Tensile Behavior of Ferrite-Carbide and Ferrite-Martensite Steels with Different Ferrite Grain Structures
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URGICAL AND MATERIALS TRANSACTIONS A
r ¼ r0 þ kL enL :
½1
The modified C–J analysis based on the Swift equation[17] can be expressed as: dr ln ½2 ¼ ð1 ns Þ ln r lnðks ns Þ; de where, r and e are the true stress and true strain, respectively; nL and ns are the strain-hardening exponents that can be calculated by linear regression from the logarithmic plots. The ln(r) vs ln(e) plots show nearly monotonic behavior following the Ludwick equation,[16] where the slope of the plots representing the strain-hardening exponent, nL, Figure 4(a). VFGF/C steel showed the minimum nL (~0.09), which is increased by the bimodal grain structure in BG-F/C steel (nL ~ 0.14) to a value close to CG-F/P steel (nL ~ 0.15), Figure 4(a). Compared to ferrite-carbide structures, ferrite-martensite dual-phase structures offered higher nL values, which increased in the order VFG-DP (nL ~ 0.14)
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