厚板多层多道焊温度场的有限元分析

考虑坡口形式对焊接热输入分布的影响及焊缝横断面形状特征,建立了超细晶Q460高强钢厚板多层多道GMAW焊有限元分析模型.利用ANSYS软件对超细晶钢多层多道焊焊缝及热影响区形状尺寸进行了模拟计算,计算结果与试验结果吻合较好.对超细晶钢多层多道焊温度场及热循环曲线进行了计算和定量分析.结果表明,后续焊缝对整个厚度方向上热影区热循环的峰值温度、高温停留时间及冷却时间有重要影响,应严格控制后续焊缝热输入或层间温度.     

焊接热输入对HQ130钢焊接热影响区组织硬度的影响

ＭＩＧ／ＭＡＧ焊接热输入包括焊接电弧热流和熔滴带入熔池的热焓量两部分,本文以作者提出的焊接热输入分布模型为基础,建立了熔流场和温度场的数值分析模型,采用数值模拟技术研究了焊接热输入对ＨＱ１３０钢焊接热影响区（ＨＡＺ）组织和硬度的影响规律,给出了不同焊接热输入时ＨＡＺ不同部位奥氏体晶粒尺寸及组织和硬度的计算结果,实验表明,ＨＱ１３０钢焊接热循环及ＨＡＺ组织,硬度的计算值和值吻合良好。     

热输入对Q890D低合金高强钢焊接性能的影响

通过分析不同焊接热输入下Q890D钢板的焊接接头金相组织及热影响区硬度,考察了不同焊接热输入对其焊接接头强度、-20 ℃低温冲击吸收能量的影响。结果表明,Q890D钢在热影响区存在明显淬硬现象。当焊接热输入由低向高变化时,热影响区的硬度有上升趋势,而表面焊道的热影响区硬度远远高于打底焊道,说明多层多道焊时,后道焊缝对前道焊缝的热处理效果比较明显,减少了热影响区的淬硬组织。打底焊道的热影响区硬度低于焊缝及母材,存在焊后软化现象,焊接时需尽量避免过大的焊接热输入。焊缝金属中粗大贝氏体组织的增加,导致焊缝金属低温冲击吸收能量普遍低于热影响区。随着热输入的减小,焊接接头的抗拉强度和冲击吸收能量(包括焊缝、熔合线及HAZ)都有很大的提升。说明焊接热输入在一定范围内的变化对整个焊接接头强度及塑韧性有较大的影响。     

S355钢激光-MIG复合焊接头显微组织和残余应力

采用激光-MIG(metal inert gas welding, MIG)复合焊接方法对12 mm厚S355钢板进行焊接,分析了9 kW激光功率下复合焊接头显微组织和硬度分布规律. 建立了适合低合金高强钢激光-MIG复合焊接的双椭球 + 三维锥体复合热源模型来描述复合热源的能量分布,采用SYSWELD软件计算了1.0,1.5,2.0 m/min三种焊接速度下激光-MIG复合焊的温度场和接头的残余应力,分析了焊接速度对焊接过程的温度场和残余应力分布的影响. 结果表明,三种焊接速度下粗晶热影响区(coarse grained heat affected zone, CGHAZ)的组织为马氏体,接头的硬度水平较高,最高硬度均在350 HV以上. 焊接速度增加,熔池最高温度下降,焊后冷却速度增加. 等效残余应力水平较高,HAZ位置出现了应力集中;随着焊接速度增加,等效残余应力、纵向残余应力、横向残余应力和厚度方向的残余应力峰值均上升;但焊接速度从1.5 m/min增加到2.0 m/min时,各应力分量的拉应力峰值上升较少,而压应力峰值显著上升.     

双丝埋弧焊接头性能研究

在16Mn钢板上进行双丝自动埋弧焊工艺试验,得到了不同焊接速度下的焊件.对不同工艺参数下得到的焊接接头试样进行了拉伸试验、硬度测试以及金属显微组织观察,并计算了双丝自动埋弧焊时的熔敷率.结果表明:采用双丝埋弧焊得到的焊缝外形美观;金属熔敷率与焊接速度成反比;随着焊接速度的降低焊接线能量相应的增大,较长的高温停留时间会促...     

