It increased the demand for steel since steel was used to make railcars and tracks.
Steel was used to make railroad tracks and cars because it was the only metal strong enough. So the expansion of the railroad industry would mean more steel had to be used and thus it would increase the demand.
The expansion of the railways was a phenomenon of great relevance for the American economy, since it connected cities and markets, allowing the transportation of cargoes in practically the whole national territory.
In this context, all industrial sectors have benefited. In particular, the steel industry, since steel was the raw material for the train tracks, with a large increase in demand during that period.
