Study of an Economical and Effective Heat Treatment Method to Improve the Performance of Gear Steels

Abstract

During heat treatment, gear steels undergo grain coarsening, so an appropriate heat treatment process that can efficiently control the austenite grain growth and ensure a good performance of gear steels is particularly important. Herein, the influence of a requenching treatment on the comprehensive behavior of low‐carbon alloy steel 20Cr2Ni4 is explored. The pristine steel samples with and without Nb microalloying subjected to conventional quenching and tempering (QT) treatment are compared with the requenched steel sample. The results show that different requenching temperatures considerably impact grain refinement and homogenization. The steel requenched at 830 °C exhibits the greatest tensile strength of 1444 MPa and excellent toughness, comparable to the mechanical properties of the steel upon Nb microalloying after the conventional QT treatment. The formation of twin martensite and uniform fine grains with a high dislocation density together with numerous low‐angle and high‐angle grain boundaries is responsible for the simultaneously improved strength and ductility of the requenched specimen; thus, the proposed requenching heat treatment is a promising, efficient, and reliable method to double‐refine prior austenite grains and their packet and block structures and improve the comprehensive properties with a combination of high strength and toughness, yielding high‐strength gear steel.