Low-carbon bainitic cold-work-strengthened non-quenched and tempered steel with excellent delayed fracture resistance

Abstract

The invention relates to low-carbon bainitic cold-work-strengthened non-quenched and tempered steel with excellent delayed fracture resistance, which belongs to the technical field of alloy steel, and is applicable to manufacturing grade 10.9 high-strength bolts with tensile strength above 1000MPa. The steel comprises the following chemical components by weight percent: 0.06-0.15% of C, not more than 0.10% of Si, 1.80-2.40% of Mn, not more than 0.010% of P, not more than 0.008% of S, 0.10-0.40% of Cr, 0.0005-0.003% of B, 0.05-0.15% of V, 0.01-0.08% of Ti, 0.005-0.03% of RE, 0.01-0.05% of Al, 0.004-0.01% of N and the balance of Fe and other inevitable impurities; simultaneously, the elements of V and Ti further meet the following relational expression of a strengthening parameter theta: V(%) plus Ti(%) is not less than 0.10 and not more than 0.20; and a metallurgical structure is a granular bainite. The low-carbon bainitic cold-work-strengthened non-quenched and tempered steel has the advantages of not only having good plasticity and cold working performance, but also having excellent delayed fracture resistance and being used for manufacturing the grade 10.9 high-strength bolts with the delayed fracture resistance.

Description

technical field [0001] The invention belongs to the technical field of alloy steel, and in particular provides a low-carbon bainitic cold-strengthened non-quenched and tempered steel with excellent delayed fracture resistance, which is suitable for making 10.9-grade high-strength bolts with a tensile strength above 1000 MPa. Background technique [0002] Fasteners such as high-strength bolts are widely used, but in the manufacturing process of high-strength bolts made of traditional medium-carbon steel or medium-carbon alloy steel, softening or spheroidizing annealing treatment is usually performed at least once, which not only takes a long period, but also consumes a lot of energy. . In this regard, people have developed a non-quenched and tempered steel wire rod that can omit softening or spheroidizing annealing and quenching and tempering treatment, that is, the wire rod produced by controlled rolling and controlled cooling, and then undergoes a certain amount of cold def...

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Problems solved by technology

[0004] For some quenched and tempered steels for delayed fracture resistant high-strength bolts currently developed internationally, the technical idea is to increase the carbon content, increase or add the content of alloy elements to achieve good delayed fracture resistance while increasing the strength. properties, which tend to worsen the cold workability of the steel, and more importantly, these measures often lack consideration of mobile dislocation suppression

A bainitic steel for grade 10.9 bolts introduced in the literature (Boratto F et al. Wire J. Inter., 1992, (9): 129-134), not only the higher Cr (0.60%) content is not only suitable for cold working The performance is unfavorable, and the lack of consideration of delayed fracture resistance limits its scope of application

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