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Three composite bronzes reinforced with steel dendrites from steels of different classes, which perform the function of a bearing surface in sliding friction, are studied. The chemical compositions of the dendrites and of the matrix are determined as a function of the heat treatment of bronze BrZhNOA 12-7-2-1. The fine structure of dendrites in bronze BrZhNKoA 9-4-1-1 is studied and the effect of the aging temperature in the intermetallic reinforcement of the dendrite with composition corresponding to maraging steel N23Yu1 is determined. The type of the crystal lattice of the dendrite is shown to affect substantially the tribological properties of bronze BrZhNKhA 12-9-3-1. © 2022, Springer Science+Business Media, LLC, part of Springer Nature.

Industrial development continues to present challenges for manufacturers. One of them is additive manufacturing (AM) with metallic materials. One promising solution is wire arc additive manufacturing (WAAM). Currently, WAAM is a more promising tool for developers, firstly due to the simplicity of its realization and secondly for its cost-effectiveness. Building materials are represented by welding wires, so the deposition rate is favorable. A pulse power source is commonly used in this scheme of realization. Much less attention has been paid to the optimization of the power source working regime, i.e., welding mode. Indeed, the power determines the whole process of WAAM. Therefore, in the present work, an attempt has been made to perform a scientifically based design for the optimal welding mode. The austenitic welding wire was chosen to eliminate phase-transition effects in the solid state of the deposited metal. As a result of the investigation, the advantages of the designed welding mode for WAAM application are made clear. Successful efforts have been made to optimize welding modes for WAAM applications. This study is important for manufacturers as well as engineers and scientists.

To compare the design, metallurgy, mechanical performance, and canal preparation of 5 rotary systems.A total of 735 25-mm NiTi instruments (sizes 0.17[0.18]/.02v, 0.20/.04v, 0.20/.07v, 0.25/.08v, 0.30/.09v) from ProTaper Gold, ProTaper Universal, Premium Taper Gold, Go-Taper Flex, and U-File systems were compared regarding overall geometry and surface finishing (stereomicroscopy and scanning electron microscopy), nickel and titanium ratio (energy-dispersive spectroscopy), phase transformation temperatures (differential scanning calorimetry), mechanical performance (torsional and bending tests), and unprepared canal surface (micro-CT). One-way ANOVA and Mood's median tests were used for statistical comparisons with a significance level set at 5%.Stereomicroscopic analysis showed more spirals and high helical angles in the Premium Taper Gold system. All sets of instruments had symmetrical spirals, no radial lands, no major defects, and an almost equiatomic ratio between nickel and titanium elements, while differences were observed in their tips' geometry and surface finishing. At room temperature (20 °C), DSC test revealed martensitic characteristics for ProTaper Gold and Go-Taper Flex, and mixed austenite plus R-phase for the Premium Taper Gold, while ProTaper Universal and U-Files had full austenitic characteristics. Overall, larger instruments had higher torque resistance and bending load values than smaller ones, while a lack of consistency and mixed values were observed in the angle of rotation. The 0.25/.08v and 0.30/.09v instruments of ProTaper Universal and U-File had the highest maximum torques, the lowest angles of rotation, and the highest bending loads than other tested systems (P .05). No significant difference was noted regarding the untouched root canal walls after preparation with the tested systems (P .05).Although differences observed in the overall geometry and phase transformation temperatures have influenced the results of mechanical tests, unprepared canal surface areas were equivalent among systems.Root canal preparation systems with similar geometries might present different mechanical behaviors but equivalent shaping ability.

In this study, microstructure and mechanical properties of thin wall austempered and intercritically austempered ductile iron with a chemical composition of 3.37%C, 2.7%Si, 0.30%Mn, 0.01%S, 0.01%P, 0.47%Cu, and 0.0371%Mg were investigated. Thin ductile iron samples with different thicknesses of 5, 10, and 15 mm were cast and then heat treated with two different austempering techniques. The first sample was austenitizing below upper critical temperature at 810 °C for an hour and then rapidly quenched in a salt bath at 375 °C and held for 1 h (IADI). The second treatment was carried out at austenitizing temperature of 900 °C, which was above upper critical temperature, for an hour and then rapidly quenched in a salt bath at 375 °C for 1 h (ADI). The mechanical properties of the austempered and intercritically austempered thin wall samples were evaluated and compared to the as-cast samples. The fatigue properties of all samples were simulated using ANSYS software, and the best condition was experimentally tested using plane bending fatigue testing machine. Maximum ultimate strength (1056) MPa and hardness (396 HV) were obtained for 5 mm ADI sample. Maximum impact toughness (43 J) was achieved for 15 mm IADI sample due to existing proeutectoid ferrite in matrix. Maximum simulated fatigue strength (435 MPa) was reported for 5-mm ADI sample and minimum simulated fatigue strength (160 MPa) was registered for as-cast DI sample. For both ADI and IADI castings, fatigue strength decreased with increasing sample thickness. For 10-mm ADI sample, the simulated fatigue strength was (407 MPa) which was close to the experimental result (417 MPa).

Novel steel of Fe-0.81C-1.9Mn-1.48Si-0.27Mo-0.95Ni-1.43Co-0.79Al composition was austenitized at 930 °C and isothermally treated at 240 °C for different intervals of time to produce carbide-free nanostructured bainite. The metastable austenite transformed to nanostructured bainite without any carbide precipitation. The transformation was slow but isothermal in nature, i.e., volume fraction of transformed product was increasing with time. The stability of phases was investigated under electropulsing at a high peak current density of 8.3 kA/mm2 and a low total pulse duration of 265 μs. Electropulsing drove cementite precipitation kinetics in both austenite and bainite even in the presence of high silicon content of 1.48 mass%. Thereby major part of metastable carbon lean austenite transformed to bainite in a few microseconds. As a result, the remaining austenite changed its morphology from a blocky form toward a desirable filmy form. Precipitation in bainite restricted its growth and nanostructure was maintained. The overall hardness of the steel was decreased due to reduction in residual strain, dislocation density although austenite was transformed to bainite, and precipitation of cementite, but hardness was much higher than that of coarse-grained ferrite. Electropulsing of nanostructured bainite increases the elastic modulus by the combined effect of transformation of retained austenite to bainite and cementite precipitation in austenite/bainite.

