Super Duplex Stainless Steel Welds Research Articles

Physical simulation of low temperature phase separation during multipass welding of super duplex stainless steel

This study aimed to investigate the degree of low-temperature phase separations and 475 °C -embrittlement in physically simulated multipass super duplex stainless steel (SDSS) welds. A single bead weld was produced using gas metal arc welding and multiple thermal cycles with different peak temperatures were applied using a Gleeble physical simulator with fixed and moving jaws to simulate the influence of constrained designs, to mimic the welding of thick SDSS components. The samples were studied using atom probe tomography and the results were correlated with toughness and ferrite microhardness. The results showed that the microhardness of the ferrite in the constrained simulated multipass reheated weld increased from 304 HV to 374 HV after 5 min aging at 475 °C. The amplitude of the Cr concentration of the same sample, showing the level of Fe-Cr phase separation, increased from 1.025 to 1.045 after 5 min aging at 475 °C. Despite the clear development of phase separation in the ferrite, the toughness did not drop. It can be concluded that reheated SDSS welds are not susceptible to 475 °C -embrittlement during short fabrication times of up to 5 min for the austenite level of 50%.

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 post-weld heat treatment on microstructure and corrosion properties of multi-layer super duplex stainless steel welds

Abstract To investigate the influence of post-weld heat treatment on the microstructure and corrosion properties of super duplex stainless steel welded joints, multi-layer multi-pass welding of 2507 super duplex stainless steel by tungsten argon arc welding was performed using an ER2594 welding wire. The microstructures of the welded joints before and after post-weld heat treatment at 1150 °C, 1170 °C and 1190 °C were observed, and the mechanical and corrosion properties were tested. The post-weld heat treatment changed the austenite content and morphology of the welded joint and improved the corrosion resistance of different parts of the weld metal. The choice of various solution heat treatment temperatures affected the change in austenite content in the weld zone and the degree of diffusion and homogenization of the alloy elements. After post-weld heat treatment at 1170 °C, the two-phase ratios in each area of the weld were the most suitable and uniform, and the overall mechanical and corrosion properties of the joint were more uniform.

Fe and Cr phase separation in super and hyper duplex stainless steel plates and welds after very short aging times

Fe and Cr phase separation in ferrite, causing 475 °C-embrittlement, was studied after very short aging times in super duplex stainless steel (SDSS) and hyper duplex stainless steel (HDSS) plates and welds. Atom probe tomography showed that hot-rolled SDSS, experiencing significant metal working, had faster kinetics of phase separations compared to the SDSS and HDSS welds after 5 min aging at 475 °C. The surface of the 33-mm SDSS plate had faster Fe and Cr phase separation and larger toughness drop. A higher density of dislocations next to the austenite phase boundary in ferrite, detected by electron channeling contrast, can promote the phase separation at the surface of the plate with lower austenite spacing. The toughness dropped in HDSS welds after aging, but SDSS welds maintained their toughness. An inverse simulation method considering an initial sinusoidal nanometric Cr and Fe fluctuation showed that Ni increases the interdiffusion of Cr in the system, resulting a higher degree of phase separation in SDSS welds than the HDSS weld. Within the composition range of the studied SDSS and HDSS materials, the processing influences the Fe and Cr phase separation more than the variation in composition during short aging or typical fabrication times.

Experimental investigation on dissimilar weld between super duplex stainless steel 2507 and API X70 pipeline steel

This work investigates the microstructure and mechanical properties of 2507 super duplex stainless steel and API X70 high strength low alloy steel weld joint. This joint finds application in offshore hydrocarbon drilling riser and oil–gas pipelines. Coated shielded metal arc welding electrodes have been designed and extruded on 309L filler and their performance compared with a commercial austenitic electrode E309L. Filler 309L solidifies in ferrite-austenite (F-A) mode with a resultant microstructure comprising skeletal ferrites with austenite distributed in the interdendritic region. Results of tensile and impact tests indicate that weld fabricated with laboratory-developed electrodes has higher ductility and impact energy than the commercial electrode. The tensile strength and weld hardness of commercial electrodes are superior. The laboratory-made electrode’s microhardness is lower than the commercial electrodes, making the former less prone to failure. An alternative welding electrode coating composition has been suggested through this work and found to be performing satisfactorily and comparable to the commercially available electrodes.

