Heat treatment of long products

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.

An in-line heat treatment of rolled materials is becoming frequently used by hot rolling plants. This method achieves the required material structure without the necessity of reheating. This paper describes a design procedure of cooling sections for obtaining the demanded structure and mechanical properties. Experimental stands, applied for the cooling study of steel samples, were built at the Brno University of Technology. The first experimental stand enables to simulate a variety of cooling regimes and evaluate the final structure of the tested samples which are instrumented by set of thermocouples indicating the temperature history of the tested material. The second experimental stand is a tool for the design of the cooling sections which can ensure obtaining demanded heat treatment procedure and demanded final structure. The heat transfer coefficient history at the surface is gained as an output of the inverse task. Mathematical model and its implementation into the software tool for computer simulation of heat treatment processes (quenching and tempering) of steel is presented. Heat transfer boundary conditions obtained from test on experimental stand are used for calculation of cooling curves followed by prediction of microstructure after austenite transformation and final mechanical properties as hardness, tensile strength and yield stress. The software QTSteel used for computer simulation of heat treatment of long products has been developed by ITA Ltd. Verification and practical examples of metallurgical predictions for long products, especially tubes and bars, are presented.