steel research international最新文献

Traditional spheroidization annealing of 100Cr6 bearing steel is time-consuming and energy-intensive. To address this, warm rolling is proposed as an efficient alternative for microstructure refinement and toughness enhancement. The influence of warm rolling at critical dual-phase (760 °C) and ferrite (700 °C, 650 °C) temperatures is investigated. At 760°C, dynamic recrystallization dominated with 90% recrystallized area, yielding equiaxed ferrite grains of 4–6 μm and normally distributed carbides averaging 0.37 μm in size with 32 vol%. Lower-temperature rolling at 650 °C intensified deformation bands to 3 μm spacing, promoting carbide precipitation to 47 vol% density at 15.7 particles μm⁻² while suppressing recrystallization (90% area with GOS >2). Nanoscale carbides of 0.094 μm pinned grain boundaries, transitioning deformation mechanisms from grain-boundary sliding to intragranular slip. Impact toughness increased by 30%–40% in ferrite-zone rolled specimens due to crack deflection by laminated fibrous grains and fine carbides. This work clarifies how distortion energy storage drives deformation-induced carbide precipitation, providing a pathway to achieve high toughness through tailored warm-rolling processes.

A coupled volume of fluid–discrete phase model (DPM) model is used to simulate the single-flow postcombustion oxygen lance gas–metal interaction behavior and dephosphorization behavior in a 250 t converter. The effects of different lance heights and operating pressures on the molten pool flow rate, phosphorus content, and endpoint phosphorus content are investigated, while the influence of phosphorus distribution ratios on the dephosphorization rate is also analyzed. The results show that as the lance height increases, the droplet fraction (percentage of droplets relative to the liquid steel mass) decreases, the average velocity of the steel surface increases, the dead zone area first increases and then decreases, and the dephosphorization rate gradually declines. When the operating pressure increases from 0.8 to 1.1 MPa, surface fluctuations intensify, more droplets are splashed, and the dephosphorization rate increases from 61.9% to 81.0%. For phosphorus distribution ratios of 40, 80, 120, and 160, the dephosphorization rates are 48.5%, 60.7%, 69.2%, and 75.1%, respectively. Industrial tests on a 250 t converter using a single-flow postcombustion oxygen lance show that the higher the total iron and CaO content in the slag, the higher the phosphorus distribution ratio; the dephosphorization rate gradually increases with the gradual increase of the phosphorus distribution ratio.

Calcium treatment is widely used to modify Al₂O₃ inclusions in molten steel. However, feeding Ca wire has the problems of unstable Ca treatment effect, deterioration of molten steel cleanliness, and influence of steel plant environment. Herein, the feasibility of replacing Ca treatment with Ca-containing ferrosilicon in ladle furnace (LF) refining process is investigated by thermodynamic calculation and industrial trials. The result of thermodynamic calculations shows that the evolution of inclusions type is similar when pure Ca wire and Ca-containing ferrosilicon are fed, and Al₂O₃ inclusions are also modified by ferrosilicon. The industrial trials of different addition methods of Ca-containing ferrosilicon shown that the molten steel had high cleanliness and well inclusions control effect with the process of one-time addition of ferrosilicon without Ca treatment (OTAF). The Ca treatment of feeding 130 m Ca wire is canceled by postponing the time of adding ferrosilicon. The fitting relationship between the addition of ferrosilicon and the increasing of Ca content in molten steel or the yield of Ca is obtained. In addition, an on-line control software for Ca increase by adding ferrosilicon is developed to predict the Si and Ca content in the LF refining process in real time.

To forecast types of inclusions formed during the real deoxidation process, thermodynamic stability diagrams and nucleation kinetics of magnesium and aluminum complex deoxidation in the liquid iron are calculated. Thermodynamic Mg–Al–O 3D stability diagram with different deoxidation products is calculated at 1600 °C using Wagner's second order model. Kinetics of homogeneous nucleation and heterogeneous nucleation of inclusions are calculated according to the classical nucleation theory. The effects of nucleation rate and frequency factors on the homogeneous nucleation are discussed. As nucleation rate increases and frequency factor decreases, inclusions nucleation becomes more difficult, causing the 3D stability diagram to shift toward the higher dissolved oxygen content. In addition, MgO·Al₂O₃ inclusions are difficult to nucleate homogeneously and heterogeneously through dissolved aluminum, oxygen, and magnesium directly.

By means of cold ring rolling (CRR), quenching and tempering treatments, microstructure observation, and mechanical-property tests, the effects of CRR on the microstructure and wear resistance of GCr15 bearing steel are studied. The results show that the carbides before heat treatment are refined by CRR, and a large number of small-sized Cr₇C₃ carbides appear. Compared with the samples without CRR, the number of undissolved carbides in the CRR samples is obviously reduced. CRR promotes the dissolution of large-sized carbides during solution treatments while retaining a large number of fine Cr₇C₃ carbides when the solution treatment temperature is below 860 °C. After tempering, the amount of carbide precipitation in the CRR samples increases, and the carbide is fine and uniform. When the solution temperature is 840 °C, the tempering hardness of the CRR samples reaches the highest of 747.31 HV₁. When the solution temperatures are above 840 °C, the tempering hardness of the CRR samples is always higher than that of the samples without CRR. When the solution temperature is 840 °C, the wear resistance of the CRR sample is the best, and the wear loss is only 0.45 × 10⁻⁴ mg/(N·m).

