Schaeffler Diagram Research Articles

Corrosion Resistance and Mechanical Properties of Cr-Rich 316 Stainless Steel Coatings Fabricated by the TIG Process Using Flux-Cored Wires.

Arc welded 316 stainless steel coatings with flux-cored wires are very promising for marine service environments due to their low cost, high efficiency, and satisfactory performance, while they suffers from Cr dilution during the preparation process. Herein, based on the consideration of increasing the Cr content and ensuring the same value of the Cr/Ni equivalence ratio (Creq/Nieq), 316-modified flux-cored wires, 316F (19Cr-12Ni-3Mo) and 316G (22Cr-14Ni-3Mo), were designed under the guidance of a Schaeffler diagram for the improvement of the electrochemical and mechanical properties of 316 stainless steel coatings. The designed flux-cored wires were welded into a three-layer cladding by the tungsten inert gas welding (TIG) process, and the microstructure, corrosion resistance, and mechanical properties of the claddings were investigated. The results showed that 316F and 316G consist of γ-Fe (austenite) and a small portion of δ-Fe (ferrite) as the Creq/Nieq is approximately 1.5. However, due to the higher value of the equivalent Cr content (ECC), 316G has an additional intermetallic phase (σ), which precipitates as a strengthening phase at grain boundaries, significantly increasing the tensile and yield strength of 316G but reducing its plasticity. In addition, the corrosion current density (icorr) and pitting potential (Eb) for 316G are 0.20447 μA·cm-2 and 0.634 V, respectively, while the values for 316F are 0.32117 μA·cm-2 and 0.603 V, respectively, indicating that 316G has better anti-corrosion performance.

Application of Schaeffler Diagram for Predicting the Structure and Mechanical Properties of Heat-Resistant Steels with More than 10 wt.% Cr

Application of Schaeffler Diagram for Predicting the Structure and Mechanical Properties of Heat-Resistant Steels with More than 10 wt.% Cr

Predictive tools for the cooling rate-dependent microstructure evolution of AISI 316L stainless steel in additive manufacturing

This study presents a thorough evaluation of advanced predictive tools for the solidification microstructure of AISI 316L stainless steel, taking into account both chemical composition and cooling rate. In order to achieve a broad range of cooling rates comparable to prominent additive manufacturing processes, autogenous laser welds were carried out on the steel plate by means of powderless directed energy deposition (DED) and selective laser melting (SLM) machines. Computational analysis of cooling rates and metallographic investigations revealed that DED welds solidify at moderate rates, exhibiting a primary ferrite (FA) solidification mode. Conversely, SLM welds solidify at significantly higher rates, showing dual solidification modes: initial austenite (A) at the fusion boundary and subsequent ferrite (F) at the interior. The WRC-1992 constitution diagram predicts the FA mode in accordance with the findings in the DED welds. An implicated Schaeffler diagram, proposed for a comparable cooling rate, also predicts the same mode. An artificial neural network model, referred to as ORFN, consistently predicts the variation of ferrite content within the DED welds based on the cooling rate variation. The dual mode observed in the SLM welds aligns with established knowledge regarding the alteration of stainless steel solidification under extremely high cooling rates. While the occurrence of the A mode at the fusion boundary is anticipated according to implicated Schaeffler diagrams for extremely high cooling rates, the transition to the F mode is not addressed explicitly.

High ductility – Good strength stainless steel alloys at the elevated temperature for nuclear reactors core

