Simulation of Runout Table Cooling

Abstract

Accelerated cooling on the runout table of hot mills has become a key technology to produce thermo‐mechanically controlled processed (TMCP) steel plates and strips. During runout table cooling austenite decomposition takes place and determines the final microstructure and, hence, the properties of the hot‐rolled steel. There is an increased tendency to produce higher strength TMCP steels with complex microstructures including bainite and martensite. To tailor these microstructures, it is required to carefully design runout table cooling paths and lower the cooling stop and coiling temperature, respectively, for producing flat products with homogeneous mechanical properties. Thus, simulation of runout table cooling is a crucial aspect of process modeling. In the present paper, the status of runout table simulation approaches is reviewed. In particular, the three boiling mechanisms of water cooling, that is, nucleate, transition, and film boiling are discussed. The development of appropriate heat transfer coefficients is rather mature for nucleate and film boiling, respectively. Modeling and controlling the transition boiling regime below the Leidenfrost temperature remains a challenge as heat extraction rates increase with decreasing steel temperature. The status of heat transfer simulations for transition boiling is thus discussed in detail. Currently, the proposed heat transfer correlations, while increasingly based on the underlying physics, still contain a number of empirical parameters that require tuning with experimental and/or mill data. The review is limited to information in the open literature while recognizing that a number of proprietary in‐house runout table cooling models exist that are developed either by equipment makers or steel companies to control accelerated cooling to lower cooling stop or coiling temperatures.

Transient Bottom Jet Impingement Cooling of Steel

“…Experimental results show the possible existence of all the boiling mechanisms i.e. nucleate, transition and film boiling for the range of temperatures relevant to run-out table cooling, as reviewed by Wolf et al 5) and Guedia et al 7) Water jet impingement cooling experiments can be conducted either under steady state or transient conditions. Run-out table cooling can be simulated by pilot scale transient experiments with stationary and moving plates, respectively.…”

“…an impingement zone close to the water jet and a parallel flow zone at a distance farther from the jet. 7,15) Top cooling experiments were conducted under transient conditions by Ishigai et al 8) on stainless steel to study heat transfer in the stagnation line, i.e. the jet centerline.…”

Modeling and Simulation of Steel Rolling with Microstructure Evolution: An Overview

“…The specific heat, thermal conductivity coefficient, and enthalpy change of each phase are obtained from thermodynamic calculations using either thermodynamic database software such as ThermoCalc, BISRA, and JMatPro or values from previous literatures. [46,178] The heat transfer at the surface is based on convection and radiation which are as follows.…”

“…There have been many reports on obtaining the most accurate thermal properties for various purposes; however, some adjustments may be required for feasible prediction results. [178][179][180] Gan and Jang developed an algorithm utilizing the conjugated-gradient method to optimize the heat transfer coefficient to achieve uniform temperature distribution and minimum residual stress during cooling of H-shaped steel beam. [180]…”

“…The specific heat, thermal conductivity coefficient, and enthalpy change of each phase are obtained from thermodynamic calculations using either thermodynamic database software such as ThermoCalc, BISRA, and JMatPro or values from previous literatures. [ 46,178 ] The heat transfer at the surface is based on convection and radiation which are as follows. where the heat transfer by radiation ( q rad ) is expressed by the Stefan–Boltzmann constant ( σ ), emissivity ( ε ), and temperature. [ 4 ] The heat transfer by convection ( q conv ) is expressed by convective heat transfer coefficient ( h ) and temperature.…”