Austenitic and ferritic stainless steel dissimilar weld metal evaluation for the applications as-coating in the petroleum processing equipment

The current study presents some fundamental observations on the effects of the welding heat input in the chemical composition, microstructure, hardness and petroleum corrosion resistance of the fusion zone, formed by the AWS E309MoL austenitic stainless steel covered electrode and the AISI 410S ferritic stainless steel, being a dissimilar welding procedure. Such welding configurations are widely used as an overlay of equipment in the petroleum and gas industries. The welds were performed with the application of three different levels in heat inputs (6, 9 and 12 kJ/cm). Samples of the weld metals were conventionally prepared for the microstructural characterization by light microscopy and scanning electron microscopy. A corrosion test with samples immersed in heavy oil heated at 300 °C, was carried out for a period of 60 h. The corrosion rate was determined by the weight loss given after the aforesaid test. The fusion zone microstructure has a typical δ-ferrite acicular morphology, from which the level of δ-ferrite was duly altered with the increases of the welding heat input, due to the variations in the composition of the weld metal caused by dilution. It was also concluded that the chemical composition and the weld metal microstructure had a slight influence in the material’s corrosion rate. As a matter of fact, the corrosion rate of the weld metals evaluated herein, was considered satisfactory with few variations between the welding heat inputs duly applied.     

Effect of heat input and weld chemistry on mechanical and microstructural aspects of double side welded austenitic stainless steel 321 grade using tungsten inert gas arc welding process

Stainless steel 321 is a stabilized austenitic grade that prevents the formation of chromium carbides at the grain boundaries and subsequently reduces the risk of corrosion attack at the weld surface by forming titanium carbide. It is primarily used in industries such as pressure vessels, boilers, nuclear reactors, carburetors and car exhaust systems. In order to assess the effect of gas tungsten arc welding process parameters on weld penetration, the proposed Taguchi L₉ orthogonal matrix has been selected with two factors and three levels for welding austenitic stainless steel 321 by adjusting the welding current and welding speed. Bead-on-plate experiments were performed on base metal of 6 mm thick plate by changing the process parameters, and corresponding weld bead measurement and macrostructure images are examined. Maximum depth of penetration −3.3017 mm is achieved with a heat input −1.4058 kJ/mm, i. e., welding current-220 A and welding speed-120 mm/min. Double-side arc welding technique is used to obtain full penetration on 6 mm thick plate. The quality of the weldment was assessed using non-destructive radiography inspection. Mechanical integrity and microstructural characteristics of the weldments were studied using tensile (transverse and longitudinal), bend, impact, microhardness, optical microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction analysis, ferrite number measurement and scanning electron microscope. The results reveal that the double side-tungsten inert gas weldment have better mechanical properties. It is corroborated from the weld metal microstructure that it contains γ-austenite, δ-ferrite and titanium carbides (intermetallic compounds). X-ray diffraction analysis and energy dispersive x-ray spectroscopy plots confirm the increase in the ferrite phase in weld metal. The ferrite measurement results show that the ferrite volume in the base metal and weld metal is 1.2 percent and 6.1 percent respectively. In addition, the higher δ-ferrite volume in the weldment helps in attaining superior mechanical integrity. Fractography shows that the failure mode of the weld metal and the base metal is ductile.     

Failure investigation of 321 stainless steel pipe to flange weld joint

Failure investigation was conducted on a refinery pipe-to-flange weld joint that suffered cracking. Both the pipe and flange are made of AISI 321 stainless steel. The flange was circumferentially welded to the pipe which is seam welded. The investigation revealed that both the circumferential and seam welds were in sound conditions, namely no evidences of sensitization, lack of weld penetration, and voids or porosities. Thus, welding practices were not suspected to be the cause of failure. The failure of the weld joint was found to have started at the δ-ferrite phase in the flange material and propagated through the circumferential and seam welds. The failure mode was concluded to be chloride stress corrosion cracking synergized by the presence of H₂S. The presence of corrosive compounds in the refinery stream and the residual stresses at the weld joint triggered active anodic dissolution of the δ-ferrite precipitates, resulting in cracking of the material.     

