Quality control

Last updated 2026-10-06 · method revision 3

Every charge ends with a measurement, or the job is not closed. We read hardness to the sampling rule and, where needed, look at the structure under the microscope.

Instruments

• A bench Rockwell tester - the main instrument for quenched and carburised parts.
• A Brinell press with a 10 mm ball at 3000 kgf - for annealed and normalised work measured in HB.
• A portable dynamic hardness tester - for large parts that will not sit on the bench tester.
• A metallography microscope to 1000×, structure read at 500×; etch is 4 % nitric acid in alcohol.

Sampling rules

On one part we take at least three points in the marked zone. A batch of up to 20 is checked in full; above 20 we check ten percent, but never fewer than three parts. For carburising the rule is tighter: a witness microsection is cut for every charge, and its case depth and structure are read.

Acceptance protocol

The result is written up as an eight-point protocol; a copy is kept for three years so the history of a given part can be pulled up.

1. Protocol number and date, customer, contract or request number.
2. Part name, steel grade, drawing number and the design section.
3. Operation and route: furnace, temperature, soak, quenchant.
4. Charge number and treatment date.
5. Measured hardness by point, with method and instrument.
6. For carburising, the case depth and structure from the witness.
7. Remarks: distortion, a decarburised layer, any straightening done.
8. Verdict - accepted, accepted with conditions, or reject - and the heat treater's signature.

When a result comes out "accepted with conditions", we write down exactly what is out of tolerance and what to do about it. What usually causes it is on the defects page.