QPQ is abbreviation of quench-polish-quench. QPQ is a kind of metal surface modification technology, with high corrosion resistance，high wear resistance and non-pollution.
The advantage of QPQ
1. High wear resistance
2. High corrosion resistance
3. High fatigue resistance
4. Little deformation
Auto valve using 4Cr9Si2 steel, the exhaust valve adopt 5Cr21Mn9Ni4N steel.
4Cr9Si2 valve stem and head hardness is 30~37HRC, valve rear hardness more than 48HRC.
5Cr21Mn9Ni4N exhaust valve stem and head hardness is 34~40HRC, valve rear hardness is 50~60HRC after solution. Can also use 4Cr9Si2 steel as the rear and 5Cr21Mn9Ni4N steel welding. The rear after high frequency quenching hardness can reach 55 ~ 63 HRC.
First valve achieve the above technical requirements after preheating process, and then start QPQ treatment , so that forming more than 5 microns compound layer on the surface, increase the high temperature condition of corrosion resistance, abrasion resistance and fatigue resistance.