Delta Ferrite Content Research Articles

Feasibility of manufacturing high-aspect-ratio hollow tubes of SS410 through wire-arc directed energy deposition

This study reports new observations from the fabrication of high-aspect-ratio hollow tubes of SS410 through wire-arc directed energy deposition (wire-arc DED) process. Characterisation work was performed on a single tube as a function of its build height. The maximum ultimate tensile strength (UTS) of 1372 MPa and maximum yield strength (YS) of 980 MPa were achieved in the middle region of the tube. The highest UTS in the middle was attributed to the low delta ferrite content. The reduction of delta ferrite was found to be linked with the repetitive heating and cooling. In contrast, the top and bottom sections exhibit a substantial presence of delta ferrite, indicating that the cyclic effects were not considerable. Nevertheless, the presence of significant ductility in the bottom region of the component indicated the occurrence of tempering effects. This observation is further supported by the lower levels of local strain observed using KAM mapping. Overall, this work proposes a novel fabrication method for producing hollow sections with superior strength and ductile properties.

Performance analysis of various fluxes in different variants of the TIG welding process on the quality of welding

The tungsten inert gas (TIG) welding process is widely used in various industries for its ability to produce high-quality welds at a low cost. However, TIG welding struggles with welding thick stainless steel in a single pass, reducing production efficiency. To address this, new TIG variants such as activated TIG (A-TIG), flux bound TIG (FB-TIG), and flux zone TIG (FZ-TIG) have been developed to enhance penetration in austenitic stainless steel. This study investigates the effects of TiO2 and Fe2O3 flux on 304 stainless steels welded using A-TIG, FB-TIG, and FZ-TIG processes. Results show a slight increase in the depth-to-width (d/w) ratio for A-TIG and FB-TIG, while FZ-TIG achieved a 59% higher d/w ratio compared to autogenous TIG welding. The increased penetration is attributed to the reversal Marangoni convection and arc constriction. Microstructural analysis reveals a higher delta ferrite content in A-TIG and FZ-TIG welds due to increased heat input. Additionally, FZ-TIG welds exhibited an 11.5% higher microhardness compared to autogenous TIG welds. FZ-TIG welding enhances penetration and mechanical properties effectively.

A NOVEL DOUBLE-SIDE LASER WELDED THICK PLATE: MICROSTRUCTURE AND NUMERICAL PREDICTION OF TENSILE TEST

The study aims to provide firsthand knowledge on finite element simulation (FES) of double-side laser welded (LW) stainless steel 304 (SS-304) thick plates used for automobile application. Double-side welding technique is an idea of achieving complete penetration with minimal heat input. The microstructural evaluation revealed the presence of dendritic growth that results in the enhancement of tensile strength (TS) for the welded sample. There is a slight increase in the delta ferrite content in weldment. The change in microstructure is due to thermal history during solidification. The TS of base metal (BM) was [Formula: see text][Formula: see text]MPa whereas the welded sample exhibited strength of [Formula: see text][Formula: see text]MPa. FES was successfully employed to simulate TS with error percentage less than 1.

Flux-cored arc welding of 316L austenitic stainless steel: the effect of different shielding gas mixtures on microstructural features and weld performance

ABSTRACT Double-pass flux cored arc welding (FCAW) of 316 L austenitic stainless steel was performed using different shielding gas mixtures. Microstructural features and weld performance were evaluated. Based on the Creq/Nieq ratio of fusion zone and cooling rate, different morphologies of ferrite (skeletal, lathy, and dendritic) and austenite with various volume fractions were produced. An increase in Creq/Nieq ratio can increase the strength level because the presence of ferrite in the weld metal acts as a second-phase strengthening agent. On the other hand, ferrite is a suitable place for sigma phase precipitation. Highest joint efficiency resulted in the specimen welded via GTAW. The ductility of welds was ranked as CO2 +Ar shielded FCAW > GTAW > CO2 shielded FCAW > self-shielded FCAW. At room temperature, variation of delta-ferrite content (Creq/Nieq ratio) does not affect toughness. However, an increased amount of CO2 in shielding gas will result in decreased toughness values because of the enhanced formation of oxide inclusions. Increasing CO2 content of shielding gas from 0% to 18% and finally to 100% will result in decreasing toughness values from the highest value of 76J to 40 J and finally the lowest value of 38J.

