Most scrap yards won't mess with small quantities of ordinary steel chips. They turn to valueless rust before they accumulate enough to make load to the foundry. Volume generators of carbon and alloy steels often have railcar sized loads that are saleable immediately. By contrast, 5 gallon buckets of copper, brass and aluminum, plus some of the more exotic materials such as Ti, and various stainless grades are worth saving if you're patient and keep them scrupulously clean. That's very keen to getting the most money for your scrap. Most yards grade your scrap by the worst sample they look at. For instance, 1 soldered fitting in a bucket of pristine copper will downgrade the entire lot.