H22 Button Bit Carbide Grade Verification: Density, Hardness and Microstructure

To verify the carbide grade in an H22 tapered button bit, do not accept a hardness value alone. Freeze the declared grade or approved reference first, then compare a traceable test set covering density, Vickers hardness, metallographic microstructure and—when the supplier uses magnetic process control—coercivity and magnetic saturation. The result is evidence of conformity to an agreed material specification; it is not a universal pass/fail grade chart. Test methods, sampling location, specimen preparation and acceptance limits must be agreed before production because cemented-carbide grades can overlap in individual properties.

What “carbide grade” means in an H22 button bit

The buttons in a tapered bit are cemented carbide: hard carbide grains held in a metallic binder. A common mining-tool family is tungsten carbide with cobalt binder (WC–Co), but the exact composition, grain-size distribution, additives and manufacturing route belong to the supplier's material specification. Those variables influence hardness, wear response, toughness and process stability together.

This is why two buttons can show similar hardness while differing in binder content, grain size, porosity or carbon balance. Conversely, a legitimate grade change intended for another rock condition may shift several properties without indicating poor manufacture. The buyer's job is therefore to verify the supplied lot against a declared, application-approved grade—not to infer performance from appearance, one portable reading or a generic grade name.

Carbide material verification also has a different boundary from whole-bit inspection. Bit diameter, taper fit, button protrusion, flushing holes and brazed or interference-fit retention still require separate checks. Use the H22 button-bit pre-shipment inspection guide for those finished-tool controls and the H22 bit-type selection guide for application choice.

Why a multi-test comparison is stronger than one certificate value

A published quality-control study for sintered carbide mining tips combined density, hardness and quantitative microstructural analysis rather than treating one result as decisive. It also highlights why specimen preparation and representative imaging matter. The practical buyer lesson is simple: ask for a coherent evidence set in which the results support the same declared material, then investigate disagreements instead of averaging them away.

Build the verification plan before placing the order

1. Freeze the commercial and technical reference

Put the carbide grade designation, supplier specification revision and intended bit configuration on the purchase document. If the supplier uses a proprietary grade name, require the corresponding controlled property ranges rather than relying on the name. Record whether the reference is a drawing, data sheet, signed sample approval or previous accepted lot. A phrase such as “high-quality carbide” is not a measurable requirement.

For H22 tapered button bits, also freeze the dimensions and compatibility items that are outside the carbide-grade test: nominal bit diameter, taper angle and matching rod, button profile, face arrangement and flushing configuration. Buyers can review the active H22 taper button-bit configuration route when preparing those RFQ details.

2. Define the lot and sampling rule

A test report is useful only when the sample can be tied to the shipped lot. Define what constitutes a lot—such as one carbide grade and production batch used in a stated purchase quantity—and require a lot code on the report and packing records. Agree who selects the specimens, when selection occurs, how they are sealed and whether the laboratory receives retained loose buttons or destructive samples taken from finished bits.

Do not invent a sample quantity after seeing a result. The number of specimens and retest rule should reflect order size, historical stability, consequence of failure and the destructive nature of the test. For a new supplier or changed material, buyers commonly need stronger evidence than for a stable, repeatedly accepted source, but the exact plan belongs in the contract or inspection instruction.

3. Use specimens that represent the delivered carbide

Density may be measured on a clean, sound carbide specimen using the agreed method. Hardness and microstructure require prepared surfaces; cutting, mounting, grinding, polishing and etching can influence the observation. Ask the laboratory to identify the specimen, preparation route, test locations, equipment and method revision.

Retained loose buttons from the same carbide batch are often easier to test without contamination from the bit body or joining process. If the contract requires testing buttons removed from completed bits, agree on removal and sectioning procedures and accept that the sample is sacrificed. Never assume a loose coupon represents the shipment unless batch traceability connects it to the buttons installed in those bits.

How to review each test

Density: compare with the declared grade, not pure WC

Density is sensitive to composition and voids, but a cemented-carbide button is not pure tungsten carbide. Binder content, other carbides and porosity affect the result. Require the method—ISO 3369 is a recognized reference for hardmetal density—plus specimen identification, fluid and temperature conditions where relevant, measured values and the declared acceptance range.

A value within range supports consistency; it does not prove the grain structure or toughness. A shift from the approved baseline may justify checking composition, porosity, sample cleanliness and measurement repeatability before deciding whether the lot is nonconforming.

Hardness: record method, load and preparation

Vickers hardness is widely used for hardmetals. A report should state the method, indenter load, surface preparation, number and location of impressions, individual results and summary statistic. ISO 3878 is the relevant hardmetal Vickers-hardness reference. Results reported only as “HV” without a load or specimen description are not adequate for comparison.

Hardness must be read beside the declared composition and microstructure. Finer WC grains or reduced binder can increase hardness, but the same change may alter toughness. Therefore, do not reward the highest number automatically. The correct result is the agreed range for the application-approved grade.