回火焊道对核电低合金钢表面镍基堆焊层热影响区性能的影响

采用钨极氩弧焊焊接方法在核电用16MND5低合金钢表面进行690镍基焊丝堆焊,分别堆焊1层和利用回火焊道方法堆焊3层,研究回火焊道对堆焊层热影响区的硬度、组织和冲击韧性的影响。结果表明:回火焊道产生的回火效应可有效降低合金钢镍基堆焊层热影响区的硬度至可接受硬度范围320HV10以下,堆焊层热影响区的冲击韧性提高27%以上,均值达到163J/cm2,热影响区板条状组织得到有效回复,获得满足RCC-M标准要求的低合金钢焊接热影响区硬度和冲击韧性指标。研究表明利用回火焊道技术可实现低合金钢镍基堆焊免除高温回火热处理。     

能量配比对激光-MIG复合焊接头残余应力的影响

采用不同激光/电弧能量配比(QRLA)对8 mm厚Q345钢板进行激光-MIG(metal inert gas,MIG)复合焊接,研究了QRLA对复合焊接头的截面形貌和显微组织的影响,并分析了不同QRLA下焊接过程的温度场和接头残余应力分布的变化规律.结果表明,随着QRLA增大,熔宽显著下降,焊接过程的最高温度略有升高...     

Metallographic structure analysis of DC pulsed SAW joint

Submerged arc welding （SAW） has shortcoming of over heat input, which increases grain size in heat-affected zone （ HAZ） and decreases welding quality and mechanical properties of the joints serioasly. With improvements of welding equipment, direct current （ DC） pulsed SAW （ PSAW） was utilized successfully in the research. Comparing DC PSAW with DC common SAW （ CSAW） , the metallographic structure was analyzed with optical and electron microscope, the width of HAZ was measured as well as the width and hardness of the coarse grained HAZ （CGHAZ）. The research shows that DC PSAW joint had higher welding penetration, narrower HAZ and CGHAZ, which benefited HAZ performance and welding quality.     

Microstructures and hardness of flat overhead weld of the high strength steel thick plate using double-sided arc welding

High strength steel thick plate is widely used in shipbuilding, pressure vessels, etc., the balance between weld quality and welding efficiency is becoming a research focus. In this paper, double sided double arc flat-overhead welding experiments for high strength steel thick plate were conducted. Microstructures of weld have been observed through optical microscope (OM) and scanning electron microscope (SEM). Transformation of microstructures under thermal cycles of multi peaks was analyzed. Macro and micro hardness were also tested. The results show that the heat-affected zone (HAZ) near the fusion line experiences thermal cycles up to three times. The microstructures there are the most complex, including coarse lath martensite in original coarse-grained zone, and net like structure along grain boundaries in critical reheat coarse grained zone. After several times of tempering for backing welding, the features of acicula and lath are weakened. Its microstructure approaches to the microstructure of base metal which is tempering sorbite. The hardness test shows that the maximum hardness occurs at critical reheat coarse-grained zone, the hardness of reticulation structure at grain boundary can be up to 450HV.     

EQ70钢激光电弧复合焊焊接热循环及其对热影响区组织演变的影响

采用Visul Environment 软件建立了EQ70钢激光电弧复合焊的三维模型,并利用SYSWELD软件对激光电弧复合焊焊接温度场进行了有限元数值模拟,结合热电偶测温法和热影响区的微观组织表征分析了激光电弧复合焊热循环特点及其对热影响区组织演变的影响. 结果表明,采用双椭球体+峰值递增锥体组合型热源可以准确模拟复合焊温度场,电弧区、过渡区、激光区相同热影响区微区具有相近的热循环,热影响区加热速度可达400 ℃/s,1 100 ℃以上停留时间为0.79～1.33 s,t_8/5为4～6 s. 粗晶区、细晶区组织为板条马氏体,临界区组织为马氏体+晶界碳化物,亚临界区组织为回火马氏体. 激光电弧复合焊具有快速加热、高温停留时间短的特点,在一定程度限制了奥氏体晶粒的长大,粗晶区和细晶区平均晶粒尺寸分别为42.7,19.8 μm.     

