The testing of steel’s properties often begins with checking hardness. This is measured by pressing a diamond pyramid or a hard steel ball into the steel at a specific load. The Vickers Diamond Pyramid Hardness tester, which measures the DPH mentioned above, uses an indenter with an included angle of 136° between opposite faces of a pyramid and usually a load of 10, 30, or 50 kilograms-force. The diagonal of the impression is measured optically, and the hardness expressed as the load in kilograms-force divided by the impressed area of the pyramid in square millimetres. Tensile and yield strength are determined by pulling a standardized machined sample in a special hydraulic press and recording the pulling force at increasing elongations until the sample breaks. The elongation at this point, and the way the fracture looks, are good indications of the steel’s ductility. Measuring the pulling force at 0.20 percent elongation and dividing it by the test bar’s cross section are a means of calculating the yield strength, a good indicator of cold formability. Impact toughness is determined by hitting a standardized, prismatic, notched sample with a test swing hammer and recording the work required to break it. This is performed at different temperatures, because brittleness increases as temperature falls.

There are many other tests used in the industry to check a steel’s mechanical properties, such as wear tests for rails, drawability tests for sheets, and bending tests for wire. Metallographic laboratories examine the microstructure of polished and etched steel samples, often on computerized and very powerful (up to 80,000× magnification) microscopes. Laboratories also check physical data such as thermal elongation and electromagnetic properties. Chemical composition is often checked by completely automated spectrometers. There are also several nondestructive tests as, for example, the ultrasonic test and magnaflux test used to check for internal and external flaws such as laminations or cracks.