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View Full Version : Neat anti rust process ,new to me



Edwin Dirnbeck
10-18-2013, 11:44 PM
I found this.

http://wot.motortrend.com/gm-plans-roll-out-of-rust-resistant-brake-rotors-on-selected-models-140867.html#axzz2i8JMeAVH


I just read about an anti rust and corosion process that GM is using on their cast iron brake rotors .They call it FNC .It is a nitrideing process.It seems to be cheap .and durable.I was just wondering if anyone knows about it and could it be used on steel or is it just for cast iron. Edwin

A.K. Boomer
10-19-2013, 12:19 AM
All I know is the Germans were big on nitrideing their cranks and cams many years ago, I have no idea about today.

JRouche
10-19-2013, 03:13 AM
I just read about an anti rust and corosion process that GM is using on their cast iron brake rotors .They call it FNC .It is a nitrideing process.It seems to be cheap .and durable.I was just wondering if anyone knows about it and could it be used on steel or is it just for cast iron. Edwin

Not in the Home Shop Machinist environment I wouldn't think. JR

Jaakko Fagerlund
10-19-2013, 03:26 AM
Nitriding is usually done in a nitrogen rich atmosphere (like ammonia) and at a temperature range of around 400-600 C, so I wouldn't say it is easy to do at home.

Martin0001
10-19-2013, 03:29 AM
One can try certain nitrogen hardening methods at home.
Cold plasma process or cyan*a*te bath is not really out of reach.
Cyan*a*te is made by smelting easy available chemicals (sodium or potassium carbonate and urea) around 400*C and can be used as formed, eg nitrided item dipped in for an appropriate time.
Btw, cyanates are not to be confused with cyanides.

Cyanate formation:
K2CO3 + CO(NH2)2 --> 2KCNO + 2H2O Reaction proceeds around 400*C, water evaporates, smelted cyanate is left.

Anyway, at least with stainless nitridind is *reducing*, not increasing corrosion resistance.

Nitriding increases hardness (considerably) and also improves tribological properties (wear resistance).

Willy
10-19-2013, 08:55 AM
Yes I too recall reading about GM's process for increasing brake rotor life while reducing corrosion.
Like the others suggested, it's not exactly a process one would undertake in a home shop environment.

Below a quote and a link to an article that describes the process.


http://www.propickupmag.com/gm-designs-anti-rust-brake-rotors-fnc-technology-reduces-annoying-brake-wear-issues/


The engineers developed an exclusive corrosion protection process that super heats the rotors at 560 degrees Celsius for a day in an oven the size of a tour bus.Inside the nitrogen-rich atmosphere, nitrogen atoms bond to the surface of the steel rotor, hardening and strengthening the rotor.
The name for the technology is Ferritic Nitro-Carburizing, or FNC, and it has most often been used to treat powertrain parts.
Since its introduction on brake rotors in 2008, FNC has helped reduce warranty claims on brakes by 70 percent.

J Tiers
10-19-2013, 09:05 AM
Some of the "dip-in and heat" case hardening compounds are really nitriding materials, so the process is not THAT far from what is fairly common to do in a "home shop".

The GM process, based on the time, will be somewhat deeper than the common surface nitriding compounds can do when used as directed, but still sounds like a surface process. I assume a case-hardened rotor has a similar set of friction properties to a non-case hardened rotor.

The description is of a reasonably normal nitriding process, but presumably the exact compounds used are the subject of the patents. Nitriding itself is quite old. Packing materials to be hardened in carbon with bits of leather and animal hoof would provide a source of nitrogen and have some effect beyond normal case hardening. Actual cyanide hardening goes back well over a hundred years.

boslab
10-19-2013, 10:03 AM
Think the process was called tufriding, not as hard as nitriding but helped with corrosion as a happy accident.
Mark

lynnl
10-19-2013, 10:08 AM
It's funny how a phantom question or supposition so often gets ascribed to a post. :) The OP said nothing about doing it at home.

vpt
10-19-2013, 10:28 AM
They should worry about the rest of the truck not the rotors! Ford too!

Peter N
10-19-2013, 12:34 PM
We've been using Nitriding for Donkeys years on our mould tools.
Most of our tool cores & cavities are made from P20 pre-toughened steel, and whilst nice and tough at around 32-35 RockwellC as its name suggests, it's fairly easy to machine but not as hard as a fully through-hardened bit of tool steel like H13/EN30B/A2 etc, so we Nitride the cores & cavities after machining to give a really hard wearing surface, particularly on sliding contact parts where it works really well. Never noticed any additional corrosion resistance but we never let the tooling get a hint of rust on the moulding surface anyway.
I think the increased wear resistance was the primary reason that GM specced it.