X80/X100异种钢激光-MIG复合焊接头显微组织和性能

采用激光-MIG复合焊对X80管线钢和X100管线钢进行焊接,研究了激光功率对复合焊接头的焊缝形貌、显微组织、硬度、强度和韧性的影响规律.结果表明,激光功率从2.0 k W增大至3.5 k W时,盖面焊缝熔宽和熔深增加,激光区熔深明显增加;激光区焊缝中AF含量增加、LB含量减少,X100侧粗晶热影响区和细晶热影响区中条状贝氏体含量减少,X80侧粗晶热影响区和细晶热影响区中准多边形铁素体含量增加.复合焊接头硬度分布并不对称,最高硬度出现在X100侧熔合区部位.复合焊接头的抗拉强度基本不随激光功率变化,拉伸试样断裂位置均为X80侧母材.随着激光功率增大,焊接接头最高硬度和韧性均下降.     

Q890高强钢焊接淬硬倾向和冷裂纹敏感性

通过焊接热模拟试验、焊接热影响区最高硬度试验以及公式计算,分析了Q890钢的焊接淬硬倾向和冷裂纹敏感性.结果表明,稻垣道夫建立的经验公式比D·Vwer建立的理论经验公式更适用于计算厚板的焊接冷却时间t8/5.Q890钢焊接热影响区的粗晶区具有较强的淬硬倾向,调整焊前预热温度以及焊接热输入,对Q890钢热影响区的淬硬倾向无明显改善,但焊前预热能有效增大冷却时间t100,降低试验钢的焊接冷裂倾向.通过计算机拟合建立了冷却时间ts/5与焊接热影响区过热区硬度的关系式,经过验证该关系式能够对Q890钢最高硬度进行合理的预测.     

工业绿色发展工程科技战略及对策

采用Formastor-F Ⅱ 全自动相变仪,结合光学显微镜(OM)和维氏硬度测试,研究不同冷却速率对1 400 MPa级超高强钢焊接热影响区(HAZ)粗晶区组织转变和性能的影响规律,绘制焊接连续冷却转变曲线(SH-CCT),结合焊接工艺试验,采用公式法确定最佳焊接工艺参数. 结果表明,1 400 MPa级超高强钢马氏体临界转变冷却速率约为5 ℃/s,当冷却速率大于5 ℃/s时,热影响区粗晶区组织为单一板条马氏体,硬度值为487 ~ 509 HV5,冷却速率小于5 ℃/s时,粗晶区组织中出现中高温相变产物,即板条贝氏体、粒状贝氏体和铁素体等组织,硬度值下降为487 ~ 260 HV5,同时组织中还出现M-A组元,其含量随冷却速率降低先增加后减少,形态也由弥散颗粒状变为断续长条状或块状分布;厚度8 mm的1 400 MPa级超高强钢焊接时,热输入控制在20 kJ/cm以内,粗晶区组织为板条马氏体,硬度维持在500 HV5左右,粗晶区不发生软化现象,满足工程使用要求.     

Numerical modelling of temperature distribution during multipass welding of plates

Abstract

Welding is a reliable, cost effective, and efficient metal joining process. Manual metal arc welding (MMAW) is a widely used welding process in industry and multipass welding is very frequently used in the MMAW process. The temperature distribution that prevails during multipass welding affects the material microstructure and hardness of the regions near the weld, and the residual stresses that will be present in the material after cooling to room temperature. These changes will consequently affect the performance of the welded joint. In the present work, a computer model based on the control volume method has been developed to predict the temperature distribution during multipass welding of plates using the MMAW process. To validate the computer model, the temperature distribution was measured experimentally in a 12 mm thickness stainless steel weld pad during multipass welding. The welding parameters were used as input data for the computer model. The computer predictions and the experimentally measured temperature distributions agree well.     

A stochastic model for austenite phase formation during arc welding of a low alloy steel

Modeling the microstructure of heat-affected zone (HAZ) in weld area can be useful in predicting mechanical behavior of the weldment. A multi-scale model is proposed to calculate the temperature distribution and to predict the microstructure evolution within the HAZ. Finite difference method was used to develop a computer model for studying the cooling curves during welding, and a stochastic method to analyze the austenite formation and its grain growth in HAZ. The droplet of liquid metal detached from electrode in manual arc metal welding is an important concern in studying the temperature distribution and the austenite grains growth. Both heat content of liquid metal detached from electrode and heat generated by electrical arc were used in calculation of temperature distribution. The stochastic model simulates the austenite phase formation and its growth during welding based on the kinetics of these processes. With this model, it is possible to visualize the topology of austenite phase. This multi-scale model was applied to the welding of low alloy steel. The observed morphology was in good agreement with that predicted by the model.     

