Preparation and performance of nonphosphating coating on steels

The technology of phosphating on steels extensively used in metal finishing industry causes eutrophication pollution and harms human beings. A new tannate and fluoferrite composite chemical conversion coating treatment process on Q195 steel surface was studied by using single factor experiment and comprehensive evaluation. A homogenized, blue-black conversion coating was formed on the Q195 steel through a solution containing KF, HNO₃, tannin, and Cr(NO₃)₃. The performance, morphology and composition of the conversion coating were investigated by neutral salt spray test, metallographic, scanning electron microscopy(SEM), energy disperse spectroscopy(EDS) and fourier transformed infrared spectra. The results showed that primary components of the conversion coatings on steel were potassium fluoferrite, tannin-Fe³⁺ and tannin-Cr³⁺ complexes. The crystalloid of coating was less than 1μm. The conversion coating improved the anti-corrosion performance of steel effectively and the salt spray test reached 9h.