I'm getting my low temp salt pot up and running in the next couple weeks, and I'm wondering about tempering times and temps.
I normally temper for two 2-hour cycles in the oven (at various temperatures, depending on the steel), but with salts it seems like I should be able to cut that time a bit, since the knife will be up at temperature as soon as the salts are back up to temperature from me putting the knife in the pot.
I'm planning to experiment, but does anyone have a good starting place or general rule of thumb? I read somewhere that some smiths do just a 20 minute soak in salts for every two hour soak they would normally do in the oven, but that seems to imply that it takes 1 hour and 40 minutes for a knife in an oven to get up to temperature...which doesn't seem right. Perhaps they are raising the temperature of the salts a bit because they have more control over the temperature and time with salts?
Any advice is welcome. (I use mainly 1084, W2, 5160, and 80CrV2.)
Steve
I have no experience with tempering in salts - but temperature is temperature.
I give my oven tempering about 20 minutes for the knife to get to the set temp.
I'm sure in salts that time is less.
But, once there, the TIME should be the same.
And hour in the oven or an hour in the salts is still an hour.
Karl B. Andersen
Journeyman Smith
Karl,
Thanks for the info. That is my intuition too--temperature is temperature, and time in the salts would be the same (at temp) as time in an oven.
I would think that the blade in the salts would be at the set temp pretty quick (within seconds). Not too many people seem interested in this topic, or perhaps not many people have experience with low temp salts...
Steve
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Karl,
Thanks for the info. That is my intuition too--temperature is temperature, and time in the salts would be the same (at temp) as time in an oven.
I would think that the blade in the salts would be at the set temp pretty quick (within seconds). Not too many people seem interested in this topic, or perhaps not many people have experience with low temp salts...
Steve
I've also heard of guys using a large tray filled with sand. Heat that up completely and then slide the knife into the sand for the tempering time. The extra mass will maintain a more steady temp without roller coaster-ing with temp fluctuations.
Karl B. Andersen
Journeyman Smith
Karl--excellent idea with the sand. I've been contemplating how to temper a sword--that might be the ticket.
I know you do a lot of hot bluing--is this part of your tempering cycle, or are these temps significantly lower?
Steve
I will tell you what I know, I use low temp. salt for thin blades. I use a lot of 15n20 for kitchen knives and hunting knives. Because of the thin blades a lot of distortion occurred. So I began quenching in low temp salt. I would bring the blades to 1475 degrees, quench in 350 degree salt. I would let is set for 3-5 minutes then let it air cool. This forms banite. You loose 1 or 2 points of rc hardness, but you will not notice it, because you save on distortion , the blades come out straight, with out any wrinkles. have also used it on e52100 and was pleased with the results. I hope this helps. Timothy
Tim Potier
Master Smith
I left something off, after it air cools and forms banite, I then temp by putting it back in the 350 degree salt for one hour , take it out, the put it back for another temper cycle in 350 degree salt for one hour. I take it out clean it up , the finish the blade. Timothy
Tim Potier
Master Smith
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I know you do a lot of hot bluing--is this part of your tempering cycle, or are these temps significantly lower?
Steve
I hot blue at 292. And it's only for 27 minutes. Doesn't change anything.
Karl B. Andersen
Journeyman Smith
|quoted:
I left something off, after it air cools and forms banite, I then temp by putting it back in the 350 degree salt for one hour , take it out, the put it back for another temper cycle in 350 degree salt for one hour. I take it out clean it up , the finish the blade. Timothy
Interesting. I appreciate you sharing what you do. It looks like I just need to do some experimenting and see how it goes.
When you temper your 1084 or 15N20 in an oven, do you temper for longer? It seems like most people do a couple two-hour cycles, whereas with the salts you just do a couple one-hour cycles. Do you use the same times in an oven?
Steve
In a tempering oven, it may take 1/2 hour for the blade to get up to the set temp. After that - the tempering time begins, so that may be why you see so many folks doing 'longer' tempering in an oven.
I place my knife in and begin timing for an hour and a half so I know I got a full hour at set temp.
When placing in salts, the blade will come up to temp almost immediately. One hour will do it.
Karl B. Andersen
Journeyman Smith
Good point Karl, time at temperature is the same with salt, open air heat ,etc, there is no warp drive tempering that I know of. If I go in a sauna at 300 degrees or a hot tub at 300 degrees It is the same heat and same time. Does that help. Mike Conner a great Mastersmith, said he like to temper in a fry daddy, the temp was consistent, and constant. There was no cycling like in an open air oven, which heats up , then when it reaches the 350 degree temp. it turns off, when it drops 5 or so degrees it turns on and brings the oven back to 350 degrees. This must be what you are thinking about. Timothy
Tim Potier
Master Smith
Timothy and Karl,
Thank you for the information.
It sounds like I can cut my tempering times, but not drastically, and only because air takes longer to heat up a blade than molten salt.
I'll need to do some experimenting.
Steve
