Vpliv bazičnosti AOD žlindre na čistost nerjavnega jekla AISI 304L

Pašić, Armin (author), Knap, Matjaž (mentor), Bradaškja, Boštjan (comentor), Burja, Jaka (comentor)

Čistost nerjavnega jekla pomembno vpliva na njegovo livnost ter na površinsko kakovost in uporabne lastnosti končnih izdelkov. Pri izdelavi jekla AISI 304L imajo pomembno vlogo nekovinski vključki, katerih število, velikost in kemijska sestava so odvisni od procesnih pogojev, sestave žlindre ter ravnanja z njo med posameznimi fazami izdelave. V magistrskem delu je bil raziskan vpliv bazičnosti žlindre med postopkom argon-kisikovega razogljičenja (angl. Argon Oxygen Decarburization, AOD) na čistost nerjavnega jekla AISI 304L. Primerjana sta bila dva tehnološka postopka. Pri prvem postopku je bila uporabljena žlindra AOD z nižjo bazičnostjo 1,2, ki je bila po končani AOD-obdelavi popolnoma odstranjena. V ponovčni peči je bila nato oblikovana nova kalcijevo-aluminatna rafinacijska žlindra. Pri drugem postopku je bila uporabljena standardna AOD-žlindra z bazičnostjo 1,5, pri čemer je bil del žlindre prenesen v ponovčno peč. V industrijskih razmerah jeklarne SIJ Acroni je bilo izdelanih šest šarž, po tri za vsak postopek. Na vzorcih jekla in žlindre so bile izvedene kemijske analize, določena je bila vsebnost skupnega kisika, izračunane pa so bile vrednosti bazičnosti, optične bazičnosti, sulfidne kapacitete in porazdelitvenega razmerja žvepla. Čistost jekla je bila ovrednotena z avtomatsko analizo nekovinskih vključkov. Rezultati so pokazali, da je standardna AOD-žlindra ugodneje vplivala na čistost taline po obdelavi v AOD-konvertorju in na učinkovitost razžveplanja. Kljub temu sta se pri postopku z nižjo bazičnostjo med nadaljnjo obdelavo v ponovčni peči učinkovito zmanjšala število nekovinskih vključkov in vsebnost skupnega kisika. Končna vsebnost skupnega kisika je pri postopku z nižjo bazičnostjo znašala 45 ppm, pri standardnem postopku pa 54 ppm. Rezultati kažejo, da na končno čistost jekla AISI 304L poleg bazičnosti AOD-žlindre pomembno vpliva tudi ravnanje z žlindro skozi celotno tehnološko pot.

• Language: Slovenian
• Keywords: AISI 304L, AOD, bazičnost žlindre, sulfidna kapaciteta, nekovinski vključki, čistost jekla
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2026
• Publication date in RUL: 13.11.2026

Secondary language

• Language: English
• Title: Influence of AOD slag basicity on cleanliness of AISI 304L stainless steel

Abstract

Stainless steel cleanliness significantly affects its castability as well as the surface quality and service properties of the final products. In the production of AISI 304L stainless steel, non-metallic inclusions play an important role. Their number, size and chemical composition depend on the process conditions, slag composition and slag-handling practices during the individual stages of production. This master’s thesis investigated the influence of slag basicity during argon oxygen decarburisation (AOD) on the cleanliness of AISI 304L stainless steel. Two process routes were compared. In the first route, AOD slag with a lower basicity of 1.2 was used and completely removed after completion of the AOD treatment. A new calcium aluminate refining slag was subsequently formed in the ladle furnace. In the second route, standard AOD slag with a basicity of 1.5 was used, with part of the slag being transferred to the ladle furnace. Six heats were produced under industrial conditions at the SIJ Acroni steelworks, three using each process route. Chemical analyses were performed on the steel and slag samples, the total oxygen content was determined, and the basicity, optical basicity, sulphide capacity and sulphur distribution ratio were calculated. Steel cleanliness was evaluated by automated analysis of non-metallic inclusions. The results showed that the standard AOD slag had a more favourable effect on melt cleanliness after treatment in the AOD converter and on desulphurisation efficiency. Nevertheless, during subsequent treatment in the ladle furnace, the process route employing the lower-basicity slag effectively reduced both the number of non-metallic inclusions and the total oxygen content. The final total oxygen content was 45 ppm for the lower-basicity process route and 54 ppm for the standard process route. The results indicate that the final cleanliness of AISI 304L stainless steel is influenced not only by the basicity of the AOD slag but also by slag-handling practices throughout the entire process route.

• Keywords: AISI 304L, AOD, slag basicity, sulphide capacity, non-metallic inclusions, steel cleanliness