O1 ??

Pelallito

Well-Known Member
Hello,
I have recently heat treated 4 blades made from O1.
The forge stayed between 1425 to1475. A propane forge b
There was considerable damage to the exterior of the blanks.
I held them to a 15 min soak. Blade where 5/32nd to 3/16th thick.
How can I minimize that damage? I am considering making a muffle.
The soak time seems excessive for something that thin.
Please help me understand what is going on in O1, that requiressuch a long soak time in something that thin.
The blades where right next to the TC.
Thank you,
Fred
 
The O1 requires a longer soak because of the alloy content. You will get a nice hard steel with almost no soak, but will miss some of the alloy benefits of the steel. Atmosphere in your forge might make a difference (not my specialty) or you could try something like TURCO or ATP641 to reduce decarb.
 
I take it that you were running a pyrometer with a thermocouple in your gas forge and that where you got the 1425° to 1475° for a spot temperature. That only says how hot your forge was running where the end of the thermocouple was located, not how hot the blade was. The blade itself could be hotter or cooler. Yes, a muffle tube would help but a regulated kiln would help more with a moderately complex hypereutictic steel such as O1. It doesn't take much time, a matter of several seconds, above the target temperatue of 1475° to put too much carbon into solution and cause the formation of a lot of retained austinite which will rob the blade of initial hardness and then cause a problem with brittleness later on as it converts to untempered martensite.

The reason that the O1 requires a long soak at low temperatures is the presence of chromium and tungsten carbides which do not go into solution as quickly as cementite (iron carbide). The temperature is kept under 1475° to retard grain growth and to control the amount of carbon to go into solution in the austinite. More complex steels like D2 or stainless steels might need something like a 30-60 minute soak at 1800°-1900° to break down their carbides and release the carbon into solution for martensite formation. It all depends on the alloy. It's more than just making sure that the blade is heated all the way through.

Doug
 
KM.ca and Doug Lester,
Thank you both for answering so promptly.
I did put on an anti scale compound before HT, it was spotty how it worked. I think I needed to preheat the blade more before putting it on next time.
The TC is in my version of a 2 brick forge( similar to Len Landrums), The blades were leaning against the TC.
I think that I need to make and install a plate so that I can control the amount of air going in.
Thanks again
 
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