Effect of clad orientation on the mechanical properties of laser-clad repaired ultra-high strength 300 M steel

Abstract

Repair of high-performance steels such as 300 M is a subject of recent interest owing to the significantly high costs of maintenance, repair and overhaul (MRO). Laser cladding is an ideal repair and surface treatment technology with benefits over conventional metal repair techniques. It is well known that steel structures subjected to rapid heating and cooling cycles, such as that administered during laser-metal processing, demonstrate anisotropic properties due to non-uniform microstructures. Despite the reported sensitivity to loading direction, there is very little literature on the effect of the orientation of single layer laser clad tracks on the mechanical properties of repaired coupons. Therefore, in this study, an investigation of the effect of clad orientation on the microstructural and tensile properties of 300 M cladded specimens was carried out. Longitudinal (LC), inclined (IC), and transverse (TC) clads were studied, with orientations 0°, 45°, and 90°, respectively, to the axis of the tensile loading direction. The cross-sectional micrographs showed the presence of untempered martensite in the core of the clad tracks and tempered martensite along the inter-track boundaries and the clad-HAZ interfaces, irrespective of the clad orientation. However, the changes in the alignment of these martensitic phases to the load direction resulted in differences in the tensile properties of the three clad orientations. TC specimens exhibited higher tensile strength and ductility compared to the LC and IC specimens, and better tensile strength and Young’s modulus compared with grind-out only specimens. This was attributed to the occurrence of alternate bands of hard untempered martensite and softer tempered martensite perpendicular to the loading axis, thereby improving the toughness of the TC specimens. Hence, better cladding strategy is required to be implemented to further enhance the mechanical properties of the laser clad repaired components.