For certain applications in the world of internal combustion engines (ICE), it has been found that nitrided valves have a better performance against wear than those which are seat hard faced and chrome plated. This alternative has not been significantly explored in the Medium Duty (MD) and Heavy Duty (HD) markets.
Fully nitrided MD/HD valves, mostly hard faceless, would be less expensive than chromed ones. They may become a cost effective product with better tribological performance, higher fatigue strength and improved resistance to thermal shock. In addition to this, a proper selection of the counterpart materials, those of the valve seat insert (VSI) and the valve guide (VG) will have a synergetic effect on the valve set performance, also leading to its cost improvement.
Not less important is the replacement of the well-known salt bath nitriding by the gas nitriding technique, an environmentally friendly process that maintains valve performance with the advantage of employing a lower nitriding temperature providing a higher tip end and seat hardness combined with a lower distortion level in the final product.
The aim of this work is to present the development and introduction of fully nitrided valves as a reliable solution for nowadays MD/HD applications. It is based on a deep process and product validation including the development of the gas nitriding process, wear, fatigue and engine tests.