What are the preparatory heat treatment processes when forging forgings?

Forgings stay at high temperature for a long time when deeply carburizing, and the cooling is slow after the end of carburizing, and the form of excess carbide precipitated is network or block, which is not ideal for carburized forgings that require fatigue strength, and is not conducive to controlling deformation and microstructure state during quenching. Especially when the surface carbon concentration is high or exceeds the limit, the effect on the performance is greater, so after the deep carburizing of the forging, the spheroidization treatment is carried out again after the carburizing cooling, so as to achieve uniform and refined distribution of carbide particles.

After carburizing and spheroidizing forgings, it is often necessary to carry out finishing processing, and the carburized layer is processed away from the parts that do not need carburizing and hardening, and a certain amount of final grinding allowance can also be left.

The carburizing quenching temperature of forgings is generally 800-820 °C, the furnace gas should have a reducing atmosphere, and it can also be filled with nitrogen to eliminate the oxidizing atmosphere, or you can use methanol to exhaust and drop some acetone, and you can also apply anti-decarburizing agent at the carburizing part.

There are no special requirements for tempering after carburizing and quenching of forgings, but in the selection of temperature, it is often higher than the tempering temperature of carburizing and quenching of small forgings. This is determined according to the required surface hardness of large forgings, but it should be noted that the surface hardness of the forgings that need to be ground last, the surface hardness after tempering should be increased by 2HRC than the required hardness, to prevent the surface hardness after the large grinding allowance is removed.

The structural properties of the cold rolling work rolls of forgings are very demanding, and a series of preparatory heat treatment processes must be carried out before the final heat treatment to meet the hardness and performance requirements of the roll neck and prepare the organization for the final heat treatment. The process includes: heat treatment after forging, conditioning after rough machining, and quenching the surface of the roll neck of the working roll of the high-speed cold rolling mill.

Heat treatment after forging. After the cold rolling work roll is forged, the air is cooled to 600-650 °C hot into the furnace, and the forgings are heat treated after forging. The heat treatment after forging focuses on completing the following three tasks: the first is to eliminate the network carbide, the second is to eliminate the stress softening structure to obtain a spherical pearlite structure, and the third is to reduce the hydrogen content in the steel to prevent the generation of white spots.

Tempering heat treatment. After rough machining and ultrasonic nondestructive testing of cold-rolled work roll blanks after forging heat treatment, the overall quenching and tempering heat treatment is carried out. The main functions of quenching and tempering heat treatment are: First, it is to prepare the organization for subsequent induction hardening. The second is to obtain high comprehensive mechanical properties to withstand intense quenching and meet the toughness requirements of the working roller neck in terms of use.