Microstructural and mechanical behavior of 4.5Cr–2W–0.25V–0.1C steel

In this paper the microstructural and mechanical properties of a hot rolled Cr–W–V steel were studied. The 4.5Cr–2W–0.25V–0.1C steel was austenitized at 1000 °C for 30 min and then tempered at 600 and 700 °C for 1 h. The physical metallurgy of this steel was studied by optical, scanning electron and transmission electron microscopes and X-ray and electron diffraction patterns. The results showed that four types of carbide were precipitated as MC, M3C, M7C3 and M23C6 along prior austenite grains and lath boundaries and within martensitic matrix. The average sizes of the M7C3 and M23C6 carbides in the specimens tempered at 600 °C were about 100 and 180 nm, and in specimens tempered at 700 °C were about 110 and 210 nm, respectively. When the tempering temperature was increased, weight percent of extracted precipitates and the formation rate of the stable carbides such as M23C6 and dissolution rate of the metastable carbides such as M3C and M7C3 were also increased. The results of hot tension tests showed the strength and elongation of tempered specimens were decreased when the test temperature was increased. The strength decrease was slow at range of 200–500 °C but sharp at test temperature of 600 °C. The results suggested tempering at 700 °C has better tensile properties at operating temperature (500–600 °C) when compared to tempering at 600 °C.