低碳含量无碳化物贝氏体钢的强韧化及低周疲劳行为研究

发布时间：2018-06-24 06:11

本文选题：无碳化物贝氏体钢 + 残余奥氏体　；参考：《燕山大学》2015年博士论文

【摘要】：本文设计和制备了三种不同铝含量(即0Al、0.6Al和1.2Al,质量百分比)的低碳无碳化物贝氏体钢,利用光学显微镜、扫描电镜、透射电镜、X-射线衍射、数字图像相关法和力学性能测试等,研究了热处理工艺参数、铝含量和加载速率对低碳无碳化物贝氏体钢微观组织及其演化、以及力学性能的影响,揭示了其强韧化的机制;利用低周疲劳试验,对低碳无碳化物贝氏体钢在不同应变幅下的低周疲劳行为进行了研究。研究了保温时间和等温淬火温度对1.2Al钢微观组织和力学性能的影响。结果表明,在320 oC等温淬火温度下,随着等温保持时间的延长,获得的无碳化物贝氏体型铁素体和残余奥氏体的含量均呈现出先增加后保持不变的趋势,其冲击韧性和总延伸率也先增加然后保持不变;随着等温保持时间的延长,虽然屈服强度基本保持不变,但是抗拉强度则先轻微下降然后保持不变。随着等温淬火温度从350 oC降低到300 oC,等温淬火后获得的贝氏体型铁素体板条的宽度、残余奥氏体的含量和尺寸均呈现出减小的趋势,屈服强度和抗拉强度轻微增加,总延伸率显著降低,而冲击韧性则表现为先增加后降低的趋势。研究了铝含量对低碳无碳化物贝氏体钢微观组织和力学性能的影响。结果表明,随着铝含量的增加,贝氏体型铁素体板条得到了明显细化,其屈服强度和冲击韧性得到了明显提高。此外,随着铝含量的增加,残余奥氏体的含量和尺寸均呈现出下降的趋势,抗拉强度、总延伸率随之下降,而冲击韧性则随之增加。这一结果表明,铝含量对实验钢的抗拉强度、拉伸延性及冲击韧性产生不一致性影响。研究了加载速率对1.2Al钢两种不同类型试样断裂吸收功的影响。结果表明,对于U型缺口试样,随着加载速率的增加,裂纹萌生功、裂纹扩展功和总吸收功均增加;对于预制裂纹试样,随着加载速率的增加,尽管裂纹萌生功基本保持不变,但是裂纹扩展功和总吸收功均逐渐增加。这主要是由于随着加载速率的增加残余奥氏体向马氏体转变的量降低的缘故。研究了两种不同等温温度(300 oC和350 oC)下等温淬火处理后1.2Al钢的低周疲劳行为。结果表明,在给定总应变幅下,两种等温淬火试样具有相似的循环应力响应行为,即初始阶段的循环硬化、然后循环软化直至失效,或者在初始阶段的循环硬化和循环饱和之后、循环软化直至失效。分析认为,初始阶段的循环硬化既不是由应变诱发的马氏体相变引起的,也不是由增加的位错引起的。原始组织中存在的高密度位错之间的相互作用、以及可移动位错的显著降低是引起初始阶段循环硬化的主要原因,而大量位错湮没和位错重排是引起初始循环硬化之后出现循环软化的主要原因。与350℃等温淬火试样相比,在低总应变幅下300 oC等温淬火试样具有较高的疲劳寿命,而在高总应变幅下300 oC等温淬火试样则显示出较低的疲劳寿命。这主要是由于300 oC等温淬火钢的屈服强度高于350 oC等温淬火钢的屈服强度、而350 oC等温淬火钢具有较高拉伸延性的综合作用所引起的。
[Abstract]:Three kinds of low carbon bainite steel with different aluminum content (0Al, 0.6Al and 1.2Al, mass percentage) were designed and prepared. The process parameters of heat treatment were studied by optical microscope, scanning electron microscope, transmission electron microscope, X- ray diffraction, digital image correlation method and mechanical properties test. The content of aluminum and loading rate of low carbon non carbonization were studied. The microstructure and evolution of bainitic steel and the influence of mechanical properties revealed the mechanism of its strengthening and toughening. The low cycle fatigue behavior of low carbon bainitic steel under different strain amplitudes was studied by low cycle fatigue test. The microstructure and mechanical properties of 1.2Al steel were studied by the heat preservation time and the isothermal quenching temperature. The results show that at 320 oC isothermal quenching temperature, with the prolongation of the isothermal retention time, the content of the bainite ferrite and retained austenite of the carbide is increased first and then remains unchanged, and the impact toughness and the total elongation at first increase then remain unchanged, with the prolongation of the isothermal retention time. However, the yield strength remained unchanged, but the tensile strength decreased slightly and remained unchanged. As the isothermal quenching temperature decreased from 350 oC to 300 oC, the width of bainite ferrite lath obtained after isothermal quenching, the content and size of retained austenite decreased, and the yield strength and tensile strength increased slightly. The total elongation rate decreased significantly, while the impact toughness was increased first and then decreased. The effect of aluminum content on the microstructure and mechanical properties of low carbon bainitic bainite steel was studied. The results showed that the bainite ferrite slab was clearly refined with the increase of aluminum content, and the yield strength and impact toughness were obtained. In addition, with the increase of aluminum content, the content and size of retained austenite showed a downward trend, the tensile strength, the total elongation decreased and the impact toughness increased. The results showed that the aluminum content was inconcomitant to tensile strength, tensile ductility and impact toughness of the experimental steel. The loading speed was studied. The effect of rate on the fracture absorption work of two different types of 1.2Al steel specimens. The results show that the crack initiation work and the total absorption work increase with the increase of the loading rate for the U notched specimen, and the crack initiation work is basically unchanged with the increase of the loading rate for the prefabricated specimen, but the crack propagation work is basically unchanged. And the total absorption work increased gradually. This was mainly due to the decrease of the amount of retained austenite to martensite with the increase of loading rate. The low cycle fatigue behavior of 1.2Al steel after isothermal quenching at two different isothermal temperatures (300 oC and 350 oC) was studied. The results showed that two isothermal quenching specimens were used under the given total strain amplitude. There is a similar cyclic stress response, that is, cyclic hardening at the initial stage, then softening until failure, or softening the cycle to failure after the initial stage of cyclic hardening and cyclic saturation. Dislocation caused by dislocation. The interaction between high density dislocation in the original tissue and the significant reduction of movable dislocation are the main causes of the initial stage of cyclic hardening. A large number of dislocation annihilation and dislocation rearrangement are the main causes of cyclic softening after initial cyclic hardening. Compared with the isothermal quenching specimens at 350 degrees C, The 300 oC isothermal quenching specimen with low total strain amplitude has a higher fatigue life, while the 300 oC isothermal quenching specimen under high total strain amplitude shows a lower fatigue life. This is mainly due to the yield strength of the 300 oC isotherm steel higher than that of 350 oC isotherm steel, while the 350 oC isotherm steel has a higher tensile elongation. Caused by the comprehensive effect of sex.
【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1

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