Edited to add: We don't of course do any of this ourselves, it all goes out to our heat treaters (Tecvac or Wallwork heat treatment as they are now called - linky:http://www.wallworkht.co.uk/content/nitride_and_nitrocarburise/)

lazlo
10-19-2013, 12:51 PM
Some of the "dip-in and heat" case hardening compounds are really nitriding materials.

I know that Evan thinks that Kasenit has a nitriding effect, but nitriding happens at lower temperature than case hardening. I tried heating a piece of 4140 to 950F in Kasenit (nitriding temperature), and found no increase in hardness whatsoever. I called Kasenit in Highland Mills, New York the last time we discussed this, and they said it (sodium ferrocyanide) was a carburizing compound, not a nitriding compound.

Edit: it was a piece of 4140 I tried. Nitriding forms nitrides with chromium, molybdenum and titanium in the alloy, so it doesn't work on carbon steel. O-1 would be another good candidate of what's commercial sold as "Nitralloy" (steel used in nitriding).

lazlo
10-19-2013, 01:08 PM
Cold plasma process or cyan*a*te bath is not really out of reach.
Cyan*a*te is made by smelting easy available chemicals (sodium or potassium carbonate and urea) around 400*C and can be used as formed, eg nitrided item dipped in for an appropriate time.

Cyanate formation:
K2CO3 + CO(NH2)2 --> 2KCNO + 2H2O Reaction proceeds around 400*C, water evaporates, smelted cyanate is left.

Thanks Martin! Sodium carbonate is washing soda -- got that. Trying to figure out a readily available source of urea on the weekend ;)

RWO
10-19-2013, 02:10 PM
Glock introduced Melonite salt bath nitriding surface hardening and finishing to the firearms industry. The process is fairly popular in the aftermarket for target shooter's barrels as it makes the barrel essentially wear-proof and very easy to clean. MMITruetech offers the service for individuals. This site describes the process and the properties imparted to the work pieces in exhaustive detail: http://www.northeastcoating.com/SaltBathNitriding_1.htm

RWO

Tilaran
10-19-2013, 02:10 PM
Nitty-gritty time. Have fun
http://industrialcoatingsworld.com/wear-resistant-coatings/hardening

Alistair Hosie
10-19-2013, 03:56 PM
BE careful toxic fumes in heating some of that stuff!!!! Alistair

Jaakko Fagerlund
10-20-2013, 03:06 AM
Thanks Martin! Sodium carbonate is washing soda -- got that. Trying to figure out a readily available source of urea on the weekend ;)
Just about any hardware store that has a gardening section should have it.

J Tiers
10-20-2013, 09:24 AM
I called Kasenit in Highland Mills, New York the last time we discussed this, and they said it (sodium ferrocyanide) was a carburizing compound, not a nitriding compound.
[

OOOOOOOKKAAAAAAAAYYYYYYYYYYYYYYY.

So......if you want carburizing, use a cyanide compound.

Apparently then, if you want nitriding, pack it in carbon????

This doesn't add up. I'm going to go out on a limb here and suggest that Kasenit DOES provide a nitriding effect. It probably ends up as a form of carbonitriding.

The stuff is a nitrogen compound, chemically closely related to the salt bath nitriding compounds. So why should I believe that it has ZERO nitriding effect, and instead is a carbon source ONLY? When you heat the material in contact with the Kasenit, the situation is similar to (but of course not identical to), a salt bath nitriding process. A cyanide compound in contact with hot metal....

There isn't any particular reason to have a cyanide compound if all you want is carbon.... OK, so sodium cyanide IS used for adding carbon.... Are you betting that there is zero nitriding effect? The stuff has more nitrogen than urea, which gives a nitriding effect.

One reason to believe in nitriding is that kasenit gives a shallow case.... Nitriding typically also gives a shallow case, AND it happens fast, compared to adding carbon via a case hardening process (both according to my reference books, in this case a Colvin and Stanley gear book). The Kasenit process is not an hours-long heating process, as far as I know, so that adds up also.

Low temps which you assumed were going to work with kasenit may work in a salt bath, but they may not work with a crude torch and powder "Bubba" type dip-and-heat process such as the Kasenit.

There is also a serious question as to your ability to detect a surface hardening in the first place. A thin case doesn't necessarily react the same way to standard tests as a many tens of thousandths thick case resulting from a long carbon-adding process. That would apply to either a nitriding or carburizing process, if they are short, as with Kasenit.

With low alloy stuff, probably carburizing.... with other alloys, almost surely a combination effect.

lazlo
10-20-2013, 11:23 AM
OOOOOOOKKAAAAAAAAYYYYYYYYYYYYYYY.

So......if you want carburizing, use a cyanide compound.

Jerry, nitriding is a more complicated chemical process -- you don't just heat the metal, provide a nitrogen source and get a hard case. Unlike case hardening, you're not driving carbon into austenite, you're forming nitrides with chromium, molybdenum, ... elements in the alloy. Which is why nitriding also doesn't work on plain carbon steels. You need to use Nitralloys (alloys that are amenable to nitriding).


