The Effects of Finish Rolling Temperature and Niobium Microalloying on the Microstructure and Properties of a Direct Quenched High-Strength Steel

This paper comprehends the effects of finish rolling temperature (FRT) and Nb-microalloying on the microstructural evolution and resultant properties of a low carbon direct quenched steel in the yield strength category of ≥900 MPa. Results indicate that a decrease in FRT close to A temperature signi...

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Bibliographic Details
Published in:Archives of metallurgy and materials 2017-06, Vol.62 (2), p.619-626
Main Authors: Kaijalainen, A., Vähäkuopus, N., Somani, M., Mehtonen, S., Porter, D., Kömi, J.
Format: Article
Language:English
Subjects:
Alloys
Bainite
CCT diagram
Direct quenching
Ferrites
Finish rolling
High strength steels
Hot rolling
Low carbon steels
Martensitic stainless steels
Mechanical properties
Microalloying
Microstructure
Nb-microalloying
Niobium
Phase transitions
Quenching
Strip
Yield strength
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Summary:This paper comprehends the effects of finish rolling temperature (FRT) and Nb-microalloying on the microstructural evolution and resultant properties of a low carbon direct quenched steel in the yield strength category of ≥900 MPa. Results indicate that a decrease in FRT close to A temperature significantly influenced the microstructure following phase transformation, especially at the subsurface (~50-400 μm) of the rolled strip. On decreasing the FRT, the subsurface microstructure revealed a fine mixture of ferrite and bainite obviously as a result of strain-induced transformation, whereas the structure at the centreline remained essentially martensitic. Further, Nb-microalloying promoted the formation of ferrite and bainite even at higher FRTs, thus influencing the mechanical properties. The microstructures of the hot-rolled strips were further corroborated with the aid of CCT diagrams.
ISSN:2300-1909
1733-3490
2300-1909
DOI:10.1515/amm-2017-0091