Wyniki wyszukiwania - Biblioteka Nauki

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Przykład obróbki cieplnej odlewów z żeliwa wysokochromowego

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Siekaniec D. , Szczęsny A. , Kopyciński D.

Archives of Foundry Engineering

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2015

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tom Vol. 15, iss. 4 spec.

109--112

PL

Żeliwo wysokochromowe jest powszechnie stosowanym materiałem w przemyśle górniczym i mineralnym, gdzie wymagana jest duża odporność na zużycie ścierne. Swoje dobre właściwości zawdzięcza obecności w mikrostrukturze twardych węglików. Żeliwo chromowe poddawane hartowaniu ma w praktyce osnowę austenityczną, austenityczno-perlityczną lub perlityczną. Istotnym procesem w czasie obróbki cieplnej jest tzw. destabilizacja austenitu, jest on ważny ponieważ dopiero po jego zajściu może nastąpić przemiana martenzytyczna. W zależności od szybkości chłodzenia, które następuje po procesie destabilizacji austenitu, może powstać perlit, bainit i martenzyt. Przeprowadzone badania dotyczyły określenia wpływu szybkości chłodzenia odlewów z żeliwa wysokochromowego po obróbce cieplnej, na mikrostrukturę i twardość. Badaniu zostało poddane żeliwo wysokochromowe o zawartości 27%Cr i 2,7%C. Przeprowadzono zabieg hartowania z temperatury 950 °C w czasie 4h, następnie odlewy poddano trzem wariantom chłodzenia – w wodzie, w kąpieli solnej i na powietrzu. Zbadano i porównano mikrostrukturę oraz twardość odlewów dla różnych wariantów chłodzenia.

EN

High Chromium Cast Iron (HCCI) is widely use in mining and mineral industry, where abrasive resistance is a principal requirement. Its good properties thanks to the hard eutectic carbides occurring in the microstructure. The effect of heat treatment on HCCI was a subject of many research. High Chromium Cast Iron have an austenitic, austenitic-pearlitic or pearlitic matrix. An important process during the heat treatment is austenite destabilization, thus until after it conduct the martensitic transformation can occur. Depending on the cooling rate that follows the process of destabilization of austenite, perlite, bainite and martensite may form. The present work, aimed at studying the influence of cooling rate after heat treatment, on the microstructure and hardness. The study were carry out on samples of High Chromium Cast Iron containing 27%Cr i 2,7%C. Samples were subjected to the tempering treatment at the temperature of 950°C for 4 hours and three variants of cooling – in water, in a salt bath and on air. Examined and compared the microstructure and hardness of castings for different variants of cooling.

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Effect of Silicon Addition on the Microstructure of Cast 24Cr-5Ni-2.5Mo-xSi Duplex Steel

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Kalandyk B. , Zapała R. , Witkowska M. , Kowalska J.

Archives of Foundry Engineering

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2018

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tom Vol. 18, iss. 1

186--190

EN

Characteristics of the microstructure of corrosion-resistant cast 24Cr-5Ni-2.5Mo duplex steel after introduction of 0.98, 1.67 and 4.3% Si were described. Based on the test results it has been found that silicon addition introduced to the corrosion-resistant cast two-phase duplex steel significantly reduces austenite content in the alloy matrix. Increasing silicon content in the test alloy to 4.3% has resulted, in addition to the elimination of austenite, also in the precipitation of Si-containing intermetallic phases at the grain boundaries and inside the grains. The precipitates were characterized by varying content of Cr and Mo, indicating the presence in the structure of more than one type of the brittle phase characteristic for this group of materials. The simulation using Thermo-Calc software has confirmed the presence of ferrite in all tested alloys. In the material containing 4.3% Si, the Cr and Si enriched precipitates, such as G phase and Cr3Si were additionally observed to occur.

3

Analiza porównawcza kształtek ceramicznych z celulozowymi wykorzystywanych do tworzenia układów wlewowych w odlewnictwie

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Zawieja Z. , Sawicki J. , Gumienny G.

Inżynieria Materiałowa

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2014

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tom Vol. 35, nr 5

434--437

PL

Rodzaj materiału z jakiego wykonuje się kształtki do tworzenia układów wlewowych ma kluczowy wpływ na proces zalewania ciekłym metalem oraz na jakość finalnego produktu jakim jest odlew. W pracy przedstawiono wyniki badań dotyczące wpływu materiału kształtki stosowanej do układów wlewowych na gradient temperatury ciekłego żeliwa oraz mikrostrukturę odlewu. Do badań wykorzystano cylindryczne kształtki wykonane z klasycznej masy ceramicznej oraz z tworzywa na bazie masy celulozowej. Ustalono, iż kształtki z masy celulozowej wytwarzają silny efekt egzotermiczny po ok. 150 sekundach od momentu zalania ciekłym żeliwem. Wynikiem efektu egzotermicznego z zastosowaniem kształtki celulozowej jest dłuższy czas istnienia żeliwa w stanie ciekłym, co opóźnia inicjację krystalizacji eutektyki w porównaniu z kształtką ceramiczną. Wydłużenie przemiany eutektycznej w przypadku zastosowania kształtek celulozowych prowadzi to stabilniejszego procesu krystalizacji, w wyniku czego dominuje równowagowa mikrostruktura perlityczna z wydzieleniami grafitu oraz węglików, a zastosowanie kształtki ceramicznej prowadzi do tworzenia mikrostruktury ausferrytu również z wydzieleniami grafitu oraz węglików.

