Hydraulic Check Valve hardness over HRC65

In the Spring Festival, I received a confirmed price for a large quantity of hydraulic check valves from Stephen. The contact between Stephen and I is only 2-3 times in the whole last year. It was noted at the end of the email that he needs me to contact him as soon as possible to discuss this hydraulic check valve. Stephen comes from American CASE company. We met the year before last. After communication, it was learned that at the beginning of last year, a bulldozer of their company needed to use hydraulic check valve, the one that AAK had made samples at the beginning. Because the price of AAK hydraulic check valve was 20% higher than that of his original supplier, Stephen did not choose to purchase hydraulic check valve from AAK. Some time ago, the customer complained that the hydraulic pump was damaged due to the sudden increase of hydraulic system pressure. Stephen communicated with the original hydraulic check valve manufacturer and the manufacturer replaced the hydraulic check valve with a new one, but 3 months later, the same problem came again. The customer was very dissatisfied that this delayed the construction and needed the problem solved at one time. Stephen went back to AAK and asked about the price of the hydraulic check valve. He needed us to maintain the quotation offered last year. I asked Stephen why he went back to AAK to purchase the hydraulic check valve. He told that since the first complaint from the customer, their engineers retested the original hydraulic check valve samples. The hardness of AAK sample was the highest, and the material hardness of each part of the hydraulic check valve was no less than HRC65. I know why their hydraulic check valve went on strike in 3 months. When we made the sample, we knew that the working pressure was more than 450bar, which was a challenge for the hydraulic check valve. The material hardness of each part of the hydraulic check valve is required to reach more than HRC65. There may be no more than 5 hydraulic valve manufacturers that can reach this level in Ningbo. Stephen wondered why the material hardness of each part of AAK hydraulic check valve can be over HRC65? 1. Material selection is the core. AAK adopts 20CrNi2MoV high carburizing bearing steel imported from Germany for this hydraulic check valve. 2. Heat treatment is the key. Through secondary quenching + cryogenic treatment + low-temperature tempering process, it is cooled to 650 ~ 700 and put into the furnace. After cooling to 450 ~ 500 , it is discharged from the furnace. The micro hardness is 237 ~ 247 HV. 3. In the later stage, point-to-point testing is the key. SonoDur3, a Rockwell hardness tester imported from Germany, adopts the UCI hardness test method, and the test program is fast and mobile to carry out nondestructive testing on the hardness of each component of the hydraulic check valve efficiently and accurately.