CN-121986181-A - Steel material, blank, and method for producing component

Abstract

The steel material has a predetermined chemical composition, wherein when the Al content in mass% is [ Al ], and the N content is [ N ], the [ Al ] and the [ N ] satisfy a predetermined relationship, and when the length of a line segment connecting the center of gravity of the cross section and the surface of the cross section closest to the center of gravity is d/2, and when the position of the surface, which is a distance d/2 in the center of gravity direction, is d/2, and the position of the surface, which is a distance d/4 in the center of gravity direction, is d/4, the solid solution Al amount is 0.018 mass% or more and the solid solution N amount is 0.009 mass% or more in a cross section perpendicular to the rolling direction, and when the number density of MnS, which is 1.0-10.0 μm 2 , in the d/4, is 70.0/mm 2 or less and the number density of MnS, which is more than 10.0 μm 2 , is 374.0 mm or less, in the d/4.

Inventors

• He Tianai
• YUYA MASATO
• JIANG TOUCHENG
• SUZUKI TAKAHISA

Assignees

• 日本制铁株式会社

Dates

Publication Date

20260505

Application Date

20240925

Priority Date

20231011

Claims (5)

1. 1. A steel material characterized by having a chemical composition comprising C：0.10~0.30%、Si：0.03~1.50%、Mn：0.35~1.50%、P：0.002~0.020%、S：0.002~0.050%、Cr：0.05~2.30%、Al：0.020~0.060%、N：0.011~0.030%、Ti：0.007% or less by mass, 0.100 or less by mass of Nb 、Mo：0~0.40%、O：0~0.0050%、V：0~0.15%、B：0~0.0050%、Cu：0~0.40%、Ni：0~0.30%、Sn：0~0.100%、Ca：0~0.0050%、Mg：0~0.0050%、 and the balance Fe and impurities, When the Al content in mass% is [ Al ] and the N content is [ N ], the [ Al ] and the [ N ] satisfy the following formulas (1) and (2), In a cross section perpendicular to a rolling direction, when d/2 is a length of a line segment connecting a center of gravity of the cross section and a surface of the cross section closest to the center of gravity, d/2 is a position of a distance d/2 from the surface in the center of gravity, d/4 is a position of a distance d/4 from the surface in the center of gravity, In either of the d/2 portion and the d/4 portion, the solid-solution Al amount is 0.018 mass% or more, and the solid-solution N amount is 0.009 mass% or more, In the d/4 portion, the number density of MnS with an area of 1.0-10.0 μm 2 is 70.0/mm 2 or less, the number density of MnS with an area exceeding 10.0 μm 2 is 4.0/mm 2 or less, 1.50≤[Al]/([N]-(-0.0013×[Al]/[N]+0.007))≤5.00 (1) 1.50≤[Al]×([N]-(-0.0013×[Al]/[N]+0.007))×10000≤10.00 (2)。
2. 2. A steel product as claimed in claim 1, wherein, The chemical composition contains at least one selected from the group consisting of, in mass%, more than 0% and not more than 0.007% of Ti, more than 0% and not more than 0.100% of Nb 、Mo：0.03~0.40%、O：0.0001~0.0050%、V：0.01~0.15％、B：0.003~0.0050%、Cu：0.01~0.40%、Ni：0.01~0.30％、Sn：0.010~0.100%、Ca：0.0001~0.0050%, and 0.0001 to 0.0050% of Mg.
3. 3. A billet having a chemical composition comprising C：0.10~0.30%、Si：0.03~1.50%、Mn：0.35~1.50%、P：0.002~0.020%、S：0.002~0.050%、Cr：0.05~2.30%、Al：0.020~0.060%、N：0.011~0.030%、Ti：0.007% or less by mass, 0.100 or less by mass of Nb 、Mo：0~0.40%、O：0~0.0050%、V：0~0.15%、B：0~0.0050%、Cu：0~0.40%、Ni：0~0.30%、Sn：0~0.100%、Ca：0~0.0050%、Mg：0~0.0050%、 and the balance of Fe and impurities, When the Al content in the chemical composition is [ Al ] and the N content is [ N ], the [ Al ] and the [ N ] satisfy the following formulas (1) and (2), At a position 5mm inward from the surface in a direction perpendicular to the surface, the number density of MnS having an area of 1.0 to 10.0 [ mu ] m 2 is 70.0 pieces/mm 2 or less, the number density of MnS having an area exceeding 10.0 [ mu ] m 2 is 4.0 pieces/mm 2 or less, The amount of precipitated Al is 0.012 mass% or more, The average size of AlN is 90nm or less, 1.50≤[Al]/([N]-(-0.0013×[Al]/[N]+0.007))≤5.00 (1) 1.50≤[Al]×([N]-(-0.0013×[Al]/[N]+0.007))×10000≤10.00 (2)。
4. 4. The blank according to claim 3, wherein, The chemical composition contains at least one selected from the group consisting of, in mass%, more than 0% and not more than 0.007% of Ti, more than 0% and not more than 0.100% of Nb 、Mo：0.03~0.40%、O：0.0001~0.0050%、V：0.01~0.15％、B：0.003~0.0050%、Cu：0.01~0.40%、Ni：0.01~0.30％、Sn：0.010~0.100%、Ca：0.0001~0.0050%, and 0.0001 to 0.0050% of Mg.
5. 5. A method for producing a component, comprising a vacuum carburizing step of vacuum carburizing the blank according to claim 3 at a temperature range of 900 to 1000 ℃.

