Forming and oxidation behavior during forging with consideration of carbon content of steel

Abstract

Developments in technology rely increasingly on the numerical simulation of single process steps up to whole process chains using commercially available or user-written software systems, mostly based on the finite element method (FEM). However, detailed simulations require realistic models. These models consider the relevant material-specific parameters and coefficients for the basic material, surface phenomena, and dies, as well as machine kinematics. This knowledge exists to some extent for certain materials, but not in general for groups of steel that depend on alloying elements. Nevertheless, the basic material and its behavior before, during, and after hot deformation must be understood when designing and describing die-forging processes by experimental and numerical simulations. This is why a new mathematical approach has been formulated for forming behavior and recrystallization kinetics, taking into account the carbon content of the base material, the initial microstructure, and the reheating mode. Furthermore, there have been no studies investigating the influence of varying a single chemical element, such as the carbon content, with regard to the oxidation behavior, including the internal structure (e.g., pores) at high temperatures. In this context the majority of studies were performed with steel grade C45 (material no. 1.0503), which was chosen as base material for the experiments conducted. To identify the effects of the alloying element carbon on the material and oxidation behavior, steel grades C15 (material no. 1.0401) and C60 (material no. 1.0601) were also investigated. The investigations revealed a dependence of the material behavior (microstructure and surface) on the alloying system. Based on the experimental results, the mathematical models formulated were parameterized and implemented in the FE-software Simufact Forming (Simufact Engineering GmbH, Hamburg, Germany) by means of user subroutines. Furthermore, a correlation between the thickness of the oxide scale layer and friction was determined in ring compression tests and accounted for in the software code. Finally, real forging tests were carried out under laboratory conditions, with all three investigated steels for calibration of the materials as well as the FE models.