P91热轧无缝钢管的TMCP模拟

TMCP Simulation for Hot Rolling of P91 Seamless Steel Pipe

基于无缝钢管PQF工艺并结合其动态相变规律研究结果,制定P91热轧无缝钢管TMCP,使用Gleeble1500-D热模拟试验机对P91钢进行TMCP穿孔、连轧及定径热变形模拟,使用SEM和TEM观察变形各阶段的精细组织结构,分析P91钢管在TMCP条件下的微观组织遗传规律,研究了形变奥氏体的细化、强化及其马氏体相变行为。结果表明:对于P91钢管,采用TMCP,穿孔及连轧真应变达1.8的高温大变形易实现再结晶、细化形变奥氏体晶粒,990℃低温定径变形累积强化形变奥氏体、诱导马氏体相变,结合1℃/s的控制冷却得到了细化至0.1~0.5μm的马氏体板条。还发现,板条内的亚结构为2~20 nm的微细孪晶及高密度位错,析出了20 nm×100 nm的(Cr,Fe,Mo)23C6纳米级碳化物。这种组织特征遗传了P91钢管TMCP细晶强化、析出强化及相变强化效果,大大提高了P91钢管的力学性能,并由实际生产验证了P91钢管TMCP的可行性。

The thermal mechanical control processing(TMCP)for hot-rolling of P91 seamless steel pipe was designed based on the features of PQF process and the relevant research results of its dynamic phase transition regularities.Then the hot deformation processes for piercing,continuous rolling and sizing of P91 pipe were simulated by means of Gleeble-1500 D thermal-mechanical simulator.Whilst the microstructural evolution of P91 pipe during TMCP was assessed by SEM and TEM,and the refinement and strengthening of deformed austenite and its martensitic transformation behavior were also investigated.The results show that the large deformation at higher temperature with true strain of 1.8 during piercing and continuous rolling may benefit the recrystallization and the refinement of deformed austenite grains,while the accumulation of sizing deformation at 990℃may strengthen the deformed austenite and induce the martensitic transformation during the TMCP of P91 pipe.Martensite laths with a thickness of0.1~0.5μm were obtained via proper controlled cooling of 1℃/s.Fine twins of 2~20 nm and high density dislocations were found in Martensite laths.The nanoscale precipitates of(Cr,Fe,Mo)23 C6 with a size of about 20 nm×100 nm were found between the laths of the martensite.This structure characteristic is the imprint of the TMCP effect of fine grain strengthening,precipitation strengthening and phasetransformation strengthening,which can greatly improve the mechanical properties of P91 pipe.The feasibility of TMCP for P91 pipe was verified by the actual production.