KR20210131724A - Steel Material for Agricultural Machine Rotary Blade with Tempering Process Omitting and Manufacturing Method of Agricultural Machine Rotary Blade Using by This - Google Patents

Abstract

The present invention increases the bainite tissue fraction in steel for rotary blades manufactured by providing an appropriate carbon equivalent, thereby reducing or suppressing the production of martensite and pearlite in the steel, and appropriately securing the effective amount of boron in the steel By doing so, it relates to a steel material for a rotary blade for omitting the tempering process to improve the wear resistance of the manufactured rotary blade, and a method for manufacturing a rotary blade using the same.

Description

Steel Material for Agricultural Machine Rotary Blade with Tempering Process Omitting and Manufacturing Method of Agricultural Machine Rotary Blade Using by This}

The present invention relates to a rotary blade for agricultural machinery that is mounted on a driven agricultural machine such as a tiller, a manager or a tractor and crushes agricultural soil, and more specifically, increases the bainite tissue fraction in steel for a rotary blade manufactured by providing an appropriate carbon equivalent, and , This reduces or suppresses the generation of martensite and pearlite in the steel, and by properly securing the effective amount of boron in the steel, thereby improving the abrasion resistance of the manufactured rotary blade. It relates to a method for manufacturing a rotary blade used.

In general, rotary blades for agricultural machinery are mounted on driven agricultural machinery such as tractors, and the rotary blade rotating at a high speed finely grinds the lumpy soil in the cultivated land to make the grains of the cultivated land even. For cultivating crops, it plays a role of evenly spreading the soil of the arable land so that the surface of the paddy field or field remains flat.

Rotary blades for agricultural machinery require excellent strength, toughness, and abrasion resistance because their ability to plow should be demonstrated in arable land with various environmental characteristics such as rough terrain, barren soil, and soil containing a lot of gravel.

In addition, if the arable land contains a lot of stones, the plastic wear resistance of the rotary blade increases, and if the soil ratio in the arable land is high, the elastic zone wear of the rotary blade increases. Abrasion resistance in the plastic region is required.

In particular, if the wear amount of the rotary blade increases, the ability to dig up the soil during plowing of cultivated land is reduced, and the lumped soil is not sufficiently crushed. The operation was not performed smoothly, and the rotary blade and the rotary blade driving part of the agricultural machine were overloaded, thereby increasing the fuel consumption of the agricultural machine, and causing damage to the rotary blade or malfunction of the driving part.

Therefore, the material of the rotary knife for agricultural machinery requires high abrasion resistance, and the abrasion resistance is improved as the hardness of the material increases. When manufacturing a rotary blade, heat treatment such as quenching and tempering is performed.

Hardened steel for rotary blades increases in hardness but becomes brittle, and fatigue failure can easily occur if residual stress remains on the surface of the quenched rotary blade. By changing the structure in the steel for rotary blade to a stable structure, toughness is imparted, and the abrasion resistance is improved by increasing the fraction of carbide in the microstructure.

However, if the tempering temperature is increased to increase the wear resistance of the rotary blade, the strength of the rotary blade is lowered due to the softening action of the steel base material for the rotary blade, and thus the wear resistance may decrease.

In addition, the quenching process usually uses oil, and during the tempering process, the oil remaining on the surface of the quenched rotary blade is vaporized and toxic gas is emitted, which may cause environmental pollution.

In addition, in order to perform the tempering process, a heating furnace must be installed to heat the rotary blade after quenching has been completed. It causes a complicated problem, and accordingly, the production speed of the rotary blade is reduced, and the production cost is increased.

Recently, smart factories are being built as an extension of the factory automation concept that optimizes each unit process according to unmanned production facilities and management automation according to the past automation of production factories.

In a smart factory, the equipment in the factory shares data between each process through the Internet of Things so that the entire process can be organically linked with each other, and the active decision-making generated by synthesizing and analyzing the collected data is delivered to each equipment in real time. Therefore, the flexibility of the production process suitable for multi-product complex production is secured, so in the smart factory, reduction of the factory scale through production line and process reduction is important.

Therefore, it is necessary to develop a steel material for a rotary blade that can omit the tempering process during the heat treatment process when manufacturing a rotary blade in order to prevent environmental pollution caused by oil vapor and build a smart factory according to the reduction of production processes and production facilities.

Steel materials that can omit the heat treatment process have been developed through a four-step process. The first generation heat treatment omitted steel is a medium-carbon steel containing vanadium (V), which is hot-formed and then air cooled to form a ferrite-pearlite structure. It is applied to crankshafts or connecting rods for automobiles that are not subjected to excessive shock or load during operation because the impact toughness is low compared to heat-treated steels with the same tensile strength.

The second-generation heat treatment omitted steel lowers the carbon content to compensate for the low impact toughness of the first-generation heat treatment omitted steel material, and at the same time increases the silicon (Si) content, and is cooled to form a needle-shaped ferrite or ferrite-pearlite structure The cooling rate was increased, and the impact toughness was improved by refining the crystal grains of pearlite by adding molybdenum (Mo) and titanium (Ti).

In order to further improve the impact toughness and strength of the third generation steel, the martensite end temperature is increased to 200°C by the mass effect by adding niobium (Nb) and molybdenum (Mo), and through controlled cooling immediately after hot forming. The carbide was uniformly dispersed to form a complex structure of bainite and martensite.

In order to improve impact toughness, strength, and formability to a similar level to that of heat-treated steel, the 4th generation non-heat-treated steel is being developed in the direction of increasing the texture fraction of bainite through controlled cooling immediately after hot forming.

As a steel for forming such a bainite structure, there is a high-strength bainite-based non-tempered steel for automobile chassis parts disclosed in Korean Patent Application Laid-Open No. 10-2003-0008852 (published on January 29, 2003), but it has a high manganese (Mn) content. Accordingly, the formation rate of martensite which adversely affects the improvement of toughness increases, and boron (B) that can delay the formation of ferrite is not contained, so that it is difficult to form a uniform bainite structure.

High-strength wear-resistant steel with excellent hardenability of Korean Patent Publication No. 10-0415626 (registered on Jun. 6, 2004), and wear-resistant steel of Korean Patent No. 10-0445890 (registered on Aug. 17, 2013) and a manufacturing method thereof It is proposed to use nickel, chromium, and molybdenum as a base to improve abrasion resistance and hardenability by adding titanium, vanadium, and niobium, which are precipitation strengthening elements, alone or in combination. there was a problem with

In addition, Korean Patent Publication No. 10-0908624 (registered on July 14, 2009) and Korean Patent Publication No. 10-1766567 (registered on August 2, 2017), respectively, describe a pre-hardened steel with improved machinability and toughness and a manufacturing method thereof. And, although posted in the hot-rolled steel sheet and its manufacturing method, since it corresponds to the manufacturing method of heat-treated steel including tempering, it reduces the space efficiency of the production plant, which is a disadvantage of heat-treated steel, and reduces environmental pollution caused by oil and heating. There was a problem in that the production cost increased due to the large amount of energy consumed for the purpose and the production speed decreased due to the increase in the number of processes that could not be solved.

