With Mexico, the U.S. has a trade surplus in steel. Yet another reason not to implement the announced tariff.
Be that as it may, the tariff ignores not only the basic economics of tariffs, but also the significance of what it means for an economy to be a mature one and a developing one. In the former economy, demand for raw materials like steel is relatively constant whereas in a developing one, the demand for such things is on the upswing.
Because the U.S. is a mature economy, while there may be incidental bumps in total demand for steel, barring some major new innovation that uses steel and of which developed economies are better positioned to avail themselves of it, non-domestic buyers of steel, particularly developing nations, will avail themselves of a U.S. steel tariff's price impacts to hasten their advance. Insofar as China is a developing economy, that's a terrible thing as goes the status of economic competition between China and the U.S. The tariff all but begs China to hasten its economic expansion, one that's powered by over 1.5B people, and do so without suffering any of the consequences of the tariff due to the fact that
only about 2% of U.S. steel imports come from China.
Then there's the matter of the tariff having the greatest impact on Canada.
Canada is the U.S.' largest buyer of U.S.-produced goods, dwarfing by huge margins all other nation's except Mexico, which is the second largest consumer of U.S. goods. Who deliberately implements a policy that adversely affects the two largest buyers of one's own products and the prices paid by consumers in one's own nation? Oh, Donald Trump does that. It's flat-out stupid to do so; even disregarding the mature vs. developing economy aspects, it's stupid.
When a large importing country implements a tariff it will cause an increase in the price of the good on the domestic market and a decrease in the price in the rest of the world. But since Trump wants to impose the tariff on raw materials, it'll raise not only the price of steel and aluminum in the U.S., but also the price of everything made from that steel and aluminum.
As for who will bear
the incidence of the tax/tariff, well, that depends on the elasticity of demand and the elasticity of supply for each given product class, and in some instances, each differentiable product.