EFFECT OF HEATREATMENT PROCESSES AND NITROGEN CONTENT ON COARSENING BEHAVIOR OF 20CrMoH AUSTENITE
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 1 000 ℃,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.
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