Sharpening R2/SG2 stainless with high grit stones

I was told by one of the Shapton reps that the passivation layer on stainless is hard enough that I should be starting on a low grit stone because the higher grit ones wouldn't cut well until that layer is broken through. Does that mean that I can't really do touch-up work on a stainless knife unless I take it to the rough stones first?

I'm specifically talking about a very thin R2/SG2 blade that has microchipping, but I do have a few standard henckels (guest knives) that I try to keep sharp as much as possible as well.

I'm using Shapton pro 320/1000/5000 stones

I run my stainless knives, including R2, on the same stones as my carbon. I do touch up on my 8000 Gesshin. If they are very dull or have small chips, it goes to the 1000 Chosera, first. Only if there are big chips or the knives need thinning do they go on anything coarser.

Sounds to me like the Shapton rep wanted to sell some extra stones.

I use a 6k arashiyama to do touchups on my stainless knives (R2 included). No problems yet.

strumke said:

I was told by one of the Shapton reps that the passivation layer on stainless is hard enough that I should be starting on a low grit stone because the higher grit ones wouldn't cut well until that layer is broken through.

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I haven't heard that before. Do you happen to have a full quote in context, and could you ask permission to share it?

It was over the phone, so I can repeat what I remember...

He was talking me through a bunch of things, some of which were a bit more salesman-y then others, but he basically said that the passivation/oxidation layer that keeps stainless stainless is quite hard, and if you start on a high grit stone, then it will feel like the stone isn't doing much cutting. He said if I hit a low grit stone first to break through the passivation layer, and then went back to the same high grit stone, it would be a totally different impact.

He also gave the example of if you did your low grit work one night and waited until the morning to finish up everything, by the morning, the passivation layer would have built up again, so you would need to break through again before using the high grit.

It you're talking specifically about Shapton stones, I've used 5 and 6k on SG2 with no problems. Micro chipping might require a lower grit initially, depends on the knife and severity of the chipping. I go to a lower grit stone first myself.

EdipisReks said:

Sounds to me like the Shapton rep wanted to sell some extra stones.

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Or maybe not too familiar with modern steels?

I got this bridge for sale too.

FWIW I've found that SG2 -- at least the knife I've been using and sharpening very regularly -- responds best to harder, more aggressive stones.

Before I got the diamond set from JKI, a Shapton Glass 1k was my stopping and starting point for that knife. It cut quick enough that even if the edge was completely dead, I could cut a new bevel and remove metal, and it was also extremely toothy and would last me a couple shifts if I couldn't find the time to do a full sharpening. With quick touch-ups before shifts, I could go two weeks or so without having to spend time on the stones.

Just my experience. Some of the stones that I liked to finish my other carbon & stainless knives, like the Rika 5k, I found I didn't really care for on this particular PM steel knife.

I've never had to drop down to the coarse grits (300-500) though because I find the 1k Shapton stones to cut extremely quick.

To my understanding the passivatin layer builds up to 70-80% emmidiately when it gets in contact with air and the remaining % a bit slower in the following 24 hour or so.
It is extremely thin also, about 0,01 mA/cm² and transparent so there is probably not much hardness to it

Sabaki said:

To my understanding the passivatin layer builds up to 70-80% emmidiately when it gets in contact with air and the remaining % a bit slower in the following 24 hour or so.
It is extremely thin also, about 0,01 mA/cm² and transparent so there is probably not much hardness to it

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Trying to jog my memory on all the talks I have had by the Australian Stainless Association down here... But I would agree with this.. From my memory I didn't think it was hard at all. Like I thought that it got scratched off very easily, but as was said above reformed almost immediately.

You essentially need to think of the protective layer on stainless as a form of rust (or oxidation for those that want to use the proper term as rust is truly iron oxide). As soon as the metal is exposed to the atmosphere it is oxidizes and forms an extremely thin translucent layer of oxidised material that protects it from rusting etc.

But again, don't necessarily quote me, am just trying to remember what I have learnt... And don't know the specific composition of SG2/R2 and if there is any additional alloying elements that may make that oxidation layer harder.

But from my experience, I strop/touch up my Itou R2 knife of a JCK 6k all the time and it renews the edge perfectly (as in general touching up between major sharpening).

Update - The Shapton Rep I was talking to on this was Harrelson Stanley, who seems to have a decent resume on this stuff. I'm still not in a position to say what's fact vs otherwise, just wanted to bring this full circle.

What's this down under (The Australian Stainless Association) I'll bet you need a large meeting hall for that.:happymug:

More like a shed in the middle of no where to keep us creepy engineer tips from scarring the general public

malexthekid said:

More like a shed in the middle of no where to keep us creepy engineer tips from scarring the general public

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At least you are an Association