Let's talk salt pots...

[Darren Ellis]

I'm getting ready to finish up my salt pots that I've had the parts for for something like 1.5 years now...about time, huh? Nick Wheeler mentioned in a recent thread that he had to grind the "salt film" off of blades, otherwise they were subject to bad corrosion. At Batson's this past weekend I talked to Chuck Robinson about this a little, and then today, on the knife list, Mike Starling made a comment about it too...good timing! Anyway, I'd love to hear how others treat their salt pots and what you do to clean up blades after heat treatment with salt pots.

Chuck thought that a soak overnight in warm TSP should resolve any residual film problems on the blades. Also, the following quote was posted by Mike Starling:

If the concern is about the corrosivity of the molten salt on blade materials themselves, I'd suggest that you're probably seeing the effect of contaminants that build up in the molten salt over time. These combined with any kind of carbon left on the knife blade can result in what appears to amount to surface burning of the blade being heat treated.

These contaminants can be removed by stirring the molten high temp salts with carbon rods and the addition of some boric acid to the pot.

So, here's what I'm wondering...what do you guys do to your blades post heat treat when using salts to neutralize the salt? For instance, if I HT 20 blades, it may be a few days or even weeks before I can finish grind them... Also, where can one get carbon rods and where's the best source for Boric Acid?

Thanks!

-Darren

[Laredo7mm]

I use a 50/50 mix of sodium chloride and calcium chloride formy salts. After the oil quench, I rinse the blade in hot soapy water (about 100°) to remove the oil and salt before I put it in the oven to temper.

I think most salts sould be easily dissolved in water, give them a washing, that works for me.

[Doc Hollywood]

You can get Boric acid in the garden center of most home builder stores (Home Depot, Lowes).

I have no idea aboutthe carbon rods.

Doc

[NickWheeler]

Darren-

I've talked to a few smiths that told me you can simply add wood-chips to the salt for the carbon addition. I tried it with my old salt vessel... and man was it ever messy.

I believe what Mike said is/can be true... but my blades had the same problem even when both salt vessels and the salt in them was new.

I've wondered about the TSP... I'll have to try it.

I know that has to be either a salt or method that works, as there are makers that do fully engraved blades out of 52100 and then use high and low temp salt to heat-treat.

I'd love to get this problem solved. I surface ground about 25 blades the other day but didn't have time to get all the other surfaces ground (edges and bevels) and by the next day the flats were already rusty. Basically wasted all the time the previous day surface grinding as I'll just have to do it again.

That's a MAJOR PITA!!!

Thanks for sharing what you've found Darren
-Nick-

http://www.wheelerknives.com

[Kevin R. Cashen]

Darren, I am not sure what could be happening on other folks blades, but you asked what others do after the heat treat, so here is my method:

After all the belt work, I hand polish both monosteel and damascus to a 400X satin finish before heat treating. My high temp have additions of a graphite powder on the surface, but this is for decarb and pitting issues while in the salts, not afterwards. My low temp salt is just the salts. I quench from one into the other, the high temp particles are removed by the quench. After the quenching and tempering I rinse the blades off in soap and water, sometimes a squirt of TSP solution, if the spray bottle is setting there, until the low temp salts are disolved.

I can then spread some oil on them and let them set until I get to them or start the final finish imediately. If you leave the low temp on the blades and let them set they will draw moisture pretty bad, but I have found the blue-gray oxide from the nitrate salts looks an awful lot like gun blue, and acts an awful lot like it in retarding corrosion.

All my belt work is long done before the heat treatment. Then next step is to either polish the monosteel to a 400x hand rub, and the damascus to an 800x before etching in FeCl. All I can say is that this has worked very well for me for quite a few years now, for what it is worth.

[Kevin R. Cashen]

Perhaps what could be happening in some of the other examples given is a chloride thing. Acids and bases are pretty easy to deal with by simple Ph balancing, but chorine atoms still on the blade will raise holy heck. This is why simple dips in baking soda just will not properly neutralize ferric chloride, but a base with a seriously aggresive rinse will. Gotta knock those chlorine atoms loose.

My salts are simple sodium chloride, but if other chorides are used they may be more tenacious in letting go I dunno.

[John Frankl]

Darren and All,

Thanks for the info so far. As one getting ready to go to salts for HT as well this is very helpful.

Not to hijack a very productive thread, but is ANYONE thinkings of stocking/fabricating 316L tube containers? I'm finding the forge building, electronic controls, etc. much easier that getting a decent piece of tube

Thanks,

John Frankl

[NickWheeler]

Kevin-

What's happening for me, is horrible corrosion after the blades being in the salt.

If I harden an O1 blade (let' say from high temp salt to AAA) and don't do my finish grinding very soon afterward... the blade will draw moisture and rust like there's no tomorrow.

I've tried cleaning the blades in soapy water, then oiling, but it doesn't seem to help much.

