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Electro-slag welding with heat input of 530kJ/cm was applied to 60mm thick shipbuilding plate EH40, and microstructure and mechanical properties of the weld joint were characterized. Different regions such as heat affected zone, fusion zone, weld metal and base metal are found across the weld joint by microstructure analysis. A narrow coarse grain heat affected zone consisting of acicular ferrite, polygonal ferrite and grain boundary ferrite is found, width of which is less than 1mm. Acicular ferrite (?? 10??m) and grain boundary ferrite is observed at weld metal, while fusion zone have a complex structure of acicular ferrite, grain boundary ferrite and ferrite side plate. Mechanical property tests show that the absorbed energy of WM, FL and CGHAZ at -20?? during Charpy impact test is more than 60J, no evident softening phenomenon occurred at heat affected zone, and other properties met the requirement.     

低合金高强钢针状铁素体组织特征和形成机理

针状铁素体是一种具有大角度晶界、高位错密度的板条状中温转变组织,该组织能有效细化晶粒并具有良好的强韧性匹配.因此,通常在低合金高强度钢焊缝和粗晶区中,利用细小的夹杂物来诱导针状铁素体形成,形成有效晶粒尺寸细小的针状铁素体联锁组织或者针状铁素体和贝氏体的复合组织,使其具有良好的韧性.然而,相关研究对针状铁素体组织的形成机理和控制原理的解释并不十分清楚,对于针状铁素体的定义和理解也存在差异.总结了针状铁素体的本质、相变、形核、形态、晶体学取向关系、长大行为、细化机理和力学性能等方面的特征,归纳了奥氏体晶粒尺寸、转变温度、冷却速度、夹杂物类型和尺寸等对针状铁素体形成的影响,提出了针状铁素体组织形态和转变机理方面几个仍需深入研究的问题和方向.     

油罐钢焊接接头的组织与力学性能分析

通过拉伸、冲击、组织观察等方法对油罐钢气电立焊焊接接头的力学性能和显微组织进行了研究。结果表明,在100 kJ/cm线能量的条件下,接头具有良好的抗剪切强度和低温韧性。粗晶区组织主要由粒状贝氏体和板条贝氏体组成,并存在一定数量的M-A岛,细晶区主要为块状和多边形铁素体组织。     

不同强度级别低合金钢焊缝金属的组织特征及其对韧性的影响

焊接区的微观组织是决定其力学性能的关键因素。为了改善低合金钢焊缝的冲击韧性,对500~1 000MPa级焊条的焊缝金属的化学组成、金相组织和力学性能进行了对比研究。采用金相显微镜和透射电子显微镜对不同强度级别的低合金钢焊缝组织进行了观察和电子衍射分析,并进行了焊缝金属拉伸强度和冲击韧性测试。结果表明,随着焊条强度级别的增加,焊缝组织由先共析铁素体、针状铁素体加珠光体变成粒状贝氏体,最后变成贝氏体加马氏体组织;当焊缝组织为粒状贝氏体时其韧性最低。     

铈和铌改性对DP780双相钢焊缝冲击性能的影响

 双相钢中铁素体马氏体两相性能差异会导致焊接接头软化,在使用过程中温度较低时,冲击功下降,使材料由韧性状态变为脆性状态。为研究铈和铌添加量对改善DP780焊缝低温脆性的问题,利用低温冲击试验与拉伸试验,开展了不同铈和铌添加量对DP780焊缝的力学性能的研究。利用金相显微镜、SEM等方法阐明了试验钢在添加不同铈和铌后的焊缝组织与形貌变化。结果表明,在-40 ℃时,无铈和铌添加时组织中出现部分残余奥氏体,焊缝冲击功为0.465 J,解理台阶面出现大量河流花样,属于脆性断裂;随铈与铌质量分数变化,焊缝冲击功与铈和铌的添加量呈现非线性关系。当铈与铌占熔敷金属质量分数分别为0.35%和0.15%时焊缝的综合性能最佳,冲击功达到3.9 J,熔敷金属组织晶界紧密,撕裂棱周围出现韧窝,呈混合断裂特征。试验研究表明,加入的适量的铈与铌,焊缝中形成的稀土化合物可增加断裂变形阻力与消耗能量,从而有效阻碍裂纹的扩展,显著提高DP780的低温冲击韧性而不会大幅降低其抗拉强度,保证双相钢焊接质量。但铈与铌影响焊缝性能无固定函数关系可循且试验样本量少,无法精确到任意添加量探究。在后续研究中可引入算法对DP780焊缝力学性能进行预测,在生产之前建立模型,寻找最佳铈和铌添加量,提高安全性能。     

