Microstructure and Corrosion Resistance of Dissimilar Weld-Joints between Duplex Stainless Steel 2205 and Austenitic Stainless Steel 316L

The microstructure and corrosion resistance of dissimilar weld-joints between stainless steel SAF 2205 and stainless steel AISI 316 L were investigated. Welding was accomplished by different types of welding wires AWS ER 347, AWS ER 316 L and AWS ER 309 L. To verify soundness of welded samples, nondestructive tests were performed. Metallographic samples were prepared from cross-section areas of weldjoints to investigate microstructure of different regions of weld-joints by optical microscopy and scanning electron microscopy. Corrosion resistance of weld-joints was evaluated in NaCl solution by potentiodynamic polarization and electrochemical impedance techniques. In the weld metal AWS ER 347, the brittle sigma phase was created, resulting in the decrease of weld-joint corrosion resistance. According to the results of metallurgical investigations and corrosion tests, welding wire AWS ER 309 L was suitable for welding duplex stainless steel(SAF 2205) to austenitic stainless steel(AISI 316L) by gas tungsten arc welding(GTAW)process.     

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.     

Degradation of mechanical and corrosion resistance properties of AISI 317L steel exposed at 550 °C

The use of austenitic stainless steel type AISI 317L has increased in the last years, in substitution to AISI 316L and other austenitic grades. The higher Mo content (3.0 wt.%. at least) gives higher corrosion resistance to AISI 317L. However, some concern arises when this material is selected to high temperature process services in refineries. Microstructural changes such as chromium carbide precipitation and sigma phase formation may occur in prolonged exposure above 450 °C. In this work, the microstructure evolution of AISI 317L steel during aging at 550 °C was analyzed. Thermodynamic calculations with Thermocalc® and detailed microstructural analysis were performed in steel plate base metal and in weld metal produced by GTAW process. The aging for 200, 300 and 400 h promoted gradual embrittlement and deterioration of corrosion resistance of both weld and base metal. The results show that the selection of AISI 317L steel to services where temperatures can reach 550 °C is not recommended.     

Microstructure,hardness and petroleum corrosion evaluation of 316L/AWS E309MoL-16 weld metal

The current work presents some observations about the effect of welding heat input on the microstructure, hardness and corrosion resistance of AWS E309MoL-16 weld metal, diluted with AISI 316L austenitic stainless steel plates. Such welds are widely used during overlay of equipment in the petroleum and gas industries. Results show that the welds contained δ-ferrite varying between vermicular to lathy morphology, typically encountered in welds which solidify in ferrite–austenite mode (FA). Conversely, contents and morphology of δ-ferrite in the weld metals were altered, showing an increase of welding heat input. The corrosion rate of the weld metal indicated that when higher levels of welding heat input are used the corrosion rate is reduced. This may be attributed to metallurgical changes, especially variations in the proportion of δ-ferrite, caused by changes in cooling rate.     

Resistance spot welding joints of AISI 316L austenitic stainless steel sheets: Phase transformations,mechanical properties and microstructure characterizations

In this paper, we aim to optimize welding parameters namely welding current and time in resistance spot welding (RSW) of the austenitic stainless steel sheets grade AISI 316L. Afterward, effect of optimum welding parameters on the resistance spot welding properties and microstructure of AISI 316L austenitic stainless steel sheets has been investigated. Effect of welding current at constant welding time was considered on the weld properties such as weld nugget size, tensile–shear load bearing capacity of welded materials, failure modes, failure energy, ductility, and microstructure of weld nuggets as well. Phase transformations that took place during weld thermal cycle were analyzed in more details including metallographic studies of welding of the austenitic stainless steels. Metallographic images, mechanical properties, electron microscopy photographs and micro-hardness measurements showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Backscattered electron scanning microscopic images (BE-SEM) showed various types of delta ferrite in weld nuggets. Three delta ferrite morphologies consist of skeletal, acicular and lathy delta ferrite morphologies formed in resistance spot welded regions as a result of non-equilibrium phases which can be attributed to the fast cooling rate in RSW process and consequently, prediction and explanation of the obtained morphologies based on Schaeffler, WRC-1992 and Pseudo-binary phase diagrams would be a difficult task.     

