New to Stainless--corrosion issues with HSS tooling?

MyrtleLake · Sep 12, 2009

I very rarely, if ever, work in SS. Of late, I have had need to. I have read---or perhaps better, read hearsay---that Stainless loses its non-corrosive/non-rusting properties if machined with steel tooling. Or polished with scotchbrite, steel wool, or other steel abrasives.

True of False?

i.e. if machined with carbide, polished with maroon then ultra-fine scotchbrite, lastly Simichrome... have I ruined its resistance to rusting?

i.e. same thing if machined with HSS instead of carbide?

of note: working with 303 SS

TeflonDave · Sep 12, 2009

Never heard that before

I never experienced that w/ 303 sst - I have only gotten bad material to start with at times. The main concern in machining 300 series stainless is workhardening. Use nice sharp good quality tools and monitor the tool life if yer doin' production work. My preferred tooling was carbide inserts KC730 turning and KC 720 cut-off. It is also important to make sure you monitor the roughing tools if you use them. I have seen many an operator go through finishing tools like crazy only to find out that the worn roughing tool was the cause of premature failed finishing tools. Oh I miss the days when 303L SST was available. :smoking:

Limy Sami · Sep 12, 2009

Bul** - I mean urban myth.

Carbon steel contamination when grinding and brushing welds? yes,........ machining - bar room engineers.

jim rozen · Sep 12, 2009

The only degradation that I'm aware of, and I don't really understand where it
is most likely to happen, is something called 'carbide precipitation' I think, and it
happens after a weld is made in stainless. The joint is more likely to rust, than
the parent metal.

Jim

SeymourDumore · Sep 12, 2009

BS or not, many prints require passivation after machining with ferrous tools:

http://www.pfonline.com/articles/119806.html

Believe me, I hate it but gotta be done if it says so.

MyrtleLake · Sep 12, 2009

So what I'm reading from the responses:
-no matter what I use to machine it, the part will more than likely be fine.
-if the part is critical, high cost, or in extreme weather situations most of its life, passivation after machining is a very good idea and safeguard.

KilrB · Sep 12, 2009

... Stainless loses its non-corrosive/non-rusting properties ...

I seriously doubt that.

Most likely what is happening is deposition of microscopic ferrous particles from the cutting tool.

When these rust, and it's "surface" rust, it appears that the SS is rusting.

This would explain the need for passivation that SeymoreDumore brings to our attention.

Limy Sami · Sep 12, 2009

Thanks Seymour, I stand corrected,......... even if I can't help thinking life's a tad too short

SeymourDumore · Sep 12, 2009

Again, I don't know if it's the corrosion resistance properties or loose rust particles from the cutting process, but the neighbor shop makes precision balls for cleanroom equipment and for gyroscopes, they all need to be passivated.
I've made some parts for nuclear powerplants, fuel valves for a missile and a few powder packing dies for a local explosives manufacturer, they all called for passivation after ALL machining processes completed.

Nowadays, It is a bitch to find an approved source too as the chemicals used are apparently highly regulated.

KilrB · Sep 12, 2009

Let's not forget, these parts are made of SS for a reason.

They are going into a highly corrosive environment of some sort.

SS is not impervious to corrosion, just much more resistant.

Giving corrosion a good place to get started on a piece of SS by imbedding microscopic pieces of iron in the surface can't be good ...

MyrtleLake · Sep 12, 2009

So then, after the carbide tooling for machining... Aluminum Oxide filing stones? http://tinyurl.com/pljhqb to get to where I can do a final buffing on a SS specific wheel? Or do I have to use Alumina Ceramic? Does Al-Ox have any ferrous properties?

SeymourDumore · Sep 12, 2009

Art

I don't know, but I've only seen Silicon-carbide restrictions for Titanium parts exclusively.
I think the notes about the finishing is that you should use a clean wheel that has not seen any iron particles. My guess that dressing the wheel sufficiently should take care of that.

Hdpg · Sep 12, 2009

KilrB said:
I seriously doubt that.

