Large steel castings are large in size and tonnage, and it is easy to produce large internal and external temperature difference and large internal stress during heat treatment, so attention should be paid to heating and cooling speed during heat treatment. The temperature difference and stress of steel castings can be reduced.

2. When charging the furnace, the casting should be placed on a pad iron with an appropriate height, and the placement of the pad iron should ensure good ventilation of the furnace gas to avoid deformation of the casting. For important large castings, the furnace loading sketch should be drawn, the technical requirements should be indicated, and the position sketch of external thermocouple should be drawn.

3. After heat treatment, welding repair, correction, machining and cutting the riser area, stress analysis must be carried out for large-scale production castings (except high manganese steel and other materials).

4. After heat treatment, a lot of cutting is not allowed.

Specification for heat treatment inspection of large steel castings;

Valve castings are complex in shape and easy to deform and crack. Annealing heat treatment is often used for large steel castings.

During the inspection, it is important to supervise whether the supplier meets the following heat treatment specifications and check the hardness value of the castings.

Because in the heat treatment process, especially for large steel castings with complex shapes, when the furnace temperature rises to 650℃~800℃, the temperature should be raised slowly, or a learning period should be maintained at this ambient temperature. Due to the phase transformation of carbon steel in this system temperature data interval, with the constant change of a certain volume, the stress that affects the phase transformation is generated. If the temperature rises, the temperature difference between the thin-walled part and the thick-walled part of the casting and between the surface layer and the central layer will easily increase, thus increasing the thermal stress of the casting and easily causing the casting to crack.

Is the heat preservation time of 1.2 enough?

The heat preservation time of thick-walled castings is longer than that of thin-walled castings, so as to keep the temperature inside and outside the castings uniform and have enough time for microstructure transformation.

1.3 When large steel castings are annealed, furnace cooling is generally adopted.

Specification for heat treatment inspection of austenitic stainless steel castings

The heat treatment technology of austenitic stainless steel castings can usually be developed by solution treatment and stabilization treatment. Good sex.

The focus of the inspection is to monitor whether the supplier conducts the inspection according to the following heat treatment specifications.