焊丝含氮量及焊接电流对高氮钢焊缝组织和性能影响

针对高氮奥氏体不锈钢焊接过程中由于N元素逸出引起气孔、导致力学性能恶化的问题,利用相图计算软件设计并制备了含氮量为0.35%和0.85%两种奥氏体不锈钢焊丝,系统地研究了氮含量和焊接电流对高氮钢焊缝气孔倾向性、微观组织以及力学性能的影响规律. 结果表明,高氮钢焊缝气孔倾向和力学性能与焊接电流、焊丝氮含量密切相关:随着焊接电流增加,氮含量0.35%的高氮钢焊缝抗拉强度和断后伸长率均增加,未出现气孔;而氮含量0.85%的高氮钢焊缝具有很高的气孔倾向,抗拉强度和断后伸长率变化不大,当焊接电流增大到一定值后,气孔倾向性明显降低.     

1Cr22Mn16N高氮钢激光焊接Ⅰ.焊接保护气体组成和热输入对焊缝氮含量及气孔性的影响

利用CO2激光对1Cr22Mn16N高氮钢进行了焊接,研究了焊接热输入和保护气体组成对焊缝氮含量、气孔的影响.结果表明,在相同激光焊接热输入条件下,随着保护气体中氮含量的增加,高氮钢焊缝中的氮含量略有增加.当采用纯氩作为焊接保护气体时,焊缝氮含量随热输入的增加而减小;当保护气体中的氮比例达到一定比例时,焊缝氮含量随热输入的增加而增大.焊接热输入较小的条件下焊缝易产生气孔,较大的热输入将抑制焊缝中气孔的产生,而且保护气体中氮含量越高,焊缝中产生气孔的倾向越小.     

1Cr22Mn16N高氮钢激光焊接I.焊接保护气体组成和热输入对焊缝氮含量及气孔性的影响

利用CO2激光对1Cr22Mn16N高氮钢进行了焊接,研究了焊接热输入和保护气体组成对焊缝氮含量、气孔的影响。结果表明,在相同激光焊接热输入条件下,随着保护气体中氮含量的增加,高氮钢焊缝中的氮含量略有增加。当采用纯氩作为焊接保护气体时,焊缝氮含量随热输入的增加而减小;当保护气体中的氮比例达到一定比例时,焊缝氮含量随热输入的增加而增大。焊接热输入较小的条件下焊缝易产生气孔,较大的热输入将抑制焊缝中气孔的产生,而且保护气体中氮含量越高,焊缝中产生气孔的倾向越小。     

1Cr22Mn16N高氮钢激光焊接——Ⅱ.焊缝组织与性能

为了研究高氮钢激光焊接接头焊缝区组织、性能特性,利用CO2激光对1Cr22Mn16N高氮钢进行了焊接,研究了焊接热输入和保护气体组成对焊缝组织、性能的影响.结果表明,高氮钢激光焊接焊缝组织均为奥氏体和少量的δ铁素体.当焊接热输入增大时,δ铁素体的尺寸显著增大.高氮钢激光焊接接头均没有出现软化区.随着热输入的减小,焊缝区的平均硬度升高;随着保护气体中氮气比例增大,焊缝区的硬度增加.当热输入减小时,焊缝韧性上升,而保护气体的组成对焊缝冲击吸收功的影响不大.     

1Cr22Mn16N高氮钢激光焊接II.焊缝组织与性能

为了研究高氮钢激光焊接接头焊缝区组织、性能特性，利用CO2激光对1Cr22Mn16N高氮钢进行了焊接，研究了焊接热输入和保护气体组成对焊缝组织、性能的影响。结果表明，高氮钢激光焊接焊缝组织均为奥氏体和少量的占铁素体。当焊接热输入增大时，占铁素体的尺寸显著增大。高氮钢激光焊接接头均没有出现软化区。随着热输入的减小，焊缝区的平均硬度升高；随着保护气体中氮气比例增大，焊缝区的硬度增加。当热输入减小时，焊缝韧性上升，而保护气体的组成对焊缝冲击吸收功的影响不大。     

