紧固件用SA-540合金钢的强韧化工艺研究

通过成分优化(/%:0.35～0.46C,0.6～1.0Cr, 1.50～2.05Ni, 0.18～0.32Mo, 0.1V)、冶炼工艺(3 t VIM+ESR)以及热处理工艺(再次热处理工艺：850℃2 h水冷+590℃5 h水冷)的合理制定，获得了满足指标要求的紧固件用高强高韧SA-540合金钢材料。结果表明，为确保SA-540合金钢高温300℃规定塑性延伸强度R_p0.2≥860 MPa,室温抗拉强度应控制在1150～1170 MPa,仅有20 MPa的强度范围。对于经850℃2 h淬火/水冷+560℃5 h回火/水冷调质处理后室温抗拉强度超标的紧固件，可再次通过重新淬火并提高回火热处理温度(850℃2 h淬火/水冷+590℃5 h回火/水冷)使合金钢拉伸性能满足指标要求。SA-540合金钢淬火后随回火的温度升高，呈现抗拉强度和屈服强度下降、伸长率和断面收缩率增加的变化趋势。添加0.1%V的SA-540合金钢，可明显提高合金钢的强度和塑性指标，但低温冲击性能降低明显。

Strengthening and Toughening of SA-540 Alloy Steel for Fasteners

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 exceeds 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.