Elastic interactions and the metallurgical and acoustic effects of carbon in the Caribbean steel drum

Abstract

Requisite amounts of carbon interact with dislocations in deformed drum steel composing the note platform for the Caribbean steel drum (or pan) to produce complex, nonlinear 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 variation (which appear to occur by splitting), which is related to characteristic deformation (or strain). This, in turn, is related to dislocation density. Similar frequency variation characteristics were also observed in actual drum notes. Detailed texture measurements revealed only about 3% variation in the elastic moduli for the undeformed and heavily deformed drum steel. Detailed tempering diagrams illustrate the variations of residual microhardness with aging temperature, time, strain, and carbon content, while stress–strain diagrams show more detailed carbon dislocation dynamic interactions. While strain aging is a prominent feature of drum tempering, high-quality instruments can be developed and tuned even without noticeable strain aging by varying the methodology to manipulate the internal stresses to produce requisite elastic–plastic interactions. This could be achieved by strain-induced ordering of interstitial carbon (Snoek effect) and by dislocation pinning and unpinning by carbon atoms in a dynamic fashion (Portevin–Le Châtelier effect). A carbon threshold occurs below about 0.02 wt.% C and an anomalous hardening occurs in drum steels heat-treated at 800 °C due to martensite nucleating and growing at the original ferrite grain boundaries upon quenching. This microstructure is carbon-dependent, increasing with increasing carbon content above the ∼0.02 wt.% C threshold. Below this carbon threshold, there is no strain aging or high-temperature hardening. Frequency spectra from heat-treated disks show an enhancement of the frequency variations and the generation of more harmonics.