Effect of Rare Earth on Microstructure and Properties of Steel(2)

The importance of rare earth elements can be imagined. I also mentioned a part in the last article, so here I will finish the rest about the influence of rare earth on the organization and properties of steel. I hope everyone can read and give an evaluation.

1. Rare earth can improve the strength, plasticity and toughness of cast steel. If the cast steel grain structure is coarse, the grain can be refined by adding rare earth. It can improve the yield strength, toughness and plasticity of cast steel. 

2. Rare earth improves the wear resistance of cast steel. The addition of rare earth reduces the precipitation of coarse carbides during crystallization, which improves the wear resistance of the cast steel. The rare earth refines the as-cast structure, improves the hardness and work hardening ability of the steel, reduces the as-cast looseness, and makes the inclusions in the steel less, smaller, and spheroidized. These are all possible reasons why rare earths improve the wear resistance of steel.

2. Rare earths can improve the high temperature oxidation resistance of steels and alloys. The rare earth element is mostly present in the metal phase state in the FCM alloy. When the alloy is oxidized at 1300 °C, the rare earth atoms diffuse from the solid solution and the rare earth intermetallic compound to the scale, alloy matrix interface or alloy surface. Forming a rare earth-containing oxide scale on the surface and forming a rare earth-containing oxidized oxide point dense region on the surface of the alloy substrate. 

4. The effect of rare earth on the room temperature strength, hardness and short-term high temperature tensile strength of steel. The rare earth element can slightly increase the room temperature strength of the cast steel by refining the as-cast structure. The amount of rare earth alloying in steel is linear with strength. For Fe crAl alloys, the dispersion of internal oxidized particles will increase the strength of the alloy matrix due to the internal oxidation of rare earths and rare earths at high temperatures. 

5. Rare earths affect the properties of steel by changing the microstructure of the steel. For example, rare earth can slow the austenite bainite transformation, which is beneficial to improve the hardenability of steel. The addition of rare earth can change the position where the carbide precipitates from the grain boundary and the intragranular distribution to become mainly distributed in the crystal, and refine the carbide and lath martensite.

6. Rare earth elements can eliminate the embrittlement tendency of FecrAl alloys when used at high temperatures. Rare earth reduces pearlite in steel, reduces band structure, and reduces white spot formation tendency. These can be attributed to the formation of rare earth composite carbides and the interaction of rare earths with hydrogen.

7. Rare earth improves the high temperature creep rupture strength and plasticity of high alloy steel. Rare earth strengthening grain boundary and reducing the content of impurity elements on grain boundaries are the main reasons for the improvement of steel heat strength.