Fatigue behavior of ultrafine grained medium Carbon steel processed by severe plastic deformation

6th International Conference on Nanomaterials by Severe Plastic Deformation

材料科学;化学

Ruffing, C.^1 ; Ivanisenko, Yu^2 ; Kerscher, E.^1

Working Group of Materials Testing, University of Kaiserslautern, Kaiserslautern, Germany^1

Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany^2

关键词: Crack initiation sites;    Elevated temperature;    Fatigue experiments;    High pressure torsions;    Medium-carbon steels;    Non-metallic inclusions;    Severe plastic deformations;    Ultra fine grained microstructure;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/63/1/012163/pdf
DOI  :  10.1088/1757-899X/63/1/012163

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

The endurance limit of materials has been observed to be significantly increased in materials with an ultrafine grained microstructure [1, 2]. As this effect, however, has not yet been investigated in steels, fatigue experiments of an unalloyed medium carbon steel with a carbon content of 0.45 wt.-%, which was treated by high pressure torsion (HPT) [3-5] at elevated temperature were carried out. The treatments were applied to discs which had different initial carbide morphologies and showed an increase of hardness after HPT by a factor of 1.75-3.2 compared to the initial states, whereby the amount of increase depends on the initial carbide morphology. The maximum hardness achieved was 810 HV. The discs were cut into fatigue specimens in the form of bars of the size of 4 mm x 1 mm x 600 gm. Until a hardness of 500 HV the endurance limits correspond linearly with the hardness. This is no longer the case at higher hardness values, where inherent and process-initiated flaws lead to lower fatigue limits. The maximum endurance limit exceeded 1050 MPa in 4-point-micro-bending and at a load ratio of R 0.1. Fractography revealed different crack initiation sites like pre cracks and shear bands [6, 7] resulting from HPT or fisheye fractures initiated from non-metallic inclusions.