KR101268736B1 - martensitic stainless steel and method of manufacturing it - Google Patents

Abstract

The present invention is in weight%, carbon (C): 0.51 to 0.59%, silicon (Si): 0.2 to 0.4%, manganese (Mn): 0.4 to 0.6%, phosphorus (P): 0.025% or less, sulfur (S) : 0.003% or less, Chromium (Cr): 13.7-14.3%, Nickel (Ni) 0.4% or less, Molybdenum (Mo): 0.4-0.6%, Copper (Cu): 0.5% or less, Tungsten (W): 0.8- 1.2%, balance iron (Fe) and other unavoidable impurities, and consists of a ferrite matrix and uniformly distributed chromium carbide microstructure, wherein the chromium carbide microstructure is 80 / 100㎛ ² to 200 / 100㎛ type martensite containing ² can provide a stainless steel and their preparation.

Description

Martensitic stainless steel and method of manufacturing the same

The present invention relates to martensitic stainless steels and a method of manufacturing the same, and more particularly, the size and distribution of fine chromium carbide in martensitic stainless steels by optimizing heating conditions (heating conditions), cooling conditions and cracking conditions. It relates to a martensitic stainless steel having a high corrosion resistance and high hardness by ensuring uniformity and a method for producing the same.

Typically, esophagus, scissors, doctor blades, razor blades, scalpels, and the like are frequently in contact with moisture when in use, so high corrosion resistance is required, and further high hardness is required to maintain cutting and wear resistance. The present invention relates to martensitic stainless steels that can satisfy these requirements.

In general, martensitic stainless steels, in particular in the case of the annealing agent of the stainless steel, have a microstructure composed of fine chromium carbide uniformly distributed in the ferrite matrix. As such, when the fine chromium carbide is uniformly distributed, it is possible to rapidly re-use carbon with high temperature austenite in a subsequent hardening process, thereby increasing the chromium concentration of about 7% in the matrix to about 12%. Can be. In addition, by increasing the concentration of chromium in the matrix, thin chromium carbide can be densely produced on the surface of a material such as a razor blade or the like. The chromium carbide produced on the surface can suppress corrosion of the razor blade matrix by moisture, and thus can improve corrosion resistance. That is, in order to manufacture a razor blade having excellent corrosion resistance, it is required to uniformly distribute fine chromium carbides in stainless steel.

In addition, in order to maintain a predetermined machinability and wear resistance, after the reinforcement heat treatment of martensitic stainless steel, it is required that the stainless steel has a high hardness. Such high hardness can be realized by the martensite structure produced by the reinforcement heat treatment.

Martensite is a very hard tissue produced by the rapid cooling of hot austenite. The higher the content of carbon dissolved in hot austenite, the higher the carbon dissolved in martensite, thereby increasing the hardness of martensite. As described above, 420 martensitic stainless steels are mainly used as materials to satisfy corrosion resistance and high hardness at the same time.

In addition, the hot rolled coil of martensitic stainless steel is very brittle due to the martensite structure generated during casting and hot working. Therefore, it was necessary to soften the martensitic stainless steel to a predetermined level so as to facilitate the processing. Therefore, when the martensitic stainless steel is heat-treated, a batch annealing furnace is provided in which heat treatment of the brittle material is easy. I have used it.

On the other hand, 420 series martensitic stainless steels commonly used have insufficient corrosion resistance. The present invention relates to a high corrosion-resistant martensitic stainless steel added with Mo and W and a method for producing the same in order to solve such inadequate corrosion resistance. In the martensitic stainless steel according to the present invention, in the chromium carbide (Cr ₂₃ C ₆ ) which is precipitated during heat treatment unlike the conventional 420 series martensitic stainless steel, some Cr may be substituted with Mo and W, which is chromium. It may affect the precipitation ability of carbides. Therefore, in order to manufacture martensitic stainless steel having high hardness and corrosion resistance and improved workability, a new type of heat treatment condition is required to uniformly distribute fine chromium carbide in the substrate.

An object of the present invention devised to solve the above-mentioned problems is to provide a high corrosion-resistant martensitic stainless steel and a method for producing the same added with Mo and W.

Another object of the present invention is to provide a martensitic stainless steel in which fine chromium carbide is uniformly distributed in a ferrite matrix.

Another object of the present invention is to provide a novel heat treatment process for producing a material having high hardness, corrosion resistance and workability.

