surface cracks

SHOKR

Well-Known Member
Just saw this when i was about to start hand sanding
Those lines across the knife appear to be surface cracks.
They only appeared after it was surface ground (after HT)
In your opinion can this blade be salvaged/used? Any thoughts?




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Rudy Joly

Well-Known Member
I've never seen that on any blade of mine after heat treat. It looks like the whole surface has crazing. Try hand sanding, even if they disappear or blend, soak the blade in kerosene or diesel fuel for a few hours. Remove the blade and clean well, let it sit in a warm place for a while (no problem where you are). If it's cracked in any place, the kero or diesel will keep weeping out of the blade where it's cracked. I do this to blades I'm suspicious of or don't "sound" right after heat treat. Good luck.



Rudy
 

rhinoknives

Well-Known Member
Shokr,
Is that a machine finish? Because some of it looks like the chatter marks you can get from having build up of grinding dust/crude on the Platen and it comes through the belt looking like that?

Take a look at your Platen.
 

SHOKR

Well-Known Member
Laurence, I found it like that right after surface grinding at a machining shop, they use grinding stones not belts. but before i gave it to the guy there was nothing on it
 

samuraistuart

Well-Known Member
SHOKR.....If you don't mind I have a question that is just BURNING inside. Was the knife tempered at all before it saw the surface grinder? The reason I ask, another gentleman on another forum had a problem very similar to yours. He was using O1 tool steel, had applied an anti scale coating, and noticed cracks along the entire length of his knife and sanding blocks (he was making some blocks out of the same O1). He quenched the blades and blocks, but couldn't remove the anti scale coating so used his surface grinder to do it, and noticed the cracks on his blocks but not the blades. Then he put the blades and blocks into LN (which probably made any cracks WAY worse) without a snap temper. The blades also had cracks on them after the cryo that he didn't notice before. The conclusion reached was the cracks were caused by using his surface grinder on the hardened untempered steel. When he put the blades in the LN, the micro cracks that were not visible before....became visible! That's why I am curious if you tempered these blades before surface grinding. Thanks for any info!

As a side note...on yet another forum....a guy was using 52100 and experienced cracks along the blade similar to yours and the other fellow. The conclusion reached there was that his quench medium was too fast.....warmed canola oil. Which I understand works very well with 52100 (works for me every time...and I've used the upper range of aust temps...never an issue with 52100). Be that as it may...he changed from canola oil to AAA (IIRC) and his problem went away. Go figure...the universe is indeed strange at times. The cracks on his blade were almost spider web like...not just one or two or three here and there. I wouldn't think it would cause those surface spider web cracks. But apparently using too fast of an oil can do that.
 
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rhinoknives

Well-Known Member
Laurence, I found it like that right after surface grinding at a machining shop, they use grinding stones not belts. but before i gave it to the guy there was nothing on it
Then may be stone marks from the surface grinding. Were they grinding the bevels for you or just polishing the flats? Do some length way sanding with some 220 or higher grit paper on the tang and see if the go away?

They look like machine marks of some kind to me?
 

Lagrange

Well-Known Member
I have to agree with Laurence. Those marks appear to be machining scratches to me. It seems that there would have to be some serious flaws with your steel if you had cracking like this.
I could be wrong, but I would try and sand the marks out.
 

SHOKR

Well-Known Member
Stuart

The blade was tempered yes

This steel is sverker21 (D2)
It was surface ground to thin it a bit when it was still soft (im starting to suspect that surface grind), then took it to another surface grinder for better finish. (the first grinder has something wrong with his machine, so it leaves very wavey surface, but i go to him when i want to remove material) then it was HTed and no problems appeared, i hand sanded it a bit with 120 and no problem, but I was going to surface grinder anyway and felt my hand sanding left bit of deep scratches from surface grinding before (I think youre starting to see how hard things arecforcme around here...)
When i got it from that SGer i saw those cracks, or at least they seem like cracks


Guys, I just want to make sure, you understand the problem is the wavey lines across the blade not the straight lines along its length, righy?

Anyway I will give it a go on my disc sander later and see how things go, probably try what kerosene trick too

Thanks

Will keep you posted
 

C Craft

Well-Known Member
SHOKR, I might be wrong but they look like marks caused by the stones. You said they were ground at a machine shop. Does the machine shop have the ability to do a magnflux process on the steel. It is not a cheap process but if you are friendly with the machine shop they may help you out on the price for a knife. The process is often used when rebuilding engines and you want to check the engine parts for any stress cracks that are not visible to the eye. Below is a definition of the magnaflux process and it will tell definitively if they are cracks! If they are then you are on your way to figuring out what went wrong!

Full Definition of MAGNAFLUX. —used for a method of testing a ferrous metal for defects by magnetizing the material and observing the patterns assumed by iron powder applied either dry or in liquid suspension.
 

SHOKR

Well-Known Member
Sounds interesting!!
Not sure who here would have it but wont hurt to ask around!
 

SHOKR

Well-Known Member
Sounds interesting!!
Not sure who here would have it but wont hurt to ask around!

Thanks! :)
 
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