Study of the Effect of Composition and Thermal Deformation Treatment on Properties of Ferritic Steels Microalloyed with Titanium and Niobium. Part 2. Phase Precipitate Characteristics*

Abstract

The effect of composition and thermal deformation treatment parameters (temperature for the end of rolling and strip winding on a coil, cooling rate after rolling) on mechanical properties, microstructure, and characteristics of precipitates (type, amount, size, morphology, distribution) in advanced ferritic automotive sheet steels is studied. It is demonstrated for the first time that these steels make it possible to obtain simultaneously high strength, ductility and formability due to a homogeneous fine ferritic microstructure additionally strengthened by volumetric system of nano-sized carbide precipitates. It is shown that the contribution to steel strengthening due to the formation of phase precipitates can reach significant values of more than 300 MPa. The main features of phase precipitate, microstructure, and property formation of ferritic steels are established.