The evolution of non-metallic inclusions in liquid steel involves a series of processes, including nucleation, growth by diffusion and Ostwald ripening, growth by collisions, floating up and removal ...of relatively large inclusions, as well as pushing and engulfment of remaining inclusions during solidification. All the evolution processes occur uniquely at the interface between inclusions and liquid steel. Therefore, interfacial properties between inclusions and liquid steel, such as interfacial energy and contact angle, play a crucial role in the evolution of inclusions, thus determining the inclusion characteristics. To effectively control the inclusion characteristics, the role of interfacial properties in the evolution processes of non-metallic inclusions is systematically reviewed in this work, based on theoretical analysis and published experimental results. In the early and middle stages of deoxidation, inclusions should have as high interfacial energy or contact angle as possible to enhance inclusion removal. In the later stage, however, the interfacial energy should be decreased as much as possible to weaken the clustering and pushing of inclusions, favoring the formation of small-sized and uniformly-distributed inclusions. To optimize the characteristics of Al2O3 inclusions, which are the most common in steel, several control strategies are proposed.
M2C eutectic carbide favours the mechanical properties of high-speed steels, but is often largely replaced by coarse M6C eutectic carbide in as-cast M42 steel. To deeply understand the formation ...behavior of M2C and M6C carbides, M2C and M6C eutectic alloys were prepared according to the composition of M2C and M6C eutectic mixtures in M42 steel, and their solidification behavior was investigated. Only one type of eutectic carbide is formed in water-quenched M2C and M6C eutectic alloys, i.e., M2C and M6C, respectively. Both M2C and M6C carbides appear in the alloys cooled at 3°C/min. However, the M2C eutectic alloy was more significantly affected in terms of carbide type by the low cooling rate. According to thermodynamic calculation, M6C carbide in the M2C eutectic alloy is only slightly more stable in thermodynamics above 1210.1°C, below which M2C carbide becomes stable. For the M6C eutectic alloy, however, only M6C eutectic carbide is thermodynamically stable. Furthermore, thermodynamic results reveal that besides raising the content of C and V, reducing the content of Mo can also greatly promote the formation of M2C carbide in M42 steel, which updates the traditional opinion on the influence of Mo element. The results in this work provide the underlying insights needed to promote the formation of M2C carbide in M42 steel by fine-tuning the composition.
•A new formation mechanism of the Type-A CsMPs is proposed.•Silicate matrix is inherited from partially oxidized FeO-bearing silica-based microparticles.•Diffusion of volatile constituents into ...FeO-bearing silica-based microparticles occurs in reducing atmospheres.
A large amount of radiocaesium-bearing microparticles (CsMPs) were released into surrounding environment during the Fukushima Daiichi Nuclear Power Plant accident. To clarify the formation mechanism of the Type-A CsMPs, which were released from Units 2/3 and have spherical or ellipsoidal morphologies, oxidation behavior of 304 stainless steel containing 1 wt.% Si at 1200 ºC in steam atmosphere was investigated in this work. Both Fe2SiO4 and Ni-Fe-Cr phases were formed and distributed in the porous oxide scale. With the progress of oxidation, Fe2SiO4 and Ni-Fe-Cr phases were oxidized, causing severe spallation of the oxide scale somewhere between 90 min and 120 min. Trace amounts of Al and Ti were detected in the silica microparticles transformed from Fe2SiO4 oxidation. Furthermore, thermodynamic calculations were performed with the aid of FactSage software, revealing that: (1) when severe spallation of the oxide scale occurs, high levels of Fe oxides can stably exist in silica-based microparticles distributed in the oxide scale; (2) the Type-A CsMPs may be formed in reducing atmospheres. Based on the experimental and thermodynamic results, a completely new formation mechanism of the Type-A CsMPs is proposed. Silicate matrix is inherited from partially oxidized FeO-bearing silica-based microparticles, which are released from the oxide scale due to spallation. Moreover, diffusion of volatile constituents into FeO-bearing silica-based microparticles occurs in the reactor pressure vessel (RPV), not out of the RPV. This new formation mechanism can well explain many characteristics of the Type-A CsMPs.
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The microstructure and mechanical properties of high-speed steels are sensitive to some surface-active additives. In this work, four M42 high-speed steel ingots containing tellurium (Te) in ...concentrations ranging from 0 to 500 ppm were prepared with a vacuum induction furnace, and their microstructure and mechanical properties were systematically investigated. Te combines with Mn and possibly forms MnTe phase located in the interdendritic regions together with eutectic carbides. Te obviously refines the primary dendrite stem and decreases the secondary dendrite arm spacing of as-cast M42 steel. Te hardly affects the fraction of eutectic mixtures, but greatly refines the size of eutectic mixtures. The presence of 163 ppm Te strongly promotes the formation of M6C eutectic carbides. This trend, however, is reversed at higher Te contents. 163 ppm Te increases the red hardness of M42 steel from 58.51 HRC to 60.8 HRC by suppressing the dissolution of secondary carbides. Further increasing Te content has no significant effect on the red hardness. Moreover, Te slightly deteriorates the tensile strength of as-cast M42 steel, while substantially improves the compressive and bending strength of tempered M42 steel. The reasons why Te affects the formation tendency of M6C eutectic carbides as well as the mechanical properties of M42 steel were discussed.
