CZ298442B6 - High-strength steel for forging - Google Patents

Abstract

In the present invention, there is disclosed a Forged steel composition containing 0.3 to 0.5 percent by weight of carbon, 0.1 to 0.4 percent by weight of silicon, 0.7 to 1.5 percent by weight of manganese, 1.2 to 3.5 percent by weight of chromium, 0.1 to 0.6 percent by weight of molybdenum, up to 0.7 percent by weight of nickel, at least one element being selected from the group consisting of vanadium. Niobium and tantalum in the total amount 0.03 to 0.35 percent by weight, and 30 to 250 ppm of nitrogen, the balance being iron and undesired impurities. The invented Forged steel forms a microstructure consisting of bainite and martensite and contains nitrogen in solid solution with vanadium, niobium and tantalum in such en amount that (total weight percentage of vanadium, niobium and tantalum + 0.001 x /N (ppm) in solid solution)\ is more than or equal to 0.068. A preferred feature of the invented forges steel is small amount of expensive alloying ingredients (particularly nickel) at maintenance of the steel high strength. The steel is particularly suitable for manufacture of big crankshafts intended for ships.

Description

High strength steel forging

Technical field

The present invention relates to a high-strength forging steel (referred to hereinafter as high-strength forging steel) and in particular to a high-strength forging steel characterized by a low price (with respect to the content of expensive alloying elements, especially nickel) and high strength . Such forging steel finds utility primarily as a material for forging large shaft bending shafts and the like. Therefore, high strength crank shafts of high-strength steel are also included within the scope of the present invention.

BACKGROUND OF THE INVENTION

Angled shafts for power transmission on ships are usually made of chromium molybdenum steel, designated as ISO 42CrMo4, ISO 36CrNiMo6 and DIN 32CrMol2. The first of these steels contains a relatively high C content and a relatively low Cr and Mo content, which results in a proportionally low strength but also a relatively low cost and is therefore used in cases where the load requirements are not so great. The latter contains a large amount of nickel as an alloying additive, which gives it the best strength and toughness between the three steels, and therefore finds application in cases where the load is particularly high. The third steel shows intermediate values in both price and strength between the two previous ones, and therefore finds application in cases where toughness is particularly important.

In recent times, it has become common to produce large crankshafts for use on ships made of ISO 36CrNiMo6 steel, which is expensive but has high strength to avoid marine hazards.

The aforementioned ISO 36CrNiMo6 steel, which is a nickel chromium molybdenum steel, has excellent strength and toughness which gives it a high nickel content as a reinforcing additive, but is therefore more expensive than other forged chromium molybdenum steels because nickel is an expensive alloying metal. This limits the widespread use of this steel.

SUMMARY OF THE INVENTION

The present invention has been developed in light of the foregoing. The object of the present invention was to develop a less expensive, high strength forging steel with comparable or better strength, toughness and curing capability (as required by current manufacturers) than 36CrNiMo6, and thus to prepare a very strong Ni-Cr-Mo steel for practical use forging. Another object of the present invention is a method of manufacturing crank shafts of said forging steel characterized by low cost, high strength and toughness, and good hardenability.

The object of the present invention is high-strength steel forgings comprising 0.3 to 0.5% carbon, 0.1 to 0.4% silicon, 0.7 to 1.5% manganese, 1.2 to 3.5% chromium, 0.1 to 0.6% molybdenum not more than 0.7% nickel, and at least one element selected from the group consisting of vanadium, niobium and tantalum in an amount of 0.03 to 0.35% in total, and 30 to 250 ppm nitrogen, while the remainder is iron and unavoidable impurities, the microstructure of which consists mainly of bainite and martensite and which contains nitrogen in solid solution and enough vanadium, niobium and tantalum to fulfill the condition expressed by the following expression 1:

[Total content (%) V, Nb and Ta] + 0.001 x [N (ppm) in solid solution]> 0.068 ... (1) (% expressed in% by weight. The same applies in the following).

-1 CZ 298442 B6

The high-strength steel forging of the present invention is characterized by a limited nickel content as described above, intentionally added nitrogen (N) and at least one of V, Nb and Ta, with such N content in solid solution and total V content. , Nb and Ta to satisfy the above expression 1, and with a microstructure composed mainly of bainite and martensite. It has a high tensile strength and good toughness with good hardenability and is comparatively cost effective.

