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.     

Evaluation of the mechanical and metallurgical characteristics of weld metals deposited by class ANSI/AWS class A5.4-06 E309 covered electrodes

The objective of this work was to evaluate the mechanical properties of weld metals of different coated electrodes, class AWS E309 (309L-15, 309L-16, 309MoL-15 and 309MoL-16) from three manufacturers available in the national market. The welds were conducted in the flat position on 1020 ABNT steel plates milled and buttered in accordance with AWS standard A5.4-06. Test pieces were removed for chemical analysis, metallographic analysis and tensile resistance testing. The test pieces were removed from the welds and the tests were also carried out in accordance with the appropriate standards. The results indicate that the level and the morphology of the δ-ferrite has a significant influence on the tensile resistance and ductility of the weld metal, and in some cases they do not comply with the requisites of the AWS standard A5.4-06 in regard to ductility. The conclusion is that electrodes manufactured to the same standard have significant differences in δ-ferrite values, tensile resistance and ductility, which resulted in significant differences in the mechanical properties of the weld metal.     

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.     

Hot-corrosion resistance of dissimilar AISI 4340 and AISI 304L weldments in the molten salt environment at 600°C

High temperature corrosion resistance of welded components in power plant industry, hot sections of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces and petrochemical installations is one of the serious necessity. The failure of hot sections of welded component is due to the deposition of molten salt which accelerates the hot corrosion reactions in the weld joint. In this research work, the oxy-chlorination of dissimilar weldments between AISI 304L austenitic stainless steel and AISI 4340 alloy steel at 600°C in eutectic mixture of K₂SO₄?+?60% NaCl under molten salt conditions was investigated. Corrosion kinetics for this dissimilar joints calculated from the thermogravimetric charts were represented. Corrosion on the dissimilar joint employing E309L filler in pulsed current gas tungsten arc welding process is found to be very aggressive, due to the fragmented delta ferrites at numerous locations resulting in the formation of the micro electrochemical cells, which act as sites for corrosion initiation and thus leading to higher corrosion rate. However, in the case of continuous current, the joint is able to protect itself better in this environment due to lower amounts of delta ferrites in weld zone, which is attributed to the higher temperature available in continuous mode leading to austenisation of delta ferrites in the multipass welding.     

电子束焊工艺对304不锈钢焊缝的抗晶间腐蚀性能影响

采用3种不同的电子束焊接工艺焊接304不锈钢,通过显微组织观察、XRD分析、极化曲线测试、动电位再活化(EPR)试验研究了不锈钢焊缝的抗晶间腐蚀性能.结果表明:减少焊接热输入量和添加熔入性焊丝这两种方法都能减少电子束焊缝中铬的碳化物的析出,降低焊缝的敏化度,提高焊缝的抗晶间腐蚀性能;与减少焊接热输入量相比,添加熔入性焊丝对晶间腐蚀的影响更大,焊缝抗晶间腐蚀性能提高更显著.     

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.     

Intergranular corrosion of welded joints of austenitic stainless steels studied by using an electrochemical minicell

An intergranular corrosion study of welded joints of austenitic stainless steels (AISI 304 and 316L) has been addressed. A specific small-scale electrochemical cell (minicell) has been used. Four different weldment zones have been studied. The electrochemical methods applied were the electrochemical potentiokinetic reactivation test and electrochemical potentiokinetic reactivation double loop test. These techniques showed that the HAZ was the most critical zone to intergranular corrosion for both materials. The weld metal was susceptible to interdendritic corrosion and the fusion line showed a mixture of intergranular and interdendritic corrosion. The effect of pre- and post-welding heat treatments for AISI 316L was analyzed. The HAZ was again the most critical zone in every heat treatment condition. The results were correlated to the microstructural features of the materials.     

