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1

Analysis of effort of carbides and austenite in austenitic cast steel cooled violently

Tuleja J.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1

205-210

EN

This work presents the analysis the effort of phases which are present in the austenitic cast steel Fe-Ni-Cr-C, applied for elements of technological instrumentation for carburising furnaces. The reduced stresses [sigma]_red in the carbides and the austenitic matrix were determined in accordance with the assumed hypotheses of effort, on the basis of the structural stresses [sigma]_x [...] calculated by the finite element method for two model location cases of the carbides towards the cast steel surface. The hypotheses referred to the crack condition were applied to evaluate the elastic carbide efforts, while for the elastic-plastic austenitic matrix - the hypotheses referred to the plasticity condition were used. There were compared the reduced stresses óred determined in accordance with various hypotheses and the correctness of their applying. It was demonstrated on the basis of the executed analysis of the effort that the carbides are destroyed only when they are not entirely surrounded by the austenitic matrix.

2

Fracture formation in austenitic cast steel during thermal fatigue

Tuleja J.

Archives of Foundry Engineering

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2008

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Vol. 8, iss. 1

139-142

EN

In the paper are presented the results of numerical analyses of carburisation and thermal shock effect on fracture formation in stable austenitic cast steel of Fe-Ni-Cr-C type used in the charge-carrying elements of carburising furnaces. Using the method of finite element method, the distribution of stresses developing in carbides and their surrounding matrix were determined during rapid temperature changes. It was showed that very large tensile stresses developed in the carbides "out–coming" onto the alloy surface, regardless of the volume, type and anisotropy of properties, which could have led to their cracking as early as in the first cycles of heating and rapid cooling.

3

The thermal fatigue behaviour of creep-resistant Ni-Cr cast steel

Piekarski B.

Archives of Foundry Engineering

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2007

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Vol. 7, iss. 4

155-158

EN

The study gives a summary of the results of industrial and laboratory investigations regarding an assessment of the thermal fatigue behaviour of creep-resistant austenitic cast steel. The first part of the study was devoted to the problem of textural stresses forming in castings during service, indicating them as a cause of crack formation and propagation. Stresses are forming in carbides and in matrix surrounding these carbides due to considerable differences in the values of the coefficients of thermal expansion of these phases. The second part of the study shows the results of investigations carried out to assess the effect of carbon, chromium and nickel on crack resistance of austenitic cast steel. As a criterion of assessment the amount and propagation rate of cracks forming in the specimens as a result of rapid heating followed by cooling in running water was adopted. Tests were carried out on specimens made from 11 alloys. The chemical composition of these alloys was comprised in a range of the following values [...]. The specimens were subjected to 75 cycles of heating to a temperature of 900oC followed by cooling in running water. After every 15 cycles the number of the cracks was counted and their length was measured. The results of the measurements were mathematically processed. It has been proved that the main factor responsible for an increase in the number of cracks is carbon content in the alloy. In general assessment of the results of investigations, the predominant role of carbon and of chromium in the next place in shaping the crack behaviour of creep-resistant austenitic cast steel should be stressed. Attention was also drawn to the effect of high-temperature corrosion as a factor definitely deteriorating the cast steel resistance to thermal fatigue.

4

Naprężenia strukturalne w stabilnym staliwie austenitycznym w warunkach nawęglania i nagłych zmian temperatury

Tuleja J., Gutowski P., Leus M.

Archiwum Odlewnictwa

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2006

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R. 6, nr 22

590-597

PL

W pracy przedstawiono wyniki analizy numerycznej naprężeń strukturalnych powstających w staliwie austenitycznym typu Fe-Ni-Cr-C w węglikach i otaczającej je osnowie w czasie gwałtownych zmian temperatury. Analizę przeprowadzono dla dwóch wariantów usytuowania węglików. W pierwszym z nich węglik był w całości otoczony austenitem, w drugim zaś był częściowo odsłonięty - "wychodził" na powierzchnię stopu. Wykazano, że niezależnie od kształtu wydzieleń w węglikach wychodzących na powierzchnię stopu powstają bardzo duże naprężenia rozciągające, mogące prowadzić do ich pękania już w czasie pierwszych cykli nagrzewania i gwałtownego chłodzenia.

EN

In the paper the results of numerical analysis of tessellated stresses in carbides and surrounding them matrix in the stable austenitic Fe-Ni-Cr-C alloys are given. These stresses are arising in the rapid changes of temperature due to differences of thermal expansion of phases. The analysis was carried out for two variants of carbides placement in austenite. In the first case the carbide was wholly surrounded by austenite and in the second one it came out onto the alloy surface. It was pointed out, that independently to the shape of the precipitation in carbides entering the surface of the alloy the great tensile stresses are arising. They may cause fracture initiation in the uncovered carbides as early as in the first cycles of heating and rapid cooling.

5

Model termodynamiczny mikronaprężeń, dyfuzji i reakcji chemicznych w nasyconych ośrodkach porowatych

Burak J., Kubik J., Czapla E.

Zeszyty Naukowe Politechniki Białostockiej. Mechanika

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2001

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Z. 24

101--108

PL

W pracy zaproponowano kontynualne, termodynamiczne podejście do opisu fizyko-mechanicznych zjawisk oddziaływania agresywnych czynników środowiska zewnętrznego w warstwach powierzchniowych materiału porowatego (betonu) oraz zachodzących procesów dyfuzji i reakcji chemicznych. Beton rozpatruje się jako nasycony roztworem wodnym materiał porowaty. Przy opisie procesów w fazach wykorzystuje się koncepcje termodynamiki procesów nierównowagowych (teorii roztworów wieloskładnikowych), a dla otrzymania równań dla ciała w całości - metody uśrednienia przestrzennego teorii ośrodków wielofazowych.

EN

The thermodynamical approach has been proposed for description of physical and mechanical processes in subsurface layers of concrete through acting aggressive factors of the surroundings accompanying their diffusion and corresponding chemical reactions. Concrete is considered as two-phase porous material saturated by water solution. For the description of the phases the concept of thermodynamics of nonequilibrium processes (the theory of multicomponent solutions) is used, and methods of space averaging of the theory of multiphase media are applied for a description of whole body.