Small cracks in blade

J.Marsillo

J.Marsillo

Joined
Nov 8, 2000
Messages
1,255
I have been working on a knife for my friends son,nothing fancy just a drop point utility.The steel was old file steel a heller bro's to be exact.I've used them before with good results. This time i'm not sure what happened,It was also my first shot at a hollowgrind.I clay coated the blade for HT,soaked in the steel tube within the forge for about 5 minutes at about 1550,quenched in peanut oil.tempered while still quite warm at 500 for 1 hour twice.
Cleaning up the blade i noticed very small cracks running the length of the blade ( I couldnt get a good pic) close to the cutting edge.none of them started at a specific point and one long one ran throught the choil halfway down the blade.I couldnt grind them out they seem to run all the way through.

That was enough for me to destroy the blade.One thing i did notice with a 15x magnifying glass was the grain looked a little irregular :confused: maybe I'm imagining things but i'm pretty sure I could pick out the difference from the clay coating too.
 
What are the things it could be from?

Over heating?
Flaw in the steel of the file from the start?
Flaw in the steel that would come into play only in the quench?
Quench in too fast of quench oil?
Too much stress in the steel after the quench?
 
it seames that realy the onley way a steel could get cracks like that was in the factory, thay might have roled it out when it was to cold or somthing. but may be quentching to fast, but unlikeley.
 
ITs a good idea (if you didnt do it) to grind the file marks off what will be the knife edge before you forge it to shape. It doesnt take much in a thin blade for a stress crack to start.
 
Sorry the first post reads like i was half asleep....I was :) More of a rant than a question
The blade was 5/32" thick at the spine,and for lack of a better measurement a heavy 1/16" at the cutting edge.I didnt have any secondary bevels either.
My question is how can i avoid this in the future, I'll be using 1095 for all my stock removal knives for a while.So I'm expecting some crackage :o
Should i grind up to 120 instead of 80?
The cracks appear only in the hollow ground section of the blade,but they dont run with them,they are pretty random and squiggly.

For the destructive test i put it in a vice edge down and flexed it long ways to see if the cracks opened up,they didnt change.Then i tryed the bend test but i couldnt get enough leverage to bend past a few degrees.So I hit it with a 4 lb cross pein/peen hammer and it snapped off.
Thanks for the help guys.
 
no, i have carcked many blades but mine allwase crack with one long crack down the centere. I have never seen tuns of long cracks in a blade befor that is why i thought it might have happend in the factory.
 
I used files and 1095 for over 15 years, never had one crack. I finished them to 100grit before heat treat, and took the edges pretty thin. Around .015, to .020. I quenched in motor oil thinned with diesel. Only time I have experienced cracking was with fire strikers of 1095, and a water quench. The cracks were longitudinal, and down the sides, the same as my grinder marks. The strikers were 1/4"x 1/4" in thickness.
 
Sounds like a problem from the factory....if you work the steel too cold (forging) the possibility of cracking can happen...since you didn't forge, it has to happen at the factory. Large grinder marks can also cause cracks, but they usually run with the marks. New 1095 flat stock should work better for you than "found" steel from salvage. Keep us informed and post some pictures. SeeYa:confused: :D
 
Unless your forge is temperature controlled (or even if it is), 5 minutes at temp for 1095 or similar can allow for grain growth. This could lead to what appears to be cracks but is accually the appearance of the grain boundaries. They can tend to look like cracked glass especially if the grain growth has been really bad. The critical temp for 1095 is I believe about 1450. It takes less than a minute at temp for simple steels in knife sized cross-sections to completly austenize.

The teeth of a file should be completely removed before heat-treat, you may not thoroughly remove them if you forge before grinding. Large scratches from grinding/sanding can also lead to stress risers that will crack.

ron
 
Joe,
Yeah what son of bluegrass said... 1450 and 350-400. Watch where you get your heat treat info from. Some of the large companies give heat treating temps that seem to be for something other than knifemaking???:confused:
Matt
 
Thanks for the help fella's . I'm pretty sure i over heated I was going by the premise that heller bro's files were W2,thats why the heat was so high.
Isnt longer,better for heat treating as far as soak time goes? For my next trick I will buy a GOOD temp probe :)

....Is it me or do the smilies keep changing place??
 
I used to have 1095 crack regularly, probably 1 out of 3. I started hand sanding blades to at least 220 grit, parallel to the edge before quenching, and I haven't cracked any of the last 10 or 12 1095 blades I've quenched. I quench in vegatable oil at about 135 degrees. If your peanut oil was too cold, that could also be the culprit. Could have had something to do with the clay, as well.

Todd
 
Joe - buy quality steel & quenching oil: McMaster.

The MOST economic way to get 1095 is to buy their 18x48 sheets - .080
is under $60.

Oil is something like $18 per gallon. A steal . Doesn't flash up as much.

For thin blades, do take it up to 220, both the perimiter and both sides
 
With simple steels, 1095, W-1, W-2 etc, longer soaks just means grain growth. That is bad for knives.

If you haven't read anything on metallurgy let me be so bold as to recommend "Metallurgy Theory & Practice" by Dell K. Allen. I've got it and the sections on heat treating and carbon steel provided a lot of information on the why. That book can usually be found used for a few $$.

This is how I do it
http://www.geocities.com/son_of_bluegrass/heattreat.html
 
You must log in or register to reply here.
Back
Top