初始组织对双向温轧中碳钢组织演变的影响

Effect of initial microstructure on microstructure evolution of bidirectional warm rolled medium carbon steel

利用扫描电镜(SEM)和电子背散射衍射技术(EBSD)对马氏体以及铁素体+珠光体组织中碳钢在550℃双向温轧后的组织演变进行了研究。结果表明:淬火马氏体温轧后渗碳体颗粒在铁素体基体上分布比较均匀,小角度晶界所占比例很高,4道次轧制后亚晶粒尺寸约为1.35μm,部分铁素体晶粒发生动态再结晶,形成大角度晶界包围的细小的等轴晶粒;而铁素体+珠光体作为轧前组织,温轧后渗碳体颗粒和亚晶粒主要集中在原珠光体区,4道次后平均亚晶粒尺寸约为1.79μm,等轴细小的铁素体晶粒主要在原珠光体与铁素体边界分布。双向温轧是淬火马氏体获得碳化物颗粒与超细晶铁素体均匀混合组织的有效方法。

The microstructure evolution of quenched martensite and ferrite ＋ pearlite of medium carbon steel after bidirectionally warm rolling at 550 ℃ were investigated by means of scanning electron miscroscope（ SEM） and electron backscatter diffraction（ EBSD）. The results indicate that when the initial microstructure is lath martensite,the cementite particles distribute on ferrite matrix homogeneously after four pass warm rolling. Because of dynamic recovery,low angle grain boundaries present a higher proportion and the subgrain size is 1. 35 μm after four passes rolling. In addition,small amount of equiaxed ultrafine ferrite grains which surrounded by high angle grain boundaries can be obtained due to dynamic recrystallization. When the microstructure before rolling is ferrite ＋ pearlite,the cementite particles and subgrains are mainly located at the areas of former pearlite colonies,the average subgrain size is 1. 79 μm after four passes warm rolling. Besides,a few equiaxed ultrafine ferrite grains with high angle grain boundaries distribute on the boundaries of pearlite and ferrite. Bidirectional warm rolling for quenched martensite is an effective method to form ultrafine ferrite with uniformly distributed cementite particles in medium carbon steel.