Emel Taban

Toughness and microstructural analysis of superduplex stainless steel joined by plasma arc welding

EN 1.4410 (UNS S32750) superduplex stainless steel (SDSS) with a thickness of 6.5 mm has been welded by plasma arc welding (PAW) process with different heat inputs. To determine the mechanical properties, impact toughness testing at subzero temperatures starting from −20 °C down to −60 °C was carried out while fractographs were examined by scanning electron microscopy (SEM). Microstructural examination included macro- and microphotographs of the cross sections, ferrite content measurements and hardness survey of the weld zones. Interpreting all data obtained, results were compared depending on the heat inputs of the joints while the relation between heat input and properties was explained. Promising low temperature toughness, results were obtained while it was concluded that the variation of the heat input influenced mainly the ferrite content and hardness of the weld zones. Results showed that PAW, which is considered immature process in welding of SDSS, can be employed for 1.4410 superduplex grade with controlled heat input so the properties.

Plasma Arc Welding of Modified 12% Cr Stainless Steel

This article deals with the plasma arc welding properties of 6 mm thick modified X2CrNi12 stainless steel conforming to the grades EN 1.4003 and UNS S 41003 with carbon content below 0.015% to improve the weldability. The butt welds produced without filler metal and with AISI 316L austenitic type of consumable were subjected to tensile and bend tests as well as Charpy impact toughness testing. Examinations including fractography, metallography, chemical analysis of the weld metal, ferrite content, grain size, and hardness analyses were carried out. Sound plasma arc welded joints of modified 12 Cr revealed the microstructure-property relationship, such as high ferrite content (≥ 70%) resulting in ferrite grain coarsening mainly at the high temperature heat-affected zone (HTHAZ) has no adverse effect on tensile or bend properties, but has negative effects on low temperature toughness. Enhanced toughness was provided in case of the low temperature heat affected zone (LTHAZ) with finer grained microstructure. The increase at the weld metal hardness in Weld 2 is related to the austenitic type of filler used.

Joining of Duplex Stainless Steel by Plasma Arc, TIG, and Plasma Arc+TIG Welding Processes

1.4462 duplex stainless steel (DSS) with a thickness of 6.8 mm was joined by plasma arc, Tungsten Inert Gas (TIG), and plasma arc + TIG welding processes. Impact toughness testing was carried out and fractographs were examined by Scanning Electron Microscopy (SEM). Microstructural analysis, ferrite content, and hardness survey of the weld zones were done while the variation in chemical composition was investigated with energy dispersive X-ray spectroscopy (EDX). Results were compared due to the heat inputs of the joints and the relation between microstructure, and toughness was explained. Promising results showed that plasma arc welding (PAW) and/or plasma + TIG welding, which are considered immature processes for DSS, can successfully be employed for increased productivity.

Trend and innovations in laser beam welding of wrought aluminum alloys

The drive toward fulfilling weight reduction obligation, superior weld quality requirement, and industrial manufacturing rationale has sprung up considerable interest in applying laser welding technology on aluminum alloys. Nevertheless, porosity, solidification cracking, and surface reflectivity have been the major banes of laser welding of aluminum alloys. However, literature has shown that positive efforts have been accomplished in reducing these fundamental concerns by adopting careful selection of welding procedure, modification of pure laser welding techniques, and the use of appropriate filler metal. Albeit, there is still upbeat progression on the application and improvement of laser welding of aluminum alloys. At present, laser welding technology has the potential of fulfilling industrial requirements in joining lightweight aluminum alloys because of its capacity for automation and intrinsic flexibility, precision and repeatability, low general heat input, high welding speed, and low weld distortion. As a result, this report examines the available and current status of laser technologies in welding aluminum alloys. It further categorizes the laser technologies of aluminum alloys into four assemblages, namely, pure or single-beam laser welding, laser-arc hybrid welding, tailored heat source laser welding, and other innovative laser welding technologies, respectively. Mechanical, corrosion, and microstructural behaviors of laser welded aluminum alloys are also studied. Conversely, some of the research areas that need further investigations are proposed. Corrosion behavioral properties, influence of micropores on fatigue and quasi-static tensile strength, and toughness characterization of laser welded aluminum alloys are insufficient in literature.

Welding behaviour of Duplex and Superduplex Stainless Steels using Laser and Plasma ARC Welding processes

Abstract1.4462 (UNS S31803) duplex stainless steel (DSS) and EN 1.4410 (UNS S32750) superduplex stainless steel (SDSS) have been welded by fibre laser welding and plasma arc welding (PAW) processes with-Cout filler metal. Impact toughness testing at various temperatures from 20 °C down to −60 °C was carried out. Microstructural examination included macro and microphotographs of the cross-sections, ferrite content measurements and hardness survey of the weld zones. Weld metal impact toughness results on the order of 100 J were obtained while values between 30 J and 60 J were measured respectively for plasma arc and laser welds of the duplex and superduplex grades even at −60 °C test temperature. Ferrite content of the welds varied generally in an acceptable range which affected the microstructure and the toughness properties. Better toughness results of plasma arc welds of both duplex and superduplex material compared to the laser welds are attributed to the balanced microstructure of the weld metal having ferrite- austenite ratio close to 50:50 % obtained by controlled heat input.

