Haijiang Hu

Wuhan University of Science and Technology | WUST · Department of Materials Science and Engineering

For the first time, investigation of twin evolution during austenite grain growth in an Fe-C-Mn-Si alloy was conducted with in-situ observation using high temperature laser scanning confocal microscopy during austenization. It was found that twins nucleated in austenite grains, some of which might disappear during isothermal holding, even as new tw...

In situ observations of austenite grain growth in Fe-C-Mn-Si super bainitic steel were conducted on a high-temperature laser scanning confocal microscope during continuous heating and subsequent isothermal holding at 850, 1000, and 1100°C for 30 min. A grain growth model was proposed based on experimental results. It is indicated that the austenite...

The effect of ausforming on the stability of retained austenite in a C-Mn-Si bainitic steel was investigated through metallography, X-ray diffraction and dilatometry. The geometrical relationships of the amount of bainite transformation and the volume fractions of retained austenite with deformation strains were studied. The results show that the d...

The relationship between the strain corresponding to the maximum amount of bainite (termed as peak value strain) and ausforming temperature is investigated by metallography, X-ray diffraction, and dilatometry. The results indicate that the peak value strain increases with the increase of ausforming temperature, whereas the corresponding maximum amo...

Unlike medium‐carbon and high‐carbon steels, the effect of the high‐temperature deformation process on bainite transformation of low‐carbon steels has is yet to be fully understood. Processes with varying high‐deformation temperatures and reductions were designed to investigate the bainitic transformation of low‐carbon steel. The results indicated...

The lengthening of bainitic ferrite laths in a model alloy containing a carbon gradient was observed in-situ using a Laser Scanning Confocal Microscope (LSCM). Results show that the observed lengthening rates increase with increasing temperature and decreasing carbon content. Crystallographic analysis was conducted by ex-situ electron backscattered...

The microstructure and wear performance of a low-carbon steel treated by austempering below and above martensite start temperature (Ms) were investigated. The results show that the bainite, fresh martensite (FM) and retained austenite (RA) were observed in samples austempered above Ms. Except for the three above phases, the athermal martensite (AM)...

The effects of boro-austempering treatment on growth kinetics of borided layers, microstructure, and properties in a medium-carbon bainitic steel were investigated. The microstructure, distribution in coatings, corrosion, and wear properties of boro-austempered steels were characterized by a microscope, field-emission electron probe micro analyzer,...

The hardness, tensile properties, low temperature impact toughness and wear resistant performance in a low-carbon bainite/martensite multi-phase wear resistant steel were investigated. The results show that the multi-phase wear resistant steel with less amount of bainite exhibits better wear resistant performance at lower applied load, while the st...

The growth behavior and crystallographic orientation of bainite in a low carbon steel were investigated by a combination of in situ observation and electron backscattered diffraction. The intersection of different bainitic ferrite (BF) laths was analyzed in detail. The results show that the growth of a given lath stops when it runs into a preexisti...

In order to investigate the effect of integrated austempering and Q&P(quenehing and partitioning) process on microstructure and mechanical properties of a medium-carbon high-strength bainitic steel, the microstructural observation, dilatometry, X-rays diffraction and tensile tests were utilized to clarify the microstructural evolution and property...

In order to investigate the changing law of the volume percent of retained austenite in a medium-carbon bainitic steel under different isothermal conditions,X-ray diffraction measurement,thermalmechanical simulation experiment and scanning electron microscope were utilized to analyze the effects of austempering on the volume percent of retained aus...

Both ausforming and austempering below the martensite start temperature (M S) have been shown to accelerate the bainitic transformation. This work investigates the combined effects of deformation and austempering below the M S on the isothermal transformation kinetics, microstructure, and hardness in a medium-carbon bainitic steel. The results show...

The transformation kinetics of a low carbon bainitic steel was investigated using in situ confocal microscopy and dilatometry for isothermal treatments above and below the martensite start (MS) temperature. Both martensite and bainite are formed during isothermal holding below the MS, but bainite was the dominant transformation product. The prior m...

Five quenching temperatures were designed to investigate the relationship between volume fraction of retained austenite and microstructure, mechanical properties of a medium carbon quenching and partitioning (Q&P) steel. It is normally accepted that the optimal mechanical property of Q&P steels is obtained by quenching at optimum temperature, which...