Low temps which you assumed were going to work with kasenit may work in a salt bath, but they may not work with a crude torch and powder "Bubba" type dip-and-heat process such as the Kasenit.

I didn't Bubba it. I packed the 4140 in Kasenit and heated it to 950F in a PID controlled heat treat furnace (I'm a bladesmith :) ), and let it soak for 2 hours. Absolutely zero difference in hardness, as measured on a Wilson AT30 Rockwell hardness tester.


The stuff is a nitrogen compound, chemically closely related to the salt bath nitriding compounds. So why should I believe that it has ZERO nitriding effect, and instead is a carbon source ONLY?

You can prove it to yourself, like I did :) Nitriding happens about 400F below austentizing (case hardening) temperature. That's the beauty of the process.
If you, or anyone else, can manage to get a hard case on any steel alloy at 950F with a home shop process -- please let use know! :)

lazlo
10-20-2013, 12:21 PM
Another great paper from the American Society of Metals about Nitriding. The low, sub-austentizing temperature and no quenching means almost no dimensional change (which is why it's very popular on rifle barrels), no warping or cracking...

http://www.asminternational.org/content/ASM/StoreFiles/06950G_Chapter_1.pdf


"The secret of the nitriding process is that it does not require a phase change from ferrite to austenite, nor does it require a further change from austenite to martensite. In other words, the steel remains in the ferrite phase (or cementite, depending on alloy composition) during the complete procedure. This means that the molecular structure of the ferrite (body-centered cubic, or bcc, lattice) does not change its configuration or grow into the face-centered cubic (fcc) lattice characteristic of austenite, as occurs in more conventional methods such as carburizing. Furthermore, because only free cooling takes place, rather than rapid cooling or quenching, no subsequent transformation from austenite to martensite occurs. Again, there is no molecular size change and, more importantly, no dimensional change, only slight growth due to the volumetric change of the steel surface caused by the nitrogen diffusion."

J Tiers
10-20-2013, 01:38 PM
I wouldn't bother trying to harden at a low temp..... a "tempering" (softening) temp.....

I am just puzzled as to why NO nitriding can take place..... it IS fairly simple..... if you provide the heat and the nitrogen, it cannot really be PREVENTED with proper steels. To do it "right" of course it takes more care.

It does seem, though, as if *you* cannot detect the hardening, whether or not it occurs..... I don't quite see how it can be avoided with proper steel.

Nitriding is stated to provide a THIN case..... -.07 mm (3 thou) up to almost 30 thou max. Detecting a thin wear resisting case on a "pasty-soft" steel base is likely to be difficult. you wouldn't check hardness, you'd check abrasion resistance.... Got an abrasion resistance tester?

Seems like some of the effect of kasenit would have to be due to carbonitriding..... depending on the base steel. How would you avoid it?

Some metallurgists apparently think that old-time case hardening may, depending on the steel, have included a nitriding effect, due to the source materials used. Since the iron wasn't a known alloy, it is hard to say, but any impurities may well have included the target elements.

Willy
10-20-2013, 02:10 PM
A very interesting read in the link below regarding the various processes used for the hardening of gears. Differing applications and alloys are also covered.
I've had this little .pdf file on my computer for a while, I just needed to find a link to it in order to post it here.
Only five pages long but a lot of insightful information that answers some of the questions raised.

http://www.mtvac.com/pdfs/gear_heat_treatment1.pdf

lazlo
10-20-2013, 05:27 PM
Good article Willy -- thanks!

So I had the right steel (4140) and the right temperature (950F). But mein Gott! 10 - 80 hours soak time??! :eek:

http://i164.photobucket.com/albums/u15/rtgeorge_album/nitriding_zpsef24702f.jpg (http://s164.photobucket.com/user/rtgeorge_album/media/nitriding_zpsef24702f.jpg.html)

Jaakko Fagerlund
10-20-2013, 10:32 PM
Yup, takes a long long time in the oven. Easy way to test for nitriding is with a file. Nitrided steel feels like a granny on ice, the file literally skids there with no bite at all.

Martin0001
10-21-2013, 06:28 AM
For those interested in nitriding here is a patent descrption dealing with a molten salt system not requiring cyanides only much safer and easier available cyanates:
http://www.google.co.in/patents/US4019928

Here I am enclosing preparation of potassium cyanate (KCNO) which have been later used in small scaled nitriding of various valves and other small items for the need of chemical labs in chemistry department:

Note:
1. Potassium cyanate *is* known to be toxic, not as toxic as cyanide but still toxic.
Lethal dose for mice resulting in half of animals dead is 320mg*kg-1, which is 32 times higher than in case of potassium cyanide (10mg*kg-1).
(Merck Index 12; 7788 &7789.)
Other cyanates, for example sodium cyanate are also toxic.
2. Excess of urea is used in discussed preparation to ensure full conversion and as a result a quantity of Ammonia, a gas of unpleasant and repugnant odor is formed as a byproduct, so some provisions for ventilation are necessary.
Ammonia is also toxic to a degree but repugnant enough to force staff out of premises before much harm is done.