A study on low magnetic permeability gas tungsten arc weldment of AISI 316LN stainless steel for application in electron accelerator

Low magnetic permeability is an important criterion in selection of the material of construction of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3–8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI 316LN stainless steel is not required to be solution annealed after the final forming operation for obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector Microtron, the study also provides useful input for design of future indigenous accelerators with vacuum chambers of austenitic stainless steel.     

Effect of rare earth elements on microstructure and oxidation behaviour in TIG weldments of AISI 316L stainless steel

The influence of rare earth addition in weld metal, on the microstructure and oxidation behaviour of AISI 316L stainless steel in dry air under isothermal condition at 973 K for 240 h is reported. Rare earth metal (REM) doped weld metal zone exhibits better oxidation resistance during isothermal holding as compared to base metal and undoped weld metal zone of 316L. Presence of both Ce and Nb in weld metal shows superior oxidation resistance than with Ce alone. TIG weld microstructures are presented by optical microscopy. The morphologies of the scales and nature of their adherence to the alloy substrates, and scale spallation have been characterized by SEM and EDAX.     

Weldability and properties of martensitic/austenitic stainless steel joints

Abstract

A series of studies has been carried out to examine the weldability and properties of dissimilar steel joints using martensitic and austenitic stainless steels F6NM (OCr13Ni4Mo) and AISI 347, respectively. This type of joint requires good mechanical properties, corrosion resistance, and a stable magnetic permeability in addition to a good weldability. Weldability tests include weld thermal simulation of the martensitic steel to investigate the influence of weld thermal cycles and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of the heat affected zone (HAZ); implant testing to examine the tendency for cold cracking of martensitic steel; and rigid restraint testing to determine hot crack susceptibility of the multipass dissimilar steel joints. The simulation results indicated that the toughness of the martensitic steel HAZ did not change significantly after the weld thermal cycles. The implant test results indicated that welds produced using nickel based filler show no tendency for cold cracking, whereas welds produced using martensitic or ferritic filler show such a tendency. Based on the weldability tests, a welding procedure (tungsten inert gas welding for root passes with HNiCrMo-2B wire followed by manual metal arc welding using ENiCrFe-3B coated electrode) was developed and a PWHT at 600°C for 2 h was recommended. Joints produced using the developed welding procedure are not susceptible to hot and cold cracking. After PWHT the joints exhibit both satisfactory mechanical properties and stress corrosion cracking resistance.

MST/1955     

Influence of filler metals and welding techniques on the structure–property relationships of Inconel 718 and AISI 316L dissimilar weldments

In the present investigation, an attempt has been made to weld the precipitation hardened Nickel based super alloy Inconel 718 and austenitic stainless steel AISI 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) process employing ER2553 and ERNiCu-7 fillers. Microstructure examination using optical and SEM analysis clearly witnessed the formation of unmixed zone at the Heat Affected Zone (HAZ) of Inconel 718 for all the joints. The studies showed the absence of deleterious phases in the CCGTA and PCGTA weldments employing ERNiCu-7. Tensile studies corroborated that the fracture occurred at the parent metal of AISI 316L in all the cases. It was inferred from the present study that PCGTA weldments employing ERNiCu-7 exhibited better metallurgical and mechanical properties. This study articulated the effect of filler metals on the structure–property relationships of the weldments.     

Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773 K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000 HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.     

