Chromium Carbide Precipitation Research Articles

Prevention of weld decay in TIG welded AISI 304 steel pipes

Weld decay due to chromium carbide precipitation at grain boundaries in the heat affected zone (HAZ) during TIG welding of austenitic stainless steels. This issue is particularly significant concerning the welding of AISI 304 steels, commonly used in the food industry. Although this problem can be overcome with different methods, there are some restrictions. A novel technique for welding AISI 304 steel pipes is introduced to reduce weld decay and improve the mechanical properties. The use of this technique, which includes faster cooling after welding, significantly minimizes the time of precipitation of chromium carbide. Temperature measurements and microstructural analyses monitor precipitation and the impact of the technique on the mechanical characteristics of AISI 304 steel pipes was assessed through hardness and hoop tensile tests. There was a 6% increase in hardness values observed in the HAZ region. Furthermore, a 16.7% increase in maximum load and a 127.4% increase in elongation. The reduction in chromium carbide precipitation observed in the microstructural analysis was confirmed through the double loop electropotentiokinetic reactivation (DLEPR) test, specifically for assessing intergranular corrosion. With the novel method, there was a 25% increase in corrosion resistance in the HAZ and a 40% increase in the weld zone.

Влияние добавок карбида и борида вольфрама на структуру и микротвердость эквиатомного CrFeNi-покрытия, сформированного короткоимпульсной лазерной наплавкой

A coating based on a single-phase medium-entropy CrFeNi alloy with a face centered cubic structure has good ductility, relatively high anti-corrosion properties, low cost, but insufficient strength for its widespread use. It is assumed that adding strengthening particles in the form of tungsten carbides and borides to the CrFeNi equiatomic coating will lead to an increase in its mechanical properties. This work studies the influence of tungsten carbide and boride additives on the structure and microhardness of a CrFeNi equiatomic coating. The coatings were formed by layer-by-layer short-pulse laser cladding with preplaced powder on a multifunctional laser installation equipped with a solid-state laser with a lamp pump based on an Nd:YAG crystal. The change in phase composition when adding strengthening particles was detected using X-ray diffraction analysis and transmission electron microscopy (TEM). Both methods confirmed the precipitation of Cr23C6 chromium carbide in the deposited coatings. TEM photographs indicate that the precipitated phase is distributed along the grain boundaries of the -solid solution. The study found that the addition of 6 wt. % WC and 3 wt. % WB increases the level of microhardness of the CrFeNi coating by 26 % (from 340±6 to 430±12 HV 0.025). This occurs due to the presence of Cr23C6, WC particles in the structure and possible microdistortions of the crystal lattice of the -phase as a result of doping with tungsten atoms released during the dissolution of tungsten borides and carbides in the process of high-temperature short-pulse laser heating.

Intergranular Corrosion in X39CrMo17-1 – A Review

Abstract The aim of this contribution is to review cases of repeated snap ring failures in large gas turbine engine service due to intergranular attack, or intergranular corrosion, IGC, and to shed some light on metallurgical aspects of the wet corrosion resistance of the subject high-alloy martensitic stainless chromium steel X39CrMo17-1, DIN 1.4122. It is important to note that only snap rings, a.k.a. retaining rings for bores or Seeger rings, were affected by those failures, namely fractures resulting from intergranular attack (IGA, Kornzerfall). It was determined that the metallurgical root cause of failure was sensitization, resulting from secondary chromium carbide precipitation at grain boundaries (GB), and the ensuing chromium depletion in narrow bands adjacent to the GB, which rendered the matrix there sensitive to selective corrosion (the chromium content in these narrow seams, measuring only a few 10 nm in width, drops below the corrosion resistance threshold of ca. 10.5 %). Snap rings, as the name suggests, require a certain “snappiness” to serve their purpose. It is because of this requirement that all snap rings that experienced failures in the field were heat treated per DIN EN 10088-2, providing for a low tempering temperature of max. 250 °C, leading to a relatively high hardness of ca. 580 HV 10, providing said “snappiness”. It turned out that the microstructure resulting from this heat treatment (H/T) is sensitized, rendering the material sensitive to IGA. To the knowledge of the authors, no other components made of this martensitic stainless chromium steel are given this H/T, but rather a high-temperature tempering of 650 °C–750 °C per DIN EN 10088-3, producing a lower hardness in the order of ca. 300 HV 10 and largely a lack of “snappiness”, the latter being not required by those non-snap ring applications. Metallurgically, it became clear that high-temperature tempering per DIN EN 10088-3 eliminates sensitization by “backfill” diffusion of chromium from the non-depleted matrix into formerly depleted regions next to GB. It was therefore decided in the authors’ organization to eliminate X39CrMo17-1 per DIN EN 10088-2 as a possible material selection. The metallurgical investigations described in this contribution corroborate and support this decision.

