大型筒节2.25Cr-1Mo-0.25V钢的组织遗传及轧后冷却控制

Structure heredity and controlled cooling after rolling of heavy cylinder 2. 25Cr-1Mo-0. 25V steel

根据大型筒节的轧制和轧后冷却模型,模拟大型筒节轧制截面的应变率和轧后冷却速度曲线;结合Gleeble-3800对金属小试样2.25Cr-1Mo-0.25V钢进行了热压缩模拟实验,得出了多道次压缩的流变应力曲线;分析了小试样热变形后不同冷却方式对其组织形貌的影响和对后期正火晶粒细化的作用。结果表明,2.25Cr-1Mo-0.25V钢轧制过程心部大部分区域温度不变;轧制压下率低,心部应变率不足10%;道次间歇时间长,静态软化率高达95%,奥氏体晶粒回复长大;轧后空冷过程心部冷却速度缓慢,冷却后基体主要为粒状珠光体组织,经后期热处理晶粒不易细化,是造成组织遗传的主要原因;增大轧后冷却速度和降低冷却转变温度有利于后期热处理晶粒细化,采用喷淋-空冷联合冷却能充分利用大型筒节的轧后余热,冷却过程热应力较小,有利于促进后期热处理组织细化。

The strain rate and cooling rate curves of heavy cylinder cross section in rolling were obtained by the models of rolling and cooling of heavy cylinder. The flow stress curves of many times-hit hot compression tests were obtained by hot compression test of small metal samples2. 25Cr-1Mo-0. 25 V steel on Gleeble-3800. The effects of different cooling methods on the microstructure and morphology of small metal samples after hot deformation and the grain refinement after heat treatment were analyzed. The results show that the temperature in most of center part of heavy cylinder is constant in the rolling process. The rolling reduction ratio is low; especially the strain rate of center part is less than 10%. The interval in pass is long and the static softening ratio is as high as 95%,so the grain size of austenitic is recovery. The cooling rate of the center part is slow with the air cooling after rolling,and the matrix is mainly spheroidal pearlite,which leads to the grain refinement difficult and becomes the main reason for the phenomenon of structure heredity. The increase of the cooling rate and the decrease of the temperature of cooling transformation are benefit to the grain refinement. The usage of spray-air combined with cooling can make full use of the rolling heat,and the thermal stress is less,which is benefit to the grain refinement after the heat treatment.