The effect of the strain path on the work hardening of austenitic and ferritic stainless steels in axisymmetric drawing |
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| Authors: | P R Cetlin E C S Corrêa M T P Aguilar |
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| Affiliation: | (1) Department of Metallurgical and Materials Engineering, the Federal University of Minas Gerais, Minas Gerais, Brazil;(2) Department of Materials Engineering and Construction, the Federal University of Minas Gerais, Minas Gerais, Brazil |
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| Abstract: | The work-hardening characteristics of metals deeply affect the analytical and numerical analyses of their forming processes
and especially the end mechanical properties of the products manufactured. The effects of strain, strain rate, and temperature
on work hardening have received wide attention in the literature, but the role of the strain path has been far less studied,
except for sheet-metal forming. Strain-path effects seem to have never been analyzed for bulk-forming processes, such as axisymmetric
drawing. In the present work, drawn bars were considered as composed of concentric layers strained along varying strain paths.
The tensile von Mises effective stress, effective-strain curves of two layers and of the full cross section of the drawn material,
were experimentally determined. The flow behavior of these regions was compared to that resulting from pure monotonic-tensile
processing. The AISI 420 and 304 stainless steels revealed a strain path and a material effect on their work-hardening characteristics.
Higher or lower hardening rates were observed in axisymmetric drawing, as compared to pure tension. These phenomena were interpreted
by considering the dislocation arrangements caused by initial drawing straining and their subsequent restructuring, associated
with the strain-path change represented by tension after drawing. The analytical and numerical analyses of the tensile behavior
of metals following axisymmetric drawing must consider the strain-path effects on the constitutive equations laws and on the
hardening behavior of the material. The redundant deformation factor in axisymmetric drawing (φ) plays a central role in the analysis of the process and on the prediction of the mechanical properties of the final products.
This parameter was evaluated considering (a) the strain distribution in the bar cross section caused by drawing or (b) the
mechanical properties of the drawn bars. The comparison of the results from these two approaches allowed an unexplained interpretation
of a material effect on this parameter. |
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