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This research employed three-dimensional optical profilometry to examine the influence of yield point elongation (YPE) on the evolution of surface topography associated with Lüders band growth. Eleven Lüders bands were examined on tensile specimens containing YPE ranging from 0.13% to 2.34%. For each sample, a cycle of loading just beyond the yield point, unloading, recording surface topography changes, then repeating the process was undertaken. All samples were prepared by aging for various times at 150°C, chemically stripping the galvanized coating, and polishing one face to a mirror finish for surface topography assessment of the Lüders band. Assessments of the Lüders bands in the scan area revealed topography ranging from a ‘local’ maximum depth to a final condition reflecting residual features.

The frictional behavior of two nominally 70 g/m2 electrogalvanized sheet steels, mechanically processed with a series of surface roughnesses and coating morphologies, were evaluated with the bending under tension test. The crystallographic textures for the as-received materials were different; one was primarily prismatic with a friction coefficient of 0.14 and the other was primarily low angle pyramidal with a friction coefficient of 0.20. The friction coefficients were changed by surface modifications and values as high as 0.31 were observed. Friction data are discussed in terms of surface roughness, interfacial contact pressure, true contact area, and crystallographic texture. Results are interpreted on the basis of the deformation characteristics of the zinc coatings and with respect to overall sheet formability characteristics.

The influences of laboratory-induced hydrogen on the tensile deformation and fracture behavior of selected sheet steels including conventional DQSK and HSLA steels as well as newer DP and TRIP grades were evaluated. The effects of cold work, simulated paint baking, and natural aging were considered. Hydrogen effects were observable by increased flow stress, decreased ductility, altered neck geometry, and altered fracture mechanisms. Differences among the steels and conditions were observed and interpreted on the basis of microstructure, fracture behavior, and theories of hydrogen embrittlement.