Effect of blade finish on rust resistance

B

Bill1170

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Dec 20, 2007
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It is generally agreed here that bead-blasted blades will rust more easily than the same blades with a satin, stonewashed, or polished finish.

It is also agreed that different steels vary in their corrosion resistance, ranging from O-1 that rusts very easily to H-1 that will not rust at all.

My question is this: What have you found in your personal experience to be the best finish for resisting rust on a blade? Since steels vary, please also say what steel and what the finish was before and after the modification, or if factory, how the various finishes compared on the same steel from the same maker.

Let's leave coated blades out of this. Patinas are fair game, since they can be done easily by the end user.

Thanks in advance.

Bill
 
i think its a polished finish. the higher the level of polish the better the resistance to corrosion. i think a ground blade though smooth and shiny has alot of small microscopic roughness from its machining/grinding process that is perfect for trapping dirt/salts etc and moisture. the better polished out those imperfections the better it will clean up after use and thus it should not rust as easy. that said, its hard to perfectly polish metal, and if not given the same care as an unpolished version, corrosion will find the spots missed just as if it hadnt been polished to begin with. so, keep um clean always, wipe off with an oily rag if its been wet. etc etc usual blade maint.
 
I suspect the same, that a high polish is best for resisting corrosion. I have a FFG Delica that I put a mirror finish on with waterstones to 6000 followed by CrO2 compound. Looking through a 100x scope, it could still be smoother but I got tired of doing it and let it go. Being VG-10, corrosion is less of an issue anyhow, but I love the look. It sure glides through what I am cutting.

ZDP has a reputation for staining more easily, and I think of polishing it, but that stuff is very slow to process with abrasives! I have a blue ZDP Stretch on B/O at KW and plan to shine it up after it comes. It seems a very hard steel like ZDP will scratch less after being polished than a softer steel will.
 
I tend to question that a polished blade will resist corrosion better though I believe it somewhat.

A small example would be my dads ZDP endura, the only spot that shows corrosion is the high polished edge. It will patina almost black while the sides of the blade above the edge show nothing.

I've also noticed this with other non stainless steels that had a polished edge.

On a side note, a full polished blade will stick more in cutting some materials because there is more surface area in contact with the material. Don't believe me? check out the kershaw groove :)
 
1. The rougher the blade finish, the more surface area moisture has to get a purchase on.

2. The smoother the blade finish, the easier it is to wipe clean of moisture.

I've never had rust on a SAK blade, but the little blade on my Leatherman keychains (Micra, Squirt) likes to rust all the time. SAK blades are fairly highly polished, while the Leatherman's blades are pretty rough.

Media blasted finishes are the worst.
 
my experience favors a high polish in rust resistance & makes cutting easier by reducing friction. the oldtimers used to do a crocus polish [black polish] on the best of there blades. this was said the process closed the pores in the steel making the blade surface more resistant to rust . having used blades with a crocus polish i agree that the steel is more rust proof. the highly polished surface not only is more resistant to rust but by reducing friction it cuts much easier. the most impelling proof came from using an endura with factory edge to cut double thick cardboard. after taking another endura with a polished edge i cut the same cardboard & it was as if i had used totally different knives. the polished endura cut twice as rasy. i,ve also noticed that the polished edges on my gec 1095 carbon tend to rust less since a smooth bevel is easier to clean completely.
dennis
 
knifenut1013 said:
I tend to question that a polished blade will resist corrosion better though I believe it somewhat.

A small example would be my dads ZDP endura, the only spot that shows corrosion is the high polished edge. It will patina almost black while the sides of the blade above the edge show nothing.

I've also noticed this with other non stainless steels that had a polished edge.

On a side note, a full polished blade will stick more in cutting some materials because there is more surface area in contact with the material. Don't believe me? check out the kershaw groove :)
Click to expand...

The Groove is an interesting case. I have not been tempted by that knife, in part because it seems like the blade would be a pain to clean.

As for very smooth surfaces sticking more, I would think something like cheddar cheese would be a prime example of this, but my polished Delica sticks no more than the factory one with the satin finish. (I have two FFG Delicas, a blue and a green. The green one I polished.)

The black patina on the polished bevel of your dad's Endura still beats red rust in my book. Is it stable or does it grow thicker and/or wipe off onto the stuff he cuts? It is curious that it responds differently than the rest of the blade. Thanks for replying.

Bill
 
Planterz said:
1. The rougher the blade finish, the more surface area moisture has to get a purchase on.

2. The smoother the blade finish, the easier it is to wipe clean of moisture.

I've never had rust on a SAK blade, but the little blade on my Leatherman keychains (Micra, Squirt) likes to rust all the time. SAK blades are fairly highly polished, while the Leatherman's blades are pretty rough.

Media blasted finishes are the worst.
Click to expand...

Good point about the moisture being easier to remove. The SAK steel is more stain resistant than many other knife steels, and of course they are also mirror finished.

