[Jnadke]

I should be able to help you out.

Both alloys are of the same class (4xx) so the alloying elements are the same for both.

The carbon content of the latter one is higher (x40) = 0.4% Carbon. This will make the steel much harder, but less flexible. This would be a great stainless steel for gears and other functional parts. Even so, I would send them off to have them heat treated if you wanted the most durable gearbox.
The A designation is because there are 3 types of 440 steels (A, B, C). C is the hardest of the three (but least corrosive-resistant), and is commonly used in high-quality stainless steel knives.

The carbon content of the former one is lower (x10) = 0.10% Carbon. This will lead to a softer, more malleable steel. Still, it's steel so it will be strong. This would be great for the structural parts of a robot. Still, aluminum would be better for such an application.

Might I ask, what would you be using it for?



There's an entire engineering field called Materials Science that specializes in the studying of various materials and their applications. Eventually, this field will become bigger as we learn how to manipulate materials for specific applications.