[Show abstract][Hide abstract] ABSTRACT: Purpose: In the following paper there have been the structure and fatigue properties of micro-alloyed 23MnB4 steel in initial state and after heat treatment evaluated.Design/methodology/approach: Fatigue test of micro-alloyed 23MnB4 steel was completed by metallographic and fracture analyses. For scope the methods of the light microscopy and SEM were used.Findings: Microstructure of examined alloy in initial state was characterized mostly by fine ferrite with pearlitic net and in state after heat treatment was formed by martensite or partly by bainite and after tempering was formed by tempered martensite. Objective of this work consisted in determination of fatigue characteristics of micro-alloyed 23MnB4 steel, including fracture analyze. Results of fatigue testing at various stress levels for the samples in initial state and after the heat treatment have confirmed that obtained values of cycles to rupture were at least 585 000 cycles. Change of fatigue properties in dependence on heat treatment of the used steel.Research limitations/implications: For define fracture area a samples must be provide with notch. The experiment was limited by occurrence a void in cast alloys.Practical implications: The results may be utilized for application of the investigated material in process of manufacturing.Originality/value: These results contribute to explanation of fracture mechanism of micro-alloyed 23MnB4 steel.
Journal of Achievements in Materials and Manufacturing Engineering. 01/2008;
[Show abstract][Hide abstract] ABSTRACT: ABSTRAKT Problematika vývoje nanostrukturních materiálu je v soucasné dobe intenzívne zkoumaná na významných vedeckých pracovištích a unive rzitách ve svete -Soul, Fukuoka, Los Angeles, Grenoble, Los Alamos apod., uznávánými vedeckými odborníky (Furukawa, Nemoto, Langdon, Stolyarov, Zhu, Lowe, Segal apod.). Jedná se zejména o vývoj technologie ECAP (Equal-Channel Angular Pressing – Pravoúhlé protlacování rovnostrannými kanály). Daná technologie prináleží k základním metodám pro dosažení ultrajemného zrna. Jedná se zejména o neželezné kovy a jejich slitiny. Neželezné kovy a jejich slitiny jsou velmi dobre recyklovatelné a nahrazují stále ve vetším merítku oceli. Zároven dochází k významnému snižování výrobních nákladu u výrobku z techto materiálu. Roste význam jejich použití zejména v automobilovém prumyslu, ve vojenském a kosmickém prumyslu.
[Show abstract][Hide abstract] ABSTRACT: The technology, ECAP – Equal Channel Angular Pressing, belongs to technologies of accelerated development and represents top items of R&D agenda in the world. The development of nano-structure materials and nanotechnologies in general represents a principal domain of EU RP 6. The R&D network development and commencement of concrete project implementation should start in 2003 and onwards. The investigation of nano-structure materials is subject of concentrated efforts of major research institutions in the world -Soul, Fukuoka, Los Angeles, Grenoble, Los Alamos, etc. – and eminent scientists -Furukawa, Nemoto, Langdon, Stolyarov, Zhu, Lowe, Segal, etc. In particular this concerns ECAP (Equal-Channel Angular Pressing) technologies. This technology represents a basic method for achieving super fine granularity structures. Especially non-ferrous metals, and their alloys are of primary concern. Non-ferrous metals, and their alloys are subject of an easy recycling process, and they increasingly tend to substitute steel on a larger scale. At the same time, a major decrease of production cost for these materials, and their products can be noted. Their importance for applications by automobile industry is ever growing that is also the case for military and space industries. Major car producers in the world -Opel, Audi, Jaguar, Ford, Fiat, Volvo, Toyota – have launched production of small cars that are largely made from Al and its alloys. The objective has been to bring down the overall vehicle weight, which is of immediate consequence, taking into account production costs, petrol consumption, CO2 and Nox emissions that are all lower, which is in favour of environmental sustainability for production industries. Aluminium alloys of super fine granularity structure are basic intermediate products realised by ECAP technologies. The state of super fine granularity facilitates forming of material in the so-called 'superplastic state'. The achievement of the desired structure depends primarily on the tool geometry, number of passages through the die, magnitude and speed of deformation, process temperature, and lubrication mode. 1 PRINCIPLES OF ECAP TECHNOLOGY Severe plastic straining is achieved in ECAP by pressing the sample through a die as illustrated schematically in Fig. 1. The sample is machined to fit within a channel which passes through the die in an L shaped configuration /1, 2/. For the situation where the angle between the two parts of the channel is equal to 90°, the test sample will undergo straining by shear as it passes from one part of the channel to the other: this shearing is illustrated in Fig. 2. It is apparent from Fig. 1 that the sample emerges from the die without any change in the cross-sectional dimensions. Thus, this process is distinct from the more conventional metal working processes such as rolling and extrusion where there is a concomitant reduction in the cross-sectional dimensions of the work piece. In practice, it is convenient to define three separate planes within the sample associated with ECAP: these planes are indicated in Fig. 1 and they are plane X perpendicular to the longitudinal axis and planes Y and Z parallel to the side face and the top face of the sample at the point of exit from the die, respectively.