Republic of Korea Patent Publication No. 10-2003-0008852 (published on January 29, 2003) Republic of Korea Patent Publication No. 10-0415626 (Registered on Jan. 6, 2004) Republic of Korea Patent Publication No. 10-0908624 (registered on July 14, 2009) Republic of Korea Patent Publication No. 10-0445890 (Registered on August 17, 2013) Republic of Korea Patent Publication No. 10-1766567 (Registered on Aug. 2, 2017)

In an embodiment of the present invention, even if the tempering process is omitted during the heat treatment process during the manufacture of the rotary knife for agricultural machinery, the strength and toughness of the produced rotary knife are at a level similar to that of the product subjected to the tempering heat treatment, thereby reducing the production cost of the rotary knife and It aims to achieve improvement in production efficiency.

In an embodiment of the present invention, in order to secure the mechanical properties and abrasion resistance of the manufactured rotary blade for agricultural machinery, the purpose is to secure the bainite structure formation rate in the steel for the rotary blade of 90% or more.

According to an embodiment of the present invention, in the steel for a rotary blade manufactured so that the tempering process can be omitted during the heat treatment process consisting of quenching and tempering, nickel (Ni) 0.003 to 0.2 wt%, copper (Cu) 0.005 to 0.2 wt%, From 0.01 to 0.5% by weight of molybdenum (Mo), 0.01 to 0.04% by weight of titanium (Ti), 0.01 to 0.04% by weight of vanadium (V), 0.001 to 0.2% by weight of niobium (Nb), and 0.001 to 0.01% by weight of aluminum (Al) At least one selected type is contained, carbon (C) 0.1 to 0.4 wt%, silicon (Si) 0.1 to 1.0 wt%, manganese (Mn) 0.1 to 1.5 wt%, chromium (Cr) 0.1 to 0.7 wt%, boron (B) 0.001 to 0.004% by weight, nitrogen (N) 0.004 to 0.015% by weight, the balance is composed of iron and other unavoidably contained impurities, the bainite tissue fraction is formed more than 90%.

According to an embodiment of the present invention, it contains molybdenum (Mo), nickel (Ni), and copper (Cu), and is expressed by the formula C + Mn/6 + (Cr + Mo)/5 + (Ni + Cu)/15 The carbon equivalent is formed within the range of 0.25 to 0.6.

According to an embodiment of the present invention, it contains a trace alloy of titanium (Ti), vanadium (V), niobium (Nb) and aluminum (Al), (1.15Ti + 0.99V + 0.58Nb + 1.99Al) / 7.66N of The microalloy addition constant expressed by the formula is formed within the range of 0.8 to 1.0.

According to an embodiment of the present invention, _{the effective amount of boron expressed by the formula of [{5.25B - (7.66N 2} - 1.15Ti + 0.99V + 0.58Nb + 1.99Al)/5.25}] x 10000 is within the range of 7 to 20 ppm is formed from

According to an embodiment of the present invention, the tissue fraction of lower-bainite formed at a relatively low temperature is 60% or more compared to upper-bainite formed by austempering.

According to an embodiment of the present invention, the carbide fraction in the bainite structure formed by the rapid cooling expressed by the formula of (addition of carbon - 0.02) x 15.2 is formed within the range of 1.22 to 5.78.

According to an embodiment of the present invention, the steel has a hardness of Hv410-525, 135-185kg/mm ² of Tensile strength, 100 ~ 140kg / mm ² yield strength, of 0.65 ~ 0.75 yield ratio, 30% to 50% cross-sectional reduction rate, 11-16% elongation of 30 to 75J / cm ² at room temperature impact toughness of 1.22 ~ 5.78 of the It satisfies the bainite carbide fraction range.

According to an embodiment of the present invention, in the tempering method for manufacturing a rotary blade using steel for a rotary blade for omitting the tempering process during the heat treatment process consisting of quenching and tempering, 0.003 to 0.2 wt% of nickel (Ni), 0.005 to 0.2 wt%, molybdenum (Mo) 0.01 to 0.5 wt%, titanium (Ti) 0.01 to 0.04 wt%, vanadium (V) 0.01 to 0.04 wt%, niobium (Nb) 0.001 to 0.2 wt%, aluminum (Al) 0.001 to At least one selected from 0.01% by weight is contained, carbon (C) 0.1 to 0.4% by weight, silicon (Si) 0.1 to 1.0% by weight, manganese (Mn) 0.1 to 1.5% by weight, chromium (Cr) 0.1 to 0.7 The process of forming the steel for a rotary blade composed of weight %, boron (B) 0.001 to 0.004 weight %, nitrogen (N) 0.004 to 0.015 weight %, the remainder iron and other unavoidably contained impurities, and turning the steel material into a plate shape It consists of a process of hot rolling, a process of hot forming into a rotary blade shape by heating a steel material, and a quenching process of rapidly cooling the formed rotary blade to form a bainite tissue fraction of 90% or more.

According to an embodiment of the present invention, the heating of the steel in the process of hot forming is performed by atmospheric heating or induction heating within a temperature range of 1050° C. or less from the A3 transformation point.

According to an embodiment of the present invention, rapid cooling of the rotary blade in the quenching process is made at a cooling rate of 20 ~ 150 ℃ / sec until the temperature of the heated rotary blade reaches room temperature.

According to an embodiment of the present invention, even if the tempering process is omitted during the heat treatment process during the manufacture of the rotary knife for agricultural machinery, the strength and toughness of the produced rotary knife can be improved to a level similar to that of the product subjected to the tempering heat treatment.

According to an embodiment of the present invention, by omitting the tempering process during the heat treatment process for improving strength, toughness and abrasion resistance when manufacturing the rotary blade for agricultural machinery, the production speed of the rotary blade according to the reduction of the process and the production cost are reduced, and tempering is achieved. By omitting the installation of a reheating furnace for the process, there is an effect of reducing the size of the factory and optimizing the flow of the production line through the reduction of facilities.

According to an embodiment of the present invention, by providing an appropriate carbon equivalent to the steel for a rotary blade, and by controlling the time axis at which the bainite nose of the continuous cooling transformation (CCT) curve is formed, the produced steel for the rotary blade It has the effect of increasing the bainite tissue fraction, preventing the martensite tissue formation rate from increasing, and improving the abrasion resistance and toughness of the manufactured rotary blade by reducing or suppressing the pearlite generation amount.

According to an embodiment of the present invention, by maximizing the production fraction of cementite, which is a bainite carbide in steel for a rotary blade, there is an effect that can improve the wear resistance of the manufactured rotary blade.

