The effects of finish rolling temperature and niobium microalloying on the microstructure and properties of a direct quenched high-strength steel
Kaijalainen, A.; Vähäkuopus, N.; Somani, M.; Mehtonen, S.; Porter, D.; Kömi, J. (2017-04-01)
Kaijalainen, A., Vähäkuopus, N., Somani, M., Mehtonen, S., Porter, D., Kömi, J. (2017) The Effects of Finish Rolling Temperature and Niobium Microalloying on the Microstructure and Properties of a Direct Quenched High-Strength Steel. Archives of Metallurgy and Materials, 62 (2), 619-626. https://doi.org/10.1515/amm-2017-0091
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https://urn.fi/URN:NBN:fi-fe202103016184
Tiivistelmä
Abstract
This paper comprehends the effects of finish rolling temperature (FRT) and Nb-microalloying on the microstructural evolu-tion 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 Ar3 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 es-sentially 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.
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