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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。
In the laboratory, three kinds of Nb, V microalloyed Q355E hot rolled H-section steels were continuously cooled and transformed by Gleeble-3500 thermal simulator. The influence of cooling rate on microstructure and hardness of the test steels was studied. The results show that when the cooling rate is 0.5 ℃ / s, bainite begins to appear in the microstructure. When the cooling rate is higher than 7 ℃ / s, the pearlite transformation is terminated. The addition of Nb promotes the formation of bainite and inhibits the nucleation of ferrite and pearlite at moderate cooling rates. The addition of Nb shifts the ferrite transformation zone to the right. The addition of Cr reduces the ferrite and pearlite transformation points at higher cooling rates and promotes the formation of martensite at high cooling rates. Due to the influence of V precipitation, the hardness of V-containing test steel has a “trough” at a cooling rate of 1 ° C / s. When the cooling rates of the three kinds of test steels are between 0.5 and 3 ℃ / s, the test steels can obtain fine quasi-polygonal ferrite with good toughness and small amount of composite structure of pearlite and bainite.