10kW光纤激光焊接缺陷的形成

研究了未熔透光纤激光焊接过程中工艺参数对小孔型气孔、热裂纹和飞溅的影响,并讨论焊接缺陷形成机理. 结果表明,随着光纤激光焊接速度的增加,焊缝气孔和热裂纹倾向降低. 当焦点位置在工件表面时,气孔倾向最大;而当焦点位置由入焦向离焦偏移时,热裂纹敏感性增加. 光纤激光焊接气孔是由小孔不稳定引起的,而小孔不稳定性同时引起了熔池后部凝固前沿形状的变化,提高了焊缝热裂纹的敏感性. 较慢速光纤激光焊接飞溅的形成主要在于小孔开口处前沿熔池的凸起,其程度可能与小孔的稳定性有关.     

氮含量对高氮钢PMIG焊接头组织和性能的影响

文中采用H307Mo焊丝,开展了高氮钢PMIG焊接工艺试验,重点分析了焊缝中氮含量对接头组织和性能的影响,并通过调整工艺参数,控制焊缝中氮的含量.结果表明,当焊缝中氮含量低于0.24%时,焊缝以FA模式凝固,焊缝组织为骨架状铁素体枝晶和奥氏体基体组成,并且随着氮含量的提高,铁素体含量降低,显微硬度逐渐下降;当焊缝中氮含量高于0.30%时,焊缝以A模式凝固,组织为单相奥氏体枝晶组织,随着焊缝氮含量的提高,奥氏体枝晶不断增大,显微硬度逐渐提高.随着氮含量的提高,焊缝中气孔逐渐增多,冲击韧性呈现先增大后减小的趋势.     

高强度奥氏体焊条仰焊气孔成因分析

针对A507焊条,采用不同药皮含水量焊条、不同氮含量焊芯、有无气体保护及不同焊接操作方法进行仰焊试板焊接,并对焊缝进行解剖,对仰焊焊缝气孔产生的原因进行了分析.试验结果表明,焊条烘焙制度及焊芯中的氮不是产生气孔的直接因素,焊接过程中熔池保护不良是产生气孔的主要原因,可通过调整药皮配方及恰当的焊接操作方法避免空气中的氮气进入焊接熔池,减少焊缝中的气孔.     

保护气体中氮气比例对高氮钢双面同轴TIG焊接工艺性的影响

针对高氮低镍奥氏体不锈钢开展了双面同轴TIG自熔焊试验，分析了保护气体成分对电弧电压、电弧形态、钨极形貌、焊缝气孔与含氮量的影响规律. 结果表明，随着保护气体中氮气比例的提高，平均弧压以三次函数的速度增大，波动程度亦随之呈增大趋势；氮气的加入导致电弧显著收缩，焊后钨极表面覆盖棕褐色氮化钨薄层，同时焊接飞溅增大，电弧出现周期性“尾焰反射”现象，焊接稳定性随氮气比例提高而变差；随保护气体中氮气比例的提高，焊缝气孔数量和最大气孔尺寸同时增加，焊缝含氮量先增大后趋于稳定；为了降低焊接不稳定和焊缝气孔的不利影响，保护气体中氮气的比例应低于20%.     

管线钢焊接接头H2S应力腐蚀试验分析

采用楔形张开加载(WOL)试样,对X56、X65管线钢不同焊接工艺下焊接接头的焊缝金属和热影响区在H2S介质中的抗应力腐蚀性能进行了试验研究.结果表明,全部平行试样都发生了少量的裂纹扩展,当应力强度因子K达到临界值(KISCC),裂纹不再扩展.在文中采用的焊接工艺下制备的X56钢和X65钢焊接接头,热影响区的抗H2S应力腐蚀性能略强于焊缝金属,且焊缝金属和热影响区性能均低于文献中介绍的母材性能,可以认为是焊缝金属和热影响区粗晶区的晶粒粗化、焊接缺陷、焊接残余应力和焊缝的高匹配等因素造成的.     

