The two main properties that make steel interesting are 1) cost 2) toughness. Toughness in a material science sense is the ability to absorb energy before fail

The two main properties that make steel interesting are 1) cost 2) toughness. Toughness in a material science sense is the ability to absorb energy before failure. This has two major components, yield strength (energy to initiate deformation) and ductility (ability to deform without fracture). The ductility of steel (and of many other metals) is what drive their use in structural applications, whereas many materials, i.e. ceramics, have higher yield strength but almost no ductility. Even though many glasses are "stronger than steel", if you drop a glass bowl and a steel bowl only one will shatter. If your I-beam shatters you are in trouble. Steel is interesting in comparison to other metals because iron and carbon are abundant and the iron-carbon system has a lot of interesting features that can increase both strength and ductility.