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Vpliv vsebnosti niklja na izotermno poboljšanje sive litine s kroglastim grafitom
ID Brence, Jan (Author), ID Mrvar, Primož (Mentor) More about this mentor... This link opens in a new window, ID Gogolin, Julius Alexander (Co-mentor)

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Abstract
Izotermno poboljšana siva litina s kroglastim grafitom (ang. austempered ductile iron oz. ADI) je nodularna litina, ki je podvržena posebni toplotni obdelavi z namenom dosega optimalne kombinacije trdnosti, duktilnosti in žilavosti. Predstavlja pomembno alternativo jeklu in aluminijevim zlitinam zaradi nižje gostote (7,2 g/cm3 proti 7,85 – 7,87 g/cm3 za jekla) in manjšim proizvodnim stroškom zaradi manjše porabe energije. Eden glavnih problemov v proizvodnji ADI je proces toplotne obdelave, posebej pri debelostenskih ulitkih. Notranji deli ulitka se namreč ohlajajo počasneje, zato lahko pred dosego temperature izotermnega poboljšanja nastane nehomogena mikrostruktura, sestavljena iz delov perlita in ferita v avstenitu. Nikelj je eden izmed legirnih elementov, ki je sposoben preložiti prehod transformacije ferita in/ali perlita proti daljšim časom in tako dati notranjim delom ulitka dovolj časa, da se ohladijo brez tvorbe nezaželenega perlita. Za preiskavo vpliva niklja na mikrostrukturo in mehanske lastnosti litine ADI, smo izdelali tri litine z različnimi vsebnostmi niklja. Poboljšanje smo izvajali pri različnih temperaturah z uporabo kalilnega dilatometra in solnih kopeli. Iz rezultatov smo določili točke faznih prehodov in izrisali TTT diagram. Analizirali smo mikrostrukturo in opravili termično analizo ter mehanske preizkuse.

Language:Slovenian
Keywords:ADI, nikelj, dilatometer, izotermno poboljšanje, TTT diagram
Work type:Bachelor thesis/paper (mb11)
Organization:NTF - Faculty of Natural Sciences and Engineering
Year:2019
COBISS.SI-ID:1845343 This link opens in a new window
Publication date in RUL:27.09.2019
Views:606
Downloads:221
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Secondary language

Language:English
Title:Effect of nickel content on isothermal improvement of gray cast iron with spherical graphite
Abstract:
Austempered ductile iron (ADI) refers to nodular cast iron, subjected to a special heat treatment process called austempering, to achieve an optimal combination of strength, ductility and toughness. It represents a strong competitor to steel and aluminium alloys due to its lower density (7,2 g/cm3 to 7,85-7,87 g/cm3 for steel), weight saving potential and lower production costs. One of the main problems in the production of ADI is the heat treatment process, especially in thick-walled castings. The inner parts cool down much slower than outer parts, which can result in a heterogenous microstructure, formed before reaching the isothermal temperature, consisting of parts of pearlite and ferrite fixed in austenite. To overcome this problem, nickel is added, which is one of the elements that is capable to postpone the transformation times of ferrite and/or pearlite, thus giving the inner parts of a casting sufficient time to cool down without the formation of unwanted pearlite. In order to investigate the influence of nickel on microstructure and mechanical properties of ADI, we made three melts with different nickel contents. Austempering was done at different temperatures using a quenching dilatometer and salt baths in order to determine the transformation points, from which we plotted the TTT diagram. Microstructure was also analysed and mechanical tests were made, followed by thermal analysis.

Keywords:ADI, nickel, dilatometer, heat-treatment, austempering

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