The content of each element was determined according to the following policies. The high strength forging steel of the present invention retains its characteristic regardless of the basic composition as long as the nickel content, V, Nb and Ta content, total nitrogen content and nitrogen content of the solid solution retain the above conditions. The high strength forging steel of the present invention must have the following basic composition in order to fully maintain the above properties.

C 0.3 to 0.5%, more preferably 0.36 to 0.45%,

Mn 0.7-1.5%, more preferably 0.8-1.2%,

Cr 1.2 to 3.5%, more preferably 1.5 to 2.5%,

Mo 0.1 to 0.6%, more preferably 0.15 to 0.35%, with the remainder mainly consisting of iron.

The high-strength steel forging, which has the above-mentioned basic composition, contains a small amount of Al as a deoxidizing element. Al is effective when its amount is greater than 0.001% but has no additional effect if its content is greater than 0.040%. It is therefore appropriate to keep the Al content below 0.040%. Another harmful element that is present in forged steel is sulfur S, which adversely affects toughness and fatigue strength. The S content should be suitably kept below 0.006%.

In addition, the high strength forging steel of the present invention is characterized by a D1 value of not less than 30 mm. (The D1 value is the critical diameter of a steel product whose middle portion exhibits 50% martensitic hardness after turbidity in water). Such characteristics make the forged steel particularly suitable for the production of large propeller shafts. The present invention therefore includes crankshafts, especially those with large dimensions, manufactured by forging of the forged steel mentioned above.

In view of these problems, the inventors have made a great effort to develop a forged steel that is less expensive but which has a comparable strength and toughness to "ISO 36CrNiMo6", which is known as high strength Ni-Cr-Mo forged steel. The forged steel contains minor amounts of nickel as an alloying additive in order to reduce costs and maintain good curing important for the production of large forgings with high strength. As a result of the foregoing, the forged steel contains no more than 0.7% nickel as a reinforcing additive, providing high strength and toughness in conjunction with an additive of at least one element selected from the group consisting of V, Nb and Ta and a very low nitrogen content. the total content of V, Nb and Ta and the amount of nitrogen dissolved in the solid solution satisfy the above condition 1. This compensates for the reduction in strength due to the reduced nickel content. The forging steel also shows very good hardenability. This discovery led to the present invention.

Cr-Mo steels for forging generally require the presence of nickel in order to have high strength and toughness and increased curing ability. Unfortunately, nickel is such an expensive additive that it increases the cost of steel beyond the price demanded by the user if its content is higher. Thus, the present invention discloses a new steel with comparable strength and hardenability compared to conventional Ni-Cr-Mo forging steel, although it has a minimum nickel content. To reduce costs, the nickel content is maintained below 0.7%, more preferably below 0.5% and most preferably below 0.3%.

-2GB 298442 B6

Reducing the nickel content reduces the strength, toughness, and hardenability caused by nickel, and therefore such a resultant steel is not required by the consumer. The inventors of the present invention have thoroughly examined the possibilities of replacing the inadequate properties due to the reduced nickel content by supplying other elements, thereby developing a new forging steel that meets the consumer's requirements in terms of both cost and performance. They have found that this requirement can be met by adding at least one element selected from the group consisting of V, Nb and Ta and nitrogen (which has hitherto been considered as a harmful trace element) to Cr-Mo steel for reduced nickel fittings, the content of V, Nb and Ta and the amount of nitrogen dissolved in the solid solution to satisfy the above requirement 1.

In order to achieve a practical effect on forging steel, it is important that the nickel content does not exceed 0.7%, the content of at least one of the V, Nb and Ta elements is from 0.03%, more preferably from 0.045% to dp 0.35%, most preferably 0.15% and the nitrogen content was from 30 ppm, more preferably from 40 ppm to 250 ppm, most preferably 100 ppm. Finally, it is important that the total content of V, Nb and Ta and the content of nitrogen dissolved in the solid solution satisfy the above requirement 1.

