| Gray cast iron is widely used in various fields of industrial production because of its excellent formability and cost performance,and is one of the most common metal materials.In the cylinder heads of gasoline and diesel engines,etc.,they are all made of gray cast iron material with good shock absorption performance.However,due to the poor corrosion resistance of gray cast iron,its use environment is limited.Studying the corrosion phenomena and laws of gray cast iron under neutral atmospheric conditions,and understanding the influence of environmental factors on the corrosion of gray cast iron,the use of cast iron parts is a very important topic.In this paper,HT250 is used as the research object to discuss the effects of adding different mass percentages of alloying elements on its microstructure,dry and wet alternating corrosion,moisture-resistant atmospheric corrosion,resistance to marine atmosphere corrosion,and matrix potential and space charge layer resistance of corrosion products.The metallographic structure was detected by ZEISS metallographic microscope.The morphology of the corrosion was observed by field emission scanning electron microscopy.The phase structure of the corrosion products was analyzed by X-ray diffractometer.The polarization curve and AC impedance were measured by electrochemical workstation.The preliminary analysis of the atmospheric corrosion mechanism of gray cast iron.The results show that in the microstructure,with the addition of Ni element,the formation of supercooled graphite is reduced,the pearlite structure is refined and stable,the structure is more dense,the aggregation of inclusions at the grain boundary is reduced;and with the addition of Ni element The increase in the content,the more obvious this phenomenon.Under dry and wet alternating environment conditions,the corrosion rate of gray cast iron samples decreases with the increase of test period;with the increase of Ni addition amount,the corrosion layer thickness of the sample increases gradually,the stability improves,and the corrosion resistance is stronger.On the 10th day,the corrosion rate of the 4#sample(with a Ni element content of 1.5%)was reduced by 15%compared to the 2#sample(with a Ni element content of 0.05%).The effect of temperature on the corrosion rate of gray cast iron is first proportional to the inverse ratio.The corrosion rate first increases with the increase of temperature.W hen the temperature exceeds the critical temperature(60℃),the corrosion rate decreases with the increase of temperature.With the increase of the amount of Ni added,the corrosion resistance of the sample in the moisture-resistant atmosphere is enhanced.When the temperature is 60℃ and the humidity is 98%,the corrosion rate of the 4#sample is reduced by 42%compared with the 2#sample.The influence of humidity on the corrosion rate of cast iron also has a critical value:when it is lower than the critical humidity(80%relative humidity),the effect of humidity on the corrosion rate of cast iron is not obvious;once the external humidity is higher than the critical humidity,the corrosion rate of cast iron will follow The humidity increases rapidly and increases rapidly.As the amount of Ni increases,the corrosion resistance of the sample in the moisture-resistant atmosphere increases.The corrosion behavior of cast iron in the atmosphere is electrochemical corrosion under a thin water film:moisture will preferentially adsorb on the active site of gray cast iron,forming a series of water droplets,and then the water droplets grow and diffuse and spread on the metal surface.Preference is given to the connection of the substrate to the graphite,which ultimately forms a continuous layer of corrosion products on the surface of the material.The mechanism of Ni element improving the corrosion resistance of cast iron is to refine the pearlite structure,increase the thickness and stability of the corrosion product layer,and increase the space charge layer resistance Rt of the corrosion product. |
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