Recommendation? Failure... Time to try again 5160

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Wags1776

Joined
Apr 20, 2017
Messages
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Hey anyone, I just finished my 4th attempt to make a knife... because It warped and cracked during heat treat. At school, we have a nice machine shop and I've made a few simple stock removal knives. The first a straight razor which came out beautiful and straight, but was accidentally thrown away over the summer. A small knife with a convex grind and paracord wrap I gave away. A small edc knife which was lost/stolen and finally by beautiful 10.5" bowie that has a serious warp and structural cracks down the spine. So its time to try again (making a big bad blade), but before I start I have a few questions:

1: What went wrong?
- I didn't normalize but didn't think I needed to for stock removal
2: What steel?
- I liked working with o1 but I feel betrayed by it, would 5160 be easier for me to heat treat for a big chopper?
3: Any Misc advice for a newb?

Thanks
-Bret
 
Are you using warm oil for quenching your blades? Also, I think if you overheat the steel before quenching could cause a similar problem also, but I'm no expert.
 
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It's not enough information for any helpful answers. What was the heat treat procedure? What was the oil it was quenched in? How much grinding prior to quench? How was it quenched? Where are the pictures of these cracks?
 
R.C.Reichert said:
Are you using warm oil for quenching your blades? Also, I think if you overheat the steel before quenching could cause a similar problem also, but I'm no expert.
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Oil was room temp, I used an oven so I doubt the blade got too hot.
 
kuraki said:
It's not enough information for any helpful answers. What was the heat treat procedure? What was the oil it was quenched in? How much grinding prior to quench? How was it quenched? Where are the pictures of these cracks?
Click to expand...

Sorry for the lack of detail. I took the blade to 1475 for about half an hour then room temperature oil quenched. As per the recommendation of our resident machinist. Lots of grinding prior to quench, I ground the whole blade from 1/4 inch stock. Probably should have done a normalizing cycle or 2.
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(not sure if the image will work) http://i.imgur.com/LZ1cmxA.jpg , http://i.imgur.com/r3XaTvq.jpg
 
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This crack is propagating from the spine? How thick is it at the crack at the spine and how thick at the edge? How long is it to either direction from the crack?

LZ1cmxA.jpg
 
r3XaTvq.jpg


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That crack is starting at the edge, not the spine, isn't it?
 
I'm wondering how thick the spine is and how fast the quench medium is because cracks like that I believe come from the edge cooling much faster than the spine. As the edge cools it contracts slightly and hardens while the spine is still hot and plastic. Then the spine cools and contacts, and tries to pull the edge around it, but being hard already, it cracks from that stress.
 
Edge probably too thin. 30 minutes maybe too long a soak. Oven temp maybe wrong.

Blades in after oven reached temp, or in while oven came up to temp?

I made hundreds of blades from 01 years ago and never had any cracks.
 
I agree, something is wrong. Those edge cracks would normally show from doing a thin edge in a too fast a quenchant. I get them when doing W-2 slicers quenched in water/brine. (That's why I recommend doing a W2 quench before grinding the bevels)

Is your quench tank outside where the tank catches rain water? The oil would float on it and you wouldn't know you were quenching in water. If your oil is old, possibly water contaminated, or of unknown type, replace it with a commercial quenchant or a coupe gallons of canola.



I suggest addressing all the issues Don mentioned:

Make a new knife in O-1 or 5160 and finish it to 400 grit. ( Both would be fine for a chopper)
Leave the edge at .020" to .030" before HT.
HT in the oven at 1500-1520F with a 10 minute soak. ( both steels use the same temperature range)
Quench in 130F medium speed oil - Parks AAA or canola
Temper immediately at 400-450F
Finish knife and give it a good field test with chopping and cutting stuff.
 
kuraki said:
I'm wondering how thick the spine is and how fast the quench medium is because cracks like that I believe come from the edge cooling much faster than the spine. As the edge cools it contracts slightly and hardens while the spine is still hot and plastic. Then the spine cools and contacts, and tries to pull the edge around it, but being hard already, it cracks from that stress.
Click to expand...

Stacy E. Apelt - Bladesmith said:
I agree, something is wrong. Those edge cracks would normally show from doing a thin edge in a too fast a quenchant.

Is your quench tank outside where the tank catches rain water? The oil would float on it and you wouldn't know you were quenching in water. If your oil is old, possibly water contaminated, or of unknown type, replace it with a commercial quenchant or a coupe gallons of canola.



I suggest addressing all the issues Don mentioned:

Make a new knife in O-1 or 5160 and finish it to 400 grit. ( Both would be fine for a chopper)
Leave the edge at .020" to .030" before HT.
HT in the oven at 1500-1520F with a 10 minute soak. ( both steels use the same temperature range)
Quench in 130F medium speed oil - Parks AAA or canola
Temper immediately at 400-450F
Finish knife and give it a good field test with chopping and cutting stuff.
Click to expand...

Thanks for the advice, I tried to leave the edge about .03 thick, and theres no way any water got in the tank, but it's 1/4 inch at the spine with a hollow grind so the difference in cooling speed for the edge and spine would be huge and I was going into oil that was about 65 degrees.
With that 10 min soak on a blade witht the same geometry as this one theres no way the spine would get to edge temp, so are you effectivley doing a differential quench. Also would preheat or stressremoval cycles be necessary, or a second tempering cycle? Or just one to 1500 for 10 min and once to 425 for 2 hrs?
Your advice has been extreamly helpful.
 
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