Stainless Steel Weld Research Articles

Investigation of zigzag line defects in friction stir welding of SS304 stainless steel

The zigzag line defect (ZLD) formed in the stir zone (SZ) affects the microstructural and mechanical properties of the materials welded by friction stir welding (FSW). In this research, the cause of ZLD formation in the FSW of SS304 steel was analyzed. The results showed that this defect is formed under incomplete penetration conditions. Under such conditions, oxygen enters the SZ from the incomplete penetration site and linearly creates micro- and nano-voids of metal oxides. The formed oxide voids had high hardness, but due to crack nucleation, they showed low fracture toughness.

Microstructure and Hardness Properties of AISI 321 Stainless Steel Welded Joints with Different Filler Metal

Austenitic stainless steel is susceptible to sensitization when exposed to high temperatures. During welding operations, they tend to form chromium depletion zones and thus become susceptible to intergranular corrosion. The microstructure and hardness properties of AISI 321 austenitic stainless steel welds have been studied in this work. The phenomenon of sensitization of AISI 321 stainless steel during GTAW has also been investigated. This experiment observed three welded samples using different filler metals, ER316, ER308, and ER347. Weld sample analysis was studied using an optical microscope and a microhardness tester. The results demonstrated that the type of filler metal significantly affected changes in the microstructure and hardness of the weld joint.

Laboratory comparison of field portable X-ray fluorescence spectrometer (FP-XRF) and inductively coupled plasma mass spectrometry (ICP-MS) for determination of airborne metals in stainless steel welding fume

Welding fume is a common exposure in occupational settings. Gravimetric analysis for total particulate matter is common; however, the cost of laboratory analyses limits the availability of quantitative exposure assessment for welding fume metal constituents in occupational settings. We investigated whether a field portable X-ray fluorescence spectrometer (FP-XRF) could provide accurate estimates of personal exposures to metals common in welding fume (chromium, copper, manganese, nickel, vanadium, and zinc). The FP-XRF requires less training and is easier to deploy in many settings than traditional wet laboratory analyses. Filters were analyzed both by FP-XRF and inductively coupled plasma mass spectrometry (ICP-MS). We estimated the FP-XRF limit of detection for each metal and developed a correction factor accounting for the non-uniform deposition pattern on filter samples collected with an Institute of Medicine (IOM) inhalable particulate matter sampler. Strong linear correlation was observed for all metals (0.72<r < 0.96). The median percent bias for chromium and nickel was less than 15%. The linear slope between the two methods for some metals (copper, manganese, and zinc) was greater than 1, indicating that the FP-XRF overestimated metal mass (median percent bias for vanadium was the largest at 94%), but the linearity of the response suggests that appropriate correction factors could be developed.

Simulation of wave propagation in austenitic stainless steel welds with solidification structure predicted by Cellular Automaton method

Austenitic stainless steel is widely used in nuclear power plants (NPPs) and a variety of occurrences of stress corrosion cracking (SCC) near its weld have been reported among NPPs. Ultrasonic testing is a critical technique for the detection and depth sizing of SCCs. However, such welds' anisotropic and heterogeneous properties cause difficulties in ultrasonic testing when ultrasonic waves propagate through welds. Deeply understanding the characteristics of ultrasonic waves with wave propagation simulation is effective to improve the accuracy of ultrasonic testing. To this end, it is necessary to take crystal orientation and grain boundary into account simultaneously in the numerical model. In this study, a model was developed so that the Cellular Automaton (CA) method can simulate the solidification structure from multilayer and multipass welding process, then the solidification structure of a 7-layer and 7-pass weld of austenitic stainless steel was predicted based on welding conditions. Finally, the finite element method was used to compute wave propagation in austenitic stainless steel weld with the solidification structure predicted. Numerical results of wave propagation in austenitic stainless steel weld were compared to those obtained by experiment.

Application of the heat treatment in the welding process of ferritic stainless steels – causes and effects

This paper aims to analyse the application, importance and impact of heat treatment operations used in ferritic stainless steel welding processes on the properties of the welds obtained. In addition, the article aimed to formulate the main problems that occur during the welding process of ferritic stainless steels, including, in particular, the phenomenon of ferrite grain growth due to thermal processes.The analysis of the available literature covered issues related to heat treatment processes used in the welding of ferritic stainless steels, taking into account the issue of the growth of the ferrite grain under the influence of heat supplied during welding and the possibility of heat treatment of the obtained welds. The analysis also included determining the possibility of inhibiting the growth of ferrite grains by using elements such as titanium, niobium, and molybdenum, thus improving the strength properties of welds.Organisation of knowledge in the field of the impact on the mechanical properties of ferritic stainless-steel welds and heat treatment processes used before, during, and after welding.Properly selected parameters of the welding process of ferritic stainless steels, especially the amount of heat input, together with appropriate heat treatment parameters, should improve the mechanical properties of ferritic stainless steels.The analysis of the possibility of a wider application of ferritic stainless steels allowed to draw one of the main conclusions stating that the limited possibilities of using ferritic stainless steels in heavy industry are related to their high susceptibility to ferrite grain growth under the influence of high temperature during welding and, consequently, decreases in strength properties of welding joints made of ferritic stainless steels. Additional heat treatment operations are introduced before, during, or after the sapping process to improve their mechanical properties.

