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The structure of austenitic steel AISI 316 after ECAP and low-cycle fatigue

Greger M., Vodárek V., Dobrzański L., Kander L., Kocich R., Kuřetová B.

Journal of Achievements in Materials and Manufacturing Engineering

2008

Vol. 28, nr 2

151-158

Purpose: The article presents results of investigation of structure and properties of austenitic steel grade AISI 316 after application of Equal Channel Angular Pressing (ECAP) at the temperature of approx. 290° C. Design/methodology/approach: The ECAP method led to significant improvement of strength of investigated material. Experiments were planned and realised at the temperature ranging from room temperature up to above mentioned temperature. Findings: It was established with use of the EBSD technique that after 8 passes through the ECAP die the sub-grains with an angle of disorientation smaller than 10° formed less than 20% of resulting structure. Average size of austenitic grains with high angle boundary after 8 passes was approx. 0.32 µm. It was proven that the ECAP method enables obtaining of ultra fine-grained austenitic structure formed by recrystallised grains with very low density of dislocations. Practical implications: The Technology ECAP was applied on austenitic steel AISI 316. It was verification of ECAP application possibility on steel AISI 316 importantly for following applying on similar kinds of steel, because ECAP technology influence on fatigue properties was confirmed. Originality/value: It can be predicted on the basis of obtained results that, contrary to low-cycle fatigue the ultra-fine grained material will manifest at fatigue load in the mode of constant amplitude of stress higher fatigue characteristics, particularly fatigue limit.

The structure and properties of chosen metals after ECAP

Greger M., Kocich R., Čížek L., Dobrzański L. A., Widomská M., Kuřetová B., Silbernagel A.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 18, nr 1-2

103--106

Purpose: This paper was aimed at verification of functionality of the ECAP technology at extrusion of the copper, alluminium alloys and steel. Design/methodology/approach: Experiments were made on equipment, which is demonstrated in the Fig 1. Deformation forces were measured during extrusion, resistance to deformation was calculated and deformation speed was determined approximately. Analysis of structure was made with use of light microscopy and TEM. Findings: The samples of Cu and Al alloys were extruded at room temperature. For the samples of steel was used the two-stage pressing, when the samples were extruded at temperature of approx. T1 = 325°C and T2 = 220°C. In order to increase concentration of deformation in volume of the sample the samples were after individual passes turned around their longitudinal axis by 90 o and they were extruded again. Research limitations/implications: research were limited to the die with constant extrusions angless within the value of 90°. In the future, it is planne to analyse the influence of changes of the angle and relative reduction ration on the ECAP process. Originality/value: Cross-section of original samples of Cu and Al alloys was 8 x 8 mm and their length was 32 mm and cross-section of original samples of Fe alloy was 10 x 10 mm and their length was 40 mm.