Diffusion-controlled growth and
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I.
INTRODUCTION
UNDERSTANDING the kinetics of manganese sulfide (MnS) precipitation in electrical steels is important in the design of rolling schedules and the selection of annealing parameters, ll'2j As is well known, MnS has been extensively used as an elementary "inhibitor" in commercial electrical steels. [3,4,5] The morphology of MnS plays a key role in improving the final texture and, therefore, the magnetic properties of these steels. 16,7,81 Since it has been found that large particles only exhibit a very small pinning effect on grain boundaries, I9'~~ it is important to know how to produce a fine dispersion of MnS precipitates during hot rolling. Similarly, the hightemperature growth and coarsening behavior of the straininduced MnS precipitates is of considerable interest and merits a detailed quantitative description. The aim of the present study was to throw some light on the growth and coarsening kinetics of MnS during the hot deformation of electrical steels. In earlier studies by the present authors, t~2"13Jthe nucleation kinetics of MnS precipitation were investigated in these steels. The resuits demonstrated that both grain boundaries and dislocations act as nucleation sites for such strain-induced precipitation. At the higher testing temperatures, nucleation at grain boundaries is dominant. As the temperature is decreased, however, nucleation on dislocations becomes more important. Following these investigations, the progress of MnS precipitation has been further analyzed in the present study. The size distribution of MnS particles during growth and coarsening has been measured by electron microscopy, and the relevant precipitation start (Ps) and finish (Ps) times have been determined by a creep technique. With the aid of these
W.P. SUN, CSIRA Research Associate, M. MILITZER, NSERC International Fellow, and J.J. JONAS, CSIRA/NSERC Professor of Steel Processing, are with the Depa~nent of Metallurgical Engineering, McGill University, Montreal, PQ H3A 2A7, Canada. Manuscript submitted December 27, 1991. METALLURGICAL TRANSACTIONS A
experimental results, the growth and coarsening mechanisms have been analyzed, and the details of this study are described below. II.
M A T E R I A L S AND T E C H N I Q U E S
A. Materials and Creep Tests Three of the four electrical steels employed previously t121were selected for investigation of the growth and coarsening behaviors. The detailed chemical compositions of these experimental materials are listed in Table I in weight percent. Cylindrical specimens 12 mm in height and 8 mm in diameter were subsequently machined from the as-received plates with their compression axes parallel to the rolling direction. Creep tests were carried out on a computerized MTS machine equipped with a high-temperature, high-vacuum furnace. Prior to application of the load, each specimen was solution treated at 1300 ~ for 30 minutes to dissolve the sulfides present in the as-received materials. After such treatment, the specimens were immediately cooled to the test temperature. On
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