Mechanical and Metallurgical Properties of Dissimilar Joining of 304 ASS: A Review

. The mechanical and metallurgical properties of dissimilar joining of 304 stainless steel (SS) and other alloys have been extensively studied in recent years. Stainless steel is a widely used material in various industries such as aerospace, chemical processing and transportation. The austenitic Chromium-Nickel stainless steel AISI 304 provides the best balance of corrosion resistance, endurance, and ductility. Due to the low carbon content, carbide precipitation during welding is less likely. The dissimilar welding of AISI 304 austenitic stainless steel using various welding techniques with various materials was thoroughly reviewed in the current paper. According to the review, the optimum material to use when intergranular corrosion is a concern is AISI 304 austenitic stainless steel. It is also among the best materials usually utilised in the production of components that cannot be heated.


Introduction
Stainless steel is a type of steel that was developed in the 20th century by adding chromium to carbon steels to create a passive protective layer that slows surface erosion.It can be further alloyed with elements like nickel, molybdenum, and titanium to achieve certain qualities as shown in Table 1.There are different categories of stainless steel, including martensitic, ferritic, duplex, precipitation hardenable, and austenitic.[1] Among them, stainless steel 304 is the most popular due to its chemical composition, mechanical properties, weldability, corrosion and oxidation resistance.Stainless steel 304L is recommended to avoid intergranular corrosion in the heat-affected zone.It finds applications in a variety of industries, including food and beverage processing, chemical and petrochemical processing, medical devices, architecture, and construction.Some common applications of SS304 include kitchen equipment, sinks, countertops, piping systems, storage tanks, heat exchangers, pressure vessels, and medical.Austenitic stainless steels are the most common type and are composed of iron, chromium, and nickel, with high levels of these two elements giving them good corrosion resistance.They are non-magnetic and non-hard, though cold working can increase their hardness.They are commonly used in corrosive environments.They are classified into "L" grades, "straight" grades, and "H" grades based on their carbon content, with L grades having less than 0.03% C and H grades ranging from 0.04-0.10%C. [2] High carbon grades are used for tougher, wear-resistant, or high temperature applications but can cause issues in the Heat Affected Zone (HAZ) during welding.
Arc welding is a common method for joining ferrous elements, including austenitic stainless steels.However, issues like chemical inhomogeneities, microporosity, cold laps, micro-fissures, and hot cracks can decrease the quality of the joint.Hot cracking is particularly common in austenitic stainless steels, but the use of filler materials with residual ferrite can help decrease it.[3] Despite the development of suitable filler materials, issues still exist at the root of weldments where the high austenite content of the parent material may dilute the filler material and decrease the amount of retained ferrite, increasing the risk of hot cracking.
Filler materials cannot prevent the formation of chrome carbides in the Heat Affected Zone (HAZ) of austenitic stainless steel during welding, which can make the material susceptible to corrosion.This issue can be addressed through the use of low carbon content and post-weld heat treatment, but these options may not be feasible for all applications.Therefore, the use of "L" grade austenitic stainless steel is recommended in situations where this is a concern.[6]

Review on different Welding procedures of SS304:
The following sections provide a complete overview of welding SS 304 Austenitic Stainless steel using various welding procedures.

Friction welding:
Friction welding offers several benefits, including no melting, excellent repeatability, quick production, and lower power input.It is useful for difficult-to-weld materials and generates less heat damage during the welding process.Friction welding techniques can be used to join different materials, and it is a solid-state joining method that involves rotating one component while applying pressure to the other.[2] High-quality joints can be created with little post-weld machining required.The quality of friction welds is influenced by variables such as friction time, forging time, pressure, rotational speed, and others.
The research conducted by Ozdemir.N, and et al. [1] studied the interface qualities of AISI 304L to AISI 4340 alloy steel friction welds at different rotational speeds.The experiment revealed that the thickness of the plastic deformed zone reduced with increased speed, causing more mass to be thrown away from the welding interface.The study also showed that the tensile strength of the welded samples increased with the width of the complete plastic deformed zone and as the rotational speed increased.The structural integrity was assessed through scanning electron microscopy, and the mechanical characteristics were evaluated using micro hardness and tensile tests.In this study by James, J.A. et al. [2], the properties of friction welded joints of austenitic stainless steel 304 and medium carbon steel AISI 1040 were investigated, comparing the properties of welds with and without a nickel interlayer at different welding parameters.The welding parameters were optimized using three input parameters and three input levels, and the experiments were designed using Taguchi Orthogonal array.The ultimate tensile strength of welds with a nickel interlayer was higher, with a maximum strength of 661 MPa achieved at the highest burn off length of 8 mm.As shown in Fig. 1 the microhardness results showed a decrease in peak hardness at the interface due to the presence of nickel, resulting in a reduction in the precipitation of chromium carbide.

