Structural State Evolution and Rolled Product Properties in Relation to Treatment Regime of Model Steels for Hot Stamping. 2. Cold-Rolled Product*

Abstract

A model steel microalloyed with vanadium is studied in detail for features of the change in microstructure, mechanical properties, and nanosize carbonitride precipitation system in relation to hot rolling, recrystallization annealing, and primarily slow cooling. The possibility is established of the occurrence during rolled product slow cooling of processes similar to recrystallization, leading to a reduction in grain elongation and size, stress relaxation, and formation of a more uniform and equilibrium condition. In addition, due to the formation a considerable amount of vanadium carbonitride precipitates with an average size of 10–15 nm dispersion hardening is realized that provides an increase in strength almost without a reduction in ductility. The intensity of development of the favorable processes described depends to a certain extent on condition of the solid solution formed during steel hot rolling. In addition, an increase in temperature at the end of hot rolling to 830–845°C with a reduction in strip winding temperature in a coil to about 600°C and below leads to improvement of the structural state, and the set of annealed cold-rolled product mechanical properties.