Stainless Steel Dissimilar Metal Research Articles

Dissimilar joining of Ti–6Al–4V to 316L stainless steel by a novel joining process based on arc additive manufacturing and combined twin-wire arc welding

The joining structure of Ti–6Al–4V to 316L stainless steel has potential demands in many fields. However, it is very difficult to avoid the formaiton of intermetallic compounds (IMCs) of the weld between Ti–6Al–4V to 316L stainless steel, which will severely decrease joint properties. In this paper, a novel joining technology that combines the single wire backing arc welding and the spatially arranged combined twin-wire arc welding was utilized to join Ti–6Al–4V and 316L stainless steel. Copper alloy wire (S214) and vanadium alloy wire (V01) were used as filler metals to produce two isolation layers, which prevented the formation of IMCs. The phase compositions at the Fe/Cu, Cu/V and V/Ti interfaces were Fe(S,S) + Cu(S,S), Cu(S,S) + V(S,S) and V(S,S)+(β-Ti, V)SS respectively. The distribution of the spherical and clustered V(S,S) particles in the matrix at the Cu/V interface contributes to dispersion strengthening and solid solution strengthening of the interface. Tensile strength of 394 MPa with an elongation of 2.53% was achieved. The joint fractured at the Cu/V interface of the single wire backing arc weld and the Cu zone of the spatially arranged combined twin-wire arc weld respectively. Dimple plastic fracture modes were detected in the joints. This technology is not only applicable to Ti–6Al–4V titanium alloy/316L stainless steel dissimilar metal joining, but also provides a new research strategy for the joining between other dissimilar metals.

Insight into the galvanic corrosion behaviour of low alloy steel A508/309 L/308 L stainless steel dissimilar metal weld at different temperatures.

Galvanic corrosion is prevalent in many dissimilar metal welds (DMW) in-service applications. Nevertheless, there is a scarcity of systematic investigations regarding the effect of different temperature conditions on the galvanic corrosion behaviour of low alloy steel (LAS)/309 L/308 L stainless steel (SS) DMW making up the reactor pressure vessel (RPV). Relevant results of this study indicate that temperature significantly affects the galvanic corrosion behaviour of LAS A508/309 L/308 L SS in simulated primary water solution. The shutdown temperature condition showed a higher influence of galvanic corrosion than the operating temperature condition. The discrepancy is ascribed to the varying difference in corrosion potential between the dissimilar metals in both conditions, which are 357 mV vs. SCE and ⁓55 mV vs. SCE for shutdown and operating temperature conditions, respectively. The specially designed immersion test simulating the actual RPV in-service environment revealed that the galvanic interaction between the dissimilar metals at the interface region is greatly affected by the anode (LAS A508) to cathode (309 L/308 L SS) area ratio, with average corrosion exceeding 0.3 mm/y occurring when the actual anode to cathode area ratio exceeds 1:6000. Finally, from the morphological evolution results it is seen that galvanic corrosion develops along the weld fusion line interface, rather than in the depth direction of the LAS A508, which is conducive for the operational reliability of the RPV.

An experimental investigation on predicting the fracture toughness distributions in ferritic-austenitic stainless steel dissimilar metal welds from spherical indentation tests

This study provides an experimental investigation on predicting the fracture toughness distributions in dissimilar metal welds (DMWs) connecting the nozzle of reactor pressure vessel (made of low-alloy steel) and the safety end of pipes (made of stainless steel). Indentation energy to fracture model with three criteria (namely the critical stress, critical strain, and critical damage variable, CDV) and the energy release rate (ERR) model were introduced into fracture toughness predictions from spherical indentation tests (SITs). It was found that consistency of the fracture toughness KIC calculated from the repeated tests using the critical strain criterion and ERR model is even higher than that from mini-CTs, while high dispersion predictions were observed in critical stress criterion. Compared with the CDV criterion, the ERR model focuses on the dissipation energy required to form unit area “equivalent-crack” (i.e., the rate) rather than the whole indentation energy till a critical depth, and thus it is less affected by the absolute value of damage variations in three repeated SITs. Source of errors were first investigated through the damage developments in uniaxial tensile specimens manufactured from different zones of the DMWs, which proves the CDV varies from 0.1 to 0.25 and thus shall not be regarded as a constant. Then, SEM observations were conducted on both the fracture surfaces from mini-CTs and the section surfaces from SITs, indicating both the changes in fracture mechanism (from ductile dominated to the joint effort of ductile void developments and cleavage micro-crack propagations) and the existence of small initial voids from welding lead to the errors in damage-mechanics-based predictions.

