Stainless Steel Joints Research Articles

Microstructure evolution and mechanical properties of copper/304 stainless-steel joints by low-temperature soldering

Pure copper (Cu) soldering joints with 304 stainless steel (SS) at different soldering temperatures (240–[Formula: see text]C) were prepared by using Sn–3.5 Ag (wt.%) as a soldering filler-metal material. The mechanical properties and microstructure evolution were investigated. Sound Cu/304 SS joints were obtained by soldering at 240–[Formula: see text]C for 90 s and the highest average joint shear strength was [Formula: see text] MPa when brazed at [Formula: see text]C. The Cu6Sn5 and Ag3Sn phases were typical intermetallic compounds (IMCs) in the joints at a soldering temperature of [Formula: see text]C. Cu3Sn IMCs were formed at the Cu/Cu6Sn5 interface as the soldering temperature increased to [Formula: see text]C and above. Shear fracture analysis by scanning electron microscopy (SEM) with energy dispersive spectroscopy showed that the joints fractured mostly inside the Cu6Sn5 layers.

Corrosion behavior of stainless steel-tungsten carbide joints brazed with AgCuX (X = In, Ti) alloys

We studied the long-term corrosion behavior of carbide/316L stainless steel joints brazed with AgCuX alloys (X = Ti, In). The results show that the Cu-based solid solution (Cu (s,s)) in the brazing alloy is the weak link of corrosion germination. Ti increases the Fermi level and decreases the *H adsorption energy (ΔG*H) of Cu(s,s), thus leading to a higher thermodynamic tendency of hydrogen evolution. In contrast, In decreases the Fermi level and the d band center of Cu (s, s) leading to a positive ΔG*H, which improves the corrosion resistance. The results agree with the mechanical performance tests.

Study of the structure and mechanical properties of electron-beam-welded dissimilar joints of copper and stainless steel with and without offset

We present the results of an investigation of the structure and mechanical properties of dissimilar joints of copper and 304L stainless steel formed by electron-beam welding. The samples studied were welded without a beam offset and with a beam offset towards either welded materials to a distance of 0.3 mm. The phase composition was determined via X-ray analysis. The structure was investigated using scanning electron microscopy. The mechanical properties, including hardness and tensile strength, were measured. The phase composition of the considered specimens consisted of a double-phase structure of face-centered cubic (fcc) and body-centered cubic (bcc) phases. The sample welded without offset exhibited the highest yield strength and tensile strength values. The microhardness of all samples increased in the fusion zone on the steel side and decreased in the fusion zone on the copper side compared to the initial hardness of the two materials.

High strength-ductility synergy in a laser welded dissimilar joint of CrCoNi medium-entropy alloy and stainless steel

CrCoNi medium-entropy alloy (MEA) and its welded joints has great potential applications in engineering structures since they present superior ultimate tensile strength (UTS) and ductility. However, the mechanical performance of the welded joints of CrCoNi and traditional metal alloys remains mysterious. Here, we applied laser welding to join CrCoNi and stainless steel (SS) 301L to achieve a dissimilar MEA-SS301L joint and investigated its microstructure evolution and mechanical properties. The fusion zone becomes a face-centered cubic single-phase non-equiatomic FeCrCoNi high-entropy alloy (HEA). Its UTS and ductility is 482 MPa and 46% at 300K, respectively; and is respectively enhanced to 791 MPa and 59% at 77K. Our dissimilar joint displays a strength-ductility synergy that exceeds that of all other dissimilar HEA joints and most similar HEA joints. Electron backscattered diffraction, transmission electron microscopy and molecular dynamics simulation uncover that extensive dislocation activities, stacking fault networks, deformation twins, and interactivity between dislocations and twin boundaries are the origin of this high strength-ductility synergy in our joint.

