Tungsten carbide balls, composed primarily of tungsten carbide and bonded with cobalt as a binder, are widely used in precision bearings, valves, and molds. Their high hardness and wear resistance are their core properties. Hardness reflects a material's ability to resist local deformation, with typical values ranging from 1500–2000 Vickers hardness (HV). The specific hardness is determined by the alloy grade (such as YG series tungsten-cobalt alloys or YT series titanium-cobalt alloys) and the sintering process. The following briefly describes hardness assessment from the perspectives of standards and test methods.
I. Hardness Standards for Tungsten Carbide Balls
The hardness assessment of tungsten carbide balls follows international and national standards, such as ISO 4498 (sintered metal materials) and China's GB/T 4340 (Vickers hardness), GB/T 230 (Rockwell hardness), and GB/T 231 (Brinell hardness). These standards specify test conditions and specimen requirements to ensure reliable results. The specimen surface must be polished to a roughness of Ra ≤ 0.8 μm to prevent defects from affecting the measurement.
1. Vickers hardness (HV): 1500–2000. Suitable for high-precision testing, it produces a small indentation and reflects surface or thin-wall properties.
2. Rockwell hardness (HRA): 85–93. Using a diamond indenter, it is suitable for rapid assessment of overall hardness.
3. Brinell hardness (HBW): 1400–1800. Due to the extremely high hardness of tungsten carbide balls, a large-diameter indenter is required to avoid indenter damage. Hardness values are affected by alloy composition. For example, the hardness of YG8 is approximately HRA 88–90, and that of YT15 is approximately HRA 89–91. Batch variation is controlled within ±5%. For actual application, refer to supplier data or calibration testing.
II. Hardness Testing Methods for Tungsten Carbide Balls
Carbide ball hardness testing primarily utilizes the indentation method. The Vickers method is preferred for its high precision, the Rockwell method is more efficient, and the Brinell method is less commonly used. Before testing, the specimen must be polished and the environment controlled (20±5°C, humidity <65%). Average values of 3–5 points are taken for each specimen. 1. Vickers Hardness Test Use a 136° face angle diamond square pyramid indenter. Apply a load of 0.05–1 kgf for 10–15 seconds. Measure the diagonal length d (μm) of the indentation and calculate it as HV = 1.854 F / d2. According to GB/T 4340.1-2009, the tolerance is ±2%. This method is suitable for testing thin, high-hardness layers. Microscopic measurement ensures accuracy. 2. Rockwell Hardness Test Using the HRA scale, apply a preload of 10 kgf, then a total load of 60–150 kgf. Using a diamond cone indenter, measure the indentation depth h and calculate HRA = 100–500 h. This method, held for 1–3 seconds, is suitable for batch testing and easy to use. 3. Brinell Hardness Test Using a carbide ball indenter (diameter 1–10 mm), apply a load of 3,000–30,000 kgf. Measure the indentation diameter d and calculate HBW = 2F / [π D (D - √(D2 - d2))], according to GB/T 231.1-2018. Tungsten carbide balls are rarely used due to their fragility. 3. Applications and Precautions The Vickers method is accurate but time-consuming, making it suitable for laboratory analysis; the Rockwell method is rapid and suitable for on-line monitoring. Hardness values are interchangeable using ISO 18265, for example, HV 1600 ≈ HRA 90. Testing requires clean specimens and a stable environment. To ensure reliability, it is recommended to entrust calibration to a national metrology institute and optimize the process based on alloy characteristics to meet the demands of high-load conditions.