Analysis Microstructure of Weld Metal for HQ130+QJ63 High Strength Steel

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Ti对大线能量焊接焊缝组织和性能的影响

对不同Ti含量的气电立焊焊缝组织及力学性能进行了对比研究。结果表明,Ti的质量分数在0.028%~0.038%范围内时,焊缝中获得大量细小的针状铁素体,焊缝组织及低温韧性得以明显改善。当Ti过量时,焊缝中的针状铁素体减少,组织以贝氏体为主,低温韧性相应下降。焊缝组织中观察到块状和条状的M-A组元,随着焊缝Ti含量增加,其总量增加。焊缝夹杂物多为以氧化物为核心,外层包裹着MnS的复合夹杂物,并随夹杂物Ti含量的增加,由Mn-Si-Al-O型向Ti-Mn-Al-O型转变,有利于促进针状铁素体形成。而当焊缝中Ti过量时,主要夹杂物又转变为对针状铁素体形核无效的Ti-Al-O型,促进了贝氏体转变。     

线能量对V-N-Ti和Nb-Ti船板焊接接头组织性能的影响

为了验证实验室研究结果,研究了100 kJ/cm线能量对V-N-Ti和Nb-Ti船板焊接接头组织和性能的影响规律.试验结果表明,2种船板钢屈服强度、抗拉强度和伸长率相当,V-N-Ti钢-40℃冲击功显著高于Nb-Ti钢;2种成分钢板焊接接头热影响区-20℃冲击功相当,而V-N-Ti钢焊缝金属冲击功显著低于Nb-Ti钢;...     

无碳化物贝氏体耐磨钢板组织与性能的研究

研究了无碳化物贝氏体耐磨钢板组织、力学性能及焊接性能。结果表明,在低碳贝氏体钢基础上,通过加入一定量的硅元素,利用其在贝氏体组织转变过程中抑制碳化物析出作用,得到由非等轴铁素体加马氏体和残余奥氏体(M-A)岛或由板条状铁素体及其板条间残余奥氏体(Ar)膜组成的无碳化物贝氏体组织,以此得到既具有高强度、高硬度,又具有较高的低温冲击韧性,同时具有较好的焊接性能。     

屈服强度460MPa级耐候钢及其焊接性能

通过连续冷却相转变行为的研究,利用试验轧机成功试制了24mm厚,屈服强度460MPa级耐候钢板,并分析了钢板微观组织、力学性能、腐蚀性能以及焊接性能。连续相转变行为和钢板试制结果表明:精轧温度不大于850℃,厚度压下率不小于0.6,冷速为4~15℃/s和终冷温度不大于465℃可得到以针状铁素体(3~10μm)和多边形铁素体(5~15μm)为主的钢板,其屈服强度不小于480MPa,抗拉强度不小于635MPa,伸长率不小于23%,-40℃冲击功不小于209J。对试制钢板进行了热输入量为72kJ/cm的双丝埋弧焊接试验,无焊前预热和焊后热处理,得到了无缺陷焊接接头,焊接热影响区-40℃冲击功不小于100J;粗晶区的高韧性与其晶内铁素体为主以及少量晶界铁素体和上贝氏体的微观组织有关。72h周浸试验结果表明:试制钢种的耐大气腐蚀能力比普碳钢Q345B提高了46%。     

40CrNiMoA钢同质焊条焊接接头组织和性能研究

分析了焊接电流70A、80A、90A对40CrNiMoA钢焊缝接头组织和力学性能的影响。随着焊接电流的增大,焊缝外观质量较好。随着焊接电流的增大,熔池区温度升高,奥氏体晶粒尺寸增大,导致马氏体组织粗大。焊缝的显微组织为马氏体及少量残余奥氏体。焊缝的硬度远高于母材的硬度,且波动较大。热影响区的硬度从母材向沿焊缝方向逐渐升高。焊接接头纵向应力在焊缝中心为压应力,向外压应力减小。焊接颜色区边界处纵向应力为拉应力,且该点拉应力最大。焊接接头横向应力在焊缝中心为拉应力,向外逐渐增大,焊接颜色区边界处变横向拉应力达到最大。焊接电流和热输入增大,降低了材料的韧性,组织中铁素体增多及焊接残余应力是诱发脆性断裂的原因。焊接电流80A是40CrNiMoA同质焊条平板对接焊接工艺的最佳的焊接电流。     

