Effect of Dynamic Transformation on the Mean Flow Stress. Issue 3 (7th September 2012)

• Record Type: Journal Article
• Authors: Jonas, John J.; Ghosh, Chiradeep; Basabe, Vladimir V.
• Is Part Of: Steel research international. Volume 84:Issue 3(2013:Mar.)
• Page Start: 253
• Page End: 258
• Publication Date: 2012-09-07
• Subjects: rolling load -- separation force -- mean flow stress -- dynamic transformation -- upper critical temperature; Steel -- Periodicals; Steel -- Metallurgy -- Periodicals; 669.142
• DOI: 10.1002/srin.201200166
• Languages: English
• ISSNs: 1611-3683

Abstract

Abstract: Flow curves were determined in torsion at a series of temperatures on four plain C steels and a Nb microalloyed steel of increasing C concentration. The mean flow stresses (MFSs) pertaining to each experimental condition were calculated from the flow curves by integration. These are plotted against inverse absolute temperature in the form of Boratto diagrams. The stress drop temperatures, normally defined as the upper critical temperature$A_{{\rm r3}}^{{\rm *}} $, were determined from these diagrams. These are shown to be about 40°C above the paraequilibrium and about 20°C above the orthoequilibrium temperatures. This type of behavior is ascribed to the occurrence of dynamic transformation (DT) during deformation. The general characteristics of the DT of austenite to ferrite are reviewed. It is suggested that some of the unexpected load drops that have been reported to take place above the A e3 temperature in strip mills may be attributable to this phenomenon. Abstract : Mean flow stresses are calculated from experimental flow curves determined on four steels of increasing C content. These are plotted against inverse temperature so as to define the stress drop or upper critical temperature applicable to rolling. These temperatures are shown to be well above the equilibrium transformation temperatures, an observation that is attributed to the occurrence of dynamic transformation.