Microstructure: look for the specified structure and defects

Metallography can assess WC grain size and distribution, binder distribution, porosity and carbon-related defects when the sample is prepared and examined correctly. The ISO 4499 series covers metallographic determination of hardmetal microstructure, including grain-size measurement and characterization of porosity, uncombined carbon and eta phase.

Request representative images with magnification, scale, specimen ID and test location. One attractive field of view is not a statistical result. If quantitative grain-size data are required, the report should identify the measurement procedure, fields assessed and distribution or classification used. Mechanical and magnetic measurements are method-dependent data that require controlled specimen preparation, calibrated equipment and documented interpretation.

Magnetic measurements: valuable process evidence with limits

Coercivity can respond to WC grain size and binder-phase condition; magnetic saturation can help monitor the state and amount of the magnetic binder. These measurements are fast and useful for batch control when the supplier has established grade-specific baselines. They are not universal grade identifiers. Require the instrument, calibration status, units, declared limits and correlation to the approved grade.

If magnetic data disagree with hardness or microstructure, open a technical review. Possible explanations include sampling mismatch, calibration, composition variation or process changes. Do not accept an unexplained conflict merely because another number is in range.

Acceptance workflow for procurement teams

1. RFQ stage: define the grade specification, test methods, lot definition, sampling, report content and change-notification rule.
2. Pre-production approval: approve a reference data set or sample only after application requirements and bit configuration are confirmed.
3. Production evidence: require lot-linked results for density, hardness and any agreed magnetic controls.
4. Periodic or risk-based verification: use an independent laboratory or witnessed test for microstructure and other destructive checks at the agreed frequency.
5. Document review: confirm specimen IDs, dates, methods, units, equipment, calibration status and signatures before comparing results with limits.
6. Deviation control: quarantine the affected lot, investigate the complete evidence set and apply the pre-agreed retest or disposition rule.

Keep the test report, lot code, packing list, supplier declaration and inspection record together. Traceability is what turns laboratory data into shipment evidence. A certificate with no connection to the delivered cartons cannot support acceptance.

Common purchasing mistakes

• Using hardness as a grade name. Different compositions and microstructures can overlap in hardness.
• Comparing results from different methods. Load, preparation and measurement procedure can change comparability.
• Accepting generic certificates. Reports need lot and specimen traceability to the delivered bits.
• Setting universal density limits. The correct range depends on the declared grade composition and approved baseline.
• Inspecting only polished images. Micrographs need scale, magnification, location and representative sampling.
• Confusing carbide quality with joint quality. A conforming button can still be poorly retained, and a sound joint cannot correct the wrong carbide grade.

RFQ and test-report checklist

• Supplier carbide grade and controlled specification revision
• Target ranges for density and Vickers hardness, including test methods and hardness load
• Required microstructural characteristics and applicable ISO 4499 part
• Magnetic properties and limits, if used for process control
• Lot definition, sampling quantity, specimen source and selection responsibility
• Independent, witnessed or supplier-laboratory testing requirement
• Report fields: lot ID, specimen ID, equipment, calibration status, method, raw results and conclusion
• Retest, quarantine and concession process
• Change notification for grade, powder source, binder content or manufacturing route
• Link from carbide batch to finished-bit packing and shipment documents

Frequently asked questions

Can hardness alone confirm an H22 button-bit carbide grade?

No. Hardness supports comparison with a declared grade, but it does not uniquely identify binder content, WC grain size, porosity or toughness. Combine it with density, microstructure and traceability; add magnetic or chemical evidence when specified.

Should every finished button bit be cut for testing?

No. Most carbide-grade tests are destructive or require prepared specimens. Agree a representative sampling plan using retained buttons, sacrificial finished bits or both, and connect every specimen to the production lot.

What should a microstructure report include?

At minimum, it should identify the specimen and location, preparation method, microscope method, magnification, scale and representative images. Quantitative claims also need the measurement procedure, assessed fields and reported distribution or classification.

Are coercivity and magnetic saturation mandatory?

Not for every purchase. They are useful process-control tools for appropriate magnetic hardmetal grades when the supplier has validated grade-specific limits. They should complement, not replace, the agreed physical and metallographic tests.

How should a buyer handle a result outside the agreed range?

Hold the affected lot, verify specimen identity and method, then follow the agreed retest and disposition rule. Review the complete evidence set before accepting, rejecting or granting a documented concession.

Prepare a traceable H22 button-bit inquiry

PerfoMax can review H22 taper, nominal diameter, button layout, flushing configuration and buyer-specified inspection documents for overseas mines, quarries, contractors and distributors. Send the matching rod details, rock conditions, order quantity, declared carbide requirements and required evidence. Start with the H22 taper button-bit inquiry route so the commercial configuration and verification plan are aligned before production.

Technical references

• An Improved Procedure for the Quality Control of Sintered Carbide Tips for Mining Applications — peer-reviewed research combining hardness, density and quantitative microstructure.