Duplex Stainless Steel Welds Research Articles

AISI 2205 DSS for body-in-white automotive structure: effect of welding current and time on the performance of spot welded joint

Duplex stainless steel is an ideal candidate in the automotive sector leading to a significant weight reduction and enhancement in product safety. In the present work, two major influencing process parameters i.e. welding current and welding time have been considered to investigate the mechanical and metallurgical performance of resistance spot welded duplex stainless steel. Other important process parameters, such as electrode force, squeeze time and hold time have been kept constant throughout the process. Results show that tensile shear strength (TSS) increases with an increase in welding current as well as welding time due to more amount of heat generation at interface. However, excessive value of both results in the expulsion of weld material which significantly alters the nugget diameter and cause decrease in TSS. Moreover, the failure mode is changed from interfacial failure (IF) mode to pull-out failure (PF) mode at the higher value of welding current and time. Microstructural observation reveals that the fusion zone (FZ) is consisted of columnar grain structure, whereas heat affected zone (HAZ) contains equiaxed grain structure. Furthermore, the phase balance of austenite and ferrite is completely disturbed in the FZ and HAZ.

Dissimilar welding of super duplex stainless steel (SDSS) and pipeline steel – A brief overview

There are different grades of stainless steels available in the market for its better corrosion resistance but super duplex stainless steel find their name due to the presence of two phase microstructure. Due to the complex metallurgical behavior the welding of super duplex stainless steel is quite difficult as compared to the normal grades of the stainless steel. Austenite and ferrite are the two main phases present in super duplex SS almost in equal proportions. To provide better strength, corrosion resistance and sulfide stress cracking than the normal stainless steels, these super duplex SS (SDSS) are specially designed to meet the requirements of structural and pressure vessel applications. This paper basically study about the dissimilar welding challenges during welding of various grades of super duplex stainless steels. Different secondary phases has been formed in the microstructure of duplex stainless steels (DSSs) when these steels are exposed to higher temperatures. These secondary phases degrade their performance at excessive higher temperatures. To minimize the degradation of the engineering performance of DSSs at higher temperatures various types of isothermal treatments have been used.

Investigation of microstructure evolution, mechanical and corrosion properties of SAF 2507 super duplex stainless steel joints by keyhole plasma arc welding

Keyhole plasma arc welding (PAW) of the super duplex stainless steel (SDSS) is expected to achieve full-penetration joints of medium-thickness plates in a single pass with higher efficiency. However, the unique key-holing processes due to the special constricted arc behaviors cause much different thermal cycles of the liquid metals as well as changed microstructures. SDSS 2507 with a thickness of 10 mm was joined by PAW to investigate the joints' microstructure and properties. Microstructure characterization reveals substantial differences in the content of austenite, ranging from 68.9% in weld metal (WM) to 32.1% in the heat-affected zone (HAZ). The oxide inclusions in the WM enhance the hardness of the welded joints, but provide the path for crack propagation to decrease its impact toughness. While complicated microstructure is found in HAZ forming ferrite and diverse austenite, such as grain boundary austenite (GBA), intragrain austenite (IGA), and Widmanstätten austenites (WA). A small amount of secondary austenite (γ2) and chromium nitride are also found in HAZ, and they significantly deteriorate its corrosion resistance. The grain boundary misorientation angle distribution of the austenite in WM is found to be dominated by the low angle boundaries (LABs). However, its content decreases from the WM to base metal (BM). Selective corrosion occurs in all samples, where ferrite is preferentially dissolved when the extrinsic voltage is low (<0.5 V) and austenite is preferentially dissolved when the extrinsic voltage is high (>0.5 V), indicating the different electrochemical activity of the two phases.

Effects of Nitrogen-Added Double Shielding Gas and Solution Treatment on Duplex Stainless Steel Weld Microstructure of Deep-Penetration Tungsten Inert Gas Welding

Effects of Nitrogen-Added Double Shielding Gas and Solution Treatment on Duplex Stainless Steel Weld Microstructure of Deep-Penetration Tungsten Inert Gas Welding

Investigating the mechanical properties and fusion zone microstructure of dissimilar laser weld joint of duplex 2205 stainless steel and A516 carbon steel