GTAW/ TIG Welding
Tungsten electrodes are used in TIG.Thorium (Th), Zirconium (Zr), Lanthanum (La), and Cerium (Ce) oxides are typically used to cover this electrode, which increases its ability to transport current and emit electrons.You can use A.C. and D.C.However, straight polarity D.C. is recommended.[4] Because when the polarity is reversed, a significant quantity of heat is produced at the electrode tip, which causes tungsten to diffuse.Argon is the most commonly used shielding gas, while helium is occasionally used.The shielding gases protect the welding zone from atmospheric pollution.Water is used to cool the electrode and prevent tungsten particle diffusion.TIG welding is used to weld reactive metals such as aluminium and magnesium, thanks to the inert gas used.Singh.D. K., and et al. [4] conducted a study on the tungsten inert gas (TIG) welding of stainless-steel grade SS 304 and medium carbon steel EN 8 with different combinations of weld parameters.They observed significant variations in the microstructures of the weld and interface depending on the welding process factors such as current, voltage, and speed.The microstructures ranged from coarse grain distributions to big grains of austenite, and there were two prominent phase boundary relationships 44°〈104〉 and 44°〈114〉, at the phase borders.The impact energy was found to be a function of in-grain disorientation and % δferrite, while the tensile strength was found to be a function of low angle grain boundary fractions.Mixed mode and ductile fractures were observed under tensile deformation, and the distribution, size, and forms of the dimples and micro voids on the cracked surfaces varied.Sharma.P., et al. [5] used A-TIG welding to join P92 steel and 304H austenitic stainless steel plates with Cr2O3, MoO3, SiO2, and TiO2 fluxes.TiO2 was found to provide the best through-thickness penetration.Microscopy, hardness, tensile, and impact toughness tests were conducted to evaluate the quality of the weld joint created using TiO2 flux.The weld joint was found to have produced ferrite stringers, polygonal austenite grains, and untendered martensite in various zones as shown in Fig. 3.The V-notch Charpy impact toughness of the weld joint was lower than that of base metals due to the creation of an untempered martensitic structure.Pandey.C., and et al. [6] studied the effect of welding different grades of austenitic stainless steel SS304L and martensitic P92 steel using autogenous gas tungsten arc welding, followed by conventional and unconventional heat treatment.The heat-treated welded joints were subjected to mechanical testing and microstructural characterization, including Charpy toughness testing, tensile testing, and hardness testing.The study found that unconventional heat treatment resulted in a stabilized microstructure and enhanced mechanical properties, with the best results in terms of Charpy toughness and tensile strength.

GMAW/ MIG Welding
Gas metal arc welding (GMAW) is a welding method that uses an electric arc between a consumable electrode and the work piece to join metals.A gas or gas mixture is supplied externally to protect the arc and molten weld pool.The core concept of GMAW was introduced in the 1920s and became commercially viable in 1948.[7] Initially used for welding aluminium, it was known as metal-inert gas (MIG) welding due to the use of an inert gas for arc shielding.The study by A.P. Johan Singh, and et al. [7] evaluated the fatigue life of Gas Tungsten Arc Welded (GTAW) cruciform joints made of AISI 304L stainless steel with Lack of Penetration (LOP) using standard S-N and crack initiation propagation (IP) techniques.The crack initiation life and crack propagation life were predicted using the local stress-life and fracture mechanics approach, respectively.The expected fatigue lives and the experimental values were contrasted, and it was discovered that joints with LOP = 2 mm for 6 mm thickness plate had considerably longer fatigue lifetimes.Patel, T. M., and et al. [8] have concentrated on improving GMAW process parameters, placing particular emphasis on determining the best welding parameters for penetrating with activated flux.It has been tried to employ activated flux as shown in Fig. 4 to increase the strength of the welding junction and the depth-to-width ratio.It has been discovered that Taguchi provides the best values for process parameters that will improve the performance of the weld joint.MgCO3 was shown to have a noticeable impact on penetration after welding with activated flux, and it also passed tests like the macro test, DP test, X-ray test, tensile test, and impact test.Ayof.M. N., and et al. [9] investigated the customised orbital welding of dissimilar materials made of British Steel (BS) 1387 and Stainless Steel (SS) 304.They used an automated fixed nozzle-rotational jig in gas metal arc welding (GMAW) and evaluated the weldment quality using a non-destructive dye penetrant test.The tensile strength and microhardness were examined to confirm the impact of welding parameter modifications.Response Surface Methodology (RSM) was used in Design of Experiment (DOE) to create a process parameter, and it was found that when arc current and voltage increased and travel speed reduced, the tensile strength and microhardness increased.No significant flaws were found.

