The effect of chemical composition and austenite conditioning on the transformation behavior of microalloyed steels

Journal Article · Sun Jan 15 04:00:00 EST 2012 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2011.11.003· OSTI ID:22066404

Rezaeian, Ahmad ^[1]; Yue, Steve ^[2]

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1. Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)
2. Department of Mining and Materials Engineering, McGill University, 3610 University Street, Montreal, Quebec, H3A 2B (Canada)

In this investigation, by using continuous cooling torsion (CCT) testing, the transformation behavior of four microalloyed steels under two circumstances of austenite conditioning and non-conditioning was studied. A full scale hot-rolling schedule containing a 13-pass deformation was employed for the conditioning of the austenite. The CCT tests were then employed till temperature of {approx} 540 Degree-Sign C and the flow curves obtained from this process were analyzed. The initial and final microstructures of the steels were studied by optical and electron microscopes. Results show that alloying elements would decrease the transformation temperature. This effect intensifies with the gradual increase of Mo, Nb and Cu as alloying elements added to the microalloyed steels. As well, austenite conditioning increased the transformation start temperature due mainly to the promotion of polygonal ferrite formation that resulted from a pancaked austenite. The final microstructures also show that CCT alone would decrease the amount of bainite by inducing ferrite transformation in the two phase region. In addition, after the transformation begins, the deformation might result in the occurrence of dynamic recrystallization in the ferrite region. This could lead to two different ferrite grain sizes at the end of the CCT. Moreover, the Nb bearing steels show no sign of decreasing the strength level after the transformation begins in the non-conditioned situation and their microstructure is a mix of polygonal ferrite and bainite indicating an absence of probable dynamic recrystallization in this condition. In the conditioned cases, however, these steels show a rapid decrease of the strength level and their final microstructures insinuate that ferrite could have undergone a dynamic recrystallization due to deformation. Consequently, no bainite was seen in the austenite conditioned Nb bearing steels. The pancaking of austenite in the latest cases produced fully polygonal ferrite structures. - Highlights: Black-Right-Pointing-Pointer Adding alloying elements would decrease the transformation temperatures. Black-Right-Pointing-Pointer Austenite conditioning increases the transformation start temperature. Black-Right-Pointing-Pointer Deformation could induce the occurrence of dynamic recrystallization in ferrite region.

• OSTI ID: 22066404
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Journal Issue: Complete Vol. 63; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AUSTENITE
BAINITE
CHEMICAL COMPOSITION
COOLING
DEFORMATION
ELECTRON MICROSCOPY
FERRITE
GRAIN SIZE
LOW ALLOY STEELS
MATERIALS TESTING
OPTICAL MICROSCOPY
RECRYSTALLIZATION
ROLLING
TORSION