Conversion of Elongation Values for Cold-Rolled Low Carbon Steel Sheets

Abstract It is often difficult or impossible to prepare tension test pieces from flat steel products to specified standard size due to inadequate sample piece size. Hence several sizes of test pieces yielding different gage lengths are envisaged. However, the value of the total elongation beyond maximum stress in tension testing depends on the gage length due to the effect of necking. Acceptance values of elongation at fracture for flat steel products are therefore specified together with corresponding gage lengths, e.g., 50 or 80 mm (fixed gage lengths) and k So (proportional gage lengths) where k takes the value of 4.00, 5.65, 8.16, or 11.30 and k √SO is the original cross-sectional area of the test piece in mm2. Methods for converting room temperature percentage elongation at fracture obtained on various proportional and nonproportional gage lengths to other gage lengths exist for austenitic, carbon, and low alloy steels as hot-rolled, normalized, annealed, etc., but not as cold-reduced. These methods are also not valid where the gage length is greater than 25 times √SO or where the width-to-thickness ratio of the test piece is greater than twenty. This paper proposes a possible solution for cold-rolled low carbon steel sheets of thickness less than 2.0 mm, which continue to be, if not the major, one of the major raw materials in the automotive industry. The solution lies in the modification of the exponent in the Oliver formula used for flat steel products other than cold-rolled low carbon steel sheets.