Stainless Steel Joints Research Articles

Achieving superior property by forming fine-sized mult-principal element layer at the weld interface of stainless steel and medium entropy alloy

The present study revealed that a strong CoCrNi medium entropy alloy (MEA)/stainless steel (SS) joint could be obtained by friction welding technique with the formation of a microscale interfacial layer composed of varying degrees of the multi-principal element. A significant refinement in grain size to (∼2.8 µm) compared to the base metals (16.6 µm for MEA and 12.2 µm for SS) was observed arising from the co-occurrence of continuous and discontinuous dynamic recrystallisation where grains nucleated at triple grain boundaries, twin boundaries as well as low angle grain boundaries. A relatively strong brass texture {112} 〈110〉 appeared in the layer after recrystallisation, which was attributed to the grain growth behaviour under large deformation. The formation process of the interfacial layer from mesoscale to nanoscale was then postulated. Nanoindentation test indicated that the grains in the layer showed hardness between two base metals, but the interfacial layer demonstrated much higher yield strength (632 ± 14 MPa) and tensile strength (916 ± 4 MPa) than base metals, being higher than the relevant values reported in the literature. It was further clarified that the grain boundary strengthening mechanism rather than dislocation strengthening or solid-solution strengthening was mainly responsible for the strength enhancement.

Interfacial Microstructure and Mechanical Properties of 1Cr18Ni9Ti/1Cr21Ni5Ti Stainless Steel Joints Brazed with Mn-Based Brazing Filler.

The problem of stainless steel brazing is still the focus of scientific research. In this work, the Mn-based brazing filler was used to braze 1Cr18Ni9Ti and 1Cr21Ni5Ti stainless steel. The typical microstructure of the 1Cr18Ni9Ti/1Cr21Ni5Ti joint was analyzed in detail, and the interface structure of the joint was determined to be 1Cr18Ni9Ti/Mn(s, s)/1Cr21Ni5Ti. The brazing temperature and holding time were shown to have a great influence on the microstructure of the brazed joint. The tensile strength of brazed joints first increased and then decreased with the rising of the brazing temperature and the holding time. The maximum tensile strength was 566 MPa when the joints were brazed at 1125 °C for 15 min. The diffusion of Mn and Cr was an important factor affecting the quality of the joints. The diffusion distances of Mn and Cr at different brazing temperatures and holding times were measured, and the diffusion activation energy and diffusion coefficient were achieved by the Arrhenius equation.

Investigations on the effect of standing ultrasonic waves on the microstructure and hardness of laser beam welded butt joints of stainless steel and nickel base alloy

Joining dissimilar metals with superior quality is important to provide tailored, lightweight, and cost-efficient components. Expensive and durable materials are exceptionally used where the cheaper material would not withstand the requirements. With laser beam welding, dissimilar metals can already be joined with high precision, low heat input, and a customizable mixing degree. Introducing ultrasonic excitation into the weld pool is a promising approach for further improvements like customizing the solidification morphology and avoiding weld defects. The experiments are carried out with round bars of 30 mm diameter made of 1.4301 steel alloy and 2.4856 nickel base alloy. Ultrasonic-assisted laser beam butt welding is conducted on rotating specimens with a laser beam power of 7.75 kW and a welding speed of 0.95 m/min. The specimens are evaluated by metallographic cross sections, hardness measurements, and energy-dispersive x-ray spectroscopy (EDX). The ultrasound is used to excite an eigenmode of the sample and the weld position is varied at stress- and displacement-nodes. Two different mechanisms of acoustic grain refinement are revealed. Heterogeneous nucleation is fostered in weld seams that are positioned in stress-nodes, and the fragmentation of dendrites is fostered in displacement-nodes. The welds' chemical compositions correspond to the change of solidification morphology.