Laser welding of dissimilar A516 low carbon steel and duplex stainless steel was conducted to evaluate the effect of fiber laser welding parameters (e.g., laser power, welding speed, nozzle distance and beam deviation) on the responses of tensile strength, depth of the melt pool, microstructure, temperature near the melt pool and melt pool hardness. The maximum tensile strength of 500 MPa and 18 percent elongation were obtained at the laser power of 400 W, welding speed of 300 mm/min and the focal point. The absorbed power of laser and linear speed of welding had the most notable impact on the tensile strength of the weld. The fusion zone microstructure was composed of a combination of ferrite–austenite distribution from duplex stainless steel (DSS) based on different cooling and heating cycles. During the nucleation process, ferrite grains were transformed to austenite grains from different areas of the fusion zone. Also, the weld fusion zone microstructure at A516 side was composed of fully martensitic structure, according to the higher heat input upper critical temperature of steel (AC3), thereby leading to rapid cooling. The EDS analysis also showed that the Fe percentage was continually reduced at the fusion line from A516 to DSS, although Ni and Cr were distributed at the fusion zone with some minor changes of weight percentage. Therefore, Cr and Ni had a crucial effect on elemental alloy composition in this laser welding process. The ductility of the A516 fracture surface with bigger and deeper fracture dimples was caused by applying higher laser energy density, which effectively improved the fracture ductility of the welded samples.

Joint-design effect on the metallurgical and mechanical behavior of duplex stainless steel welds

In the present investigation, the influence of joint design on the microstructure and the mechanical properties of SAF 2205 duplex stainless steel welds are reported. Plates with two different joint designs were welded using the gas tungsten arc welding process. To investigate the sole effect of joint design, the joints were designed in such a way that both joints have similar groove volumes. The weldments were investigated for microstructural characterization, ferrite content, and microhardness study; later, they were subjected to Charpy V-notch impact test, transverse tensile test, and fatigue testing in order to investigate the mechanical performance. Both the weld joints were able to achieve 100% joint efficiency in view of the transverse tensile test. Different weld joint configurations demonstrated the influence of the differential heat dissipation characteristics of the joints, evident from different morphological features revealed through optical microscopy of the weldment. The welding affected the ferrite(α)-austenite(γ) ratio of the weld metals and differed the welds in terms of ferrite content in the root and weld pass. The weld zone of the U-joint showed a 65.8% ferrite fraction and thus showed 18% more hardness as compared to the V-joint, while the V-joint had the highest yield stress of 617 MPa. The study revealed that the U-joint performed better in comparison to the V-joint in terms of microhardness, impact toughness, and fatigue behavior. The U-joint could resist around 15% more fatigue cycles than the V-joint under high cycle fatigue.

Mechanism for enhanced age hardening of 22 % Cr duplex stainless steel weld metal fabricated with grade 2209 filler material

In industrial applications, 22 % Cr duplex stainless steel is extensively used to manufacture welded components. However, the steel becomes brittle on thermal exposure at 250–500 °C (known as 475 °C embrittlement). Most existing studies have focused on the solution-treated material, leaving the weld metal largely unexplored. In this study, we characterized a nanoscale structure of 22 % Cr duplex stainless steel weld metal, fabricated using a grade 2209 filler wire and aged at 400 °C for 1,000 h. The presence of Ni-Mn rich solute clusters within BCC-structured ferrite phase was evident, along with spinodal decomposition in the weld metal. A simulation conducted using Thermo-Calc indicated that the clusters were the precursors of the G-phase. The residual stress and the higher Ni content are considered to accelerate the spinodal decomposition of the weld metal. The solute clusters and pronounced spinodal decomposition contributed to an enhanced age hardening of the ferrite in the weld metal.

Effect of welding current on properties of activated gas tungsten arc super duplex stainless steel welds

Abstract A comparative evaluation of the influence of welding current on Tungsten Inert Gas (TIG) welding and Activated Tungsten Inert Gas (ATIG) welding on the depth of penetration and microstructure properties was performed. Various super duplex stainless steel (SDSS) beads on plate weld joints were studied. Visual observation showed that lower welding current resulted in partial weld penetration in the case of both TIG and ATIG weldments. Weld joints obtained by the ATIG process have a higher depth of penetration and depth/width ratios than weld joints obtained in the conventional TIG process at comparatively lower welding currents. Further, microstructural characterizations were performed using optical microscopy. The weld zone microstructure consists of grain boundary austenite (GBA), widmanstätten austenite (WA) and intragranular austenite (IGA). Ferrite percentage in bulk material and each weldment was measured using ferrite scope. The TIG-welded heat affected zone (HAZ) joints showed higher ferrite content than activated flux TIG-welded HAZ joints for various welding current conditions. Ferrite content measured in the weld-zone, HAZ and base material was within the ranges of the standard values. The TIG weld zone showed higher hardness than that of the ATIG weld zone.

Effect of solution treatment on duplex stainless steel weld microstructure of deep-penetration TIG welding

The double-layer gas shielded welding method was adopted in this study. The pure argon gas was used in the inner layer, while a small amount of active gas was added to the outer layer. The welding efficiencies and phase ratios in weld microstructure of 2205 duplex stainless steel under different outer shielding gas conditions were compared. Different solution treatment conditions were applied to the welded joints after welding to explore the effect of solution treatment temperature and time on the weld microstructure. The experimental results showed that the welding efficiency could be improved effectively by adding a proper amount of active gas into the outer protective gas. Proper solution treatment could increase the austenite phase proportion in 2205 duplex stainless steel welds. With the increase of the solution temperature and time, the content of austenite gradually increased, the grain became fine, and the two phases were of uniform distribution.

