Higher melting point of anti-corrosion spiral steel pipe processing

  It is found that most anti-corrosion spiral steel pipes have higher melting point than the main elements, and still have strength and hardness at high temperature. The superalloy has good tempering softening resistance at high temperature. For example, After 70o~1000 ℃ and 72h aging heat treatment, the hardness of Ao.2CoCrFenic1 high entropy alloy has not decreased, but has been greatly improved. However, traditional alloys such as high-speed steel soften at 550 ℃. For example, AIZnMnSnSbPbMg alloy has strong oxidation resistance at 750 ℃, and the thermogravimetric increase rate is only 004%; Under the same conditions, the thermogravimetric increase rate of pure magnesium is as high as 274%. The high entropy alloy shows rare high-temperature precipitation hardening phenomenon and excellent high-temperature oxidation resistance, and its oxidation resistance is comparable to that of the anti-oxidation alloy Ni-22Cr-10A1-1Y on the jet turbine blade. NiCocraIsiY high entropy alloy coating was prepared by arc ion plating method. The results show that the mass of the coating with high A content increases rapidly at the initial stage of oxidation, but increases slowly with time, and the weight gain is only 0.5 mgcm2 at 1000 ℃ and 10 oh; After oxidation, A2O3 dense oxide films with different morphologies were formed on the surface to isolate oxygen diffusion to the coating and even the alloy matrix; The higher A storage capacity during isothermal oxidation can timely repair the damaged oxide film, slow down the cracking and peeling of the oxide film during cyclic oxidation, so as to ensure that the material can resist long-term high-temperature oxidation. As mentioned above, the high mixing entropy effect of anti-corrosion spiral steel pipe is prominent under high temperature conditions, which can better reduce the Gibbs free energy of the alloy system, Therefore, relatively stable microstructure and properties of the alloy can be obtained, which indicates that high entropy alloy has potential application in high temperature. On this basis, Senkov et al. studied the high-temperature mechanical properties of two high melting point and high entropy alloys and compared them with nickel base superalloys. It can be seen that these two refractory alloys show excellent high temperature yield strength, especially at temperatures higher than 1000 ℃. Compared with nickel base superalloys, they have very obvious advantages.

Irradiation resistance Generally speaking, in terms of microstructure, irradiation will lead to an increase in the density of crystal defects in materials, such as vacancy and interstitial atoms, dislocation and dislocation ring, poor stability of structure and phase, segregation and local ordering. In terms of properties, irradiation will lead to the increase of brittleness, volume swelling and creep of materials until fracture and failure. At present, there are few research results on the radiation resistance of high entropy alloys, but their excellent performance has attracted extensive attention of researchers. Zhang et al. Egam et al. conducted in situ electron irradiation studies on Zrhfnb body centered high entropy alloy and CoCrCuFeN face centered cubic high entropy alloy. The irradiation study of Ni, NCo, NiCoR and NiCoFeCrMn shows that the high entropy alloy has good radiation resistance. The disordered solid solution phase structure mainly formed by high entropy alloys is characterized by large lattice distortion and high configuration entropy due to the difference in atomic size, which may result in atomic level stress, making them have special properties, and may break through the performance limits of existing materials. The excellent performance of high entropy alloy radiation resistant materials provides a new idea for nuclear materials and promotes the development of nuclear energy.

In addition, radiation resistant materials are also required in the aerospace field, and radiation resistant treatment is also required for equipment and other surfaces operating in a radioactive environment. Low temperature irradiation can also reduce the fracture toughness of materials. The most typical example is the increase of ductile brittle transition temperature of BCC materials under irradiation. After irradiation, the relationship between yield stress and ductile brittle transition temperature is consistent with the existing theoretical model. In this theoretical model, the ductile brittle transition temperature, the yield stress strongly dependent on temperature and the fracture stress not significantly dependent on temperature are consistent with the changing trend of these three under irradiation. The ductile brittle transition temperature is generally obtained by impact test of notched specimen, and then the fracture toughness of the material is indirectly obtained by the ductile brittle transition temperature. In the experiment, the fracture toughness of materials can be measured by the sharp cracks on the materials, and the sharp crack area is a representative stress strain gradient area in the structural components. In recent years, with the development of elastic-plastic fracture mechanics theory, the relationship between fracture toughness and temperature of many iron base alloys has been found out some general laws. The ion irradiation damage mechanism of ceramic and cermet materials, the relationship between the two can be normalized by the size parameters of samples. This general relationship can also be used to predict the relationship between the fracture toughness of nuclear materials and temperature. At present, the prediction results for some small-scale samples are in good agreement with the experimental results.