發(fā)布時間：2019-03-15 20:15

【摘要】：大型鍛件制造是重大裝備制造的關(guān)鍵技術(shù)之一,其質(zhì)量直接影響到重大裝備的整體水平和運行可靠性,是發(fā)展電力、船舶、冶金、石化、重型機械和國防等工業(yè)的基礎(chǔ),是發(fā)展先進裝備制造業(yè)的前提。大型鍛件在高溫成形及其降溫過程中,由于氫析出并偏聚于鍛件內(nèi)部的微缺陷中,所產(chǎn)生的內(nèi)高壓和微裂紋極易導(dǎo)致零件突然斷裂,稱之為氫脆,是大鍛件質(zhì)量控制中最為危險和棘手的問題。近年來的研究成果雖然在熱-力-微觀組織耦合方面取得了一些新的進展,但對于大鍛件的氫脆問題一直沒有得到很好的解決。為研究氫脆損傷的產(chǎn)生機理,本文以氫脆敏感性高的合金鋼為研究對象,采用物理模擬及有限元分析相結(jié)合的方法對大型鍛件中的氫濃度、氫擴散以及氫脆損傷的機理進行了綜合研究。由于氫原子是自然界中質(zhì)量最輕和半徑最小的原子,想要準確地測量鍛件中的氫含量一直是困擾工業(yè)界和科學(xué)界的一項難題。為了對鍛件中的氫含量及氫濃度分布進行研究,本文利用有限元方法建立了大型鍛件鍛后熱處理過程的擴氫計算有限元模型,分析得到了材料在熱處理過程中的氫擴散規(guī)律。對于大型鍛件來說整個熱處理過程都是在擴氫的,為了能時刻檢測鋼中氫的含量,必須要掌握鋼中氫的滲透速率。本文以菲克第二定律為依據(jù),利用電化學(xué)工作站及配套測試軟件對不同成分的合金鋼進行了氫擴散系數(shù)的測定實驗,給出了一種適合于金屬材料氫擴散系數(shù)測定的實驗方法。為了對材料的氫脆損傷機理進行研究,通過充氫實驗使外界的氫原子不斷的向鍛件內(nèi)部擴散,并對試件的緩慢拉伸過程進行數(shù)據(jù)記錄,分析了40Cr和45號鋼在不同充氫電流和充氫時間條件下的氫致鼓包的形貌特征、抗拉強度、延伸率等力學(xué)性能參數(shù),以延伸率的變化量為氫脆指標對氫脆程度進行度量,且通過充氫-拉伸實驗和充氫-放置-拉伸實驗驗證了氫致?lián)p傷的不可逆性。為了對鍛件內(nèi)孔洞的氫壓及氫含量進行定量分析,在電化學(xué)充氫實驗的基礎(chǔ)上結(jié)合有限元方法對氫鼓包內(nèi)部的氫壓進行了反算研究,建立氫濃度與微孔隙氫壓的聯(lián)系,對氫鼓包的長大規(guī)律和鼓包內(nèi)氫壓計算進行研究,用以解決金屬材料中的微孔隙或氫偏聚區(qū)往往位于零件內(nèi)部且很難進行直接測量的問題。為研究大型鍛件成形過程中微孔隙氫壓強度的變化,以氫壓原理為基礎(chǔ),建立了大型鍛件氫壓場分析的有限元模型,得到了不同條件下鍛件內(nèi)部微孔隙氫壓強度和氫濃度的變化規(guī)律,研究了不同氫濃度下氫壓應(yīng)力場的分布及相鄰微孔洞間的耦合作用。
[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.
【學(xué)位授予單位】：燕山大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG316

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本文編號：2440951