The Influence of Multi-Pass Hot Rolling Parameters and Subsequent Heat Treatment on Microstructure and Mechanical Properties of Medium-Carbon Steel

In this study, the influence of the number of roll passes in hot rolling process to microstructural and mechanical properties of medium-carbon steel within applying the same amount of total deformation was investigated under as-rolled and quenched and tempered conditions. Tensile strengths of as-rolled specimens were increased depending on the higher volume percentage of martensite at lower roll passes. The size and distribution of martensite/austenite formations directly contribute to toughness rather than tensile strength, and the coarser martensite/austenite islands give rise to differences between actual and software predicted tensile strengths. It was revealed that fracture surfaces of as-rolled specimens were influenced by the rolling pass number changes. Spherical chromium (Cr) and molybdenum (Mo)-rich precipitates were formed more intensively in samples produced with 4 roll passes compared to 5 and 6 roll passes. Finer carbide formations and smaller dimples were found in heat-treated specimens compared to as-rolled ones. Furthermore, the positive contribution of initial martensite microstructure to mechanical properties was observed in heat-treated specimens.