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Crack Analysis and Solutions for Mining Machinery Rack Front Seat
The rack front seat is a key load-bearing component in mining machinery. This study analyzes flange cracks in a 3.5t GS‑25CrMo4 alloy steel casting, identifies hot cracking caused by oxide bi‑films and inclusions, and provides effective process improvements.
1. Basic Part Information
- Part name: Mining machinery rack front seat
- Material: GS‑25CrMo4 alloy steel
- Weight: 3.5 t
- Wall thickness: 50–65 mm
- Crack location: flange area (near gate and riser)
2. Test and Analysis Methods
- Sample size: 20 mm × 20 mm × 20 mm
- Optical microscope (OM) and FESEM
- EDS energy spectrum analysis
- Metallographic corrosion: 4% nitric alcohol
3. Key Test Results
- Obvious decarburization layer on both sides of the crack
- Maximum effective decarburization depth: 846.1 μm
- Crack is intergranular hot crack with oxidized brown appearance
- A large number of oxide inclusions at crack: 20–400 μm
| Element | Mass Fraction (%) |
|---|---|
| Fe | 68.69 |
| O | 28.65 |
| Na | 1.04 |
| Ca | 1.01 |
| Mn | 0.61 |
4. Root Cause of Cracking
- Crack type: hot cracking during solidification
- Main source: oxide bi‑films with inclusions
- Internal inclusions: Fe₂O₃, MnO
- External inclusions: Na₂O, CaO (from slag)
- Shrinkage stress + grain boundary weakness → crack initiation
- Slow cooling near riser promotes crack growth
5. Effective Solutions
- Optimize gating and riser layout; move riser 35 mm inward
- Enlarge riser diameter to 300 mm for better feeding
- Add chromite sand at flange for chilling effect
- Use composite rare earth for deoxidation and refining
- Strengthen raw material control and slag management
- Improve operator skill and standardization
6. Field Application Result
- Over 180 pieces produced with improved process
- No similar hot cracks occurred
- Casting quality and stability significantly improved
7. Conclusion
- Flange crack is typical intergranular hot cracking
- Oxide bi‑films and inclusions are the main crack sources
- Process optimization and metallurgical improvement completely solve cracking
- The solution is reliable for large alloy steel mining castings
Summary
By analyzing oxide inclusions, decarburization layers, and solidification stress, the study confirms that oxide bi‑films induce hot cracks. Optimized casting and refining solutions effectively eliminate cracks and ensure stable production of heavy mining machinery components.