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Technical Paper

Effects of Steel Surface Texture on Appearance After Painting

An extensive investigation was conducted to assess the influence of steel sheet surface finish (i.e. topography or “texture”) on painted surface appearance. Ten sets of steel panels representing a variety of shot blast, EDT, laser, and bright surface textures were painted simultaneously using advanced solvent-based luxury vehicle paint systems. Paint appearance was measured using a relatively new Autospect instrument and also in terms of conventional Distinctness of Reflected Image (DOI). The results are discussed in detail with respect to 1) the influence of different steel surface textures on paint appearance, 2) the evolution of surface topography during painting, and 3) the implications of this work.
Technical Paper

New Method for Categorizing Low Carbon Automotive Sheet Steel

More stringent mechanical property requirements in automotive sheet steels, coupled with improvements in steel processing techniques, have made traditional methods for categorizing sheet steel obsolete. In particular, classification of steel quality by terms such as CQ, DQ and DQSK is no longer appropriate. SAE's Division 32 has addressed this issue and written a recommended practice for classifying sheet steel. The new method is based on nominal yield strength coupled with yield strength uniformity. Also included are provisions for differences in surface quality. The methodology has applicability to hot rolled, cold rolled, and coated sheets in the low to medium strength range.
Technical Paper

The Edge Formability of High-Strength Cold-Rolled Steel

Little information is available about the influence of inclusions and edge condition on the edge Formability of cold-rolled steels. For this reason a series of high-strength cold-rolled steels was evaluated through the hole expansion test. The steels examined were a rephosphorized steel microalloyed 50 and 60 ksi steels and recovery annealed 60 and 70 ksi steels. Edge formability has been found to be greatly influenced by the condition of the punched edge. Samples that were “dressed” (i.e. by removal of the shear burr along with the worked metal at the edge) exhibited a larger percentage hole expansion when compared to those evaluated in the as-blanked condition. The effect of inclusions on crack initiation is more significant in the de-burred condition than in the as-blanked condition because of the lower incidence of defect sites present at the edge. Hole expansion was found to be better in materials having higher total elongation and plastic anisotropy rm.
Technical Paper

Improvements in the Dent Resistance of Steel Body Panels

A computer-controlled body panel testing machine has been used to quantify stiffness and dent resistance of body panels at Chrysler. The influence of yield strength and local reinforcement on the mechanical behavior of automotive door panels has been investigated. Medium strength steels in the range of 210 -240 MPa yield strength have produced significant improvements in dent resistance over a 160 MPa yield strength steel. Considerable improvements in dent resistance can also be attributed to the use of local, adhesively attached, glass fiber reinforcement patches. The effects of boundary conditions and panel shape on stiffness and dent resistance are illustrated in this application.