A novel 2 GPa grade low alloy ultra-high strength steel and heat treatment process

doi:10.13251/j.issn.0254-6051.2024.03.028

Abstract

Abstract: A novel low alloy ultra-high strength steel 40CrMnSi2Mo with a 2 GPa grade tensile strength was developed by adding Si and small amount of Mo in the traditional 35CrMnSiA steel. The effects of quenching temperature (875-975 ℃) and tempering temperature (200-300 ℃) on the mechanical properties of the 40CrMnSi2Mo steel were systematically investigated. The results show a higher martensite starting temperature (Ms) decreases the formation tendency of twinning martensite structures, which benefits the toughness of the 40CrMnSi2Mo steel. A small amount of Mo can effectively inhibit the temper brittleness, which makes the impact absorbed energy of the steel tempered at 300 ℃ only decrease 7.7%, while tempering at 275 ℃ and 300 ℃ reduces the retained austenite quantity which leads to the decrease of fracture toughness. In general, a well combination of tensile strength (over 2 GPa) and fracture toughness (over 85 MPa·m^1/2) of the 40CrMnSi2Mo steel can be obtained when the studied steel quenched at 950 ℃ and tempered at 200 ℃ and 225 ℃, which outperform that of AISI 4340 steel and 300M steel. It is expected that this novel low-cost steel has a significant application prospect.

Key words: 2 GPa grade ultra-high strength steel, 40CrMnSi2Mo steel, heat treatment, tensile strength, fracture toughness

CLC Number:

TG142.1

Yu Linran, Yang Zhuoyue, Su Jie, Ding Yali, Liu Geng. A novel 2 GPa grade low alloy ultra-high strength steel and heat treatment process[J]. Heat Treatment of Metals, 2024, 49(3): 164-167.

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