Analiza mikrostrukture i svojstava zavarenog spoja čelika Hardox 450

master's thesis

• Title (english): Analysis of the microstructure and properties of the Hardox 450 steel welded joint
• Author: Davor Marić
• Mentor: Vera Rede (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2022-12-15, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Cilj ovog rada bio je karakterizacija zavarenog spoja čelika otpornog na trošenje oznake Hardox 450. U teorijskom dijelu rada opisana su svojstva konstrukcijskih čelika poboljšane otpornosti na trošenje te njihovo ponašanje u eksploataciji. Detaljno je opisano zavarivanje Hardox čelika i naknadna toplinska obrada zavarenih spojeva. U eksperimentalnom dijelu rada prikazani su rezultati analize kemijskog sastava, mikrostrukturne analize i ispitivanja mehaničkih svojstava. Analizirani čelik Hardox 450 sadrži oko 0,2 % ugljika i ima relativno sitnozrnatu martenzitnu mikrostrukturu. Zbog velikog unosa topline pri zavarivanju, u zoni utjecaja topline zavarenog spoja, narušena je osnovna mikrostruktura i došlo je do pogrubljenja zrna. Linija staljivanja jasno je izražena, a metal zavara ima tipičnu ljevačku dendritnu mikrostrukturu. U odnosu na mikrotvrdoću osnovnog materijala koja je oko 430 HV0,2, tvrdoća u ZUT-u je niža i iznosi približno 250 HV0,2, a najniža tvrdoća izmjerena je u metalu zavara oko 210 HV0,2. U istim područjima izmjerene su nešto niže vrijednosti tvrdoće HV10. Vlačna čvrstoća zavarenog spoja znatno je niža od čvrstoće osnovnog materijala. Kod savojnog ispitivanja nije došlo do pojave pukotina na ispitnim uzorcima pri kutu savijanja od 180°. Pri ispitivanju udarnog rada loma, zona utjecaja topline imala je veću žilavost od metala zavara.

Abstract (english)

The aim of this master thesis was to perform the characterization of the welded joint of wear resistant steel grade Hardox 450. The properties of structural steels with improved wear resistance and their behaviour in exploitation were described in the theoretical part of the thesis. The welding of Hardox steels and the subsequent heat treatment of welded joints are described in detail. The results of the analysis of the chemical composition, microstructural analysis and testing of the mechanical properties are presented in the experimental part of the thesis. The analysed Hardox 450 steel contains about 0.2 % carbon and has a relatively fine-grained martensitic microstructure. Due to the high heat input during welding, in the heat-affected zone of the welded joint, the basic microstructure was disturbed, and the grain coarsening occurred. The fusion line is clearly defined, and the weld metal has a typical casting dendritic microstructure. Compared to the microhardness of the base material, which is around 430 HV0.2, the hardness in HAZ is lower and is approximately 250 HV0.2, while the lowest hardness is measured in the weld metal, around 210 HV0.2. Slightly lower HV10 hardness values were measured in the same areas. The tensile strength of the welded joint is significantly lower than the strength of the base material. During the bending test, no cracks appeared on the test samples at a bending angle of 180°. While testing fracture toughness, the heat affected zone had higher toughness than the weld metal.

• Keywords: Hardox čelik; zavareni spoj; mikrostruktura; mehanička svojstva
• Keywords (english): Hardox steel; welded joint; microstructure; mechanical properties
• Language: croatian
• URN:NBN: urn:nbn:hr:235:865285
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2022-11-30 12:32:06