REVERSE TRANSFORMATION OF LOW CARBON LOW ALLOY STEELS.

Abstract

The process of formation of austenite was studied in two 0. 12% C, 3. 5Ni, 0. 35% Mo steels, one of them containing 0. 0020% B. Specimens with acicular structures such as martensite, bainite, or tempered martensite were heated at temperatures between Ac, and Ac//3. Metallographic investigation showed that the austenitizing process is divided into two stages. In the first, globular austenite is formed accompanying the dissolution of cementite. Acicular austenite is also formed at an early stage. In the second stage, a globular austenite is formed by the coalescence of the acicular austenite grains, and those formed in the both stages grow to form elongated austenite grains. Gamma prime transformation prevails in the boron-containing steel. It is suggested that reverse transformation is controlled primarily by the rate of recrystallization of austenite.