Two methods of annealing glass products
Two methods of annealing:
1. Complete annealing is applied to alloys with solid-state phase transformation (recrystallization) occurring during balanced heating and cooling. The annealing temperature is a certain temperature above or within the phase transition temperature range of each of the alloys. Both heating and cooling are slow. The alloy undergoes a phase transformation and recrystallization during the heating and cooling processes, so it is called recrystallization annealing, which is often referred to as annealing. This annealing method is fairly commonly used in steel. The recrystallization annealing process of steel is: slowly heating to 30-50℃ above Ac3 (hypo-eutectoid steel) or Ac1 (eutectoid steel or hyper-eutectoid steel), keep it for an appropriate time, and then slowly cool down. Through the transformation of pearlite (or also pro-eutectoid ferrite or cementite) to austenite (recrystallization of the first transformation) that occurs during heating and a second, opposite, that occurs during cooling Back-phase recrystallization. It forms pearlite (or pro-eutectoid ferrite or cementite) with finer grains, thicker lamellae and uniform organization. The annealing temperature is above Ac3 (hypo-eutectoid steel) to make the steel completely recrystallized, which is called complete annealing, and the annealing temperature is between Ac1 and Ac3 (hypo-eutectoid steel) or between Ac1 and Acm (hypereutectoid steel). ), which causes partial recrystallization of the steel, which is called incomplete annealing. The former is mainly used for castings, forgings, and weldments of hypoeutectoid steels to eliminate structural defects (such as Widmanstler structure, banded structure, etc.), make the structure thin and uniform, and improve the plasticity and toughness of steel parts . The latter is mainly used for forging and rolling of medium carbon and high carbon steel and low alloy structural steel. If the cooling rate after forging and rolling of this kind of forging and rolling is large, the pearlite formed is finer and the hardness is high; if the temperature of stopping forging and rolling is too low, there will be large internal stress in the steel. At this time, incomplete annealing can be used instead of complete annealing to recrystallize pearlite and make the grains finer. At the same time, it also reduces hardness, reduces internal stress, and improves machinability. In addition, the spheroidizing annealing of hypereutectoid steel with annealing temperature between Ac1 and Acm is also incomplete annealing. Recrystallization annealing is also used for non-ferrous alloys, such as titanium alloys, which undergo allotropic transformation when heated and cooled, low temperature is α phase (close-packed hexagonal structure), high temperature is β phase (body-centered cubic structure), and the middle is " α+β" two-phase region, that is, the phase transition temperature range. In order to obtain near-equilibrium room temperature stable microstructure and refined grains, recrystallization annealing is also carried out, that is, slowly heating to a temperature not much higher than the phase transition temperature range, and holding for an appropriate time to transform the alloy into fine grains of β phase; Then slowly cool down, so that the β phase is transformed into the fine grains of the α phase or the α+β phase.
2. Incomplete annealing Incomplete annealing is an annealing process in which the iron-carbon alloy is heated to a temperature between Ac1-Ac3 to achieve incomplete austenitization, followed by slow cooling. Incomplete annealing is mainly suitable for medium and high carbon steel and low alloy steel forgings and rolling parts. Its purpose is to refine the structure and reduce the hardness.
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