Friction Welding Of Stainless Steel Research Articles

Optimizing weld strength and microstructure in CP-titanium and 304 stainless steel friction welds with chromium interlayer

This study investigates the effect of a Cr-interlayer on the hardness and friction-welded joint strength between CP-titanium and 304 stainless steel. Rotary friction welding, with its adjustable parameters such as upset pressure, is the preferred method for this dissimilar joint. Due to the difference between these two base metals, a metallic interlayer like chromium, is crucial for controlling the formation of intermetallic compounds (IMCs). Welding was conducted at three different upset pressures, both with and without the Cr-interlayer. Tensile and microhardness tests were performed, complemented by phase analysis and microstructural characterization using XRD and SEM. Our findings reveal that employing a chromium layer and higher upset pressures enhances strength while reducing the presence of brittle IMCs in the welds. At the CP-titanium side, dynamic recrystallization occurs due to increased heat generation at the interface and strain occurred by materials flow, facilitating IMC formation, especially evident at 250 MPa upset pressure. Interestingly, relatively higher strength at 150 MPa is attributed to the absence of IMCs. Conversely, higher strength results at 350 MPa due to from the flow of softened material, effectively purging IMCs from the weld zone. Notably, both β-titanium and chromium-based IMCs form in the presence of the chromium interlayer, resulting in decreased joint hardness and increased overall ductility. In conclusion, our study's findings contribute to bridging the gap between theoretical strength and practical application, significantly advancing joint performance.

Study of the Effect of Friction Time and Preheating on the Joint Mechanical Properties of Friction Welded SS 316-Pure Zn

Friction Welding (FRW) is a solid-state welding method. This technology also permits the connecting of dissimilar and similar materials while consuming less electricity than conventional electric welding. Friction welding is frequently used to join a variety of components because it generates high-quality joints and is capable of joining a wide range of materials and their complexity. This research examined the friction welding of stainless steel and pure zinc. The investigation concentrated on the welding parameters, specifically the effect of friction time and provision of preheating on parameters with high joint strength, as well as the mechanical properties, microstructure, and characterization of the joint material. The results of the experimental research indicated that the welding settings had a significant impact on the friction welding process. The tensile strength increased as a result of the reduced friction duration during the welding process, as demonstrated by the experimental findings. The longer the friction period, the more an oxide layer will form on the surface of the metal, preventing the diffusion process and impacting the production of the intermetallic phase for the joint’s strength.

Improving Mechanical Properties of Dissimilar Material Friction Welds

Friction welding of stainless steel to titanium with aluminum insert metal was investigated to improve the mechanical properties of the joints. Two different methods were used to insert the aluminum as a barrier between to substrates. The process parameters were found to be different for these two methods to obtain the sound welds. The friction welds between stainless steel and titanium with aluminum insert prevented the formation of brittle intermetallic compounds in the weld interface. A new intermetallic compounds such as AlTi and Al3Ti were formed between titanium and aluminum insert metal interface which are more ductile than the FeTi and CrTi intermetallic compounds. The joints characterized that the aluminum insert metal improved the metallurgical reaction at the weld interfaces thus indicates the results of decrease in microhardness of the intermetallic compounds which have major influence on the strength of the joints. The tensile strength of the aluminum insert welds was higher than the direct joints between the stainless steel and titanium. Higher tensile properties were attained at higher upset pressure condition due to the effect of higher force upon the welded materials and the remnant narrower thickness of insert metal.

Influence of silver interlayer in dissimilar 6061-T6 aluminum MMC and AISI 304 stainless steel friction welds

Aluminum MMCs are finding greater utility in automobile and aerospace industries. To boost up the application of aluminum MMCs in real-time applications, it is essential to weld these specimens to other engineering materials. There are several research works reporting the lacuna in arc welding of dissimilar aluminum/steel joints, viz., preferential melting of the aluminum alloy and formation of brittle iron-aluminum intermetallics. However, friction welding process illustrates positive sign for its employment to join dissimilar aluminum/steel. Conversely, intermetallic formation is still of concern. Consequently, to overcome this prevailing problem, interlayers are introduced in this study. At first, dissimilar Aluminum MMCs and AISI 304 stainless steel friction welds are experimented with and without the presence of silver interlayer for conceptual understanding and to clarify and confirm the phenomenal terminologies based on literature. Based on this experience, a few trials of dissimilar Aluminum MMCs and AISI 304 stainless steel friction welds with silver interlayer are experimented on trial and error basis to find optimized friction welding parameter values and these values are used in ANOVA software to plot and analyze the parameters inter dependencies. Then, upper and lower limits of friction welding parameters are fixed to achieve good-quality welds. These limits are fed into ANOVA to obtain full factorial trials based on design of experiment (DoE). The weldments are also evaluated using destructive and non-destructive tests. The metallurgical characterizations of weldments are analyzed. Further, a preliminary attempt is made to develop a finite element model to investigate temperature governing phenomenon such as deformation, stress and strain.