Deformation and fracture behaviour, and thermal stability of ODS-Cu/ODS-Cu and SUS/ODS-Cu joints fabricated by advanced brazing technique

A joint of oxide dispersion strengthened copper alloy (ODS-Cu; GlidCop®), i.e., GlidCop®/GlidCop® joint and a joint of stainless steel (SUS) and GlidCop®, i.e., SUS/GlidCop® joint were prepared by using the advanced brazing technique (ABT). Deformation and fracture behavior, and thermal stability of these joints were investigated by means of three-point bending test, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Firstly, in the case of the GlidCop®/GlidCop® joint, plastic deformation occurred predominantly in the diffusion layer with lower hardness. The fracture proceeded approximately at the center of the diffusion layer. In the case of the SUS/GlidCop® joint, on the other hand, plastic deformation occurred widely in the bulks, GlidCop® and SUS near the interfaces between the bulk and the bonding layer. The fracture proceeded mainly along the interface between the bonding layer and the bulk GlidCop®, and substantially along the interface between the bonding layer and the bulk SUS. Secondly, influences of 2nd-step heat on the GlidCop®/GlidCop® and SUS/GlidCop® joints were examined from viewpoints of microstructure and mechanical strength. Almost no obvious changes in the width of the diffusion layer (GlidCop®/GlidCop® joint) or the bonding layer (SUS/GlidCop® joint), and in the element distribution in these layers after the 2nd-step heat were recognized. In addition, any obvious changes in the shape of stress-strain curve and yield strength were not recognized for both joints.

Microstructure and Mechanical Properties of Laser-Welded Joint of Tantalum and Stainless Steel

Bimetallic components welded by Ta and stainless steel have great promise for engineering applications, but there is relatively little relevant research. In this study, 0.6 mm-thick Ta and 304L stainless steel plates were laser welded, and the forming characteristics, microstructure, and mechanical properties of the welded joints were analyzed. First-principles calculations were also performed to explore the structural stabilization mechanisms of the two intermetallic compounds, TaFe2 and TaCr2, in terms of mechanical properties as well as electronic structure. The results showed that the weld surface was smooth and free from any defects. Fe-based solid solutions formed grains, while TaFe2, TaCr2, and some Fe-based solid solutions formed intergranular and eutectic structures. In addition, due to the presence of the brittle phases of TaFe2 and TaFe, the microhardness of the weld area can reach 650HV, with an average hardness of 530HV, which is much higher than that of the base material. The tensile shear of the joint at room temperature was 154.77 N/mm, and the fracture occurred in the weld zone on the steel side, showing brittle fracture. TaFe2 is a brittle intermetallic compound, while TaCr2 is ductile. Both TaFe2 and TaCr2 systems have dual properties of metallic and covalent bonding within them, and metallic bonding dominates.

Investigations of Tungsten Inert Gas and Metal Active Gas Joints of SUS301L Stainless Steel: Electron Backscatter Diffraction Characterization and Fatigue Performance

Investigations of Tungsten Inert Gas and Metal Active Gas Joints of SUS301L Stainless Steel: Electron Backscatter Diffraction Characterization and Fatigue Performance

Effect of Laser Shock Peening on High-Cycle Fatigue Performance of 1Cr18Ni9Ti/GH1140 Weld

The welded joints of 1Cr18Ni9Ti austenitic stainless steel and GH1140 nickel-based superalloy dissimilar materials used in certain types of aero-engine combustion liner components are prone to crack initiation during service, seriously affecting the service life of the combustion liner. In this study, laser shock peening (LSP) was applied to the dissimilar metal weld of 1Cr18Ni9Ti and GH1140, which are used in the combustion liner parts of aero engines. The effects of LSP on the residual stress, microhardness, microstructure and high-cycle fatigue performance of the weld were analyzed. The results show that the residual stress in the weld and heat-affected zones was converted from tensile residual stress to high amplitude compressive residual stress via LSP. Furthermore, the surface hardness of every region of the combustion liner weld was increased, especially in the weld zone, where an increase of 41.4% from 162 HV to 229 HV was observed. Simultaneously, with the introduction of grain refinement, gradient plastic deformation in the depth direction and the dislocation structure of the surface material, the high-cycle fatigue limit of the weld specimen was significantly increased and the fatigue limit of the 1Cr18Ni9Ti/GH1140 welded joint was improved by 65.39%, from 289 to 478 MPa.

