Special features of the formation of welded joints in vertical laser-arc welding of low-alloy steels

ABSTRACT

Investigations were carried out into the special features of the technology of vertical laser-arc welding of large structures made of high-strength and low-alloy steels with a variable welding gap and a large root face.

The parameters of the conditions of vertical laser-arc welding of root passes in the low-alloy steel 30–40 mm thick with a root face of 10 mm (welding speed, the amplitude and frequency of transverse oscillations, the intensity of welding current, arc voltage, laser radiation power) resulting in the formation of high-quality welded joints are determined. The experimental results show that the laser radiation power, required for producing continuous penetration of the root face, depends on the thickness of the parent metal: for the metal thickness of 14–30 mm the sufficient laser radiation power is 3.8 kW, for a thickness of 40 mm it is no less than 4.6 kW to penetrate a depth of 5 mm.

The welded joints have a fine-dispersed acicular structure of the martensitic – bainitic type. The experimental results were used to develop a technology of welding of low-alloy steels of different thickness using robotic equipment.     

Hot cracking investigation during laser welding of high-strength steels with multi-scale modelling approach

Hot cracking during laser welding of advanced high-strength steels is reported to be a serious problem by automotive manufacturers. In this work, hot cracking susceptibilities of transformation-induced plasticity (TRIP) and dual-phase (DP) steels are studied based on a multi-scale modelling approach. Transient temperatures measured from welding experiments are used to validate a finite element (FE) model. The temperature, thermal gradient and cooling rate in the weld fusion zone are extracted from the FE model and pre-defined as boundary conditions to a phase field model. The welding-induced microstructural evolution is simulated considering thermodynamic and mobility data. Results show that, compared to the DP steel, the TRIP steel has a broader solidification range, a greater pressure drop at the inter-dendritic regions, and an increased phosphorus segregation at the grain boundaries; all these make this steel more susceptible for hot cracking.     

Special features of metallurgical processes in plasma welding of chromium bronze

The metallurgical processes taking place in the weld pool in plasma welding of chromium bronze are investigated. The reasons for the formation of defects, hot cracks, and pores are determined, and measures that should be taken to prevent the formation of these defects are indicated.     

分段冷补焊在火力汽轮机修复中的应用

在火力汽轮机自动主汽门结合面大型铸钢件裂纹补焊时,因补焊坡口的形状、位置等原因,无法一次完成敷焊层焊接。通过研究现场结构实际情况,采用分段冷补焊工艺圆满完成了汽轮机自动主汽门结合面大型铸钢件裂纹的修复工作。     

不锈钢冷金属过渡焊角接接头应力及变形规律研究

在高速列车轻量化课题中,不锈钢薄板作为车体结构的关键部分越来越受重视。针对异种厚度的SUS301L不锈钢薄板,采用冷金属过渡技术进行角接试验,通过热电偶采集焊接时距焊缝不同位置的温度变化。用3D激光扫描仪测量焊接变形,由于采用焊缝悬空的约束方法,底板焊后发生了较大的呈波浪状的变形,最大变形量达到6.545 mm。用μ-X360分析仪检测接头残余应力,应力呈M型分布。     

高强度低焊接裂纹敏感性钢焊接热影响区的冲击韧度

采用埋弧自动焊接方法焊接高强度低焊接裂纹敏感性钢,分析了高强钢焊接热影响区中不同微区的显微组织特征与冲击韧度之间的关系.焊接接头粗晶区和细晶区的显微组织分别为粗大的粒状贝氏体和细小的准多边形铁素体组织,其-20℃的平均冲击吸收功分别为45 J和170 J.粗晶区中粒状贝氏体的有效晶界为原始奥氏体晶界,晶内存在大量的小角度晶界和亚晶界,有效晶粒尺寸较大,冲击韧度显著降低;细晶区中准多边形铁素体的平均有效晶粒尺寸约为5.3μm,大角度晶界可以有效阻碍了裂纹的扩展,具有较好的冲击韧度.     

