Utjecaj brzine hlađenja na tvrdoću i žilavost mikrolegiranih čelika

doctoral thesis

• Title (english): Influence of cooling rate on hardness and toughness of micro alloyed steels
• Author: Marko Dunđer
• Mentor: Slobodan Kralj (mentor)
• Committee member: Vinko Ivušić (predsjednik povjerenstva)
• Committee member: Slobodan Kralj (član povjerenstva)
• Committee member: Nikša Krnić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2005-05-10, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering
• Universal decimal classification (UDC): 621 - Mechanical engineering. Nuclear technology. Machinery ; 669 - Metallurgy

Abstract

U radu se obrazlaže usporedba simulacije toplinskog ciklusa zavarivanja s realnim ciklusom zavarivanja. U teorijskom dijelu istraživanja u okviru ovog rada istražen je utjecaj temperaturnih polja na transformaciju mikrostrukture i na mehanička svojstva zavarenog spoja. U eksperimentalnom dijelu ispitivana je tvrdoća i udarna radnja loma na različitim položajima u zoni utjecaja topline unutar cjelovitog zavara. \Napravljena je fraktografska analiza karakterističnih prijeloma i ispitivanje na elektronskom scanning-mikroskopu koja se koristila za ocjenu karakterističnih prijeloma, odnosno ocjene da li se radi o interkristalnom, transkristalnom ili žilavom lomu. Pri ispitivanjima se koristio mikrolegirani čelik povišene čvrstoće TStE 420, a simulacija je provedena na simulatoru toplinskog ciklusa TCS 1405 SMITWELD. Provedena istraživanja su potvrdila polaznu hipotezu ovog rada - primjenom simulacije toplinskog ciklusa zavarivanja i odgovarajućim ispitivanjima na cikliranim uzorcima moguće je ubrzati i skratiti opseg trajanja aktivnosti kod izbora parametara zavarivanja. Također je utvrđeno da svako višeprolazno zavarivanje koje se prakticira u realnim zavarima ima niže vrijednosti tvrdoće i više vrijednosti udarne radnje loma u odnosu na simulirane uzorke. Na kraju su predloženi optimalni parametri pri MAGpostupku zavarivanja ovog čelika.

Abstract (english)

This paper explains comparison between welding thermal cycle simulation and real welding cycle. In the theoretical part of the investigations provided in this paper, the influence of temperature fields' distribution on transformation of microstructure and weld joint mechanical properties was investigated. In experimental part of this paper the investigations of hardness and toughness in different locations of heat-affected zone of complete welded joint were performed. The fractographic analysis on scanning microscope of specific broken specimens was used for fracture type evaluation to determine intergranular, transgranular or ductile fracture. The micro alloyed steel TStE 420 was used for experimental investigations and welding thermal cycle simulation was performed on thermal cycle simulator TCS 1405 SMITWELD. The investigations performed in this work confirmed start hypothesis of this work, i.e. by the application of thermal simulation of welding cycle it is possible to accelerate and shorten duration of activities at welding parameters selection. Beside that, it was determined that multipass welding which is often used in real welding had lower hardness and higher toughness values in relationship to simulated specimens. Finally, the optimal welding parameters for MAG welding of this steel were proposed.

• Keywords: mikrolegirani čelici povišene čvrstoće; temperaturna polja; vrijeme hlađenja ∆t8/5; brzina hlađenja w8/5; tvrdoća; udarna radnja loma
• Keywords (english): high strength micro alloyed steels; temperature fields; cooling time ∆t8/5; cooling rate w8/5; hardness; notch
• Language: croatian
• URN:NBN: urn:nbn:hr:235:604414
• Study programme: Title: Mechanical Engineering and Naval Architecture; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje tehničkih znanosti (doktor/doktorica znanosti, područje tehničkih znanosti)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2021-02-03 10:15:59