Corrosive Pitting in LionSteel M7 satin finish

F

FCCBCT

Joined
Jul 23, 2014
Messages
239
Hi everyone, my questions are; Is Sleipner alloy from Uddeholm really suitable for outdoor knife manufacture? It has less Chromium (Cr) than D2 and it's primary application is in the tooling industry where non corrosive lubricants would be used around the tools. Or are we really just reinventing the wheel? My D2 blades don't chip, my AISI440C/N695 blades chip even less. I don't dispute the supposed added toughness of the Sleipner, though remembering LionSteel do not guarantee the M7 against anything other than cutting tasks more or less-correct me if I'm wrong here.

Also if the Sleipner is PVDed then this ceramic nitride coating will definitely add corrosion resistance EVEN if there are alloy defects (pleanty of metallurgy papers discussing this) I know from correspondence with Gianni that the black coated version of the M7 is chemically blacked, so it's not a nitriding.

My M7 after a brief submersion in fast flowing freshwater (a flooding river actually) has undergone corrosive pitting (the satin finish). I know it is NOT a stainless steel as far as the definition of stainless steel goes, as I would expect some rust without care even with the limited Cr but Mn around 0.5%, 0.2% might be better to resist corrosion but then this would not be the same alloy, ok.
I wrote to Uddeholm requesting some comments but am still awaiting any reply. The pitting is confined towards the last 5-6cm of blade from the tip backwards and present more on one side than the other. This was not saltwater submersion but river water. Anyway here are some pictures:
Apologies for the large image, I have indicated the various regions with an overlay in Photoshop, other than that these are the original images.

Corrosive+Pits+Sleipner+alloy_DSC_5311+copy.jpg



For full details please see the following:

http://hardcorecampingtools.blogspot.com/2014/08/lionsteel-m7-and-sleipner-steel-ok-here.html


I'm not after a warranty issue (that is unless the situation changes drastically-ie the blade continues to pit, especially on the edge surfaces) just trying to understand why. The blog explains some of the science behind the process. General rusting,corrosion is ok for example most carbon steels such as 1095, but pitting can be a problem if the pits migrate into the blade un noticed because they are small. The only way to stop them is to physically remove them; protect from galvanic reactions (pretty difficult in real life usage of a knife meant for the outdoors) and or protect from oxygen, ok the latter can be effected by a light coating of edible oil.

All comments welcomed
Has anyone else notice this on their M7.

BTW the liquid you see is NOT water but sunflower oil.



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I have a few tiny rust pits in my SR-2A. Funny thing is that they're just on one side of the blade and one on the spine. I used Flitz to get rid of the rust but the tiny pits are there. The pits are so tiny that they may not show up in pictures but I'll try to get some pictures tomorrow.

I don't carry it much but I live about 7.5 miles from Pacific Ocean. I'm going to start carrying it more now to see what happens. May be even when I go for walks to add the sweat factor.
 
I am far from a metals expert, so far that I can't claim to even know a thing but,

The photos make the rust spots look superficial and appear easy to be removed with no damage to the steel. Is this the case or will there be damage?
 
wolfmann601 said:
I am far from a metals expert, so far that I can't claim to even know a thing but,

The photos make the rust spots look superficial and appear easy to be removed with no damage to the steel. Is this the case or will there be damage?
Click to expand...

No the rust spots should be able to be removed with no damage. The concern of mine was the pitting action as it can develop (into the blade) if left unchecked (which I won't be doing this, ie leaving it unchecked!)
 
molletta said:
Remove oil and clean blade with a metal polish.
Click to expand...

Ok Uddeholm just got back to me, the product manager for Sleipner alloy. and I quote some lines of text from the lengthy email:

"Looking at the photos I do not see the corrosion as something unexpected".

he went on to talk about the Cr in solution of both D2 and Sleipner being not significantly different from one another (I forgot this, which was pretty stupid) and that they both have about the same behaviour when subjected to water. He said that in both D2 and Sleipner almost all the Cr is tied up in carbide formation. But of course both D2 and Sleipner has less than the minimum of 12% Cr in solution in the "base steel" to be considered corrosion resistant eg like ELMAX.

