Zaostale napetosti v prekrovnih laserskih zvarnih spojih

Hostnik, Miha (author), Klobčar, Damjan (mentor), Trdan, Uroš (comentor)

Nerjavna jekla in visokotemperaturne superzlitine so zaradi dobrih mehanskih in protikorozijskih lastnosti v uporabi tudi za izdelke v agresivnih okoljih ter povišanih temperaturah. Pogosto se v praktičnih aplikacijah pojavlja potreba po spajanju teh raznorodnih materialov, kar predstavlja velike izzive. Med glavne izzive spada pojav zaostalih napetosti in pokanje varov v vročem. V zaključni nalogi smo analizirali vzdolžne in prečne zaostale napetosti v zvarnih spojih nikljeve superzlitine Inconel 602 (EN 2.4633) in izločevalno utrjevalnega martenzitnega nerjavnega jekla S17400 v stanju H1150M. Prekrovni zvarni spoji cevi iz nikljeve zlitine in jeklene tankostenske cevi so bili izdelani s postopkom kontinuirnega laserskega varjenja z diskastim laserjem ob uporabi treh različnih varilnih parametrov. Za primerjavo smo izmerili tudi zaostale napetosti na osnovni/nenavarjeni, nenatisnjeni cevki in na nenavarjeni cevki natisnjeni na cev. Na vsakem vzorcu so bile, s postopkom rentgenske difrakcije, opravljene meritve na dveh merilnih mestih v vzdolžni in prečni smeri glede na var. Na vidno razpokanih varih smo s pomočjo makroskopa izmerili dolžine razpok ter z makrostrukturnimi analizami v prečnem preseku preučili značilnosti razpok. Ugotovili smo, da obstaja povezava med dolžino razpok in varilnimi pogoji in da so razpoke prisotne tudi pod površino z značilnim pokanjem le po sredini zvarnega spoja.

• Language: Slovenian
• Keywords: lasersko varjenje, zaostale napetosti, razpoke v vročem, rentgenska difrakcija
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FS - Faculty of Mechanical Engineering
• Place of publishing: Ljubljana
• Publisher: [M. Hostnik]
• Year: 2019
• Number of pages: 50 str.
• PID: 20.500.12556/RUL-106795
• UDC: 621.791.725:620.18(043.2)
• COBISS.SI-ID: 16527643
• Publication date in RUL: 18.03.2019

Secondary language

• Language: English
• Title: Residual stresses in overlap laser welds

Abstract

Stainless steels and high-temperature superalloys are commonly used in aggressive thermal conditions because of their good mechanical and anti-corrosive properties. In practical applications it is often required to join these dissimilar materials, which is usually very challenging. The main challenges are residual stresses and hot cracking of the welds. In this work we analysed longitudinal and transversal residual stresses in welded joints of nickel superalloy Inconel 602 (EN 2.4633) and precipitation-hardened martensitic stainless steel S17400 in condition H1150M. Nickel alloy tubes and steel tubes were continuously laser welded using disk laser with three different sets of parameters in overlapping joint configuration. For comparison we also measured residual stresses on a basic/non-welded tube and on a non-welded tube pressed on another tube. On each sample we measured longitudinal and transversal residual stresses with X-ray diffraction on two places of each sample. On visibly cracked samples we measured the lengths of the cracks with a macroscope and analysed crack characteristics on the sections of the samples. We made some macrographs to confirm presence of cracks under the surface of the weld. We concluded that there is a link between crack lengths and welding conditions and that cracks are also present under the surface with the characteristic cracking only in the centre of the welds.

• Keywords: laser welding, residual stresses, hot cracking, x-ray diffraction