2 broken blades, why?

T

TigerBlades

Joined
Sep 21, 2021
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I just dropped my new fruit bat bushcraft knife. It was supposed to be done by Sunday, but I guess I can scrap that now.
Both are from the same bar of 80crv2. The first one, which turned out perfect was from a different bar. Not sure if it's the steel or me.

2 blades heat treated how I normally heat treat them have snapped. Normalized 3 times, heat treated right at magnetic, and tempered 3 times. Both had the same dark spot on the spine. This has put me behind and out of a little money. Can someone explain?

https://imgur.com/GeRq9WU

https://imgur.com/3fAj23g
 
The dark spot indicates a previous crack. These microcracks may not even show to the naked eye. The crack prorogated with the quench, and then broke afterwards. All the normalizing in the world won't undo a crack.
I am guessing the blade was forged and you worked it too cold. Stop all forging at 1600F or bright red color.
 
Stacy E. Apelt - Bladesmith said:
The dark spot indicates a previous crack. These microcracks may not even show to the naked eye. The crack prorogated with the quench, and then broke afterwards. All the normalizing in the world won't undo a crack.
I am guessing the blade was forged and you worked it too cold. Stop all forging at 1600F or bright red color.
Click to expand...
Could that happen from quenching it twice? First time it didn't harden. But, I only did that on the second knife. First one broke after quench when I file tested it.
 
1) Multiple quenches may lead to cracking the blade. You said it didn't harden. How did you determine that?
2) After the quench a carbon steel blade is brittle martensite. It is as fragile as glass. We all love to see the shows where they take a file and file away to see if it got hard, but that also risks snapping the blade.
3) Additionally, with carbon steels, the temper should be very soon after quench. If delayed, micro-cracks may form, and sometimes the blade will break while sitting on the bench. Dropping the blade or any shock can easily crack or break te blade until it is tempered.
 
Stacy E. Apelt - Bladesmith said:
1) Multiple quenches may lead to cracking the blade. You said it didn't harden. How did you determine that?
2) After the quench a carbon steel blade is brittle martensite. It is as fragile as glass. We all love to see the shows where they take a file and file away to see if it got hard, but that also risks snapping the blade.
3) Additionally, with carbon steels, the temper should be very soon after quench. If delayed, micro-cracks may form, and sometimes the blade will break while sitting on the bench. Dropping the blade or any shock can easily crack or break te blade until it is tempered.
Click to expand...
1. Definitely didn't harden. Wouldn't even skate my dullish file.
2. Yeah, forged in fire kind of got me started on a knifemaking tangent, now here I am. Working on a mora-type puuko at the moment.
3. I see that now.

What kind of steel do you primarily use, and how long have you making blades?
 
You want help ? Put some details in your first post, don't make us drag it out of you.

Temperatures

quench media ? Water ?

what does normalize, quench and temper mean to you ?


It was supposed to be done by Sunday, ?
If we haven't said it before, this is why you are not ready to sell yet.
Get some skills and equipment first.
 
12345678910 said:
You want help ? Put some details in your first post, don't make us drag it out of you.

Temperatures

quench media ? Water ?

what does normalize, quench and temper mean to you ?


It was supposed to be done by Sunday, ?
If we haven't said it before, this is why you are not ready to sell yet.
Get some skills and equipment first.
Click to expand...
Way to make a blade forums noob feel welcomed :).

Any ways, Normalize at glowing red 3 times. Quench at just past magnetic in water, Temper at 500F twice.

Also, just because I forgot to mention my process, doesn't mean I'm that bad at knifemaking. And yes, 2 weeks is a perfect amount of time for me (doesn't have all the fancy tools), not sure where you were headed with that.
 
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Any time you water quench, you risk developing a microfracture (brown spot), so multiple quenches will increase those chances. To reduce the likelihood of cracks, add salt to the water (I do 1 cup of salt for every 10 cups of water) and heat it to 120*F.

I recently forgot to heat up my brine (salt water) and developed microfractures in 4/5 blades. the fifth blade developed a regular fracture lol
 
TigerBlades said:
Way to make a blade forums noob feel welcomed :).

