Correlation of Mechanical Properties with Fracture Surface Features in a Newly Developed Dual-Phase Steel

Dual-phase (DP) steels were produced by a newly developed method utilizing simple cold-rolling and subsequent short intercritical annealing of a martensite-ferrite duplex starting structure. Tensile testing revealed an excellent strength-elongation balance (UTS x UE a parts per thousand 110-150 J/cm(3)) for the DP steels in comparison with the commercially used high strength steels. Fracture surfaces of the tensile specimens were studied by scanning electron microscopy analysis and image processing. Mechanical properties were correlated with fracture surface features. It was found that the variation of the total elongation and strength-elongation balance with the martensite volume fraction could be well correlated with the variation of the average dimple area. The variation of the yield strength and dimple areal density with the martensite volume fraction followed the same trend.