The Tooth Bending Strength of Gears of JIS Materials (The Fatigue Test Result of Case Hardened Gears, Nitrided Gears and Through Hardened Gears and the Relationship with the Allowable Stress of the ISO Calculation System)

Abstract

Tooth strength of case hardened, nitrided or through hardened gears depends on the property and quality of gear material, manufacturing and the heat treatments. When Japanese designs gears, tooth bending fatigue strength data for the JIS gear steels is needed. Tooth bending endurance tests for JIS low-alloyed steels for gears and JIS wrought nitriding steels were conducted with pulsator over a six year period. It was found that the tooth bending fatigue strength of the case hardened SNC 815, SCM 420 H and SCM 822 H gears is 500-824 N/mm2, 490-588 N/mm2 and 392-530 N/mm2 respectively. Results for nitrided gears made from 31 CrMo 12 and others and for through hardened gears made from SNCM 439 and SNCM 630 were obtained. The maximum strength value in these tests was 157% of the maximum value of ISO's allowable stress data in case hardened gears, 142% in nitrided gears and 165% in through hardened gears respectively.