Case Tru Sharp Pitting

A

Ace Rimmer

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Jul 4, 2017
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I wasn't sure where to post this, but since it involves a traditional (Case 6318 SS) I'll try it here.

I've just noticed some pitting on both sides of all three blades on my 6318 stockman (2017 date stamp). I think this is the result of something I did (explained below). I thought I'd post this for information and possible general interest, and to solicit any possible comments, thoughts, ideas, suggestions, etc. I doubt it really matters on a "user" knife.

I have re-dyed this knife twice. Both times I've used a hot (near-boiling but not boiling) dye bath containing Rit dye, a drop or two of dish soap, and a "splash" of white vinegar. The first time I had the blades open and sticking out of the water to facilitate removing the knife at the end of the process, and the pitting appears (perhaps) to correspond to about where the water surface would have been. I discontinued this practice (open blades) after dying a couple of knives because this left a haze on the surface of the blades (above the water line) that wouldn't easily rub off, but did come off after a bit of polishing. I didn't notice the pitting after the first re-dye treatment.

I just completed re-re-dying this knife with all blades closed. I immediately noticed the pitting when cleaning up the knife because some of the dye water was trapped in the pits. The only other knife done with the blade open and extending above the water (a Rough Rider) has not been re-re-dyed and exhibits no pitting.

I think that pretty well covers all I know about this. It would be interesting to know if anyone has ever seen anything like this.


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I have never had stainless blades pit like that, but I have never dyed any covers either. I imagine, as you are thinking, that the marks are a result of the dying process that you use.
 
One way to verify if a pit or a stain:
Use a needle or pin to see if the "defect" goes below the surrounding surface.

It seems strange to me that Case's steel would be pitted by your dye solution.
 
They are definitely pits; some can even be felt by running a fingernail over them, especially those near the spine of the blade. I'm thinking there was some interesting chemistry going on at or just above the surface of the water. There should be no oxygen in the water since it had been brought to a boil just before putting the knife in.
 
420HC (AKA Case Tru-sharp) is reasonably corrosion resistant as knife steels go. However, I would not expect any steel with a carbon content of ~.5% and a chromium content of 15% to do particularly well in a boiling acidic solution. While there are grades of stainless steel which will totally shrug at those conditions, they have way less Carbon and way more chromium. That haze you polished off was actually corrosion.

304 stainless does well in that type of environment. But its composition is
0.05% carbon, That's 1/10th the carbon compared to 420HC
18% chromium
 
Yes, Rit will pit stainless. I've dyed a few knives and experienced this myself. I don't own any Case TruSharp, but I've pitted the stainless springs on a Case knife and the blades of a few Rough Riders.
 
Ace Rimmer said:
They are definitely pits; some can even be felt by running a fingernail over them, especially those near the spine of the blade. I'm thinking there was some interesting chemistry going on at or just above the surface of the water. There should be no oxygen in the water since it had been brought to a boil just before putting the knife in.
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Bad news. Boiling water still contains free dissolved oxygen unless chemicals have been added to deplete it.
 
Interesting. I have used the hot RIT dye process on several Case SS knives with no issues. It pits the heck out of Case CV though. Learned my lesson after two of those - no more stovetop RIT dye for my Case CV knives.
 
knarfeng said:
420HC (AKA Case Tru-sharp) is reasonably corrosion resistant as knife steels go. However, I would not expect any steel with a carbon content of ~.5% and a chromium content of 15% to do particularly well in a boiling acidic solution. While there are grades of stainless steel which will totally shrug at those conditions, they have way less Carbon and way more chromium. That haze you polished off was actually corrosion.

304 stainless does well in that type of environment. But its composition is
0.05% carbon, That's 1/10th the carbon compared to 420HC
18% chromium
Click to expand...

Interesting, and thanks for the details. And the haze was all above the water level which adds to my suspicion that the most chemical activity was going on in the vapor region (and probably the interface) rather than in the liquid.

solphilos said:
Yes, Rit will pit stainless. I've dyed a few knives and experienced this myself. I don't own any Case TruSharp, but I've pitted the stainless springs on a Case knife and the blades of a few Rough Riders.
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Thanks, good to hear that my experience is not unique.

Jody744 said:
Color the pits with a #2 pencil, then wipe clean.
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Thanks, I'll give that a try.

Mora2013 said:
Just curious how much use this knife has already seen. That’s a lot of blade scratches for a 2017 knife!
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When viewed "in person" it doesn't look that scratched. The longitudinal "scratches" are actually just streaks from me wiping the blade with my finger. The mark at the far left is from blade rub (good ol' stockman behavior). Otherwise I always seem to generate a certain amount of scratches when I sharpen and I'm not sure how or why -- I think I'm being careful! :confused:

Hickory n steel said:
Any potential issues with the small pits ?