The Influence of Various Welding Methods on the Microstructure and Mechanical Properties of 316Ti Steel.

Austenitic stainless steels are very popular due to their high strength properties, ductility, excellent corrosion resistance and work hardening. This paper presents the test results for joining AISI 316Ti austenitic steel. The technologies used for joining were the most popular welding techniques such as TIG (welding with a non-consumable electrode in the shield of inert gases), MIG (welding with a consumable electrode in the shield of inert gases) as well as high-energy EBW welding (Electron Beam Welding) and plasma PAW (plasma welding). Microstructural examinations in the face, center and root areas of the weld revealed different contents of delta ferrite with skeletal or lathy ferrite morphology. Additionally, the presence of columnar grains at the fusion line and equiaxed grains in the center of the welds was found. Microstructural, X-ray and ferroscope tests showed the presence of different delta ferrite contents depending on the technology used. The highest content of delta ferrite was found in the TIG and PAW connectors, approximately 5%, and the lowest in the EBW connector, approximately 2%. Based on the tests carried out on the mechanical properties, it was found that the highest properties were achieved by the MIG joint (Rm, 616, Rp0.2 = 335 MPa), while the lowest were achieved by the PAW joint (Rm = 576, Rp0.2 = 315 MPa).

Influence of Induction Preheating and Post Weld Heat Treatment for Reducing Delta Ferrite Content and Improving Mechanical Properties of Induction Assisted Gas Metal Arc Welding of Modified 9Cr-1MoV Steel

Influence of Induction Preheating and Post Weld Heat Treatment for Reducing Delta Ferrite Content and Improving Mechanical Properties of Induction Assisted Gas Metal Arc Welding of Modified 9Cr-1MoV Steel

Study on the Effect of Hydrogen in Argon-Nitrogen Shielding Gas on Pitting Corrosion for Austenitic Stainless Steel by GTA Welding Process

The addition of hydrogen in shielding gas has been found to contribute to increasing the productivity of gas tungsten arc (GTA) welding compared to the processes using argon-nitrogen shielding gas. In this report, the GTA welding joints of AISI 304 stainless steel with Ar-N2 and Ar-N2-H2 addition were fabricated. The microstructure and pitting corrosion resistance were studied in this work. The corrosion characterisation of welds metal was investigated by a potentiodynamic method in NaCl solution. It was found that H2 addition also had effects on delta-ferrite microstructures and corrosion behaviour. Increasing hydrogen in argon-nitrogen shielding gas increased the delta-ferrite content and improved pitting corrosion resistance.

Delta ferrite formation and evolution during slab processing from an 80-ton industrial heat of AISI 304 austenitic stainless steel

Although delta ferrite is a very common phase in most austenitic stainless steels, studies about its formation and evolution during slab processing from industrial heats of tens of tons are scarce. The main objective of this research is to study the evolution of delta ferrite (quantity, chemical composition, morphology, and distribution) along the production route from the cast slab to the coil of an industrial heat of 80 tons of 304 stainless steel. Samples were extracted after the following processing steps: continuous casting, first and second hot-rolling pass, and solution-heat-treating, arriving at the final commercial condition. Sample analyses were carried out with several complementary microstructural characterization techniques: optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (EDS), X-ray diffraction, and magnetic measurements of delta ferrite content (feritscope). Thermocalc® indicates that the present continuous cast slab solidifes according to the FA (ferrite-austenite) mode and the final microstructure should be completely austenitic in equilibrium conditions. Nevertheless, delta ferrite is detected along the processing steps, indicating that the steel is out of phase equilibrium. The ferrite content measured after solidification varies significantly across the as-cast slab thickness. Lower values are detected on the surfaces, followed by a gradual increase when moving into the slab, reaching a peak, and finally decreasing at the slab center. This pattern of delta ferrite content is named “M type” distribution. The average content of delta ferrite decreases after each subsequent processing step, namely the two hot-rolling passes and the solution heat-treating.