Studying the strengthening mechanisms and mechanical properties of dissimilar laser-welded butt joints of medium-Mn stainless steel and automotive high-strength carbon steel

In this study, a post-weld heat treatment (PWHT) at a high temperature of 700 °C for 10 min was proposed to significantly improve the mechanical performance of dissimilar laser-welded butt joints between medium-manganese stainless steel (MMn-SS) and high-strength carbon steels (HS-CS) as base metals (BMs). Electron backscatter diffraction and transmission electron microscopy were employed to characterise the microstructures and study the deformation mechanisms in the paired metals of the dissimilar joints during PWHT and tensile straining. Micro-indentation hardness tests were performed to analyse the mechanical responses in the weld zones after PWHT. The results revealed that PWHT at 700 °C significantly affected the microstructure and mechanical strength of the BMs and their weldments. A fully tempered martensitic microstructure with recrystallised grain regions was formed in the fusion zones (FZs) of the weldments, which were processed at low and high specific point energies (SPEs) of 19, 25, and 30 J. BM HS-CS was significantly strengthened owing to the interphase precipitation hardening of vanadium carbide precipitates during the proposed PWHT. The strength-ductility balance of BM MMn-SS was improved by combining the martensitic transformation and mechanical twinning mechanisms. Although, the tensile strength of BM HS-CS increased from 500 to 630 MPa and that of the metal in the FZ decreased from 1100 to 800 MPa owing to PWHT. Hence, HS-CS is a weak metal for dissimilar joints, and joint failure was promoted in it.

Simultaneously enhanced strength-ductility synergy and corrosion resistance in submerged friction stir welded super duplex stainless steel joint via creating ultrafine microstructure

In this paper, submerged friction stir welding (SFSW), capable of significantly weakening the welding thermal cycle compared to conventional FSW, was employed on SAF2507 super duplex stainless steel (SDSS). An ultrafine grained (UFG) dual-phase microstructure, characterized by more uniformly distributed and balanced alpha (α) and gamma (γ) phases with average grain sizes of 0.96 and 0.77 µm, respectively, was achieved in the stir zone (SZ). Such unique microstructure leads to a synergistic enhancement of tensile strength and ductility in the longitudinal SZ at room temperature, which increases from 840 MPa to 18% under AFSW condition to 915 MPa - 22%. As well, this UFG dual-phase microstructure plays a crucial role in determining the resultant higher corrosion resistance. Combining with the reduced width of entire joint, a transverse SFSW joint with a remarkable increased total elongation was successfully achieved. In addition, the relatively lower residual stress across the whole joint actually contributed to the increment of ductility in the SFSW joint, as compared to the traditional FSW joint. The aforementioned results demonstrate an effective strategy in achieving a completely balanced UFG microstructure across the whole SZ during SFSW and a concurrent improvement of strength, elongation and corrosion resistance.

Effect of Solution Heat Treatment by Induction on UNS S31803 Duplex Stainless Steel Joints Welded with the Autogenous TIG Process

In the oil and gas industry, the manufacture of equipment using materials that resist aggressive media is one of the greatest challenges. UNS S31803 duplex stainless steel is widely used for this purpose owing to its good combination of mechanical and corrosion resistance. The objective of this work was to evaluate the effect of induction solution heat treatment using autogenous TIG welding on UNS S31803 DSS sheets. Sheet samples were subjected to two different treatment parameters for a duration of 10 s and at temperatures of 1050 and 1150 °C. The results obtained with the treatments were compared with those of the as-welded condition, which was the reference condition. Quantitative and qualitative analyses of the samples were carried out, in addition to microstructural characterization using confocal microscopy and a corrosion resistance study as per ASTM G48 standard. We observed that the best results were obtained with a treatment of 10 s at 1150 °C, which was able to eliminate chromium nitrides and re-establish the proper balance of the ferrite and austenite phases. In addition, the treatment was able to reduce hardness and provide welds free of cracks and discontinuities, also presenting a low corrosion rate.

