The role of finely divided retained austenite on the mechanical properties of QP and ART processed novel 0.3C ultrahigh strength steels
Kantanen, Pekka (2023-03-10)
https://urn.fi/URN:ISBN:9789526236070
Kuvaus
Tiivistelmä
Abstract
Both 0.3C (high) Si-Al and 0.3C medium-Mn steels are considered ideal recipes for developing the third-generation advanced high strength steels using the innovative quenching and partitioning (QP) and austenite reversion transformation (ART) treatments, respectively. This study reports the effects of QP and ART processing on the evolved microstructural characteristics, focusing on phase transformation behavior and resultant mechanical properties, augmented by the presence of finely divided retained austenite (RA). While QP processing trials were carried out with (high) Si-Al steels, both QP and ART treatments were utilized to optimize the processing of medium-Mn steels to achieve high strength-ductility combinations. The processes were later scaled up for laboratory rolling simulations, involving thermomechanical rolling followed by direct quenching and partitioning (TMR-DQP) in the case of (high) Si-Al steels, and TMR-QP and TMR-ART treatments for medium-Mn steels. The prime objective was to gain in-depth knowledge about the effects of processing on evolved microstructures, operating structural mechanisms and corresponding mechanical properties.
Physical simulation experiments were conducted on a Gleeble simulator, followed by scaling up of the experiments on a laboratory rolling mill. Detailed microstructural characterization, including the differences in fractions, morphology, C-content, and stability of RA were performed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA), besides using various materials characterization and electron microscopy techniques. Mechanical properties were evaluated in respect of hardness, tensile and impact toughness properties, and structure-property correlations established.
The result showed that fine division of RA between martensitic laths, besides the refinement of martensitic packets and laths, notably improved the low-temperature impact toughness. Various combinations of high tensile strengths with good elongations could be achieved with QP and ART treatments, depending on the volume fraction, size, shape, distribution and carbon content of RA and morphology of martensite. Implementation of TMR-DQP and TMR-QP and TMR-ART processing on the laboratory rolling mill was challenging, as the properties were known to be sensitive to the processing parameters, particularly the quenching temperature (TQ).
Tiivistelmä
0.3C (korkea) pii- ja alumiiniseostetut sekä 0.3C keskimangaaniteräkset ovat houkuttelevia kandidaatteja uudeksi kolmannen sukupolven autoteollisuuden muovattavaksi suurlujuusteräkseksi. Tässä väitöskirjassa on tutkittu näiden teräksien mikrorakenteiden ominaisuuksia, austeniitti-martensiitti- ja martensiiti-austeniittifaasimuutosilmiöitä sekä näiden vaikutusta mekaanisiin ominaisuuksiin. Keskeytettyä sammutusta yhdistettynä matalan lämpötilan hehkutus (QP) prosessiin sekä austeniitin reversiomuutos (ART) -prosessiin on käytetty hyvien lujuus-sitkeysominaisuuksien saavuttamiseksi. Tavoite oli lisätä tietoa siitä, kuinka mikrorakenteen eri piirteet vaikuttavat termomekaanisesti valssatun suorasammutetun QP (TMR-DQP) ja termomekaanisesti valssatun ART (TMR-ART) teräksen ominaisuuksiin.
Termomekaanista Gleeble-simulaattoria ja laboratoriokuumavalssainta on käytetty mikrorakenteen ominaisuuksien ja jäännösausteniitin hajaantumisen tutkimisessa. Lisäksi käytettiin erilaisia elektronimikroskooppeja ja analysaattoreita. Mekaanisten ominaisuuksien määrittämiseen käytettiin kovuusmittareita, veto- ja iskusitkeyskokeita.
Tulokset osoittivat, että iskusitkeyteen vaikuttaa jäännösauteniitin määrän lisäksi myös rakenteen sälekoko. QP- ja ART-käsittelyillä voidaan saavuttaa erilaisia suuria vetolujuus-/venymäyhdistelmiä riippuen jäännösausteniitin määrästä, koosta, muodosta, jakaantumasta ja jäännösausteniitin hiilipitoisuudesta sekä martensiitin ja mahdollisen bainiitin morfologiasta. On haasteellista ottaa DQP-käsittely käytäntöön, koska keskeytetyn sammutuksen lämpötila vaikuttaa teräksen ominaisuuksiin ja sen hallinta tarkasti teollisessa mittakaavassa on haasteellista. ART-käsittelyssä haasteena on kapean prosessi-ikkunan (lämpötila ja hehkutusaika) hallinta ART-hehkutuslämpötiloissa.