The microstructure and properties of a medium‐carbon high‐strength bainitic steel treated by integrated technology of austempering and boriding treatments (boro‐austempering) were investigated by metallographic method and electrochemical impedance spectroscopy etc. The results show that the carbide‐free bainite of substrate and the borided layers o...

The transformation behavior and microstructure in a medium-carbon bainitic steel were investigated by combination of metallography and dilatometry. The fine micro-structural units of carbide-free bainite in non-ausformed and ausformed materials were measured by a transmission electron microscope. Mechanical stabilization of austenite in deformed ma...

It is commonly accepted that single ausforming with small strain at low temperature promotes isothermal bainite transformation and leads to more retained austenite. In the present study, the effects of two-step ausforming on the bainite transformation and retained austenite in a Fe-C-Mn-Si medium-carbon bainitic steel were investigated by thermo-me...

Carbide‐free bainitic steels present microstructures containing bainitic ferrite, carbon‐enriched retained austenite and may contain martensite. The effects of deformation during austempering on the subsequent bainite transformation and the final volume fraction of retained austenite have not been reported. In the present study, compressive true st...

A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation, microstructure, and strength of Fe–C–Mn–Si superbainitic steel. The results indicate that the strength of the samples decreases and the elongation increases with the isothermal transformati...

The martensitic transformation in a Fe–C–Mn–Si bainitic steel was examined by in situ high-temperature laser scanning confocal microscopy (LSCM) and dilatometry. The phenomenon of continuous martensitic transformation during austempering was firstly dynamically observed by LSCM. Differing from the commonly accepted viewpoint on martensite formation...

Effects of austenisation temperature on martensite and bainite transformation behaviour, microstructure, and mechanical properties of a bainitic steel austempered below martensite starting temperature were investigated in this study. Results show that the amount of athermal martensite gradually increased with the increase of austenisation temperatu...

The industrial trials of two cooling modes, i e, water cooling in forepart + air cooling in later part (WAC) and air cooling in forepart + water cooling in later part (AWC), were carried out for a Ti-Nb microalloyed steel. The average cooling rates and coiling temperature were the same for two modes. The continuous cooling transformation (CCT) curv...

The authors have indicated that they mistakenly provided the wrong TEM micrograph for Fig. 8 of their paper. The authors have provided the correct TEM micrograph, which is shown below.

In the present study, the thermo‐mechanical controlled processing (TMCP) technology was applied to produce Ti–Nb–Mo microalloyed hot‐rolled steels. The strength at the tail of a strip coil is often found to be non‐uniform. The microstructural and the mechanical properties of the specimens in the outermost circle as well as in the third circle and t...

The effects of aluminum addition on bainite transformation and properties of carbide-free bainitic steels containing 0.22 wt.% carbon were investigated by two different types of heat treatment processes: continuous cooling process (CCP) and isothermal transformation process (ITP). The results indicate that for the CCP treatment, Al addition signifi...

Four low-carbon bainitic steels with different nickel (Ni) and chromium (Cr) contents were designed to analyze the influences of Ni and Cr on bainitic transformation, microstructure and properties by metallographic method and dilatometry. The results showed that compared to the base steel, the kinetics of bainitic transformation in Ni or Cr additio...

In the present study, the relationship between initial austenite grain size and mechanical properties of a 5% nickel cryogenic steel was investigated. The microstructures of initial austenite grains and tempered martensites were analyzed by an optical microscope. In addition, a transmission electron microscope was employed to examine the morphologi...

Both ausforming and transformation temperature affect the successive bainitic transformation and microstructure. The individual influence of each case is clear, whereas the combined effects are still unknown. Thermomechanical simulation and metallography were used to investigate the combined effects of ausforming and transformation temperature on b...

The effects of deformation temperature on phase transformation and microstructure in nanostructured bainite steel were studied. The results indicate that the deformed austenite with a strain of 0.3 at 300°C presents accelerated kinetics of bainitic transformation. However, the amount of bainite in ausformed austenite then reduces with the increase...

In the present study, low-carbon steel was first evenly cryorolled by 50% reduction at liquid nitrogen temperature (LNT) and then annealed at 400–550 °C for 1800 s. A transmission electron microscope was employed to analyze the microstructures and the tangled dislocations in the processed steel. The presence of Fe3C particles in the steel was confi...

The effect of strain rate on the kinetics of the bainitic transformation in a Fe-C-Mn-Si medium-carbon bainitic steel was investigated by dilatometry, metallography, and X-ray diffraction. The results indicate that the bainitic transformation is affected by the strain rate. The bainitic transformation is significantly promoted by deformation at a l...