Spring steel wires are extensively utilized in automotive engines valve and suspension applications. Owing to spring often work under high-frequency dynamic loads and periodic alternation stress, ...non-deformable inclusions often act as fatigue fracture origin of spring steel. The control of inclusions in spring steel for automobile are extensively reviewed. On the one hand, the new perspective on the problems left over the past decades, include the new viewpoint on whether FeO is an inherent constituent of inclusions, the new understanding of the origin of CaO-based inclusions, the new perspective of whether the VD treatment progress should be removed but RH retain, have been discussed. On the other hand, the new approaches, via, calcium treatment, alkali oxide treatment, rare earth treatment, new refractory application, have also been summarized. Finally, the unsolved problems, the source of CaO-based inclusions, the mechanism of alkali metals modified inclusions, the based thermodynamic data for reactions between rare earth yttrium (Y) and non-metallic inclusions, the operability of CaO-containing refractory in industry, that should be explored further are also been discussed.
In the present study, high-speed steel (HSS)/ductile cast iron (DCI) composite roll was manufactured by the electroslag remelting cladding (ESRC) technology. The compositional variation, grain size, ...microstructure, hardness, and tensile strength of the HSS layer and the bimetallic interface were investigated systematically. The obtained results illustrated that the chemical composition of the cladding layer (HSS) changed dramatically due to the surface melting of the roll core (DCI) and the mechanical mixing of the bimetallic liquids. The different solidification rates and chemical compositions in different regions of the HSS layer led to great variations of the grain size, the carbide content, and the hardness. In addition, a bimetallic transition zone (about 9.47 mm) was generated between the HSS layer and the DCI core due to the elemental migration and diffusion between the bimetals. Carbides of different types, morphologies, sizes, and compositions had direct influences on interfacial properties.
The effects of V–Nb microalloying on the microstructure and mechanical properties of ultra-high-strength spring steel at various austenitizing and tempering times were investigated. To achieve this, ...scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron backscatter diffraction, and tensile tests were performed. The equations for austenite grain coarsening at 900 °C and (V,Nb)C carbide growth at 400 °C were obtained. The results indicated that the tensile properties of the investigated steel significantly improved after V–Nb microalloying with the same quenching-tempering treatment. With increasing austenitization or tempering time, the tensile properties of the experimental steels dramatically declined owing to the coarsening of the grain size or of the martensite lath width and carbide size. Because V–Nb microalloying increased the densities of the grain boundaries and carbides, the full width at half maximum 211α, microstrain, and dislocation density decreased slowly with prolonged tempering time. The strength increment among the investigated steels mainly resulted from the grain refinement strengthening, dislocation strengthening, and most importantly, precipitation strengthening of (V,Nb)C carbide.
Background The mechanism of long non-coding RNA MIR137HG in human gastric cancer (GC) is currently unknown. In the present study, we aimed to explore the function and mechanism of MIR137HG in gastric ...cancer. Methods The expression of lncRNA-MIR137HG in 69 gastric cancer samples and their paired surgical margin (SM) tissue samples were tested by QRT-PCR. UCSC was used to find the gene location relationship among MIR137HG and its embedded miRNAs. TargetScan was used to predict the targets of miR-2682-3p. Starbase was used to predict the candidate proteins that interacted with MIR137HG. Western blot, co-focus, and RIP assay were used to verify the direct interaction between MIR137HG and FUS (fused in sarcoma/translocated in liposarcoma, FUS/TLS), while dual-luciferase reporter assay was used to confirm the interaction between miR-2682-3p and FUS. Cell migration assays, colony formation, and xenografts assay were used to investigate the function of MIR137HG and miR-2682-3p to tumor growth and metastasis. Western blot assay was used to explore the downstream candidate protein of FUS. Results Data showed that MIR137HG expressed significantly higher in GC than in SM. MIR137HG promoted colony formation and migration in vitro and promoted tumor formation and metastasis in vivo. MIR137HG is distributed in both the nucleus and cytoplasm. It was co-located with FUS and could directly interact with FUS, which might interact with other proteins, such as MET(MET-proto-oncogene, receptor tyrosine kinase), RHOC(ras homolog family member), and CTNNB1(catenin beta1). These proteins may involve different signaling pathways to regulate gastric cancer progression. By contrast, the embedded miR-2682-3p could antagonize the series functions of its host lncRNA-MIR137HG by targeting FUS. Conclusions lncRNA-MIR137HG promoted growth and metastasis in gastric cancer by interacting with FUS, while miR-2682-3p could inhibit the function of MIR137HG via the same target FUS. Keywords: LncRNA, MIR137HG, miR-2682-3p, FUS, Gastric cancer
In this paper, the effect of solidification pressure on the dendrite structure and characteristics of carbides in H13 die steel ingot was investigated by experimental and calculational methods. Based ...on the effect of pressure on the cooling rate, a formula is proposed to calculate the secondary dendrite arm spacing: λ2 = 71.45 × R−0.37. It is applicable when the maximum value of pressure is around 2 MPa and the cooling rate is between 0.5 and 3 K/s. With increasing pressure from 0.1 to 2 MPa, the effects of pressure on the segregation ratio of V, Mo, Cr and C are little and can be neglected, which caused by the combined effect of equilibrium partition coefficient, diffusion coefficient and cooling rate. Therefore, the characteristics of carbides are determined by the decreasing the secondary dendrite arm spacing and increasing cooling rate with the increment of pressure. With increasing pressure from 0.1 to 2 MPa, the types of carbides are not change, which are MC and M2C in H13 die steel ingot. Meanwhile, the mean area of carbides decreases obviously with increasing pressure, and the decrement in mean area at the edge is larger than that at the center of ingot.
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