INFLUENCE OF SIGMA PHASE ON GENERAL CORROSION OF AUSTENITIC STAINLESS STEEL

Austenitic stainless steel is mostly used at high temperatures. It is known that during heating of the austenitic stainless steel with increasing temperature and time of annealing a microstructure is changed i.e. there is the precipitation of carbides followed by precipitation of secondary phases as a sigma phase. The presence of the delta ferrite in austenitic stainless steel enhances the formation of the sigma phase. This study represents the influence of delta ferrite on the sigma phase formation and the effect of the sigma phase on general corrosion. Corrosion tests were conducted in the corrosion cell according to Standard ASTM G5, on instrument potentiostat/galvanostat, Princeton Applied Research, model 263A-2, with the software PowerCORR® (Standard, ASTM G5-94). Examinations were carried out in 1% HCl and 10% FeCl3 solutions. The Tafel extrapolation method was used for the investigation of general corrosion. The results of corrosion testing indicated that the intensity of the general corrosion increases with the increase of the delta ferrite and sigma phase contents.

Improving the Corrosion Resistance of AISI 316L Steel for Semiconductor Piping by Controlled Delta-Ferrite Content

This study evaluated changes in delta-ferrite content depending on the preheating of AISI 316L stainless steel. We also determined the reasons for the variation in delta-ferrite content, which affects corrosion resistance. Changes in delta-ferrite content after preheating was confirmed using a Feritscope, and the microstructure was analyzed using optical microscopy (OM). We found that the delta-ferrite microstructure size decreased when preheating time was increased at 1295 oC, and that the delta-ferrite content could be controlled through preheating. Potentiodynamic polarization test were carried out in NaCl (0.5 M) + H2SO4 (0.5 M) solution, and it was found that higher delta-ferrite content resulted in less corrosion potential and passive potential. To determine the cause, an analysis was conducted using energy-dispersive spectroscopy (EDS), which confirmed that higher delta-ferrite content led to weaker corrosion resistance, due to Cr degradation at the delta-ferrite and austenite boundaries. The degradation of Cr on the boundaries between austenite and delta-ferrite can be explained by the difference in the diffusion coefficient of Cr in the ferrite and austenite. A scanning electron microscopy (SEM) analysis of material used for actual semiconductor piping confirmed that corrosion begins at the delta-ferrite and austenite boundaries. These results confirm the need to control delta-ferrite content in AISI 316L stainless steel used for semiconductor piping.

Effect of Heat Input in Dissimilar Welding on SS304H and T22 to Hardness Distribution and Delta Ferrite Content with GTAW Process

In this paper, a study was carried out on the effect of various heat input on the hardness distribution and delta ferrite content in dissimilar welding on T22 and SS304H tube boilers in power plants using Gas Tungsten Arc Welding (GTAW). The heat input used in this study is 2.9 KJ/mm, 3.1 KJ/mm and 3.6 KJ/mm. Controlling the heat input parameter is one method to reduce problems in dissimilar welding. The general problem occurs in dissimilar welding is the failure on the weldment to occur due to differences in chemical composition, mechanical properties and thermal coefficients of the two materials where it makes degradation in the microstructure in the fusion zone and creating residual stress than susceptibility to fatigue in material or cracks. All variation of heat input in this study is safe to operate in the welding process and low tendency to hot cracking. Using the lowest variation of heat input 2.9 KJ/mm has the highest value of hardness distribution and lowest FN value.

