Gas Nitride Issues: Blistering & Flaking on H-13

[Jerry Van]

We manufacture parts out of H-13 forgings. A typical dimension is 18"L x 11.5"W x 4.5"H. Parts are machined and heat treated to Rc 44/47. They are then rough ground in several areas, allowing .002 per surface for final grind after gas nitride. They are then nitrided to a case depth of .012". On several recent occasions, the parts are received back from nitride with considerable blistering on surfaces that had not been rough ground prior to nitride. However, not all parts in a nitride run will exhibit blistering, and of the blistered parts, the blistering may be scattered, with perhaps one or two sides blistered, but the others clean. Our last nitride run was the worst we've experienced, with not only blistering, but with flaking as well. Our long time heat treat source is at a loss to explain the issue, as runs for other customers, done before and after our parts, have no problems. Any thoughts on this issue??

Thanks,

Jerry Van

 

[Jerry Van]

Here's some pics...

 

[Jerry Van]

Here's another pic...