Ferrite Grains Research Articles

The Mechanisms of Nano‐AlN Content in the Microstructure and Mechanical Properties of Fe–25Mn–9Al–8Ni–1C–0.2Ti Alloy

In order to design a high‐strength, tough alloy for structural components, Fe–25Mn–9Al–8Ni–1C–0.2Ti–xAlN (x = 0, 0.25, 0.5, 0.75, and 1 wt%) alloys are prepared by powder metallurgy combined with vacuum arc melting. It can be seen from microstructure that the AlN/Al preform obtained by homogenizing mixing followed by vacuum pressureless sintering is added to the arc melting in the form of raw materials, and the AlN phase can exist stably and be uniformly distributed in the matrix. The main phases of the alloys are composed of austenite, ferrite, and TiC. With the increase of AlN content, the ferrite content is decreased and the grains are refined. The distribution of ferrite grains is changed from network to needle‐like and dot‐like morphology. Mechanical property test results reveal that the addition of the nano‐AlN can maintain the stability of the tensile strength while significantly improving its elongation after fracture. Specifically, when the AlN content is 0.5 wt%, the elongation after fracture reaches the maximum value of ≈55.8%, representing ≈98.5% improvement compared to the matrix alloy. It is attributed to the promotion of slip line formation by nano‐AlN, resulting in a higher density of slip lines within the alloy.

Microstructure and mechanical properties of the wire arc additively manufactured 316L/ER70S-6 bimetal structure

ABSTRACT The wire arc additive manufacturing (WAAM) process often begins printing on a substrate. In some cases, the substrate could act as a functional part of the WAAM-fabricated parts. In this work, ER70S-6 is directly deposited onto a 316L substrate using the WAAM process. Microstructural studies reveal good fusion and bonding at the interface. Due to the dilution of ER70S-6 and 316L, a gradient change in composition and microstructure was observed in the first six layers. The first layer (Fe-10Cr-5.5Ni-1Mo-1Mn) and the second layer (Fe-4Cr-2Ni-1Mn-0.5Mo) exhibit a bainite microstructure. Ferritic grains were observed from the third layer onwards. The microhardness is high at 336.9 ± 6.3 HV for the first layer and 302.7 ± 5.7 HV for the second layer. A decrease in microhardness was observed with the increase of the building layer until layer six. The yield strength is 356.6 MPa and the UTS is 502.3 MPa for the 316L/ER70S-6 bimetal joint. The digital image correlation (DIC) method is used to analyse the deformation behaviour. During the tensile test, the 316L substrate side yields first, and then the deformation shifts to the ER70S-6 side. This study also holds the potential for the development of novel alloys.

The effect of air-cooling heat treatment on the microstructure and phase transformations of structural steels

The aim of this study was to investigate the microstructure, phase transformations, and hardness changes of S235JR, S275JR, and S355JR structural steels after air-cooled heat treatment. The steel samples were austenitized at 1000°C and then cooled in air, and the sample temperatures were recorded with a thermocouple during cooling. The microstructure and phase transformations of the samples were analyzed both experimentally and with the Computerized Combining Phase Diagrams and Thermochemistry (CALPHAD) material property software. It was observed that higher carbon and manganese levels in structural steels lower the phase transformation temperatures, promote bainite formation, reduce the average ferrite grain size, and consequently lead to an increase in hardness. The phase ratios and hardness values were determined by the predicted experimental results with a deviation of less than 3%. These results show that a balanced ferrite and bainite phase distribution is achieved air cooling and the software effectively models these transformations.

Phase Formation, Microstructure, and Permeability of Fe-Deficient Ni-Cu-Zn Ferrites (II): Effect of Oxygen Partial Pressure

