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High-strength steel product excelling in fatigue strength and process for producing the same

A technology of fatigue strength and manufacturing method, which is applied in the field of auto parts, can solve the problems that cannot meet the requirements of bending fatigue strength, and achieve the effect of improving the effect

Inactive Publication Date: 2005-11-23
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in this method, the maximum value of fatigue strength is only about 770MPa, which cannot meet the recent requirements for bending fatigue strength.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0080] After wire rolling the steel materials having the composition shown in Table 1, warm forging was performed under the conditions shown in Table 2 to obtain a product of 60×60×120 mm. From this product, tensile test pieces, rotational bending fatigue test pieces, and machinability test pieces were taken. Table 2 lists the results of research on ferrite grain size, cementite content, pearlite content, tensile strength, rotational bending fatigue strength and machinability of the products. The amount of deformation during warm forging was calculated based on the finite element analysis method, with the coefficient of friction of the forged surface being 0.3. In addition, the machinability was evaluated as follows: if the tool life in the outer cylindrical cutting test is the same as or higher than the SC material of JISG5101, ◯ is marked, and if it is inferior to the SC material, × is marked.

[0081] As can be seen in Table 2, according to the present invention, if the st...

Embodiment 2

[0085] After wire rolling the steel materials having the composition shown in Table 3, warm forging was performed under the conditions shown in Table 4 to obtain a base material of 60×60×120 mm. Tensile test pieces, rotational bending fatigue test pieces, and machinability test pieces were taken from the base material. Next, induction hardening was performed on the rotating bending fatigue test piece under conditions of heating temperature: 900° C. and frequency: 12 kHz. The ferrite grain size, cementite amount, pearlite amount, tensile strength, machinability, prior austenite grain size of the quenched structure after induction hardening, and the Table 4 also lists the results of the study on the rotational bending fatigue strength of the test pieces. The amount of deformation during warm forging was calculated based on the finite element analysis method, with the coefficient of friction of the forged surface being 0.3. In addition, the machinability was evaluated as follow...

Embodiment 3

[0092] After wire rolling the steel material having the composition shown in Table 5, warm forging was performed under the conditions shown in Table 6 to obtain a base material of 60×60×120 mm. Tensile test pieces, rotational bending fatigue test pieces, and machinability test pieces were taken from the base material. Next, nitriding treatment was performed on the rotating bending fatigue test piece under the conditions shown in Table 6. The results of a study on the ferrite grain size, cementite amount, pearlite amount, tensile strength, machinability, ferrite grain size of the surface layer after nitriding treatment, and rotational bending fatigue strength of the base metal And recorded in Table 6. The amount of deformation during warm forging was calculated based on the finite element analysis method, with the coefficient of friction of the forged surface being 0.3. In addition, the machinability was evaluated as follows: if the tool life in the outer cylindrical cutting ...

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Abstract

A high-strength and high-fatigue-strength steel having a base metal strength of 1000 MPa or more and a rotating bending fatigue strength of 550 MPa or more is provided. The steel contains 0.3-0.8 percent by mass of C, 0.01-0.9 percent by mass of Si, 0.01-2.0 percent by mass of Mn, and Fe and unavoidable impurities as the remainder. The steel has a ferrite-cementite structure having a grain size of 7 mum or less or a ferrite-cementite-pearlite structure having a grain size of 7 mum or less. A surface metal of the steel after high-frequency induction quenching has a martensite structure having a prior austenite grain size of 12 mum or less. Alternatively, a surface metal of the steel after nitriding has a fine structure having a ferrite grain size of 10 mum or less.

Description

technical field [0001] The present invention relates to a high-strength steel material with excellent fatigue strength suitable for automobile parts using bar steel, such as constant velocity joints, transmission rods, crankshafts, connecting rods, wheel axles, and the like, and a manufacturing method thereof. Background technique [0002] Products such as connecting rods and axles are manufactured by high-temperature forging or roll forming, followed by cutting. Products such as constant velocity universal joints, transmission rods, crank shafts, and wheel shafts are subjected to high-temperature forging or roll forming after annealing or spheroidizing annealing to improve machinability, and then high-frequency quenching is performed partially or entirely , or manufactured by nitriding treatment. In order to reduce the weight of the vehicle body, high strength and long fatigue life are required for products for such applications. [0003] Conventionally, it has been known...

Claims

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Application Information

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IPC IPC(8): C21D8/06C22C38/00C22C38/04C22C38/58
Inventor 林透松崎明博
Owner JFE STEEL CORP
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