Process parameter influence on performance of friction taper stud welds in AISI 4140 steel

Friction taper stud welding is a new variant of friction welding which has been developed from the principles of friction hydro-pillar processing. This paper considers the effect of weld process parameters on weld defects, macrostructure and mechanical properties in AISI 4140 steel. It also presents 3D residual stress data for a typical friction taper stud weld. Applied downwards force, rotational speed and plunge depth (equivalent to consumable length) of the stud tool were systematically varied whilst measuring tool torque and temperature at several locations during welding. A simple Taguchi analysis was then used to relate process parameters and weld tensile strength. The combinations of parameters leading to high tensile strength are identified and linked to the occurrence of specific weld defects.     

Study of the characteristics of duplex stainless steel activated tungsten inert gas welds

The purpose of this study is to investigate the effects of the specific fluxes used in the tungsten inert gas (TIG) process on surface appearance, weld morphology, angular distortion, mechanical properties, and microstructures when welding 6 mm thick duplex stainless steel. This study applies a novel variant of the autogenous TIG welding, using oxide powders (TiO₂, MnO₂, SiO₂, MoO₃, and Cr₂O₃), to grade 2205 stainless steel through a thin layer of the flux to produce a bead-on-plate joint. Experimental results indicate that using SiO₂, MoO₃, and Cr₂O₃ fluxes leads to a significant increase in the penetration capability of TIG welds. The activated TIG process can increase the joint penetration and the weld depth-to-width ratio, and tends to reduce the angular distortion of grade 2205 stainless steel weldment. The welded joint also exhibited greater mechanical strength. These results suggest that the plasma column and the anode root are a mechanism for determining the morphology of activated TIG welds.     

Fatigue behaviour of friction welded medium carbon steel and austenitic stainless steel dissimilar joints

This paper reports the fatigue behaviour of friction welded medium carbon steel–austenitic stainless steel (MCS–ASS) dissimilar joints. Commercial grade medium carbon steel rods of 12 mm diameter and AISI 304 grade austenitic stainless steel rods of 12 mm diameter were used to fabricate the joints. A constant speed, continuous drive friction welding machine was used to fabricate the joints. Fatigue life of the joints was evaluated conducting the experiments using rotary bending fatigue testing machine (R = −1). Applied stress vs. number of cycles to failure (S–N) curve was plotted for unnotched and notched specimens. Basquin constants, fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated for the dissimilar joints. Fatigue strength of the joints is correlated with microstructure, microhardness and tensile properties of the joints.     

Effect of welding procedure on wear behaviour of a modified martensitic tool steel hardfacing deposit

In the last years hardfacing became an issue of intense development related to wear resistant applications. Welding deposits can functionalize surfaces and reclaim components extending their service life. Tool steels are widely used in hardfacing deposits to provide improved wear properties. Nevertheless systematic studies of wear behaviour of new alloys deposited by hardfacing, under different service conditions are scarce. In this work the effects of shielding gas, heat input and post-weld heat treatment on the microstructural evolution and wear resistance of a modified AISI H13 martensitic tool steel deposited by semi-automatic gas shielded arc welding process using a tubular metal-cored wire, were studied. Four coupons were welded with different welding parameters. The shielding gases used were Ar–2% CO₂ and Ar–20% CO₂ mixtures and two levels of heat input were selected: 2 and 3 kJ/mm. The as welded and 550 °C–2 h post-weld heat treated conditions were considered. From these coupons, samples were extracted for testing metal–metal wear under condition of pure sliding with a load of 500 N. Chemical compositions were determined; microstructure and microhardness were assessed. It was found that content of retained austenite in the microstructure varied with the welding condition and that heat-treated samples showed secondary hardening, associated with precipitation phenomena. Nevertheless, as welded samples showed higher wear resistance than heat treated specimens. Under these test conditions post-weld heat treatment led to a reduction in wear resistance. The best wear behaviour was observed in samples welded with low heat input and under the lowest oxygen potential shielding gas used here, in the as welded condition. The intervening mechanism was mild oxidative. These results were explained in terms of the relative oxidation resistance stemming from different welding conditions.     