If the total V, Nb and Ta content and the nitrogen content are accidentally outside the above specified range and the requirements of claim 1 are not met, the resulting pendulum steel does not have high strength and toughness and good hardenability as envisaged by the present invention.

The inventors of the present invention do not explain why the steel for low nickel forgings so significantly increases the strength and toughness limit in the presence of such a total content of V, Nb and Ta and the nitrogen contained in the solid solution to meet the requirement of requirement 1. Possible reason is that nitrogen combined with V, Nb and Ta forms nitrides and dissolved nitrogen itself causes an effective increase in the breaking strength. Since strength enhancing elements such as V, Nb and Ta are very expensive, it is economically advantageous to add them in small amounts in conjunction with inexpensive nitrogen dissolved in solid solution to increase strength.

Effective strength enhancement occurs only when strength enhancing elements and nitrogen are added to Cr-Mo steel forging, containing no more than 0.7% Ni. This effect does not occur when added to high-grade forged steel containing more than 0.7% Ni.

The forging steel of the present invention is based on Cr-Mo steel forging containing not more than 0.7% Ni. When alloying one or more strength elements (V, Nb, Ta) and nitrogen so that the total content of V, Nb and Ta and the total content of nitrogen dissolved and undissolved in the solid solution and total nitrogen meet the above requirement 1, the required forging steel comparable in strength, toughness and hardenability to the comparatively expensive high-grade, high-grade Cr-Mo forging steel with a high nickel content.

As mentioned above, the forging steel of the present invention is characterized by a limited nickel content. It is further characterized by containing at least one of the elements V, Nb and Ta and nitrogen (and nitrogen dissolved in the solid solution) in a specific amount. Forged steel is not specifically limited in the basic composition. For the preparation of steel for forging with the properties of the present invention, i.e. strength, toughness and hardenability, suitable for the production of crankshafts etc., it is possible to use Cr-Mo steel for forging with the following basic composition:

C 0.3 to 0.5%, more preferably 0.36 to 0.45%,

Si 0.1 to 0.4%, more preferably 0.15 to 0.4%,

Mn 0.7-1.5%, more preferably 0.8-1.2%,

Cr 1.2 to 3.5%, more preferably 1.5 to 2.5%,

Mo 0.1 to 0.6%, more preferably 0.15 to 0.35%.

The content of each of the elements listed above was determined on the basis of the reasons explained below.

-3GB 298442 B6

C 0.3 to 0.5%, more preferably 0.36 to 0.45%.

Carbon determines hardenability as well as strength. For greatest efficiency, carbon must be present in an amount of from 0.3%, more preferably 0.36% or more, and most preferably 0.38% or more. However, the excess carbon has a negative effect on toughness and causes inverted V-shape segregation. Therefore, an upper carbon content of 0.5% or less, more preferably 0.45% or less, and most preferably 0.42% or less is suitable.

Si 0.1 to 0.4%, more preferably 0.15 to 0.4%.

Silicon contributes to strength. For greatest effect, the silicon content should be from 0.1% or more, more preferably 0.15% or more, and most preferably 0.20% or more. Conversely, however, silicon in excessive amounts promotes the formation of inverted V-shaped segregation, resulting in low ingot purity. Therefore, the upper limit of the silicon content should not exceed 0.4% or less, and more preferably 0.3% or less.

Mn 0.7-1.5%, more preferably 0.8-1.2%.

Manganese contributes to curing as well as to strength. For greatest effect, it should be present in an amount of 0.7% or more, 0.8% or more, and most preferably 0.9% or more. However, the excess manganese content promotes the formation of inverted V-shaped segregation. Therefore, the upper limit of the manganese content should be 1.5% or less, more preferably 1.2% or less, and most preferably 1.1% or less.

Cr 1.2 to 3.5%, more preferably 1.5 to 2.5%.

Chrome supports toughness as well as strength. For the greatest effect, the chromium content should be 1.2% or more, more preferably 1.5% or more, and most preferably 1.75% or more. Conversely, however, excess chromium promotes the formation of inverted V-shaped segregation, resulting in low ingot purity. Therefore, the upper limit of chromium content should be 3.5% or less, more preferably 2.5% or less.

