【作者】 丛振华；

【导师】 王沿东；

【作者基本信息】 东北大学 ， 材料学， 2008， 硕士

【摘要】 本论文基于同步辐射源大型科学装置的原位高能X射线衍射技术,研究了形变诱发塑性钢(TRIP钢)及双相钢(DP钢)的微观力学行为。TRIP钢由铁素体、贝氏体和少量残余奥氏体相组成,DP钢由铁素体和马氏体相两相组成。对于TRIP钢来说,由于其体心立方相(铁素体+贝氏体)与面心立方结构相(奥氏体)晶体结构差异明显,两种不同相具有完全不同的hkl衍射峰,故易根据不同相衍射峰对应的晶格常数变化提供的定量信息,从而获得不同应力状态下奥氏体相的hkl点阵应变分布。然而对于TRIP钢中的铁素体和贝氏体相以及DP钢中的铁素体和马氏体相而言,由于其具有相同的晶体结构,故衍射峰相互交叠,很难利用单峰拟合技术获得各相的点阵应变。本论文通过选取两个具有不同峰宽和峰位的Gaussian函数对各相的衍射强度与20关系曲线进行拟合,能够很好区分TRIP钢中铁素体相和贝氏体相以及DP钢中铁素体相和马氏体相(200)晶面的衍射峰峰位,从而确定不同载荷下两种材料各相的点阵应变及平均相应力。通过使用双相弹塑性自洽模型(EPSC)对材料微观力学行为进行了模拟。模拟与实验结果符合良好,从而证明该模型能够较好模拟多相材料的微观力学行为。基于以上工作,我们得到如下结论：1、外加载荷较小时,TRIP800及DP980钢内部微观应力主要为各相平均应力,随外加载荷不断增加,与晶粒取向相关应力(晶间应力)取代相应力,成为微观应力的主要来源。2、奥氏体含量14%的TRIP800钢中γ相(奥氏体相)所承受的平均应力和晶粒取向相关应力大于α相的对应应力；奥氏体含量4%的TRIP800和DP980钢中,贝氏体和马氏体相所承载的平均应力和晶粒取向相关应力均大于铁素体相的相对应应力。3、奥氏体含量14%的TRIP800钢中α相与γ相弹塑性转变点分别为300MPa和600MPa；奥氏体含量为4%的钢中α相与γ相弹塑性转变点分别为300MPa和750MPa。DP980钢中铁素体和马氏体的弹塑性转变点分别为830和900MPa。4、弹塑性自洽模型能够很好模拟双相材料中的微观力学行为,可以提供无法通过实验手段直接获得的微观力学信息,为材料性能预测提供有力工具。更多还原

【Abstract】 The micromechanical behavior of transformation induced plastic (TRIP) steel and dual phase (DP) steel was studied by the in-situ high-energy X-ray diffraction technique based on the synchrotron source. The microstructure of the studied TRIP steel consists of the ferrite, bainite and the residual austenite; while the DP steel is composed of ferrite and martensite. For TRIP steels, due to the obvious difference of the positions of diffraction peaks of the face-centred cubic phases (ferrite and bainite) and the body-centred cubic phase (austenite), it is easy to separate them from each other by the different positions of the respective diffraction peaks. Then, the lattice strains of the austenitic phase as a function of applied stress can be obtained.However, as for ferrite and bainite in the TRIP steel as well as the ferrite and martensite in the DP steel, it is difficult to separate them from each other by the single peak fitting. Although the ferrite/bainite and ferrite/martensite exhibit the same crystal structure, the (200) lattice strains of each phase can be determined by separating their overlapping diffraction peaks. This is achieved through fitting the lattice strain vs.20 curve by adopting two Gaussian functions with the different peak widths and positions. In this way, specific lattice strains of respective phases are determined for all the phases in both TRIP steel and DP steel.We also used an Elastic-Plastic Self-Consistent (EPSC) model to construct the respective constitutive laws for both phases from the experimental lattice strains and macrostress-strain curve. It is confirmed that the EPSC model can capture well the micromechanical behaviour of two-phase materials.Based on the work mentioned above, the following conclusions could be drawn:1. The microstresses in the materials mainly come from the phase stress caused by the phase-to-phaseinteraction when the macro-stress is low. With increasing the applied stress, grain-orientation-dependent stress is developed and dominate the microstresses in the 2. In the two-phase materials, such as TRIP800 and DP980 steels, the average stress in each phase and grain-orientation-dependent stress subjected by austenite, bainite and martensite are larger than the corresponding stresses by ferrite under the applied loading.3. The critical shear stress of TRIP800 composed by 14% austenite is approximately 300MPa in a phase and the corresponding stress of y phase is 600MPa. The critical shear stress of TRIP800 composed by 5% austenite is 300MPa in a phase and the corresponding stress of y phase is 750MPa. Similarly, the shear stress of ferrite and martensite in DP980 is 830 and 900MPa, respectively.4. The EPSC model can capture well the micromechanical behaviour in the two-phase materials. The EPSC model provides useful information on the phase-to-phase and grain-to-grain interations in the materials, which could not be obtained by simply performing experiments. It is proved to be a powerful tool in predicting the mechanical properties of the materials.更多还原