What are the common annealing methods of steel materials

The common annealing methods of steel materials are as follows:

① Complete annealing.
The purpose is to refine the coarse overheated structure of medium and low carbon steel with poor mechanical properties after casting, forging and welding.

The method is as follows: the workpiece is heated to 30-50℃ above the temperature at which all ferrite is transformed into austenite and kept for a period of time, and then slowly cooled with the furnace. During the cooling process, the austenite transforms again and the microstructure of the steel is refined.

② Spheroidizing annealing.
The purpose is to reduce the high hardness of tool steel and bearing steel after forging.

The method is as follows: the workpiece is heated to 20-40℃ above the temperature at which austenite begins to form in the steel, and then slowly cooled after heat preservation. In the cooling process, the lamellar cementite in pearlite becomes spherical, thus reducing the hardness.

③ Isothermal annealing.
The purpose is to reduce the high hardness of some alloy structural steels with high nickel and chromium content for machining.

The method is as follows: generally, the austenite is cooled to the most unstable temperature of austenite at a relatively fast speed, and the hardness can be reduced after the austenite is transformed into troostite or sorbite after holding for an appropriate time.

④ Recrystallization annealing.
The purpose is to eliminate the hardening phenomenon of metal wire and sheet during cold drawing and cold rolling.

The method is as follows: the heating temperature is generally 50-150℃ below the temperature at which austenite begins to form. Only in this way can the work hardening effect be eliminated and the metal be softened.

⑤ Graphitization annealing.
The purpose is to make the cast iron containing a lot of cementite into malleable cast iron with good plasticity.

The method is as follows: the casting is heated to 950℃ and cooled properly after holding for a certain time to decompose the cementite into flocculent graphite.

⑥ Diffusion annealing.
The purpose is to homogenize the chemical composition of alloy casting and improve its performance.

The method is as follows: on the premise of no melting, the casting is heated to the highest possible temperature and kept for a long time, and slowly cooled after the diffusion of various elements in the alloy tends to be uniform distribution.

⑦ Stress relief annealing.
The purpose is to eliminate the internal stress of steel castings and weldments.

The method is as follows: for steel products, the temperature below which austenite begins to form after heating is 100-200℃, the internal stress can be eliminated by cooling in air after heat preservation.