Morphology, Microstructure, and Mechanical Properties of S32101 Duplex Stainless-Steel Joints in K-TIG Welding.

In this paper, the S32101 duplex stainless steel welded joints were produced by a K-TIG welding system. The weld geometry parameters under different welding speeds were analyzed by combining the morphological characteristics of the keyhole. The microstructure and impact toughness of the base metal and weld metal zone under different welding speeds were studied. The experiment results show that the welding speed has quite an effect on the geometry profile of the weld. In addition, the characteristic parameters of the keyhole can effectively predict the geometry profile of the weld. The test results prove that the microstructure, Σ3 coincidence site lattice grain boundary, and phase boundary of ferrite and austenite have an effect on the impact property of the weld metal zone. When the proportion of the austenite, Σ3 coincidence site lattice grain boundary and random phase boundary increased, the impact property of the weld metal zone also increased.

Corrosion, Heat Treatment, and Microstructural Studies of GTA Welded 316 Austenitic Stainless-Steel Joint

The formation of a protective chromium carbide passive film makes austenitic stainless steel (ASS) alloys suitable for corrosive and high-temperature environments. This paper examined the transformation of the microstructure, corrosion, and mechanical properties of gas tungsten arc welded 316 austenitic stainless steel. The scientific principles governing metallurgical transformation and corrosion dynamics were discussed. The review shows that passive film on 316L ASS gradually erodes as the concentration of chloride ion rises. Metallurgical properties of FZ are completely changed, and solid-state transformation occurs at HAZ during the GTA welding process. These transformations affect the microstructure, corrosion, and mechanical properties of GTA welded ASS alloys.

Effect of beam oscillation on the mechanical properties of fiber-laser-welded thin-plate X2CrTiNb18 ferritic stainless-steel joints

This study adopted fiber laser welding (FLW) and oscillating fiber laser welding (OFLW) to weld 1.2 mm-thick X2CrTiNb18 ferritic stainless steel (FSS) in the form of square butt joint. The microstructure and mechanical properties of two types of joints were characterized and compared. The results showed that beam oscillation had a marginal effect on the unidirectional tension properties of the joints. However, the plasticity and fracture toughness of the joint were markedly increased. The beam oscillation changed the morphology and microstructure of the weld. It transformed the outer profile of the weld cross-section into an inverted trapezoid, and formed an equiaxed grain zone in the weld. Beam oscillation decreased the angle between the growth direction of columnar crystals around the equiaxed grains and the weld centerline, which improved the deformation coordination of the grains. The plasticity and fracture toughness of X2CrTiNb18-FSS joints were also improved accordingly.

Study on the Effects of Multiple Laser Shock Peening Treatments on the Electrochemical Corrosion Performance of Welded 316L Stainless Steel Joints

To study the influence of laser shock peening on the electrochemical corrosion resistance of welded 316L stainless steel joints, welded 316L stainless steel joints are treated with different laser shock peening treatments (i.e., one, two, and three times). Our analysis employs electron backscattering diffraction (EBSD), scanning electron microscopy (SEM), X-ray diffraction (XRD), an X-ray stress meter, and electrochemical corrosion tests to observe and analyze the microstructure, structural composition, residual stress, and corrosion resistance in different areas of the surface of 316L before and after the laser shock peening. The results show that the residual stress distribution of the welded joints is optimized after laser shock peening, with a maximum residual compressive stress near the matrix of 171 MPa. When the number of laser shock peening treatments is two, the corrosion current reaches a minimum of 9.684×10−7 A/cm2, and optimal pitting resistance is obtained. However, when the number of laser shock peening treatments is further increased to three, the corrosion current increase and the pitting resistance decreases. In summary, the electrochemical corrosion resistance of the welded joints effectively improves after laser shock peening, but its performance begins to decline after three repeated shocks, which is related to the combined effects of stress change and microstructure phase transformation.