1a and 1b are graphs showing the cooling rate of a rotary blade made of conventional heat treatment omitted steel, respectively, and a cooling process of a rotary blade made of steel for rotary blade for omitting the tempering process according to the present invention.
2 is a graph showing a continuous cooling transformation (CCT, continuous cooling transformation) curve showing the phase transformation according to the cooling rate of the steel for a rotary blade.
3 is a graph showing a phenomenon in which the starting temperature of the phase transition temperature changes while the CCT curve moves according to the carbon equivalent, and FIG. 3a is a carbon equivalent of 0.25 or less, FIG. CCT curve shift in the above is shown.
4 is a graph showing the volume ratio range of retained austenite that does not affect the yield strength according to the carbon content of the steel for rotary blades.
5 is a graph showing an ideal effective range of boron for securing an ideal bainite structure by delaying ferrite transformation.
6 is a graph showing the hardness value of the rotary blade formed according to the cooling rate in the quenching process during the manufacturing process of the rotary blade.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

It will be described in detail focusing on the parts necessary to understand the operation and operation according to the present invention.

While describing the embodiments of the present invention, descriptions of technical contents that are well known in the technical field to which the present invention pertains and are not directly related to the present invention will be omitted.

This is to more clearly convey the gist of the present invention without obscuring the gist of the present invention by omitting unnecessary description.

In addition, in describing the components of the present invention, different reference numerals may be assigned to components of the same name according to the drawings, and the same reference numerals may be given even though they are different drawings.

However, even in this case, it does not mean that the corresponding components have different functions depending on the embodiment or that they have the same function in different embodiments, and the function of each component is the corresponding embodiment. It should be judged based on the description of each component in

In addition, the technical terms used in this specification should be interpreted in the meaning generally understood by those of ordinary skill in the art to which the present invention belongs, unless otherwise specifically defined in this specification, and excessively comprehensive It should not be construed as meaning or in an excessively reduced meaning.

Also, as used herein, the singular expression includes the plural expression unless the context dictates otherwise.

In the present application, terms such as "consisting of" or "comprising" should not be construed as necessarily including all of the various components or various steps described in the specification, some of which components or some steps are It should be construed that it may not include, or may further include additional components or steps.

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention is 0.003 to 0.2% by weight of nickel (Ni), 0.005 to 0.2% by weight of copper (Cu), 0.01 to 0.5% by weight of molybdenum (Mo), 0.01 to 0.04 wt% of titanium (Ti), 0.01 to 0.04 wt% of vanadium (V), 0.001 to 0.2 wt% of niobium (Nb), and 0.001 to 0.01 wt% of aluminum (Al) At least one or more is contained as Cr), 0.001 to 0.004% by weight of boron (B), 0.004 to 0.015% by weight of nitrogen (N), the balance iron and other unavoidably contained impurities.

Hereinafter, the action and content of essential components excluding iron and other unavoidably contained impurities constituting the steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention are as follows.

1) Carbon (C)

In the steel containing the above components and content, the bainite structure fraction is formed at 90% or more, and the heat treatment omitted steel having the existing bainite structure is 1250 at the A3 transformation point while going through the p0 to p1 process as shown in FIG. 1a. A steel material heated to an austenitizing temperature between ℃ is hot formed while going through the p1 to p2 process, and the hot-formed rotary blade is subjected to constant temperature transformation from p3a to p4 or controlled cooling from p3a to p4 to obtain bainite (bainite). ) to form an organization.

In contrast, in the embodiment of the present invention, as shown in FIG. 1b , a bainite structure is formed through the rapid cooling of the process p2 to p3c. Although a separate tempering process is not required in common, the rapid cooling process has an advantage in that the time required to complete the process is greatly shortened compared to the controlled cooling or constant temperature transformation process.

At this time, when the fraction of the bainite structure formed by rapid cooling is less than 90%, it is difficult to secure the mechanical properties and durability characteristics of the manufactured rotary blade, and the carbide fraction contributing to the improvement of the wear resistance of the rotary blade is reduced. It is preferable to form 95% or more of the fraction.

As shown in the continuous cooling transformation curve (CCT curve) of FIG. 2 according to the content and cooling rate of the alloy, bainite is formed within a temperature range of 400 to 650 ℃, which is the temperature at which pearlite and martensite are formed. As a microstructure of steel, austenite is one of the decomposition products formed when austenite is cooled beyond the critical temperature of 727°C. .

In addition, bainite has a fine non-lamellar structure, and is composed of cementite and dislocation-rich ferrite. Due to the high density of dislocations contained in ferrite, it has higher hardness than conventional ferrite. will have

In addition, the bainite microstructure has a two-phase structure composed of lath-shaped ferrite and carbide, and depending on the composition and cooling rate of austenite, upper-bainite and upper bainite In comparison, a lower-bainite structure formed at a relatively low temperature is generated.

Upper bainite is an aggregate of ferrite laths forming plate-shaped regions by forming parallel groups. The carbides precipitated at the austenite grain boundary (inter-lath region) before the formation of the bainite structure are complete carbides between the lath boundaries depending on the carbon content. While forming a film, it may cause deterioration of the toughness of bainite steel.

On the other hand, the lower bainite is composed of lath-shaped ferrite and a fine-scale carbide (Fe ₃ C) aggregate, and the carbide precipitated inside the ferrite plate has a rod or blade shape. Even if omitted, sufficient strength and toughness are ensured.

Therefore, by forming the lower bainite tissue fraction larger than the upper bainite tissue fraction, the abrasion resistance, strength, hardness and toughness characteristics of the manufactured rotary blade can be improved, and it is preferable to form the lower bainite tissue fraction of 60% or more do.

When the lower bainite tissue fraction is less than 60%, the toughness of the manufactured rotary blade decreases as the upper bainite tissue fraction of the steel for rotary blade becomes relatively high. This is because the effect of shortening the process by omitting the tempering process cannot be obtained because it must be carried out by adding

The tissue fraction of the lower bainite is maximized at the cooling rate approaching the nose of the bainite diagram as shown in the continuous cooling transformation curve shown in FIG. 2, and is increased at the cooling rate away from the nose. In order to increase the tissue fraction of bainite, rapid cooling must be performed, and it is preferable to cool the molded rotary blade at a cooling rate of 20 to 150° C./sec until it reaches room temperature.

At this time, the cooling rate of 20 ~ 150 ℃ / sec can be applied differently depending on the volume of the rotary blade rapidly cooled.

As shown in FIG. 3, the bainite texture fraction of the steel for a rotary blade is greatly affected by the carbon equivalent. If the carbon equivalent is low, the bainite nose of the CCT curve is short-lived as shown in FIG. 3a. As it moves to the side, the upper bainite tissue fraction increases relatively, and when the carbon equivalent is high, as the bainite nose of the CCT curve moves toward the long-term side, as shown in FIG. 3c, the amount of martensite produced increases than that of bainite. .

Therefore, the steel material for a rotary blade according to an embodiment of the present invention is limited to contain 0.1 to 0.4% by weight of carbon.

When the carbon content is less than 0.1% by weight, it is not possible to secure the proper distribution of carbides necessary for strength and wear resistance that can satisfy the performance required by the manufactured rotary blade, and the hardenability (quenching property) of the steel material for the rotary blade itself is poor. It becomes insufficient, and difficulty arises in forming a bainite structure.

