First time working with stainless- CPM154 rust question

phorizt

phorizt

Joined
Aug 26, 2013
Messages
358
Up until now I've worked exclusively in carbon steels but just got some CPM154 and AEBL to work with. I know "stainless" is not stain proof and that it becomes more corrosion resistant once it is heat treated. However, I started grinding my first knife in CPM154 tonight and by the time I ground the 2nd bevel the other side was already all rusted over as if I were working with 1084. I took the CPM 154 blade, an 01 blade and an AEBL blade and sprayed each one with water after a pass on the grinder to compare and the CPM blade rusted worse than the 01 blade. AEBL didn't rust. Before I get too far into grinding several more blades in the CPM154 I just wanted to see if this was normal or if I should worry about possibly having mislabeled steel?
 
Well, it certainly does sound like it is not CPM154. Sure if a little rust showed that would be normal but for it to react and oxidize so quickly makes me think it's some type of carbon or mild steel.
Frank
 
When grinding there are four things that make a blade "Rust while you watch".
1) fine particles of steel
2) oxygen
3) moisture
4) heat

You provide the steel dust, Texas provides the rest.

The blade surface isn't actually rusting, it is the fine powered steel dust and microscopic grooves with very thin apexes that react with the air/water/heat. Add to that constant dunking in water and the blade getting hot enough in grinding bevels to evaporate the water...and you get what is called "flash rust". It just rubs off with a towel or a single pass with sandpaper. When done grinding for the day, it is a good idea to wipe down the blade well to remove loose dust/grit/rust as well as dry the blade. In very warm and humid places ( like Texas) a light oiling is also good. This is especially important if you will not be continuing the grinding/sanding the next day.

Also, many steels are spheroidized to make them easier to grind. This is good for grinding, but the matrix is nearly pure iron, which reacts with the air and moisture even faster. This is why some steel seems to rust faster than others pre-HT.
 
Also you say you work mainly with carbon steels, if you use the same belts for both small particle of carbon steel will transfer to the stainless and rust, also carbon dust from your dip bucket will also cause this.
 
Thanks for the info guys. Texas is certainly providing more than our share of moisture right now.
 
I would never imagine that would be the cause. Sure great that we got the right answer. That's why we come here though isn't it?
Frank
 
I would have to imagine your getting some sort of high carbon dust on it somehow during your process.

Jay
 
SBuzek said:
Also you say you work mainly with carbon steels, if you use the same belts for both small particle of carbon steel will transfer to the stainless and rust, also carbon dust from your dip bucket will also cause this.
Click to expand...

Bingo. I won't use files that I've used on carbon steel on stainless.
 
Stacy and Stan explained it well... I suspect it's mostly a function of cross-contamination. (Plus of course humidity... a little fine 1084 dust on a nice clean blade in 70 or 80% humidity will indeed "rust before your eyes".)

Since I work with both low-alloy and high-alloy steels in the same shop and my housekeeping/dust control procedures are less than perfect, I just assume that everything is contaminated with nearly pure iron dust. That reminds me to clean blades off at the end of the day, lightly oil or spray them with dykem to keep more dust off the surface as it settles, or even oil and wrap them if they're going to sit around for a while.

As for contamination from your slack bucket, a few drops of dish soap in the water will break the surface tension and allow the dust and grit to sink to the bottom. A couple tablespoons of baking soda helps as well.

This reduces "flash rust" and also helps prevent your belts getting glazed over and gunked up. (if you pull a blade out of the bucket with a bunch of swarf on it and go right back to the belt, in about 2 revolutions all that gunk is smeared between the crystals and structures on the belt itself, and just ends up getting pushed into the new scratches you're making). It helps in getting crisp, consistent grinds, too... a bunch of 60-grit swarf on your blade when you're trying to clean it up with a 400-grit belt will make you say very bad words.

You still want to change the water fairly often, of course... in a perfect world we'd run our grinders like machinists run mills, with a constant stream of coolant that is either replaced or re-filtered to keep all that gunk under control and off the tooling and workpiece.
 
Thanks again for all of the tips and info. I'll add some dish soap to my bucket. It certainly doesn't get changed often but I do use a separate bucket for dunking blades than the one under my grinder so it isn't too terribly dirty but definitely not clean water either. I ground some more 154 last night and didn't seem to have the same issues this time. It was the from the same bar stock so at least I'm fairly confident it was just cross contamination as y'all said.
 
So I just received my cpm154, cpm3v and 1084, and the cpm154 os the only one with surface rust. I asked on a thread I started a few weeks ago, b7t it seems to have gone "dead" so after searching and finding this thread I figured I'd ask. I have a picture but I'm not sure how to post it....thanks in advance guys.

Marc
 
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