Reactors materials are the backbone of reactor life extending and making it safer. Accordingly, unabated research continues for the improvement of nuclear reactor materials, especially the reactor core materials. Hence, in the present article, two developed tungsten/molybdenum stainless steel grades MoW1 (0.843 wt% of Mo and 1.801 wt% of W) and MoW2 (0.251 wt% of Mo and 2.433 wt% of W) were produced. AISI316 standard stainless steel was used as a base material. Microstructural features of the produced alloys were investigated using Schaeffler diagram, optical microscopy, SEM-EDS, and X-ray diffraction. The mechanical properties of the produced alloys were studied at room temperature RT and elevated temperatures of 300 and 500 °C. W addition by 1.801 wt% at the expense of Mo (MoW1 steel) strengthened yield strength YS and ultimate tensile strength UTS by 42.344% and 32.022% at room temperature compared to the standard stainless steel AISI316, while a high affinity was found between YS and UTS results for steel containing 2.433 wt% of W (MoW2) and the AISI316. On the other hand, the elongation El% of MoW1 decreased by 20.861% and MoW2 by 17.219% compared to the AISI316. At 300 and 500 °C, the MoW1 stainless steel alloy has higher YS (by 4.865% and 7.865%) and UTS (by 17.580% and 41.077%) than AISI316. While, MoW2 has slightly lower YS (by 7.568% and 3.371%) and higher UTS (by 10.046% and 36.261%) than AISI316. Both of MoW1 and MoW2 has much higher El% than AISI316 at both 300 and 500 °C. As a comparison between the developed stainless steel alloys MoW1 and MoW2 for both 300 and 500 °C, MoW1 gave better YS (by 13.450% and 11.628%), UTS (by 6.8465% and 3.534%), and El% (18.3024% and 18.037%) results than MoW2. Accordingly, depending on the distinctive mechanical properties of the developed MoW1 stainless steel alloy at 300 and 500 °C, it is a strong candidate as an appropriate material for high-temperature conditions of the nuclear reactors core.

Developed borated austenitic stainless steel alloys as nuclear reactor control rods

Modified austenitic stainless steel alloys reinforced with B and B/Ti were fabricated and their suitability as nuclear reactor control rods was tested. A standard stainless steel AISI 316L was used as a base alloy and inlaid by 0.58 wt% of B (SSB). The structural examination of the modified SSB stainless steel, which was conducted through the Schaeffler diagram, optical micrographs (OM), and X-ray diffraction (XRD) patterns had referred to the domination of the austenite phase with the appearance of boride (M2B) and carboborides (M23X6) phases along the grain boundaries. Mechanically, an augmentation in the hardness, yield strength (YS), and ultimate tensile strength (UTS) values was observed with the incorporation of B into the AISI 316L stainless steel. However, the addition of B led to a reduction in the values of elongation (El), reduction area (RD), and impact energy. Then, the SSB stainless steel was reinforced by 0.33 wt% of Ti (SSTiB1). The structural examination showed the formation of M2B, M23X6, TiC, TiN, and TiB2 phases along the grain boundaries of the austenite matrix as well as little ferrite phases. Ti led to a significant increase in hardness, YS, UTS, El, RD, and impact energy of the SSB steel. Finally, a further addition of B and Ti (1.13 & 1.77 wt% of B & Ti, SSTiB2) was tested, as this increase led to the more enhancement of hardness, YS, UTS, and impact energy but reduced the El slightly. Due to the high slow neutrons absorption cross-section of B, the slow neutrons attenuation ability of the modified stainless steel increased effectively with increasing boron concentrations. The obtained distinctive mechanical properties and high attenuation efficiency of slow neutrons of the produced SSBTi2 stainless steel, make it a suitable choice for use as control rods in nuclear reactors.

The effects of Cr and Ni equivalents on the microstructure and corrosion resistance of austenitic stainless steels fabricated by laser powder bed fusion

In this study, two gas-atomized austenitic stainless steel (ASS) powders with a predominant difference in Cr contents, Mod.-A (18Cr-14Ni-2.6Mo) and Mod.-B (22Cr-14Ni-2.5Mo), were applied in the laser powder bed fusion (LPBF) process. The two kinds of powders and the Mod.-B LPBF sample contained a certain amount of ferrite, whereas, the Mod.-A LPBF sample was found to contain no ferrite. Furthermore, the ferrite content of the Mod.-B LPBF sample determined by ferrite scope (about 5.5 %) was lower than that estimated by Schaeffler diagram (over 10 %). The rapid solidification of the LPBF process tended to reduce the ferrite contents of the fabricated sample as compared with the amount of ferrite present in the feedstock powder or estimated by Schaeffler diagram. It was noted that the chemical compositions of the austenite and ferrite in the Mod.-B LPBF sample had no noticeable differences. Moreover, few ferrites in the LPBF sample caused a significant grain refinement, which resulted in obvious increases in yield and ultimate tensile strength but a decrease in ductility. The corrosion behavior of the 316L plate and two LPBF samples was investigated in 3.5 wt% NaCl, 1 M HCl and 0.5 M H2SO4 solution in this work. The corrosion resistance of the LPBF samples were higher than that of 316L plate in 3.5 wt% NaCl and 1 M HCl solution. In 0.5 M H2SO4 solution, all three tested samples exhibited nearly the same potentiodynamic polarization curves. Overall, the Mod.-B LPBF sample exhibited corrosion resistance equivalent or superior to that of the 316L plate and Mod.-A LPBF sample.

