Abstract
It is known that non-metallic inclusions (NMI) that are formed during steel production and heat treatment can significantly affect the properties of final steel products. Therefore, it is very important to be able to determine the content of harmful NMI in steels. Nickel-based alloys are widely used in the oil and gas recovery industry, due to a good combination of strength and corrosion properties. Earlier studies have shown that the corrosion properties in immersion test and electrochemical tests for Ni-based EP718 alloys are slightly lower than that for 718 alloys. The focus in this study was the influence of different NMI on the corrosion resistance of these alloys. The characteristics of inclusions (such as size, morphology, and chemical composition) were analysed by using the electrolytic extraction method followed by three-dimensional investigations using SEM in combination with EDS. It was found that some non-metallic inclusions in EP718 alloys significantly reduce its corrosion resistance. It was also shown that a primary dissolution of the metal matrix occurs around certain inclusions during electrolytic extraction. Based on obtained results, the corrosion active non-metallic inclusions can be determined in these Nickel-base alloys and some recommendations for optimization of their production technology can be formulated.
Highlights
It is known that non-metallic inclusions (NMI) that are formed during steel production and heat treatment can significantly affect the properties of final steel products
This study focused on precise assessments of nonmetallic inclusions in corrosion resistance nickel-based alloys (EP718 and 718) by using the electrolytic extraction method
The electrolytic extraction method was applied for evaluation of non-metallic inclusions in corrosion resistance nickel-based alloys (EP718 and 718)
Summary
It is known that non-metallic inclusions (NMI) that are formed during steel production and heat treatment can significantly affect the properties of final steel products (such as workability, mechanical properties, corrosion resistance, etc.). It has been found that various non-metallic inclusions observed on polished metal samples of EP718 alloys can significantly reduce its corrosion resistance. A number of studies [2,3,4] performed during the last 10-20 years showed that the three-dimensional (3-D) investigations of inclusions and clusters on a film filter after electrolytic extraction (EE) from metal samples have major advantageous in comparison to the conventional two-dimensional (2-D) investigations of NMI on polished surfaces of metal samples. This study focused on precise assessments of nonmetallic inclusions in corrosion resistance nickel-based alloys (EP718 and 718) by using the electrolytic extraction method. Based on comparative analysis of inclusions characteristics, the most harmful NMI were determined with respect to the corrosion resistance of the investigated nickel-based alloys
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