The biggest steel-producing country in the world in 2016 was China, which accounted for about half of the world's steel production and more than half of the U.S. trade deficit. Imposing tariffs on such products is a way to balance trade.
What of fears of a trade war? Most of the above countries are already participating in a trade war with the United States, except that the United States has not been fighting back. The governments of these countries have been manipulating the terms of trade to enhance their exports to the United States and keep out U.S. products. As a result, we get debt, and they get the new factories and the R&D that needs to locate near factories.