Performance of tungsten carbide parts depends heavily on raw material formula and sintering quality. Without reliable lab testing, hidden internal defects may lead to unexpected tool failure after delivery. Our in-house QC lab runs a full set of standard tests to verify carbide quality before shipment. Four core tests form our standard inspection package: hardness test, density measurement, transverse rupture strength (TRS) test, and metallographic analysis. All test results are recorded and can be attached to the Certificate of Analysis (COA) for buyers. This article explains each test and what quality risks they help identify.

2. Hardness Test (HRA / HV)

Hardness is the most commonly used index to judge carbide wear resistance. For cemented carbide, we mainly use HRA Rockwell A scale or Vickers HV hardness test. The hardness value is controlled by cobalt content and WC grain size. Higher cobalt binder usually lowers hardness but improves toughness.

During the test, a diamond indenter presses into the polished carbide surface under fixed load. The indentation size is measured to calculate hardness. Multiple points are tested on one sample to check uniform hardness distribution. If hardness fluctuates widely, it indicates uneven powder mixing or abnormal sintering.

Hardness out of tolerance is a major rejection reason. It will directly cause either fast abrasive wear or easy chipping during service.

3. Density Test

Carbide density is measured by the Archimedes water immersion method. We weigh the sample in air and in pure water, then calculate the actual density. The theoretical density is fixed for each WC-Co grade.

Low density usually means incomplete densification or internal pores after sintering. Too high density rarely happens but may signal wrong cobalt ratio. Density test is a fast screening method to catch abnormal sintering before doing expensive TRS or metallography tests.

4. TRS Transverse Rupture Strength Test

TRS, or bending strength, evaluates the material’s ability to resist fracture under bending load. Standard rectangular carbide test bars are placed on two support points, then force is applied at the center until the sample breaks.

TRS reflects the overall toughness and internal defect level. Porosity, coarse grain or inclusion defects will greatly reduce TRS value. This test is critical for cold forging dies, pin cores and impact-resistant carbide parts. High TRS means better anti-fatigue performance under cyclic load.

5. Metallography Inspection

Metallography is a microscopic inspection. The carbide sample is cut, mounted, ground and polished, then observed under a metallurgical microscope. Our lab checks porosity rating, WC grain size distribution, free carbon, eta phase and non-metallic inclusions.

It can find tiny hidden defects invisible to naked eyes: micro pores, abnormal grain growth, carbon imbalance. Free carbon or eta phase will drastically reduce strength and service life. For HIPed carbide products, metallography report is the key proof to confirm near-zero porosity.

6. Summary of 4 Core QC Tests

7. Test Data & COA Certificate

All lab test data can be compiled into the COA document for each batch. Buyers can specify required test items before production. For standard low-stress wear parts, hardness and density are usually enough. For high-performance tooling like cold forging dies and HIP carbide components, we suggest full inspection including TRS and metallography.

We keep test records and sample archives for traceability. If customers have quality doubts after receiving goods, we can review original lab data quickly.

8. FAQ