热处理工艺及氮含量对20CrMoH奥氏体粗化行为的影响

EFFECT OF HEATREATMENT PROCESSES AND NITROGEN CONTENT ON COARSENING BEHAVIOR OF 20CrMoH AUSTENITE

利用马弗炉热处理和光学金相显微镜对20CrMoH钢原始奥氏体金相组织进行了观察和晶粒尺寸测量,研究了热处理工艺和不同N含量对20CrMoH钢原始奥氏体组织生长规律的影响。研究表明:在热轧组织均匀和细小的情况下,热处理工艺和氮含量均对钢中奥氏体晶粒的影响显著。当N含量为78 ppm时,890℃热处理时晶粒长大不明显;随着加热温度升高,晶粒异常长大现象逐渐显著;当加热温度达到950℃时,晶粒粗化明显,并呈现出不均匀长大现象,出现混晶。当N含量为110 ppm时,890℃和950℃热处理时晶粒长大程度不明显;但是当加热温度达到甚至超过1000℃时,原始奥氏体晶粒出现快速、不均匀长大现象,加热2 h以内即出现混晶。整体而言,热处理温度对20CrMoH材料的原始奥氏体晶粒尺寸和均匀性有显著影响。相比较而言,110 ppm氮含量较78 ppm氮含量材料抵抗晶粒粗化的能力大幅度提升。氮含量的增加能够较大幅度提高20CrMoH齿轮钢的热处理粗化临界温度,拥有更宽的工艺窗口,更有助于产品后续热处理工艺的制定与执行。

The austenitic microstructure and grain size of 20CrMoH steel was observed and measured by Muffle furnace heat treatment and optical metallography microscope.The effects of heat treatment and different N content on the growth of the original austenitic microstructure of 20CrMoH steel were studied.The results show that the influence of heat treatment and nitrogen content on austenite grain is significant when the microstructure is uniform and fine.When the N content is 78 ppm,the grain growth is not obvious at 890℃.With the increase of heating temperature,the abnormal grain growth becomes more and more obvious.When the heating temperature reaches 950℃,the grain coarsening is obvious,and the phenomenon of uneven growth appears,and mixed crystals appear.When the N content is 110 ppm,the grain growth is not obvious at 890℃and 950℃.However,when the heating temperature reaches or even exceeds 1000℃,the original austenite grains grow rapidly and unevenly,and mixed crystals appear within 2 hours of heating.Overall,the heat treatment temperature has a significant effect on the original austenite grain size and uniformity of 20CrMoH materials.In comparison,the resistance to grain coarsening of materials with 110 ppm nitrogen content is significantly improved than that with 78 ppm nitrogen content.The increase of nitrogen content can significantly increase the critical temperature of 20CrMoH gear steel for heat treatment coarsing,and has a wider process window,which is more conducive to the formulation and execution of subsequent heat treatment processes of products.