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Abstract In this work, the effect of solidification rate on the microstructure and impact toughness of high boron high speed steel is systematically investigated. The theoretical and experimental results indicate that the as-cast microstructure of high boron high speed steel consists of α-Fe matrix and eutectic borocarbide. Without Ca-Ti addition, borocarbide presents a continuous and reticular structure. After Ca-Ti modification, borocarbide possesses an isolated, fine structure. Besides, cooling rate obviously affects the extent of spheroidization. In modified high boron high speed steel, calcium possesses surface activity, which restrains the growth of eutectic borocarbide during solidification. Titanium exists in the form of dispersedly distributed TiC particles which act as heterogeneous nuclei for eutectic borocarbide. The impact toughness of high boron high speed steel is remarkably improved by Ca-Ti modification, which can be further improved by cooling rate. The effect of cooling rate on improving of the toughness can provide a scientific basis for the foundry process designing. [ABSTRACT FROM AUTHOR]

In this work, the microstructure, alloying element distribution, and borocarbide mechanical properties of high-boron multi-component alloy with Fe-2.0 wt.%B-0.4 wt.%C-6.0 wt.%Cr-x wt.%Mo-1.0%Al-1.0 wt.%Si-1.0 wt.%V-0.5 wt.%Mn (x = 0.0, 2.0, 4.0, 6.0, 8.0) are investigated. The theoretical calculation results and experiments indicate that the microstructure of high-boron multi-component alloy consists of ferrite, pearlite as a matrix and borocarbide as a hard phase. As a creative consideration, through the use of first-principles calculations, the comprehensive properties of borocarbide with different molybdenum concentrations have been predicted. The calculations of energy, state density, electron density and elastic constant of Fe2B crystal cell reveal that substitution of the molybdenum atom in the Fe2B crystal cell can remarkably improve its thermodynamic stability, bond strength, and covalent trend. For verifying the accuracy of this theoretical calculation, nano-indentation testing is carried out, the results of which indicate that the actual properties of borocarbide present favorable consistency with the theoretical calculations. [ABSTRACT FROM AUTHOR]

This work investigated the microstructure and mechanical property of high-boron multi-component alloy with Fe, B, C, Cr, Mo, Al, Si, V, Mn and different contents of Ti. The results indicate that the as-cast metallurgical microstructure of high-boron multi-component alloys consist of ferrite, pearlite and borocarbide. In an un-modified alloy, continuous reticular structure of borocarbide is observed. After titanium addition, the structure of borocarbide changes into a fine and isolated morphology. TiC is the existence form of titanium in the alloy, which acts as the heterogeneous nuclei for eutectic borocarbide. Moreover, impact toughness of the alloy is remarkably improved by titanium modification. [ABSTRACT FROM AUTHOR]

In this work, the microstructure, the formation characteristics, and the growth mechanism of eutectic borocarbide during solidification in high boron high speed steel with 2.0 wt% B–0.4 wt% C–6.0 wt% Cr–4.0 wt% Mo–2.0% Al–1.0 wt% Si–1.0 wt% V–0.5 wt% Mn are investigated utilizing liquid quenching technology. The experimental results illustrate that the as‐cast microstructure of high boron high speed steel consists of α‐Fe matrix, eutectic borocarbide M2(B,C) with continuous network structure, M3(B,C) boron‐cementite, and M7(C,B)3 (M = Fe, Cr, Mo, V, Mn). Different precipitating sequences of eutectic borocarbides with various compositions are revealed. During solidification, order of precipitation is Cr‐rich borocarbide and Mo‐rich borocarbide, respectively. Mo‐rich borocarbide precipitates from the existing Cr‐rich borocarbide rather than forming independently. Additionally, the growth mechanism of different borocarbides is systematically studied, which clearly explains the reason of continuous reticular formation of borocarbide. Cr‐rich borocarbide is the proeutecitc phase, which grows in the form of faceted‐nonfacetedgrowth. As the significant finding of this work, the "hexagon" growth mechanism of Mo‐rich borocarbide is discovered. This mechanism feasibly describes the paralleled lamina and faveolated structure of Mo‐rich borocarbide. These results render a consideration for the elimination of elemental segregation through reasonable foundry process designing. The as‐cast microstructure of high boron high speed steel consists of α‐Fe matrix, eutectic borocarbide M2(B,C), M3(B,C) boron‐cementite, and M7(C,B)3 (M = Fe, Cr, Mo, V, Mn). During solidification, order of precipitation is Cr‐rich borocarbide and Mo‐rich borocarbide, respectively. Cr‐rich borocarbide is the proeutecitc phase, which grows in the form of faceted‐non faceted growth. The "hexagon" growth mechanism of Mo‐rich borocarbide is discovered. [ABSTRACT FROM AUTHOR]