Conditions for the Efficient Crushing of the As-Cast Microstructure of 30Cr10Ni Duplex Stainless Steel
- PDF / 1,204,005 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 29 Downloads / 206 Views
INTRODUCTION
BECAUSE of their excellent corrosion resistance as well as their mechanical and physical properties, duplex stainless steels (DSS) are becoming increasingly important. They have found applications in various industries as welding materials and, because of their good corrosion properties, also in the chemical, oil-extraction, food-processing, and paper industries. The properties of DSSs are a result of their two-phase microstructure (i.e., austenite and ferrite) in which the austenite contributes to the toughness and the ferrite improves the mechanical and welding characteristics. Their properties have been improving continually as a result of an optimization of the alloying, casting, hot and cold forming, heat treatment, etc.[1–4] It is well known that, in general, a large difference persists in the hot workability between the as-cast and the wrought states, which is attributed to the different distributions of the alloying elements, the grain size and the geometry, the morphology of microstructure, etc. Thus, the hot forming of the as-cast state is a critical step in the production of a DSS because a two-phase, ascast microstructure is prone to cracking, especially on the ferrite–austenite grain boundaries, where carbides, impurities, and secondary phases precipitate. The twophase structure additionally contributes to the complexity of the hot forming as a result of the different MILAN TERCˇELJ, Associate Professor, MATEVZ FAZARINC, and DAVID BOMBACˇ, Researchers, and GORAN KUGLER, Assistant Professor, are with the Faculty for Natural Sciences and Engineering, University of Ljublijana, Askerceva 12, 1000 Ljubljana, Slovenia. Contact e-mail: [email protected]. Manuscript submitted December 3, 2009. Article published online August 17, 2010. 1328—VOLUME 41B, DECEMBER 2010
deformation modes of both phases as a consequence of their different crystallographic structures. Some authors suggest that the strain partitioning between the ferrite and the austenite results in internal stresses at the phase boundaries, which may lead to crack formation during hot deformation. Therefore, the volume fractions of both phases have a large influence on the hot workability of DSSs.[5–14] The complexity during hot deformation also contributes to the different softening mechanisms of the ferrite and the austenite. Namely, during hot deformation, the ferrite phase, which is softer, exhibits dynamic recovery (DRV) or extended DRV, as was discussed in detail by the authors,[15,16] but some authors also report the occurrence of dynamic recrystallization (DRX) in the ferrite.[11,17] However, austenite, which is harder, usually exhibits DRX even at temperatures below 1373 K (1100 C); although, some authors observed that DRX only occurs above 1473 K (1200 C).[18] Additionally, the beginning of the precipitation of secondary phases, such as the sigma phase, chromium nitride, secondary austenite, the chi phases, etc., which usually takes place[19–22] in the temperature range 873 K (600 C) to 1273 K (1000 C), represents the lo
Data Loading...
