In this paper

the SA-540 high strength and high toughness steel for fasteners is obtained by the optimization of composition(/%:0.35-0.46C

0.6-1.0Cr

1.50-2.05Ni

0. 18-0.32Mo

0. 1V)

the reasonable formulation of smelting process(3t VIM+ ESR)and heat treatment process(re-heat treated at 850 ℃ for2 h water cooling+590 ℃ for 5 h water cooling). The results show that in order to ensure the specified plastic elongation strength R

p0.2

≥860 MPa of SA-540 steel at 300 ℃

the tensile strength at room temperature should be controlled in the range of 1150- 1170 MPa

with only a strength window of 20 MPa. For the materials whose tensile strength at room temperature exceed

s the standard after quenching at 850℃ for 2 h/water cooling +tempering at 560℃ for 5h/water cooling

the tensile properties of the alloy steel can meet the index requirements by reheating and quenching at 850 ℃ for2 h/water cooling + tempering at 590 ℃5 h/water cooling. With the increase of tempering temperature after quenching

the tensile strength and yield strength of SA- 540 steel decrease

and the elongation and reduction of area of steel increase. Adding 0. 1% vanadium to SA-540 steel can obviously improve the strength and plasticity of steel

but the low-temperature impact property decreases significantly.