Alloy Tube Eliminates Hydrogen Embrittlement

- Jan 17, 2019-

[1] To reduce the amount of hydrogen permeation in T22 alloy steel tubes, it is necessary to minimize the pickling of high strength/high hardness steel T22 alloy steel tubes because pickling can exacerbate hydrogen embrittlement. When removing rust and scale, try to use sandblasting and shot blasting. If the T22 alloy steel tube with Rockwell hardness equal to or greater than HRC 32 is pickled, it is necessary to ensure that the T22 alloy steel pipe is soaked in acid when the pickling process is established. The maximum time is no more than 10 minutes. The concentration of the acid solution should be reduced as much as possible, and the time for immersing the parts in the acid should not exceed 10 minutes; in the case of degreasing, the chemical degreasing method such as cleaning agent or solvent degreasing, the amount of hydrogen permeation is less, if electricity is used Chemical degreasing, first cathode and anode, high-strength T22 alloy steel pipe is not allowed to use the cathode to remove oil; in heat treatment, the amount of methanol and propane is strictly controlled; in electroplating, alkaline plating or high current efficiency plating The amount of liquid hydrogen permeation is small.

[2] Coating with low hydrogen diffusivity and low hydrogen solubility

It is generally believed that when Cr, Zn, Cd, Ni, Sn, and Pb are electroplated, hydrogen infiltrated into the steel member is likely to remain, and T22 alloy steel pipe coatings such as Cu, Mo, Al, Ag, Au, and W have low hydrogen diffusivity and Low hydrogen solubility, less hydrogen permeation. In the case of meeting the technical requirements of the product, a coating that does not cause hydrogen permeation, such as a mechanically galvanized or non-chromium-zinc-aluminum coating, can be used without hydrogen embrittlement, high corrosion resistance, good adhesion, and ratio. Electroplating environmental protection.

[3] De-stressing before plating and de-hydrogenation after plating to eliminate hydrogen embrittlement. If the parts are subjected to quenching, welding and other processes, the internal residual stress is large. Before plating, tempering should be performed. The tempering and stress relief can actually reduce the parts. The number of traps, thereby reducing the risk of hydrogen embrittlement.

[4] Control the thickness of the coating. Since the coating covers the surface of the fastener, the coating will act as a hydrogen diffusion barrier to a certain extent, which will hinder the diffusion of hydrogen to the outside of the fastener. When the thickness of the plating exceeds 2.5 μm, it is very difficult to diffuse hydrogen out of the fastener. Therefore, the hardness of the fastener <32HRC, the thickness of the coating can be required to be 12μm; the high-strength bolt with hardness ≥32HRC, the thickness of the coating should be controlled at 8μmmax. This requires that the risk of hydrogen embrittlement of high-strength bolts must be taken into consideration when designing the product, and the plating species should be reasonably selected.