Rolled steel bar or wire for hot forging
A hot forging and wire rod technology, applied in heat treatment furnaces, manufacturing tools, heat treatment equipment, etc., can solve problems such as coarse grains and difficulty in ensuring toughness
Active Publication Date: 2014-12-31
NIPPON STEEL CORP +1
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- Application Information
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Problems solved by technology
) grain coarsening, so it is difficult to ensure good toughness especially at low temperature
Method used
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[0087] Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" of content of each element means "mass %".
[0088] (A) Chemical composition of bar or wire
[0089] C: 0.10 to 0.20%
[0090] C has the effect of increasing the martensite hardness of the steel after quenching, and also has the effect of suppressing the coarsening of crystal grains during heating for quenching by forming TiC together with Ti. In order to sufficiently secure this effect, it is necessary to contain 0.10% or more of C. On the other hand, C increases the hardness of the HAZ, resulting in weld cracks. Therefore, an upper limit is set, and the content of C is set at 0.10 to 0.20%. The C content is preferably not less than 0.12% and not more than 0.18%.
[0091] Si: 0.01 to 0.30%
[0092] Si is an element effective in deacidification of steel and also contributes to improvement of hardenability. In order to ensure these effects, it is necessary to conta...
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Abstract
Disclosed is a rolled steel bar or wire for hot forging, which has a chemical composition that contains 0.10-0.20% of C, 0.01-0.30% of Si, 1.00-2.30% of Mn, 0.040% or less of S, 0.10-0.80% of Cr, 0.010-0.080% of Al, 0.0002-0.0050% of B, 0.010-0.080% of Ti and 0.0020-0.0080% of N, with the balance made up of Fe and impurities, while limiting P to 0.040% or less, Cu to less than 0.10%, Ni to less than 0.10%, Mo to less than 0.05% and V to 0.01% or less among the impurities, in said chemical composition [Ti - 3.4N = 0.001] being satisfied, Ceq represented by a specific formula of C, Si, Mn, Ni, Cr, Mo and V being 0.57 or less, and DI represented by a specific formula of C, Si, Mn, P, S, Cr, Ni, Mo and Cu being 70-170. The rolled steel bar or wire for hot forging has 10 or more Ti precipitates having a circle-equivalent diameter of 0.07-1.0 µm and 10 or more Ti precipitates having a circle-equivalent diameter of 0.01-0.05 µm in an area of 100 µm2. Since the rolled steel bar or wire for hot forging is weldable and has excellent strength and toughness of the matrix and excellent toughness of HAZ, the rolled steel bar or wire for hot forging is suitable as a material for underbody components of automobiles such as a spindle.
Description
technical field [0001] This invention relates to rolled bar or wire for hot forging. Specifically, it relates to a steel bar or wire rod for hot forging that is weldable and has excellent strength and toughness (especially toughness at low temperature). Background technique [0002] Vehicle running parts such as axles require high strength and excellent toughness. [0003] As the raw material of the above-mentioned parts, medium-carbon "carbon steel and alloy steel for machine structures" such as S48C specified in JIS G 4051 (2009) and SCM 435H specified in JIS G 4051 (2009) are generally used. [0004] Usually, the above-mentioned steel is heat-treated by quenching and tempering after hot forging, and then processed into a predetermined shape by cutting. Furthermore, in order to join with another member, processing, such as bolt hole processing and spline shape processing, is performed, and a desired part is finished. [0005] However, machining of high-strength componen...
Claims
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IPC IPC(8): C22C38/00C21D8/06C22C38/58
CPCC22C38/54C22C38/50C22C38/46C22C38/42C22C38/06C21D9/0075C22C38/02C22C38/58C22C38/44C22C38/00C21D8/065
Inventor 桥口国男长谷川达也松本齐江头诚棚桥努塚本达也新川雅树
Owner NIPPON STEEL CORP