Vpliv z varjenjem dovedene toplote na lastnosti zvarnega spoja v TWIP jeklih

Švab, Nino (author), Zorc, Borut (mentor)

Cilj magistrske naloge je bil raziskati vpliv z varjenjem dovedene toplote na mehanske lastnosti in mikrostrukturo sočelnih zvarov pri TWIP (ang. Twinning Induced Plasticity) jeklih. Uporabili smo jekli debeline 2,5 mm različnih kemijskih sestav, ki smo jih varili z MAG (ang. Metal active gas) in TIG (ang. Tungsten inert gas) načinom. S spreminjanjem varilnih parametrov smo vplivali na količino dovedene toplote pri varjenju. V okviru eksperimentalnega dela smo opravili rentgensko analizo zvarov, preizkušanje zvarjencev z nateznim preizkusom, izmerili trdoto v sestavnih področjih zvara, določili velikost kristalnih zrn v toplotno vplivani coni (TVC) in širino TVC. Opravili smo tudi mikrostrukturno analizo izhodnega stanja jekel ter stanja po varjenju. Ugotovili smo, da dovedena toplota negativno vpliva na mehanske lastnosti, predvsem na napetost tečenja in trdoto. Dovedena toplota vpliva na rast kristalnih zrn v TVC in širino same TVC. Z analizo izhodnega mikrostrukturnega stanja obeh jekel smo prišli do ugotovitev, da je jeklo TWIP-Cr-Si nekoliko hladno utrjeno, jeklo TWIP-Al-Si pa v gašenem stanju. Pri varjenju materiala TWIP-Al-Si so v zvaru prisotne interdendritne razpoke ter izceje Si, P in Mn.

• Language: Slovenian
• Keywords: TWIP jekla, mehanske lastnosti, mikrostruktura, varjenje, dovedena toplota.
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2018
• PID: 20.500.12556/RUL-103706
• COBISS.SI-ID: 1751647
• Publication date in RUL: 23.09.2018

Secondary language

• Language: English
• Title: Influence of the welding heat input on the properties of the welds in TWIP steels

Abstract

The purpose of master's thesis was to determine the effect of heat input on the mechanical properties and microstructure of the butt welds in TWIP (Twinning Induced Plasticity) steels. Steel sheets of two TWIP steels with different chemical composition and thickness of 2,5 mm were used. GMAW (gas metal arc welding) and GTAW (gas tungsten arc welding) were used as welding techniques. Heat input was influenced by different welding parameters. In the experimental part following procedures were carried out on the welded material: tensile tests, hardness measuring, x-ray weld analysis, determination of grain size in HAZ (heat affected zone) and diameter of HAZ. Furthermore, microstructure analysis was made on initial and welded material. It was discovered that the increased heat input has negative effect on mechanical properties, especially on yield strength and hardness. Heat input also effects grain growth and growth of the HAZ. With microstructure analysis on the initial material it was discovered that steel TWIP-Cr-Si has cold worked microstructure and TWIP-Al-Si has quenched microstructure. After GTAW of TWIP-Cr-Si dendrites occured of Si, P and Mn carbides on boundaries. After welding of TWIP-Al-Si interdendritic cracks and segregation occured.

• Keywords: TWIP steels, mechanical properties, microstructure, welding, heat input.