steel research international最新文献

Seamless steel pipes classified as API 5CT are widely used in oil and gas exploration wells, with K55-grade steel commonly subjected to quenching and tempering (Q&T) to meet mechanical requirements. This study investigates an alternative heat treatment strategy based on austempering post-intercritical austenitizing to develop ferrite–bainite biphasic microstructures aiming to reach this grade. Experimental procedures include computational simulations, dilatometric analysis, scanning electron microscopy/optical microscopy microstructural characterization, Vickers microhardness testing, and tensile tests. The combination of intercritical austenitizing at 750 °C and austempering at 400 °C results in a well-balanced microstructure, achieving a yield strength of 532 MPa, tensile strength of 779 MPa, total elongation of 16%, and a hardness of ≈270 HV, meeting the API 5CT K55-grade requirements. Compared to Q&T conventional treatments, this route improves ductility while maintaining strength and eliminating the need for a tempering stage. These results demonstrate the potential of austempering after intercritical austenitizing as a viable alternative for manufacturing K55-grade pipes, enabling better mechanical performance.

The dynamic deformation characteristics of AISI type 316LN stainless steel (316LN) with five different nitrogen contents (0.07, 0.11, 0.12, 0.14, and 0.22 wt%) have been investigated at intermediate strain rates. The experiments were conducted on flat tensile specimens using an accelerated drop-weight testing setup synchronized with a high-speed camera. The acquired digital images of planar specimen surface with speckle patterns are analyzed using the digital image correlation technique for assessment of local strain fields. The loads vs. displacement response of the materials, along with local strain fields, and the appropriate constitutive behavior at intermediate strain rates have been established. The flow stress of all test specimens was found to increase with both strain rate and nitrogen content. For 316LN with 0.07 wt% N, the flow stress at strain rate, 200 s⁻¹ increased nearly twice compared to the quasi-static strain rate. However, the ductility measure in terms of percentage elongation shows nearly 50% drop with increasing strain rates. Scanning electron microscopy (SEM) studies on fracture morphology reveal a combination of dimples and void sheets at quasi-static and high strain rates. The failures of specimens at all strain rates are found to be plastic instability induced ductile fracture.

To elucidate the mechanisms of the refining process for high Mn–high Al steel, kinetic calculations are performed based on effective equilibrium reaction zone model. Combined with laboratory-scale thermal experiments, a comprehensive discussion is conducted regarding 1) mass transport of elements, 2) potential reoxidation of the steel melt, and 3) kinetics of Mg evaporation. In the initial 0–5 min, the mass transfer coefficients in the slag and the steel are 1.62 × 10⁻⁵ and 2.43 × 10⁻⁴ m s⁻¹, respectively. From 5 to 60 min, these coefficients decrease to 1.08 × 10⁻⁵ and 1.62 × 10⁻⁴ m s⁻¹. After the slag addition, the evaporation loss of Mn is negligible, while that of Mg is quite significant. The escape of Mg vapor leads to continuous reduction of MgO in molten slag, which accelerate the erosion of MgO refractory and decrease the yield of Al. The Mg evaporation process is determined by the mass transport in the slag phase. As the reaction progressed, the apparent viscosity of the slag increases with the accumulation of solids, which in turn inhibit the volatilization of Mg.

Hot deformation of two dual-phase low-density steels Fe11Al5Mn1C1Nb (Alloy 1) and Fe11Al10Mn1C1Nb (Alloy 2) (all compositions in wt%) is studied using a Gleeble thermomechanical simulator. The steels are compressed to a true strain of 0.69 at temperatures ranging from 900 to 1200 °C at strain rates of 1–0.001 s⁻¹. Electron backscattered diffraction studies suggest that at higher strain rates and lower temperatures, dynamic recovery (DRV) is the primary softening mechanism. Dynamic recrystallization (DRX) is activated at intermediate strain rates and temperatures leading to a partially recrystallized microstructure. Dominating DRX is observed at low strain rates and high temperatures due to sufficient time and driving force available for DRX. Optimized hot deformation parameters are determined based on DRX fraction (f_drx) and average grain size (D_avg). Deformation at 1100 °C which falls in the intercritical region leads to a fine-grained microstructure. The presence of uniformly distributed NbC particles leads to a significant refinement in grain size. Particle stimulated nucleation is observed near coarse NbC and κ carbides which assist in DRX. Fine NbC particles can provide significant precipitation strengthening in these alloys. It is suggested that Nb may be an important alloying addition to low-density steels.

