Utjecaj zaštitnoga plina i načina prijenosa metala na svojstva zavarenoga spoja čelika X80

Jurica, Maja (2015) Utjecaj zaštitnoga plina i načina prijenosa metala na svojstva zavarenoga spoja čelika X80. = Influence of the shielding gas and metal transfer on the X80 weld joint properties. Doctoral thesis , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Kožuh, Zoran.

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Abstract (Croatian)

U ovom doktorskom radu obrađena je i analizirana problematika utjecaja zaštitnog plina i novorazvijenog načina prijenosa metala (eng. CBT – Controlled Bridge Transfer) na svojstva zavarenog spoja visokočvrstog čelika API 5L X80. U uvodnom dijelu rada iznesen je pregled dosadašnjih spoznaja i istraživanja na području proizvodnje TMCP (eng. Thermo Mechanical Controlled Process) čelika, MAG zavarivanja visokočvrstih čelika (eng. Metal Active Gas) s posebnim naglaskom na CBT način prijenosa metala te utjecaja zaštitnih plinova na mikrostrukturu zavarenog spoja. Također su postavljene hipoteze i definirani ciljevi rada. U eksperimentalnom dijelu rada opisan je plan provedbe zavarivanja, ispitivanja i analize rezultata. Zavarivanje uzoraka u eksperimentalnom dijelu rada izvedeno je prema plošno centriranom centralno kompozitnom planu pokusa (eng. CCF – Face Centered Composite Design), te je prema tome definirano 22 stanja pokusa, s 3 ponavljanja u centru. Prema planu pokusa definirane su 3 varijable koje su bile varirane na 2 i 3 razine. Od spomenute 3 varijable, dvije su numeričke (brzina dodavanja žice, m/min i udio CO2 u zaštitnom plinu, %) i jedna je kategorijska (način prijenosa metala). Za svako stanje pokusa su iz sučeljeno zavarenih ploča izrađeni uzorci za kemijsku i mikrostrukturnu analizu. Karakterizacijom su definirani kemijski sastavi zavarenih spojeva, uključci u zavarenim spojevima i osnovni materijal, mikrostrukturni sastav tj. udio konstituenata u zavarenim spojevima kao i mikrotvrdoće pojedinih prolaza i faza. Cijeli eksperimentalni dio rada proveden je u Laboratoriju za zavarivanje, Laboratoriju za tribologiju, Laboratoriju za analizu materijala i Laboratoriju za materijalografiju na Fakultetu strojarstva i brodogradnje, Sveučilište u Zagrebu. Dobiveni rezultati i podaci o kemijskom i mikrostrukturnom sastavu zavarenog spoja statistički su analizirani pomoću programskog paketa Design Expert. Izrađeni su matematički modeli iz kojih je vidljiva značajnost utjecaja variranih faktora i njihovih interakcija na ispitivana svojstva zavarenog spoja. Također su Monte Carlo simulacijom procijenjeni utjecaji varijacija ulaznih veličina na kvalitetu rezultata mjerenja kemijskog sastava i analize mikrostrukture zavarenog spoja.

Abstract

This doctoral thesis focuses on the influence of the shielding gas and newly developed metal transfer mode (CBT – Controlled Bridge Transfer) on the HSLA API 5L X80 weld characteristic. The introduction includes detailed literature overview on the subject of the TMCP steel production, MAG welding process (with emphasis on the newly developed CBT welding process) and effect of the shielding gas on the welded joint characteristics. Goals and hypothesis are also defined in the introductory part of the thesis. Experimental part of thesis specifies the complete welding procedure of the workpieces, conduction of the samples testing and finally the analysis of the obtained results. The entire welding was conducted according to the central composite experiment design, face centered (CCF), which resulted in 22 runs with 3 replicates in the center. The design consisted of 3 factors varied over 2 and 3 levels. Out of the 3 varied factors, 2 of them are numeric (wire feed speed, m/min and CO2 content in the shielding gas, %) and the third one (metal transfer mode) is categorical. For each run from the experiment design a sample from the butt welded joints were prepared in order to conduct chemical and microstructural characterization. Analysis of the chemical characterisation provided information on the exact chemical composition of the weld metal, heat affected zone and base metal as well as of inclusions. Also, microstructure of the welded joint was analysed in order to get information of the portion of different constituents. In the end micro hardness of the each individual phase and weld pass was measured. Entire experimental work was conducted in Laboratories of the Faculty of mechanical engineering and naval architecture, University of Zagreb. All of the gathered data on the chemical and microstructural composition of the weld metal were statistically analyzed with the Design Expert software program. As of the result of the analysis, mathematical models were defined from which the influences of the varied parameters were defined and their interactions on the weld metal characteristics were observed. Also, Monte Carlo Simulation was used in order to estimate the influence of the input values variations on the properties of the microstructural and chemical analysis results.

Item Type: Thesis (Doctoral thesis)
Uncontrolled Keywords: TMCP čelici; X80; CBT MAG zavarivanje; acikularni ferit; uključci
Keywords (Croatian): TMCP steel; X80; CBT MAG welding; acicular ferrite; inclusions
Subjects: TECHNICAL SCIENCE > Mechanical Engineering
Divisions: 1100 Department of Welded Structures > 1110 Chair of Welded Structures
Date Deposited: 07 Mar 2016 13:07
Last Modified: 07 Mar 2016 13:07
URI: http://repozitorij.fsb.hr/id/eprint/5201

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