Rusting Stainless

Howard1

Howard1

Joined
Jan 16, 2017
Messages
207
Yet another 2 roadblocks. I am using s35v for some chefs knives. I am cooling with water through the non HT grinding so I don't burn my hands too badly. When I set the unfinished blanks aside rust formed in the puddles of water left on the blade. Is that normal. This has 16% chromium. How can it rust? I ran a test with one of my heat-treated blanks and no rust. The blanks come from two different sticks.
I ordered 3/32 x 2' stock. As I got less than precision milled and it mics at just under 1/8. When I try to reduce them by grinding them on the glass platten with a 36 blaze, very little happens. My understanding is that the blaze is glazing over ( I am grinding at 3500 SFPM). If so what can I use. The steel came from Admiral. I am currently making the thickest Santoku knives on the planet. One recommendation I had was to use aluminum oxide belts. They don't last long but they are said not to glaze. Any takers on these world shaking problems?
 
I have heard tell that martensitic steels do not become fully corrosion resistant until they are hardened.
 
^ this

The chromium is currently tied up with carbon in carbides. When you heat treat it the carbon goes into solution and some of the chrome is left free which gives it corrosion resistance. It will be fine after you harden it.

BTW, don't grind stainless with belts that have been used on carbon steel, you'll get cross contamination.
 
Nathan the Machinist said:
^ this

The chromium is currently tied up with carbon in carbides. When you heat treat it the carbon goes into solution and some of the chrome is left free which gives it corrosion resistance. It will be fine after you harden it.

BTW, don't grind stainless with belts that have been used on carbon steel, you'll get cross contamination.
Click to expand...
How about very low carbon steel like they sell at Home Depot, puddle steel I think it is called. That is my practice steel. The only time I use it now is to push it into my belts that seem to have glazed. I use the sharp edges until sparks start to fly off the belt. Jeff at True Grit seemed to indicate that it was a good way to re-cut the crystals on the ceramic belts if the belt speed doesn't generate enough friction and heat.
 
When you use anything that handled carbon steel , abrasive paper , files , machining etc particles of carbon steel stick the the stainless , begin to rust , the rust then continues into the stainless .That's why we keep tooling separate - tooling for stainless and tooling for carbon steels !! That' also why we invented "passivation" which removes the carbon steel and other contaminants and gives a thicker oxide layer on the stainless !! Passivation uses nitric acid though now citric acid is used as it's easier on the environment !
 
Ceramic belts like Blaze and Cubitron 984 are made to run hard and fast.
Howard1 said:
How about very low carbon steel like they sell at Home Depot, puddle steel I think it is called. That is my practice steel. The only time I use it now is to push it into my belts that seem to have glazed. I use the sharp edges until sparks start to fly off the belt. Jeff at True Grit seemed to indicate that it was a good way to re-cut the crystals on the ceramic belts if the belt speed doesn't generate enough friction and heat.
Click to expand...
 
mete said:
When you use anything that handled carbon steel , abrasive paper , files , machining etc particles of carbon steel stick the the stainless , begin to rust , the rust then continues into the stainless .That's why we keep tooling separate - tooling for stainless and tooling for carbon steels !! That' also why we invented "passivation" which removes the carbon steel and other contaminants and gives a thicker oxide layer on the stainless !! Passivation uses nitric acid though now citric acid is used as it's easier on the environment !
Click to expand...
Well that certainly has added a new complexity to this. Just what I needed. I'm not ungrateful just intimidated by the mountain that I am climbing. I Googled passivation. Very cool. There are businesses that do it for industry. Can the bath be homemade?
 
mete said:
When you use anything that handled carbon steel , abrasive paper , files , machining etc particles of carbon steel stick the the stainless , begin to rust , the rust then continues into the stainless .That's why we keep tooling separate - tooling for stainless and tooling for carbon steels !! That' also why we invented "passivation" which removes the carbon steel and other contaminants and gives a thicker oxide layer on the stainless !! Passivation uses nitric acid though now citric acid is used as it's easier on the environment !
Click to expand...
I'm glad that I asked. I would have never figured this out. Thanks
 
I have never passivated my self but it is possible . One problem , especially for nitric acid is disposal of the acid. I should have added that corrosion resistance is often a matter of the oxide layer on metals. Destroy that layer and your corrosion resistance can be greatly reduced !
Corrosion can be a very complex process !!!
 
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