摘要
采用连铸坯生产18CrNiMo7-6齿轮锻件经正火后,机加工面出现了局部"花纹".为了明确"花纹"形成机理,采用多种分析方法进行研究,结果表明:"花纹"区和正常区均遗传了原连铸坯凝固枝晶偏析特征,但"花纹"区的枝晶间偏析聚集度更高、颜色更深.枝晶间偏析区碳化物多,显微硬度高,使加工面粗糙度增加,是导致机加工"花纹"的直接原因.
Abstract
After normalizing,heat-treatment and machining,local point-like"pattern"appeared on the machining surface of gear forgings produced of 18CrNiMo7-6 continuous casting billet.In order to clarify the formation mechanism of"pattern",a variety of analysis methods were used to study the"pattern"area,and the results showed that there were dark and light areas distributed between the"pattern"area,with a typical morphomorphic dendrite structure,the light area was the dendrite arm,and the elements were evenly distributed in this area,with a microhardness of 174.1HV;the dark area was the typical interdendrite segregation area,with higher carbon content,more carbides,with a microhardness of 217.4HV.Above results show that the coarse dendrites of raw materials and dendrite segregation are the direct causes of machining"pattern".Therefore,avoiding coarse dendrites and reducing dendrite segregation in the continuous casting production process are the key point to solve the surface pattern of forgings.After normalizing,the 18CrNiMo7-6 gear forgings produced by continuous casting billet,a local dotted"pattern"appeared on the machined surface.In order to clarify the formation mechanism of the"pattern",the"pattern"area was studied with a variety of analysis methods.The results show that:in the"pattern"area,there are alternatively distributed dark and light-colored microstructure areas,with typical solidification dendrite characteristics.The light-colored area is the dendritic crystal arm,and all elements are evenly distributed in this area,and the microhardness is 174.1HV.The dark area is the interdendrite segregation area,with high carbon content and more carbides,and a microhardness of 217.4HV.The above research results show that local dendritic crystal thickening and dendrite segregation of continuous casting billet are the direct causes of machined"pattern".Therefore,avoiding coarse dendrites and reducing segregation between dendrites in the process of continuous casting are the key measures to solve the"pattern"of forging.
万方数据