Welding of Super Duplex Stainless Steel and Austenitic Stainless Steel:#xd; Influence and Role of Bicomponent Fluxes

ABSTRACT This study investigated dissimilar tungsten inert gas and activated tungsten inert gas welding experimental results of austenitic 202 with a super duplex 32760 stainless steel. Their microstructural study revealed a balanced austenite-ferrite morphology that mainly consisted of Widmanstatten austenite (WA), grain boundary austenite (GA), and intergranular austenite (IGA). The study showed that the use of flux reduced the heat input necessary to achieve complete penetration, which tends to increase ferrite count in the heat-affected zone and the weld zone of weldment, resulting in minimizing the hot cracking propensity. Further, structure-property connections were also established by evaluating these two weldments’ tensile strength, impact strength, and microhardness. It was determined that weldments of activated tungsten inert gas weldment had better mechanical properties than traditional tungsten inert gas weldment. A weld zone fracture occurred near the austenitic weld interface in both weldments. It was noticed that unmixed zone formation on the side of the austenitic steel was to blame for the poor mechanical properties and failure of tungsten inert gas and activated tungsten inert gas weld joints. In both cases, the hardness distribution in the weld zones is ranked as super duplex stainless steel base metal > heat-affected zone of super duplex steel side > welded zone > heat-affected zone of austenitic steel side > austenitic base metal.

Correction to: Hot cracking in duplex stainless steel weldments — a review

Correction to: Hot cracking in duplex stainless steel weldments — a review

Spatially resolved EDS, XRF and LIBS measurements of the chemical composition of duplex stainless steel welds: A comparison of methods

Duplex steels (DSS) are used in all industries where corrosion problems play a major role. Examples include the chemical industry, the food industry and shipping industries. DSS have a balanced phase ratio of ferrite (α) and austenite (γ). Unlike single-phase stainless steels, DSS combine the advantages of these and can therefore fit many industry requirements, such as weight saving or high mechanical strength. When these steels are welded, alloying elements can burn off and condense as thin layers on cold surface regions. This loss of chemical elements can lead to changes in the microstructure. With the help of Laser-Induced Breakdown Spectroscopy (LIBS), chemical element distributions were visualized. The results were compared with those of conventional measurement methods, such as energy dispersive X-ray analysis (EDS) and X-ray fluorescence analysis (XRF), and the results from LIBS could be validated. LIBS is suitable as a fast, straightforward measurement method for producing line scans along the weld seam and provides spatially resolved information on accumulation phenomena of burned off alloying elements. LIBS is very well suited for the detection of sub-surface elements due to the exclusively superficial ablation of the material. In addition, the measurement method has been calibrated so that quantitative statements about element concentrations can also be made.

Hot cracking in duplex stainless steel weldments — a review

Hot cracking in duplex stainless steel weldments — a review

Initiation mechanism of pitting corrosion in weld heat affected zone of duplex stainless steel

The pitting corrosion resistance of duplex stainless steel welds was investigated. Pitting corrosion mainly occurs in high-temperature heat-affected zone (HT-HAZ), where the peak temperature reaches ferrite single-phase region. Most pitting corrosion in the HT-HAZ initiates from (Ti,Cr)N in the ferrite. Even the titanium content is less than 50 ppm, titanium-containing nitrides precipitate in the HT-HAZ. While no clear Cr-depleted zone develops around (Ti,Cr)N, almost no passive film forms on (Ti,Cr)N surface. Therefore, pitting corrosion is initiated not only by Cr-depleted zone around Cr nitride but also by the lack or vulnerability of the passive film on the (Ti,Cr)N surface.

Analyzing the Effects of Heat Treatment on SMAW Duplex Stainless Steel Weld Overlays

Duplex stainless steel (DSS) has a reasonably high resistance to chloride stress corrosion cracking for offshore and marine applications. However, DSS weld overlay has not been successfully demonstrated due to some inherent problems in achieving pitting and crevice corrosion resistance. In this research work, isothermal heat treatments (350, 650 and 1050 °C) with and different cooling rates have been performed DMR249 Grade A by using shield metal arc welding (SMAW) with an E2209 electrode. Micrographs have shown two phase microstructures of the DSS weld metal, the amounts of austenite phase increased with increment of post-weld heat treatment (PWHT) temperatures. The dilution has maintained consistent values except solution annealing that has shown the disappearance of the heat affected zone in micrographs. The weld metal hardness values increased with PWHT temperatures and remained low at solid solution annealing temperatures. The major alloying elements (C, Mo, Cr, Ni, N, and Fe) were analyzed, as these elements can contribute to intermetallic phases. The results showed that C and Cr content slightly increased with PWHT except for solid solution annealing, Mo showed consistently low content due to dilution effects. Ni maintained higher content, although the heat-treated samples showed slight fluctuations. Nitrogen produced consistent values, as recommended to prevent critical involvement in nitride precipitation.

