Grain interaction in local plastic deformation of welded structural steel - Influence of length scale on sub-grain deformation behaviour for polycrystalline BCC material

Pauli Lehto

Grain interaction in local plastic deformation of welded structural steel - Influence of length scale on sub-grain deformation behaviour for polycrystalline BCC material

Julkaisun otsikon käännös: Kiteiden välinen vuorovaikutus hitsatun rakenneteräksen paikallisessa deformaatiossa

Pauli Lehto

Energia- ja konetekniikan laitos

Tutkimustuotos: Doctoral Thesis › Monograph

Abstrakti

Rakenneteräkset ovat yleisimmin käytetty materiaali kuljetusvälineteollisuudessa. Jotta perusmateriaalin ominaisuuksia voidaan hyödyntää parhaalla mahdollisella tavalla hitsatuissa rakenteissa kuten laivoissa, tarvitaan syvällistä tietoa materiaalin käyttäytymisestä. Tämä väitöskirja tutkii monikiteisiä teräksiä, joissa on tilakeskeinen kuutiollinen kiderakenne. Olennaista teräksen tehokkaassa hyödyntämisessä on mikrorakenteen ja lujuuden välisten tekijöiden määrittäminen. Tässä työssä keskitytään hitsatun rakenneteräksen mikrorakenteen ja plastisen deformaation karakterisointiin. Mikrorakenne ja plastinen deformaatio mitataan elektronisuihkumikroskopian (SEM) avulla, sekä mikrorakenteen geometrisia mittoja verrataan paikallisiin materiaalin lujuusarvoihin. Lujuutta mitataan instrumentoidulla kovuuskokeella eri mittakaavoissa, kattaen deformaatioalueen koon yksittäisen kiteen murto-osasta kymmeniin kiteisiin. Kovuusmittauksista tehdään mikrorakenneanalyysiin soveltuvat poikkileikkaukset, jotta deformaatioprosessin tilastollinen vaihtelu pystytään määrittämään. Kideorientaatioanalyysiä varten kehitetään jälkikäsittely- ja analysointimenetelmät, joilla paikalliset deformaatioalueet voidaan määrittää kiteeseen muodostuvien alirakenteiden perusteella. Työn tulokset osoittavat, että kidekokojakauma vaikuttaa huomattavasti hitsatun teräksen lujuuteen ja plastisen deformaatioalueen laajuus osoitetaan riippuvaiseksi teräksen keskimääräisestä kidekoosta. Lisäksi eri kokoisten kiteiden vuorovaikutus vaikuttaa oleellisesti deformaatioprosessiin. Kovuusmittausarvojen hajonta on suurinta kidevuorovaikutuksen takia, kun kovuusmittausjäljen diagonaalimitta on 0.1 – 2 kertaa keskimääräinen kidekoko (dv). Tämä mittakaava sijaitsee yksittäiskiteen deformaation ja kontinuumimekaniikan rajapinnassa. Mitattu kovuuden hajonta pienenee huomattavasti, kun kovuusmittausjäljen koko on moninkertainen keskimääräiseen kidekokoon nähden. Tässä mittakaavassa lujuuteen vaikuttaa eniten keskimääräinen kidekoko ja kidekoon hajonta. Nämä tekijät voidaan ottaa huomioon lujuuden ennustamisessa käyttämällä tilavuuspainotettua keskimääräistä kidekokoa (dv). Tätä parametria käytetään modifioidussa Hall-Petch yhtälössä lujuuden ennustamiseen, ja suoritettujen validointivertailujen perusteella sen todetaan soveltuvan laaja-alaisesti kidekokoriippuvaisten mekaanisten ominaisuuksien ennustamiseen.

