THE EFFECTS OF ROLLING PROCESSES ON THE MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF ULTRALOW CARBON BAINITIC STEELS

In this work, experimental ultralow carbon bainitic steels were prepared to study the effects of rolling parameters on the bainitic structure and on the strength-toughness properties. In order to obtain the desired bainitic structure, the reheating temperature should be high enough to allow more NbC to dissolve in austenite. It was also shown that the finish-rolling temperature had a strong effect on the mechanical properties. Both yielding and tensile strengths decreased with decreasing finish-rolling temperature, whereas toughness increased with decreasing finish-rolling temperature. However, the final thickness of the finish-rolling plate was found to have little influence on the strength. It was also found that the steels studied became considerably harder when heated at a temperature of around 600-degrees-C, owing to the precipitation of NbC in a bainitic ferrite matrix.