Effect of magnetic field applied during gas metal arc welding on the resistance to localised corrosion of the heat affected zone in AISI 304 stainless steel

Resistance to localised corrosion at the heat affected zone (HAZ) of AISI 304 stainless steel gas metal arc welded (GMAW) in presence of magnetic fields of different intensity was studied. Samples of HAZ, 8 mm away from the weld centre, were subjected to electrochemical potentiokinetic reactivation to assess the degree of sensitisation (DOS). The application of magnetic field during welding induced lower DOS and better resistance to pitting corrosion in 3.5% NaCl solution than samples welded without it. Experimental findings suggest that magnetic fields enable Cr redistribution in the austenitic base metal during the welding thermal cycle reducing Cr depletion.     

堆内构件304L焊接件在除氧和氯离子环境中的应力腐蚀开裂研究

采用高温高压慢应变速率拉伸试验方法(SSRT),研究了在除氧环境下不同浓度氯离子对304L焊接件在模拟一回路高温高压硼锂水介质中氯致应力腐蚀开裂的影响。结果表明:当氯离子浓度为1 mg/L时,其各项力学性能指标与惰性氮气空白样一致,表明在低浓度氯离子除氧条件下,304L焊接件没有应力腐蚀敏感性。随着氯离子含量(1~50mg/L)的增加,304L焊接件应力腐蚀敏感指数变化呈增加趋势。断口侧面没有观察到明显的裂纹,氯离子浓度越低,断口缩颈现象越明显,表明主要是机械断裂。氯离子浓度较高时,棱角部分出现微裂纹源,可能与棱角部分应力更为集中相关。所有样品的断裂位置都在焊缝和热影响区,在焊缝和热影响区发生了巨大的形变,离断口越近,变形越严重。焊接部位是304L堆内构件中薄弱环节,应该成为应力腐蚀开裂和其他性能检测的重点部位。     

Fatigue life prediction using two stage model for AISI 304L cruciform joints,with different fillet geometry,failing at toe

Abstract

Reports in the literature indicate that the fillet geometry affects the fatigue properties of cruciform welded joints in structural steels. In an attempt to study the above effect with respect to stainless steel sheet metal welded joints, load carrying transverse fillet welded cruciform joints having a two fillet geometry were fabricated from AISI 304L stainless steel using gas tungsten arc welding and gas metal arc welding with 308L electrodes. The objective of the present work is to predict the fatigue life of AISI 304L cruciform joints failing at the weld toe using a two stage model. The local stress life method was applied to calculate the fatigue crack initiation life, whereas the fatigue crack propagation life was estimated using fracture mechanics concepts. Constant amplitude fatigue tests with stress ratio R ~ 0 were carried out using a 100 kN servohydraulic Dartec universal testing machine at a frequency of 30 Hz. An automatic crack monitoring system based on crack propagation gauges was used to obtain the propagation data during the fatigue process. The predicted lives were compared with the experimental values.     

304/Q235复合板多主元高熵化焊缝的组织与性能

对304/Q235复合板进行激光填粉焊接试验,利用光学显微镜、扫描电镜、X射线衍射、材料万能试验机及电化学工作站等,对比分析了多主元高熵化CrNi₂MnTi_0.5Al_0.5焊料及Fe基焊料所得焊接接头的微观组织、物相结构、力学性能与电化学腐蚀性能,探索了焊缝填充材料对不锈钢复合板焊缝微观组织、接头性能的影响规律。结果表明,CrNi₂MnTi_0.5Al_0.5焊料焊缝区形成了FCC及Ti₃Al颗粒的双相结构,焊缝显微硬度仅为Fe基焊料焊缝区硬度的69%~75%。两种焊接接头都有较好的抗拉强度,拉伸试样都在母材区断裂。CrNi₂MnTi_0.5Al_0.5焊料焊缝区具有最佳的耐蚀性能,其腐蚀速率约为304不锈钢的41%。     

