Boriding as a post-treatment to homogenize mechanical and tribological properties in weld-repaired AISI D2 tool steel

This study evaluates boriding as a post-treatment to improve the surface and tribological performance of AISI D2 tool steel repaired by GTAW using ER308L filler. Compared to quenching and tempering, boriding increased surface hardness, reaching 34.5 ± 0.4 GPa in the repaired zone and 31.8 ± 3.3 GPa in the base material. XRD confirmed the presence of FeB, Fe₂B, and CrB phases in the boride coating formed on both regions. Severe perpendicular cracks were predominantly observed in the base material. VDI 3198 testing showed lower adhesion in the base material, whereas scratch tests revealed lower critical loads in the repaired zone. Microabrasion tests showed that boriding reduced volume loss and friction coefficient by 28 % and 40 %, respectively, while also eliminating differences between the base and repaired zones. In dry reciprocating sliding tests where both regions were simultaneously evaluated, boriding reduced total wear volume by ∼80 % and decreased the coefficient of friction by 25 %. Wear mechanisms and material loss were also more uniform across the borided surfaces. These results demonstrate that boriding improves surface hardness, adhesion, and wear resistance in weld-repaired tool steels while promoting more uniform mechanical and tribological performance. Optimization of boriding parameters is still needed to reduce crack formation in the coating.