Sudanese iron spear, 1930s, made and used by the Jur tribe of Sudan

Around 1000BC it was discovered that iron with a small amount of carbon could be hardened by quenching in water after heating.This was followed by a reheating process called tempering.However it was not until Henry Sorby (1826-1908) developed the metallographic technique for observing the microstructures of metals and alloys under the microscope, and also theories of thermodynamics were developed, which provided a scientific basis for the study of alloying, that the effects of carbon in steel were appreciated.The effects of quenching and tempering could also be explained.