Experimental findings and their theoretical interpretation related to the achieving of a 1.1m grain size in structural steels with a microstructure of ferrite and pearlite are summarised. Several ...laboratory processing methods can be used to achieve this grain size. It seems that only DIFT (deformation induced ferrite transformation) offers the possibilty of industrial use for thin sheets, while for thicker products DIFT can ensure the small grain size only for a thiN surface layer. By very small grain size yield stress and tensile strength are increased, while elongation, reduction of area and strain hardening are decreased. For a grain size of 1.3 mum upper shelf notch toughness is smaller, toughness transition temperature is lower and lower shelf notch toughness is higher than by the steel with the grain size of 6.8 mum.
The degradation process of an X20CrMoV 121 steel with an initial microstructure of tempered martensite was investigated. The effects of the change of microstructure type, and of the carbide ...particles' size and distribution were determined. Accelerated creep tests showed that the change of the mode of distribution of the carbide particles decreases more strongly due to creep resistance than the increase of the particle-to-particle distance. In the temperature range 550 DGC to 800 DGC, for annealing times from 2 h up to 1344 h, the hardness decreases faster at lower temperatures. It is possible to determine with sufficient reliability whether the steel's resistance to creep deformation was reduced below a safe level with non-destructive verification of the steel's microstructure and hardness.
Based on experimental data and transmission electron micrographs an explanation of the mechanism of the change of Charpy notch transition temperature after strain ageing is proposed. The explanation ...involves the interplane ordering of carbon atoms at ageing annealing at 250 deg C as a synergy of the dislocation structure and the redistribution of carbon atoms in solid solution in ferrite. The induced internal stresses decrease the cleavage fracture strength of the ferrite matrix and increase the Charpy notch toughness transition temperature.
The effect of microstructure on creep resistance of the low carbon chromium steel X20CrMoV121 after 100‐hours of static‐load test at a temperature of 580 °C and constant stress of 170 MPa was ...investigated. The specimens for the experiments were extracted from steam pipes of a steam power plant and heat treated. The effect of isothermal annealing on the microstructure and hardness as well as the kinetics of the precipitation of the carbide particles were determined.
Investigations into the fretting behaviour of the AlSi7Mg-T6 aluminium alloy are presented in this paper. With regard to the surface finishing conditions of the material, two types of specimen were ...considered: (i) machined and (ii) machined and shot peened specimens. The research was focused on investigations into the influence of the number of cycles, normal load (contact pressure) and the amplitude of slip on the fretting behaviour of the material. Fretting tests were performed under various running conditions with regard to normal load levels and slip amplitudes. The coefficient of friction between the surfaces at the fretting junction was continuously recorded. The fretting damage on the aluminium specimens was studied by means of microscopic and EPM analyses. With regard to the evolution of coefficient of friction curves, two modes of fretting process were identified. They differ in the transition from the initial phase to the steady-state fretting regime and depend primarily on the severity of the running conditions and the material properties. In general, higher values of the coefficient of friction were observed with machined and shot peened specimens as compared with those which were machined. It was found that for a given normal load, the coefficient of friction increases with an increased amplitude of slip while, for a given amplitude of slip, it decreases with an increased normal load.
The description of various techniques for the elimination of the locking phenomenon in degenerated finite-elements based on the Timoshenko–Mindlin hypotheses is presented. The use of these techniques ...is illustrated by the problem of the hydrostatic forming of thin metal sheet.
Proučavano je površinsko izdvajanje antimona na površinama polikristalne legure FeSi sa 0.05 tež.%, u ultravakuumu i na temperaturama od 450 do 950 ◦C. Izdvajanje na granicama zrna je zanemarivo. ...Ustanovljeno je da je nastajanje teksture posljedica smjerovno–ovisnih učinaka antimona na površinsku energiju pa stoga i na granice zrna. Upravljavano površinsko izdvajanje potiče poseban rast zrna.