According to a feature of the present invention for achieving the above object, the present invention is a weight%, carbon (C): 0.51 ~ 0.59%, silicon (Si): 0.2 ~ 0.4%, manganese (Mn): 0.4 ~ 0.6%, phosphorus (P): 0.025% or less, sulfur (S): 0.003% or less, chromium (Cr): 13.7-14.3%, nickel (Ni): 0.4% or less, molybdenum (Mo): 0.4-0.6%, Copper (Cu): 0.5% or less, Tungsten (W): 0.8-1.2%, containing ferrous matrix and other unavoidable impurities, consisting of a ferrite matrix and a uniformly distributed microstructure of chromium carbide, 80 High carbon martensitic stainless steel comprising a microstructure of chromium carbide of about / 100 μm ² to 200/100 μm ² .

The microstructure of the chromium carbide is spherical, and the chromium carbide microstructure may have a maximum diameter of 5 μm or less.

In addition, as another feature of the present invention, in weight%, carbon (C): 0.51 to 0.59%, silicon (Si): 0.2 to 0.4%, manganese (Mn): 0.4 to 0.6%, phosphorus (P): 0.025% Sulfur (S): 0.003% or less, Chromium (Cr): 13.7-14.3%, Nickel (Ni): 0.4% or less, Molybdenum (Mo): 0.4-0.6%, Copper (Cu): 0.5% or less, Tungsten (W): In the heat treatment of martensitic stainless steel containing 0.8 to 1.2%, balance iron (Fe) and other unavoidable impurities, after heating the stainless steel to 800 ℃ to 900 ℃, 10 hours to 30 hours Maintaining the first cracking step; A cooling step of cooling the stainless steel that has undergone the first cracking step to 650 ° C to 750 ° C; And a second cracking step of maintaining the stainless steel cooled to 650 ° C to 750 ° C at a constant temperature for 5 hours to 10 hours.

At this time, the temperature increase rate in the first cracking step may be less than 200 ℃ / hour.

In the cooling step, the cooling rate may be greater than 10 ℃ / time.

According to the present invention as described above, it is possible to provide a high corrosion-resistant martensitic stainless steel and a method for producing the addition of Mo and W.

In addition, the present invention can provide a martensitic stainless steel in which fine chromium carbides are uniformly distributed in a ferrite matrix.

In addition, the present invention can provide a novel heat treatment process for producing a material having high hardness, corrosion resistance and workability.

1 is a temperature graph with respect to the time of the heat treatment process of martensitic stainless steel according to the present invention.
FIG. 2 is a SEM photograph of martensitic stainless steel according to Comparative Example 1 heated to a temperature of 850 ° C. at a rate of 40 ° C./hour.
FIG. 3 is a SEM photograph of martensitic stainless steel according to Comparative Example 2 heated to a heating temperature of 850 ° C. at 100 ° C./hour.
4 is a SEM photograph of the martensitic stainless steel according to Example 1 cooled to 650 ° C. at a cooling rate of 10 ° C./hour.

Specific details of other embodiments are included in the detailed description and the drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. In the following description, it is assumed that a part is connected to another part, But also includes a case in which other elements are electrically connected to each other in the middle thereof. In the drawings, parts not relating to the present invention are omitted for clarity of description, and like parts are denoted by the same reference numerals throughout the specification.

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

The present invention relates to martensitic stainless steel having a high chromium carbide uniformly distributed, ensuring high corrosion resistance and high hardness. The present invention also relates to a method for producing martensitic stainless steel including a novel heat treatment process to have high corrosion resistance and high hardness.

1 is a temperature graph with respect to the time of the heat treatment process of martensitic stainless steel according to the present invention. Referring to Figure 1, the manufacturing method of martensitic stainless steel in weight%, carbon (C): 0.51 ~ 0.59%, silicon (Si): 0.2 ~ 0.4%, manganese (Mn): 0.4 ~ 0.6%, phosphorus ( P): 0.025% or less, sulfur (S): 0.003% or less, chromium (Cr): 13.7 to 14.3%, nickel (Ni): 0.4% or less, molybdenum (Mo): 0.4 to 0.6%, copper (Cu): 0.5% or less, tungsten (W): 0.8-1.2%, in the heat treatment of martensitic stainless steel containing residual iron (Fe) and other unavoidable impurities, after heating the stainless steel to 800 ℃ to 900 ℃, A first cracking step maintained for 10 to 30 hours; A cooling step of cooling the stainless steel that has undergone the first cracking step to 650 ° C to 750 ° C; And a second cracking step of maintaining the stainless steel cooled to 650 ° C to 750 ° C at a constant temperature for 5 hours to 10 hours. In addition, after the second cracking step, the stainless steel may be cooled by air cooling.

The method for producing martensitic stainless steel according to the present invention may include first and second cracking steps. The first and second cracking steps are for spheroidizing the fine particles of the chromium carbide formed in the layered form by heat treatment, and the martensitic stainless steel spheroidized by such heat treatment may improve ductility.

