Exploring the mechanical performance and deformation mechanism of non-magnetic steel repaired through laser metal deposition under various strategies

The repair of non-magnetic drilling tools is crucial for improving the cost-efficiency of directional drilling operations. In this study, P530 non-magnetic steels containing keyholes, grooves, and surface defects were repaired using laser metal deposition (LMD). A systematic investigation was conducted to examine the effects of repair ratios and strategies on microstructure, phase composition, magnetic properties, and mechanical performance. Across the repair interface, the microstructure evolved in a gradient manner, from columnar grains in the deposited region to dislocation-free recrystallized fine grains in the heat-affected zone (HAZ), and finally to quasi-equiaxed grains in the base material (BM). This transition was determined by local heat accumulation and repair geometry. The coating was mainly composed of austenite with trace Cr 2 N, with a dominant {100}<001> cube texture accounting for stable paramagnetism. The repaired regions exhibited hardness values comparable to the BM, while the HAZ showed the lowest hardness and served as the primary fracture site. At 10% and 30% repair ratios, keyhole and T-groove repaired specimens achieved ultimate tensile strength close to that of the BM, showing favourable strength matching; elongation remained similar to the BM in T-groove specimens but was significantly reduced in keyhole repairs. At 50% repair ratios, both strategies showed reduced strength and ductility, with quasi-cleavage fracture in keyhole repairs and ductile–brittle mixed fracture in T-groove repairs. Deformation was governed by twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP), which varied with repair geometry. Surface-repaired and clad specimens showed moderate properties, confirming the effectiveness of LMD in restoring non-magnetic steels.