Ferritic Stainless Steel Welds Research Articles

Optimization and Evaluation of Mechanical and Electrochemical Properties of Ferritic Stainless Steel Welding Using Taguchi Design

The main objective of this work is to optimize welding parameters of AISI 430 FSS welds, focused to minimization of ferrite grains size using Taguchi’s design. Two input parameters of speed and welding current; were chosen to select the minimum grain size and to ascertain their effects on ferrite grain size. ANOVA method was used to evaluate the influence of varying factors on the overall quality of welds. Optimal combination of the parameters were be predicted by S/N analyses, it was accessed on employing an 80 A with 6mm/s. Experimental characterizations of optimum weld joint were performed by using tensile test assisted by image correlations, optical and electronic microscopy. As a result, welding speed had the main influence on grain size by 84.30%. Optimum welding parameter offered finest microstructure with low rate of martensite precipitates in both fusion zone and heat affected zone, and best combination of strength and ductility, it presented a homogeneous distribution of tensile stresses that caused a ductile fracture in base material. ,it is found that that optimized welding parameters permit to give greater resistance to corrosion, which exhibit a lower corrosion current, indicating that coarse ferrite grains are more susceptible to corrosion compared to fine grains.

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.

Understanding and Controlling the Weld Microstructure of Steels

In this article, selected studies are reviewed with a focus on the analysis of microstructure development in steel weld metals. In the study of austenitic stainless steel weld metals, microstructure development in the primary ferrite solidification mode (FA mode) was clarified and related to why FAmode welds are resistant to hot cracking. In studies of duplex stainless steel weld metals and high-Cr ferritic stainless steel weld metals, nitrogen-driven microstructure development and TiN-assisted grain refinement, respectively, were described, and discussions about the mechanism of equiaxed grain formation in the weld metals were added in the latter. In the study of low-alloy steel weld metals, the roles of titanium oxide and titanium nitride (TiN) inclusions on intragranular ferrite formation and the refinement of weld microstructure were described based on crystallographic analysis and the first principles calculation. At the end, the potential importance of the application of different multiscale, multiphysics simulations to welding research was pointed out.

Application of the heat treatment in the welding process of ferritic stainless steels – causes and effects

This paper aims to analyse the application, importance and impact of heat treatment operations used in ferritic stainless steel welding processes on the properties of the welds obtained. In addition, the article aimed to formulate the main problems that occur during the welding process of ferritic stainless steels, including, in particular, the phenomenon of ferrite grain growth due to thermal processes.The analysis of the available literature covered issues related to heat treatment processes used in the welding of ferritic stainless steels, taking into account the issue of the growth of the ferrite grain under the influence of heat supplied during welding and the possibility of heat treatment of the obtained welds. The analysis also included determining the possibility of inhibiting the growth of ferrite grains by using elements such as titanium, niobium, and molybdenum, thus improving the strength properties of welds.Organisation of knowledge in the field of the impact on the mechanical properties of ferritic stainless-steel welds and heat treatment processes used before, during, and after welding.Properly selected parameters of the welding process of ferritic stainless steels, especially the amount of heat input, together with appropriate heat treatment parameters, should improve the mechanical properties of ferritic stainless steels.The analysis of the possibility of a wider application of ferritic stainless steels allowed to draw one of the main conclusions stating that the limited possibilities of using ferritic stainless steels in heavy industry are related to their high susceptibility to ferrite grain growth under the influence of high temperature during welding and, consequently, decreases in strength properties of welding joints made of ferritic stainless steels. Additional heat treatment operations are introduced before, during, or after the sapping process to improve their mechanical properties.

