About Nitrate quecnhing
Nitrate Bath Quenching
Nitrate bath quenching is a metal heat treatment process in which a workpiece, after being austenitized by heating, is immersed into molten salt liquid at a specific temperature for rapid cooling (quenching) to achieve the required microstructure and properties.
1. Core Principle
• Medium: Molten salt (such as chloride, nitrate mixture) is used as heating/cooling medium.
• Process:
1. The workpiece is heated quickly and uniformly to quenching temperature in salt bath (isolated from air to prevent oxidation and decarburization).
2. Quickly transferred to low-temperature salt bath (for marquenching/isothermal annealing) or cooled directly in salt bath.
3. The controllable cooling rate of salt bath (between water and oil) is used to reduce deformation and cracking.
2. Main Types
• Marquenching (Grade Quenching): Insulated in salt bath above Ms point (martensite start temperature), cooled uniformly then air-cooled.
◦ Application: Complex and thin-walled parts (tools, dies), minimal deformation.
• Isothermal Quenching (Bainite Quenching): Long-term insulation in salt bath near Ms point, austenite directly transformed into bainite.
◦ Features: High hardness + high toughness, excellent comprehensive performance.
3. Main Advantages
• Small deformation, low cracking risk: uniform cooling,