Micropitting damage, commonly seen in case-hardened gears, gradually deteriorates the contact surface geometries, potentially leading to macropitting and fatigue failure. A previous CETIM [1] study based on gear contact fatigue tests investigated the effect of shot peening on the micropitting and its development to macropitting on case-hardened gears. A specific shot peening is employed to optimize the surface roughness of the flanks. Initial inspection of gear specimens revealed that shot peening resulted in higher surface residual stresses and lower surface roughness compared to ground tooth flanks (without shot peening). Experimental results showed that while both specimens exhibited micropitting, it was more pronounced on the shot-peened tooth flanks, with greater tooth profile loss. However, it was found that shot peening delayed the onset of macropitting, extending the gear’s durability by more than 50%. This work seeks to explore why shot-peened gears, despite exhibiting higher surface residual stresses and reduced surface roughness, deteriorate more quickly. Analyses were carried out, including surface damage assessments using microscopy and interferometric profiles, and damage mechanism analysis through EBSD technique. Results showed micropitting craters of 10-100 μm in size and 1-5 μm in depth, with significant crystallinity reduction in worn areas. Tribological tests were also conducted on tribometer according to ASTM G-133 in crossed cylinder/cylinder mode to measure the friction coefficient. These tests allowed the reproduction of micropitting on the non-peened surface of cylinder extracted from gear after 20 000 cycles, while no micropitting was observed on a shot-peened surface even after 340 000 cycles. Keywords: Spur gears, micropitting, fatigue, shot peening, roughness, residual stress, EBSD [1] D. Jbily, F. Lefebvre, A. Simonneau, The influence of shot peening on gear teeth micropitting and contact fatigue failure, Procedia Structural Integrity, Volume 57, 2024, Pages 199-216, ISSN 2452-3216