Effect of manganese during the stabilization of austenite in quench and partitioning (Q&P) steels

Abstract

Nowadays, automobile emissions are one of the leading causes of air contamination. In this regard, the weight reduction of the vehicles structures and parts is vital, while the passenger’s safety is the first issue. Therefore, high demand for Advanced High Strength Steels (AHSS), is constantly increasing in the automotive industry, which can adequately fulfill both safety and emissions issues through reduction in thickness. A new generation of AHSS covers these demands owing to excellent forming and mechanical properties. Accordingly, Quenching and Partitioning (Q&P) steels have been developed with a special microstructure composed of an initial fraction of martensite and a slight fraction of stabilized retained austenite. The aim of the present work is to assess the effect of different amounts of manganese in Q&P steel under various heat treatment cycles relevant to an industrial process. A 0.2C-1.5Si base steel with different amount of Mn, namely 1.5, 3.5 and 5.5 (in wt%) were selected to promote different amounts of retained austenite after Q&P process. In order to determine the critical transformation temperatures such as Ac1, Ac3, Ms and Mf, which are needed to design Q&P thermal cycles, dilatometric experiments were carried out. The results are presented according to the chemical composition, the final microstructure and the hardness obtained in each condition.