G'day,

I just wanted to share some info that I found out today, I have spoken to a few locals recently who have changed over standard alloy steel bolts to stainless steel bolts while restoring their cars, now I can understand why people would consider doing this as it has less corrosion and also looks good. BUT, it does not have the same strength as alloy steel bolts, so one has to be careful where you use them. Alloy steel bolts are quenched and tempered making them harder where stainless steel bolts have not been. Below is a table of the differences:
Class & Material.....Min. Yield Strength (Mpa).....Min Tensile Strength (Mpa)
Class 8.8.......................640-660.................................800-830 med. carbon steel
Class 10.9.....................940......................................1040 alloy steel
Class 12.9....................1100.....................................1220 alloy steel
A-2 Stainless..................210 min.................................500 min.
....................................450 typical.............................700 typical
Yield Strength: The maximum load at which a material exhibits a specific permanent deformation.
Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.

Edited by user Wednesday, 14 March 2012 9:54:17 AM(UTC)  | Reason: Not specified

Off the shelf, a Stainless steel Bolt isnt as strong as a Grade 8.8, but don't write off the Stainless bolt yet.

I say this with caution, because you have to know what your doing, but a Stainless bolt can be made tougher than a Grade 8.8 with the know how. It's all about the heating and cooling process to harden it.
I won't go into detail on here - but I will say the bolt is cooled very slowly in common Lime as found in the Gardening section of your local plant nursery or Hardware store. You will also require a Rockwell Hardness Test rig/machine - which costs a couple of grand.

Edited by user Wednesday, 14 March 2012 4:16:52 PM(UTC)  | Reason: Not specified

Stainless steel is an steel alloy as well, just a different alloy of ferrous metals.
Knowing the tensile strength of bolts and where to use them is the important part.

also consider there is stainless steel and stainless steel.
i have come across so called stainless steel which was highly magnetic and also had some rust properties.

316 stainless is used in marine enviroments and is not attracted by magnets and will not rust. 316 nuts, bolts etc are expensive. 304 is considered stainless, is attracted by magnets and will rust although it takes a long time. 304 can still be polished up to look good. Bolts etc are far cheaper.

There is some good answers here and wise words, most stainless bolts would really only be good for holding the guards and bonnet on. However as stated there are better stainless bolts around, in fact they can be close to the best. I have some of these in my con rods, the composition is made up roughly as follows,

Nickel 35%, Cobalt 35%, Chrome 20% and Moly 10%

This gives a heat treated Mpa of approx 2,200. It is extremely good in hostile chemical environments, It also resists stress corrosion.

One material that beats the MP35N in terms of tensile strength is C-350, a Maraging steel with a Mpa strength of 2400. It is about 65% iron with the rest being made up of Ni,Co,Mo,Ti, Al but it has no carbon. I use this material in the piston pins. All materials are super clean to achieve these strengths.

Edited by user Tuesday, 20 March 2012 8:55:38 AM(UTC)  | Reason: Not specified