People have been aware of and worked iron for approximately 4,000 years. However, its usage only became recognized around 1200 BC. This is because it was extremely difficult to smelt, melt, cast or forge because of temperature required.

The composition of the furnace atmosphere created by an endothermic generator is as follows: CO ~ 20%, CO2 ~ 1.0%, Hydrogen ~ 40%, Nitrogen ~ 35% and 4% methane.

The reason for the metallurgical heat-treatment process of stress relieving is primarily to remove residual, induced stresses from the steel. These stresses will occur as a result of rolling, forging, machining, welding, etc.