Microstructure and Pitting Corrosion Resistance of AISI 430 Ferritic Stainless Steel Joints Fabricated by Ultrasonic Vibration Assisted Cold Metal Transfer Technique

The influences of ultrasonic vibration during cold metal transfer welding process on the microstructure, element distribution and pitting resistance of AISI 430 ferritic stainless steel joints with ER 308L as filler metal were investigated. The combined effects of mechanical vibration, acoustic streaming and cavitation of ultrasonic vibration significantly refined the primary ferrite grain in the weld metal and then impacted the subsequent solid-phase transition process, leading to the ~45% reduction of ferrite content in the weld metal. Moreover, these effects also resulted in the homogenization of alloying elements in the weld metal. The pitting corrosion resistance of the welded joints with ultrasonic vibration was increased compared with that of without ultrasonic vibration, but lower than the base metal. The pitting resistance of the weld metal with ultrasonic vibration was higher than that of the weld metal without ultrasonic vibration and base metal, while that of the one without ultrasonic vibration was lower than the base metal.

Mechanical Properties and Corrosion Resistance of Cold Metal Transfer Small-Bore Thin-Walled Tube Butt Welded Joints of UNS S32205 Duplex Stainless Steel

Mechanical Properties and Corrosion Resistance of Cold Metal Transfer Small-Bore Thin-Walled Tube Butt Welded Joints of UNS S32205 Duplex Stainless Steel

Effect of Multi-Objective Optimization for Double Pulse Resistance Spot Welded Joints of Ferritic Stainless Steel

In this research work, an attempt is made to optimize the parameters of double pulse resistance spot welding process of AISI 409M ferritic stainless steel sheets by multi objective Taguchi approach. The tensile shear strength of the weld joint and indentation at the weld surface are taken as the response quality characteristics, which are required to be maximized and minimized respectively. Three control parameters, such as second pulse current, second pulse weld time and cooling time were taken for the analysis. Furthermore, a linear response surface model has been developed to correlate tensile shear strength and indentation values with process parameters. The results showed that, the second pulse current value was found to be the most influential parameter affecting tensile shear strength and indentation in double pulse resistance spot welding. Results of the optimization process were also validated by confirmation test.

Microstructures and Mechanical Properties of 304 Stainless Steel Joints by Focused Ultrasound-Assisted TIG Welding

Microstructures and Mechanical Properties of 304 Stainless Steel Joints by Focused Ultrasound-Assisted TIG Welding

Fatigue performance of butt-welded austenitic stainless-steel joints evaluated by peak-stress method

In this study, the fatigue performance of butt-welded austenitic stainless-steel joints is investigated by fatigue test, nominal-stress method and peak-stress method. Welding profiles and misalignment were analyzed, residual stresses were measured, and fatigue tests were conducted. The experimental fatigue data are regressed to the stress range versus life-to-failure (S–N) curve of the nominal stress method, and the factor affected dispersion is analyzed by using the peak-stress method. The following conclusion can be drawn: (1) The fatigue strength is 155 MPa in nominal stress method, which is higher than that of structural steel (80 MPa) in the international fatigue design standards. (2) The influence of the welding misalignment and distortion can be accurately estimated by the combing the reference S-N curve and stress magnification factor formulae from the international fatigue design standards.

Interface Structure in Friction Welded Joints between Stainless Steel 304 and Mild Carbon Steel

Friction welding is a solid-state welding process using heat generated through friction. Dissimilar materials can be joined properly with friction welding. This study is a continuation of the previous study and aimed to determine the interface structure occurred on stainless steel and carbon steel joints. Stainless steel 304 and mild carbon steel are joined with this method at 2000 rpm rotation for 15 seconds and forging time of 5 seconds with a pressure of 5 MPa. The results of a micro-observation using a scanning electron microscope show good bonding in the interface area. The carbon steel is more welded to the stainless steel in the periphery than in the center. The spectrum results of Energy Dispersive X-Ray of the interface show Fe, C and Cr elements content. This is what causes the strong welding bond.