Effect of nitrogen addition to shielding gas on residual stress of stainless steel weldments

Abstract

The objective of the present study was to investigate the effect of nitrogen additions to the shielding gas on the ferrite content and residual stress in austenitic stainless steels. Autogenous gas tungsten arc (GTA) welding was applied on austenitic stainless steels 304 and 310 to produce a bead on plate weld. The delta ferrite content of the weld metals was measured using a Ferritscope. The residual stress in the weldments was determined using the hole drilling strain gauge method. The present results indicated that the retained delta ferrite content in type 304 stainless steel weld metals decreased rapidly as nitrogen addition to the argon shielding gas was increased. The welding residual stress increased with increasing quantity of added nitrogen in the shielding gas. It was also found that the tensile residual stress zone in austenitic stainless steel weldments was extended as the quantity of added nitrogen gas in the argon shielding gas was increased.     

含氮奥氏体不锈钢在焊管领域中的应用前景

传统的304、316等奥氏体不锈钢焊管的焊缝很难保持全奥氏体组织状态,而含氮Cr-Ni奥氏体不锈钢既具有高奥氏体稳定性及由此带来的优良塑性、韧性和加工性能,又具有高强度及高耐腐蚀性,将是应用前景更为广泛的不锈钢焊管新品种。详细介绍了含氮奥氏体不锈钢的发展情况、氮在其中所起的作用、焊接特性及其在焊管生产上的应用,并对国内不锈钢及其焊管生产提出了建议。     

冷却速率对高氮钢焊缝组织和性能的影响

研究了水冷和空冷条件下高氮不锈钢焊缝金属微观组织和力学性能的变化规律,讨论了冷却速率对高氮不锈钢焊缝微观组织和力学性能的影响规律. 结果表明,冷却速率增加能够有效增加高氮钢焊缝金属中的氮含量,尤其对于含氮量0.85%的高氮含量焊丝,增氮效果更明显. 冷却速率增加对高氮钢焊缝金属抗拉强度提高程度取决于焊丝中的氮含量,对于低氮含量高氮钢焊丝,冷却速率增加能够显著提高焊缝金属抗拉强度,当焊丝中氮含量超过0.58%时,冷却速率增加对焊缝金属抗拉强度影响不大,最终接头强度达到850 MPa.     

Development of laser welding technology for fully austenitic stainless steel

The radial stainless steel plates (RPs) used for Toroidal field (TF) coils in the International Thermonuclear Experimental Reactor (ITER) are 13 m long, 9 m wide and 10 cm thick, which are quite large. Even though they are very large structures, high manufacturing tolerances and high mechanical strength at 4 K are required. It is also required that each RP should be fabricated every three weeks. Therefore, the authors intend to develop efficient manufacturing methods for an ITER TF coil RP. Laser welding is then selected as a welding method for RP. Especially, the development of high technology laser welding is necessary to prevent hot cracking in the material used for the RP; namely, fully austenitic stainless steel with high nitrogen content. The authors carried out trial laser welding experiments aiming at its application to RP. As a result, it was effective to make the angle of back inclination of the weld head at a uniform welding speed. It also seemed that the sensitivity of hot cracking could be reduced by optimizing the chemical compositions of material used for RP. The base material and the welded joints satisfied mechanical properties in 4 K. The application of the laser welding technology to the fully austenitic stainless steel was therefore demonstrated.     

Evaluation of solidification cracking susceptibility of Fe–18Mn–0·6C steel welds

Solidification cracking susceptibilities of high Mn steel welds were evaluated in the present study. A longitudinal Varestraint technique was utilised to assess the solidification cracking behaviours of the fusion zone. High Mn steel welds were more susceptible to solidification cracking than 304 and 202 austenitic stainless steel welds, however, they were less susceptible than 310S austenitic stainless steel welds. Extensive segregations of Mn and C took place at the dendritic and grain boundaries in the weld metal, and accordingly contributed to the increase of the hot cracking susceptibility of high Mn steel by the enlargement of solidification temperature range. Further, continuous γ-(Fe,Mn)₃C eutectic phases formed at 1090°C along the grain boundary primarily resulted in the increase of solidification cracking sensitivity in high Mn steel.     