Q345B钢板焊接热循环及实时角变形测试

对Q345B钢板进行多层多道焊接,使用K型接触式热电偶测温模块和激光位移传感系统测量焊接过程中的热循环和角变形。结果表明,多层多道焊的热循环峰值温度随焊道的逐渐靠近而升高;距离焊缝越近,峰值温度越高,对应的升温速度也越快;焊接角变形主要产生于焊接阶段,表现为逐渐增加,而在层间冷却阶段很小,最终焊接角变形约为4.78°。     

X80管线钢焊接热模拟热影响区疲劳裂纹扩展行为的分析及预测

通过焊接热模拟方法对X80双相管线钢不同焊接热影响区疲劳裂纹扩展行为进行了研究,并分析实际焊接试样与焊接热模拟试样的热影响区疲劳裂纹扩展行为的差异,讨论了焊接热模拟技术应用于疲劳裂纹扩展寿命预测的可行性。结果表明,当裂纹在粗晶热影响区(CGHAZ)和临界热影响区(ICHAZ)上扩展时,由实际焊接试样与焊接热模拟试样热影响区所测得的疲劳裂纹扩展速率曲线(da/dN-DK曲线)存在明显差异,其原因与显微组织变化引起的裂纹扩展阻力大小不同有关。因此,建议采用实际焊接试样完整的热影响区所测得的da/dN-DK曲线来评估疲劳裂纹扩展寿命。     

Investigation of the structure and mechanical properties of welded joints in steels of the K56 strength grade in different welding conditions

The results of investigations of the effect of the welding conditions of manual arc welding on the structure and mechanical properties of the welded joints in low-carbon, low-alloyed pipe steels of the K56 strength grade are presented. It is shown that in welding in different combinations of welding current and welding speed, the superheated zone of the heat-affected zone (HAZ) is characterized by the formation of ferrite and pearlite in the form of grains and Widmanstätten structure. The experiment planning method is used to determine the regression dependences of the hardness and impact toughness of the metal of the superheated zone on the controllable welding parameters.     

碳铌含量对微合金钢中贝氏体热稳定性的影响

采用冷弯实验、等温热处理结合硬度测量、光学金相技术和透射电子显微术观测分析了微合金钢中贝氏体组织在A1以下温度受热时的组织演化历程。结果表明,提高微合金钢的碳铌浓度积可以显著延缓贝氏体组织趋于平衡的演变,阻碍钢的软化进程。冷变形在增加钢的初始硬度的同时也加快了随后的受热过程中钢的软化和显微组织向平衡组织演化的进程。张应变和压应变这两种不同类型的应变对组织演变的促进效果几乎相同。冷变形提高了钢中位错密度,也加剧了位错分布的不均匀性,后者是预应变加速组织演变的直接原因。在等温受热过程中贝氏体组织的演变首先是贝氏体板条内的位错发生重新分布,在板条边界附近形成高位错密度区,并同时伴随有低位错密度区出现,然后低位错密度区跨越板条边界形成铁素体晶核并不断吞噬高位错密度区,最终完全演变为平衡组织多边形铁素体。     

Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength

Geometrical distortions occur while welding, but the understanding of how and why they occur and how to control them is limited. The relation between the weld width, weld metal volume, total energy input, width of hard zone and distortions when laser welding three different thin sheet steels with varying strength has therefore been studied. Weld metal volume and total energy input show a good correlation with distortion for one steel at a time. The best correlation with the when including all three steel grades was the width of the hard zone composed of weld metal and the martensitic area in the heat affected zone.     

CPR1000核电站核岛主管道预制焊接变形研究及应用

针对CPR1000核电站核岛主管道用厚壁不镑铜核岛主管道预制焊接中的焊接变形问题,采用理论分析与模拟试验相结合的研究方法,系统地研究了核电站核岛主管道预制焊接不同装配结构的焊接变形特点,确立了主管道预制焊接的反变形措施,保证了主管道预制焊接质量.     

Investigation of the thermal electromotive force of steels and alloys of different structural grades in electron beam welding

The results of investigations of the thermoelectric properties of steels of different structural grades and also nickel- and cobalt-based alloys are presented. The temperature dependencies of the absolute thermal electromotive force and the thermal electromotive force coefficient of materials are determined.     

