Annealing and normalizing defects and remedies

Annealing and normalizing due to heating or cooling properly, there will be some contrast with the intended purpose of the organization, resulting in defects.
 

An over-burning

Since the heating temperature is too high, there grain boundary oxidation, even partial melting of the grain boundary, resulting in the scrapping.
 

2 black brittle

Carbon tool steel or low alloy tool steel after annealing, although sometimes found hardness is low, but brittle is great, a discount on the break, fracture grayish black, so called black brittle microstructure is characterized by partial cementite transformed into graphite.

The main reason for this phenomenon is due to the annealing temperature, holding time is too long, slow cooling, pearlite transformation by a more stable equilibrium Fe-C phase diagram due. High carbon steel, manganese content is too low, containing traces of promoting graphitization than the impurity element (such as aluminum), etc. can promote graphite.

 

3 abnormal tissue

Sacrifice their organization is: sub-eutectoid steel, prior eutectoid ferrite grain boundaries on the presence of coarse cementite, pearlite lamellar spacing is large, the eutectoid steel, prior eutectoid cementite a very wide around the body of the ferrite, and the eutectoid cementite is very wide. Appear abnormal tissue because: when sub-eutectoid steel or eutectoid steel annealing, cooling near the Ar1 too slow, especially just below Ar1 point, for example, less than 10 degrees Celsius for a long stay. The formation of such an organization is to be precipitated eutectoid phase, in turn, in the subsequent pearlite, ferrite or cementite free growth, and the formation of free ferrite or cementite. Results appear in sub-eutectoid steel non-eutectoid cementite, while in eutectoid steel in a one of the free ferrite. This is the opposite of normal tissue, so called abnormal tissue. Abnormal tissue will result in elimination quenching soft spots. Re-emergence of such organizations should first annealing eliminated.

 

4 meshwork

Meshwork mainly due to heating temperature. The cooling rate is too slow caused. Because mesh ferrite or a carbon-carbon experience reduced mechanical properties of steel, in particular network cementite in the subsequent quenching is difficult to eliminate, it is necessary to control

Reticular tissue re-normalizing approach generally taken to eliminate.

 

5 high hardness

Annealing of high carbon steel is one of the important objectives of lower hardness, ease of machining, and thus the hardness after annealing has certain requirements. However, if the annealing temperature is too high, heating, cooling speed, especially for a high content of alloying elements, the cold stability of austenite steel, there will be sorbite, troostite, and even lower body shell, MA 's tissue, and thus higher hardness than the hardness range specified

  In order to obtain the desired hardness, should be re-annealed.