The Structure And Mechanism Of The Oxide Film Formed In The Process Of Electric Heating Of Cr20Ni80 Alloy

Cr20Ni80 alloy is a typical Ni-Cr electric heating alloy, because of its high melting point, stable resistivity, strong oxidation resistance and good mechanical properties, long service life and many other advantages is widely used in machinery,metallurgy,industrial furnace etc. Because of the special working environment of Cr20Ni80 alloy wire, the high temperature oxidation resistance is the most important performance, therefore, the study on the oxidation resistance of nickel based electric heating alloy at home and abroad, but these studies are based on the oxidation method of heating in a furnace, the actual situation of the electric heating is not consistent with the use of alloy wire. In the furnace, the temperature of the electric heating alloy is transferred from the outside to the inside of the alloy, but when the electric heating,the alloy wire is the heating body, and the temperature is transferred from the alloy to the surrounding. There may be difference in temperature field distribution. In this paper, the high temperature oxidation process of Cr20Ni80 alloy was studied by means of an electric heating device.The service temperature of the Cr20Ni80 alloy is 950?1100?,the laboratory generally used to improve temperature accelerated experimental determination of the service life, the fast life of Cr20Ni80 alloy electric "GB/T 1234-2012 high resistance alloys for electrical heating" provisions of the determination of the temperature of 1200?. So this paper test fast life of Cr20Ni80 alloy wire at 1200?, drawing resistance curve changes with time, according to the curve, selection of Cr20Ni80 alloy with different heating time at 1200?, morphology and composition of the surface oxide film is analyzed, The isothermal oxidation experiments also select the temperature range of 900-1100?,analysis of Cr20Ni80 alloy in different heating temperature difference of alloy surface oxide film, the oxidation mechanism of preliminary exploration of Cr20Ni80 alloy.The experimental results show that: oxidation process of Cr20Ni80 alloy at 1200? may be divided into 3 stages, the rapid oxidation phase, oxide film is mainly composed of Ni oxide and Cr oxide,and NiO and Cr2O3 react with solid phase to generate NiCr2O4 covering the surface the substrate; in Steady state oxidation phase,oxide film the surface is mainly composed of dense Cr2O3,reduce the oxidation rate of substrate; in the unstable phase,because of the existence of stress in oxide film,leading to a large number of outer film peeling, the inner oxide film is exposed and porous, and the substrate is oxidized rapidly, at this time, Cr20Ni80 alloy wire is about to break. The morphology observation and composition analysis of Cr20Ni80 alloy wire,it's believed that the pores and inclusion in the alloy are the cause of the failure of the alloy wire, When the Cr20Ni80 alloy wire is heated at different temperatures, it's found that with the increase of temperature. surface oxide content of Cr also increased, as the temperature increases, the diffusion rate of metal ions increases.