Hydrogen-induced cracking usually occurs in aqueous solutions and results in embrittlement and cracking of the steel due to the diffusion of hydrogen into the steel matrix. Hydrogen-induced cracking often occurs when hydrogen enters the steel matrix as a result of accidental factors during the forming or finishing process. It is usually influenced by three factors, material properties, environmental factors and stress factors.

Hydrogen-induced cracking (HIC). Hydrogen-induced cracking usually occurs in aqueous solutions and results in embrittlement and cracking of the steel due to the diffusion of hydrogen into the steel matrix. Hydrogen-induced cracking often occurs when hydrogen enters the steel matrix as a result of accidental factors during the forming or finishing process. It is usually influenced by three factors; material properties, environmental factors and stress factors.

During the Second World War, a British Air Force Spitfire crashed out of the sky due to mechanical failure, killing the pilot instantly. The authorities took this matter very seriously and all the parts of the crashed aircraft were collected and a special investigation team was set up to investigate the cause of the crash. The cause of the crash was a broken spindle, and many tiny cracks were found inside the broken spindle, which was called hairline at that time.

Around 1940, the founder of the Institute of Metals of the Chinese Academy of Sciences, Mr. Li Xun, started to work on this research at the University of Sheffield in the UK after graduating with a Ph.D. The prerequisite for solving this problem was how to quantitatively test and analyse the hydrogen content in steel. Subsequently, Kaoru Lee invented the Hydrogen Determination Meter, which was used to determine the hydrogen content of steel. It was eventually proved that it was hydrogen that caused the fracture of aircraft spindles. Kaoru Lee became the founder of the field of hydrogen cracking.

High-strength steels containing chromium and nickel are very sensitive to hydrogen; steels with higher carbon content have a greater tendency to hydrogen cracking; mild steels are less susceptible to hydrogen cracking; and forgings with a dense organisation are more susceptible to hydrogen cracking than castings with a loose organisation. Hydrogen atoms penetrate into the steel, will reduce the atomic bonding force between the grains, so that the toughness of steel decline.

Hydrogen cracking fracture is very similar to other brittle fracture, high-strength materials are prone to fracture along the crystal. For low carbon steel, in the small surface along the crystal is prone to small, incomplete development of the tough nest, some people call ‘chicken claw pattern’.

Hydrogen cracking with hysteresis, for welding components, hydrogen cracking occurs suddenly, will pose a serious threat to people and property, need to pay great attention.

How to eliminate hydrogen from metals is a major concern. Certain steels or parts used under special conditions must be dehydrogenated, for example, galvanised parts used in aircraft are dehydrogenated. Galvanising on elastic parts and high strength steels also requires dehydrogenation. Dehydrogenation uses a heating process to drive the hydrogen out of the part. The effect of dehydrogenation is related to the dehydrogenation temperature and holding time. The higher the temperature and the longer the holding time, the better the dehydrogenation.

Usually, the components to be dehydrogenated can be placed in a vacuum oven, at a temperature of 200 ~ 250 ℃ treatment 2 ~ 3 h. Dehydrogenation in hot oil can be obtained with the same effect as dehydrogenation in the oven, the heat is uniform, the requirements of the equipment is also more simple.