發(fā)布時(shí)間：2021-06-17 17:23

　　奧氏體不銹鋼是應(yīng)用最廣泛的不銹鋼,由于其優(yōu)異的機(jī)械性能、耐腐蝕性和可加工性,幾乎覆蓋了不銹鋼結(jié)構(gòu)應(yīng)用范圍的60-70%。焊條電弧焊（SMAW）因其成本低、適應(yīng)性強(qiáng)和便攜性好,是不同AISI等級(jí)不銹鋼系列最常用的焊接方法。巴基斯坦的主要工業(yè)中（特別是Heavy Mechanical Complex和Heavy Industries Taxila）,大部分的制造都依賴SMAW。這種焊接方法在巴基斯坦的其他行業(yè)（制糖廠、水泥廠等）的維修部門中也很常用。因此,本文作者采用SMAW方法制備奧氏體不銹鋼接頭,并對(duì)其焊接接頭進(jìn)行研究。在循環(huán)和沖擊載荷的條件下,焊接接頭易產(chǎn)生疲勞和韌性失效。不同焊接條件下的焊縫組織演變對(duì)于焊接接頭的最終壽命產(chǎn)生很大的影響。本研究對(duì)于揭示顯微組織演變對(duì)奧氏體不銹鋼SMAW接頭疲勞壽命和沖擊韌性的影響機(jī)理有著重要的意義。多層多道焊縫中不同焊接區(qū)域的凝固和再凝固以及隨后的相變對(duì)于焊接接頭的力學(xué)性能起著至關(guān)重要的作用。本研究目的之一是研究多層多道焊對(duì)焊縫顯微組織和接頭力學(xué)性能的影響。使用金相顯微鏡測(cè)定了奧氏體中的δ鐵素體相。不同于傳統(tǒng)的依賴于一般鐵素體數(shù)（F.N.）的方法,本... 

【文章來(lái)源】：山東大學(xué)山東省 211工程院校 985工程院校 教育部直屬院校

【文章頁(yè)數(shù)】：208 頁(yè)

