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The roles of pre-formed martensite (PM) in below-Ms bainite formation, microstructure, crystallography, strain partitioning and mechanical properties of a low-carbon bainitic steel were investigated using electron-backscattered diffraction, transmission electron microscopy, micro digital image correlation technique and mechanical tests. It is demonstrated that the pre-formation of martensite eliminates the incubation time for bainite transformation at various austempering temperatures below Ms, indicative of its acceleration effect at the early stage of transformation. This effect is mainly attributed to the surfaces or tips of the PM acting as the nuclei of subsequently-formed bainite, with initial bainite tending to form around the PM. However, the finishing time for below-Ms bainite transformation, especially at even lower temperatures, is retarded, owing to the dividing effect of PM on parent austenite grains, the decreasing effect of lowered isothermal temperature on the diffusion rate of carbon atoms and the strengthening effect of lowered isothermal temperature on supercooled austenite. PM and its adjacent bainitic laths have nearly the same crystallographic orientation and belong to the same block. The pre-formation of martensite largely refines the bainitic blocks/laths and retained austenite. The specimens with PM show relatively uniform strain partitioning among various phases, contrasting with the specimens without PM, for which strains are highly concentrated in the bainite region nearby fresh martensite/austenite (M/A) blocks or between adjacent M/A blocks. The impact absorption energies of the specimens with PM, when austempered at 30–60 °C below Ms, are more than twice higher than those of the specimens without PM, at no expense of tensile properties.

In this paper, martensite-to-austenite reversion during intercritical annealing was applied to a conventional low-alloy transformation-induced plasticity steel to form reverted austenite, which was followed by austempering to form bainite, and hence the resulting microstructures and mechanical properties were investigated. The obtained microstructure is composed of alternating lamellae of intercritical ferrite and reverted austenite on microscale, with the latter consisting of bainitic ferrite laths and retained austenite films on nanoscale. This unique microstructure exhibits excellent strength–ductility combinations, which surpass those of conventional polygonal blocky-structured counterparts, providing a strategy for developing high-performance structural materials at low production cost.

Nanobainite was produced in medium-C Si-rich steel through ausrolling at 500 °C and subsequent austempering at temperatures slightly above the martensite start temperature. The tensile properties were studied and compared to high-C nanobainite steels. Extremely high ultimate tensile strength (2223–2581 MPa) and appreciable total elongation (6.2–8.5%) were achieved in the medium-C nanobainite steel, which were comparable and even correspondingly superior to high-C nanobainite steels. In addition, the strengthening mechanism was briefly discussed.

A metastable austenitic stainless steel was repetitively cold rolled and reversely annealed. The strain-hardening behavior and deformation mechanism during tensile testing were comparatively studied for the specimens annealed at 800 °C and 1000 °C. Fine-grained austenite with uniformly distributed carbides was formed in the 800 °C-annealed specimen, whereas coarse-grained austenite without carbides was obtained with annealing at 1000 °C. Continuous strain hardening was achieved in all specimens, which could be attributed to the strain-induced martensite and deformation twining for the annealed specimens at 800 and 1000 °C, respectively. The carbide precipitation promoted the formation of strain-induced martensite due to the depletion of austenite stabilizers.

In quenching-tempering (QT), limiting factors such as hardenability, temper embrittlement, quenchant pollution, and quenching distortion and cracks have to be considered. In order to avoid these limitations, we propose a thermomechanical process to fabricate spheroidized cementite in ferrite matrix in a medium-C steel with mechanical properties that are comparable to QT, which is based on multi-pass caliber rolling at start rolling temperature (SRT) in two-phase α+γ region. In this study, the effect of the SRT (in the range from 720 °C to 820 °C) on microstructures, mechanical properties, and impact fracture behavior were investigated by using 45 steel as experimental material. Results indicate that the rolling can result in a fibrous “ferrite + pearlite” microstructure. If the SRT is at 740 °C to 760 °C, then the multi-sized ferrite grains with intensive α-fiber texture ( //RD) and the completely spheroidized cementite distributed in the fine ferrite grain region can be formed. The spheroidization of cementite is attributed to the deformation-induced divorced eutectoid transformation. The mechanical properties significantly exceeded the requirements of the Chinese National Standard GB/T 699−1999 for quenched-tempered 45 steel. When the SRT decreased from 780 °C to 820 °C to 720 °C to 760 °C, the Charpy impact absorbed energy ( A KV ) increased from approximately 50 J to 100 J, and the impact fracture behavior changes from dimple along with some splits into quasi-cleavage. This thermomechanical process is a potential alternative to QT of medium-C steels.

