Investigation Of Chromium Content On Elevated Oxidation Resistance Of Iron-Based Coating

In the article four kinds of high-temperature oxidation-resistant iron-based coatings were deposited on the surface of Q235 low carbon steel by arc spraying process. The morphologies, composition, and phase structures of the oxidation products were investigated by scanning electron microscopy (SEM), Energy spectrum analysis (EDS) and x-ray diffraction analysis (XRD) and contrastive study of four kinds alloy coatings. Corrosion-resistance performance of coatings was evaluated by means of high temperature oxidation test, corrosion with salt coating test and thermal shock test. And the corrosion mechanisms were discussed. The following is the result:1. Fe-based cored wires were prepared by using 430 steel strip to wrap metal powder of Cr, Fe. Fe-based coatings were prepared by electric arc spraying process, which have compact surface. Typical layered Fe-based coatings were fabricated. Fe-based coatings contained Cr, oxide and spinel structure of Fe-Cr as the major constituent by analysis of SEM, EDS, XRD. The chromium content of iron-based coatings had a certain influence on the. Micro-hardness of coatings, but which isn't the main factors. with increase of Cr rate, the micro-hardness of coatings has a little increasing; The average micro-hardness are about lower than 500HV0.1. The thermal shock test showed: For the thermal shock test the 40wt.%Cr is the best coating, and the 20wt.%Cr is the worst coating. Among other two kind of test specimen's heat-resistant knocking can be situated.2. High temperature oxidation test showed: the Cr content plays an important role in the oxidation resistance. Under the identical experiment temperature, the oxidation rate of coating is lower than the substrate's. When the Cr content contained in the coating is more than 40wt.%, a continuous Cr2O3 passivation layer is developed on the surface of the coating, leading to good high temperature oxidation resistance.3. The research of corrosion with salt coating's property indicated that: four kinds of coating's corrosion rates are lower than the substrate's, and the Cr44 corrosion resistance performance is most superior. Compared with the substrate, When the Cr content contained in the coating is more than 40wt.%, which can further restrain the oxidation process effectively. The weight gain of the Q235 steel after 100h corrosion test was 7.87 times of that of the FeCr coating under the same test condition. However, in the low Cr- contained coating. which the content is lower than 30wt.%, most of the oxidation products are loose structured Fe2O3, resulting in a poor effect in substrate protection, As time goes by, the corrosion layer gradually became seriously, till eroded the substrate.