Characterization of the texture evolution in AISI 430 and AISI 433 ferritic stainless steels during simulated hot rollin
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.408
Characterization of the texture evolution in AISI 430 and AISI 433 ferritic stainless steels during simulated hot rolling K. A. Annan, C.W. Siyasiya, W.E. Stumpf
Department of Materials Science and Metallurgical Engineering, University of Pretoria 0002, South Africa. Corresponding author: KA Annan, e-mail: [email protected]
Abstract
Multi-pass compression tests were carried out on the Gleeble-1500D® and Gleeble3800TM® thermo-mechanical simulators to investigate the effect of temperature, strain rate and inter-pass time on the development of the texture in ferritic stainless steels (FSS) AISI 430 and 433, the latter an Al-containing variant. Orientation Distribution Functions (ODFs) through the electron backscattered diffraction (EBSD) technique was employed to characterise and study the texture present in the steels after hot working. The mean flow stress analysis showed that, the dynamic recrystallization to dynamic recovery transition temperature decreases with an increase in strain rate in both grades of stainless steels possibly allowing texture optimisation at lower hot rolling temperatures. Higher finishing rolling temperatures, lower strain rates and longer inter-pass times led to improvement in the formation of the desired γ-fibre texture which contributes to ductility or drawability in these steels. Dynamic recrystallization which promotes the formation of the desired γ-fibre texture was found to occur in both AISI 430 and 433 at temperatures above 1000 oC and strain rates less than 5 s-1. Generally AISI 433 develops a stronger gamma texture than the AISI 430 when hot rolled under similar conditions.
INTRODUCTION Ferritic Stainless Steels (FSS) containing approximately 16 wt% Cr have been found to be prone to the development of severe surface defects or “ridges” during stretch forming and deep drawing operations [1]. Through EBSD studies, it has been established that the spatial orientation distribution in the RD–ND and TD-ND sections exhibits inhomogeneity but no alignment [2]. It has also been found that the origin of this defect in stainless steels is linked to a number of factors including the crystallographic texture effects, which originate from anisotropic plastic flow of mixed textures [3, 4]. The origin of these textures may also be traced to textural and microstructural banding during hot working [3]. It has been shown by others [2, 4] that the alignment of similarly oriented grains occurs along the RD in the RD-TD plane and the stronger the alignment, the more
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severe the ridging during deep drawing. It is therefore appropriate to study ridging by analysing the texture in the RD-TD (or rolling plane) [2, 4]. For BCC metals such as AISI 430 and 433, cross slip and climb o
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