Mo 0.1 to 0.6%, more preferably 0.15 to 0.35%.

Molybdenum promotes strength, toughness and hardenability. For greatest effect, molybdenum should be present in an amount of 0.1% or more, more preferably 0.15% or more, and most preferably 0.20% or more. Molybdenum, however, is prone to microsegregation (normal segregation) due to its small partition coefficient. Therefore, an upper limit of molybdenum content of 0.6% or less, more preferably 0.35 or less, and most preferably 0.30% or less is suitable.

The forging steel of the present invention has the aforementioned base composition in which Fe is the base. It undoubtedly also contains trace amounts of undesirable impurities, or may optionally contain other elements that are harmless to the effect of the present invention. Examples of such supplemental elements include B (which contributes to hardenability), Ti (contributes to deoxidation) and Ca, Mg, Ce, Zr and Te (controlling the form of MnS). They can be used alone or in combination with each other. Their total amount should be less than about 0.03%.

In addition to the aforementioned base composition, the forging steel of the present invention contains aluminum as one of the unwelcome impurities. Aluminum (as a deoxidizing agent) is added to reduce the oxygen content of the forging steel. For good oxygen reduction effect, aluminum should be present in an amount of about 0.001% or more. However, the aluminum present in excess binds nitrogen and forms AIN (thus avoiding an increase in the breaking strength due to the addition of N and V), and also merges with a number of other elements to form non-metallic inclusions and intermetallic compounds (thereby negatively affecting toughness). Therefore, the maximum aluminum content should be 0.10% or less, more preferably 0.04% or less. In order to prevent the formation of AIN, the addition of V and the like is important from the point of view of increasing the breaking strength. and nitrogen. If the nitrogen content is very low, namely about 0.001%, the amount of AIN formed is small and the firming effect is induced even though the nitrogen content is about 30 ppm. However, if the aluminum content is high, namely about 0.03%, a considerable amount is formed

As a result, it is desirable to increase the nitrogen content to only about 250 ppm or to increase the content of V and etc. in order to obtain the desired strength enhancement effect as desired.

Another contaminant is sulfur, which is derived from sulfides contained in coke for the production of iron. Sulfur in steel creates sulfides (such as MnS) that interfere with fatigue characteristics. To avoid similar problems, it is necessary to keep the sulfur content below 0.006%, more preferably below 0.005%.

The forging steel of the present invention is characterized in that it has the aforementioned basic composition and its microstructure consists mainly of bainite and martensite. However, it will not achieve as high a strength as envisaged by the present invention when the fracture area is more than 10% of ferrite and perlite. The term "mainly composed of bainite and martensite" means that the structure cut-off, which can be distinguished under an optical microscope, is mostly bainite and martensite and the fracture area of ferrite and perlite is less than 10%. Unfortunately, there is no reliable way of quantitatively determining the amount of bainite and martensite in the fracture surface. However, it is possible to empirically distinguish a microstructure composed mainly of bainite and martensite in structural photographs.

A microstructure composed mainly of bainite and martensite can be obtained for steel with the above chemical composition when the steel is heat treated at an average cooling rate of about 0.5 ° C to 100 ° C / min. from a temperature range of 870 ° C to 500 ° C.

The forging steel of the present invention has a chemical composition as described above. Due to the limited nickel content (less than 0.7%), it exhibits a high strength without addition of a significant amount of alloying additives due to the presence of at least one element of V, Nb and Ta and nitrogen added in a specific amount. It is advantageous in its curing capacity, as shown by the high D1 value above 30 mm (i 32 mm) according to the Jomini test. (D1 is the critical center diameter to obtain hardness due to the formation of 50% martensite after turbidity in water). For this reason the steel is very suitable for forgings which are hardened after forging, ie for the production of crankshafts, especially shafts with large dimensions for use on ships.

Due to the remarkable hardenability denoted by the D1 value, the steel for forgings of the present invention is particularly advantageous for large forgings such as crankshafts with a diameter of 150 to 1000 mm, which require high centering and hardness after turbidity on the surface.

