Work hardening behaviour in banded dual phase steel structures with improved formability

Abstract

In this work, we show how the presence of microstructural banding and segregation affects the work-hardening behaviour of a dual phase steel with improved formability. This steel contains chemical segregation inherited from the casting process. Our previously developed 3D cellular automaton model allowed us to design thermo-mechanical processes to either promote or suppress banding. The bands are properly described as in-plane sheets of martensite grains.Mechanical testing data revealed a significant reduction in tensile strength in banded structures for a similar level of ductility. The work-hardening behaviour in the pre-yield regime, including the yield strength itself, is not correlated to the incidence of segregation and/or microstructural banding. The reduction in ultimate tensile strength in banded structures stems from a reduced work-hardening capacity in the post-yield regime. This is due to increased austenite stability in the banded steels, coupled to the anisotropic strain localisation in the ferritic matrix between martensite bands.

The Influence of Segregation of Mn on the Recrystallization Behavior of C-Mn Steels

“…Many steels display the effects of casting in the form of segregation, for example, in microstructural banding of the ferrite and martensite in dual-phase steels [7] and in inhomogeneous Nb precipitation in HSLA steel, [8] to name just two. In common, C-Mn automotive forging grades segregation can be seen by local variations in Mn and Cr levels, and a banded ferrite + pearlite structure in the soft condition.…”

Strength and Fracture Behaviour of Dual Phase Steel Dp450 in Static and Dynamic Conditions

“…Using the Hencky theory for the plane strain indentation slips it is possible to calculate the approximate yield strength of the sample. Values of the yield strength are shown in Table 2 [12][13][14].…”

Deformation Response of Dual Phase Steel in Static and Dynamic Conditions

“…Using Hencky theory for plane strain indentation slip it is possible to calculate the approximate yield strength of the sample. Values of the yield strength are shown in Table 2 [11][12][13]. Fig.11 shows the force-depth graph near the fractured end obtained from the indentation test after dynamic impact test.…”