Steel Refining Research Articles

Cleanliness Improvement and Microstructure Refinement of As-Cast High-Nitrogen Stainless Bearing Steel by Magnesium Treatment

Cleanliness Improvement and Microstructure Refinement of As-Cast High-Nitrogen Stainless Bearing Steel by Magnesium Treatment

An Improved Inclusions Modification Strategy Through Barium-Alloyed Cored Wire Injection in Steel Refining

An Improved Inclusions Modification Strategy Through Barium-Alloyed Cored Wire Injection in Steel Refining

Microstructure, Tensile Properties, and Fracture Toughness of an In Situ Rolling Hybrid with Wire Arc Additive Manufacturing AerMet100 Steel.

As a type of ultra-high strength steel, AerMet100 steel is used in the aerospace and military industries. Due to the fact that AerMet100 steel is difficult to machine, people have been exploring the process of additive manufacturing to fabricate AerMet100 steel. In this study, AerMet100 steel was produced using an in situ rolling hybrid with wire arc additive manufacturing. Microstructure, tensile properties, and fracture toughness of as-deposited and heat-treated AerMet100 steel were evaluated in different directions. The results reveal that the manufacturing process leads to grain fragmentation and obvious microstructural refinement of the AerMet100 steel, and weakens the anisotropy of the mechanical properties. After heat treatment, the microstructure of the AerMet100 steel is mainly composed of lath martensite and reversed austenite. Alloy carbides are precipitated within the martensitic matrix, and a high density of dislocations is the primary strengthening mechanism. The existence of film-like austenite among the martensite matrix enhances the toughness of AerMet100 steel, which coordinates stress distribution and restrains crack propagation, resulting in an excellent balance between strength and toughness. The AerMet100 steel with in situ rolling is isotropy and achieves the following values: an average ultimate strength of 1747.7 ± 16.3 MPa, yield strength of 1615 ± 40.6 MPa, elongation of 8.3 ± 0.2% in deposition direction, and corresponding values in the building direction are 1821.3 ± 22.1 MPa, 1624 ± 84.5 MPa, and 7.6 ± 1.7%, and the KIC value up to 70.6 MPa/m0.5.

Refining of High-Carbon Steel and Reduction of CO<sub>2</sub> Emissions by Using Lignite Upgraded Coal Briquettes

Refining of High-Carbon Steel and Reduction of CO<sub>2</sub> Emissions by Using Lignite Upgraded Coal Briquettes

Kinetic Analysis of Bubble Thermal Expansion in High‐Temperature Molten Steel

The refinement of clean steel is significantly influenced by the behavior of bubbles in high‐temperature molten steel. However, the thorough examination of the thermal expansion behavior of bubbles and its effects on two‐phase flow dynamics in high‐temperature molten steel is scarce. This study investigates the thermal expansion process of low‐temperature bubbles in high‐temperature molten steel and the resulting dynamics of two‐phase flow, employing a volume of fluid model coupled with the energy equation method. The water model physics experiment investigates the rising characteristics of bubbles inside a water–air system and validates the accuracy of numerical simulations. Results reveal that bubble temperature reaches 1873 K during a 0.1 s periodic variation, exhibiting three stages: severe heating, expansion cooling, and contraction heating. The inertia of the fluid causes the bubble to overexpansion and overcontraction, and the energy conversion between the two phases causes expansion cooling and superheating (max temperature: 2642 K). A mathematical model is built to characterize the dynamic behavior of two‐phase flow and the thermal expansion behavior of gas bubbles of arbitrary initial size in molten steel.

Microstructure Evolution and Austenitic Grain Refinement of Ti-Modified High Mn Steels During Solution Annealing Heat Treatment

Microstructure Evolution and Austenitic Grain Refinement of Ti-Modified High Mn Steels During Solution Annealing Heat Treatment

As-Cast Grain Refinement of H13 Steel by Cerium Sulfide Formed During Solidification

As-Cast Grain Refinement of H13 Steel by Cerium Sulfide Formed During Solidification

On Joint Deoxidation and Refining of Steel with Complex Alloys

On Joint Deoxidation and Refining of Steel with Complex Alloys

Superficial Grain Refinement of 316L Stainless Steel by Rolling with Rough Rolls.

