Effect of low cycle fatigue damage on tensile behavior of sensitized stainless steel

Abstract

The aim of this report is to effect of sensitization treatment of the low cycle fatigue and post-fatigue tensile properties of a non-conventional austenitic stainless steel. The metallurgical investigation of solution annealed as well as sensitizedstainless steels were carried out in order to determine the microstructural characteristics, hardness, grain size distribution, tensile and low cycle fatigue properties and finally to determine the dislocation densities of the deformed specimens. The microstructure of the selected steel in solution annealed condition reveals that the steel owns nearly equiaxed austenite grains with annealing twins throughout the matrix. The grain size measurement was carried out by the aid of line intercept method for all materials and average grain size of as-received steel was found 23.49 ± 4.40 µm. Tensile and low cycle fatigue tests of the samples were carried out by using universal testing machine of ±100 kN capacity. The results indicate that the steel cyclically softens in both solution annealed as well as sensitized conditions. This nature of softening is also seen in the post-fatigue tensile tested samples. The fractographic analyses indicate that the fracture surfaces of the sensitized specimens are predominantly of typical rock candy type fracture whereas dimple fracture was observed in the solution annealed sample. Typical dislocation density in the deformed specimen assessed by X-ray diffraction profile analyses, is 6.2804 × 1015 m-2 in case of solution annealed sample while in sensitized steel specimens this range is 9.0575 × 1014 m-2. Thus, an increase of nearly an order of magnitude in the dislocation density was found.