ISSN: 1546-962X
CODEN: JAIOAD
Published Online: 4 April 2011
Page Count: 12

Control Strategies for an Inline Cooling Device in Hot Strip Processing of Innovative Steel Materials

Rieger, Thomas
Dept. of Ferrous Metallurgy, RWTH Aachen Univ., Aachen, NRW

Bülters, Oliver
Institute for Metal Forming, RWTH Aachen Univ., Aachen, NRW

Bian, Ing. Jian
ThyssenKrupp Steel Europe AG, Duisburg,

(Received 21 July 2010; accepted 1 March 2011)

Abstract

Heat treatment of steel is used to adjust different microstructures and mechanical properties. The Quenching and Partitioning (Q&P) process or cyclic annealing for grain refinement lead to increased strength and ductility. Both approaches demand a strict temperature control and a close strip temperature tracking. A control strategy for optimal properties is developed. Herefore a one-stand laboratory scale hot rolling process line was equipped with a water cooling section. A detailed temperature control during the cooling process was established accounting for strip thickness and velocity, set point temperatures, and amount of water cooling. While industrial set points and parameters of closed-loop controllers are often empirical, the presented control system and strategies are investigated by MatLab-Simulink. The improved material properties were evaluated in annealing tests. The control system for the cooling track reduces the temperature gradient within the strip to 12 K. The simulation of the cooling track gives an optimal set point. As a prerequisite for a controlled design of time-temperature-cycles, it can be calculated for various process parameters. Grain sizes <5 μm are achieved by cyclic annealing and accompanied by increased strength and ductility. The Q&P treatment produces tempered martensite and retained austenite with improved mechanical properties.

Keywords:
temperature control, heat treatment, steel

Paper ID: JAI103279
DOI: 10.1520/JAI103279
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