Effect of Material Change from 20MnCr5 to EN 353 on Fatigue Performance of Crown Wheel Pinion ( Hypoid Gear Sets) of Full Float Axles - Case study

Abstract

Crown wheel pinion is a prime member in transferring the power from transmission to wheel ends in automotive truck axles. Gear material is one of the deciding factors to estimate the fatigue life of the part. Higher the fatigue characteristics of the material better the fatigue performance of the part. In this case study, heavy truck axle with particular size having deep gear ratio is considered for material change from DIN 20MnCr5 to BS-EN 353, because its challenging to meet the life requirement in deeper gear ratios typically above 6. The basic material comparison conducted for metallurgical properties, jominy values, heat treatment properties, fatigue endurance limits, impact strength & fracture toughness. The analysis shows the EN 353 has 50% better impact strength, 35% better fracture toughness & 6.5% better endurance limit than that of 20MnCr5. The impact strength of EN 353 is 50J where as 20 MnCr5 is 25J, the fracture toughness of EN353 is 99.5 MPa√m & that of 20MnCr5 is 64.3MPa√m. The fracture toughness is calculated using Roberts-Newton formula. The endurance limit for EN 353 is 1000MPa & that of 20MnCr5 is 935MPa. The case carburized results show EN 353 has better case structure than 20MNCr5. The total 12 Numbers of gear sets, 6 each for 20 MnCr5 & EN 353, are validated for gear set fatigue on bench for particular torque. The performance of EN 353 is 24% better than 20MnCr5. The fatigue life of EN 353 is 39983 Cycles & that of 20MnCr5 is 30212 Cycles. The fracture mode is same in both the grades & typical fracture is on the Pinion. This study shows us the material change over is contributed significantly by improving the fatigue life of crown wheel pinion particularly for deeper gear ratios in heavy truck axles.