Original papers
Original papers are not included in the electronic version of the dissertation.
Kantanen, P. K., Javaheri, V., Somani, M. C., Porter, D. A., & Kömi, J. I. (2021). Effect of deformation and grain size on austenite decomposition during quenching and partitioning of (high) silicon‑aluminum steels. Materials Characterization, 171, 110793. https://doi.org/10.1016/j.matchar.2020.110793
Somani, M. C., Porter, D. A., Karjalainen, L. P., Kantanen, P. K., Kömi, J. I., & Misra, D. K. (2019). Static recrystallization characteristics and kinetics of high-silicon steels for direct quenching and partitioning. International Journal of Materials Research, 110(3), 183–193. https://doi.org/10.3139/146.111744
Kantanen, P. K., Somani, M. C., Porter, D. A., Kömi, J. I., & Misra, D. K. (2018). Microstructures and mechanical properties of tough ductile ultrahigh-strength steels processed through direct quenching and partitioning. Materials Science Forum, 941, 468–473. https://doi.org/10.4028/www.scientific.net/MSF.941.468
Kantanen, P., Somani, M., Kaijalainen, A., Haiko, O., Porter, D., & Kömi, J. (2019). Microstructural characterization and mechanical properties of direct quenched and partitioned high-aluminum and high-silicon steels. Metals, 9(2), 256. https://doi.org/10.3390/met9020256
Haiko, O., Somani, M., Porter, D., Kantanen, P., Kömi, J., Ojala, N., & Heino, V. (2018). Comparison of impact-abrasive wear characteristics and performance of direct quenched (DQ) and direct quenched and partitioned (DQ&P) steels. Wear, 400–401, 21–30. https://doi.org/10.1016/j.wear.2017.12.016
Kantanen, P., Anttila, S., Karjalainen, P., Latypova, R., Somani, M., Kaijalainen, A., & Kömi, J. (2022). Microstructures and mechanical properties of three medium-Mn steels processed via quenching and partitioning as well as austenite reversion heat treatments. Materials Science and Engineering: A, 847, 143341. https://doi.org/10.1016/j.msea.2022.143341
Osajulkaisut
Osajulkaisut eivät sisälly väitöskirjan elektroniseen versioon.
Kantanen, P. K., Javaheri, V., Somani, M. C., Porter, D. A., & Kömi, J. I. (2021). Effect of deformation and grain size on austenite decomposition during quenching and partitioning of (high) silicon‑aluminum steels. Materials Characterization, 171, 110793. https://doi.org/10.1016/j.matchar.2020.110793
Somani, M. C., Porter, D. A., Karjalainen, L. P., Kantanen, P. K., Kömi, J. I., & Misra, D. K. (2019). Static recrystallization characteristics and kinetics of high-silicon steels for direct quenching and partitioning. International Journal of Materials Research, 110(3), 183–193. https://doi.org/10.3139/146.111744
Kantanen, P. K., Somani, M. C., Porter, D. A., Kömi, J. I., & Misra, D. K. (2018). Microstructures and mechanical properties of tough ductile ultrahigh-strength steels processed through direct quenching and partitioning. Materials Science Forum, 941, 468–473. https://doi.org/10.4028/www.scientific.net/MSF.941.468
Kantanen, P., Somani, M., Kaijalainen, A., Haiko, O., Porter, D., & Kömi, J. (2019). Microstructural characterization and mechanical properties of direct quenched and partitioned high-aluminum and high-silicon steels. Metals, 9(2), 256. https://doi.org/10.3390/met9020256
Haiko, O., Somani, M., Porter, D., Kantanen, P., Kömi, J., Ojala, N., & Heino, V. (2018). Comparison of impact-abrasive wear characteristics and performance of direct quenched (DQ) and direct quenched and partitioned (DQ&P) steels. Wear, 400–401, 21–30. https://doi.org/10.1016/j.wear.2017.12.016
Kantanen, P., Anttila, S., Karjalainen, P., Latypova, R., Somani, M., Kaijalainen, A., & Kömi, J. (2022). Microstructures and mechanical properties of three medium-Mn steels processed via quenching and partitioning as well as austenite reversion heat treatments. Materials Science and Engineering: A, 847, 143341. https://doi.org/10.1016/j.msea.2022.143341
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