Odd pattern on blade after heat treat

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elementfe

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May 3, 2008
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blade%252520heat%252520treat%252520002.JPG


First time posting an image, hope it comes through.
This is an odd pattern (the diagonal striping near the edge) that I noticed after quench on a prototype made from some sawmill blade- spark test suggests 1070 or thereabouts.
Heated slowly in a propane forge to about 1600 (a little hot, but...) quenched to about 150 in ATF, then scrubbed with scotchbrite so I could watch the temper color.
Perhaps this is common, but this is the first time I've actually looked at it- anyone know what causes this pattern?

Thanks!
Andy G.
 
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are you talking about the top half of the blade? that looks like pits from getting the blade way too hot in that area but its hard to tell in that picture.
 
No, the diagonal striping near the edge- it's not from sanding, it appeared during heating/quench.
The pitting is because I made a quick proto from skanky old sawmill blade that's been under my table for ten years.
 
Possibly grain direction? If it was from a circular saw blade, You can't expect the grain to run with the shape, can you?
 
OK, this is what I think: having re-read Mr. Cashen's excellent article on quenching, I noticed that the tracks are on an angle that would be vertical when the blade was being quenched. I think that they're tracks from vapor bubbles, since I wasn't agitating as much as I should have been.
Haven't tested the blade yet, but it'll be interesting, lacking a Rc tester, to see how well it hardened- probably could have used water and gotten better results.
Andy
 
My guess is that the pattern you see is alloy banding. I saw a lot of this when I was playing with 1075 a few years back.
 
Justin , my assumption also - alloy banding. Certainly not from vapour bubbles !
 
mete - I disagree -
I think that there was too much cellular traffic in his area and the RF ionized the vapor bubbles in the quench. This allowed magnetic flux lines to affect the steel molecules, especially the ferrite, as they transitioned through the austenite-martensite barrier. The lines look exactly like the lines formed by iron filings on a glass sheet in a magnetic field.

Either that or it is alloy banding?
 
Scratches and irregularities left on a blade prior to heat treat can and will grow deeper that the bottom of the scratch.
 
OOOhhh....I LIKE it!
Let me be sure to put on my aluminum foil hat next time before I quench, leave my phone in the lead lined box! (or would stainless foil be more appropriate?)
Hm! Perhaps that's why this pattern doesn't appear on stainless- because the EMF rays from the black helicopters can't get through the foil!

Thanks all for your replies- blade seems to have hardened fine, I'll assume it's banding and use better steel on the next ones.
 
Ed Fowler said:
Scratches and irregularities left on a blade prior to heat treat can and will grow deeper that the bottom of the scratch.
Click to expand...

So polishing before heat treat is recommended, or just be prepared to grind off more than thought necessary after heat treat to get rid it?
 
I always sand down to a 220 grit before hardening. The same goes for the spine and the edge - any scratches deeper than a 220 will show up below the bottom of the scratch. I left a blade that had been hardened and tempered lay on my bench after I started grinding it down for a student this summer, leaving 36 grit scratches on the surface of one side of the blade. Months later I finished grinding the blade and tested for edge flex, 36 grit scratches left over the period of several months on a hardened blade resulted in 36 grit chips out of the blade edge. I was able to grind below them and no more edge chipping.

We still have a lot to learn about stress risers, but the pattern you achieved (could see - it was there before tempering but you could not see it)
during tempering supplied a lot of information. So does etching your blades, etching every blade provides a great opportunity for learning.

Pits like you left on the top of the blade will also grow deeper, but if you don't harden the spine you won't have as much to grind off if you want to get rid of them.
 
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