Effect of electrode composition over performance of dissimilar stainless-steel welds

In this study, the effect of composition of the electrodes ER347 and ER310 is investigated on the microstructure, mechanical and corrosion properties of dissimilar weld between AISI 430 and AISI 304L; made using gas metal arc welding. The mechanical properties were investigated by uniaxial tensile tests whereas corrosion properties were analyzed via polarization tests in H2SO4 (acidic) and NaOH (alkaline) solutions with varying concentrations − 0.1 M, 0.3 M and 0.5 M. It has been found that electrode composition does not change the hardness of the weldments; however it has affected the hardness of heat affected zones (HAZ). Hardness of HAZ near AISI 304L was higher, when the weldment was made using ER 347 due to presence of finer grains in HAZ. In contrast to this, hardness of HAZ near AISI 430 was higher, when the weldment was made using ER 310 due to carbide formation at grain boundaries. Unlike hardness, strength of welded specimens was approximately 54% and 14% lower than AISI 304L and AISI 430 respectively due to the presence of HAZ zones. Width of HAZ zones has also decided the extent of decrease in elongation values, showing the lowest elongation for the welded specimen made using ER347. The higher carbon content can lead to wider HAZ zone, thus not only results in degradation of mechanical properties but also decreases the passivation ability of the welds. At very low pH level (0.44), passive layer can get ruptured and Ni wt. % plays a detrimental role over corrosion resistance of the welds.

Nucleation of equiaxed δ-ferrite by accelerating TiN formation controlled by oxide during welding of ferritic stainless steel

The accelerating effect of oxides on TiN formation to promote the nucleation of equiaxed ferrite was investigated under simulated gas tungsten arc (GTA) welding conditions. This revealed that the formation of oxides such as Ti2O3, (Ti, Al)2O3, and MgAl2O4 is essential for the solidification of equiaxed δ-ferrite. MgAl2O4 significantly accelerates the formation of TiN and produces a fine-grained equiaxed structure. Minor alloying with Ti, Al, and Mg significantly influenced the composition and crystal structure of the oxides. Ti2O3 and (Ti, Al)2O3 were identified as corundum structures with the same orientation relationship as TiN on the {0001} crystal plane. Ti2O3 and (Ti, Al)2O3 could act as heterogeneous nuclei for TiN because low lattice misfits of 0.6% and 0.6–8.1% could be reached for Ti2O3 and (Ti, Al)2O3 for {0001}oxide//{111}TiN and [10–10]oxide//[110]TiN, respectively. Spinel type MgAl2O4 was found to have a fully paralleled orientation relationship with TiN, resulting in a 4.8% misfit with TiN in each crystal plane. This indicates that all the crystal planes of MgAl2O4 could accelerate the formation of TiN. Baker-Nutting orientation relationship was confirmed for TiN and δ-ferrite. Therefore, the TiN formed by oxide acceleration could nucleate δ-ferrite. The multiple accelerating planes of MgAl2O4 and a high quantity of MgAl2O4-TiN as nucleation sites showed an optimal effect on equiaxed solidification under a high-temperature gradient.

Interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening of δ-ferrite in 308L stainless steel weld metal

In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors, the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously, which can induce microstructural evolution and hardening of the material. Since it is quite difficult to achieve this simultaneous process out of the pile, two kinds of combined experiments, i.e., post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work. The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening of δ-ferrite in 308 L weld metal was investigated by combining atom probe tomography, transmission electron microscopy and nanoindentation tests. The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation, thus enhancing hardening of irradiated δ-ferrite. For the effect of irradiation on the microstructure and hardening of thermally aged δ-ferrite, however, intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition, leading to a limited effect on hardening of thermally aged δ-ferrite. Furthermore, the interaction of thermal aging and irradiation can promote G-phase precipitation. Meanwhile, the interaction can cause δ-ferrite hardening, which is mainly influenced by spinodal decomposition, followed by G-phase and dislocation loops, where spinodal decomposition and G-phase cause hardening by inducing strain fields.