On the reasons for the premature failure of safety valve springs in the equipment of the primary oil refining

The reasons for the premature failure of a spring made of steel 50KhFA used in the safety valve of the column head part of the flare facility were analyzed. The failure of the spring occurred after 7 years of operation at a temperature below 90°C in a working environment of light oil products (sulfurous gasoline). Visual and measurement control, chemical analysis of the steel composition, energy-dispersive X-ray spectroscopy (EDS) of metal in local areas, macro- and microstructural analysis, macro- and electron fractography, phase chemical and X-ray structural analysis, hardness and microhardness tests and reductive heat treatment were used in the research. The data on the characteristic external signs, typical micro damages, and the mechanism of destruction under low-temperature hydrogen sulfide corrosion of steel 50KhFA with hydrogenation, the most dangerous accompanying process, were gained in the study. According to the results obtained, the chemical composition and hardness of the spring metal meet the requirements of the standards for steel 50KhFA. The microstructure of the studied metal is tempered martensite with a decarburized layer up to 0.158 mm in thickness present on the surface. The analysis of the results showed that the premature failure of the spring is attributed both to technological heredity and contact with the working environment unauthorized by the project. An ulcerative damage of the metal surface and penetrating of corrosion products into the depth of metal due to violation of the integrity of the spring coating were revealed, which indicates a low resistance of 50KhFA steel to low-temperature hydrogen sulfide corrosion. The failure occurs predominantly near non-metallic inclusions along the boundaries of primary austenitic grains, where the largest precipitates of chromium carbides are located, as well as along the interphase boundaries of oriented carbide plates.

Effect of Heat Treatment on Microstructure and Properties Evolution of Stainless Steel Cladding Plate.

Heat treatments are necessary sometimes in order to improve comprehensive properties of stainless steel cladding plate (SSCP). However, carbon atoms in carbon steel diffuse into stainless cladding during the heat treatment process, thus decreasing its corrosion resistance. In this paper, optical microscopy, scanning electron microscopy, and microhardness and shear testing were employed to characterize the microstructure and mechanical properties of the bonding interface in SSCP. Then, the corrosion resistance of the stainless steel cladding surface was evaluated by electrochemical tests. The results showed that the diffusion of carbon atoms played an important role in enhancing the bonding strength of SSCP, but might lead to intergranular sensitization of the cladding surface because of chromium carbide precipitation. Notably, this precipitation could be induced by quenching and tempering treatment, and hindered by solution treatment. Hence, the cladding surface on SSCP after single solution treatment possessed the superior corrosion resistance, and SSCP with continuous solution and tempering treatment exhibited the highest bonding strength.