55Cr17Mo1VN high nitrogen martensitic stainless steel is usually applied to the high-quality mold, which is largely produced by the pressurized electro slag remelting process. The microstructure evolution of quenching and tempering heat treatment were investigated and an optimal heat treatment process to achieve excellent mechanical properties was found out. The main precipitates in the steel included carbon-rich type M23C6 and nitrogen-rich type M2N. With increasing austenitizing temperature, the equivalent diameter of the precipitates got fined, and retained austenite content increased significantly when the austenitizing temperature exceeded 1020 °C. The fracture mode gradually changed from brittle fracture to ductile fracture with increasing tempering temperature from 200 to 550 °C. The experimental steel tempered at 350 °C achieved a good combination of hardness (60.6 HRC) and strength (2299.2 MPa) to meet service requirements. Flake M23C6 precipitated along martensite lath boundaries and the secondary hardening phenomenon occurred when the tempering temperature was 450 °C. Due to the high nitrogen content, M2N precipitated from the inside of laths and matrix when tempered at 550 °C.

This paper provides a mechanistic understanding of hydrogen-microstructure-strain interactions in a finely-grained 25Cr-7Ni super duplex stainless steel subjected to dynamic tensile loading. Miniature-sized tensile specimens were hydrogen-charged for up to nine days, and the microstructure was imaged, in-situ, during mechanical tensile testing. Digital image correlation analysis of the recorded images revealed that the austenite phase underwent softening while the ferrite phase hardened due to uptaken hydrogen. Severe strain localization occurred due to dissolved hydrogen in the microstructure resulting in hydrogen-induced cracks. Mobile hydrogen atoms caused softening of the microstructure while trapped hydrogen reasoned hardening. The austenite's hydrogen absorption capacity is decisive for the susceptibility to hydrogen embrittlement.

Quenching and partitioning (Q&P) treatment is a novel method to produce advanced high strength steel with excellent mechanical properties. In this study, combination of multiple-cyclic annealing and Q&P process was compared with traditional cold-rolled Q&P steel to investigate the microstructural characteristics and austenite retention. The results showed that retained austenite in traditional Q&P sample was principally located in the exterior of austenite transformation products, while those in multiple-cyclic annealing samples were mainly distributed inside the transformation products. With the increase in cyclic annealing number, both of austenite fraction and austenite carbon content increased, attributing to higher initial austenite carbon content and larger number of austenite/neighbored phase interface to act as carbon partitioning channel. In traditional Q&P sample, the deformed ferrite was recrystallized by sub-grain coalescence, while the austenite was newly nucleated and grew up during annealing process. As a comparison, the ferrite in multiple-cycle annealing samples was formed by means of three routes: tempered martensite that completely recovered with retention of interior martensite variant, epitaxial ferrite that formed on basis of tempered martensite, ferrite that newly nucleated and grew up during the final annealing process. Both of lath martensite and twin martensite were formed as initial martensite and then tempered during partitioning process to precipitate e carbide with C enrichment, Mn enrichment and homogeneous Si distribution. Compared with the traditional cold-rolled Q&P steel, the Q&P specimens after multiple-cyclic annealing show smaller strength and much larger elongation, ascribing to the coarser microstructure and more efficient transformation induced plasticity (TRIP) effect deriving from retained austenite with high carbon content and larger volume fraction. The application of double annealing treatment can optimize the mechanical properties of Q&P steel to show a striking product of strength and elongation as about 29 GPa%, which efficiently exploit the potential of mechanical performance in low carbon steel.

Carbon diffusion at the solid–liquid interface is of fundamental importance in scrap melting. Herein, the scrap microstructure at the melt interface and the carbon and silicon distributions are described using optical microscopy and electron microprobe analysis (EPMA). The microstructural path from the surface to the interior of the scrap was primary carbide → acicular martensite → dislocation martensite (original structure). The corresponding carbon concentration gradient was > 4 wt.% → 1–1.5 wt.% → 0.2 wt.%. This was consistent with the observed microstructural changes. Furthermore, the depth of the carbon diffusion layer was 200 μm and 220 μm at 1300°C and 1350°C, respectively. The silicon-enriched layer may be a retarding factor for carbon dissolution. The area of the austenite phase region in the Fe-Fe3C phase diagram was reduced owing to the presence of silicon. Therefore, acicular martensite formed after water quenching decreased, which reduced the thickness of the carburized layer.

A multi-component multi-phase-field model was conducted to simulate the solidification process of Fe-Mn-C-Al high-Mn steel with different solidification modes, especially that with the peritectic phase transition. The evolution of the microstructure and solute distribution during the solidification process was analyzed. In addition, the influence of the C content, cooling rate, and thermal undercooling was discussed. The results reveal that the area of interfaces and solute distribution influence the evolution of phase fractions. The amount of initial ferrite phase, the solute distribution formed by the initial ferrite phase, and the nucleation position of austenite phase are key factors affecting the microstructure morphology and microsegregation. The microstructure and microsegregation have an interactive effect. Increasing C content changes the solidification mode, leading to different microstructure and microsegregation. For all the steel with different C contents, the cooling rate and undercooling do not influence the phase transition sequence, while they affect the microstructure and microsegregation. The cooling rate and thermal undercooling have more influence on the solidification process of hypo-peritectic high-Mn steel than hyper-peritectic steel. The present study contributes to providing significant reference for the process control of the microstructure morphology and microsegregation of peritectic high-Mn steel.

Hydrogen embrittlement can occur in steels with metastable phases, due to activation of the hydrogen-enhanced decohesion mechanism upon transformation. Meanwhile, recent investigations suggest that alloys undergoing e-martensite transformation may exhibit resistance to hydrogen embrittlement. To better understand hydrogen effects in these alloys, we investigate the hydrogen-induced microstructural transformations in a metastable Fe45Mn35Co10Cr10 alloy. To this end, we electrochemically charge unstrained samples, quantify the hydrogen evolution by thermal desorption spectroscopy, and observe microstructural transformations by scanning electron microscopy techniques. Through these analyses, we find that the hydrogen-induced e-martensite formation is dependent on the crystallographic orientation of the austenite grains, and takes place preferentially along Σ3 boundaries. Further charging of hydrogen induces extension twinning within the martensite. We examine the microstructural factors influencing these transformations to better understand the hydrogen-microstructure interactions.

