High-speed steel composite rolls are widely used in hot continuous rolling finishing mill units due to their excellent hardness, wear resistance, and thermal stability. However, in the practical application of a certain steel plant, a large-scale peeling phenomenon occurred on the surface of the rolls, resulting in steel stacking accidents and production disruptions. This paper combines the measured data and failure analysis to explore the causes of spalling and puts forward improvement suggestions, providing a reference for the industry.
Description of Failure Conditions
This steel plant uses high-speed steel composite rolls with a specification of ϕ805mm×700mm. During the rolling process of DC01 low-carbon steel, large-scale spalling occurred on the drive side of the rolls. The spalling area accounts for approximately 1/6 of the entire working surface. The cracks start from the junction of the middle layer and the core and expand along the radial and axial directions, eventually leading to the fragmentation and scraping of the roller surface.
Composition and Performance Analysis
1. Chemical composition
After analyzing the three layers of materials of the flaking fragments, it was found that:
The composition of the surface high-speed steel complies with the standard.
The composition of ductile iron in the middle layer and the core basically meets the design requirements, but the carbon content is slightly lower.
2. Hardness and strength
Measured average hardness:
Surface layer: 80.0 HS (conforming to the standard).
Middle layer: 58.5 HS.
Heart part: 33.0 HS (slightly lower than the manufacturer’s requirements).
Tensile tests show that the tensile strength of the middle layer is relatively low and it is prone to become the crack initiation area.
Analysis of the Causes of Peeling
Improper control of the casting process.
During the third centrifugal pouring, the pouring time control of the middle layer was unreasonable, resulting in:
Poor interface integration.
Local loose holes.
The thickness of the high-speed steel layer is insufficient or the adhesion is weak.
The purity of the ductile iron liquid is insufficient.
The core contains high levels of harmful gases such as oxygen and nitrogen. During the solidification process, inclusions float up, forming an inclusion-enriched zone at the junction of the middle layer and the core, which severely weakens the interfacial bonding strength.
The distribution of carbides is unreasonable
There are large-sized brittle carbides near the interface, which are prone to become crack propagation channels and accelerate the failure process.
Suggestions for Improvement.
To prevent similar failures from happening again, the following measures are recommended:
- Optimize the casting process.
- Precisely control the pouring time and temperature of the intermediate layer.
- Ensure the metallurgical bonding quality among the three layers.
- Improve the purity of molten iron.
- Strengthen the deoxidation and denitrification in the smelting process;.
- Use more effective purification technologies to reduce the generation of inclusions.
- Optimize the heat treatment process.
- Refine the carbide structure.
- Improve the matching of toughness and strength between high-speed steel and the intermediate layer.
Conclusion
High-speed steel composite rolls are a key component with excellent performance, but their manufacturing process is complex, and interface bonding quality is crucial. This failure indicates that merely meeting the composition design is far from enough; it is also necessary to strictly control the pouring process and the purity of raw materials. By optimizing the production process and quality control measures, the service life of the rolls can be significantly prolonged, ensuring the stable production of the steel plant.
Contact us：cykc@cykcgroup.com.cn