Comparative study on microstructure and mechanical properties of a C-Mn-Si steel treated by quenching and partitioning (Q&P) processes after a full and intercritical austenitization

A C-Mn-Si steel with lean microalloy elements was treated by a series of quenching and partitioning (Q&P) processes after a full or intercritical austenitization (hereinafter referred as F-QP and I-QP process, respectively). The discrepancy in microstructure and mechanical properties of the samp...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2017-01, Vol.684, p.261-269
Main Authors: Yan, Shu, Liu, Xianghua, Liu, Wayne J., Liang, Taosha, Zhang, Bin, Liu, Lizhong, Zhao, Yang
Format: Article
Language:English
Subjects:
Austenite
Carbon manganese steels
Comparative studies
Elongation
Exponential functions
Grains
Heat treatment
Mechanical properties
Mechanical stability
Microstructure
Partitioning
Phase transitions
Product of strength and elongation
Q&P process
Quenching
Retained austenite
Silicon steels
Strain
Strength
TRIP effect
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Summary:A C-Mn-Si steel with lean microalloy elements was treated by a series of quenching and partitioning (Q&P) processes after a full or intercritical austenitization (hereinafter referred as F-QP and I-QP process, respectively). The discrepancy in microstructure and mechanical properties of the samples under these two heat treatment processes was investigated. The results indicate that the austenite grains are mainly film-like in the F-QP samples, while blocky austenite grains account for the majority in the I-QP samples. And the later contains a larger amount of retained austenite than the former. In addition, the reason why the austenite fraction decreases with the increasing of partitioning time after the peak value can be related to the bainite transformation due to the dynamic change of phase region in the continue cooling transformation (CCT) diagram of untransformed austenite with carbon enrichment. The I-QP samples show higher product of strength and elongation (PSE) but relatively lower strength, while the F-QP samples are just the reverse. Notably, the one-step I-QP samples show an excellent strength–ductility balance, of which the tensile strength and total elongation are 1140–1280MPa and 17–22%, respectively. The exponential function and Olson-Cohen (O-C) model were utilized to fit the variation of retained austenite fraction with strain. By comparison, retained austenite in the I-QP sample is more sensitive to the increasing strain, i.e., lower mechanical stability.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2016.12.026