The paper deals with the change of the structure and mechanical properties of the austenitic steels after the exposure at the critical temperature. The effect of the bend radius of tubes on the mechanical properties and the structure was studied. The effect of solution annealing was studied too. The grades TP347 HFG, Super 304H and HR3C were chosen in the study. The bend radii R60, R80 and R100 were on the matter. The mechanical properties were studied using small punch test and miniaturized tensile tests. From the results can be concluded that the mechanical properties and the structure have been influenced due to one year exposure at the working temperature significantly. Various amounts of σ-phase were found in the pulled part of the bend side of the tubes even after only thermal exposure without any loading.Keywords: σ-phase, stainless steel, small punch test
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