Effect of weld metal chemistry and heat input on the structure and properties of duplex stainless steel welds

Study on microstructure and mechanical properties of 304 stainless steel joints by TIG, laser and laser-TIG hybrid welding

Abstract: This paper investigated the microstructure and mechanical properties of 304 stainless steel joints by tungsten inert gas (TIG) welding, laser welding and laser-TIG hybrid welding. The X-ray diffraction was used to analyze the phase composition, while the microscopy was conducted to study the microstructure characters of joints. Finally, tensile tests were performed and the fracture surfaces were analyzed. The results showed that the joint by laser welding had highest tensile strength and smallest dendrite size in all joints, while the joint by TIG welding had lowest tensile strength, biggest dendrite size. Furthermore, transition zone and heat affected zone can be observed in the joint of TIG welding. The fractograph observation showed that the TIG welding joint existed as cup–cone shaped fracture, while the laser welding and hybrid welding joints existed as pure-shear fracture. The laser welding and hybrid welding are suitable for welding 304 stainless steel owing to their high welding speed and excellent mechanical properties.

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Abstract: Additive manufacturing technologies based on melting and solidification have considerable similarities with fusion-based welding technologies, either by electric arc or high-power beams. However, several concepts are being introduced in additive manufacturing which have been extensively used in multipass arc welding with filler material. Therefore, clarification of fundamental definitions is important to establish a common background between welding and additive manufacturing research communities. This paper aims to review these concepts, highlighting the distinctive characteristics of fusion welding that can be embraced by additive manufacturing, namely the nature of rapid thermal cycles associated to small size and localized heat sources, the non-equilibrium nature of rapid solidification and its effects on: internal defects formation, phase transformations, residual stresses and distortions. Concerning process optimization, distinct criteria are proposed based on geometric, energetic and thermal considerations, allowing to determine an upper bound limit for the optimum hatch distance during additive manufacturing. Finally, a unified equation to compute the energy density is proposed. This equation enables to compare works performed with distinct equipment and experimental conditions, covering the major process parameters: power, travel speed, heat source dimension, hatch distance, deposited layer thickness and material grain size.

Effect of heat input on the microstructure and mechanical properties of gas tungsten arc welded AISI 304 stainless steel joints

Abstract: Influence of heat input on the microstructure and mechanical properties of gas tungsten arc welded 304 stainless steel (SS) joints was studied. Three heat input combinations designated as low heat (2.563 kJ/mm), medium heat (2.784 kJ/mm) and high heat (3.017 kJ/mm) were selected from the operating window of the gas tungsten arc welding process (GTAW) and weld joints made using these combinations were subjected to microstructural evaluations and tensile testing so as to analyze the effect of thermal arc energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that the joints made using low heat input exhibited higher ultimate tensile strength (UTS) than those welded with medium and high heat input. Significant grain coarsening was observed in the heat affected zone (HAZ) of all the joints and it was found that the extent of grain coarsening in the heat affected zone increased with increase in the heat input. For the joints investigated in this study it was also found that average dendrite length and inter-dendritic spacing in the weld zone increases with increase in the heat input which is the main reason for the observable changes in the tensile properties of the weld joints welded with different arc energy inputs.

Investigation on AISI 304 austenitic stainless steel to AISI 4140 low alloy steel dissimilar joints by gas tungsten arc, electron beam and friction welding

Abstract: This paper presents the investigations carried out to study the microstructure and mechanical properties of AISI 304 stainless steel and AISI 4140 low alloy steel joints by Gas Tungsten Arc Welding (GTAW), Electron Beam Welding (EBW) and Friction Welding (FRW). For each of the weldments, detailed analysis was conducted on the phase composition, microstructure characteristics and mechanical properties. The results of the analysis shows that the joint made by EBW has the highest tensile strength (681 MPa) than the joint made by GTAW (635 Mpa) and FRW (494 Mpa). From the fractographs, it could be observed that the ductility of the EBW and GTA weldment were higher with an elongation of 32% and 25% respectively when compared with friction weldment (19%). Moreover, the impact strength of weldment made by GTAW is higher compared to EBW and FRW.

Effect of welding processes and conditions on the microstructure, mechanical properties and corrosion resistance of duplex stainless steel weldments—A review

Abstract: Dual phase duplex stainless steel comprised with ferrite and austenite shows its strength and corrosion resistance in many aggressive environments based on outstanding performance over the last 20 years establishment is a great attention for researchers, manufacturers and end users. The current worldwide rapid growth, demand, and consumption of duplex- stainless steels, particularly in petrochemical, marine, power plant and other engineering applications, where the multiphase steels are being utilized that require welding for fabrication of components. On the other hand, largest production and applications sectors are captured by austenitic stainless steels globally, but the Ni price volatility breaching the backbone of producers and end users. In such conditions for the cost flexibility, joining of dissimilar metals also reflects the overall industrial need. Joining of duplex alloys is a challenging, due to number of embrittling precipitates and metallurgical changes. On the other hand inappropriate welding conditions, imbalance phase ratio of austenite/ferrite leads to solidification cracking, corrosion susceptibility, and lower ductility. As the demand for higher productivity is increasing worldwide in many domains like oil pipeline, shipbuilding sectors etc., where the thick sections are used, which endorses the requirement of higher heat input, optimization of interpass temperature, cooling rate, proper selection of consumables, defect free joints for fast and rapid productivity. However, many advanced techniques like plasma, laser, PCGTAW, A-TIG and hybrid welding processes are developing to fulfill the requirements for higher productivity without distortion. But high ferritization is another issue with those processes. Moreover, suitability and standardization of duplex alloys for high current and large heat input are still in doubt. Even, no comprehensive accounts of the dissimilar welding operation on the effect of processes and welding conditions are found in the literature. This review paper systematically highlights the effect of welding processes and conditions on microstructure, mechanical properties and corrosion resistance of duplex stainless steels and its various combinations on the basis of structure–property co-relationship.

Duplex stainless steels : microstructure, properties and applications

Abstract: Developments, grades and specifications Alloy design Microstructure Forming and machining Physical and mechanical properties Corrosion Stress corrosion cracking Welding metallurgy Welding processes Weld properties Non-destructive testing of welds Applications Service experience.