高强度管线钢焊接热影响区显微组织精细表征

Fine Characterization of High Strength Pipeline Steel Welding HAZ Microstructure

为了认清焊接过程显微组织的演变过程,对显微组织进行了精细化表征。结合多年来对高性能管线钢的研究实践,认为粗晶热影响区性能较易通过调整热输入量来改善,而对于临界粗晶热影响区,由于二次热循环峰值温度不可避免地会落在Ac1~Ac3的两相区,致使高C含量的脆性链状M-A形成,且其占比含量高,尺寸粗大,极易成为脆性裂纹的起裂源,进而恶化低温冲击韧性。为了改善临界粗晶区韧性,必须严格控制脆性M-A尺寸、分布及含量。有效方案是合理设计管线钢关键合金成分(Nb、Ni等),控制粗晶区奥氏体尺寸,促进二次热循环过程奥氏体相变更完全,以此来抑制链状M-A的形成和改善低温韧性。

In order to understand the evolution of microstructure in welding process, fine characterization of microstructure is carried out. Based on years of research and practice of high performance pipeline steel, it is concluded that the performance of coarse crystal heat affect zone(HAZ) is easy to be improved by adjusting heat input. For the critical coarse crystal HAZ, the peak temperature of the secondary thermal cycle inevitably falls into the two-phase zone between Ac1 and Ac3 , resulting in the formation of brittle chain M-A with high C content. Due to the high proportion and large size of M-A, it is easy to become the initiation source of brittle crack, which further worsens the low-temperature impact toughness. Therefore, in order to improve the toughness of critical coarse crystal zone, the size, distribution and content of brittle M-A must be strictly controlled. The effective scheme is to reasonably design the key alloy composition of pipeline steel , such as Nb/Ni and so on, control the austenite size of coarse crystal zone, promote the complete change of austenite phase in the secondary thermal cycle process, so as to inhibit the formation of chain M-A and improve the low temperature toughness.