Complete annealing refers to a heat treatment process method in which the hypoeutectoid steel is heated to 30~50℃ above Ac3, kept warm, and then slowly cooled with the furnace to obtain a heat treatment process close to the equilibrium structure (pearlite structure). It is mainly used for castings and forgings of hypoeutectoid steel, such as excavator bases, boring bars of boring machines, etc. The heating temperature is 30~50℃ above Ac3, and the temperature is kept warm for a period of time, so that the original structure of the steel is completely transformed into a single uniform austenite, and then in the slow cooling, the austenite is transformed into ferrite and pearlite to achieve the purpose of refining the structure, reducing hardness and eliminating internal stress.
After pouring and mold cooling, the ingots and cast steel parts, or the hot forged parts with too high final rolling termination temperature, have coarse grains, are easy to obtain Widmanstatten structure, and have internal stress. Complete annealing can be used to refine grains, make the structure uniform, eliminate internal stress, reduce hardness, facilitate cutting, and prepare the structure for quenching of processed parts.
Complete annealing is only applicable to hypoeutectoid steel and not to hypereutectoid steel. If hypereutectoid steel is heated to a single-phase austenite zone above Acm, a network of secondary cementite will precipitate after slow cooling, which greatly reduces the strength, plasticity and toughness of the steel.
Carbon Steel Thick Wall Pipe
