应力作用下A508-3钢的连续冷却相变行为研究
发布时间：2018-07-27 14:49
【摘要】：A508-3钢是一种低碳低合金钢,其大锻件作为核电站压力容器而广泛应用,在热处理过程中因体积巨大,不同部位的传热速率不同,从而产生热应力和相变应力,所以涉及温度、应力、相变三者的交互作用,以往的研究大都忽略了应力这一参数,针对这一实际现象,本文选取A508-3钢作为研究对象,研究不同冷却速度下应力对相变动力学及显微组织的影响,以期不仅在理论上解释相变机制,而且为实际工程应用提供参考,主要试验研究和结论如下:利用高温相变仪对A508-3钢非等温相变过程开展试验,获得连续加热和冷却膨胀曲线,确定各组织转变点,绘制出连续冷却转变曲线,并分别对先共析铁素体、珠光体、贝氏体及马氏体相变开展研究,研究发现,A508-3钢的先共析铁素体相变开始点与冷速之间的关系能够很好地满足Scheil叠加法处理的兰格模型;所得珠光体和贝氏体体积分数与时间之间满足指数关系模型;在高冷却速度下的马氏体转变满足变温马氏体相变动力学方程;依据CCT曲线,珠光体和贝氏体的临界冷速均低于0.1℃/s;马氏体的临界冷速介于2℃/s和5℃/s之间。利用Gleeble-1500D热力模拟试验机对压应力作用下连续冷却过程中的组织转变展开研究,结果表明:连续冷却过程中,单轴压应力增加了先共析铁素体的冷速范围,促进了先共析铁素体和珠光体相变的进程,且压应力越大,促进作用越明显;压应力减缓了贝氏体相变速率,促进形核,抑制长大,且压应力值越大,抑制作用越明显;随压应力增加,珠光体的显微形貌变化不明显;粒状贝氏体中呈线性沿一定方向规则排布的M/A岛长径比下降,数量也减少,弥散分布的颗粒状M/A岛尺寸减小,数量增加。利用Gleeble-1500D热力模拟试验机对拉应力作用下连续冷却过程中贝氏体相变展开研究,结果表明:连续冷却过程中,单轴拉应力促进冷速为0.5℃/s的贝氏体转变,对冷速为1~2℃/s下的贝氏体相变起抑制作用,贝氏体形貌受拉应力的影响与压应力作用下保持基本一致。
[Abstract]:A508-3 steel is a kind of low carbon low alloy steel. Its large forgings are widely used as pressure vessels in nuclear power plants. Because of their huge volume and different heat transfer rates in different parts during heat treatment, they produce thermal stress and phase transformation stress, so they involve temperature. The interaction of stress and phase transformation has been neglected in previous studies. In view of this practical phenomenon, A508-3 steel is chosen as the object of study in this paper. The effect of stress on phase transformation kinetics and microstructure at different cooling rates is studied in order not only to explain the mechanism of phase transition theoretically, but also to provide a reference for practical engineering application. The main experimental results and conclusions are as follows: the non-isothermal phase transformation process of A508-3 steel was tested by high temperature phase transformation instrument, the continuous heating and cooling expansion curves were obtained, the transformation points of each microstructure were determined, and the continuous cooling transformation curves were drawn. The transformation of proeutectoid ferrite, pearlite, bainite and martensite were studied respectively. It was found that the relationship between the starting point of preeutectoid ferrite transformation and the cooling rate of A508-3 steel could well meet the Lange model treated by Scheil superposition method. The obtained volume fraction of pearlite and bainite satisfies the exponential model of time, the martensite transformation at high cooling rate satisfies the dynamic equation of martensite transformation at variable temperature, and according to the CCT curve, The critical cooling rate of pearlite and bainite is lower than 0.1 鈩，
本文编号：2148163
[Abstract]:A508-3 steel is a kind of low carbon low alloy steel. Its large forgings are widely used as pressure vessels in nuclear power plants. Because of their huge volume and different heat transfer rates in different parts during heat treatment, they produce thermal stress and phase transformation stress, so they involve temperature. The interaction of stress and phase transformation has been neglected in previous studies. In view of this practical phenomenon, A508-3 steel is chosen as the object of study in this paper. The effect of stress on phase transformation kinetics and microstructure at different cooling rates is studied in order not only to explain the mechanism of phase transition theoretically, but also to provide a reference for practical engineering application. The main experimental results and conclusions are as follows: the non-isothermal phase transformation process of A508-3 steel was tested by high temperature phase transformation instrument, the continuous heating and cooling expansion curves were obtained, the transformation points of each microstructure were determined, and the continuous cooling transformation curves were drawn. The transformation of proeutectoid ferrite, pearlite, bainite and martensite were studied respectively. It was found that the relationship between the starting point of preeutectoid ferrite transformation and the cooling rate of A508-3 steel could well meet the Lange model treated by Scheil superposition method. The obtained volume fraction of pearlite and bainite satisfies the exponential model of time, the martensite transformation at high cooling rate satisfies the dynamic equation of martensite transformation at variable temperature, and according to the CCT curve, The critical cooling rate of pearlite and bainite is lower than 0.1 鈩，
本文编号：2148163
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