Paper analyses the influence of different values of the angle of the deformation zone in the forming tool on severe plastic deformation (SPD) process and on mechanical properties of resulting steel strip. Forming equipment using the severe plastic deformation (SPD) process and DRECE (Dual Rolling Equal Channel Extrusion) method builded and installed in the laboratory for the development of new technologies at the Faculty of Mechanical Engineering of VSB -Technical University of Ostrava is described. Tests were carried out at selected low-carbon deep-drawing steel DC01. By magnetoelastic method the residual stresses in material after separate passes were analyzed. DRECE method of forming brings compression stress into the material, which is favorable for further use.
The DRECE method belongs to the severe plastic deformation (SPD) processes used for the refinement of sheet metal elements. A forming device used in this method is currently being installed in the workplace in the Centre of Advanced Innovation Technologies, VSB Technical University of Ostrava. In the present work the structural characteristics and fracture morphology of Ck55 carbon steel after the application of the DRECE method with a forming tool angle of 118? are presented. The microstructure results are linked to selected mechanical properties. The tensile, hardness, and fatigue tests are performed. The methodology of non-destructive residual stresses measurement in the carbon steel after the extrusion and application of tensile tests on small samples are important for their use in technical practice. The paper presents the original results of selected properties after the application of the DRECE method on Ck55 steel, which will be used in the future to assess the application of the DRECE method and to determine other directions of the processing of ferrous alloys and steels.
Original scientific paper This paper deals with detection of surface damage after grinding through non-destructive micro magnetic technique based on Barkhausen noise. Paper compares the high and low frequency techniques and their sensitivity to detect surface burn and thickness of heat affected zone. The results of investigation indicate that the low frequency technique can more clearly detect surface burn than the high frequency technique due to relatively high thickness of heat affected zones obtained after grinding operations. The paper also discusses additional aspects of micro magnetic testing as a multi parametric technique where such parameters as Peak Position of Barkhausen noise loop correlate with the thermal load of machined surface. The paper also reports about corresponding structure transformations and associated stress state beneath the surface. Keywords: Barkhausen noise; detection; grinding; surface burn Otkrivanje brusne opekline putem visoke i niske frekvencije Barkhausenovog šumaIzvorni znanstveni članak Rad razmatra pojavu oštećenja površine nakon brušenja putem nedestruktivnog mikro magnetskog načina rada temeljenog na Barkhausenovom šumu. Uspoređuju se metode visoke i niske frekvencije i njihova osjetljivost u otkrivanju površinske opekline i debljine zone pod utjecajem topline. Rezultati istraživanja pokazuju da se metodom niske frekvencije može jasnije otkriti površinska opeklina nego metodom visoke frekvencije zbog relativno velike debljine zona pod utjecajem topline nastalih nekon brušenja. U radu se također raspravlja o dodatnim aspektima mikro magnetskog ispitivanja kao multi parametrijske metode u kojoj su parametri kao što je vršni položaj petlje Barkhausenovog šuma u korelaciji s toplinskim opterećenjem obrađivane površine. U radu se također daju odgovarajuće promjene u strukturi i s tim povezano naprezanje ispod površine.
Introduction into problems -This paper deals with the application of Barkhausen noise for investigation of residual stresses after hard turning. The results illustrate the differences in the stress distribution after hard turning and grinding. The analysis of the stress and structure state shows that the conventional evaluation of Barkhausen noise fails and monitoring of surface integrity will require a subsequent modified approach. The main reason for it is a more complicated relationship between stresses, surface hardness and structure. And so the modified approach is described for monitoring surface integrity after hard turning operations. This modification is based on the biaxial stress with the high correlation to the tool wear. The main idea is based on the non proportional increase of stress in the different directions.
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