Cranes are structures that require great strength, so they must be created from materials that give them these properties. Most cranes are made from steel, which is an alloy of carbon and iron. The amount of carbon used in creating steel is important, if low levels of carbon are used the steel will be much stronger, and vice versa.
Certain cranes are designed to lift very heavy objects and cannot be made from steel which contains high levels of carbon. Instead, these high load capacity cranes are created from a variety of substances known as high-strength low-alloy (HSLA) steels. HSLA steels contain relatively low levels of carbon, typically about 0.05%. They also contain a small amount of one or more other elements that add strength. These elements include chromium, nickel, molybdenum, vanadium, titanium, and niobium. As well as being very strong, HSLA steels are resistant to atmospheric corrosion and are better suited to welding than carbon steels.