Abstract
Large size forged ingots, made of high strength steel, are widely used in aerospace, transport and energy applications. The presence of internal voids in the as-cast ingot may significantly affect the mechanical properties of final products. Thus, such internal defects must be eliminated during first steps of the open die forging process. In this paper, the effect of in-billet void positioning on void closure throughout the ingot breakdown process and specifically the upsetting step in a large ingot size steel is quantitatively investigated. The developed Hansel-Spittel material model for new high strength steel is used in this study. The ingot forging process (3D simulation) was simulated with Forge NxT 1.0® according to existing industrial data. A degree of closure of ten virtual existing voids was evaluated using a semi-analytical void closure model. It is found that the upsetting process is most effective for void closure in core regions and central upper billet including certain areas within the dead metal zone (DMZ). The volumetric strain rate is determined and two types of inertial effects are observed. The dependence of void closure on accumulated equivalent deformation is calculated and discussed in relation to void in-billet locations. The original combination of information from both relative void closure and the volumetric strain rate provides a way to optimize the forging process in terms of void elimination.
Highlights
Internal voids can have harmful consequences on material integrity if left unchecked
{ } 1 (σ1 − σ 2 )2 + (σ 2 − σ3 )2 + (σ1 − σ3 )2 (1). These parameters give a significant amount of information for successful void closure [5], their applicability to industrial size forgings demands the use of powerful simulation tools [6]
A full field finite element simulation was generated in order to obtain significant data for macroscopic equivalent strain and stress tensor components using Forge NxT 1.0®
Summary
Internal voids can have harmful consequences on material integrity if left unchecked. Voids, developed during the solidification of a large cast steel ingot [2] and mostly found in the central upper ingot and in core regions along the central axis [3], are significantly affected Their closure ensuresa sound material, an effective forming process and industrial progress in this field. These parameters give a significant amount of information for successful void closure [5], their applicability to industrial size forgings demands the use of powerful simulation tools [6]. The effects of the combined criteria are discussed for a plausible optimisation of the forging process
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