Contact reactive brazing of TC4/304 stainless steel dissimilar metals by interrupted arc pulsed welding

The most challenging aspect of producing durable joints between titanium alloy and stainless steel (Ti/SS) is preventing the formation of brittle Ti–Fe intermetallic compounds, particularly the TiFe2 phase. In this paper, the interrupted pulsed arc welding (IPAW) was proposed to join TC4 and 304SS dissimilar metals. The joining mechanisms, microstructures and shear strength of the joints were investigated. The precise regulation of arc pulsed time in the millisecond range enabled the creation of a joint without the formation of the TiFe2 phase through contact reactive brazing. A Ti-rich reaction layer consisting of β-Ti and TiFe phases was formed in the brazing joint, and the shear strength of the joint reached 106.3 MPa. By increasing the arc pulsed current or time, the brazing joint was transformed into the fusion joint. The formation of two reaction layers was observed: Ti-rich phases (TiFe and β-Ti) near the TC4 and Fe-rich phases (TiFe2 and TiCr2) near the 304SS, which exhibited high brittleness. The presence of a high brittleness fusion zone resulted in immediate cracking post-welding.

SA508 low alloy steel to 316L stainless steel dissimilar metal joint made by powder metallurgy hot isostatic pressing

Joining ferritic SA508 low alloy steel (LAS) and austenitic 316 L stainless steel (SS) via powder metallurgy hot isostatic pressing (PM-HIP) was evaluated as an alternative method to welding. This study investigated the mechanical and microstructural evolutions of the bimetallic interface under different joint designs and heat treatments. The direct joining of dissimilar metal alloys by PM-HIP method resulted in two designs: 1) powder SA508 to solid bar 316 L (P508–B316L) and 2) powder 316 L solid bar SA508 (P316L-B508). In both cases, P508–B316L and P316L-demonstrated satisfactory tensile strength, however, high hardness and severe depreciation in toughness were located on the bimetallic interface. The mechanisms responsible for the detrimental mechanical properties were verified. Large oxides were observed in P508–B316L due to the prior powder boundary (PPB) oxides present in SA508 powder. The intense sensitization occurred from the formation of M23C6 carbides, consequently from the slow cooling after PM-HIP in P316L-B508. Post-HIP heat treatments were explored to reduce the distance of carbide formation; however, the heat treatment could not eliminate the carbides. The experimental results were compared to the diffusion couple simulation as a function of carbide formation with distance. The analysis also showed the high hardness at the bimetallic interface was primarily contributed by solid solution strengthening. In conclusion, the direct joining of P316L-B508 and P508–B316L via PM-HIP was deemed to be unfeasible, and a transitional material is necessary to impede the diffusion of carbon.

Microstructure and mechanical properties of laser indirect brazed titanium/steel composite joint with a CuZn filler metal

In this study, the research on the laser welding TC4 alloy and stainless steel dissimilar metals with composite welding mechanism was investigated. Dissimilar joints of TC4 alloy and stainless steel were generated by indirect laser brazing. Moreover, in order to further explored the bonding mechanism of joints, CuZn metal was used as the filler material to study the welding process of TC4 alloy and 304 stainless steel with indirect laser brazing and transition section. The filler was extruded into metal droplets due to the metal expansion during laser welding, which increased the tightness of the joint. With the increase of heat input, the reaction between the filler and the base metals on both sides was more intense. In addition, the tensile strength reached 210 MPa (41% of stainless steel) when the laser power was 624 W.

Effect of pulse energy on microstructure and properties of laser lap-welding Hastelloy C-276 and 304 stainless steel dissimilar metals

Nd:YAG pulsed laser lap-welding of Hastelloy C-276 and 304 stainless steel was conducted. The effect of pulse energy on weld morphology, element distribution, microstructure, phase structure, tensile-shear property and corrosion property of weld joint was analyzed. The results indicated that, with the increase of pulse energy, both the penetration depth and bead width of weld metal (WM) and dilution level of 304 base metal (BM) were linearly increased. Unmixed zone between WM and 304 BM was reduced, however, the grains sizes in WM became coarser. The precipitated phase with higher content of Mo and W is mainly p phase, with the increase of pulse energy, segregation potential of Mo element was increased, however, the amount of precipitated phase was decreased due to a decline in Mo element in WM. The fracture mode of weld joint transferred from interfacial fracture to tensile fracture with the increase of bead width, and the maximum load capacity of which was achieved at a pulse energy of 4.0 J. The average micro-hardness value of WM was decreased with the increase of pulse energy due to the depletion of Mo and W strengthening elements and the coarser grain size in WM. The corrosion resistance of WM was weakened with the increase of pulse energy ascribed to the reduce of Ni and Mo elements.

