Heating and cooling transformation diagrams for the rapid heat treatment of two alloy steels

Abstract

In rapid heat treatments, such as laser and induction hardening, a thin surface layer of austenite is formed on a part during heating. After cooling for only a few seconds, this layer transforms into martensite, pearlite, bainite, and/or proeutectoid ferrite/cementite, depending on the cooling rate, dissolved carbon content, homogeneity of the dissolved carbon, austenite grain size, and steel composition. In this work, transformation diagrams suitable for rapid heat treatments were determined by dilatometry for two alloy steels, one hypoeutectoid and one hypereutectoid. A short austenitizing time after fast heating was used. Models for computer calculations of phase transformations with the use of isothermal diagrams are also discussed. Calculations of continuous heating diagrams from the isothermal heating diagrams gave good agreement in comparison with the observed diagrams.