Abstract: Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength (σb), total elongation (δ) and the product of ultimate tensile strength and total elongation (σb•δ) reach the maximum values (791 MPa, 36% and 28476 MPa%, respectively) at optimal processes.

Key words: Hot deformation, Austempering, Hot rolled multiphase steels, Mechanical properties