The effect of alloying elements on pearlite growth
- PDF / 655,901 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 232 Views
I.
INTRODUCTION
THE effect of
different alloying elements on the pearlite transformation has been studied by a number of workers. ~-~0 All alloying elements in steels, with the exception of cobalt, retard the pearlite transformation. The austenite stabilizing elements, like Mn, Ni, etc'., decrease the eutectoid temperature (Ael), and hence are generally expected to retard the pearlite transformation because of the decreased thermodynamic driving force for the transformation. The ferrite stabilizing elements, like Mo, Cr, Si, etc., increase the Ae~ temperature. In their presence, pearlite transformation starts at temperatures higher than the binary Fe-C Ae~ temperature; however, at lower temperatures the transformation rates are generally slower than the plain carbon eutectoid steel. It is now generally agreed that during pearlite growth the alloying element partition between the ferrite and cementite at low supersaturations and the growth is controlled by alloying element boundary diffusion, whereas at high supersaturations pearlite growth occurs without any partitioning of the alloying element and is controlled by carbon volume diffusion. ~'a8 The partitioning of alloying elements has been experimentally observed by Picklesimer et al. ,3 Razik et al., 4'5 A1-Salman et al.,9 and Chance and Ridley 6 in a number of Fe-C-Mn, Fe-C-Si, and Fe-C-Cr alloys. In all these studies, the partitioning was observed at low supersaturations, down to a certain temperature characteristic of the alloy composition, below which no partitioning was observed. For a given alloying element the partition-nopartition transition temperature decreased with increasing alloy content. The theory of the partitioning of alloying elements and the partition-no-partition transition during the ferrite transformation is fairly well developed, u-~5 Sharma ~and Sharma et al. 2 extended this to describe satisfactorily the kinetics of pearlite growth in Fe-C-Cr alloys. Razik et al. 4,s used similar arguments to explain their results on the partitioning of Mn and Cr during the pearlite transformation. From these studies, the following general conclusions may be drawn S.K. TEWARI, formerly a Graduate Student at the Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, India, is now with the Mishra Dhatu Nigam Ltd., Hyderabad, India, ROMESH C. SHARMA is Assistant Professor, Department of Metallurgical Engineering, Indian Institute of Technology,Kanpur, India, and is presently on leave at The Universityof Wisconsin, Madison, WI 53706. Manuscript submitted luly 24, 1984. METALLURGICALTRANSACTIONSA
regarding the mechanism by which the alloying elements affect the pearlite growth: (i) The partitioning of alloying elements is thermodynamically required and occurs at low supersaturations. (ii) At high supersaturations pearlite growth without any partitioning of the alloying elements is feasible and generally occurs. (iii) In the partitioning range growth is controlled by the alloying element boundary diffusion, whereas in the no-partit
Data Loading...
