大型预硬化718塑料模具钢不同区域的抛光性能

Polishing Performance of Different Zones in Large-size Plastic Die Steel 718

用光学显微镜和扫描电镜对截面尺寸为1 360mm×715mm的大型预硬化718塑料模具钢块不同区域的显微组织进行了分析,用原子力显微镜对不同显微组织的表面形貌进行了观察,分析了珠光体/回火贝氏体混合组织区域的抛光去除机制。结果表明:模具钢边部为均匀的回火索氏体组织,边部和心部的中间部位存在带状偏析,组织为回火贝氏体、珠光体以及偏析处形成的索氏体+粒状碳化物,心部为珠光体组织;回火索氏体组织细小,回火碳化物分布均匀,具有良好的抛光性能;回火贝氏体组织由于具有粗大的贝氏体铁素体板条和粗大的不均匀分布的颗粒状碳化物,其抛光性能较差;珠光体以及偏析处形成的异常组织的抛光性能也较差,可观察到橘皮形貌;具有不同组织的表面,其组织间的屈服强度相差越大,则表面抛光性能越差。

The microstructure of pre-hardened 718 plastic die steel bloom with a cross-section size of1 360mm×715 mm was studied using OM and SEM.The surface morphology of different microstructure were characterized by AFM.The polishing removal mechanism of the microstructure containing tempered bainite and pearlite was analyzed.The results show that the microstructure at the edge of the tested bloom was uniform tempered sorbite.Segregation banding was found in the area between the edge and the core,and the microstructure in this area was tempered bainite,pearlite,sorbite+ granular carbide in segregation banding.The microstructure in core was pearlite.The tempered sorbite had excellent polishing performance due to fine microstructure and uniform carbide distribution.The polish performance of tempered bainite decreased because of containing large bainitic ferrite laths and uniformly distributed coarse carbides.Pearlite and abnormal microstructure in segregation banding had poor polishing performance,the morphology like orange peel could be observed.The larger the yield strength difference of the microstructure on the surface having different microstructure,the poorer the surface polishing performance.