He went on the say the following and I quote the entire paragraph:

"The extent of corrosion here is perhaps a little worse than I would expect after only a few minutes in water but the extent of attack is also affected by other factors like for example the surface finish and how the steel has been heat treated. In this case it seemed like the surface finish of the knife in the photo was a little rough aside from the grinding which could have contributed to the fast attack. It could also be due to the heat treatment since that will affect both Cr content in solution and also how the carbides are distributed which can in turn affect the speed of the corrosion attack".

Anyway the bottom line for me, is a reminder of the metallurgy I was once taught but clearly forgotten and I now know more about the behaviour of the Sleipner alloy. The surface finish might explain some of this corrosion seen as you can indeed see the milling tool marks and also might explain why on a D2 blade I have (which is almost a mirror polish) has not suffered any type of corrosion when subjected to water. Who knows, as a scientist, my observations are only based on a "n number" of one! and let's face it that's not very scientific.


I will be removing the corrosion with something like "Brasso" which i've found to be very good for similar things and continue to see how the M7 performs.


It would be good to know from other forum members their experience with Sleipner if working around water. Generally all of my work is based near rivers, so I can't avoid it LOL. Maybe I'll go back to taking the N690 knives out again.
 
RamZar said:
I have a few tiny rust pits in my SR-2A. Funny thing is that they're just on one side of the blade and one on the spine. I used Flitz to get rid of the rust but the tiny pits are there. The pits are so tiny that they may not show up in pictures but I'll try to get some pictures tomorrow.

I don't carry it much but I live about 7.5 miles from Pacific Ocean. I'm going to start carrying it more now to see what happens. May be even when I go for walks to add the sweat factor.
Click to expand...

The rust spots here too, on this M7, are also confined to the first 5-6cm (couple of inches) back from the tip there are no indications of corrosion anywhere else on the knife (I haven't removed the handle yet as it's still under warranty) but the whole knife got submerged for a couple of minutes crossing a river.
 
FCCBCT said:
The rust spots here too, on this M7, are also confined to the first 5-6cm (couple of inches) back from the tip there are no indications of corrosion anywhere else on the knife (I haven't removed the handle yet as it's still under warranty) but the whole knife got submerged for a couple of minutes crossing a river.
Click to expand...

I started the test today carrying my SR-2A with Sleipner. As I said about 7.5 miles from Pacific Ocean, it has been more humid than usual (50%+) and it's strapped to my running shorts so it gets exposed to heat, sweat and humidity. After each day I do wash with detergent and tap water. Dry and lube. Ready for the next day. Saturday it'll go to my USPSA shooting match. Lots of heat, sweat, dust and gunpowder! Sunday cross country walk.

It does very light cutting too.
 
RamZar said:
I started the test today carrying my SR-2A with Sleipner. As I said about 7.5 miles from Pacific Ocean, it has been more humid than usual (50%+) and it's strapped to my running shorts so it gets exposed to heat, sweat and humidity. After each day I do wash with detergent and tap water. Dry and lube. Ready for the next day. Saturday it'll go to my USPSA shooting match. Lots of heat, sweat, dust and gunpowder! Sunday cross country walk.

It does very light cutting too.
Click to expand...

Hi yeah it will be good to see. The M7 was actually submerged for about 2 min or less, the time it took me to cross this river, so it got a proper dunking. To be honest I also like the guy from Uddeholm was surprised at the rapidity. I'm going to also be testing some polished D2 blades with supposedly the same amount of based metal Cr in solution as Sleipner and see how they compare. Salt spry can be pretty rough on knives that's for sure.:)
 
FCCBCT said:
Hi yeah it will be good to see. The M7 was actually submerged for about 2 min or less, the time it took me to cross this river, so it got a proper dunking. To be honest I also like the guy from Uddeholm was surprised at the rapidity. I'm going to also be testing some polished D2 blades with supposedly the same amount of based metal Cr in solution as Sleipner and see how they compare. Salt spry can be pretty rough on knives that's for sure.:)
Click to expand...

The best side by side test would be to compare LionSteel SR-1 Ti in Sleipner versus LionSteel SR-1 Al in D2. Assuming similar heat treat and grind by LionSteel for both.

The D2 is Bohler K110.

