Razvoj nekovinskih vključkov pri izdelavi jekla PK346 : magistrsko delo

Božank, Jure (author), Medved, Jože (mentor), Balaško, Tilen (co-mentor), Šuler, Blaž (co-mentor)

Magistrsko delo z naslovom “Razvoj nekovinskih vključkov pri izdelavi jekla PK346” je bilo izvedeno z namenom pregleda nekovinskih vključkov, ki so bili prisotni po oksidaciji v EOP (elektroobločna peč), redukciji žlindre v EOP, po prebodu, po legiranju na VOD (angl. Vacuum Oxygen Decarburization), po oksidaciji na VOD, po degazaciji na VOD, pred dodatkom CaSi, 5 min po dodatku CaSi, 10 min po dodatku CaSi, v koreniki (tehnološki odpad livnega sistema), po mehanski obdelavi in po EPŽ (elektropretaljevanje pod žlindro). S termodinamičnimi izračuni s programskim orodjem Thermo-Calc se je simulirala tudi procesna pot (VOD). Nekovinski vključki so bili analizirani z mikroskopom SEM (angl. Scanning Electron Microscope) s pomočjo EDS (angl. Energy-dispersive X-ray Spectroscopy) analize. Pri procesih na EOP in vse do konca oksidacije na vakuumski postaji so bili najpogostejši MnS in Cr2O3. Po degazaciji na vakuumski postaji so bili najpogostejši nekovinski vključki iz sistema Al2O3-SiO2-CaO. Po dodatku CaSi je modificiranih vedno več nekovinsikh vključkov in 10 min po dodatku CaSi je v jekleni talini prisotnih največ Al2O3•CaO. Za povečano obdelovalnost jekla se doda žica S, zaradi česar zavzamejo največji delež vključki Al2O3+MnS, pogosti pa so tudi nekovinski vključki iz sistema Al2O3-SiO2-CaO, ki so vsebovali fazo CaS. V šaržo 1 se CaSi in S nista dodala, zato so nekovinski vključki v koreniki in po mehanski obdelavi ter EPŽ nemodificirani Al2O3. Na optičnem mikroskopu se je ocenila čistost jekla po standardu DIN 50602, in sicer po standardni metodi K. Najslabšo oceno je imel vzorec po redukciji žlindre v EOP, ki se je skozi proces izdelave jekla izboljševala. S primerjavo šarž 2, 3, 4 in EPŽ šarže 1 smo ugotovili, da je EPŽ vzorec čistejši, vendar vsebuje trdne nemodificirane Al2O3 vključke, medtem ko drugi vzorci vsebujejo nekovinske vključke iz sistema Al2O3-SiO2-CaO, ki so globulitne oblike in MnS. S primerjavo žlindre in nastalih faz v jeklu smo se osredotočili na Cr in smo primerjali delež Cr2O3 v žlindri in vse nastale faze v jeklu, ki vsebujejo Cr. Ugotovili smo, da je največji delež nekovinskih vklljučkov z vsebnostjo Cr po oksidaciji, kjer je tudi delež Cr2O3 v žlindri največji, ko žlindra ne vsebuje več Cr2O3, pa se Cr oksidi v jeklu ne pojavljajo več. S termodinamičnimi izračuni s programskim orodjem Thermo-Calc smo simulirali procesno pot izdelave jekla (VOD).

• Language: Slovenian
• Keywords: jeklo PK346, nekovinski vključki, termodinamičnimi izračuni, delež nekovinskih vključkov
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: J. Božank
• Year: 2023
• Number of pages: XVIII, 67 f.
• PID: 20.500.12556/RUL-150800
• UDC: 669
• COBISS.SI-ID: 168070403
• Publication date in RUL: 23.09.2023

Secondary language

• Language: English
• Title: Development of non-metallic inclusions in production of PK346 steel : master's thesis

Abstract

The master thesis on the development of non-metallic inclusions in production of PK346 steel was prepared with the aim of investigating non-metallic inclusions occurring after oxidation at EAF (Electric Arc Furnace), slag reduction at EAF, tapping into the ladle, after alloying at VOD (Vacuum Oxygen Decarburization), after degassing at VOD, before addition of CaSi wire, 5 min after addition of CaSi wire, 10 min after addition of CaSi wire, in samples of the residue in the casting system and after mechanical processing and after electroslag remelting (ESR). The process path (VOD) was simulated with thermodynamic calculations using the Thermo-Calc software. Non-metallic inclusions were analysed with a SEM microscope (Scanning Electron Microscope), equipped with an EDS detector (Energy-dispersive X-ray Spectroscopy). After oxidation in the EAF and until the end of oxidation in the vacuum station, MnS and Cr2O3 were the most common. After degassing, the most common non-metallic inclusions were from the Al2O3-SiO2-CaO system. After the addition of CaSi wire, more and more non-metallic inclusions were modified. 10 min, after the addition of CaSi wire, the Al2O3•CaO were most common. To improve the machinability of steel the S-wire is shot into the molten steel, making the Al2O3+MnS most common and inclusions from the Al2O3-SiO2-CaO system, where the CaS phase occur. In batch 1, no CaSi and no S-wire were added, so that the non-metallic inclusions in the remains of the casting system and the ESR consistent predominantly of Al2O3. The purity of the PK346 steel was determined using the DIN 50602 standard method K under the optical microscope. The worst K1 grade was found in a sample taken after slag reduction at EAF, but the grade improved during the process. The best grade was in a sample taken 10 minutes after the addition of CaSi wire. Comparing batches 2, 3, 4 and ESR batch 1, we found that the ESR sample was cleaner but contained unmodified Al2O3, while the other samples had non-metallic inclusions MnS and non-metallic inclusions from the Al2O3-SiO2-CaO system, which were in liquid globulite form. When comparing the slag and the phases formed, we focused on the Cr phases. We found that the highest proportion of non-metallic inclusions containing Cr occurs after oxidation, where the proportion of Cr2O3 in the slag is highest. When the slag no longer contains Cr2O3, no Cr oxides are present in the steel.

• Keywords: Steel PK346, non-metallic inclusions, thermodynamic calculations, content of non-metallic inclusions