Four different isothermal treatment processes were designed to investigate the effect of isothermal treatment parameters on the comprehensive property in an ultrafine bainite steel. Four different isothermal treatment processes, including two kinds of one-step bainite transformation procedures at temperature above MS and below MS, respectively, and...

Ultrafine grained low‐carbon steels are fabricated by cryorolling and cold‐rolling martensite starting microstructure at liquid nitrogen temperature and ambient temperature, respectively. The results indicate that cryorolling process at liquid nitrogen temperature present more potential in refining ferrite grains in low‐carbon steel (132 nm) than a...

Deformation experiments for two bainite steels at different strain rates are conducted to analyze the effects of strain rate on deformation resistance during ausforming of two bainite steels. The results indicate that deformation resistance for medium‐carbon steel increases with strain as well as strain rate due to work hardening. However, for low‐...

A novel method of cryorolling martensite for fabricating ultrafine grained low-carbon steel with attractive strength was proposed. The results indicate that ultrafine-grain structured steel could be manufactured by cryorolling and the subsequent annealing of martensite. The mean ferrite size of 132.0 nm and the tensile strength of 978.1 MPa were ob...

An advanced bainite rail with high strength–toughness combination was produced in a steel mill and the effects of tempering on the microstructure and properties of the bainite rail steel were investigated by optical microscopy, transmission electron microscopy, electron back-scattering diffraction and X-ray diffraction. Results indicate that the te...

The effects of Nickle (Ni) addition on bainitic transformation and property of ultrahigh strength bainitic steels are investigated by three austempering processes. The results indicate that Ni addition hinders the isothermal bainite transformation kinetics, and decreases the volume fraction of bainite due to the decrease of chemical driving force f...

The relationship between the passivation period of Si-containing steel and oxygen concentrations was investigated by conducting the oxidizing experiments employing four different oxygen concentrations on a simultaneous thermal analyzer (STA) at a heating temperature of 1260°C. The results show that the duration of passivation period increased with...

Four isothermal heat treatment schedules are designed to study the effects of transformation temperature below and above martensite starting temperature (MS) on bainitic transformation kinetics, microstructure, and mechanical properties of a low-carbon bainitic steel. The results indicate that the product of tensile strength and elongation (PSE) of...

Thermal simulations were conducted on a Gleeble 3800 simulator. The main purpose is to investigate the effects of stress on the kinetics of bainitic transformation in a Fe-C-Mn-Si advanced high strength bainitic steel. Previous studies on modeling the kinetics of stress affected bainitic transformation only considered the stress below the yield str...

In this study, medium-carbon steel was subjected to warm deformation experiments on a Gleeble 3500 thermosimulator machine at temperatures of 550°C and 650°C and strain rates of 0.001 s –1 to 1 s –1 . The warm deformation behavior of martensite and the effects of strain rate on the microstructure of ultrafine grained medium-carbon steel were invest...

A method to reduce the scale of silicon-containing steels by adjusting the heating route has been proposed in the present study. The influence of heating rate on the oxidizing behavior of steels containing Si was studied by simultaneous thermal analyzer with various heating rates under the condition of the fixed heating time and same heating temper...

Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon bainitic steels were investigated by dilatometry, met...

The evolution of lengthening rate of bainite sheaves during continuous cooling process in a Fe–C–Mn–Si superbainitic steel was investigated by in situ observation on high-temperature laser scanning confocal microscope. The lengthening rates of bainite sheaves in three temperature ranges were calculated. The results indicate that the lengthening rat...

To investigate the effects of Nb addition on transformation kinetics and microstructure properties in low-carbon bainitic steels, two C–Si–Mn bainitic steels were designed, one of which was added with 0.025 (wt%) Nb and the other was C–Si–Mn steel. Heat treatment experiments were carried out on thermal simulator. The microstructures were observed b...

Mechanism of burning loss of ZG40Cr25Ni20 austenitic heat-resistant steel was investigated by optical microscope (OM), energy dispersive spectrometer (EDS) analysis, X-ray diffractioin (XRD) and in situ observation on laser scanning confocal microscopy (LSCM). The results show that with the temperature increasing, austenite grain grows up, Cr23C6 c...

The varying trends of the amount and rate of bainitic transformation with strains at low temperature were investigated through metallography, X-ray diffraction and dilatometry. The results show that deformation at 573 K promotes bainitic transformation, whereas the promotion degree on bainite transformation by ausforming is nonlinear with strains....

