Results

During the 1st reporting period, the following research activities were conducted:

The manufacturing of industrial casts of one reference carburizing steel grade and three other steels suitable for alternative surface hardening treatments, with the aim to produce gears working at rotating speeds as high as 15,000 rpm without suffering relevant fatigue and scuffing problems. Besides the reference 27MnCr5, an alternative carburizing steel for a new carburizing and quenching process (20NiCrMo2) and, for nitriding and nitrocarburizing, one Q&T steel (40CrMoBi4) and one F-P microalloyed steel (36MnSiV4) have been casted, hot rolled and characterized.

In order to guarantee that the modification of the traditional route of gear manufacturing does not affect drastically the total cost of the component, the main process steps were evaluated. Hot forgeability has been assessed, showing a good performance for all the studied steels, although slightly lower for the Q&T steel 40CrMoBi4. Rough and hard machinability have been evaluated, showing opposite results due to the different hardness of steels for each condition of machining.

Optimization of the surface hardening parameters has been done to achieve the specified surface hardness and case hardening depth (CHD) for each steel and heat treatment (conventional carburizing and HPGQ, LPC+WSQ, nitriding and nitrocarburizing). Besides the difficulties to achieve the narrow window for the Stellantis specification of CHD for the four steels, the optimization of the process LPC+WSQ has been longer than expected due to the random occurrence of quenching microcracks.

A detailed metallurgical analysis of the hardened case has been carried out for the six combinations of steel grades and heat treatments. Fatigue and tribological tests have started, but they accumulate a delay of six months due to the drawbacks to optimize the surface hardening treatments.

Dissemination activities include the creation of a project website (www.topgear-project.eu), which is regularly updated with TOPGEAR events and outcomes.