TY - JOUR
T1 - Bainite Formation in Medium-Carbon Low-Silicon Spring Steels Accounting for Chemical Segregation
AU - Goulas, C.
AU - Mecozzi, M. G.
AU - Sietsma, J.
N1 - Funding Information:
This research was carried out under the project number M22.12.476 in the framework of the Research Program of the Materials innovation institute (M2i) ( www.m2i.nl ). The authors would like to thank Mr. R. Huizenga and Mr C. Kwakernaak from the Surfaces & Interfaces group of TU Delft for performing the XRD and EPMA measurements, respectively. Dr. T. Sourmail from ASCO Metal is acknowledged for performing the interrupted dilatometry experiments. The authors would like to thank Professor Fourlaris, Dr. Tsakiridis, and Dr.-ing S. Papaefthymiou of National Technical University of Athens for the STEM-EDS measurements.
Publisher Copyright:
© 2016, The Author(s).
PY - 2016/6/1
Y1 - 2016/6/1
N2 - In this paper, the effect of chemical inhomogeneity on the isothermal bainite formation is investigated in medium-carbon low-silicon spring steel by dilatometry and microscopy. The analysis of the microstructure at different times during transformation shows that chemical segregation of substitutional alloying elements resulting from casting strongly affects the bainite formation by retarding the transformation kinetics and limiting the maximum achievable bainite fraction. During holding at temperatures close to and above the martensite start temperature, a homogeneous lower bainitic microstructure can be eventually obtained, whereas at higher temperatures, incomplete bainitic reaction is evident. It was also found that at the early stages of the transformation, differences in the bainite formation kinetics, due to local inhomogeneities in Cr and Mn concentration, result in retardation of the growth of bainite in the high Mn and Cr concentration regions. The calculated difference in driving force for nucleation between the enriched and the depleted areas is not by itself sufficient to explain the microstructures obtained and thus significant influence of growth on bainite formation is observed. Particularly, it was calculated and experimentally observed that Cr partitions in the carbides in the high Mn, Cr regions during the isothermal treatment, limiting the transformation kinetics.
AB - In this paper, the effect of chemical inhomogeneity on the isothermal bainite formation is investigated in medium-carbon low-silicon spring steel by dilatometry and microscopy. The analysis of the microstructure at different times during transformation shows that chemical segregation of substitutional alloying elements resulting from casting strongly affects the bainite formation by retarding the transformation kinetics and limiting the maximum achievable bainite fraction. During holding at temperatures close to and above the martensite start temperature, a homogeneous lower bainitic microstructure can be eventually obtained, whereas at higher temperatures, incomplete bainitic reaction is evident. It was also found that at the early stages of the transformation, differences in the bainite formation kinetics, due to local inhomogeneities in Cr and Mn concentration, result in retardation of the growth of bainite in the high Mn and Cr concentration regions. The calculated difference in driving force for nucleation between the enriched and the depleted areas is not by itself sufficient to explain the microstructures obtained and thus significant influence of growth on bainite formation is observed. Particularly, it was calculated and experimentally observed that Cr partitions in the carbides in the high Mn, Cr regions during the isothermal treatment, limiting the transformation kinetics.
UR - http://www.scopus.com/inward/record.url?scp=84960090883&partnerID=8YFLogxK
U2 - 10.1007/s11661-016-3418-6
DO - 10.1007/s11661-016-3418-6
M3 - Article
AN - SCOPUS:84960090883
SN - 1073-5623
VL - 47
SP - 3077
EP - 3087
JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
IS - 6
ER -