Abstract
An investigation was undertaken to obtain information on (a) the relationship, if any, between the aluminum and nitrogen contents of a steel and the susceptibility of the steel to graphitization, (b) the manner in which chromium influences the process, and (c) the effect of normal amounts of Mn, Si, S, and P in the graphitization of steel. Toward these objectives, twelve laboratory heats of iron-carbon alloy were made from specially prepared melting stock. Various amounts of Al, N, Cr, Mn, Si, S, and P were added to these heats. They were forged to ⅝-in-square bars, variously heat-treated, bead-welded, and tested for graphitization at 1025 F for periods of time extending to 8000 hr. Information on the progress of graphitization in the specimens was obtained by metallographic examination. The data obtained included the number of graphite nodules per unit area (as a measure of nucleation), the average nodule diameter, and the per cent conversion of carbide to graphite—all as functions of time. The evidence generally indicated that the graphitization process, whether occurring in the weld-heat-affected zone or in unaffected parent metal, took place by means of a nucleation and growth mechanism, which envisages a time rate of nucleation.