EN

Liquid metal casting process and the final casting product quality is highly depending on the kind of material used for tube fittings manufacturing in order to create the feeding channels. The following study presents the influence of type of the material used for feeding channels on the temperature gradient of the liquid iron as well on the microstructure of the iron casting. Ceramic classic and cellulose based fittings both cylindrical tube shaped have been used for the investigation. 150 seconds after pouring liquid iron the cellulose based tube fittings are generating very high exothermic effect. Compared to the ceramic fitting the cellulose tube, due to such an exothermic phenomena, keeps the iron as a liquid in longer period and it is providing consequently later the eutectic crystallization. Longer eutectic crystallization reaction leads to more steady process therefore perlit equilibrium phase including graphite and carbides microstructure is dominating when cellulose based fitting are in use. Ausferrite including graphite and carbides is more observed when ceramic tube fittings for iron processing are taken.

4

Influence of the heat treatment on the microstructure and properties of austenitic cast steel

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Bała P. , Krawczyk J. , Pawłowski B.

Archives of Foundry Engineering

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2010

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tom Vol. 10, iss. 3

35--38

EN

Exploitation investigations of a centrifugally cast pipe of austenitic cast steel indicated a significant influence of its microstructure on functional properties. Determination of the possibility of forming the microstructure and properties of the investigated cast steel by heat treatments was the aim of the presented paper. According to the Standard ASTM A 297, material from which the pipe was made is determined as HF type cast steel. The solution heat treatment from a temperature of 1080 °C was performed and followed by the microstructure observations and hardness measurements. It was found, that the solution heat treatment from this temperature will not significantly improve the material strength properties. However, it will visibly influence its fracture toughness. An influence of aging performed after the solution heat treatment on microstructure and hardness was also investigated. Cast steel was aged for 1 hour at 600 °C (solution heat treatment from 1080 °C). On the basis of the obtained results it was found, that the solution heat treatment temperature should be the maximum permissible by the Standard i.e. 1150 °C. Heating the supersaturated material (from 1150 °C) even to a temperature of 600°C should not cause the carbide precipitation in a form of the continuous network in grain boundaries, which would decrease fracture toughness of the investigated cast steel. Due to fracture toughness a service exposure of this material should not exceed 600 °C. The permissible service exposure up to 900 °C, given for this material in the Standard, is correct only on account of heat and high temperature creep resistance but not fracture toughness.

5

Flow Effect on Si Crystals and Mn-Phases in Hypereutectic and Eutectic Al-Si-Mn Alloys

80%

Mikołajczak P.

Archives of Foundry Engineering

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2023

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tom Vol. 23, iss. 4

72--86

EN

During mold filling and casting solidification, melt flow caused by gravity is present. Otherwise, forced flow may be a method applied for casting properties improvement. The flow effect generated by an electromagnetic field on the growing phases and a whole microstructure in Al-Si-Mn alloys was studied by slow solidification conditions. The hypereutectic and eutectic alloys were chosen to allow independent growth or joint growth of forming: Si crystals, Mn-rich α-Al15Si2Mn4 phases and Al-Si eutectics. In eutectic alloys, where Mn-phases precipitate as first and only one till solidus temperature, flow decreased number density of pre-eutectic α-Al15Si2Mn4. In the hypereutectic alloys, where Mn-phases grow in common with Si crystals, forced convection increased the overall dimension, decreased number density of pre-eutectic Mn phases and strengthened the tendency to growth in the outside of the sample. In the alloys, where Si crystals grow as first, stirring reduce number density of Si and moved them into thin layer outside cylindrical sample. Also by joint growth of Si crystals and Mn-phases, in hypereutectic Mn/Si alloy, flow moved Si crystals outside, reduced number density and increased the dimension of crystals. Stirring changed also AlSi eutectic spacing, specific surface Sv of α-Al and secondary dendrite arm spacing λ2. The results gave insight of what transformation under stirring take place in simple Al-Si-Mn alloys, and helps to understand what modifications in technical alloys may occur, that finally lead to changes in castings microstructure and properties. The possibility to control dimension, number density and position of Mn-phases and Si crystals is completely new and may help by metallurgical processes, continuous casting of billets and in the production of Si for the solar photovoltaic industry.