We have investigated the phase formation, microstructure, and permeability of stoichiometric and Fe-deficient Ni-Cu-Zn ferrites of composition Ni0.30Cu0.20Zn0.50+zFe2−zO4−(z/2) with 0 ≤ z ≤ 0.06 sintered at 1000 °C in various oxygen partial pressures pO2, which range from 0.21 atm down to 10−5 atm. The density of the sintered samples is almost independent of the pO2, whereas the grain size of the Fe-deficient ferrites decreases in more reducing atmospheres. Stoichiometric ferrites show a regular growth of single-phase ferrite grains if sintered in air. Sintering at pO2 ≤ 10−2 atm leads to the formation of a small amount of Cu2O at grain boundaries and triple points. Fe-deficient compositions (z > 0) form Cu-poor stoichiometric ferrites, which coexist with a minority CuO phase homogeneously distributed between the grains after sintering in air. At pO2 ≤ 10−2 atm, the CuO grain boundary phase starts to transform into Cu2O, which concentrates at some triple points at pO2 = 10−2 atm, and it is more homogeneously distributed between the ferrite grains at the lower pO2. Formation of the Cu oxide second phases is investigated using XRD, SEM, and EDX. The permeability at 1 MHz of the stoichiometric ferrites (z = 0) is between µ′ = 200 and µ′ = 300 within the studied range of the pO2. The permeability at 1 MHz of the Fe-deficient samples decreases with the pO2, e.g., from µ′ = 750 at pO2 = 0.21 atm to µ′ = 320 at pO2 = 10−5 atm for z = 0.02, respectively.

COMPOSITION DESIGN OF 316LN AUSTENITIC STAINLESS STEEL FOR LIQUID-HYDROGEN STORAGE BASED ON HIGH-FLUX PREPARATION

Designing multi-element alloy compositions to achieve target performance was the first step in the development of modern materials, but the traditional trial-and-error experiment seriously restricted the development of new materials due to its low efficiency. In this investigation, the composition design of 316LN austenitic stainless steel for enhanced liquid-hydrogen storage using multi-crucible synchronous metallurgy in a high-flux experiment was proposed. Sixteen groups of as cast austenitic stainless steel samples with different compositions were smelted using high-flux material preparation. Then, through the observation of their microstructures, the chemical composition that best matched the target performance was finally selected. The results show that high-throughput experiments can greatly improve the efficiency of composition design optimization of new stainless steel products. At the same time, this investigation also analyzed the elemental composition of δ-ferrite and the method for effectively controlling the δ-ferrite content. In 316LN stainless steel, Cr and Mo were easily enriched in ferrite grains or grain boundaries, forming Cr and Mo enriched regions. This resulted in a gradient transition of Cr and Mo from the ferrite region to the austenite region, forming galvanic corrosion. In this study, the distribution of Cr, Mo and other elements in 316LN stainless steel was studied by means of a metallographic microscope, electron probe microanalysis, transmission electron microscope and scanning electron microscope. In addition, the relationship between the ferrite content and chemical composition was explored. Finally, it was determined that high-temperature, long-term sensitization treatment is an effective method for controlling the δ-ferrite content.

Effect of Elevated Temperature on Microstructure and Mechanical Properties of Hot-Rolled Steel

The mechanical properties and microstructure of hot-rolled steel are critical in determining its performance in industrial applications, particularly when exposed to elevated temperatures. This study examines the effects of varying temperatures and soaking times on these properties through a series of controlled experiments. The primary objective was to optimize the key response parameters, including tensile strength, yield strength, and elongation, by analyzing the influence of temperature and time. A full factorial design approach was used, applying the desirability function theory to explore all possible combinations and identify optimal processing conditions. The experimental results showed that the soaking time played a critical role, significantly influencing the mechanical properties with an impact ratio of 62%. The microstructural analysis displayed that higher temperatures and longer soaking times resulted in the formation of coarser ferrite and pearlite grains, contributing to a decrease in strength and an increase in ductility. The optimum process condition - 650 °C for 60 min - produced the highest values for tensile strength (400.32 MPa), elongation (36.78%) and yield strength (288.52 MPa). The study also highlighted the temperature-dependent nature of the mechanical behavior of hot-rolled steel. While tensile strength and yield strength initially increase with temperature, prolonged exposure, particularly at 600 °C and 750 °C, results in significant grain coarsening and a corresponding degradation of these properties. Conversely, elongation improves at moderate temperatures (150 °C to 300 °C) but decreases with prolonged exposure, especially at higher temperatures. These findings underscore the importance of precise control of thermal processing parameters to optimize the mechanical properties of hot-rolled steel. The findings offer significant insights that can be leveraged to optimize material performance in industrial applications, where thermal exposure is a critical consideration.