Plasma nitrocarburizing has been widely used to improve the hardness of stainless steels without affecting their good corrosion resistance property. The process is usually carried out by using gas discharge of N and C containing gases, with admixing H2 or Ar gas or H2-Ar in combination. The aim of the present work was to study and compare the effects of H2, Ar and H2-Ar gas in combination, admixed with N2-C2H2 gas mixture on the surface properties of austenitic stainless steels (viz. AISI 304 and 304L). The process was carried out at 400 °C and 500 Pa for 5 h. The treated samples were analyzed for their structural, mechanical, and electrochemical properties using x-ray diffractometer, scanning electron microscope, Vickers microhardness tester and potentiodynamic polarization testing instruments. Nitride- and carbide-free S-phase dual-layers were observed after plasma nitrocarburizing and their thicknesses varied with the different gas mixtures. Also, optical emission spectra of the gas discharges were recorded during the process and it was seen that the intensities of CH radical (431.44 nm) and CN radical (388.43 nm) lines were greater for Ar containing discharges. Hardness and pitting corrosion resistance were observed to be better with hydrogen compared to the other gas mixtures. Moreover, AISI 304 exhibited greater improvements in the surface hardness and corrosion resistance properties compared to AISI 304L.

Severe abrasive wear of drill pipe and casing often occurs in exploration drilling operations. To achieve the surface enhancement of the drilling components in terms of abrasive wear resistance, various flux-cored wires (FCWs) containing multiple alloying elements were developed, and the Fe-based hardfacing layers were developed by metal active-gas (MAG) welding process. The macro morphology, microstructure, and phase composition of the alloys were characterized by using OM, SEM, XRD, and EDS methods, while the wear resistance performance was measured by using an abrasion tester. The results showed that the hardfacing layer prepared by Fe-Cr-C FCW is hypoeutectic that mainly consisted of austenite matrix and (Fe,Cr)7C3-type carbides. On this basis, a higher C content in combination with Nb, Ti, and B additives resulted in the microstructure comprised of martensite-based matrix and the precipitations of (Nb,Ti)C and Fe2B hard phases. With the removal of Cr, the further addition of Nb, Ti, and B, the hard phases change from particles to bulk and lath shapes. The hard phases with higher microhardness values than the matrix contributed to an improved Rockwell hardness and a highly decreased wear weight loss of hardfacing layer. Accordingly, the wear mechanism changed from severe plastic fracture to micro-cutting going with a slight brittle micro-peeling. The interlaced distribution of (Nb,Ti)C and Fe2B provided a stable skeleton that enables an further enhanced abrasive wear resistance.

The steel 42CrMo4 with improved machinability was studied. The steel containing high amount of sulfur was calcium treated during metallurgical production stage. The size and area distribution of non-metallic inclusions present in the studied steel was analyzed and compared to the conventional Cr–Mn–Mo steels with low sulfur and calcium content. The dilatometric investigation was performed to reveal the features of the austenite transformations in studied Cr–Mn–Mo steels with various content of alloying elements. The mechanical properties of the high and low sulfur steels were analyzed in heat treated condition (oil quenching and tempering). The results proved that calcium treated 42CrMo4 steel with high sulfur content possessed almost the same characteristics of hardenability and mechanical behavior as the conventional low-sulfur steels. This implies that the steel with improved machinability can be successfully applied for the production of the heavy duty and high strength parts using automated lines and machines.

Effect of active screen plasma nitriding (ASPN) on microstructure, hardness, and wear loss of 347H austenitic stainless steel (AuSS) was studied at various processing parameters. Scanning electron microscopy, x-ray diffraction (XRD), hardness, and wear tests were performed on samples. The XRD analysis showed the presence of S-phase (γN-expanded austenite) in samples nitrided at 350 °C and 400 °C. In contrast, samples nitrided at higher temperatures ranging from 450 to 550 °C showed the presence of various types of nitride phases in the nitrogen-enriched layer. The case depth and mass of nitrided samples increased with the increase in nitriding temperatures owing to the increase in diffusivity of nitrogen at a higher temperature. The wear loss of samples nitrided at higher temperatures was lower than those nitrided at lower temperatures due to the formation of a higher amount of hard nitride phase(s) in the nitrogen-enriched layer at temperature ≥ 450 °C.

In this research, the effect of solidification pressure on phase transformation temperature and sequence, amount of proeutectoid ferrite, characteristics of pearlite and carbonitrides have been investigated by microstructure observation, crystal structure and component analysis, and thermodynamic calculation. The microstructure of 30Cr15Mo1N ingot is mainly composed of martensite, austenite, pearlite, ferrite, M23(C,N)6 and M2(C,N). With increasing solidification pressure, M23(C,N)6 precipitation temperature, austenite (γ) and ferrite (δ) formation temperature increase, and M2(C,N) precipitation temperature and ferrite (α) formation temperature decrease. Under 0.5 MPa, the precipitation sequence during solidification process of 30Cr15Mo1N ingot is “L → δ → γ → M2(C,N) → M23(C,N)6 → α + martensite/retained austenite → pearlite”. There is a negligible change in phase transformation sequence with increasing solidification pressure from 0.5 to 2 MPa. In addition, the increment in solidification pressure is beneficial to significantly increase the amount of proeutectoid ferrite and reduce pearlite lamellar spacing by enhancing cooling of 30Cr15Mo1N ingot. Meanwhile, with increasing solidification pressure from 0.5 to 2 MPa, the size of M2(C,N) and the amount of precipitated phases (pearlite and carbonitrides) have a decreasing trend, and the change in the size of M23(C,N)6 can be neglected.

This study investigates the microstructure and the hardness of thermomechanically processed joints of ultra-high-strength steel (UHSS) S1100MC, which were butt-welded by means of metal active gas (MAG) welding and electron beam welding (EBW). In MAG welding, the microstructure of the fusion zone (FZ) consisted predominantly of fine ferrite grains. Due to the formation of martensite/austenite (M/A) constituents, the hardness of the reheated weld metal (WM) was higher for vertical-up (PF) than for horizontal flat (PA) welding position. The microstructure of the heat-affected zone (HAZ) of the last welding pass consisted mainly of hard martensite in consequence of fast cooling. However, necklace-type M/A constituents and bainite phases of lower hardness formed when the HAZ of prior welding passes were reheated by subsequent welding passes. The microstructure of the EBW fusion zone was dominated by martensite. Therefore, the fusion zone had considerable higher hardness than the base material (BM). The width of the HAZ in EBW weldments is less than in MAG weldments.

