Steel for steel structure bolts

Abstract

The invention relates to steel for steel structure bolts. The steel material comprises, by mass, 0.1-0.3% of C, 0.10-0.35% of Si, less than or equal to 1.5% of Mn, less than or equal to 0.01% of S, less than or equal to 0.015% of P, 0.5-1.4% of Cr, 0.6-1.2% of Mo, the balance Fe and inevitable impurities, wherein tempering temperature is more than or equal to 600 DEG C during the final heat treatment of the steel material. According to the steel for the steel structure bolts, on the basis of the fracture morphology analysis according to practical steel structure application environment and existing application delayed breakage and fracture, the precipitation quantity and precipitation morphology of intergranular carbide are improved by optimizing alloy components, and the delayed fractureresistance of the material is improved. After the steel for the steel structure bolts is subjected to heat treatment, the tensile strength can reach 1040 MPa or more, and the upper limit can reach 1240 MPa. The fastener performance grade meets the GB / T1231-2006 standard 10.9S grade, and has excellent delayed fracture resistance.

Description

technical field [0001] The invention belongs to the field of fastener materials, and specifically relates to a high-strength steel structure bolt steel with good delayed fracture resistance and formability, which is suitable for the manufacture and production of large hexagon head bolts and flange surface bolts for steel structures. application. Background technique [0002] Steel structure large hexagonal head bolts have large size and specifications, large hexagonal opposite sides, large deformation of the head for upsetting and forging, and high requirements on the plasticity of the bolt material. For example, the common size of large hexagonal head bolts for railway steel structure bridges is M22 ~ M30. For example, in the GB / T1231-2006 standard, the 10.9S grade bolt materials are: 20MnTiB, ML20MnTiB, 35VB, etc. Medium and low carbon B steel has been widely used in the field of fasteners due to its low content of alloy elements, good plastic formability, and low cost. ...

AI Technical Summary

Problems solved by technology

[0008] In improving the delayed fracture resistance of the material matrix, the crack source area of ​​the delayed fracture bolts in practical applications shows intergranular fracture morphology, and the existing patents rarely have targeted solutions.

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