Broken blade-some insight?

[john0270]

I have been using some scrap spring steel to make knives with great luck, excellent toughness/strength, with an 'ok' edge holding ability. I recently had a 10" clip point blade on the go, out of 1080 since I wanted a little more edge retention(is my thinking right)? Anyway, this blade I did a clay coated spine heat treat(something I have never done before).... for more toughness I thought(still tempered at 425f). So wile doing some tests that my other blades would have passed easy(spliting bone by hitting the spine with a rubber mallet), i managed to chip out the edge, and then the next blow broke the blade in two even with the spine dead soft! Did I learn something????.... you tell me.

I am definitely going to source some real 5160 one of these days, and keep drawing the spine with a torch instead.... since it seems to work so well.

Here you can see the difference between the coated and non coated parts in grain size/texture:

http://img.photobucket.com/albums/v314/BigJD/broken.jpg

 

[Will Leavitt]

Ummm I have no idea what happened unless there was a crack already in it. I regularly baton my small 1084 blades through wood with no problems.

After you heat treated did you whack the blade on the anvil to see if it may have cracked during quench? I usually do that, you'll hear a difference between a cracked blade and a normal blade.

 

[silver_pilate]

Give some more information about your heat treating. What is your heat source? Is it temperature controlled? How were you judging temperature prior to quench? What are you quenching in?

Hard to tell from the picture, but is the spine portion of that cracked blade discolored compared to the rest? If so it may have been there from the heat treatment.

--nathan

 

[john0270]

This one rang true. I chipped it on bone the first blow, then I belive it just kept going. You have to try cutting bone(deer) to understand, its worse than mild steel on edges.

The spine is discolored because of the clay coating heat treat I thought? Anyway it was heated in a propane forge, to aproximately 1500-1550f and qenched in trans hydralic fluid.

 

[Will Leavitt]

John I live in Alabama where our hunting season is from Mid October through January 31 and I can harvest a buck and a doe per day...... I've dealt with a few deer.

1080ish steels given proper geometry and heat treat processes shouldn't have chipped out in my opinion. How sure are you on the temperature when tempering? Did you do a brass rod test? Can you do a brass rod test on the remaining pieces.

Usually discoloration is a sign of a crack.

What temp was the oil? A crack could have formed due to the expansion differences. What grit was the blade finished to prior to heat treat? Is is possible there was a large grit scratch you didn't know about?

 

[john0270]

oil temp was aproximately 140. I will do the brass rod test, but this is what the end use is for, dismembering deer. Looking at the geometry again it probably was to shallow. I will try and break a few more peices again to see If I get some more discoloration spots. I thought it was just the difference in the perlite vs the martenesite. The tempering temp is accurate. As for scratches, I belive I finished it to 220grit.

Actualy the picture is showing a contrast that I can't realy see in person, it might just be the light refracting off the different grain structure.

Here is another pciture, probably shows the geomitry better. With access to that many deer I bet you regularly chop deer up with swords just for testing?

http://img.photobucket.com/albums/v314/BigJD/broken2.jpg

In all likelyhood its probably the result of a few factors, stress from differential quench, not the greatest most accurate heat treating, maybe even some left over stress from forging, edge geometry.

 

[Will Leavitt]

With access to that many deer I bet you regularly chop deer up with swords just for testing?

No but with access to that many deer I know I don't have to chop through bones to dismember a deer.... Why would I chop a deer up? I eat deer.

If you haven't done anything but pick up the pieces and take pictures of them there's a rather glaring clue in the second picture.

Tell ya what, I reckon since you got it all figured out so I'll just leave you to it. Have a good one.

 

[Phil Dwyer]

No but with access to that many deer I know I don't have to chop through bones to dismember a deer.... Why would I chop a deer up? I eat deer.

If you haven't done anything but pick up the pieces and take pictures of them there's a rather glaring clue in the second picture.

Tell ya what, I reckon since you got it all figured out so I'll just leave you to it. Have a good one.

Hey Will,

Some of the rest of us haven't got squat figured out. How about filling us in?

I never quite understood the need to chop through bone to dismember a carcass. Joints are fairly easy to disjoint. Well there are three areas I often resort to cutting bone: in the front center of the pelvic section, down the backbone to separate into two sides and then the spine halves into quarters one or two ribs up from the bottom. At least that's how we typically quarter a beef carcass (mostly with a saw).

Anyway, all the best, Phil