This study presents a novel approach to producing superficial micro- and nanostructures using a cold rolling process with rough rolls, followed by low-temperature annealing. The proposed technique attempts to recreate the superficial deformation occurring in the sandblasting process. It allows for the generation of an inhomogeneous network, or tangle, of high-deformation zones on the material's surface that act as nucleation centers during the subsequent annealing process. However, the proposed method has a significant advantage over sandblasting: it is a continuous process with high productivity. An austenitic stainless-steel sheet, previously normalized, was used as the raw material. The samples were cold rolled using rough rolls (rhombic-based pyramids of 2.08 mm, 1.04 mm, and 1.5 mm in length, width, and height, respectively) and annealed at temperatures between 200 °C and 400 °C for one hour. An optical and electronic microstructure analysis showed the presence of small, heterogeneously distributed surface grains of 200-300 nm in diameter. Finite element analysis revealed significant deformation that was inhomogeneous and likely responsible for the uneven distribution of the recrystallized grains. Additionally, surface nanohardness results showed a 20% increase with respect to the central zone of the material. Finally, wear tests of the treated samples showed lower wear than samples rolled with conventional rolls.

Layered hardening and grain structure refinement of low-alloyed tool steel applying two-stage surface morphology modification by laser phase transformation and ultrasonic peening

Layered hardening and grain structure refinement of low-alloyed tool steel applying two-stage surface morphology modification by laser phase transformation and ultrasonic peening

Prediction of residual stress, surface roughness, and grain refinement of 42CrMo steel subjected to shot peening by combining finite element method and artificial neural network

Prediction of residual stress, surface roughness, and grain refinement of 42CrMo steel subjected to shot peening by combining finite element method and artificial neural network

A Computational Fluid Dynamics Study on Physical Refining of Steel Melts by Filtration

In this paper, a previous experimental investigation on physical refining of steel melts by filtration was numerically studied. To be specific, the filtration of non-metallic alumina inclusions, in the size range of 1–100 µm, was stimulated from steel melt using a square-celled monolithic alumina filter. Computational fluid dynamics (CFD) studies, including simulations of both fluid flow and particle tracing using the one-way coupling method, were conducted. The CFD predicted results for particles in the size range of ≤5 µm were compared to the published experimental data. The modeled filtration setup could capture 100% of the particles larger than 50 µm. The percentage of the filtered particles decreased from 98% to 0% in the particle size range from 50 µm to 1 µm.

Effect of Heat Treatment on the Passive Film and Depassivation Behavior of Cr-Bearing Steel Reinforcement in an Alkaline Environment

Using Cr-bearing low-alloy steel is an effective preventive measure for marine structures, as it offers superior corrosion resistance when compared to plain carbon steel. However, it remains unclear how quenching and tempering heat treatment, which is commonly applied to steel reinforcement in some specific environments to improve its mechanical properties, affects its corrosion resistance. In the present work, the impact of heat treatment on the passive film and depassivation behavior of the 0.2C-1.4Mn-0.6Si-5Cr steel are studied. The results reveal that quenching and tempering result in grain refinement of the Cr-bearing steel, which increases its hardness. However, this refinement causes significant degradation in its corrosion resistance. The critical [Cl−]/[OH−] ratio after quenching and tempering is determined to be approximately 6.6 times lower than that after normalization, and the corrosion rate is 1.6 times higher. After quenching and tempering, the passive film predominantly comprises iron oxides and hydroxides, with relatively high water content and defect density. Additionally, the FeII/FeIII ratio and film resistance are relatively low. In comparison, after normalization, the steel exhibits high corrosion resistance, with the passive film formed offering the highest level of protection.