SMAW
Lee, W. S., and et al. [10] studied the impact characteristics of shielded metal arc welded (SMAW) joints made of 304L stainless steel at different strain rates ranging from 10−3 to 7.5 × 103 s−1 using a compressive split-Hopkinson bar.They found that the weldments are sensitive to strain rate, and changes in strain rate impact the flow stress, fracture strain, and work hardening rate.The strain rate sensitivity and activation volume vary with strain rate and are related to various work hardening stress levels.The weldments fail due to adiabatic shearing, and the fracture surfaces of the fusion zone and base metal regions are characterized by elongated dimples.The impact stress-strain curves are consistent with the observed dimple features with strain rate.Mishra.D., and et al. [11] conducted a study to create a strong weld between two grades of stainless steel (310 and 304) using shielded metal and gas tungsten arc welding methods.They formed single and double "V" butt joints to test compatibility for the intended purpose as shown in Fig. 5. Weld faults were examined using dye penetrant inspection, which revealed no defects.Tensile testing on the welded specimens showed maximum values of 594 MPa for a double "V" shielded metal arc butt joint and 556 MPa for a double "V" butt joint using gas tungsten arc welding.This study provides insight for selecting an efficient welding procedure for butt welding dissimilar alloys of stainless steel grades 310 and 304 with single or double "V" edges.Fig( 5): (a) single V butt, and (b) double V butt joints [11] Patil.U.S., and et al. [12] investigated the effects of welding current, welding speed, electrode angle, and root gap on performance parameters, such as welding strength, metal deposition rate, and microstructure, when manually(shielded) metal arc welding stainless steel 304 to mild steel 1018.The primary concern when welding these two materials is carbon transfer, which can lead to carbide precipitation and failure of the welded connection.A welding strength of 403 N/mm2 was achieved using a welding current of 85 A, a welding speed of 8 mm/sec, an electrode angle of 30, and a root gap of 0.75 mm.The metal deposition rate was 9.3 gms, and the microstructure showed fewer dendrites of carbide precipitation.

Plasma Arc Welding
The "transferred arc method" or "liquid refrigerated tight nozzle" uses a nonconsumptive tungsten electrode to generate heat through a constrictive arc with the workpiece (non-transferred arc process).Plasma is formed by positive ions, electrons, and neutral gas particles.The plasma produced has a small volume.This method can be used to weld various metals and for plasma coating.[14] Since the workpiece is not part of an electrical circuit, the plasma arc torches transfer from one workpiece to another without igniting their arcs.
In order to find the best Plasma Arc Welding tensile strength parameters, Pargaonkar, H. M., and et al. [13] have conducted research.Following the testing, it was discovered that 230A of current, 28V of voltage, and 740 mm/min of wire feed resulted in the maximum tensile strength of 687.53 MPa.These findings are supported by a confirmation test performed on three samples, for which tensile strengths of 686.14, 680.33, and 682.68 MPa were determined.The ANOVA analysis reveals that, with a contribution of 67.825%, current is the most important factor influencing tensile strength, followed by voltage at 21.92%.Keyhole Plasma Arc Welding (K-PAW) was used by Harish, T. M., and et al. [14] to join 6 mm thick stainless steel 304H.The results of the X-ray radiography confirmed that a sound keyhole weld for the specified parameters was obtained without any flaws and that full penetration was attained in a single pass.According to microstructural analyses, the weld solidified in the Ferrite-Austenite (FA) mode and included 6-7% delta ferrite as shown in Fig. 6.The weld is less prone to hot cracking and sensitization when ferrite is present.Due to the creation of finer grains and a smaller heat-affected zone, keyhole plasma welds demonstrated good strength and toughness in mechanical properties testing and met the requirements for boiler components.The plasma arc welding between SS304 and SS316 was done by Rajesh, K. D., and et al. [15] It describes the effectiveness and improvement of stainless steel's performance in a marine environment.It explains how direct fusion can make superior welds more quickly.The corrosion rate is determined as SS 316, SS 304, and alloy of SS 316 and 304, in that order from low to high.

