| The relationship between the tensile properties and the microstructure in a dual phase steel containing 0.2%C and 1.5%Si was studied. Specimens were intercritically annealed at 790℃ for 8min. and then, isothermally transformed at 320∼480℃ for various times. The effect of the retained austenite on the tensile properties and TRIP phenomena was studied. The steels examined in the present investigation were found to exhibit upper and lower bainites. In the lower bainite region, morphology of the retained austenite was finely dispersed film type, but, in the upper bainite region, bulky type retained austenite was examined. Steels transformed in the lower bainite region showed better tensile property than steels transformed in the upper bainite region, because film type retained austenite in the lower bainite was more stable than bulky type retained austenite in the upper bainite during deformation of the specimens. |
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