열교환기용 스테인레스강 열화 용접부의 고온 인장 및 피로특성

Purpose: This study aims to determine the most suitable material for heat exchangers by analyzing the tensile and fatigue strengths of different types of stainless steel, i.e., AISI 310S, AISI 316L, and AISI 347 after welding and aging at both room and high temperatures. BRMethods: Tensile and fatigue tests were performed on three types of stainless steel for heat exchangers using samples aged at 800℃ for 1000 hours and samples that were welded and aged at both room temperature and 800℃. The microstructures of the base material and aged samples were observed using an optical microscope and SEM. The fatigue tests were conducted using a stress ratio of 0.1 and a stress constant test; the fracture surface was then observed using SEM.BRResults: Chromium carbides tend to precipitate more in aged stainless steel samples than in the base material. It was found that AISI 316L stainless steel has the best elongation and fatigue strength at room temperature and 800℃.BRConclusion: In terms of aged and welded samples, AISI 316L stainless steel has the highest elongation and endurance limit. In particular, it has the smallest amount of chromium carbide precipitation at 800℃. In conclusion, it is determined to be an excellent heat exchanger material in terms of weldability, formability, and durability.

The effect of small additions of Nb and Ti on the sliding wear behavior of a Co–30Cr–5Mo alloy

This work studies the addition of 0.5%Nb and 0.5%Ti in a Co–30Cr–5Mo alloy as well as the increase of carbon from 0.1 to 0.3%. The main goal is to increase the wear resistance of the alloy with such additions due to the formation of primary carbides (TiC and NbC). The additions of carbon, niobium and titanium were as ferroalloys, which implies the addition of iron into the chemistry of the alloy. Microstructural prediction studies by JMatPro indicate that the addition of all of these elements promotes an increase in the amount of the sigma phase, an undesirable phase because it is a hard brittle intermetallic compound. However, this undesirable phase could be eliminated from the structure by means of a solubilization heat treatment undertaken at 1200 °C for 2 h; this heat treatment lowered the values of hardness of the alloys. An additional aging heat treatment promoted the precipitation of chromium carbides of the type M23C6 as dispersed elongated bars within the cobalt matrix, which notably increased the hardness of the alloys. Each alloy was wear tested under two loads 52 and 78 N and under dry sliding and also under lubricated sliding using Hank solution as lubricant; the tests were undertaken at a sliding speed of 0.5 m/s. Results indicate that the addition of Ti and Nb produced small amounts of TiC and NbC in addition to a light increase in the amount of the sigma phase which increased hardness in the as-cast conditions. These alloys, with Ti and Nb additions, shown the higher hardness values in the as-aged conditions. The wear resistance of the alloys are in agreement with the hardness results particularly for the dry sliding tests. Wear resistance was higher for the harder alloys (those with Nb and Ti additions in the as-aged conditions) and it is lower for the higher applied load. For the case of the lubricated wear tests, such a trend is also observed but not so clearly as for the unlubricated tests. However, friction and wear for the lubricated experiments shown values extremely low compared to these observed for the unlubricated sliding wear tests.

Behavior in Oxidation at 1000°C of Carbon-Containing Equimolar CoNiFeMnCr Alloys Added with Hafnium or Tantalum with High Contents

In this work, HfC–and TaC–reinforced cast versions of the equimolar CoNiFeMnCr alloy (Cantor) were tested in oxidation at 1000°C in laboratory air. Chromium seemingly shared, with manganese, its role as a selectively oxidized element. The principal oxide to form externally was an M2O3 one in which Mn and Cr were present in various proportions depending on the proximity with the alloy’s surface. The HfC carbides close to the oxidation front were oxidized in situ in HfO2, with the release of carbon diffusing inwards after that and inducing the solid-state precipitation of blocky or acicular chromium carbides. The behavior of the TaC carbides present close to the oxidation front was different since they dissolved, and Ta diffused towards the oxidation front to form CrTaO4 oxides. Even after 50 hours at 1000°C, the subsurfaces were more or less deeply impoverished in Cr and Mn, with minimal contents meager, especially for Mn. The evaluation of the Cr and Mn quantities and the exploitation of results in terms of equivalent oxide thickness and kinetic oxidation constant demonstrates that the resistance of the alloys against oxidation is feeble and must be significantly improved to allow benefiting of the superior high-temperature mechanical resistances of such alloys in practical application. For that, some ways are proposed.

