Failed HT on 5160

Bühlmann

Bühlmann

North Lake Forge
Joined
Jan 6, 2022
Messages
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I had two blades come out of HT soft. They both had a 10 min soak at 1525F and quenched in AAA. Came out at 45-50 HRC after 2x 385F tempering cycles. I’m confused as to how this happened, but more importantly what is the best way to “reset” the steel for another attempt at austenitization?

ETA: Not decarb. Surfaces were properly prepared post-HT for hardness testing. They are definitely soft.
 
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IF it is 5160 and the specs stated are ACURATE, then it has to be one of two things:
1) Decarb - to test this grind a good layer off both sides of the tang and test the Tang area. If the hardness is more correct that was the issue.
2) It isn't 5160.

All this assumes the HT oven was actually at 1525.
 
It was bar stock 5160 from a reputable knife supply house, and I prepped deep to avoid the decarb answer. Digitally controlled kiln. But all that secondary mystery aside, my real question is what is the best approach to get the steel ready for a second attempt?
 
Honestly it sounds like your kiln temperate is not accurate for where the blades were.
You want to do a normalisation cycle and try again, but that's only useful if you calibrate the oven.
 
Nevermind. I wasn't asking for possible reasons for it happening. That is a different topic. I was was asking for guidance on how best to prepare the steel for another attempt. I got the information I was looking for elsewhere. Thank you for your responses.
 
Understand I'm NOT the expert here, but is AAA fast enough for 5160? I was thinking Parks 50 was the recommended quenchant, which is more like water. If you've got a small piece (coupon) of 5160 for testing you might try quenching in water to see how that works. Also, depending on the state you received the steel in it might need normalizing by heating up to 1600F, or even 1700F for 10 minutes or so then air cooling which is going to give you large grain. Then go thru 3 cycles of 1500F or so for grain reduction.

That would take care of getting the blades to a state for reheating anyway.
 
AAA is a good quench oil for 5160.

To answer the question presented "....with all the mystery aside", you don't need to do anything to simply try and re-harden the blade. No need to anneal, just try again.

But something is rotten in Denmark as the saying goes. If it is indeed 5160, that heat treat and temper should have been ~59HRC. I probably would have extended the soak in the as supplied condition.

Try to re harden. If that doesn't work, normalize it once, maybe cycle once or twice, and then try again. It may be heavily spheroidized.

Let us know what you learn.
 
Will give away my formula that always worked for 5160, my Favorite steel
Take it to 1550 10 mins
Edge quench in https preheated : //www.mcmaster.com/3202K4/ maybe 4-5secs
Immediately into heated water 1-2 sec
Back into oil to cool making certain to agitate back and forth to prevent a steam jacket
Right into the tempering oven 400deg 2hrs
There are a few other variants "Tricks" that you can use but they are personal preference
 
Hankins said:
Will give away my formula that always worked for 5160, my Favorite steel
Take it to 1550 10 mins
Edge quench in https preheated : //www.mcmaster.com/3202K4/ maybe 4-5secs
Immediately into heated water 1-2 sec
Back into oil to cool making certain to agitate back and forth to prevent a steam jacket
Right into the tempering oven 400deg 2hrs
There are a few other variants "Tricks" that you can use but they are personal preference
Click to expand...
There’s really no reason to quench in oil then go to water, also 5160 is a very deep hardening steel and there is no reason to use water at all. The only reason you see smiths in areas like Nepal working with “5160” and water quenching is likely due to not having anything else to quench blades in. With some shallow hardening steels you can quench in water first then oil, the reason for doing a 2 step interrupted quench is to have a really fast cooling rate to pass the pearlite nose but then a slow cooling rate during the transformation to martensite where you no longer need the fast speed and a slower cooling rate reduces the chance of cracks. Doing what you suggest is reversing that and cooling faster than needed after already passing the pearlite nose and unnecessarily risking cracks and distortion. Also I wouldn’t recommend 1550 for your hardening temp, another Forum member did a study and found anything over 1525 started to have significant drops in toughness.
 
Bühlmann said:
I had two blades come out of HT soft. They both had a 10 min soak at 1525F and quenched in AAA. Came out at 45-50 HRC after 2x 385F tempering cycles. I’m confused as to how this happened, but more importantly what is the best way to “reset” the steel for another attempt at austenitization?

ETA: Not decarb. Surfaces were properly prepared post-HT for hardness testing. They are definitely soft.
Click to expand...
Just a follow up question, what did you temper the blades in and did you double check it was accurate?
 
Additional questions:
How was the hardness test done?
On what part of the blade?
If a standard Rockwell hardness tester was used, were the two surfaces flat and parallel?

As said already, Just redo the HT with no additional steps and see what happens.
If you suspect the steel is heavily spheroidized, do a structure refining set of steps and then redo the HT. Start at 1700°F for 15 minutes and cool to black.. Then 1600, 1500, and 1400. Final is 1500-1525F for 10 minutes and quench in medium oil. Temper twice at 400F.
 
Joshua Fisher said:
Just a follow up question, what did you temper the blades in and did you double check it was accurate?
Click to expand...
I use a toaster oven. It has a digital thermometer, but I use a secondary thermocouple for monitoring & graphing heats.
 
Stacy E. Apelt - Bladesmith said:
Additional questions:
How was the hardness test done?
On what part of the blade?
If a standard Rockwell hardness tester was used, were the two surfaces flat and parallel?

As said already, Just redo the HT with no additional steps and see what happens.
If you suspect the steel is heavily spheroidized, do a structure refining set of steps and then redo the HT. Start at 1700°F for 15 minutes and cool to black.. Then 1600, 1500, and 1400. Final is 1500-1525F for 10 minutes and quench in medium oil. Temper twice at 400F.
Click to expand...
Hardness was tested on a Wilson 3JR. These were unground blanks, so surfaces were flat, parallel, & finish to 400 grit. I tested dozens of points on each blade across the entire blade profile looking for irregularities.

I did a DET anneal & repeated my process with similar results.
 
Bühlmann said:
Hardness was tested on a Wilson 3JR. These were unground blanks, so surfaces were flat, parallel, & finish to 400 grit. I tested dozens of points on each blade across the entire blade profile looking for irregularities.

I did a DET anneal & repeated my process with similar results.
Click to expand...
I’d be curious what the as quenched hardness is, just to take the tempering out of the equation.
 
Those samples do not look ground in the photo. After HT they should be surface ground on both sides before testing. I'm not saying that is the only issue, but without it the test isn't accurate.
 
Stacy E. Apelt - Bladesmith said:
Those samples do not look ground in the photo. After HT they should be surface ground on both sides before testing. I'm not saying that is the only issue, but without it the test isn't accurate.
Click to expand...
Those samples are absolutely ground, on both sides. 120, 220, then finished @ 400. Don’t let the lighting & poor framing fool you. It would be a waste time otherwise.

The 1600 sample is not flat in the pic, because after the hardness test I put it in a vise & gave it a few whacks to see if it’d snap.
 
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