Effects of silicon, nickel, and vanadium on impact toughness in spring steels

Abstract

The effects of alloying elements silicon, nickel, and vanadium, and the tempering temperatures on the mechanical properties, especially impact toughness, in 0.6C–(1.0–2.5)Si–(0.7–1.8)Ni–(0.1–0.2)V steels (wt-%), were investigated by performing hardness tests, impact tests, and TEM examination. The results obtained showed that the addition of silicon up to 2.5 wt-% shifted the embrittlement temperatures to higher temperatures, owing to the silicon retarding the formation and growth of cementite at boundaries. Additionally, it was found that the temperature of the peak in Charpy impact toughness v. tempering temperature curves coincided with the onset of the decomposition of retained austenite. The temperatures of the conversion of ε carbide to cementite and of the onset of tempered martensite embrittlement were not changed by the addition of nickel up to 2.0 wt-% in the present steels. However, the decomposition of retained austenite was delayed and the toughness was increased over all the tempering temperatures. The effect of the vanadium addition in the present steels was limited to the increase in hardness and impact toughness.