Microstructures And Properties Of Cold Rolled DP590

In order to satisfy new generation automobile steel development currently and accelerate domestic cold-rolled dual phase steel developing and using, it is of great significance to study the microstructure and property of dual-phase steel. Combining with metallographic analysis and mechanical property testing, the effect of intercritical annealing temperature, holding time, quenching speed and over-aging temperature during continuous annealing process on microstructures and properties of dual-phase steels was researched in this thesis based on the background of some company in China, applying Multi-functional continuous annealing simulator. Meanwhile industrial tests of DP590were introduced. The main works and achievements were shown as follows:(1) The effect of annealing temperature on microstructures and properties of dual-phase steel was studied. It was found that as the annealing temperature increasing, the volume fraction of martensite increased, island-like martensite transformed to massive martensite, and its strength increased but elongation decreased.(2) The effect of holding time on microstructures and properties of dual-phase steel was studied. It was found that strength was high and elongation was poor at a very short holding time. The comprehensive mechanical properties would not get better and the productivity couldn’t be improved at a too long holding time. Thus the holding time should be controlled in a certain range.(3) The effect of cooling rate on microstructures and properties of dual-phase steel was studied. It was found that the strength increased while the elongation decreased as the cooling speed increased within a certain speed range. The microstructures and mechanical properties changed slightly at a high cooling rate.(4) The effect of over-aging temperature on microstructures and properties of dual-phase steel was studied. It was found that the strength decreased while elongation increased with over-aging increasing. Bainite transformation occurred when over-aging temperature was higher than320℃.(5) DP590was trial-produced according to a group of optimized simulation technique and its strength and elongation could meet the enterprise requirents.