Abstract
The inhomogeneous hardness distribution of high pressure torsion (HPT) processed IF steel disks along different directions is investigated. The results indicated that there exists inhomogeneous distribution in HPT processed IF steel disks, giving lower hardness in the center and higher hardness in the edge regions. However, on the axisymmetrical section testing plane of the disks’ thickness direction, there is a soft zone near the surface of disks. Further results from radius testing plane of different depths from the surface of HPT processed disks show that the inhomogeneity rules of hardness distribution on the radius direction are similar to that on the thickness direction. Compared with the initial state, different stages of HPT (compression and compression + torsion) can both remarkably increase the hardness of IF steel disks. Microstructure investigation results can give a well support to verify the rules of hardness distribution, showing hardly no change of grains in center and sever plastic deformation in edge. The inhomogeneous distribution of stress and strain with the huge friction between anvil and disks in the process of HPT play an important role of hardness and microstructure distribution.
Highlights
The processing of bulk metals through the application of High Pressure Torsion (HPT) is considered to be the most successful procedure for producing ultrafine-grained (UFG) materials with exceptionally small grain sizes on submicrometer or nanometer level, and with a high fraction of boundaries having high angles of misorientation [1,2,3]
The results indicated that there exists inhomogeneous distribution in high pressure torsion (HPT) processed IF steel disks, giving lower hardness in the center and higher hardness in the edge regions
We investigate the inhomogeneity of hardness and microstructure distribution on the different direction of IF steel disks processed by HPT
Summary
The processing of bulk metals through the application of High Pressure Torsion (HPT) is considered to be the most successful procedure for producing ultrafine-grained (UFG) materials with exceptionally small grain sizes on submicrometer or nanometer level, and with a high fraction of boundaries having high angles of misorientation [1,2,3]. Interstitial-free (IF) steel is widely used for automotive deep-drawing applications with micro-alloying elements (Ti, Nb and V) forming precipitates with carbon and nitrogen. There is a significant limitation with HPT because of the inhomogeneous strain, at least in principle, across the diameter of the samples during the HPT deformation, which can lead to the homogeneity of hardness and microstructure of disks and be verified by materials such as Al, Ni, Cu and austenitic steel for giving the lower values of hardness in the centers but higher hardness in the edge of disks [1,5]. The study on inhomogeneity of HPT processed IF steel disks is concerned by materials researchers.
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