3Cr2Mo is a plastic die steel widely used in the world. It has good comprehensive mechanical properties and high hardenability, which can make large section steel obtain uniform hardness, good polishing performance and high die surface smoothness. Generally, this steel is quenched and tempered with a hardness of HRC28~35 (i.e. pre-hardening), and then cold-worked as a mold, which can be used directly. This not only ensures the performance of the die, but also avoids the deformation of the die caused by heat treatment. Therefore, this kind of steel is suitable for manufacturing. Suitable for medium and precision plastic molds and die casting molds with low melting point of tin, zinc and lead alloys.

Chemical composition:

Si-Mn-P-S-Cr-Mo-Ni

0.28-0.4 0.2-0.8 0.6- 1 ≤0.03 ≤0.03 1.4-2 0.3-0.55 0.85- 1. 15

Physical properties:

1) Density: 7.3 1g/cm3.

2) linear expansion coefficient: temperature18 ~100℃/18 ~ 200℃/18 ~ 300℃//kloc-0 ~ 400℃//8. kloc-0//0 13. 1 1× 10-6K- 1/ 10-6K- 1/ 13.7 1× 10-6K- 1

3) Elastic modulus: (20 C) 212000 MPa, shear modulus? (room temperature) is 825000MPa, and Poisson's ratio is 0.288.

4)? Thermal conductivity: temperature 20℃/ 100℃/200℃/300℃/400℃, thermal conductivity 36.0 [w/(m k)]/33.4 [w/(m k)]/31.4]

Hardness treatment:

In order to improve the service life of the die to more than 800,000 times, the pre-quenched steel can be quenched and tempered at low temperature. When quenching, preheat at 500-600℃ for 2-4 hours, then keep the temperature at 850-880℃ for a certain time (at least 2 hours), put it in oil and cool it to 50- 100℃, and the hardness after quenching can reach 50-5248HRC. In order to prevent cracking, tempering at 200℃ should be carried out immediately, and the hardness can be maintained after tempering.