The isothermal transformation kinetics, microstructure and mechanical properties of a low-carbon bainitic steel, subjected to below-Ms/above-Ms austempering with or without prior ausforming, have been investigated via dilatometric measurements, microstructural characterization and mechanical tests. The results show that for all austempered samples, prior ausforming largely refines the bainitic laths and enhances the mechanical stability of supercooled austenite, the latter leaving more austenite untransformed at the finish of isothermal treatment. Nevertheless, divergent consequences on the final microstructure arise: for the above-Ms austempered samples, prior ausforming increases the amount of large, unwanted brittle martensite/austenite blocks and decreases the volume fraction of retained austenite at room temperature; however, for the below-Ms austempered samples, prior ausforming decreases the size and amount of martensite/austenite blocks and increases the volume fraction of retained austenite. Accordingly, the below-Ms austempered samples with prior ausforming exhibit a product of strength and ductility of ∼ 43 GPa% and impact toughness of ∼180 J/cm2, in sharp contrast with those of the above-Ms austempered samples with prior ausforming, ∼33 GPa% and ∼80 J/cm2, respectively. The present results clearly demonstrate a favorable effect of the combined process of ausforming and below-Ms austempering against the adverse combining effect of ausforming and above-Ms austempering. Keywords: Mechanical properties, Carbide-free bainite, Transformation kinetics, Isothermal treatment, Ausforming

In this work, fully recrystallized ultrafine-grained (UFG) Fe-30Mn-0.11C steel with mean grain size of 1 μm was successfully produced by using traditional cold rolling and annealing process. The UFG Fe-30Mn-0.11C steel exhibited high tensile ductility (∼60.4%) and yield strength (381 MPa). Grain refinement and source hardening were responsible for achieving this combination of strength and ductility in the studied material. Keywords: Fully recrystallized, Ultrafine-grained, Grain refinement, Source hardening

The excellent properties of transformation-induced plasticity (TRIP) steels with a lamellar structure are generally claimed to mechanically stabilize retained austenite (RA) grains, enabling the TRIP effect to persist up to higher strains. Nevertheless, the present work finds that nearly no RA grains are transformed into martensite at the strain range of 0.10–0.14 in lamellar-structured specimens. Furthermore, the strain-hardening exponent remains nearly unchanged. To explain the underlying mechanisms of this strain-hardening behavior, the block/packet/prior austenite grain boundaries of the hierarchically lamellar-structured TRIP steel were reconstructed. Moreover, the evolutions of full-field strain distribution and back stress hardening with straining were examined through the in situ micro digital image correlation technique and cyclic loading–unloading–reloading tensile tests. Results show that the block structure controls the microstructural deformation behavior of lamellar-structured specimens. Within a block, ferrite and bainite layers could deform synergistically. However, next to block boundaries, ferrite layers are susceptible to a large strain gradient due to the different deformation tendencies of adjacent blocks. Compared to conventional polygonal-structured specimens, the more refined ferrite grains of lamellar-structure specimens reduce the strength difference between ferrite and bainite layers. The strains are more uniformly partitioned among various constituents, thus delaying the occurrence of tensile necking. Back stress hardening dominates the strain-hardening in conventional polygonal-structured specimens, facilitating the increase of flow stress but decreasing the toughness. In lamellar-structured specimens, combined moderate back stress and dislocation hardening should be responsible for the persistent strain-hardening exponent after the strains exceed 0.10.

