Temperature of Molybdenum rolling and Annealing

-Key to the Successful Processing of Molybdenum and its Alloys

Molybdenum Rolling and Annealing Temperature

The complexity of molybdenum rolling, with the unique properties of the metal and its alloys, is formidable. It demands deep knowledge and exacting attention to detail at every point in a multi-stage process. Moly and moly-alloyed metals have high melting points, significant resistance to deformation, and an equiaxed grain structure that make them susceptible to low-temperature brittle fracture. For these and other reasons, precise rolling and annealing temperature management is essential to the successful processing of these materials.

Challenges of Low-Temperature Molybdenum Rolling

When rolling molybdenum sheets at low temperatures, the metal’s high deformation resistance can lead to complications, including development of internal micro-cracks. In extreme cases, the moly sheet may fracture completely. Moreover, complications intensify as rolling temperatures decrease due to elongation of grains in the direction of the roll. If the rolling temperature falls below the recrystallization temperature, the molybdenum sheet may adopt a banded cell structure. This phenomenon imparts anisotropy to the microstructure, potentially impeding further processing and the finished product’s suitability for intended purposes.

Challenges of High-Temperature Molybdenum Rolling and Temperature Management

Temperature optimization during molybdenum’s pre-form rolling stage is crucial, often requiring an increase in rolling temperature up to, and sometimes beyond, the metal’s recrystallization temperature. This helps achieve optimal yield rate—an advantage that becomes apparent as the material thins. As rolling advances, deformation amplifies and self-stored energy builds, effectively lowering the recrystallization temperature of the rolled parts. Controlled decreases of rolling temperature in the subsequent hot, warm, and cold rolling stages thus becomes a necessity. Meticulous control of rolling temperatures across all stages of the process is essential to quality and performance of the product.

Appropriate Annealing Temperature in Molybdenum Rolling Production

In molybdenum rolling production, the specific characteristics of different molybdenum/alloy materials determines the appropriate annealing process. The correct annealing treatment manifests as temperature rises, tensile strength and micro hardness decrease, and the elongation rate increases. The preservation of recovered grains significantly enhances the product’s mechanical properties, such as tensile strength and elongation rate, which facilitate subsequent rolling and deep processing.

Conversely, setting an incorrect annealing temperature can increase the likelihood of crystal defects in the metal. During low-temperature recovery, the movement of point defects significantly reduces their density. In contrast, during moderate and high-temperature recovery, the movement of linear defects, known as lattice dislocations, causes polygonization, accompanied by the slip and climb of the grains. The result is a decrease in dislocation density and sub-grains in the microstructure. As the temperature continues to rise, the molybdenum material undergoes a recrystallization transformation.

Pure molybdenum sheets have a lower recrystallization temperature than molybdenum alloy sheets. To prevent excessive grain growth, the annealing temperature for pure moly sheets is set lower. Balancing annealing temperature is critical to producing high-quality products with optimum mechanical properties.

The precise, highly technical process of molybdenum rolling is fundamentally an exercise in meticulous rolling and annealing temperature regulation. The understanding of and capability to applying this regulation is required to achieve desired results to customer specifications when working with these exceptional materials.