Microstructure of Butt Joint of High-Silicon Steel Made Using CO2 Laser Welding and Inconel 82 Filler

A nickel-based filler wire, Inconel 82, was applied to weld a high-silicon steel plate with a chemical composition in wt% of 2.6 Si, 0.5 Al and Fe balance. The chemical composition of the heterogeneous weld bead was deviated from that of the conventional alloy due to incomplete mixing/convection between the filler wire and base metal in the weld pool. The microstructure of the weld bead was examined in greater depth by FESEM/EBSD, EPMA/WDS and STEM/EDS in the experiment. The heterogeneous weld bead was primarily composed of austenite and martensite, and mainly governed by the Ni concentration. A Schaeffler diagram based on the ratio of Cr and Ni equivalents in the selected positions of the weld bead was used to predict the structure and phase(s) of the Fe-based weld bead. A methodology for the analysis of a weld metal with an unconventional alloy composition has been proposed in the study.

Description of a new concept for the development of adapted hot-work tool steels for laser-powder bed fusion

This work presents a new approach for developing carbon-martensitic hardenable hot work tool steel, which can be processed to defect-free components by laser powder bed fusion (L-PBF). The alloy approach is based on low transition temperature steels (LTT), which are characterized by a low martensite start temperature at which the austenite transforms into martensite. With this transformation, a volume expansion occurs, which causes a reduction in the tensile residual stresses previously formed in the austenite phase during cooling. At the same time, low martensite start temperature counteracts the further formation of high residual stresses as the material continues to cool down to room temperature. A modified Schaeffler diagram was used to find an appropriate alloy composition as starting point for alloy development. This diagram was adapted to the L-PBF process by laser-remelting the surfaces of cast specimens with different Ni- and Cr-equivalents. The resulting retained austenite content and the associated residual stresses of the remelted surfaces were determined using x-ray diffraction. Knowing the interaction between the chemical composition, the retained austenite volume fraction, the martensite start temperature, and the residual stress state, an optimal alloy window for L-PBF-processable hot work tool steels could be determined with the help of the adjusted Schaeffler diagram. Finally, a suitable commercially available alloy X38CrMo7–2 was adapted that can be processed using L-PBF without preheating of the build platform. The microstructure and the properties associated (hardness, strength) of the L-PBF-processed and heat-treated steel X38CrMo7–2 were compared with the frequently used tool steel X40CrMoV5–1 (L-PBF-processed with preheating of the build platform of 300 °C).

Effect of welding parameters on the mechanical and metallurgical properties of armor steel weldment

The effect of welding parameters on the mechanical and metallurgical properties of armor steel weldment was studied using gas tungsten arc welding process with two filler wires: carbon steel and austenitic stainless-steel filler wires (AWS A5.18 ER 70S-6 and AWS A5.9 ER 307, respectively). The joint configurations were mainly single V and single bevel grooves. Using both AWS A5.18 ER70S-6 carbon steel filler wire and AWS A5.9 ER307, austenitic filler wire for the two joints passed the required tensile strength by the military standard. The joints successfully regained the base metal hardness at a distance of less than 15 mm. The ultimate tensile strength of the joints welded in a single bevel groove is 906 MPa which is higher than the joints welded using a single V groove is 865 MPa. This could be attributed to the increase in dilution percentage with the single bevel joints. Both single V joint and single bevel joints passed the required Charpy V-notch impact test whether using both carbon and stainless-steel wires. The effect of heat input and cooling rate on the mechanical and microstructure of welded joints was studied. The reduction of heat input caused a narrow HAZ with a small reduction in its hardness values with much reduction in the width of softening microstructure zone. SEM observations show that the base metal has a martensitic structure, but the weld metal microstructures depend on the filler: carbon steel or austenitic steel types. Using a single bevel groove with an austenitic steel filler metal, the weld metal shows a martensitic/austenitic microstructure by SEM observation, and this was verified by the Schaeffler diagram which showed a high dilution percentage (about 35% dilution). This resulted in a significant increase in joint strength and a higher weld metal impact resistance.

