| Summary: | Annealing process is critical to mechanical properties and microstructure of DP steel. For DP steel with strength grade of 590MPa, experiments with different combinations of intercritical annealing temperature and over-aging temperature were carried out during annealing. The tensile tests of the final products and nanohardness tests of different phases were made, and the microstructures were analyzed. The results indicated that higher intercritical annealing temperature was favorable to higher volume fraction of martensite and lower nanohardness of martensite with lower C density. The ultimate tensile strength increased monotonously with the volume fraction of martensite increasing. Higher over aging temperature would make martensite islands be partially resolved and carbides precipitate, which made lower volume fraction of martensite, and resulted in lower nanohardness of martensite. The revealed rules could provide important guide to control material properties of DP steel by manipulating annealing process.
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