Investigation of the effect of deformation stored energy on the allotropic transformation temperature Zsolt Csepeli 1,2a * , Péter Bereczki 1,b , Balázs Verő 1,c , Ibolya Kardos 2,d and Péter János Szabó 3,e 1 College of Dunaújváros, Dunaújváros, Hungary 2 ISD Dunaferr Co. Ltd., Dunaújváros, Hungary 3 Budapest University of Technology and Economics, Budapest, Hungary a zscsepeli@mail.duf.hu, b bereczkip@mail.duf.hu, c verob@mail.duf.hu, d kardos.ibolya@isd-dunaferr.hu, e szpj@eik.bme.hu Keywords: DIFT, deformation stored energy, austenite transformation temperature, physical simulation, ferrite grain refinement Abstract. The aim of our investigation was to study the effect of deformation on the start temperature of the austenite-ferrite transformation. The deformation was carried out during cooling before the beginning of the transformation. The transformation start temperature was determined by dilatometric measurement with a Gleeble 3800 thermomechanical simulator. A novel method was developed to study the deformation induced ferrite transformation (DIFT) effect and successful experiments were carried out on S460MC grade steel specimens to determine the effect of the deformation stored energy on the transformation temperature of the austenite. Evaluating the dilatograms a strong relationship was observed between the temperature of the deformation and the austenite transformation start and finish temperatures. Lower deformation temperature resulted finer microstructure after austenite transformation. Introduction DIFT process is a promising technology to decrease ferrite grain size at industrial scale. The deformation stored energy increases the A3 temperature that results in metastable state above the equilibrium transformation temperature and the austenite-ferrite transformation takes place at a larger undercooling than during equilibrium transformation [1,2]. The result of the DIFT process can be an ultra fine grained microstructure with enhanced mechanical properties [3,4]. Using traditional production technologies the smallest attainable ferrite grain diameter is 5 µm, while exploiting the advantages of DIFT process steel strips with 1 µm ferrite grain diameter can be produced [5]. According to the Hall-Petch relationship this grain size reduction results in a significant increase in the yield strength. The aim of this study was to characterize the effect of the deformation stored energy on the start and finish temperature of the austenite transformation in a Nb microalloyed steel by physical simulation. The effect of the temperature of the deformation on the ferrite grain size was studied by light microscope and scanning electron microscope with EBSD detector. Experimental procedure The experiments were carried out on Gleeble 3800 thermo-mechanical simulator equipped with Hydrawedge System. This physical simulator provides a method for simulation of different technological processes even at high temperature on various metals and alloys. Due to the two synchronized hydraulic servo system on each side of the specimen, the applied strain and strain rate can be controlled during the deformation. In addition, the fully integrated mechanical system includes different transducers (for example longitudinal and transversal strain gauges, load cell, dilatometer, etc.), which provides feedback to insure accurate control of the hydraulic compression rams. The heating of the specimen can be realized by a direct resistance heating system. There are Materials Science Forum Vol. 812 (2015) pp 23-28 © (2015) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.812.23 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 193.225.187.99, Regional Centre of Excellence on Materials Science and Technology, Dunaújváros, Hungary-04/02/15,14:07:04)