Abstract
The kinetics of copper sulfide growth has been investigated using low carbon steel samples such as Fe-0.3mass%Cu-0.03mass%S-0.1mass%C and Fe-0.1mass%Cu-0.01 mass%S-0.1mass%C. The samples were heat-treated at 1273, 1423 and 1573 K for 100 s – 14.4 ks for precipitation of copper sulfides and then subjected to observation by a scanning electron microscope (SEM) and a transmission electron microscope (TEM) to measure the size of copper sulfides precipitated in the samples. The growth kinetics of copper sulfides has been found to be well described by the Ostwald ripening model, as follows:
where
Rt and
R0 are the radii of copper sulfide precipitates, respectively, at
t =
t and
t = 0 where
t is time,
kO is the rate constant in this model and
T is thermodynamic temperature. The diffusion coefficients and activation energy derived from values of
kO are close to those of copper in austenitic iron. On the basis of the growth kinetics, it has been proposed that the heat-treatment for as-cast strip steel should be conducted at around 1273 K, at which the size of copper sulfide precipitates can be controlled to be as small as 20–30 nm in several tens of minutes.
