Bolts – Cross Ref Steel to Stainless & Corrosion

[Swiss_Toni]

Does anyone have a cross reference for metric bolt grades from steel to stainless steel?

e.g 8.8 = XXX, 10.9 = XXX, 12.9 = XXX

Also which has a bigger issue, if any, with dissimilar metal corrosion. Steel to aluminium OR Stainless Steel to aluminium?

The installation application is engine mounts (solid), bellhousings, gearbox moutning, etc). Of course with liberal amount of antiseize (eg copperslip)

Thanks

[Steve_D]

I stand to be corrected but I don't believe any of the normal stainless fixings come anywhere near 8.8 or above.
No doubt there are stainless grades that can be that strong but they would be very specialized and expensive.

Stainless to ali is worse.
If you want to use the two together then us a product called Duralac. This is specified by the UK navy for all fixings that will or may be in contact with sea water and SS to ali anywhere.

Steve

[harry b]

Swiss_Toni said:

Does anyone have a cross reference for metric bolt grades from steel to stainless steel?


Also which has a bigger issue, if any, with dissimilar metal corrosion. Steel to aluminium OR Stainless Steel to aluminium?

The installation application is engine mounts (solid), bellhousings, gearbox moutning, etc). Of course with liberal amount of antiseize (eg copperslip)

Thanks

Hi Toni,
I did some tests in the past to find out the application of bolts on magnesium, the worst material in the perspective of galvanic corrosion.
It is known how bad the corrosion of magnesium is, but nobody knew the timescale of the corrosion to appear in a 3 years timeperiod.
The test conditions where however not the regular sea and salt environment (salty winter roads) but just sportscar conditions, so from spring to autumn useage. (our cars don't float in the sea, and aren't used in winter.
Resulting image below has on top stainless steal screw, right bottom galvanised steel, and left bottom cupraslip on steel.



As you can see there is hardly any corrosion between the galvanised and stainless steel on magnesium, but the cupraslip is not a good solution, because it corroded quite heavy.

The galvanised and stainless steel screws just came out with no problem at all.
But beware, read the testing conditions good, and realise if it applies to your usage.

Good reading stuff:
http://corrosion.ksc.nasa.gov/galcorr.htm
http://www.azom.com/details.asp?articleID=1177
http://corrosion-doctors.org/Forms-galvanic/galvan...


For bolt strength there are different strength classifications, but not clearly marked on the head of a bolt.
I assume you know that a 8.8 has a tensile strength of 8x8= 64Mpa.

see at table2 in the link below
http://www.bssa.org.uk/topics.php?article=1

[MarkWebb]

as a boating man I can agree with steve on the corrosion issuehowever my car has many stainless bolts into aluminum and corrosion does not seem to be an issue in the generally oily engine atmosphere