Laser Spot Welding
Laser spot welding (LSW) is a fast and precise method of laser welding that is suitable for welding heat-sensitive parts such as precision parts, sheet metal, and automotive components.LSW has the advantages of low heat input to the weld, minimal deformation, and a small heat-affected zone (HAZ), which make it a viable option for the manufacturing sector, especially the automobile sector.[16] LSW is known for its high mechanical qualities and repeatability of welds.Shanmugarajan.B., and et al. [16] conducted research on laser welding of incompatible combinations of stainless steel (304) and titanium to increase weld strength and ductility while minimizing hazardous intermetallics.They performed autogenous welds by adjusting laser power, welding speed, and position relative to the joint centre, but were unable to produce crack-free autogenous welds for all parameter combinations tested.The study found that even with high welding speeds or by changing the beam position, the autogenous welds showed extensive cracking as shown in Fig. 7.The use of vanadium as an interlayer failed to produce crack-free joints, but tantalum was able to create a junction with 40 MPa strength.Attar.M. A., and et al. [17] developed a mathematical model for laser welding of dissimilar metal sheets, specifically copper and stainless steel types 304.They used a simulation of the continuous disc laser welding process to estimate the temperature distribution, weld shape, and dimensions of the fusion zone and heat-affected zone.The simulation included six heat flux distribution models, and the results were validated by comparing them to experimental findings.The simulation showed that dissimilar welding resulted in a smaller heat-affected zone and lower temperature at the fusion zone centre due to the higher thermal conductivity of copper.The validity of the simulation was confirmed

Flux Cored Arc Welding
Three welding sequences were adopted without the use of mechanical restraints on the plates.Fig. 8 shows the welding route of each sequence.Three sequences drastically altered the residual stresses, which are produced during the arc welding process as a result of the temperature's direct impact on distortions, according to Rodrigues, L. A. and et al. [18] Robotized FCAW was used to achieve a greater welding velocity (100 cm/min) and a low heat input (0.64 KJ/mm).The behaviour of residual stresses and distortions is significantly influenced by the welding sequences; hence, these effects are closely related.S3 had the lowest residual stresses (86%), distortions (59%), and longitudinal and transversal compressive stresses, respectively.The S3's transverse residual stresses switched from compressive to tensile, and it behaved similarly to the reference plate.

Conclusion:
The following conclusions are reached from the review of welding of AISI 304 Austenitic Stainless steel by various welding processes: The rotating speed is primarily responsible for determining the diameter of the fully plasticized deformed zone region.The tensile strength of the weld zone increases with rotation speed.The tensile strength is inversely correlated with the friction pressure.Tensile strength and bonding time are inversely related.
Untempered lath martensite, PAGBS, and partially tempered martensite are some of the distinct features present in the microstructure of the TIG welded DWJ (dissimilar weld joint).The weld fusion zone has very little precipitation, and the coarse grain precipitation that is there has completely dissolved along the P91 side of the fusion boundary.TiO2 flux induces Marangoni's convection to reverse, which results in depth of penetration.When compared to UHT, the hardness of the DWJ in the as-welded and CHT states changes considerably, although the hardness of the SS304 L base and HAZ is essentially unaltered in either state.
The GMAW (Gas Metal Arc Welding) welding settings had no effect on the weldment's mechanical characteristics.When the arc current and voltage were raised while the trip speed was lowered, the tensile strength and microhardness values increased.As a result, there is a relationship between the welding parameters and the weldment's mechanical characteristics.
An increase in strain rate in SMAW (Shielded Metal Arc Welding) causes a rise in flow stress and a fall in fracture strain.According to SEM data, adiabatic shearing is the primary cause of fracture in welded joints, with cracking happening at an oblique angle of 40 to 50 degrees to the direction of impact.While the welding current is low, the likelihood of carbide precipitation is low, but as the welding current rises, the likelihood of precipitation increases.
When using plasma arc welding, the weldments' increased tensile strength in comparison to the base metal and the percentage of elongation in the tensile specimen meet the requirements to be considered boiler grade materials.
In laser spot welding, the higher the yield stress, the lower the distortion and the greater the storage of residual stress.Dendrites predominated the microstructure of the weld, and the phenomena of sensitization was not seen in the HAZ.The High angle grain boundaries (HAGB) proportion is higher than the LAGB fraction, according to the grain boundary character distribution of the weld.
Better heat transfer from the inside out in FCAW directions results in a smaller influence on the stiffened panels.In this instance, the welding procedure began from the inside out with an alternate simple pass deposition (opposite directions) between the inner stiffeners and both sides for each one of the stiffened panel's four stiffeners.

Fig 1 :
Fig 1: microhardness along the length of specimen.[2] Vivekananthan.M, and et al.[3] have studied the Inertia friction welding as shown in Fig. 2 on stainless steel studies on stainless steel 304 and 410 combination.The effect of process parameter speed, friction time and forging time were studied.More over the joint strength is measured by the tensile test and Hardness of the joints.The following results are drawn from the study: The friction pressure is directly proportional to the tensile strength.The bonding time is indirectly proportional to the tensile strength; The inherent characteristics of stainless steel deformation have strong influence on the interface and consequently on the welding strength.