burnt steel????

[ScottRoush]

I had stuff going on yesterday... and I'm not sure it went well. I had a roughed out blade of 5160 that was given to me... I have no idea what kind of HT was done on it... but it was flat ground with the plunge going all the way to the back so I assumed it had been annealed. Well right off the bat I realized that the spine area was softened but the edge was as hard as could be. So I decided to anneal it myself in my electric ceramics kiln. I've used the kiln for quenching before with great results... but never for annealing... and I've never annealed 5160. This kiln is 110 Volt and 20 amps and struggles to get up to 1500F on the pyrometer. This an analog pyrometer and I've checked it's accuracy in boiling water and, at those temps, it seems to be accurate.

So I put the blade in and ramped it up to a 1500 (a minor household emergency came up and it held at that temperature for 45 minutes or so... this may be the problem!) and then opened the door so that it would rapidly cool to 1300 and then gradually cool to 1200. When I opened the door the blade was a very pale yellow! I proceeded to bring down in temperature as I described above. It held at 1200 for several hours and then came down gradually to air temp in the kiln. It now has the thickest layer of scale that I've ever seen, it warped and is VERY easy to bend at the ricasso. The scale started to crack as soon as I brought it out of the kiln.

So did I burn this steel by leaving it at 1500 for too long and getting it up to pale yellow... even though the pyrometer only read 1500? It reads up to 2500?

Anyway.... I just want to make sure this blade is still worth working on.

 

[mete]

The term "burnt" has a certain technical meaning -heated to very high temperature ,above about 2300 F where the grain boundaries have oxidized ! That means scrap !
If your pyrometer is correct you have just annealed the steel with grain growth and scale. You would have to reHT to get the grain size down then start from the beginning.

 

[ScottRoush]

Thanks Mete.... What about the color of the steel though? According to the color (pale, almost whitish yellow), the temperature of the steel was much higher than what my pyro was reading. Can the blade somehow build up temperatures if sitting too long above that which the pyro is reading? That probably doesn't make sense... but I just can't figure that color. Since I've been using this kiln for hardening, I've never seen that color... And I've never let metal sit that long at those temps.

Well... I wanted it annealed anyway if that is all that happened.

 

[Don Hanson III]

You will likely need to normalize a couple times and grind the skin off to get past the decarb. But it's probably OK.

I don't anneal simple carbon steels anymore, just normalize.