Preheating is a key process to ensure the welding repair performance and quality of steel castings. The preheating temperature required for the weld repair area should be determined based on factors such as the material of the steel casting to be repaired and the ambient temperature of the welding site. The recommended preheating temperatures for welding repair areas of different steel casting materials are shown in the table, and the preheating temperatures for welding repair of steel castings of other materials can be determined by reference.
| Cast steel grade | Heat treatment status | General defects (℃) | Major defects (℃) |
| ZG230-450 | As-cast state | ≥ 5 | ≥ 150 |
| Grade B steel ZG310-570 | As-cast state | ≥ 5 | ≥ 150 |
| Grade C steel | Normalizing | ≥ 100 | 200 ～ 250 |
| Grade C steel | Quenching and tempering treatment | ≥ 180 | 200 ～ 250 |
| Grade E steel ZG25MnCrNiMo | Quenching and tempering treatment | ≥ 180 | 200 ～ 250 |
For steel castings that require preheating treatment before welding repair, overall preheating is preferred, such as using a resistance furnace for overall heating; When the overall preheating method is limited, or the local preheating method can be used, the preheating range shall extend at least three times the width of the weld section thickness to both sides of the weld.