Abstract
The thermodynamic heat-transfer mechanisms, which occur as a heated billet cools in an air environment, are of clear importance in determining the rate at which a heated billet cools. However, in finite element modelling simulations, the convective heat transfer term of the heat transfer mechanisms is often reduced to simplified or guessed constants, whereas thermal conductivity and radiative emissivity are entered as detailed temperature dependent functions. As such, in both natural and forced convection environments, the fundamental physical relationships for the Nusselt number, Reynolds number, Raleigh parameter, and Grashof parameter were consulted and combined to form a fundamental relationship for the natural convective heat transfer as a temperature-dependent function. This function was calculated using values for air as found in the literature. These functions were then applied within an FE framework for a simple billet cooling model, compared against FE predictions with constant convective coefficient, and further compared with experimental data for a real steel billet cooling. The modified, temperature-dependent convective transfer coefficient displayed an improved prediction of the cooling curves in the majority of experiments, although on occasion a constant value model also produced very similar predicted cooling curves. Finally, a grain growth kinetics numerical model was implemented in order to predict how different convective models influence grain size and, as such, mechanical properties. The resulting findings could offer improved cooling rate predictions for all types of FE models for metal forming and heat treatment operations.
Highlights
IntroductionThe industrially focused processing of bulk metal forming, and the associated manufacturing operations such as open-die and closed-die forging, played a significant role in global industrialisation and subsequent manufacturing growth and development [1]
Using the Borisov and Gorland [10] experimental data as validation, the graphs presented in Figure 5a illustrate that for the natural cooling experiment, the finite element (FE) model using the temperature-dependent function improved the match compared to the experiment for the measurement taken on the outer edge
A temperature-dependent function for describing the convective heat transfer coefficient between a heated billet and the atmosphere, for both natural and forced convection, has been constructed by using fundamental properties of air-flow including thermal conductivity, air velocity, dynamic and kinematic viscosity and density, forming the Reynolds, Rayleigh, Grashof, and Prandtl numbers. These tabular datasets were used in an FE model to compare cooling curve predictions against a constant convective coefficient model and against the experiment
Summary
The industrially focused processing of bulk metal forming, and the associated manufacturing operations such as open-die and closed-die forging, played a significant role in global industrialisation and subsequent manufacturing growth and development [1]. Whilst forging methods and techniques have developed to allow for smaller, more intricate forging objects to be accurately formed through the process, the development of hydraulic presses and very large forging hammers has, in parallel, driven the use of forging techniques to manufacture huge forgings for very heavy industry, weighing an excess of 50 tonnes. The use of various steels as the primary material for structural use has dominated the global metals industry for over a century, largely due to its superior materials properties, the abundance of iron, and the cost efficiency of manufacture [2]. By alloying with additional elements including vanadium, nickel, molybdenum, chromium, cobalt, and others, in small quantities, specialised alloy steels, for specific purposes, can be produced [3], ranging from corrosion resistant stainless steels to the ultra-hard tool steels
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
