Carbon and oxidation

[langchop]

hi guys,
A twofold question if anyone can enlighten me. I have recently read from a few sources that 'it is the high amount of carbon in steel that causes corrosion' and that 'stainless steels with more carbon corrode more because of the high levels of carbon'
common sense tells me that carbon would be fairly inert and have very little effect on reactivity of a steel? (unless a carbon compound is produced as a byproduct during the formation of iron oxide?)
Does the carbon play that significant a role in the corrosion resistance of a steel?

Secondly, just a thought about the oxidising layer on stainless steels: has anyone ever tested or investigated the actual effect of this layer on the performance of the blade edge? Ie. Is it possible that the oxide formed (being a ceramic) adds to the durability or sharpness of the edge?

 

[Dan Pierson]

Stainless steels with lots of carbon do corrode more but the cause is a bit indirect:

When you add more carbon and more chromium to the mix they tend to combine as chromium carbides, thus reducing both the carbon available for martensite and the chromium available to form the protective oxide.

Verhoeven's "Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel" discusses this in a rather hard to follow appendix. Maybe one of the metallurgists here can explain what happens more simply.

 

[mete]

Dan has the important point - available chromium is the most significant.
I don't know of any study of the effects of the oxide layer. I wonder if the razor makers have made such a study.