400MPa级超细晶粒钢电弧焊焊接接头组织与性能

采用普通电弧焊方法（手工电弧焊、二氧化碳气体保护焊、埋弧焊）对400MPa级超细晶粒钢进行焊接,并对不同工艺条件下的焊接接头的组织与性能进行了分析。结果表明,400MPa级超细晶粒钢电弧焊焊接接头热影响区存在着明显的晶粒长大现象;手工电弧焊和埋弧焊焊接接头性能明显下降,而二筘化碳气体保护焊焊接接头性能下降不明显。根据试验结果,实际生产中可以利用二氧化碳气体保护焊方法焊接400MPa级超细晶粒钢。     

Study on heat source model in twin-arc GMAW with a common weld pool

The heat input from arcs to weld pool in twin-arc gas metal arc welding (GMAW) with a common weld pool is investigated by high-speed photography. The characteristics of arc shapes and droplet transfer are studied and then the models for heat flux distribution on top surface of weld pool and enthalpy distribution of metal droplets transferred into weld pool are established. By using the model, 3-D geometries of weld pools in twin-arc GMAW with a common weld pool are predicted. Corresponding welding experiments on mild steel plates are carried out and the results indicate that the predicted shape of weld bead on cross section shows good agreement with measured one.     

Novel method of thermite welding

Abstract

This article presents a novel method of thermite welding. A hand operated portable welding can be conveniently realised using self-made thermite welding pencil without any welding equipments. A butt junction was obtained between two low carbon steel plates. Morphological, microstructure and mechanical analyses of the weld bead were carried out. The results demonstrated that the two steel plates were jointed by fusion bonding with the filler. No defects such as porosity and microcrack were found. The hardness test showed the low hardness of the fusion zone compared with the base material. In addition, the grain growth in HAZ did not affect the hardness of the base material. The average tensile strength of welds was 285·4 MPa, ～70% of the average tensile strength of low carbon steel.     

400 MPa级超细晶粒钢板焊接热影响区的组织和力学性能

超细晶粒钢的强度和韧性比普通晶粒钢有大幅度的提高，其焊接性是该钢能否获得广泛应用的关键。通过采用实际焊接和焊接热模拟方法，研究了焊接热输入对超细晶粒钢组织和力学性能的影响。研究结果表明，超细晶粒钢的奥氏体晶粒长大倾向与普通晶粒钢相近，在热影响区和母材之间存在一再结晶软化区，板厚小于3mm时，粗晶热影响区的裂纹扩展吸收能大于母材，板厚大于5mm时，粗晶热影响区韧性比母材有较大幅度降低。对影响粗晶热影响区韧性的机理进行了探讨。     

Role of Welding Parameters Using the Flux Cored Arc Welding Process of Low Alloy Steels on Bead Geometry and Mechanical Properties

Welding parameters have direct effects on the bead geometry, microstructure, and mechanical properties of low alloy steels. A series of experiments have been carried out to examine some of these parameters using the flux cored arc welding process (FCAW). In this article, an experimental study was conducted to investigate the influence of welding parameters in FCAW process particularly welding voltage and travel speed on weld bead dimensions. The study also includes the effects of bead overlap and deposition sequence on the parent material and the heat-affected zone (HAZ) properties. It was found that an increase in the welding voltage leads to an increase in the weld bead width, and the increase in the welding traverse speed leads to a decrease in the weld bead width. When studying the bead overlap percentages, it was found that the 50% bead overlap can be considered to be practically a better option than the higher percentages of bead overlap (i.e., 70-90%). The experimental investigation of studying the deposition sequence showed that there were no significant differences in the microstructure, hardness, and the size of the refined HAZ between the two proposed deposition sequences. However, a significant improvement in the microstructure and the size of the refined HAZ, and a reduction in the hardness were achieved after depositing the second welding bead, irrespective of the depositing sequence.