Data Sheets:

UDDEHOLM SLEIPNER
BOHLER K110 (D2)

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FCCBCT said:
The rust spots here too, on this M7, are also confined to the first 5-6cm (couple of inches) back from the tip there are no indications of corrosion anywhere else on the knife (I haven't removed the handle yet as it's still under warranty) but the whole knife got submerged for a couple of minutes crossing a river.
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If the knife was carried in a sheath the water would run out the drain hole. So it should have the majority of the residual water near the bottom of the sheath, which could explain why the corrosion is centered around the tip.
On my knives I like to polish the blade faces up with sandpaper. Make sure to work through the grits; up to 1500-2000 is what I usually go to. After that I avoid sandpaper and prefer not to flitz. If you can build a patina it should be more resistant to rusting. I read somewhere that old timers stuck their knife in a potato overnight to start a patina.
BTW your picture looks like typical stainless rusting to me. With little islands of rust that develop into pitting. I've actually tried bluing an MVS-8 (Variation of AUS8) knife and it blued in pockets.
 
Jhansenak47 said:
If the knife was carried in a sheath the water would run out the drain hole. So it should have the majority of the residual water near the bottom of the sheath, which could explain why the corrosion is centered around the tip.
On my knives I like to polish the blade faces up with sandpaper. Make sure to work through the grits; up to 1500-2000 is what I usually go to. After that I avoid sandpaper and prefer not to flitz. If you can build a patina it should be more resistant to rusting. I read somewhere that old timers stuck their knife in a potato overnight to start a patina.
BTW your picture looks like typical stainless rusting to me. With little islands of rust that develop into pitting. I've actually tried bluing an MVS-8 (Variation of AUS8) knife and it blued in pockets.
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Yes that's the interesting thing for me the rusting is very much like a stainless steel. It was pretty hot around 30C plus after exiting the river and can't imagine any residual water playing that much of a role as the whole knife was submerged but of course I didn't look in side the scabbard and can't rule this out what you say, good point. :thumbup:
 
It was pretty hot around 30C(86f) plus after exiting the river and can't imagine any residual water playing that much of a role as the whole knife was submerged
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Keep in mind that your sheath isn't very well ventilated. Air will only absorb so much water so the interior could easily maintain a high humidity as it slowly dries out. Heat will also speed up the chemical reaction of rusting and make you sweat which in turn will maintain a higher humidity in the area next to your skin.
I wear my SR2 with the same sleipnir steel blade on my neck in my turnouts while doing firefighter training. Believe me, it is flipping hot and humid. It gets soaked with sweat so it has salt in it as well. The first time I did it the blade had light rust all over it. I just clean it off with some remington oil and and a nylon gun brush. Now having done it several times it really doesn't have any problems. Maybe i'm crazy but IMO Sleipnir will develop a patina.
 
I carried my SR-2 in Sleipner for 10 days. The pitting did not increase at all. I did not rinse it every day. It was exposed to humidity, water, sweat and dust.

What actually happened is that the blade is now stained as in patination. The black spots are the tiny old pits and the discolorations are the stains/patinations. The pits are only on one side (lock side) and from lower front to tip. The stains will not go away with Flitz.

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Wow, I had no idea these discolored so easily.

What is the situation with the black-bladed M7? It is not coated, so the black finish will not rub off so easily?

My satin M7 looks so nice, I'd hate to have it get discolorations I cannot remove with polish. Thinking about sending it in to swap for a black one, but I love the look of the satin so much...

Aubrey, how's yours doing?
 
Hey, it is a knife, and any knife, which sees use, will show signs of wear.


And when buying a non stainless blade, one can only expect signs of corrosion.

I get, that crisp new knife looks good, and especially so an M7.
But if you plan on using it, staining should be expected...
 
jmclfrsh said:
Wow, I had no idea these discolored so easily.

What is the situation with the black-bladed M7? It is not coated, so the black finish will not rub off so easily?

My satin M7 looks so nice, I'd hate to have it get discolorations I cannot remove with polish. Thinking about sending it in to swap for a black one, but I love the look of the satin so much...

Aubrey, how's yours doing?
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Hi if I have this right Gianni told me the blackened blades are chemically blackened eg like " blueing", it's a common process. Sleipner can of course be PVDed and my understanding from reading the relevant metallurgical papers a PVD coating would increase the corrosion resistance of Sleipner. You will see PVD Sleipner for milling tools.
 
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