Introduction Chylopericardium is a rare complication following orthotopic heart transplant (OHT). Chylous pericardial effusions are characterized by an accumulation of lymph and emulsified fats in the pericardial sac that has a milky appearance with triglyceride levels in high concentration. Ongoing leakage of chyle in the pericardial space can have detrimental effects on nutrition, metabolism, and the immune system. We report one of the first cases of chylopericardium following orthotopic heart transplant that was successfully treated with thoracic duct embolization. Case Report A 37 year old male with dilated nonischemic cardiomyopathy on home milrinone presented for OHT. The operation was uncomplicated with a bicaval anastomosis and allograft ischemic time of 178 minutes. The early postoperative course was complicated by 2R acute cellular rejection, for which he was treated with pulse steroids with good effect. The post-biopsy echocardiogram revealed a large circumferential pericardial effusion with fibrinous strands and evidence of tamponade. He was taken for pericardiocentesis where 1.2 liters of pink milky fluid were removed, with improvement in pericardial pressure from 14 mmHg to 0 mmHg. Pericardial fluid triglycerides resulted at 1645 mg/dL consistent with chylous fluid. Unfortunately, the effusion reaccumulated in less than 24 hours suggestive of thoracic duct injury. He was taken for pericardial window and placed on a low-fat lymphatic diet. Subsequent lymphangiogram confirmed thoracic duct injury, for which successful coil embolization of the thoracic duct was performed. He was restarted on a regular diet and follow up echocardiogram showed normal graft function and no further reaccumulation of the effusion. He convalesced well and his post-transplant course was unremarkable on a standard maintenance immunosuppression regimen. Summary Chylopericardium may occur rarely as a complication of cardiothoracic surgery, trauma, malignancy, infection, or congenital abnormalities. Conservative management with dietary modification has resulted in only variable success while surgery (ligation of the thoracic duct and pericardial window) can carry higher risks due to its invasive nature. We report a case of chylopericardium following orthotopic heart transplant that was successfully managed with a percutaneous option of thoracic duct embolization.

Large-strain ausforming and low-temperature bainite transformation were carried out in a medium C - Si rich alloy steel on a thermomechanical simulator. Then, temperature–time–transformation curves of the bainite transformation after ausforming at different temperatures were obtained by dilatometry. The effects of ausforming on transformation kinetics, microstructure, and hardness of samples were studied. Results show that the entire process of bainite transformation can be accelerated by ausforming. With decreasing ausforming temperature, the transformation rates greatly increased at the initial transformation stage but slightly decreased at the final stage. Compared with non-ausformed sample, not only was the maximum growth rate in the ausformed samples larger, but the maximum growth rate also appeared earlier. In addition, the maximum rate of the ausformed bainite transformation was increased and the time of reaching the maximum rate was shortened with decreasing the ausforming temperature. The effect of ausforming on bainite transformation kinetics depended not only on the ausforming temperature and strain but also on the isothermal transformation temperature. The reduction in transformation time was increased under decreased isothermal transformation temperature. Ausforming refined the bainite plates and increased the fraction of retained austenite formed in the subsequent low-temperature isothermal transformation. Consequently, nanostructured bainite with enhanced hardness was prepared in the medium C - Si rich alloy steel.

Mo containing high-C-Cr bearing steel was modified with Si (0.8–1.5 wt.%) and 0.8Si–1.0Al to prepare nanostructured bainite by low-temperature isothermal heat treatment. The modified steels were isothermal held at 220 to 240 °C after partial austenitization in an intercritical gamma+carbide region, and the resultant microstructure and mechanical properties were studied. Carbide-free nanostructured bainite with plate thickness below 100 nm and film retained austenite, as well as a small amount of undissolved carbide particles, was obtained in the modified steels except in 0.8Si steel, in which carbides precipitated in bainitic ferrite. As Si content increased, the mean thickness of bainitic ferrite plates modestly decreased, whereas the fraction of retained austenite markedly increased. The thickness of bainitic ferrite plate and the fraction of retained austenite in Si-Al-modified steel were smaller than those in Si-modified steels. The hardness and elongation of the Si-Al-modified steel were lower than those of Si-modified steels. The yield strength of Si-Al-modified steel was superior to that of Si-modified steels. Mid-level ultimate tensile strength and impact toughness were achieved in Si-Al-modified steel. For bearing applications, Si-modified steels could provide higher hardness and toughness but lower dimensional stability. Meanwhile, Si-Al-modified steel could offer higher dimensional stability but lower hardness and toughness.

