Physical and Numerical Simulations of Closed Die Hot Forging and Heat Treatment of Forged Parts

Abstract

The paper describes physical and numerical simulations of a manufacturing process composed of hot forging and controlled cooling, which replace the conventional heat treatment technology. The objective was to investigate possibilities and limitations of the heat treatment with the use of the heat of forging. Three steels used to manufacture automotive parts were investigated. Experiments were composed of two sets of tests. The first were isothermal (TTT) and constant cooling rate (CCT) dilatometric tests, which supplied data for the identification of the numerical phase transformation model. The second was a physical simulation of the sequence forging-cooling on Gleeble 3800, which supplied data for the validation of the models. In the numerical part, a finite element (FE) thermal-mechanical code was combined with metallurgical models describing recrystallization and grain growth during forging and phase transformations during cooling. The FE model predicted distributions of the temperature and the austenite grain size in the forging, which were input data for further simulations of phase transformations during cooling. A modified JMAK equation was used to calculate the kinetics of transformation and volume fraction of microstructural constituents after cooling. Since the dilatometric tests were performed for various austenitization temperatures before cooling, it was possible to include austenite grain size as a variable in the model. An inverse algorithm developed by the authors was applied in the identification procedure. The model with optimal material parameters was used for simulations of hot forging and controlled cooling in one of the forging shops in Poland. Distributions of microstructural constituents in the forging after cooling were calculated. As a consequence, various cooling sequences during heat treatment could be analyzed and compared.

Physical and Numerical Simulations for Predicting Distribution of Microstructural Features during Thermomechanical Processing of Steels

“…Three-step forging of the part shown in Figure 17a was considered. The details of the industrial forging process for this part are given in [36], where more information on the application of Forge 3D to simulations of hot forging can be found. The results of FE simulations in the form of temperature distribution after subsequent stages of forging are presented in Figure 17b-d The solution of the stochastic evolution Equation (1) can be performed for each Gauss point of the FE mesh, accounting for the current local temperatures and strain rates.…”

Experimental and Numerical Investigation of Folding Process—Prediction of Folding Force and Springback

“…Various examples of processes where coupled thermomechanical models are commonly used have been illustrated in the literature. In thermoforming and hot forming processes, coupled thermomechanical models are crucial [26][27][28]. They enable the prediction of material behavior, including plastic deformation and springback, accounting for temperature changes during forming.…”