1. Mechanical properties: the influence of quenching temperature.The normal quenching and heating temperature of GCr15 steel is 830-860℃, and it is cooled with oil. The optimal quenching temperature is 840℃, and the hardness after quenching reaches 63-65HRC.Under the actual production conditions, the quenching temperature can be slightly different depending on the effective section size of the die and the quenching medium.For molds with larger size or with nitrate graded quenching, a higher quenching temperature (840-860℃) should be selected in order to improve hardenability and obtain sufficient depth of hardening layer and higher hardness;Smaller size or oil-cooled molds are generally used at a lower quenching temperature (830-850℃).For skH51 of the same specification, the heating temperature in the box furnace should be slightly higher than that in the salt bath furnace.Effect of tempering temperature.As tempering temperature increases, the hardness decreases after tempering.When the tempering temperature exceeds 200℃, it will enter the first type of tempering brittle zone.Therefore, the tempering temperature of GCr15 steel is generally 160-180℃.
2. Process performance: forging.GCr15 steel has good forging performance and wide forging temperature range.The forging process specifications are generally as follows: 1050-1100℃, initial forging temperature 1020-1080℃, final forging temperature 850℃, air cooling after forging.The forged tissue should be a fine lamellar pellet, which can be spheroidized without normalizing.Is the fire.The normal heating temperature of GCr15 steel is generally 900-920℃, and the cooling speed should not be less than 40-50℃/min.Small molds can be cooled in still air;Larger molds can be blown or sprayed without cooling;Large molds with a diameter of more than 200mm can be cooled in hot oil until the surface temperature is about 200℃ and then taken out for air cooling.The internal stress formed by the latter cooling method is large and easy to crack. Spheroidizing annealing or stress relieving annealing procedure should be carried out immediately.Spheroidizing annealing.The spheroidizing annealing process specification for GCr15 steel is generally as follows: heating temperature 7700-790℃, holding temperature 2-4h, isothermal temperature 690-720℃, isothermal time 4-6h.After annealing, the microstructure is fine and uniform spherical pearlite with a hardness of 217-255HBS and good cutting performance.
The hardenability of GCr15 steel is better than skH9 (the critical quenching penetration diameter of oil is 25mm), and the depth of the hardening layer obtained in the case of oil quenching is similar to that of the carbon tool in the case of steel quenching.