回火工艺对BJ890钢组织和力学性能的影响

Effect of tempering process on microstructure and mechanical properties of BJ890 steel

以BJ890臂架用无缝钢管为实验对象,利用光学显微镜、扫描电子显微镜,电子背散射衍射、透射电子显微镜、万能试验机以及冲击试验机等测试手段,研究了不同调质工艺对钢的微观组织与力学性能的影响规律。结果表明:随回火温度升高,钢中马氏体组织分解,碳化物析出,强度降低,韧性升高。BJ890钢的最佳调质工艺为920℃淬火+620℃回火。在620℃回火温度下,60min内晶粒尺寸基本不变;120min回火时,晶粒显著增大。随回火时间延长,碳化物析出长大,从“短棒状”逐渐转变为“球形”。同时钢强度降低,冲击韧性升高,但回火60min以上冲击韧性变化不明显。最佳热处理工艺为920℃+14min淬火,620℃+60min回火。钢材抗拉强度为1025MPa,屈服强度为983MPa,伸长率为19.56%,-20℃冲击功为110J,-40℃冲击功为69J,ETT韧脆转变温度为-30.1℃,AFTT韧脆转变温度为-43.4℃。

The microstructure and mechanical properties of BJ890 seamless pipe for boom were studied using optical microscope(OM),scanning electron microscope(SEM),electron backscatter diffraction(EBSD),transmission electron microscope(TEM),universal testing machine and impact testing machine.The results show that with the increase of tempering temperature,the martensite decomposes,the carbides precipitate,the strength decreases,and the toughness increases.The optimal quenching and tempering process for BJ890 steel is 920℃quenching+620℃tempering.Tempering at 620℃within 60min,the grain size remains basically unchanged,and the grain size obviously increase after tempering for 120min and the precipitation and growth of carbides were observed.With the increase of tempering time,the shape of carbides is gradually changing from"short rod shape"to"spherical shape".Moreover,the strength of the tested steel decreases and the impact toughness increases,but the change of impact toughness is not obvious after tempering for more than 60min.The optimal heat treatment process is 920℃for 14min quenching,620℃for 60min tempering.The tensile strength is 1025MPa,the yield strength is 983MPa,the elongation is 19.56%,the impact energy at-20℃is 110J,the impact energy at-40℃is 69J,the ductile-brittle transition temperature is-30.1℃in ETT code,and the ductile-brittle transition temperature is-43.4℃in AFTT code.