I'm very confused, the article says:<p><i>'The MTA had good reason to believe the program would succeed. Just a few years prior, it had dropped more than 1,000 Redbird trains in the ocean. They remain on the ocean floor to this day, in part because they were made of carbon steel, which helps prevent corrosion.</i><p><i>By comparison, Brightliners were made of stainless steel. When the subway cars debuted in 1964, they were a mechanical and aesthetic innovation. The stainless steel made the train cars lighter on the tracks, but this worked against them underwater.'</i><p>Few questions here. First, isn't carbon steel ... steel? Steel is primarily iron and carbon, so my understanding is that carbon steel is mostly just a marketing term to have at least an adjective of some sort, just like 'aircraft grade aluminium', which is in fact one of the cheapest, bulk types of aluminium (hence use in bulk in aircraft)<p>Second, how does regular steel fare better than stainless steel in a corrosive environment? The article says the stainless steel started to corrode from the welds, which is fair enough, but wouldn't regular steel just corrode wholesale?