Evaluate Effect of Pulsed Current Gas Tungsten Arc Welding Process Parameter on Intergranular Corrosion of SS304L Weld

Austenitic stainless steel (ASS) is the most common type of stainless steel which offers excellent weldability and mechanical properties. ASS is being used for various applications i.e. automotive, oil and gas and chemical industries in which the welding process plays a prominent role. Welding process selection is the main factor that emphasizes mechanical and corrosion resistance properties in various aggressive environments. There are various corrosion occurs in ASS but intergranular corrosion (IGC) forms during welding at elevated temperatures. IGC mainly occurs at grain boundaries of structure and resulting chromium depletion due to precipitation of chromium carbide at the grain boundary. In present work pulsed current gas tungsten arc welding (PCGTAW) process was used to investigate intergranular corrosion by oxalic acid test as per ASTM A262 Practice A. Experiments performed based on Taguchi L9 using design of experiments and corrosion rates are evaluated at base metal, heat affected zone and weld zone. This work is aimed to optimize process parameters followed by regression analysis to IGC susceptibility in the weldment. In this investigation, it has been found from ANOVA and main effects plots that peak current and base current are the most significant parameters in the PCGTAW process. The results of the corrosion test revealed that heat affected zone is more susceptible to IGC. At the end, it has been observed that the optimum value of peak current, base current and frequency based on regression analysis are 100 A, 50 A and 6 Hz respectively.

Grain growth and precipitation behaviour of AISI 430 ferritic stainless steel subjected to pulsed laser beam welding using free-form pulse shaping

Ferritic stainless steels are prone to grain coarsening and precipitation of chromium-rich grain boundary phases during fusion welding, which increase intergranular corrosion susceptibility. State-of-the-art techniques to overcome these challenges mainly feature heterogeneous nucleating agents with regard to grain coarsening or alternating alloy concepts as well as post-weld heat treatments as for restoration of intergranular corrosion resistance. The present investigation seeks to depart from these traditional approaches through the use of a tailored heat input during pulsed laser beam welding by means of free-form pulse shaping. Grain size analysis using electron backscatter diffraction shows a substantial reduction of grain size as compared to continuous-wave lasers due to a distinctive columnar to equiaxed transition. Moreover, phase analyses reveal the overcoming of chromium carbide precipitation within the heat-affected zone. As corrosion tests demonstrate, intergranular attack is therefore concentrated on the weld metal. In comparison to continuous-wave laser beam welding, intergranular corrosion susceptibility is substantially reduced for very short pulse durations. From these results, it can be derived that pulsed laser beam welding using free-form pulse shaping enables direct control of heat input and, thus, tailored grain growth and precipitation formation properties.

Weldability of ductile cast iron using AISI-316L stainless steel ER rod

This paper analyzes the corrosion resistance and the mechanical and microstructural properties of a welded joint of ductile cast iron using AISI316L stainless steel as filler material and three different heat treatments: preheating at 250 and 450 ºC and a post-weld annealing treatment. The results show the presence of ledeburite at the interface between the weld bead and the heat affected zone and at the root pass, along with a loss of strength and ductility when the welding coupons are preheated. An annealing does not eliminate the presence of ledeburite and leads to a massive precipitation of chromium carbides at the areas of the weld bead where dilution is higher. Corrosion rate was lower for the annealed coupon, but in that case, the corrosion of the weld bead increases due to the precipitation of chromium carbides.

