Microstructures and Mechanical Properties of an Ultrahigh‐Strength and Ductile Medium‐Carbon High‐Silicon Spring Steel

Abstract

Herein, the microstructure and mechanical properties of medium‐carbon high‐silicon spring steel are studied, which is alloyed and/or microalloyed with Cr, Mo, Ni, Cu, Nb, and V, and subjected to various austenitizing and tempering processes. The steel has a mixed microstructure consisting of fine lath martensite, nanoscale cementite, ε‐carbide, and an amount of retained austenite (10.4 vol%). At room temperature, the steel exhibits ultrahigh tensile strength (2002 MPa) and yield strength (1775 MPa) with total elongation of 11.1%, while a good toughness is obtained characterized by Charpy impact energy as 38 J. The ultrahigh strength of this steel is attributed to the dislocation and precipitation strengthening, while the excellent total elongation is closely associated with the retained austenite. In addition, tempered martensite embrittlement is found in this steel when tempered at 450 °C. This is due to the retained austenite decomposition and cementite coarsening along the prior austenite grain and martensite laths.