Kinetics of Ostwald ripening—an analysis of models and errors with reference to MnS inclusions in steel

Abstract Kinetic studies were carried out in temperature range 950–1,350°C to determine the coarsening behavior of type II manganese sulfide inclusions in plain carbon/manganese steel. The influence of additions of selenium and of mechanical deformation (forging) on the kinetics was also sought. Detailed quantitative optical metallographic studies were carried out to determine the sources and the extent of errors introduced into the conventionally determined parameters (such as mean particle radius and the total number of particles per unit volume) used in the study of kinetics. The errors were shown to rise from three sources, viz.: 1. 1. from methods used for sectioning correction. 2. 2. the system under study. 3. 3. the instruments employed. A comparison of the data of the present and earlier studies on the basis of the experimental errors has shown that the large number of precautions taken to minimize the errors was effective and the present data are the most precise to date. However, attempts to prove the existence of a particular rate-controlling mechanism based on a comparison of conventionally used parameters proved ineffective, because of the associated errors. The effort involved in reducing this error to a level sufficient to permit the “proof” of a mechanism based on the above parameters was shown to be very large. However, alternative methods of collecting and interpreting data (such as mean inclusion diameter and growth rates deduced from volume fraction distributions) were more promising, because of the greater accuracy and sensitivity of their parameters. The findings of this study on the quantitative metallographic aspects would be applicable not only in coarsening kinetic studies but also in other fields of metallurgy and materials.