When the carbon content exceeds 0.4 wt%, the strength of the manufactured rotary blade can be improved, but as the martensite production rate rapidly increases, the toughness is greatly reduced and breakage is easy to occur, so the carbon content is reduced to 0.4 wt% It is limited to the following to form a level of strength that meets the performance required for a rotary blade.

2) Silicon (Si)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention contains 0.1 to 1.0% by weight of silicon, and when the silicon content is less than 0.1% by weight, the decarburization and solid solution strengthening effect does not occur sufficiently.

In addition, when the silicon content exceeds 1.0 wt%, the toughness and plastic workability of the bainite-structured rotary blade steel material is reduced, and the surface of the rotary blade manufactured by excessive decarburization of the material surface of the rotary blade steel material Hardness and durability are greatly reduced.

3) Manganese (Mn)

The steel for rotary blade for omitting the tempering process according to an embodiment of the present invention contains 0.1 to 1.5 wt% of manganese, and manganese generates solid solution strengthening of ferrite contained in bainite to improve the strength of the steel for rotary blade and improve the toughness of the steel for rotary blades by refining the bainite structure.

At this time, when the manganese content is less than 0.1% by weight, it is insufficient to promote hardenability and bainite structure formation, and when the manganese content exceeds 1.5% by weight, the hardenability greatly increases and the martensite structure formation rate increases. It adversely affects the toughness of the rotary blade, making it difficult to ensure the homogeneity of the bainite structure.

4) Chromium (Cr)

The steel for rotary blades for omitting the tempering process according to an embodiment of the present invention contains 0.1 to 0.7 wt% of chromium, which improves the strength, fatigue strength, and wear resistance of the steel for rotary blades, and improves hardenability. The bainite structure is stably generated, and the impact resistance is increased by forming a composite carbide with molybdenum and vanadium.

At this time, when the chromium content is less than 0.1% by weight, it becomes difficult to obtain the effect according to the chromium content, and when the chromium content exceeds 0.7% by weight, the martensitic structure occurs and the brittleness of the manufactured rotary blade increases, so that the use of the rotary blade The risk of breakage increases.

5) Boron (B)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention contains 0.001 to 0.004% by weight of boron. As the atomic boron contained in the steel segregates at the austenite grain boundary, the grain boundary free energy is lowered to suppress the formation of proeutectoid ferrite, thereby promoting the formation of the bainite structure.

When the boron content is less than 0.001% by weight, the effect of promoting bainite structure formation becomes insignificant, and when the boron content exceeds 0.004% by weight, boron, which has a high affinity with nitrogen and oxygen, forms oxides and nitrides in the dissolution process, so that hot _{Since borocarbides such as M 23} (CB) ₆ or Fe ₂ B are formed at the rolling or forging processing temperature to promote the formation of proeutectoid ferrite, it becomes difficult to secure the bainite tissue fraction.

In particular, if the cooling rate is slow when performing the quenching process of the rotary blade, boron nitride is formed at the grain boundary, and the produced nitride acts as a nucleation site of ferrite, thereby reducing the strength and toughness of the manufactured rotary blade.

Therefore, in order to prevent the formation of boron nitride, titanium, vanadium, niobium, aluminum, etc. must be added to appropriately secure the effective amount of boron that exists in an atomic state without bonding with nitrogen.

6) Nitrogen (N)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention contains 0.004 to 0.015% by weight of nitrogen, and nitrogen is combined with titanium, aluminum and vanadium contained in the steel for a rotary blade to form carbonitride, , the formed carbonitride refines the austenite grains to improve the strength and toughness of the bainite steel.

At this time, when the nitrogen content is less than 0.004% by weight, it is difficult to obtain the effect of improving the strength and toughness of the bainite steel, and when the nitrogen content exceeds 0.015% by weight, the carbonitride is coarsened and the growth of austenite grains during heat treatment lowers deterrence.

In addition, when the content of titanium, aluminum and vanadium is insufficient compared to the amount of nitrogen contained, nitrogen is dissolved in the steel for a rotary blade to greatly reduce the toughness of the rotary blade.

In the steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention, in addition to the carbon, silicon, manganese, chromium, boron, and nitrogen, in order to omit the tempering process in the manufacturing process of the rotary blade, the characteristics of the steel structure for the rotary blade are One or more of nickel, copper, molybdenum, titanium, vanadium, niobium and aluminum may be selectively added and contained to change or improve the performance of the manufactured rotary blade, such as strength or toughness, The action and content will be described as follows.

1) Nickel (Ni)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention may additionally contain 0.003 to 0.2% by weight of nickel, and nickel improves the hardenability of the steel to stably form a bainite structure, It is possible to increase the strength without reducing the toughness of the manufactured rotary blade, and improve the corrosion resistance.

At this time, if the nickel content is less than 0.003 wt%, the effect of improving the strength and corrosion resistance of the steel for rotary blades and the effect of securing toughness at low temperatures cannot be obtained, and when the nickel content exceeds 0.2 wt%, the critical point of the effect is reached and more An improved effect may not be obtained, and manufacturing cost may be increased.

2) Copper (Cu)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention may additionally contain 0.005 to 0.2% by weight of copper. It improves the tensile and yield strength of the rotary blade according to the solid solution strengthening and precipitation strengthening effects, Improves corrosion resistance.

At this time, when the copper content is less than 0.005 wt%, the corrosion resistance improvement effect is insufficient, and when the copper content exceeds 0.2 wt%, the critical point of the effect is reached and a more improved effect is not obtained. When charging into a heating furnace for rolling, grain boundary embrittlement may cause surface defects or deterioration in toughness of the manufactured rotary blade.

3) Titanium (Ti)

The steel for a rotary blade according to an embodiment of the present invention may additionally contain 0.01 to 0.04 wt% of titanium, and titanium is combined with nitrogen in the bainite steel to which boron is added to fix nitrogen, thereby suppressing the generation of boron nitride. Thus, it is possible to secure the effective amount of boron in the atomic state.

At this time, TiN, the most stable of the grain refining element compounds, has a low solid solubility at high temperature and a slow grain growth rate, which can contribute to grain refinement. .

As the bainite transformation initiation temperature decreases as the austenite crystal grain size decreases, the formation of upper bainite is reduced, the fraction of lower bainite is increased, and the lower bainite tissue fraction is more easily secured by suppressing the formation of martensite. It is possible to increase the tensile strength and yield strength of the manufactured rotary blade.

At this time, when the titanium content is less than 0.01% by weight, the effect becomes insignificant, and when the titanium content exceeds 0.04% by weight, the improvement effect reaches a saturated state and does not show the improved effect, and the toughness of the manufactured rotary blade is reduced. do.

4) Molybdenum (Mo)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention may additionally contain 0.01 to 0.5 wt% of molybdenum, and molybdenum increases the hardenability of the steel for a rotary blade to obtain a bainite structure stably. And, molybdenum carbide improves the strength and toughness of the manufactured rotary blade by refining the grain size.

When the heat treatment cooling rate of the rotary blade is slow, the toughness of the rotary blade manufactured by dispersing the coarse precipitates of molybdenum may decrease. Densification can occur to increase the toughness of the rotary blade.