Grain refinement and mechanism of steel in ultrasound assisted wire and arc additive manufacturing

The small volume molten pool of wire and arc additive manufacturing (WAAM) undergoes complex non-equilibrium solidification process, resulting in the formation of columnar grains that severely limits the mechanical properties of the fabricated components. For refining the microstructure of deposition layers, the optimized ultrasonic equipment and loading methods are installed on a deposition platform, and the ultrasonic energy is coupled synchronously with the WAAM process using ER70S-6 welding wire as the filling material. Experimental results show that high-intensity ultrasound can transform coarse columnar grains into fine equiaxed grains, the area and degree of grain refinement increase with the ultrasonic amplitude. A computational fluid dynamics model of ultrasound assisted WAAM was developed to study the pressure field distribution in the molten pool. The region of acoustic cavitation in molten pools is highly consistent with the region of grain refining, showing that acoustic cavitation is the key factor in changing the grain structure. The collapse of cavitation bubbles generates cyclic alternating local high pressure, resulting in high velocity melt flow near the grain, which causes fatigue fracture of growing columnar grains exceeding the yield strength. A theoretical model is proposed to calculate the maximum length of grain growth under acoustic cavitation, which is in agreement with the experimental statistics of grain size. This work reveals the effect area and mechanism of ultrasound on the rapidly solidified molten pool, and provides a theoretical basis for grain refinement in ultrasound assisted WAAM.

Grain refinement and strengthening of PH 13-8Mo martensitic stainless steel through TiC/TiB2 inoculation during wire arc additive manufacturing

This research investigates the role of TiC/TiB2 nano-inoculants’ addition to the PH 13-8Mo martensitic stainless steel structure during wire arc additive manufacturing (WAAM). The microstructural analysis revealed that the introduction of the ceramic-based inoculants promoted the transition of columnar-to-equiaxed grain structure, refined the primary δ-ferrite grains, slightly increased the retained austenite content, and provoked the precipitation of in-situ TiC/M3B2 phases. Additionally, mechanical properties investigations showed that the TiC/TiB2 inoculation abated the anisotropic ductility as compared to the non-inoculated sample, and also improved the microhardness and tensile strength. Moreover, post-printing solutionizing and aging treatments were found to further enhance the hardness and strength of both TiC- and TiB2-reinforced components owing to the precipitation of nano-sized β-NiAl phases, while the accumulation of M3B2 phases in the intergranular regions led to the embrittlement of the TiB2-inoculated sample. This work, for the first time, illustrates the great potential for the adoption of ceramic-based nanoparticles as reinforcing/grain refining agents during the WAAM process for the fabrication of reinforced-PH 13-8Mo stainless steel components with a homogenous microstructure, nearly isotropic behavior, and superior mechanical performance.

Microstructural Refinement of Hot-Rolled Steels via Ferrite Dynamic Recovery and Recrystallization

Microstructural Refinement of Hot-Rolled Steels via Ferrite Dynamic Recovery and Recrystallization

The effect of renewed melting process under electrical slag on the fatigue life of the precipitation hardened stainless steel Custom-450

The aim of this study was to investigate the effect of under electro slag re-melting (ESR) process on the fatigue behavior of GTD-450 steel used for manufacturing gas turbin blades. These parts are always at risk of failure due to fatigue. Refining of steel by ESR process is one of the most important modern methods of steelmaking in order to achieve a homogeneous structure, minimal elemental and structural segeregation, as well as reducing non-metallic impurities in terms of their number and size and most importantly their uniform distribution in the steel structure. Due to dependency of fatigue properties of steels on structural factors of steel, the role of ESR process using different slag compositions on this important property of GTD-450 steel was investigated. Microstructural studies by optical and electron microscopes showed that grain size of ESR samples were averagely 10% finer than non-ESR ones. As well as performing various mechanical tests including tensile and fatigue on samples prepared in different conditions, showed that although ESR had a minor effect on tensile properties of steel but impact energy of steel in ESR condition were averagely 16% more than non-ESR condition. Finally, the core finding of this paper is that, fatigue life of GTD-steel turbine blade produced via ESR method can be improved by 30%.