超(超)临界火电机组SA335P91钢与12Cr1MoV钢焊接性能

国内超临界（SC）、超超临界（usc）火力发电机组锅炉制造及管道安装中,主蒸汽管道及锅炉受热面的再热器采用SA335P91钢与12CrlMoV钢实施的焊接,对其异种铁素体耐热钢的焊接机理进行研究,阐述了两种耐热钢的金属结构特点和焊接性能．通过理论分析和实践确认了该两种异种耐热钢在焊接过程产生热冷裂纹、韧性降低、脆化及Ⅳ型软化开裂的倾向和主要因素．有针对性的采取了相适应的工艺措施和合理的热处理方案,获得了优良的焊接接头．对即将应用到实际生产的其它异种耐热钢,特别是铁素体异种钢的焊接具有较好的参考价值．     

Special features of heating and melting electrodes with an exothermic mixture in the coating

Experimental results show that exothermic reactions in the heating and melting stages of electrode coating take place when the coating contains more than 35% of the exothermic mixture. Data for the effect of the amount of exothermic mixture in the electrode coating on heating and melting of the electrodes are presented. The thermal balance of melting the electrodes with the exothermic mixture in the coating is calculated. The results show that the temperature of 1273 K at which the efficiency of the exothermic reaction is high is reached at a distance of approximately 1 mm from the electrode tip. It is confirmed that the addition of up to 53.4% of the exothermic mixture to the electrode coating increases the effective efficiency of heating the parent metal (η_m) from 0.715 to 0.815 and of the electrode (η_el) from 0.28 to 0.415.     

热输入对800MPa级水电用钢焊缝组织性能的影响

采用三种热输入对800 MPa级水电用高强钢进行埋弧焊接,研究不同热输入对焊缝金属组织、强度、塑性和冲击韧性的影响。结果表明,三种热输入下焊缝金属组织均以粒状贝氏体为主,并含有少量的板条贝氏体、铁素体和残余奥氏体,随着热输入的增加,板条贝氏体减少,而粒状贝氏体和铁素体量增加。焊缝金属的屈服强度和抗拉强度稍有下降,当热输入为28.7k J/cm时强度最高,抗拉强度和屈服强度分别为784 MPa和702 MPa;当热输入升高为35.2 k J/cm时,抗拉强度和屈服强度分别下降23 MPa和18 MPa,塑性得到改善;当热输入为35.2 k J/cm时,其延伸率达到峰值,为22.5%,较热输入为28.7 k J/cm时升高5.5%。而冲击功则先升后降,三种热输入下随着热输入的升高,其冲击功依次为85 J、106 J和94 J。     

TC4钛合金激光焊缝形貌与残余应力数值分析

针对激光深熔焊特点,采用均匀体热源模型、双椭球热源模型和组合热源模型,对TC4钛合金CO₂激光深熔焊的焊缝形貌和残余应力进行了数值模拟与试验.结果表明,在进行激光深熔焊焊缝形貌与残余应力数值计算中,应根据激光焊接热输入选择激光热源模型,并提出了均匀热源模型适合较大热输入,双椭球热源模型适合中等热输入,而组合热源模型适合较小热输入的选择原则;组合热源模型和双椭球热源模型均能体现热输入随深度的递减变化,焊缝轮廓呈现圆锥形和钉子形;均匀体热源的上下表面的残余应力分布基本一致,而双椭球热源和组合热源模型的下表面残余应力明显低于上表面.     

铝对大线能量焊接条件下HSLAA焊接热影响区粗晶区M-A组元及冲击韧性的影响

采用热模拟试验方法分析了HSLA在100 kJ/cm大线能量条件下添加不同铝元素(0.027％,0.038％,0.070％)对焊接热影响区粗晶区的M-A组元内部组织、含量的影响.通过透射电镜分析M-A组元的内部组织转变,发现铝元素可以促进M-A组元内部残余奥氏体的稳定性,减少M-A组元中马氏体的含量.M-A组元统计和低温冲击试验结果表明,添加铝元素能够有效减少焊接热影响区粗晶区中M-A组元的含量,含有较高铝元素的试样冲击吸收功明显提升且较为稳定.