Improving Strength of Stainless Steel/Aluminum Alloy Friction Welds by Modifying Faying Surface Design

Conventionally in friction welding, the rubbing or faying ends of the base material rods are square turned. For the case of dissimilar friction welding, this design is not optimum because of differential flow behavior of the materials. When, only one of the materials deforms preferentially, the actions of cleaning and expulsion of oxides and impurities from the interface would not be as effective. This will adversely affect the joint properties. In this study, alternate designs of faying surfaces such as providing taper (external and internal) and smoother surfaces are compared with the square cut design. The aim was to study how the faying surface conditions of the stronger material affect the flow behavior of the weaker material. By affecting better flow behavior, the intention was to expel intermetallics and other impurities from the interface, and thereby improve joint properties. Friction welding of stainless steel with aluminum alloy (aluminum-magnesium-silicon) was studied. The joints were evaluated for strength and it is found that the external tapered system has the best strength. Different characterization techniques such as optical microscopy, scanning electron microscopy, x-ray diffraction were carried out to observe different phases, microstructure zones, etc., at the interface. Finally, possible reasons for the better strength of tapered system were discussed.

Optimization of friction welding parameters using evolutionary computational techniques

The purpose of this study is to propose a method to decide near optimal settings of the welding process parameters in friction welding of stainless steel (AISI 304) by using non conventional techniques and artificial neural network (ANN). The methods suggested in this study were used to determine the welding process parameters by which the desired tensile strength and minimized metal loss were obtained in friction welding. This study describes how to obtain near optimal welding conditions over a wide search space by conducting relatively a smaller number of experiments. The optimized values obtained through these evolutionary computational techniques were compared with experimental results. The strength and microstructural aspects of the processed joints were also analyzed to validate the optimization.

Microstructure and pitting corrosion of similar and dissimilar stainless steel welds

Pitting Corrosion behaviour of similar and dissimilar metal welds of three classes of stainless steels, namely, austenitic stainless steel (AISI 304), ferritic stainless steel (AISI 430) and duplex stainless steel (AISI 2205), has been studied. Three regions of the weldment, i.e. fusion zone, heat affected zone and unaffected parent metal, were subjected to corrosion studies. Electron beam and friction welds have been compared. Optical, scanning electron microscopy and electron probe analysis were carried out to determine the mechanism of corrosion behaviour. Dissimilar metal electron beam welds of austenitic–ferritic (A–F), ferritic–duplex (F–D) and austenitic–duplex stainless steel (A–D) welds contained coarse grains which are predominantly equiaxed on austenitic and duplex stainless steel side while they were columnar on the ferritic stainless steel side. Microstructural features in the central region of dissimilar stainless steel friction welds exhibit fine equiaxed grains due to dynamic recrystallisation as a result of thermomechanical working during welding and is confined to ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Beside this region bent and elongated grains were observed on ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Interdiffusion of elements was significant in electron beam welding and insignificant in friction welds. Pitting corrosion has been observed to be predominantly confined to heat affected zone (HAZ) close to fusion boundary of ferritic stainless steel interface of A–F electron beam and D–F electron beam and friction weldments. The pitting resistance of stainless steel electron beam weldments was found to be lower than that of parent metal as a result of segregation and partitioning of alloying elements. In general, friction weldments exhibited better pitting corrosion resistance due to lower incidence of carbides in the microstructure.

