MATERIALS ENGINEERING, Vol. 18, 2011, No. 2
published on August 2010
CONTENTS and ABSTRACTS
Jurči, P., Dlouhý, I. (pp. 36-43)
FRACTURE BEHAVIOUR OF P/M Cr-V LEDEBURITIC STEEL WITH DIFFERENT SURFACE ROUGHNESS Full text (PDF 2536 kB) - Available online 13 July 2011
The samples made from the Vanadis 6 PM ledeburitic tool steel were surface machined to different quality and heat treated by standard regime of the processing. Three point bending tests were carried out on processed samples. It was found that the flexural strength decreased with decreasing surface quality. The lowering of flexural strength has been accompanied with the decrease of the plastic component of plastic straining preceeding to fracture initiation (work of fracture) of the material. It indicates that the surface roughness leads to the crack initiation before a larger plastic deformation of the material can be developed. Based on the results it can be suggested that to prevent the cracking of tools in the practice it is essential to make a surface machining (grinding, lapping, polishing) to as high quality as possible.
Dulebová, Ľ., Greškovič, F. (pp. 44-48)
INFLUENCE OF REGRIND ON PROPERTIES OF PLASTICS PRODUCED BY INJECTION MOULDING Full text (PDF 1357 kB) - Available online 14 July 2011
The contribution deals with the evaluation of results of selected mechanical tests. Materials Crastin® PBT (with 30 % glass fibre) and Celanex® 2004-2 PBT (without filler) were used at tests with various percentage of added regrind into basic material. The mechanical properties were obtained by tensile test and Shore hardness test. Utilization of regrind at the production of new moulded parts is important from aspect of reduction plastics waste and pollution abatement of environment.
Kolařík, K., Ganev, N., Jersák, J. (pp. 49-56)
APPLICATION OF X-RAY DIFFRACTION AND BARKHAUSEN NOISE ANALYSIS FOR STABILITY CONTROL DURING MACHINING Full text (PDF 445 kB) - Available online 14 July 2011
The contribution is focused on the recent experience of X-ray Diffraction Laboratory of the Czech Technical University in Prague and Department of Machining and Assembly of the Technical University of Liberec with industrial applications of X-ray diffraction residual stress measurement and Barkhausen noise analysis. Both methods are used for control and optimization of technological parameters during final surface machining of camshafts. They verify whether the required level of residual stresses in given subsurface areas was achieved and serve also as a fast output inspection of machine parts´ surface quality.
Micheľ, J., Buršák, M., Vojtko, M. (pp. 57-62)
MICROSTRUCTURE AND MECHANICAL PROPERTIES DEGRADATION OF CrMo CREEP RESISTANT STEEL OPERATING UNDER CREEP CONDITIONS Full text (PDF 2 436 kB) - Available online 28 July 2011
In this contribution microstructure degradation of a steam tube is analysed. The tube is made of CrMo creep resistant steel and was in service under creep conditions at temperature 530°C and calculated stress level in the tube wall 46.5 MPa. During service life in the steel gradual micro structure changes were observed, first pearlite spheroidization, precipitation, coagulation and precipitate coarsening. Despite the fact that there were evident changes in the micro structure the strength and deformation properties of the steel (Re, Rm, A5, Z), the resistance to brittle fracture and the creep strength limit, were near to unchanged after 2.1x105 hours in service. The steam tube is now in service more than 2.6x105 h.
Rosenberg, G., Gaško, M., Sinaiová, I., Kočík, M., Juhár, Ľ. (pp. 63-67)
FATIGUE BEHAVIOR OF HOT-ROLLED STEEL INTENDED FOR COLD FORMING Full text (PDF 95 kB) - Available online 28 July 2011
In the work, there are presented measured tension and fatigue properties of eight low-carbon steels moulded in form of 20 kg ingots that were processed by controlled regime of rolling /cooling and then exposed to simulated effect of two coiling temperatures. The experimental results presented in the work show, that steels with ferrite-martensite or ferrite-bainitic microstructure have in comparison to ferrite-pearlitic or ferrite-carbidic microstructure better strength-plastic properties, but worse resistance to cyclic loading.
Rosenberg, G.(pp. 68-72)
EFFECT OF SHOT PEENING ON FATIGUE PROPERTIES OF STEEL IN DIFFERENT STRUCTURAL STATES Full text (PDF 2773 kB) - Available online 29 July 2011
The aim of this paper is to evaluate the effect of shot peening on fatigue properties of dual-phase steels DP 600 in received condition, as well as in condition after different regimes of heat treatment. In the work, there are presented results of tests on smooth samples as well as on samples with stress concentrator (a drilling hole, size d = 4mm). The expectations, that shot peening of flat steel samples improves resistance to fatigue failure, were approved by all tested structural states. The tests on samples with the drilled hole showed, that effect of shot peening on fatigue properties may be negative, if the hole was drilled after shot peening of surface of samples.
Výrostková, A., Kepič, J., Macko, R., Homolová, V. (pp. 73-78)
EFFECT OF SHOT PEENING ON FATIGUE PROPERTIES OF STEEL IN DIFFERENT STRUCTURAL STATES Full text (PDF 4508 kB) - Available online 06 August 2011
Degradation of 0.5Mo-0.5Cr-0.25V material after long-term high-temperature service has been studied by means of microstructure and mechanical properties analysis. Samples were taken from the pipeline with steam leaking found after almost 200,000 h service at 565 °C. The microstructure and properties have been compared with similar materials at similar exposure conditions without any signs of the rupture. Highly tempered ferrite contains secondary particles of MC, M2C and a kind of Cr-rich carbide (M23C6 and/or M7C3) in all materials studied. The difference have been found in the values of hardness. Fractures of samples after the impact test at various temperatures with typical embrittled features are also described. Analysis of the material service history like warm and cold starts-up, conditions of thermal and mechanical fatigue, together with microstruc¬ture and mechanical properties lead to the conclusion that the material was overtempered. The exhaustion of material deformationability resulted in the rupture-leakage of a component in the place of highest stresses.
© University of Žilina, Faculty of Mechanical Engineering, ISSN 1335-0803