Combining CaO–SiO2–TiO2 and CaO–SiO2–Al2O3 ternary phase systems for design of bimetallic welds

The bimetallic welds are frequently utilized for pipeline transport system of the nuclear power plants. The occurrences of welding defects generally depend on the filler electrode as well as the electrode coatings during shielded metal arc welding process. This study involves the design of austenitic stainless steel welding electrodes for SS304L–SA516 bimetallic welds. The objective of research work includes the novel design of Al2O3–TiO2–CaO–SiO2 coatings by combining two ternary phase systems using extreme vertices mixture design methodology to analyze the effect of key coating constituents on the weld metal chemistry and mechanical properties of the welds. The significant effect of electrode coating constituent CaO on weld metal manganese content is observed which further improves the toughness of bimetallic weld joints. Various regression models have been developed for the weld responses and multi objective optimisation approach using composite desirability function has been adopted for identifying the optimized set of electrode coating compositions. The role of delta ferrite content in promoting the favourable solidification mode has been studied through microstructural examination.

A New General Paradigm for Understanding and Preventing Li Metal Penetration through Solid Electrolytes

Summary The use of lithium (Li) or sodium (Na) metal anodes together with highly ion-conductive solid electrolytes (SEs) could provide batteries with a step improvement in volumetric and gravimetric energy densities. Unfortunately, these SEs face significant technical challenges, in large part because Li and Na dendrites can penetrate through SEs, leading to short circuits. The ability of such a soft material (Li or Na metal) to penetrate through ceramic is surprising from the point of view of models widely used in the Li-battery field. We introduce a concept, new to the battery field, for preventing penetration of lithium dendrites through SEs by putting the SE surfaces into a state of residual compressive stress. For a sufficiently high compressive stress, cracks have difficulty forming, and cracks that do form are forced to close, inhibiting dendrite penetration. This approach is widely used to solve commercially important stress corrosion cracking problems in metals and static fatigue problems in ceramics and glasses (e.g., Gorilla Glass). However, the technique will not be useful for SEs if the Li-ion transport rate through a SE is substantially reduced when the SE is under compression. Our molecular dynamics calculations for Li-ion transport through a common SE demonstrate that the introduction of even very high residual compressive stresses (∼10 GPa) has only a modest effect on Li-ion transport kinetics, suggesting that this approach is viable and capable of providing a new paradigm for developing high-performance and mechanically stable SEs.

Effect of Co Addition on the Creep Rupture Properties of 9Cr-1.8W-xCo Weld Metals

In this study, the effect of Co addition on the microstructure and creep rupture properties of 9Cr-1.8W-xCo weld metals is investigated. Herein, stick electrodes were fabricated for producing weld metals with 0.5, 1.0, and 1.5 wt pct Co and without Co, which were then processed by post-welding heat treatment at 760 °C for 4 hours. The microstructures of weld metals, including the prior austenite grain size, tempered martensite lath size, delta ferrite content, and precipitate quantity and size, were characterized via optical microscopy, scanning and transmission electron microscopy, and electron backscattered diffraction. The precipitates were identified by X-ray diffraction after they were extracted from the matrix. The Curie temperature was determined via differential scanning calorimetry, which allowed the evaluation of diffusion rate as a function of Co content. The weld metals were mechanically characterized by creep rupture tests conducted at 675 °C under 150 MPa and by hardness and tensile tests conducted at room temperature as well as Charpy impact tests conducted at various temperatures from − 40 °C to 60 °C. The results obtained herein suggest that the addition of Co significantly increases the creep rupture time of 9Cr-1.8W steel (by approximately 20 times than that of Co-free steel), reduces the prior austenite grain size and tempered martensite lath size, hinders the formation of detrimental delta ferrite, and promotes the formation of precipitates with slightly larger size. Herein, the highest creep resistance from the viewpoint of creep rupture time was obtained for 9Cr-1.8W weld metal with 1.5 wt pct Co. Furthermore, the results suggest that a finer and more stable substructure is required for improving the creep resistance.

