*2.1. Material Properties*

Experimental work was conducted on the 300-grade X2NiCoMo18-9-5 maraging steel, which was provided by Deutsche Edelstahlwerke. The given chemical composition of the maraging steel is presented in Table 1. Specimens prepared for fatigue tests were cut out of a delivered maraging rolled plate with a thickness of 9.5 mm (the width of the fatigue test specimen) and then heat-treated. The specimens were first solution annealed for 1 h at a temperature of 820 ◦C, followed by quenching, and artificially ageing for 3 h at 480 ◦C, cooled in air (this process was called maraging precipitation hardening (MPH)). The mechanical properties of the precipitation-hardened maraging steel are listed in Table 2. Before performing the LSP, all the specimens were ground and polished to ensure surface roughness uniformity.

**Table 1.** Nominal chemical composition of the X2NiCoMo18-9-5 maraging steel (unit in wt. %).



**Table 2.** Mechanical properties of the X2NiCoMo18-9-5 maraging steel after the maraging precipitation hardening (MPH) process.
