Effect of Yttrium Addition on the Microstructure Evolution and Mechanical Properties of the 0.5C–1Cr–0.2Mo–0.1V Spring Steel

The 0.5C – 1Cr – 0.2Mo – 0.1V spring steel without and with 0.0061 wt% rare earth (RE)‐yttrium (Y) addition is prepared via vacuum induction melting, hot rolling, quenching and tempering, and the effects of Y addition on the microstructure evolution and mechanical properties of spring steel are investigated. The results show that Y addition can reduce the degree of microsegregation, refine the size of prior‐austenite grains during the austenitization process after hot rolling, and effectively remove and modify oxide inclusions during the solidification process. The martensite block tends to be equiaxed and refined, and the size of the martensite lath within the block also decreases with Y addition after quenching. The lamellar M 3 C carbide precipitates along the prior martensite lath boundary during tempering. Y addition can refine the lamellar M 3 C carbides and promote the formation of spherical M 7 C 3 carbides that are evenly distributed in laths. On the basis of the microstructure analysis mentioned above, the microstructure of 0.5C – 1Cr – 0.2Mo – 0.1V spring steel can be improved by the addition of Y, resulting in a significant increase in the strength, yield ratio and ductility of the steel.