Postweld heat treatment of rotary friction welded AISI 1018 steel: microstructure, mechanical properties and corrosion resistance evaluation

The present study investigated the effect of post-heat treatment (PWHT) on the microstructure, mechanical properties and corrosion resistance of rotary friction welded AISI 1018 low-carbon steel. Metallographic analysis revealed that as-welded sample showed heterogenous microstructure consisted of fine grains of polygonal ferrite in weld zone (WZ) and coarse grains of ferrite and elongated pearlite in thermomechanical affected zone (TMAZ), while the postweld heat treated sample showed homogenous microstructure consisted of equiaxed grains ferrite and pearlite both in WZ and TMAZ. Mechanical test results showed that as-welded sample exhibited 36% tensile elongation and 82% bending elongation relative to base metal. After applying PWHT, the tensile elongation enhanced by 178% and bending elongation enhanced by 243% relative to the as-welded sample. The improved elongations after PWHT was caused by homogeneous microstructure consisted of equiaxed grains of ferrite and pearlite in weld joint. Electrochemical results revealed that the order of the corrosion rate is heat treated > base metal > as-welded in 0.5 M H2SO4 environment. The difference in corrosion behavior is primarily related to microstructure development where fine grain structure of as-welded sample with low volume fraction of pearlite showed lowest corrosion rate.

The influence of intercritical temperature, ferrite-austenite morphology, and orientation relationship on martensitic transformation in dual phase steels

Two different morphologies of martensite in dual-phase (DP) steel were obtained through two processing routes. In the first method, the steel was water quenched from a fully austenitic state, followed by intercritical annealing (IA). In the second method, the steel was water quenched, cold rolled, and then subjected to intercritical annealing (C-IA). For IA and C-IA steels, the intercritical temperatures varied from 735oC to 765oC to obtain different fractions of ferrite. To understand the effect of ferrite content, morphology, and the orientation of ferrite/austenite on martensitic transformation, a combination of scanning electron microscopy, electron backscattered diffraction, and dilatometric tests were conducted. It was observed that layered martensite presented in IA samples, and blocky martensite appeared only at prior austenite boundaries at 765oC. In C-IA samples, equiaxed martensite grains were present, which become coarser by elevating the temperature to 765oC. In IA samples, martensitic transformation was much faster than in C-IA samples; the difference in martensitic transformation rate is particularly significant at lower annealing temperatures. Carbon enrichment of the partial austenite had a converse effect on the martensitic transformation at 745°C in both samples. The highest transformation rate was recorded in IA samples at 745°C among all IA and C-IA samples. The ferrite/martensite in IA samples maintained Kurdjumov–Sachs orientation relationship (K-S OR) with prior austenite and selected the same variant in the same block. Whereas, in polygonal samples, ferrite/martensite had an irrational OR with the prior austenite, no variant selection appeared in ferrite and martensite grains. Martensite nucleation accelerated on the ferrite surface when it had a K-S OR with the matrix grain, forming a low-energy interface with the ferrite. In contrast, ferrite surfaces irrationally oriented with the matrix grain did not promote martensite nucleation. This was likely due to the large misorientation and higher carbon build-up near the boundary during intercritical holding. The lower activation energy for martensitic nucleation in IA samples compared to C-IA samples resulted in an accelerated rate of martensite transformation in IA samples.

Effect of purity on the tensile mechanical behavior of pure iron

The current work systematically investigated the microstructures, mechanical properties, textures, dislocation density and dislocation substructures of 3N2, 4N2 and 5N2 pure irons (3N2, 4N2 and 5N2 pure irons represent that the content of Fe are 99.9264 wt%, 99.9925 wt% and 99.9992 wt%, respectively) using SEM, EBSD, XRD and TEM. The results indicated that the recrystallization temperature decreased with increasing purity, and higher purity accelerated grain growth. 4N2 and 5N2 pure irons both presented equiaxed ferrite grains, while the microstructure of 3N2 pure iron was consisted of irregular polygonal ferrites and equiaxed ferrite grains. Low-density LAGBs were observed in annealed pure irons. The fraction of LAGBs increased significantly after deformation, and the LAGBs density decreased as the purity increased. The dislocation substructures of 3N2 and 4N2 pure irons were dominated by sub-grain boundaries with high dislocation densities and dislocation tangles, whilst 5N2 pure iron primarily consisted of fewer sub-grain boundaries and random dislocations. Work hardening was the primary strengthening contribution of pure irons. As the purity decreased, the capacity of work hardening increased, which resulted from the effective obstacles to dislocations by higher fraction of LAGBs, sub-grain boundaries with high dislocation densities and dislocation tangles. Therefore, the improved mechanical properties may be attributed to the increase of work hardening ability with the decrease of purity. 3N2 pure iron presented discontinuous yielding behavior, while 4N2 and 5N2 pure irons exhibited continuous yielding behaviors. The continuous yielding was attributed to the minimal interstitial atoms rarely segregated on mobile dislocations to form Cottrell atmosphere.