EPR法评价HR3C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研究了HR3C钢焊接接头的晶间腐蚀敏感性,并通过金相显微镜、X-射线衍射仪、扫描电子显微镜及能谱仪研究了HR3C钢焊接接头的微观组织.结果表明,HR3C钢焊缝金属和焊接热影响区均为奥氏体+析出相组成,焊接接头具有较低的晶间腐蚀倾向.由于焊缝金属中Cr和Nb等元素含量高及晶界和枝晶界铌、铬元素偏析等原因提高了晶界耐腐蚀性,使其具有优异的抗晶间腐蚀性能;而热影响区由于受焊接热循环作用晶界析出M23C6引起晶界贫铬,具有一定的晶间腐蚀敏感性.     

Microbially influenced corrosion on stainless steels in waste water treatment plants: Part 1

Abstract

Field tests on stainless steels have been carried out at five waste water treatment plants for one year. Three grades of stainless steel, i.e. AISI 304 (UNS S30400), AISI 316 (UNS S31600), and duplex 2205 (UNS S31803) were tested in the final settling tank in the plants. The time dependence of the open circuit potential (OCP) was measured for all coupons. Ennoblement of the OCP, similar to that reported from investigations in sea water, was found in one of the plants. Waters from three of the exposure sites, containing dispersed deposits from exposed coupons, were chemically analysed. Pitting corrosion was observed after the field test on steel grade AISI 304 in three of the five plants, and on AISI 316 in one plant. No corrosion was found on 2205 in any of the plants. Laboratory measurements of the OCP were carried out for the AISI 304, AISI 316, and duplex 2205 steels in water collected from one of the plants. Cathodic polarisation curves were recorded in waste water from the same plant. T he cathodic reaction rate increased at the highest OCP. Simulation of the ennoblement was carried out by potentiostatic polarisation in a 600 ppm chloride solution. The current response indicated corrosion of welded AISI 304 material and of AISI 304 and AISI 316 steels in crevice assemblies after a long induction time. Part 2 of this study presents the results of further testing and a risk assessment design.     

Microstructure and Mechanical Behavior in Dissimilar SAF 2205/API X52 Welded Pipes

The welding of a duplex stainless steel SAF 2205 DSS(UNS 31803) and high strength low alloy steel API X52 by shielded metal arc welding process was conducted using two different filler metals,the duplex E2209 and austenitic E309 grade.The microstructures of the dissimilar metal joints have been investigated by optical microscopy,scanning electron microscopy,energy-dispersive spectroscopy(EDS) and X-ray diffraction.EDS analysis at the interface X52 weld metal showed an evident gradient variation of Cr and Ni between boundaries of fusion and type II,where the highest hardness value was recorded.Tensile strength and toughness values of the weld metal produced by E309 electrode are slightly higher than those of the weld metal produced by E2209 electrode.Potentiodynamic polarization tests of different regions of the welded joints evaluated in 3.5%NaCl solution exhibit a high corrosion resistance of both weld metals.     

玻璃喷丸处理提高304不锈钢焊接接头抗应力腐蚀性能的研究

基于对304不锈钢焊接试板表面喷丸处理前后的表层残余应力X射线衍射测量，研究了在42％沸腾MgCl2溶液中，表面玻璃喷丸和铸钢喷丸对304不锈钢焊接试板应力腐蚀开裂敏感性的影响，比较了采用不同铸钢喷丸和玻璃喷丸处理工艺的304不锈钢焊接试板抗应力腐蚀开裂的能力．试验结果表明：未喷丸处理的焊接试板6h就发生开裂，50％、100％覆盖率的铸钢喷丸焊接试板分别在试验310h和3500h开裂，而200％覆盖率的铸钢喷丸焊接试板，50％、100％、200％覆盖率的玻璃喷丸焊接试板经历3500h也未见开裂．因此，喷丸处理工艺能够很好地提高焊接构件抗应力腐蚀开裂能力；且在同样喷丸强度下，焊接接头经玻璃喷丸工艺处理后的抗应力腐蚀能力明显优于铸钢喷丸处理工艺．     

