Preparation of Two-Phase Ferritic-Martensitic Steels of Different Alloy Systems in Continuous Annealing Units

Features of structure and property formation, processing aspects for preparation of cold-rolled, including hot-dip galvanized, product of two-phase ferritic-martensitic steels with the most typical alloying system (silicon, manganese, and chromium), and also additional alloying with molybdenum, are studied with heat treatment in continuous annealing units (CAU). Cold-rolled product of different thickness is heat treated (HT) in the intercritical temperature range established from results of dilatometric measurements. It is established that there is formation in the test steels of a ferritic-martensitic structure with some proportion of bainite and residual austenite in the form of an MA-component (region with a size of several microns consisting of martensite and residual austenite). With modeling of the HT regime typical for CAU steel alloyed with molybdenum has strength 100–150 MPa higher than steel of the typical alloy system, and this is connected with a higher proportion of strengthening phase within the structure.