Nanostructured bainite and dispersed carbide particles were formed in Si–Mo-alloyed high-C–Cr bearing steels by low-temperature austempering after partial austenitizing in the intercritical gamma + carbide region. Comparing with conventional quenched and tempered high-C–Cr bearing steel, the impact toughness is remarkably enhanced; the hardness is still adequate for the bearings even though it is slightly decreased. Keywords: Austempering, Steels, Hardness, Impact behavior, Nanostructured bainite

The microstructures and mechanical properties of a novel bainitic bearing steel subjected to austenitizing at 950 °C for 40 min followed by low-temperature austempering at 200 °C for 2 h, 6 h, 12 h and 72 h were studied. Nano-bainite microstructure with bainitic ferrite plate thickness about 50±15 nm was obtained by austempering at 200 °C for 6 h, 12 h and 72 h. Besides nano-scaled bainitic ferrite plates, there were small amount of retained austenite and undissolved carbides in the microstructure. The volume fraction of retained austenite is 7.2% in the samples austempered at 200 °C for 72 h. The ultimate tensile strength of samples austempered at 200 °C for 72 h reaches 2373 MPa, which is superior to the sample austempered at 200 °C for 2 h, whose microstructure is almost full martensite. The weight loss values are 0.0100 g and 0.0273 g for samples austempered for 72 h and 2 h respectively and the wear resistance of the sample austempered for 72 h is about 1.7 times higher than that for 2 h. Because of the excellent strength and wear resistance of the low-temperature bainite, this low-temperature austempering could be a potential technology for manufacturing bearings.

An Fe-34.5Mn-0.04C steel has been processed by cold rolling and annealing to prepare samples with a lamellar structure, a recrystallized grain structure and a composite structure of layers of recovered and recrystallized structures. For the recrystallized grain structure and the lamellar structure, the flow stress has been analyzed by applying Hall-Petch formulations. For the composite structure, the rule of mixture has been applied to calculate the flow stress, revealing an extra strengthening from a constraint effect. An excellent combination of strength and ductility has been found in a composite with 10% hard lamellae in a recrystallized grain structure.

The effects of ausforming temperature, strain and strain rate on isothermal bainite transformation behaviour and microstructural refinement in medium-carbon Si–Al-rich alloy steel were determined by thermomechanical simulation. Results show that ausforming decreased the martensite start temperature and enabled isothermal transformation at low temperatures, resulting in the formation of nanostructured bainite. Decreasing the ausforming temperature and increasing the ausforming strain did not only reduce the incubation of isothermal transformation but also refined bainite lath and enhanced the hardness of the alloy steel. Strain rate showed a weak influence on the transformation behaviour and microstructure of the obtained nanostructured bainite.

The microstructures of a low carbon Nb-microalloyed steel processed with the Heat-treatment On-line Process (HOP) technology, whose highest heating temperature ranges from 560 °C to 720 °C, were characterized. The tensile properties were evaluated from the ThermoMechanical Control Process (TMCP) treated samples. The results indicate that the microstructure is primarily composed of non-equiaxed ferrite grains with martensite/austenite (M/A) constituent dispersed at grain boundaries for the specimens with different HOP temperature. The refinement of niobium precipitate particle and increase of volume fraction of precipitation could induce the enhancement of the yield strength when increasing the HOP temperature. The relationship between the average size and volume fraction of the precipitate particles and the precipitation strengthening part of yield strength follows the Orowan–Ashby equation. Moreover, the yield ratio slightly reduces with the increasing amount of M/A constituent, and a platform of yield ratio emerges when the HOP temperature ranges from 590 °C to 720 °C.

Deformation behavior of austenite/supercooled austenite in a medium-carbon Si–Al-rich alloy steel is investigated on a thermomechanical simulator and an optical microscope. Effects of ausforming temperature, strain rate and strain on martensite start temperature ( M S ) and ausformed martensite microstructure are studied in detail. Results show that power-law-type work hardening is caused during supercooled austenite deformation at 300 °C; and the work hardening followed by steady-state flow is caused during the deformation at 600 and 900 °C. The ausforming can decrease M S , refined lath martensitic microstructure and slightly enhanced hardness. With decreasing the ausforming temperature the M S and martensite lath thickness decrease markedly. The strain and strain rate do not have strong effects on the M S and lath thickness. In addition, the ausforming can decrease the tetragonality of martensite and facilitate the formation of dislocation substructured martensite.