Effect of rare earth element yttrium addition on microstructures and properties of a 21Cr–11Ni austenitic heat-resistant stainless steel

In this comparative study, the microstructure and the mechanical properties of a 21Cr–11Ni austenitic heat-resistant stainless steel with and without addition of rare earth (RE) element yttrium have been investigated. The results show that a number of fine spherical yttrium-rich oxide particles are not uniformly distributed in the matrix of steel with yttrium; instead, they are aligned along the rolling direction. The grains surrounding the alignment are nearly one order of magnitude smaller than those farther away from the alignment. The approximate calculation results indirectly show that the grain refinement may be mainly attributed to the stimulation for nucleation of recrystallization rather than to pinning by particles. Furthermore, the alignment has resulted in significant loss in transverse impact toughness and tensile elongation at room temperature. There is a trough in the hot ductility–temperature curve, which is located between 973 and 1173 K. The ductility trough of steel with yttrium becomes shallow within a certain temperature range, especially around 1073 K, indicating that improvement on hot ductility is achieved by yttrium addition. The results may be attributed to the increase of grain boundary cohesion indicated by the effective improvement on intergranular failure tendency, and the inhibitory effect of yttrium on sulfur segregation to grain boundaries is believed to be an important cause.     

Processing map for hot working characteristics of a wrought 2205 duplex stainless steel

Processing map on a wrought 2205 duplex stainless steel under hot compression conditions has been developed based on the dynamic material model theories in the range 1223–1473 K and 0.01–10 s⁻¹. The various domains in the map corresponding to different deformation characteristics have been discussed in combination of microstructural observations. The results show that the power dissipation efficiency (η) depends strongly on the dynamic recrystallization (DRX) of austenite which plays a dominant role in microstructural evolution, while the ferrite phase mainly continues to exhibit relatively well-developed dynamic recovery (DRV) at large strain. The optimum hot working domain of wrought 2205 duplex stainless steel is obtained to be in the temperature range 1373–1473 K and at strain rate of 0.01 s⁻¹, with peak efficiency 50% occurring at about 1423 K, in which more uniform microstructure is developed due to the occurrence of complete DRX of austenite. The unstable hot working regimes are predicted by Prasad instability criterion, in good agreement with the macro-and microstructural observations. As predicted, flow instability, which are manifested as twinning, bands of flow localization and the absence of DRX in austenite are observed at lower temperatures and higher strain rates (1223–1273 K and 1–10 s⁻¹); in other cases, wedge cracking is responsible for instability phenomena observed at the temperature range 1373–1423 K and strain rate of 10 s⁻¹.     

Microstructure and properties of austenitic stainless steel reinforced with in situ TiC particulate

Austenitic stainless steel reinforced with 5 vol.% TiC particulate was in situ synthesized by in situ reaction during melting process successfully and its microstructure, mechanical properties as well as oxidation behavior were investigated. Microstructure observations revealed that in situ TiC particulates with an average size of 2–10 μm distributed uniformly in the matrix and the interface boundaries between TiC particulates and austenite matrix were clean without any impurities and contaminations. Addition of TiC particulates refined the grain structure of austenitic matrix, but did not cause formation of any new phases in microstructure. Beneficial effects of TiC addition to austenitic stainless steel on both mechanical properties and oxidation resistance were found. Both at ambient and elevated temperature, tensile strengths of the steel with TiC addition were notably higher than those of its matrix alloy, however, a decrease in ductility also appeared, as exhibited by other particulate reinforced alloys. Besides tensile strengths, creep resistance of austenitic stainless steel was also significantly increased by TiC addition at elevated temperature of 923 K. Oxidation test at 1073 K revealed that TiC addition to austenitic stainless steel raised the oxidation resistance of the steel remarkably.     

