The difference of 379HB between the surface hardness of 2Cr13 surfacing Stellite NO.6 and that of 379HB is more than 50HB. The 17-4PH steel is heat-treated with 1040 ℃ for 1h, air cooling, 610 ℃ for 4h, and air cooling. Its hardness is 329HB. During the heat treatment of forging blanks, attention should be paid to the starting point of martensite transformation and the temperature of aging treatment. Transformation point The martensite starting transformation point Ms of 17-4PH steel is about 121 ℃, and the transformation ending point Mf is about 32 ℃. The valve seat is a large section part, which should be preheated at 650 ℃, then heated to 1040 ℃ in a high temperature furnace for 1h, air cooled, and needs to be quickly cooled to below 32 ℃, that is, air cooled, water cooled or oil cooled. In order to prevent cracking, air cooling is often used.

Question 2: If there is a lack of air source, how to ensure the opening and closing of pneumatic butterfly valve? It is very clear to all that pneumatic butterfly valve is used to realize various actions of the device with the help of air source, including valve opening and closing. It is not difficult to imagine that if the butterfly valve lacks such an important medium as air source, can it still operate normally? Even with manual pneumatic device, can the goal be achieved? Please remember that if the pneumatic butterfly valve can be started normally, the corresponding air source must be available first, so as to complete the opening and closing action. If the air source is gone, a manual device can be installed, which can have a double fuse.