Study of Microtopography of Free Surface of if-Steel at the Uniaxial Stretching

Abstract

Study of the process of final microtopography of automobile-body sheet surface forming revealed increase of roughness of free surface of sheet at its uniaxial deformation. A necessity to account this factor was noted, since the regulation ranges of microtopography parameters of some kinds of sheet products are narrow. Results of the study of variation of microtopography surface of automobile-body sheet of IF-steel depending on grain size and value of uniaxial deformation presented. It was shown that with the growth of ε, a complicated character of forming of free surface microtopography at various scale levels is observed. Amplitude values (Ra, Rq) and step (Rрc) parameters increase in a nonlinear way when ε grows for high frequency component of microtopography. While ε grows, on the surface of IF steel the grains form structural elements of deformation (SED). The step parameters of SED increase while ε grows slightly, whereas the amplitude parameters of SED show considerable growth. Stages of variation of surface microtopography of IF-steel at uniaxial stretching considered. It was shown that at early stages of deformation, intensive formation of ledges of micro-asperity of rough layer and forming of SED boundaries on the surface takes place. During next stages of deformation, the process of spatial decomposition of the roughness profile asperities at the constant spatial parameters of SED takes place. The intensity of growth of the rough layer roughness heights decreases and that of growth of height sizes of SED increases. At the stages close to destruction, the roughness profile is becoming even and the amplitude characteristics are increasing sharply. The amplitude characteristics of SED profile Raгарм considerably exceed the analogue characteristics of the roughness profile Raслуч.The results of the study should be used to take into consideration formation of free surface microtopography during production of cold-rolled sheet.