The rate of dynamic recrystallization in 17-4 PH stainless steel

The hot working behavior of 17-4 PH stainless steel (AISI 630) was studied by hot compression test at temperatures of 950–1150 °C with strain rates of 0.001–10 s⁻¹. The progress of dynamic recrystallization (DRX) was modeled by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetics equation. The flow softening was directly related to the DRX volume fraction and the DRX time was determined by strain rate. For quantification of recrystallization rate, the reciprocal of the time corresponding to the DRX fraction of 0.5% or 50% was used. Analysis of the sigmoid-shaped recrystallization curves revealed that the rate of DRX increases with increasing deformation temperature and strain rate. The Zener-Hollomon parameter (Z) was found to be inappropriate for analysis of DRX kinetics. Therefore, the dynamic recrystallization rate parameter (DRXRP) was introduced for this purpose. The DRXRP may be determined readily from the Avrami analysis and can precisely predict the rate of DRX at hot working conditions.     

Interface microstructure and mechanical properties of arc spot welding Mg–steel dissimilar joint with Cu interlayer

A novel technology was developed for the arc spot welding of AZ31 Mg alloy to Q235 steel with Cu as interlayer. The mechanisms of bonding dissimilar materials were investigated using mechanical and metallurgical examinations. Results show that the joining of Mg alloy to steel with Cu involved two bonding mechanisms: weld-brazing by the Cu transition layer at the interface edge and bonding by a micron-scale composite transition layer of Al₃Cu₄Fe₃ and Fe₄Cu₃ intermetallic phases at the interface center. The additional reaction of Cu increased the reaction temperature and composition ranges at the interface. It also elicited a bridge effect that improved the weldability of Mg alloy and steel by new formed phases.     

Characterization of microstructure,mechanical properties and corrosion resistance of dissimilar welded joint between 2205 duplex stainless steel and 16MnR

The joint of dissimilar metals between 2205 duplex stainless steel and 16MnR low alloy high strength steel are welded by tungsten inert gas arc welding (GTAW) and shielded metal arc welding (SMAW) respectively. The microstructures of welded joints are investigated using scanning electron microscope, optical microscope and transmission electron microscopy respectively. The relationship between mechanical properties, corrosion resistance and microstructure of welded joints is evaluated. Results indicate that there are a decarburized layer and an unmixed zone close to the fusion line. It is also indicated that, austenite and acicular ferrite structures distribute uniformly in the weld metal, which is advantageous for better toughness and ductility of joints. Mechanical properties of joints welded by the two kinds of welding technology are satisfied. However, the corrosion resistance of the weldment produced by GTAW is superior to that by SMAW in chloride solution. Based on the present work, it is concluded that GTAW is the suitable welding procedure for joining dissimilar metals between 2205 duplex stainless steel and 16MnR.     

Synergistic investigation into the marine parameters’ effect on the corrosion rate of AISI 316 stainless steel

In this paper, the corrosion rate of the austenitic stainless steel AISI 316, under the synergistic effect of environmental factors, has been assessed via potentiodynamic polarization scan. Salinity, velocity, pH and temperature are the factors that induce effects on the corrosion rate of the considered metal. Quantitative analysis is applied using the full two-level factorial experimental design method. This analysis calculates the contribution value of each parameter in changing the quantity of average corrosion rate in both individual and synergistic cases. In addition, qualitative analysis has been used to predict the variation direction. These two analyses show the important role of the synergistic action that changes the variation direction of corrosion rate and the contribution percentage of each parameter in varying the value of corrosion rate. Applying both quantitative and qualitative analyses can show the magnitude and quality of each parameter’s effect, which is remarkably valuable in marine application designs.     

A comparative study of laser-arc double-sided welding and double-sided arc welding of 6 mm 5A06 aluminium alloy

In order to study the interactions between the two heat sources in both laser-arc double-sided welding (LADSW) and double-sided arc welding (DSAW), some welding characteristics including weld configuration, energy efficiency, weld microstructure and mechanical properties of the both processes were contrastively investigated. The results show that the weld cross-section of LADSW within the proper welding parameter takes on the combination of typical weld profiles of gas tungsten arc welding and laser welding, while the DSAW takes on a quasi-symmetrical shape. The energy efficiency of LADSW is higher than DSAW, probably due to the higher heat transfer efficiency in laser welding and stronger effect of laser on the arc. The weld microstructures of the both processes characterized by scanning electron microscope mainly consist of α and β phase, whereas the grain size and second-phase particle size vary a great deal for the different heat input. The tensile strength of LADSW is 91.7% of base metal, compared with that of 82.3% of DSAW, and the elongation is also higher than DSAW. The fracture micromorphology of LADSW indicates a more typical dimple fracture than that of DSAW. It is considered that the better mechanical properties of LADSW are attributed to the finer grain size.     

