The strength level of large steel casting is similar to the forged steel casting, but the plasticity and toughness are poor, the internal structure is uneven and not dense, the deviation of internal chemical composition is larger, the thermal conductivity is poor, and the structure is complex. Therefore, in the heat treatment, special attention should be paid to the elimination of internal stress, to prevent cracking problems, but do not have to consider the hydrogen hazard. In the formulation of heat treatment process, it refer the same steel grade. However, the effects of uneven chemical composition, coarse grain and other casting defects must be noted.
Notes on large steel castings:
1. Large steel castings due to its large volume and weight, easy to cause the temperature difference between inside and outside .And large internal stress of the heat treatment, the heat treatment should pay attention to the heating and cooling speed,it can reduce the temperature difference between the steel castings and reduce the stress.
2. Furnace,the steel castings should be placed at the proper height and it should ensure that the furnace gas has good circulation and avoid deformation of steel castings. For the important large castings, the draft of the furnace shall be drawn up and the technical requirements shall be specified. When the external thermocouple is indicated, the position diagram shall be drawn.
3. Large steel castings (except high manganese steel casting and other materials) after heat treatment,welding, correction, machining, cutting riser etc must be carried out to deal with stress.
4. After heat treatment, does not allow a large number of cutting.