I agree on the media blasted finishes corroding fastest of all.

Bill
 
DennisStrickland said:
my experience favors a high polish in rust resistance & makes cutting easier by reducing friction. the oldtimers used to do a crocus polish [black polish] on the best of there blades. this was said the process closed the pores in the steel making the blade surface more resistant to rust . having used blades with a crocus polish i agree that the steel is more rust proof. the highly polished surface not only is more resistant to rust but by reducing friction it cuts much easier. the most impelling proof came from using an endura with factory edge to cut double thick cardboard. after taking another endura with a polished edge i cut the same cardboard & it was as if i had used totally different knives. the polished endura cut twice as rasy. i,ve also noticed that the polished edges on my gec 1095 carbon tend to rust less since a smooth bevel is easier to clean completely.
dennis
Click to expand...

Dennis,

The crocus polish fascinates me. One thing I have read about high polishes is that, in the final stages of polishing, there is actually melting of the metal at the very surface going on, due to the localized high friction. Blew my mind to read that! There may be pore-filling going on with the crocus polish, too.

I also know from direct experience that cast iron machine tables can be made slippery and protected from rust by means of burnishing talcum powder into the surface with a dry sponge or blackboard eraser. I read it and did not believe it, so I stripped the wax off my jointer and talc'd it. After a whole year, zero rust. The idea is that the talc fills the pores in the surface that are where the rust begins. That whole experience confirmed for me just how little I really know about the world around me.

Were both Enduras cutting the cardboard with identical edge bevels and sharpness levels? If so, the results are very impressive.

Bill
 
bill1170 the enduras were slightly different in bevel since i polished one down to convex. it's impossible [almost] to mirror polish an edge & it retain same bevel as one polished on spydie fine ceramic hone. the other spydie was taken on down on green rouge. unit [ken] did a great test about 2 or three months back showing how different levels of polish took less force to cut same cord. a fectory endura will not appear to be same knife as the endura with polished bevels. i have confirmed this with zdp. vg10 & 1095 on cardboard. i make no conclusions only my personal experience. dennis
 
Dennis,

I watched all the videos on Ken's test, enjoyed it very much. I like how he came up with a simple way to quantify his findings, cutting cord in his jig on a digital scale. The main point I came away with was the significant reduction in cutting force due to the reduction in bevel angle.

I have mentioned in other threads that I was unhappy with the performance of my saber ground ZDP Delica when slicing corrugated cardboard. I realized a tremendous reduction in required cutting force simply by rounding the transition from the saber grind to the flat sides of the blade, without making any change at all to the final bevel or cutting edge.

Bill
 
i concur that the ffg endura certainly outcuts the saber ground endura. my observation is that a polished bevel with equal degree as an unpolished bevel will cut with less resistance on any medium. i'm not trying to debate anyones opinion, i only mentioned my personal experience cutting with polished versus unpolished bevels.really the dynamics of bevel polishing are best impressed on ones self when they actually do the cutting. thanks for the response.
dennis bill did you see the cutting of tire sidewalls with polished vg10 , s30 & zdp?
 
Planterz said:
1. The rougher the blade finish, the more surface area moisture has to get a purchase on.

2. The smoother the blade finish, the easier it is to wipe clean of moisture.

I've never had rust on a SAK blade, but the little blade on my Leatherman keychains (Micra, Squirt) likes to rust all the time. SAK blades are fairly highly polished, while the Leatherman's blades are pretty rough.

Media blasted finishes are the worst.
Click to expand...

I've had the exact same experience, my LM Wave and Micra are all about rusting, its there go to move, while the SAK's don't have a spot. All are generally the same age/ware/use.

Nothing against leatherman though, I still love them and the for what they are, the bit of rusting doesnt bother me.
 
DennisStrickland said:
i concur that the ffg endura certainly outcuts the saber ground endura. my observation is that a polished bevel with equal degree as an unpolished bevel will cut with less resistance on any medium. i'm not trying to debate anyones opinion, i only mentioned my personal experience cutting with polished versus unpolished bevels.really the dynamics of bevel polishing are best impressed on ones self when they actually do the cutting. thanks for the response.
dennis bill did you see the cutting of tire sidewalls with polished vg10 , s30 & zdp?
Click to expand...

Yeah, I saw the sidewall cutting video(s). Very impressive.
 
Planterz said:
1. The rougher the blade finish, the more surface area moisture has to get a purchase on.

2. The smoother the blade finish, the easier it is to wipe clean of moisture.

I've never had rust on a SAK blade, but the little blade on my Leatherman keychains (Micra, Squirt) likes to rust all the time. SAK blades are fairly highly polished, while the Leatherman's blades are pretty rough.

Media blasted finishes are the worst.
Click to expand...

I agree.
 
Has anyone here experienced a rust problem on an uncoated steel blade that got worse when that blade was polished?
 
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