Effects of boron addition on tempering processes in an Fe-9Cr-0.1C alloy martensite

Abstract

The effects of boron addition on the tempering processes of 0.1C-9Cr martensite have been studied. The alloys with and without 98 ppm boron were prepared. The specimens austenitized at 1200°C for 1.2 ks were quenched into iced brine. The structure was consisted of a′ martensite laths. They were heated at 10°C/min to 900°C. Temperature derivative of electric resistivity, dρ/d T, exhibited small increase at temperature around 740°C (reaction A), gradual decrease at temperatures between 750°C and 800°C (reaction B), large decrease at around 815°C (reaction C) and small increase at around 830°C (reaction D). Transmission electron microscopic observations showed that the reactions in the alloy with boron were related to the dissolution of cementite, the precipitation of M23(B·C)6 and M7(B·C)3, the austenite formation, and the dissolving of the carbides with further increase of austenite, respectively. In the alloy without boron, they corresponded to the dissolution of cementite, the precipitation of M7C3, the austenite formation, and the dissolving of M7C3 with further increase of austenite, respectively. The boron addition to Fe-lowC-highCr alloy promotes M23(B·C)6 formation and retards the α → y transformation.