Effects of heat treatment on microstructure and mechanical properties of Fe-Co-Ni-Cr-Mo-C alloy

Abstract

A kind of Fe-Co-Ni-Cr-Mo-C alloy was designed for valve seat use. The effects of the quenching temperature, tempering time and tempering temperature on the mechanical properties and microstructure of the alloy were investigated. The results show that the hardness decreases, while tensile strength (σ_b), transverse rupture strength (σ_bb) and impact toughness (K_ic) increase after the alloy is quenched and tempered. The best complex property (σ_b, 446 MPa; σ_bb, 793 MPa; K_ic, 2. 96 J/cm²) can be obtained when the alloy is quenched at 1100°C and tempered at 650°C. The results of X-ray diffraction and energy dispersive X-ray analysis (EDX) show that the major strengthening phases are carbides such as (Fe, Cr)₇C₃ and Fe₂MoC. The obvious secondary hardening appears when the alloy is tempered at 550°C, which results from the precipitated carbides of Cr and Mo in the alloy from the matrix and the heat-resistant retained austenite.

Keywords

valve seat / Fe-Co-Ni-Cr-Mo-C alloy / heat treatment / microstructure / property

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