Julkaisun otsikon käännös	Kiteiden välinen vuorovaikutus hitsatun rakenneteräksen paikallisessa deformaatiossa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Remes, Heikki, Vastuuprofessori Romanoff, Jani, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-8806-8
Sähköinen ISBN	978-952-60-8807-5
Tila	Julkaistu - 2019
OKM-julkaisutyyppi	G4 Monografiaväitöskirja

Tutkimusalat

kidekoko
paikallinen plastinen deformaatio
Hall-Petch yhtälö
heterogeeninen monikiteinen materiaali
EBSD

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-8807-5

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title = "Grain interaction in local plastic deformation of welded structural steel - Influence of length scale on sub-grain deformation behaviour for polycrystalline BCC material",

abstract = "Polycrystalline body-centred cubic (BCC) steel is the most commonly used structural material in the transportation industry. In order to optimize sustainable use of steel materials in welded structures such as ships, better fundamental understanding of the factors affecting material behaviour is required in different length scales. This thesis studies the length scale interface between microstructural features and continuum scale deformation in BCC steel materials. Special attention is paid on characterization of microstructure and local plastic deformation in heterogeneous steel weld metals. In this work, microstructural characteristics are correlated with plastic deformation response, and the fundamental deformation mechanisms are resolved using electron backscatter diffraction. The local deformation process is characterized for welded steel using instrumented indentation testing in different length scales, ranging from a fraction of one grain to tens of grains. A serial sectioning procedure is developed in order to consider the stochastics of the plastic deformation process in heterogeneous microstructures. Furthermore, advanced orientation data post-processing and misorientation analysis are utilized to identify the plastic deformation zone and formation of dislocation cells beneath hardness indentations. The results of the thesis reveal the importance of grain size dispersion to mechanical properties, and the significance of grain interactions for the plastic deformation process in polycrystalline BCC steel. Comparison between base and weld metal revealed that the size of the plastic deformation zone is proportional to the average grain size. A transition region was defined between continuum and single crystal material behaviour, where the interaction of grains of different size controls the local plastic deformation of polycrystalline steel. The strongest influence grain interaction on hardness variation was found to take place at indentation diagonal lengths 0.1 – 2dv, when slip transmission primarily occurs between two grains. When the size of the plastic deformation zone is considerably larger than the average grain size, spatial hardness variation decreases significantly. In this regime, hardness and strength are affected by average grain size and grain size dispersion. To consider these aspects, a modified Hall-Petch relationship is introduced utilizing the volume-weighted average grain size based on the rule of mixtures. The modified Hall-Petch relationship is validated with literature data, showing its applicability to a wide range of materials that show grain size dependent mechanical properties.",

keywords = "grain size, local plastic deformation, Hall-Petch relationship, heterogeneous polycrystalline material, EBSD, kidekoko, paikallinen plastinen deformaatio, Hall-Petch yht{\"a}l{\"o}, heterogeeninen monikiteinen materiaali, EBSD, grain size, local plastic deformation, Hall-Petch relationship, heterogeneous polycrystalline material, EBSD",

author = "Pauli Lehto",

year = "2019",

language = "English",

isbn = "978-952-60-8806-8",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "206",

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TY - BOOK

T1 - Grain interaction in local plastic deformation of welded structural steel - Influence of length scale on sub-grain deformation behaviour for polycrystalline BCC material