Comparative analysis of GTAW+SMAW and GTAW welded joints of duplex stainless steel 2205 pipe

Duplex stainless steel (DSS) has good oxidation resistance, mechanical properties and corrosion resistance because of the austenite and ferrite two-phase coexistence characteristics, so it has been widely used in the petrochemical, ocean engineering and other industries. In this paper, the butt welding of DSS 2205 pipes were conducted by the combination welding of gas tungsten arc welding and shielded metal arc welding (GTAW + SMAW), and full automatic GTAW respectively. The microstructure, mechanical and corrosion resistance properties of two welded joints were observed and measured. The results show that the ferrite content in the weld and the heat-affected zone (HAZ) of the GTAW + SMAW joint is higher than that of GTAW joint. The weld Charpy energy of GTAW joint is much higher than that of GTAW + SMAW joint, while the Charpy energy of both the fusion line and the HAZ of GTAW joint is slightly higher than that of GTAW + SMAW joint. The strain concentration occurs at the grain boundaries greater than 45°, and the smaller the grain size is, the more dispersed the strain is. The effect of the temperature on the pitting corrosion resistance is obvious. The pitting corrosion resistance of GTAW + SMAW joint is significantly lower than that of GTAW joint, and the pitting corrosion resistance of the root weld is poor, and the SMAW weld is worse than the GTAW weld (except for the root weld). The ferrite phase proportion is related to the pitting corrosion resistance. In a word, the performance of GTAW joint is better than that of GTAW + SMAW joint.

Mechanical behavior of austenitic stainless-steel welds with variable content of [formula omitted]-ferrite in the heat-affected zone

δ-ferrite solidified in the fusion zone (FZ) mitigates the microfissuring susceptibility in multi-pass welded joints performed on austenitic stainless steel (ASS). The herein investigation studied welded joints between two 304L grade ASS with different chemical compositions, which varied δ-ferrite content in the heat-affected zone (HAZ). The pulsed-current gas tungsten arc welding (GTAW-P) process was used along with filler metals ER 308L and ER309L. Additionally, an autogenous joint was made with stainless steel (SS) of high δ-ferrite content (10%). A thermo-mechanical finite element (FE) model was applied to estimate the thermal history, residual stress (RS) and distortion distributions on SS joints. Then, numerical results were correlated with the fracture analysis. The tensile test corroborated the increment in ductility due to δ-ferrite content increasing in the HAZ. The enhancement of mechanical strength observed in the autogenous welded joint was associated with the pinning effect produced by δ-ferrite stringers formed in the HAZ, which inhibited grain growth. Despite the high joint efficiency of SS 304L weldments, the FZ was fractured due to the microfissuring and precipitated particles. The FZ rupture starts in the FZ-HAZ interface of the first weld bead related to the ductility loss with the heat input. Microfissures found in the FZ of all weldments were related to the tensile stress concentration caused by the uneven distortion distribution and the ductility increment (up to 39%) provided by the high δ-ferrite content. Some chromium carbides in the FZ acted as stress raisers.

