Effect of carbon and nitrogen content on microstructure and properties of Nickel Alloy UNS N07718

摘要

In oil and gas fields high levels of hydrogen sulphide, carbon dioxide, chloride and sulphur at high pressures and high temperatures require material fine tuning in terms of chemical composition, microstructure and mechanical properties to assure required stress corrosion cracking resistance. The precipitation hardenable alloy 718 (UNS N07718) alloy is applied in upstream oilfield technology due to its high strength and high corrosion resistance. Compositions and production process parameters affect microstructure features with a direct consequence on mechanical properties and corrosion resistance. However, a complete understanding of the influence of microstructural features on the corrosion resistance of alloy 718 has not been reached to date. To address this a large research program dealing with the effect of precipitates on the susceptibility of alloy 718 to localised corrosion and hydrogen embrittlement was conducted. The effect of carbon and nitrogen content has been invstigated in this work. Plates of Alloy 718 (wt 16 mm) were manufactured on pilot scale varying carbon and nitrogen contents in order to assess mechanical and microstructural properties as well SCC behaviour after solubilisation heat treatment followed by ageing hardening treatment.