Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel
Main target of the present work is to elucidate the effect of both initial microstructure and heating rate on phase transformations that occur during ultrafast processing. For this purpose, two initial microstructures, a ferritic-pearlitic and a soft-annealed microstructure were considered. We appli...
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| Format: | Article |
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MDPI AG
2019-01-01
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| Series: | Metals |
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| Online Access: | http://www.mdpi.com/2075-4701/9/1/72 |
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| author | Spyros Papaefthymiou Vassilios Karamitros Marianthi Bouzouni |
| author_facet | Spyros Papaefthymiou Vassilios Karamitros Marianthi Bouzouni |
| author_sort | Spyros Papaefthymiou |
| collection | DOAJ |
| description | Main target of the present work is to elucidate the effect of both initial microstructure and heating rate on phase transformations that occur during ultrafast processing. For this purpose, two initial microstructures, a ferritic-pearlitic and a soft-annealed microstructure were considered. We applied different heating rates (10 °C/s, 200 °C/s, 300 °C/s) up to the peak austenitization temperature, θ ≅ 900 °C. The evolving microstructure is analysed via SEM and EBSD, whereas the carbide dissolution and austenite formation is simulated with Thermocalc® and DICTRA software. Data obtained in this research proves that, when the heating rate increases, the carbide dissolution rate is disseminated. Compared to a conventional heating rate, where the local chemical composition homogenizes as a result of diffusion, rapid reheating leads to intense segregation of the substitutional atoms at the cementite/austenite interface and turns diffusion to a sluggish process. This fact, combined to the infinitesimal time for diffusion, forms an inhomogeneous carbon distribution along the microstructure. This inhomogeneity is further enhanced by the presence of increased carbides’ size present in the initial microstructure. Due to rapid heating, these carbides cannot be decomposed since the diffusion distance of alloying elements increases and the diffusion of alloying elements is impeded during ultrafast heating, thus, remain undissolved at peak austenitization temperature. Their presence and effect in heterogeneous ferrite nucleation restrict austenite grain growth. Consequently, fine austenite grains in conjunction with their chemical heterogeneity lead to the coexistence of fine martensite, bainite laths and undissolved carbides in the final microstructure after quenching. |
| first_indexed | 2024-12-20T02:58:47Z |
| format | Article |
| id | doaj.art-47a2a24d6a5f49239a248ac52fc43f47 |
| institution | Directory Open Access Journal |
| issn | 2075-4701 |
| language | English |
| last_indexed | 2024-12-20T02:58:47Z |
| publishDate | 2019-01-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Metals |
| spelling | doaj.art-47a2a24d6a5f49239a248ac52fc43f472022-12-21T19:55:50ZengMDPI AGMetals2075-47012019-01-01917210.3390/met9010072met9010072Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo SteelSpyros Papaefthymiou0Vassilios Karamitros1Marianthi Bouzouni2National Technical University of Athens, School of Mining and Metallurgical Engineering, Division of Metallurgy and Materials, Laboratory of Physical Metallurgy, 9, Her. Polytechniou str., Zografos, 15780 Athens, GreeceNational Technical University of Athens, School of Mining and Metallurgical Engineering, Division of Metallurgy and Materials, Laboratory of Physical Metallurgy, 9, Her. Polytechniou str., Zografos, 15780 Athens, GreeceNational Technical University of Athens, School of Mining and Metallurgical Engineering, Division of Metallurgy and Materials, Laboratory of Physical Metallurgy, 9, Her. Polytechniou str., Zografos, 15780 Athens, GreeceMain target of the present work is to elucidate the effect of both initial microstructure and heating rate on phase transformations that occur during ultrafast processing. For this purpose, two initial microstructures, a ferritic-pearlitic and a soft-annealed microstructure were considered. We applied different heating rates (10 °C/s, 200 °C/s, 300 °C/s) up to the peak austenitization temperature, θ ≅ 900 °C. The evolving microstructure is analysed via SEM and EBSD, whereas the carbide dissolution and austenite formation is simulated with Thermocalc® and DICTRA software. Data obtained in this research proves that, when the heating rate increases, the carbide dissolution rate is disseminated. Compared to a conventional heating rate, where the local chemical composition homogenizes as a result of diffusion, rapid reheating leads to intense segregation of the substitutional atoms at the cementite/austenite interface and turns diffusion to a sluggish process. This fact, combined to the infinitesimal time for diffusion, forms an inhomogeneous carbon distribution along the microstructure. This inhomogeneity is further enhanced by the presence of increased carbides’ size present in the initial microstructure. Due to rapid heating, these carbides cannot be decomposed since the diffusion distance of alloying elements increases and the diffusion of alloying elements is impeded during ultrafast heating, thus, remain undissolved at peak austenitization temperature. Their presence and effect in heterogeneous ferrite nucleation restrict austenite grain growth. Consequently, fine austenite grains in conjunction with their chemical heterogeneity lead to the coexistence of fine martensite, bainite laths and undissolved carbides in the final microstructure after quenching.http://www.mdpi.com/2075-4701/9/1/72ultrafast heatingphase transformationmoving boundariesDictrananostructured steelmartensite/bainite |
| spellingShingle | Spyros Papaefthymiou Vassilios Karamitros Marianthi Bouzouni Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel Metals ultrafast heating phase transformation moving boundaries Dictra nanostructured steel martensite/bainite |
| title | Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel |
| title_full | Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel |
| title_fullStr | Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel |
| title_full_unstemmed | Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel |
| title_short | Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel |
| title_sort | ultrafast heating and initial microstructure effect on phase transformation evolution of a crmo steel |
| topic | ultrafast heating phase transformation moving boundaries Dictra nanostructured steel martensite/bainite |
| url | http://www.mdpi.com/2075-4701/9/1/72 |
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