Keyhole gas tungsten arc welding of AISI 316L stainless steel

Keyhole gas tungsten arc welding (K-TIG) was used to weld AISI 316L stainless steel of mid-thickness (thickness ranging 6–13 mm). 316L plates of 10-mm thickness were jointed using an I-groove in a single pass without filler metal. The effects of welding parameters on the fusion zone profile were investigated. The weld properties, including mechanical properties, microstructure, and corrosion resistance, were analyzed. The primary weld microstructures were austenite and δ-ferrite. The tensile strength and impact property of the weld were almost the same as those of the base metal, while the corrosion resistance of the weld was even better than that of the base metal. High-quality 316L stainless steel joints can be realized through K-TIG welding with high productivity and low processing cost. The practical application of K-TIG welding to join mid-thickness workpieces in industry is well demonstrated and an ideal process for welding AISI 316L of mid-thickness with high efficiency and low cost is presented.     

Microstructure evolution and mechanical properties of 316H weld metal during aging

ABSTRACT

A standard 316H welding wire was used to obtain 6% δ-ferrite in the weld metal by the automatic tungsten inert gas welding. The effect of aging time at 750°C on microstructure and mechanical properties of the weld metal were analysed. The results showed that as the aging time increased, the δ-ferrite fraction decreased, and finally, δ-ferrite was no longer seen, the M₂₃C₆ fraction first increased and then decreased, and the σ phase fraction increased. Finally, the fractions of M₂₃C₆ and σ phase kept stable, but the size increased. Accordingly, as the aging time increased, the yield and tensile strengths first decreased significantly, then increased obviously and finally decreased slightly again, while the elongation and impact energy decreased all the time.     

Structure morphology effect of Ti and Nb stabilized austenitic stainless steel welds on corrosion properties

In this preliminary study the microstructure morphology of the austenitic stabilized stainless steel deposited by manual metal arc (MMA) welding on corrosion has been investigated as part of a study attempting to establish a quantitative correlation between the morphology and corrosion properties. It was found that corrosion resistance of the developed complex microstructure depends on the particular structure morphology at the parent metal-weld bead interface. For a given composition, the developed morphology is controlled by the interrelated parameters of heat input, cooling rate and joint geometry. Extensive precipitation of -ferrite results in a significant reduction of corrosion resistance.     

MODIFICATION OF THE COMPOSITION OF LASER WELDS IN ELECTROGALVANIZED STEEL AND THE EFFECT ON CORROSION PROPERTIES

Compositional modification of the weld metal during laser welding of electrogalvanized steel sheet was achieved by the injection of metal powder or by a technique in which zinc that had been volatilized as a result of the welding operation was redeposited on the weld bead. Corrosion testing by means of the linear polarization technique showed that the coating corrosion rate in the case of laser welds containing redeposited zinc was substantially lower for an initial period than for normal laser welds. Only a small decrease in corrosion rate was achieved by the injection of tool steel powder during laser welding while an increase in coating corrosion rate was produced by the injection of nickel powder or stainless steel powder     

金属焊接件海运包装防护技术研究

目的研究新型包装防护技术对焊接件的防护效果及其对后续焊接、涂装等工艺的影响,解决常规包装无法解决的焊接部位腐蚀防护问题。方法通过自然环境暴露实验、中性盐雾实验对焊接件常规包装防护方式和改进后的新型包装防护方式,即PE袋密封包装、气相防锈袋和气相防锈袋+冷喷锌的防护效果进行对比研究。结果 30 d盐雾实验后,PE袋密封包装防护下焊接件基材、焊缝都出现了腐蚀迹象,其中焊缝部位相对于基材锈蚀更加严重。气相防锈袋密封包装防护下焊接件基材基本上无锈蚀,焊缝部位出现轻微腐蚀。气相防锈袋+冷喷锌包装防护下焊接件基材以及焊缝部位都相对完好,未出现任何锈蚀现象。结论常规的包装防护方式对焊接件基材有一定的保护作用,但是对焊接部位并不能起到较好的保护。改进后的气相防锈袋+冷喷锌包装防护方式综合了气相防锈技术和冷喷锌的双重优势,对焊接件的基材、焊缝及热影响区均具有较好的保护效果,且不影响后续的喷涂焊接工艺等,该组合型防护方式可有效应用到焊接件的海运包装防护中。     

