Tensile Properties of Steel Tubes for Hydroforming Applications

With the increased use of tubular steel products, especially for automotive hydroforming applications, there is increased interest in understanding the mechanical properties measured by tensile tests from specimens of different orientations in the tube. In this study, two orientations of tensile specimens were evaluated -- axial specimens with and without flattening and flattened circumferential specimens. Three steels were evaluated -- two thicknesses of aluminum killed drawing quality (AKDQ) steel and one thickness of high strength low alloy (HSLA) steel. Mechanical property data were obtained from the flat stock, conventional production tubes and quasi tubes. Quasi tubes were produced from the flat stock on a 3-roll bender, but the quasi tube was not welded or sized. The intent of this paper is 1) to describe the relationship between the tensile properties obtained from the various types of test specimens, 2) to relate the tensile properties to the strain history, both in tube making and in specimen preparation, and 3) to discuss the effect of tube mill processing and sample preparation on measured tensile properties. An axial specimen without flattening is the best sample for obtaining representative mechanical properties for the tube. The cumulative strain from both producing tube and preparing tensile samples is a good measure of the effect of deformation on the subsequent tensile properties.