The influence of full and partial austenitization temperatures on the quench and partition heat treatment process for an advanced high strength steel

Abstract

The effect of full and partial austenitization on the microstructural evolution of a medium carbon steel with 2.2 mass %Si was studied during the quench and partitioning heat treatment process. The quench and partition process is designed to ensure that carbon partitions to retained austenite to obtain martensite and carbon-stabilized retained austenite. The full and partial austenitization temperatures were established after determining the Ac3 and Ac1 temperature from dilatometer runs. Heat treatment was carried out in a Bähr Dilatometer and replicated in salt bath furnaces. Phase transformations were studied by dilatometry, scanning electron microscopy and EBSD analysis. Hardness tests were carried out to evaluate the mechanical properties. The results indicate that full austenitization treatment at 940°C resulted in thin films of retained austenite along with a lath martensite structure. The partial austenitization at 800°C resulted in plate-like martensite with blocky retained austenite. The full austenitization gave rise to a higher volume fraction of retained austenite of about 22% which led to better mechanical properties.