Selection of process parameters for induction heating elbow tempering treatment

The tempering treatment of the bent pipe is completely carried out by traditional heating process. The selection of parameters such as tempering temperature, holding time and tempering cooling method are all based on obtaining better overall performance.

(1) The relationship between tempering temperature and strength

When the tempering treatment temperature is between 600 and 650°C, the obtained yield strength value is the largest, and decreases when it exceeds 650°C. The tensile strength reaches its highest value when tempered at 600°C and begins to decrease above 600'C. According to the relationship between strength and tempering temperature, in order to make the yield strength and tensile strength meet the standard requirements, the tempering temperature should be selected between 600 and 650°C.

(2) Relationship between tempering temperature and low temperature impact toughness

At all tempering temperatures (all held for 60 minutes), the impact energy values are higher than the standard value. This phenomenon shows that the test steel itself does not have temper brittleness and has a very low brittle transition temperature. Therefore, low-temperature toughness does not need to be considered when determining the tempering temperature.

(3) Tempering holding time and tempering cooling method

During tempering, the carbide phase has fully precipitated and the strength has reached its peak (600~650℃). After exceeding this temperature, the carbide begins to coarsen and the strength begins to decrease. This phenomenon reflects that the 60min tempering holding time is sufficient. From the relationship curve between the tempering temperature and low-temperature impact toughness of steel, it can be seen that this steel type does not have low-temperature brittleness and temper brittleness. Therefore, air cooling can be used after tempering treatment.

To sum up, the tempering treatment process of elbows can adopt a tempering temperature of 600~650℃, and then air cooling after 60 minutes of heat preservation.