Mechanisms for Improving Chemical and Structural Homogeneity of Hot-Rolled Product for Objects Prepared by Hot Stamping

Abstract

Redistribution of components forming the structure and properties during hot rolling of microalloyed steels, similar in chemical composition to hardened steels during hot stamping, of an industrial melt containing carbon from 0.098 to 0.219%, is studied in detail. It is established that a key production parameter controlling the intensity of occurrence of these processes is the temperature at the start of rolling in the finishing group of stands, i.e., T₆. An increase in T₆ leads to significant enrichment with respect to carbon content, and a finer structure due to the formation of niobium carbonitride precipitates in surface layers compared with the rolled product axial zone. An increase in carbon content and a reduction in the concentration of niobium and other microalloying components within steel reduces the intensity of development of these processes. It has been shown by experiment that significant metal chemical and structural inhomogeneity forming in the continuous billet casting stage may be avoided or significantly reduced during hot rolling on the basis of controlling excess phase precipitation. This leads to a marked increase in the level of production and service properties of both hot-rolled product and metal objects prepared from it by hot stamping.