According to the simulation results of the gear box, the prototype is trial-produced. The mechanical properties, metallography, magnetic particle inspection and radiographic inspection of the trial-produced ductile iron castings meet the requirements of the technical conditions. The chemical composition of the material is shown in Table 1, the mechanical properties are shown in Table 2, the metallographic structure and hardness are shown in Table 3, and the finished product drawing is shown in the figure. It can be seen that the mechanical properties and metallographic structure of gear box ductile iron castings meet the technical requirements.
| Texture of material | C | Si | Mn | P | S | Mg | Re |
| QT400-18L | 3.71 | 2.18 | 0.18 | 0.025 | 0.008 | 0.040 | 0.020 |
| Texture of material | Tensile strength Rm/MPa | Elongation after fracture A/% | Specified plastic extension strength Rp0.2/MPa | Impact absorption energy at -40 ℃ Kv2/J |
| QT400-18L | 412 | 286 | 24.8 | 15 15 14 |
| Texture of material | Graphite condition | Matrix structure | Brinell hardness (HBW5/750) |
| QT400-18L | 85%VI6/7+15%V6/7 | Ferrite | 152 |
(1) By controlling the composition and quality of pig iron, scrap steel and return charge, the mechanical properties and metallographic structure requirements of the material are ensured by adopting the pitting spheroidizing process of rare earth magnesium spheroidizing agent and the three-time inoculation process.
(2) Semi-closed bottom pouring process, upper and lower small sprues, large cross sprue, flat inner sprue and other process measures have effectively reduced the occurrence of slag inclusion, air entrainment and other defects in ductile iron castings.
(3) Based on Magma simulation calculation, the riser and chill are reasonably designed to control the solidification temperature field of ductile iron castings, and the qualified ductile iron castings with dense interior are obtained.