Ferritic Stainless Steel Joints Research Articles

Study on the Microstructure and Mechanical Properties of Ultrasonic-Assisted TIG Welded 441 Ferritic Stainless Steel Joints

A self-designed ultrasonic-assisted welding platform was built to improve the poor microstructure and properties of conventional TIG welded ferritic stainless steel. The ultrasonic vibration was transmitted to the weld pool through the base metal in the manner of point–surface contact in the optimal position after calculation. The results show that the coarse columnar grains in the welded joint can be transformed into very fine equiaxed grains under ultrasonic vibration, especially the coarse columnar grains near the fusion line where cliff-like refinement occurs. The maximum grain size in the weld seam is reduced from 420 μm to 260 μm, and the average size is reduced by 60%. At the same time, the grain orientation tends to be harmonized. The microhardness of the welded joint is greatly improved on the whole, and the softening of the heat-affected zone caused by grain coarsening is effectively inhibited. Compared with the welded joints without ultrasonic assistance, the tensile strength and yield strength can be increased by 61 MPa and 47 MPa, respectively, under 130 W ultrasonic vibration. By strengthening the weak part of the welded joint, the weldability and toughness reserve of 441 ferritic stainless steel can be significantly improved.

Improving Plasticity of Ferritic Stainless Steel Welded Joints via Laser Spot Control.

The plasticity of welded 441 ferritic stainless steel joints was controlled by varying the laser beam spot diameter during laser welding. A stainless steel plate thickness of 1.2 mm was used. The microstructures of the welded joints were analyzed for various spot diameters. The elongation of breaks and the reduced area of tensile specimens were analyzed to study the effects of spot diameter on plasticity of the welded joints. The results showed that the weld melt width and weld column crystal size increased with the spot diameter, but isometric crystals in the center of the weld were gradually reduced. Increasing spot diameter resulted in decreased tensile strength, elongation after breaks, and area reduction. So the parameter must be controlled during the laser welding.

Numerical investigation of the influence of friction stir welding parameters on the microstructure of AISI 410S ferritic stainless steel joints

Stainless steels are widely used in industry due to their corrosion resistance properties. Ferritic stainless steels are cheaper than austenitic steels because the former do not contain nickel, an expensive alloying element. However, when ferritic stainless steels are used in manufacturing industries, they undergo microstructure transformations that can result in corrosion. Furthermore, the conventional welding processes that are most commonly used can also cause microstructural changes, such as high grain growth, due to the high thermal inputs applied, and precipitation of deleterious phases. On the other hand, Friction Stir Welding (FSW) avoids such problems due to its intrinsic features and has, therefore, become a viable option for the welding of ferritic stainless steels. This technique imposes high deformation rates, enough heat to soften the material and provides the necessary conditions to promote dynamic recrystallisation and, consequently, prevent the grain growth that occurs in conventional welding. The current investigation is clearly justified due to the vast potential of ferritic stainless steels in the industry using FSW. The main goal of this work is to simulate the FSW process, analyse the possible structural changes in the material and provide the factors that most influence the quality of welds when using this process, such as temperature, strain rate, and changes in the viscosity of the material. The results were able to predict the regions with the smallest grain sizes due to dynamic recrystallisation. Furthermore, the calculated Zener-Hollomon values could be directly linked to the grain size: when the Zener-Hollomon parameter increases the grain size decreases.

Microstructure characteristics and mechanical properties of the thin-plate AISI 430 ferritic stainless steel joints by interrupted pulsed arc welding

The feasibility of the interrupted pulsed argon arc welding (IPAW) of the 0.5 mm-thick AISI 430 ferritic stainless steel (FSS) was studied. The results showed that the sound appearances of the butt joints were obtained by the IPAW under different welding parameters. Two joining modes were obtained: (1) typical fusion pool structure with continuous coarsen columnar grain by short interrupted time and low welding speed; (2) snowflake-shape melting pool structure with relatively independent radially grew columnar grain by long interrupted time and high welding speed. The fusion zone (FZ) and heat-affected zone (HAZ) of the joints showed higher microhardness compared to the base metal because of the carbide precipitation and martensite transformation. The joint with a typical fusion pool structure fractured at the fusion zone with a low tensile strength and elongation rate because the weak bonding region between the columnar grains was perpendicular to the tensile direction. The joint with the snowflake-shaped structure displayed a high tensile strength and elongation rate, which was fractured at the BM, as a result of the randomness of the intergranular bonding interface to the tensile direction caused by dendritic radial growth.