Influence of ultrasonic impact treatment on microstructure and mechanical properties of nickel-based alloy overlayer on austenitic stainless steel pipe butt girth joint

Ultrasonic impact treatment (UIT) is carried out on the Ni-based alloy stainless steel pipe gas tungsten arc welding (GTAW) girth weld, the differences of microstructure, microhardness and shear strength distribution of the joint before and after ultrasonic shock are studied by microhardness test and shear punch test. The results show that after UIT, the plastic deformation layer is formed on the outside surface of the Ni-based alloy overlayer, single-phase austenite and γ type precipitates are formed in the overlayer, and a large number of columnar crystals are formed on the bottom side of the overlayer. The average microhardness of the overlayer increased from 221 H V to 254 H V by 14.9%, the shear strength increased from 696 MPa to 882 MPa with an increase of 26.7% and the transverse average residual stress decreased from 102.71 MPa (tensile stress) to −18.33 MPa (compressive stress), the longitudinal average residual stress decreased from 114.87 MPa (tensile stress) to −84.64 MPa (compressive stress). The fracture surface has been appeared obvious shear lip marks and a few dimples. The element migrates at the fusion boundary between the Ni-based alloy overlayer and the austenitic stainless steel joint, which is leaded to form a local martensite zone and appear hot cracks. The welded joint is cooled by FA solidification mode, which is forming a large number of late and skeleton ferrite phase with an average microhardness of 190 H V and no obvious change in shear strength. The base metal is all austenitic phase with an average microhardness of 206 H V and shear strength of 696 MPa.

Influence of parameters on the microstructure of a duplex stainless steel joint welded by a GMAW welding process

Duplex stainless steels (DSSs) are widely used in industry for their desirable properties. Any fusion welding technique modifies the microstructure and, consequently, the properties of the material. This paper presents a parametric study of the variables that determine the energy contribution (current, voltage and welding speed) and the structural modifications produced during gas metal arc welding. The analysis comprises metallographic study, phase balance, dimensioning of the weld beads and tensile and hardness tests. The influence of the variables studied on the thermal cycles obtained (temperatures reached and cooling rate) was determined by using a finite element model. The results showed that, in addition to the indicated parameters, the parameter power transfer per volume (W/m3) and the geometry in the bead must be controlled due to their influence on the heat flow distribution and phase balance.

Effect of the microstructure on the corrosion behavior of dissimilar friction stir-welded 304 austenitic stainless steel and Q235 low-carbon steel joints

To investigate the effect of the microstructure on the corrosion behavior of the dissimilar friction stir welded (FSW) joint between 304 stainless steel (SS304) and Q235 low-carbon steel, the microstructure of the joint in this work was characterized by optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction. The corrosion behavior in different zones of the joint was evaluated by the electrochemical tests, and the corresponding corrosion morphologies were illustrated via SEM and laser confocal scanning microscopy. According to the results, plenty of low-angle grain boundaries (LAGBs) and a low proportion of twin boundaries (TBs) deteriorated the corrosion resistance on the SS304 side of the joint. The corrosion products of the SS304 side mainly included γ-Fe2O3, FeCrO4, and Cr2O3, while those of the Q235 steel side were α-Fe2O3 and α-FeOOH. The corrosion mechanism in the stir zone (SZ) was galvanic corrosion between proeutectoid ferrite and pearlite on the Q235 steel side, during which the austenite remained uncorroded, whereas the proeutectoid ferrite, pearlite, and bainite were severely corroded. The above results indicated that the uniform distribution of mixed structures and a small area proportion of austenite (cathode) would improve the corrosion resistance in the SZ.

Experimental study of the effect of oxygen in argon as a shielding gas on corrosion behaviour of dissimilar weld joints of austenitic and ferritic stainless steels

In this study, Austenitic AISI 304L stainless steel was welded with Ferritic AISI430 stainless steel by MIG–welding using welding electrode ER347 and pure Ar and Ar+2%O2 as the shielding gases. The welded samples were polished and dipped into different concentration of HCL solutions of 0.1M, 0.2M, 0.3M and 0.5M concentrations. Weight change of the samples per week in different concentration of HCL solution was noted for 4 weeks and with the help of weight loss, corrosion rate was calculated. The percentage weight loss was observed to be more when welding was done using pure-Ar as a shielding gas compared to Ar+2%O2. Welded samples were also characterized by means of microscopic and electrochemical investigation.