The formation and control of Laves phase in superalloy 718 welds

Weld heat input/cooling rate (affected by welding process, parameters, technique, tooling, etc.) was found to influence the microstructural characteristics and segregational features in alloy 718 welds, with low heat inputs proving beneficial. Laves phase formed in the interdendritic regions of the weld metals as a result of segregation. The morphology and composition of Laves phase depended strongly on heat input/cooling rate and influenced its response to subsequent homogenization post-weld heat treatment. The various factors affecting the formation and control of Laves phase in alloy 718 welds are highlighted. This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of heat input/multiple passes and post weld heat treatment on strength/electrochemical characteristics of friction stir weld joint

The V-95 and D-19 precipitation hardened Russian aluminum alloys are widely used in the Russian aircraft industry and these alloys are not weldable by conventional fusion weld techniques. This paper intends to evaluate the effect of spindle and weld speed on joint strength characteristics of a single pass (SP) and double pass (DP) friction stir lap weld through a common heat index and to analyze the effect of retrogression and re-ageing treatment (RRA) on joint strength and corrosion characteristics. The strength characteristics were analyzed by welding and shear testing of specimens and corrosion susceptibility of joint through immersion in EXCO solution as per ASTM G34. The trials revealed that the joint strength of the welded alloy is inversely proportional to the heat index and the DP weld provided significantly higher strength than an SP weld. The heat affected zone of the joint was found most sensitized to corrosion. The RRA treatment was found to improve the strength of the joints welded with higher heat input while it slightly degraded the joint strength for low heat input welds. The corrosion characteristics of the welded joint is also significantly improved by the post weld RRA treatment.     

Characterisation of dissimilar P91 and P92 steel welds joint

In the present study, dissimilar weld joint was prepared using the P91 and P92 steel plate of 8-mm thickness, using the multi-pass gas tungsten arc (GTA) welding with filler (weld 1) and autogenous tungsten inert gas welding (A-TIG) process (weld 2). Evolution of δ-ferrite patches was studied in weld zone and heat affected zone (HAZ) for both weld 1 and weld 2. Effect of varying post weld heat treatment (PWHT) duration was also studied on δ-ferrite patches and mechanical properties of the dissimilar weld joint. PWHT was carried out at 760°C. For weld 2, weld zone showed poor impact toughness and higher peak hardness as compared to weld 1. After the PWHT, a considerable reduction in hardness was obtained for both weld 1 and weld 2,while impact toughness of weld zone showed a continuous increment with PWHT duration. For weldments characterisation, optical microscope, scanning electron microscope (SEM) and microhardness tester were utilised.     

The effect of thermal ageing on low cycle fatigue behaviour of 316 stainless steel welds

It is well known that welds are the weak links in any structure. Therefore, it is of out most importance to characterize the mechanical properties of welds. Moreover, the changes in the microstructure that occur in welds on exposure to high temperatures affect the mechanical properties and must be studied by ageing the welds at high temperature. In this paper the low cycle fatigue behaviour of thermally aged 316 stainless steel weld metal is presented. Weld pads with single V configuration were prepared by the shielded metal arc welding process using 316 electrodes. Thermal ageing was done for 10,000 h at 823 and 873 K. Total strain controlled low cycle fatigue tests were conducted at a constant strain rate of 3 × 10^?3 s^?1 with strain amplitudes in the range ±0.25% to ±0.6% at 823 and 873 K. Weld metal exhibited initial hardening followed by cyclic softening prior to failure. The aged samples exhibited higher stress response as compared to the unaged samples. At both the temperatures and all strain amplitudes fatigue life was inferior to that of unaged samples. The metallography of the aged and tested material was studied through optical, scanning and transmission electron microscopy. The effect of transformation of δ-ferrite to sigma phase and carbides in the weld metal on low cycle fatigue behaviour was evaluated.     

