Experimental Determination of a Strain State in a Bulk Forming of a Low Carbon Steel

An experimental metallographic method for determining strain distribution in a cold formed workpiece is presented in this paper. The method, based on the dependence of recrystallized grain size on prior deformation, was applied to a bulk formed element made of low carbon steel. Strain distribution was obtained by the calibration curve which gives the relation between recrystallized grain size and prior deformation. To determine strain values, the average grain size was measured in the longitudinal cross-section of the formed element. To accurately differentiate deformation zones, additional observation of carbides and nonmetallic inclusions morphology was utilized, also. The grain size and strain noticeably differ through the cross-section. It is observed that in the middle part, material flows freely through the die opening without significant deformation. From this zone, strain increases gradually, reaching the highest value at the contact surface of the die slope, while the top part flows radially having intermediate values of strain.