On thermal and mechanical behavior of cast irons at elevated temperatures

Kalle Jalava

On thermal and mechanical behavior of cast irons at elevated temperatures

Julkaisun otsikon käännös: Valurautojen termisestä ja mekaanisesta käyttäytymisestä korotetuissa lämpötiloissa

Kalle Jalava

Konetekniikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Valaminen on valmistusmenetelmä, joka mahdollistaa monimutkaisten komponenttien tuotannon monessa kokoluokassa. Valutuotteiden tehokas käyttö vaatii kattavaa tietoutta niin tuotantotekniikoista kuin seosten materiaaliominaisuuksista. Valuraudat ovat keskeisiä konstruktiomateriaaleja käyttökohteissa, joissa yhdistyy tarpeet hyvistä termisistä ja mekaanisista ominaisuuksista. Pallografiittiraudat ovat valurautojen alatyyppi, jonka tiettyjen mikrorakenteen ja seostuksen yhdistelmillä on potentiaalia korvata suomugrafiittirautoja termisesti kuormitetuissa käyttökohteissa. Tässä työssä tutkittiin tiettyjen valurautatyyppien termistä ja mekaanista käyttäytymistä korotetuissa lämpötiloissa huoneenlämmöstä noin 400 °C asti. Transient Plane Source-tekniikkaan perustuvaa mittauslaitteistoa käytettiin karakterisoimaan suomu-, tylppä- ja pallografiittirautojen lämmönjohtavuutta. Pallografiittirautojen lämmönjohtavuutta tutkittiin tarkemmin piiseostuksen välillä 1.5 - 4.3 p-% ja eri ferriitti-perliittisuhteilla. Testien tuloksia käytettiin regressiomallien luomisessa, joka mahdollistaa termisten ominaisuuksien arvioimisen. Mekaanisen testauksen puoli tässä työssä keskittyy dynaamisen myötövanhenemisen vaikutusten esiintymiseen ferriittisperliittisillä pallografiittiraudoilla. Myötövanhenemiseen liittyvät testit koostuivat vetokokeista ja venymäohjatuista syklisistä testeistä useilla venymänopeuksilla ja -amplitudeilla huoneenlämpötilasta 450 °C:seen asti. Työn tulosten perusteella voidaan sanoa, että käytetty lämmönjohtavuuden mittaustekniikka soveltuu valurautojen karakterisoimiseen, kunhan tietyt käyttäjään ja mittaustulosten analyysin haasteet otetaan kunnolla huomioon. Pallografiittirautojen lämmönjohtavuuksia voidaan optimoida tai arvioida testiparametrien ja luodun regressiomallin avulla. Tämä on mahdollista, koska grafiittipallojen vaikutus lämmönjohtavuuteen on suhteellisen pieni. Myötövanhenemiseen liittyvät testit osoittavat, että siihen liittyviä ilmiöitä esiintyy kaikilla testatuilla ferriittis-perliittisillä mikrorakenteilla tiettyjen venymänopeuksien ja lämpötilojen yhdistelmillä. Koska myötövanhenemiseen liittyy mm. negatiivinen muodonmuutosnopeusherkkyys, venymäarvojen heikentyminen ja positiivinen lämpötilakorrelaatio myötymisjännitykseen, on se otettava huomioon termomekaanisen jännityksen alaisten komponenttien suunnittelussa. Tämä työ lisää tietoa valurautojen käyttäytymisestä korotetuissa lämpötiloissa, jättäen sen hyötykäytön tulevaisuuden tutkimuskohteeksi. Lisää materiaalitestausta ja dataa tarvitaan kattamaan ferriittisperliittisten pallografiittirautojen tuotantoikkuna, jonka kautta mahdollistuu paikallisten materiaaliominaisuuksien huomioonottaminen valunsimulaatioissa ja muissa optimointityökaluissa.