Modelling of Sigma Phase Precipitation in Super Duplex Stainless Steel Weld Metal

Modelling of Sigma Phase Precipitation in Super Duplex Stainless Steel Weld Metal

Bead by bead study of a multipass shielded metal arc-welded super-duplex stainless steel

The present study aims at investigating bead geometry and the evolution of microstructure with thermal cycles in multipass shielded metal arc welding of a V-groove 13-mm type-2507 super-duplex stainless steel (SDSS) plate. The weld consisted of 4 beads produced with arc energies of 0.81–1.06 kJ/mm. The upper beads showed lower base metal (BM) dilution than the first bead. Thermal cycles were recorded with thermocouples, indicating that the cooling rate decreased in the as-deposited weld zone when adding a new bead. Ferrite fraction in the as-welded condition was lower for the upper beads. The austenite grain morphology in reheated passes varied depending on the local peak temperatures and the number of reheating passes. Sigma phase precipitated in a location reheated by the third and fourth passes that was subjected to a critical peak temperature for sigma precipitation. Ferrite content, measured using image analysis and Fisher FERITSCOPE technique, showed that the ferrite fraction moved toward 50/50% in the weld metal with an increasing number of reheating cycles. Finally, a schematic map showing an overview of the microstructure in the multipass SDSS weld was introduced.

The Effect of Welding Heat Input on the Structure–Property Relationship of a New Grade Super Duplex Stainless Steel

Herein, microstructural and mechanical characteristics and corrosion resistance of the UNS S32906 super duplex stainless steel (SDSS) welds are investigated. The gas tungsten arc welding technique is used with direct current electrode negative polarity. Welding is conducted in 1.19, 1.46, and 1.87 kJ mm−1  to evaluate the effect of heat input. The results show that the amount of ferrite phase decreases from 59.4% to 49.4% as the heat input increases. Moreover, only ferrite and austenite phases are observed in the microstructure without any other detrimental phases. Hardness test results show that the hardness of the weld metal rises up in comparison with that of the base metal. Furthermore, the more the heat input, the less the weldment hardness. The impact test shows that the toughness of the samples increases with heat input. Polarization tests show that base metal has a better corrosion behavior irrespective of the heat input of the weldments. With an increase in the heat input, the corrosion behavior is improved. It can be said that whether in terms of microstructure or mechanical properties or corrosion resistance, the specimens that are welded with the highest heat input show the best properties.

Effect of Welding Processes on the Microstructure and Mechanical Properties of Duplex Stainless Steel Weld Joints

Abstract The objective of the present investigation involves studying the microstructure and mechanical properties of duplex stainless steel (DSS) alloy 2205 and super DSS (SDSS) alloy 2507 weld joints fabricated by tungsten inert gas (TIG) welding and its variant, activated TIG (A-TIG) welding. Square butt weld joints were fabricated from 10-mm-thick plates of DSS and SDSS using single pass A-TIG and multi-pass TIG welding processes. The filler wire ER2209 was used for multi-pass TIG welding of DSS 2205, and ER2594 filler wire was used for multi-pass TIG welding of SDSS 2507. The microstructure in the A-TIG weld metals was found to be coarser, which was caused by high peak temperatures during A-TIG welding. The microstructures exhibited different forms of austenite, including grain boundary allotriomorphs, Widmanstätten side plates, and intragranular precipitates in the weld metal. In the A-TIG weld metals, the microstructure exhibited a balanced ferrite-to-austenite ratio. The hardness values of multi-pass TIG weld joints were higher compared to A-TIG weld joints. The tensile and yield strengths of multi-pass TIG weld joints were higher compared to A-TIG weld joints, which was mainly due to higher delta ferrite content and finer microstructure. The toughness values obtained by Charpy impact testing were higher in A-TIG weld joints compared with multi-pass TIG weld joints at room temperature, which was mainly due to the balanced ferrite-to-austenite ratio in the weld microstructure. However, at subzero temperatures, the A-TIG weld joints exhibit lower impact toughness because of their coarser weld metal structure.

