Materials science and metallurgy of the Caribbean steel drum
The fabrication of a steel drum (or steelpan), especially the sinking of the drum head by hand with a hammer, has been examined in detail utilizing light metallography (LM) and transmission electron microscopy (TEM). Residual microstructures corresponding to reductions in thickness of up to 50% at the bottom of the drum-head indicate that dislocation densities in the low carbon (0.04 to 0.09% C), ferritic steels, can exceed 1010 cm –2. This substructure in conjunction with a grain structure consisting of elongated grains produces hardness increases of up to 45% at the bottom of the drum head. The heat treatment (or “burning”) of the Caribbean steel drum is an essential stage in the fabrication process and has been found to involve strain aging, which increases the hardness by an additional 5 to 20%. This is especially prominent in drum steels containing from 0.04 to 0.09% C. The strain aging combined with the strain hardening applied to the drum head sinking and note fabrication process, produces a requisite elastic-plastic interaction which allows for multi-harmonic tuning and the creation of the unique chromatic tones and harmonic overtones which are characteristic of the various instruments. These unique features of note vibrations were observed by comparing impact hardness profiles with the corresponding static Vickers hardness measurements for actual, tuned notes and the same, corresponding notes extracted from the drum head, respectively. Elastic-plastic and plastic hardness profiles were compared in unique color maps. In an effort to understand the influence of deformation on the sound of the steel drum, circular disks simulating free, ideal notes, and utilizing 316 stainless steel plates (0.05% C), were cold rolled to reductions up to 40%. Disks were hung on a wire through a hole drilled on the edge of the disk, and hit with a heavy (tungsten alloy) mallet to record the acoustic sound spectra. Requisite amounts of carbon interact with dislocations in deformed drum steel composing the note platform for the Caribbean steel drum to produce complex, non-linear behavior, especially notable in harmonic frequency spectra. Experiments on flat, circular disks prepared from high-quality, low-carbon (0.04 wt.% C) drum steel illustrate harmonic spectrum changes and frequency peak splitting which is related to characteristic deformation (or strain); which in turn is related to dislocation density. (Abstract shortened by UMI.)
Ferreyra Tello, Everaldo, "Materials science and metallurgy of the Caribbean steel drum" (2000). ETD Collection for University of Texas, El Paso. AAI9997670.