Julkaisun otsikon käännös	Valurautojen termisestä ja mekaanisesta käyttäytymisestä korotetuissa lämpötiloissa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Orkas, Juhani, Vastuuprofessori
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-0060-0
Sähköinen ISBN	978-952-64-0061-7
Tila	Julkaistu - 2020
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

valurauta
lämmönjohtavuus
dynaaminen myötövanheneminen
korotetut lämpötilat

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-64-0061-7

Siteeraa tätä

@phdthesis{5b5a83b1350a46418f5e735d21438fe1,

title = "On thermal and mechanical behavior of cast irons at elevated temperatures",

abstract = "Casting is a production process that lends itself superbly to creation of complex shapes in many scales. To get every sliver of performance from a casting, one needs to combine the knowledge of shaping methods to a deep understanding of properties and behaviour. Cast irons in particular are widely used in thermally loaded applications, where both mechanical and physical properties are required. Spheroidal graphite cast irons hold potential in becoming a replacement for lamellar graphite alloys with certain combination of microstructure and alloying. In this work, thermal and mechanical properties of select cast iron types are explored at elevated temperatures, from room temperature (RT) to around 400 °C. A Transient Plane Source-measurement system is used to characterize thermal conductivities of lamellar, compacted and spheroidal graphite irons. Secondly, the effects of silicon alloying in the range of 1.5 to 4.3 w-% and different ferrite-pearlite fractions to spheroidal graphite thermal conductivity at elevated temperatures are tested and models for estimation purposes are made. Mechanical property side of this work concentrates on evaluating the occurrence of Dynamic Strain Aging (DSA) in ferritic to pearlitic microstructures of spheroidal graphite cast iron. DSA testing consisted of tensile and cyclic load cases with various strain rates and amplitudes from RT to 450 °C. The results in this thesis indicate that the used TPS measurement system is capable of characterizing cast irons at elevated temperatures, when care is taken in analysis and certain operator related challenges are considered. Additionally, spheroidal graphite cast iron thermal conductivities can be optimized or estimated with the chosen test parameters as the contribution of graphite in spheroids is relatively minimal. The mechanical property experiments show that DSA related phenomena are evident in all tested ferritic and pearlitic microstructures with certain combination of strain rates and temperatures. As DSA effects include negative strain rate sensitivity, ductility minimums and positive temperature dependence for flow stress and work hardening, it should be considered in analysis of components that are used in the range of 200-400 °C. This work fills gaps in knowledge regarding cast irons at elevated temperatures. However, taking the outlined approaches further remains a topic for future research. Additional testing is required to cover the full production window of spheroidal graphite cast irons to be fully usable in production simulation, optimization tools and local property approaches",

keywords = "Cast iron, thermal conductivity, dynamic strain aging, elevated temperatures, valurauta, l{\"a}mm{\"o}njohtavuus, dynaaminen my{\"o}t{\"o}vanheneminen, korotetut l{\"a}mp{\"o}tilat, Cast iron, thermal conductivity, dynamic strain aging, elevated temperatures",

author = "Kalle Jalava",

year = "2020",

language = "English",

isbn = "978-952-64-0060-0",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "148",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - On thermal and mechanical behavior of cast irons at elevated temperatures

