釉化用钢热轧和热处理过程奥氏体—铁素体转变的数值模拟

发布时间：2018-01-16 01:31

本文关键词：釉化用钢热轧和热处理过程奥氏体—铁素体转变的数值模拟　出处：《东南大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文采用模拟和实验相结合的方法,对釉化用钢热轧和热处理过程中显微组织和C浓度分布的演化进行研究。在实验基础上,建立耦合热力学数据库以及有限元模拟的温度场和应力场的二维元胞自动机(cellular automaton,CA)模型。该模型包含了奥氏体(Y)和铁素体(α)的连续形核、由C浓度场、应变能和界面迁移率所控制的相变、溶质C在γ/α界面处的再分配以及在αα和γ中的扩散。应用该CA模型模拟了形变诱导铁素体相变(dynamic strain induced transformation,DSIT)热轧和连续热轧过程、在αα-Y两相区的保温、以不同冷却速度的连续冷却、以及不同温度下回火的热处理过程中的显微组织与C浓度场的演化,在此基础上分析工艺-组织-力学性能之间的关系。此外,采用实验方法研究了不同保温时间对冷、热轧釉化用钢在不同温度保温冷却后的组织和性能的影响。热轧过程的CA模拟结果表明,DSIT过程中第四道次轧前降温过程,随温度降低,αα相分数增长速率先慢后快再逐渐减小。轧制过程中温度迅速升高且有应力作用,但由于持续时间较短,显微组织无明显变化,α/γ相界面周围出现贫C区。在轧后降温过程中,发生α→γ逆转变,随后开始γ→α相变。因此,αα相分数先降低后升高,室温时显微组织主要为晶粒尺寸较细小的α相和沿晶界分布的富C块状相。在连轧第七道次降温过程中发生γ→α转变,α相分数增长速率先慢后快再逐渐减小。室温时显微组织主要为晶粒尺寸较粗大的α相和晶界处尺寸较大的富C块状相。热处理过程的CA模拟结果表明,在α-γ两相区的815℃保温过程中α→γγ相变由界面控制逐渐转变为扩散控制,呈现出混合控制模式,保温300 s后αα相与γ相中的C浓度均达到各自的平衡值。在随后的连续冷却过程发生γ→α相变,以1.5℃/s冷速冷却至室温后的C浓度场比5.0℃/s时的C浓度场更均匀。以5.0℃/s冷却至室温后的试样在300℃和500℃温度下回火5 min,C分布均匀性随回火温度升高而提高。模拟结果可合理解释相关实验现象的机理。保温不同时间的热处理实验结果表明,C、Mn、Si含量较低的2#冷轧钢板经不同温度保温空冷后,与轧制态相比,屈服强度降低,并随保温温度升高而下降,不同保温时间对屈服强度影响不大。C、Mn、Si较高的18#冷轧钢板经700～870℃保温砂冷后,屈服强度高于空冷及轧制态的屈服强度,在760℃和840℃保温10 min砂冷的屈服强度比保温5 min砂冷的屈服强度分别提高46 MPa和27 MPa;在760～870℃温度范围内保温10 min空冷的屈服强度比保温5 min空冷的屈服强度提高约15 MPa。与18#成分相同的17#热轧钢板在不同温度保温空冷后,在700～815℃区间,延长保温时间对屈服强度影响不大;在840℃和870℃时,延长保温时间能提高屈服强度约25 MPa。
[Abstract]:This paper uses the method of combination of simulation and experiment, the glaze and microstructure evolution of C steel hot rolling and heat treatment process of concentration distribution is studied. On the basis of experiment, a coupled thermodynamic database and finite element simulation of temperature field and stress field of two-dimensional cellular automata (cellular, automaton, CA) model. The model consists of austenite and ferrite (Y) (a) of the continuous nucleation, C concentration field, strain energy and interface mobility under the control of the phase transition, the solute C in gamma / alpha at the interface and redistribution in the alpha alpha and gamma diffusion in the application of the CA model. The deformation induced ferrite transformation (dynamic strain induced transformation, DSIT) and continuous hot rolling process, thermal insulation in the alpha alpha -Y two-phase region, with continuous cooling with different cooling rate, microstructure and heat treatment under different temperature tempering process of fabric and C concentration field of play Analysis of the relationship between technology and organization of mechanical properties on this basis. In addition, an experimental study of different cold preservation time on the effect of hot rolling, glaze microstructure and properties of steel at different temperature after cooling the hot rolling process. The simulation results show that CA, DSIT in the process of fourth times before rolling the cooling process, with the decrease of temperature, the alpha alpha phase fraction the growth rate of the first slow fast and then decreased gradually. In the process of rolling temperature increased rapidly and the stress, but due to short duration, no significant changes in microstructure, alpha / gamma phase interface around the C area. In the poor cooling after rolling process. To have alpha gamma gamma inverse transformation, then began to alpha transformation. Therefore, alpha alpha phase fraction increased firstly and then decreased, the microstructure at room temperature is mainly a phase and grain size smaller distributed along the grain boundaries of C rich phase, alpha gamma. Block occurred in the rolling seventh cooling process Change, phase fraction growth rate soon after the first slow then decreases. When the room temperature microstructure of C rich massive large phase and grain boundary grain size coarse phase. The heat treatment process of CA simulation results show that the insulation in the alpha gamma phase region 815 DEG C during alpha to gamma gamma phase from the interface control gradually transformed into diffusion control, presents a hybrid control mode, after holding for 300 s and alpha alpha gamma phase C concentration reached their equilibrium values. And phase change in continuous gamma alpha cooling to 1.5 DEG C, C concentration field /s cooling rate and cooling to room temperature than the concentration of C 5 C /s is more uniform. The sample /s 5 degrees of cooling to room temperature after tempering for 5 min at 300 DEG C and at a temperature of 500 DEG C, C distribution uniformity with the tempering temperature increases. The simulation results can explain the mechanism of the experimental phenomena. The experiments of heat treatment for different holding time. The results show that C, Mn, 2# cold rolled steel plate with low content of Si with different temperature after air cooling, compared with rolling, the yield strength decreased, and decreased along with temperature, different holding time has little influence on the yield strength of.C, Mn, 18# cold rolled steel Si higher by 700 ~ 870 DEG C sand cold, yield strength is higher than that of air cooling and rolling, the yield strength in the yield strength of 760 degrees and 840 degrees heat 10 min sand cold insulation cold sand than 5 min were increased by 46 MPa and 27 MPa; in 760 ~ 870 degrees Celsius temperature range 10 min insulation cooling yield strength more than 5 min air cooling insulation yield strength is increased by about 15 MPa. with the same 18# components of 17# hot rolled steel at different temperature after air cooling, in 700 ~ 815 degrees interval, time has little influence on the yield strength; at 840 DEG and 870 DEG C, holding time can improve the yield strength of about 25 MPa.

【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1;TG335.11;TG161

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