At this time, when molybdenum is contained together with boron, hardenability is controlled during cooling to optimize the balance between tensile strength and toughness.

In addition, when the molybdenum content exceeds 0.5% by weight, the hardenability is increased more than necessary and the martensite production rate is increased, and a saturation state is reached in which the improvement effect is no longer increased.

In particular, since boron and molybdenum are expensive elements, it is preferable not to contain more than the necessary amount because the production cost of the rotary blade is greatly increased if the content is more than necessary.

5) Vanadium (V)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention may additionally contain 0.01 to 0.04 wt % of vanadium, and vanadium is formed by combining with carbon in the steel to form fine carbides in the steel for a rotary blade. It plays an important role in hardenability control to secure an appropriate bainite structure by improving strength and preventing grain growth of austenite phase by forming vanadium carbonitride (VC, VCN) at a temperature of 900°C or higher.

Vanadium improves the strength of the manufactured rotary blade through precipitation strengthening and dispersion strengthening while forming fine precipitates of vanadium carbonitride inside the ferrite structure while the steel for rotary blade is cooled.

In particular, since fine precipitates of vanadium carbonitride are unstable at high temperatures, it is very important to control the cooling rate to form fine precipitates of vanadium carbonitride. do.

At this time, when the content of vanadium is lower than 0.01 wt %, the effect caused by the vanadium content is insignificant, and when the content of vanadium exceeds 0.04 wt %, the improvement effect does not increase any more, and the saturation state is reached.

In particular, when coarse carbonitride is formed according to an excessive amount of vanadium, the toughness of the manufactured rotary blade is lowered and the steel is brittle.

6) Niobium (Nb)

The steel material for a rotary blade for omitting the tempering process according to an embodiment of the present invention may additionally contain 0.01 to 0.04% by weight of niobium, and niobium is niobium carbonitride (NbC, As NbN) precipitates at the grain boundary, a fixing effect appears to refine the grains, and the strength and toughness of the bainite structure can be improved.

At this time, when the content of niobium is less than 0.01% by weight, it is difficult to compensate for the fixing effect due to niobium carbonitride and the effect of improving hardenability accompanied by lowering the carbon content, bainite transformation is not easy, and the content of niobium When it exceeds 0.04 wt%, it is preferable to contain an appropriate amount of niobium because coarse niobium carbonitride may be formed and the toughness of the bainite structure may be reduced.

7) Aluminum (Al)

The steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention may additionally contain 0.001 to 0.01% by weight of aluminum. Aluminum is a powerful element that removes oxygen contained in the steel for a rotary blade while forming aluminum oxide. It acts as a deoxidizer and combines with nitrogen to refine bainite grains.

At this time, when the content of aluminum is less than 0.001 wt%, the effect of deoxidation or bainite grain refining action is reduced, which is undesirable, and when the content of aluminum exceeds 0.01 wt%, the amount of aluminum oxide non-metallic inclusions increases. It may cause deterioration of the toughness of the manufactured rotary blade or the occurrence of nozzle clogging during casting of steel for rotary blades.

In addition, the steel for a rotary blade for omitting the tempering process of the present invention contains oxygen (O) of 0.003% by weight or less, phosphorus (P) of 0.01% by weight or less, and sulfur (S) of 0.01% by weight or less desirable.

Specifically, phosphorus is segregated at the grain boundary (inter-lath region) to reduce the toughness of the steel for rotary blades.

In addition, sulfur is combined with manganese and iron during steel making for rotary blades to form emulsions (MnS) and iron oxides (FeS) that reduce the toughness of bainite steels, and the emulsions increase the anisotropy of steel while stretching during hot working This reduces the mechanical properties of the steel for rotary blades, and the iron oxide becomes a path for surface defects due to inclusions (foreign substances) contained in the composition during hot or cold working due to its low melting point.

In addition, oxygen is combined with the oxidizing element of the rotary blade steel to form non-metallic inclusions, thereby inhibiting the mechanical properties and fatigue properties of the bainite steel, so it is preferable not to contain in excess of the above content.

In the case of containing molybdenum (Mo), nickel (Ni) and copper (Cu) in the steel for a rotary blade for omitting the tempering process according to an embodiment of the present invention, carbon equivalent satisfying the range of 0.25 to 0.6 wt% (equivalent) It is preferable to form

The carbon equivalent is derived by the formula below.

Carbon equivalent (wt%) = C + Mn/6 + (Cr + Mo)/5 + (Ni + Cu)/15

When the carbon equivalent is less than 0.25 (wt%), especially at the carbon equivalent of 0.20 (wt%) or less, when the rapid cooling is performed during the production process of the rotary blade, the structure of the steel for rotary blade is transformed into ferrite and pearlite, resulting in a bainite structure It is difficult to secure, and as the CCT curve moves to the short-time side as shown in FIG. 3a, the upper bainite tissue fraction increases.

In addition, when the carbon equivalent exceeds 0.6 (wt%), as shown in FIG. 3c, as the CCT curve moves to the long-time side, the amount of martensite production increases, the amount of bainite production decreases, and the effect of the content of manganese decreases. do.

At this time, among the constituent factors of the bainite microstructure, retained austenite distributed at grain boundaries after phase transformation greatly reduces the yield strength of the manufactured rotary blade. Yield of the manufactured rotary blade during quenching by continuous cooling of the rotary blade As a result of studying the correlation between the amount of carbon equivalent and the amount of retained austenite that does not lower the strength, the limit conditions as shown in the graph of FIG. 4 were obtained.

Specifically, when the amount of retained austenite of 5 vol% or less and the carbon equivalent of 0.25 to 0.6 (wt%) corresponding to the range of the square box indicated by the broken line in the graph of FIG. 4 is maintained, the yield strength of the manufactured rotary blade decreases doesn't happen

In the steel for rotary blade for omitting the tempering process according to an embodiment of the present invention, the minor alloy addition constant made of titanium (Ti), vanadium (V), niobium (Nb) and aluminum (Al) is in the range of 0.8 to 1.0 is preferably satisfied, and the microalloy addition constant can be expressed by the following formula.

Trace alloy addition constant = (1.15Ti + 0.99V + 0.58Nb + 1.99Al) / 7.66N

If the microalloy addition constant is less than 0.8, the effect of boron addition is lowered, making it difficult to secure a bainite structure. As this is formed, the toughness of the manufactured rotary blade may be reduced.

In the case of including titanium (Ti), vanadium (V), niobium (Nb) and aluminum (Al) in the steel for rotary blade for omitting the tempering process according to an embodiment of the present invention, effective to satisfy the range of 7 to 20 ppm It is desirable to form an effective Boron.

The effective amount of boron is derived by the formula below.

Effective boron amount (ppm) = [{5.25B - (7.66N ₂ - 1.15Ti + 0.99V + 0.58Nb + 1.99Al)/5.25}] x 10000

The relationship between the effective amount of boron in the steel for rotary blade and the ideal bainite grain size of the manufactured rotary blade is shown as the graph of FIG. A value in the range of 7 to 20 ppm can be obtained by obtaining the effective amount of boron according to the effective boron content formed in the broken line box of FIG. 5 through the above formula to induce night transformation.

