spark test of S-7

Hi. I bought a few drops marked as S-7 on E-Bay. I spark tested them, and although they show evidence of a medium carbon molybdenum allow (bursts and arrows), I wonder if some one with a more calibrated eye can double check the photo (Alvin? :-))

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Mild steel baseline photo is also available in the same album.

Thanks, Eric

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Cool. :) I finally fooled someone into spark testing stuff. ;)

I'm not all that good at it. :/ I have to have known samples that I compare, side by side. :/

Also... the darker the better. I've spark tested when I couldn't see the grinder, like an arc welder, just hope for the best and make adjustments as needed. :)

The books can't say that. ;) You might "hurt yourself". :/

Carbon makes the bursts. Moly tends to make the pronounced-type "spear points" Si suppresses the carbon bursts Cr is orange and suppresses both the bursts and the stream Ni same as Cr but not orange V tends to brighten the spark stream W in low amounts can look like Mo

Mn is discounted as not showing much if anything... but I want to know what causes O1 to have that hollow-round "puff ball" little "dandelion flower" look.

For an novice like me, spark testing isn't about knowing-off-hand.

It's about side by side comparisons and coming up with something like... "it's like a cross between this and that, more like that" a doggone sucessful spark test. :)

But more often than that it's about... "does it have enough carbon bursts to be blacksmith heat treatable?" Your S7 is showing that it needs time at temperature like a medium allow steel. :/

From the pictures it sure enough could be S7. :) From the pictures it sure as heck ain't 1095 or HSS. :)

That's where I'd start and then continue to narrow it down as far as I could.

Alvin in AZ

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You probably didn't buy this S7 to make sparks, so why not forge it, harden and temper as though it was S7 and see if it works that way.

S7 is air hardening, so as a first test, I'd forge an end out to about

1/2" round or rectangular, make it into a chisel that you need, then harden it (takes a few hundred degrees above non-magnetic, a BRIGHT orange to low yellow, then let it cool in still air. It should get real hard. Now, get a good forge fire going. Heat a 5 pound piece of scrap to orange or so and place your newly hardened part beside it. Cover it all with coke and kaowool or even fiberglass insulation and turn the blower off. Let the fire go out. If the part got soft enough to file, it may well be S7. If it is soft enough to file, it's something else. (This test was to see if it can be annealled without having to cool at 25 degrees per hour or less down to about 1000 degrees, which is what S7 needs). If it won't file,, temper to straw to red, and use it. If it stays sharp for a long time whil cutting cold or hot steel and doesn't crack, it probably is S7.

I know I left a couple of "if its nots" hanging, Pete Stanaitis

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Hi Alvin. Thanks for the reply. One reason that I was a little confused was that the spark tests shown in the following link:

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showed a much larger effect of molybdenum.

I have the typical junk steels: grade 2 bolt, HC railroad spike, C-J railroad spring, file, old hammer head. These give me a pretty good run of the scale of carbon content. I also have large drill bits. I agree; the sparks look nothing like 1060, 1095 or HSS.

As for the darkness, these tests were done at night with little lighting. The reason it looks bright is because of the digital camera's flash. If you suppress the flash in "night shot" mode, the shutter speed is too slow, and it doesn't work. "Auto mode" also does not work, because the shutter speed is to fast and only the flash is seen, no sparks. The newer model has "fireworks" mode, but I bought last year's model on sale.

Thanks, Eric

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Hi Pete. Thanks for the reply. Just to clarify, the "if not" that you left out was:

"If the part got soft enough to file, it is something else. If it is not soft enough to file, it may well be S7."

That is a good suggestion to just try forging it. I have not been able to get to the forge for a while. Maybe this weekend.


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Hi Pete. I was able to get to the forge on the weekend. It does seem like S-7. It was much harder to move than 1060 rail springs. I needed a striker, and even then it was slow going. If it was hit while red (carefully!) it made a clanking noise. I air cooled the end and it skated an old file. My striker told me that it was not worth forging down from 3/4" round. I should just bite the bullet and buy from Mojave or stick with old coil spring.

Meanwhile, I bought a drop from a different vendor on EBay. It spark tested almost identically. Two people on iforgeiron posted pictures of S-7 spark tests, and they were almost the same, given the differences between a bench grinder, a belt sander and an angle grinder. BTW, I am going to have to try that angle grinder. Much more action at the arrow tips. Maybe the bench grinder is deceiving. Also, the vendor is sending me some 4140 so I can calibrate with molybdenum composition.

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Yeah, you don't want that nasty ol' stuff making your life hard. Tell you what - you can send it to me. I expect I can find something to do with it :-)


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Kyle J.

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