Hydrogen embrittlement 氫脆化
Quoted from Wikipedia, the free encyclopedia 錄自: 維祺百科
Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel , become brittle and crack following exposure to hydrogen. Hydrogen cracking can pose an engineering problem especially in the context of a hydrogen economy. However, commercially workable and safe technology exists globally in the hydrogen industry, which produces some 50 million metric tons per year.
發生過程: 單獨H原子鑽入鋼內, 後來又在晶界上集結成分子, 產生將晶粒推開的力道.
The mechanism starts with lone hydrogen atoms diffusing through the metal. At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in(Martensite / prior Austenite grain boundaries). This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible. 高強度與低合金鋼最易氫脆化. Steel with an ultimate tensile strength of less than 1000 MPa or hardness of less than 30 HRC are not generally considered susceptible to hydrogen embrittlement.
Hydrogen embrittlement can occur during various manufacturing operations or operational use - anywhere that the metal comes into contact with atomic or molecular hydrogen. Processes that can lead to this include phosphating, pickling, 鍍鉻,磷酸膜, 酸洗.and electroplating. A special case is arc welding, in which the hydrogen is released from moisture (for example in the coating of the welding electrodes; to minimize this, special low-hydrogen electrodes are used for welding high-strength steels). Other mechanisms of introduction of hydrogen into metal are galvanic corrosion, chemical reactions of metal with acids, or with other chemicals (notably hydrogen sulfide in sulfide stress cracking, or SSC, a process of importance for the oil and gas industries).
一般除氫須在零件 電鍍完1小時內, 即需送入烤箱200度c烤2-4小時 De-hydrogen baking should be performed within one hour after eletrical plating/coating.
硬度越高的產品,電鍍完 烘烤除氫時間越長. Higher hardness of parts require higher baking temp.
Aerospace Material Spec. AMS 2460 requires 中規定:
HRC 191 C, 烘烤除氫(最少要_
小時) min baking hours
36~39 3
40~45 8
> 46 以上 23
* Steel in annealed state have the matrix of Ferrite. Ferrite is very ductile and has extremely low solubility of hydrogen and therefore will not have hydrogen embrittlement problems.
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