Influence of post-weld heat treatments on microstructure and mechanical properties of AISI 431 martensitic stainless steel friction welds

The relative effects of different post-weld heat treatments (PWHTs) on microstructure and mechanical properties of friction welded martensitic stainless steel type AISI 431 were studied. The weld microstructure consists of acicular martensite in equiaxed prior austenite grains and with heat treatment, the martensitic microstructure experiences coarsening. It was observed that retained austenite content decreases with an increase in the PWHT tempering temperature. The tensile properties of welds under different PWHTs were comparable to those of parent metal in the respective treatments. Welds exhibited higher notch tensile strengths than the parent metal in the respective heat treatment condition. Double tempering (670°C + 600°C) led to maximum reduction in hardness. Welds exhibited poor impact toughness in the as welded condition. The improvement in impact toughness was found satisfactory in welds subjected to double tempering, although did not match to the level of the parent metal at respective conditions. The mechanism and reasons for the observed behaviour have been discussed, correlating the microstructure, fracture features and mechanical properties.

INFLUENCE OF WELDING PROCESSES ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF DISSIMILAR AUSTENITIC-FERRITIC STAINLESS STEEL WELDS

Dissimilar metal welding of austenitic (AISI 304)-ferritic (AISI 430) stainless steel has been taken up to understand the influence of the welding process on microstructure and mechanical properties. Fusion welding processes, namely, gas tungsten arc welding (GTAW), electron beam welding (EBW), and friction welding, have been employed. The GTAW and EBW processes were selected to understand the heat input effects, while friction welding was included to compare fusion and solid-state welding processes. The material used for fusion welding studies is 20-mm-thick, hot-rolled, and annealed plate. Rods of 18 mm diameter machined from the same plate material were used for friction welding studies. In GTAW, ER 430 filler material was employed for dissimilar metal combination, while other welds are autogenous. Gas tungsten arc welds consisted of coarse columnar grains. In electron beam welds, the microstructure consisted of predominantely equiaxed grains on the austenitic stainless steel side, while columnar grains were observed on the ferritic stainless steel side. Epitaxial solidification was noted on the ferritic stainless steel side, while no such features were evident on the austenitic stainless steel side. Electron probe micro analysis (EPMA) revealed that inter diffusion of elements was significant in GTAW, intermediate in EBW, and insignificant in friction welds. Notch tensile and impact properties of ferritic stainless steel and dissimilar metal combination of austenitic-ferritic stainless steel friction welds are superior to gas tungsten arc welds and electron beam welds. Electron beam welds of austenitic stainless steel exhibited superior notch tensile and impact toughness compared to friction welds. Gas tungsten arc welds exihibited the lowest pitting corrosion resistance, while friction welds possessed the highest pitting corrosion resistance. In general, pitting was confined to Cr-depleted regions adjacent to the carbide precipitates.

Metallurgical and Mechanical Properties of High Nitrogen Austenitic Stainless Steel Friction Welds.

Friction welding of high nitrogen austenitic stainless steels was carried out using a pressure servo-control system brake type device. The welding parameters were 2 400 rpm for rotational rate, 70 MPa for 4, 7, 10 and 15 s for friction pressure, and 150 MPa for 6s for upset pressure. As the friction time increased, the fully plastically deformed zone (Region I) in the vicinity of the bond-line increased. In contrast, an increase in friction time decreased the region (Region II) where the grains were partly deformed and grown. The TEM examination suggested that the intergranular phases precipitated in the vicinity of the bond-line are Cr2N (Hexagonal, a=0.48113 nm, c=0.44841 nm) and CrN (Cubic, a=0.4140 nm). Tensile test results indicated that high nitrogen stainless steel joints are considerably higher in the tensile strength than the commercial stainless steel SUS316L or SUS304 joints. However, for all the welding conditions, the joint strength of high nitrogen HNS-1 or HNS-2 joints was slightly lower than that of the base material. Furthermore, the detailed fractographic observation confirmed that the rupture occurred near the bonding interface. The inferior tensile strength of the nitrogen-containing austenitic stainless steel joint could be attributed to the Cr-nitrides precipitated near the bonding interface.

