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Comment by uticus | Hacker News Reader

i don't get it. my kitchen sink is stainless, as are various cookware, and they are regularly exposed to water with no problems. what's the difference?

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First, 'Stainless' is not a single item and in fact a wide variety of alloys with sliiiightly differing compositions which confer more or less corrosion resistance in favor of other mechanical attributes of the finished product. I have read (but must admit I do not know the accuracy of the claim) that Tesla went with a harder yet less corrosion resistant form of stainless for the cybertruck.

Second, while they see regular use the profiles of wear for e.g. cookware are very different than that of a car's body. For one, you likely thoroughly clean your cookware relatively soon after using it. How often is the car thoroughly washed down? The outside chemicals, road de-icer, quantity of UV or other environmental effects that differ between the daily life of your average chef's knife and a given cybertruck also very much play into it.

The comparison point is a kitchen sink, not a chef’s knife, and Cybertrucks rust after only a few days in the rain, and somewhere it doesn’t snow. Some stainless steels don’t even rust in salt water. They could have chosen a stainless steel that wouldn’t rust, they just didn’t. It could be a mechanical compromise, but the shell isn’t pushing mechanical requirements. I think it’s much more likely cost cutting, supplier problems, aesthetics, ineptitude, or a sleazy attempt to sell more wraps. Whatever it is, it was avoidable.

Kitchen sink is washed with water and left to dry immediately. Additionally, it is exposed only to mildly chlorinated water (or detergents that will protect the sink).

The Cyberpuck does not always get the luxury of air drying even. It is consistently exposed to acid rain and sometimes to high concetrations of road salt and sand eating the smooth surface making it vulnerable.

Different types / grades of stainless steel

There isn’t just one “stainless steel” everyone uses there are a vast number of grades and types for all applications and rust resistance is only one attribute

Iirc kitchen sinks are 304 and the cyber truck is a special 301 Tesla formulated. Marine is 316

https://en.m.wikipedia.org/wiki/SAE_steel_grades

There are also different ways to “finish” it citric vs nitric acid baths for instance

Here's a fairly decent breakdown of the types of steels used for knives: https://knifeinformer.com/discovering-the-best-knife-steel/

There are lots of different 'stainless steels', some are more resistant to rust than others. Stainless steel just means 'less susceptible to rust and staining than other steels'.

Unverified reports based on statements made before the truck came out discusses 301 stainless, most cookware is made from 304, 301 is cheaper and less resistant to staining and rust. The delorian was also built with 301 laid over fiberglass for the body-panelling (maybe so that the rust would be where you could see it and scotchbrite the fuck out of it). 301 isn't particularly salt-resistant though, so if you have a cybertruck anywhere that regularly salts their roads or near the coast salt air...

I think it’s because your kitchen sink and cookware aren’t regularly exposed to other corrosive elements that damage that a car left parked outside would be.

The article mentions this: > Once the chromium oxide barrier is breached, corrosion takes hold. And caveat emptor, because Tesla's owner's manual advises promptly removing corrosive substances, emphasizing not to wait until the Cybertruck is scheduled for a "complete wash,”

I think kitchenware will eventually suffer from the same problems, but it’s just not exposed to the same level of wear and tear as a car, so you’ll see things rust after maybe 10+ years, versus <=1 like with CyberTrucks

Pretty sure it’s more the steel grade in a cybertruck (301) is < the grade in most kitchen sinks (304)

> it’s just not exposed to the same level of wear and tear as a car

is it because the kitchenware is washed more regularly than a car would be?

also, to add anecdotal evidence, I have some stainless, non-coated hardware on my deck, directly exposed for 18 months now, and there is zero rust.

not trying to be contrary, just saying i have used stainless things but never experienced rust on them. either it's coming, or the stainless i have is somehow all better, or something else is up.

I put a plastic item in a stainless steel bowl and added bleach. I left it for several days because I was trying to remove some persistent stains from the item. When I checked it, the bleach had corroded through the stainless steel.

I would imagine that road salt stuck into seams would, over time, also corrode stainless steel. If there are small gaps, it can get in there and be hard to clean out. Just like getting food caught between your teeth and not flossing.

The difference is what's in the water.

still confused, what could possibly be in rainwater or coastal humidity that isn't in dirty dishwater? i get the focus is on salty water on the coastline, but i can guarantee the dish sink has been exposed to extremely concentrated salt solutions.

the difference is velocity. salt and dirt at 60mph velocity makes a big impact

I have no idea if this is the salient difference, but rainwater is actually slightly acidic -- it absorbs CO2 as it forms in the air, which combines with the water and turns into carbonic acid, H2CO3.

Various unfriendly-to-metal compounds free in the air (such as sulfur) that can precipitate out into the rain and thus onto the vehicle.

> i can guarantee the dish sink has been exposed to extremely concentrated salt solutions.

It also is usually rinsed after use, and sits dry in a climate controlled indoor environment 99.9% of the time.

There's dozens of varieties of stainless, all with slightly different properties. All of them can rust under varying conditions.

Most sinks and silverware are typically fairly rust resistant varieties of stainless, and are exposed to pretty minimally demanding conditions.

Try salt water.

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