改善大截面20SiMn3MoV贝氏体钢组织和性能的热处理工艺

利用X射线衍射分析(XRD)、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)等研究了930℃加热空冷及930℃加热水冷-空冷交替冷却对Φ53 mm无碳化物贝氏体钢20SiMn3MoV组织和力学性能的影响。结果表明:930℃加热空冷处理后,实验钢的组织较粗大,为贝氏体铁素体(BF)和分布在贝氏体铁素体板条之间的残留奥氏体(AR)组织,晶粒度等级为6.5~7.5级,抗拉强度为1288 MPa,-40℃冲击吸收能量为22.8 J。经930℃加热水冷-空冷交替冷却处理后(先水冷到400~450℃后空冷),实验钢的组织细小,为贝氏体铁素体(BF)和分布在贝氏体铁素体板条之间的残留奥氏体(AR)组织,晶粒度等级为7.5~8.0级,抗拉强度为1393 MPa,-40℃冲击吸收能量为38.8 J,表明水冷-空冷交替冷却工艺细化了实验钢的晶粒,提高了实验钢的强度及韧性,与930℃加热空冷相比,实验钢的强度提高了8.2%,低温韧性提高了70%。

Heat treatment process for improving microstructure and properties of large section 20SiMn3MoV bainitic steel

The effects of normalizing at 930℃with air-cooling and normalizing at 930℃with alternate water cooling and air-cooling on microstructure and mechanical properties of carbide-free bainitic steel 20 SiMn3 MoV were studied by means of X-ray diffraction(XRD),optical microscope(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that after normalizing at 930℃with air cooling,the microstructure of the experimental steel is coarse,and composed of bainite-ferrite(BF)and retained austenite(AR)distributed between the bainite-ferrite lath,the grain size grade is 6.5-7.5,the tensile strength is 1288 MPa,and the impact absorption energy at-40℃is 22.8 J.After normalizing at 930℃followed by alternate water cooling and air-cooling(first water-cooling to 400-450℃and then by air cooling),the microstructure of the experimental steel is fine,and composed of bainite-ferrite(BF)and retained austenite distributed between the bainite-ferrite lath,the grain size grade is 7.5-8.0,the tensile strength is 1393 MPa,and the impact absorption energy at-40℃is 38.8 J,indicating that the alternate water-cooling and air-cooling process can refine the grains of the experimental steel and improve the strength and the toughness.Compared with that after normalizing at 930℃with air-cooling,the tensile strength and the low-temperature impact toughness of the steel after normalizing at 930℃with alternate water cooling and air-cooling increase by 8.2%and 70%,respectively.