【學(xué)位級(jí)別】：博士

【文章目錄】：
Abstract
摘要
Chapter 1 Introduction
    1.1 Significance of Research
    1.2 Scientific Objectives
    1.3 Research Methodology
Chapter 2 Literature Review
    2.1 Welding zones generation
    2.2 Overview of different welding techniques
    2.3 Current status of Shielded Metal Arc Welding (SMAW) process
        2.3.1 Consumable electrodes
        2.3.2 Weld heat input
        2.3.3 Chemical Composition
        2.3.4 Influence of welding parameters
    2.4 Current status of evolved microstructure in steel weldments
        2.4.1 Grain nucleation
        2.4.2 Solidification process
        2.4.3 Microstructure and weldment properties
    2.5 Current status of impact toughness of steel weldments
        2.5.1 Impact toughness at weld interfaces
        2.5.2 Chemical composition influence on Impact toughness
    2.6 Current status of Fatigue life of steel weldments
        2.6.1 Fatigue crack propagation rate FCPR in steel
        2.6.2 Numerical Simulation of Fatigue
Chapter 3 Welding experiments and tensile testing
    3.1 Selection of material
    3.2 Chemical compositions of BM used to produces different specimens
        3.2.1 Chemical composition of base metal
        3.2.2 Mechanical properties of as-received base metal
        3.2.3 Austenitization of as-received base metal
    3.3 SMAW welding for different specimens
        3.3.1 Welding conditions for weldments used to study impact toughness
        3.3.2 Welding conditions for weldments used to study cooling rate effect on fatigue life
        3.3.3 Welding conditions for weldments used to study chemical composition effect on fatigue life
        3.3.4 Welding conditions for weldments used to study multipass welding effect on fatigue life
    3.4 Procedure to measure the cooling rate of pre-heated welded plates
    3.5 Tensile testing of weldments
        3.5.1 Tensile test specimen preparation
        3.5.2 Samples for hardness tests
    3.6 Experimental procedure for different testing
        3.6.1 Tensile test
        3.6.2 Hardness test
    3.7 Tensile tests results
        3.7.1 Multipass weldments
        3.7.2 Variation in cooling rate
        3.7.3 Variation in chemical composition
        3.7.4 Force-displacement curves
    3.8 Hardness tests results
        3.8.1 Multipass weldments
        3.8.2 Effect of cooling rate
Chapter 4 Effect of microstructure on impact toughness
    4.1 Impact toughness testing procedure
    4.2 Impact toughness results
        4.2.1 Effect of chemical composition and cooling rate
    4.3 Quantitative Analysis of microstructure
        4.3.1 Schaeffler Diagram: Estimation of delta ferrite percentage
        4.3.2 Determination of localized δ-ferrites
    4.4 Effect of microstructure on impact toughness
        4.4.1 Impact energy based on δ/γ ratio
        4.4.2 Effect of chemical composition on microstructure evolution, ferrite number and impact toughness
        4.4.3 Effect of multipass welding on impact toughness
Chapter 5 Fatigue test specimens and results
    5.1 Details of specimens used in fatigue test
        5.1.1 Compact Tension (CT) specimen
        5.1.2 Bend test specimen
        5.1.3 Specimens for metallographic study
        5.1.4 Specimens for fractographic study
    5.2 Experimental procedure
        5.2.1 Fatigue crack length measuring
        5.2.2 Fatigue tests on CT specimen
        5.2.3 Bend fatigue tests
        5.2.4 Metallography of weldment
        5.2.5 Fractography of Fracture Surfaces
    5.3 Effect of Multipass welding on Fatigue Test
        5.3.1 Microstructure evolution and its effect on FCPR in single pass welding
        5.3.2 Microstructure evolution and its effect on FCPR in double pass welding
        5.3.3 Microstructure evolution and its effect on FCPR in triple pass welding
    5.4 Microstructural evolution due to variation in chemical compositions and its effect on fatigue life
        5.4.1 Fatigue results of weldments W4, W5 and W6
        5.4.2 Microstructural evolution of weldments W4, W5 and W6
        5.4.3 Discussion on microstructural evolution effect on fatigue life of weldments W4, W5 and W6
    5.5 Effect of cooling rate of pre-heated plates on microstructural evolution and fatigue life of weldments
Chapter 6 Numerical calculation of COD, SIF and analytical modeling of crack tip plasticity
    6.1 Stress intensity factor calculation
        6.1.1 Displacement method
        6.1.2 Singular finite element method
        6.1.3 Energy release rate criteria
    6.2 Numerical model
        6.2.1 J-Integral and COD as damage parameters
        6.2.2 Finite element model (Based on J-integral singularity)
        6.2.3 Working equations developing relationship between COD (δ_t) and stressintensity factor (K)
        6.2.4 Assumption made while adopting this model
        6.2.5 Limitations of the model
    6.3 Numerical simulation procedure
        6.3.1 Material
        6.3.2 Boundary conditions
        6.3.3 Meshing
        6.3.4 J-Integral calculations
    6.4 Simulation results
        6.4.1 Stress intensity factor calculation by COD and J-integral
        6.4.2 Effect of loading range on COD
    6.5 Plastic zone size calculation
        6.5.1 Plastic zone calculation through numerical values of J-integral
        6.5.2 Plastic zone calculation through analytical modeling
Chapter 7 Conclusion and Future work
    7.1 Conclusion
    7.2 Future work
References
Acknowledgement
List of Publications
學(xué)位論文評(píng)閱及答辯情況表


【參考文獻(xiàn)】：
期刊論文
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[2]Effect of welding processes on mechanical and microstructural characteristics of high strength low alloy naval grade steel joints[J]. S.RAGU NATHAN,V.BALASUBRAMANIAN,S.MALARVIZHI,A.G.RAO.  Defence Technology. 2015(03)
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[4]Effect of Aging on the Toughness of Austenitic and Duplex Stainless Steel Weldments[J]. Omyma Hassan Ibrahim,Ibrahim Soliman Ibrahim,Tarek Ahmed Fouad Khalifa.  Journal of Materials Science & Technology. 2010(09)



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