304H钢埋弧焊工艺

对304H钢采用埋弧焊的焊接方法进行了工艺试验,分析了304H耐热奥氏体不锈钢埋弧焊的特点,提出了合理的埋弧焊焊接工艺,检验焊缝质量,分析焊接接头的显微组织,测试其力学性能.结果表明:焊接工艺参数合理,在焊接接头未发现任何焊接缺陷,焊缝质量良好;焊接接头强度、塑性均可达到与母材相当的水平.304H耐热奥氏体不锈钢采用此工艺方法焊接,完全可以获得优良的焊接接头.     

304不锈钢/T2紫铜电子束焊接熔池凝固行为及组织性能研究

采用电子束作为焊接热源,通过调节功率输出及不同的焊接偏置,研究了304奥氏体不锈钢与T2紫铜熔化焊的熔池凝固行为及组织性能特征。采用光学显微镜、扫描电镜、能谱、拉伸等分析测试方法对接头特征进行了表征,其结果表明,304不锈钢和T2紫铜电子束焊接可获得良好的焊缝成形,接头无明显气孔,微裂纹等缺陷。接头最高拉伸强度可达246 MPa,接近等强于铜基材。束流偏置对接头强度具有很大影响,铜侧偏置易引起铜侧热影响区晶粒粗大,钢侧偏置易引起熔合不良及热裂纹形成。钢和铜之间不形成脆性金属间化合物,焊缝的相组成主要为ε相、γ相及晶间α相。     

超超临界机组用Super304H钢焊接接头的组织和性能

采用光学显微镜、扫描电子显微镜及能谱仪等手段,通过拉伸试验、弯曲试验、冲击试验和硬度试验,研究超超临界机组用Super304H奥氏体耐热钢焊接接头的微观组织和力学性能。结果表明:Super304H钢焊接接头的组织均为γ+析出相,热影响区的晶粒尺寸有明显的长大,焊缝组织是典型的胞状树枝晶,枝晶界上的析出相主要为Nb(C,N)。Super304H钢焊接接头具有较高的强度和良好的塑韧性,但接头的组织形态对韧性有重要影响,粗大的柱状晶是焊缝韧性降低的重要原因,熔合区因Nb(C,N)析出强化硬度较高。     

X2CrNiN18-7不锈钢CMT焊与MIG焊对比试验

使用CMT,MIG这2种焊接方法对X2CrNiN18-7不锈钢焊接,对得到的焊缝进行了外观形貌、组织构成、力学性能等方面的对比分析。结果表明:2种焊接方法焊缝外观形貌相似,CMT焊所得焊缝熔宽小于MIG焊的熔宽,CMT焊所得焊缝先析出δ铁素体,以FA模式凝固。室温组织由γ奥氏体、少量δ铁素体构成。接头由母材、热影响区、部分熔化区、焊缝柱状晶区构成,熔合线在母材部分熔化区和焊缝柱状晶区之间,靠近部分熔化区的热影响区部分析出条状平行铁素体,可抑制此区域热影响区晶粒的长大。相比CMT焊所得焊缝,MIG焊的特征区域缺少了部分熔化区以及等轴晶区。CMT焊接所得接头力学性能明显优于MIG焊。     

254SMO/Q235B异种钢焊接接头显微组织的研究

在膨胀节生产过程中,发现管道的部分焊道出现了裂纹,为找出裂纹产生的原因,分别选用ERNiCrMo-3,ERNiCrMo-10及ERNiCrMo-14镍基合金焊丝,采用手工TIG焊对254SMO/Q235B异种钢进行焊接.焊后利用金相显微镜和扫描电子显微镜对焊接接头的显微组织进行了分析研究.发现采用ERNiCrMo-10焊丝进行焊接时,焊缝成形良好,未出现焊接裂纹;选用ERNiCrMo-3和ERNiCrMo- 14焊丝时,焊缝均有不同数量的微裂纹出现.研究结果表明,焊接裂纹为凝固裂纹,焊丝成分是造成焊接裂纹的主要原因之一,焊缝凝固模式为全奥氏体模式,有明显的凝固亚晶界(SSGB)、凝固晶界(SGB)和迁移晶界(MGB).     

