Gas Nitriding problems in a GGG60 cast iron punching die

[danava71]

Attached you will find three micrographs of a punching die, made of a gray cast iron (GGG60), that was gas nitrided for 60 Hr, at 520 C; whit ammonia dissociation of 30%.

The surface shows a flaky appearance and spalls easily, in some areas it seems like blisters. I think the porosity on the tool affected the results of the nitriding process. This defects does not appear in all areas of the piece only in some of them.

We have nitrided other pieces made of the same material and under the same process conditions, and this failure didn´t appear.

The surface hardness is 32 Rc.

I will appreciate all your inputs, because we don’t know why it happens.

My best regards!

 

[TVP]

There is an excellent discussion of this topic in the following article by Edward Roli?ski from Advanced Heat Treat Corp.:

http://www.ahtweb.com/upload/d8cb7I...as NitridedNitrocarburized Gray Cast Iron.pdf

 

[danava71]

Thank you very much for your info, I'll read the article
Regards!