Alloying Strategy Boosts Powertrain Performance（合金策略提高动力性能）.pdf

TECHNICAL Alloying Strategy Boosts Powertrain Performance Patrik Ölund and Garry Wicks The development of a new, gas-carburized gear steel, necessitated by a customer-driven specification, has not only increased the power density in an existing gearbox design, but has done so without requiring any significant change to production processes or heat treatment equipment. Introduction under rotating bending fatigue When a customer specified an increase conditions. The literature sug- in the power throughput of an existing gested that if the internal oxida- gearbox design, they approached Euro- tion could be reduced to 2 µm, a pean steel maker Ovako AB with a re- potential gain of 100 MPa in the quest for a new-generation gear steel. fatigue limit could be achieved Patrik Ölund, head of research and de- (Fig. 2). The customer confirmed velopment at Ovako, and Garry Wicks, that if this increase in the fatigue Ovako research engineer, demonstrate limit could be achieved in the here how a novel approach to alloy- gear steel, the powertrain would ing strategy enabled them to increase be able to handle the increased the fatigue limit of the steel by 20 per- power transmission levels. cent and still meet tough production The cause of the oxidation was constraints. Improvements in the sur- depletion of the alloying ele- face fatigue strength of atmosphere- ments near the surface during carburized steel gears have enabled a the carburizing process, which manufacturer to increase the power was reducing hardenability and throughput of an existing gearbox de-