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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 03-02-2016, 12:02 PM
torchart torchart is offline
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what am I doing wrong?

I am trying to make 3 knives. One got hard the other two did not. I am using 5160 and I have a electric kiln. I made a small salt bath. brought the temp up to 1550. put one knife in and let it soak for 30 min or so, till the temp came back up to 1550. quickly quenched one in oil at 125. Then ran the others through the same way. one made it, the other 2 did not. I put one back through. It is still soft. What can I do?

Last edited by torchart; 03-02-2016 at 12:04 PM.
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  #2  
Old 03-02-2016, 12:37 PM
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Andrew Garrett Andrew Garrett is offline
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How much oil was in the quench reservoir when you started and what temperature was it at?

It may have been too cold for the first knife, but warm enough for the second, and too hot for the 3rd (or some variation of that phenomenon).

When you do a batch of knives in sequence, you have to manage your quench temps between each blade. The more oil you have, the more forgiving it is.
I keep several bars of steel handy. I use a couple to get it heated up to 120* at first, then a stack of cold bars to keep it there as the red hot knives keep heating it up.
A good meat thermometer with a long probe is a must.

Then again, that may not be the problem. It could be that you steel was misidentified.


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Old 03-02-2016, 12:58 PM
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Assuming all the temperatures are accurate then I'd say the steel is likely not 5160. Could easily be the oil temps as Andrew said but if that '5160' is locally salvaged it would be very suspect to me. Most leaf springs manufactured in the last few decades are not 5160 and some of the substitutes probably don't heat treat the same way.

If you make some knives with 1084 and go through your whole process with known steel until you can consistently make good blades then when something like this happens you'll know right away the problem is in the steel .

All that being said, I'm not clear on why you are using a salt bath if you have an electric furnace unless you have it just for tempering. Anyway, you mentioned both but only specified using one so that leaves us 'assuming' and you know what that does ...


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Last edited by Ray Rogers; 03-02-2016 at 01:01 PM.
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Old 03-02-2016, 03:18 PM
torchart torchart is offline
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I am using the salt bath to reduce the oxidation and pitting. it works well.
my oil bath is a turkey fryer. probably 4 gallons. The oil was 150 for the first one. some cooler for the other two.
I feel sure the steel is 5160. I bought it from a dealer. 4- 5 ft joints. other knives from the same lot have don well
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Old 03-02-2016, 04:37 PM
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If you're confident about the steel then what about the oil? If 150F worked well but the others were cooler that could be the problem Andrew pointed out. Depends on the oil but oil below 100F is almost always a bad idea ...

PS

You said you have several 5ft bars of steel....were all three knives from the same bar?


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Last edited by Ray Rogers; 03-02-2016 at 04:40 PM.
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Old 03-02-2016, 05:08 PM
torchart torchart is offline
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They were all from the same bar. I don't recall which was first. I thank the one that hardend was first. But I know the oil was over 100 on all of them. What is the range of temperature of the quench oil that should be good?
also what is the highest I should go in the Kiln with 5160 before quenching?
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Old 03-02-2016, 05:14 PM
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The temp of the oil depends on what oil it is

This time you said 'kiln' when heating the blade before quenching. Did you mean 'salt pot'? In either case, how are you measuring the temperature?

We won't have much chance of figuring this out without a lot of accurate details....


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Old 03-02-2016, 06:54 PM
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If everything you posted is accurate, The most important question is what are you using to determine hardness?
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Old 03-02-2016, 09:07 PM
torchart torchart is offline
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I have a small SS pan in my kiln, it holds about a pound of salt. just enough to submerge the knife. I have a pyro
meter on the kiln. and a thermometer that came with the turkey fryer. I have peanut oil for quenching. I use a good file to test for hardness.

Last edited by torchart; 03-02-2016 at 09:09 PM.
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Old 03-02-2016, 11:47 PM
Doug Lester Doug Lester is offline
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I'm wondering if your kiln is recovering temperature after the first blade but your salt bath is not. You are measuring the temperature of the kiln not the salt bath. Most people when they set up a molten salt tank have the thermocouple in a stainless steel tube that is in the molten salt itself.

Doug


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Old 03-03-2016, 05:22 PM
torchart torchart is offline
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The problem may be that the salt bath did not have time to recover. Making the knife under the critical temperature.
thanks for your help. Ill give them a longer soak next time.
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Old 03-08-2016, 03:21 PM
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Whimpy Whimpy is offline
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Have you tried water or brine quenching the steel? It might need a faster quench than you are getting with oil.
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Old 03-08-2016, 08:28 PM
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GHEzell GHEzell is offline
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Quote:
Originally Posted by Whimpy View Post
Have you tried water or brine quenching the steel? It might need a faster quench than you are getting with oil.
It would be a very, very bad idea to water or brine quench 5160... it has enough chromium and manganese that it will harden in most any oil. It will actually air harden in thin enough sections.


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