Karakterizacija zavarenog spoja dupleks nehrđajućeg čelika

undergraduate thesis

• Title (english): Characterization of the duplex stainless steel welded joint
• Author: Ivan Petrinšak
• Mentor: Vera Rede (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2022-03-02, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

U ovom radu provedena je karakterizacija zavarenog spoja cijevi od dupleks nehrđajućeg čelika oznake X2CrNiMoN 25-7-4. Analizirana je makrostruktura i mikrostruktura te mikrotvrdoća HV0,2 u osnovnom materijalu, zoni utjecaja topline i metalu zavara. U teorijskom dijelu rada opisana je sistematizacija i osnovna svojstva konstrukcijskih nehrđajućih čelika. Detaljno su opisani dupleks nehrđajući čelici, osobito njihova zavarljivost. Analizom makrostrukture utvrđeno je da je zavar pravilnog simetričnog oblika, bez vidljivih pukotina i drugih pogrešaka, s jasno izraženom linijom staljivanja. Mikrostruktura osnovnog materijala sastoji se od ferita i austenita u podjednakim udjelima. U zoni utjecaja topline narušena je pravilna dupleks struktura. Udio ferita viši je od 50 %, vide se krupna feritna zrna, a mjestimice u njima ima izlučenih kromovih nitrida. Također se vide zrna sekundarnog austenita. Metal zavara ima tipičnu ljevačku dendritnu mikrostrukturu s podjednakim udjelom ferita i austenita. Vrijednosti mikrotvrdoće HV0,2 zavarenog spoja dosta se razlikuju u osnovnom materijalu, ZUT-u i metalu zavara. Najmanje vrijednosti mikrotvrdoće izmjerene su u metalu zavara. Podjednake su u tjemenu, sredini i korijenu zavara i iznose od 245 do 272 HV0,2. Mikrotvrdoća u osnovnom materijalu podjednaka je u vanjskom rubu, sredini i unutarnjem rubu stijenke cijevi i iznosi između 311 i 321 HV0,2. Mikrotvrdoća osnovnog materijala viša je od mikrotvrdoće u tjemenu i sredini ZUT-a. Najviša mikrotvrdoća izmjerena je u zoni utjecaja topline, u korijenu zavara i iznosi 360 HV0,2.

Abstract (english)

In this study, the characterization of welded joint of grade X2CrNiMoN 25-7-4 duplex stainless steel pipe was performed. The macrostructure and microstructure as well as the microhardness HV0.2 in the base material, heat-affected zone, and weld metal were analyzed. In the theoretical part of the study, the systematization and basic properties of structural stainless steels were described. Duplex stainless steels were described in detail, especially their weldability. Analysis of the macrostructure determined that the weld is of the correct symmetrical shape, without visible cracks and other defects, with a clearly defined fusion line. Microstructure of the base material consists of ferrite and austenite in equal parts. In the heat-affected zone, the proper duplex structure is disrupted. The ferrite content is higher than 50 %, large ferrite grains can be seen, and chromium nitrides are excreted in some places. Grains of secondary austenite can also be seen. The weld metal has a typical as-cast dendritic microstructure with an almost equal ratio of ferrite and austenite. The HV0.2 microhardness values of the welded joint differ considerably in the base material, HAZ, and weld metal. The lowest values of microhardness were measured in the weld metal. They are almost the same in the face, middle, and root of the weld and range from 245 to 272 HV0.2. The microhardness in the base material is almost the same in the outer edge, middle and inner edge of the pipe wall and ranges between 311 and 321 HV0.2. The microhardness of the base material is higher than the microhardness at the face and middle of the HAZ. The highest microhardness was measured in the heat-affected zone, at the root of the weld and equals 360 HV0.2.

• Keywords: nehrđajući dupleks čelik; zavareni spoj; karakterizacija
• Keywords (english): stainless duplex steel; welded joint; characterization
• Language: croatian
• URN:NBN: urn:nbn:hr:235:201867
• Study programme: Title: Mechanical 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: Open access
• Created on: 2022-02-23 22:07:31