Three low-carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition is effective for improving the strength of low-carbon ba...

In this study, two silicon-containing steels with different P contents were used, and reheating tests were conducted in an industrial furnace in a hot strip plant. The effect of P on the microstructure and melting temperature of Fe2SiO4 in silicon-containing steels was investigated using a backscattered electron (BSE) detector and energy-dispersive...

Red scale defect is known to be mainly caused by net-like Fe2SiO4–FeO. In the present study, the morphology of Fe2SiO4–FeO in a Si-containing steel was investigated by simultaneous thermal analysis, high-temperature laser scanning confocal microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Only liquid Fe2SiO4–FeO can form...

Bainitic transformation under stress is an interesting subject. The present study investigates the effect of large stress above the yield strength of austenite on the microstructure and kinetics of bainitic transformation at different transformation temperatures. Scanning electron microscope, X-ray diffraction examination and dilatometry were used....

There has been a continued interest over the past years in the effects of external stress or prior deformation on the bainite transformation. In this study, the combined effect of prior deformation and stress on the bainite transformation was investigated and the interaction between the effects of prior deformation and stress was discussed in detai...

In this work, three low-carbon bainitic steels, with different Mo contents, were designed to investigate the effects of Mo addition on microstructure and mechanical properties. Two-step cooling, i.e., initial accelerated cooling and subsequent slow cooling, was used to obtain the desired bainite microstructure. The results show that the product of...

Effects of deformation on kinetics of bainite transformation in a carbide-free bainitic steel were investigated by SEM, dilatometry and XRD. The results show that a 0.25 pre-strain at 300℃ accelerates bainite transformation and thus the final volume fraction of bainite increases. The content of retained austenite at room temperature increases with...

The thermal simulation experiments on bainitic transformation were conducted on Gleeble 3800. The microstructures of specimens were examined by scanning electron microscopy. The main purpose is to investigate the relationship between the dilatation of specimens and bainitic transformation under stress. Results show that the radial strain cannot rep...

The dynamic observations of bainitic transformation in a Fe-C-Mn-Si superbainite steel were conducted on a high temperature laser scanning confocal microscope. It is indicated that the mutual intersection of bainite sheaves often occurs during growth of bainite ferrite, resulting in an interlocked bainite microstructure. Moreover, bainite transform...

Superbainite steel is a new high strength steel, widely used in mechanical machinery, structure, bridge engineering etc. The effects of transformation and austenization temperatures on bainitic transformation in an Fe-C-Mn-Si superbainite steel were investigated by the combination of high temperature metallography and dilatometry. The experimental...

To investigate the dynamic process of bainite transformation, in situ observation of bainite transformation in a 0.42%C superbainite steel was conducted on a high temperature laser scanning confocal microscope. It is found that the bainite embryos nucleate not only in parent austenite grain, on grain boundary and previously formed bainite platelet,...

The CCT curve of a C-Si-Mn steel was investigated. The hot simulation tests at different cooling rates were conducted on Gleeble-1500 simulator and microstructures were observed. Based on transformation temperatures recorded by dilation curves and microstructures, the CCT curve diagram for tested steel was plotted. The effects of cooling rate on mi...

The growth rates of bainite plates in an Fe-C-Mn-Si superbainitic steel were investigated by in situ observation. The lengthening rates of ferrite bainite during both cooling and isothermal holding processes were observed and the growth rates of bainite plates nucleating at grain boundaries, within grains and on preformed bainite were measured. It...

In situ observation of dynamic process of austenite grain growth in an advanced bainite steel was carried out on high temperature laser scanning confocal microscope (LSCM). Three kinds of grain growth behavior are directly observed, i.e. expansion and migration of austenite grain, combination of some small grains as well as segmentation and merger...

The precipitation in continuously casting slabs of a Ti-Nb microalloyed steel was studied. The samples were taken from different places along cross section of slabs and the precipitations were observed by TEM. The results show that the centre area of slab contains more precipitates of Ti-Nb and carbonitrides more uniformly distribute in the centre...

In situ observation of bainitic nucleation and growth in a superbainite steel was conducted by high-temperature laser scanning confocal microscopy. The morphological development of bainite transformation was directly observed. Moreover, thermal simulation tests were carried out in which bainite transformation was recorded by dilatometry. The bainit...