what steel-based weapons were invented between 1800-1900?

Answer 1

William Armstrong invented the breech-loading big gun about 1860, which from 1880 onwards became the standard armament for large steel-hulled warships.

Answer 2

Virtually all of the weapons invented during that century were made of steel. So the the submarine, monitor, and Gatling gun of the civil war, the the early tank and maxim gun of Europe, the steam engines, steel rails, the armor of the ships and fast lightweight metal ship, bridges and finally the skyscraper buildings.