Ex-situ observation of ferrite grain growth behavior in a welded 9Cr-1Mo-V-Nb steel during aging at 740 °C

It has recently been reported that ferrite grains coarsened to several hundred micrometers were occasionally observed in long-term serviced 9Cr-1Mo-V-Nb steel welds. To clarify the factors that cause ferrite grain growth in martensite during high-temperature exposure, alternating aging heat treatment and observation of the same field of view was performed using a welded 9Cr-1Mo-V-Nb steel. Such ex-situ observations revealed that the rapid grain growth of ferrite by consuming martensite occurred in the weld metal during aging at 740 °C. In the test material used in this study, some δ-ferrite grains were observed in the weld metal near the fusion line. In the region where δ-ferrite grains were observed, the concentrations of austenite-forming elements such as Mn and Ni were locally decreased in the matrix due to dilution by the base metal, promoting δ-ferrite retention after welding. Ex-situ observation indicated that no significant grain growth of δ-ferrite occurred during aging. Therefore, it was suggested that a new ferrite grain formation followed by rapid grain growth consuming martensite occurred during aging. The elastic strain energy density of the dislocations PMdis and the interfacial energy density PMsurf in martensite can affect the driving force for ferrite grain growth by consuming martensite. Based on the evaluation results for PMdis and PMsurf after 500 h of aging, PMsurf was considered to be the main driving force for ferrite grain growth. Although the ferrite-formation process could not be directly observed, it is possible that ferrite was formed by the recrystallization of martensite through the bulging mechanism.

Deformation behavior and fracture mechanisms of 430 ferritic stainless steel after dual-phase zone annealing via quasi in-situ tensile testing

This study systematically investigated the deformation behavior and fracture mechanisms of AISI 430 ferritic stainless steel (FSS) following dual-phase zone annealing with varying martensite contents, using quasi in-situ tensile testing. In 430 FSS with a low martensite volume fraction, significant deformation occurred through dislocation slip in the ferrite phase, involving the activation of multiple slip systems and dislocation transmission at grain boundaries. In contrast, in sample with high martensite fraction, dislocation slip within the ferrite was restricted, leading to an overall decrease in plasticity. During the tensile process, ferrite grains exhibited different responses under external stress. Additionally, strain concentration mainly occurred at ferrite-martensite phase boundaries and at interfaces between large and small grains. As deformation progressed, strain distribution gradually homogenized in the low martensite fraction sample. However, in the high martensite fraction sample, fracture occurred before strain distribution could become uniform. Weak bonding at ferrite-martensite phase boundaries renders these interfaces critical sites for crack initiation. The combined effects of dislocation accumulation and strain incompatibility lead to the initiation and propagation of cracks, ultimately causing material failure. Optimizing the dual-phase zone annealing processes enables ferrite grains to achieve moderate and uniform sizes while maintaining the continuous distribution of ferrite and the discontinuous distribution of martensite. This microstructural control can effectively reduce interphase stress concentration, enhance the coordinated deformation capabilities of ferrite, and thereby significantly improve the overall performance of 430 FSS.

Interfacial boron segregation in a high-Mn and high-Al multiphase lightweight steel

Interface segregation affects the microstructure evolution and mechanical properties of alloys, including strength, ductility and damage tolerance. This is particularly true for multiphase high-strength steels containing multiple types of interfaces whose characteristics are key factors influencing the steels’ mechanical performance. The different tendencies of solute segregation to different types of interfaces can lead to complex segregation behavior, which needs to be understood. Here, we focus on the segregation behavior of B in a high-Mn, high-Al lightweight steel with a two-phase austenite-ferrite microstructure. We find distinct B segregation at both austenite and ferrite grain boundaries as well as at austenite-ferrite phase boundaries after high temperature annealing (1100°C) and fast quenching. The segregation process is governed by local equilibrium between bulk and interfaces as discussed in terms of thermodynamic and ab initio calculations. Our findings reveal a dependence of B segregation on the interface structure regardless of the adjacent phases, which can be explained in terms of respective interfacial energy in accord with the Gibbs adsorption isotherm. In addition, co-segregation of B and C is observed at both high-angle and low-angle ferrite grain boundaries due to the attractive interaction between the two solutes in the bulk ferrite phase. In contrast, for austenite grain boundaries, C depletion is observed owing to its site competition effect and repulsive interaction with B in austenite. These observations help to guide interface segregation engineering in complex multiphase lightweight steels to improve their mechanical performance.

