Characteristic of martensite–austenite constituents in coarse grained heat affected zone of HSLA steel with varying Al contents

Abstract

The fine microstructure of martensite–austenite (M–A) constituents in simulated coarse grained heat affected zone (HAZ) of high strength low alloy steel with varying aluminium content (0·038 and 0·070 wt-%) at 100 kJ cm⁻¹ heat input welding was investigated. The result shows that M–A constituents with 0·038%Al consisted of lath martensite and retained austenite. The retained austenite was distributed along the martensite lath. Whereas, the M–A constituents with 0·070%Al consisted of lath martensite and retained austenite, as well as a small amount of twinned martensite. The amount of retained austenite in M–A constituents with 0·070%Al was becoming higher slightly than that with 0·038%Al. Accordingly, the volume fraction of M–A constituents was reduced with 0·070%Al. Appropriate aluminium addition could decrease not only the area fraction but also the size of M–A constituents, which are beneficial for improving the toughness of HAZ.