| The effect of tempering temperature on the tensile properties of dual phase steels, obtained from different microstrctures, were studied. The starting microstructures of the studied dual phase steels were three kinds ; ferrite+coarse pearlite(F+P₁), ferrite+fine pearlite(F+P₂) and martensite(M). By increasing the tempering temperature, tensile strength was decreased, independently of the starting microstructures. Yield strength of the F+P starting structures was increased at the tempering temperature around 200 C and then decreased with the increased tempering temperature. However, the DP steel of M-starting structure has shown progressive decrease in yield strength with increased tempering temperature. The tempering effect on the elongation was similar, independently of the starting structures. At the early stage of tempering, tensile properties were influenced predominantly by the segregation of carbon at dislocation sites. At the later stage of the tempering, softening effect by the decomposition of martensite is more effective. |
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