Effect of TIG and activated flux TIG welding processes on weld bead geometry, microstructure, and hardness of SAF 2507 grade super duplex stainless steel joints

Tungsten inert gas (TIG) welding is frequently used to fabricate super duplex stainless steel weldments due to its superior mechanical qualities and attractive appearance in contrast with other arc welding techniques. The broad use of TIG welding remains constrained despite all of its advantages. Thus, the process of activated flux tungsten inert gas (A-TIG) welding is created. In the current study, ATIG welding with different oxide fluxes is used to execute bead-on-plate welding on 6 mm thick super duplex (SS) SAF 2507 grade. The TIG and ATIG processes are used for bead-on-plate welding, and the macrostructure, microstructure, and mechanical features of super DSS weld beads are analysed. When different oxide fluxes are used, the A-TIG technique achieves a greater depth of penetration and a narrower weld bead width than the standard TIG process. SiO2 flux with ATIG welding gives the highest depth of penetration (5.42 mm) among all other fluxes used. Also, A-TIG welding using SiO2 flux has a finer grain structure and a higher hardness value than other fluxes. The primary microstructure in the A-TIG weld zone was austenitic, but delta ferrite was still present.

Evolution mechanism of fracture interface wave and microstructure during resistance butt spot welding

In this work, the interface wave was first shown in resistance butt spot welding of titanium (Ti) alloy and stainless steel (SS) as in explosive welding and magnetic pulse welding. Interface wave exhibited a fracture mode in the joint, so which were called fracture interface waves. The wavelength and the peak of the fracture interface wave weaken from the center of the joint to the outer edge. The formation of the wave is closely related to the interface microstructure. Fracture interface wave would have a direct impact on the joint properties. Analysis of the formation of fracture interface wave is helpful to improve the quality of the joint. Thermo-electric-mechanical-magnetic-flow coupling in resistance butt spot welding makes it difficult to explain the forming mechanism completely by existing theory and experiment methods. The key conditions of fracture interface wave propagation were analyzed by means of thermo-electric-mechanical numerical simulation. The formation process was explained in addition to the microstructure, mechanical properties.

Revealing microstructural evolution and mechanical properties of resistance spot welded NiTi-stainless steel with Ni or Nb interlayer

Dissimilar welding of NiTi and stainless steel (SS) for multifunctional device fabrication is challenging due to the brittle nature of intermetallic compounds (IMCs) that are formed in the weld zone. In this work, Ni and Nb interlayers were applied for the resistance spot welding (RSW) of NiTi and SS to replace the harmful Fe2Ti phase and to restrict the mixing of dissimilar molten metals, respectively. Microstructural evolution and mechanical properties of the joints were investigated. It was shown that a conventional weld nugget was created in the absence of any interlayer in the welded joint suffering from traversed cracks due to the formation of brittle IMCs network in the fusion zone (FZ). By the addition of Ni from the interlayer, Fe2Ti dominated weld nugget was efficaciously replaced by Ni3Ti phase; however, the presence of the large pore and cracks reduced the effective joining area. The use of a Nb interlayer resulted in a fundamentally different joint, in which FZs at NiTi and SS sides separated by the unmolten Nb would suppress the mixing of dissimilar molten metals. Nb-containing eutectic structures with low brittleness formed at the interfaces, contributing to the enhancement of joint strength (increased by 38% on fracture load and 460% on energy absorption). A high-melting-point interlayer showed great potential to realize a reliable and high-performing RSWed NiTi-SS joint.

Effects of Flowrate of Additional Shielding Gas on the Properties of Welded Seam Using Twin-Wire GMAW Welding for Duplex Stainless Steel

Aiming to diminish the defects caused by high-speed pulsed GMAW (Gas Metal Arc Welding), such as lack of penetration, lack of fusion, humping and undercut, this paper proposes an improved twin-wire GMAW welding process by introducing the impact of additional shielding gas on the molten pool, and the effects of different shielding gas flowrates on the mechanical properties and microstructure of the welded seams were investigated. The purpose of introducing additional shielding gas was to use the airflow hood formed by gas injection to isolate air. The impact force generated by the jet might change the original natural solidification mode of the molten pool, which had the effect of improving weld formation and stirring the pool. The airflow hood formed during the process of the additional shielding gas jet impact welding of the molten pool might extend the protection time for the surface of the welding molten pool. The 2205 duplex stainless steel plate was used as the base material for the butt welding test, and the welded seams were subjected to a tensile test, hardness analysis, and metallographic analysis. The results indicated that as the flowrate of additional shielding gas increased in the range of 8 L/min~16 L/min, the width of the welded seam increased and the height of reinforcement decreased gradually. However, a weld seam with a lower middle region and higher sides would appear when the gas flowrate became excessively large. Under the identical welding current and for welding speeds of 160 cm/min, 180 cm/min and 200 cm/min, respectively, the joint formed under the flowrate of 12 L/min had the highest tensile strength (824.3 MPa) among the test specimens under different flowrates of 8 L/min, 12 L/min and 16 L/min. The test results indicated that the jet impact force was relatively moderate when the flowrate of the additional shielding gas was 12 L/min, and thus was optimal for the welded seam.