12CrlMoV低合金钢管的焊接组织与性能

通过对12Cr1MoV低合金钢管试验及分析,结果表明,其力学性能符合标准.焊缝及热影响区组织为贝氏体 铁素体,焊缝和细晶区晶粒细小、显微硬度较高;粗晶区晶粒粗大、硬度较低;基体组织为铁素体 珠光体,硬度更低.总体焊接性能良好,尚能满足使用要求.     

12%Cr铁素体不锈钢焊接接头组织及韧性研究

对四种不同成分的12%Cr铁素体不锈钢做了焊接性试验。分析焊接接头的组织,测量了焊接接头的低温冲击功。试验结果表明,随着碳含量的增加,焊接粗晶区组织由单相铁素体逐渐转变成以马氏体为主,粗晶区宽度变窄,晶粒尺寸变小。细晶区组织以马氏体为主,组织细小均匀。熔合线处和热影响区的低温冲击功相比母材均显著降低。断裂路径分析结果表明,窄的粗晶区宽度和小的晶粒尺寸使断裂路径经过更多的奥氏体焊缝区,提高了整体的冲击韧性。     

焊后热处理对07MnCrMoVR钢热影响粗晶区-20℃冲击韧性的影响

采用光学显微镜、扫描显微镜、透射电镜和冲击韧性试验机对07MnCrMoVR钢热影响粗晶区在460～660℃ 2h焊后热处理工艺下的组织性能进行了分析。结果表明,随着焊后热处理温度的升高,焊缝热影响粗晶区-20℃冲击韧性呈现先降低再升高的现象。焊后热处理钢在580℃和620℃出现再热裂纹倾向,冲击试样为脆性断口,解理断裂,沿着晶界出现了微裂纹,主要是因为碳化物沿着晶界析出并长大弱化了晶界的结合能,导致低温冲击韧性出现降低。≥620℃焊后热处理,07MnCrMoVR钢出现再结晶的现象,位错消失,铁素体晶粒合并长大使其低温冲击韧性又重新升高。该钢最优焊后热处理为460～500℃ 2 h。     

Correlation Between Microstructure and Low-Temperature Impact Toughness of Simulated Reheated Zones in the Multi-pass Weld Metal of High-Strength Steel

A large fraction of reheated weld metal is formed during multi-pass welding, which significantly affects the mechanical properties (especially toughness) of welded structures. In this study, the low-temperature toughness of the simulated reheated zone in multi-pass weld metal was evaluated and compared to that of the as-deposited zone using microstructural analyses. Two kinds of high-strength steel welds with different hardenabilities were produced by single-pass, bead-in-groove welding, and both welds were thermally cycled to peak temperatures above Ac₃ using a Gleeble simulator. When the weld metals were reheated, their toughness deteriorated in response to the increase in the fraction of detrimental microstructural components, i.e., grain boundary ferrite and coalesced bainite in the weld metals with low and high hardenabilities, respectively. In addition, toughness deterioration occurred in conjunction with an increase in the effective grain size, which was attributed to the decrease in nucleation probability of acicular ferrite; the main cause for this decrease changed depending on the hardenability of the weld metal.     

Investigations on Dissimilar Weld of UNS S32205 DSS and ASTM A517 Steel

In the present research, microstructure and mechanical properties of 2205 duplex stainless steel/A517 quench and tempered low alloy steel dissimilar joint were investigated. For this purpose, gas tungsten arc welding was used with ER2209 filler metal. Characterizations were conducted by optical microscopy, scanning electron microscopy equipped with an energy dispersive spectroscopy and X-ray diffraction. Mechanical properties were evaluated in micro-hardness, tensile and impact tests. Microstructure in the weld zone included an austenitic continuous network in the matrix of primary ferrite. No brittle phases were formed in the weld metal and stainless steel heat affected zone (HAZ). The weld metal/A517 interface showed higher hardness than other regions. Tensile tests indicated that the values of the yield and tensile strength were 663 and 796 MPa, respectively. Impact tests indicated that the weld zone had almost the same impact energy as base metals. The minimum impact energy of 12 J was related to A517 HAZ. The results of scanning electron microscopy for fracture surfaces indicated that weld zone, 2205 HAZ and A517 HAZ had ductile, ductile–brittle and brittle fracture mode, respectively.     