Effects of temper condition and corrosion on the fatigue performance of a laser-welded Al–Cu–Mg–Ag (2139) alloy

The effects of temper condition and corrosion on the fatigue behavior of a laser beam welded Al–Cu–Mg–Ag alloy (2139) have been investigated. Natural aging (T3 temper) and artificial aging (T8 temper) have been applied prior to welding. Corrosion testing has been performed by exposing the welded specimens to a salt spray medium for 720 h. Aging influences the corrosion behavior of laser welds. In the T3 temper, corrosion attack is in the form of pitting in the weld area, while in the T8 temper corrosion is in the form of pitting and intergranular corrosion in the base metal. In the latter case corrosion is attributed to the presence of grain boundary precipitates. Corrosion degrades the fatigue behavior of 2139 welds. The degradation is equal for both the T3 and T8 tempers and for the corrosion exposure selected in this study corresponds to a 52% reduction in fatigue limit. In both cases fatigue crack initiation is associated with corrosion pits, which act as stress raisers. In the T3 temper, the fatigue crack initiation site is at the weld metal/heat affected zone interface, while for the T8 temper the initiation site is at the base metal. Fatigue crack initiation in uncorroded 2139 welds occurs at the weld toe at the root side, the weld reinforcement playing a principal role as stress concentration site. The fatigue crack propagates through the partially melted zone and the weld metal in all cases. The findings in this paper present useful information for the selection of appropriate heat treatment conditions, to facilitate control of the corrosion behavior in aluminium welds, which is of great significance for their fatigue performance.     

Laser-beam welding of SiC fibre-reinforced Ti-6Al-4V composite

Three- and ten-ply SiC fibre-reinforced Ti-6Al-4V composites were joined using a laser beam. With a 300 m thick Ti-6Al-4V filler metal, fully penetrated welds without apparent fibre damage, could be obtained in welding directions both parallel and transverse to the fibre direction by controlling the welding heat input. Excess heat input resulted in the decomposition of SiC and subsequent TiC formation, and also caused degradation of joint strength. The welding of the three-ply composite in which full penetration was achieved at lower laser power, exhibited higher flexibility in heat input than that of the ten-ply composite. Heat treatment at 1173 K after welding improved the joint strength because of the homogenization of the weld metal and decomposition of TiC. The strengths of the transverse weld joints after the heat treatment were approximately 650 and 550 MPa for the three- and ten-ply composites, respectively. With the welding direction parallel to the fibre direction, the strengths both parallel and transverse to the weld joint were equivalent to those of the base plate.     

Incoloy 825/L360复合管焊接接头耐蚀性研究

目的研究Incoloy 825/L360复合管焊后的焊缝耐蚀性能。方法以Incoloy 825/L360复合管为研究对象,选用Inconel625焊材进行了镍基合金焊缝的焊接,并对焊缝和Incoloy 825母材在质量分数为3.5%的NaCl溶液、6%的FeCl_3溶液中进行电化学试验,并对其耐蚀性进行了对比分析。结果在质量分数为3.5%的NaCl溶液中,不同温度下母材自腐蚀电位均高于焊缝,自腐蚀电流密度均小于焊缝,随着温度的升高,母材的自腐蚀电位和焊缝的自腐蚀电流密度均增加,母材的自腐蚀电流密度变化不明显;在质量分数为6%的FeCl_3溶液中,母材与焊缝的自腐蚀电位整体较高,母材的自腐蚀电流密度高于焊缝,不同温度下焊缝极化曲线均存在明显的钝化平台。结论 Incoloy 825母材和焊缝在两种溶液中的耐蚀性存在一定差异;在质量分数为3.5%的NaCl溶液中,母材腐蚀对温度不敏感,焊缝的腐蚀敏感倾向性随着温度的升高而增大,腐蚀敏感性高于母材;在质量分数为6%的FeCl_3溶液中,不同温度下的焊缝极化曲线均存在明显的钝化平台,腐蚀敏感性低于母材。     