Description

Steel material, blank, and method for producing component Technical Field The present invention relates to a steel material, a blank obtained using the steel material, and a method for manufacturing a member using the blank. The present application claims priority based on japanese patent application No. 2023-175737 of the application of japan, 10/11 of 2023, the contents of which are incorporated herein by reference. Background In recent years, further enhancement of mechanical driving members such as gears has been demanded due to miniaturization of driving units accompanied by electric driving of automobiles, construction vehicles, and the like. In addition, in the gear, a bending load is applied to the teeth when the teeth mesh. Therefore, the teeth of the gear are required to have bending fatigue strength. Moreover, in the gear, the tooth surfaces slide with a short period from each other. Therefore, on the tooth surface, inhibition of pitting is required. That is, mechanical parts typified by gears used in automobiles, construction vehicles, and the like are required to have not only bending fatigue strength but also surface fatigue strength (pitting corrosion characteristics). It is known that carburizing treatment (carburizing and quenching) is very effective for improving the surface fatigue strength of a mechanical component. In general, therefore, mechanical parts such as gears are often manufactured by machining steel materials such as bar steel as a blank by forging or the like to form a blank, cutting the blank into a part shape as required, and then performing carburizing treatment (carburizing and quenching). As the carburizing treatment, a vacuum carburizing treatment for reducing the CO 2 discharge amount is used instead of the gas carburizing treatment which has been conventionally used in many cases. The gas carburizing treatment is a surface treatment performed by heating an object to a carburizing temperature in a carburizing gas, and the vacuum carburizing treatment is a surface treatment performed by heating an object to a carburizing temperature under vacuum, then introducing the carburizing gas into an atmosphere at a low pressure, and holding the object in the vacuum atmosphere so that a diffusion period for diffusing carbon is set at least once. In the vacuum carburization treatment, a hydrocarbon gas is used as a carbon supply source. Therefore, the vacuum carburization process does not generate CO 2 in the carburization reaction. Therefore, the vacuum carburization treatment can produce a member in a process friendly to the earth environment. On the other hand, in the carburization treatment, since the object is heated to the carburization temperature, abnormal grain growth occurs in the steel material, which may cause a decrease in fatigue characteristics and the like. Particularly in the vacuum carburization treatment, the surface is denitrified while being heated to the carburization temperature, and thus abnormal grain growth is more likely to occur. To solve the problem of suppression of abnormal grain growth during carburization, patent document 1 discloses a rolled steel bar for surface hardening excellent in grain coarsening prevention property during high-temperature carburization, which is composed of steel containing C：0.05~0.25%、Si：0.05~2.0%、Mn：0.01~1.5%、S：0.005~0.2%、Cr：0.4~1.5%、N：0.0085~0.0219%、Al：0.058~0.062%、Nb：0.038~0.100%、Ti：0.008~0.012%, in mass% and the balance being Fe and unavoidable impurities, and in which all of carbides, nitrides and carbonitrides, two or more of which are adhered, or the number of composite precipitates is 0.5x10 12/m 2 or less, each of which contains at least one element selected from Al, nb and Ti in equivalent circle diameter of 100nm or more. Further, patent document 2 discloses a high-temperature carburized steel which contains 0.001 to 0.10% Nb (meaning of mass%), 0.01 to 0.15% Al, 0.01 to 0.03% N, and a content [ N ] of N satisfying the formula (1), and a solid solution Al amount after hot working represented by the formula (2) of 0.01 to 0.10%, respectively, as a high-temperature carburized steel capable of preventing occurrence of coarsening, abnormal growth, and the like of austenite grains at the time of carburization treatment. Patent document 2 discloses that by containing an appropriate amount of Al in a solid solution state without precipitating Al after hot working, fine composite precipitates of AlN, nbC or NbCN and AlN can be obtained at the time of subsequent heat treatment, which exhibit pinning effect at the time of high temperature carburization, and can suppress coarsening of crystal grains to high temperature. Further, regarding coarsening of crystal grains at the time of vacuum carburization, for example, patent document 3 discloses, as a coarse blank for vacuum carburization capable of suppressing abnormal crystal grain growth of a treated surface portion or the like at the time of vacuum carburization, a coar