SUS304/Q235B双金属冶金复合螺旋管激光-CMT复合焊+埋弧焊接头组织及性能

采用激光-CMT复合焊+埋弧焊的焊接工艺对SUS304/Q235B双金属冶金复合螺旋管进行了生产试制,利用OM,EDS研究了复合管焊缝微观组织特征及合金元素分布,同时检验了焊接接头的力学性能和耐腐蚀性能。结果表明,焊缝合金成分合理,合金元素稀释率低。内焊焊缝(CMT区域)微观组织为奥氏体+铁素体+碳化物析出相,内焊焊缝(LBW区域)微观组织为奥氏体+铁素体+马氏体,Q235B基层焊缝微观组织为铁素体+珠光体;焊接接头抗拉强度平均值为451 MPa,-10 ℃下焊缝及热影响区的冲击吸收能量平均值分别为167 J和236 J,焊接接头面弯、背弯180°拉伸面无裂纹(弯轴直径45 mm),焊缝硬度最高值为285 HV10;晶间腐蚀试验后,管体与焊缝弯曲180°拉伸面无裂纹(弯轴直径4 mm)。SUS304/Q235B双金属冶金复合螺旋管激光-CMT复合焊+埋弧焊接头的各项性能均符合相关标准的要求,能够满足饮用水输送工程的应用需求。 创新点： 区别于传统螺旋焊管的双面埋弧焊,采用了激光-CMT复合焊(内焊)+埋弧焊(外焊)的工艺对SUS304/Q235B双金属冶金复合螺旋管进行焊接,形成了“Y+V”形的焊接接头形貌,减小了内、外焊缝的重合量,有效地控制了不锈钢复层一侧焊缝合金元素的稀释及碳钢基层一侧焊缝合金元素的过量裹入,避免了内、外焊缝高硬相的产生,提升了焊接接头的综合性能。     

Super304H奥氏体耐热钢摩擦焊焊接接头持久强度研究

利用"等温线法"对Super304H奥氏体耐热钢摩擦焊焊接接头625℃持久强度试验数据进行外推,表明焊接接头在超超临界机组工作环境下服役是安全可靠的。结果表明,高应力条件,试样断口主要为韧窝断裂,以穿晶断裂为主;低应力条件,试样断口主要为解离断裂,以蠕变断裂为主;蠕变断裂是以孔洞和微裂纹的形核与长大为基础。析出相沉淀强化是Super304H奥氏体耐热钢焊接接头的主要强化手段。     

T92/Super304H异种钢焊接接头的组织结构和力学性能

采用钨极氩弧焊(GTAW)技术,采用ERNiCr-3和ERNiCrMo-3两种镍基焊丝实施T92/Super304H异种钢焊接,并对接头的显微组织结构及力学性能进行测试分析。结果表明:T92侧热影响区(HAZ)中粗晶区析出大量的第二相颗粒,细晶区则为细小的索氏体组织;Super304H侧HAZ奥氏体晶粒长大,晶界析出明显;ERNiCr-3焊接的焊缝组织呈胞状结构,晶粒粗大;ERNiCrMo-3焊接的焊缝组织呈柱状晶组织特征。ERNiCrMo-3焊接的接头强度、塑性及硬度较大,拉伸断裂位于Super304H母材;而ERNiCr-3焊接的接头强度、硬度较低,但冲击韧性较高,拉伸断裂位于焊缝。     

大厚度电子束焊接接头厚度方向的组织差异性

利用K110型电子束焊机焊接50 mm厚的304不锈钢板,并对焊接接头深度方向的微观组织及硬度进行分析. 结果表明,利用电子束焊接方法能够一次性焊透50 mm厚不锈钢板,得到成形良好的焊接接头. 焊缝深宽比较大,约为18:1. 焊缝组织由奥氏体和铁素体组成. 从焊缝上表面到深约39 mm处,铁素体形态依次为网状,板条状/骨架状和树枝状分布于奥氏体枝晶间或晶界处. 在焊缝的下层,亚稳的胞状奥氏体将取代稳定铁素体相作为初生相直接从熔体中析出. 沿焊缝中心深度方向,接头的凝固模式由primary ferrite with second-phase austenite,FA转变成primary austenite with second-phase ferrite,AF模式,晶粒尺寸减小,硬度呈波动性增加趋势.     

