ISOTHERMAL TRANSFORMATION AND STRUCTURAL CONSTITUENTS AFTER QUENCHING

Hot-Bath Quenching of a Low W-Cr Tool Steel (SKS 2) in Low Temperature Range-I

Abstract

In order to obtain a fundamental information on an applicability of hot-bath quenching below Ms temperature to an improvement of properties of a 1.0% C-1.0% Cr-1.4% W tool steel, its isothermal transformation and structural constituents after hot bath quenching were investigated by means of microscopic observation, dilatometric and magnetic analysis, as well as hardness test.
The main results obtained are summarized as follows: In hot-bath quenching below the Ms (162°C), there take place, at earlier stage, athermal and isothermal austenite-martensite reactions, and then, at later stage, austenite-lower bainite reaction, which promotes the stabilization of austenite markedly in a similar way as an isothermal reaction in austempering at above the Ms; thus, a mixed structure of tempered martensite and lower bainite containing a lot of retained austenite is obtained by a quenching under certain conditions.