1. Nitriding

• Principle: The die is placed in a nitrogen - containing medium at 500 - 600 °C. For hot work die steel, ammonia decomposes to release nitrogen atoms, which diffuse into the die surface and form nitrides with alloying elements.

• Advantages: The nitriding layer has high hardness, improving wear resistance. It also offers good corrosion resistance and minimal die deformation, crucial for high - precision dies.

• Application: Widely used in die - casting and plastic molds. For die - casting aluminum alloy molds, nitriding enhances mold cavity wear and corrosion resistance, extending die life.

2. Carburizing

• Principle: The die is heated in a carbon - rich medium at 900 - 950 °C. Gas (using methane, propane) or solid carburizing methods are common. Carbon atoms diffuse into the die surface, forming a high - carbon layer.

• Advantages: Greatly improves die surface hardness and wear resistance. The core maintains toughness, allowing the die to withstand complex stress.

• Application: Mainly for cold working dies under heavy load and impact, like cold - heading and cold - extrusion dies. Cold - heading dies need to resist high impact and friction, and carburizing meets this need.

3. Hardening Film Deposition

• Physical Vapor Deposition (PVD)

• Principle: In a vacuum, the source material is evaporated or sputtered and deposited on the die surface. For ion plating (a PVD method), argon gas is ionized, the die surface is cleaned and activated, and metal or compound films (e.g., TiN, ZrN) are deposited.

• Advantages: High - hardness, wear - resistant films with strong adhesion to the die matrix. Low - temperature deposition results in minimal die deformation, and film thickness and composition can be precisely controlled.

• Application: Used in precision molds like injection molds. For molds injecting high - hardness plastics, PVD - deposited TiN film improves release and wear resistance.

• Chemical Vapor Deposition (CVD)

• Principle: A chemical reaction occurs on the die surface using gaseous precursors. For SiC film deposition, silane and methane decompose and react on the die surface at 800 - 1200 °C with a catalyst.

• Advantages: Deposits a uniform, dense film on complex - shaped dies. The film has high quality, hardness, wear, and corrosion resistance, and can be customized with various components.

• Application: For molds with high film - quality requirements and harsh working conditions, such as hot working molds. CVD - deposited high - temperature - resistant films protect the die surface.

4. Polishing

• Manual Polishing: Operators use sandpaper and stones, starting with coarse (80 - 120 mesh) to remove marks and burrs, then finer sandpaper, and finally polishing paste with a wool wheel. It's flexible but has low efficiency and high operator - skill requirements.

• Mechanical Polishing: A polishing machine drives a polishing wheel with polishing paste. It's more efficient than manual polishing and can achieve better surface finish. Cloth polishing wheels are used for high - gloss requirements.

• Electrolytic Polishing: The die, as the anode in an electrolyte, has its surface microscopic bulges preferentially dissolved under direct current, smoothing the surface. It can handle complex - shaped molds, like those with deep holes and narrow grooves.

5. Electroplating

• Chromium Plating: The die, as the cathode in a chromium - plating electrolyte (containing chromic acid), has chromium ions deposited on its surface. The chromium layer has high hardness, wear resistance, and chemical stability, improving mold release and wear resistance, and providing a good gloss.

• Nickel Plating: The die is placed in a nickel - ion - containing electrolyte. Nickel plating offers corrosion resistance, hardness, and decoration. Different nickel - plating processes yield different appearance and performance.

• Composite Plating: Solid particles (e.g., ceramic, diamond) are added to the plating solution and deposited with metal ions on the die surface. The composite coating combines metal's conductivity and machinability with particles' high hardness and wear resistance.

6. Laser Processing

• Laser Quenching: A high - energy - density laser beam scans the die surface, rapidly heating it to the quenching temperature and then cooling to form a martensitic structure. It's suitable for local surface strengthening of large dies, with fast heating, minimal deformation, and the ability to handle complex surfaces.

• Laser Cladding: Pre - designed cladding material (metal powder) is fed to the die surface and melted with the die surface by a laser beam, then solidified. It can repair die - surface defects and improve surface performance, such as for die - casting mold surface wear.

7. Surface Coating

• Polytetrafluoroethylene (PTFE) Coating: PTFE has a low friction coefficient, good chemical stability, and high - temperature resistance. Coating die surfaces by spraying or dipping improves die release. It's used in injection and rubber molds, especially for viscous plastics.

• Diamond - like (DLC) Coating: DLC is a carbon - based coating with diamond - like properties. Deposited by PVD or CVD, it offers high hardness, wear resistance, and a low friction coefficient. It's used for molds with high - hardness and wear - resistance requirements.

• Ceramic Coating: Ceramic coatings (e.g., alumina, zirconia) have high hardness, high - temperature resistance, and corrosion resistance. Thermal - sprayed ceramic coatings improve die performance in harsh environments, such as enhancing hot - working mold thermal fatigue and oxidation resistance.