Quality verification is critical before accepting tungsten carbide shipments. Even if your carbide parts look good visually, hidden issues such as wrong cobalt content, out-of-tolerance dimensions or unstable hardness can lead to premature tool failure. Professional carbide suppliers provide official inspection documents together with each batch, the most important three being COA, dimension inspection report and hardness test report. These documents serve as quality proof for buyers, support incoming quality control (IQC), and can be used for traceability if quality disputes occur later. This article explains what each document covers and what details you should verify.

Certificate of Analysis (COA)

COA, short for Certificate of Analysis, is the material certification document for tungsten carbide batches. It records raw material composition and basic material properties of the carbide grade. A standard COA is batch-specific and cannot be reused across different production lots.

Key information included on a carbide COA:

• Batch number, order number and production date
• Cobalt (Co) content and WC grain size
• Material grade designation (YG6, YG8 or custom grade)
• Density and transverse rupture strength (TRS)
• Signature or stamp from the factory quality department

Note: A COA certifies material chemistry and bulk material performance. It does not replace dimensional inspection reports for machined features.

Dimension Inspection Report

The dimension report verifies whether finished carbide parts meet drawing tolerances. For ground carbide rods, custom carbide blades, die blanks and wear plates, dimensional accuracy directly affects assembly and tool performance. Inspectors use micrometers, optical comparators or coordinate measuring machines (CMM) according to drawing requirements.

Reports should list sampling quantity, measured actual values, tolerance range and pass/fail results. For high-precision carbide components, full inspection records can be requested in advance.

Hardness Test Report

Hardness is one of the most frequently checked mechanical indicators for tungsten carbide. Hardness is usually measured by HRA scale, sometimes HV. Hardness correlates with wear resistance and toughness. A deviation from the specified hardness range often signals inconsistent sintering or wrong cobalt percentage.

Important points about carbide hardness testing:

• Test location: Hardness should be tested on representative sample surfaces after grinding
• Sampling method: Random sampling from the same batch
• Data: Record individual readings, average value and acceptable range

Keep in mind: Hardness alone cannot fully judge carbide quality. Always combine hardness results with COA and dimension reports.

Checklist for Valid Inspection Documents

• ✅ Documents match your order batch number
• ✅ Measured values fall within agreed tolerance and material specifications
• ✅ Test methods and standards are clearly stated
• ✅ Documents have factory QC stamp or authorized signature
• ✅ No generic blank documents reused for multiple orders

You can negotiate with your supplier to send scanned copies of inspection documents before shipment, and deliver original documents together with goods.