Anisotropies and inhomogeneities in the microstructure of the case hardening steel SAE 5120

Abstract

AbstractDistortion is an effect of inhomogeneous strain behavior. It can be initiated by plasticity due to thermal or transformation stresses (such as yielding, creep and transformation plasticity), phase transformations or strains during phase transformations. Inhomogeneities in microstructure and anisotropies constitute a distortion potential. Based on this knowledge several investigations were carried out on forged disks with a centered hole made of low alloy steel SAE 5120 (EN 20MnCr5) because both inhomogeneity and anisotropy have been observed in the microstructure of this material. Disks have been forged from continuous cast and hot rolled bar material. They show an inhomogeneous banded microstructure that is explicitly orientated in the direction of the two manufacturing processes. By forging, the initial microstructure of the bar material is influenced significantly: the segregation bands parallel to the rolling direction are deformed into a typical pattern. Besides this inhomogeneity in microstructure also the inhomogeneities of the bar material, such as center segregations from continuous casting, can still be observed in the deformed material. Gear blanks were machined from these disk blanks. It has been shown that the original position of the gear blank inside the disk blank influences the distortion [1]. The underlying reason remained unclear and investigations on this topic are discussed in this paper.