Effect of beam oscillation on the mechanical properties of fiber-laser-welded thin-plate X2CrTiNb18 ferritic stainless-steel joints

This study adopted fiber laser welding (FLW) and oscillating fiber laser welding (OFLW) to weld 1.2 mm-thick X2CrTiNb18 ferritic stainless steel (FSS) in the form of square butt joint. The microstructure and mechanical properties of two types of joints were characterized and compared. The results showed that beam oscillation had a marginal effect on the unidirectional tension properties of the joints. However, the plasticity and fracture toughness of the joint were markedly increased. The beam oscillation changed the morphology and microstructure of the weld. It transformed the outer profile of the weld cross-section into an inverted trapezoid, and formed an equiaxed grain zone in the weld. Beam oscillation decreased the angle between the growth direction of columnar crystals around the equiaxed grains and the weld centerline, which improved the deformation coordination of the grains. The plasticity and fracture toughness of X2CrTiNb18-FSS joints were also improved accordingly.

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.

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.

Metallurgical and Mechanical Properties Variation Along the Thickness of Electron Beam Welded Ferritic Stainless Steel Joints After Postweld Heat Treatment

Metallurgical and Mechanical Properties Variation Along the Thickness of Electron Beam Welded Ferritic Stainless Steel Joints After Postweld Heat Treatment

Microstructure and mechanical properties of gas metal arc welded AISI 430/AISI 304 dissimilar stainless steels butt joints

Nowadays, there is an increasing demand for the use of joining dissimilar metals in various industrial applications owing to the economic benefits and better joint performance. Ferritic stainless steel grades is a good alternative for austenitic ones in several applications as they display higher ductility and strength as well as better corrosion resistance in chloride environments. However, the poor ductility and low impact toughness of ferritic stainless-steel welded joints limit their wide-spread application. Thus, the demand for joining dissimilar ferritic and austenitic stainless steels is ever increasing in several engineering applications in various industries such as nuclear power plants, coal fired boilers, automobile manufacturing industry, chemistry and petro-chemistry industries, etc. Therefore, successful joining of these two different types of stainless steel grades using conventional fusion welding methods is rather important. In this study, the weldability of AISI 430 ferritic and AISI 304 austenitic steel plates using gas metal arc welding and the effect of heat input on microstructure and the mechanical properties were investigated. For this purpose, AISI 430 and AISI 304 plates with a thickness of 5 mm were joined using different heat input values. The microstructures evolved in the weld region of the joints and their mechanical properties were determined by detailed optical microscopy investigations, micro-hardness measurements and tensile tests. Thus, the influence of the heat input on the weldability of these two different stainless-steel plates using gas metal arc welding was also studied.

Investigation on aisi 430 ferritic stainless steel weldment by Tig, Mig welding and continuous drive friction welding

This work describes the study conducted on the macrostructure, microstructure and Tensile strength characteristic of AISI 430 Ferritic stainless steel joints by TIG Welding, MIG Welding and Friction Welding. A detailed analysis was conducted on mechanical property by ANOVA for each of the weldment. The output of the investigations exhibits that the weldment made by MIG has the high tensile strength (580 MPa) than the weldment made by FW (536 MPa) and TIG (492 MPa). The influence of process parameters on mechanical characteristics of weldment by MIG, TIG and FW were individually discussed. The fracture surface analyzed using SEM and found that FW weldment free from defects like carbide precipitation, stress corrosion cracking, sigma phase formation, high heat affected zone, joint distortion were usually occurs in stainless steel weldment by TIG and MIG. The microstructure of the weldment by MIG and TIG is found to be heterogeneous and the same is found by schaeffler diagram.

Galvanic corrosion behaviors of the low-carbon ferritic stainless steel ERW (electrical resistance welding) joint in the simulated seawater

PurposeThe purpose of this paper is to focus on the galvanic corrosion behaviors of the low-carbon ferritic stainless steel electrical resistance welding (ERW) joint in the simulated seawater.Design/methodology/approachThe electrochemical methods such as electrochemical noise, galvanic current and TOEFL polarization curve tests were used to study the galvanic corrosion behaviors of ERW joints of low-carbon ferritic stainless steel in simulated seawater. On this basis, a reliable accelerated corrosion method was developed.FindingsThe corrosion type of the base metal and joint is the typical local corrosion. The order of corrosion resistance from strong to weak is: weld zone > base metal > low-temperature heat-affected zone (HAZ) > high-temperature HAZ. The results of constant current-constant potential accelerated corrosion test show that after constant current-constant potential accelerated corrosion, the joints present a typical groove corrosion pattern. The groove initiating area is located in the HAZ, and the corrosion degree in the weld zone is relatively light, which is consistent with the electrochemical test results.Originality/valueThis paper has clarified the galvanic corrosion behaviors of low-carbon ferritic stainless steel ERW joints. Moreover, a reliable accelerated corrosion method for the low-carbon ferritic stainless steel ERW joint has been developed.