In this study, the carbide precipitation at 925 °C in austenite (γ) of a 0.04C–1.5Mn–0.10Ti–0.39 W (wt%) low-carbon steel was investigated by stress relaxation (SR) high-resolution transmission electron microscopy and atom probe tomography. First-principles calculations were employed to reveal the precipitation mechanism. Results indicate that a high dispersion of W- and Fe-rich MC-type ultrafine carbides (

A superior combination of yield strength (1001 MPa) and − 20 °C impact toughness (166 J) was obtained in Nb–V–Ti-microalloyed Ni–Cr–Mo–Cu steel treated by direct quenching and tempering route (DQT). The tested steels treated by DQT route and re-austenitization and tempering route (QT) were compared with each other in terms of mechanical properties and microstructures characterized by optical microscopy, transmission electron microscopy, X-ray diffraction, electron back-scattered diffraction method and so on. Strength and Vickers hardness of the tested steel treated by the above two routes vary with isothermal aging temperature (400–600 °C), shown as under-aged state, peak-aged state and over-aged state. All DQT specimens show higher strength and Vickers hardness than QT specimens with the same aging condition. Furthermore, the largest difference of yield strength between DQT and QT specimens was shown in DQT600 and QT600 specimens. DQT600 or QT600 specimens refers to direct quenched (DQ) or quenched (Q) specimens isothermally aged at 600 °C. The main disparities in quenched microstructure between DQ and Q specimens are mainly in morphology of prior austenite grains, dislocation density of martensite matrix and solution amount of Nb and Mo elements dissolving in martensite matrix, which play key roles in affecting microstructure and mechanical properties of DQT and QT specimens. Higher dislocation density of matrix and finer average diameter of both MC (M is any combination of Nb, Mo and V) and Cu-rich particles were shown in DQT600 specimens than in QT600 specimens. Strengthening from dislocations and nanosized MC and Cu-rich particles mainly leads to the largest difference of yield strength between DQT600 and QT600 specimens. In addition, strong dislocation strengthening and precipitation strengthening in DQT600 specimen also elevated its ductile-to-brittle-transition-temperature, compared with QT600 specimen.

Mathematical analysis of experimental data for low-alloy steel 09G2S austenite recrystallization after hot rolling is provided. An original mathematical model is proposed that relates the volume fraction of recrystallized structure to degree of hot deformation, temperature, and recrystallization annealing duration. The prediction accuracy for this model evaluated in terms of dispersion of deviation for experimental data from predicted results standardized for the average value of experimental results comprises ≈ 20%.

Cavitation plays a central role during creep-fatigue. During recent years, fundamental models for initiation and growth of creep cavities that do not involve any adjustable parameters have been developed. These models have successfully been used to predict creep rupture data for austenitic stainless steels again without using adjustable parameters. However, it appears that basic models have not yet been applied to creep-fatigue assessments. A summary of the fundamental cavitation models is given. A model for monotonous deformation is transferred to cyclic loading. The parameter values are kept except that the dynamic recovery constant is raised due to increased interactions between dislocations during cycling. This model is successfully compared with observed LCF and TMF hysteresis loops. A new model for cavity growth due to plastic deformation is presented. The model is formulated in such a way that the condition for constrained growth is automatically satisfied. In this way, it is avoided to overestimate the growth rate.

Considering the thermophysical properties of materials and the latent heat of phase change, the temperature field, HAZ microstructure evolution, residual stress and post-weld deformation of S355JR-316L dissimilar metals were numerically simulated using SYSWELD software and verified by experiments. After welding, the phase transition only occurs on the HAZ side of S355JR, in which the maximum content of martensite is 9.8%, the maximum content of residual austenite is 0.3%, and the remaining is bainite. Along the weld direction, the longitudinal and transverse residual stresses of S355JR and 316L appear near the weld centerline. The maximum longitudinal residual stress is 410 MPa, and 310 MPa, respectively, and the maximum transverse residual stress is 204 MPa, and 188 MPa, respectively. The overall deformation of the welded joint is V-shaped symmetrical with respect to the weld centerline. The deformation of S355JR is smaller than that of 316L, and the maximum edge deformation is 3.1 mm. The result of angular deformation is 4.1°. The overall deformation and angular deformation of welded joints welded with dissimilar steel are greater than those welded with the same steel.

Ever-leaner compositions are targeted for nominal type 16–8-2 weld metals in attempts to limit sigma-phase formation during elevated temperature operation. Three variants of type 16–8-2 weld metals were exposed to aging at 750 °C for up to 3500 h. Evaluation of the resultant structures by magnetic measurements, neutron diffraction (at ambient and cryogenic temperatures), and electron backscatter diffraction established that the leaner variants were susceptible to forming martensite after aging. This is ascribed to a local increase in the martensite start temperature due to sensitization taking place during elevated temperature aging. The extent of martensite formation diminished during aging treatments exceeding 1000 h owing to diffusion of solute elements from the austenitic matrix to the sensitized regions (recovery). Subsequent elevated temperature aging of the microstructures containing martensite also resulted in a decrease in martensite content: the mechanism, however, differs from that for single-cycle exposure. This observation is explained by martensite reversion to austenite. Martensite formation was completely absent from the higher-alloyed variant. This variant experienced intergranular carbide precipitation and delta ferrite decomposition into secondary austenite and carbides. This work demonstrates significantly different aging responses for composition variants within the allowed ranges for type 16–8-2 weld metals.

