steel research international最新文献

Systematic and pioneering exploration is conducted on the effect of postforging residual heat normalizing on the static recrystallization (SRX) and grain refinement of 55# hub bearing steel applied in automotive industry. Through dual-pass hot compression tests, the impacts of deformation temperature (1040, 1100, 1160 °C), strain rate (0.1, 1, 10 s⁻¹), interval time (5, 15, 60 s), and strain (0.05, 0.07, 0.1) are investigated. Key findings show that the recrystallization activation energy is determined as 233 623 J mol⁻¹, and kinetic and grain size models are developed. Higher deformation temperatures and strain rates promote SRX and grain refinement, enhancing material performance. Postforging normalizing notably accelerates recrystallization and refines grains, especially at higher temperatures. Extended normalizing time leads to a more uniform grain structure, improving strength and toughness. Treated steel exhibits a higher recrystallization volume fraction and better mechanical properties. Finite element simulations with Deform software validate the results, offering insights for optimizing forging and normalizing processes. This research provides a new basis for heat treatment optimization of 55# hub bearing steel.

The steel industry is a major contributor to global energy consumption and pollutant emissions. This study focuses on optimizing the production of magnesium–calcium–carbon (Mg–Ca–C) bricks, a crucial refractory material in steelmaking, to reduce pollution and carbon emissions. The effects of curing temperature and time on Mg–Ca–C brick properties are investigated using an orthogonal experimental design. Furthermore, a novel air excess coefficient measurement instrument, based on an electrochemical zirconium oxygen analyzer, is developed for real-time monitoring of drying kiln conditions. The optimal curing process is determined to be 170 °C for 12 h, resulting in a bulk density of 2.76 g cm⁻³, apparent porosity of 8.15%, compressive strength of 66.34 MPa, and flexural strength of 22.46 MPa. The measurement instrument demonstrates an average accuracy of 98.1% and an average response time of 2.35 s. Optimization of the curing process, coupled with precise control of the air excess coefficient, leads to a significant improvement in Mg–Ca–C brick properties, contributing to reduced pollution and enhanced energy efficiency in the steel industry.

The steel industry is a major contributor to global energy consumption and pollutant emissions. This study focuses on optimizing the production of magnesium–calcium–carbon (Mg–Ca–C) bricks, a crucial refractory material in steelmaking, to reduce pollution and carbon emissions. The effects of curing temperature and time on Mg–Ca–C brick properties are investigated using an orthogonal experimental design. Furthermore, a novel air excess coefficient measurement instrument, based on an electrochemical zirconium oxygen analyzer, is developed for real-time monitoring of drying kiln conditions. The optimal curing process is determined to be 170 °C for 12 h, resulting in a bulk density of 2.76 g cm⁻³, apparent porosity of 8.15%, compressive strength of 66.34 MPa, and flexural strength of 22.46 MPa. The measurement instrument demonstrates an average accuracy of 98.1% and an average response time of 2.35 s. Optimization of the curing process, coupled with precise control of the air excess coefficient, leads to a significant improvement in Mg–Ca–C brick properties, contributing to reduced pollution and enhanced energy efficiency in the steel industry.

To develop a high strength [yield strength (YS) of minimum 460 MPa] and high-impact toughness (Min. 27 J at −50 °C) steel in thick normalized plate (>50 mm thickness), three different types of steel are prepared with varying nitrogen (90–150 ppm), vanadium (0.1–0.15 wt%), and niobium (0.03 wt%) levels. The cast steels are hot rolled and normalized at 900 °C. The microstructures are characterized by optical microscopy, scanning electron microscopy, electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM) to correlate with the tensile properties. The complex mechanism of precipitate dissolution, grain boundary pinning, and reprecipitation is involved in the case of vanadium precipitation in the normalized steel. The increase in nitrogen content from 90 to 150 ppm seems to have no positive effect on strength in the normalized condition. The strengthening is calculated for both as-rolled and normalized conditions, and the highest precipitation strengthening is observed in 0.15V–90N in the as-rolled state, and the highest grain size strengthening and precipitation strengthening are observed for 0.1V–0.03Nb–100N steel in the normalized state. Based on the above laboratory-based study, a successful commercial heat is processed, and ≈450 MPa YS and 110 J (−50 °C) are observed in the hot-rolled and normalized plate.

To develop a high strength [yield strength (YS) of minimum 460 MPa] and high-impact toughness (Min. 27 J at −50 °C) steel in thick normalized plate (>50 mm thickness), three different types of steel are prepared with varying nitrogen (90–150 ppm), vanadium (0.1–0.15 wt%), and niobium (0.03 wt%) levels. The cast steels are hot rolled and normalized at 900 °C. The microstructures are characterized by optical microscopy, scanning electron microscopy, electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM) to correlate with the tensile properties. The complex mechanism of precipitate dissolution, grain boundary pinning, and reprecipitation is involved in the case of vanadium precipitation in the normalized steel. The increase in nitrogen content from 90 to 150 ppm seems to have no positive effect on strength in the normalized condition. The strengthening is calculated for both as-rolled and normalized conditions, and the highest precipitation strengthening is observed in 0.15V–90N in the as-rolled state, and the highest grain size strengthening and precipitation strengthening are observed for 0.1V–0.03Nb–100N steel in the normalized state. Based on the above laboratory-based study, a successful commercial heat is processed, and ≈450 MPa YS and 110 J (−50 °C) are observed in the hot-rolled and normalized plate.

