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Molybdenum slab is a semi-finished plate material formed by subjecting molybdenum metal to specific processing techniques, such as rolling or forging for subsequent plastic processing. Below is a detailed introduction:

I. Definition and Properties

1. Definition: Molybdenum slab is a semi-finished plate material with a specific shape, size, and internal structure, obtained through preliminary processing (such as forging or pre-rolling treatment) after molybdenum metal has undergone melting, casting, or powder metallurgy processes. It serves as an important raw material for producing molybdenum plates, molybdenum foils, and other molybdenum products.
2. Properties:
   • High Melting Point: Molybdenum has a melting point as high as 2620℃, enabling molybdenum slabs to maintain stable physical and chemical properties under high-temperature environments.
   • High Strength: Molybdenum slabs possess high tensile strength and yield strength, allowing them to withstand significant external forces without undergoing deformation or fracture.
   • Excellent Thermal and Electrical Conductivity: Molybdenum slabs exhibit outstanding thermal and electrical conductivity, making them suitable for applications requiring efficient heat or electrical conduction.
   • Corrosion Resistance: Molybdenum slabs demonstrate good resistance to various acids, alkalis, and salts, enabling long-term use in harsh chemical environments.

Causes of Layering

1. Improper Rolling Process Parameters:
   • Insufficient Reduction: When the reduction is less than 20%, the surface of the molybdenum slab undergoes deformation, while the central layer remains undeformed, leading to differences in mechanical properties across metal layers and subsequent layering.
   • Low Rolling Temperature: During low-temperature rolling, the deformation resistance of the molybdenum slab increases, resulting in an uneven rolling process and a tendency to layer. Additionally, low-temperature rolling may cause recrystallization brittleness, further exacerbating the layering tendency.
   • Single Rolling Direction: Unidirectional rolling (such as full longitudinal or full transverse rolling) leads to anisotropy in the molybdenum slab, with a fibrous microstructure along the rolling direction. This type of microstructure exhibits poor strength and plasticity in the perpendicular direction, making it prone to layering.
2. Slab Quality Issues:
   • Internal Defects: The presence of voids, cracks, or other defects within the molybdenum slab can act as crack initiation sites during the rolling process, leading to layering.
   • Uneven Powder Particle Size: For molybdenum slabs produced through powder metallurgy, uneven powder particle size or improper sintering processes can result in a loose internal structure of the slab, increasing the risk of layering.
3. Rolling Equipment Problems:
   • Uneven Roll Wear: Uneven wear on the rolls can lead to uneven distribution of rolling forces, causing uneven deformation of the molybdenum slab during rolling and subsequent layering.
   • Abnormal Equipment Operation: Abnormal equipment operation can result in vibrations or impacts during the rolling process, imposing additional stress on the molybdenum slab and increasing the risk of layering.

Solutions

1. Optimizing Rolling Process Parameters:
   • Increasing Reduction: During the initial stages of rolling, a larger reduction (generally greater than 20%-25%) should be employed to ensure uniform deformation across the entire cross-section of the molybdenum slab. This helps eliminate the undeformed central layer and reduces the risk of layering.
   • Raising Rolling Temperature: Appropriately increasing the rolling temperature can reduce the deformation resistance of the molybdenum slab, resulting in a more uniform rolling process. However, care should be taken to avoid recrystallization brittleness caused by high-temperature rolling. For example, increasing the first-pass rolling temperature during hot rolling from 1200℃ to 1250℃.
   • Adopting Cross Rolling: Cross rolling can alter the deformation direction of the molybdenum slab, helping to eliminate anisotropy and improve the overall performance of the plate. Through cross rolling, more uniform deformation can be achieved in the thickness direction of the molybdenum slab, reducing the tendency for layering.
2. Improving Slab Quality:
   • Optimizing Powder Metallurgy Process: Select molybdenum powders with uniform particle size and good morphology for pressing and sintering to enhance the density and uniformity of the slab’s microstructure. Optimize sintering process parameters (such as temperature and time) to ensure a dense, defect-free internal structure in the slab.
   • Strengthening Slab Inspection: Conduct quality inspections (such as ultrasonic testing and metallographic examination) on the molybdenum slab before rolling to promptly identify and address internal defects, preventing defective slabs from entering the rolling process.
3. Maintaining Rolling Equipment:
   • Regularly Inspecting Rolls: Regularly inspect the wear condition of the rolls and promptly replace severely worn rolls to ensure uniform distribution of rolling forces.
   • Ensuring Normal Equipment Operation: Strengthen equipment maintenance and upkeep to ensure normal equipment operation, avoiding vibrations or impacts during the rolling process that could impose additional stress on the molybdenum slab.
4. Other Auxiliary Measures:
   • Recrystallization Annealing Treatment: Subjecting the rolled molybdenum plate to recrystallization annealing treatment can eliminate internal stresses and result in more uniform plate properties. The annealing temperature and time should be reasonably selected based on the material and thickness of the molybdenum plate.
   • Surface Cleaning and Protection: Clean the surface of the molybdenum plate (such as through alkali washing or sandblasting) to remove surface oxide layers and impurities, improving surface quality. During handling and storage, protect the surface of the molybdenum plate from scratches and impacts.