Many kinds of stainless steel alloys are totally immune to corrosion under a normal conditions. For example, everything used in the food industry are a such grade. Some of it doesn't rust even at temperatures much higher than 100degC in a much more corrosive atmosphere, than water vapors.

Do they have mechanical properties and costs that make them acceptable as car parts? No steel is totally immune to corrosion.

What are "normal conditions"? Because for instance plenty of stainless steel alloys are very much not totally immune to the accelerated corrosion caused by saltwater...and think of how many people live and drive beside seas and oceans.