Failure analysis of laser directed energy deposited high-strength alloys on the bainitic crossing noses in a rolling-sliding contact

The 17-4PH, 420SS, and 18Ni300 deposits were prepared to repair the bainitic crossing nose via laser directed energy deposition (L-DED) technology, and their mechanical properties, wear and rolling contact fatigue (RCF) damage behaviors and microstructure evolution were analyzed. The findings indicate that 420SS and 18Ni300 deposits exhibit higher yield strength compared to the bainitic crossing nose, and 18Ni300 and 17-4PH deposits demonstrate better impact work. The wear mechanism of bainitic crossing nose is fatigue wear, which changes to adhesive wear after preparing high-performance deposits by L-DED. The microstructure evolution law within the deposits is as follows: dislocation accumulation gives rise to the formation of low-angle grain boundaries. Subsequent strain accumulation transforms austenite into martensite within the multiphase structure, leading to the development of subgranular boundaries that evolve into high-angle grain boundaries and eventually nanocrystalline grains. Among the three martensitic steel deposits examined, the 18Ni300 deposit stands out for its good wear and RCF resistance. This superiority is attributed to several factors: the retained austenite hinders RCF crack propagation via the transformation-induced plasticity effect, and numerous nano-precipitates enhance the shakedown limit. Under rolling-sliding contact, the austenite fully transforms into martensite consistent with the parent phase, without micro-regional stress concentrations. These findings can lay a theoretical foundation for regulating the microstructure and performance of deposits, ultimately preventing wear and RCF failures at railway crossings.