O papel crucial do hidrogênio no aço: prevenção de rachaduras induzidas por hidrogênio

The crucial role of hydrogen in steel: preventing hydrogen-induced cracking

Hydrogen is known to cause embrittlement and cracking in steel, commonly called hydrogen-induced cracking (HIC). HIC typically occurs in aqueous solutions, as hydrogen can diffuse into the steel matrix, resulting in embrittlement and cracking of the steel.

HIC is mostly discussed today as it is a major concern in many industries. It is often caused by accidental factors during the forming or finishing process that allow hydrogen to enter the steel matrix.

HIC is influenced by three main factors: material performance, environmental conditions and stress.

Bubbling on sample surface after hydrogen charging

During the Second World War, an RAF Spitfire fighter crashed out of the air due to mechanical failure, killing the pilot instantly. The incident was considered of great importance, which led authorities to collect all parts of the plane and establish a special investigation team to determine the cause of the accident.

The investigation revealed that the aircraft crash was caused by the fracture of the main shaft. The fracture showed multiple small fissures, known at the time as hairline fractures.

In 1940, Mr. Li Xun, founder of the Metals Research Institute of the Chinese Academy of Sciences, began research work at the University of Sheffield after graduating. The prerequisite for solving this problem was to find a way to quantitatively test and analyze the hydrogen content in steel.

Later, Mr. Li Xun invented a hydrogen tester to measure the hydrogen content in steel. It ended up being proven that hydrogen was responsible for the fracture of the aircraft's main axis. As a result, Mr. Li Xun became the founder of the field of hydrogen-induced cracking.

High-strength steels containing chromium and nickel are highly susceptible to hydrogen. Steels with a high carbon content are more prone to hydrogen-induced cracking, while steels with a low carbon content are less prone to this phenomenon.

Forgings with a dense structure are more susceptible to hydrogen-induced cracking than castings with a loose structure. When hydrogen atoms penetrate the steel, the atomic bonding strength between the grains decreases and the steel's toughness is compromised. The fracture caused by hydrogen-induced cracking is similar to other brittle fractures, and high-strength materials are more susceptible to intergranular fracture.

In low-carbon steel, small, incomplete dimples are likely to appear in the small facets along the grain, forming what is known as a “chicken claw pattern.”

Hydrogen embrittlement fracture

Hydrogen-induced cracking has hysteresis.

The occurrence of hydrogen-induced cracks in welded components can be sudden and poses a serious threat to people and property. This issue requires great attention.

Explosion accident

The elimination of hydrogen in metals is a critical issue that requires attention. Certain steels or components used in specific conditions must undergo dehydrogenation treatment. For example, galvanized parts used in aircraft must go through this process. Hydrogen removal is also necessary for zinc plating on elastic parts and high-strength steel.

The process of removing hydrogen from parts involves heat treatment. The effectiveness of hydrogen removal depends on the hydrogen removal temperature and retention time. The higher the temperature and the longer the time, the more effective the hydrogen removal will be.

Typically, the component to be treated can be placed in a vacuum oven and treated at a temperature of 200-250°C for 2-3 hours. Hot oil can also be used to achieve the same hydrogen removal effect as the oven. This method offers the benefit of uniform heating and simpler equipment requirements.

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