X90管线钢的低温冲击韧性和断口形貌分析

Analysis on low temperature impact toughness and fracture morphologies of X90 pipeline steel

采用系列温度冲击试验法测定了X90管线钢在-100~0℃的冲击吸收能量和剪切断面率,用扫描电镜观察了不同温度下试验钢的冲击断口形貌。结果表明,该管线钢具有良好的低温冲击韧性,-80℃时的冲击吸收能量可达219 J,韧脆转变温度ETT50为-78.5℃、FATT50为-83.5℃;冲击断口形貌在0、-20℃下以大而深的等轴状韧窝为主,在-40、-60、-80℃下以抛物线韧窝为主,且韧窝尺寸和深度开始减小,在-100℃以扇形解理花样为主。试验钢在-80^-40℃温度区间,冲击断口发生显著分离现象,导致冲击吸收能量与剪切断面率曲线斜率减小。

The charpy impact absorbed energy and shear fracture ratio of X90 pipeline steel at the temperature range of -100-0 ℃ were determined by conducting series temperature impact tests.The fracture morpholoties at different temperatures were observed by means of SEM.The results show that the X90 pipeline steel has a good low-temperature impact toughness.The average impact absorbed energy at-80 ℃is 219 J; the ductile-btittle transition temperature of ETT50 is -78.5 ℃ and FATT50 is -83.5 ℃.The primary microscopic fracture morphology of the tested steel at 0 ℃ and -20 ℃ is equiaxed dimple with comparatively large size and depth, which turned into parabolic dimple at -40, -60,-80 ℃ and fan-shaped cleavage at -100 ℃.The obvious fracture seperation occurs at the temperature range of -80--40 ℃, which causes the slope decrease of impact absorbed energy and shear fracture ratio curve.