1. Material requirements
The steel casting product is made of medium carbon medium chromium alloy steel. The chemical composition requirements are shown in Table 1, and the mechanical properties requirements are shown in Table 2.
| Component | C | Cr | Mn | Si | So | S | P |
| Content | 0.5~0.7 | 4.0~5.5 | 0.5~1.0 | 0.5~0.8 | 0.4~0.6 | ≤0.025 | ≤0.025 |
2. Smelting process
The melting temperature of molten steel shall be controlled between 1570 ℃ and 1590 ℃, and it shall be slightly killed after being discharged. The pouring temperature should be controlled between 1460 ℃ and 1490 ℃. Theoretically, it is better to lower the pouring temperature. If the pouring temperature is too high, secondary slagging is easy to occur, and defects such as shrinkage cavity, shrinkage porosity and air hole are easy to appear in the steel castings. Although the fluidity of the material is good, the temperature drops quickly. When there is oxide film on the surface, it is too late to operate properly. On-site observation found that when the oxide film was about to come out (the dotted film appeared at the edge of the ladle first), the pouring should be carried out immediately. In other words, on the premise that the steel castings do not produce cold shut defects, the pouring temperature should be appropriately lower. In the production practice, we should constantly summarize our experience and master the control of the furnace temperature and pouring temperature.
Aluminum with a mass fraction of about 0.15% and rare earth with a mass fraction of about 0.35% are washed into the furnace for deoxidation and modification.
The steel castings shall be unpacked when they are cooled to below 250 ℃ in the mold. The pouring riser is brittle and can be smashed during cleaning.
3. Heat treatment process and mechanical properties of steel castings
Quenching process of steel castings: heating to 930 ℃ for 2 h~3 h, quenching out of furnace (air cooling in winter, spray cooling in summer). Tempering process: lower than 150 ℃ into the furnace, heating to 300 ℃~350 ℃ for 2 h~2.5 h, and air cooling out of the furnace. The performance requirements after heat treatment are shown in Table 2.
| State | Hardness (HRC) | Impact value/J · cm^-2 | Tensile strength/MPa |
| As-cast state | 49.5 | 9.5 | — |
| Heat treatment | 52~55 | 19~25 | 1 400~1 600 |
4. Use of metallographic structure and material
The metallographic structure of the material after heat treatment is tempered martensite+lower bainite+broken point carbide. The hardenability of this material is good, and the lining plate with a thickness of 70 mm can be fully hardenable. The wear resistance of the steel castings produced by this material is three times higher than that of high manganese steel after the installation test.