Microstructure and mechanical performance of dissimilar metal joints of aluminium alloy and stainless steel by cutting-assisted welding-brazing

The 5052 aluminium alloy and 304 stainless steel were successfully joined by cutting-assisted welding-brazing (CAWB) method without using flux. Dual-scale interfacial structures were achieved by designing the geometry of cutting tool. Results indicated that the macroscale self-locking interface was produced when the taper step-shape cutting tool was adopted. Especially when the cutting tool step was increased to 6 steps, the microscale interface took on a micrometre-sized self-locking morphology and a layer of wavy intermetallic compound (IMC) with an average thickness of 3.3 μm was formed at the interface. The τ4 IMC particles and the FeAl6 phases on a small scale were dispersed homogeneously in the welded seam. The maximum tensile strength of the joints reached 152.3 MPa, 75% that of the 5052 aluminium base metal. The robust Al/steel dissimilar joints were attributed to the particle-reinforced weld metal and the macro- and microscale dual self-locking structure at the interface.

Microstructure and mechanical properties of dissimilar NiTi and 304 stainless steel joints produced by ultrasonic welding

Superelastic NiTi alloy and 304 stainless steel (304 SS) were joined with a Cu interlayer by ultrasonic spot welding (USW) using different welding energy inputs. The surface morphology, interfacial microstructure, mechanical properties, and fracture mechanisms of the dissimilar NiTi/304 SS USWed joints were studied. The results showed that the surface oxidation intensified with increasing ultrasonic welding energy due to mutual rubbing between tools and sheets. The weld interface microstructure exhibited voids or unbonded zones at low energy inputs, while an intimate contact was established at the joining interface when applying a higher energy input of 750 J. With increasing energy input to 750 J, the weld interface shows two interfaces due to the behavior of plastic flow of Cu interlayer. The lap-shear load of the joints first increased, achieving a maximum value of ∼690 N at an energy input of 750 J, and then decreased with further increase in welding energy. Interfacial failure was observed at NiTi/Cu interface at all energy inputs, and no intermetallic compounds were found on the fracture surfaces of both the NiTi/Cu and Cu/304 SS interfaces.

A new numerical model to predict welding-induced sensitization in SUS304 austenitic stainless steel joint

In this paper, a SUS304/P92 dissimilar metal butt-welded joint was fabricated, and the welding-induced sensitization of SUS304 austenitic stainless steel in this joint was investigated via the numerical simulation and experiment. In the proposed new numerical model, the time–temperature-precipitation diagram and the time–temperature-sensitization diagram were used to simulate the region and the degree of sensitization, respectively. The predicted degree of sensitization (DOS) in the weld decay zone matched the electrochemical measurements well. Based on the simulation results, the evolution of DOS at the austenitic stainless steel side during the multi-pass welding process was examined in detail. The obtained results can help evaluate the material susceptibility to stress corrosion cracking in austenitic stainless steel joints.

Effect of Wire Composition on Microstructure and Penetration Crack of Laser-Cmt Hybrid Welded Cu and Stainless Steel Joints

Effect of Wire Composition on Microstructure and Penetration Crack of Laser-Cmt Hybrid Welded Cu and Stainless Steel Joints

Effect of Thermo-Mechanical Distribution on the Evolution of Imcs Layer and Mechanical Properties of 2219 Aluminum Alloy/304 Stainless Steel Joints by Inertia Friction Welding

Effect of Thermo-Mechanical Distribution on the Evolution of Imcs Layer and Mechanical Properties of 2219 Aluminum Alloy/304 Stainless Steel Joints by Inertia Friction Welding

Studying The Strengthening Mechanisms and Mechanical Properties of Dissimilar Laser-Welded Butt Joints of Medium-Mn Stainless Steel and Automotive High-Strength Carbon Steel

Studying The Strengthening Mechanisms and Mechanical Properties of Dissimilar Laser-Welded Butt Joints of Medium-Mn Stainless Steel and Automotive High-Strength Carbon Steel

Experimental investigation on aluminium alloy AA6061 and AA8011 using friction stir welding

Friction Stir Welding (FSW) is a solid-state joining process that involves joining of metals without fusion or filler materials. The process is particularly applicable for aluminum alloys but can be extended to other products also like steels. The project was mainly founded by National Technological Agency of Finland. The friction stir welded joints of austenitic and ferrite stainless steels were implemented at different rotational speeds 500 ∼ 1100 rpm. The results showed that increasing rotating speed enhanced heat input and material movement in the welded zone, and the nugget zone had a blocky, laminated, and vortex structure of austenite and ferrite. In this investigation, different combinations of tool rotation speeds and tool transverse speeds are used to connect different types of stainless steel. Following an overview of the macroscopic characteristics, the micro structure development and associated hardness tensile and impact results and distributions are discussed.

