The key to preparing materials that maintain a fine-grained structure at high temperatures lies in introducing fine, dispersed second-phase particles to pin grain boundaries and controlling processing and heat treatment to prevent abnormal grain growth during high-temperature service.
1. Metallurgical and Compositional Design: Adding Microalloying Elements
Ti, Nb, V, Al: Adding these elements during the smelting process forms highly stable carbides (such as TiC, NbC, VC) or nitrides (AlN), which precipitate during solidification and heating, effectively pinning grain boundaries.
W, Mo: Improve the red hardness and temper softening resistance of steel. Their carbides remain stable at high temperatures, hindering grain boundary migration.
Practical Recommendation: Select microalloyed or inherently fine-grained steels such as H13+Ti and Al-Killed H13, ensuring that the content of key elements meets standards (e.g., Ti >= 0.015%, Al >= 0.02%).
2. Powder Metallurgy Process: Obtaining Ultrafine Original Microstructure
PM-H13, ASP-23: Through gas atomization powder preparation + hot isostatic pressing (HIP) molding, segregation in traditional ingots is avoided, resulting in a uniform microstructure with an original grain size of 8-10.
Advantages: Dispersed carbide distribution, good isotropy, and significantly superior resistance to grain growth compared to traditional cast and forged steel.
Applications: High-precision injection molds in medical and optical applications, improving fatigue life by over 30%.
3. Thermomechanical Processing Control: Refining Grain Size
Controlled Rolling and Cooling (TMCP): During forging or rolling, the deformation temperature and cooling rate are controlled, allowing for multiple deformations in the austenite region, promoting dynamic recrystallization and refining the grain size.
Isothermal Annealing + Rapid Cooling: Slow furnace cooling is avoided; air cooling or wind cooling is used, shortening the high-temperature residence time and inhibiting grain agglomeration and growth.
Contraindications: Slow cooling or prolonged high-temperature holding is prohibited to prevent secondary recrystallization that could lead to abnormal coarsening.
4. Surface and Composite Structure Design (Cutting-Edge Direction)
Ceramic Matrix Composites (CMCs): Such as SiC/SiC, Al₂O₃/ZrO₂, which do not have grain growth issues and can withstand temperatures exceeding 1400℃, making them suitable as nozzle liners;
Metal-Ceramic Composite Structures: Embedding ceramic cores or coatings within a metal matrix to improve localized high-temperature stability.
