INFLUENCE OF REHEATING AND COOLING CONDITIONS ON STRUCTURE AND MECHANICAL PROPERTIES of C-Mn-Si STEEL

The paper deals with structure and properties development of AHSS (advance high-strength steel) and UHSS (ultra high-strength steel) steel grades for various groups of automotive parts. C-Mn-Si type steel properties are evaluated based on the results of laboratory controlled rolling and cooling. The important influence on mechanical and plastic properties, amount of residual austenite (RA) and final structural type has, except for cooling rate, also starting temperature of intensive cooling (TIC) which follows after hot plastic deformations. If TIC is from interval of 620-760 deg C the final structure predominantly consists of ferrite with RA. Mostly acicular ferrite with RA, as well as bainite with RA was obtained when TIC was kept in the range of 760-850 deg C.