On 2018-08-08 14:48:54
On 2018-08-08 14:47:24
On 2018-08-08 11:45:46
The transformation of well type annealing furnace depends on the phase relationship between new and old carbides and parent phase and the habitual surface, the recovery and recrystallization of phase A. due to the precipitation of K, C% in M and squareness ↓. When C < 0.25% in M, it becomes BCC phase a. When t > 400 ℃, the dislocation substructure in phase a recovers.
(1) "In situ" transformation - on the basis of the old carbides, it is gradually transformed into new carbides through composition reorganization and lattice reorganization.
(2) "Independent" transformation a new carbide is formed independently by nucleation and growth in other parts, i.e. "independent" nucleation and growth transformation. At this time, due to the precipitation of new carbide, the carbon content of the parent phase decreases, so the fine old carbide will dissolve into the matrix again until it disappears.
Recovery: the dislocation lines and dislocation cells gradually disappear, the dislocation density is apricot, the remaining dislocations are rearranged into dislocation network, and a grain is divided into sub grains by dislocation network. Organization after reply:. The microstructure of the phase remained strip like.
Recrystallization (600-700 ℃): strip like. It transforms into equiaxed grains and grows gradually. After tempering at high temperature for a long time, the polygon is obtained. Phase and uniformly distributed spherical K constitute complete recrystallization structure. If the temperature of well annealing furnace continues to rise, the grain A and K will grow.
Note also the first and second tempering brittleness temperature regions:
The first kind of temper brittleness occurs in 200-350 ℃, which occurs in different degrees in all quenched steels. It is also called "irreversible temper brittleness".
The second kind of temper brittleness is formed between 450 ℃ and 650 ℃. That is to say, the impact toughness of steel decreases. One of its characteristics is that the brittle state is formed when the fast cooling does not occur and the slow cooling does not. In addition, for the samples with toughness, after tempering embrittlement treatment, they will become brittle state to reduce the impact toughness, so this kind of tempering embrittlement is also called "reversible tempering embrittlement".
The precipitation of carbide, the transformation of retained austenite, the decomposition of martensite, the recovery and recrystallization of phase a are all very complicated during tempering.