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 pulsater over a six year period. It was found that the tooth bending fatigue strength of the case hardened SNC815, SCM420H and SCM822H gears is 500〜824N/mm^2, 490〜588N/mm^2 and 392〜530N/mm^2 respectively. Results for nitrided gears made from 31CrMol2 and others and for through hardened gears made from SNCM439 and SNCM630 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.