Influence of Filler Material on the Microstructural and Mechanical Properties of 430 Ferritic Stainless Steel Weld Joints

Tungsten Inert Gas (TIG) welding is a commonly used welding technique for ferritic stainless steel, due to its ability to produce high-quality, clean, and precise welds. This welding method provides excellent control over the heat input, making it suitable for thin-walled, high-alloy materials such as ferritic stainless steel. The purpose of this study was to investigate the effect of using two different filler materials, 310 (austenitic) and 410 (ferritic), on the microstructural and mechanical properties of Tungsten Inert Gas (TIG) weld butt joints of 430 ferritic stainless steel (FSS). The results showed that the choice of filler material significantly impacted the dilution percentage, the chromium-nickel equivalent ratio, microstructure, microhardness, and tensile characteristics of the welded joint. The use of 310 filler resulted in a columnar microstructure, whereas the use of 410 filler resulted in a ferritic (acicular ferrite) microstructure with the presence of martensite and austenite. The sample welded with 410 filler demonstrated superior mechanical properties compared to the sample welded with 310 filler. These findings emphasize the importance of selecting the appropriate filler material in order to achieve the desired microstructural and mechanical properties in 430 FSS welded joints.

Novi nalazi o koroziji feritnih varova od nerđajućeg čelika - pregled

This study covers the review of the degradation of ferritic stainless-steel weldments between 2015 and 2022. The industrial and automotive sectors make extensive use of ferritic stainless steel (FSS) due to its superior oxidation and corrosion resistance, low price, high thermal conductivity, and low thermal expansion. However, it has been reported that ferritic stainless steel is harder to weld than austenitic stainless steel and that doing so would probably result in a weaker welded joint owing to the coarsening of grains high welding temperatures. According to past research, the amount of heat applied during the welding procedure affected how soon the FSS (409 M) weldment degraded after being exposed to NaCl (3.5%) medium. The coarsening of the grains was considered to be the cause of this. When the shielding gas' CO2 content increased, the intergranular corrosion of the FSS weld metal was found to increase. Welds made with the ER430LNb filler metal had significantly lower intergranular corrosion of FSS (AISI 441) than those made with the ER430Ti filler metal. It was discovered that boiling Cu-CuSO4 - 50% H2SO4 solution increased the corrosion rate for the FSS (AISI 430) weldment more than boiling 40% HNO3 Solution. Weldments made of FSS (AISI 430) were found to be negatively affected by the CuCuSO4 - 50% H2SO4 environment in terms of intergranular corrosion attack.

Microstructural and Statistical Investigation on Dissimilar Friction Stir Spot Welding of Austenitic and Ferritic Stainless-Steels

The increasing use of austenitic and ferritic stainless steel sheets, especially in the power plant industry, highlights the importance of research into the mechanical and metallurgical properties of these joints. Friction stir spot welding of these sheets was investigated using full-factorial experimental design. Considering the three main parameters of rotational speed, plunge depth and dwell time, each of which had three levels, led to 27 tests. The highest strength (6400 N) was related to sample number 8 with parameters 900 rpm, 2.7 mm and 20 s and this sample was selected for microstructural studies. The metallurgical properties of this sample were investigated and the microstructures of heat affected zone, thermos-mechanically affected zone and stir zone were extracted. Thermomechanical changes during the process and especially dynamic recrystallization in the stir zone due to heat application and severe plastic deformation by the process reduce the grain size, which in turn increases the bond strength. Using analysis of variance, it was found the direct effect of rotational speed and plunge depth on the lap shear strength is significant. The interaction effect of rotational speed and plunge depth and also, rotational speed and dwell time on the response were significant.

Tailoring the Process Parameters for Ti-Stabilized 439 Ferritic Stainless Steel Welds by Cold Metal Transfer Process

Tailoring the Process Parameters for Ti-Stabilized 439 Ferritic Stainless Steel Welds by Cold Metal Transfer Process

Effect of titanium content on solidification structure of ferritic stainless steel gas-tungsten and gas-metal arc welds

