Physical Property Determination for Process Monitoring and Control

Abstract

Cold rolled and recrystallised steel strips in general are applied where the fitness for use asks for a high degree in deep drawability and surface quality features like low roughness and waviness. The good characteristic deep drawability of the steel grades developed for this purpose is achieved by low carbon contents (< 0.05%) and is described today by the properties of the standard tensile test: yield strength, tensile strength, percentage elongation before reduction and elongation at rupture. Futhermore, properties for anisotropy induced by crystallographic texture (Bleck, Bode and Hahn, 1990), i. e. the vertical (rm) and planar (Δr) anisotropy parameters are of interest. A good deep drawability — for instance for complex shaped car body parts — asks for a high value of the vertical anisotropy rm describing the resistance of the material against a reduction in thickness during the deep drawing process. The planar anisotropy value Δr is a measure for the direction-dependent yield resistence of the material in the strip plane. The value should be as small as possible in order to avoid earing during deep drawing (Schmidt and Schaffrath, 1993). The mechanical properties of the cold rolled steel strips are determined by the recrystallisation process after cold rolling. After laser welding to a strip of some kilometer length in a hot dip galvanising line the coils of cold rolled steel run through the recrystallisation furnace followed by the zinc-coating-line.