Intergranular corrosion behaviour of FeCoCrNi high-entropy alloy fabricated by selective laser melting

Recently, high-entropy alloys (HEAs) show a wide application prospect in the marine field to achieve excellent corrosion resistance. In this paper, the intergranular corrosion (IGC) behaviour of FeCoCrNi high-entropy alloy fabricated by selective laser melting (SLM) at different laser powers (140, 170, 200, 230, and 260 W) was studied by microstructure analysis and double-loop electrochemical potentiokinetic reactivation. All specimens show high IGC resistance, and the degree of sensitisation of SLMed FeCoCrNi HEAs increased with the increase of laser power. Interestingly, no chromium carbides precipitation was found at the grain boundary, which indicates the intergranular corrosion mechanism of SLMed FeCoCrNi HEAs is totally different from that of most alloys caused by Cr depletion. It is found that the superior IGC resistance in SLMed FeCoCrNi HEAs produced by low laser power can be attributed to larger grain size, a higher fraction of [Formula: see text][Formula: see text] ([Formula: see text] 3), and low-[Formula: see text] coincidence site lattice boundaries. This work provides a strong insight into the application of additive-manufactured HEAs in harsh corrosion environments.

Study of effect of hardening cooling rate on microstructure of 12Kh17G9AN4-Sh steel

Currently, sheet rolling made of stainless austenitic steels are in demand and are widely used in various fields of industry and the national economy. It is used for the manufacture of welded structures, products for the aviation and food industries, as well as other industries. The main requirement for this type of sheet rolled is corrosion resistance and good plastic properties. Technological operations in the production of sheet rolling from corrosion-resistant steels of the austenitic class are selected in such a way as to ensure maximum resistance against corrosion, and the plastic properties are ensured by a homogeneous single-phase austenitic structure. Chromium is the main alloying element of corrosion resistant steels. With increasing chromium content, the corrosion resistance of steel increases. For maximum corrosion resistance, the chromium in the steel must be dissolved in the austenite. The precipitation of its carbides from the solid solution during cooling is an extremely undesirable process, since this will lead to a decrease in the percentage of chromium in austenite and a decrease in the resistance to intercrystalline corrosion. Insufficient cooling during quenching can lead to the precipitation of chromium carbides and deterioration of the corrosion resistance of the steel. The paper presents the results of a study of the effect of various cooling media (air, water) during quenching of thin-sheet rolled products made of corrosion-resistant steel 12Cr17Mn9NNi4-SH. An X-ray phase structural analysis was carried out, the thermodynamically equilibrium phase composition was calculated, and the microstructure and microhardness of steel were studied. Using chemical analysis, the distribution of alloying elements over the cross section of austenite grains was estimated. To assess the obtained values of microhardness, a statistical analysis was carried out.

The Effect of Boriding and Heat Treatment on the Structure and Properties of 100Cr6 Steel

The main aim of this case study is to present the changes caused by heat treatment on the structure and properties of 100Cr6 steel by annealing, hardening, and tempering in combination with previous chemical-heat treatment (CHT) by boriding. The boriding causes changes to the microstructure of the steel samples, which include a change in the morphology of the deposited cementite and a change in the volume of the chromium carbide particles. The cementite is transformed from its original granular form to a lamellar form. An increase in the proportion of chromium carbide particles in the sample occurs due to the higher affinity of chromium for carbon. This leads to precipitation of chromium carbides rather than carbides of iron. A multi-phase diffusion layer Fe2B-FeB with a thickness of 31 ± 2.8 µm is formed during boriding, with a typical tooth-like texture. Although the diffusion layer does not have the same toughness and resistance as the single-phase Fe2B diffusion layer, samples after boriding increase their resistance to tribological abrasion by 29 % compared to samples without this treatment. After quenching and tempering of the borided samples, a maximum tensile strength of Rm = 1779 MPa is measured. Compared to samples which are only quenched and subsequently tempered, this is an increase in tensile strength of about 59 %.