Grain refinement of A517 steel by inoculation with Al–5Ti–B master alloy

The edge-to-edge matching model was used to identify TiB2 as a potential grain refiner to refine the high temperature δ-ferrite in low carbon steels. To effectively introduce the grain refiner, Al–5Ti–B master alloy (MA) was used to add TiB2 particles into an A517 steel. However, there was no grain refinement in the as-cast A517 steel, attributed to the decomposition of TiB2 particles in the molten A517 steel, into Ti and B. As a result, BN particles formed on the pre-existing Al2O3 particles were detected within prior austenite grains. Nevertheless, there was significant grain refinement after reheating the A517 ingots to 1150 °C, isothermally holding for 2 h and air cooling. The austenite grain size of the reheated A517 steel was decreased from 318 ± 70 μm to 38 ± 4 μm using 0.1 wt% Al–5Ti–B MA. Grain refinement was caused by Ti-containing nanometre-sized precipitates along prior austenite grain boundaries inhibiting the grain growth. The grain refinement improved the strength and ductility of ingots after reheating and improved workability for the production of hot worked products.

Grain refinement of stainless steel by strontium oxide heterogeneous nucleation site particles during laser-based powder bed fusion

The effect of SrO heterogeneous nucleation site particles on the formability, microstructure, and mechanical properties of additive manufactured 316 L (Fe-17%Cr-11%Ni-2%Mo) stainless steel samples produced by laser-based powder bed fusion has been investigated. The relative densities of the samples produced with SrO under medium and low energy density conditions were higher than those produced without SrO, although addition of SrO negatively affected the relative density under the high energy density condition. SrO addition showed significant grain refinement (about 15%) on the 316 L stainless steel alloy during laser-based powder bed fusion. Although it was found that SrO had a negative effect on the mechanical properties under the high energy density condition, significant improvements of the microstructure and mechanical properties was achieved by addition of SrO under the low energy density condition with high scanning velocity. It can be concluded that addition of heterogeneous nucleation site particles is a potential way to control the microstructure and mechanical properties of samples made by laser-based powder bed fusion.

Characterization of local deformation and fracture behavior in ferrite + martensite dual-phase steels having different grain sizes

Low carbon dual-phase (DP) steels composed of soft ferrite and hard martensite have been widely used in the automotive industry due to their good strength-ductility balance and large strain hardening ability. DP steels have a wide variation in mechanical properties depending on several microstructural features such as grain size, phase fraction and distribution. Among them, the grain refinement of DP steels is known to be an effective option for enhancing mechanical performance in strength and ductility (especially post-uniform elongation). However, the exact reason for the significant improvement of post-uniform elongation by grain refinement has not been fully understood. It is considered that the characterization of local deformation behavior and micro-void formation/growth behavior in connection with microstructures is an essential approach for understanding the enhanced post-uniform elongation realized in the fine-grained DP specimen. In the present study, we prepared two kinds of DP specimens with mean ferrite grain sizes of 14.9 μm (coarse-grained DP) and 7.1 μm (fine-grained DP), and carefully investigated local strain distribution of tensile specimen and micro-void formation/growth behavior using digital image correlation (DIC) analysis and SEM observations. The fine-grained DP specimen exhibited a gradual strain localization after necking and had sufficient strain capacity that could endure against fracture. The fine-grained DP structure had a great number of micro-voids in the necked region, but almost all the micro-voids maintained a very small size, which was contrasted with the case of coarse-grained DP specimen containing very large-sized micro-voids. Such a significant difference in micro-void size/number characters between two kinds of DP specimens would be one possible reason for exhibiting greatly different post-uniform elongation behavior.