Effect of Rare Earth on Microstructure and Properties of Steel(1)
As we all know, the development of the rare earth element has made great progress. It plays an important role in all fields. And let us talk about the performance impact of the rare earth elements in steel.
1. The rare earth element can improve the fatigue performance of steel. The metamorphism of rare earth on oxidized inclusions (such as AL2O3) leads to the formation of rare earth inclusions such as REAlO3 and RE2O2S. They will cause an increase in the fatigue life of certain steels, such as silicon manganese spring steel, 40MmB steel and 25 MntiB gear steel. The extent of the increase will vary depending on the loading conditions, the strength of the steel, the number and size of the inclusions.
2. Improve the cutting performance of free-cutting steel. In free-cutting steels such as 20 CrRES, 20 CrMnTire and lCrl8Ni9RES. Due to the formation of more rare earth inclusions and wrapped composite rare earth inclusions, the number of hard spots present alone is greatly reduced. At the same time, the rare earth inclusions from a layer of lubricating film and inclusions in front of the tool to cause stress concentration during cutting. Thereby the cutting performance of the steel is significantly improved.
3. Improve the pitting resistance of the stainless steel. The rare earth element changes the composition of sulfide inclusions in steel, the form of impurities in steel and reduce the sulfur content in steel. This is the main reason for the corrosion resistance of rare earth to improve steel.
4. Improve the hot workability of high alloy steel. The addition of rare earth in steel can eliminate the segregation of sulfur, purify the grain boundary and improve the thermoplasticity of the steel.
5. Rare earth inhibits temper brittleness of steel and lowers ductile-brittle transition temperature. When the rare earth mass fraction is high (0.2%~0.3%), the rare earth weakens the temper brittle sensitivity of the steel.
6. Rare earth improves the atmospheric corrosion resistance of phosphorus-containing steel. After the addition of rare earth, the segregation of phosphorus and sulfur between dendrites is reduced. The degree of segregation of phosphorus in profile steel is reduced by about 30%. The uniform distribution of phosphorus in the steel allows the full effect of phosphorus.
7. Rare earth elements improve the ability of high alloy steel weld metal to resist intergranular crack formation. In the austenitic weld metal containing niobium, the addition of cerium or yttrium prevents the segregation of niobium and improves the crack resistance of the weld metal. In the austenitic weld metal containing no niobium, cerium and calcium are added. Not only improve the crack resistance of the weld, but also improve its resistance to intergranular corrosion.
8. Effect of rare earth on the hardenability of steel. In steels with lower carbon content, the addition of cerium increases the incubation period of pro-eutectoid ferrite transformation. The right-temperature transition curve of the supercooled austenite is shifted to the right, and the nucleation rate and the growth rate of the pro-eutectoid ferrite are decreased and the uniform nucleation of the pro-eutectoid ferrite at the austenite grain boundary into uneven nucleation only at the edge of the grain boundary.
1. The rare earth element can improve the fatigue performance of steel. The metamorphism of rare earth on oxidized inclusions (such as AL2O3) leads to the formation of rare earth inclusions such as REAlO3 and RE2O2S. They will cause an increase in the fatigue life of certain steels, such as silicon manganese spring steel, 40MmB steel and 25 MntiB gear steel. The extent of the increase will vary depending on the loading conditions, the strength of the steel, the number and size of the inclusions.
2. Improve the cutting performance of free-cutting steel. In free-cutting steels such as 20 CrRES, 20 CrMnTire and lCrl8Ni9RES. Due to the formation of more rare earth inclusions and wrapped composite rare earth inclusions, the number of hard spots present alone is greatly reduced. At the same time, the rare earth inclusions from a layer of lubricating film and inclusions in front of the tool to cause stress concentration during cutting. Thereby the cutting performance of the steel is significantly improved.
3. Improve the pitting resistance of the stainless steel. The rare earth element changes the composition of sulfide inclusions in steel, the form of impurities in steel and reduce the sulfur content in steel. This is the main reason for the corrosion resistance of rare earth to improve steel.
4. Improve the hot workability of high alloy steel. The addition of rare earth in steel can eliminate the segregation of sulfur, purify the grain boundary and improve the thermoplasticity of the steel.
6. Rare earth improves the atmospheric corrosion resistance of phosphorus-containing steel. After the addition of rare earth, the segregation of phosphorus and sulfur between dendrites is reduced. The degree of segregation of phosphorus in profile steel is reduced by about 30%. The uniform distribution of phosphorus in the steel allows the full effect of phosphorus.
7. Rare earth elements improve the ability of high alloy steel weld metal to resist intergranular crack formation. In the austenitic weld metal containing niobium, the addition of cerium or yttrium prevents the segregation of niobium and improves the crack resistance of the weld metal. In the austenitic weld metal containing no niobium, cerium and calcium are added. Not only improve the crack resistance of the weld, but also improve its resistance to intergranular corrosion.
8. Effect of rare earth on the hardenability of steel. In steels with lower carbon content, the addition of cerium increases the incubation period of pro-eutectoid ferrite transformation. The right-temperature transition curve of the supercooled austenite is shifted to the right, and the nucleation rate and the growth rate of the pro-eutectoid ferrite are decreased and the uniform nucleation of the pro-eutectoid ferrite at the austenite grain boundary into uneven nucleation only at the edge of the grain boundary.
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