Usually in the manufacture of steel.
Boron is used to make control rods.
you use it in technology and car care you use the steel ruler for straight lines for wood and plastic and other things.
He must have nerves of steel.The steel marbles are usually ball bearings.I hope this "smart car" has a steel frame.
One use of boron is to make magnets.
Use exactly what the manufacture of your car recommends and nothing else.
Because it lowers the weight of the car.
Stainless steel, like the Delorean.
air craft
if you mean the exhaust pipes it depends on the car. older cars were usually made of steel. now they use stainless steel alot.
For automotive use steel is inexpensive and easy to form. Kitchen sinks use stainless steel because it won't rust but it is harder to form.
You can if the manufacture recommends that particular weight of oil.