Due to the increased integration of functions, many components have to meet high and sometimes contradictory requirements. One way to solve this problem is Tailored Forming. Here, hybrid semi-finished products are manufactured by a joining or cladding process, which are then hot-formed and finished. For the design of hybrid components for a possible later industrial application, knowledge about properties of hybrid components is required. In this paper it is investigated how the respective process steps of the Tailored Forming process chain change the surface and subsurface properties of the applied cladding layer. For this purpose, shafts made of unalloyed steel are provided with a high-alloy austenitic steel X2CrNiMo19-12 cladding by laser hot-wire cladding. Subsequently, hot forming is carried out by cross-wedge rolling and the finishing by turning and deep rolling. After each process step, the subsurface properties of the cladding such as microstructure, hardness and residual stress state are examined. Thus, the influence of different process steps on the subsurface properties in the process chain of manufacturing hybrid shafts can be analyzed. This knowledge is necessary for the specific adjustment of defined properties for a required application behavior.

The kinetic transition of partitionless proeutectoid ferrite transformation from austenite, experimentally reported earlier in an Fe–C–Mn–Si alloy, is simulated incorporating interfacial segregation of carbon and alloy elements. The time-dependent diffusion equations of solutes are solved within the α/γ interface to evaluate the transient effects of solute accumulation on the migration of interface. The carbon concentration at the interface in the matrix decreased faster and the interface migration ceased, or the so-called stasis occurred, when the carbon concentration gradient in the immediate front of the interface turned to null or reversed. This can happen earlier than the partitionless-to-partitioned growth transition predicted from conventional theory in the absence of interfacial segregation, depending upon austenite grain size, i.e., the extent of soft impingement of carbon diffusion fields in the matrix in which a large carbon supersaturation remained. The subsequent transformation may be resumed accompanying the bulk partitioning of Mn (and probably Si) and/or nucleation of new ferrite crystals.

This paper describes the development and characterisation of bainitic steel for rail applications based on carbide-free, low-alloy steel. The results show that after rolling and subsequently cooling, the designed carbide-free bainitic steel exhibits better mechanical performance than standard pearlitic steel. This is because of its fine, carbide-free bainitic microstructure, which consists of bainitic ferrite and retained austenite laths. Microstructural and mechanical property analysis was carried out using scanning and transmission electron microscopy, X-ray diffraction, hardness measurements, tensile and low-cycle fatigue tests. The obtained results demonstrate that during low cyclic deformation, a partial transformation of the retained austenite into deformed martensite α′ takes place, and strain-induced martensitic transformation occurs. The initial strengthening of the material during low-cycle fatigue was caused by the transformation of austenite into martensite and the increase in the dislocation density of the steel. In addition, an optimal amount of retained austenite in the form of thin layers and islands (dimensions not exceeding 1 µm) made it possible to obtain a high yield while maintaining the high plasticity of the steel. These microstructural features also contributed to the high crack resistance of the tested carbide-free bainitic steel.

The hot deformation characteristics, microstructure evolution, and dynamic recrystallization (DRX) mechanism of the newly developed austenitic heat-resistant steel Fe–18Cr–10Ni–0.3Nb–2.5Cu were systematically investigated by thermal compression tests combined with microstructure characterizations. The activation energy (Q) map, Zener–Hollomon parameter (Z) map, and processing map were plotted according to the stress–strain curves to reveal the inherent connection between the three maps and the hot deformation characteristics of this alloy. The high η region in the processing map does not precisely correspond to the region where DRX developed. Nevertheless, the flow instability map accurately predicts the microstructure. The variation pattern of Z corresponded more closely to the hot deformation microstructure evolution than did the variation pattern of Q. The degree of DRX increases with decreasing Z. The optimal process parameters are 1000 °C/0.01 s−1/0.8 and 1100 °C/10 s−1/0.8 (temperature/strain rate/strain), and they result in complete DRX and a narrow range of Z values. The DRX mechanism at high strain rate is characterized by the combined enhancement of discontinuous DRX (DDRX), continuous DRX (CDRX), and twin-DRX (TDRX). The dominance of the particle-stimulated nucleation (PSN) mechanism at intermediate strain rate results in the formation of incompletely recrystallized microstructures with approximate orientation. Sufficient time at low strain rate promotes the development of DDRX and CDRX.

Instead of conventional quenching and tempering, fast austenitization from an initial microstructure of lamellar pearlite followed by quenching and tempering was carried out, leading to the formation of inhomogeneous microstructure. It comprised different morphologies of lath martensite and retained austenite (RA). The effect of tempering temperature on microstructure evolution and tensile properties was systematically investigated. With increasing tempering temperature from 150 to 250 °C, transition carbides gradually coarsened and their amount increased, the dislocation density in martensitic laths gradually decreased, and RA fraction decreased from 10.9% to 2.2%. The precipitation and dislocation strengthening can ensure a high strength, while RA can ensure a good ductility, leading to a simultaneous increase in the strength and ductility when decreasing tempering temperature. Specifically, the best combination of tensile properties (ultimate tensile strength of 2133 ± 41 MPa and total elongation of 11.1% ± 1.3%) was achieved after tempering at 150 °C.

Large gains in surface hardness and corrosion resistance of EN41B have been achieved for the AS_PN process. However, the effect of the AS_PN process parameters, like treatment time and temperature, on the hardness, corrosion, and wear of EN41B have not been investigated. Thus, in this study, EN41B samples have been treated at 500 °C and 550 °C for 2 h, 4 h and 6 h with a gas flow ratio of $${\text{H}}_{2} /{\text{N}}_{2} = 4:1$$ . Scanning electron microscopy analysis showed that the compound layers varied from 15.251 µm to 25.045 µm, and also revealed the formation of transformed austenite phases. X-ray diffraction analysis has revealed the formation of $$\varepsilon - {\text{Fe}}_{2 - 3} {\text{N}}$$ and $$\gamma^{\prime} - {\text{Fe}}_{4} {\text{N}}$$ phases on the surface of the samples. The microhardness test has revealed that the maximum gain in the hardness after treatment is 4.2 times that of the base material. Finally, it was observed from potentiodynamic polarization testing that the sample treated at 550 °C for 6 h has a minimum corrosion rate of 419.10 mm/year ×10−3.

