Effect of Low-Carbon Steel 20GFL Heat Treatment Regime on Structure and Mechanical Properties

Abstract

Results are given for a study of the effect of heat treatment parameters on supercooled austenite transformation kinetics in steel 20GFL. Specimen microstructure is studied in specimens 10 × 10 mm in cross section with the following regimes: soaking at 860 and 940°C, cooling in an air stream 3–8 m/sec through a channel 100 mm in diameter. The change in microstructure features in the course of high-temperature soaking at 940°C for 30 and 60 min after specimen cooling in salt water is determined. It is established that in cast steel there is chemical composition microliquation inhomogeneity with respect to carbon and manganese, which decreases during soaking (60 min) and is accompanied by austenite grain growth. Critical cooling rates are determined with which a structure forms containing upper and lower bainite. A dependence is obtained for impact strength KCV⁻⁶⁰ on soaking temperature and time in the γ-region. The effect is demonstrated of alloying with vanadium on the possibility of stimulating the formation of globular lower bainite components.