Photo of broken steel

D

deloid

Joined
Dec 19, 2007
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I was testing some steel (I think 5160). It is a car spring but I wasn't worried about the mystery steel issue since I was going to use this for the D guard, not the blade.

I annealed a piece (tested and soft ), hammered it down to the estimated thickness after a few heats then I let it cool and tested it's brittleness in a vise. It broke really fast. The photo shows the grain pattern.
I do need to be able to bend the steel a bit and I suspect that normalizing would have solved the problem but I thought that a photo would help with some more concrete advice.
Thanks for looking.

dsc6814.jpg
 
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My guess is that a normalizing cycle would have helped reduced the brittleness by resetting the grain size. At forging heat, you are bound to grow the grain, and it needs to be reduced. Looks large to me.

--Nathan
 
Did you leave it too cool overnight in the forge? I wonder if we're seeing coarse pearlite with possible grain boundary carbide. hum...

"paging Mr. Cashen"...
 
Go ahead and post your fractures and have them all discussed at one time.
I'd like to get a bit more detail about the HT procedures .At this point grain size looks like the most likely suspect.
 
p1060463.jpg


its T1, salt bath heat treated and triple tempered to 64 Rc
I cut about 1/4 the way through with a cut off wheel on my dremmel, then broke it with a pair of vice grips. it didn't bend at all
as you can see I etched one piece. that color is the result of only 10 min in vinegar, which I though was fascinating.
so I am concerned about the micro structure of the steel (the grain structure appears to be supper fine,
even under 5x magnification the etched end looked like 800-1200 grit black silicon carbide sand paper),
but I am also really interested in the mechanics of the fracture. it did not break in a clean line,
but with bulbous lumps I am also greatly intrigued by the ripples/ridges located mainly along the compression side of the fracture
 
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so I was thinking about this some more, and i was wondering about what happens mechanically when it breaks. I assume that it bends a little before it breaks, so half the break (in my photo the half that is cut partially) is in tension, and the other half is in compression. so how the hell do you compress something at 64 Rc, and are those ridges the natural consequence
 
deloid said:
I was testing some steel (I think 5160). It is a car spring but I wasn't worried about the mystery steel issue since I was going to use this for the D guard, not the blade.

I annealed a piece (tested and soft ), hammered it down to the estimated thickness after a few heats then I let it cool and tested it's brittleness in a vise. It broke really fast. The photo shows the grain pattern.
I do need to be able to bend the steel a bit and I suspect that normalizing would have solved the problem but I thought that a photo would help with some more concrete advice.
Thanks for looking.

dsc6814.jpg
Click to expand...
You seem to have pretty coarse grain there. Most likely cause the fact you didn't anneal or at least normalize after the severe forging heat.
I did a destructive test on a purposedly overheated blade some times ago and got a structure exactly like that.
Kavin Kashen can say much more for sure. He has studied the topic in great depth.
 
Nebulae, good photo and exactly what you would expect from that alloy at that hardness. It will fracture in tension before compression.

Note the grain size difference between Nebulae's and Deloid's .Deloid's grain size makes for a brittle steel !!
 
I don't know, the ridges are driving me nuts. It seems like they are there for a reason, its just too convenient to see them placed where they are. Good point about the tension fracture vs compression, that is kinda obvious should have seen that.
 
"Kavin Kashen can say much more for sure. He has studied the topic in great depth."




Awaiting Kavin's response to this one. Should be interesting, to say the least. ;) :)
 
another observation. The ridges in my photo seem to be parallel to... something, I dont know what you would call it, perhaps the direction of force? or fracture? Fracture plane? This would mean it arcs along the edge of the curve along the ''lumps". furthermore the ridges seem to be pretty evenly spaced, and evenly sized, yet much larger than a single grain?
:confused:??????

just throwing this out there, I also I did the same thing to D2 at 58 Rc (different beast I know, but I think Perhaps the largest difference as far as the fracture goes is the hardness) and I got realitivly straight fractures, no lumps and no ridges to speak of. perhaps an artifact of hardness?

We deffinitly need Kevin Cashen, how often does he frequent our humble abode?
 
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