Selection of quenching temperature in heat treatment

Heat treatment is a kind of metal hot working technology, which puts the metal material in a certain heating furnace for heating, heat preservation and cooling in the cooling medium, and changes its properties by changing the crystal structure on the surface or inside of the material. Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the performance of the workpiece by changing the microstructure inside the workpiece or the chemical composition on the surface of the workpiece. The characteristic of heat treatment is to improve the internal quality of the workpiece, which is generally not visible to the naked eye.

Today we mainly discuss the selection of quenching temperature in heat treatment. See the following points for details:

(1) If the parts of the same steel are quenched with a coolant with large cooling capacity (such as sodium hydroxide water for water quenching and diesel oil for oil quenching), the temperature shall be taken as the lower limit, otherwise the upper limit.

(2) If the section area is large, the quenching temperature of the hardener should be taken as the upper limit, or even slightly higher. If the section area is small, the lower limit should be taken.

(3) The lower limit should be taken for workpieces that are easy to deform or crack. In order to prevent deforming and cracking of thin carbon steel, quenching oil should be used for 3m / M thin parts in the spinning factory. (whether 45 steel or T10 steel)

(4) It is only required that the lower limit of the surface wear-resistant and hardener free (cold working die) should be taken, and the carburized workpiece can be lowered a little more.

(5) The lower limit shall be taken for the workpiece with low hardness.

(6) High speed, uniform, small deformation, less decarburization and short heating time of the salt bath furnace are the upper limit, while the long heating time of the box furnace is the lower limit.

(7) The lower limit shall be taken for the reworked and re quenched workpieces (large parts must be annealed or tempered at high temperature).

(8) The upper limit shall be taken for workpieces requiring high red hardness.

(9) The upper limit shall be taken for globular quenched microstructure, the middle value for flaky quenched microstructure and the lower limit for point pearlite.

(10) The upper limit shall be taken if the workpiece size is required to expand a little. The lower limit shall be taken if the size of workpiece is required to be reduced a little.