Source: https://www.researchgate.net/profile/Didier_Chicot/publication/45690155_Caracterisation_physique_et_mecanique_de_l'acier_4140_nitrure_et_implante/links/55e6deb708aed3ee06b4d2ad/Caracterisation-physique-et-mecanique-de-lacier-4140-nitrure-et-implante.pdf