The microstructures of an acicular ferrite (AF) and martensite/austenite (M/A) constituent steel processed with cooling rate from 5 to 25 °C/s after hot deformation were characterized. The tensile properties were evaluated from the thermomechanical control process (TMCP) treated samples. The results indicate that as the cooling rate increased, AF grain is refined, M/A constituent becomes smaller and distributes more dispersively accompanied by the slight decrease of amount. The refinement of AF effective grain and the rising dislocation density could significantly induce the enhancement of yield strength (YS), and the relationship between the YS and the AF effective grain size defined with the low boundary tolerance angle (2–6°) follows the Hall–Petch approach. The increasing yield ratio (YR) shows that the strain hardening capacity reduces as a result of the microstructure evolution while increasing the cooling rate.

A 35MnSiCrNiAlMo bainitic steel whose mechanical properties approached those of 140-maraging steel was developed. The steel was continuously cooled from a temperature slightly higher than its martensite start temperature (Ms) to Ms − 20 °C at a cooling rate of 0.5 °C min−1, after which the overall mechanical properties are better than those of austempered samples at any constant temperature. Mixed microstructures consisting of fine plates of carbide-free bainitic ferrite and thin films of retained austenite were obtained.

Nanostructured bainite was prepared in medium-carbon Si–Al-rich alloy steel by low-temperature austempering of deformation-strengthened supercooled austenite. The deformation strengthening of supercooled austenite can depress the martensite start temperature, allowing austempering at a lower temperature to form nanostructured bainite with high hardness.

The martensitic transformation behaviour of deformed supercooled austenite and the resulting microstructure in a medium-carbon Si–Al-rich alloy steel were studied. The deformation of supercooled austenite can depress the martensite start temperature and create nanostructured lath martensite with high hardness.

a b s t r a c t The softening behaviour of cold-rolled dual-phase low-carbon steel during annealing and the resulting microstructure and tensile properties were investigated. Ferrite–martensite dual-phase structures were produced by intercritical heat treatments (IHT): (A) intercritical quenching at 760 ◦ C after quenching at 1000 ◦ C; (B) furnace cooling from 1000 to 760 ◦ C and immediate quenching. The results show that an excellent strength–ductility balance is achieved by the cold rolling and appropriate annealing of these two IHT samples. Completely recrystallized ultrafine-grained ferrite with a bimodal distribution and dispersively nanoscale carbide particles are obtained. The annealing softening activation energy of coldrolled sample (A) is far less than that of cold-rolled sample (B). In addition, the effect of IHT on the softening behaviour, resulting microstructure and tensile properties was discussed.

This research studied the effect of austempering temperature on the sliding wear resistance of high-Si–Al steel, with a nanostructured bainitic microstructure obtained by austempering, and compared it with a tempered martensitic microstructure obtained by tempering. Results show that the sliding wear resistance of the nanostructured bainitic microstructure increases as the austempering temperature is decreased from 260 to 220 °C. The wear resistance of these austempered samples is 21–51%, greater than that of tempered ones, although austempered samples have a lower hardness than tempered ones. In addition, the worn surface microstructure of samples tempered and austempered at 240 °C was also examined, indicating that the single-phase α nanograins were formed in the worn surface of both samples. The mean size of nanograins, in the worn surface of samples austempered at 240 °C, is less than that of the tempered ones.

The microstructure and mechanical properties of a high-carbon Si–Al-rich steel austempered at 220–260 °C were studied by optical microscopy, X-ray diffraction, transmission electron microscopy and tension and impact tests. Results show that the nanostructured bainite microstructure composed of 38–57 nm-thickness laths of bainitic ferrite and retained austenite is produced and the excellent combination of mechanical properties is achieved. The high yield strength 1534–1955 MPa and high ultimate tensile strength 2080–2375 MPa are obtained and accompanied by the elongation 6.7–7.8% and the Charpy impact energy 7.8–22.2 J. Fracture surface observations by scanning electron microscopy indicate that both the impact and tension fracture are in a mixed mode of the brittle quasi-cleavage fracture and the ductile dimple fracture, while the ductile dimple fracture is predominant in the tension crack propagation.

