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

5.  Non-pollution

Process case                                                                    

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.