The N-bearing 19Cr-LDSS (Lean Duplex Stainless Steel, LDSS) with heterostructure consisting of coarse-grained ferrite and ultrafine-grained austenite was prepared by combining severe plastic deformation with High Temperature-Short Time (HTST) heat treatment. The microstructural observations and measurements were performed on deformed and annealed samples to correlate the excellent strength-plasticity matching to the grain refining and transformation-induced plasticity (TRIP) effect. The heterogeneous structure revealed a remarkable improvement of the strength compared to the counterparts processed by the conventional solution treatment. A yield strength (YS) of 800 MPa, ultimate tensile strength (UTS) of 1100 MPa and total elongation (TE) of 45% were achieved by the HTST treatment. Therefore, the higher YS and UTS of 19Cr-LDSS under HTST treatment were obtained on the premise of ensuring the excellent strength-plasticity matching. The high strength was provided by the grain refinement, and the high uniform elongation was attributed to the persistent high strain hardening rate due to the hetero-deformation-induced stress associated with the activation of TRIP effect. Meanwhile, the strain accommodation of coarse-grained ferrite phase also contributed to the improvement of plasticity for the experimental steel.

Maraging steels are precipitation hardened steels with high-strength and excellent toughness. Maraging steels being the key player in the strategic sector, demands welding of thick sections up to 12 mm for critical applications. They are readily weldable in the soft solution-annealed condition and further strengthened by post-weld heat-treatment (PWHT). However, welding of thick sections, on the other hand, necessitates a longer welding time, more number of passes and a higher heat input. This paper elucidates the influence of different PWHTs on the metallurgical and mechanical behavior of 12-mm-thick plates of MDN 250 grade maraging steel by using multi-pass gas metal-arc welding (GMAW). The different PWHTs adopted for the study include; Direct Aging (DA), Solutionizing + Aging (SA) and Homogenizing + Solutionizing + Aging (HSA). The microstructures of the fusion zone (FZ) with DA and SA condition reveal the presence of reverted austenite (RA) along the cell boundaries. However, in the weldment with HSA treatment was free from RA. Metallographic analysis of the as-welded FZ showed nickel, molybdenum and titanium segregation along the cell boundaries. This resulted in the formation of RA on subsequent aging. The SA treatment was not effective in complete elimination of reversion. The HSA treatment, on the other hand, had completely eliminated both elemental segregation and reversion. The welded joint with HSA treatment had an ultimate tensile strength (UTS) of 1582 MPa and a fracture toughness of 92.9 MPa√m, respectively. HSA treatment also shows a remarkable improvement in fracture toughness compared to other PWHTs. The present study underscores the fact that multi-pass GMAW with HSA treatment provides optimal mechanical properties.

Austenite and ferrite phases share equal fractions in the steel and thus coins the name austenitic-ferritic steels, widely known as duplex steels, among researchers. The current study focuses on revealing the sliding wear behavior of the steels, which is of great industrial importance in oil & gas and chemical processing industries, where it is used as valves in pipelines. Austenitic-ferritic steel and its niobium (Nb) added castings were produced through the induction melting route. Thermodynamic analyses of the systems were performed using Thermo-calc software. Isopleths generated through thermodynamic simulation predicted niobium carbide (NbC) formation in the system, and the same was asserted through x-ray diffraction peaks. Scanning electron microscope (SEM) with energy-dispersive spectroscopy (EDS) study also confirmed the presence. The dry sliding wear performance of these castings was investigated. Experiments have been performed where cast austenitic-ferritic steel pins, slid against non-shrinking, oil-hardened steel disk, with sliding speeds 1, 1.5, and 2 m/s, under loads of 20, 30, and 40 N, without lubrication at room temperature. Variations in wear rate, friction coefficient, and volume loss were studied with respect to sliding distance, load, and sliding velocity. SEM was used to understand the wear phenomena and mechanisms involved, and white light interferometry analysis over the worn-out surfaces gives insight to the understanding. NbC formed in the system imparts stability to the steel against sliding wear. The results show that Nb addition can be beneficial in applications like valves, elbows, and other fittings in the pipelines, where degradation of a material due to wear is high and thus improves the productivity of the industry.

The improvement of the intergranular corrosion resistance of aged 316L stainless steel (316L) heat-affected zone by electropulsing treatment was studied. The results showed that the intergranular corrosion resistance of aged 316L HAZ increased with the increase of electropulsing frequency. As electropulsing frequency reached 170 Hz, most of M23C6 produced in austenite and δ-ferrite was dissolved during the aging process, and the intergranular corrosion resistance was basically restored. Thermodynamics and kinetic analysis clarified that electropulsing could reduce the thermodynamic dissolution barrier of M23C6 and improve the atomic diffusion flux, thereby promoting the dissolution and discontinuous distribution of M23C6 below its thermodynamic dissolution critical temperature and improving the intergranular corrosion resistance of aged 316L HAZ.

The motivation for this paper evolved from the question “when is a cast iron eutectic?” raised by a recent paper. The simple answer is when the carbon equivalent of the iron is 4.2%. This raises another question: How does one calculate the carbon equivalent (CE)? The paper summarizes the many different equations used for this purpose. It demonstrates that Mg and inoculation affect the calculation of CE and that the Si contribution in classic CE equations is inaccurate for all practical purposes. The use of isopleths is limited as they cannot consider the effect of elements such as Mg and oxygen, or that of the metal quality (nucleation potential). They also cannot illustrate the effect of small differences in silicon resulting from inoculation. Corrections for the contribution of Si and Mg are proposed. Yet, CE can be used to determine the eutectic carbon if enough data are available to find the intersection of the austenite and graphite liquidus. Despite its limitations, because of its repeatability for a given process, the foundry can rely on TA and CE for composition control.

Compact components are prone to failure at brazed joints. A comprehensive understanding of the effect of brazing temperature on the metallurgical reactions and microstructure evolution of 316L/BNi-2 brazed joints will provide support for optimization of the brazing process and improving joints strength. In this paper, the brazing process was carried out at 966°C 991°C, 1033°C, 1065°C, 1100°C, 1137°C and 1170°C in a vaccum furnace. The morphology and crystal structure of different zones of the brazed joints including athermal solidification zone (ASZ), isothermal solidification zone, and diffusion-affected zone (DAZ) were investigated. Results show that the DAZ begins to form, and the Ni3B, Ni3Si, CrB, and γ-Ni in the ASZ gradually coarsen below 1033°C. When the temperature reaches 1065°C, the filler alloy completely liquidizes. The boron in the filler alloy diffuses into the base metal, resulting in isothermal solidification. The residual liquid phase generates binary and ternary eutectic reactions. According to TEM patterns analysis in the DAZ, borides, and carbon-boride are mainly distributed on grain boundaries and within grains, respectively. In addition, M5B3 boride in the DAZ gradually transforms into M2B boride due to its better thermodynamic stability. Above 1170°C, the borides in the DAZ partly dissolve, and meanwhile, the matrix transforms from martensite to austenite, forming the alternating distribution of austenite and boride. During the heating process, with increasing brazing temperature, the hardness and elastic modulus of brazed joint microregions gradually decrease.

