MATERIALS ENGINEERING, Vol. 16, 2009, No. 4
published on December 2009

CONTENTS and ABSTRACTS

Kalincová, D. (pp. 1-4)
AN INFLUENCE OF THE SURFACE ROLLING ON MECHANICAL PROPERTIES OF THE BAND SAW BLADES Full text (PDF 2762 kB)
The article present the experiment focused on the band saw blade surface mechanical properties analysis after plastic deformation process. The deformation of the band saw blade is caused by rootling in order to increase operating reliability. Mechanical properties were evaluated by hardness measurement and by microstructure analysis.

Němcová, A., Zapletal, J., Juliš, M., Podrábský, T. (pp. 5-10)
CYCLIC FATIGUE RESISTANCE OF AZ91 MAGNESIUM ALLOY Full text (PDF 2760 kB)
The paper deals with determination of principal mechanical properties and the investigation of fatigue behaviour of AZ91 magnesium alloy. The experimental material was made by squeeze casting technique and heat treated to obtain T4 state (solution annealing), when hard, brittle Mg17Al12 intermetallic phase is dissolved. The basic mechanical properties (Young’s modulus, ultimate tensile strength, yield strength, elongation to fracture and reduction of area) were determined by static tensile test. Furthermore, fatigue parameters were investigated. The S-N curve on the basis of smooth test bars tested under symmetrical push-pull loading at room temperature was evaluated. The measured data were subsequently used for fitting with suitable regression functions (Kohout & Věchet and Stromeyer) for determination of the fatigue parameters. Fatigue limit ?C of the studied alloy for 108 cycles is approaching 50 MPa. In addition, the fracture surfaces were observed by scanning electron microscopy. The failure analysis proved that the striations were observed in fatigue crack propagation area and in the area of static fracture was observed the transgranular ductile fracture. The structure of the studied alloy in the basic state and after heat treatment was observed by light and scanning electron microscopy.

Vaško, A. (pp. 11-14)
CHOSEN FACTORS INFLUENCING MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AUSTEMPERED DUCTILE IRON Full text (PDF 1910 kB)
The paper deals with some factors influencing microstructure and mechanical properties of austempered ductile iron (ADI). Final structure and properties of ADI are obtained by exactly controlled process of heat treatment of nodular cast iron. The influence of conditions of isothermal heat treatment on microstructure and mechanical properties of austempered ductile iron, especially different temperature of isothermal transformation of austenite and different holding time at this temperature, is shown in the paper.

Sobotová, J. (pp. 15-20)
THE STUDY OF KINETIC RECRYSTALLIZATION OF HOT FORMED AUSTENITIC Ti STABILIZED STAINLESS STEEL Full text (PDF 1561 kB)
The paper deals with the study of recrystallization of hot formed austenitic Ti-stabilized stainless steel X6CrNiTi18-10. Kinetic recrystallization was studied in the selected material by means of plastometric and upsetting tests. The effect of the strain temperature was studied in the temperature range 900-1250°C by plastometric tests. A drop hammer was used for the upsetting tests in the deformation temperature 1200°C. The height reduction in the tests was determined in a way that made it possible to compare specimens formed both by plastimetry and upsetting. Recrystallization was evaluated in the paper on the basis of stress-strain analysis, metallography (recrystallized fraction, grain size), hardness measurements (HV10), calculation of dehardening from values of hardness measurements and x-ray analysis (volume fraction of mosaic blocks larger than 10 µm). Parameter Z was determined for all conditions of strain, value of the activation energy of the tested material Q = 415 kJ/mol was used for the calculations. The monitored characteristics were compared after forming on a plastometer and upsetting at comparable strain intensity.

