| Dual phase steels with 0.03％ carbon and various manganese contents of 1.4％, 1.9％ and 2.3％ were made in laboratory, and their mechanical properties and ageing behaviors were studied. In the water-quenched dual phase steels, as manganese content increased, work hardening rate and strength-ductility combination increased. Due to the higher manganese content, dual phase steels of ferrite and martensite were able to be obtained by slow cooling instead of water-quenching. Mechanical properties of dual phase steels made by slow cooling were superior to those made by water-quenching, because slow cooling made the ferrite matrix cleaner by decreasing the solute carbon content. The activation energy for ageing was estimated as 27±3 ㎉/mole in 1.4％ Mn dual phase steel. This value is higher than that for carbon diffusion in ferrite, 20 ㎉/mole. This difference seems to be attributed to the attraction between carbon and manganese atoms. |
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