Effect of Mechanical Arc Oscillation on the Grain Structure of Mild Steel Weld Metal

The effect of mechanical arc oscillation on the weld metal grain structure in mild steel gas tungsten arc welds has been studied. For welds made without arc oscillation, columnar grains were observed in the weld metal; however, for the same welding parameters, the weld made with arc oscillation had smaller sized relatively equiaxed grains in the weld metal. The strengths for weld made with arc oscillation was higher than that for weld made without arc oscillation, with appreciable increase in ductility; this could be attributed to the reduction in grain size diameter due to arc oscillation. Lower weld metal hardness and increase in heat affected zone hardness was observed in weld made with arc oscillation; this could be attributed to increase in pro-eutectoid ferrite formation with absence of Widmanstatten ferrite structures in the weld metal and less coarsening of grains in the heat affected zone due to increased cooling rate.     

TMCP工艺对低碳Ni-Nb钢组织转变和力学性能的影响

 为了研究TMCP工艺对低碳Ni-Nb钢显微组织转变类型和晶粒尺寸的影响规律,研究了不同TMCP工艺下的显微组织特征及其对力学性能的作用机理。结果表明,在未变形轧制情况下,当冷却速度小于5 ℃/s时,显微组织为铁素体和珠光体,铁素体晶粒尺寸随着冷却速度的增大而减小;在变形轧制情况下,随着冷却速度的增加,组织中的铁素体晶粒尺寸明显减小;当冷却速度增大到5 ℃/s时,微观组织中出现了大量粒状贝氏体。试制钢板试验表明,当冷却速度为4 ℃/s时,试验钢的组织为准多边形铁素体,可以有效提高钢的低温韧性;当冷却速度达到6 ℃/s时,试验钢微观组织中出现大量粒状贝氏体,明显降低钢的低温韧性。     

Hybrid Laser-Arc Welding of X90 Pipeline Steel: Effect of Laser Power on Microstructure and Mechanical Properties

In this work, hybrid laser-arc welding process was applied to X90 pipeline steel which has wide potential applications in the future pipeline project. The effect of different laser power (1.0, 1.5 and 2.5 kW) on microstructure and mechanical properties of weld joints was investigated. It has been found that a macroscopic morphology of “wine cup like” is observed in the weld joint with increasing laser power, where fusion zone (FZ) and heat-affected zone (HAZ) can be clearly identified. The FZ microstructure mainly includes massive ferrite, acicular ferrite (AF), and increased laser power resulting in a decrease in AF content. The HAZ consists of coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ) and mixed-grained HAZ (MGHAZ). The hardness ranging from the weld center to base metal decreases and then increases, and the effect of laser power on hardness is not significant. The increased laser power leads to an evident decrease in the ultimate tensile strength and impact toughness of weld joint. The highest ultimate tensile strength and impact energy are 815 MPa, 239.1 J respectively at a laser power of 1.0 kW. A number of inclusions are observed at the bottom of dimples, which may be the (Ti,Mn)₂O₃ particles.     

LNG用镍基合金焊条熔敷金属的组织与性能

目前国产LNG用镍基低温焊条存在的主要问题是无法同时满足强韧性要求。采用金相显微镜和扫描电镜对自主生产的3种ENiCrMo-6焊条熔敷金属的显微组织进行观察,应用硬度、冲击和拉伸试验对接头力学性能进行测试分析。结果表明:焊缝金属主要由奥氏体以及析出物构成,晶界间存在的低熔点共晶物,易形成沿晶裂纹,降低熔敷金属的拉伸、冲击和弯曲性能。随着合金含量的升高,强度和硬度总体呈上升趋势,对塑性和韧性有所损害,Nb的碳化物析出对裂纹扩展具有阻碍作用,有利于提高韧性。新研制的镍基焊条满足LNG设备对焊缝金属的性能要求。