| The effects of heat treatment paths and chromium addition on tensile properties in austenite dual phase steel obtained by isothermal heat treatment in the two phase region directly from the austenite region and intercritical dual phase steel obtained by intercritical annealing were investigated. As a specimen Fe/1.1.Mn/0.12C and Fe/1.0Mn/1.1Cr/0.12C steels were used. It was found that austenite dual phase steel had a increased volume fraction of martensite than the intercritical dual phase steel over the same time of heat treatment. Chromium addition decreased the volume fraction of martensite at the same isothermal heat treatment temperature. The isolated coarse martensite particles were obtained with little effect of chromium addition in austenite dual phase steel, but in the case of intercritical dual phase steel, coarse and finely dispersed martensite particles were observed with the addition of chromium caused by initial structure before intercritical annealing. As for the effect of chromium on tensile properties, total elongation of austenite dual phase steel was remarkably decreased with low tensile strength, but tensile strength increased and total elongation decreased slightly in intercritical dual phase steel. In Fe/1.0Mn/1.1Cr/0.12C steel, the total elongation of intercritical dual phase steel was excellent than that of austenite dual phase steel due to the fact that the mean size of martensite was so small and the number of martensite particles per unit area were remarkably increased at the same volume fraction. |
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