Effects of types of GTAW including superior GTAW-PC with superimposed HF current on mechanical and metallurgical properties of super duplex stainless steel weld joints

The manufacturing of a product with super duplex stainless steel generally involve joining using fusion welding techniques. The industries are continuously striving to produce better quality product through use of advanced techniques of welding. Investigation has been done to study the effects of types of GTAW including superior advanced GTAW-PC with superimposed HF current on mechanical and metallurgical properties of super duplex stainless steel weld joints. The weld joints of super-duplex stainless steel (UNS S32750) are prepared using continuous current gas tungsten arc welding (CCGTAW), CCGTAW with superimposed high frequency current, pulse current gas tungsten arc welding (GTAW-PC) and superior advanced GTAW-PC with superimposed high frequency current utilizing super duplex grade electrode over alloyed with 2%–3% nickel (ER2594). The association of high frequency either to CCGTAW or GTAW-PC is a novel technique being utilized in present research. The super imposed high frequency current restricts the arc with almost equal root and projected diameter. The weld joints are characterized with respect to quality of mechanical and metallurgical properties. Both these properties are found superior in case GTAW-PC with superimposed high frequency current as compared to all other types of CCGTAW. The association of high frequency with GTAW and GTAW-PC leads to reduction of weak section of weld joint of width of HAZ along with significantly improvement of associated properties. The superiority of properties due to involvement of high frequency current is explained and justified with the associated science involved.

Ferrite content measurement in super duplex stainless steel welds

Approaches to determining ferrite fraction (%) and ferrite number (FN) were examined for super duplex stainless steel (SDSS) welds. A reference sample was produced by bead-on-plate gas–tungsten arc welding of a type-2507 SDSS plate. By comparing different etchants and measurement practices, it was realized that etching with modified Beraha followed by computerized image analysis (IA) was the most accurate and quickest technique to measure ferrite fraction, which determined the same ferrite fraction (68.0 ± 2.6%) as that measured by electron diffraction backscattered analysis (67.6 ± 2.3%). A Round Robin test was performed on a reference sample at University West, Swerea KIMAB, Outokumpu Stainless, and Sandvik Materials Technology to investigate the repeatability of the technique. The ferrite fraction measurements performed at different laboratories showed very small variations, which were in the range of those seen when changing microscope in the same laboratory. After verification of the technique, the relationship between ferrite fraction and ferrite number (measured with FERITSCOPE®) was determined using 14 single (root) pass welds, including butt, corner, and T-, V-, and double V-joint geometries. The best-fit equation found in this study was ferrite number (FN) = 1.1 × ferrite fraction (%). To conclude, the ferrite fraction technique suggested in the present paper was accurate and repeatable, which made it possible to determine a ferrite fraction–ferrite number formula for SDSS single-pass welds.

Pitting corrosion resistance properties of super duplex stainless steel weld metals and influencing factors

Thanks to the excellent combination of strength, low temperature toughness, and good corrosion properties, particularly resistance to pitting corrosion attack, super duplex stainless steels have found wide applications in the offshore–onshore oil and gas industries and petrochemical industries. In the meantime, due to the special thermal process of welding, super duplex weld metals in the as-welded condition, when comparing with the base steels, always show considerably inferior corrosion properties. However, in order to maximize the performance capability of processing facilities built with super duplex steels, oil companies have been continuously trying to push the required pitting temperature for weld metals to more and more challenging levels. This has made the design of relevant welding consumables even more difficult. This paper explores the possible solution through optimizing the alloying design so that the weld metals can consistently meet the increased requirements of various specifications. This includes a balanced alloying system that will provide good pitting corrosion resistance (typically expressed as high critical pitting temperatures) while is still capable to maintain adequate mechanical properties, particularly low temperature impact toughness. Major aspects that may have considerable influence on these properties are investigated and discussed.