The high-cycle bending fatigue behaviour of high-carbon Si–Al-rich steel with a nanostructured bainitic microstructure was studied. A fatigue limit for no failure in 107 cycles of the nanostructured bainitic steel is determined not only by hardness or strength, which determines the fatigue limit of conventional high- and ultrahigh-strength low-alloy steels, but also by microstructure. Retained austenite and secondary cracks in fatigue fractures of the nanostructured bainitic steel have positive effects on the fatigue property.

A kind of technology was proposed for the development of low-temperature bainitic microstructure in the surface layer of low-carbon gear steel 20CrMnMo, which is based on carburization and succedent low-temperature austempering. The carbon content in the surface carburization layer increases to 0.81 wt.%, making the martensite starting point depressed. Low-temperature bainite formed in the carburization layer and lath martensite with low carbon content in the center by austempering at a low temperature slightly higher than the martensite starting point of the surface layer. Aluminum is added as alloying elements with the purpose of enhancing the driving force of bainitic transformation and retarding the precipitation of cementite during austempering. With the excellent toughness of low-temperature bainite, this low-temperature austempering technology could be a potential substitute of the traditional quenching and tempering heat treatment in the manufacture of gear.

To reduce cost production, a bainitic steel with a new chemical composition was designed using MUCG83 thermodynamic model. The steel was cast as cylinder bar using a high frequency induction furnace under argon gas atmosphere. The cast cylinder was electro-slag remelted (ESR) for obtaining clean steel. Hot rolling was carried out after ESR to reduce the thickness and to change the cast structure to a wrought structure. To obtain a bainitic structure the austenitized samples were transformed isothermally at the temperature range of 200–300 °C for different times and finally were quenched into water. The microstructures were characterized by X-ray diffraction, scanning electron and transmission electron microscopes. The tensile and Charpy impact tests were carried out to evaluate the mechanical properties. The results show a good combination of high tensile strength and impact toughness which is ideal for high performance applications. The prominent mechanical properties are due to the unique microstructural characteristics which are evolved during isothermal transformation.

A process primarily based on carburization and successive low-temperature austempering, was proposed for the generation of low-temperature bainitic microstructure in the surface layer (∼2.5 mm in thickness) of low-carbon steel. For a potential use in the manufacture of heavy-duty gears, wear properties of this type of microstructure were studied. Comparisons were made with carburized commercial steel of 20CrMnTi subjected to quenching followed by tempering, which is widely used in the area of gear. The result showed that the experimental steel and the control steel present different wear mechanisms under the same sliding wear process. The low-temperature bainitic steel exhibits an excellent wear resistance as a consequence of the following three main factors: (i) high strength plus high toughness, (ii) carbon enriched austenite, and (iii) extremely fine α-phase microstructure. The low-temperature bainitic microstructure exhibits high strength and high toughness due to the refinement of the microstructure. Secondly, the film-like carbon enriched austenite (∼30 nm in thickness) uniformly distributed between the carbide-free bainitic ferrite plates can retard the crack propagation during sliding friction and play an advantageous role in wear resistance. Lastly, an extremely fine single α-phase microstructure was promptly induced in the dry sliding friction of the surface layer of the low-temperature bainitic steel; such fine refined microstructure lead to an increase in hardness, which can improve wear resistance.

A new process to fabricate ultrafine-grained low-carbon steel was proposed. Low-carbon steel plates were intercritically quenched to obtain martensite–ferrite structure, and then warmly rolled at 700 °C. The processed samples revealed bimodal ultrafine ferritic grains and nanoscale carbide particles, and showed excellent mechanical properties.

The thermoplastic characteristics of high manganese austenitic steels were investigated using a Gleeble-3500 type thermal simulation testing machine. The results indicate that the zero-ductility temperature of the steels was low and the temperature range for plasticity was small. Through comparing the high-temperature thermoplasticity of several high manganese austenitic steels with different phosphorus and sulfur contents, the nature of thermoplasticity of the steels was explored. The results showed that phosphorus was concentrated at the boundaries of austenite grains and formed (FeMn)3P, a low-melting-point eutectic, which tended to melt the boundaries of the austenite grains. Furthermore, sulfur and manganese tended to form MnS inclusions, which were incompatible with the plastic deformation of the austenite matrix when deformed at high temperatures. Hence, the zero-ductility temperature and the plasticity temperature range of the high manganese austenitic steels were reduced significantly with an increase in the content of phosphorus or sulfur. It is thus believed that the large amount of low-melting-point eutectic of phosphorus in the grain boundaries of the austenite and the MnS inclusions were responsible for the poor thermoplastic performances of the high manganese austenitic steels. The relationship between the zero-ductility temperature of the high manganese austenitic steel and the content of phosphorus and sulfur can be expressed by T = 1248 − 1530 w s − 1651 w p . Consequently, a process for forged high manganese austenitic steel crossing was proposed based on which the mechanical properties of the forged steel was almost doubled when compared with the conventional cast high manganese austenitic steel crossing.

