要約
Steel is made two ways. The blast furnace uses coking coal to strip oxygen from iron ore and produces most of the world's steel and a large share of its emissions. The electric-arc furnace melts scrap with graphite electrodes and needs no ore at all.
段階ごと
Banded iron formation
Almost all iron ore comes from rock laid down over two billion years ago, when oxygen first appeared in the oceans and precipitated dissolved iron.
Pilbara or Carajás
Ore is drilled, blasted, crushed and screened. High-grade hematite needs no concentration at all.
Sinter, pellets and coke
Fines are agglomerated; coking coal is baked into coke, which acts as both fuel and chemical reductant.
Blast furnace or direct reduction
Carbon strips oxygen from iron oxide. Direct reduction can use hydrogen instead of carbon, which removes the CO2 at the cost of needing clean hydrogen.
Basic oxygen or electric-arc furnace
Carbon is burned out of the iron and alloying elements are added: manganese always, plus chromium, nickel, niobium or vanadium.
