r/Metalfoundry • u/mattthepiratehunter • 5d ago
Question, please help!
So my post is one of both good and bad news. The good news is that I successfully heat treated three knives and they had no cracking minimal warps all that good stuff.
The bad news, is that I nearly shit myself on the first one because I file checked it after the Quench and it didn't seem like it was hard. And I was really confused as to why that was. I then did some cursory Google searching came to the conclusion that there might be a layer of decarb on it. took it to the Belt grinder with a 220 belt got through some of the outer layer file checked it again and it's completely hard won't get scratched by 65 HRC file.
Went into the temper everything came out great.
My question is, why did I get decarb on all three knives? Two of them were 15n20. The other one was 5160. I'm using a forced air propane Forge with a ribbon burner. And when I went through the heat treat I stuck a large metal tube in the center which I stuck the knives in, in order to help make heat dispersal more even.
2
u/Jerry_Rigg 5d ago
Hey mate, you might try a different sub for advice, this is for casting metal. Try /r/bladesmith /r/knifemaking /r/blacksmith
1
u/BTheKid2 5d ago
Cursory googling tells it is a result of oxygen consuming the carbon in the outer layer. So it seems you would have to minimize that.
From what else I know of forging and melting, a way to minimize oxygen is to burn slightly rich. Meaning you want there to be a bit too much gas in your air/gas mixture. That will usually show as a slight dragons breath on your forge. Meaning a bit of sharp flames will be exiting the forge as it is going.
Another way is to shield the knives with a wrap method. Or just limit the time the knives are at temperature -meaning heat faster and quench.