The optimism of 1960, vs the reality of today…
Not all stainless steels are entirely “stainless.” One look at a 3 year old exhaust on a modern car proves that. While not rusty… it isn’t shiny anymore but is a reddish-brown color. 400 series stainless steels are like that. The stuff in your kitchen is made from 300 series stainless steels that stay shiny. Many aftermarket exhausts are made from this and stay shiny.
400 series stainless is pretty easy to bend and stamp. A little bit more difficult than carbon steels to form. 300 series with its added nickel and chrome, does not want to be stamped or bent. It tends to spring back. It is very hard on stamping dies, too.
They way you get form-ability is to reduce the chrome and nickel a bit which leads to some corrosion. This is the stuff your refrigerator is made of… but it doesn’t roam around on salted roads, now does it?
Me-thinks the Tesla may be using refrigerator stainless and not kitchen-ware stainless.
3 Likes
Rusting is not uncommon for stainless steels exposed to the atmosphere. This can be especially true in industrial and city areas with polluted air. The materials used for washing can accelerate rusting too. If the owner buffs the surface with an abrasive cloth, that would rub off the passivation layer. When the steel is passivated the free iron is dissolved and an oxide coating is deposited in the surface. Depending on how they did this, the surface passivation might not be optimal. California has extreme pollution laws as you know and hot nitric acid passivation might not be allowed. This method of passivation in the driveway is impractical. Maybe citric acid passivation would be allowed.
There are several levels of Stainless steel depending percentage of Chromium (and other metals are added). The more Chromium and Nickle the less likely it’ll rust. Nova did a great episode years ago about the reconstruction of Statue of Liberty and the stainless steel structure. Before that I had no idea of the many different levels of Stainless there were.
When I read about this problem, my first thought was that Tesla isn’t using enough nickle in their steel.
The pervasive belief that “stainless steel” doesn’t rust is just one of the misconceptions about metals and their various formulations. I’ve run across numerous legacy mechanical drawings specifying the base material as “stainless steel”, “brass” or “aluminum”. I always wondered how the machine shop tasked with making those parts resolved that ambiguity. Then again, I recall the time when a quality guy checking parts noticed that a hole had no dimension on the drawing and yet they were cranking them out by the toteful. A visit to the machinist and he said he noticed it and decided that is where it looked like it should go… 
Magnets will stick to some types of stainless steel, and not others. I’m guessing Tesla is using the kind that magnets will stick to.
They should be using the stainless steel the Delorean is made with.
1 Like
Some years ago I was at a scrap yard and picked out a piece roughly what I was looking for. The guy at the counter said that’s stainless. You can’t drill it, weld it, bend it, etc. ok I kept on looking. I prefer paint though.
One other thing common between the Tesla and Delorean- flat body panels. Stainless steel doesn’t form as easily into complex curves.
More than you want to know:
1 Like
Supposedly, most DeLorean owners avoid driving in the rain because of the rain’s effect on the stainless steel.
I suspect it’s more like improper surface preparation before passivation, poor passivation, or improper care after purchase. IMO this all points more to poor materials selection for the body.
The Delorean use 304 stainless and the Cyber truck uses 301 grade. 304 uses less carbon and a little more Cr, it’s corrosion resistance is a little better than 301.
1 Like
They may start their trip in the rain, but once they reach 88mph the can abruptly change :).
2 Likes
Scrap yards require non-magnetism to pay for stainless steel.