The strength level of large steel castings is close to forged steel, but with poor plasticity and resistance. At the same time, large steel castings also have problems such as uneven and not dense inside, large internal chemical composition error, poor thermal conductivity and messy structure.
Therefore, it is necessary to pay special attention to eliminate internal stress and prevent cracking during heat treatment. However, there is no need to take the harm of hydrogen into account. When formulating the heat treatment process, you can refer to the TTT, CCT and hardenability curve of same steel grade. Meanwhile, we should also take the influence of uneven chemical composition, coarse grains and other casting defects into account.
Precautions for the heat treatment of large steel castings
Suitable temperature adjustment.
Due to large volume and tonnage, large steel castings simply form large internal and external temperature differences and stress during heat treatment. Therefore, we should pay attention to its heating and cooling rate. This can largely reduce the temperature difference and stress of steel castings.
To ensure excellent circulation of the furnace gas.
When installing the furnace, the casting should be placed on the horn of appropriate height. The placement of the horn should ensure excellent circulation of the furnace gas and prevent the deformation of the casting. For important large castings, a sketch of the furnace installation should be made to specify the technical requirements, and indicate the orientation of the thermocouple when drawing an external thermocouple.
It is necessary to stress relief after heat treatment.
Large-scale castings (except high-manganese steel) should relief stress after heat treatment, welding repair, correction, machining, and cutting riser waiting.
After heat treatment, too many cuts are not allowed.
Yide casting has rich experience in heat treatment of casting, with 27 years’ experience. If you have any problem with iron casting, brass casting, or steel casting, or you are looking for an experienced casting manufacturer in China, please don’t hesitate to contact us for more details.