[1] To reduce the amount of hydrogen permeation in T22 alloy steel pipes, it is necessary to minimize the pickling of high-strength/high-hardness steel T22 alloy steel pipes, because pickling can aggravate hydrogen embrittlement. When removing rust and scale, use sandblasting and shot blasting as much as possible. If the T22 alloy steel pipe with Rockwell hardness equal to or greater than HRC 32 is pickled, the T22 alloy steel pipe must be soaked in acid when formulating the pickling process. The maximum time does not exceed 10 minutes. The concentration of the acid should be reduced as much as possible, and the parts should be immersed in the acid for no more than 10 minutes; when degreasing, chemical degreasing methods such as cleaning agents or solvent degreasing are used, and the amount of hydrogen permeation is less. Chemical degreasing, first cathode followed by anode, high-strength T22 alloy steel pipes are not allowed to use cathode electrolysis to remove oil; during heat treatment, strictly control the amount of methanol and propane dripping; during electroplating, alkaline plating solution or high current efficiency plating The amount of liquid hydrogen permeation is small. [2] Adopt a coating with low hydrogen diffusivity and low hydrogen solubility.
It is generally believed that when electroplating Cr, Zn, Cd, Ni, Sn, Pb, the hydrogen infiltrated into the steel is easy to remain, while Cu, Mo, Al, Ag, Au, W and other T22 alloy steel pipe coatings have low hydrogen diffusivity and Low hydrogen solubility, less hydrogen permeation. In the case of meeting the requirements of product technical conditions, coatings that will not cause hydrogen penetration, such as mechanical galvanizing or chromium-free zinc-aluminum coatings, will not occur hydrogen embrittlement, have high corrosion resistance, good adhesion, and Electroplating is environmentally friendly.
[3] Stress relief before plating and hydrogen removal after plating to eliminate hydrogen embrittlement. If the internal residual stress of the parts is large after quenching, welding and other processes, tempering treatment should be carried out before plating. Tempering to eliminate stress can actually reduce the internal The number of traps, thereby reducing the hidden danger of hydrogen embrittlement.
[4] Control the thickness of the coating. Because the coating covers the surface of the fastener, the coating will function as a hydrogen diffusion barrier to a certain extent, which will hinder the diffusion of hydrogen to the outside of the fastener. When the plating thickness exceeds 2.5 μm, it is very difficult for hydrogen to diffuse out of the fastener. Therefore, for fasteners with hardness less than 32HRC, the coating thickness can be required to be 12μm; for high-strength bolts with hardness ≥32HRC, the coating thickness should be controlled at 8μmmax. This requires that in product design, the hydrogen embrittlement risk of high-strength bolts must be considered, and the plating species must be reasonably selected.