Residual stress is the critical cause of material distortion, but there is a lack of effective control means in practical applications. In this paper, the combination of finite element calculation and stress characterization by crack compliance method is used to study the influence law of different cooling histories on residual stress. It is found that the residual stress can be effectively controlled by interrupted quenching process, i.e., adjusting the cooling rate at the appropriate phase transformation point and suppressing the growth of eigenstrain in the pre-phase transformation zone. In the above process, the phase transformation point at which the cooling rate adjustment is carried out is crucial for controlling residual stress. Based on this, this paper establishes a theoretical model of low-stress quenching and verifies it on NM400 steel. The results show that after adjusting the cooling rate at the appropriate phase transformation point, the eigenstrain of NM400 steel can be reduced from 2.78 × 10⁻³ to 1.51 × 10⁻³, the residual stress is reduced from 219.27 to 120.28 MPa, and the transverse warpage is reduced from 8.3 to 2.8 mm under the premise of keeping the microstructure and properties unchanged. The finding provides a new path to controlling residual stress.

This study aims to understand the fracture mechanisms within the hot ductility trough by investigating four microalloyed steels with varying Ti content and balanced Nb. Variations in the cooling rate and Ti content significantly influence intergranular cracking by affecting proeutectoid ferrite formation and TiNb(CN) precipitation. Thermomechanical tests are conducted at three critical temperatures (700, 800, and 900 °C), under cooling rates of 10 and 1 K·s⁻¹, and a strain rate of 0.001 s⁻¹. The effect of cooling rate on hot ductility is examined by analyzing ferrite thickness, and TiNb(CN) precipitates through microstructural investigation and MatCalc simulation. At 700 °C, a thin ferrite layer at grain boundaries causes intergranular cracking. A slower cooling rate increases ferrite thickness, thereby, reducing crack susceptibility. At 800 and 900 °C, precipitation behavior and dynamic recrystallization dominate the hot ductility. Coarser precipitates formed under slow cooling result in lower microvoid density at TiNb(CN)-grain boundary interfaces, thereby limiting crack propagation. Among the Ti-containing steels, steel S1 exhibits the highest ductility recovery, while steel S2 demonstrates the most favorable overall hot ductility performance. The high Ti content in S3 promotes excessive TiNb(CN) formation, which increases microvoids and suppresses the recovery of hot ductility.

Additive manufacturing (AM) of metallic parts has gained significant attention in the materials manufacturing industry. Despite the advantages of complex shape, flexibility, rapid prototyping, and ease of processing, AM parts have associated disadvantages of surface roughness and esthetics that limit wider industrial applications. Specifically, the problem of roughness is more severe in complex intricate geometries that involve high internal surface area. The present study aims to decrease the roughness with minimal material loss of in-house fabricated direct energy deposition specimens using the electropolishing technique. The control over polishing time, in minimizing surface roughness and its associated material loss is demonstrated. Furthermore, surface passivation of electropolished surfaces is determined with potentiodynamic polarization, Mott–Schottky, and electrochemical impedance spectroscopy. Electropolishing performed at 60 °C for 40 min, show a maximum mass loss of 6%. The methodology reported in this study, optimized to reduce the surface roughness (R_a) by 48% with an associated improvement in corrosion resistance by 99%. The results indicate a significant positive shift in corrosion mitigation, with current density of 7.722 μA cm⁻² and 0.024 μA cm⁻² for as-fabricated and polished surface, respectively. Furthermore, the passive film formed on the 40 min polished surface, demonstrates 2-orders of magnitude reduced carrier density demonstrating improved passivation to Cl⁻ penetration.

The evolution characteristics of inclusions during reaction process between low-density steel and CaO-Al₂O₃-based mold flux are studied. The results show that the chemical reaction between [Al] and (B₂O₃) mainly occurs, followed by that between [Al] and (SiO₂). The mass transfer coefficient of [Al] in steel decreases from 33.86×10⁻⁵ to 9.47×10⁻⁵m s⁻¹ owning to the reduction in content of [Al] and the increase in interfacial mass transfer resistance caused by the deterioration of mold flux properties. The main inclusion is AlN, followed by AlON. With the increase in reaction time, the number density of inclusions decreases from 281.5 to 176.8 mm⁻², and then, slightly increases to 193 mm⁻². The average diameter of inclusions shows an overall increasing trend from 1.81 to 3.45 μm. Moreover, the number density of inclusions in argon-cooled steel ingot is 360 mm⁻², and the average diameter is 2.75 μm. AlN inclusions float up to the steel–slag interface, and there are three removal paths: 1) AlN inclusions self-decompose to generate [Al] and N₂; 2) AlN inclusions react with (B₂O₃) to form BN solid particles; and 3) AlN inclusions react with (SiO₂) to form Si₃N₄, dissolving in the mold flux.

The evolution characteristics of inclusions during reaction process between low-density steel and CaO-Al₂O₃-based mold flux are studied. The results show that the chemical reaction between [Al] and (B₂O₃) mainly occurs, followed by that between [Al] and (SiO₂). The mass transfer coefficient of [Al] in steel decreases from 33.86×10⁻⁵ to 9.47×10⁻⁵m s⁻¹ owning to the reduction in content of [Al] and the increase in interfacial mass transfer resistance caused by the deterioration of mold flux properties. The main inclusion is AlN, followed by AlON. With the increase in reaction time, the number density of inclusions decreases from 281.5 to 176.8 mm⁻², and then, slightly increases to 193 mm⁻². The average diameter of inclusions shows an overall increasing trend from 1.81 to 3.45 μm. Moreover, the number density of inclusions in argon-cooled steel ingot is 360 mm⁻², and the average diameter is 2.75 μm. AlN inclusions float up to the steel–slag interface, and there are three removal paths: 1) AlN inclusions self-decompose to generate [Al] and N₂; 2) AlN inclusions react with (B₂O₃) to form BN solid particles; and 3) AlN inclusions react with (SiO₂) to form Si₃N₄, dissolving in the mold flux.