There are fairly 3 reasons for the decline of iron and smelting industry in nineteenth century.They are
1) New forest laws were adopted.This law prevented people entering into the forest.therefore they could not collect wood for the smelting process.
2) In some areas the government gave access for the use of forest but high tax has to be paid. This reduced the income of the iron smelters.
3) By the late 19th century iron and steel was being imported from britan. So the Ironsmiths began using the imported iron and steel to manufacture implemants