Two-step method to evaluate equibiaxial residual stress of metal surface based on micro-indentation tests

The present study proposed a method to evaluate the equibiaxial compressive residual stress of a metal surface by means of a depth-sensing indentation method using a spherical indenter. Inverse analysis using the elastic–plastic finite-element model for an indentation test was established to evaluate residual stress from the indentation load–depth curve. The proposed inverse analysis utilizes two indentation test results for a reference specimen whose residual stress is already known and for a target specimen whose residual stress is unknown, in order to exclude the effect of other unknown mechanical properties, such as Young’s modulus and yield stress. Residual stress estimated by using the indentation method is almost identical to that measured by X-ray diffraction for indentation loads of 0.49–0.98 N. Therefore, it can be concluded that the proposed method can effectively evaluate residual stress on metal surface.     

On the behavior of nitrogen in a low-Ni high-Mn super duplex stainless steel

The present work describes an investigation on a new series of low-Ni high-Mn super duplex stainless steels (DSSs) 25Cr–2Ni–3Mo–10Mn–xN with nitrogen concentrations varying in the range between 0.37 and 0.50 wt.%. It was observed that these alloys have a ferrite–austenite structure. Under the same heat-treatment conditions, the austenite shows a marked upward tendency with an increase in N content. Nitrogen delays the precipitation of σ phase. The increase in nitrogen enhances the yield strength (YS), ultimate tensile strength (UTS) and ductility as well as the pitting corrosion potential of the materials. The pitting corrosion occurs in the austenite phases in the case of low N content (0.37 wt.%), but in the case of high N content (0.50 wt.%) it happens in the ferrite phases.     

Analysis of residual stresses in thick aluminum friction stir welded butt joints

Plates of aluminum alloys 2219-T62 were joined in a butt joint by friction stir welding. The residual stresses on the top and bottom surfaces were measured using the hole-drilling strain-gauge method. In the test specimen, it was found that the residual stresses on the top surface peaked at about 171 MPa, while the value reached 243 MPa for the weld with tunnel defect and had the conventional “M” profile with tensile stress peaks in the heat-affected zone. Those attached on the bottom surface had the inverted “V” profile with tensile stress peaks in the weld centre and the corresponding value was 99.4 MPa. Meanwhile, with the increase of rotary speed, the longitudinal residual stress decreased on the top surface, but increased on the bottom surface.     

Anisotropic property of material arrangement in friction stir welding of dissimilar Mg alloys

Microstructure and mechanical properties of friction stir weld joints of dissimilar Mg alloys AZ31 and AZ80 were investigated in the present work. Several different welding parameters were adopted in the study, and the effects of rotation speed and welding speed on the joint quality were discussed comprehensively. In addition, material arrangement which means that AZ31 alloy was at advancing side or at retreating side has significant influence on the joint formation, including the joint microstructure and mechanical properties. A few kinds of defects were observed when the improper parameters were taken in the experiment, and the reasons for generating these defects were revealed in this work. Sound joints with good mechanical properties could be easily obtained when AZ31 was at retreating side, but it was difficult to obtain the sound joint with the contrary material arrangement. These results suggest that the material with inferior plastic deformability should be set at the advancing side and the material with superior one should be set at the retreating side in order to get sound FSW joint of dissimilar Mg alloys.     

