EFFECT OF SEVERE PLASTIC DEFORMATION ON STRUCTURE AND PROPERTIES OF AUSTENITIC AISI 316 GRADE STEEL
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. The ECAP method leads to significant improvement of strength of investigated material. Investigation of structure was made by combination of TEM and FEG SEM together with EBSD. Statistic evaluation of angular disorientation and of size of grains/sub-grains was also made with use of electron diffraction (EBSD) in combination with scanning electron microscope FEG SEM Philips. It was proven that the ECAP method enables obtaining of ultra fine-grained austenitic structure. It was established with use of the EBSD technique that after 8 passes through the ECAP die the sub-grains with misorientation angles smaller than 10 formed less than 20% of the final structure. Average size of austenitic grains with high-angle boundaries after 8 passes was approx. 0.1m.
DEVELOPMENT OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AUSTENITIC STAINLESS STEEL AFTER ECAP DEFORMATION
Cold and hot Equal-Channel Angular Pressing (ECAP) is an effective method to refine metallic grains. In this paper structure and mechanical properties including low cycle fatigue of austenitic stainless steel were evaluated and effect of hot ECAP at 280 o C on graing refinement was investigated. Testing results show that the refinement of grains can not be infinitely increased with increasing of ECAP passes (or total strain). The equivalent strain was ~1,0 per pass and the applied equivalent strain varied from 1,0 to 6. Under isothermal ECAP condition of the present study, optimum passes for investigates steel are between 4 and 6 passes. Microstructure evolution was observed by transmission electron microscopy (TEM). The effect of severe plastic deformation was studied at 280 o C, further deformation led to the formation of grain subdivision inside deformation bands and the onset of new grains formation after 2 ECAP passes. The deformation at 280 o C up to 6 passes lead to the formation of recrystallized grains of the order of 100-250 nm size.
Surface roughness monitoring by singular spectrum analysis of vibration signals
Abstract This study assessed two methods for enhanced surface roughness (Ra) monitoring based on the application of singular spectrum analysis (SSA) to vibrations signals generated in workpiece-cutting tool interaction in CNC finish turning operations i.e., the individual analysis of principal components (I-SSA), and the grouping analysis of correlated principal components (G-SSA). Singular spectrum analysis is a non-parametric technique of time series analysis that decomposes a signal into a set of independent additive time series referred to as principal components. A number of experiments with different cutting conditions were performed to assess surface roughness monitoring using both of these methods. The results show that singular spectrum analysis of vibration signal processing discriminated the frequency ranges effective for predicting surface roughness. Grouping analysis of correlated principal components (G-SSA) proved to be the most efficient method for monitoring surface roughness, with optimum prediction and reliability results at a lower analytical-computational cost. Finally, the results show that singular spectrum analysis is an ideal method for analyzing vibration signals applied to the on-line monitoring of surface roughness.