They certainly don't effect my carbon steel blades.
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I doubt it in any normal use. Might create stress risers if I used it as a pry bar. ;)

yablanowitz said:
Bad news. Boiling water still contains free dissolved oxygen unless chemicals have been added to deplete it.
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Thanks, I didn't realize that. Helps explain how complex the chemistry is here.

jc57 said:
Interesting. I have used the hot RIT dye process on several Case SS knives with no issues. It pits the heck out of Case CV though. Learned my lesson after two of those - no more stovetop RIT dye for my Case CV knives.
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I did a CV Texas Jack and anticipated issues. It was a $25 knife that I purchased to use in the experiment and already had some pitting. Actually, it cleaned up fairly well. I may need to declare that I've learned all I need to know about dying and give up on it. :D
 
Oh, and one other thought -- since the pits didn't show up until after the second bath, I wonder if the first bath didn't cause some grain boundary corrosion (primarily occurring in the region of the vapor-liquid interface), and then thermal stresses (or something else?) from the second bath caused the weakened areas to pop out. (I have some water chemistry and metallurgy training, but it was a long time ago. :confused: )
 
Do you recall how long you kept it in the pot?

I've only dyed one Case knife, a Beer Trapper in SS, and I didn't have any issues. I didn't add vinegar, though; I just had water, RIT, dish soap, and a dash of salt. My dye mix was at a very low simmer, and the knife took close to an hour (intermittent as I would take it out and rinse it to see how the dye was taking) to get it where I wanted it.
 
Ive dyed both case stainless and cv.
Stainless was ok but the cv got some big time stains. Both large stockmans.
I dyed a csse tb saddlehorn trapper production model that is stainless and its fine.
Rit solution is v salty.
 
Ace Rimmer said:
They are definitely pits; some can even be felt by running a fingernail over them, especially those near the spine of the blade. I'm thinking there was some interesting chemistry going on at or just above the surface of the water. There should be no oxygen in the water since it had been brought to a boil just before putting the knife in.
Click to expand...

A complete lack of oxygen in the environment is a bad thing for stainless steel. Putting stainless steel in a corrosive environment in which there is no oxygen can lead to depletion of the oxide layer on the steel. The oxide layer is what keeps stainless steel from corroding. Deplete it and your stainless steel is no longer stainless.

But you are correct. There is some interesting and complex chemistry which happens when you put any steel in a corrosive environment.
 
Not surprised by this, boiling in water and acid make for a harsh environment.

Can't get RIT here but I've used very strong tea dye with salt with very good results especially on Stag (that takes some nerve as the slabs get bloated and look horrible at first, goes back to normal with a slow dry out) CV of course gets blackened and even stainless goes dark. Don't think I noticed pitting but I didn't boil it, just left it to soak for some hours in tea water that had boiled.

As a side note to pitting on brand new GEC carbon. Left a Churchill overnight in a lime slice, blackened nicely but it gave it some very nasty pits which shocked me.
 
Thanks, everyone, for sharing your experiences. I've learned some new things, which was a goal here, along with changing the look of some knives. (One thing I found was that blue dye didn't take very well, but brown and red both produced good results.)

Wurrwulf said:
Do you recall how long you kept it in the pot?

I've only dyed one Case knife, a Beer Trapper in SS, and I didn't have any issues. I didn't add vinegar, though; I just had water, RIT, dish soap, and a dash of salt. My dye mix was at a very low simmer, and the knife took close to an hour (intermittent as I would take it out and rinse it to see how the dye was taking) to get it where I wanted it.
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I brought the dye mixture to a boil and then turned off the heat. I believe that I used 15 minutes for the brown and then ten for the red. By the way, in general I've had no problems with the glued shields. I did one Rough Rider for which I left the mixture on a low simmer and the shield fell out. I replaced it with superglue.

The Rit instructions call for adding salt for some fabrics and vinegar for others. For bone, I just took a guess at vinegar. :p
 
knarfeng said:
A complete lack of oxygen in the environment is a bad thing for stainless steel. Putting stainless steel in a corrosive environment in which there is no oxygen can lead to depletion of the oxide layer on the steel. The oxide layer is what keeps stainless steel from corroding. Deplete it and your stainless steel is no longer stainless.

But you are correct. There is some interesting and complex chemistry which happens when you put any steel in a corrosive environment.
Click to expand...

Good point! I think we tend to think of "stainless" steel as magically rustproof or even inert, when actually there are complex things going on at the surface. One CO I had in the Navy always referred to it as "CRES" for "corrosion resistant steel". Thinking of it that way helps to remember that it is "resistant" and not "proof".
 
Ace Rimmer said:
The Rit instructions call for adding salt for some fabrics and vinegar for others. For bone, I just took a guess at vinegar
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I just used a little salt with mine, not vinegar. Perhaps that's why my stainless knives were unaffected.

I have used heated vinegar before (not with dye) when experimenting with patina on CV blades, and it produced a rather vigorous reaction. I can see how that could probably affect stainless too.
 
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