Peľák, S., Mišičko, R., Fedáková, D., Bidulská, J. (pp. 21-28)
BETWEEN THE DENDRITE STRUCTURE QUALITY, THE CASTING TECHNOLOGY AND THE DEFECTS IN CONTINUOUSLY CAST SLABS Full text (PDF 382 kB)
The paper presents the results of analysis of surface defects of continuously cast slabs. Longitudinal central cracks of type II, accompanied by local depression, were found. The local depressions were formed in areas with the thinnest slab chill zone. We suppose that they were caused by heterogeneous contraction of solidified shell. The second part of the paper analyzes the relationships between the chemical composition, the dendrite structure parameters, the casting technology parameters and the occurrence of defects in continuously cast slabs. To determine the susceptibility of the steel to longitudinal cracking, we analyzed the relationships between a large variety of data (slab chemical composition, casting speed, casting and overheating temperatures, primary and secondary dendrite arm spacing, etc.). The longitudinal defects were more frequent in overheated steel, with a small central zone, great dendrite arm spacing and with a higher than recommended sulphur and phosphorus content. Numerically expressed, cracking developed at the segregation index values IS?100, with the surface cracking index IPT?60.

Petrík, J. (pp. 29-32)
THE APPLICATION OF Ni FOR IMPROVEMENT OF Al-Si-Fe ALLOYS Full text (PDF 151 kB)
Iron, often present in secondary material (scrap) forms brittle and hard needles in Al-Si alloys.These particles decrease the mechanical properties of castings. A reliable and economic method of iron elimination from aluminium alloys has not been well-known yet in metallurgical practice. The influence of nickel as an iron corrector (up to 0.7 %) and iron (up to 2.5 %) on the fluidity, microstructure and mechanical properties of the Al alloy with 9.75 % Si, 0.2 % Mg was evaluated. The presence of Ni results in shortening of the needles, but the segmentation of ß needles was not observed. Improvement of mechanical properties was observed despite of low affecting of microstructure.

Černý, I. (pp. 33-39)
AN EFFECT OF SHOT PEENING ON GROWTH AND RETARDATION OF PHYSICALLY SHORT FATIGUE CRACKS IN AN AIRCRAFT Al-ALLOY Full text (PDF 850 kB)
Results of an investigation of effect of shot peening on development of physically short fatigue crack in an aircraft V-95 Al-alloy, which is of a similar type as 7075 alloy, are described and discussed in the paper. The first part deals with adaptation and verification of direct current potential drop method for detection and measurement of short crack initiation and growth. The specific material and quite large dimensions of flat specimens with side necking of a low stress concentration factor had to be considered when position of electrodes was specified and the measurement method verified. The specimen type and dimensions were proposed taking account of the investigation of shot peening effects. Physically short fatigue cracks of the length from 0.2 mm to more than 3 mm, most of them between 0.8 – 1.5 mm, were prepared under high cycle fatigue loading of a constant nominal stress amplitude ?160 MPa. Specimens with existing short fatigue cracks were shot peened using two different groups of parameters. Development of crack growth after shot peening was measured and compared with crack growth in specimens without shot peening. Retardation of crack growth was significant particularly with cracks shorter than 2 mm. For the specific stress amplitude, evaluated results enable to estimate threshold length of defects, which after the application of shot peening will be reliably arrested.

Jurko, J. (pp. 40-43)
PLASTIC DEFORMATION ON THE MACHINED SURFACE OF STEEL Cr20Ni10MoTi AT DRILLING Full text (PDF 617 kB)
Information about material machinability is very important for the machining technology. Precise and reliable information on the machinability of a material before it enters the machining process is a necessity, and this brings the verification of technological methods in practice. This article presents the conclusions of machinability tests on austenitic stainless steel according to EN-EU (ISO): steel Cr20Ni10MoTi. This article presents the conclusions of VEGA grant agency at the Ministry of Education SR for supporting research work and co-financing the projects: Grant work #01/3173/2006 with the title „Experimental investigation of cutting zones in drilled and milled stainless steels

Hlavatý, I., Sigmund, M., Krejčí, L., Mohyla, P. (pp. 44-50)
THE BAINITIC STEELS FOR RAILS APPLICATIONS Full text (PDF 1052 kB)
Actual trends of worldwide railway transport development are characterized by increasing speed and growth of railway’s axels load. Increasing load together with transverse, longitudinal wheel displacement and braking on the rails results into heavy surface tension. One of many applications for bainitic steel is in railway transport for highly strength and wear resistant rails. Rail steel must be designed to be able to resist plastic deformation, wear, rolling contact fatigue, bending stress and thermal stress during rail welding process and rails resurfacing.


© University of Žilina, Faculty of Mechanical Engineering, ISSN 1335-0803