Development of Mathematical Model for Percentage of Elongation of TIG Welded Duplex Stainless Steel

Quality strongly depends on good mechanical properties of any manufacturing material. Similarly, quality of Tungsten Inert Gas (TIG) welding of Duplex Stainless Steel (DSS) depends on good mechanical properties like percentage of elongation, ultimate tensile strength etc. Better Percentage of Elongation (PE) is produced using proper welding parameters and their values at the time of TIG welding. In this study, TIG welding has been done on ASTM/UNS 2205 duplex stainless steel materials. A new mathematical model is developed using non-linear regression analysis for the prediction of percentage of elongation. The variables used in the prediction models are selected welding parameters like welding current, gas flow rate and speed of welding. A residual plot for PE has been developed to validate the mathematical model. Calculation of percentage deviation for PE has been made. Comparison of measured and predicted PE value has been done by graphical representation. The relationship between percentage of elongation and the welding parameters has been illustrated graphically by surface plots and contour plots as well. Combined effects of any pair of input parameters on PE are represented graphically with the help of three-dimensional surface plots. According to this analysis, the models provide good PE with the data used in this study.

Relationship between ferrite–austenite phase transformation and precipitation behavior of sigma phase in super duplex stainless steel weldment

Relationship between ferrite–austenite phase transformation and precipitation behavior of sigma phase in super duplex stainless steel weldment

Study on fracture properties of duplex stainless steel and its weld based on micromechanical models

The application of stainless steel in structures is increasing recently, but few related seismic studies have been conducted. The purpose of this paper is to study the ductile fracture behavior, especially under Ultra-low-cycle fatigue (ULCF) of duplex stainless steel and its weld based on micromechanical fracture models. A total of 148 specimens covering multiple geometries were manufactured from duplex stainless steel base metal, heat-affected zone, and weld metal. To investigate the mechanical properties of these materials and calibrate the parameters of constitutive models, monotonic and cyclic tests of smooth round bars were conducted. Moreover, monotonic and cyclic tests of notched round bars were performed, followed by the finite element method analyses to calibrate the fracture models including void growth model (VGM), the stress modified critical strain (SMCS) model, and the cyclic void growth model (CVGM). VGM and SMCS were verified to be effective for these materials to predict ductile fracture under monotonic loading, but CVGM cannot calculate the accurate damage under different cyclic test conditions. Then the CVGM was modified by a novel damage variable. Desirable fitting results were obtained by adopting this damage variable. While duplex stainless steel base metal exhibits excellent ductility, that of the welds is much lower with large dispersion. The reason for the low toughness of welds was found to be related to the unbalanced microstructure formed in welding. The study contributes to developing fracture prediction models of duplex stainless steel, and benefits the research on the seismic behavior of duplex stainless steel structures.

Microstructural and Mechanical Properties of Post Weld Heat Treated 2205 Duplex Stainless-Steel and 316l Austenitic Stainless-Steel Dissimilar Weldments

Microstructural and Mechanical Properties of Post Weld Heat Treated 2205 Duplex Stainless-Steel and 316l Austenitic Stainless-Steel Dissimilar Weldments

Inhomogeneity of Microstructure along the Thickness Direction in Stir Zone of Friction Stir Welded Duplex Stainless Steel

Inhomogeneity in microstructures along the thickness direction in the stir zone of a duplex stainless steel (SUS329J4L) welded at rotational speeds of 275 rpm, 400 rpm, and 800 rpm were investigated using the electron back scattered diffraction method. The changes in volume fractions and average grain sizes of ferrite and austenite along the thickness direction may reflect the temperature gradient along the thickness direction. However, near the top surface, significant grain refinement occurred presumably due to the introduction of the additional strain by the shoulder. The KAM values in the stir zone exhibited a higher value in austenite than in ferrite through all the thickness direction, which is inferred to be related to the difference in dynamic recrystallization behavior governed by stacking fault energy; i.e., lower in the austenite phase than in ferrite phase. The layer thickness per unit length of the layered structure became smaller than that of base metal as the rotational speed of FSW was reduced to 275 rpm, which implies that new grains nucleate during FSW. Furthermore, some ferrite grains nucleated at austenite/austenite grain boundaries were confirmed to satisfy the Kurdjumov-Sachs orientation relationship. FSW is assumed to promote the nucleation of new grains with different phases probably owing to the stirring effect of elements by FSW. In a duplex structure formed in the stir zone of FSW, a linear relationship between the ferrite and austenite grain sizes was found to hold irrespective of rotational speeds.