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Open AccessArticle

Tracing Microalloy Precipitation in Nb-Ti HSLA Steel during Austenite Conditioning

1
Department of Materials Science, Saarland University, Campus D3.3, D-66123 Saarbrücken, Germany
2
Materials Engineering Center Saarland (MECS), Campus D3.3, D-66123 Saarbrücken, Germany
3
AG der Dillinger Hüttenwerke, D-66763 Dillingen, Germany
4
Engineering Office and Consultant, Salzgitter, Germany
5
Department of Materials Engineering (MTM), KU Leuven, 3001 Leuven, Belgium
6
NiobelCon bvba, 2970 Schilde, Belgium
*
Author to whom correspondence should be addressed.
Metals 2020, 10(2), 243; https://doi.org/10.3390/met10020243
Received: 23 January 2020 / Revised: 7 February 2020 / Accepted: 9 February 2020 / Published: 12 February 2020
(This article belongs to the Special Issue Thermomechanical Processing of Steels)
The microalloying with niobium (Nb) and titanium (Ti) is standardly applied in low carbon steel high-strength low-alloy (HSLA) steels and enables austenite conditioning during thermo-mechanical controlled processing (TMCP), which results in pronounced grain refinement in the finished steel. In that respect, it is important to better understand the precipitation kinetics as well as the precipitation sequence in a typical Nb-Ti-microalloyed steel. Various characterization methods were utilized in this study for tracing microalloy precipitation after simulating different austenite TMCP conditions in a Gleeble thermo-mechanical simulator. Atom probe tomography (APT), scanning transmission electron microscopy in a focused ion beam equipped scanning electron microscope (STEM-on-FIB), and electrical resistivity measurements provided complementary information on the precipitation status and were correlated with each other. It was demonstrated that accurate electrical resistivity measurements of the bulk steel could monitor the general consumption of solute microalloys (Nb) during hot working and were further complemented by APT measurements of the steel matrix. Precipitates that had formed during cooling or isothermal holding could be distinguished from strain-induced precipitates by corroborating STEM measurements with APT results, because APT specifically allowed obtaining detailed information about the chemical composition of precipitates as well as the elemental distribution. The current paper highlights the complementarity of these methods and shows first results within the framework of a larger study on strain-induced precipitation.
Keywords: niobium-titanium microalloyed steel; electrical resistivity; atom probe tomography; scanning electron microscopy niobium-titanium microalloyed steel; electrical resistivity; atom probe tomography; scanning electron microscopy
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MDPI and ACS Style

Webel, J.; Herges, A.; Britz, D.; Detemple, E.; Flaxa, V.; Mohrbacher, H.; Mücklich, F. Tracing Microalloy Precipitation in Nb-Ti HSLA Steel during Austenite Conditioning. Metals 2020, 10, 243.

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