With the continuous expansion of the application field of low alloy wear-resistant steel, higher processing plasticity and toughness are prioritized on the basis of ensuring strength and hardness. In this article, a low alloy wear-resistant steel Hardox400 was studied: by adding a mass fraction of 0.0030% of rare earth cerium as microalloying treatment, the pilot scale simulation of the rare earth wear-resistant steel was carried out using vacuum induction furnace and a four-high reversible laboratory mill. The effects of the rare earth on the occurrence state of the inclusions, microstructure, mechanical properties and wear resistance of the steel were studied by means of optical microscope (OM), scanning electron microscope (SEM) and wet sand/rubber wheel wear tester. The results show that the fine spherical CeAlO₃, CeAlO₃-MnS and elliptical Ce₂S₂O-CaO are formed by adding 0.0030% Ce, which enhances the binding force between the inclusions and matrix. The addition of rare earth Ce helps to refine the as-cast structure, prevent the transformation of proeutectoid ferrite of overcooled austenite and promotes the formation of bainite ferrite, whilst simultaneously increasing the yield strength, yield ratio and surface hardness, especially the low-temperature impact toughness approximately between −40 °C~−20 °C of the tested steel. Simultaneously, the ability to resist abrasive embedment and crack propagation is enhanced, and the wear resistance is obviously improved. The research results will provide a reference for the development of high-quality rare earth wear-resistant steel utilizing national featured resources.

This study systematically investigated the influence of high nitrogen (N) addition (0.205 wt.%) on microstructure and mechanical properties of as-cast M42 high speed steel. The results demonstrate that the conventional and high-nitrogen M42 cast ingots are mainly composed of martensite, retained austenite and various precipitates (M2C, M6C as well as MC in M42 cast ingot or M(C, N) in M42N cast ingot). The addition of N could increase the retained austenite content, trigger the transformation of MC to M(C, N), favor the formation of M2C at the expense of M6C, and improve the distribution uniformity of M6C at the macroscopic scale. Moreover, the addition of N could lead to the reduction of the secondary dendrite arm spacing as well as the decrease of the thickness and area fraction of eutectic carbides, and improve the distribution uniformity of eutectic carbides at the microscopic scale. The M(C, N) particles form directly from the liquid phase prior to the formation of primary austenite, which could act as the heterogeneous nuclei of primary austenite and thus promote the refinement of the as-cast microstructure. The addition of N slightly decreases the macro-hardness and ultimate compression strength of the cast ingot but increases its ductility, which could be ascribed to the increase of retained austenite content and the reduction in the amount of eutectic carbides. Therefore, high N addition can significantly improve the as-cast microstructure of M42 high speed steel, which is promising for the further enhancement of the mechanical property and service life of the final product.

The formation mechanism of the clogging layer of the alumina-carbon submerged entry nozzle in the smelting process of rare earth Q355 steel was investigated in this paper. First, the inclusions in the molten steel were discovered to be primarily composed of CaAl₂O₄, MgO, CaS, and CeAlO₃. The mass fraction of solid inclusions increases as the rare earth content increases, and the proportion of inclusions, primarily CaAl₂O₄, changes. Calcium titanate and cerium aluminate formation can be inhibited by high [Ca] content. XRD and scanning electron microscopy were then used to examine the phase composition and morphology of the inner and outer arcs of the clogging nodules. The clogging was found to be divided into three layers: the nozzle matrix, the reaction layer, and the steel layer. Finally, it is concluded that the dissolution of C element in refractory material is the cause of nozzle blockage, and the core cause of nozzle blockage is the deposition of Al₂O₃, CaAl₂O₄, and rare earth compounds. Meanwhile, solutions to nozzle blockage are provided from the perspectives of top slag optimization, the deoxidization process, the calcium treatment process, and protective pouring.

CeO₂ can be applied to refining slag to minimize the size of inclusions, speed up the deoxidization process, and adsorb Al₂O₃ inclusions. The impact through which CeO₂ content affects slag’s melting efficiency is still uncertain. The thermal analyzer was used to measure the thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) curves of the slag melting process. According to the study results, with the increase in CeO₂ content, the melting temperature of slag decreased first and then increased. The slag’s melting point fell from 1364 °C to 1324 °C and then rose to 1503 °C. XRD and SEM were used to analyze the CaO-Al₂O₃-SiO₂-MgO-CeO₂ slag’s microstructure. The mineral-phase structure of CeO₂-containing refining slag was primarily composed of Ca₂SiO₄ and 3CaO·Al₂O₃, MgO, SiO₂, CaO·Al₂O₃, and Ca₈Ce₆Al₆O₂₆. The proportion of 3CaO·Al₂O₃, CaO·Al₂O₃, and Ca₂SiO₄ decreased as the rare-earth-oxide content increased, while the proportion of Ca₈Ce₆Al₆O₂₆ increased. FactSage was used to estimate the equilibrium-phase compositions of slags with various compositions, and a model for predicting melting points was carried out by a linear regression model. Results were obtained through the analysis of equilibrium-phase composition and crystal structure transformation. The main reasons for the melting point decrease were the change of degree of polymerization and the decrease in contents and complete melting temperature of high-melting-point Ca₃Al₂O₆ and Ca₂SiO₄ compounds. The latter increase in melting point was due to the number of Ca₈Ce₆Al₆O₂₆ compounds and precipitation temperature increases and the complexity of the structural-network increases.