Hybrid (plasma + gas tungsten arc) weldability of modified 12% Cr ferritic stainless steel

This paper deals with the hybrid (plasma + gas tungsten arc) welding properties of 12 mm thick modified 12% Cr ferritic stainless steel complying with EN 1.4003 and UNS S41003 steels with a carbon content of 0.01% to improve the weldability. The root passes of the butt welds were produced with plasma arc welding (PAW) without filler metal while gas tungsten arc welding (GTAW) was used to accomplish filler passes with 309 and 316 austenitic stainless steel type of consumables, respectively. The joints were subjected to tensile and bend tests as well as Charpy impact toughness testing at −20 °C, 0 °C and 20 °C. Examinations were carried out in terms of metallography, chemical analysis of the weld metal, ferrite content, grain size and hardness analyses. Although 309 consumables provided higher mean weld metal toughness values compared to 316 (90 J vs. 75 J), 316 type of consumables provided better mean HAZ toughness data for the joints (45 J vs. 20 J) at −20 °C. Toughness properties of the welds correspond with those of microstructural features including grain size and ferrite content.     

Formation and evolution of layered structure in dissimilar welded joints between ferritic-martensitic steel and 316L stainless steel with fillers

Dissimilar high-energy beam (HEB) welding is necessary in many industrial applications. Different composition of heat-affected zone (HAZ) and weld metal (WM) lead to variation in mechanical properties within the dissimilar joint, which determines the performance of the welded structure. In the present study, appropriate filler material was used during electron beam welding (EBW) to obtain a reliable dissimilar joint between reduced-activation ferritic-martensitic (RAFM) steel and 316 L austenitic stainless steel. It was observed that the layered structure occurred in the weld metal with 310S filler (310S-WM), which had the inferior resistance to thermal disturbance, leading to severe hardening of 310S-WM after one-step tempering treatment. To further ameliorate the joint inhomogeneity, two-step heat treatment processes were imposed to the joints and optimized. δ-ferrite in the layered structure transformed into γ-phase in the first-step normalizing and remained stable during cooling. In the second-step of tempering, tempered martensite was obtained in the HAZ of the RAFM steel, while the microstructure of 310S-WM was not affected. Thus, the optimized properties for HAZ and 310S-WM in dissimilar welded joint was both obtained by a two-step heat treatment. The creep failure position of two dissimilar joints both occurred in CLAM-BM.     

A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study,crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels(AISI 304,AISI 316L and DSS 2205)were investigated and discussed.Crevice repassivation potential(ER,CREV),which was measured by the potentiodynamic-galvanostatic-potentiodynamic(PDGS-PD)test,was applicable to crevice corrosion evaluation of 304 and 316 L stainless steels.However,much lower(ER,CREV values were obtained for DSS 2205 and LDSS 2002.These abnormal(ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase,the lower corrosion potential in the crevice-like solution,and more crevice corrosion sites in the PD-GS-PD test.A critical chloride concentration of crevice corrosion(CCCCREV)measurement was introduced for crevice corrosion evaluation of various stainless steels.The derived CCCCREVwas proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels.An order of crevice corrosion resistance of AISI 304≈LDSS 2002相似文献   

Influence of Heat Input on Martensite Formation and Impact Property of Ferritic-Austenitic Dissimilar Weld Metals

The effect of heat input on martensite formation and impact properties of gas metal arc welded modified ferritic stainless steel (409M) sheets (as received) with thickness of 4 mm was described in detail in this work. The welded joints were prepared under three heat input conditions, i.e. 0.4, 0.5 and 0.6 kJ/mm using two different austenitic filler wires (308L and 316L) and shielding gas composition of Ar + 5% CO2. The welded joints were evaluated by microstructure and charpy impact toughness. The dependence of weld metal microstructure on heat input and filler wires were determined by dilution calculation, Creq/Nieq ratio, stacking fault energy (SFE), optical microscopy (OM) and transmission electron microscopy (TEM). It was observed that the microstructure as well as impact property of weld metal was significantly affected by the heat input and filler wire. Weld metals prepared by high heat input exhibited higher amount of martensite laths and toughness compared with those prepared by medium and low heat inputs, which was true for both the filler wires. Furthermore, 308L weld metals in general provided higher amount of martensite laths and toughness than 316L weld metals.     

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.     

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.     

