Effect Of Composite Powders On Corrosion Properties Of Ductile Iron

Ductile iron has been widely used in many industries such as automobile,machinery manufacturing and wind power because of its good elongation,tensile properties,wear resistance and low cost.Most of China's wind turbines are located in windy areas such as the coast and the northern deserts.Their environmental and climatic conditions are extremely harsh,and they are facing the effects of natural environments such as seawater,tides,and salt fog.Work under wind speed,high temperature difference,high and cold environment.Therefore,the atmospheric corrosion phenomena and rules of nodular cast iron must be studied.In this paper,QT400-18 L is taken as the research object to study the effect of adding composite powders with different mass fractions on the matrix structure,tidal atmosphere corrosion,alternating wet and dry corrosion,electrochemical corrosion and their corrosion products on corrosion performance.The atmospheric corrosion mechanism of spheroidal graphite cast iron and the effect of composite powder on the corrosion resistance were preliminarily discussed.The test results show that: adding compound powders with different mass fractions to QT400-18 L,the spheroidization rate is increased from 79.40% to 90.08%,the spheroidization level is increased from 3 to 2,and the pearlite content is reduced from 20.84% to 11.16%,Its structure is obviously refined;in the constant damp heat test,QT400-18 L corrosion rate has a critical value with the change of humidity and temperature.With the increase of humidity,the corrosion rate of the QT400-18 L sample gradually increases.When the humidity exceeds the critical humidity(80%),the corrosion rate is rapidly accelerated;when the humidity is 98% and 60?,when adding 0.15% composite powder The corrosion rate is reduced by 29.29%.The corrosion rate of the QT400-18 L sample gradually increases with increasing temperature.When the critical temperature exceeds 60?,the corrosion rate decreases.In the salt spray test,the corrosion rate of the QT400-18 L increases first with the increase of the test period.After it is large,it decreases to be stable.After adding 0.10% composite powder,the corrosion rate(6h)is reduced by 26.03%.Among the micro-scale corrosion products,the "rod-shaped" corrosion products gradually become thicker and shorter and become "cotton ball-shaped" corrosion products.It is believed that the transformation of ?-Fe OOH to ?-Fe OOH in this process is the main factor that the corrosion rate gradually decreases and tends to be gentle.Ductile iron corrosion in the atmosphere occurs preferentially at the junction of graphite and the substrate with a large potential difference,at which point droplet adsorption and spreading occurs,and eventually expands into a continuous corrosion product layer.The mechanism of composite powder to improve the corrosion resistance of spheroidal graphite cast iron is mainly to refine the structure of spheroidal graphite cast iron,increase the electrode potential of the matrix,improve the stability of the corrosion product layer,and improve the transfer resistance(Rct)of the charge resistance.