Softened zone formation and joint strength properties in dissimilar friction welds

The mechanical properties of dissimilar MMC/AISI 304 stainless steel friction welds with and without silver interlayers were examined. The notch tensile strengths of MMC/AISI 304 stainless steel and MMC/Ag/AISI 304 stainless steel friction welds increased when high friction pressures were applied during the joining operation. The higher notch tensile strengths of dissimilar MMC/AISI and MMC/Ag/AISI 304 stainless steel friction welds resulted from the formation of narrow softened zones in MMC material immediately adjacent to the bondline. The influence of softened zone width and hardness (yield strength) on the notch tensile strengths of dissimilar welds was analysed using finite element modelling (FEM). FEM in combination with the assumption of a ductile failure criterion was used to calculate the notch tensile strengths of dissimilar joints. The key assumption in this work is that dissimilar weld failure wholly depended on the characteristics (mechanical properties and dimensions) of the softened zone formed in MMC material immediately adjacent to the bondline. The modelling results produced based on this assumption closely correspond with the actual notch tensile strengths of dissimilar MMC/Ag/AISI 304 stainless steel and MMC/Ag/AISI 304 stainless steel friction welds.

Characterisation and generation mechanism of residual stress and plastic strain in Ti/AISI304L stainless steel friction welds

Summary This paper describes detailed FEM modelling performed to clarify the characteristics of residual stress and plastic strain generated during dissimilar metal friction welding operations. The results obtained may be summarised as follows: When bonding problems of dissimilar materials are being numerically analysed by an FEM thermal elastic‐plastic analysis, comparisons undertaken in the radial direction of both the distribution and magnitude of the z axis stress σz generated in both base metals adjacent to the bondline, as determined from the uniform cooling model from 800 °C to room temperature, provide a sound basis for a decision as to the suitability of the FEM mesh used. A comparison of the yield stress σY and temperature relationships in both base metals shows that the Ti base metal has the lower zero‐σY temperature (mechanical fusion temperature). Thermal diffusion in Ti/AISI304L stainless steel friction welds mainly occurs within a narrow region of around 20 mm from the bondline, and this st...

Improving tensile strength and bend ductility of titanium/AlSI 304L stainless steel friction welds

The metallurgical and mechanical properties of friction welds between titanium and AISI 304L stainless steel were examined. Joint tensile strength increased when high friction pressure (>196 MN m−2) and high upsetting pressure (294 MN m−2) were used during welding. Although the surface roughness of the titanium substrate had no effect on joint strength, decreasing the surface roughness of the AISI 304L material did increase the tensile strength of completed joints. As welded dissimilar joints had poor bend test ductility and failed in the interface region. Detailed microscopy and X-ray diffraction analysis confirmed that the poor bend ductility was caused by a combination of high hardness of the titanium material immediately adjacent to the joint interface, the presence of unrelieved residual strain at the joint interface, and intermetallic phases formed during the welding operation. Detailed transmission electron microscopy and X-ray analysis confirmed that a thin layer rich in intermetallics was present in the as welded joints. (FeNiCr)Ti phases were formed during seizure formation and disruption; this provided the necessary conditions for anomalously high rates of diffusion of titanium in stainless steel, and of iron, chromium, and nickel in titanium. Low temperature post-weld heat treatment (PWHT), involving heating to 500–600°C followed by immediate air cooling, reduced intermetallic precipitation, promoted stress relaxation, and facilitated complete bonding across the whole joint interface. This treatment markedly improved bend ductility and had a negligible effect on joint tensile strength. High PWHT temperatures (≥900°C) and long holding times at temperature markedly reduced joint tensile strength and bend ductility, owing to excessive formation of intermetallic phases at the joint interface.MST/1521

Improving tensile strength and bend ductility of titanium/AlSI 304L stainless steel friction welds

AbstractThe metallurgical and mechanical properties of friction welds between titanium and AISI 304L stainless steel were examined. Joint tensile strength increased when high friction pressure (>196 MN m−2) and high upsetting pressure (294 MN m−2) were used during welding. Although the surface roughness of the titanium substrate had no effect on joint strength, decreasing the surface roughness of the AISI 304L material did increase the tensile strength of completed joints. As welded dissimilar joints had poor bend test ductility and failed in the interface region. Detailed microscopy and X-ray diffraction analysis confirmed that the poor bend ductility was caused by a combination of high hardness of the titanium material immediately adjacent to the joint interface, the presence of unrelieved residual strain at the joint interface, and intermetallic phases formed during the welding operation. Detailed transmission electron microscopy and X-ray analysis confirmed that a thin layer rich in intermetallics was...