Precipitation behavior of boron-carbide hard phase comprising a new high-boron high-speed steel

Abstract

The solidification process and the precipitation behavior of the boron-carbide hard phase comprising a new high-boron high-speed steel were investigated through the combination of phase balance calculations (by Thermo-Calc software) and experimental tests. The results revealed that a primary austenite precipitation reaction (L → γ), ternary eutectic reaction (L → γ + M2 (B, C) + M2C), and secondary boron carbide precipitation reaction (γ → M (B, C) and γ → M3 (B, C)) occurred during the solidification process of the steel. These reactions occurred at characteristic temperatures of 1350 °C, 1220 °C, 1100 °C, and 1000 °C, respectively. The precipitation reaction of primary austenite yielded a primary austenite dendrite and a eutectic structure distributed along the grain boundary. The ternary eutectic reaction products were austenite, M2 (B, C) and M2C, which were distributed in the grain boundaries in a manner consistent with interdependence and mixed growth. Similarly, the secondary M3 (B, C) boron carbide, converted from the (Fe, Cr)3C carbide, was precipitated from the austenite matrix. The solidification process consisted of four stages: diffusion of alloying elements, aggregation of alloying elements at grain boundaries, nucleation of M3 (B, C) phases and growth of M3 (B, C) phases. This new high-boron high-speed steel can be widely used in rolls and other fields where wear resistance is required.