AU - Jalava, Kalle

PY - 2020

Y1 - 2020

N2 - Casting is a production process that lends itself superbly to creation of complex shapes in many scales. To get every sliver of performance from a casting, one needs to combine the knowledge of shaping methods to a deep understanding of properties and behaviour. Cast irons in particular are widely used in thermally loaded applications, where both mechanical and physical properties are required. Spheroidal graphite cast irons hold potential in becoming a replacement for lamellar graphite alloys with certain combination of microstructure and alloying. In this work, thermal and mechanical properties of select cast iron types are explored at elevated temperatures, from room temperature (RT) to around 400 °C. A Transient Plane Source-measurement system is used to characterize thermal conductivities of lamellar, compacted and spheroidal graphite irons. Secondly, the effects of silicon alloying in the range of 1.5 to 4.3 w-% and different ferrite-pearlite fractions to spheroidal graphite thermal conductivity at elevated temperatures are tested and models for estimation purposes are made. Mechanical property side of this work concentrates on evaluating the occurrence of Dynamic Strain Aging (DSA) in ferritic to pearlitic microstructures of spheroidal graphite cast iron. DSA testing consisted of tensile and cyclic load cases with various strain rates and amplitudes from RT to 450 °C. The results in this thesis indicate that the used TPS measurement system is capable of characterizing cast irons at elevated temperatures, when care is taken in analysis and certain operator related challenges are considered. Additionally, spheroidal graphite cast iron thermal conductivities can be optimized or estimated with the chosen test parameters as the contribution of graphite in spheroids is relatively minimal. The mechanical property experiments show that DSA related phenomena are evident in all tested ferritic and pearlitic microstructures with certain combination of strain rates and temperatures. As DSA effects include negative strain rate sensitivity, ductility minimums and positive temperature dependence for flow stress and work hardening, it should be considered in analysis of components that are used in the range of 200-400 °C. This work fills gaps in knowledge regarding cast irons at elevated temperatures. However, taking the outlined approaches further remains a topic for future research. Additional testing is required to cover the full production window of spheroidal graphite cast irons to be fully usable in production simulation, optimization tools and local property approaches

AB - Casting is a production process that lends itself superbly to creation of complex shapes in many scales. To get every sliver of performance from a casting, one needs to combine the knowledge of shaping methods to a deep understanding of properties and behaviour. Cast irons in particular are widely used in thermally loaded applications, where both mechanical and physical properties are required. Spheroidal graphite cast irons hold potential in becoming a replacement for lamellar graphite alloys with certain combination of microstructure and alloying. In this work, thermal and mechanical properties of select cast iron types are explored at elevated temperatures, from room temperature (RT) to around 400 °C. A Transient Plane Source-measurement system is used to characterize thermal conductivities of lamellar, compacted and spheroidal graphite irons. Secondly, the effects of silicon alloying in the range of 1.5 to 4.3 w-% and different ferrite-pearlite fractions to spheroidal graphite thermal conductivity at elevated temperatures are tested and models for estimation purposes are made. Mechanical property side of this work concentrates on evaluating the occurrence of Dynamic Strain Aging (DSA) in ferritic to pearlitic microstructures of spheroidal graphite cast iron. DSA testing consisted of tensile and cyclic load cases with various strain rates and amplitudes from RT to 450 °C. The results in this thesis indicate that the used TPS measurement system is capable of characterizing cast irons at elevated temperatures, when care is taken in analysis and certain operator related challenges are considered. Additionally, spheroidal graphite cast iron thermal conductivities can be optimized or estimated with the chosen test parameters as the contribution of graphite in spheroids is relatively minimal. The mechanical property experiments show that DSA related phenomena are evident in all tested ferritic and pearlitic microstructures with certain combination of strain rates and temperatures. As DSA effects include negative strain rate sensitivity, ductility minimums and positive temperature dependence for flow stress and work hardening, it should be considered in analysis of components that are used in the range of 200-400 °C. This work fills gaps in knowledge regarding cast irons at elevated temperatures. However, taking the outlined approaches further remains a topic for future research. Additional testing is required to cover the full production window of spheroidal graphite cast irons to be fully usable in production simulation, optimization tools and local property approaches

KW - Cast iron

KW - thermal conductivity

KW - dynamic strain aging

KW - elevated temperatures

KW - valurauta

KW - lämmönjohtavuus

KW - dynaaminen myötövanheneminen

KW - korotetut lämpötilat

KW - Cast iron

KW - thermal conductivity

KW - dynamic strain aging

KW - elevated temperatures

M3 - Doctoral Thesis

SN - 978-952-64-0060-0

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

On thermal and mechanical behavior of cast irons at elevated temperatures

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

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