弛豫及冷却过程对大变形管线钢组织及性能的影响

Influence of Relaxation Time and Cooling Rate on Microstructure and Hardness of X70 Pipeline Steels with High Deformation Resistance

利用Gleeble-3800模拟X70大变形管线钢奥氏体再结晶区和非再结晶区的双道次变形、弛豫及加速冷却过程。采用金相显微镜、SEM等试验方法,研究了空冷驰豫时间及冷却速度对显微组织的影响。结果表明:从770℃弛豫到700℃后开始快冷的冷速为8.1℃/s时,驰豫时间(53.8～100 s)对组织、硬度的影响较小;不同弛豫时间对应的组织均为双相组织,马氏体/贝氏体呈岛状分布在铁素体基体上,铁素体晶粒大小不一,碳化物多且密集;从770℃弛豫到700℃后采用水冷时,随着驰豫时间延长,双相组织中铁素体增多,硬度降低;相同驰豫时间及水淬方式冷却试样的硬度及马氏体/贝氏体数量明显高于8.1℃/s冷却的试样。

The process of rolling in the recrystallized region and the nonrecrystallized region of austenite, relaxation and cooling in X70 pipeline steels with high deformation resistance were simulated using Gleeble-3800. The influence of relaxation time and cooling rate on the microstructure and hardness was investigated by OM and SEM. The results indicate that the influence of relaxation time on the microstructure and hardness was not obvious when cooling at 8.1 ℃/s after relaxation from 770 ℃ to 700 ℃. Dual-phase microstructure with martensite/banite inlands in ferrite matrix can be obtained for relaxation time between 53.8 s and 100 s, which has different size ferrite grain with dense carbides. The amount of ferrite increases and hardness decreases with relaxation time increasing, when water-quenched after relaxation from 770℃ to 700℃. Under the same relaxation time, the hardness and amount of martensite/banite with water quenching are higher than those with cooling rate of 8.1 ℃/s.