Heat Treatment Process of Cemented Carbide Balls

The heat treatment process of cemented carbide balls is mainly used to optimize their properties, such as improving hardness, wear resistance and fatigue resistance, while ensuring dimensional accuracy and surface quality.

1. Material Properties of Cemented Carbide Balls

Cemented carbide balls are usually made of tungsten carbide (WC) and binders such as cobalt (Co) through powder metallurgy. Its heat treatment process is different from that of ordinary steel, and is mainly concentrated in the sintering and subsequent heat treatment stages to adjust the microstructure and properties.

2. Main Heat Treatment Process Flow

The heat treatment process of cemented carbide balls usually includes the following steps:

(1) Powder preparation and molding

Raw material ratio: Select the appropriate ratio of tungsten carbide and cobalt according to the application.

Pressing molding: Press the powder into a ball blank by cold isostatic pressing or die pressing to ensure uniform initial density.

(2) Pre-sintering

Purpose: To remove the binder added during the molding process (such as paraffin or polyvinyl alcohol) and to initially enhance the strength of the blank.

Process parameters:

Temperature: 400-600°C (depending on the type of binder).

Atmosphere: Usually carried out in a hydrogen or vacuum environment to avoid oxidation.

Time: 1-2 hours, slowly increasing the temperature to prevent cracking.

(3) High-temperature sintering

Purpose: To densify the cemented carbide ball blank and form a microstructure with high hardness and high strength.

Process parameters:

Temperature: 1350-1500°C (adjusted according to the alloy composition).

Atmosphere: Vacuum sintering or low-pressure sintering (HIP, hot isostatic pressing) to reduce pores and defects.

Time: 1-3 hours, depending on the size of the ball blank and the type of furnace.

Cooling: Control the cooling rate to avoid cracks caused by thermal stress.

(4) Hot isostatic pressing (HIP, as needed)

Purpose: Further eliminate internal micropores and improve density and mechanical properties.

Process parameters:

Temperature: 1300-1400°C.

Pressure: 100-200 MPa.

Atmosphere: Argon or other inert gas.

Time: 1-2 hours.

Applicable scenarios: Especially important for high-precision, high-performance cemented carbide balls (such as those used in precision bearings or valves).

(5) Post-treatment (optional)

Low-temperature tempering: Performed at 200-400°C to eliminate residual stress and enhance toughness.

Surface treatment: Improve surface finish and dimensional accuracy through grinding or polishing.

Coating treatment: Such as PVD or CVD coating (such as TiN, TiC) to further improve wear resistance and corrosion resistance.

3. Key Process Control Points

Temperature control: The temperature must be precisely controlled during high-temperature sintering. Too high a temperature may cause grain growth and reduce hardness; too low a temperature may result in insufficient density. Atmosphere Protection: A vacuum or inert gas (such as argon) environment is crucial to prevent oxidation and carbon content changes.

Cooling Rate: Rapid cooling can lead to thermal stress cracking, so the cooling curve must be optimized based on the ball diameter and material properties.

Dimensional Accuracy: Carbide balls shrink during sintering, which must be compensated for in mold design and process parameters.

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