Enhanced creep lifetime in P91 steel weldments via stabilizing tempered martensite structure

P91 steel weldments are susceptible to Type IV creep cracking during high-temperature service, significantly reducing the creep lifetime of impacted components. For enhancing the creep lifetime of P91 steel weldments, the present work proposes a novel post-weld heat treatment strategy to stabilize the tempered martensite structure and avoid Type IV creep cracking. Compared to conventional post-weld tempered treatment weldments, the creep lifetime of as-welded weldment is improved by 1.7 times, while the creep lifetime of weldment subjected to post-weld normalizing followed by tempering is enhanced by 4.6 times, effectively preventing Type IV cracking. It has been revealed that creep weakness zones, that is, soft zones, occur in as-welded weldment and post-welded tempering treatment weldment, where the microstructure is predominantly recrystallized ferrites. Creep fracture always occurs in the region of the highest fraction of recrystallized grains. Post-weld normalizing and subsequent tempering can enhance prior austenite grain size and stabilize tempered martensite structure. For as-welded weldment and post-welded tempering treatment weldment, creep cavities preferentially grow along ferrite grain boundaries as compared to prior austenite grain boundaries, which could easily lead to intergranular premature cracking. For post-weld normalizing and subsequent tempering weldment, cavities form along prior austenite grain boundaries of base metal and are elongated together with martensitic packets/blocks under stress. Finally, the final fracture is caused by the rupture of elongated grains.

An empirical model of the kinetics of hydrogen-induced cracking in pipeline steel, using statistical distribution models and considering microstructural characteristics and hydrogen diffusion parameters

This study proposes an empirical model to predict the kinetics of hydrogen-induced cracking (HIC) growth rate in pipeline steels based on experimentally measured hydrogen diffusion parameters and spatial distribution of microstructural features previously identified to have a role on HIC kinetics. In the experimental work, the HIC was induced by electrochemical cathodic charging and the crack growth was monitored by ultrasonic inspection. Optical and scanning electron microscopy were used to determine the spatial distribution parameters of non-metallic inclusions, and the ferrite grain and second phase characteristics. The hydrogen microprint technique used to visualize hydrogen diffusion path in the microstructure and the hydrogen diffusion parameters were determined by hydrogen permeation tests. Results show that NMI shape affects HIC nucleation sites, using student's t-distribution, while ferrite grain characteristics affect HIC growth rates, with X70–2 and X56 steel plates recorded highest HIC growth rate. The Log-Normal distribution model, supported by statistical analysis, effectively predicts HIC growth rates compared with Weibull and Gamma distribution models.

Effect of Si on the Yield Strength of Medium-Carbon Steels Consisting of Ferrite and Pearlite

To enhance the intrinsic yield strength of the ferrite-pearlite microstructure that inevitably forms in a non-quenched-and-tempered steel for large structural components, this study analyzed the effect of adding Si. The resulting ferrite-pearlite microstructure in medium-carbon steels was examined, and the resulting increase in yield strength was interpreted based on strengthening mechanisms. Hot-rolled sheets of 0.3C-1.5Mn steels were fabricated with Si ranging from 0.22 to 2.21 wt. %. Austenitization was conducted at 880°C followed by slow continuous cooling, and ferrite-pearlite microstructures were formed. With increasing Si, the yield strength increased from 409.1 to 573.6 MPa. Although there was a negligible change in the austenitic grain size, the mean diameter of the ferritic grains decreased from 8.8 to 5.0 μm, while the mean interlamellar spacing of the pearlites decreased from 196.6 to 109.9 nm. Using these quantitative data about microstructural features and considering possible strengthening mechanisms, a model to predict yield strength was derived via a constrained optimization method. The resulting model indicated that the major mechanisms are the refinement of pearlitic interlamellar spacing and the solid solution strengthening of ferrite by Si. Their contribution to the increment in yield strength was over 75 %, while others such as ferritic grain refinement and increased pearlitic volume fraction have limited influence.