Submerged arc welding of thick ferritic martensitic 12Cr stainless steel with a variety of consumables

Abstract Modified X2CrNi12 stainless steel, conforming to EN 1·4003 and UNS S41003 grades, has been designed with less carbon (<0·015%) and impurities to improve the weldability and mechanical properties. The present paper deals with submerged arc welding (SAW) of 30 mm thick plates of this steel with austenitic and duplex stainless steel consumables. Several samples extracted from the welded joints were subjected to mechanical testing by means of tensile, bend, Charpy impact and crack tip opening displacement (CTOD) fracture toughness tests. Microstructural examination including grain size analysis, hardness and ferrite measurements was carried out. Salt spray and blister tests as corrosion testing were applied. Considering all data obtained, it can be recommended to use austenitic filler metals as an economic alternative for SAW of this steel in the areas where impact is anticipated and adequate atmospheric corrosion resistance is needed since the weld made with austenitic wires exhibited very encouraging low temperature impact toughness properties related with finer grained microstructure and adequate strength and corrosion properties.

Friction stir spot welding of aluminum alloys: A recent review

Abstract The application prospect of aluminum alloys in aerospace, high speed train manufacturing, shipbuilding and automotive industries is increasing and friction stir spot welding (FSSW) is adjudged to be a non-fusion and suitable joining technology for it. Conversely, friction stir spot welding has challenging attributes such as objectionable FSSW tool pin performance and short life span in mass production stage, creation of crack initiation sites like hook defect, material flow voids and probe hole, as well as restrictions on thickness of materials that can be welded. These challenges have caused a lot of tool profile innovative modifications and technological advancement in friction stir spot welding of aluminum alloys. Nevertheless, some of these vital issues are still unresolved and this notion makes FSSW an evolving solid state joining technology. A succinct view of literature on FSSW of aluminum alloys reveals that most researchers have limited their research to the characterization of microstructure and mechanical properties of aluminum welds; thus leaving a blatant research gap in post-weld tool examinations. Tool wear mechanism and void formation mechanism in FSSW processes as well as characterization of friction stir spot welded aluminum alloys are research areas that need critical examinations. Nevertheless, this publication combines the innovative and recently developed friction stir spot welding technologies of aluminum alloys and assesses their generalized process parameters; it also covers microstructural and mechanical properties of aluminum alloys available in literature. This report classifies FSSW of aluminum alloys based on three criteria namely, probe amendment, shoulder adjustment and complexity of tool movement.

Possibilities and Limitations to Improve the Weldability of Low Carbon 12Cr Ferritic Stainless Steel for Expanded Industrial Applications

Ferritic stainless steel X2CrNi12 (EN 10088) is generally appreciated for its relatively low cost and good resistance to wet abrasion and mild environments, but unfortunately its weldability is restricted. Typical applications up to now include railway wagons for coal and iron ore, mining and mineral process and transport equipment, bus frames and chassis, silos, etc. This steel grade nowadays can be fabricated cost effectively with low carbon and impurity levels appreciably improving both the weldability and mechanical properties. In this case, long-term maintenance costs of assemblies produced using this ‘clean’ X2CrNi12 stainless steel will be low, with a suitable coating providing sufficient protection for several decades. For other applications, the use of weldable X2CrNi12 is also more economical than higher alloyed stainless steels. Moreover, joining the steel by laser welding without filler metal should be considered. The present paper provides an overview of results of a research project initiated by the Belgian Welding Institute investigating the possibilities of this modified low carbon ferritic stainless steel. The main objective of this work was to demonstrate that it offers great application ranges for constructing purposes which should expand its application field substantially. In the near future broadening this steel family with even higher mechanical properties allowing further reduction of plate or wall thickness and of production costs will be explored.

Effect of the Purging Gas on Properties of Ti Stabilized AISI 321 Stainless Steel TIG Welds

Abstract Gas purging is necessary to provide a high quality of stainless steel pipe welding in order to prevent oxidation of the weld zone inside the pipe. AISI 321 stabilized austenitic stainless steel pipes commonly preferred in refinery applications have been welded by the TIG welding process both with and without the use of purging gas. As purging gases, Ar, N2, Ar +N2 and N2 + 10% H2 were used, respectively. The aim of this investigation is to detect the effect of purging gas on the weld joint properties such as microstructure, corrosion, strength and impact toughness. Macro sections and microstructures of the welds were investigated. Chemical composition analysis to obtain the nitrogen, oxygen and hydrogen content of the weld root was done by Leco analysis. Ferrite content of the beads including root and cap passes were measured by a ferritscope. Vickers hardness (HV10) values were obtained. Intergranular and pitting corrosion tests were applied to determine the corrosion resistance of all welds. Type of the purging gas affected pitting corrosion properties as well as the ferrite content and nitrogen, oxygen and hydrogen contents at the roots of the welds. Any hot cracking problems are not predicted as the weld still solidifies with ferrite in the primary phase as confirmed by microstructural and ferrite content analysis. Mechanical testing showed no significant change according to the purge gas. AISI 321 steel and 347 consumable compositions would permit use of nitrogen rich gases for root shielding without a risk of hot cracking.

12.2 – A New Potential for Welded Structures in Modified X2CrNi12: Characterization of Dissimilar Arc Weld with S355 Steel

In this study, modified X2CrNi12 ferritic stainless steel conforming in composition to grades UNS S41003 (ASTM A240) and Wr. Nr. 1.4003 (EN 10088-2 and EN 10028-7) has been welded to non-alloy S355 steel by means of flux cored arc welding (FCAW) process. A dissimilar butt welded joint was subjected to a series of tests in order to investigate all aspects of the weld properties. Mechanical testing was carried out by means of Charpy impact, tensile and bend tests. Microstructural examinations including hardness surveys, ferrite content measurements and grain size analyses of various weld regions were realised. Salt spray and blister tests were also applied as exposure testing. Rather promising results have been obtained yielding a correlation between microstructure and impact toughness.