Analysis of thermal cycles in resistance flash welding of steels

A comparative study of the clad electrode and tubular wire processes was carried out, looking at the mechanical and micro-structural properties of weld metals of high-resistance steel, in the ‘as-welded’ and ‘stress-relief heat treatment’ (PWHT) conditions. The results show that the procedures adopted for welding with tubular wire and clad electrodes allow satisfactory levels of mechanical resistance to be obtained, with the exception of the value of percentage lengthening of the tubular wire, in the as-welded condition. The impact tests show that both the weld metals showed satisfactory impact resistance, in both the as-welded and PWHT conditions, observing that, for the tubular wire, the impact resistance is lower for the clad electrode in both conditions, lying close to the limit applied for the acceptance criterion of 50 J at 0°C in the PWHT condition. It was confirmed that the productivity achieved by the tubular wire process was approximately twice as high as that for the clad electrode process. As a result, the inherent advantage of the tubular wire process must be complemented with a consideration of all the mechanical properties obtained, orienting suitable selection of the welding process, in particular, for application in equipment that operates in fatigue conditions.     

Toughness recovery of modified 9Cr–1Mo steel weld metals after long-term thermal ageing and its evaluation by electrochemical measurement

Recently, thermal power plants have tended to operate under higher temperature and pressure steam conditions for CO₂ reduction. Modified 9Cr–1Mo steels are used in the ultra-super critical power plant because of their excellent creep properties. However, the toughness of base metal decreases after long-term thermal ageing at operation temperature. Moreover, toughness of weld metal is lowest in the MIG weldment. In this study, metallurgical factors of toughness of the modified 9Cr–1Mo steel weld metals by thermal ageing at operation temperature were investigated. And the evaluation method of toughness by the electrochemical measurement used with 5% sulphuric acid aqueous solution was investigated.

The weld metal that received post-welding heat treatment (PWHT: 1023 K and 5.4 ks) decreased toughness by thermal ageing in 873 K and 31.5 Ms. However, toughness of the welds after thermal ageing was recovered to the same level as PWHT welds when the thermal aged welds received the same thermal history as PWHT. A lot of the large Laves phase was observed in the weld metal after the thermal ageing. However, almost all of the Laves phase dissolved in parent phase by the same thermal history as PWHT. Therefore, it seemed that the decrease and the recovery of toughness were mainly determined by the behaviour of precipitation of the Laves phase. The peak of the current density (Ip) in the electrochemical measurement appeared in the weld metals that precipitated a lot of large Laves phase. It seemed that appearance of Ip was caused by the dissolution of the Laves phase. A good correlation between toughness and Ip was observed. Therefore, it can be said that toughness of the weld metals is supposed to be predicted using an Ip of the electrochemical measurement.     

微合金钢焊缝组织中针状铁素体形核与长大驱动力

利用KRC模型对焊缝金属中针状铁素体转变的热力学驱动力进行了理论计算。计算结果表明，焊缝金属中AF(针状铁素体)相变开始温度的理论值为1100K(827℃)。试验所测得的焊缝金属中针状铁索体转变开始温度实际值为670℃，针状铁素体的相变热力学驱动力数值为△G^→AF γ1≤-570J／mol。随着转变温度的降低和焊缝金属中碳含量的降低，针状铁素体的形核和长大驱动力增加针状铁索体的总相变驱动力小于其形棱和长大的驱动力．这种差距随转变温度的降低而增大。     

Technological special features of ultrasound welding polymer films

The design of permanent joints with fillet welds characterized by bevelling of the edges with the depth decreasing with an increase in the distance from the weld edge to the centre of the weld is proposed. The experimental results show that in producing permanent joints with the edge bevel of variable depth, the volume of the deposited metal is reduced by 35% with the corresponding reduction in the material requirement of the process without reducing the load-carrying capacity of the welded joint.     

热处理状态对沉淀硬化模具钢动态断裂韧度的影响

测定了１０Ｎｉ３ＭｎＣｕＡｌ马氏体沉淀硬化型塑料模具用钢在固溶淬火态及不同时间时效后的动态断裂韧度Ｋ＿（１ｄ）。组织为板条状低碳马氏体且条间分布有少量残余奥氏体的固溶态钢，Ｋ＿（１ｄ）值明显高于时效后的Ｋ＿（１ｄ）值，这是由于时效过程中脱溶析出细小弥散的Ａｌ＿３Ｎｉ型沉淀相并对基体产生强烈的应力场所致。试验还表明，此钢的Ｋ＿（１ｄ）冲击速度很敏感，不论是固溶态或时效态，Ｋ＿（１ｄ）都随冲击速度的提高而下降，应用位错动力学理论可对此现象作出解释。     

锆对X70钢焊缝微观组织及韧性的影响

通过在埋弧焊焊剂中添加铁锆合金粉末，以此向焊缝金属过渡锆元素，研究了金属锆对X70钢焊缝金属微观组织和性能的影响。结果表明，锆的加入增加了焊缝金属中针状铁素体的含量，改善了焊缝金属的微观组织。夏比冲击韧性试验显示，锆含量在0．006％时焊缝金属韧性最好。超过0．006％，焊缝金属中虽然也保持了较高的铁素体含量，但由于出现了小岛状的M-A组元，导致韧性降低。     

