Diffusion of Sulfur in Gamma Iron

Abstract

Study on the diffusion behaviour of sulfur in pure iron in the temperature range from 950°C to 1 250°C, was carried out by means of radiotracer. A thin film of radioactive sulfur was deposited as a diffusion source on iron specimens by heating with ferrous sulfide in vacuum sealed capsule.
The surface residual radioactivity counting method was applied to determine the coefficients of volume diffusion and of grain boundary diffusion.
As a result, the volume diffusion coefficient of sulsur in pure iron is given by: D_v=1.7 exp (-53000/RT) cm²/sec. The measured grain boundary diffusion coefficient below 1100°C follows the rule that was determined for grain boundary diffusion in alpha iron. However, the grain boundary diffusion of sulfur above 1100°C is more rapid and temperature dependence may be given by: D_gbδ=1.1×10^-5 exp (-23000/RT) cm³/sec., where δ is grain boundary width.
Microscopic observation shows that rod-like sulfide precipitates appear in the crystal grain after cooling from the diffusion temperature above 1 200°C.