Next Article in Journal
Influence of Stress on Kinetics and Transformation Plasticity of Ferrite Transformation Based on Hysteresis Effects
Previous Article in Journal
Interfacial Characteristics of Dissimilar Ti6Al4V/AA6060 Lap Joint by Pulsed Nd:YAG Laser Welding
Article Menu
Issue 1 (January) cover image

Export Article

Open AccessArticle
Metals 2019, 9(1), 72; https://doi.org/10.3390/met9010072

Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel

1
National 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, Greece
2
Hellenic Research Centre for Metals (ELKEME S.A.), Department of Physical Metallurgy and Forming, 61st km Athens—Lamia Nat. Road, 32011 Oinofyta, Viotia, Greece
*
Authors to whom correspondence should be addressed.
Received: 19 November 2018 / Revised: 21 December 2018 / Accepted: 8 January 2019 / Published: 12 January 2019
Full-Text   |   PDF [4890 KB, uploaded 14 January 2019]   |  

Abstract

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. View Full-Text
Keywords: ultrafast heating; phase transformation; moving boundaries; Dictra; nanostructured steel; martensite/bainite ultrafast heating; phase transformation; moving boundaries; Dictra; nanostructured steel; martensite/bainite
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
SciFeed

Share & Cite This Article

MDPI and ACS Style

Papaefthymiou, S.; Karamitros, V.; Bouzouni, M. Ultrafast Heating and Initial Microstructure Effect on Phase Transformation Evolution of a CrMo Steel. Metals 2019, 9, 72.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Metals EISSN 2075-4701 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top