Influence of the microstructure on the corrosion resistance of plasma‐nitrided austenitic stainless steel 304L and 316L

Austenitic stainless steels are widely used in medical and food industries because of their excellent corrosion resistance. However, they suffer from weak wear resistance due to their low hardness. To improve this, plasma nitriding processes have been successfully applied to austenitic stainless steels, thereby forming a thin and very hard diffusion layer, the so‐called S‐phase. In the present study, the austenitic stainless steels AISI 304L and AISI 316L with different microstructures and surface modifications were used to examine the influence of the steel microstructure on the plasma nitriding behavior and corrosion properties. In a first step, solution annealed steel plates were cold‐rolled with 38% deformation degree. Then, the samples were prepared with three kinds of mechanical surface treatments. The specimens were plasma nitrided for 360 min in a H₂–N₂ atmosphere at 420 °C. X‐ray diffraction measurements confirmed the presence of the S‐phase at the sample surface, austenite and body centered cubic (bcc)‐iron. The specimens were comprehensively characterized by means of optical microscopy, scanning electron microscopy, glow discharge optical emission spectroscopy, X‐ray diffraction, surface roughness and nano‐indentation measurements to provide the formulation of dependencies between microstructure and nitriding behavior. The corrosion behavior was examined by potentio‐dynamic polarization measurements in 0.05 M and 0.5 M sulfuric acid and by salt spray testing.     

Effect of post weld heat treatment on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel weldments

The effect of postweld heat treatment (PWHT) on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel joints with ER316LMn filler material was investigated. PWHT aging was performed for 1 h at four different temperatures of 600 °C, 760 °C, 870 °C and 920 °C, respectively. The microstructure revealed the sigma phase precipitation occurred in the weld metals heat-treated at the temperature of 870 °C and 920 °C. The PWHT temperatures have the less effect on the tensile strength, and the maximum tensile strength of the joints is about 630 MPa, reaching the 95% of the base metal, whereas the elongation is enhanced with the rise of PWHT temperatures. Meanwhile, the sigma phase precipitation in the weld metals reduces the impact toughness.     

Microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for welding of a 12%Cr duplex stainless steel

Abstract

The microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for the welding of a duplex 12% Cr corrosion resisting steel, as well as the experimental procedures used, are described. During the development, it was found that weld metals having matching compositions (and thus duplex structures) to those of 3CR12 had very poor impact properties. This was largely because of the inability to control weld metal grain size. By increasing the proportion of austenite stabilising elements, to produce a predominantly low carbon martensitic weld deposit, it was found that acceptable toughness (≥30 J at 20°C) could be achieved in the as welded condition. The electrochemical properties were designed to be similar to, yet slightly more noble than, those of the wrought 3CR12 plate, thus guarding against possible inhomogeneities in the as cast structure. Cost was also an important consideration throughout the development of these closely matching consumables, since the austenitic filler metals used (e.g. AWS E 309 Mo) were substantially more expensive than the parent plate. It has been shown that cost effective, metallurgically compatible filler metals for 3CR12 can be produced.

MST/651     

奥氏体不锈钢离子渗碳后的腐蚀行为

为了提高奥氏体不锈钢零件的使用寿命,利用低温离子渗碳技术对AISI 316L奥氏体不锈钢进行了表面渗碳处理.用X射线衍射仪和光学显微镜分析了渗碳层的微观组织结构,用显微硬度计测试了渗碳层的硬度分布,通过电化学极化曲线测试技术和化学腐蚀试验研究了离子渗碳AISI 316L不锈钢的腐蚀行为.渗碳层为单相碳过饱和奥氏体固溶体,由此明显提高了AISI 316L不锈钢的抗腐蚀性能,渗碳层硬度梯度平缓,表面显微硬度高达900 HV.结果表明,奥氏体不锈钢低温离子渗碳处理不仅提高了其表面硬度,而且提高了不锈钢表面的耐腐蚀性能,从而提高了其使用寿命.