Due to the small temperature difference between the inside and outside of the parts, the internal stress of the parts is reduced and the cracking tendency of the parts is reduced.
For example, the ball screw quenched and tempered parts of 50crmo steel require a hardness of 25-30hrc and adopt the stage heating and quenching method. The blank specifications of the screw are various, such as 25 mm × 600 mm, 35 mm × 600 mm, ~ 40 mm × 600 mm, 460 mm × 800 mm, etc.
The stage heating and quenching method is adopted in the resistance furnace. The process is 750 ℃× 1 h-840 ℃× 3 h oil cooling (calculated as 2.5 s / R AM). After taking out the white smoke, it is cooled in the air. The hardness is tested to be 50-53 HRC, and then it is tempered to the required hardness at high temperature immediately.
For another example, for CrWMn steel mold, we use a salt bath furnace at 800 ℃ to install the furnace, and after the temperature is kept at 20 min, it rises to 840 ℃ (the holding time is calculated as 1 min / mm), and then people cool it i n 160 ℃ nitrate to prevent the mold from cracking.
On 2018-08-08 11:45:46