There are no significant manufacturing limitations in the processing of steel for the forging of the present invention. The production can be carried out by casting after mixing the desired components in a high-frequency induction furnace, electric furnace or converter. The mixing of the components is followed by degassing under vacuum. Casting can be accomplished by casting large forging ingots or by continuous casting for small forging. However, according to the present invention, a strict control of the nitrogen content present in the forging steel is necessary. A suitable way of meeting this requirement is to add raw materials to molten steel containing nitrogen in the form of a nitride, such as manganese nitride and nitride, or by blowing nitrogen into the molten metal. Under appropriate conditions, it is possible to reduce the nitrogen content by vacuum degassing.

The forging steel of the present invention may be formed into a crankshaft or the like. in any way that is unaffected by anything. A common method involves the following steps:

• Production of steel of the desired composition in an electric furnace or similar.

• Removing contaminants (such as sulfur) and gaseous components (such as oxygen) by vacuum cleaning.

• Production of ingot.

• Ingot heating and heated ingot forging.

-5GB 298442 B6 • Intermediate check, reheat and forged to the required crankshaft shape.

• Homogenization by heating and hardening by hardening.

• Finishing.

Forging the shape of the desired crankshaft can be done by either free forging or R-R (or T-R) forging. The free forging creates crankshaft arms and crankshaft pins in a single block, which is then finished to the required shaft shape by gas cutting and machining. The R-R (or T-R) fitting is performed so that the ingot axes coincide with the main shaft axis. The advantage of this forging method is that the central part contaminated by segregation becomes the central part of the crankshaft. Therefore, the resulting crankshaft has a clean surface and hence better strength and toughness characteristics.

Due to the high strength and low cost, the steel for fitting according to the present invention is suitable for any forgings other than crankshafts, such as propeller shafts and screw shafts for ships, built-in, respectively. Pivot shafts as well as hollow items where welding is not required.

BRIEF DESCRIPTION OF THE DRAWINGS

Giant. 1 and 2 are graphical representations of the relationship between nickel content and tensile strength and the relationship between tensile strength and nitrogen content of test steels. These graphs were prepared on the basis of data presented in Tab. 1 and 2. It is apparent from FIG. 1 that the maximum increase in strength is achieved by introducing nitrogen and any amount of V, Nb and Ta at 0.7% nickel in steel or less. From Figure 2 it can be seen that the most effective nitrogen content is 30 ppm or more, more preferably 40 ppm or more, and most preferably 50 ppm or more. Further, it can be seen that the effect of nitrogen decreases when its amount exceeds 60 to 70 ppm. This demonstrates that an excess of nitrogen (especially in amounts above 100 ppm) has no effect in terms of strength increase but increases the nitride content with a negative impact on toughness. Therefore, the nitrogen content should be less than 100 ppm, more preferably less than 80 ppm.

Giant. 3 is a graphical representation of DI values in test and comparative examples. This figure shows a comparison of the effect of the DI value from the samples and the comparative samples. It is evident from the figure that the forged steel specimens have higher DI values and thus better hardenability than the comparative specimens.

Giant. 4 is a graphical representation of the tensile strength versus the V content of steel and the N content of a solid solution. It can be seen that the samples containing V and nitrogen according to the requirement of the previously mentioned relation 1 have higher strength. As can be seen from the figure, if the total content of V, Nb and Ta is greater than 0.068%, the forging steel has sufficient strength when the amount of nitrogen dissolved in the solid solution is practically zero.

Giant. 5 is a graphical representation of a method for determining the nitrogen content of a solid solution.

Industrial applicability

As mentioned above, the present invention is directed to a new Ni-Cr-Mo steel for forging that is inexpensive and yet has high utility. Forged steel is characterized by a controlled low nickel content (to reduce costs) and high strength due to the presence of added trace amounts of V, Nb and Ta. The forging steel also has excellent hardenability, making it suitable for use with large size products, especially large crankshafts.

