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Open access

I. Olejarczyk-Wożeńska, A. Adrian, H. Adrian and B. Mrzygłód

Parametric Representation of TTT Diagrams of ADI Cast Iron

The method of parametric representation of TTT diagrams on example of selected austempered ductile cast irons is presented. TTT diagrams were digitalised and n, k parameters of Johnson Mehl equation were calculated. The relationships between n, k parameters and transformation temperature were analysed for two ADI irons. Knowledge of these parameters enables to calculate the progress of austenite to bainite transformation.

Open access

H. Adrian and K. Wiencek

Abstract

Linear section of grains in polyhedral material microstructure is a system of chords. The mean length of chords is the linear grain size of the microstructure. For the prior austenite grains of low alloy structural steels, the chord length is a random variable of gamma- or logarithmic-normal distribution. The statistical grain size estimation belongs to the quantitative metallographic problems. The so-called point estimation is a well known procedure. The interval estimation (grain size confidence interval) for the gamma distribution was given elsewhere, but for the logarithmic-normal distribution is the subject of the present contribution. The statistical analysis is analogous to the one for the gamma distribution.

Open access

I. Olejarczyk-Wożeńska, H. Adrian and B. Mrzygłód

Abstract

The paper presents a mathematical model of the pearlite - austenite transformation. The description of this process uses the diffusion mechanism which takes place between the plates of ferrite and cementite (pearlite) as well as austenite. The process of austenite growth was described by means of a system of differential equations solved with the use of the finite difference method. The developed model was implemented in the environment of Delphi 4. The proprietary program allows for the calculation of the rate and time of the transformation at an assumed temperature as well as to determine the TTT diagram for the assigned temperature range.

Open access

E. Głowacz, H. Adrian and W. Osuch

The work examines the effect of nitrogen and micro-additions V and V+Al on the austenite grain size and the coagulation of carbonitride precipitates in 40Cr8 steel. The analyzed materials underwent heat treatment consisting in holding the material at 1200ºC for 1h, which was next exposed to furnace cooling down to 820ºC and maintained at this temperature for 20hrs, and subsequently quenched in water. With the application of electron microscopy, the microstructure and the formed carbonitride precipitates were examined. The SigmaScanPro software was used to perform the quantitative metallographic analysis of the precipitates. The study demonstrated that increase in the content of nitrogen inhibits the coagulation rate of carbonitrides, whereas aluminium favours the tendency for coagulation and efficiently inhibits the austenite grain growth.

Open access

P. Skubisz, H. Adrian and J. Sińczak

Controlled Cooling of Drop Forged Microalloyed-Steel Automotive Crankshaft

Certain aspects of determination of continuous cooling conditions directly after forging and their applicability to industrial conditions are discussed. On example of high-pressure-pump crankshaft problems concerning realization of drop forging of microalloyed-steel forged shaft with thermomechanical treatment involving subsequent direct controlled cooling are presented.

The paper is focused on determination of both forging conditions and subsequent cooling parameters, which in combination with modelling of precipitation kinetics in the analysed steel allowed accomplishment of required final mechanical properties of the forged part. For the determined conditions of thermomechanical treatment experimental trials in industrial conditions were carried out. Obtained in simulation pattern of continuous cooling was realized with a line consisting of six stages of controlled rate of stirred air flow. Satisfactory level of mechanical properties, exceeding minimum of the assumed requirements was reported, as well as uniform fine grained microstructure regardless of cross-sectional dimensions, meeting the requirements of automotive industry.

Open access

I. Telejko, H. Adrian and B. Guzik

Over-all mechanical properties of alloys are extremely low at the last stage of solidification where alloy exists at brittle temperature range (BTR). When the solidification process is completed a sudden and marked change in strength and ductility of metal is observed. It means that as long as liquid phase is present, metal will fail in a brittle manner. There are known different theories of brittleness of alloys in existence of liquid phase. The idea involved by authors of the paper is as follows: three major factors caused by presence of liquid may be taken into account:

- decreasing the energy needed for crack nucleation,

- increasing atomic diffusional flux out of the crack tip,

- creating a path for abnormally quick diffusion of atoms from the crack tip.