Transmission Electron Microscopy Study on the Precipitation Behaviors of Laser-Welded Ferritic Stainless Steels and Their Implications on Intergranular Corrosion Resistance

The intergranular corrosion susceptibility of ferritic stainless-steel weldments is strongly dependent on chromium carbide precipitation phenomena. Hence, stabilization is widely used to mitigate the aforementioned precipitation. In contrast, stabilization has proved ineffective to fully prevent intergranular corrosion due to segregation of unreacted chromium during solid-state heat-treatments. To analyze the precipitation behavior of 17 wt.-% chromium ferritic stainless steels during laser welding, sheets of unstabilized and titanium-stabilized ferritic stainless steels were welded in a butt joint configuration and characterized with special consideration of precipitation behavior by means of transmission electron microscopy. While unstabilized ferritic stainless steels exhibit pronounced chromium precipitate formation at grain boundaries, titanium-stabilization leads to titanium precipitates without adjacent chromium segregation. However, corrosion tests reveal three distinctive corrosion mechanisms within the investigated ferritic stainless steels based on their inherent precipitation behaviors. In light of the precipitation formation, it is evident that immersion in sulfuric acid media leads to the dissolution of either grain boundaries or the grain boundary vicinity. As a result, the residual mechanical strength of the joint is substantially degraded.

Effect of environmental condition on corrosion susceptibility of GTA welded AISI 202 austenitic stainless steel

Austenitic stainless steels with low nickel content or nickel-free content are currently considered structural materials for nuclear fusion reactor applications. Even though the base metal achieves excellent performance, welding may result in premature failures due to morphological and compositional heterogeneities. The presence of pollutants in the environment results in environmental acidification, which influences the corrosion susceptibility of the weldment. This paper it is aimed to examine the influence of the gas tungsten arc welding (GTAW) process on localized corrosion and the degree of sensitization (DOS) of AISI 202 austenitic stainless steel (ASS) butt joints in three distinct regions: base-zone (BZ), heat-affected zone (HAZ), and weld-zone (WZ) in 3.5% NaCl under pH-5 environmental conditions. The localized corrosion behavior of the weldment was studied using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and degree of sensitization (DOS) using the double loop electro-chemical potentiokinetic reactivation (DL-EPR) technique. Optical microscopy (OM) is used to understand the microstructural features of weldments and pit morphologies before and after polarisation studies. The present study establishes that the heat-affected zone (HAZ) has low corrosion resistance, high DOS%, and low intergranular corrosion (IGC) resistance compared to the base and weld zones. This could be due to the thermal cycles involved in HAZ during welding, resulting in chromium depletion and the formation of chromium carbide precipitation.

Analytical modeling of the evolution of the nonlinearity parameter of sensitized stainless steel

Austenitic stainless steels are subject to the precipitation of chromium carbides (M23C6) during exposure to high temperatures, causing these alloys to be susceptible to intergranular corrosion due to chromium depletion along grain boundaries. The acoustic nonlinearity parameter, β, shows sensitivity to the formation of carbides in these alloys. The Thermo-Calc TC-PRISMA module was used to model the nucleation and growth of grain boundary M23C6 carbides. The model was verified with scanning transmission electron microscopy analysis that allowed measurements of the grain boundary precipitates. The paper introduces a reduced-order model of the acoustic nonlinearity based on the formation of misfit dislocations at the interface of the grain boundary precipitate and matrix to explain the change in β during isothermal aging. A direct relationship between the radius of the M23C6 grain boundary carbides and β was observed and verified with nonlinear ultrasound measurements on 304L and 316L stainless steels.

Shielded metal arc welding of AISI 409M ferritic stainless steel: study on mechanical, intergranular corrosion properties and microstructure analysis