The microstructure in the worn surfaces of a failed bainitic steel railway crossing was investigated using optical microscopy, SEM, TEM, nanoindentation and Mossbauer spectroscopy. The results indicated that a nanocrystalline layer had formed in the surface of a worn crossing during service. The formation of the nanocrystalline layer was due to the severe plastic deformation (SPD) caused by the repeated heavy loading in service by high speed train wheels. The mechanism of formation of the nanocrystalline layer was strain induced dynamic recrystallization, and the nanocrystalline grains were nucleated from the original crystals of the steel directly. The alloying elements in the worn surfaces of the steel segregated slightly by diffusion during the process of recrystallization. The nanocrystalline layer does not display the white etching layer commonly observed in ordinary railway rails, the reason may be the differences of its microstructure and carbon content with the ordinary rail steel.

High tensile ductility and high strength were simultaneously obtained in UFG low-carbon steel prepared by appropriate annealing of cold-rolled martensite–ferrite dual-phase structure. High tensile ductility and high strength are attributed to the coexistence of fully recrystallized ferrite grains with bimodal size distribution and dispersive nanoscale carbides.

We studied the microstructure and impact toughness of low-alloy high-carbon steel austempered at low temperature. Ultrafine carbide-free bainitic microstructure was obtained, which is composed of lath-like bainitic ferrite and retained austenite. The impact absorbed energy of austempered samples is much greater than that of the low-temperature tempered sample, while the hardness is slightly lower than the tempered sample. Crack propagation occurs via a combination of brittle quasi-cleavage fracture and ductile dimple fracture.

The warm deformation behavior of quenched 0.45C steel was investigated, and the constitutive equation of the warm deformation was established. The effect of warm deformation on the microstructure and mechanical properties was analyzed. Results show that the ultrafine grain microstructure composed of submicron ferrite grains and nanoscale cementite particles can be created in the steel by quenching and warm deformation under moderate conditions. Compared to conventional quenching and high-temperature tempering, quenching and subsequently warm deformation at 600 °C can result in much higher tensile strength (861 MPa), nearly double the yield strength (777 MPa), and about the same total elongation (19.1%) and uniform elongation (9.3%).

The microstructures on the damaged surfaces of two served bainitic steel crossings were investigated using optical microscope and scanning electron microscope (SEM). The tensile properties of the bainitic steel with different contents of hydrogen were measured. The results showed that the plasticity of the bainitic steel, such as the reduction of area and elongation, decreases sharply with the increase of hydrogen content. There was a critical content of hydrogen without the hydrogen embrittlement for the commercial bainitic steel used for crossing, which was 7 × 10 −5 wt%. When the content of hydrogen in a bainitic steel was lower than the critical value, during the used process of the crossings, the wear failure appeared during the early stage; however, the fatigue spalling appeared in the end of the process. When the content of hydrogen was higher than the critical, brittle fracture was responsible for the failure of the crossing in a short time during use.

We investigated the fracture behavior of intragranular particle-reinforced alumina–mullite composites in terms of the effect of inter-phase microstresses on grain and grain boundary toughness. First, we calculated the residual matrix microstresses in the composites and validated the results by experimental measurement. Then, we analyzed the influence of the stress state on crack propagating and calculated the ratios of grain boundary toughness to grain toughness and deduced the percentage of transgranular fracture (PTF) that increases with the matrix microstress increase. On basis of the above results, we established the relationship between the microstructural features, matrix microstresses, and PTF. The results agree qualitatively with the experimental observations. Finally, we interpreted the strengthening mechanism and explained the excellent wear resistance of the alumina–mullite composites in terms of fracture-mode transition.