-6GB 298442 B6

Table 1

r- E “E R · φ cx £ 2Γ _J -J 10 CM 34 I WITH with 10 CM T CM what 01 Ol O O O IN" O CU about what 20 ABOUT WHAT CU 10 > oz _o E CL Q- b * co O Xj · m xř WHAT co CM xt σι co CO Xt Cb CM XT CM CO CM C0 01 b * b- WHAT 01 uo Xt O 10 00 10 and> 10 of < what about O XT o o o * what about o Xf o o O what about o * xT O O O UO O O o o> o o o * what about o bo o o what about o what about o what about © what about o what about o what about o what about o CD O O O* © o o o CM o o o eo H O O O O O O O O O O O O O O O O O O O O O E j5 XJ Z O O O O O O O O O O O O O O O O O O O © with? c Φ MM O > What about co uo o XT uo o what LO o what u> o IO IO o s o CM U> o co m o co 10 o 10 0 O uo 10 o o what o O C0 Φ o what o o CO o O CO xt o XT m o 10 uo O (0 O O O O O O O O O O O O O O O O O O O ‘Φ E o p CM CM 10 CM <0 CM 10 CM co CM u> CM 10 CU 1Λ CM <0 CM 10 CM CD CM co CM 3 co CM b <0 CM C0 01 XT CM CO CM XT CM Φ O O O O O O O O O O O O O O O O O O O O O O 0) Xt T ' 10 0> N Cl in- «XT CM * L0 XT CU 5 cm xT σι cm ' CM 01 ao 0) r ~ b01 01 01 b01 01 cu ' 01 CM * CM CM cm " WHAT XT CM * what 01 T ~ <0 01 CD 01 00 e> chin CM o o CM O o CM o o CM O o CM o o CM o 01 O o CM O o CM o O o tn o o CM o O O O o CM o 01 T “· O* o CM o o CM o w what about CO o o what § what about CO o o CO O o CO o o what about WHAT § CO O O what about CM o o CO O O CM O O CM O o CM O O CM O O what about what about XT o o O O O O O O O O O O O O O O O O O O O O c s CM CO χτ o XT o LO o 3 10 o uo O b * 01 b * bb * 01 b * co b * ABOUT WHAT xr 01 10 01 b ^ 01 b> what about cu O xr o O <r » X ” X ^- X ” O O O O O O O O O O T ~ XT CM co CM Μου co CM CM M CM «Τ CM O <0 CM - what CM what b> CM bCM CD CM Xt CM XT CM 10 CM XT cu O O O O O O O O O O O O O O O O O O O O O 10 CO io co O XT CM CO About Xt CD co O XT WHAT co what what b * co § WHAT co O XT 0> co σ> co CD CO 0> CO 0> CO O XT cu XT O O O O O O O O O O O O O O O O O O O O CM what XT it what b- 00 CT> O T ~ XJ CO * o Λ TJ ca TJ (ti TJ (0 TJ (ti T3 Cti ie Cti T3 <0 0 <0 TJ (0 áÉ jg YEAH áÉ áĚ £ O. and 'cl O. 'O. 'O. CL CL Q. O. *and (0 > Xti c> o ž r— O <o XX CL CM Ό WHAT JO »u. CL what about ® JC H— Q. JX L CL IO Ό CO uť Η » 0l <0 TJ φ 3c > * - CL Š • íš c δ ΙΟ a. O (ti > Jti CL > O uo CL o honor • honor c> o w O CL o (ti> Mti c> o k. O CL o (ti> * «c > o o CL > Mti> O w O CL o (ti> '<0 c. > 2 o CL o (ti> (0c> o w o OL O <0> '(ti c> o o CL <w of c> o km> O CL b * XI (0 xz Q- co TJ (0 32 Q 01 TJ (ti XX CL