Microstructural features and mechanical behavior of duplex stainless steel/low carbon steel friction stir dissimilar weld

This paper aims to understand the effect of friction stir butt welding on the microstructure and mechanical performance, measured in terms of hardness characteristics, transverse tensile test, and shear punch, of dissimilar weld of duplex stainless steel (DSS) and low carbon steel (LCS). The dynamic recrystallization, material intermixing, and atomic interdiffusion between DSS and LCS governed the microstructure of the stirred zone. The stirred zone was free from harmful intermetallic phases like the sigma phase. It was identified that three distinct metallurgical regions feature the stirred zone, including (i) dual-phase zone (DPZ) with an unbalanced fine duplex microstructure of austenite and ferrite, (ii) ferrite phase zone (FPZ) with fine-grained ferrite strengthened by an enhanced Ni and Cr content, (iii) martensite zone (MRZ), which was formed due to the formation of thermally unstable austenite at high temperatures due to Cr, Ni, and C interdiffusion between DPZ and FPZ. Furthermore, when LCS was positioned on the advancing side, a higher fraction of martensite was formed in the stirred zone due to the more efficient material mixing. The shear punch test indicated that the shear strength of the stirred zone in the dissimilar welds was ∼130% and ∼16% higher than that in the LCS and DSS base metals, respectively. The contributions of solid solution hardening and grain boundary hardening to the hardness/strength of the stirred zone were elucidated.

Corrosion behaviors of super austenitic stainless steel weldment by GTAW welding for ships desulfurization system

This study aims to clarify how filler-typed metals which were ERNiCrMo-3 and ERNiCrMo-4 affect corrosion resistance characteristics in the weldment of super austenitic stainless steel joints under the simulated desulfurization environment for ships. The desulfurization environment includes high temperature, chlorides, and acidic conditions, which, inevitably, can cause severe corrosion to great extent. For exact clarification, the variations of microstructure and the composition distribution in the weldment before and after welding was examined by using scanning electron microscope and energy dispersive X-ray spectroscopy. Then, the corrosion resistance characteristics were comparatively evaluated through the cyclic potentiodynamic polarization test together with potential measurement under the desulfurization simulated environments. In addition, the correlation between passive film and corrosion resistance characteristics was investigated after identifying the formed features of the passive film through the X-ray photoelectron spectroscopy analysis. Through these studies, it made certain, ERNiCrMo-4 filler metal with high Mo content is advantageous for the formation of MoO3 oxide on the surface, which belongs to form a stable passive film and maintains the corrosion resistance characteristics under the simulated desulfurization environment.

EBSD Analysis of 316L Stainless Steel Weldment on Fusion Reactor Vacuum Vessel

EBSD Analysis of 316L Stainless Steel Weldment on Fusion Reactor Vacuum Vessel

Effect of ferrite morphology on pitting corrosion resistance of austenitic stainless steel weld metals

The effect of the ferrite morphology on the pitting corrosion resistance of austenitic stainless steel weld metals solidified with primary ferrite was investigated. Most of the pitting corrosion occurred at the interface between ferrite and austenite—particularly at the vermicular ferrite/austenite interface; less pitting corrosion occurred at the lacy ferrite/austenite interface. This was because a Kurdjumov–Sachs orientation relationship was established between lacy ferrite and austenite. Consequently, Cr carbide was less likely to precipitate owing to the low interfacial energy, and the lacy ferrite/austenite interface was less likely to be an initiation site of pitting corrosion.

