At present, all countries are actively researching and developing ultra-supercritical heat-resistant steel, in 2007, the United States developed an austenitic wear-resistant plate that can spontaneously form an Al2O3 protective film, which takes Al2O3 as a protective layer and can withstand high temperatures of 650 ~ 900 ° C, and the cost is lower than that of Ni-based superalloys. Subsequently, in 2010, China successfully developed another AFA wear-resistant plate through composition optimization on the basic composition of the traditional austenitic wear-resistant plate NF709, which can generate a continuous dense Al2O3 protective layer under the condition of water vapor at 800 ° C.
In the process of high temperature operation of the gas turbine used in power generation and ship industry, the combustion of sulfur-containing fuel and the salty environment of the ocean will deposit sulfate, oxygen and other corrosive gases on its blades, which will cause accelerated corrosion of the blades and wear phenomenon. In order to make AFA corrosion-resistant wear-resistant plate more widely used, it is particularly necessary to study its wear resistance and mechanism. Compared with nickel-based K417 superalloy and 316L wear-resisting plate, the new AFA wear-resisting plate has excellent resistance to sodium sulfate molten salt. Limiting the diffusion of S element in the alloy is beneficial to improve the wear resistance of the alloy. At 1273K, the diffusion coefficient of S in Co is only half that of S in Ni, indicating that Co is beneficial to the wear resistance of the alloy. Therefore, in order to better improve the wear resistance of the new AFA wear plate, it is necessary to study the influence of alloying element Co on its wear resistance.
A research institution selected a new type of AFA wear-resistant plate, its chemical composition (mass fraction, %) is Ni25.00, Cr18.00, Al3.00, Mo1.50, Nb1.50, Si0.15, C0.08, B0.01, P0.04, Hf0.15, Y0.01, Fe50.56.
The alloy is smelted by non-consumable vacuum arc furnace. Before melting, the arc furnace is vacuumed to below 5×10-3Pa, filled with high purity argon, and high purity titanium ingot is smelted first to absorb the residual O. Because there are many kinds of elements in this alloy, and the melting point, density, thermal expansion rate and other physical properties of each element are quite different, it is necessary to melt the pre-alloy first in the melting process: 1) Mo, Nb, C, B and a part of Ni and Fe with high melting point are put in a crucible; 2) Low melting point of Al, Si and Cr, Co, Fe-P and another part of Ni, Fe in another crucible, due to the low boiling point of Al, melting should be prevented from overheating to avoid Al burning. The above prealloys are melted 4 times each, and then one alloy is synthesized and melted 10 times. After the alloy is melted and cast, the wear resistance test is carried out after heat treatment and cutting into the sample. The results show that:
(1) Adding Co element to the new AFA wear plate can improve the wear resistance of sodium sulfate molten salt to a certain extent.
(2) The Co element can increase the relative content of Cr in the oxide film, promote the formation of a continuous protective oxide film, and enhance the adhesion and densification of the oxide film, delay the rupture time of the oxide film, and extend the wear-resistant inoculation period.
(3) The Co element can also effectively delay the diffusion of S element in the AFA wear-resisting plate, reduce the vulcanization-oxidation rate in the wear-resisting process, and thus improve the wear resistance of the alloy.