Recrystallization and austenite reversion are two crucial physical metallurgical phenomena occurring during the intercritical annealing process of cold-rolled medium Mn steel (MMnS), which can produce an ultrafine dual-phase microstructure essential for achieving the superior strength-ductility balance. To elucidate the microstructural behavior of concurrent recrystallization and austenite reversion, a tracing method based on the heterogeneous Mn distribution induced by softening annealing is employed to identify the distinct recrystallization modes in deformed ferrite and martensite. The potential interactions between recrystallization and austenite reversion are then assessed by monitoring Mn redistribution during intercritical annealing. Furthermore, the influences of recrystallization extent, controlled by different rolling reductions on austenite reversion, are also analyzed. These findings indicate that recrystallization significantly enhances both the nucleation and growth of reversed austenite in cold-rolled MMnS. Grain boundaries (GBs) formed during recrystallization serve as rapid diffusion channels, thereby facilitating the efficient partition of Mn atoms to reversed austenite during intercritical annealing. The freshly nucleated finer austenite subsequently pins the GBs, inhibiting the coarsening of recrystallized ferrite. This process not only assists in preserving the refined dual-phase microstructure, but also ensures a greater amount of austenite stabilized in the final microstructure at room temperature.

The effects of bismuth (Bi) content on the microstructure, mechanical, and corrosion behaviors of Al–Zn–Mg–Cu–Sc–Zr–Bi are systematically investigated. Al–Zn–Mg–Cu–Sc–Zr–Bi alloys with Bi content ranging from 0 to 0.5 wt% are synthesized via casting. The addition of Bi significantly refines the grain size from 52.6 to 23.2 nm, promoting the discontinuous precipitation of second phase particles along grain boundaries for Bi contents of 0.3–0.5 wt%. These Bi-rich particles are identified through scanning electron microscopy/energy dispersive spectroscopy analysis. The tensile strength is substantially enhanced, with the synthesized alloy with 0.3 wt% of Bi achieving the highest 367.42 MPa. This improvement is attributed to lattice distortion caused by Bi dissolution and the Hall–Petch effect. However, excessive Bi content (>0.3 wt%) leads to stress concentration at grain boundaries, reducing tensile strength. Moreover, the synthesized alloy with 0.2 wt% of Bi exhibits the highest corrosion resistance, as indicated by electrochemical impedance spectroscopy results, which suggests improved capacitive characteristics due to Bi addition. This work highlights the potential of Bi as a microalloying element to optimize mechanical and corrosion properties of Al–Zn–Mg–Cu, offering a valuable insight for developing high-performance structural materials with enhanced strength and corrosion resistance.

Product development routes for new generation ultrahigh-strength structural steels such as S1300 are currently not well-defined, warranting studies on their alloy design, processing, and microstructure–property correlations. This study aims to bridge the gap in understanding of these aspects by investigating a boron-treated, low-carbon, S1300-type alloy steel produced via the direct-quench and tempering (DQ&T) route. The study includes detailed characterization of microstructure development under widely varied tempering temperatures using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), dilatometry, and hardness measurements. It reveals three tempering stages of martensite, based on changes in hardness and corroborated by full width at half maximum (FWHM), microstrain, crystallite size, and lattice distortion of martensite. A strong linear correlation between hardness and FWHM is found. The microstructure remained predominantly martensitic (BCT) from its DQ to all tempered states up to 700 °C. Furthermore, EBSD analysis reveals the presence of bainite alongside tempered martensite. Nucleation of fine η-Fe₂C, formation and growth of Fe₃C and other alloy carbides, and secondary hardening are responsible for the three distinct stages of tempering. Finally, a new parameter named “microstrain-crystallite size parameter” is proposed to establish an empirical relationship for predicting hardness changes during tempering of S1300-type steels.

In this work, a low-carbon Nb + V microalloyed steel has been thermo-mechanically processed at 1100 °C, followed by water-quenching. The sample processing results in dynamically recrystallized (DRX) austenite along with coarse deformed pancake grains at a high strain rate deformation. The primary objective brings into inspection the effects of austenite processing and parent austenite grain sizes on lath martensite nucleation and growth. A high surface/volume ratio of DRX grains enhances the nucleation rate; however, the observed grain size of ≈2–3 μm interrupts the growth to a premature halt. The unannihilated crystal defects and dynamically recovered sub-boundaries inside pancake-shaped grains also constrain martensitic reaction with a selective variant growth by maintaining Kurdjumov–Sachs orientation relationships. The orientation mismatch between the variants leads to delving deep into the hierarchical structure of martensite such as packets, blocks, sub-blocks, and laths, forming differentially in DRX versus pancake grains. Fundamentally, the austenite to martensite lattice change incorporates dilatation (≈0.03) and shear (≈0.22) strain. The demonstration of variant pairing helps to conceptualize the large shear strain component minimization. The stress concentration at the hierarchical structure has been analyzed. A comprehensive nature of this work also enlightens the effect of crystallographic texture on slip, retarding lath-formation from deformed austenite.

The impact toughness, microstructure, and carbide precipitation behavior of austenitic hot-forging die steel after holding at different temperatures (740–780 °C) for various times (0–48 h) are investigated. The results showed that the hardness of SDHA steel decreases with increasing holding time due to the precipitation and coarsening of M₂₃C₆ and M₂C carbides. During the holding process, M₂₃C₆ carbides precipitate on the grain boundaries and inside the grains (near grain boundaries), and M₂₃C₆ carbides precipitate on the grain boundaries are interconnected to form a chain-shaped distribution. The impact toughness of materials severely deteriorates due to this distribution of carbides, and the fracture morphology is characterized by intergranular fracture and secondary cracks. The maturation equations of M₂₃C₆ carbides at the grain boundaries at 740, 760, and 780 °C are obtained. Besides, the nanoscale MC carbides maintain a coherent relationship with the matrix after a long holding time at high temperatures, so it is an important secondary precipitation for maintaining the thermal stability of materials.