Examination of Microstructure, Mechanical Properties, and Fatigue Strength in a Wire Arc Additively Manufactured Material Comprising Dissimilar Materials: AISI 316L Stainless Steel and Carbon Steel

This study provides a comprehensive investigation into the microstructure, hardness, tensile strength, and bending fatigue behavior of a Wire Arc Additively Manufactured (WAAM) component composed of dissimilar materials—Carbon Steel (CS) and 316L stainless steel. Microscopic analysis reveals distinct microstructural characteristics, such as equiaxed ferrite grains in WAAM CS and a coarse columnar structure with delta-ferrite phases in WAAM 316L. A macroscopic phase map indicates a predominantly Body-Centered Cubic (BCC) structure near the interphase, suggesting element migration between CS and 316L due to high heat input. Higher magnification scans highlight martensitic structures on both sides of the interphase, with the CS side exhibiting larger grain sizes. Hardness assessment along the built direction shows a peak hardness of 407 HV near the interphase on the 316L side, contrasting with the CS side's average interphase hardness of 316 HV due to larger grain sizes. The yield strength of both WAAM CS and WAAM dissimilar material was consistently measured at 392 MPa. In comparison, WAAM 316L exhibited a slightly lower yield strength of 359 MPa. Notably, WAAM 316L demonstrated the highest tensile strength among the materials, reaching 656 MPa. Meanwhile, WAAM CS displayed a robust tensile strength of 503 MPa, and the WAAM dissimilar material exhibited a yield strength of 520 MPa. In terms of elongation, WAAM CS and WAAM 316L showcased values of 44.9% and 49.6%, respectively. On the other hand, WAAM dissimilar material exhibited a somewhat lower elongation of 20.4%, suggesting a different mechanical behavior in terms of ductility. Bending fatigue tests on WAAM 316L, WAAM CS, and the dissimilar material reveal a fatigue limit of approximately 225 MPa for WAAM 316L, 210 MPa for WAAM CS, and approximately 210 MPa for the dissimilar material. In the low-cycle and medium-cycle regimes, the dissimilar material exhibits slightly superior fatigue strength, potentially due to its marginally higher static strength. Notably, consistent fractures on the CS side during fatigue tests underscore a recurring behavior in the dissimilar material.

Comparison of Novel 1 GPa Low‐Carbon, Low‐Alloyed Steel Produced with Simulated and Laboratory‐Scale Thermomechanical Controlled Processes

A laboratory‐scale hot‐rolled Ti–Mo–V–Nb steel with 1 GPa tensile strength is produced, and its microstructure and tensile properties are characterized using advanced analysis techniques and uniaxial tensile testing. A Gleeble 3800 thermomechanical simulator is used to determine a process window for the thermomechanical controlled processing (TMCP) procedure. Although the simulated TMCP specimens are fully ferritic at coiling temperatures (CT) of 590 and 630 °C, the bainitic and mixed (bainitic + ferritic) microstructure is formed in the hot‐rolled steels. The variation in the microstructure causes variations in the dislocation density through the sheet thickness, which significantly reduces the steel's ductility properties, whereas a 16% elongation is achieved with the fully bainitic microstructure. Another significant difference between the simulated TMCP and hot‐rolled specimens is the precipitation behavior. No nanosized interphase‐precipitated (IP) carbides are formed in the hot‐rolled steel during the austenite‐to‐ferrite phase transformation, although the formation of the nanosized spherical IPs is observed within the polygonal ferrite grains of the simulated TMCP specimens at the CT of 630 °C. Relatively coarse (5–20 nm) spherical (V,Mo,Ti,Nb)C carbides do not strongly affect the tensile properties of the hot‐rolled Ti–Mo–V–Nb steel. The results show that the dislocation and grain boundary strengthening mainly contribute to the strength properties of this steel.