Assessment of the universality of duplex stainless steel powder in laser additive repair based on Schaeffler diagram

The type and quantity of repair materials used in ocean or field environment is unclear. This study investigated the effective methods for evaluating the universality of a specific powder for multiple materials using a self-made universal duplex stainless steel powder (UDSS) as the object and tensile strength (σ) of the additive repair part in the normal direction of the interface as the index. Based on the Schaeffler diagram, the equivalent distances of Cr and Ni were used to characterize the chemical composition difference between the material to be repaired and the UDSS powder, and the angle θ was used to characterize the difference in microstructures. Three models, σ-(Cr eq , Ni eq ) , σ-ρ equivalent distance linear, and σ -( ρ,θ ) polar coordinate models, were proposed for predicting the strength of the additive repaired part. These models were verified using the results of repair tests on five substrates. The mean prediction error, pf, of the σ -( ρ, θ ) polar coordinate model was minimum, that is, approximately 9.68%. Under the conditions of this study, the maximum normal strengths of the repaired specimen interface in the normal direction were 689, 704, and 957 MPa in the austenite, ferritic, and ferrite + austenite regions, respectively, thus proving the universality of the UDSS powder used. This study provides a novel and a reliable method for evaluating the universality of UDSS powder for laser-additive repair. The relationship between the tensile strength and evolution of the microstructure, chemical composition, and microhardness near the interface is discussed.

Uticaj unete toplote na zatezne karakteristike austenitno-feritnih zavarenih spojeva

Introduction/purpose: During exploitation tests of gasoline storage tanks, cracks can form in an austenitic-ferrite welded joint, which can compromise the entire tank. Methods: In order to obtain a welded joint of satisfactory strength and durability, the paper analyzes the influence of heat input on the tensile characteristics of welded joints. In the current literature and practice, additional materials for welding the tank elements are selected according to the chemical compositions of the elements of basic materials, with the help of the Schaeffler diagram. In this paper, the characteristics of welded joints of gasoline storage tanks are examined, when the largest part of the tank is made of fine - grained microalloyed steel NIOMOL 490 K, while the roof part of the tank is made of austenitic steel. Slabs of these two materials were welded by the MIG process with additional material MIG 18/8/6, at different amounts of heat input. Conclusion: The analysis of the results obtained by tensile testing according to SRPS EN ISO 6892-1: 2020 standard concluded that the behavior of the joint as a whole depends on the properties of each individual part of the welded joint and their mutual influence. It was also concluded that the mutual influence is better if welding is performed with a lower amount of heat input, because then a lower degree of mixing of additional material with basic materials is achieved.

Dissimilar metal weld failure of steam piping in a hydrogen unit of petroleum refinery

Steam generation from hot reformer effluent in a hydrogen unit of a petroleum refinery increases the refinery margin. Upstream and downstream piping in hydrogen plant were constructed by SA335 P22 (AS) and type SS304L (SS) materials, respectively. This paper reports failure of dissimilar pipe weld after six months of high pressure steam service. Visual inspection indicates several ratchet marks initiated from outer wall surface at heat affected zone (HAZ) of AS pipe accompanied with brittle fracture. Further, failed samples were examined for chemical analysis, micro-hardness, fractography & elemental analysis and microstructural analysis. Fractographic results indicated that the dissimilar weld was failed due to thermal fatigue. Moreover, microstructural analysis revealed the presence of martensite in AS HAZ region with higher micro-hardness. In-spite of fixed operating temperature at 600 °C, there was a difference in thermal expansion that induced large strain gradient at interface and result in low cycle thermal fatigue failure. Type 308L filler metal was directly employed for dissimilar welding without buttering at interface layer was the main cause of failure. The principal factors that were responsible for Dissimilar Metal Weld (DMW) failure are discussed with respect to Schaeffler diagram and correct welding procedure for failure prevention is proposed. It is further recommended to employ 309/309L filler metal at interface layer according to ASME codes & standards to avoid DMW failure.

