What's the difference between ordinary steel used to make submarines and military steel?

Submarine should be built on the basis of safety, stealth and attack ability, so submarine steel is very different from ordinary useful steel:

First, submarine steel must be low magnetic steel. As we all know, steel is a special form of iron, so after World War II, people invented magnetic detectors to find submarines in water and magnetic mines. If the magnetic characteristics of the submarine are obvious, then the probability of its being discovered and accurately positioned is very high, and being discovered means being annihilated.

Second, the steel used for submarines must be of high strength, because submarines have to bear dozens or even hundreds of water pressures underwater. If the strength of the shell is too poor, once the shell breaks, people will be crushed into a ball of meat by water pressure and will never die again. If the shell is too thick, it will increase the weight of the submarine and itself, and the internal space will become smaller, which will greatly affect the maneuverability and combat effectiveness of the submarine.