In the manufacturing process and service environment of threaded fasteners, under the reaction of cathodic protection or corrosion, the matrix of steel or other metals may be penetrated by hydrogen atoms and stay in the matrix, which is under the stress of yield strength. In the state, it may cause a reduction or loss of extensibility or load-bearing capacity, and cracks, which may cause sudden fracture during storage or service, causing serious brittle failure. Threaded fasteners, especially high-strength fasteners, are subjected to hardening heat treatment and electroplating after cold drawing, cold forming, thread rolling, machining, and grinding, and are extremely susceptible to hydrogen embrittlement. There are many reasons for hydrogen embrittlement of fasteners. Among them, what is caused by the electroplating process is one of the key factors.
The hydrogen embrittlement of fasteners is not a slow and continuous process like corrosion. The hydrogen embrittlement of fasteners is a phenomenon of sudden fracture. Because of its suddenness, the consequences are often more serious than corrosion. Especially when safety performance is required, reducing hydrogen embrittlement is a very necessary or indispensable important measure, especially in the process of electroplating fasteners.
The situation and characteristics of fasteners prone to hydrogen embrittlement failure risk
A. High tensile strength or hardening or surface hardening;
B. Adsorption of hydrogen atoms;
C. Under tensile stress.
As the hardness of the parts increases, the carbon content increases, and the degree of cold work hardening is strengthened, in the pickling and electroplating process. The solubility of hydrogen and therefore the total amount of hydrogen absorbed will also increase, that is to say, the more sensitive the parts are to hydrogen embrittlement. Parts with smaller diameters are more sensitive to hydrogen embrittlement than parts with larger diameters.