I have wondered if it's the brand of salt I'm using (Houghton). Or if there's just some simple step I'm leaving out in preventing the problem.

Thanks Kevin!
-Nick-

http://www.wheelerknives.com

[Matt Shade]

Going in a different direction a little bit. I wonder what would happen if you just found a way to store blades away from moisture until you can finish grind them. Anybody got one of those low temp welding rod ovens? They can keep the moisture content under 1%, and I'm pretty sure they stay under tempering temps.
I guess some tupperware and a couple silica packs might do the trick for a day or two as well

[bladsmth]

Carbon rods can be bought from any casting supply company,or a jewelers supply.

[Kevin R. Cashen]

Originally Posted by NickWheeler

Kevin-

What's happening for me, is horrible corrosion after the blades being in the salt.

If I harden an O1 blade (let' say from high temp salt to AAA) and don't do my finish grinding very soon afterward... the blade will draw moisture and rust like there's no tomorrow.

I've tried cleaning the blades in soapy water, then oiling, but it doesn't seem to help much.

I have wondered if it's the brand of salt I'm using (Houghton). Or if there's just some simple step I'm leaving out in preventing the problem.

Thanks Kevin!
-Nick-

http://www.wheelerknives.com

Hmmmm. I will quench my shallow hardening stuff into Park #50 and still not get the same problem. I feel for you as that would frustrate me to no end. If I had more than a couple scoops of Park Nu-sal left I would send you some to see if there was a difference. Do you have any info on the Houghton stuff? What salts are others that are suffering from this issue using? I would love to help get to the bottom of it, since that could put a serious crimp in ones productivity

What do the blades look like after leaving the oil? Are there flakes of salt left? is there any pitting or etching at this point? My oil quenched blades will be slightly grayish with some very slight color deviations from where the salt got blown off.

[Darren Ellis]

Hey everybody, thanks for the great info, this is good stuff!

Kevin, are you using the Parks Salts?

-Darren

[NickWheeler]

Kevin-

I've tried to get Nu-Sal...but we know how friendly HeatBath is.

I was amazed when I finally got them to send me quenching oil. I'm also using #50 on shallow hardening steels... and get the same problem.

Right after quenching the blades are a light grey color....very clean looking and NO decarb.

I'll scrape/wire-brush the little flakes of salt off, wipe them down real quick and then they go into either a digitally controlled tempering oven or low temp salts.

In the photo pictorial about me making blade blanks that my friend Randy recently put together, you can see a pic of an O1 blade. It's covered in thick, nasty rust, and the pic was taken only 1 week after it had been heat-treated.

http://outdoors-magazine.com/s_artic...id_article=188

This is the second part of a three part series, but the pic is right near the top.

Thanks Kevin!!!
-Nick-

http://www.wheelerknives.com

[Dan Gray]

great tid-bits here

BTW Nick
I have your link up..
http://www.knivesby.com/knifemaking.html

[twistedneck]

Are these carbon jewelry rods required for salt pot quenching? I assume they will help eliminate decarb on the part while in the salt pot.

Has anyone tried a stainless mini agitator (prop) and slight water addition? I need to speed up the salt quenching rate.

Finally, what is the best way to clean the parts free of chlorides and acids after the salt quench? I'd like to store these with an oil film for a few days.

Thanks!

[jhiggins]

What if you coated the blades with some of that waxy coating you sometimes get on endmills, drillbits and other tooling? That stuff is melted in a pot, and is full of oil. Might be a good solution to to the rust problem you have, Nick.

Another idea I had was that perhaps your blades simply were not clean enough. Maybe try running them through the dishwasher, then just store them in a bucket of oil?

[Dan Gray]

Originally Posted by twistedneck

Has anyone tried a stainless mini agitator (prop) and slight water addition? I need to speed up the salt quenching rate.

Thanks!

you are not talking about water in the salts are you BOOM

[twistedneck]

Originally Posted by Dan Gray

you are not talking about water in the salts are you BOOM

Oh yes...

Not the same as adding a wet part to salt. Water addition takes place under lower temp salt at about 750F and full agitation. This is recommended by ASM Heat Treaters Guide. I'm going to run it by the Houghton quench guru next week when we meet for work.

[Dan Gray]

Originally Posted by twistedneck

Oh yes...

Not the same as adding a wet part to salt. Water addition takes place under lower temp salt at about 750F and full agitation. This is recommended by ASM Heat Treaters Guide. I'm going to run it by the Houghton quench guru next week when we meet for work.

very interesting
use your safety gear

[jhiggins]

Since we are talking salt pots, what would be the length of the inside tube? I mean, what would be good dimensions for the salt tubes? I'm considering making some for sale out of 316L and tigging the bottoms on if there is enough interest.

Right now, I am thinking of lengths of 18", 24" and 36"... What do you guys think?