Open access

H. Adrian and K. Wiencek

Linear section of grains in polyhedral material microstructure is a system of chords on a test line. The mean chord length is the linear grain size of the material. In the prior austenite microstructure of low alloy structural steels, the chord length is a random variable which has the gamma distribution. The distribution parameters are closely related to the austenite linear grain size. Because the sequent chord lengths are statistically independent, the grain size interval estimation (confidence interval) may be performed by the chi-square distribution.

Open access

J. Augustyn-Pieniążek, H. Adrian, S. Rzadkosz and M. Choroszyński

Abstract

The high mechanical properties of the Al-Li-X alloys contribute to their increasingly broad application in aeronautics, as an alternative for the aluminium alloys, which have been used so far. The aluminium-lithium alloys have a lower specific gravity, a higher nucleation and crack spread resistance, a higher Young’s module and they characterize in a high crack resistance at lower temperatures. The aim of the research planned in this work was to design an aluminium alloy with a content of lithium and other alloy elements. The research included the creation of a laboratorial melt, the microstructure analysis with the use of light microscopy, the application of X-ray methods to identify the phases existing in the alloy, and the microhardness test.

Open access

I. Olejarczyk-Wożeńska, H. Adrian, B. Mrzygłód and M. Głowacki

Abstract

A mathematical model of austenite - bainite transformation in austempered ductile cast iron has been presented. The model is based on a model developed by Bhadeshia [1, 2] for modelling the bainitic transformation in high-silicon steels with inhibited carbide precipitation. A computer program has been developed that calculates the incubation time, the transformation time at a preset temperature, the TTT diagram and carbon content in unreacted austenite as a function of temperature. Additionally, the program has been provided with a module calculating the free energy of austenite and ferrite as well as the maximum driving force of transformation. Model validation was based on the experimental research and literature data. Experimental studies included the determination of austenite grain size, plotting the TTT diagram and analysis of the effect of heat treatment parameters on the microstructure of ductile iron. The obtained results show a relatively good compatibility between the theoretical calculations and experimental studies. Using the developed program it was possible to examine the effect of austenite grain size on the rate of transformation.

Open access

Benedikt A. Gasser, Adrian M. Stäuber, Glenn Lurmann, Fabio A. Breil, Hans H. Hoppeler and Michael Vogt

Abstract

Purpose. This study explored the effects of unstable shoe design on oxygen consumption. Methods. Oxygen consumption (VO2) and heart rate (HR) were measured in 16 individuals while barefoot, wearing unstable shoes (Masai Barefoot Technology) and wearing conventional sport shoes while standing and walking on a treadmill and for 5 individuals while walking around a 400 m track. Results. When wearing the MBT shoes, a significant (p < 0.01) increase of 9.3 ± 5.2% in VO2 was measured while standing quietly for 6 min. No differences in VO2 and HR were observed between the MBT shoes or weight-adjusted conventional shoes (to match the weight of the MBT shoes) while walking on a treadmill. However, significant increases (p < 0.01) in VO2 (4.4 ± 8.2%) and HR (3.6 ± 7.3%) were observed for the MBT shoes compared with being barefoot. No significant differences in VO2 and HR were recorded while walking around a 400 m track either with MBT shoes, weight-adjusted conventional shoes or barefoot. Nonetheless, a comparison of the MBT shoes with barefoot revealed a tendency for VO2 to be higher when wearing the MBT shoes (7.1 ± 6.5%, p < 0.1) although HR was not significantly affected. Conclusions. The unstable shoe design predominantly effects oxygen consumption while standing, most likely due to increased muscle activity of the lower extremities.