Most likely what is happening is deposition of microscopic ferrous particles from the cutting tool.

When these rust, and it's "surface" rust, it appears that the SS is rusting.

This would explain the need for passivation that SeymoreDumore brings to our attention.

I worked in a place making pulp digesters once and the explanation I got, which is chemically valid, is that the ferrous particles act as a sort of catalyst and the stainless does corrode around them and will eventually develop large pits or even holes; it is a localized galvanic reaction. The passivating literally dissolves these ferrous particles away and establishes a thick protective oxide coating over the stainless.

It is possible if you had a tool, HSS or even carbide, that had been used on mild steel and then went straight to stainless you could embed ferrous particles in the surface of the stainless. HSS tools in particular are prone to getting a little build up of steel right on the tip. But I think this is stretching things a bit.

MyrtleLake · Sep 12, 2009

Just went to Wikepdia: Aluminum Oxide = Al2-O3
I don't see any Fe's in there, so I will figure it doesn't cause an issue unless its touched steel/iron beforehand.

The real Leigh · Sep 12, 2009

Particle transfer from one job to another is the problem

I believe the problems related to abrasives are not related to the abrasives. :smoking:

The problem arises when the same abrasive (grinding wheel, sanding belt, etc.) is used for plain steel then for stainless steel. The abrasive picks up particles (obviously) from the regular steel and deposits them on the next workpiece through the machine, i.e. the stainless.

So always use new abrasives, or isolate one set ONLY for use on stainless, and you should be fine.

- Leigh

KilrB · Sep 12, 2009

Hdpg said:
I worked in a place making pulp digesters once and the explanation I got, which is chemically valid, is that the ferrous particles act as a sort of catalyst and the stainless does corrode around them and will eventually develop large pits or even holes; it is a localized galvanic reaction. The passivating literally dissolves these ferrous particles away and establishes a thick protective oxide coating over the stainless.

It is possible if you had a tool, HSS or even carbide, that had been used on mild steel and then went straight to stainless you could embed ferrous particles in the surface of the stainless. HSS tools in particular are prone to getting a little build up of steel right on the tip. But I think this is stretching things a bit.

You know how on C.S.I. they say the criminal always leaves some of himself at the scene?

I'm willing to bet that when your tool dulls, even just a little, it rubs and leaves iron particles behind.

Run near any tool long enough in SS and see what kind of wear you get on the cutting edge.

The real Leigh · Sep 12, 2009

Hdpg said:
...the explanation I got, which is chemically valid, is that the ferrous particles act as a sort of catalyst and the stainless does corrode around them...

Excuse me

Stainless Steel IS ferrous.

The addition of chromium as an alloying element makes it resistant to corrosion.

Passivation removes the ferrous material near the surface, enhancing the corrosion resistance.

- Leigh

Limy Sami · Sep 12, 2009

OK OK, you guys have scared me enough, I'm putting out a worldwide recall on all the stainless parts I've made

KilrB · Sep 12, 2009

Question ... Would using new (unused) ceramic inserts solve this problem?

mm · Sep 12, 2009

Sixty percent of the work I do in my small shop is with 300 series stainless. ALL stainless projects are passivated before they go out the door. Originally passivation was outsourced to a local factory which used nitric acid.

The cost and lead time kept increasing. I started doing my own passivation in house, using citric acid. The cost was not too high, even now, you can probably get set up for under $400.

Any time steel or iron touches stainless there will be iron molocules transferred. These iron molocules will rust. Also, welding brings iron to the surface. Passivation removes the iron and may increase the chrome surface layer.

About 1/4 of my projects have some or total polishing done. It is much safer to passivate before and after polishing. My stainless does not show any rust.

mm

New to Stainless--corrosion issues with HSS tooling?

Stainless

Aluminum

Diamond

Diamond

Diamond

Stainless

Stainless

Diamond

Diamond

Stainless

Stainless

Diamond

Stainless

Stainless

Diamond

Stainless

Diamond

Diamond

Stainless

Aluminum

Similar threads