高钢级X100管线钢的韧性和显微组织

Toughness and microstructure of high grade X100 pipeline steel

通过OM、SEM、示波冲击和落锤试验研究了高钢级X100管线钢的显微组织、冲击和落锤断裂性能。结果表明,终冷温度为400℃时,试验钢具有更好的显微组织、冲击韧性和落锤断裂性能。400℃终冷试验钢组织均匀,LB、GB和M/A组元细小,原始奥氏体被LB板条束分割细化;终冷温度提高至520℃,试验钢组织均匀性变差,GB和M/A组元粗化,LB对组织的分割细化作用减弱。落锤断裂过程中,原始奥氏体晶界(PAGB)、LB和AF改变裂纹扩展方向,提高止裂性能。冲击试验温度降低,400℃终冷试验钢冲击吸收能量(E)、裂纹形成能(E1)、韧性扩展能(E2)和脆性裂纹扩展能(E3)变化不大。表征材料韧脆倾向的-60℃冲击(E2+E3)/E1值为2.83,呈韧性断裂;520℃终冷试验钢E、E1、E2和E3逐渐降低,-60℃冲击(E2+E3)/E1值为0.95,呈脆性断裂。

High grade X100 pipeline steel's microstructure, impact fracture and drow weight tear test ( DWTT) properties were investigated by OM, SEM, instrumented.impact test and DWTT test.The results indicate that the tested steel shows better toughness and DWTT properties with the 400 ℃ final cooling temperature.The test steel's microstructure consists of fine lath bainite ( LB ) , granular baintie ( GB) , acicular ferrite ( AF) and martensite/austenite ( M/A) constituents.Prior austenite grain is segmented and refined by LB lath.Final cooling temperature raises to 520 ℃, microstructure's uniformity becomes worse, GB and M/A constituents coarsen, LB's refining effect weakens.Crack propagation direction changes at prior austenite grain boundary ( PAGB) , LB and AF during the DWTT fracture process. With the reducing of impact test temperature, the 400℃final cooling test steel's impact energy ( E) , crack formation energy ( E1 ) , ductility fracture propagating energy ( E2 ) and brittle fracture propagating energy ( E3 ) change a little.The ( E2 +E3 )/E1 value which characterizes the materials'ductile-brittle transition tendency at -60 ℃is 2.83, taking on ductile fracture.When the final cooling temperature raises to 520 ℃, the E, E1, E2, E3 decrease significantly, and the (E2 +E3)/E1 value at -60 ℃is 0.95, taking on brittle fracture.