Note: -: not measured

Table 2

Chemical composition% wt. | N in solid 1 solution (ppm) o CM • 5 CO CM kO co what CM CM O WHAT bCM 1 34 I ID 03 / O with CD CO «r · CM E o. Q. OF FROM I OS <o U> CM | 09 / O T— AT) i ss ¹ ....................... 03 / 00 About what 48 89 I 54 CM XT O O 03 hx M- < 0.003 I εοο'ο 0.003 I 0.003 I 0.003 I 0.003 I xt o o O 0.003 I about CM About I 0.005 I 0,005 i CD O O O | 0.014 0,036 I 0,014 I 0.017 I 0.025 I 0,003 | 0.003 I 0,003 CM O O O The O O O O O O O O O O O O O O O O O O O CM C3 o ” O -Q Z O O O O O O O O O O O O O O O O O O O O I 0,03 > 0.050 I 0.051 0,080 0.025 I 0.015 I : 0,016 | 0.055 I I 0,056) I 0,077) | 0,049 | | 0,048) 00 o <5 | 0,055) 0,097) lo '· 1Γ © I 0,049 | 0,070 | 0,047 | 0,084 I 0.051 | 0,043 O 2 IO ou o 5T CM o CM CM o ' 0.23 I xr CM o «· CM o ! 0.26 I 5T CM O T ' CM O | 0.26) I 0.25 I xr CM o I 0,27 | 0.23 ’ ID CM O CM o I 0,24 I 0,25 I 0.23 j 18'0) | 0.28 w o 00 <33 03 Ch 1.50 I 55 WHAT 03 / 00 xt CM 1,99 | | 1.50 I I 1.46 I I 1.96 I i ^. 03 / r- what 03 / b · 03 / T * 1 2.02 I 1.93 WHAT 03 / IN" O CM 11,98 | I 1.52 I CM O CM b · of I 0.75 I what O 1,52 | | 85'I-) CM O | 0J9 0,20 | CM o 1 1.44 03 / O Φ IN" O O T O* CM O I 0,20 I 0,21 03 / O" I 0.20 I I 0.19 I AND About CM o ” o CM o (Λ | 0,003 1 CO o o O 1800'0 CO o o O | 0.0031 | 0,002) 0,0021 | 0,002) | 0,002) CM O O O I 0,002] what about o | 0.003! | 0.004 | 0,003) ) 800'0 I | 0.002 I | 0.003 I | 0,003) CM O O o | 0.003 Μη I 0.98 I CM O | 0,60 | | 0.63 I | 0.99 I [0.98 | m bo ’ CO o Y— | 0.59 I I 1.03 I xr o what about I 1.07 03 / ID o γ— O IN" | 1.02 I I 1.06 I | 0.63 I O In “O. ώ 0.23 ! 0,24 | LO CM O 0,26 | XT CM O CO CM O 0,25 | «T CM O I 0.22 I to CM O co CM O CM o I 0,24 I 0,26 I 0.27 I I 0,24 I 0.25 I I 0,23) 03 CM o ' 1 0,23, I 0.25 I O 1 0,40 I I 0.39 I I 0,36 h * co O I 0.38 I I 0.34 I | 0,39 | | ivo | | 0,35 | | 0.39 I | 0.391 03 CO O I 0.40 I o Ί- Ο I 0.39 I | 0.38 I XT o | 0,38 | I 0.36 I 1 ° · 41 ° O xr o ‘ 1 Comparative example 12] | Comparative example | Comparative example Comparative Example Comparative Example | Comparative example | Example 10 | Example 11 I Comparative example 18) Comparative Example | Comparative Example 20 CM Ό <e £ Mm Q_ [Example 13) xr T— Bu m £ Mbu »0. | Example 15) | Comparative Example | Example 16 | Example 17] | Comparative Example 22] | Example 18 | Example 19

-8EN 298442 B6

Table 3

0,2% yield strength (MPa) Tensile stress (MPa) Elongation (%) Narrowing (%) Impact work (J) Value Dl (mm) Comparative Example 1 803.8 947.4 18.6 65.7 72.9 27 Mar: Example 1 764.4 915.3 18.7 67.2 64.2 30 Example 2 806.5 963.3 18.4 67.4 58.3 32 Example 3 769.3 817.3 20.0 70.2 60.2 34 Example 4 762.4 919.2 17.7 67.6 48.7 38 Example 5 760.5 909.4 20.0 71.2 55.1 41 Example 6 772.2 934.9 19.4 69.5 48.1 44 Comparative Example 2 720.3 886.9 20.1 70.6 106.4 27 Mar: Comparative Example 3 720.3 885.9 20.1 70.6 75.6 25 Comparative Example 4 699.7 872.2 17.8 69.4 42.7 23 Comparative example 5 705.6 887.9 18.7 66.7 42.2 22nd Comparative example 6 723.2 898.7 19.9 68.2 67.7 27 Mar: Comparative example 7 711.2 896.7 19.3 69.8 54.4 27 Mar: Comparative example 8 685.0 874.0 20.3 68.7 79.0 29 Comparative example 9 705.0 898.0 19.5 66.2 73.0 30 Comparative Example 10 677.0 873.0 20.3 68.5 81.3 31 Comparative example 11 702.6 888.9 19.3 63.9 39.2 24 Example 7 775.0 935.0 19.6 66.2 53.9 32 Example 8 825.0 989.0 12.7 64.6 46.3 32 Example 9 819.0 979.0 18.6 65.2 36.5 33