AU - Lehto, Pauli

PY - 2019

Y1 - 2019

N2 - Polycrystalline body-centred cubic (BCC) steel is the most commonly used structural material in the transportation industry. In order to optimize sustainable use of steel materials in welded structures such as ships, better fundamental understanding of the factors affecting material behaviour is required in different length scales. This thesis studies the length scale interface between microstructural features and continuum scale deformation in BCC steel materials. Special attention is paid on characterization of microstructure and local plastic deformation in heterogeneous steel weld metals. In this work, microstructural characteristics are correlated with plastic deformation response, and the fundamental deformation mechanisms are resolved using electron backscatter diffraction. The local deformation process is characterized for welded steel using instrumented indentation testing in different length scales, ranging from a fraction of one grain to tens of grains. A serial sectioning procedure is developed in order to consider the stochastics of the plastic deformation process in heterogeneous microstructures. Furthermore, advanced orientation data post-processing and misorientation analysis are utilized to identify the plastic deformation zone and formation of dislocation cells beneath hardness indentations. The results of the thesis reveal the importance of grain size dispersion to mechanical properties, and the significance of grain interactions for the plastic deformation process in polycrystalline BCC steel. Comparison between base and weld metal revealed that the size of the plastic deformation zone is proportional to the average grain size. A transition region was defined between continuum and single crystal material behaviour, where the interaction of grains of different size controls the local plastic deformation of polycrystalline steel. The strongest influence grain interaction on hardness variation was found to take place at indentation diagonal lengths 0.1 – 2dv, when slip transmission primarily occurs between two grains. When the size of the plastic deformation zone is considerably larger than the average grain size, spatial hardness variation decreases significantly. In this regime, hardness and strength are affected by average grain size and grain size dispersion. To consider these aspects, a modified Hall-Petch relationship is introduced utilizing the volume-weighted average grain size based on the rule of mixtures. The modified Hall-Petch relationship is validated with literature data, showing its applicability to a wide range of materials that show grain size dependent mechanical properties.

AB - Polycrystalline body-centred cubic (BCC) steel is the most commonly used structural material in the transportation industry. In order to optimize sustainable use of steel materials in welded structures such as ships, better fundamental understanding of the factors affecting material behaviour is required in different length scales. This thesis studies the length scale interface between microstructural features and continuum scale deformation in BCC steel materials. Special attention is paid on characterization of microstructure and local plastic deformation in heterogeneous steel weld metals. In this work, microstructural characteristics are correlated with plastic deformation response, and the fundamental deformation mechanisms are resolved using electron backscatter diffraction. The local deformation process is characterized for welded steel using instrumented indentation testing in different length scales, ranging from a fraction of one grain to tens of grains. A serial sectioning procedure is developed in order to consider the stochastics of the plastic deformation process in heterogeneous microstructures. Furthermore, advanced orientation data post-processing and misorientation analysis are utilized to identify the plastic deformation zone and formation of dislocation cells beneath hardness indentations. The results of the thesis reveal the importance of grain size dispersion to mechanical properties, and the significance of grain interactions for the plastic deformation process in polycrystalline BCC steel. Comparison between base and weld metal revealed that the size of the plastic deformation zone is proportional to the average grain size. A transition region was defined between continuum and single crystal material behaviour, where the interaction of grains of different size controls the local plastic deformation of polycrystalline steel. The strongest influence grain interaction on hardness variation was found to take place at indentation diagonal lengths 0.1 – 2dv, when slip transmission primarily occurs between two grains. When the size of the plastic deformation zone is considerably larger than the average grain size, spatial hardness variation decreases significantly. In this regime, hardness and strength are affected by average grain size and grain size dispersion. To consider these aspects, a modified Hall-Petch relationship is introduced utilizing the volume-weighted average grain size based on the rule of mixtures. The modified Hall-Petch relationship is validated with literature data, showing its applicability to a wide range of materials that show grain size dependent mechanical properties.

KW - grain size

KW - local plastic deformation

KW - Hall-Petch relationship

KW - heterogeneous polycrystalline material

KW - EBSD

KW - kidekoko

KW - paikallinen plastinen deformaatio

KW - Hall-Petch yhtälö

KW - heterogeeninen monikiteinen materiaali

KW - EBSD

KW - grain size

KW - local plastic deformation

KW - Hall-Petch relationship

KW - heterogeneous polycrystalline material

KW - EBSD

M3 - Doctoral Thesis

SN - 978-952-60-8806-8

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Grain interaction in local plastic deformation of welded structural steel - Influence of length scale on sub-grain deformation behaviour for polycrystalline BCC material

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

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