To improve the quality of the engine valve, so that its service life is longer, the valve surface must be strengthened treatment, common strengthening treatment methods are as follows:

1、 rolling

Rolling can make the metal surface plastic deformation, the formation of a large residual compressive stress, improve the fatigue strength and wear resistance of the material. Rolling to avoid valve locking clip groove fracture has a significant effect, rod rolling not only improves wear resistance, but also reduces the wear of the valve guide, when the valve taper rolling, its roughness up to 0.2 or less, the hardness of the surface can be increased HRC6 ~ 8.

2、Aluminum infiltration

Aluminum infiltration on the surface can significantly improve the oxidation resistance, heat resistance and wear resistance of the valve. Aluminum infiltration of many methods, and the better process is a high-frequency heating spray plating aluminum, that is, first in the preheating coil in the valve head heated to about 300 ℃, and then to the cone surface spraying aluminum and further high-frequency heating to 700 ~ 1000 ℃, so that the aluminum spraying layer of part or most of the formation of ferro-aluminum alloy layer, the thickness of the aluminum diffusion layer needs to be reached 15 ~ 25 μm, the highest of 40 μm, the iron and aluminum alloy layer of the Vickers hardness is slightly improved. The Vickers hardness of the ferro-aluminum alloy layer is slightly increased.

3、Chrome plating

For poor sliding performance in the valve guide valve steel (such as austenitic steel), most of the rod can be chromium plating, chromium plating can be abrasion-resistant and not easy to build up carbon, rod chromium plating layer thickness of about 0.03 ~ 0.04mm, plating for fine grinding.

4、Nitriding

Nitriding has significant effect on improving the wear resistance and fatigue strength of the valve. As the nitriding layer is generally thin, nitriding can be done after micro-grinding, does not allow other heat treatment and cutting, so the nitriding parts before finishing and tempering treatment. In order not to affect the mechanical properties of the material and the accuracy of the parts in the nitriding process, the nitriding temperature is generally 500 ~ 570 ℃, not more than the tempering temperature in the tempering treatment, valve nitriding most of the low-temperature vacuum ion nitriding or nitrocarburizing.

5、Surface quenching

Valve made of martensitic heat-resistant steel or alloy structural steel, the general use of surface quenching to improve the hardness of the rod end, at the same time, the valve stem surface and the intake valve cone surface can also be used to improve the wear resistance of surface quenching.

With the engine power, burst pressure and other enhancements to improve the degree of the load, temperature and other gradual increase in the valve cone surface, the more complex and harsh conditions make the valve surface strengthening is particularly important.