【作者】 康国旺；

【导师】 崔占全；

【作者基本信息】 燕山大学 ， 材料学， 2005， 硕士

【摘要】 近年来,研究发现以铁素体及弥散分布的碳化物为特征的贝氏体组织具有良好的力学性能。对此,人们研究了多种因素对贝氏体相变及贝氏体组织的影响,而关于贝氏体区形变对其影响的报道,还未曾见到。 本文以 3Cr-1Mo-0.25V 钢为实验材料,利用 Gleeble-3500 热模拟试验机,测定了该钢的转变点和 CCT 曲线,并对该钢在贝氏体区形变进行了研究。采用金相、扫描电镜、透射电镜、硬度等实验方法对处理后的试样进行了组织和性能的分析。 相变点及 CCT 曲线测定结果表明: 3Cr-1Mo-0.25V 钢的相变点 Ac₁ 800℃、Ac₃ 890℃、Ar₁ 720℃、Ar₃ 845℃。在所测冷速范围内,CCT 图中存在两种相变区,即高冷速的马氏体转变区和低冷速的贝氏体相变区。当冷速大于 30℃/s 时,可获得马氏体组织;当冷速为 15-30℃/s 时获得马氏体、贝氏体混合组织;当冷速小于 15℃/s 时获得贝氏体组织。 贝氏体区形变对贝氏体相变及贝氏体组织的影响表现在: 在贝氏体相变后形变,随形变温度的降低、形变量的增加,贝氏体铁素体条片状特征趋于明显,硬度增加。在贝氏体相变中形变,随形变温度的降低贝氏体铁素体条片状特征趋于明显,碳化物尺寸变小,弥散度减小,硬度增加;随形变量的增加,贝氏体铁素体条片状特征趋于明显,析出物尺寸变小、弥散度增加,硬度增加。在贝氏体相变中形变,有促进碳化物在铁素体片条中析出的作用。在相同的形变条件下,相变中形变的试样由于析出软化而硬度较低。更多还原

【Abstract】 In recent years, the study demonstrates that the bainitic microstructure consisting of bainitic ferrite and carbide precipitates possesses excellent comprehensive mechanical properties. Numerous studies have been done on it. But few studies on the effects of deformation in bainitic transformation region on bainitic microstructure and transformation have been reported. In this paper, 3Cr-1Mo-0.25V steel was selected for experiments. The critical points, the CCT curve and the effects of deformation in bainitic transformation region on the microstructure and mechanical property of the steel were investigated by using of Gleeble-3500 thermal simulator, optical microscope, SEM, TEM and hardness measurement. It is observed that the critical points Ac₁, Ac₃, Ar₁and Ar₃ of the steel are 800℃, 890℃, 720℃ and 845℃ respectively, the CCT curve exists martensitic transformation region at high cooling rate and bainitic transformation region at lower cooling rate. Martensite can be obtained at the cooling rate higher than 30℃/s, mixed microstructure with martensite and bainnite can be obtained at the cooling rate in a range from 15℃/s to 30℃/s, bainite can be obtained at the cooling rate lower than 15℃/s. When deformation was performed after bainitic transformation, with the deformed temperature decreasing or the reduction increasing, the lath character of bainitic ferrite is evident and the hardness of the specimen increases. When deformation was performed during bainitic transformation, with the deformed temperature decreasing, the lath character of bainitic ferrite is evident, the dimension and dispersion of the precipitates decreases and the hardness of the specimen increases, and with the reduction increasing, the dimension of the precipitates decreases, the dispersion increases, the hardness of specimen increases. Deformation performed during bainitic transformation promotes carbide precipitate in bainitic ferrite laths. In the same deformation conditions, the hardness of the specimen deformed during bainitic transformation is lower than that deformed after bainitic transformation, because of soften due to precipitation.更多还原