Ti-V-Nb微合金钢第二相粒子在焊接热循环过程中的变化规律

利用萃取复型技术，对Ti-V-Nb微台金钢母材、焊缝及模拟粗晶区中第二相粒子进行了研究结果表明，母材中的粒子为含有Ti，V，Nb的碳氮化台物复合粒子，其尺寸均在100nm以下；粒子的形状不规则，不同粒子具有不同的成分．焊接过程中，溶池中的碳氮化合物粒了绝大部分发生溶解，溶解到溶池中的Ti通过冶金反应生成TiO，TiO与溶池中的其它脱氧(脱硫)产物结合成尺寸较大的夹杂物；而溶解到溶池中的Nb及V未重新忻出．分析表明，TiO位于夹杂物的表面，且其附近一般有MnAl2O4相，两者具有相同晶体位向．焊接热循环旨，焊接粗晶区中仍保留了较多的粒子，但粒子尺寸显著增大，粒子的形状由母材中的不规则状变为方形，粒子的Ti含量显著提高。     

微合金钢焊缝金属中针状铁素体相变动力学分析

采用热膨胀法成功地测出不同热输入下微合金钢焊缝金属组织中针状铁素体（AF）相变开始温度及终止温度，并绘制出AF转变开始温度和终止温度曲线，得出焊缝金属组织中AF相变温度范围为668—541℃。在热模拟和定量金相试验基础上，通过对试验数据的分析，建立了微合金钢焊缝金属中AF相变的各种T-tc-f动力学曲线。通过对AF各种相变动力学曲线的分析和讨论，得出微合金钢焊缝金属组织中AF相变的一般规律。     

微合金非调质钢的断裂韧性与断裂机理分析

本文测试了两种微合金中碳钢35MnVN和40MnVTi的断裂韧性K_IC值及不同正火处理状态下35MnVN的J_R阻力曲线。对热加工条件及组织参数对K_IC值及J积分值的影响进行了分析。结果表明,采用降低了的始锻温度以及相应低的终锻温度可提高K_IC值。组织状态相似条件下,40MnVTi的断裂韧性值比35MnVN略高些。860～950℃正火处理对改善断裂韧性效果明显,温度过高则无效果。本文还对脆性断裂机制进行了讨论。     

20Cr2MoV钢焊缝金属微观分析

２０Ｃｒ２ＭｏＶ高强度热强钢用埋弧自动焊进行多道多层焊,经调质热处理后,焊缝金属的冲击性值急剧下降,不能满足使用要求。用扫描电镜分析的结果表明：焊缝金属中有较多的非金属夹杂物,特别是夹杂物附近存在微裂纹及晶界碳化物析出是造成焊缝金属低温冲击韧性值低的主要原因。     

温度对焊接热模拟X80管线钢断裂韧性的影响

通过试验和3D有限元模拟相结合的方法分析了焊接热模拟X80管线钢在不同温度（-90,-60,-30和0℃）下的断裂韧度.文中选取标准三点弯曲试样在不同温度下进行断裂韧度测试,同时对测试件进行三维有限元实体建模与分析计算.结果表明,X80管线钢的断裂韧性随温度减低显著减小,并使其倾向于脆性断裂.材料在不同温度下的真实应力-应变曲线行为从光滑拉伸到断裂力学试样具有良好的可传递性,温度对材料的硬化行为没有明显影响,有限元计算的结果表明,应用该方法可以准确地计算X80钢焊接热影响区不同温度下的CTOD值.     

多层多道平焊接头冲击性能不稳定的原因分析

以X70管线钢用药芯焊丝多道焊平焊接头为研究对象.用光镜和扫描电镜观察焊接接头和冲击试样金相组织、寻找冲击断口起裂源，对焊缝冲击韧性不稳定且出现低值的原因进行了研究.结果发现，冲击试样的取样位置不同，冲击吸收功不同；冲击试样开缺口处柱状晶所占比例是冲击韧性出现波动的一个主要原因，但不是其出现低值的原因；缺口前沿焊接缺陷的位置以及粗大晶粒是冲击韧性波动以及出现低值的主要原因，试样冲击吸收功为54.2 J时是解理断裂，解理断裂试样的起裂源为夹杂、未熔合等焊接缺陷，且这些缺陷的位置距缺口越近，冲击韧性越低.     

New methods of predicting dissimilar steel weld metal microstructures by Schaeffler Diagram(Part 2)

On the base of the methods of predicting weld metal microstructures of pearlitic dissimilar steel welded joints using austenitic type filler materials by Schaeffler Diagram, the other new methods of predicting and expressing weld metal microstructures of two kinds of dissimilar steel welded joints (pearlite/pearlite and austenite/pearlite) using austenitic filler materials by Schaeffler Diagram are suggested. Those new methods resolve some difficult problems which the microstructure kinds in two heterogeneous mixture zones of weld metal neighbouring two kinds of welded base metals are difficult to be accurately ascertained and the fluctuations of weld metal microstructures across fusion line are difficult to be conveniently expressed according to the traditional predicting method. The new predicting methods are more concise and practical.     

