Strain hardening exponent and strain rate sensitivity exponent of dual-phase steels at quasi-static strain rates during tensile testing

The effects of quasi-static strain rates on the tensile properties of two commercial ferrite-martensite dual-phase DP 600 and DP 800 steels were investigated using strip-shaped samples. The investigation was done by uniaxial tensile tests, covering applicable quasi-static strain rates. The two dual-phase steels show positive strain rate sensitivity. It is found that, as the flow stress increases, the strain-rate sensitivity exponent m decreases. The drop in the strain-rate sensitivity exponent m with strain is largely attributed to the decreased true strain rate caused by the increased instantaneous length of the specimen as the deformation progresses. To better describe the flow behavior of DP steels, a relationship combining the effect of both strain hardening exponent n and strain-rate sensitivity exponent m on the slope of the stress-strain is correlated. A good agreement between the extended Hollomon model and experimental tensile test data from stress-strain measurements is found.