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Wootz quench question


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This is a blade I forged (with the help of some great friends here in Greece) using some of the wootz produced during last year's masterclass in Belgium run with Klaas Remmen and Niko Hynninen. The composition is white cast, and armco pure iron.

I normalized the blade three times, around non-magnetic, quenched it in olive oil from slightly over non-magnetic, tempered 2hours at 200C, and sanded up to 1000 grit with water so as not to burnish the surface. Then etched in 2% nitric acid for 10 min, and cleaned up with fine steel wool.

 

I have run across two issues, and I will be grateful if anybody here can shed some light.

 

One is some decarburization on the right side, which I will probably have to go back and grind away, right?

 

The second one is that the patterns appear really strong at the tip (on both sides of the blade) but are difficult to see on the rest of the blade. Is it possible that the tip somehow heated up more than the rest of the knife, or that it soaked enough, and the rest of the blade did not, and that is why this is happening? Should I reheatreat the blade, soaking it more at non-magnetic, or maybe even higher?

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check the hardness with a file - it looks like only the tip hardened. If that's the case, then either the tip was the only part that got hot enough, or else it was the only part that cooled fast enough. I'd bump up your temp about 25 degrees f, and try again. Remember that a magnet only gives you the Curie temp - 1418f - which is useful for calibrating your eye, checking how evenly your steel is heating, and getting you in the right ballpark, but it doesn't tell you the quench temp - for that you have to watch for decalescence. I don't have much experience with wootz, but I suspect that you're better off raising the temp a little rather than increasing soak time, which I'd guess would be more likely to wash out the pattern. If going hotter doesn't work, then you need a faster quench - probably brine if you don't have access to a fast oil. If the whole blade is hard, then it looks like you over heated the tip which is not ideal, but the wootz structure may make it acceptable. I'd also go with a longer, deeper etch, and polish with loose abrasives to bring out the structure.

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Hi Athan.

 

It all ways quite hard make good judgement from any given photo, but

it might be that there is some level of decarb at steel surface.

This you need to work by grinding...yep...it sucks if your blade is all ready thin but only way.

Also I never keep any Wootz in solution that long. Even weak solution will greate pitting and makes surface more or less " burned" look a like if that long soak is used.

 

First I would recomend you re grind it whit 600, 800, and make light 5-10s ecth whit Nital ( alcohol + Nitric acid) neutralize whit bakingsoda water mix and wipe dry...also you can use alcohol rinsing after neutralizing and wipe it dry.Dont use any pumice or wool, just cotton or soft paper tissue.

You should see pattern...if not do new etch 5-10s.

 

If you see spots in steel that holds grey / light grey colours whit out any pattern they usually are decarb. ....more grinding that is then.

 

If you re do the whole HT you need to draw steel soft (softer) before..Steel might be cranky if you re do it from that phace. If you have kiln set it +700C and cool it slow to +600C after this whit kiln...If not you can use gasforge but it needs to be cold../ first heat up...

Get it gently to +700 C and re heat you blade on top of gas forge first during forge heat up....then in side...get it even colour ( that is really low red ) dont over heat it...soak 5min kill the gas forge and blug all holes whit wool or some other insulative material...leat it cool down whit gasforge..

Open the surface and re do the HT. One normalization ( non mag) heat and cool down in open air..

 

Take heat +760 C on the blade as you like ( just the edge or whole blade) and be sure you have +80 C oil ready.

Quenc horizontal or vertical...what you like to do..and do the file test to be sure it hard...temper +200 C at least hour.

( Before tempering you can grid window to see is there pattern or not..and to see hows the HT whent.) Martensite turns darker/black)

 

I hope you get at least some tips from this to try out.

 

-N-

 

( Multiple normalisations have tendesy to make steel harder to get quenched...as grain can be really small) spesially in oil.

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Hello Niko,

 

Thank you, that was much more than a few tips!

I have a kiln, so I will do what you proposed and post the results.

The blade is pretty thick so more grinding will be OK. I will definitely soften the steel before HT, learnt that lesson when a whole ax cracked on a second quench...

I was a bit fearful making nital, is it safe? Do you use ethanol or methanol?

What we learned in your and Klaas's masterclass last year has been of great value, especially how to forge down wootz ingot to bar, we even managed to break down 2Kg ingot using a 5Kg sledgehammer with slow, deep hits! I have 20ton press so maybe I can use that too, if I go really slow.

 

It is great work what you do with wootz, and appreciate your help immensely. This has been a huge lesson to me.

 

(As I said last year, you and Klaas are both welcome to stay with us whenever you come to Greece for some sun.)

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  • 2 months later...

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Hello again, here are some photos of the finished blade, after following the HT proposed by Niko. Quench was from 760 in a kiln, into 80 degrees olive oil.

The watering refused to appear very clear, even after several attempts with different echants (FeCl, nitric, oxalic, metabisulphide), and the best appeared to be a 50/50 mix of 2% nitric, with 5% oxalic.

 

Well, onto the next wootz blade now... Thinking I might have to bump the temp up to 780 maybe.

 

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Edited by Athan Koumantos
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  • 2 months later...

Hi Athan,

Good job on the blade, it is a pity that you lost the pattern a bit at the end. It is hard to tell from the picture, but from what I can see, you probably turned it all to martensite which as Niko mentioned that it masks the pattern and makes it dark. I have had this happen on some blades, the pattern is still there, but it creates a ghosting of the pattern when you etch it. Also each time you do a heat treat in the forge, you have to take the small layer of new decarb off the surface of the blade or it will hide the pattern. You can still etch it deeply and show pits where the pattern was, like a negative of the pattern, but the carbides are gone and you have to sand past that in order for the pattern contrast to come back.

 

Hope you have better luck on your next blade.

 

Regards,

Tim.

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