Temperature and effect of complete annealing

Metal products must be annealed before they can be considered as qualified products. There are many ways to anneal, such as isothermal annealing, homogenization annealing, and full annealing. What is the full annealing temperature and what is the complete annealing effect?

What is the full annealing temperature? What is the complete annealing effect?
 


What is the complete annealing temperature?

Full annealing is to heat the metal to 20~30 °C above Ac3, and then slowly cool with the furnace after heat preservation, in order to obtain a heat treatment process close to the equilibrium structure (pearlite type structure). Also known as recrystallization annealing. Mainly used in casting and forging parts of hypoeutectoid steel, such as excavator base, trampoline mast and so on. The heating temperature is 30~50 °C above Ac3, and the temperature is kept for a period of time, so that the original microstructure of the steel is transformed into a single uniform austenite. Then, in the slow cooling, the austenite is transformed into ferrite and pearlite to achieve refinement. Organize, reduce hardness and eliminate internal stress. Hypereutectoid steel cannot be completely annealed. Since the secondary cementite is precipitated in a network after being heated to Acm (carbon dissolution limit line in austenite), the mechanical properties of the steel are remarkably lowered, and it is easy to crack at the time of quenching.


What is the role of complete annealing?

Refine the austenite grains and eliminate the Wei's structure. One of the reasons for the formation of Wei's structure is that the austenite grains are too large (the temperature of stop rolling, stop forging is too high or the heating temperature is too high during heat treatment), while when it is completely annealed, the heating temperature is lower, after recrystallization The crystallites are inevitably refined. As shown in the figure, it can be seen that when the spheroids are transformed into austenite, the grains are remarkably refined, and even after cooling slowly, the newly formed spheroids are fine. of. Therefore, after complete annealing, the austenite grains are finer and the ferrite Weiss structure can be eliminated.



There are many metal products that need to be fully annealed after being smelted. It is understood that the heating temperature for complete annealing is 20 to 30 degrees Celsius above Ac3.