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Application of rare earth in steel making
The use of rare earth elements in steel has a long history, spanning nearly 30 years. Through extensive research on the behavior and mechanisms of rare earth metals in steel, scientists have clearly defined their roles. Experimental studies on the addition process have helped establish optimal conditions for introducing rare earths, including the types and quantities used. By the late 1980s, there were no major technical barriers to applying rare earths in steel production. China's rare earth steel output grew significantly, rising from 110,000 tons in 1985 to nearly 600,000 tons by 1997, with over 80 different varieties. During the "Eighth Five-Year Plan" period, one company, WISCO, produced 1.6 million tons of rare earth steel, generating economic benefits of 320 million yuan, social benefits of 1.83 billion yuan, and saving 50 million U.S. dollars in foreign exchange.
When rare earth elements are added to steel, they serve multiple functions such as deoxidation, desulfurization, and modifying inclusions, contributing to the purification and transformation of the steel. In certain types of steel, they can also act as micro-alloying agents. Rare earth elements enhance the oxidation resistance, high-temperature strength, and ductility of steel. They also improve fatigue life, corrosion resistance, and crack resistance, making the material more durable and reliable.
**The main roles of rare earths in steel include:**
**Purification:** Adding rare earths to molten steel helps replace oxygen and sulfur in inclusions like manganese sulfides, alumina, and aluminosilicates, forming rare earth compounds. These compounds tend to float to the surface and enter the slag, reducing the number of inclusions and purifying the steel.
**Refinement of Microstructure:** The rare earth compounds formed during the reaction with inclusions have higher melting points and precipitate before solidification. These fine particles act as nucleation sites, reducing the degree of supercooling during crystallization. This leads to a finer microstructure, reduced segregation, and improved mechanical properties.
**Inclusion Morphology Control:** When rare earths are introduced into steel, manganese sulfides are replaced by rare earth oxides or sulfides that have low plasticity at high temperatures. These compounds remain spherical during rolling, causing less damage to the steel’s mechanical properties. As a result, the toughness and fatigue resistance of the steel are enhanced.
In atmospheric corrosion-resistant steel, rare earths help create a dense inner rust layer that bonds strongly with the matrix, preventing the penetration of oxygen and water. This reduces the corrosion rate, increasing the corrosion resistance of the steel by 0.3 to 2.4 times compared to non-rare earth steel. In MnNb low alloy high-strength steel, rare earth additions significantly improve cold bending, impact, low-temperature impact, and wear resistance, enhancing both processing performance and service life. In railway rails, rare earths boost wear and spalling resistance, extending rail life by 1.5 times after prolonged use.
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**Tags:** Rare earth steelmaking
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