Ti-Mo微合金钢铁素体中的析出物

用MMS-300热力模拟机研究了变形量、保温温度及保温时间对钛钼微合金钢铁素体基体上析出物尺寸的影响规律,获得了铁素体区析出动力学特征。结果表明,实验钢铁素体基体中析出物主要为钛钼的碳氮化物,其中尺寸较大析出物为圆形、方形或长条形,随机分布;尺寸细小析出物为圆形或椭圆形,其析出形态为排列整齐的相间析出及弥散析出,当保温温度较高时,其分布形式主要为相间析出;随着变形量的增加及保温时间的延长,析出物尺寸减少,随着保温温度的升高,析出物尺寸先增加后减少,铁素体区析出动力学曲线中600℃和700℃为最小尺寸析出温度。     

低合金高强钢焊缝强韧性研究

通过焊丝向焊缝中加入不同合金元素，研究这些合金元素对焊缝强度、冲击韧性尤其是低温冲击韧性的影响。结果表明．尽管所加合金元素不同，焊缝金属冲击功与温度关系曲线上平台能均具有较高水平，但焊缝金属低温冲击韧性受合金化程度的影响较大。采用Ti、B及M等元素多元合全化的焊缝金相组织中针状铁素体比例高，具有较高的低温冲击韧性和强度。     

2205 双相不锈钢管焊缝韧度分析

2205双相不锈钢具有优异的力学性能和耐腐蚀性能,广泛用于运输、石油、天然气、海洋和化工等行业.与普通奥氏体不锈钢相比,双相不锈钢焊接有许多特点,被公认为是一种较难焊接的材料.某天然气集输管道最高操作压力13.3 MPa,最低操作温度-30℃,对韧度提出了较高的要求.对该高压天然气管道钢管纵、环焊缝的冲击韧度和断裂韧度(CTOD)进行了试验、分析.结果表明,纵焊缝(SAW焊接方法)的冲击韧度和断裂韧度比环焊缝(TIG SMAW焊接方法)明显好.其主要原因是采用的填充金属不同,以及因热输入量差异、焊后固溶处理与否而引起显微组织中两相比例的差异造成的.     

热处理工艺对含Nb焊缝金属组织与力学性能的影响

采用含Nb及不含Nb两种焊丝对高速列车转向架用S355J2G3钢板进行焊接,分析了焊态下接头各区域的性能差别,研究了合金元素Nb和焊后热处理制度对焊缝金属组织和性能的影响.结果表明:焊缝金属的韧性是焊接接头性能的薄弱环节.焊态下Nb的加入提高了焊缝金属的强度,但对塑性和韧性无明显影响.经去应力退火后,不含Nb焊缝金属的强度降低,延伸率和冲击功升高,而含Nb焊缝金属的强度升高,延伸率和冲击功降低,退火后含Nb焊缝金属中NbC颗粒析出是影响焊缝金属组织和性能的主要因素.在焊后正火处理条件下,随着正火温度的升高,不含Nb焊缝金属的组织和性能均无明显变化,而含Nb焊缝金属的强度明显升高,延伸率和冲击功显著降低.严格控制正火温度是含Nb焊缝金属获得高强韧性的关键.含Nb焊缝中魏氏组织的含量随正火温度的升高而明显增多.电镜观察表明,经920℃正火处理后,焊缝中的NbC颗粒尺寸大于退火态焊缝金属中的NbC相,而在1200℃正火处理后NbC颗粒溶解消失.     

微合金元素对V-N中碳微合金钢组织和性能的影响

采用金相显微镜和透射电镜等分析方法研究了微合金元素对V-N中碳微合金钢组织和性能的影响.结果表明,V-N中碳微合金钢的热轧态组织为铁素体+珠光体组织,随着钢中V、N含量增加,铁素体含量增多,晶粒变细;微合金钢中的V、Ti、N等元素主要以V(C,N)和V(C,N)+Ti(C,N)形式析出,其中V(C,N)颗粒细小,而V(C,N)+Ti(C,N)颗粒较粗大;细小、弥散分布在钢中的V(C,N)相以析出强化的方式改善了中碳微合金钢的综合力学性能;而适量的Ti在钢中形成弥散分布的TiN相阻止热加工过程中奥氏体晶粒的过分长大,细化了微合金钢的组织.     

Nb-V复合微合金化高钢级管线钢的奥氏体连续冷却转变

利用热模拟试验机研究了3种不同成分的Nb、V微合金化高钢级管线钢的过冷奥氏体连续冷却转变行为,绘制了动态CCT曲线,分析和比较了3种试验钢的显微组织、显微硬度值和动态CCT曲线。结果表明,0.05Nb-0.03V配比能提高多边形铁素体的开始转变温度,从Nb钢的650~700 ℃,提高到700~800 ℃,并缩小多边形铁素体温度转变区间,扩大贝氏体温度转变范围,从Nb钢的400~650 ℃,扩大到350~680 ℃,同时抑制多边形铁素体相变,使管线钢更易获得所需的贝氏体针状铁素体组织。