Ferritic stainless steel is utilized to fabricate automotive exhaust systems using a ferritic weld metal. Ductility of the weld metal is higher if its microstructure contains a significant proportion of equiaxed grains. The formation of equiaxed (rather than columnar) grains is favoured by a higher titanium weld metal content. In this study, the Ti content of ferritic stainless steel weld metal was changed by using Ti-free (Type 436) and Ti-containing (441) ferritic stainless steel as base metals. The metal-cored welding consumable contained 0.4% Ti. Gas-tungsten arc welding and gas-metal arc welding processes were compared. The weld metal Ti content ranged from zero to 0.5% Ti, as determined from scanning electron microscopy supplemented by inductively coupled plasma optical emission spectroscopy. Cross-sections of the weld beads were subjected to point counting (to estimate the fraction of equiaxed grains) and image analysis (to estimate the average grain size). Point counting proved to be more reliable. The fraction of equiaxed grains was sensitive to the Ti content, but not to the welding process. Below 0.4% Ti, the fraction of equiaxed grains gradually increased with an increase in the weld metal Ti content; above 0.4% Ti, the fraction of equiaxed grains rapidly increased with increasing Ti content. The transition in behaviour at 0.4% Ti corresponded to a Ti content at which Ti-rich precipitates became stable at the estimated liquidus temperature of the weld metal.

A Novel Approach to Inhibit Intergranular Corrosion in Ferritic Stainless Steel Welds Using High-Speed Laser Cladding

Ferritic stainless steels are prone to localized corrosion phenomena such as pitting corrosion or intergranular corrosion, in particular when jointed by fusion welding processes. State-of-the-art techniques to avoid intergranular corrosion mainly consist of alternating alloy concepts or post-weld heat-treatments—all of which are associated with increased production costs. Hence, the present investigation seeks to introduce a novel approach for the inhibition of intergranular corrosion in ferritic stainless steel welds through the use of high-speed laser cladding. Here, vulnerable sites prone to intergranular corrosion along the weld seam area are coated with a chemically resistant alloy, whereby an overlap is achieved. Optical and electron microscopy as well as computer tomography and tensile tests reveal that the detrimental effects of intergranular corrosion in both stabilized and unstabilized ferritic stainless steel are substantially reduced. In addition to that, the effects of varying overlap widths on the identified corrosion phenomena are studied. Moreover, the resulting dilution and precipiation phenomena at the clad–sheet interface are thoroughly characterized by electron backscatter diffraction and energy dispersive X-ray spectroscopy, whereby interrelationships to corrosion resistance can be drawn. As a result of this investigation, the number of techniques for the inhibition of intergranular corrosion is enlarged, and substantial cost-saving potentials in the manufacturing industry are unlocked.

Behavior of weld pool convection and columnar-to-equiaxed grain transition in gas tungsten arc welds of ferritic stainless steels with different aluminum contents

Abstract In gas tungsten arc welding (GTAW), columnar grains typically grow from the fusion line of a weld to its centerline because of high temperature gradient and small growth rate. This columnar grain often causes premature failure during bending or expansion in the center of the fusion zone. Equiaxed grains, on the other hand, reduce the occurrence of cracks and improve the ductility, strength, and toughness in the fusion zone. Microstructural solidification has a significant effect on the mechanical properties; the columnar-to-equiaxed grain transition (CET) is one factor that significantly improves fusion zone mechanical properties. During GTAW, a thermal gradient occurs on a molten pool owing to the uneven mixing of the elements or the unequal compositions of the base materials, leading to a non-uniform surface tension. This is called the Marangoni effect, which creates a flow inside the molten metal and affects the overall weld shape. The Marangoni effect is associated with a coefficient called the surface tension gradient or the thermal gradient of surface tension that affects the direction of molten metal flow. The content of oxygen and flux affect the surface tension gradient. If the content of oxygen and flux are high, the surface tension gradient becomes positive, with a narrow and deep-penetrating pool. In this study, various experiments and a numerical simulation were performed to analyze the weld pool behavior and CET in GTA welding of ferritic stainless steels with aluminum contents of 100 and 300 ppm. In the experiment, 300 ppm of aluminum was observed to have a wider bead width than that observed for the 100-ppm sample; further, the growth of equiaxed grains in the centerline was promoted. In the numerical simulation, it was confirmed that when the aluminum content was 300 ppm, the outward flow occurring in the arc center formed a wide and shallow penetration. Furthermore, it was revealed that aluminum combines with oxygen to form aluminum oxide, thereby reducing the oxygen content. Therefore, as the aluminum content increased, the surface tension gradient was observed to become negative and affect CET.