In the first cracking step, the stainless steel is heated up to 800 ° C. to 900 ° C., wherein the temperature increase rate may be less than 200 ° C./hour. In addition, at this time, after the temperature increase, the stainless steel may be maintained for 10 hours to 30 hours.

When the temperature increase rate is 200 ° C./hour or more, the transit time in a temperature section in which the size of the precipitated chromium carbide microstructure becomes coarse may be reduced. Therefore, the size of the chromium carbide microstructure can be reduced, thereby inducing an increase in the density of chromium carbide in the local region where the microstructure is small in size. That is, the diffusion rate of the precipitated chromium carbide may decrease in a region where the size of the microstructure is relatively large, and may cause distribution nonuniformity of the chromium carbide. Therefore, in order to ensure uniform distribution of chromium carbide, it may be preferable that the temperature increase rate is less than 200 ° C / hour.

When the temperature of the stainless steel is less than 800 ℃ or more than 900 ℃ in the first cracking step, since the spheroidized fine particles of the chromium carbide in the stainless steel is not made well, the ductility of the stainless steel may be reduced. In addition, it may be preferable to maintain the first cracking time for 10 hours to 30 hours. When the first cracking time is less than 10 hours, the heat treatment time of the stainless steel is not sufficient, so that the size of the chromium carbide microstructure is It may decrease, and thus may cause a distribution nonuniformity of chromium carbide. In addition, when the first crack time exceeds 30 hours, the heat treatment time is increased to reduce the process efficiency and increase the energy consumption to increase the production cost.

The martensitic stainless steel may include a cooling step of cooling the stainless steel that has undergone the first cracking step to 650 ° C to 750 ° C. In the cooling step, the cooling rate may be greater than 10 ℃ / time.

If the cooling rate in the cooling step is 10 ° C / hour or less, the time passing through the temperature range of, for example, 750 ° C ~ 850 ° C which is a temperature range in which the size of the chromium carbide microstructure is coarse, may be increased, thus martensite Chromium carbide microstructures can be coarsened within stainless steels, which can represent microstructures that are not suitable for materials of materials requiring high corrosion resistance and hardness, such as razor blades. Therefore, the cooling rate in the cooling step is preferably limited to more than 10 ℃ / time.

In addition, the second cracking step may maintain the stainless steel cooled to 650 ℃ to 750 ℃ at a constant temperature for 5 hours to 10 hours.

The reason why the temperature range is 650 ° C. to 750 ° C. and the crack time is 5 hours to 10 hours in the second cracking step is reduced when the chromium carbide is excessively grown when the microstructure of the chromium carbide is spheroidized. And to suppress the decrease in ductility.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the scope of the present invention is not limited by the following examples.

Comparative Example and Example

Table 1 is a composition of the hot rolled coil of martensitic stainless steel according to Comparative Examples 1, 2 and Example 1 of the present invention, Table 2 is a heat treatment condition of the hot rolled coil of martensitic stainless steel according to Table 1 and each Hardness, elongation and chromium carbide density results.

The hot rolled coil of martensitic stainless steel according to the present invention is, in weight%, carbon (C): 0.51 to 0.59%, silicon (Si): 0.2 to 0.4%, manganese (Mn): 0.4 to 0.6%, phosphorus (P) ): 0.025% or less, sulfur (S): 0.003% or less, chromium (Cr): 13.7-14.3%, nickel (Ni): 0.4% or less, molybdenum (Mo): 0.4-0.6%, copper (Cu): 0.5 % Or less, tungsten (W): 0.8-1.2%, balance iron (Fe) and other unavoidable impurities may be included. In Example 1, a hot rolled coil of martensitic stainless steel having a composition shown in Table 1 was used, and heat treatment was performed using a thickness of 2 mm of the hot rolled coil.

C Si Mn P S Cr Ni Mo Cu W Fe and impurities 0.54 0.30 0.49 0.023 0.002 14.03 0.26 0.49 0.04 0.86 Remainder

Each component in Table 1 above is weight percent. Comparative Examples 1 and 2 and Example 1 having a composition as shown in Table 1 were prepared with a hot rolled coil having a thickness of 2 mm, and heat treatment was performed under different conditions as shown in FIGS. 1, 2, and 3. The hardness, elongation, and chromium carbide density of Comparative Examples 1 and 2 and Example 1, which were subjected to the heat treatment as described above, were measured, and the results are shown in Table 2 and FIGS. 2 to 3.

