深海用X70管线钢焊接粗晶热影响区组织和性能研究

Study on Microstructure and Properties of CGHAZ of X70 Pipeline Steel for Deep Sea

采用Gleeble-3800热模拟机对深海用X70厚壁管线钢进行热模拟试验,研究在不同焊接线能量下粗晶热影响区的组织转变及性能变化。结果表明:不同焊接线能量下焊接粗晶热影响区组织主要是板条状贝氏体和粒状贝氏体。冷却时间t_(8/5)在12~50s内,适量的粒状贝氏体以不同位向分割板条贝氏体,M-A组元呈块状弥散分布,粗晶区的韧性最好。t_(8/5)<12s时,组织由粗大的板条束贝氏体和条状M-A岛组成;t_(8/5)>50 s时,粒状贝氏体和多边形铁素体增多。这些组织导致冲击韧性降低。

The thermal simlation tests of X70 thick wall pipeline steel for deep sea were carried out by using Gleeble-3800 simulator. The microsturcture and corresponding properties of coarse grain heat affected zone （CGHAZ） under different thermal cycles with various heat inputs were studied. The results show that the microstructure of CGHAZ mainly consists of slab bainite ferrite and granular bainite under different linear welding energies. When the cooling time t8/5is within 12-50 s, a proper amount of granular bainite splits slab bainite ferfite in different directions, the M-A component is distributed in block, and the toughness of CGHAZ is the best. When the t8/5 is lower than 12 s, the microstructure is composed of coarse slab bainite ferrite and strip M-A islands. When the t8/5 is bigger than 50 s, the granular bainite and polygonal ferrite increase. These microstructure leads to the reduction of impact toughness.