I am no historian, but a quick search produces some results. Solingen was a center for sword production in medieval times. Naturally, when swords fell out of favor, the city adapted to crafting razors, razor blades, and cooking cutlery.
Sheffield is an incredibly important city with regard to steel. Many innovations to steel came from that city including the invention of stainless steel.
At one time, Sheffield was the cutlery capital of the world. In time, Solingen took its place. Now, who knows if there is a "cutlery capital of the world?"
As far as razor steels go, you have high carbon steel and stainless steel (usually 440C stainless steel). Nowadays, the stainless steel used in custom razor manufacturing can get complicated. I'll let our custom razor guys chime in on the properties of the steels.
Some helpful links:
Solingen - Wikipedia, the free encyclopedia
Sheffield - Wikipedia, the free encyclopedia
Carbon steel - Wikipedia, the free encyclopedia
Stainless steel - Wikipedia, the free encyclopedia
Straight razor - Wikipedia, the free encyclopedia