Influence of liquid nitrogen on residual circumferential distortion, weld penetration and delta-ferrite distribution in clamped tungsten inert gas welded butt joint of 316 stainless steel

AISI 316 stainless steel (SS316) is an attractive material for industrial applications. Welding of this alloy can lead to severe distortion that often results in dimensional inaccuracies. With the help of specially designed fixture and clamping mandrels, tungsten inert gas (TIG) welding on SS316 pipes is employed to investigate the effect of liquid nitrogen on the circumferential distortion, weld penetration and delta-ferrite distribution in different welding zones. The experimental results reveal that the presence of trailing heat sink in TIG welded butt joint has almost zero distortion at a distance of 30 mm from the weld centerline and 64% decrement in residual circumferential distortion at the center of the weld bead. A metallurgical microscope is used to find the weld penetration, (fusion zone) FZ and (heat affected zone) HAZ. The results illustrate that increase in current and the presence of intensive cooling media yield deeper penetration in TIG welding. Liquid nitrogen (LN2) also constricts the FZ and HAZ. Instead of evaluating delta-ferrite contents using the ferrite number technique, a MATLAB® code for image processing is developed to evaluate the delta-ferrite distribution in the different regions of a single-pass weldment. Delta-ferrite contents are maximum in the presence of intensive cooling media near HAZ and increase with an increase in the current value. Hence, TIG welding with LN2 as trailing heat sink is the most suitable scheme to weld industrial pipes owing to its higher weld penetration, higher delta-ferrite contents and minimum circumferential distortion.

Optimization of TIG welding parameter in dissimilar joints of low nickel stainless steel AISI 205 and AISI 216

Abstract Low nickel 200 series grade austenitic stainless steels are popular due to their low price and the welding of these materials is of interest to engineers and fabricators. Therefore, the dissimilar joining of AISI 205 and AISI 216 stainless steels are examined in this paper. The study used a TIG welding process with an ER307 filler metal and stepped up welding speeds with varying mixtures of H2 in the argon shielding gas. The weldments on the weld bead (shape and size), solidification mode (predicted on WRC-1992) and the delta-ferrite content (compared between the predicted and calculated lath ferrite with vermicular ferrite) were examined. The microstructure (volume and formation of delta-ferrite in the austenite matrix), mechanical properties (hardness and tensile strength tests) and pitting corrosion resistance (pitting potential and pitted initial) are also studied. The results indicate that the welding speed can be stepped up from a minimum of 1 to a maximum of 3.5 mm/sec. This parameter affected to an increase weld bead size, delta-ferrite, hardness, tensile strength and pitting corrosion resistance of the weld metals. The role of H2 can help heat collection in the weld pool during welding allowing the welding speed to increase up to a maximum 5.2 mm/sec. This was achieved with a 6 vol.% of H2 in the argon shielding gas. These results can help increase productivity and thus be considered a successful outcome for this work.

Effect of thermal aging on metallurgical, tensile and impact toughness performance of electron beam welded AISI 316 SS joints

Abstract Electron beam welding was used to fabricate a fully penetrated joint of 18 mm thick AISI 316 stainless steel plates. The effects of carbide precipitation on the metallurgical and mechanical properties of the weld were evaluated after aging at 750 °C for 300 h. The optical microstructure analysis showed that the weld zone consists of skeletal, vermicular, lathy, and lacy ferrite which further transformed into carbides after thermal aging. The weld zone was weaker in terms of ultimate tensile strength as compared to the base metal, as the presence of ferrite content (varied from 8% to 2.9 %) in the weld zone. Analysis along the thickness of the welded joint revealed that the bottom of the weld bead possessed 6% higher ultimate tensile strength as compared to the top of the weld bead. The microhardness and impact toughness in as-welded specimens got increased by 12.5 % and 49.5 % respectively while traversing from top to root of the weld bead. Thermal aging promoted the formation of Cr rich carbides (Cr23C6) on the grain boundaries and reduced the delta ferrite content near to zero. Further, it led to a reduction in the impact toughness by 62 % at the bottom of WZ and increased the ductility and the microhardness of the weld bead.