Influence of Welding Energy on Intergranular and Pitting Corrosion Susceptibility of UNS S32205 Duplex Stainless-steel Joints

This study analysed the integrity of welded joints of a UNS S32205 duplex stainless steel, using different welding energies: 0.5 kJ.mm-1, 1.0 kJ.mm-1, and 3.5 kJ.mm-1. Microstructural characterisation, tensile testing, intergranular attack susceptibility testing (ASTM A262 practice A) and pitting/crevice corrosion resistance tests (critical pitting temperature test, ASTM G48 practice C) were performed in these welded joints. The results showed that the tensile properties of the welded joints did not vary significantly with the welding energy. The microstructure's ferrite content in the molten zone (MZ) was proportional to the welding energy: the ferrite concentration in the 0.5 kJ.mm-1 weldings was approximately 75%. When the welding energy increased to 3.5 kJ.mm-1, the amount of ferrite dropped to 54%. The 3.5 kJ.mm-1 welded joint featured a comparatively higher proportion of coarser austenite grains. The HAZ of the 3.5 kJ.mm-1 welded joint was comparatively more susceptible to the intergranular attack along the α/γ interfaces, while in the base metal and the other two welded joints, the intergranular attack along the α/γ interfaces was not prominent. Additionally, the pitting corrosion took place preferentially in the ferrite phase of the HAZ for all welding conditions.

Heat input effects on mechanical constraints and microstructural constituents of MAG and laser 316L austenitic stainless-steel welded joints

<abstract> <p>This study aims to investigate the optimum heat input required to overcome the negative consequence of the thermal properties of austenitic stainless steel to produce welded joints free of distortion. An experimental investigation using robotic-MAG and fiber-laser welding processes has been used in other to investigate angular, longitudinal distortion (bending), and microstructural constituents in the heat-affected zone (HAZ) of different welded joints. Ten 316L steel, butt-joints were made by different travel 25 speeds at the range of (7–11 mm/s). A highly sensitive 2D-laser device has been used to measure the distortion then, a microstructural investigation was done using an optical micrograph, Scanning Electron Microscopy (SEM) coupled with the Electron Dispersive Spectrometer (EDS). The laser-fiber welding process results indicated optimum parameters to prevent distortion when applying welding speed of 2.2 m/min, the power source of 2.5 kW, and the focal position of 3 mm. In MAG welding, test results revealed an increase of longitudinal distortion (bending) from 1.2 mm to 3.6 mm when raising the heat input from 0.3 to 0.472 kJ/mm. When increases welding speed (11 mm/s), angular distortion was approximately 2.1° on the left side and 1.7° on the right side. Microstructural investigations revealed the proportionality between heat input and carbides formations on the grain boundaries of HAZ. They were also the formation of etching pores and some ferrite content (10%) on the weld center.</p> </abstract>

Inspecting Power Network Analysis on Eddy Current Test of SMAW Joints

Eddy Current Test (ECT) is proven to be the most reliable non-destructive assessment for electrically conductive materials. This assessment works based on the emerging Eddy Current when an alternating current is induced into conductive materials. The ECT system consists of three elements, i.e. current injection, the pick-up, and the conductive target. This system is then treated as an altered wireless power network between aforementioned elements. The use of alternating current (A/C) in this network provides a wide variety of power spectra for various analysis techniques. This paper introduces novel technique of subsurface crack assessment on SMAW welded joint of stainless steel 316 L by applying network altered response to ECT system. The analysis of the network is done by constructing mathematical models of the frequency domain in each component in the network to achieve the gain of the system. The mathematical model was constructed either for the defectless and the defected speciments, and then both result was compared to investigate and extract the information about the crack. The experiment also performed to confirm the simulation from the modeling. The experiment succeeded to differentiate the size of the subsurface crack on certain working frequencies.