Super304H钢焊接接头的晶间腐蚀敏感性

利用电化学动电位再活化法(EPR)测试了Super 304H钢焊接接头焊缝和母材的晶间腐蚀敏感性.结果表明,Super 304H钢焊缝和母材均呈现出较低的晶间腐蚀倾向.进一步用扫描电子显微镜、X射线衍射仪和透射电镜研究了它们的微观组织结构,焊缝和母材均为单一的奥氏体组织+少量析出相,二者都未探测到明显的Cr23C6析出相,所以未出现明显的基体贫铬现象,但是焊缝金属因与母材合金元素等存在差异,导致其在H2SO4和KSCN溶液中的耐晶间腐蚀性能稍好于母材.     

Effect of Austenitic and Austeno-Ferritic Electrodes on 2205 Duplex and 316L Austenitic Stainless Steel Dissimilar Welds

This study addresses the effect of different types of austenitic and austeno-ferritic electrodes (E309L, E309LMo and E2209) on the relationship between weldability, microstructure, mechanical properties and corrosion resistance of shielded metal arc welded duplex/austenitic (2205/316L) stainless steel dissimilar joints using the combined techniques of optical, scanning electron microscope, energy-dispersive spectrometer and electrochemical. The results indicated that the change in electrode composition led to microstructural variations in the welds with the development of different complex phases such as vermicular ferrite, lathy ferrite, widmanstatten and intragranular austenite. Mechanical properties of welded joints were diverged based on compositions and solidification modes; it was observed that ferritic mode solidified weld dominated property wise. However, the pitting corrosion resistance of all welds showed different behavior in chloride solution; moreover, weld with E2209 was superior, whereas E309L exhibited lower resistance. Higher degree of sensitization was observed in E2209 weld, while lesser in E309L weld. Optimum ferrite content was achieved in all welds.     

Microstructure and mechanical properties of dissimilar welds between 16Mn and 304L in underwater wet welding

Dissimilar joint between 304L austenitic stainless steel and low-alloy steel 16Mn was underwater wet welded using self-shielded nickel-based tubular wire. Microstructure, mechanical properties and corrosion behaviour of dissimilar welded joints were discussed. Ni-based weld metal was fully austenitic with well-developed columnar sub-grains. Type II boundary existed between Ni-based weld metal and ferritic base metal in underwater welds similar to that in air welds. Major alloying elements distributed non-uniformly across the austenitic weld metal/16Mn interface. Maximum hardness values in wet welding appeared in a coarse-grained heat-affected zone at the 16Mn side, which possessed very low impact toughness. Underwater Ni-based welded joints fractured at Ni-based weld metal under tensile test. Ni-based weld metal had favourable corrosion resistance similar to 304L base metal.     

预置镍基合金片对异种钢UNGW接头组织及性能的影响

研究了预置镍基合金片对15CrMo/1Cr18Ni9Ti异种钢超窄间隙焊接接头组织及性能的影响。结果表明,预置镍基合金片厚度小于0.6 mm时,15CrMo熔合线附近焊缝区部分区域以A模式凝固并形成奥氏体胞状晶,而其它区域仍以FA模式凝固,其组织为等轴晶奥氏体+枝晶状铁素体,并且焊缝中心无凝固裂纹形成。预置0.9~1.2 mm厚的镍基合金片时,焊缝中心因镍偏聚而以A模式凝固,形成粗大的奥氏体柱状枝晶,并有凝固裂纹形成。预置镍基合金片厚度在0.6~0.9 mm时,可使15CrMo熔合线附近焊缝区的Ni质量分数比填充金属(ER347L)的提高约2%,明显比未预置镍基合金片的接头具有更好的抑制碳扩散效果,但当镍基合金片厚度在0.3~1.2 mm范围内变化时接头抑制碳扩散的效果并无明显变化。焊态的异种钢接头不均匀混合区内存在马氏体层,而热时效后在熔合线附近会形成一定宽度的富碳硬化区及贫碳软化区。     