Hybrid manufacturing of steel construction parts via arc welding of LPBF-produced and hot-rolled stainless steels

AbstractThe demand for free-form steel structures having improved performances, reducing labour and resource usage is increasing in the construction sector. Structural nodes are some of the most critical regions for steel structures characterised often by large dimensions. These nodes can exploit the geometrical freedom of metal additive manufacturing (MAM) processes. Laser powder bed fusion (LPBF) is arguably the most developed MAM process, which has limitations regarding the size of the parts to be produced. A way to overcome the size limits of LPBF for producing structural nodes while still exploiting its geometrical capacity is producing hybrid components by welding them to traditionally manufactured beams. Such hybrid joints would constitute a complex system from a mechanical design perspective requiring a systematic analysis in order to be certified for structural use. Accordingly, this work studies the mechanical behaviour of hybrid steel components generated by welding LPBF plates and quarto plates made of AISI 316L stainless steel. The work was guided by a case study based on a large steel node, which helped defining the requirements to fill the gap of the international standards. The mechanical characterisation of LPBF-produced plates and quarto plates, as well as the welded hybrid components revealed a maximum of 10% difference between the properties of the differently manufactured plates. Through the digital image correlation (DIC) analyses, the anisotropic deformation behaviour along the LPBF, weld seam, and quarto plate regions have been identified, and the properties after welding did not show relevant modifications. The tests allowed to define that the failure behaviour is mainly governed by interlayer bounds, and a 0.9 safety reduction parameter for considering the reduction of ductility induced by arc welding to LPBF. Finally, design and production suggestions have been provided for a correct evaluation of gross and effective sections of the designed nodes.

Effect of ultrasonic impact peening on stress corrosion cracking resistance of austenitic stainless-steel welds for nuclear canister applications

In nuclear applications, the utilization of austenitic-based stainless steel (ASS) components is an ideal material choice for storing spent nuclear fuels in dry storage canisters (DSC). However, due to the chloride rich environments in which they operate, failure in the form of stress corrosion cracking (SCC) frequently occurs. The following study assesses the efficacy of ultrasonic impact peening (UIP) on SCC susceptibility of gas tungsten arc welded (GTAW) stainless steel (SS) components, with an aim to control the SCC failure. The UIP induces residual compressive stresses (RCS) and a severely plastically deformed (SPD) layer containing nanograins on the surface. The superior SCC resistance of UIP'ed specimens is due to the synergistic effect of grain refinement and RCS. The underlying mechanisms for these findings were elucidated based on the modification of microstructural features and mechanical properties. These findings demonstrate that UIP is a potential technique for DSC application to mitigate the SCC susceptibility of ASS weld joints.

Effects of ferrite content and concentrations of carbon and silicon on weld solidification cracking susceptibility of stainless steels

In the welding of austenitic stainless steels, the formation of approximately 5% δ-ferrite phase is often used to decrease the susceptibility to solidification cracking. The partition coefficients of impurity elements such as phosphorous and sulfur of the ferrite phase are high, which expand the temperature range of solidification. At the same time, it is well known that the solidification cracking susceptibility increases with increasing δ-ferrite content above 20%. Thus, high δ-ferrite content increases the solidification cracking susceptibility, even though the δ-ferrite phase has high solubility of the impurity elements. The aim of this work was to investigate the effects of the δ-ferrite content and the concentration of carbon and silicon on the solidification crack susceptibility of Fe–18%Cr stainless steel with various nickel concentrations. The ferrite content was controlled by adding various amounts of nickel. The brittle temperature range (BTR) hardly changed with increasing δ-ferrite content, regardless of the type and concentrations of carbon and silicon. Therefore, the effect of the ferrite content on solidification cracking susceptibility must be small. In addition, the BTR increased with the concentrations of carbon and silicon. The specimens containing higher concentrations of carbon exhibited higher BTRs than those containing silicon. It is considered that the solidification segregation corresponding to the partition coefficient of carbon to the δ-ferrite phase induces an increase in cracking susceptibility. In addition, the formation of austenite during solidification reduces cracking susceptibility owing to the higher solubility of carbon.

The influence of shielding gases on keyhole-induced porosity and nitrogen absorption in SS 304 stainless steel fiber laser welds

Regarding porosity formation and gas content, choosing the appropriate shielding gas for laser welding is essential for achieving high-quality joints. Keyhole-induced porosity formation tendency and nitrogen content in SS 304 stainless steel welds were investigated based on the nitrogen content in shielding gases during fiber laser welding. Beads-on-plate autogenous welds were made at 5 kW continuous wave (CW) fiber laser in N2 and Ar mixtures. Optical metallography, micro-focused X-ray, X-ray radiography, and high-speed images of the molten pool were used to investigate the porosity formation. In addition, a gas analyzer was used to study the weld metal nitrogen content. The results show that nitrogen significantly impacts the reduction of porosity in the melting zone and increases the dissolved nitrogen in the solidified weld metal, as using pure nitrogen leads to an increase in dissolved nitrogen by 36% higher than the nitrogen content in the base metal. In contrast, it has almost no significant effect on the keyhole mode.