학술논문
Effects of Foil Thickness to Grain Size (t/d) Ratio and Prestraining on Tensile Response, Microformability and Crystallographic Texture of Ultra-Low Carbon Steel Thin Foils
Document Type
Article
Source
(2024): 348-359.
Subject
Language
Korean
ISSN
15989623
Abstract
Ultra-low carbon (ULC) steels, containing a carbon content ~ 0.055 wt%, have been used in several applications in the formof thin foils. However, there are limited studies on the effects of foil thickness (t) to grain size (d) ratio and foil condition onthe tensile response and formability of thin ULC steel foils. In the present work, the tensile and forming behaviours of ULCsteel foils of thickness about 400 μm were evaluated in both annealed and prestrained (by cold reduction to 2–7%) conditionsas a function of t/d ratio and followed by detailed texture evolution analysis. Vacuum annealing was used to achievevarying t/d ratios in the specimens. Additionally, thin ULC steel foils of 100 μm thickness in annealed condition were alsoused for examining the thickness effect. Microstructural analysis was performed using the electron backscattered diffractiontechnique. Microformability was assessed by a miniaturised Nakazima test setup with specimen geometries designed toproduce three different strain paths. The annealed foils displayed a typical yield-point phenomenon, but the total yield-pointelongation decreased with decreasing thickness and grain size. The foils exhibited typical Hall–Petch strengthening, coldwork hardening, and forming limit curves; however, there were substantial reductions in both tensile strength and ductility,and consequently, the forming strains, with decreasing the t/d ratio. The tensile response and formability of the foils wereadversely affected by both thinning and prestraining. The texture studies revealed the formation of a γ-fibre i.e., < 111 >||normaldirection, and its intensity varied significantly with the t/d ratio and mode of strain path.
Ultra-low carbon (ULC) steels, containing a carbon content ~ 0.055 wt%, have been used in several applications in the formof thin foils. However, there are limited studies on the effects of foil thickness (t) to grain size (d) ratio and foil condition onthe tensile response and formability of thin ULC steel foils. In the present work, the tensile and forming behaviours of ULCsteel foils of thickness about 400 μm were evaluated in both annealed and prestrained (by cold reduction to 2–7%) conditionsas a function of t/d ratio and followed by detailed texture evolution analysis. Vacuum annealing was used to achievevarying t/d ratios in the specimens. Additionally, thin ULC steel foils of 100 μm thickness in annealed condition were alsoused for examining the thickness effect. Microstructural analysis was performed using the electron backscattered diffractiontechnique. Microformability was assessed by a miniaturised Nakazima test setup with specimen geometries designed toproduce three different strain paths. The annealed foils displayed a typical yield-point phenomenon, but the total yield-pointelongation decreased with decreasing thickness and grain size. The foils exhibited typical Hall–Petch strengthening, coldwork hardening, and forming limit curves; however, there were substantial reductions in both tensile strength and ductility,and consequently, the forming strains, with decreasing the t/d ratio. The tensile response and formability of the foils wereadversely affected by both thinning and prestraining. The texture studies revealed the formation of a γ-fibre i.e., < 111 >||normaldirection, and its intensity varied significantly with the t/d ratio and mode of strain path.
Ultra-low carbon (ULC) steels, containing a carbon content ~ 0.055 wt%, have been used in several applications in the formof thin foils. However, there are limited studies on the effects of foil thickness (t) to grain size (d) ratio and foil condition onthe tensile response and formability of thin ULC steel foils. In the present work, the tensile and forming behaviours of ULCsteel foils of thickness about 400 μm were evaluated in both annealed and prestrained (by cold reduction to 2–7%) conditionsas a function of t/d ratio and followed by detailed texture evolution analysis. Vacuum annealing was used to achievevarying t/d ratios in the specimens. Additionally, thin ULC steel foils of 100 μm thickness in annealed condition were alsoused for examining the thickness effect. Microstructural analysis was performed using the electron backscattered diffractiontechnique. Microformability was assessed by a miniaturised Nakazima test setup with specimen geometries designed toproduce three different strain paths. The annealed foils displayed a typical yield-point phenomenon, but the total yield-pointelongation decreased with decreasing thickness and grain size. The foils exhibited typical Hall–Petch strengthening, coldwork hardening, and forming limit curves; however, there were substantial reductions in both tensile strength and ductility,and consequently, the forming strains, with decreasing the t/d ratio. The tensile response and formability of the foils wereadversely affected by both thinning and prestraining. The texture studies revealed the formation of a γ-fibre i.e., < 111 >||normaldirection, and its intensity varied significantly with the t/d ratio and mode of strain path.