Any ways, Normalize at glowing red 3 times. Quench at just past magnetic in water, Temper at 500F twice.

Also, just because I forgot to mention my process, doesn't mean I'm that bad at knifemaking. And yes, 2 weeks is a perfect amount of time for me (doesn't have all the fancy tools), not sure where you were headed with that.
Click to expand...
Quench at just past magnetic in water

Super obvious.


Not welcome ?
So many just pass by and don't even bother any more.

"red hot" is so subjective and you can be out by hundreds of degrees
I would guess you overheated it too.

Why not get some books, videos, whatever you prefer
Everything you need to know is available, no need to have it all come out here in peice-meal posts one question and answer at at time.

A few books, the right books can put you years ahead in skills and knowledge.

Try reading the stickies at least.
That would have at least steered you away from water and towards a suitable oil.

Try stock removal, get a pro heat treat, work on quality and fit and finish.
 
I'm all for low tech backyard knifemaking an heat treat, but maybe check out Larrin 's wisdom at knifesteelnerds.com so you can tweak and taylor your method to suit the materials and processes you have available. People have been doing this well for hundreds of years with simple steels and materials...but "there is no knowledge that is not power"
 
While a bit blunt, The Count is trying to point out your errors. Trust me, he has helped hundreds of new makers here over the years.

A water quench is very risky in a steel like 80CrV2. You should be quenching in oil. If a commercial fast oil is not available, use canola oil warmed to 120°F. Water or brine is too harsh for the steel you are using and has a high failure rate.

The double quench has two issues.
The first is that if the steel truly didn't harden in the first water quench, something was way off. It could have been severe decarb, or the temperature you see as "glowing red" may be a good 100-200 degrees off the 1500-1525°F you need for the quench. Because color is subjective to the viewer and changes depending on the light, many smiths that use a forge for HT do it at night with low lighting in the forge.
The second is that a micro-crack that formed in the first quench would almost surely propagate in the second.

Quenching at just past magnetic in water for 80CrV2 will get a poor result. It is the wrong quenchant and the wrong temperature. The Counts "super obvious" comment was that this is obvious to people who have read up on the steel and proper HT procedures. Obviously, it was not obvious to you at the time. This is all part of the learning process. Finding a smith near you and spending a day in the forge doing HT may help you learn a lot that is very hard to learn by yourself.

A good way to get a feel for what the proper temperature is is to put some coarse salt on a piece of bar stock and hold it in the forge. Move it around and watch as the blade heats up and the point where the salt melts is 1475°F. For 80CrV2 you want it a shade redder.

Telling us about your equipment and procedures is how we can help you improve. Some things you do may be fine and others may need changes.
 
No, a shade redder is brighter ... hotter. The way it looks to most folks is: dull red, red, bright red, orange red yellow ....
As you can see from the charts below, it looks different to different folks. You have to find out what color is what to your eyes and lighting conditions.
1649435078285.png1649435106549.png
, orange
 
If you look at the charts you will see that a dull red/blood red is 300°F too cold for HT of 80CrV2.
Even cherry red is 100°F too low.
 
Thanks for the clarification. I guess I'm used to comparing oranges and yellows for comparing forging temps.
 
T TigerBlades do your research! when I first got started I made a couple knives just because I have always loved knives and wanted to make them, and I found that I did love making them, and after making a couple I realized that I didn’t know hardly anything and had no idea what I was doing, so I did countless hours of research trying to learn as much as I possibly could (all the while still making knives) and I am SO glad I did! and I’m still constantly doing research and learning, and the more I learn the more I realize there is too learn. So long story short I recommend you do what I did, do as much research and learn as much as you possibly can, I promise you that you won’t regret it.
Another thing is don’t believe everything you see, you need to figure out what’s good info and what is not.
For starts I highly recommend Larrin Thomas’s book “knife engineering” there is so much good information in there along with http://knifesteelnerds.com/, also there is a ton of great info on this forum.

Good luck on your endeavors!
Best regards, Joseph
 
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