Heat Treatment Of Fasteners | Inspection Of Hydrogen Embrittlement

In addition to general quality inspection and control, there are also some special quality inspections and controls for the heat treatment of fasteners. Now let's talk about the inspection of hydrogen embrittlement in several control points of heat treatment.

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The heat treatment of fasteners can make them have a certain strength, good plasticity, toughness, etc. so that they can be used better while reducing relaxation and ensuring the quality and reliability of fasteners.

1. Preparation of specimens: In order to examine hydrogen embrittlement, samples need to be taken from heat-treated fasteners. The selection of these samples should be representative of the material properties of the entire batch, either by random sampling or as specified in a specific standard.

2. Pretreatment: Before conducting hydrogen embrittlement inspection, the sample may need to undergo some pretreatment to ensure the accuracy of the test results. This may include cleaning and removing surface impurities to ensure that the surface of the specimen is clean.

3. Hydrogen embrittlement detection methods: There are several common methods used to detect hydrogen embrittlement, including:

Slow strain test: The specimen is loaded to a specific strain level at room temperature and then loaded at a slow rate to observe whether a fracture occurs. Hydrogen embrittlement materials are prone to fracture at low strain rates.

Barcol hardness test: By applying a load on the sample and then measuring the hardness, observe whether there are abnormal hardness values. Hydrogen embrittlement usually results in an abnormal increase in hardness.

Hydrogen transmission test: Immerse the sample in an acidic medium and observe whether hydrogen gas is released. Hydrogen embrittlement materials release hydrogen gas in acidic environments.

4. Standard reference: To ensure the reliability of testing, it is recommended to use international or national standards as a reference for hydrogen embrittlement testing. These standards include specific experimental methods, test conditions, and interpretation of results to help ensure consistent testing.

5. Corrective Action: If a hydrogen embrittlement problem is detected, appropriate corrective action must be taken. This may include redesigning the heat treatment process, changing material formulations, using different process conditions, etc. to ensure that future fasteners are not affected by hydrogen embrittlement.

Susceptibility to hydrogen embrittlement increases with the strength of the fastener. For externally threaded fasteners of grade 10.9 and above or surface-hardened self-tapping screws and combination screws with hardened steel washers, hydrogen removal treatment should be carried out after electroplating. The hydrogen removal treatment is generally performed in an oven or tempering furnace and kept at 190~230°C for more than 4 hours to allow hydrogen to diffuse out. Threaded fasteners can be tightened on a special fixture until the screw is subjected to sufficient tension to ensure the stress, and held for 48 hours. The threaded fastener will not break after loosening.

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