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High-strength steel member

a high-strength steel and member technology, applied in the field of high-strength steel members, can solve the problems of deterioration in ductility or toughness, cracking after quenching, etc., and achieve the effect of excellent delay in fracture resistan

Inactive Publication Date: 2020-04-30
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The technical effect of this patent is to provide a high-strength steel that is resistant to delayed fractures and hydrogen embrittlement.

Problems solved by technology

However, absorption of hydrogen into steel members from atmosphere during heating may cause quenching crack after quenching.
Further, for example, a low tempering temperature of from 150 to 200° C. as in the case of high-strength steel members may cause deterioration in ductility or toughness after tempering, since hydrogen absorbed into the steel members during quenching is not sufficiently released by the tempering.

Method used

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  • High-strength steel member

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examples

[0134]Hereinafter, the present disclosure will be more specifically described with reference to Examples. It is noted that the respective Examples are not intended to limit the scope of the present disclosure.

[0135]A test material having a chemical composition shown in Table 1 was heated to a temperature shown in Table 2, thereafter hot-rolled at a finish rolling temperature shown in Table 2, and cooled to 700° C. at an average cooling rate shown in Table 2 for rolling to a diameter ϕ of 20 mm, thereby producing a circularly notched test piece (notch depth of 2 mm, notch bottom radius of 0.25 mm, and notch angle of 60 degrees) made of a round rod steel having a size of 10 mm in diameter ϕ×50 mm in length L.

[0136]The test piece was heated in a carburizing heating atmosphere or in a condition simulating RX gas heating (1 atm, mixed atmosphere of 50% of hydrogen and Ar, heating temperature of 1,000° C., and heating duration of 30 minutes), cooled to 20° C. with water at a cooling rate ...

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Abstract

A high-strength steel member having a predetermined chemical composition, having a tensile strength of 1,000 MPa or higher, containing 0.10% or more of, in terms of percent (%) by area, at least one Ti precipitate that has an average size of from 30 to 200 nm in terms of an average equivalent circle diameter and is selected from the group consisting of a Ti carbide, a Ti nitride, and a composite compound thereof, at a location of 1 mm in depth from a surface of the steel member, and containing 0.5 ppm by mass or more of non-diffusible hydrogen that is released in a temperature range of from 400 to 800° C. in a thermal desorption hydrogen analysis.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a high-strength steel member.BACKGROUND ART[0002]Among steel members used for machines, automobiles, bridges, or buildings, steel members that are required to have particularly high strength are, for example, those in which chromium steels or chromium-molybdenum steels defined in JIS G 4104 or JIS G 4105 have been subjected to a quenching / tempering treatment. Some steel members, such as gears, are carburized and then quenched to have high strength.[0003]Quenching is made after heating steel members to high temperatures at which austenite phases are formed. However, absorption of hydrogen into steel members from atmosphere during heating may cause quenching crack after quenching. Further, for example, a low tempering temperature of from 150 to 200° C. as in the case of high-strength steel members may cause deterioration in ductility or toughness after tempering, since hydrogen absorbed into the steel members during quenching is n...

Claims

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Application Information

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IPC IPC(8): C22C38/50C22C38/32C22C38/28C22C38/26C22C38/24C22C38/22C22C38/20C22C38/06C22C38/04C22C38/02C22C38/00C21D8/06C21D6/00
CPCC22C38/04C22C38/001C22C38/24C22C38/22C22C38/28C21D6/005C21D6/008C22C38/26C22C38/20C22C38/50C22C38/004C21D6/002C21D8/065C22C38/02C22C38/32C22C38/06C21D1/06C21D8/06C22C38/38C22C38/58C22C38/44
Inventor YAMASAKI, SHINGOMANABE, TOSHIYUKI
Owner NIPPON STEEL CORP
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