Microstructure and mechanical properties of AISI 430 ferritic stainless steel joints fabricated by cold metal transfer welding

AISI 430 ferritic stainless steel joints were fabricated using ER308L austenitic filler metal via cold metal transfer welding technique. The weld metal consisted of ferrite and austenite, and the heat affected zone (HAZ) can be divided into coarse and fine grain zones. The precipitation of carbides, the formation of martensites at ferrite grain boundaries (intergranular martensites) and the growth of ferrite grains occurred in the coarse grain zone of HAZ. The content of intergranular martensite and precipitated carbide increases with the increase of heat input. The microhardness values increased from the weld metal to the coarse grain zone of HAZ, and decreased significantly in the fine grain zone. The increase of microhardness value from the weld metal to the coarse grain zone of HAZ is mainly due to the formation of a large amount of intergranular martensite and intragranular carbides. The microhardness of the base metal was lower than that of weld metal and HAZ. The welded joints showed good tensile properties and the fracture was located at the base metal for all samples. The fracture surface with uniformly distributed dimples indicated the typical ductile fracture feature.

Microstructural Development and Mechanical Properties of Friction Stir Welded Ferritic Stainless Steel AISI 409

This work investigates the effect of friction stir welding process parameters (rotation rate and traverse speed) on the microstructural evolution of friction stir welded (FSWed) ferritic stainless steel (FSS) AISI 409. Optical microscope, scanning electron microscope and electron backscattering diffraction are used to quantitatively assess the development in grain structure and texture. The microstructural development suggested that thermo-mechanical deformation occurs in the stir zone within the austenite/ferrite phase region, ultimately transforming upon cooling into bainitic/ferritic microstructure. The fraction and size of the bainitic/ferritic grains are found to vary through the thickness of the joints. High fractions of coarse ferritic grains are found near the top of the stir zone, and low fraction of fine ferritic grains is found near the bottom of the stir zone. This bainitic/ferritic grain structure resulted in an increase in the hardness of the stir zone by about 74% relative to the base material. The tensile strength of the FSWed FSS joints is almost at the same level of the base material with reduction in the ductility as a result of the increased hardness of the weld zone.

Effects of melting-mixing ratio on the interfacial microstructure and tensile properties of austenitic–ferritic stainless steel joints

In this study, the microstructure and mechanical properties of dissimilar austenitic–ferritic stainless steel joints welded by gas tungsten arc welding were investigated. Different offsets of the tungsten electrode's tip from the centerline of the assembled workpieces were used to obtain different elemental melting-mixing ratios. In tensile tests, two failure modes were found: the weld/workpiece interface failure mode (low strength and ductility) and the AISI 430 base metal failure mode (high strength and ductility). With a large offset (≥0.5mm) toward the AISI 304 side, additional elemental Ni was melted into the welding pool, which changed the solidification mode from ferritic to ferritic–austenitic. This leads to a dramatic microstructure and local property change at the weld/workpiece interface. The local stress–strain curves of various heat-affected zones from different joints were obtained by the digital image correlation technique. This technique showed that the steep local microstructural and mechanical property transition of the dissimilar austenitic–ferritic joints will lead to failure at the weld/workpiece interface.

Impact Toughness and Fracture Structure about Welded Joints of Low Chromium Nickel Ferritic Stainless Steel Containing Ce/Ti

In order to improve the impact toughness and reduce inclusion, rare earth element Ce and stable element Ti are added in the low chromium nickel ferritic stainless steel welded joints and heat treatment. The Charpy test and tensile test are carried out and fracture structure are analyzed. The results show that when the ratio of Ce is 0.24% and Ti is 0.72% in welded joints of ferritic stainless steel, the mechanical properties is the best. The impact energy of welded joint is 9.4 times more than the samples without Ce and Ti, the impact toughness is also increased by 123.6% after heat treatment and the tensile strength increases by 41.9% The fracture structure is main ductile fracture and dimple, the shape of dimples is parabolic. The dimple is large and deep, and in the bottom of dimple has second phase particles. There is a few cleavage facets and river patterns in the fracture. After thermal cycling, the number of oxide particles reduce and the second phase particles are refined, so the impact toughness is improved.

Improving mechanical performance of resistance spot welded joints of AISI 409M steel by double pulse current

Abstract This study aims to investigate the effect of double pulse current in improving the mechanical performance of resistance spot welded joints of AISI 409M ferritic stainless steel. Mechanical performance was evaluated in terms of load bearing capacity and energy absorption capacity of the joint. Samples were resistance spot welded with different values of double pulse current and the corresponding values of failure peak load and failure energy were measured and compared with that of samples welded with single pulse current alone. It was found that the mechanical performance of spot welded joint of AISI 409M steel could be improved by the application of double pulse current.