At this time, when the effective amount of boron is less than 7 ppm, the effect of adding boron becomes insignificant, and when the effective amount of boron exceeds 20 ppm, it becomes difficult to secure the bainite structure while the hardenability of the steel for rotary blade decreases.

It is preferable that the carbide fraction of the bainite structure formed inside the rotary blade is formed within the range of 1.22 to 5.78 when the rapid cooling is performed during the production process of the rotary blade for omitting the tempering process according to the embodiment of the present invention. The nite carbide fraction is derived from the formula below.

Bainite Carbide Fraction = (Carbon Addition - 0.02) x 15.2

If the carbide fraction in the bainite structure of the steel for rotary blades subjected to rapid cooling is less than 1.22, it is difficult to secure the wear resistance performance of the manufactured rotor blades, and if the carbide fraction exceeds 5.78, the wear resistance of the manufactured rotor blades Although the performance can be improved, the amount of the carbide-forming element added in the steel must also be increased in order to increase the carbide fraction, which is undesirable because it can lead to an increase in manufacturing cost.

In addition, the steel for rotary blades has a hardness in the range of Hv410 to 525, and a hardness in the range of 135 to 185 kg/mm ² Tensile strength, yield strength in the range of 100 to 140 kg/mm ² , yield ratio in the range of 0.65 to 0.75, reduction in area in the range of 30 to 50%, elongation in the range of 11 to 16% and elongation in the range of 30 to 75 J/cm ² It satisfies the mechanical properties with room temperature impact toughness.

A method of manufacturing a rotary blade using a steel material for a rotary blade for omitting the tempering process according to an embodiment of the present invention is as follows.

When the steel for the rotary blade is formed, hot rolling is performed in the shape of a plate, and the steel processed in the shape of the plate is heated, and then a hot forming process is performed to form the shape of the rotary blade through rolling or forging. Rapid cooling forms 90% or more of the bainite tissue fraction in the steel of the rotary blade.

At this time, it is preferable that the heating of the steel for performing the hot forming process is performed by atmospheric heating or induction heating within a temperature range of 1050° C. or less from the A3 transformation point.

In addition, when the heating temperature for hot forming is less than the Ac3 transformation point, the bainite generation fraction decreases as abnormal ferrite is precipitated, and the fraction occupied by the upper bainite in the generated bainite increases, and the reheating temperature is 1050° C. If it exceeds, it becomes difficult to secure the toughness of the manufactured rotary blade as the grains are coarsened.

Rapid cooling of the rotary blade in the quenching process is made at a cooling rate of 20 ~ 150 ℃ / sec until the heated rotary blade reaches room temperature, as shown in the graph of Figure 6, the cooling rate of less than 20 ℃ / sec In the ferrite or pearlite transformation occurs, it becomes difficult to secure the structure of bainite, and thus it becomes difficult to secure high toughness of the manufactured rotary blade.

In addition, at a cooling rate exceeding 150 ° C / sec, the effect of securing the structure of bainite reaches a saturated state, It is undesirable because shape deformation of the rotary blade may occur.

The table below compares the mechanical properties of the steel for rotary blades according to the component composition.

The steel materials for the rotary blade according to the test example were each cast into an ingot and then hot rolled and cooled, and the rolling ratio of all steel materials was 80% or more.

In addition, Test Examples 1 to 12 were heated at a temperature of 900 to 1050 ° C for 1 hour and then cooled at a rate of 20 to 150 ° C / sec, and Test Examples 13 to 24 were heated to a temperature of 900 to 1050 ° C for 1 hour. After heating for a while, it was cooled at a rate of 70 °C/sec.

Component composition of steel for rotary blades by test example test example Ingredient composition (%) C Si Mn Cr B Ni Cu Mo Ti V Nb Al N ₂ One 0.1 One One 0.4 0.0018 0.05 0.019 0.5 0.025 0.025 0 0 0.007 2 0.12 0.6 0.3 0.1 0.0025 0.012 0.016 0.3 0.02 0.01 0.01 0.005 0.007 3 0.1 0.1 0.3 0.7 0.0038 0.011 0.021 0.2 0.031 0.03 0.029 0.009 0.015 4 0.2 0.2 0.49 0.31 0.002 0.15 0.09 0.1 0.034 0.014 0.01 0.001 0.008 5 0.17 0.6 0.5 0.3 0.0015 0.15 0.09 0.05 0.015 0.01 0.01 0.01 0.007 6 0.23 0.6 0.5 0.7 0.0013 0.015 0.02 0.1 0.03 0.024 0.02 0.01 0.0118 7 0.3 One 0.1 0.1 0.0015 0.013 0.018 0.05 0.015 0.008 0.008 0 0.004 8 0.25 0.6 0.7 0.1 0.0015 0.09 0.05 0.05 0.01 0.02 0 0.01 0.007 9 0.3 0.1 0.1 0.2 0.004 0.08 0.004 0.1 0.03 0.02 0.02 0.01 0.013 10 0.33 0.1 0.8 0.6 0.002 0 0 0.05 0.02 0.01 0.01 0.005 0.007 11 0.34 0.15 1.29 0.13 0.002 0.05 0.019 0.08 0.029 0.02 0 0 0.007 12 0.4 0.1 0.5 0.5 0.0035 0.003 0.008 0.01 0.019 0.01 0.009 0.009 0.009 13 0.1 One 0.2 0.1 0.003 0.01 0.005 0.05 0.03 0.015 0.015 0.001 0.008 14 0.1 0.6 0.2 0.1 0.002 0.03 0.019 0.05 0.022 0.02 0.02 0 0.008 15 0.1 0.1 0.2 0.1 0.002 0.04 0.019 0.1 0.02 0.01 0.01 0.003 0.007 16 0.2 0.7 0.1 0.1 0.004 0.009 0.019 0.05 0.02 0.01 0.01 0 0.005 17 0.13 0.6 0.2 0.5 0.001 0.009 0.019 0.3 0.01 0.01 0.01 0.004 0.005 18 0.35 0.1 0.6 0.5 0.003 0.009 0.019 0.1 0.01 0 0.01 0.007 0.006 19 0.35 One 1.3 0.7 0.0035 0.009 0.019 0.05 0.03 0.015 0.015 0.001 0.008 20 0.33 0.6 One 0.8 0.0019 0.009 0.019 0.1 0.026 0.01 0.001 0.002 0.007 21 0.4 0.1 One 0.4 0.002 0.009 0.019 0.4 0.03 0.01 0.015 0.002 0.008 22 0.1 One 0.2 0.1 0.0033 0.01 0.005 0.05 0.03 0.03 0.02 0.01 0.008 23 0.2 0.7 0.1 0.1 0.004 0.009 0.019 0.05 0.03 0.02 0.02 0 0.005 24 0.33 0.6 One 0.8 0.0035 0.009 0.019 0.1 0.03 0.02 0.02 0.01 0.007