Effect of governing metal thickness and stack orientation on weld quality and mechanical behaviour of resistance spot welding of AA5754 aluminium

A study was carried out to investigate the effect of governing metal thickness (GMT) and stack orientation on weld quality and mechanical behaviour of resistance spot welded (RSW) AA5754 aluminium. Individual samples from 27 different joint stacks in three test geometries; lap-shear, coach-peel and cross-tension were evaluated for quasi-static and fatigue performance; micro examination was also conducted on some of the samples to assess weld quality. The results derived from over 1000 samples show that: the GMT has a significant effect on welding quality by controlling progression of weld nugget from under-developed to over penetrated. The GMT also determines the feasible quasi-static joint strength regardless of stacks in the three joint geometries tested, though the effect differs with respect to test geometry. The fatigue behaviour is dominated by the effect of GMT on attainable weld size, overall joint stiffness and stress concentration, providing good quality of weld nuggets is achieved. No notable effect of stack orientation on weld quality and joint strength was found with respect to the joint stack asymmetry and welding orientation to the electrodes. These fundamental relationships between weld qualities, joint strength, GMT and stack orientation for RSW of aluminium will have significant relevance to design and manufacturing communities.     

Failure analysis of dissimilar thickness resistance spot welded joints in dual-phase steels during tensile shear test

Investigating the failure mode and failure mechanism of the dissimilar thickness dual phase sheets resistance spot welding joints was the objective of this study. Three distinct failure modes were observed during the tensile shear test: interfacial, partial interfacial and pullout failure. The results of the stress analysis of welded joints show that the tensile stress leads to the interfacial failure and the shear stress leads to the pullout failure. Due to more serious stress concentration and heat affected zone (HAZ) softening of DP780 side, the fracture is initiated from the DP780 steel.     

Experimental and numerical studies on the forming behavior of tailor welded steel sheets in biaxial stretch forming

Stretch forming is an important process in making complex stampings for autobody components. In the present work formability of three different types of tailor welded blanks (TWBs) in biaxial stretch forming modes has been studied by conducting limiting dome height (LDH) tests. The TWBs are laser-welded samples of low carbon and ultra low carbon steel sheets with difference in thickness, grade and surface conditions. In TWBs with difference in thickness, the LDH decreases as the thickness ratio increases and the thickness of the thinner side is also crucial. A high thickness ratio causes two major strain peaks on thinner side and fracture takes place due to strain localization at the peak close to the pole. The weld ductility and the extent of difference in properties are the two crucial parameters for formability in TWBs with difference in properties. In both these TWBs, the fracture takes place perpendicular to the weld line and propagates towards the stronger side. Significant weld line movement occurs towards the thicker/stronger side in biaxial stretch forming. The maximum weld line movement occurs at the pole and it increases with increase in thickness ratio and becomes constant beyond a certain thickness ratio. The peak load required to deform the TWB specimens is less compared to the corresponding parent sheets. In case of TWBs with difference in thickness, as the thickness ratio increases, the peak load reduces due to decreasing punch-blank contact area.     

Improvement of weld temperature distribution and mechanical properties of 7050 aluminum alloy butt joints by submerged friction stir welding

Submerged friction stir welding (FSW) in cold and hot water, as well as in air, was carried out for 7050 aluminum alloys. The weld thermal cycles and transverse distributions of the microhardness of the weld joints were measured, and their tensile properties were tested. The fracture surfaces of the tensile specimens were observed, and the microstructures at the fracture region were investigated. The results show that the peak temperature during welding in air was up to 380 °C, while the peak temperatures during welding in cold and hot water were about 220 and 300 °C, respectively. The temperature at the retreated side of the joint was higher than that at the advanced side for all weld joints. The distributions of microhardness exhibited a typical “W” shape. The width of the low hardness zone varied with the weld ambient conditions. The minimum hardness zone was located at the heat affected zone (HAZ) of the weld joints. Better tensile properties were achieved for joint welded in hot water, and the strength ratio of the weld joint to the base metal was up to 92%. The tensile fracture position was located at the low hardness zone of the weld joints. The fracture surfaces exhibited a mixture of dimples and quasi-cleavage planes for the joints welded in cold and hot water, and only dimples for the joint welded in air.