High strength bolt having excellent hydrogen embrittlement resistance

A high-strength bolt, hydrogen embrittlement resistance technology, used in bolts, nuts, threaded fasteners, etc., to achieve the effect of less alloying elements and excellent recyclability

Inactive Publication Date: 2006-08-02
KOBE STEEL LTD +1
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[0026] When using tempered martensitic steel or martensite + ferrite steel that has been generally used as a high-strength steel, it is considered that the delayed fracture due to hydrogen is caused by the old austenitic steel. In order to reduce the susceptibility to delayed failure, the following methods are generally used as mentioned in the prior art in order to reduce the susceptibility to delayed failure by accumulating hydrogen and forming voids at the crystal grain boundaries, etc., and then generating the voids. , Carbide etc. are uniformly and finely dispersed as a hydrogen trap site to reduce the diffusible hydrogen concentration. However, even if many carbides and the like are dispersed as hydrogen trap sites, the trapping ability is limited, so delayed destruction due to hydrogen cannot be sufficiently suppressed.

[0027] For this reason, the inventors have reconsidered a specific method for achieving high hydrogen embrittlement resistance (delayed destruction resist...

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Abstract

The present invention provides a high strength bolt that has excellent hydrogen embrittlement resistance. The high strength bolt having excellent hydrogen embrittlement resistance which bolt comprises 0.20 to 0.60% of C, 1.0 to 3.0% of Si, 1.0 to 3.5% of Mn, higher than 0% and not higher than 1.5% of Al, 0.15% or less P, 0.02% or less S, and balance of iron and inevitable impurities, and the structure includes: 1% or more residual austenite; 80% or more in total content of bainitic ferrite and martensite; and 10% or less (may be 0%) in total content of ferrite and pearlite in the proportion of area to the entire structure, and also the mean axis ratio (major axis/minor axis) of the residual austenite grains is 5 or higher and the bolt has tensile strength of 1180 MPa or higher.

Description

technical field [0001] The present invention relates to a high-strength bolt (bolt) excellent in hydrogen embrittlement resistance, and particularly relates to a high-strength bolt having a tensile strength of 1180 MPa or more, which suppresses hydrogen embrittlement or self-generated cracks and delays failure, which are problematic for bolts. Background technique [0002] As general steel for bolts, low-alloy high-toughness steels, especially SCM435 or SCM440, are widely used. These steels have a tensile strength of 120-130kgf / mm 2 (1180-1270MPa) high strength, but when higher strength is required, tempering is required. [0003] However, the quenched and tempered bolts obtained by quenching and tempering tend to cause delayed failure called sudden failure if a long time passes after installation. Therefore, in order to solve such a problem, for example, Patent Document 1 points out that it is only necessary to add alloy elements such as Cr, Mo, Ti, V to the basic compone...

Claims

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Application Information

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IPC IPC(8): C22C38/06C21D9/00C21D11/00C22C38/16C22C38/08F16B33/00
Inventor 汤濑文雄齐藤贤司池田周之杉本公一
Owner KOBE STEEL LTD
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