K2CO3 + 2CO(NH2)2 --> 2KCNO + CO2 + 2NH3 + H2O

Procedure:
140g of anhydrous potassium carbonate(*) and 160g of Urea(**) is powderized and placed in porcelain crucible(***) and strongly heated for example with gas burner and stirred with a glass rod(***).
Mixture is initially partially smelting and ammonia is liberated (hence some provision for fume extraction is necessary) and after a while it is solidifying again.
Stronger heating is resulting in mixture being smelted again, onto colorless clear liquid.
No more liberation of gas is seen at this point.

Small sample is being taken by wetting glass rod, dissolved in water and treated with solution of Barium (or calcium) nitrate (or chloride).
Lack of precipitation shows that conversion is complete, otherwise 1g of urea is added to a smelt and after gases are no longer liberating test is repeated again until conversion is complete (****).

Now smelt can be brought to nitriding temperature (450-600*C; different grades of steel are requiring different temperatures - one must check what material he has), your article immersed for appropriate time (few hours is enough) and taken out.
During nitriding some cyanides and carbonates are formed, so if the bath is to be reused many times, one should pass a stream of air through it (to reoxidize cyanides) and add some urea from time to time (to convert formed carbonates back to cyanates).
However if bath is for *single use* or 2-3 rounds of use it is not necessary.
Spent bath will contain some cyanides and if it is to be disposed off one should add to it about 5-10g of sulfur (*****) to it, while it is still molten.
Sulfur is to be added carefully, in small portions.
After about half an hour of so reaction is complete.
That converts toxic cyanide into relatively harmless thiocyanate (KSCN)


Alternatively smelted cyanate can be poured on the tray and after cooling down transferred to an air tight jar for further use.

(*) non restricted chemical available from chemical suppliers, also from those supplying laundries.
Laundry soda is a sodium carbonate.
One may try to use it instead of potassium carbonate and then 106g of it should be used in procedure above, instead of 140g of potassium carbonate.
One must make sure that he has *anhydrous* material at his hand, if not it can be dried by placing hydrate in cooking oven (250*C) for few hours.
Sodium or potassium carbonates are not toxic, actually used sometimes in baking (in hydrogen carbonate form) so domestic oven is OK for drying.

(**) Urea, non restricted chemical is available from any gardening/fertilizer store.
White hygroscopic powder sold under name "Urea". It is nitrogen fertilizer.
Not to be confused with other nitrogen fertilizer, ammonium nitrate.
Such mistake will most likely result in explosion.

(***) Crucible welded from stainless steel (304 or 316 SS) is also OK. Stainless rod may be also used for stirring.
It will not break easily in use as porcelain does but it will also get nitrided in use like your components but slower (304 and 316 SS is nitriding only slowly).
It should be of material 2mm thick at least and height cannot exceed diameter (or you might end up with mixture being thrown out during heating).
It should not be filled with more than half of its nominal volume.
Its life might be limited to hundred, maybe few hundreds of hours in nitriding environment.
Once "nitrided through* it will probably become metallurgically unsound.

In industry they are using titanium crucibles, probably for this reason.

(****) this analysis is done to ensure production of pure chemical but if your cyanate is to be directly heated for nitriding, it is not necessary and actually useless to piddle with it.

(*****) Available from gardening store. 5-10 g is a quantity suitable for stated amounts of starting materials used to make cyanate in the first place.
Yellow granules.
Flammable.

Hope, that will help for those contemplating home nitriding.
Looks much simpler than traditional carburization and hardening.

Disclaimer:
Described procedure of making/handling cyanates even if seems trivial for me, may prove dangerous to someone who lacks sufficient practice in chemistry (I am professional chemist).
Anyone attempting to repeat it doing it solely on his/her own risk and assumes all responsibilities associated with it.

Edwin Dirnbeck
10-21-2013, 02:11 PM
Yes I too recall reading about GM's process for increasing brake rotor life while reducing corrosion.
Like the others suggested, it's not exactly a process one would undertake in a home shop environment.

Below a quote and a link to an article that describes the process.


http://www.propickupmag.com/gm-designs-anti-rust-brake-rotors-fnc-technology-reduces-annoying-brake-wear-issues/

The GM brake rotors are heated to 560C-1040F.This seems like this would be hot enough to release stress.and warp the parts.Also the photo appears to show only rotors that dont have intergral bearings .Maybe the type shown are less likely to distort.But anyway the many replies have been very informative and good reading.Edwin