Intensive laser repair through additive manufacturing of high-strength martensitic stainless steel powders (II): evaluation of intensive repair ability of high strength martensitic steel powder based on Schaeffler diagram

As one of the key technologies for intensive additive repair (i.e., using a type of powder to repair various substrates), the method of accurately predicting the strength of repaired samples based on the chemical composition of filling materials and base materials needs to be explored urgently. An intensive additive repair experiment based on the laser coaxial powder feeding cladding technology was carried out using an independently designed intensive high-strength martensitic stainless steel (IHMSS) powder and eight types of substrates. A new approach was presented: the distance between the composition points of the IHMSS powder and the substrate to be repaired, as shown in Schaeffler's diagram (D), and their orientation relationship (θ) can provide a basis for describing the bonding strength of the repaired interface between the aforementioned materials. With the increase in D and θ, the ratios of tensile strength and elongation of additive repair parts to those of base materials decreased. When θ was below 1.12, the tensile strength of repaired interface in the normal direction was more than 83% that of the substrate to be repaired. Incomplete fusion and cracks were found on the cross section of the additive parts when θ exceeded 1.12. When D exceeded 13%, a high microhardness phase was formed near the interface. Further analysis results show that, with the increase in D and θ, the gradients of microstructure, composition, and microhardness at the repaired interface will be increased.

Study on the microstructural variation and fatigue performance of microplasma arc welded thin 316L sheet

Welding is a venerable and reliable fabricating technique to integrate materials into complex geometry desired for various industrial applications. However, localized heat concentration leading to microstructural variations can deteriorate the fatigue life of welded components. The present study explains tensile and high cycle fatigue performance of microplasma arc welded 316L SS thin sheet (0.5 mm thickness) material. The square butt joint configuration with a single pass weld was achieved for 316L SS similar sheet material. The skeletal and lathy delta-ferrite-austenitic structures were observed in the fusion zone (FZ) due to non-equilibrium solidification, which is attributed to the different thermal cycle behaviour of the FZ. This morphology is explained by the pseudo phase diagram and the Schaeffler diagram of SS material. The tensile test showed that the microplasma arc welding process achieved a joining efficiency of 93%. The high cycle fatigue performance of welded specimens was analysed at different alternating stress amplitude. The presence of a dense delta ferrite phase in the austenitic matrix is responsible for fatigue failure of the welded specimen. However, the development of deformation-induced martensite in the crack initiation site promotes fatigue life. The crack initiation, propagation, and sudden failure site were investigated to explain the fatigue fracture behaviour.

Influence of process parameters on microstructural evolution, solidification mode, and impact strength in joining of stainless steel thin sheets

ABSTRACT Incorrect selection of process parameters corresponds to 45 % of the entire weld imperfections. Selection of process parameters becomes even more critical when the joining is reduced to micro-level. The current experimentation and computational work emphasise the influence of process parameters on joint characteristics of AISI316L and AISI310 thin sheets. Thin sheets fabricated by a micro-plasma arc welding process at different process parameters (PP) PP1 (~524 J/cm), PP2 (~629 J/cm), and PP3 (~733 J/cm) are experimentally analysed to study the variation in microstructural morphology, mode of solidification, and impact toughness. The dependence of the temperature gradient (G) and solidification velocity (R) on the process parameters are also established. Microscopic images confirm the presence of equiaxed and cellular structure depending on the G/R ratio. As the cooling rate decreases, the transformation from δ-ferrite ⟶ γ-austenite is restricted, which changes the δ-ferrite percentage for different weld conditions. Elemental analysis is used to evaluate the Creq/Nieq ratio that predicts the solidification mode using the Schaeffler diagram. The outcome of the present investigation indicates that the highest G/R and maximum G*R corresponds to enhanced joint behaviour due to favourable changes in the metallurgical properties.

Effect of Heat Input on Dilution, Hardness, and Microstructure in DMW Stainless Steel and Carbon Steel

The success of Dissimilar Metal Welding (DMW) occurred in optimal Heat-input (HI) parameters. The quality of welding joints was affected by dilution, hardness value, and intermetallic microstructure. DMW quality research was carried out on stainless steel SA SS312-TP304 and SA 53GrB carbon steel using the GTAW (Gas Tungsten Arc Welding) process with Heat-input of 1866.6 to 2362.2 J/mm. Visual observation on weld joints was not found weld defects. The optimal dilution area in the Schaeffler Diagram was obtained 35.35% austenitic area and without ferrite content. The lowest hardness value on carbon steel was 145 HV. The highest hardness value of 197 HV occurred in filler-metal dilution on carbon steel, so the difference in the value of hardness was high. The hardness value on stainless steel was 184 HV and in filler-metal stainless steel dilution was 172– 90 HV, so the difference in hardness value was low. Microstructure filler-metal dilution on stainless steel was austenite-dendritic, filler-metal dilution on carbon steel was fine-grained dendritic, and on allweld metal coarse-grained dendritic metal. HAZ stainless steel austenite microstructure and ferrite-pearlite carbon steel with an indication of a ferrite net. Observation of dilution, hardness value, and microstructure in DMW did not have a significant effect. This welded joint could be used as a reference in the DMW fabrication process for stainless steel and carbon steel pipe connections.

