T_(8/5)时间对X80管线钢热影响区组织和韧性的影响

为了研究T_(8/5)时间对X80管线钢热影响区粗晶区组织和性能的影响,在Gleeble 3500热模拟试验机上对其分别进行4个焊接工艺(T_(8/5)时间分别为21、27、33和40s)的加热冷却后,对粗晶区夏比冲击性能进行测试,并对其显微组织和冲击后断口形貌进行分析。结果表明,T_(8/5)时间为21s的焊接工艺下热影响区粗晶区具有较稳定且优异的低温夏比冲击性能;随着T_(8/5)时间由21延长至40s,热影响区粗晶区的低温冲击韧性下降,断裂方式由韧性断裂向脆性断裂转变,-20℃下冲击断裂方式由部分韧性断裂转变为完全脆性断裂;延长T_(8/5)时间促进了热影响区粗晶区近熔合线侧长条大块状M/A组元的形成,使得贝氏体板条间距变大。

Effect of T8/5 time on microstructure and toughness in heat affected zone of X80 pipeline steel

The effect of T8/5 time on the coarse-grained microstructure and properties in heat affected zone of X80 pipeline steel was investigated by Gleeble 3500 thermal simulator with four T8/5 time ranged from 21 to 40 s. The Charpy V-Notch impact toughness on a coarse grained region was measured,and the microstructure and the fracture morphology after the impact toughness measurement was analyzed. The results showed that the coarse-grained heat affected zone with T8/5 of 21 s exhibits excellent and steady low temperature Charpy V-Notch impact toughness. The low temperature impact toughness decreases as the T8/5 time increases from 21 to 40 s,and the fracture mechanisms is transformed from ductile fracture to brittle rupture. The impact fracture model changes from a partly ductile fracture to a totally brittle fracture as well at －20 ℃. Prolonging the T8/5 time can promote the formation of long strip M/A constituents in the coarse-grained heat affected zone and the space between the bainitic laths.