CASE HARDENING STEEL

• Main Authors: AIHARA KENJI, MURAI NOBUHIRO, KANBARA SUSUMU
• Format: Patent
• Language: English
• Published: 02.07.1990
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; METALLURGY; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PURPOSE:To drastically improve the bending fatigue resistance and rolling fatigue resistance after carburizing and hardening in the subject steel by adding specific amt. of B to a case hardening steel having specific compsn. in which an imperfect hardening layer, intergranular oxidation and the grain boundary segregation of P are reduced. CONSTITUTION:The case hardening steel contains, by weight, 0.1 to 0.4% C, <0.15% Si, <0.5% Mn, <0.015% P, <0.30% Cr, 0.20 to 2.5% Mo, <5.0% Ni, 0.0010 to 0.0050% B, 0.010 to 0.060% sol Al, 0.0060 to 0.0200% N and the balance Fe. Each 0.01 to 0.10% of one or more kinds among Nb, V and Ti may furthermore be incorporated into the steel. In the steel, B is added not to improve the hardenability but for the purpose of strengthening the grain boundaries in the carburizing layer; it segregates into the original austenitic grain boundaries in the carburizing layer to strengthen the grain boundaries. As for the quantity to be added, for the upper limit or more, AlN is reduced and the coarsening of austenite is generated during the carburizing to deteriorate the bending fatigue limit and rolling fatigue limit and, for the lower limit or less, the effect of strengthening the grain boundaries is reduced.