Due to their high hardness, high wear resistance, high compressive strength, and excellent bending resistance, tungsten cemented carbide balls are widely used in key applications such as high-load precision bearings, oilfield valve ball seals, and high-temperature mold components. Their strength characteristics stem from the combined effects of material composition, microstructure, and process control, as analyzed below:
I. The Determining Role of Material Composition and Microstructure on Strength
1. Strengthening Effect of Tungsten Carbide (WC) Grains
WC grains are the "skeleton" of carbide, and their size significantly affects strength. Generally, finer grains increase the grain boundary area, leading to more complex crack propagation paths and significantly improved fracture toughness.
Grain refinement also enhances hardness through the "dispersion strengthening" mechanism. However, excessive grain refinement may lead to abnormal grain growth, which in turn reduces strength.
2. Plastic Adjustment of the Binder Phase (Cobalt/Nickel)
Cobalt (Co) or nickel (Ni) acts as a binder, hindering crack propagation through plastic deformation at low temperatures and improving flexural strength. At high temperatures, the cobalt phase softens, but plastic deformation of the carbide skeleton becomes dominant, resulting in a relatively small decrease in high-temperature strength.
The relationship between cobalt content and strength generally exhibits an inverted U-shaped relationship: too low a cobalt content (such as YG3) may lead to increased brittleness; too high a cobalt content (such as YG20) improves toughness but reduces hardness. Among typical grades, YG6 (6% cobalt content) achieves a relatively high flexural strength (approximately 2200-2500 MPa), offering excellent overall performance.
3. Solid Solution Strengthening with Titanium Carbide (TiC)
In YT-type cemented carbides, TiC forms a solid solution with WC, strengthening the carbide skeleton and improving high-temperature strength.
II. The Critical Impact of Process Control on Strength
1. Optimizing the Sintering Process
Vacuum sintering or hot isostatic pressing (HIP) can effectively eliminate porosity and increase density, thereby significantly enhancing compressive strength and fatigue resistance.
Sintering temperature requires precise control: too low a temperature may result in insufficient bonding; too high a temperature may cause grain coarsening and reduce strength.
2. Enhancing the Effectiveness of Surface Treatment Technologies
Grinding and polishing can reduce surface roughness, reduce stress concentration points, and improve flexural strength.
Coating technologies (such as TiN and TiAlN) can further extend fatigue life by isolating corrosive media.
III. Quantitative Performance of Strength Properties
1. Compressive Strength
The compressive strength of tungsten cemented carbide balls typically reaches 6000-7000 MPa, significantly higher than that of ordinary steel balls (approximately 3-5 times that of ordinary steel balls).
2. Flexural Strength
Typical grades have a flexural strength range of: YG3 (approximately 2500-2800 MPa) > YG6 (approximately 2200-2500 MPa) > YG8 (approximately 2000-2300 MPa). YT grades, due to TiC reinforcement, generally have slightly higher flexural strength than YG grades with the same cobalt content.
3. High-Temperature Strength Stability
Below 500°C, hardness remains virtually unchanged; at 1000°C, hardness remains high (HRA73-76, equivalent to HB430-477), far exceeding that of high-speed steel (which may drop below HRC50 at 600°C).
IV. Applications of High-Strength Tungsten Cemented Carbide Balls 1. High-Load Precision Bearings
YG6 or YT15 are typically selected, leveraging their high compressive and flexural strengths to withstand dynamic loads under high-speed rotation. 2. Oilfield Valve Ball Seals
YG8, due to its high cobalt content, offers both high bending strength and impact resistance, making it suitable for high-pressure, corrosive environments downhole.
3. High-Temperature Mold Accessories
YT-type cemented carbide balls offer high heat resistance and are suitable for high-temperature applications such as die-casting molds and hot extrusion molds.
