Papers by Keyword: Salt Bath Nitriding

Abstract: When the pressure of CO₂ is 2 MPa, through the autoclave corrosion tests of annealed N80 steel specimens in simulated oil field water solution at different temperature, the mechanism of corrosion and the change rule of corrosion resistance with the change of temperature were discussed. In the autoclave tests, some iron elements of the specimens become Fe²⁺ ions and the Fe²⁺ ions go into the solution, which results in the corrosion weight loss. Scaling develops because the CO₃^2- ions in the simulated oil field water solution react with iron elements of the specimen. To QPQ treated specimens, with the increase of temperature, the compactness of the scaling increase, the corrosion weight loss and the weight of scaling decrease. In the same temperature, the corrosion weight loss and the weight of scaling of QPQ treated specimens are both lower than that of untreated specimens.

Abstract: By constant stress tensile test, the corrosion mechanism of high temperature QPQ treated 25CrMnMo steel specimen in H₂S environment was analyzed and discussed. The γ′-Fe₄N in the ε compound layer turns into corrosion substance in the test and expands. At the surface of the ε compound layer, the corrosion layer is visible. The compound layer breaks off in little blocks for volume expansion of the corrosion substance and the exterior tensile stress. The coefficient of diffusion of hydrogen atom in the ε compound layer is very low, that decrease the probability of the hydrogen-induced corrosion of high temperature QPQ treated specimens in H₂S environment.

Abstract: The QPQ complex salt bath treatment is a type of surface technology which contains mainly salt bath nitriding and post-oxidizing processes. The effect of QPQ oxidizing temperature and duration on the corrosion resistance of QPQ treated specimens has been explored by immersion tests and salt spray tests in this paper. All the specimens were post-oxidized after being nitrided at 570! for 2 hours. The material used in this study were 1020 steel. In the immersion tests, the specimens were immersed in 3‰ H2O2 and 10% NaCl water solution. In the salt spray tests, specimens were salt spray tested using 5% NaCl neutral solution. From the experimental data, for high corrosion resistance, conclusions can be drawn:(1) appropriate temperature should be selected carefully in post-oxidizing stage .Too low or too high temperature would decrease the corrosion resistance. (2) The best post-oxidizing duration should generate magnetite film in porous area and should not collapse. (3) In second oxidizing stage, the porous area has been partly eliminated, so the duration should be less than the duration of post-oxidizing.

Abstract: The QPQ complex salt bath treatment is a type of surface strengthening technology which contains mainly salt bath nitriding and salt bath post-oxidizing processes. The effect of nitriding temperature and duration on the corrosion resistance of QPQ treated specimens is explored by immersion tests and salt spray tests in this paper. The material used in this study was 1020 annealed steel. In the immersion tests, the specimens were immersed in 3‰H2O2 and 10% NaCl water solution. In the salt spray tests, specimens were salt spray tested using a 5% NaCl neutral solution. The data indicate that, when the nitriding duration is less than 2 hours at temperature below 590
(phase change will exist when the nitriding temperature is above 590
according to Fe-N phase diagram) , the higher temperature of the salt bath nitriding , the specimens will have the higher corrosion resistance. In addition we have found that nitriding for too short a time generates a thin compound layer, and nitriding for too long generates too much porosity. Both will deteriorate the corrosion resistance.