Sensitivity Analysis of Oxide Scale Influence on General Carbon Steels during Hot Forging

Abstract

Abstract:Increasing product requirements have made numerical simulation into a vital tool for the time-and cost-efficient process design. In order to accurately model hot forging processes with finite, element-based numerical methods, reliable models are required, which take the material behaviour, surface phenomena of die and workpiece, and machine kinematics into account. In hot forging processes, the surface properties are strongly affected by the growth of oxide scale, which influences the material flow, friction, and product quality of the finished component. The influence of different carbon contents on material behaviour is investigated by considering three different steel grades (C15, C45, and C60). For a general description of the material behaviour, an empirical approach is used to implement mathematical functions for expressing the relationship between flow stress and dominant influence variables like alloying elements, initial microstructure, and reheating mode. The deformation behaviour of oxide scale is separately modelled for each component with parameterized flow curves. The main focus of this work lies in the consideration of different materials as well as the calculation and assignment of their material properties in dependence on current process parameters by application of subroutines. The validated model is used to carry out the influence of various oxide scale parameters, like the scale thickness and the composition, on the hot forging process. Therefore, selected parameters have been varied within a numerical sensitivity analysis. The results show a strong influence of oxide scale on the friction behaviour as well as on the material flow during hot forging.

Forming and Oxidation Behavior During Forging with Consideration of Carbon Content of Steel

“…The determination of the flow curves of the individual iron oxides was based on Hensel-Spittel approach 8 taking into account the forming temperature and the strain rate [22].…”

“…However, additional boundary conditions were necessary for the thermo-mechanical simulation. Based on the studies of Tominaga et al [23] and Sun [24], an oxide composition with 64% wustite, 30% magnetite, and 6% haematite was determined for an oxidation temperature of 1000 • C for the first numerical investigations [22]. Other previous studies have shown that the heat transfer coefficient for undamaged scale coatings is lower by a factor of 10-15 than for steel [25,26], whereby the heat loss to the tools is decreased.…”

Advances in Plastic Forming of Metals

“…They use the modeling tool to design multiple-pass dies as an alternative to single-pass extrusions which would be prone to central-burst. Behrens et al [3] numerically examine the formation of an oxide scale during hot forging of steel and it effect on material flow and frictional conditions. Alexandrov et al [4] examine the formation of a severely-deformed layer near the surface due to friction-induced shearing.…”

Reduction of Die Wear and Structural Defects of Railway Screw Spike Heads Estimated by FEM

“…They proposed a multi-objective optimization approach on A309 aluminum alloy through the design of experiments, simulation and hydraulic press forming. They found that by combining the operational parameters, the lifespan of the dies could be increased by 23.5% compared to the original process condition. Additionally, replacing the forging dies significantly impacts the process costs, which can reach up to 30% [17].…”

“…After producing parts with the adjusted process, they did not present surface defects and their mechanical properties were 10% higher than those specified in the technical drawing. Additionally, Behrens and coworkers [23] developed a finite element model describing scale behavior to be incorporated into commercial software used to simulate these processes, given the influence of scale formation on friction and material flow in forging die cavities.…”