Local mechanical properties of radial friction welded supermartensitic stainless steel pipes

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their microstructures and local mechanical properties (hardness, fracture toughness and micro-tensile strength) were characterized in the as-welded condition. Defect-free RF welds were produced with a matching consumable ring (CR) under optimized welding conditions. The formation of a fine structure consisting of a mixture of virgin martensite and some stable austenite retained in the CR region was observed. On the other hand, the presence of virgin martensite plus δ-ferrite was found in the microstructures of the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). A ductile fracture was detected in the CR and weld interface regions at −40 °C. Moreover, both the CR and weld interface regions showed higher hardness and strength values than those of the base material (overmatching), without presenting significant losses in ductility and fracture toughness, which was attributed directly to the fine transformed microstructure of the weld region.     

线能量对06CuNiCrMoNb钢焊缝组织与性能的影响

系统研究了焊接线能量对06CuNiCrMoNb钢焊缝金属组织与性能的影响。结果显示,线能量对焊缝金属组织与性能有显著影响,随着线能量的增加,针状铁素体含量逐渐减少,粒状贝氏体量增多,先共析铁素体宽度增加;焊缝金属低温冲击韧性降低。     

焊前热处理对压铸镁合金GTAW焊气孔的影响

在不同温度下对压铸AM60B母材进行焊前热处理,待冷至室温后对其实施不填丝GTAW重熔焊接。焊后用扫描电镜对焊缝截面的气孔分布及形貌进行观察,并用粒径分析软件Nano measurer 1.2测量焊缝中气孔尺寸,用基于Matlab二次开发的图像分析程序识别和计算焊缝气孔率。结果表明:焊缝气孔主要分布在焊缝熔融区及熔合线附近;与未经焊前热处理母材对应的焊缝相比,经焊前热处理后所得焊缝中的气孔率及气孔尺寸均降低;随着焊前热处理温度升高,焊后气孔率及气孔尺寸均逐渐增加。     

热输入对E36钢SAW焊缝组织及韧性的影响

为提高建造海洋采油平台的效率、减少生产周期,进而为实际生产提供数据支持,采用3种不同热输入对海洋采油平台用E36钢进行埋弧焊焊接,通过光学显微镜(OM)、透射电镜(TEM)、扫描电镜(SEM)和电子背散射衍射技术(EBSD)对焊缝微观组织及夹杂物形貌进行了观察,研究了不同热输入对焊缝组织及韧性的影响,并分析了不同热输入对焊缝夹杂物尺寸分布和成分的影响.结果表明:热输入为50 k J/cm时,焊缝金属韧性较好;随着焊接热输入的增加,焊缝的冲击韧性降低,但仍能满足性能指标,焊缝金属中夹杂物成分相差较大,有效夹杂物数量减少,焊缝金属中大角度晶界比例减少;对于E36钢,热输入为160 k J/cm时不仅能使韧性符合要求还能提高生产效率.     

热输入对Q1100钢焊接接头低温韧性及耐蚀性能的影响

采用10 kJ/cm和15 kJ/cm两种焊接热输入对Q1100超高强钢进行熔化极气体保护焊,研究焊接接头的组织性能及局部腐蚀行为。结果表明：两种热输入焊接接头的焊缝组织主要为针状铁素体和少量的粒状贝氏体,粗晶区组织均为板条贝氏体,细晶区组织均为板条贝氏体和粒状贝氏体,临界相变区组织为多边形铁素体、马奥岛和碳化物的混合组织。两种热输入焊接接头中电荷转移电阻均为母材>热影响区>焊缝区,母材耐蚀性最好,热影响区次之,焊缝区耐蚀性最差。在腐蚀过程中,焊缝区作为阳极最先被腐蚀,当腐蚀一定时间后,腐蚀位置发生改变,阳极腐蚀区域转移到母材区,而焊缝区作为阴极得到保护。热输入为10 kJ/cm时,焊接接头具有更好的低温韧性和耐蚀性,其焊缝和热影响区-40℃冲击功分别为46.5 J和30.2 J。