焊接工艺对TP304/SS400异种钢焊接接头组织和性能的影响

利用扫描电子显微镜并通过常温拉伸弯曲、低温冲击以及显微硬度等试验研究了FCAW，SMAW和GTAW三种不同的焊接工艺对TP304/SS400异种钢焊接接头组织和性能的影响. 结果表明，三种焊接工艺条件下，焊缝金相组织都为δ铁素体+奥氏体，但δ铁素体含量及形态分布有明显差异；FCAW焊缝中蠕虫状δ铁素体和GTAW焊缝中针状δ铁素体可有效提高韧性，故冲击韧性较高，SMAW焊缝中骨骼状δ铁素体对韧性不利，冲击韧性最低，且随冲击吸收能量的降低断口由韧性断裂转变为脆性断裂；三种焊接工艺条件下，焊接接头综合力学性能表现良好，整体显微硬度值变化不大.     

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.     

Improving austenitic stainless steel resistance spot weld quality using external magnetic field

A ring-shaped permanent magnet is applied in resistance spot welding to improve the weld quality of austenitic stainless steel. Under the action of an external magnetic field, the profile of the weld nugget became peanut-shaped instead of ellipsoidal. The crystal orientation near the faying surface was less directional, and equiaxed grains were formed in weld nugget centre. Moreover, the shrinkage cavities tendency in traditional resistance spot welds was reduced. The relatively slow cooling speed could cause element segregation and thus change solidification mode and significantly affect weld microstructures. The mechanical performance of the welds was finally improved by the applied external magnetic field in terms of microhardness and lap-shear strength.     

Influence of polarity on mechanical properties of dissimilar resistance spot welds of DP 600/AISI 304 steels

The influence of polarity during resistance spot weld (RSW) of dissimilar lap joints on mechanical properties and failure mode is assessed in this work. A dissimilar lap joint was set using DP 600 dual phase steel with AISI 304 stainless steel. The experiments were performed on a medium-frequency direct current spot welding machine with proper data acquisition of voltage and welding current. Temperature evolution was also acquired by using IR camera. The mechanical properties of spot welds were evaluated by using a coach peel testing. The effect of welding current and welding time on mechanical properties was also evaluated. Correlations between polarity with the welding nugget size, failure mode, tensile strength, temperature evolution and dynamic resistance were analysed. The analysis confirmed that the polarity on dissimilar lap joints affects the behaviour of dissimilar RSWs.     

Effect of austenitic fillers on microstructural and mechanical properties of ultra-low nickel austenitic stainless steel

In the present investigation effect of austenitic fillers namely E308, E309 and E310 on microstructural and mechanical properties of ultra-low nickel austenitic stainless steel weldment was analysed. The WRC-1992 diagram has been used to predict δ-ferrite and solidification mode of weld metal. Microstructural exploration confers the variation in magnitude and morphologies of δ-ferrite for different Cr_eq/Ni_eq ratio. It was observed that greater amount of δ-ferrite resulted in improved tensile strength. On the other hand, it lowered the impact strength of weld joint. The results indicated that E308 exhibits higher hardness and tensile strength, whereas E310 demonstrates higher impact strength and this may be attributed to the variation in δ-ferrite content and solidification mode. During tensile test joints failed in heat affected zone for all weld specimen. Surface morphology of fragmented specimens was analysed using scanning electron microscopy and different morphologies were recognised for samples failed before and after Strauss test.     

Effect of energy transfer modes on solidification cracking in pulsed laser welding

Abstract

In this study, solidification cracking in pulsed laser welding of fully austenitic, AISI Type 316 stainless steel has been analysed at different energy transfer modes. The pulse parameters have been selected appropriately to obtain conduction, transition and keyhole mode welds. Conduction and transition mode welds exhibit higher susceptibility to cracking than keyhole mode welds. It is observed that both heat input and energy transfer mode affect the cooling rate and hence influence solidification cracking. Microstructures of the fusion zone have been analysed, and the cooling rate experienced by the weld is estimated from the mean cell size in the weld. It is found that the critical cooling rate below which cracking does not occur is ～10⁴ K s^??1.