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Stainless vs. Carbon Steel



Stainless Steel vs Carbon Steel ...

Extracts from Boxerworks.com and its many authors summarized here

In stressful (metallurgical, not mental) situations, it's NOT a good idea to use SS nuts and bolts. The highest grade of stainless listed as an OTC item is called Class 80, it's tensile strength is equal to a normal bolt steel grade 8.8 (these are DIN specs that relate to the SAE grades 5 and 8). Typical stainless steel hardware has approximately 2/3 the tensile strength of carbon steel. Worse yet is that it work hardens, and can fail by brittle fracture far easier than carbon steel, which tends to fail by stretching. It's also very tough on aluminium it comes in direct contact with. Stainless steel fasteners are not as strong as regular steel fasteners, provided the non-stainless fasteners are of good quality and high grade.
Heat Transfer: The thermal conductivity of stainless is much lower than other metals and won't respond at the same rate as steel. so stainless does not transfer heat as well as plain steel (e.g. brake mounting where temperatures can raise significantly).
Chemical reactions: stainless has some other bad characteristics too, threaded things are liable to gall when torqued. Stainless in contact with "normal" steel and subject to environmental exposure (water splashed from the road) WILL rust, and the plain steel will rust more near the junction, too.
Stainless should be used only for non-critical, non-structural, non-load bearing, "decorative" purposes only. Where you use it, be sure use an copper-based anti-seize paste (to prevent an electrolytic reaction) where you bolt into aluminum castings.

Quote from the Boxerworks site: "Ever wonder why spark plugs get stuck in aluminum heads? Well, the iron or stainless plug material forms an oxide layer on the plug body. These metals are more noble than aluminum. The oxide from a more noble metal is a corrosive substance for a less noble metal leading to the iron or nickel oxide from the plug reacting with the aluminum in the head forming aluminum oxide and reverting the iron oxide back to metallic iron, or actually yet another form of iron oxide. This chemical reaction transfers electrons from one oxide to the other, causing the plug to stick to the aluminum head. The solution for the above problem is copper. Copper is quite inert to oxidation that is it does not corrode much. Put some copper paste between the iron and aluminum will prevent the reaction described above from happening as copper is more noble than nickel and will not be oxidized by nickel oxide. The same thing happens to stainless steel bolts in aluminum casings so use it there too and anywhere there is exposure to water, salt, heat etc."