The cover image is based on the article Prediction and Optimization of Water Flux Distribution for Flat Nozzles in Slab Continuous Casting by Huisheng Wang et al., https://doi.org/10.1002/srin.202400738.

This study investigates solidification microstructure evolution in 420LA automotive steel during thin-slab casting using a validated 2D thermal-fluid model coupled with confocal laser microscopy experiments. The framework correlates casting parameters with secondary dendrite arm spacing (SDAS) and shrinkage porosity. Experiments quantified SDAS variations under controlled cooling rates (4.0 m min⁻¹ casting speed, 30 °C superheat, 1.67 L kg⁻¹ specific water flow rate), confirming model accuracy. Parametric analysis reveals that increasing casting speed from 4.0 to 5.0 m min⁻¹ elevates porosity volume, while raising specific water flow rate to 3.28 L kg⁻¹ reduces SDAS through enhanced cooling intensity. Critically, combining reduced superheat (20 °C) with optimized water flow (3.28 L kg⁻¹) simultaneously refines dendritic structures and suppresses macroporosity formation. These findings establish a thermal management strategy enabling concurrent microstructure refinement and defect mitigation in high-strength steel casting. The results provide practical guidelines for improving metallurgical quality in lightweight automotive components requiring stringent porosity control while maintaining industrial production rates through parameter coordination. This work advances defect prediction capabilities in solidification engineering for advanced steel processing.

Heat treatments of a commercial 40CaF₂–30CaO–30Al₂O₃ slag are explored to study their effect on quality of ingots produced using cold start electroslag remelting (ESR). Reducing heat treatment (or roasting) time or temperature for slag degassing can lead to energy savings as well as longer lifetimes for various components. Heat treatments in vacuum with pressure monitoring and air are investigated along with several temperatures, heating rates, and/or holding times. A research scale ESR furnace is used with steel electrodes. Significant differences in ingot quality, such as the occurrence of pores and a rough sidewall near the bottom of the ingot produced using slag heat treated in air at 580 °C, are observed. Adjustments in the heat treatment temperature for heat treatment in air eventually lead to an ingot quality comparable to that obtained using slag degassing in a controlled atmosphere at higher temperatures. Using differential thermal analysis, it is found that moisture is primarily removed from the slag at ≈460 °C and 700 °C. A safe slag roasting temperature is concluded to be 750 °C. Improper slag heat treatment leads to hydrogen concentrations from 8 to 15 ppm in about one-quarter of the ingot volume.

Composite materials based on a matrix copper alloy (CuAl9Mn2) have been obtained through the addition of low-alloyed steel (13Mn6) in a volume fraction ranging from 5% to 95% by means of multiwire-feed electron beam additive manufacturing. At the optimal manufacturing parameters, the samples exhibit no evidence of porosity, inclusions, imperfections, or delamination. It is shown that the addition of 13Mn6 steel, ranging from 5% to 95% by volume, influences the dendritic grain size, morphology, and mechanical properties. The primary factors influencing structure formation are the solidification of bronze inclusions in interdendritic regions or along the boundaries of steel dendrites, particularly when a smaller volume fraction of steel is added. In addition, the precipitation of small steel inclusions from the solid solution of copper in γ-Fe is observed during cooling. In composites with a close ratio of bronze to steel, a homogeneous structure of bronze grains and steel dendrites is formed. The strength properties of the composites obtained are significantly superior to those of the matrix bronze. A moderate degree of anisotropy is observed between samples tested by static stretching in perpendicular directions.

The effect of shot peening on the interfacial element diffusion, microstructure, and mechanical properties of high-manganese steel/304 stainless-steel clad plate is studied. The modified diffusion constitutive model of the clad plate, which considers the effect of shot peening, has been established. Due to shot peening, a gradient structure is developed in the depth direction of high-manganese steel, which promotes metallurgical bonding and corresponds to a sharp increase in shear strength from 236.6 ± 6.2 to 336.3 ± 8.5 MPa, an increase of 42%. Such a significant increase in shear strength results from the rise in dislocations on the composite interface, which provides diffusion pathways for the further diffusion of elements, leading to the increase in the diffusion distance of elements and the thickness of the interface layer.