Design and evaluation of nitrogen-rich welding wires for high nitrogen stainless steel

Three nitrogen-rich welding wires with nitrogen content of 0.15 %, 0.6 % and 0.9 % for high nitrogen stainless steel welding were developed by a modified Schaeffler diagram and equilibrium phase diagram calculation. The effect of the chemical compositions especially the nitrogen on the weld defects, element distribution, microstructure, mechanical properties and droplet transfer were studied to evaluate the performance of the welding wires. Nitrogen element in the droplets of nitrogen-rich welding wires was partially lost due to the escape of nitrogen during the welding process, so nitrogen in the welding materials was not completely transported to the weld as designed, resulting in a deviation of actual weld from the design. The joint of the welding wire with 0.6 % nitrogen content had the highest mechanical properties, the tensile strength reached 912.5 MPa, and the impact energy of the weld reached 138.17 J. Full-austenite weld was only obtained in the weld of the wire with 0.15 % nitrogen content, but the tensile strength of the joint was lowest because of the low nitrogen content in the weld. Welding wire with 0.9 % nitrogen content had the most serious nitrogen loss, a few of pores were found in the weld. Moreover, the content of skeleton ferrite in the weld with the welding wire containing 0.9 % nitrogen content was high, resulting in the decrease of the weld impact energy.

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.

Microstructure, mechanical properties and pitting corrosion of TIG weld joints alternative low-cost austenitic stainless steel grade 216

This present work aims to study 200 series austenitic stainless steel as a replacement for 300 series austenitic stainless steel. This is due to 200 series austenitic stainless steel being inexpensive and also due to its popularity in Southeast Asia. This study investigated the behavior and properties of the weld metal produced from 216 grade austenitic stainless steel. The microstructure, mechanical properties and pitting corrosion resistance that were produced by the tungsten inert gas welding process (TIG) with filler metal ER316 are studied in this paper. The variable parameters of the welding process were heat inputs at high (0.78 kJ/mm), medium (0.52 kJ/mm) and low (0.39 kJ/mm) ranges. It was found that the weld metal with a high heat input level increased the width of the face weld, root weld, PMZ and HAZ. However, the opposite result was achieved when the heat input was reduced. The microstructure of all the weld metals formed delta-ferrite content in the austenite matrix. This was shown to be greater in the weld metal with a low heat input, under the solidification mode FA. The results were shown to agree with the predictions outlined in the Schaeffler diagram. In addition, it was discovered that a high heat input level produced a more discontinuous form of delta-ferrite content than for the low heat input model. This corresponded to the dendrite length and inter-dendrite spacing in the weld zone. The hardness, ultimate strength and elongation tended to decrease when the heat input increased. The fractures for all the weld metals were found to occur in the location of the weld zone. The pitting corrosion resistance increased when the heat input was reduced, which related to the volume of delta-ferrite content in the weld metal zone. This corresponds to the pitting corrosion resistance in the weld metals being higher than for the base metal material. Furthermore, it was found that pitting occurred initially at the interface between the delta-ferrite and austenite phase and the corrosion then spread into the austenite phase.

Análisis de falla de soldaduras en filete con corrosión prematura en compuertas deslizantes de acero inoxidable 316L usando diagramas de constitución

The service environment of the slide gates may cause localized corrosion at welds. In this work, a failure analysis was conducted to determine the causes of the prematurecorrosion of the fillet welds before the commissioning. According to the contractor, the slide gates were manufactured in ASTM A240 Type 316L stainless steel and welded with GMAW using an ER316LSi filler metal. Test samples of the fillet weld metals were extracted from gates after a preliminary visual inspection. The samples were analyzed using ferrite number measurements, Optical Emission Spectrometry, chemical analysis, metallographic examination and Scanning Electron Microscopy with microanalysis. The analysis of results using the Schaeffler and WRC-92 constitution diagrams showed that the estimatedchemical composition of the filler metal differs with the filler metal specified in the WPS suggesting that an incorrect carbon steel filler metal was used during the construction of the gates