Achieving balanced mechanical properties in Fe–0.16C plain low-carbon steel by trimodal microstructure and fine cementite

In the present study, for the first time, a trimodal microstructure (including coarse, fine, and ultrafine ferrite grains) was created in plain low-carbon steel by simple thermomechanical processing including intercritical annealing (at 770 °C, 800 °C, and 830 °C), 75% cold rolling, and finally heat treatment at 550 °C. The results showed that martensite with two different morphologies consisting of lath (low-carbon) and plate (high-carbon) were created in the microstructures of 800-75% and 830-75% sheets due to the non-homogeneous distribution of carbon atoms as a result of not using the homogenization treatment. After the final heat treatment, the samples exhibited trimodal grain size distribution of ferrite including coarse grains (larger than 5 micrometers), fine grains (between 1 and 5 micrometers), and ultrafine grains (UFGs) (smaller than 1 micrometer). The formation of ultrafine grains was ascribed to the presence of martensite with lath morphology in the 800-75% and 830-75% samples. The size of cementite particles in the 770-75%-550 sample was larger than the other two samples (800-75%-550 and 830-75%-550) owing to the presence of martensite phase only with plate morphology in 770-75%-550 steel. Unlike the 800-75%-550 sheet, the entire microstructure of the 770-75%-550 and 830-75%-550 samples had not undergone complete recrystallization and several deformed ferrite grains were still visible in the microstructures. The strength and hardness of the heat-treated sheets was larger than that of the as-received steel due to the presence of fine spherical cementite particles and fine ferrite grains in the microstructure of the heat-treated samples. Based on the obtained results, the 800-75%-550 sample revealed the best combination of strength-ductility-toughness due to trimodal microstructure along with the formation of fine spherical cementite particles. The failure mode of all heat-treated samples was ductile and there were both fine and coarse dimples in the fracture surfaces.

An extensive analysis of GTAW process and its influence on the microstructure and mechanical properties of SDSS 2507

The Gas Tungsten Arc Welding (GTAW) process is well-known for its accuracy, simplicity, and economical, making it the optimum method for joining Super Duplex Stainless Steel (SDSS) materials. This review paper investigates the influence of the GTAW process on the microstructure, tensile strength, micro-hardness and corrosion resistance of SDSS welded joints. The optimum constant current GTAW process parameters are discovered by various researchers who found that the welding current range should be 65A–160A for joining up to 6 mm thick SDSS material. The pulsed current GTAW process optimum Peak current range (120–165A) and back current (60–80A) range for joining 4–14 mm thick SDSS material. Microstructural analysis revealed that coarse grain is in the welded joint's weld zone (WZ) and heat-affected zone (HAZ) because of the weld thermal cycle. The Widmanstatten austenite with ferrite grain boundary is found between HAZ and WZ due to thermal cooling. Welded joint tensile strength (740 MPa–896 MPa) is sometimes greater or the same as the base metal. It shows the GTAW best parameters selection. The microhardness of HAZ (380 HV) and WZ (370 HV) of the welded joint is increased with respect to base metal (310HV) GTAW process. Multiple studies have shown that using the best GTAW parameters can improve the microstructural properties of SDSS, resulting in increased tensile strength. The charge transfer resistance analysis of GTAW welded joint revealed that higher charge transfer leads to a lower corrosion rate having ER2594 filler material with icorrs value of 0.0139 μA/cm2.

Annealing temperature-dependent microstructure, mechanical, and tribological properties of intercritically heat-treated dual-phase steel

Abstract This study investigates the role of intercritical annealing temperature on microstructural characteristics, mechanical performance, and wear resistance of DP1000 steel. As-received DP1000 steel samples in cold-rolled conditions were subjected to intercritical annealing between 730 and 880 °C with an interval of 30 °C, followed by water quenching. After heat treatment, the specimens were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), mechanical tests consisting of hardness, impact, and tensile tests, and dry sliding wear tests. The findings revealed that equiaxed ferrite grains replaced elongated ones, and the martensite ratio increased from 21% up to 64% with increasing annealing temperature. Due to the formation of equiaxed grains, the impact strength was at least doubled for each specimen by heat treatment, reaching a peak value (9.55 J cm−2) at 760 °C. The hardness (311 HB) and tensile strength (1007 MPa) of the as-received sample were higher than that of the annealed steels up to 820 °C. The mechanical strength of the samples improved at 850 and 880 °C by approximately 10%, and accordingly, the lowest wear rate was obtained at the specimen annealed at 850 °C. The increase in temperature up to 880 °C caused a decrease in wear resistance due to excessive brittleness.