北极海洋平台用Q355E热轧H型钢连续冷却转变规律

Continuous cooling transformation of Q355 Ehot rolled H-beam steel for offshore platform in an Arctic environment

在实验室利用Gleeble-3500热模拟试验机对3种Nb、V微合金化Q355E热轧H型钢进行了连续冷却转变规律测试,研究了冷却速度对试验钢组织与硬度的影响。结果表明:在冷速为0.5℃/s时,组织中开始出现贝氏体;冷速大于7℃/s时,珠光体转变即终止。在中等冷速下,Nb的加入促进了贝氏体的形成,抑制了铁素体与珠光体的形核;并且Nb的加入使铁素体转变区右移。Cr的加入降低了较高冷速下铁素体与珠光体相变点,并促进了高冷速下马氏体的形成。由于受V析出的影响,含V试验钢在冷速为1℃/s时其硬度曲线有一个"波谷"。3种试验钢的冷速在0.5~3℃/s之间时,试验钢可获得强韧性较好的细小准多边形铁素体、少量珠光体与贝氏体的复合组织。

Continuous cooling transformation of three kinds of Nb or V micro-alloyed Q355 Ehot rolling H-beam steels were tested to study the influence of cooling rate on microstructure and micro-hardness by using a Gleeble-3500thermal-mechanical simulation machine in the laboratory.The results show that bainite begins to grow when the cooling rate is as low as 0.5℃/s,and the pearlite transformation is terminated when the cooling rate is greater than 7℃/s.With the addition of Nb,the formation of bainite is promoted and the nucleation of ferrite and pearlite is restrained in the medium cooling rate.And Nb is added to the tested steel,the ferrite phase area is shifted to the right.The addition of Cr decreases the phase transition temperature of ferrite and pearlite at higher cooling rate,and promotes the formation of martensite at high cooling rate.Due to the influence of vanadium precipitation,the hardness of the V-bearing tested steels is smallest at a cold speed of 1℃/s.Fine quasi polygonal ferrite and a small amount of pearlite and bainite with better strength and toughness can be obtained when the cooling rate of three kinds of tested steel is between 0.5℃/s and 3℃/s.