Flash rust on cast iron

[chromeitout]

Quick question. I am pc'ing an old Mopar cast iron intake for a customer. I have done a few smaller cast iron pieces before. Degrease, brake cleaner, wipe down, sand blast, outgas, allow to cool to around 150 degrees, coat, cure. I did this same process today on the intake as I've done before, but during outgassing in the oven it flash rusted (bad). It turned completly brown. I am wondering is this normal for cast iron? I don't remember the smaller pieces doing this, or maybe I just didn't notice, they were test pieces. I didn't feel good about coating the intake after seeing the rust so I guess I'll re-blast it tomorrow and go again. Any help would be appreciated.

[jbotti1]

I had a similar thing happen to me when i did a smaller cast iron piece. I didn't worry about the iron turning that brownish color. I figured it was nothing to worry about and the product came out just fine.

[chromeitout]

Thanks, I don't know what happened, but I reblasted it and coated it today and it came out fine. I did preheat it today but not as hot or as long as yesterday.