Ferrite recrystallization and austenite formation in cold-rolled intercritically annealed steel
- PDF / 1,107,043 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 216 Views
.
INTRODUCTION
THEformation of austenite during intercritical annealing of low carbon steels has been the subject of a number of investigations. 1 7 Most of these studies have been performed on hot rolled or hot rolled and normalized steels with microstructures consisting of ferrite and pearlite. In the latter type of microstructure, austenite first forms at ferrite grain boundaries or pearlite colonies and carbide particles associated with ferrite grain boundaries. On cooling, the austenite transforms to martensite or other austenite decomposition products depending on hardenability and cooling rate. Because the austenite has formed on the ferrite grain boundaries, the various austenite transformation products of intercritically annealed hot rolled or normalized steels are also located on ferrite grain boundaries. Significant partitioning of manganese to austenite,l"3"6'7 and to some extent silicon to ferrite, 8-11 occurs during intercritical annealing. Little systematic investigation has been performed on intercritically annealed steels with microstructures which have been initially cold roiled. In such steels-the austenite transformation products (or retained austenite) are located not only on the ferrite grain boundaries but also within ferrite grains. 12 Austenite formation in cold rolled steels is complicated by the recrystallization of the cold worked ferrite. In experiments where cold-rolled ferrite-spheroidized cementite microstructures were subjected to intercritical annealing, Garcia and DeArdo s found that ferrite recrystallization precedes austenite formation and that, as in ferrite-pearlite microstructures, austenite formation occurs only in association with ferrite grain boundaries. The latter studys therefore does not explain the presence of secondphase particles removed from ferrite grain boundaries in cold-rolled dual-phase steels. The present investigation was performed to evaluate ferrite recrystallization and austenite formation in a cold-rolled D.Z. YANG is Lecturer, Harbin Institute of Technology, Harbin, People's Republic of China. E.L. BROWN, Research Associate Professor, D.K. MATLOCK, Charles F. Fogarty Professor, and G. KRAUSS, AMAX Foundation Professor, are with Colorado School of Mines, Golden, CO 80401. Manuscript submitted August 6. 1984.
METALLURGICALTRANSACTIONS A
Fe- 1.45Mn-0.08C-0.21Si steel. The starting microstructure consisted of ferrite and pearlite, and the emphasis of the experiments was to determine the effects of cold rolling, recrystallization, and intercritical annealing on the formation of austenite and the subsequent distribution of phases in dual-phase steel. This information is of importance to the production of high strength, formable sheet by continuous annealing of cold-rolled steel. 13
II.
EXPERIMENTAL P R O C E D U R E
The steel investigated contained, in wt pct, 0.08C, 1.45Mn, 0.21Si, 0.045A1, and 0.005N. Air-melted, 45 Kg ingots were heated to 1232 °C and hot-rolled to a 2.5 mm thick strip. Finishing temperatures ranged from 788 °C to 843 °C. Specimens of
Data Loading...