Process Window for Nd:YAG Laser Welding of Super Duplex Stainless Steel

Super duplex stainless steel (SDSS), an advanced duplex stainless steel with higher alloying concentration, is employed widely in acidic atmospheres. In this study, we make an attempt to develop a process window for the pulsed mode Nd:YAG laser welding of SDSS, as reference maps, to identify the range of process parameters viz., laser power, welding speed, defocusing distance, and pulse frequency for obtaining a defect free full penetration welds. The eminence of the welds, based on the macrostructure, microstructure, and tensile strength, is reported. We obtain a complete penetration weld devoid of undercut, crating at the top and minimum heat affected zone (HAZ) with a overlapping factor of 80–90% and heat input at 100–200 J/mm. The experimental settings prevailing inside the preferred region of the process window exhibit a higher tensile strength as well.

Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal

Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.

Microstructure evolution and mechanical properties of briefly heat-treated SAF 2507 super duplex stainless steel welds

The effects of brief post-weld heat treatment at different temperatures on the microstructure evolution and mechanical properties of SAF 2507 super duplex stainless steel welds were investigated. The results showed that the weld zones were high in hardness and low in toughness due to their far deviation from the equilibrium state. After brief post-weld heat treatment, the austenite volume fraction in the weld zones was elevated significantly. The highest impact toughness of SAF 2507 super duplex stainless steel welds was achieved when the specimens were briefly heat-treated at 1080 °C.

Correction to: Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals

Unfortunately due to typesetting mistakes, Tables 4–6 have been displayed erroneously in the article.

Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals

Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.

Effect of Dynamic Reheating Induced by Weaving on the Microstructure of GTAW Weld Metal of 25% Cr Super Duplex Stainless Steel Weld Metal

The importance of the additional growth and/or transformation of the austenite phase that occurs in weld metals of super duplex stainless steel upon reheating is known. However, the effects have not been fully investigated, especially with respect to reheating induced by weaving during single-pass welding. In this work, bead-on-pipe gas tungsten arc welding (GTAW) was conducted on super duplex stainless steel to understand the effect of weaving on the microstructure of weld metal. Microstructural analysis, electron backscatter diffraction (EBSD), and focused ion beam transmission electron microscopy (FIB-TEM) were carried out to investigate the relationship between weaving and microstructural change. The weaving of GTAW produced a dynamic reheated area just before the weld bead during welding. It was revealed that extensive reheated weld existed even after one welding pass, and that the content of the austenite phase in the reheated area was higher than that in the non-reheated area, indicating the existence of a large quantity of intragranular austenite phase. In addition, the Cr2N content in the reheated area was lower than that in the non-reheated area. This reduction of Cr2N was closely related to the reheating resulting from weaving. TEM analysis revealed that Cr2N in the non-reheated area was dispersed following heating and transformed to secondary austenite.

Dissimilar welding between SAF 2507 stainless steel and Incoloy 825 Ni-based alloy: The role of microstructure on corrosion behavior of the weld metals

The effect of the filler metal type, welding process and the welding pass number on the corrosion behavior of Incoloy 825 Ni-based alloy to SAF 2507 super duplex stainless steel weld zones were addressed utilizing scanning electron microscopy, cyclic potentiodynamic polarization and electrochemical impedance spectroscopy. The results detailed the formation of some secondary phases in the weld metals. The welds employing Ni-based filler wires revealed the highest general corrosion resistance, while super duplex stainless steel weld metals displayed the best pitting corrosion behavior. Pulsed current gas tungsten arc welding and super duplex stainless steel filler metal were recommended to obtain the optimum surface corrosion resistance.

Erratum to: Studies on the pore formation in super duplex stainless steel welds

Erratum to: Studies on the pore formation in super duplex stainless steel welds