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.
Austenite decomposition in carbon steel under dynamic deformation conditions
Purpose: The main purpose of this paper was to estimate the effect of the dynamic conditions resulting from deformation process on the austenite decomposition into ferrite and pearlite (A→F+P) in the commercial carbon steel. Design/methodology/approach: In the paper flow stress curves and microstructure of deformed steel within the range of discontinuous (austenite to pearlite) and austenite to ferrite transformation at different strain rates and cooling rates were presented. The microstructure of hot deformed samples was tested by means of an optical and electron microscopy. Findings: It was shown that the flow localization during hot deformation and preferred growth of the pearlite colonies at shear bands was very limited. The most characteristic feature of the microstructure observed for hot deformed samples was the development of carbides that nucleated along elongated ferrite grains. Research limitations/implications: In spite of intense strain hardening due to deformation and phase transformation overlapping, microstructural observation of deformed samples did not reveal significant flow localization effects or heterogeneous distribution of the eutectoid components. Therefore, complementary tests should be carried out on the steel with higher strain above the 0.5 value. Originality/value: There was no data referred to particular features of the dynamic processes, such as dynamic recrystallization and recovery, dynamic precipitation, that can occur during austenite decomposition into ferrite, and especially during discontinuous transformation of austenite to pearlite.
Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact
There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.