How does the low profile head machine screws reduce hydrogen embrittlement?

Hydrogen embrittlement generally occurs on low profile head machine screws made of carbon steel. Especially when the screw is high-strength, hydrogen embrittlement occurs, which makes people particularly troublesome. So how does the flat head screw reduce hydrogen embrittlement?

★Measures to reduce stress

Fasteners with a cold work hardness greater than or equal to 320 HV and electroplated can increase the stress relief process. If the process is carried out in accordance with the requirements of GB/T 5267.1-2002 electroplating, the temperature and duration of the process shall vary according to the design of the part, the process and the heat treatment conditions of the part, and the electroplater shall be notified in a timely manner. Machining, grinding, cold forming, or cold-rolling heat treatment of parts with a hardness exceeding 320 HV shall comply with ISO 9587.

In the case of intentional introduction of residual stress, the stress release is not satisfactory, such as a low profile head machine screws that is threaded after heat treatment.

★Cleaning process

The cleaning process may cause hydrogen to adhere to the steel and cause brittle fracture after plating.

Unless otherwise agreed, parts with heat or work hardening hardness greater than or equal to 320 HV should be cleaned using corrosion-resistant acid, alkaline or mechanical means. The time to immerse in the corrosion-resistant acid depends on the state and minimum duration that the surface of the part can accommodate. Note: Adding a suitable corrosion-resistant acid can reduce corrosion and hydrogen adhesion to steel.

Parts that have a hardness of more than 385 HV or a performance level of 12.9 or higher for heat treatment or cold work hardening are not suitable for pickling treatment. Pretreatment with a special acid-free method is reasonable, such as dry grinding, sand blasting or alkaline rust removal.

For electroplating. The surface of the steel low profile head machine screws should be specially treated, that is, after minimum immersion time cleaning.

★Electroplating process

For fasteners that have been heat treated or cold hardened and have a hardness of more than 365 HV, it is reasonable to use a large cathode power plating solution.

★Drying process

As hardness increases, the degree of hard work hardening increases, and the carbon content of steel parts or some other element increases, the solubility of hydrogen and the resulting total amount of hydrogen absorbed during pickling and plating will also increase. . At the same time, the limit number of hydrogen that can cause brittle fracture is reduced.

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