一次淬火马氏体对淬火配分钢微观组织和力学性能的影响

发布时间：2018-05-21 06:43

本文选题：淬火配分 + 马氏体　；参考：《西安建筑科技大学》2015年硕士论文

【摘要】：淬火配分(Quenching and Partition,QP)工艺先通过不完全淬火获得马氏体,再控制碳从马氏体向未转变奥氏体的配分,最后淬火至室温获得马奥组织,可以有效地提高强度钢的塑性和韧性。Speer等提出了根据一次淬火马氏体计算各项比例的方法,王存宇据马氏体相变组织不均匀性初步探讨了理论计算和实测值得差异,本文在此基础上,用含碳量为0.2-0.5wt.%的5种高硅CrNiMo系合金结构钢为对象,利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和单轴拉伸试验等多种方法,系统研究了一次淬火马氏体比例对试验钢微观组织、残留奥氏体量和单轴拉伸性能的影响。试验钢经QP工艺热处理后获得一次淬火马氏体、二次淬火马氏体、残留奥氏体构成的多相组织,随着一次淬火马氏体比例的增加二次淬火马氏体的尺寸和数量都逐渐减少,残留奥氏体的量先增大后减小,当一次淬火马氏体比例为30%-50%时,未转变奥氏体的尺寸相对均匀细小,容易吸收更多的碳而使残留奥氏体的量增大,不同含碳量的试验钢的微观组织和力学性能随着一次淬火马氏体比例的变化规律相同。随着一次淬火马氏体比例的增加,试验钢抗拉强度逐渐降低,屈服强度和断面收缩率逐渐升高,断后伸长率和强塑积先升高后降低,残留奥氏体的量和稳定性决定了钢的塑性,残留奥氏体的TRIP效应使钢获得了高塑性和高强塑积,随着一次淬火马氏体比例的增加,一次淬火马氏体和二次淬火马氏体的纳米硬度逐渐增加,含碳量高以及板条细小决定了二次淬火马氏体的纳米硬度高于一次淬火马氏体,单轴拉伸条件下微孔洞主要形成于大尺寸夹杂物,未发现二次淬火马氏体形成微孔洞的现象。
[Abstract]:Quenching and Partition (QP) process is used to obtain martensite by incomplete quenching, then to control the partition of carbon from martensite to untransformed austenite, and finally to obtain Mao microstructure by quenching to room temperature. The plasticity and toughness of strength steel can be improved effectively. Speer and others have put forward a method to calculate the proportion of martensite based on primary quenching. According to the inhomogeneity of martensite transformation microstructure, Wang Cunyu has preliminarily discussed the difference between the theoretical calculation and the measured value. On this basis, five kinds of high silicon CrNiMo alloy structural steels with a carbon content of 0.2-0.5 wt.% were used as objects, and various methods such as scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and uniaxial tensile test were used. The effect of martensite ratio of primary quenching on microstructure, residual austenite content and uniaxial tensile properties of test steel was studied systematically. After heat treatment with QP process, the multiphase structure of primary quenched martensite, secondary quenched martensite and residual austenite is gradually reduced with the increase of the ratio of primary quenching martensite to secondary quenched martensite. The amount of retained austenite first increases and then decreases. When the ratio of primary quenching martensite is 30% to 50%, the size of untransformed austenite is relatively uniform and fine, and it is easy to absorb more carbon, thus increasing the amount of retained austenite. The microstructure and mechanical properties of the tested steels with different carbon content are the same as those of the primary quenching martensite ratio. With the increase of martensite ratio of primary quenching, the tensile strength of test steel decreases gradually, the yield strength and section shrinkage increase gradually, and the elongation and strong plastic product increase first and then decrease. The plasticity of the steel is determined by the quantity and stability of retained austenite. The TRIP effect of residual austenite makes the steel gain high plasticity and high strength plastic product. With the increase of martensite ratio, the nano-hardness of primary quenching martensite and secondary quenched martensite increases gradually. The high carbon content and fine lath determined that the nano-hardness of secondary quenching martensite was higher than that of primary quenching martensite. Under uniaxial tensile condition, the micropores were mainly formed in large size inclusions, and no micropores formed in secondary quenching martensite.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG142.1

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