Beginner problem: brittle blade

K

Karoo

Joined
Jan 26, 2017
Messages
15
Good Day.
I read the thread with interest on tempering, but admit that I will have to study the technical aspects to get a better understanding of it all.
I don't want to repeat the same issues, so will try and be specific:
I made a knife out of a file as per Walter Sorrells's video tutorial.
1) Normalized the file by heating in a fire and cooling overnight;
2) Shaped the blade, etc. with simple tools;
3) Heat treated by bringing the steel to non-magnetic and then plunging into warmed used motor oil.
Now, I may have gone a bit too hot, but the blade was hardened as a new file "skated" over the blade.
4) Put it in a simple oven at 400 F for two cycles of one hour.
The blade edge chipped badly on its first working day.
Questions:
a) Can I assume that all was fine until after step 3)? If it was hardened successfully (assuming), does all the fault lie at step 4? It is possible that the oven was irregular in temperature. (I have a better oven if needed!)
b) What to do next time?
Any advice will be appreciated.
 
Seems like the issue is the heat treatment unless one of those simple tools was a hammer :)

What you can do for this blade - maybe sharpen at a greater angle, to have more "meat" supporting the edge apex, that is if the chips are small.

Now, what you can do for the next one:
1) be careful heating the blade to non magnetic - start bringing the heat in handle first, move the blade around, to avoid the tip and thin edge getting too bright when comparing rest of the blade, if you are heating in with a solid fuel (coal, coke, charcoal) then at least for longer blades consider building a muffler to spread the heat more evenly)

2) are you certain that the oven is operating at temp? those things are known to be quite inaccurate, heat treatment at 320 vs 400 could make worlds of difference. Maybe find an external thermometer to validate the oven temps, also consider doing a longer temper (maybe 2x2 h or 3 x 1 h).

3) also a saftey tip, dont use motor oil, the fumes could be cancerogenic (lots of additives to modulate the engine oil viscocity) regular canola oil works fine and is cheap.

If possible add images of the blade, will help people to get what happened in a more accurate manner.
 
Koduu's suggestion about increasing the edge angle is a good start.

If the edge angle doesn't fix the problem and it is still chipping, try this:
Remove the handle and re-temper for two hours at 450F ( just one time). For a file knife, 400F temper may be too hard.

Or, you can try and hour at 425F , clean the edge up and sharpen, then do a brass rod test, and if it is still too hard, temper again at 450F for a second hour.
 
You can greatly improve toughness by lowering the quench temperature. That won’t help with this one unless you redo the heat treat.

I see a lot of home heat treaters that go too hot. Files have a high amount of carbon which needs to be hardened from the lower end of the range.

Hoss
 
Thank you all for your input. My next project will be using an old vehicle leaf-spring and I'll keep up with the research.
 
From one beginner to another here comes the best advice I can give. Use a known steel if you want successful results. I heat treat in my backyard and I get successful, repeatable results using 1080 steel and the method you listed. The only time I have ever had a heat treat not come out properly I was making a blade from an annealed file. I didn't know the steel type and therefore didn't know how to properly heat treat the steel. The ability to keep an edge comes from proper heat treatment and you can't typically get repeatable, successful results without knowing your steel type as a beginner.

The second best advice is to use sandpaper like it's free. Actually that may be the best advice.
 
Last edited:
ten-six said:
From one beginner to another here comes the best advice I can give. Use a known steel if you want successful results. I heat treat in my backyard and I get successful, repeatable results using 1080 steel and the method you listed. The only time I have ever had a heat treat not come out properly I was making a blade from an annealed file. I didn't know the steel type and therefore didn't know how to properly heat treat the steel. The ability to keep an edge comes from proper heat treatment and you can't typically get repeatable, successful results without knowing your steel type as a beginner.

The second best advice is to use sandpaper like it's free. Actually that may be the best advice.
Click to expand...
Use a known steel .......use a known steel...............I read this many time on this forum ? So , what is the known steel ? What steel you think Ford , Toyota , BMW or Maruti from India.........USE for coil spring and for leaf spring ? What steel is used to make good file ??? What steel is used to make HSS circular saw , what steel use SKF for ball bearing ...I can bet that it is better/CLEAN one then we get from knife supplier !!
Come on....almost every steel on planet earth was made for something else not for KNIFE ! Find good file , temper twice on 250 Celsius grind bevels and you have perfect knife ! Take leaf spring from ANY vehicle from Planet Earth and you will make perfect knife ! And probably you will have better steel from leaf spring then one made in some small mill from recycled steel !!
I just finished this one from maybe 40 year old leaf spring ......................:D

eupJ4jp.jpg

And imagine .................... this unknown steel can cut toilet papir :p

thfIFVZ.jpg
 
Last edited:
Natlek,
I am sorry but your post is pure bunk. It is always better to use a known steel. It is not proof that a steel is good because it can cut toilet paper ( a blade of mild steel will do that). The notion that recycled steel from a car spring is probably superior to steel from a mill is just plain nonsense.
 
Hey Natlek, I think the point is that if you want repeatable results, you have to know what the material you are using is...
Sure you can make a great knife from almost any steel that has high enough carbon content.
However, if you don’t know the steel’s composition, you have to do a bunch more experiments to find the best best treat.
But if you’re not concerned with doing the best you can, then carry on and have fun doing it!
 
Stacy E. Apelt - Bladesmith said:
Natlek,
I am sorry but your post is pure bunk. It is always better to use a known steel. It is not proof that a steel is good because it can cut toilet paper ( a blade of mild steel will do that). The notion that recycled steel from a car spring is probably superior to steel from a mill is just plain nonsense.
Click to expand...
Sorry ,but I don t think so .Blade from mild steel will not pass nail test or knot in the wood :) Spring steel is spring steel ! And I will get repeatable results milion times from million different leaf spring .....same from any good file ,ball bearing steel or carbon steel saw for wood .
 
At risk of jumping into the middle of this with both feet, i'll add my 2 cents.

A.McPherson said:
if you don’t know the steel’s composition, you have to do a bunch more experiments to find the best best treat.
Click to expand...

This is the main point to this ongoing debate.

Natlek, I think what we all are saying is that for someone with very little to no experience with heat treating, using a known steel will at least give a "recipe" for how to get the best heat treatment as well as take at least one out of his 3 unknowns at this point.
 
You must log in or register to reply here.
Back
Top