城市输水用Q235B+304不锈钢复合管环焊焊接工艺

不锈钢复合管内侧为具有耐腐蚀性能的不锈钢,外侧为具有一定强度的碳钢,成为新一代环保型输水管。为了研究8 mm+2 mm厚城市输水用Q235B+304不锈钢复合钢管的环焊焊接工艺,试验选用合理的焊接材料及坡口形式等,获得了复合板与复合板、复合板与碳钢板的焊接接头。通过拉伸、冲击、弯曲试验评价两种焊接接头的力学性能;通过检测接头不锈钢焊道化学成分,评估复合管焊接接头内侧不锈钢焊道的耐晶间腐蚀性能。结果表明,所采用的焊接工艺获得的接头力学性能满足技术要求且富余量较大,复合管接头不锈钢焊缝获得了A+(5%~10%)δ组织,耐晶间腐蚀性能优异。     

Corrosion Resistance of Friction Surfaced AISI 304 Stainless Steel Coatings

Corrosion resistance of friction surfaced AISI 304 coating in boiling nitric acid and chloride containing environments was found to be similar to that of its consumable rod counterpart. This was in contrast to the autogenous fusion zone of GTAW weld which showed inferior corrosion resistance with respect to the consumable rod. The superior corrosion resistance of friction surfaced coatings was attributed to the absence of δ-ferrite in it.     

Determination of the sensitized zone extension in welded AISI 304 stainless steel using non-destructive electrochemical techniques

Extension of sensitized zone (SZ) in welded AISI 304 stainless steel was determined by two non-destructive electrochemical tests: double loop electrochemical potentiokinetic reactivation technique (DLEPR) and local electrochemical impedance spectroscopy (LEIS). Welding was carried out using the shielded metal arc with two selected welding energies: the first one (0.7 kJ mm⁻¹) does not promote the sensitization of the 304 steel and it constitutes the reference sample and the second one (2.2 kJ mm⁻¹) which leads to the precipitation of chromium carbides in the grain boundaries after the welding process. The non-destructive DLEPR and LEIS tests allowed the length of the SZ to be determined and a good agreement between the two techniques and the microstructure of the two welded samples was shown. The presence of an inductive loop on the local impedance diagrams seems to reflect a galvanic coupling between the weld string (anode) and the welded stainless steel plates (cathode) which will be very prejudicial to a good corrosion resistance of the welded system. The results showed that the two electrochemical tests could be applied in practical cases in industrial field.     

Failure Analysis of an Oxidative Chlorination Reactor Clad with AISI 304L Stainless Steel

Failure analysis of the hermetical AISI 304L stainless steel cladding in oxidative chlorination reactor shows that its pitting and stress corrosion arose due to the presence of chlorine ion in the working environment. In order to improve its corrosion resistance, AISI 316L stainless steel should be utilized.     

Effects of microplasma arc AISI 316L welds on the corrosion behaviour of pipelines in LiBr cooling systems

The effect of microplasma arc welding (MPAW) on the electrochemical and corrosion behaviour of AISI 316L stainless steel tubes has been studied. Scanning electrochemical measurements were performed in sodium chloride to evaluate the difference in the electrochemical activity of base (non-welded) and welded samples. Oxygen reduction rates increase in AISI 316L due to the heat treatment effect induced by welding, indicating a higher electrochemical activity in the welded samples. Additionally, the use of MPA weldments in lithium bromide (LiBr) absorption machines was also analysed at typical operating temperatures and Reynolds numbers. The welding process increases corrosion rates, hinders passivation and increases the susceptibility to pitting attack in LiBr. However, zero-resistance ammeter and localization index measurements show that the galvanic pair generated between the base and welded alloys is weak, both electrodes being in their passive state. Temperature greatly affects the corrosion process.