Hydrogen embrittlement is a phenomenon in which hydrogen penetrates into the metal and causes damage, resulting in delayed fracture of the metal material under static stress lower than the yield strength of the material.
Author: Marisa
Hydrogen embrittlement is a phenomenon in which hydrogen penetrates into the metal and causes damage, resulting in delayed fracture of the metal material under static stress lower than the yield strength of the material.
Hydrogen embrittlement is a common phenomenon in engineering, especially in the electroplating process, which can easily lead to hydrogen embrittlement of metal materials. Hydrogen embrittlement in the electroplating process mainly occurs in the processes of pickling and electroplating.
Therefore, many parts will be dehydrogenated after electroplating to avoid the harm caused by hydrogen embrittlement. The following is an introduction to the dehydrogenation method by Jiechang Electroplating Factory.
1. General dehydrogenation method
(1) Place the plated parts to be dehydrogenated in an oven (preferably in a vacuum furnace) or in hot oil (suitable for hard chrome plated parts) at 200~250℃ for more than 3 hours.
(2) Dehydrogenation in hot oil can achieve the same effect as dehydrogenation in an oven. Because it is heated evenly, it can also fill the pores in the coating, which is beneficial to improve the protective function of the coating and has simple equipment requirements.
2. Propose a dehydrogenation method according to the requirements of the workpiece
For example, in hard chrome plating, due to the low current efficiency of only 13%~18%, most of the current is consumed in the precipitation of hydrogen. Hydrogen easily diffuses into the lattice of the coating and the base metal, and hydrogen permeation is more serious, which causes a decrease in fatigue strength and affects the dynamic and static load strength. Therefore, the requirement for dehydrogenation treatment after chrome plating should be proposed in the design. After dehydrogenation treatment, 60%~70% of the hydrogen that penetrates into the coating and the base can be removed, thereby greatly reducing the brittleness without reducing its hardness.
3. Hot oil instead of dehydrogenation in the oven
The current efficiency of chrome plating is very low, so the porosity of the coating is high, and the coating is very easy to passivate. At the same time, due to the dominant cathodic coating of the chromium layer on the surface of the steel part, it is very easy to cause rust when the coating thickness is thin. In order to improve this defective link, hot oil dehydrogenation can be used instead of the dehydrogenation process in the oven under the same process conditions. Practice has proved that this process can not only maintain uniform temperature of each part of the workpiece to achieve complete dehydrogenation effect, but also effectively fill grease into the pores and cracks of the chromium layer, thereby improving the protective ability of the chromium layer.
4. The dehydrogenation temperature cannot be too high
For example, after galvanizing, dehydrogenation is carried out by heating to drive hydrogen out of the metal. The effectiveness of dehydrogenation is related to the dehydrogenation temperature and the length of the insulation time. The higher the dehydrogenation temperature and the longer the time, the more thorough the dehydrogenation. However, it cannot exceed 250 degrees Celsius. Because at this temperature, the crystalline structure of the galvanized layer will deform, become brittle, and its corrosion resistance will decrease.
The following points should also be noted when dehydrogenating:
(1) The safety factor of the part. For parts with high safety importance, the dehydrogenation time should be appropriately extended.
(2) The geometric shape and cross-sectional area of the part. Small and thin parts with notches, small angles, etc. that are prone to stress concentration should strengthen dehydrogenation.
(3) The degree of hydrogen permeation of the part. Parts that produce more hydrogen during surface treatment and take longer to treat should strengthen dehydrogenation.
(4) The stress properties of the parts during use. When the parts are subjected to high tensile stress, dehydrogenation should be strengthened. When only compressive stress is applied, hydrogen embrittlement will not occur.
(5) The surface of the coating must be kept clean before dehydrogenation. Dehydrogenation should be carried out before passivation to ensure the dehydrogenation effect and the quality of the passivation layer.
(6) Dehydrogenation should be carried out continuously and should not be stopped in the middle. Wait until the oven cools down to room temperature before opening the oven to take out the parts.
(7) Try not to rework the parts after electroplating. If electroplating is necessary, an alkaline solution can be used to remove the coating and the dehydrogenation time can be extended after electroplating.
(8) Dehydrogenation should be carried out within 3 hours after electroplating.