| The effect of distribution of martensite particles on tensile properties in dual phase steels heat treated by the intercritical annealing and the repeated treatment before intercritical annealing with the initial structures of both ferrite plus pearlite and martensite were investigated. For this investigation Fe/1.4%Mn/0.08%C and Fe/1.4%Mn/0.12%C alloys were prepared throughout the experiment. The results obtained from this study are summarized as follows. The relationships between tensile strength and uniform elongation were improved by decreasing the ferrite grain size. With increasing the volume fraction of martensite, the uniform elongation of 0.12%C-1.4Mn steel appeared nearly to remain unchanged due to the fact that the ferrite matrix became clean by decreasing carbide precipitation with increasing intercritical annealing temperatures for the same period of annealing time. Repeated heat treatment before intercritical annealing was found to increase the number of martensite (austenite) particles per unit area on polish surface after intercritical annealing. After intercritical annealing, the specimen of the initial martensite structure showed greater number of martensite particles per unit area than the specimen containing ferrite plus pearite initial structure. For the specimen of the initial martensite structure, repeated heat treatment before intercritical annealing was found to decrease the tensile strength and to increase the uniform elongation after intercritical annealing, whereas for the specimen of ferrite plus pearlite initial structure, repeated heat treatment before intercritical annealing was found to increase the uniform elongation without the decrease in tensile strength after intercritical annealing. |
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