division Heating rate
(℃ / hour) First crack condition
(℃, hour) Cooling rate
(℃ / hour) Second crack condition
(℃, hour) Hardness
(Hv) Elongation
(%) Density of Chromium Carbide
(ea / 100㎛ ² ) Comparative Example 1 200 850, 20 10 650 233 17.8 250 Comparative Example 2 40 850, 20 10 650 210 19.9 60 Example 1 40 850, 20 20 650 220 20.1 120

FIG. 2 is a SEM photograph of martensitic stainless steel according to Comparative Example 1 heated to a temperature of 850 ° C. at 40 ° C./hour, and FIG. 3 is a comparative example 2 of a temperature rise rate of 850 ° C. at 100 ° C./hour. SEM picture of the martensitic stainless steel according to the present invention, FIG. 4 is a SEM picture of the martensitic stainless steel according to Example 1 cooled to 650 ° C. at a cooling rate of 10 ° C./hour.

Comparing Comparative Example 1 and Example 1, the temperature and time are the same under the first cracking condition, but the temperature is increased by varying the heating rate up to the temperature of the first cracking condition at 200 ° C./hour and 40 ° C./hour, respectively. I was.

Referring to FIG. 2, which is Comparative Example 1, when the temperature rising rate up to the first cracking step presented in the present invention is 200 ° C./hour or more, the time passing through the temperature section in which the chromium carbide formed through the grain boundary becomes coarse decreases. Therefore, the chromium carbide has a small grain size, and also causes an increase in the chromium carbide density in the localized region, resulting in nonuniform distribution of the chromium carbide. On the other hand, referring to Figure 4, Example 1, it was confirmed that the crystal grains of the chromium carbide is uniformly distributed. In regions where the grain size is relatively large, as in Comparative Example 1, the chromium carbide distribution may be uneven due to the slow diffusion of the produced chromium carbides, resulting in an elongation of less than 18%. It could be confirmed that µm ² was shown. Therefore, it can be seen that the temperature increase rate should be limited to less than 20 ° C / hour to ensure uniform heat treatment hardness, corrosion resistance, and workability improvement by securing uniformity of chromium carbide.

Comparing Comparative Example 2 and Example 1, the temperature and time are the same in the second cracking condition, but the cooling rate in the cooling step from the first cracking condition to the second cracking condition is 10 ° C./hour and 20 ° C./hour, respectively. Otherwise the temperature was lowered.

Referring to FIG. 3, which is Comparative Example 2, it was confirmed that the chromium carbide density analysis through microscopic observation showed about 60/100/100 μm ² . On the other hand, referring to Figure 4, Example 1, the spherical chromium carbide microstructure has a maximum diameter of 5㎛ or less, it was confirmed that the density of the chromium oxide 120 / 100㎛ ² . As shown in FIG. 3, the chromium carbide coarsening in Comparative Example 2 may cause a decrease in carbide density, which leads to a decrease in hardness and a decrease in corrosion resistance of the material after heat treatment of the material. Therefore, it can be seen that the cooling rate should be limited to more than 10 ℃ / time in order to secure the fine chromium carbide density which greatly affects the heat treatment hardness and internal resistance.

Referring to FIG. 4, Inventive Example 1, it was confirmed that the fine chromium carbides were spheroidized and uniformly distributed by heat treatment within the range of the temperature increase rate and the primary cooling rate of the present invention. It can be seen that the density is 120/100 µm ² .

The hot rolled coil of martensitic stainless steel having the composition shown in Table 1 was used, and the heat treatment was performed as shown in Table 3 with a thickness of 2 mm of the hot rolled coil. After the heat treatment, the maximum diameter and distribution form of the spherical chromium carbide and the density of the chromium carbide were measured.

division Heating rate
(℃ / hour) First crack condition
(℃, hour) Cooling rate
(℃ / hour) Second crack condition
(℃, hour) Maximum diameter of chromium carbide
(탆) Distribution form Density of Chromium Carbide
(ea / 100㎛ ² ) Comparative Example 1 200 850, 20 10 650 2 Unevenness 250 Comparative Example 2 40 850, 20 10 650 5 Uniformity 60 Example 1 40 850, 20 20 650 7 Uniformity 120 Example 2 100 850, 20 20 650 4 Uniformity 80 Example 3 40 850, 20 30 650 5 Uniformity 100

