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对低碳贝氏体钢进行热模拟实验,在非再结晶区变形后以不同的冷却速度冷却,研究了不同冷却速度下低碳贝氏体钢的组织结构特征和第二相析出规律。结果表明,冷却速度对组织亚结构的影响较大。以20~50℃/s的高速冷却后,该钢的组织以板条贝氏体为主,小角度晶界较多。随着冷却速度的降低,组织中板条贝氏体减少,粒状贝氏体增加,大角度晶界比例增加,但板条间取向差极小。当冷速降低到5℃/s时,粒状贝氏体的体积分数显著增多,并形成有明显取向差的胞状亚晶。以3℃/s冷却后,组织以粒状贝氏体为主,出现先共析铁素体晶核,开始发生铁素体相变;以低于2℃/s的冷速冷却后,形成由块状铁素体、多边形铁素体和粒状贝氏体组成的混合组织,大角度晶界比例较高。实验钢中的析出相主要有矩形(Ti,Nb)(N,C)及球形Nb(N,C)或NbC两种,在冷却过程中,以NbC相析出为主,随着冷却速度降低,析出相尺寸略有增大。
The thermal simulation experiment of low carbon bainitic steel was carried out. The non-recrystallized zone was deformed and cooled at different cooling rates. The microstructure and secondary precipitation regularity of low carbon bainitic steel were studied under different cooling rates. The results show that cooling rate has a great influence on the microstructure. After cooling at a high speed of 20-50 ° C / s, the microstructure of the steel is dominated by lath bainite with more small-angle grain boundaries. With the decrease of cooling rate, the bainite decreases, the granular bainite increases and the ratio of large-angle grain boundaries increases, but the difference in orientation between slats is very small. When the cooling rate decreased to 5 ℃ / s, the volume fraction of granular bainite significantly increased, and the formation of obvious disordered cellular subgrain. After cooling at 3 ° C / s, the microstructure was dominated by granular bainite, and pro-eutectoid ferrite nuclei appeared and ferrite transformation started. After cooling at a cooling rate lower than 2 ° C / s, Bulk ferrite, polygonal ferrite and granular bainite mixed organization, a large proportion of high-angle grain boundaries. In the experimental steel, the precipitated phases mainly consist of rectangular (Ti, Nb) (N, C) and spherical Nb (N, C) or NbC. During the cooling process, NbC phase is mainly precipitated. With the decrease of cooling rate, Precipitated phase size slightly increased.