Galvanic corrosion study between low alloy steel A508 and 309/308 L stainless steel dissimilar metals: A case study of the effects of oxide film and exposure time

The effects of oxide film and exposure time on the galvanic corrosion between low alloy steel (LAS) A508 and 309/308L stainless steel (SS) dissimilar metals were studied by several electrochemical techniques and surface composition analytical tools. The zero resistance ammeter (ZRA) result shows that the trend of galvanic corrosion current between the coupled LAS A508 and 309/308L SS changes with respect to exposure time. Furthermore, from the ZRA measurement, the quantitative relationship between galvanic current and dissolution rate of the coupled LAS A508 anode metal was established by statistical approach. Electrochemical impedance spectroscopy (EIS) results and analyses demonstrated that the increasing galvanic corrosion rate observed between the coupled dissimilar metals as exposure time prolonged was suppressed by the oxide film effect. The suppression occurred as a result of the transformation of unstable oxides to stable oxide forms, and the oxide film thickening phenomenon experienced on the LAS A508 surface as exposure time prolonged. Generally, a synergy between both effects was observed in this study.

Effect of Disk Laser Beam Offset on the Microstructure and Mechanical Properties of Copper—AISI 304 Stainless Steel Dissimilar Metals Joints

Deoxidized oxygen free copper C12200, 1 mm in thickness, was welded to 1-mm thick AISI 304 stainless steel with disk laser. The butt-welded joints were produced with different welding parameters. Full factorial design of experiment (DoE) approach consisting of three factors and two levels was utilized. Laser powers used for welding were 1.3 and 1.9 kW and welding speeds of 20 and 30 mm/s. Two beam offsets were tested, namely, 100 μm toward copper side and 200 μm toward AISI 304 steel. It was found that beam offset possesses the largest influence on the welded joints’ tensile strength. Tensile strengths attained values more than 3.7 times higher in comparison to the AISI 304 steel beam offset. When lower laser power was used, the higher tensile strength was attained for copper sheet offset. Higher microhardness was observed when laser beam was offset to AISI 304 steel side. The average microhardness of the weld metal was higher than that of the weaker base material, copper sheet. Energy dispersive X-ray spectroscopy (EDS) analysis confirmed the heterogeneity in elemental composition across the welded joint interface, being lower when laser beam was offset to AISI 304 steel side. On the other hand, the copper content dropped to the average composition of weld metal at the distance of about 140 μm from copper-weld metal interface.

Investigation on the control of interfacial layer uniformity in laser-metal inert-gas hybrid welded-brazed Al/steel butt joint

Abstract Obtaining a homogeneous distribution of interfacial layer in the Al/steel butt joint could further improve the tensile properties of well-formed joint, which is of great significance to the application of Al-steel hybrid structures in engineering. This article successfully used laser-metal inert-gas (MIG) hybrid welding-brazing technology to obtained 2-mm-thick 6061-T6 aluminum alloy and 301 stainless steel dissimilar metals butt joint. The penetration ability of the hybrid heat source was improved by increasing the laser power within an appropriate range. The interfacial layer with the most uniform thickness (4.5 μm–5.2 μm) and phase composition (τ5 phase and θ phase) could be obtained at laser power of 2000 W. Numerical simulation results revealed that reducing the difference of peak temperature along Al/steel interface could effectively improve the uniformity of the interfacial layer. The smallest difference of interfacial temperatures in the joint produced at laser power of 2000 W was responsible for the most uniform interfacial layer. The tensile strength of the Al/steel butt joint with the most uniform interfacial layer could reach the maximum value of 198 MPa (about 70 % of the 6061-T6 tensile strength).

Mechanical Behavior Characterization of a Stainless Steel Dissimilar Metal Weld Interface : In-situ Micro-Tensile Testing on Carburized Martensite and Austenite

Stainless Steel Dissimilar Metal Welds (SS DMW) between low-alloy steel 18MND5 and austenitic 316L stainless steel are critical junctions in the currently operating reactors because of their heterogeneous microstructure and mechanical properties. The presence of a narrow hard layer of carburized martensite and austenite in the ferritic-austenitic interface creates an important hardness gradient which affects the crack behavior of the SS DMW. In order to evaluate the plastic properties of this hard layer, a micro tensile testing method was developed. Tensile specimens of 15 x 80 x 6 μm were extracted from the martensitic and carburized austenitic layers by focused ion beam (FIB) micro-processing and tested using an in-situ tensile testing device. A platinum FIB deposition was used to measure local strain in the specimen during the test through digital image correlation (DIC). Isotropic elasto-plastic constitutive laws for the martensite and carburized austenite were obtained from the true strain-stress curves calculated from the micro-tensile tests. It was found that the corresponding plastic properties were in a good agreement with nanoindentation measurements and with values obtained from macroscopic tensile tests on crossweld specimens machined perpendicularly to the ferritic-austenitic interface and characterized using laser beam local diameter measurements. In-situ tensile testing is a promising technique for plastic behavior characterization of small scale materials and local hard layers in dissimilar metal welds.

