Some scrap buyers and brokers are a little troubled about what steelmakers will melt for the rest of this year. The supply of scrap has not reached the shortage stage, but it has dried up. How can that be when no one was buying much scrap for the first six months of this year?

The perception is not true. There were more than a few buyers in the U.S. market—most of them from Asia. Exports to South Korea, India, Turkey and several smaller nations like Vietnam rose to levels that had not been seen for years. China, that bottomless abyss for scrap and iron ore, was the top buyer for much of the first half of this year until prices reached $350 a tonne, when they backed away from the international scrap market.

The mechanism of offshore markets has changed radically in the past few years. One sign of that change is the volume of shredded being shipped overseas in containers. Virtually every major scrap processing equipment maker is now offering machines to load 20- and 40-foot containers with shredded and heavy melt. This has drawn a whole new network of scrap sellers to the...