I'm not totally aware of the correct translation of the technical terms in English but i'll try to add up a bit:
standard steel used to be called Fe360, Ferro is latin for steel. 360 means that it will snap at a tension of 360 Newton (roughly 1/10 kilogram) per square millimeter.
Nowadays they call it S235, Steel 235 because the steel that snaps at 360 n/mm2 will start to deform at 235N/mm2
Now we dont want to bend our roof so the max tensile strength is in most cases, a useless variable, unless we want to use it as a safety device such as a shear bolt.
between 235 N/mm2 and 360 N/mm2 the steel will deform plastic, it does not return to the original length. Between 0 and 235 N/mm it will only stretch and turn back to original length when the load is taken off, which is called elastic deformation (or transformation ??)
The 235 N/mm2 is also called the "flow limit" because above this limit it will start to flow, or stretch permanently.
Carbonic steels, and wear resistant alloys usually have a lower max. breach tension in relation to the flow limit.
A material with an extremely small difference between flow limit and breach limit is glass: We can use it in lightweight high strength applications as fiberglass. But when you bump a grain of gravel to a window, it will break.
The same goes for over-hardened mower blades: When they are too hard, they'll smash apart when they hit a stone because they dont allow enough material flow to absorb the impact.
At the technical engineering school, we were ot allowed to smash two hardened hammers against each other, because both hammers were hard and would splatter sparks of metal around.