PurposeThe purpose of this study is on AISI 409 M ferritic stainless steel (FSS) which is developing a preferred choice for railway carriages, storage tanks and reactors in chemical plants. The intergranular corrosion behavior of welded SS 409 M has been studied in H2SO4 solution (0.5 M) with the addition of NH4SCN (0.01 M) with different heat input. As this study is very important in context of various chemical and petrochemical industries.Design/methodology/approachThe microstructure, mechanical properties and intergranular corrosion properties of AISI 409 M FSS using shielded metal arc welding were investigated. Shielded metal arc welding with different welding current values are used to change the heat input in the joints resulted in the microstructural variations. The microstructure of the welded steel was carefully inspected along the width of the heat-affected zone (HAZ) and the transverse-section of the thin plate.FindingsThe width of heat affected zone (3.1,4.2 and 5.8 mm) increases on increasing the welding heat input. Due to change in grain size (grain coarsening) as HAZ increased. From the microstructure, it was observed that the large grain growth which is dendritic and the structure become finer to increase in welding heat input. For lower heat input, the maximum microhardness value (388HV) was observed compared with medium (351 HV) and higher heat input (344 HV), which is caused by a rapid cooling rate and the depleted area of chromium (Cr) and nickel (Ni). The increase in weld heat input decreases tensile strength, i.e. 465 MPa, 440 MPa and 418 MPa for low, medium and high heat input, respectively. This is because of grain coarsening and chromium carbide precipitation in sensitized zone and wider HAZ. The degree of sensitization increases (27.04%, 31.86% and 36.08%) to increase welding heat input because of chromium carbide deposition at the grain boundaries. The results revealed that the higher degree of sensitization and the difference in intergranular corrosion behavior under high heat input are related to the grain growth in the HAZ and the weld zone.Originality/valueThe study is based on intergranular corrosion behavior of welded SS 409 M in H2SO4 solution (0.5 M) with the addition of NH4SCN (0.01 M) with different heat input which is rarely found in literature.

Effect of number of welding passes on the microstructure, mechanical and intergranular corrosion properties of 409M ferritic stainless steel

PurposeThis paper aims to study the effect of number of welding passes on microstructure, mechanical and corrosion properties of 409 M ferritic stainless steel. Shielded metal arc welding (SMAW) process is used to weld two metal sheets of 409 M having 3 mm thickness as bead-on-plate with single, double and triple passes. Microstructures were observed at transverse section with the help of optical microscope and with increasing number of passes grain growth, and the width of heat-affected zone (HAZ) increases. The results of tensile tests revealed that as number of passes increases, there is reduction in tensile strength and ductility. Double loop electrochemical potentiokinetic reactivation (DL-EPR) test revealed that as number of passes increases, the degree of sensitization increases. This is due to the deposition of chromium carbides at the grain boundaries and the associated depletion of chromium.Design/methodology/approachThree welded plates of single, double and triple pass were welded by SMAW process. From three welded plates (single, double and triple passes), samples for microstructural examination were cut in transverse direction (perpendicular to welding direction) with the help of wire-cut electrical discharge machine (EDM). The welded plates were sliced using wire-cut EDM along transverse direction for preparing optical microscopy, tensile testing, microhardness and DL-EPR testing specimens.FindingsFrom the microstructure, it was observed that the large grain growth, which is dendritic, and the structure become finer to increase in number of welding passes. As number of passes increases, the width of HAZ increases because of the higher temperature at the welded zone. The tensile strength decreases to increase the number of welding passes because of grain coarsening and chromium carbide precipitation in sensitized zone and wider HAZ. The maximum microhardness value was observed for single-pass weld as compared to double- and triple-pass welds because of the fast cooling rate. The degree of sensitization increases to increase the number of passes because of chromium carbide deposition at the grain boundaries.Originality/valueThe authors declare that the manuscript is original and not published elsewhere, and there is no conflict of interest to publish this manuscript.

Tribological behavior and microstructural characterization of austenitic stainless steel stabilized with Nb and V

This study deals with the influence of the addition of vanadium and niobium with concentrations of 1.2% and 0.14%, respectively, on the variation of the microstructure, and the tribological behavior of an AISI309 austenitic stainless steel. The studied specimens were structurally characterized by optical microscopy, scanning electron microscopy (SEM) X-ray diffraction and and differential scanning calorimetry (DSC). These samples were also subjected to a tribological study using the friction wear test. The results show that the addition of vanadium and niobium causes a precipitation of stable carbides (VC, NbC) which in mm causes a decrease of the chromium carbide precipitation rate. Tribological test results have also shown that the addition of these two elements improves the wear resistance of AISI309 austenitic stainless steel by decreasing the coefficient of friction fr om 0.824 to 0.554.