Table 4

0,2% yield strength (MPa) Tensile stress (MPa) Elongation (%) Narrowing (%) Impact work (d) Value Dl (mm) Comparative example 12 774 935 18.9 68.4 72.0 - Comparative example 13 770 930 19.1 68.6 74.0 - Comparative example 800 942 19.0 66.0 71.9 28 Comparative example 788 930 18.8 65.8 77.0 29 Comparative example 16 740 901 18.6 67.7 55.3 31 Comparative example 17 728 878 2,0 68.9 56.3 - Example 10 791 946.5 18.7 67.9 60.5 - They did 801 952 18.6 66.2 49.6 - Comparative example 18 779 928 18.1 65.0 47.3 25 Comparative example 19 722 900 19.7 68.6 94.0 - Comparative Example 20 724 904 19.5 67.2 75.0 - Example 12 775 935 19.6 66.2 54.0 32 Example 13 805 959 18.9 66.8 87.5 33 Example 14 803 966 17.7 66.0 64.0 33 Example 15 790 945 21.4 682 103.5 32 Comparative example 718 902 20.5 67.6 115.8 30 Example 16 775 924 19.1 65.2 83.0 33 Example 17 84 992 16.3 62.7 37.7 32 Comparative example 809 951 18.1 62.8 82.7 32 Example 18 783 930 17.2 62.1 45.0 29 Example 19 806 954 176 64.1 12.0 32

Note: -: not measured

-9EN 298442 B6

Claims (9)

PATENT CLAIMS 1. A high-strength forging steel, comprising: C 0.3 to 0.5% by weight, Si 0.1 to 0.4 wt.%, Mn 0.7 to 1.5% by weight, Cr 1.2 to 3.5 wt.%, Mo 0.1 to 0.6 wt.%, Ni not more than 0.7 wt%, at least one element selected from the group consisting of V, Nb and Ta 0.03 to 0.35 wt%; total, and N 30 to 250 ppm, the remainder being iron and unavoidable impurities, the forging steel being a microstructure composed mainly of bainite and martensite and containing N in solid solution and enough V, Nb and Ta to meet the condition expressed by the following expression 1 : [Total (wt%) V, Nb and Ta] + 0.001 χ [N (ppm) in solid solution]> 0.068 ... (1) High-strength steel forging according to claim 1, characterized in that the content of each component is specified as follows: C 0.36 to 0.45% by weight, Si 0.15 to 0.4 wt.%, Mn 0.8 to 1.2% by weight, Cr 1.5 to 3.0 wt. Mo 0.15 to 0.35% by weight, 0.035 to 0.17 wt. 3. The high-strength forging steel of claim 1, further comprising: Al 0.001 to 0.10 wt. High-strength steel forging according to claim 1, characterized in that it does not contain more than 0.006% by weight. open. 5. The high strength steel forging according to claim 1, wherein its Dl value is less than 30 mm, wherein the D1 value is a critical diameter of the steel product, the central part of which contains 50% martensitic hardness after turbidity in water. . A high-strength forging steel according to any one of claims 1 to 5, characterized in that it is used for the production of large-sized crankshafts. High strength forging steel according to claim 6, characterized in that it is used for the manufacture of large shaft crankshafts. A method of manufacturing a crankshaft, characterized in that the high-strength forging steel as defined in any one of claims 1 to 5. -10GB 298442 B6 A method of manufacturing a large-sized crankshaft for ships, characterized in that the high-strength forged steel is defined in any one of claims 1 to 5.