Precautions for heat treatment of large steel castings:
Large steel castings are large in volume and heavy in tonnage, and are prone to large internal and external temperature differences and large internal stresses during the heat treatment process. Attention should be paid to heating and cooling rates. It can reduce the temperature difference of steel castings and reduce stress.
2. When loading the furnace, the castings should be placed on pads of appropriate height. When placing the pads, ensure good air circulation in the furnace to avoid deformation of the castings. For important large-scale castings, a sketch of the furnace installation should be drawn, the technical requirements should be noted, and a sketch of the location of the external thermocouple should be drawn.
3. Large-scale production castings (excluding high manganese steel and other material information) must undergo stress relief analysis after heat treatment, welding repair, correction, machining, and cutting the riser area.
4. After heat treatment, large amounts of cutting are not allowed.
Inspection procedures for heat treatment of large steel castings:
Valve castings have complex shapes and are prone to deformation and cracking. Annealing heat treatment is often used for large steel castings.
During the inspection process, it is important to supervise the supplier's compliance with the following heat treatment specifications and check the hardness value of the casting.
Because during 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 kept at this ambient temperature. Work and study for a while. Because the carbon steel changes phase in this system temperature data range, along with the constant change of a certain volume, the phase change stress is generated. If the temperature is raised, it is easy to cause the thin-walled part and the thick-walled part of the casting, as well as the gap between the surface layer and the central layer. The temperature difference increases, which increases the thermal stress of the casting and easily causes cracking of the casting.
1.2 Is the insulation time sufficient?
The insulation time of thick-walled castings is longer than that of thin-walled castings to maintain uniform temperature inside and outside the castings and to allow sufficient time for structural transformation.
1.3 When annealing large steel castings, furnace cooling is generally used.
Inspection Specifications for Heat Treatment of Austenitic Stainless Steel Castings
The heat treatment technology of austenitic stainless steel castings can usually use solid solution treatment and stabilization treatment to make their development have better performance.
The focus of the inspection is to monitor whether the supplier is performing inspections in accordance with the following heat treatment specifications.