The Role of Hydrogen in Steel – Hydrogen Induced Cracking

Hydrogen often causes hydrogen embrittlement and cracking in steel.

Today, hydrogen induced cracking is mainly discussed.

Hydrogen-induced cracking (HIC) usually occurs in aqueous solution.

Because hydrogen diffuses into the steel matrix, steel embrittlement and cracking occur.

Hydrogen induced cracking is often caused by hydrogen entering the steel matrix due to accidental factors in the process of forming or finishing.

It is usually affected by three factors: material performance, environmental factors and stress factors.

The Role of Hydrogen in Steel - Hydrogen Induced Cracking 1

Bubbling on the sample surface after hydrogen charging

During the Second World War, an RAF Spitfire fighter fell from the air due to mechanical failure, and the pilot was killed on the spot.

The authorities attached great importance to this incident.

All the parts of the plane were collected and a special investigation team was set up to investigate the cause of the plane crash.

The aircraft crash was caused by the fracture of the main shaft, and many small cracks were found inside the fracture main shaft, which was called hairline at that time.

Around 1940, Mr. Li Xun, the founder of the Institute of Metal Research of the Chinese Academy of Sciences, began to engage in this research work at the University of Sheffield after his graduation.

The prerequisite for solving this problem is how to quantitatively test and analyze the hydrogen content in steel.

Subsequently, Mr. Li Xun invented a hydrogen determinator to determine the hydrogen content in steel.

It was finally proved that hydrogen caused the fracture of the main shaft of the aircraft.

Mr. Li Xun also became the founder of the field of hydrogen induced cracking.

High strength steels containing chromium and nickel are very sensitive to hydrogen.

Steels with high carbon content have a greater tendency to hydrogen induced cracking.

Low carbon steels are less prone to hydrogen induced cracking.

Forgings with dense structure are more prone to hydrogen induced cracking than castings with loose structure.

After hydrogen atoms penetrate into the steel, the atomic bonding force between grains will be reduced, and the toughness of steel will be reduced.

The fracture of hydrogen induced cracking is similar to other brittle fracture, and intergranular fracture is easy to occur in high-strength materials.

For low carbon steel, small and incomplete dimples are easy to appear on the small facets along the grain, which is called “chicken claw pattern”.

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Hydrogen embrittlement fracture

Hydrogen induced cracking has hysteresis.

For welded components, the occurrence of hydrogen induced cracking is sudden and will pose a serious threat to people and property, which requires great attention.

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Explosion accident

How to eliminate hydrogen in metals is the most concerned problem.

Some steels or parts used under special conditions must undergo dehydrogenation treatment.

For example, galvanized parts used in aircraft must undergo dehydrogenation treatment.

Hydrogen removal is also required for zinc plating on elastic parts and high-strength steel.

The hydrogen is removed from the parts by heating treatment.

The hydrogen removal effect is related to the hydrogen removal temperature and holding time.

The higher the temperature and the longer the time, the more thorough the hydrogen removal.

In general, the component to be hydrogen removed can be placed in a vacuum oven and treated at a temperature of 200-250 ° C for 2-3h.

The hydrogen removal in hot oil can achieve the same effect as that in the oven.

The heating is uniform and the equipment requirements are simpler.

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