High-strength low-carbon steels, having satisfactory weldability, are distinguished by an improved set of properties. One of the approaches to upgrading the combination of strength and impact strength in these steels is the development of compositions, providing martensite formation at minor rates of cooling. The data on phase transformation, taking place in manganese nickel steels in their cooling from the austenite region and subsequent heating are insufficient. The purpose of this study is to investigate into the features of overcooled austenite decay in high strength low carbon steels and into the patterns of reverted austenite formation in repeated heating.