Deformation Behavior of High Strength Steel Sheets

In this paper the tensile deformation behavior of dual-phase steel and the effect of mechanical properties of various types of high strength steel sheets on surface wrinkles during forming have been studied. A continuum model based on the “rule of mixture” is proposed to explain the tensile deformation behaviour of dual-phase steels which are composed of ferrite and martensite. In the model, the size of martensite and the strain ratio of martensite to ferrite are considered. Moreover, one of the assumptions of this theory is that the flow curves of the ferrite and martensite follow the equations σ = K∊ⁿ and σ = A ln∊ + B∊ + C respectively, where K, n, A, B and C are constants. Agreement between the calculated results and the experimental results is good for low volume fraction of martensite. The occurrence and growth of wrinkles under non-uniformly distributed stretching load depended mainly on the yield ratio and n-value in a small strain range. On the other hand, the occurrence, growth and disappearance of surface wrinkles during press forming were closely related to strength at the low strain state and r value. The steel sheets having low strength at the low strain state and high r value were hardly subject to wrinkles and when wrinkles occurred they were easily eliminated.