Effect of weld metal chemistry on stress corrosion cracking behavior of AISI 444 ferritic stainless steel weldments in boiling chloride solution

The influence of the weld metal chemistry on the susceptibility of AISI 444 ferritic stainless steel (FSS) weldment to stress corrosion cracking (SCC) in hot chloride was investigated by constant load tests and metallographic examination. Two types of filler metal of austenitic stainless steel (E316L and E309L) were used in order to produce fusion zones of different chemical compositions. The SCC test results showed that the interface between the fusion zone (FZ) and the heat affected zone (HAZ) was the most susceptible region to SCC. Results also showed that the AISI 444 stainless steel weldment with E309L weld metal presented the best SSC resistance. Microstructural examinations indicated that the cracks initiated in the weld metal and propagated to the HAZ of the AISI 444 FSS, where the fracture occurred and it was observed a considerable amount of precipitates. Additionally, the higher SCC resistance of the AISI 444 FSS weldment with E309L weld metal may be attributed to the presence of a discontinuous delta‐ferrite network in its microstructure, which acted as a barrier to cracks propagation from the fusion zone to the HAZ/fusion zone interface of AISI 444 FSS. Fractrography analyses showed that the transgranular quasi‐cleavage fracture mode was predominant in the AISI 444 weldment with E316L weld metal and the mixed fracture mode was the predominant in the AISI 444 weldment with E309L weld metal.     

Ultrasonic hardness measurements

Abstract

When austenitic high-alloy steel weld metal sustains single-phase solidification generally described as A-mode solidification, this is well-known to result in heightened solidification cracking susceptibility.^1–3 To reduce the solidification cracking susceptibility of austenitic stainless steel, it is known to be effective to undertake component modification such as to obtain a solidification mode called the AF mode or FA mode involving the ä phase being crystallized or retained.^{1, 2} To obtain a complete γ solidification mode in the case of high Nibase alloys, such as Fe–36%Ni alloy, however, it is necessary to arrange for high Cr addition in order to achieve component modification facilitating AF or FA mode solidification such as affects austenitic stainless steel. The result of such addition, however, is that impairment of base metal properties also self-evidently cause heavy loss of hot workability in a way that makes this approach difficult to describe as effective.     

不锈钢管道对接焊缝焊接热裂纹超声波检测技术

由于安装制造工艺的原因,核电站辅助系统奥氏体不锈钢对接焊缝极易产生焊接热裂纹,此类热裂纹具有长度短、高度小、多集中于焊缝表面和近表面区域等特征,同时又由于奥氏体材料自身的影响,依据标准采用的体积性检测方法不能获得较好的检测效果。笔者针对特定对象,介绍了核辅助系统奥氏体不锈钢对接焊缝焊接热裂纹超声波检测技术及验证结果,为此类焊接热裂纹检测技术提供了参考。     

Evaluation of TIG flux welding on the characteristics of stainless steel

Abstract

The aim of the present study was to investigate the effect of specific oxide fluxes on the surface appearance, weld morphology, retained δ ferrite content, hot cracking susceptibility, angular distortion and mechanical properties obtained with the tungsten inert gas (TIG) process applied to the welding of 5 mm thick austenitic stainless steel plates. An autogenous gas tungsten arc welding process was applied to stainless steels through a thin layer of activating flux to produce a bead on plate welded joint. The MnO₂ and ZnO fluxes used were packed in powdered form. The experimental results indicated that the 80% MnO₂–20% ZnO mixture can give full penetration and also a satisfactory surface appearance for type 304 stainless steel TIG flux welds. TIG welding with MnO₂ and/or ZnO can increase the measured ferrite number in welds, and tends to reduce hot cracking susceptibility in as welded structures. It was also found that TIG flux welding can significantly reduce the angular distortion of stainless steel weldments.