My story is somewhat related to Mario's. We are using sleeves manufactured from CF8M by investment casting (followed by SA at about 2000 F then quenched). The sleeves are then machined to size (a few thousands of an inch taken out) then permanently mounted within the choke assembly by "crushing" it (the crush area is a thinner section at the top of the sleeve). We never had any problems with 316, duplex or inconel. But the CF8M rezulted in a crack in the crush zone. What could be the culprit? The ferrite content is 10% (per microanalysis). Will a stress relieve prior to installation (after machining) help? Shall we control the ferrite content? How can you tell if too much srinkage after casting occurred (the final dimensions were OK) and can it be detrimental to the toughness?
Thanks,
Irina
