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Luke Shearer

cracks from water quench?

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ok well I recently heat treated a few blades, and as a bonus one of them survived! Actually the other two that cracked are still in one piece and I think there may be some hope for them...which is why I started this topic. Both of the blades that cracked were water quenched. I quenched the tanto in 140+ degree water after 3 normalizations. 3 seconds in the water, 1 second out, 2 seconds in water, 1 second out, in until cool. Its from the low manganese 1075 from Aldo.

The sax is 5 bar with wrought, 1075, 8670, RR spike, and some wierd steel I recycled from a punch for the edge. It was also normalized 3 times but it was quenched at room temp (or garage temp...in Texas that means hot ~95+)3 seconds in water then edge quench into canola oil.

 

picture time

 

pw crack.jpg

 

heres the sax. Its alot easier to see the cracks in this one.

 

tanto crack point.jpg

 

tanto crack  point 2.jpg

 

this may be the most apparent crack on the tanto. It follows the hamon, but not exactly

 

tanto crack.jpg

 

I know that these cracks do not go all the way through because on this side of the blade there are four or five cracks and on the other side theres just one.

I would love to hear if these can be salvaged. I had some pretty cool plans for them. Anything on how to prevent this on the next ones or how to fix it would be appreciated.

Edited by Luke Shearer

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no luck. on the whole, cracks are considered fatal, as they inherently weaken the blade. that said, if these are just for yourself, there's no harm in finishing them up and even using them, just don't trust your life to them.

 

some thoughts on what went wrong:

 

1. always quench mystery steel in oil. many steels will not survive a water quench, no matter what you do.

 

2. the only reasons for a water quench are to produce sori, to produce a more active hamon, or if the steel won't harden in oil.

 

3. the edge quench after the water quench was probably not a good idea - just adds one more area of stress.

 

to minimise the risk, next time:

 

1. normalise at descending heats, starting about 170f above critical, and finishing right at critical. you want to basically bring the whole blade up to forging temp to wash out the unevenness in structure produced by only bringing sections up to temp to forge, the fact that the tip and tang probably took more heats, etc.

 

2. leave the edge pretty thick - i always leave at least 2mm, usually 2.5mm before a water quench. this will very slightly decrease hamon activity, and lessen sori, but it vastly improves the chances of survival.

 

3. pay close attention to your grinding - everything needs to be as even as possible, and all the grinder marks should run parallel to the edge.

 

4. temper immediately. no admiring the shape,no checking for straightness, don't even bother to scrape off the clay.

 

5. 3 seconds water, straight into oil - won't produce any sori, but i've never had a crack doing this.

 

6. don't fall in love with a blade until you've tempered it twice.

 

7. don't water quench a pattern welded blade unless you absolutely have to - even very slight differences in hardenability will increase the chances of cracking, and you've invested too much time, effort, fuel etc, to lose it needlessly.

 

8. use a magnet to get in the ballpark for quenching temp, but the final judgement should be done by eye - if in doubt, pull it out the forge and watch the recalescence, then back in and watch the decalescence, and quench as soon as the shadows are gone.

 

9.stick with it, and better luck next time...

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Jake, that's the most succinct summation of water quench issues I've ever read! May have to sticky that one. B)

 

Luke, I know it hurts, but yep, total loss in both cases. :(

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Yes indeed well said Jake. The only thing I would add is that 8670 or L-6 will crack in water every time, in my experience.

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Thats hard to hear but thanks for the advice. I'll try again when I have more courage...and money for propane, belts, etc...

 

I hear Parks 50 is similar to a water quench but isn't as likely to crack a blade. Is that right? what kind of hamon does it produce?

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Luke, parks 50 is much safer than water, due to the slower convection phase of the quench, when most cracks occur, though this also causes negative sori, so you have to account for that. and as for hamons - take a look at Don Fogg's knives - apart from the japanese swords,he quenches pretty much everything in parks 50, and the hamons speak for themselves...

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