40Cr钢转向节锻造后表面鼓包研究

40Cr钢汽车转向节锻坯常常出现鼓包等缺陷。为此,对产生鼓包的锻件进行了化学成分分析、金相检验和能谱分析。结果表明:锻件的成分符合要求,鼓包金属为碳含量为3.5%~4.0%的铸铁,鼓包附近基体金属有0.4~0.5 mm的增碳层。鼓包是连铸坯表面的粘渣在锻造过程中以液态形式存在于锻件表面,随后冷却过程中凝固并与基体金属焊合而产生的。通过优化铸造工艺、稳定浇铸过程及选用黏度小、熔点低和熔速快的保护渣等,消除了40Cr钢转向节锻件的鼓包缺陷。

Study on Surface Bulge of 40Cr Steel Knuckle after Forging

40Cr steel forgings used for automobile knuckle offered frequently a defect in the form of bulge.For this fact,the forging which developed bulge was subjected to chemical composition analysis,microstructure survey and EDS.The results demonstrated that chemical composition of the forging conformed the requirement;the bulge metal was a cast iron having 3.5 to 4.0%C;the base metal near the bulge exhibited 0.4 to 0.5 thick carburized layer.The process of bulge formation was follows:sticky slag on the continuously cast steel stock was melted into liquid and left on the surface of forging during forging,then solidified and was bonded to the base metal during cooling.The bulge defect of the 40Cr steel forging used for knuckle has been eliminated by optimization of the casting technology,stabilization of the casting process and selection of the protecting slag having low viscosity,low melting point and fast melting speed.