The heating furnace consists of shuttle loading and batch types, and the use of a preheating furnace prevents heat loss from rapid heating by preheating materials in the furnace. The preheating furnace is used for special materials and high quality products. The heat source, either natural gas or electricity, is determined by the type of material to reduce the internal temperature difference and allow uniform heating, ensuring the quality of the product. The temperature is automatically controlled by a computer program according to the material. Step heating is also available particularly for alloying steel.