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·m1/2)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.
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