Tissue formation according to heating and cooling conditions of rotary blade steel for each test example carbon equivalent Trace alloy addition constant valid boron
(ppm) heating temperature
(℃) cooling rate
(℃/sec) bainite
(vol%) bottom
bainite
(vol%) bainite
Carbide fraction
(vol%) One 0.45 1.00 17.8 1050 150 95 75 1.22 2 0.25 0.91 15.5 970 150 95 80 1.52 3 0.33 0.87 9.8 900 150 95 85 1.22 4 0.38 0.99 19.0 1000 100 95 75 2.74 5 0.34 0.99 13.5 970 70 95 70 2.28 6 0.48 0.99 11.8 1000 50 95 65 3.19 7 0.35 0.97 13.4 950 100 95 75 4.26 8 0.41 0.95 10.4 950 100 95 80 3.50 9 0.38 0.86 13.8 1000 100 95 75 4.26 10 0.59 0.91 10.5 950 20 95 75 4.71 11 0.60 0.99 19.1 1050 20 95 70 4.86 12 0.59 0.80 9.3 970 20 95 75 5.78 13 0.16 0.98 27.6 970 70 50 10 0.61 14 0.17 0.93 11.3 900 70 70 30 0.85 15 0.18 0.83 3.0 950 70 50 20 0.61 16 0.25 0.91 33.7 1050 70 30 10 0.82 17 0.33 0.92 4.0 950 70 30 10 0.50 18 0.57 0.68 1.9 950 70 30 10 0.50 19 0.72 0.98 32.6 950 70 30 10 1.50 20 0.68 0.83 1.4 950 70 30 10 1.41 21 0.73 0.93 12.0 950 70 10 5 0.58 22 0.16 1.56 33.0 900 70 30 15 0.36 23 0.25 1.72 40.0 900 70 30 15 0.82 24 0.68 1.60 35.0 900 70 30 15 1.41

Mechanical properties and abrasion resistance of steel for rotary blades by test example residual
austenite
(vol%) mechanical properties Durability Hardness
(Hv) tensile strength
(kg/㎟) yield strength
(kg/㎟) yield ratio
(YS/TS) section reduction rate
(%) elongation
(%) room temperature
impact toughness
(J/cm2) beating
wear
(%) soil
wear
(%) One 4.5 440 150 106 0.71 50 15 65 0.6 0.08 2 0.8 410 135 94 0.69 50 16 75 0.8 0.11 3 1.3 430 145 102 0.70 50 15 70 0.6 0.09 4 1.8 450 151 112 0.75 45 14 70 0.6 0.07 5 0.8 435 145 108 0.74 50 15 65 0.6 0.08 6 4 470 160 116 0.73 40 14 60 0.5 0.07 7 1.5 430 145 106 0.73 46 13 35 0.6 0.08 8 2 455 155 115 0.74 46 13 60 0.6 0.07 9 1.8 440 150 111 0.74 46 13 60 0.6 0.08 10 1.8 510 181 129 0.71 35 12 40 0.4 0.04 11 4 525 185 132 0.71 30 11 50 0.4 0.04 12 4 515 181 129 0.71 30 12 30 0.4 0.04 13 0 280 90 60 0.67 50 15 60 4.0 0.55 14 0 310 100 70 0.70 50 15 55 3.8 0.51 15 0 280 90 60 0.67 50 15 70 3.0 0.4 16 One 370 125 80 0.64 50 17 75 2.6 0.34 17 1.3 372 120 80 0.67 50 17 70 2.7 0.36 18 4.2 372 125 75 0.60 50 17 5 2.6 0.35 19 5.2 510 120 90 0.75 10 3 5 2.7 0.36 20 6 570 170 130 0.76 30 15 4 1.5 0.2 21 8 550 190 180 0.95 10 3 3 1.3 0.17 22 0 310 100 70 0.70 60 15 65 3.8 0.51 23 One 315 110 70 0.64 50 17 60 3.7 0.49 24 6 515 180 150 0.83 10 3 5 1.4 0.19

The comparative steel for rotary blades in Tables 4 and 5 below is a steel typically applied to the manufacture of rotary blades for agricultural machinery, and is heated and quenched at 930~970℃ for 1 hour, then at 420~470℃ for 1 hour During the tempering treatment was performed.

Component composition of comparative steel for rotary blades comparative example Ingredient composition (%) C Si Mn Cr B Ni Cu Mo Ti V Nb Al N ₂ SUP9 0.56 0.23 0.76 0.75 0 0.009 0.019 0 0.002 0.002 0.002 0.001 0.007 SUP9A 0.59 0.25 0.85 0.86 0 0.003 0.003 0 0.003 0.002 0.003 0.001 0.008 SUP9D 0.58 0.25 0.84 0.84 0 0.009 0.018 0 0.002 0.001 0.032 0.001 0.006 SUP11A 0.60 0.25 0.82 0.86 0.0011 0.09 0.018 0 0.01 0.006 0.005 0.001 0.006

Mechanical properties and wear resistance of comparative rotary blade steel residual
Auste
Night
(vol%) mechanical properties wear resistance Hardness
(Hv) Seal
burglar
(kg/㎟) surrender
burglar
(kg/㎟) yield ratio
(YS/TS) section
decrease rate
(%) elongation
(%) room temperature
Shock
tenacity
(J/cm2) Carbide fraction
(vol%) beating
wear
(%) soil
wear
(%) SUP9 4 410 136 128 0.94 23 10 9 0.86 1.5 0.25 SUP9A 3 400 134 124 0.93 29 11 7 0.91 1.4 0.20 SUP9D 4 430 143 1133 0.93 30 13 8 0.90 1.3 0.19 SUP11A 3 435 146 135 0.92 26 10 7 0.93 1.3 0.17

In order to evaluate mechanical properties such as tensile and impact properties and abrasion resistance from the hot-rolled test materials, test specimens were taken in the rolling direction of the test material.

The bainite microstructure phase fraction and the carbide fraction of the Test Examples and Comparative Examples were measured by a point count method for a surface to be inspected of 1000 mm 2 using an electron microscope and an image analyzer after cooling the steel for a rotary blade.

At this time, the total retained austenite phase fraction in the bainite structure was measured using X-ray (Cu radiation), and the tensile test was performed using a KS standard (KS B0801) No. 4 specimen at a cross head speed of 5 mm. Tested at /min.

In addition, the impact test piece was manufactured according to the KS standard (KS B0809) No. 3 test piece, and the notch direction was processed from the side (L-T direction) in the rolling direction.

And due to the characteristics of rotary blades for agricultural machines that must exhibit the ability to plow in arable land with various environmental characteristics such as rough terrain, barren soil, and soil containing a lot of gravel, the abrasion resistance test is based on the impact wear test and ASTM G40-83 method. It was evaluated by the soil abrasion test according to ASTM G65-85 method.

