Primerjava mehanskih lastnosti sive litine s kroglastim grafitom ulite v različne forme : diplomsko delo

Košmerl, Luka (author), Petrič, Mitja (mentor)

Ohlajevalna hitrost ima velik vpliv na transformacijo avstenita v ferit in grafit ter perlit. Večje ohlajevalne hitrosti pripomorejo k večjemu deležu perlita v mikrostrukturi, zaradi katerega posledično dobimo višje mehanske lastnosti kot so Rm in Rp0,2 ter manjši raztezek A. Uporabili bomo 3 različne režime hlajenja vzorcev. Prvi je bil tak, da je Y proba ostala v formi do konca strjevanja, drugi, da je bila forma razformana 30 minut po ulitju taline in nato puščena na zraku ter tretji, ki smo ga razformali 30 minut po ulitju taline in nato prenesli, da je nadaljeval pot skupaj s serijskimi ulitki, kateri so bili kasneje tudi uporabljeni kot vzorci za meritve. Iz vseh teh tipov ter serijskih ulitkov smo nato pripravili vzorce za natezni preizkus. Ugotovili smo, da večje ohlajevalne hitrosti povzročijo večjo vsebnost perlita v mikrostrukturi, kateri posledično povzroči višje mehanske lastnosti ter manjši raztezek. Y probe, ki so bile v formi do konca strjevanja so imele mehanske lastnosti najbolj podobne ulitkom, medtem ko so bile najmanj podobne tiste, ki so bili po 30 min puščene na zraku. Y probe puščene na zraku so imele končno razmerje perlita in ferita 94,5 % in 5,5 %, medtem ko so imeli ulitki razmerje 39,46 % in 60,53 %. V mikrostrukturah je bilo največ prisotnih kroglastih grafitnih delcev tipa VI po standardu ISO 945-1 velikosti do 3 mm pri 100 × povečavi. Ugotovljeno je bilo, da imajo Y probe z največjo ohlajevalno hitrostjo najvišje mehanske lastnosti ter najmanjši raztezek, medtem ko so imele najpočasneje ohlajane Y probe ter serijski ulitki najnižje mehanske lastnosti ter hkrati največji raztezek, oboje v tolerancah standarda EN-GJS-500-7C, po katerem naj bi bili narejeni.

• Language: Slovenian
• Keywords: kroglasti grafit, ohlajevalna hitrost, mehanske lastnosti, perlit
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: [L. Košmerl]
• Year: 2021
• Number of pages: XII, 37 f.
• PID: 20.500.12556/RUL-131353
• UDC: 669
• COBISS.SI-ID: 83853059
• Publication date in RUL: 25.09.2021

KOŠMERL, Luka, 2021, Primerjava mehanskih lastnosti sive litine s kroglastim grafitom ulite v različne forme : diplomsko delo [online]. Bachelor’s thesis. Ljubljana : L. Košmerl. [Accessed 1 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=131353

Secondary language

• Language: English
• Title: Comparison of mechanical properties of ductile cast iron cast in different moulds : diploma work

Abstract

The cooling rate has a great influence on the transformation of austenite into ferrite and graphite and perlite. Higher cooling rates contribute to a higher proportion of perlite in the microstructure, which results in higher mechanical properties such as Rm and Rp0.2 and lower elongation A. We used 3 different cooling regimes of Y probes. The first was that the Y probe remained in sand form until it cooled to room temperature, the second, that the sand form was deformed 30 minutes after the melt was cast and then left to cool on the air, and the third that the form was deformed 30 minutes after the melt was cast and then transferred to continue the journey along with serial casts, which were later also used as samples for measurements. Samples for tensile testing were then prepared from all these types and serial casts. We found out that higher cooling rates result in higher perlite content in the microstructure, which in turn results in higher mechanical properties and lower elongation. Y probes that were in form until the end of solidification, had the most similar mechanical properties to serial casts, while those that were left to cool on the air after 30 min were the least similar. Y probes left to cool on the air had a final perlite to ferrite ratio of 94.5% and 5.5%, respectively, while casts had a ratio of 39.46% and 60.53%. In the microstructures, the most present were spheroidal graphite particles of type VI according to the ISO 945-1 standard, up to 3 mm in size at 100 × magnification. Y samples with the highest cooling rate were found to have the highest mechanical properties and the lowest elongation, while the slowest cooled Y probes and serial casts had the lowest mechanical properties and at the same time the maximum elongation, both within tolerances of EN-GJS-500-7C standard, according to which they are supposed to be made.

• Keywords: spheroidal graphite, cooling rate, mechanical properties, perlite