海洋平台用钢EH36-Z35连续冷却转变及正火工艺

Continuous cooling transformation and normalizing process of EH36-Z35 steel for offshore platform

利用热模拟试验机绘制了海洋平台用钢EH36-Z35的连续冷却转变曲线,并用光学显微镜观察不同正火工艺下的显微组织,找出了生产现场出现正火欠热组织的原因,并优化了正火工艺。结果表明,EH36-Z35钢的Ac_(3)为859℃,在<2℃/s的冷速下可获得高温转变组织铁素体+珠光体;在相同的冷却制度下,820℃和850℃正火处理后存在正火欠热组织,经890℃正火处理后获得了铁素体+弥散珠光体的合格组织。通过改变加热速度和冷却速度得到EH36-Z35钢较为合理的正火工艺为从室温用时130 min加热至890℃并保温10 min,先以5℃/s的冷速冷却到730℃,再以0.2℃/s的冷速冷却到650℃,然后以0.15℃/s的冷速冷却到400℃,之后空冷。

Continuous cooling transformation curves of EH36-Z35 steel for offshore platform were obtained by using thermal simulation testing machine,and the microstructure of the steel under different normalizing processes was studied by using optical microscope to find out the reason of normalizing underheated structure appeared in production and to optimize the normalizing process.The results show that the Ac_(3) of the EH36-Z35 steel is 859 ℃,and the high temperature transformation structure of ferrite+pearlite can be obtained under the cooling rate of 2 ℃/s.Under the same cooling process,underheated structure appears after normalizing at 820 ℃ and 850 ℃,while normal ferrite plus dispersed pearlite is obtained after normalizing at 890 ℃.Through changing the heating rate and cooling rate,the reasonable normalizing process of the EH36-Z35 steel is as taking 130 min to heat from room temperature to 890 ℃,holding for 10 min,cooling to 730 ℃ with a cooling rate of 5 ℃/s,then cooling to 650 ℃ with a cooling rate of 0.2 ℃/s,and then cooling to 400 ℃ with a cooling rate of 0.15 ℃/s,followed by air cooling.