控轧控冷工艺对厚规格X80M热轧钢带DWTT性能的影响

Effects of TMCP on DWTT property of thick X80M hot rolled steel strip

采用2 250 mm热轧线生产的厚规格(21.4 mm和22.0 mm)X80M钢带,其低温落锤撕裂(DWTT)断口剪切面积分数提升一直是热轧带钢领域的关键技术攻关课题,通过合适的成分设计与控轧控冷工艺调控,以实现细小均匀的组织形态控制,是确保产品DWTT性能的关键基础。采用低碳微合金化(Mn-Nb-Ti-Cr-Mo-Ni-Cu)成分体系设计,利用热模拟试验与金相组织分析以及DWTT性能检测相结合的方法,系统研究了铸坯加热温度、均热时间对高温奥氏体晶粒尺寸的影响和变形工艺对再结晶奥氏体晶粒尺寸的影响,以及轧后冷速对组织转变的作用。研究结果显示,低碳微合金化X80M钢采用1 160~1 180℃的加热温度、40~120 min的均热时间,粗轧道次间隔时间不大于20 s,临界再结晶区形变率不小于25%,未再结晶形变率为68%,以及轧后以冷却速率为20~30℃/s冷却至温度430℃进行卷取的控轧控冷工艺,可获得晶粒度为11~12级、组织主要为针状铁素体+粒状贝氏体+少量残余马/奥(M/A)复相组织的钢带。产品低温(-20℃)DWTT剪切面积不小于85%的合格率可达98%以上,钢带和钢管的DWTT韧脆转变温度均小于-20℃,材料具有良好的抗低温止裂性能,并在生产实践中验证了该工艺的有效性。热轧钢带制管后已批量应用于陕京四线和中俄东线工程中。因此,研究结论具有较高的实际生产指导价值,为提高厚规格X80M热轧带钢低温DWTT性能提供了有效的技术途径。

The improvement of the percentage of low-temperature drop hammer tear(DWTT)fracture shear area in thick specification(21.4 mm and 22.0 mm)X80M steel strips produced on the 2250 mm hot rolling line has always been a key technical research topic in the field of hot rolled strip steel,through the appropriate composition design and controlled rolling and cooling process,achieving a fine and uniform microstructure is the key foundation to ensure the DWTT performance of the product.A low-carbon microalloying(Mn-Nb-Ti-Cr-Mo-Ni-Cu)composition system design was adopted,combined with thermal simulation experiments,metallographic structure analysis,and DWTT performance testing methods to systematically study the effects of heating temperature and soaking time on high-temperature austenite grain size,deformation process on recrystallized austenite grain size,and the effect of post rolling cooling rate on microstructure transformation.The research results show that low-carbon microalloyed X80M steel adopts a heating temperature of 1160-1180℃,a soaking time of 40-120 min,and the controlled rolling and controlled cooling process that a rough rolling pass interval time not greater than 20 s,a critical recrystallization zone deformation rate not less than 25%,an unrecrystallized deformation rate of 68%,and cools to a temperature of 430℃at a cooling rate of 20-30℃/s after rolling,which the steel strips with a grain size of 11-12 grades and a microstructure mainly composed of acicular ferrite,granular bainite,and a small amount of residual martensite/austenite(M/A)duplex structure can be obtained,that the qualification rate of the low-temperature(-20℃)DWTT shear area not less than 85%of the produced steel strip can reach over 98%,and the DWTT ductile brittle transition temperature of both steel strip and steel pipe is less than-20℃,indicating that the material has good low-temperature crack resistance performance.The effectiveness of this process has been verified in production practice,and the hot-rolled steel strip has been widely used in the natural gas transportation of the Shaanxi Beijing Fourth Line and the China Russia East Line.Therefore,the research conclusion has high practical production guidance value and provides an effective technical approach to improve the low-temperature DWTT performance of thick specification X80M hot-rolled strip steel.