An experimental study of nitrogen gas influence on the 443 ferritic stainless steel joints by double-shielded welding

This study addressed the comparison of microstructures and mechanical properties of gas tungsten arc welding (GTAW) of 443 super pure ferritic stainless steel which are protected by three different kinds of shielding gas during welding process: pure argon, argon in the inner layer combined with nitrogen in the outer layer (simple double-layer gas), and argon-5 %nitrogen in the inner layer combined with nitrogen in the outer layer (mixed double-layer gas). As a result, in the center of the welds protected by nitrogen and argon, it formed equiaxed grains which achieving the purpose of grain refinement, while there were all columnar grains in the weld protected by pure argon. The experimental results showed that the depth/width ratio of the welds shielded by simple double-layer gas had been increased. Additionally, with the addition of nitrogen in the shielding gas, the hardness and impact toughness of the weld metal and heat-affected zone (HAZ) were improved when the heat input was the same. The relationships between microstructures and mechanical properties of 443 ferritic stainless steel joints were studied by optical microscope and scanning electron microscope combined with energy-dispersive spectrometer.

Dissimilar spot welding joints of AZ31-443 ferritic stainless steel with cover plate

Magnesium alloy AZ31B sheets and 443 ferritic stainless steel were welded using the technique of resistance spot welding with cover plates under relatively low welding current condition. The interface layer can produce, and the molten Mg can wet the surface of the interface layer of Fe-Al intermetallic compound. Metallurgical study of spot joints shows the cracks situated in only sideway of AZ31 weldment in nugget under long welding time. The cause of cracks considering the Fe-Mg equilibrium phase diagram is associated with the possible thermal behavior of various elements in nugget during spot welding process. The almost amount of reaction product FeAl3 somewhere near the interface can produce almost vertical tension stress, resulting in parallel crack. The tensile strength of the spot joint increases at first and decreases afterward.

Investigation of Microstructure and Mechanical Properties of Resistance Spot Welded Dissimilar Joints Between Ferritic Stainless Steel and Weathering Steel

Resistance spot welding is widely used in automobile and rail car manufacturing industries. In this research work, resistance spot welded dissimilar joints of ferritic stainless steel and weathering steel sheets is investigated for mechanical and metallurgical properties. Ferritic stainless steel AISI 409M and weathering steel corten A (ASTM A 242) of 2mm thickness were used in this work. Spot welding was done at different current values, keeping other parameters such as electrode force, electrode tip diameter and weld time as constant. Test specimens were subjected to tensile shear test and micro hardness test to assess the mechanical properties of the weld joints. The influence of welding current on nugget growth, fusion zone hardness, peak load, and failure energy and failure mode during tensile shear test, was investigated at various current ratings. The results showed that, with increasing value of current, peak load increased correspondingly. Nugget shape was found to be near symmetrical. Nugget diameter was found to be increasing with increase in current, in expulsion free welds. Interfacial mode of failure was noticed at low current values, whereas, at higher current values, pull out mode of failure was observed. Presence of martensite was observed in the fusion zone. Micro hardness values at fusion zone were found to be more than that of both heat affected zones and base metals.

Mechanical Properties and Microstructure of Resistance Spot Welded Joints of AISI 409M Ferritic Stainless Steel

Resistance spot welding is widely used as a sheet metal joining process, especially in automotive and rail coach manufacturing industries. Ferritic stainless steel (FSS) is used for structural applications in these areas, owing to its superior corrosion resistance compared to conventional carbon steels. In this paper, mechanical properties and microstructure of resistance spot welded FSS joints to grade AISI 409M was investigated. Tensile shear test and micro hardness test were carried out to assess the mechanical properties and failure characteristics of weld joints. Microstructure was evaluated with optical microscopy. The effect of welding current on nugget growth, peak load, fusion zone (FZ) hardness, failure energy and failure mode were analyzed at various current ratings, keeping electrode force, weld cycle time and electrode tip diameter as constants. The results showed that, with the increment in welding current, tensile shear strength increased. Nugget diameter was found to be increasing with increase in current, in expulsion free welds. At low currents, failure mode was found to be interfacial and the pull out mode of failure occurred, at relatively higher current values. Average FZ hardness was found to be more than that of base metal (BM) but less than that of maximum hardness at heat affected zone. Grain enlargement was noticed at high temperature heat affected zone. FZ microstructure consists of predominantly columnar ferrite. Failure occurred at the BM region in all the samples welded above 10 KA current.