Martensitic stainless steel according to the present invention in terms of weight%, carbon (C): 0.51 ~ 0.59%, silicon (Si): 0.2 ~ 0.4%, manganese (Mn): 0.4 ~ 0.6%, phosphorus (P): 0.025 % Or less, sulfur (S): 0.003% or less, chromium (Cr): 13.7-14.3%, nickel (Ni): 0.4% or less, molybdenum (Mo): 0.4-0.6%, copper (Cu): 0.5% or less, Tungsten (W): 0.8-1.2%, balance iron (Fe) and other unavoidable impurities, and consists of a ferrite matrix and a microstructure of chromium carbide, the microstructure of the chromium carbide 80/100 ㎛ ² to It may contain 200 / 100㎛ ² . In the case of Comparative Examples 1 and 2 it was confirmed that the microstructure of the chromium carbide is 250/100 ㎛ ² and 60/100 ㎛ ² , respectively. In particular, in the case of Comparative Example 1, the maximum diameter of the chromium carbide was 2 μm or less, and the size was too small, and it was confirmed that the distribution of the chromium carbide was uneven. In Comparative Example 2, the distribution of chromium carbide itself was uniform, but the maximum diameter of the chromium carbide was 7 μm or less. When the maximum diameter of the chromium carbide is more than 5㎛, it may be difficult to high chromium of the chromium in the subsequent process, which was confirmed that the strength of the stainless steel is lowered.

On the other hand, in Examples 1 to 3 according to the present invention, the microstructure of the chromium carbide is spherical, and the chromium carbide microstructure has a maximum diameter of 5 μm or less, and at the same time, it is confirmed that all of the chromium carbides are uniformly distributed. Could. In Examples 1 to 3 are respectively the density of chromium carbides of 120 / 100㎛ ^2, 80 / 100㎛ ² and 200 / 100㎛ ² to 80 / 100㎛ ² to ^200/2 range of 100㎛ It was confirmed that the inclusion within. If the density of the chromium carbide is less than 80 / 100㎛ ² , the size of the chromium carbide may be formed too large, thus reducing the strength of the stainless steel. In addition, when the density of the chromium carbide is more than 200 / 100㎛ ² , the size of the chromium carbide is small, but the distribution of the chromium carbide is formed non-uniform, the characteristics of the stainless steel may be non-uniform.

It was confirmed that the elongation of the stainless steels according to Examples 1 to 3 were all 18% or more. Thus, martensitic stainless steels having high corrosion resistance and high hardness were obtained by securing uniformity in size and distribution of chromium carbides in the stainless steel. Could get

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing detailed description, and all changes or modifications derived from the meaning and scope of the claims and the equivalents thereof are included in the scope of the present invention Should be interpreted.

Claims (5)

By weight%, carbon (C): 0.51 to 0.59%, silicon (Si): 0.2 to 0.4%, manganese (Mn): 0.4 to 0.6%, phosphorus (P): greater than 0 to 0.025% or less, sulfur (S) : More than 0 to 0.003% or less, chromium (Cr): 13.7 to 14.3%, nickel (Ni): more than 0 to 0.4% or less, molybdenum (Mo): 0.4 to 0.6%, copper (Cu): more than 0 to 0.5% Tungsten (W): 0.8-1.2%, including residual iron (Fe) and other unavoidable impurities,
Martensitic stainless steel comprising a ferrite matrix and a uniformly distributed chromium carbide microstructure, including 80/100 μm ² to 200/100 μm ² chromium carbide microstructures. The method of claim 1,
The chromium carbide microstructure is spherical, and the chromium carbide microstructure has a maximum diameter of 5 μm or less. By weight%, carbon (C): 0.51 to 0.59%, silicon (Si): 0.2 to 0.4%, manganese (Mn): 0.4 to 0.6%, phosphorus (P): greater than 0 to 0.025% or less, sulfur (S) : More than 0 to 0.003% or less, chromium (Cr): 13.7 to 14.3%, nickel (Ni): more than 0 to 0.4% or less, molybdenum (Mo): 0.4 to 0.6%, copper (Cu): more than 0 to 0.5% Hereinafter, in heat-treating martensitic stainless steel containing tungsten (W): 0.8 to 1.2%, residual iron (Fe) and other unavoidable impurities,
A first cracking step of maintaining the stainless steel at 800 ° C. to 900 ° C. and then maintaining the mixture for 10 hours to 30 hours;
A cooling step of cooling the stainless steel that has undergone the first cracking step to 650 ° C to 750 ° C; And
A second cracking step of maintaining the 650 ℃ to 750 ℃ cooled stainless steel at a constant temperature for 5 hours to 10 hours; manufacturing method of martensitic stainless steel comprising a. The method of claim 3,
Method of producing a martensitic stainless steel, characterized in that the temperature increase rate in the first cracking step is less than 200 ℃ / hour. The method of claim 3,
Cooling rate in the cooling step is a manufacturing method of martensitic stainless steel, characterized in that more than 10 ℃ / hour.

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