Hot deformation behavior of a ferritic stainless steel stabilized with Nb during hot rolling simulation at different tem
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Diana Pérez Escobar, Nilton José Lucinda de Oliveira, and Margareth Spangler Andrade SENAI Institute of Innovation in Metallurgy and Special Alloys, Center for Innovation and Technology SENAI FIEMG - Campus CETEC, Belo Horizonte, Minas Gerais 31035-536, Brazil (Received 28 July 2015; accepted 28 January 2016)
The aim of the present work was to study the effect of the finishing rolling temperature on interpass recrystallization promotion of an Nb-stabilized AISI 430 steel, via torsion tests simulation of a Steckel mill. The occurrence of interpass recrystallization was investigated by interrupting the tests before predetermined passes and analyzing the samples via electron backscatter diffraction (EBSD). The results revealed that interpass recrystallization can be promoted by decreasing the initial hot rolling temperature; which results in increased strain hardening during the passes and therefore, increased stored energy for recrystallization. The torsion test results concurred with those obtained by EBSD measurements. Furthermore, an optimum temperature range of 900–840 °C was found to promote interpass recrystallization during hot rolling.
I. INTRODUCTION
The use of ferritic stainless steels for different applications has increased over the last years due to their resistance to corrosion and combination of good mechanical properties and low maintenance requirements1 with lower cost of production compared to those of the austenitic stainless steels.2 This reduction in costs stems mainly from the low additions or absence of nickel, which, in some cases, makes these steels a viable alternative to the austenitic stainless steels. Ferritic stainless steels can develop an undesirable surface defect, after the cold rolling and/or deep drawing stage, called ridging or roping.3 This phenomenon, detracts from the aesthetics of the surface and is related with the crystallographic texture developed from solidification.4–7 After solidification, this type of steel presents mostly f001gÆuv0æ oriented columnar grains, which is generally considered harmful.8 It is well known that cold rolled ferritic stainless steels inherit their texture from hot rolling,9 which in turn, inherit their texture from solidification. To decrease ridging, this solidification texture must be somehow reduced/eliminated. This can be achieved via either phase transformation or mechanical straining and recrystallization. However, Nb-stabilized Contributing Editor: Yang-T. Cheng a) Address all correspondence to this author. e-mail: flaviafi[email protected] DOI: 10.1557/jmr.2016.57 J. Mater. Res., Vol. 31, No. 5, Mar 14, 2016
AISI 430 ferritic stainless steel, the object of the present study, does not transform on cooling. Therefore, the only possibility to change the solidification texture after thermomechanical processing is by recrystallization.10,11 In the case of ferritic stainless steels, it is well known that dynamic recovery (DRV) is the dominating softening mechanism.12–14 This mechanism reduces the stored energy from deformation, decreasing the driving fo
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