低温下X70大变形管线钢的冲击韧性和断口特征

Impact toughness and fracture surface features of X70 high deformability pipeline steel at low temperatures

通过夏比V型缺口冲击试验研究X70大变形管线钢20℃至-100℃的低温韧性,采用扫描电镜观察断口形貌并分析其断裂特征,讨论冲击温度、断口分离、分层裂缝等对管材低温韧性的影响,以及断口分离的影响因素。结果表明：随着冲击温度降低,纵向管材的冲击吸收能量没有明显减小,横向管材的冲击吸收能量以9%降速逐渐减小,-100℃时管材并没有发生脆性转变;随着温度降低而形成管材断口分离并趋于严重;断口起裂区和纤维区的微观形貌较为相似,以韧窝断裂为主,而放射区的微观形貌差异较大,温度低于-40℃时,放射区呈韧窝、滑移分离、解理断裂交互出现的混合型断裂特征;断口分离的主要影响因素是冲击温度和试样缺口方向,-40℃为管材冲击吸收能量转变和断口分离现象产生的临界温度点。

The impact toughness and fracture surface features of X70 high deformability pipeline steel at 20 ℃ to-100℃ were investigated by means of charpy V-notch impact test and scanning electron microscopy.The effects of impact temperature,fracture separation and delamination crack on impact toughness of the steel and the influencing factors for fracture separation were discussed.The results show that the impact absorbed energy of the transverse pipeline steel decreases gradually at a rate of 9% as the impact temperature decreasing,while the longitudinal pipeline steel still has high impact absorbed energy,and the ductile to brittle transition temperature of the pipeline steel is lower than-100 ℃.The macroscopic examination of the fracture surface is characterized by the phenomenon of fracture separations,and tends to be more serious as the impact temperature decreases.The morphology of the fracture initiation zone and the fiber zone is similar,mainly dimple fracture,while the crack propagation zone has great difference.When the temperature is lower than-40 ℃,the fracture characteristics of the crack propagation zone are ductile dimple,slip separation and cleavage fracture.The main influencing factors of fracture separation are the impact temperature and the notched direction of the specimen.-40 ℃ is the critical temperature point for the transition of impact absorbed energy of pipe and the phenomenon of fracture separation.