The present study revealed that the martensitic stainless steel AISI 420 and mild/low carbon steel AISI 1018 could be successfully joined by using friction welding technique at different parameters such as friction time and friction pressure. Macro and microstructural characterizations of welded materials were performed by optical microscope (OM), X-ray diffractometer (XRD) and scanning electron microscope with energy-dispersive X-ray spectroscop. Also, tensile and microhardness tests were performed to determine the mechanical properties. The most interesting aspect of this study is the determination of ferrite, retained austenite and chromium phases in the weld zone by XRD analysis, and in tensile tests, the fracture occurred outside the weld zone at a maximum tensile strength of 527 MPa. Moreover, the diffusions of phases such as chromium and carbon were observed in the weld zone, and the microhardness measured in the weld zone was found to be higher with 591 HV than the one measured in the base materials.

The variations in the austenite–ferrite dual-phase structure of hyper-duplex stainless steels subjected to tensile deformation were analysed in the present work. The blocks of ASTM A890 7A hyper-duplex steel were cast and heat treated to obtain a clean dual-phase structure. Unilateral tensile stress was applied on specimens prepared from the blocks. Heat-treated specimens were deformed under a displacement control mode for various percentage elongations. Scanning electron microscope and metallurgical microscope images revealed that the austenite phase was more deformed compared to that of the ferrite phase. X-ray diffraction analysis was carried out to find the crystallographic planes where maximum deformation has occurred and to explain how different phases participated in the deformation process. The austenite phase was found to be far more deformed than the ferrite phase, with the greatest deformations in the (111) and (200) planes. The distribution of constituent alloying elements was evaluated using energy-dispersive X-ray analysis (EDAX) and area-scan techniques and it was found that there were no substantial changes in the concentration of alloying elements as a result of deformation.

In this research, ultrasonic melt treatment (UST) was used to produce a new ultrafine grade of spheroidal graphite cast iron (SG iron) and austempered ductile iron (ADI) alloys. Ultrasonic treatment was numerically simulated and evaluated based on acoustic wave streaming. The simulation results revealed that the streaming of the acoustic waves propagated as a stream jet in the molten SG iron along the centerline of the ultrasonic source (sonotrode) with a maximum speed of 0.7 m/s and gradually decreased to zero at the bottom of the mold. The metallographic analysis of the newly developed SG iron alloy showed an extremely ultrafine graphite structure. The graphite nodules’ diameter ranging between 6 and 9 µm with total nodule count ranging between 900 to more than 2000 nodules per mm2, this nodule count has never been mentioned in the literature for castings of the same diameter, i.e., 40 mm. In addition, fully ferritic matrix was observed in all UST SG irons. Further austempering heat treatments were performed to produce different austempered ductile iron (ADI) grades with different ausferrite morphologies. The dilatometry studies for the developed ADI alloys showed that the time required for the completion of the ausferrite formation in UST alloys was four times shorter than that required for statically solidified SG irons. SEM micrographs for the ADI alloys showed an extremely fine and short ausferrite structure together with small austenite blocks in the matrix. A dual-phase intercritically austempered ductile iron (IADI) alloy was also produced by applying partial austenitization heat treatment in the intercritical temperature range, where austenite + ferrite + graphite phases coexist. In dual-phase IADI alloy, it was established that introducing free ferrite in the matrix would provide additional refinement for the ausferrite.

Austempered Ductile Iron (ADI) is a candidate material to replace case-hardened steel in many applications. The mechanical properties of ADI can be tailored by the chemical composition and heat treatment conditions. In this study, different nickel content Ductile Irons (DI) were cast and heat treated. In order to design the austempering process, time–temperature–transformation diagrams were generated with the Calculation of Phase Diagrams method. For each chemical composition, one group was tested in its as-cast state while the second and third groups were austempered. For austempering, the casting is reheated to austenitization temperature (900 °C) and then quenched in a salt bath at a temperature of 300 °C and held at this temperature for 2 h. The third group was cryo-treated (−196 °C for 6 h) and tempered (200 °C for 2 h) after the austempering process. Microstructural examination was performed using an optical microscope and X-ray diffraction technique. The effect of heat treatment on the hardness, toughness, and tribological behaviors of samples was investigated. The results showed that austempering with correct parameters significantly improved the hardness, toughness, and wear resistance of DI. The nickel content of DI plays a significant role in determining the properties of the alloy, and the optimum Ni amount among the tested compositions was found to be 1.64%. It was observed that cryogenic treatment facilitates some of the austenite to martensite transformations and improves wear resistance (20%); however, it has a limited effect on hardness (2–3 HRc) and toughness (±3 J).

To elucidate the dynamic strain aging (DSA) mechanism that causes serrated flow in the tensile curves of an intercritical annealed steel with retained austenite (RA) and intercritical ferrite, the multi-aspect microstructural characterization and micromechanical deformation behavior were systematically investigated in this study. Our results demonstrate that the DSA phenomenon is dependent on the strain rate, deformation temperature, and strain. This is accompanied by deformation-induced martensitic transformation (DIMT) and the generation of crystallographic defects in nucleating and propagating Portevin-Le Chatelier bands. An increase in the deformation temperature and strain rate leads to an increase in the stacking fault energy of RA. This inhibits the growth of martensitic embryos and retards the kinetics of martensitic transformation of RA, consequently decreasing or suppressing the DSA phenomenon. Furthermore, neither the long-range diffusion model of carbon atoms nor the short-range diffusion model on the reorientation of C-Mn complexes could reasonably explain the DSA phenomenon in this study. Based on the in situ synchrotron X-ray diffraction results and established mathematical models stemming from the dislocation multiplication theory, the DSA could be attributed to the periodic instantaneous dislocation multiplication in constituent phases caused by burst DIMT.

