Metallurgists - A little help...

[pryord]

So, the last time I put my muffler and cat conv. on, I thought I would be smart and use stainless nuts and bolts. The old regular steel ones were rusted and required cutting to remove. After only a year, I went to remove the stainless bolts and they are locked tight. All but a few required me to break the heads off. Heck, it's taking me longer to remove these than the old rusty ones.

What's up? Is there somethings about stainless and heat that causes them to bond together?

What should I use this time in order to facilitate easy removal. Is regular steel and "anti-seize" the way to go?

Thanks!

[MotoSook]

Did you use anti-seize on the stainless fasteners?

[Zef]

Titanium fasteners will do the job...!

[slammed1000]

regular stainless requires anti-seize or it will lock on under heat.

[Rot 911]

The heat will gaul the stainless steel nuts and studs as you have discovered. Either use stainless steel studs with bronze nuts or use regular steel studs and nuts with some anti-sieze.

[MotoSook]

Originally posted by slammed1000
regular stainless requires anti-seize or it will lock on under heat.

Even with anti-seize the nuts will lock. As a matter of fact they seem to lock "better" with anti-seize! That's why I asked if he used anti-seize.

[Zeke]

Originally posted by Kurt V
The heat will gaul the stainless steel nuts and studs as you have discovered. Either use stainless steel studs with bronze nuts or use regular steel studs and nuts with some anti-sieze.

Why not steel and bronze nuts?

[pryord]

Nope, I didn't use anti-seize. Steel and bronze sounds like a good idea.

[Steve@Rennsport]

On the subject of anti-seize compounds,....

There are several kinds and using the wrong one is akin to not using them at all. :0

1) Aluminum-based

2) Copper-based

3) Nickel-based

Copper & nickel based products are the preferred ones for exhaust hardware or anything that is exposed to extreme heat.

[Quicksilver]

Stainless bolts and bronze nuts is a common combination but it you can find copper nuts they work even better.

As far as finding anything other then aluminum anti-seize...
The last time I went looking for copper based anti-seize everyone at the various autoparts and fastener supply houses looked at me like I had three heads. I know that permatex used to make it because I had some but I am coming up short now...

[roadhog]

I read in an engineering manual using SS nuts and bolts of a different hardness will prevent seizing.Try a hard grade bolt and soft nut.I've seen SS nuts and bolts seize without heat.

[Ken911]

you need to use the nickle based or graphite based. the copper will also seize, use felpro or locktite n-5000, or n-7000, we used to use the copper based n-4000 several years back on our steam generators and some of the bolts would seize up, and we had to use a hytorque to remove them. now we use n-7000 which is graphite based on the primary side and n-5000 which is nickle based on the secondary side and never have problems. some of these bolts are torqued to 1200 ft pounds and operate for 18 months straight at 574F

[David]

Originally posted by pryord
Is regular steel and "anti-seize" the way to go?

Thanks!

Yes

[heirplane]

As is often recommended on this site, to source hard to find hardware, etc., try McMaster-Carr-- www.mcmaster.com.

McMaster has antiseize compounds for most applications.

[unclebilly]

The nickle stuff may also sieze. We used stainless hardware at one point on our ceramic fuel cells (they run at 750°C). We tried all of the commercial high temp antisieze compounds with varied luck. In the end we settled on our own home made concoction that worked quite well.

There are 2 things working against you here:

High temp oxidation which tends to cause the threads to jam together and the fact that the bolts become fully annealed in use (totally soft) so the threads want to gall together when you try to loosen them.

I'm not sure that I agree 100% on the brass nuts because they would be quite weak at operating temp but they would come off nicely once cooled down. If you could get 400 series stainless steel bolts and nuts and use some of the high temp nickel based antiseize (the nuke plant stuff) you will be OK. Other wise just get some good quality un plated steel bolts and nuts and run the nickel antiseize.

[pryord]

Thanks for all the info. Nothing is simple, is it? Off to the hardware store I go...

[chris_seven]

Diffusion bonding of stainless steel fasteners is quite a common problem particulalry if you use an Austenitic Stainless Steel.

Ferritic alloys may be a little better but even then there may be problems.

The tooling used in high temperature materials testing machines suffers with these problems on a routine basis and for many years carbon 'dags' were all that was available but this was messy and not 100% successful.

For the last few years Boron Nitride Dags have been used in this type of applications and have much improved performance and I have been using this type of product for years.

It is fairly readily available and is a white compund and not too messy.

[randywebb]

what is Diffusion bonding ?

are metal atoms diffusing across the boundary??


BTW, the Copper anti-seize is all over the place - I suspect the parts place worker bees just don't know what it is - look for a copper color.