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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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  • Abstract
  • Description
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Problems solved by technology

However, in this technology, if you want to get more excellent hydrogen embrittlement resistance, you need to further improve

Method used

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Embodiment Construction

[0026] When tempered martensitic steel or martensite + ferrite steel, which is generally used in the past, is used as a high-strength steel, it is believed that the delayed fracture caused by hydrogen is caused by the old austenite Hydrogen accumulates at grain boundaries and the like to form voids, etc., which are then generated starting from this portion. Therefore, in order to reduce the susceptibility to delayed fracture, the following method is generally adopted as mentioned in the conventional art, that is, , Carbide etc. are evenly and finely dispersed as hydrogen capture sites to reduce the concentration of diffusible hydrogen. However, even if many carbides and the like are dispersed as hydrogen trapping sites, the delayed destruction due to hydrogen cannot be sufficiently suppressed because the trapping ability is limited.

[0027] For this reason, the present inventors re-examined a specific method for realizing high hydrogen embrittlement resistance (delayed failur...

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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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