World War Two production was about manpower, not metal.

The reason why an extensive discussion of iron mining is relatively uncommon in WWII economic historiography is because it wasn't a bottleneck in the production process. The chief bottlenecks for most belligerents were labor, trace mineral resources (e.g. tungsten, manganese, chromium and nickel), rubber and, for the Axis, petroleum with Labor being by far the most important bottleneck.

The main thing that most belligerents did to increase military production was to curtail civilian good production. Civilian automobile and part production was quickly reduced to nearly zero during wartime. Other civilian goods that used metals, like cookware, other transportation uses, and housing were sharply reduced. This freed up not only the metal, but more importantly the labor that went into producing the goods. The civilian economy simply ran on it's existing supplies of these goods for 3-6 years, building up a huge latent demand that was an important element of the postwar economic boom.

Labor was the basic bottleneck of WWII production. If enough labor could be found, iron mines and furnaces could run double and triple shifts, and older facilities that were mothballed due the depression could be put back into production. A few facilities that were specific to military grade steel making, like electric blast furnaces, were expanded rapidly, but on the whole a crash program to expand iron and steel capacity wasn't needed. The reason is because economies didn't have the labor to turn all the iron and steel they could produce into military goods. Munitions factories and armed forces placed huge demands on the labor pool and as a result the economy couldn't use all the metal that it might have been able to produce.

That doesn't mean that a few trace or rarely produced metals were not in short supply. WWII saw a huge increase in demand for armor plate and high strength steel alloys, and these often required trace metals like tungsten, manganese, chromium and nickel which are less widely distributed in nature than iron ore. The Axis countries in particular had labor intensive workarounds and quality issues due to these shortages. This problem was solved by imports for the Allies, but the Axis had little access to world trade and were unable to solve it.

A further bottleneck that restricted wartime demand for steel goods was the lack of rubber and petroleum. A truck or tank or warship isn't much good without fuel or tires. The United States had a crash program to increase artificial rubber production, and drew down a small pre-war stockpile of natural rubber. Axis countries ultimately had their war economies crippled by petroleum shortages which could not be remedied. Germany and Japan would have been hard pressed to use more steel for ships and vehicles given the fuel situation.

Lastly, Aluminum was in something of a special place in terms of metal production. Since the Aluminum industry was relatively new, essential for aircraft production, and depended heavily on large scale use of electricity, the US and other counties had special programs to boost the production of aluminum and located aluminum facilities near sources of cheap electric power like hydroelectric dams.

All of the above is not to say that metal, especially iron and steel, wasn't in short supply during wartime. It was, in the sense that everything was, from shoes, to food, to housing, to heat. However other shortages were "tighter" and formed a more import element of the economic history of the war.