Microstructure and mechanical properties of AISI 439 ferritic stainless steel welds without filler metal

In literature, it has been reported that a current intensity lower than 120 A leads to a microstructure without grain growth in the heat affected zone (HAZ) of ferritic stainless steel welds. Nevertheless, in technical literature there is little information about the reduction in mechanical properties of ferritic stainless steel welds without filler metal due to grain growth in the HAZ. In this work, thin plates of ferritic stainless 439 steel were welded using pulse current gas tungsten arc welding (P-GTAW) without filler metal. The microstructures in the HAZ were analyzed and the mechanical properties on the welded joint were found by tensile test. This was carried out by cutting samples for the tensile test from the weldments and then tested in a universal testing machine. The fracture surface were observed using scanning electron microscope.

Microstructure and Mechanical Behavior of AISI 430 FSS Welds Produced with Different Elemental Metal Powder Addition

In this study the effect of the Titanium and aluminum powder addition on microstructure and mechanical properties of AISI 430 ferritic stainless steel welds produced by gas tungsten arc welding was investigated. It’s observed that the addition of aluminium (Al) or titanium (Ti) reducing the grains size, increase the equiaxed grains fraction and improve the mechanical properties with varying degrees. While the addition of mixture (Al+Ti) leads to better improving in mechanical properties and reducing of grains size up to 85 %. The details of tensile tests, optical microscopic observations, microhardness, tensile test and Scanning electron microscopy (SEM) fractography, are discussed.

Effect of shielding gas composition on intergranular corrosion of stabilized ferritic stainless steel GMA welds

The effect of shielding gas composition on intergranular corrosion of the fusion zone formed by bi-stabilized ferritic stainless steel plates (AISI 441) and ER430Ti and ER430LNb filler metals during gas metal arc welding was investigated. Double loop electrochemical potentiokinetic reactivation tests were conducted to examine the influence of the shielding gas content (Ar + 2%O2, Ar + 8%CO2 and Ar + 25%CO2) on intergranular corrosion of the ferritic stainless steel welds. It was possible to observe an increase in the tendency toward sensitization with the increase in the CO2 content in the shielding gas, especially with the ER430Ti filler metal. Analysis of the formed precipitates by means of optical microscope, scanning electron microscope an energy-dispersive X-ray spectroscopy allowed to notice that high levels of CO2 blended in the shielding gas increase the intergranular precipitates and lead to significant intergranular corrosion, which was induced by the Cr-depletion zone formation, especially for the welds produced with the ER430Ti filler metal.

Early stage oxidation behavior of Al‐ and Si‐alloyed stainless steels as well as Ni‐based alloys in air at elevated temperatures

Several alloys including Al‐alloyed austenitic and ferritic stainless steels, Ni‐based alloy and Si‐alloyed ferritic stainless steel were annealed at 550, 750, and 950 °C for up to 700 h. AISI 347HFG and 10CrMo910 were used as reference materials. Weight gain was measured and the samples were analyzed with SEM/EDS and XRD. Materials having high enough Al‐content performed best due to ability to form a continuous protective Al2O3‐oxide layer on their surface at elevated temperatures. Lower Al‐content materials were not able to form a continuous protective Al‐oxide on their surface and suffered from accelerated internal Al‐oxide formation due to alloying elements. Si‐alloying improves the oxidation resistance of the studied materials and their performance was practically in the same level as that of the best Al‐alloyed materials. In Al‐alloyed materials the crystallinity of Al2O3 on ferritic stainless steel weld metal was higher than that on welded and wrought austenitic stainless steels.

