STP1532: 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, NRW

    Pages: 18    Published: Apr 2012


    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: STP153220120007

    Committee/Subcommittee: D02.L0

    DOI: 10.1520/STP153220120007


    CrossRef ASTM International is a member of CrossRef.