高钢级厚壁管线钢低温断裂韧性控制技术研究

Research on Controlled Technology of Low Temperature Fracture Toughness on High-grade Thick-wall Pipeline Steels

针对厚规格X80管线钢低温断裂韧性控制难题,从理论层面揭示了DWTT断裂韧性的影响机制,并通过实验室轧钢试验和工业试验证实了相变前奥氏体晶粒尺寸和室温组织中的马奥岛是影响厚规格X80管线钢DWTT性能的两大主要因素。借助热模拟试验研究得出了细化奥氏体晶粒尺寸和马奥岛的主要技术措施。结果表明,尽量避免粗轧高温区在5%~8%变形、适当提高Nb含量、提高粗轧最后两道次变形量和缩短间隔时间,可以使奥氏体再结晶晶粒尺寸控制在20μm以下;适当降低终轧温度、提高冷却速率、选择合理的终冷温度,可以将组织中马奥岛体积分数降低到10%以下,平均颗粒尺寸减小到1μm以下。

This research focuses on the DWTT fracture toughness control problem of large diameter and thick gauge X80 pipeline steel and reveals the influence mechanism of DWTT fracture toughness in theoretically level. The austenite grain size before transformation and the M/A constituent in the room temperature are the two main factors to influence the performance of DWTT property of the thick gauge X80 pipeline steel, which have been proven by laboratory rolling experiments and industrial experiments. The main technical measures to refine the austenite grain size and martensite-austenite constituent are studied by means of thermal simulation experiments. The results show that by avoiding the deformation at 5%~8% deformation during rough rolling at high temperature zone, increasing the Nb content properly, increasing the last two-pass deformations of the rough rolling and shortening interval time are effective ways to control the recrystallized grain size of austenite below 20 μm;by decreasing the final roll temperature properly,increasing the cooling rate,and selecting an appropriate final cooling temperature can reduce the volume fraction of M/A constituent under 10% with average grain size below 1 μm.