Behaviour and influence of slag islands in ferritic stainless steel welds

The nature and detailed behaviour of slag islands in ferritic stainless steel welds have been analysed via weld pool video imaging, welding parameter monitoring, scanning electron microscopy, and in situ optical emission spectroscopy. The aim of the investigation was to understand how changes in weldability in 31 commercial very low-sulphur steels of EN 1.4509 (“441”, S43940) can be attributed to in situ slagging phenomena. The results showed that three slagging mechanisms can co-exist and alter the properties of the weld pool. Very stable, up to O 3 mm, aluminium-based, titanium-containing glassy films were observed directly underneath the welding arc in steels with excessive aluminium deoxidation. Such films could occasionally maintain their stability throughout the weld cycle. Steels with excessive aluminium deoxidation also showed stable, <O 1 mm, calcium-aluminium-titanium clusters in various places along the weld pool, occasionally on the glassy films, if present. Sudden movement of these clusters to the fusion line led to an irregular fusion line and abrupt changes in the fluid flow. In low-aluminium steels, the majority of slags were rich in calcium and titanium and they accumulated to the rear of the weld pool. Various build-up and breakdown mechanisms of slagging are discussed.

Influences of Energy Input and Metal Powder Addition on Carbide Precipitation in AISI 430 Ferritic Stainless Steel Welds

In the present work, 16% chromium AISI 430 ferritic stainless steel weld produced under different conditions of energy input and metal powder addition using TIG torch melting is investigated for carbide precipitation. A Box Behnken experimental design paradigm is invoked with current, speed and metal powder concentration as the primary variables while type of powder is the categorical variable. The result indicates that for a given concentration of metal powder in the melt pool, the sensitized geometry increases with energy input. Titanium as well as the mixture of aluminum and titanium powders reduces the width of the sensitized zone while aluminum powder increases the width of the zone. Titanium powder prevents the development of completely ditched structure in the high temperature heat affected zone (HTHAZ) whereas aluminum powder accelerates the formation of ditched structure in the HAZ.

Metallurgical response of weld metal to different filler metal and joint design combinations of laser-arc hybrid welded lean duplex and novel ferritic stainless steels

Laser and laser-arc hybrid welding of duplex and ferritic stainless steels is demanding, because microstructure of the welds tends to be highly ferritic. Therefore, filler metal must be used for maintaining corrosion and mechanical properties of the welds. In this study, different filler metals including duplex, basic, and overalloyed austenitic grades were used with laser-arc hybrid method to weld lean duplex 1.4162 and novel ferritic stainless steels grades 1.4622 and 1.4509. Several sets of joint design and welding parameter combinations were used to adjust the amount of filler metal in the weld. The purpose of the trials was to evaluate whether weld metal microstructures (grain morphology, austenite/ferrite balance, etc.) can be modified by using an applicable joint preparation and an “overmatched” filler metal addition. Weld characterization included several research methods such as: Macro- and microscopic examination using light microscope¸ cross-sectional dilution ratio determination from the metallographic cross sections, electron backscatter diffraction method in order to assess austenite, and ferrite phase proportions in the test welds. The effects of used groove geometry, filler metal composition, and content on resulting metallurgical features of the welds are discussed in detail.

Preliminary Outcome on Grain refinement in Ferritic Stainless Steel Welds

Preliminary Outcome on Grain refinement in Ferritic Stainless Steel Welds

페라이트계 스테인리스강 재현 용접 열 영향부의 석출거동 및 열피로 특성에 미치는 구속응력의 영향

Abstract Thermal fatigue life of the automobile exhaust manifold is directly affected by the restraint force according to the structure of exhaust system and bead shape of the welded joints. In the present study, the microstructural changes and precipitation behavior during thermal fatigue cycle of the 18wt% Cr ferritic stainless steel weld heat affected zone (HAZ) considering restraint stress were investigated. The simulation of weld HAZ and thermal fatigue test were carried out using a metal thermal cycle simulator under complete constraint force in the static jig. The change of the restraint stress on the weld HAZ was simulated by changing the shape of notch in the specimen considering the stress concentration factor. Thermal fatigue properties of the weld HAZ were deteriorated during cyclic heating and cooling in the temperature range of 200to 900due to the decrease of Nb content in solid solution and coarsening of MX type precipitates, laves phase, M 6 C with coarsening of grain and softening of the matrix. As the restraint stress on the specimen increased, the thermal fatigue life was decreased by dynamic precipitation and rapid coarsening of the precipitates.Key Words : Thermal fatigue, Ferritic stainless steel, Heat affected zone, Precipitation