GTA Weld Brazing a Joint of Aluminum to Stainless Steel

The relationship between heat input, microstructures, and mechanical properties was studied in the gas tungsten arc (GTA) weld brazing process of aluminum alloy and stain-less steel dissimilar metals with a pure aluminum core wire (ER1100). The mechanisms involved were further revealed by hot-dip aluminizing experiments. The intermetallic compounds (IMCs) of the brazing interface consisted of a thin layer of -Fe2Al5 next to the steel, and a thick layer of -Fe4Al13 adjacent to the Al joint, surrounded by eutectic identified to be Al-FeAl6 and Al-Fe2Al9 distributed uniformly in the weld metal. With increasing heat input, the total thickness of the IMCs decreased first, reaching a minimum value of 3.5 m, and then increased. The decrease in IMC thickness with heat input was observed for the first time and had never been reported before in welding or brazing processes. The joint strength increased to a maximum value of 238 MPa and then declined, suggesting an inverse relationship between IMC thickness and joint strength. The results of the hot-dip aluminizing, regarding the relationship between IMC thickness and temperature, were consistent with the change of IMC thickness in the welds. A possible mechanism in action is that interfacial kinetics and thermodynamics play a role in the dissolution and decomposition of the thick layer of -Fe4Al13 into the FeAl6 and Fe2Al9 phase. Promoting the IMC dissolution or decomposition by adjusting welding procedures is a promising new way to control the IMC growth and improve the joint strength.

Development of Low Silver AgCuZnSn Filler Metal for Cu/Steel Dissimilar Metal Joining

The microstructure and properties of a Cu/304 stainless steel dissimilar metal joint brazed with a low silver Ag16.5CuZnSn-xGa-yCe braze filler after aging treatment were investigated. The results indicated that the addition of Ce could reduce the intergranular penetration depth of the filler metal into the stainless steel during the aging process. The minimum penetration depth in the Ag16.5CuZnSn-0.15Ce brazed joint was decreased by 48.8% compared with the Ag16.5CuZnSn brazed joint. Moreover, the shear strength of the brazed joint decreased with aging time while the shear strength of the AgCuZnSn-xGa-yCe joint was still obviously higher than the Ag16.5CuZnSn joint after a 600 h aging treatment. The fracture type of the Ag16.5CuZnSn-xGa-yCe brazed joints before aging begins ductile and turns slightly brittle during the aging process. Compared to all the results, the Ag16.5CuZnSn-2Ga-0.15Ce brazed joints show the best performance and could satisfy the requirements for cost reduction and long-term use.

Microstructure characterization and properties of carbon steel to stainless steel dissimilar metal joint made by friction welding

Abstract Dissimilar metals of 1045 carbon steel and 304 stainless steel are joined successfully by friction welding. The microstructure variation and mechanical properties are studied in detail. The weld interface can be clearly identified in central zone, while the two metals interlock with each other by the mechanical mixing in peripheral zone. On carbon steel side, a thin proeutectoid ferrite layer forms along weld interface. On stainless steel side, austenite grains are refined to submicron scale. The δ-ferrite existing in stainless steel decreases from base metal to weld interface and disappears near the weld interface. Severe plastic deformation plays a predominant role in rapid dissolution of δ-ferrite compared with the high temperature. Carbide layer consisting of CrC and Cr23C6 forms at weld interface because of element diffusion. Metastable phase CrC is retained at room temperature due to the highly non-equilibrium process and high cooling rate in friction welding. The fracture appearance shows dimple fracture mode in central zone and quasi-cleavage fracture mode in peripheral zone. Further analysis indicates that welding parameters govern tensile properties of the joint through influencing the thickness of carbide layer at weld interface and heterogeneous microstructure in thermo-mechanically affected zone on carbon steel side.

Strength Prediction of Aluminum–Stainless Steel-Pulsed TIG Welding–Brazing Joints with RSM and ANN

Pulsed TIG welding–brazing process was applied to join aluminum with stainless steel dissimilar metals. Major parameters that affect the joint property significantly were identified as pulsed peak current, base current, pulse on time, and frequency by pre-experiments. A sample was established according to central composite design. Based on the sample, response surface methodology (RSM) and artificial neural networks (ANN) were employed to predict the tensile strength of the joints separately. With RSM, a significant and rational mathematical model was established to predict the joint strength. With ANN, a modified back-propagation algorithm consisting of one input layer with four neurons, one hidden layer with eight neurons, and one output layer with one neuron was trained for predicting the strength. Compared with RSM, average relative prediction error of ANN was <10% and it obtained more stable and precise results.