Effect of Residual Stress on Cracking of Hot Die-Forged Brass Fittings

Abstract

Lead brasses, i.e. copper-based alloys with additions of zinc and lead, are widely used for production of specific components in the industry and commerce. Brass components are usually produced under hot conditions, i.e. via hot die forging (with the advantageous applications of induction heating), the semi-products for which are typically rods extruded from cast billets. Finally, the components are machined to their exact shapes. Nevertheless, such a complicated production process is prone to introduce defects in the structures of the final components. The herein presented paper deals with investigations of a brass component (pre-shaped gas valve, i.e. fitting) manufactured via hot die forging. The fitting exhibited cracking in a specific location after forging and the presented investigation attempts to characterize the factors, which could have possibly induced the occurring cracking, from the viewpoint of stress distribution. The experimental investigation focused on characterization of the structure in the vicinity of the cracked area with the particular focus on the occurrence of residual stress via scanning electron microscopy. This analysis was supported with the results of stress-strain distribution during forging acquired via numerical simulation of the die forging processing step (with implemented induction heating prior forging, in accordance with the real industrial conditions) performed using the finite element method (FEM). According to the acquired results, the cracking occurred in a location featuring local inhomogeneity of stress. The inhomogeneous distribution of stress in the particular location most probably developed as the result of the geometry of the forging die, which also introduced instabilities in the material plastic flow during forging.