As shown in the table, in Test Examples 1 to 12, the ideal amount of effective boron suitable for maximizing the tissue fraction of bainite is formed within the range of 7 to 20 ppm, whereas in Test Examples 13 to 24, the effective amount of boron is in the ideal numerical range got out of

Accordingly, a bainite structure fraction of 90% or more was formed in the steel microstructure for a rotary blade of Test Examples 1 to 12, and a bainite structure fraction in the range of 10 to 70% in the steel microstructure for a rotary blade of Test Examples 13 to 24 was formed. formation can be observed.

Therefore, it can be confirmed that the performance improvement in terms of the bainite structure fraction can be maximized when rapid cooling is performed on the steel material for a rotary blade of the embodiment of the present invention, and an appropriate effective boron amount is secured.

In addition, as shown in the above table, Test Examples 1 to 12 are hardness Hv410 to 525, tensile strength 135 to 185 kg/mm2, yield strength 100 to 140 kg/mm2, yield ratio 0.65 to 0.75, reduction of area 30 to in the quenched state. 50%, elongation 11~16%, room temperature impact toughness 30~75 J/cm2, had mechanical properties and wear resistance within the range of bainite carbide fraction of 1.22~5.78, and these values were compared to Test Examples 13~24 Thus, it can be seen that the values are remarkably excellent.

In addition, it can be confirmed that the steel for rotary blades according to Test Examples 1 to 12, in which only quenching heat treatment was performed, mechanical properties and wear resistance properties of equal or greater than that of the steel materials for rotary blades of Comparative Examples in which both quenching and tempering heat treatment were performed together. have.

When manufacturing a rotary blade through the steel material for a rotary blade according to the present invention, by omitting the tempering process during the heat treatment process, the production speed of the rotary blade is improved and production cost is reduced, and heating for heating when performing the tempering process of the rotary blade By reducing the size of the factory and optimizing the flow of the production line through the reduction of the installation line, it is possible to prepare the foundation for building a smart factory.

Although embodiments of the present invention have been described with reference to the above, those skilled in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof.

Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all respects, and the scope of the present invention described in the above detailed description is indicated by the following claims, meaning and All changes or modifications derived from the scope and its equivalents should be construed as being included in the scope of the present invention.

T: temperature
t: time
Fs: ferrite transformation starting point
Ps: Pearlite transformation start point
Bs: the starting point of bainite transformation
Ms: the starting point of martensitic transformation

Claims (10)

In the steel material for a rotary blade manufactured so that the tempering process can be omitted during the heat treatment process consisting of quenching and tempering,
Nickel (Ni) 0.003 to 0.2 wt%, Copper (Cu) 0.005 to 0.2 wt%, Molybdenum (Mo) 0.01 to 0.5 wt%, Titanium (Ti) 0.01 to 0.04 wt%, Vanadium (V) 0.01 to 0.04 wt%, At least one selected from niobium (Nb) 0.001 to 0.2 wt%, aluminum (Al) 0.001 to 0.01 wt% is contained, carbon (C) 0.1 to 0.4 wt%, silicon (Si) 0.1 to 1.0 wt%, manganese (Mn) 0.1 to 1.5% by weight, chromium (Cr) 0.1 to 0.7% by weight, boron (B) 0.001 to 0.004% by weight, nitrogen (N) 0.004 to 0.015% by weight, remainder iron and other unavoidably contained impurities. and steel for rotary blades for omitting the tempering process, characterized in that the bainite tissue fraction is formed at least 90%. According to claim 1,
Contains molybdenum (Mo), nickel (Ni) and copper (Cu), and has a carbon equivalent expressed by the formula of C + Mn/6 + (Cr + Mo)/5 + (Ni + Cu)/15 Steel for rotary blades for omitting the tempering process, characterized in that it is formed within the range of 0.25 to 0.6. According to claim 1,
Contains trace alloys of titanium (Ti), vanadium (V), niobium (Nb), and aluminum (Al), adding trace alloys expressed by the formula (1.15Ti + 0.99V + 0.58Nb + 1.99Al) / 7.66N Steel for rotary blades for omitting the tempering process, characterized in that the constant is formed within the range of 0.8 to 1.0. 4. The method of claim 3,
The effective amount of boron expressed by the formula of [{5.25B - (7.66N ₂ - 1.15Ti + 0.99V + 0.58Nb + 1.99Al)/5.25}] x 10000 is characterized in that it is formed within the range of 7 to 20 ppm Steel for rotary blades to omit the tempering process. According to claim 1,
Omission of the tempering process, characterized in that the tissue fraction of lower-bainite formed at a relatively low temperature compared to upper-bainite formed by austempering is 60% or more steel for rotary blades for According to claim 1,
(Carbon addition amount - 0.02) x 15.2 The carbide fraction in the bainite structure formed by the rapid cooling expressed by the formula is formed within the range of 1.22 ~ 5.78 Rotary blade steel for omitting the tempering process. According to claim 1,
The steel has a hardness of Hv410-525, 135-185kg/mm ² of Tensile strength, 100 ~ 140kg / mm ² yield strength, of 0.65 ~ 0.75 yield ratio, 30% to 50% cross-sectional reduction rate, 11-16% elongation of 30 to 75J / cm ² at room temperature impact toughness of 1.22 ~ 5.78 of the Rotary blade steel for omitting the tempering process, characterized in that it satisfies the bainite carbide fraction range. In the anti-tempering method for manufacturing a rotary blade using steel for a rotary blade for omitting the tempering process during the heat treatment process consisting of quenching and tempering,
Nickel (Ni) 0.003 to 0.2 wt%, Copper (Cu) 0.005 to 0.2 wt%, Molybdenum (Mo) 0.01 to 0.5 wt%, Titanium (Ti) 0.01 to 0.04 wt%, Vanadium (V) 0.01 to 0.04 wt%, At least one selected from niobium (Nb) 0.001 to 0.2 wt%, aluminum (Al) 0.001 to 0.01 wt% is contained, carbon (C) 0.1 to 0.4 wt%, silicon (Si) 0.1 to 1.0 wt%, manganese (Mn) 0.1 to 1.5% by weight, chromium (Cr) 0.1 to 0.7% by weight, boron (B) 0.001 to 0.004% by weight, nitrogen (N) 0.004 to 0.015% by weight, remainder iron and other unavoidably contained impurities. The process of forming a steel material for a rotary blade to be;
The process of hot rolling a steel material into a sheet shape;
The process of heating a steel material and hot forming into a rotary blade shape;
A quenching process of rapidly cooling the molded rotary blade to form a bainite tissue fraction of 90% or more;
Rotary blade manufacturing method using steel for rotary blades for omitting the tempering process, characterized in that consisting of. 9. The method of claim 8,
The steel material heating in the hot forming process is performed by atmospheric heating or induction heating within the temperature range of 1050 ° C or less from the A3 transformation point. How to make a rotary blade. 9. The method of claim 8,
The rapid cooling of the rotary blade in the quenching process is performed at a cooling rate of 20 ~ 150 ° C / sec until the temperature of the heated rotary blade reaches room temperature. Rotary blade using steel for rotary blade for omitting the tempering process manufacturing method.

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