This article investigated the solidification structure evolution for a typical high-carbon steel billet under strong cooling intensity during the process of continuous casting. The results suggested that a regular solidification phase transformation route of ‘austenite → lamellar pearlite’ was obtained in the center surface of billet; however, an abnormal microstructure evolution route of ‘austenite → martensite → tempered sorbite (fine spheroidized cementite in the ferrite matrix)’ appeared around the corner of billet. Besides, the secondary dendrite arm spacing for the center surface was 90.92 μm, and it reduced to 49.01 μm for the corner part because of different cooling conditions. In addition, the billet corner with a major tempered sorbite phase shows higher values of tensile strength, elongation and hardness, indicating sorbite phase could improve high carbon steel mechanical properties more significantly than the phase of lamellar pearlite because of its unique homogeneously distributed spheroidized structure. Furthermore, a laboratory experiment was conducted to verify the formation mechanism of tempered sorbite, and the results suggested that martensite phase would be formed around the billet corner under strong cooling intensity during the second cooling zone, and then the quenched martensite would be transferred to tempered sorbite, as the billet was out of the second cooling zone and reheated by its inner solidification heat.

The corrosion behavior of ferritic (Fe-11Cr) and austenitic (Fe-18Cr) steels has been investigated in static liquid lead containing 5 × 10–7 wt.% oxygen at 550°C and exposure up to 1000 h. It was determined that corrosion damage of surface layers occurs along grain boundaries. This is accompanied by etching of grain boundaries and penetration of liquid lead into the matrix, with simultaneous dissolution of the main alloying elements (Ni, Cr, and Mn) of the steels. It was established that the applied loads accelerated the corrosion processes in the contact of the steels with liquid lead. The austenitic steel showed better corossion resistance under loads than did the ferritic steel.

The sliding wear property of high-carbon nanostructured bainitic bearing steel with the equal initial hardness and different microstructures was investigated, and the reasons for the difference of wear resistance between the cementite-bearing (CB) and cementite-free (CF) specimens were analyzed. The results show that CF specimens have lower mass loss and surface roughness and shallower wear depth than CB specimens during wear process. Compared with CB specimen, CF specimen presents superior wear resistance. This is due to two reasons: (1) a lot of retained austenite in CF specimen is easy to produce TRIP effect and be transformed into martensite during wear process, which notably increased the surface hardness of worn specimen; (2) there is a nondestructive oxide layer in the surface of cementite-free worn specimen, which can protect the surface of worn specimen from destruction. Under the combined effect of retained austenite and oxide layer, the loss of matrix is reduced. Thus, CF specimen exhibits high wear resistance. It reveals that the wear mechanism of high-carbon nanostructured bainitic bearing steel with different microstructures can provide a reference for improving the wear resistance in high-carbon nanostructured bainitic bearing steel in future.

A lean alloyed low carbon Si and Mn steel was austenitized at three different temperatures in the inter-critical zone (790, 810 and 830 °C) followed by austempering in salt bath in the temperature range of 425 and 525 °C to develop an attractive combination of strength and ductility with a TRIP assisted bainitic ferrite microstructure. The microstructure revealed a combination of ferrite, bainite along with martensite/retained austenite. Superior tensile strength and ductility were found in the steel austempered at about 450 °C due to the presence of higher bainitic, lower ferrite and moderate martensite/retained austenite. The product of tensile strength and percentage of elongation obtained were greater than 20 GPa% at some of the heat-treated conditions qualifying for third generation AHSS. The microstructural evolutions were correlated with the theory of bainite formation.

The objective of this paper is to study the surface texture behavior of low and medium-carbon steels machine elements in acidic environment using Abbott Firestone curve depending upon MATLAB software. The chemical composition of low-carbon steel is 0.16C-0.27Si-1.47Mn-0.02Al while medium-carbon steel is 0.49C-0.30Si-0.91Mn-0.03Al. They were hot-rolled at 1200°C for 30 min followed by air cooling. Two different heat treatment processes were applied on the hot-rolled samples. The first treatment was quenching after martensite finish (QAMf) and the second one was quenching and partitioning (Q&P). For 0.16C, the microstructure gives bands of ferrite and pearlite after hot-rolled steel. However, 0.49C produces coarse pearlite islands surrounded by ferrite phase. While, the microstructure after QAMf and Q&P processes contain ferrite, bainite, lath martensite, and retained austenite for 0.16C steel, and polygonal ferrite, lath martensite, and retained austenite for 0.49C steel, respectively. In low-carbon steel (0.16C), after hot-rolling, steel suffers from low exploitation zone (44%) of surface texture. However, after QAMf, low-carbon steel (0.16C) gives lower surface texture (36%). In addition, hot-rolled steel (0.16C) produces 40% voids zone while after QAMf, voids zone increases to 52% of surface texture. In medium-carbon steel (0.49C), after hot-rolling, steel produces 78% exploitation zone of surface texture. Furthermore, Q&P slightly enhances surface texture (exploitation zone) to 82%. At the same time, hot-rolled and Q&P of 0.49C steels exhibit very small number of voids for surface texture (1–4%). Therefore, 0.16C steel (hot-rolled and QAMf) is highly subjected to severe failure in etchy environment. However, 0.49C steel (hot-rolled and Q&P) is highly recommended in case of moderate safety factor.

Electron beam welding was used to fabricate dissimilar butt weld joints of AISI 321 and AISI 409 stainless steel 18-mm-thick plates. On both sides, i.e., fusion boundary of AISI 321 and fusion boundary of AISI 409 and along the thickness of the joint, the microstructure evolutions were studied using optical microscopy and scanning electron microscopy. The results revealed that martensite was the major phase formed in the WM. The thickness of HAZ was more on side of AISI 409 as compared to AISI 321. In comparison with the WM, the HAZ was softer. The mechanical testing revealed that the root region was more ductile in comparison with the weld’s top region. The brittle fracture was demonstrated when the notch was formed at the HAZ of AISI 409 SS and the impact toughness reduces to 2 J. However, when the notch was formed in the HAZ of AISI 321 SS, the impact toughness improved to 32 J.