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大型锻件氢脆损伤机理的研究

发布时间:2019-03-15 20:15  文章来源:笔耕文化传播
【摘要】:大型锻件制造是重大装备制造的关键技术之一,其质量直接影响到重大装备的整体水平和运行可靠性,是发展电力、船舶、冶金、石化、重型机械和国防等工业的基础,是发展先进装备制造业的前提。大型锻件在高温成形及其降温过程中,由于氢析出并偏聚于锻件内部的微缺陷中,所产生的内高压和微裂纹极易导致零件突然断裂,称之为氢脆,是大锻件质量控制中最为危险和棘手的问题。近年来的研究成果虽然在热-力-微观组织耦合方面取得了一些新的进展,但对于大锻件的氢脆问题一直没有得到很好的解决。为研究氢脆损伤的产生机理,本文以氢脆敏感性高的合金钢为研究对象,采用物理模拟及有限元分析相结合的方法对大型锻件中的氢浓度、氢扩散以及氢脆损伤的机理进行了综合研究。由于氢原子是自然界中质量最轻和半径最小的原子,想要准确地测量锻件中的氢含量一直是困扰工业界和科学界的一项难题。为了对锻件中的氢含量及氢浓度分布进行研究,本文利用有限元方法建立了大型锻件锻后热处理过程的扩氢计算有限元模型,分析得到了材料在热处理过程中的氢扩散规律。对于大型锻件来说整个热处理过程都是在扩氢的,为了能时刻检测钢中氢的含量,必须要掌握钢中氢的渗透速率。本文以菲克第二定律为依据,利用电化学工作站及配套测试软件对不同成分的合金钢进行了氢扩散系数的测定实验,给出了一种适合于金属材料氢扩散系数测定的实验方法。为了对材料的氢脆损伤机理进行研究,通过充氢实验使外界的氢原子不断的向锻件内部扩散,并对试件的缓慢拉伸过程进行数据记录,分析了40Cr和45号钢在不同充氢电流和充氢时间条件下的氢致鼓包的形貌特征、抗拉强度、延伸率等力学性能参数,以延伸率的变化量为氢脆指标对氢脆程度进行度量,且通过充氢-拉伸实验和充氢-放置-拉伸实验验证了氢致损伤的不可逆性。为了对锻件内孔洞的氢压及氢含量进行定量分析,在电化学充氢实验的基础上结合有限元方法对氢鼓包内部的氢压进行了反算研究,建立氢浓度与微孔隙氢压的联系,对氢鼓包的长大规律和鼓包内氢压计算进行研究,用以解决金属材料中的微孔隙或氢偏聚区往往位于零件内部且很难进行直接测量的问题。为研究大型锻件成形过程中微孔隙氢压强度的变化,以氢压原理为基础,建立了大型锻件氢压场分析的有限元模型,得到了不同条件下锻件内部微孔隙氢压强度和氢浓度的变化规律,研究了不同氢浓度下氢压应力场的分布及相邻微孔洞间的耦合作用。
[Abstract]:The manufacture of large forgings is one of the key technologies in the manufacture of major equipment. Its quality has a direct impact on the overall level and operational reliability of the major equipment, and is the basis for the development of industries such as power, ship, metallurgy, petrochemical, heavy machinery and national defense, etc. It is the premise of developing advanced equipment manufacturing industry. During high temperature forming and cooling of large forgings, due to hydrogen precipitation and segregation in the internal micro-defects of the forgings, the internal high pressure and micro-cracks can easily lead to the sudden fracture of the parts, which is called hydrogen embrittlement, which is called hydrogen embrittlement. It is the most dangerous and thorny problem in the quality control of large forgings. In recent years, although some new progress has been made in the thermal-mechanical-microstructure coupling, the hydrogen embrittlement of large forgings has not been well solved. In order to study the mechanism of hydrogen embrittlement damage, the hydrogen concentration in large forgings was studied by means of physical simulation and finite element analysis, and the alloy steel with high sensitivity to hydrogen embrittlement was taken as the research object in this paper. The mechanisms of hydrogen diffusion and hydrogen embrittlement damage were comprehensively studied. Since hydrogen atom is the lightest and smallest atom in nature, it is a difficult problem for industry and science to accurately measure the hydrogen content in forgings. In order to study the hydrogen content and the distribution of hydrogen concentration in forgings, the finite element model of hydrogen diffusion calculation in post-forging heat treatment process of large-scale forgings is established by using the finite element method, and the hydrogen diffusion rule of the material in the heat treatment process is analyzed. For large forgings, the whole heat treatment process is in the process of hydrogen expansion. In order to detect the hydrogen content in steel at all times, it is necessary to master the penetration rate of hydrogen in steel. Based on Fick's second law, the hydrogen diffusion coefficient of alloy steel with different composition was measured by electrochemical workstation and matching software. An experimental method suitable for the determination of hydrogen diffusion coefficient of metallic materials was given. In order to study the damage mechanism of hydrogen embrittlement of the material, the hydrogen atoms from the outside were diffused to the inner part of the forgings through the hydrogen filling experiment, and the data of the slow tensile process of the specimens were recorded. The morphology characteristics, tensile strength and elongation of hydrogen-induced bulging of 40Cr and 45 # steel under different hydrogen charging current and time were analyzed. The degree of hydrogen embrittlement was measured with the change of elongation as the index of hydrogen embrittlement. The irreversibility of hydrogen-induced damage was verified by hydrogen-filled tensile test and hydrogen-filling-placement-tensile test. In order to quantitatively analyze the hydrogen pressure and hydrogen content in the pores of forgings, the hydrogen pressure inside the hydrogen drum was inversely calculated with the finite element method based on the electrochemical hydrogen charging experiment, and the relationship between the hydrogen concentration and the hydrogen pressure in the micropore was established. The growth law of hydrogen drum and the calculation of hydrogen pressure in the drum are studied in order to solve the problem that the micropore or hydrogen segregation zone in metal materials is usually located in the part interior and it is difficult to measure directly. In order to study the change of hydrogen compression strength of micropore in the forming process of large forging, the finite element model of hydrogen pressure field analysis of large forging is established on the basis of hydrogen compression principle. The variation of hydrogen compressive strength and hydrogen concentration in the internal micropores of forgings under different conditions is obtained. The distribution of hydrogen compressive stress field and the coupling between adjacent microvoids under different hydrogen concentrations are studied.
【学位授予单位】:燕山大学
【学位级别】:博士
【学位授予年份】:2016
【分类号】:TG316

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