Effect of Tempering Conditions on Inhomogeneous Deformation Behavior of Ferrite–Martensite Dual-Phase Steels

Abstract

Synopsis :Inhomogeneous deformation in DP steel has been investigated by SEM-EBSD method and high-precision markers drawn by electron beam lithography. Particular emphasis is laid on the effects of initial hardness of martensite on the development of inhomogeneity in ferrite during tensile deformation. The hardness of each phase in DP steels has been examined using a Berkovich-type indenter. Difference of the hardness between ferrite and martensite in the specimen tempered at 423K was larger than that tempered at 673K. Changes of local orientation obtained by SEM-EBSD method inside the ferrite in the steel tempered at 423K was more noticeable than that tempered at 673K. In addition, we employed a high-precision marking method using electron beam lithography in order to measure the local displacement. Not only the equivalent plastic strain in ferrite but also the one in martensite were obtained by using the method due to tensile deformation. It is clarified that the hardness of martensite effects the development of deformation inhomogeneity in both of ferrite and martensite. On the basis of results, the influence of the characteristic of deformation inhomogeneity on the mechanical property of the DP steels is discussed.

Tensile Behavior of Ferrite-martensite Dual Phase Steels with Nano-precipitation of Vanadium Carbides

“…Similar tendencies have also been observed in other studies, 26,30) where the effect of tempering on strain partitioning has been investigated in ferrite-martensite DP steels. In such cases, a strength difference between the two phases was reduced by reducing the strength of the martensite, leading to a decrease in the overall strength of the DP steels.…”

“…38,39) Strain and stress partitioning between the phases in DP steels or other multiphase steels has experimentally been quantified by EBSD, [40][41][42] in-situ neutron diffraction, [42][43][44] high-energy X-ray diffraction, 38,45) DIC 22,30,[46][47][48][49] and lithography. 26,48,50) In this study, DIC is applied to quantify strain partitioning between ferrite and martensite phases during insitu tensile tests carried out in a SEM. For this experiment and analysis, we choose V-free and V-added samples with VF = ~50%, where the V-added sample shows a higher strength while still retaining sufficient elongation compared with the V-free sample (Figs.…”

“…8 the constituent properties (strength, formability, etc.) [23][24][25][26][27][28][29][30] of the ferrite/martensite phases. In order to understand the deformation mechanisms of nano-precipitated DP steels, the effect of these factors on mechanical properties should systematically be investigated.…”

Hydrogen Embrittlement Behavior of Ultra-high Strength Dual Phase Steel Sheet under Sustained Tensile-loading Test

“…Strain concentration in dual phase steels as a result of uniaxial deformation has been observed in ferrite neighboring martensite. 18,[22][23][24] In dual phase steels having a high volume fraction of martensite, the martensite is also deformed when large strain is applied, 25) and this deformation of the martensite may enhance hydrogen embrittlement. However, since the applied strain in this study was small, the strain is probably concentrated in the ferrite neighboring the martensite, as shown in Fig.…”

“…Additionally, dual phase steel for automobile parts is usually used after cold-press forming, i.e., plastic deformation, and in this case, the ferrite phase is considered to be preferentially subjected to plastic deformation. 18) If such deformation has marked effects on the hydrogen embrittlement behavior of the dual phase steel, it would be the first observation of this phenomenon and would also be an important finding. Therefore, an evaluation of the effects of pre-deformation on hydrogen embrittlement behavior is essential to understanding the optimum approach to using dual phase steel.…”