Earlier quoted context omitted.
China produces more steel in a month than the US does in an entire year of all types. US steel production is around 7% of Chinese steel production. Could the US ramp up steel production etc. on a crash basis under war conditions? Yes, but the overall picture is not great, given that China could also ramp up its production under the same constraints.
China could not ramp up steel production because it imports the raw materials from far away, mostly from Australia. Most of the raw materials, including energy and even food are imported into China. None of those supply chains would be left untouched in a war.
China is food-safe in calories. Not in dollars, because China produces less expensive food than they import.
While yes the raw materials are currently imported from Australia, in war-time they would be imported from Russia and Central Asia. Preparations are being made right now to facilitate this.
China is also #4 in iron ore reserves, they just aren't as economical as Australia's. Of course that doesn't matter much in wartime.