Influence of Chemical Composition and Thermo-Mechanical Processing on the Formation of Delta Ferrite in 10.7CrMoVNbN Steel

M/S Toshiba JSW Turbine & Generator Pvt. Ltd. reported the failure of 10.7CrMoVNbN steel turbine blades used in its power plant for the production of electricity. The basic reason for its failure was the higher content of delta ferrite. The objective of the present study is to reduce the failure of 10.7CrMoVNbN steel caused by delta-ferrite inclusion. 10.7CrMoVNbN steel is used for the fabrication of steam turbine blades by M/S Toshiba JSW Turbine & Generator Pvt. Ltd. Four Heats with chemical composition as well as thermo-mechanical processing and heat treatment were prepared. The main variation in all Heats was the variation in $${\text{Cr}}_{\text{eq}}$$ . Samples were prepared as per standard metallographic technique. Samples etched with kalling’s-1 agent revealed a tempered martensite morphology. The morphology of tempered martensite got refined with the reduction in $${\text{Cr}}_{\text{eq}}$$ . Further, the samples when etched with sulfuric acid etchant revealed the delta-ferrite morphology. Delta ferrite decreased with a decrease in $${\text{Cr}}_{\text{eq}}$$ . FESEM-EDS analysis revealed the presence of carbides and various phases in the steel. Further, to confirm the presence of different phases in the steels, microhardness analysis was performed. Microhardness analysis revealed the presence of tempered martensite matrix, different carbides, and delta ferrite. Further, the decrease in $${\text{Cr}}_{\text{eq}}$$ led to a marginal increase in yield strength, ultimate tensile strength, whereas a significant increase in impact strength was observed. Overall, Heat 4 with $${\text{Cr}}_{\text{eq}}$$ of 11.59 showed the maximum improvement in the mechanical properties. Further, the δ-ferrite content of Heat 4 was 0.3% which was lower than the permissible limit of 2%. Hence, Heat 4 fulfilled the material specifications specified by Toshiba and reduced the material failure caused by δ-ferrite inclusions.

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.

Evaluation of microstructure, mechanical properties and pitting corrosion in dissimilar of alternative low cost stainless steel grade 204Cu and 304 by GTA welding joint

In this present work, solutions are sought regarding the problems of dissimilar welding of austenitic stainless steel for industrial fabrication work. There is support for the popular 200 grade stainless steel as a low-cost alternate to for 300 series grade in developing countries in Southeast Asia, especially Thailand, Vietnam, Myanmar, Laos and Cambodia. This study evaluates the microstructure, mechanical properties and pitting corrosion of dissimilar welding of the alternative low cost stainless steel grades 204Cu and 304 employing a GTA welding process by using different filler metals, namely 309L and 316L. It was found that for both weld metals and both filler metals the melting area in 204Cu BM side was larger than the 304 BM side. The delta-ferrite content in the weld metal of 309L was lower than 316L, HAZ and PMZ on the 204Cu side was wider than the 304 side of both welded metals. For the mechanical properties, the hardness volume of the welded metal of the 309L was higher than the 316L. Hardness adjacent to the fusion line of the 304 side was lower than the 204Cu side of both the filler metals. The tensile strength of the welded metal of 316L was more than the 309L and both welded metals ductile fractured in the welded zone (close to the 304 BM side). The pitting corrosion resistance of the welded metal for 309L was higher than for 316L and both welded metals initiated pitting at the boundary between the austenite phase and the delta-ferrite phase.