Take a look at the steel statistics on pages 5-7 of this report: https://minerals.usgs.gov/minerals/pubs/historical-statistic...
US apparent steel consumption was 97.8 million tons in 2012, the latest date available. That's a bit lower than the 106 million tons in 1968. American steel consumption has declined about 40% per capita. The US steel industry would have had to ramp up exports very aggressively to remain as large a portion of the US economy as it was in the 1960s.