A complex B-C-N diffusion coating was produced at 580 degrees C for 1 h on AISI M35 steel substrate and compared with a reference coating formed at 880 degrees C for 2.5 h. The surface and the cross-sections of the samples were subjected to detailed characterisation. The surface roughness, hardness, residual stresses and adhesion of the coatings were also evaluated together with cutting tests using drills on coated and uncoated samples while monitoring cutting force and torque. The surface of the steel treated at 580 degrees C revealed Fe2B, boron nitride and boron iron carbide, but FeB was noted to be absent. The 580 degrees C coating had the fine-scale microstructure, which resulted in the excellent adhesion and enhanced wear resistance, relative to reference samples that contained coarse borides. The results established that a complex fine-scale diffusion coating enhanced the wear resistance and reduces the cutting force and torque during drilling, thereby increasing the drill life by a factor of 2.2. (C) 2017 Elsevier B.V. All rights reserved.