| As-rolled dual phase steels were produced in a laboratory scale by a controlled rolling process. The relationship between mechanical properties and microstructures were investigated on the tensile specimens which were produced by varying finish-rolling temperatures, cooling methods and coiling temperatures. The Fe, 0.036-0.06％ C, 1.1-1.7％ Si, 1.3-1.7％ Mn compositions showed the ferrite-martensite dual phase structures and the tensile properties of strength 55-80㎏/㎟, total elongation 25-39％ and yield ratio 553％ after finish rolling 30％ at 780-840℃ followed by oil quenching. Air cooling down to A₁temperature (720℃) before oil quenching was found to decrease the optimum finish rolling temperatures by 30-50℃ through annihilation of hot-worked microstructures. Addition of 0.4％ Cr could raise the coiling temperature to 350℃ without deteriorating the dual phase steel properties. |
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