How does hydrogen embrittlement occur when screws are broken?
What is hydrogen embrittlement? The term hydrogen embrittlement often appears when carbon steel screws are heat treated. Hydrogen embrittlement refers to the phenomenon of metal materials in the process of smelting, processing, heat treatment, pickling, electroplating, etc., or long-term use in hydrogen-containing media, the material's mechanical properties are seriously degraded due to hydrogen absorption or hydrogen permeation, and brittleness occurs.
So where are screws prone to hydrogen embrittlement? One is the neck at the lower end of the head, and the other is the incomplete thread.
How to make screws so as not to be prone to hydrogen embrittlement?
1. Avoid the introduction of excessive hydrogen. In the process of metal smelting, the relative humidity is reduced, and various additives and ingot molds are baked to keep dry.
2. Dehydrogen treatment. Slow down the cooling rate of the steel ingot to allow enough time for hydrogen to escape, or put the steel in a vacuum furnace to anneal and remove hydrogen.
3. Appropriate alloying elements are added to the steel to form a dispersed second phase, which acts as an irreversible trap for hydrogen, so that the active hydrogen content in the material is relatively reduced, thereby reducing the hydrogen embrittlement tendency of the material.
4. When pickling or electroplating, add a corrosion inhibitor to the acid or electrolyte, so that a large number of hydrogen atoms generated in the solution are combined on the metal surface to form hydrogen molecules and directly escape from the solution to prevent hydrogen atoms from entering the metal internal.
How to remove hydrogen from carbon steel screws after electroplating? Generally, heat treatment is used to expel the atomic hydrogen to prevent hydrogen embrittlement.