Utjecaj dodatnog materijala na pojavu pukotina pri MAG zavarivanju konstrukcijskog i visokolegiranog austenitnog čelika

undergraduate thesis

• Title (english): Influence of the filler material on crack appearance during MAG welding of structural and high alloyed austenitic steel
• Author: Bruno Belačić
• Mentor: Ivica Garašić (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2024-12-05, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; Production Mechanical Engineering

Abstract

Zavarivanje konstrukcijskih i austenitnih nehrđajućih čelika često se primjenjuje prilikom proizvodnje konstrukcija s ciljem smanjenja troškova, a zadržavanja antikorozivnih svojstava ili osiguravanja nemagnetičnosti dijelova konstrukcije. Zavarivanje takve kombinacije predstavlja brojne izazove zbog nepravilnosti koje se mogu pojaviti poput toplih pukotina, korozijskih pukotina uzrokovanih interkristalnom ili napetosnom korozijom, pojave martenzita na granici staljivanja, bandinga i makrosegregacije. Nečistoće poput sumpora i fosfora u dodatnom i osnovnom materijalu glavni su utjecajni faktor na podložnost nastanka toplih pukotina u materijalu zavara zbog niske topivosti tih elemenata u austenitu. Nizak stupanj miješanja dodatni je faktor koji treba osigurati tijekom zavarivanja raznorodnih čelika kako bi se smanjio prijelazni sloj između materijala i tako spriječilo smanjenje korozijske postojanosti i pojavu nepoželjnog martenzita. Zavarivanje konstrukcijskog i austenitnog čelika najčešće se provodi MAG postupkom zavarivanja s dodatnim materijalom austenitne mikrostrukture i zaštitnim plinom visokog udjela Ar i malog udjela CO2 ili O2. U eksperimentalnom dijelu rada ispitan je utjecaj 3 vrste dodatnog materijala (ESAB ER309LSi, Oerlikon ER309LSi i ER307) na nastanak pukotina i nepravilnosti u 3 kombinacije spojeva konstrukcijskih i austenitnih nehrđajućih čelika: S355J2+N zavaren za X2CrNi18-9, X5CrNi18-10 i X6CrNiMoTi17-12-2. Zavarivanje je provedeno na robotskoj stanici uz konstantne parametre kako bi se eliminiralo što više utjecajnih parametara na kvalitetu zavarenih spojeva. Mjerenjem feritnog broja zavara te makrostrukturnom i mikrostrukturnom analizom ispitnih uzoraka zaključeno je da bi sve tri vrste dodatnog materijala uz daljnju optimizaciju parametara bile pogodne za postizanje kvalitetnog zavarenog spoja. Makrostrukturnom i mikrostrukturnom analizom nisu uočene značajne greške i nepravilnosti u metalu zavarenog spoja, ali su primijećene pukotine i nepravilnosti na liniji staljivanja osnovnih materijala iza korijena zavara što je posljedica nepravilne tehnologičnosti spoja.

Abstract (english)

Welding of structural and austenitic stainless steels is commonly used in the production of structures to reduce costs while maintaining corrosion resistance or ensuring the non-magnetic properties of certain parts. Welding of dissimilar steels is often challenging due to various difficulties that may arise, such as hot cracks, corrosion cracks caused by intergranular or stress corrosion, the formation of martensite at the fusion boundary, banding, and macrosegregation. Impurities like sulphur and phosphorus in the filler and base materials are the main influencing factors on the susceptibility to hot cracks in the weld metal due to their low solubility in austenite. A low degree of mixing is another factor that must be ensured during dissimilar welding to reduce the transition zone between materials and thus prevent a decrease in corrosion resistance and the appearance of unwanted martensite. For welding of structural and austenitic steels, MAG welding process is most commonly used with austenitic filler materials and a shielding gas mixture with a high proportion of argon and a small amount of CO2 or O2. In the experimental part of the study, the influence of three types of filler materials (ESAB ER309LSi, Oerlikon ER309LSi and ER307) on crack formation and defects were tested in three combinations of joints between structural and austenitic stainless steels: S355J2+N welded to X2CrNi18-9, X5CrNi18-10, and X6CrNiMoTi17-12-2. Welding was performed on a robotic station with constant parameters to eliminate as many influencing factors on the quality of the welded joints as possible. By measuring the ferrite number of the welds and performing macrostructural and microstructural analyses of the test samples, it was concluded that all three types of filler materials, with further parameter optimization, would be suitable for achieving high-quality welded joints. No significant defects or irregularities were observed in the weld metal through macro and microstructural analysis, but some issues were detected at the fusion line of the base materials behind the root of the weld. These issues can be attributed to improper joint design.

• Keywords: Zavarivanje raznorodnih čelika; austenitni nehrđajući čelik; ER309LSi; ER307
• Keywords (english): Welding of dissimilar steels; austenitic stainless steel; ER309LSi; ER307
• Language: croatian
• URN:NBN: urn:nbn:hr:235:970804
• Study programme: Title: Mechanical Engineering; specializations in: Design, Process and Energy Engineering, Production Engineering, Engineering Modelling and Computer Simulation, Marine Engineering, Industrial Engineering and Management, Materials Engineering; Course: Production Engineering; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka strojarstva (sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2026-12-05
• Created on: 2024-12-02 18:59:57