Effects of rolling and coiling temperature on the microstructure and mechanical properties of hot-rolled high strength complex phase steel

The effects of rolling and coiling temperature on the microstructure and mechanical properties of complex phase hot-rolled high strength steel were investigated by varying rolling temperature and coiling temperature. The results showed that the strengthening of steel is mainly due to the combination of precipitation hardening and grain refinement. With the finish rolling temperature decrease, the accumulation of local strains promote the transformation from austenite to ferrite during coiling process, making ferrite grain more fine and homogeneous. With the coiling temperature decrease, the width of ferrite slabs and the average size of martensite/austenite islands (M/A islands) decrease, the main strengthening method is transformed from precipitation strengthening to fine grain strengthening. The final rolling temperature at 890 degrees C and coiling at 550 degrees C was found to provide a good combination of tensile and elongation properties.