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Corrosion Resistant Alloys
Description of material
EG1 is a single phase solid solution Nickel – Copper alloy with very high corrosion resistance in marine and chemical environments and excellent mechanical properties at sub-zero temperatures, as well as good high temperature properties up to 450 C°. The yield and tensile strength of this grade can only be increased by cold working. Depending on the chemical balance of each heat, EG1 could have a ferromagnetic behavior and this should be evaluated if magnetic permeability were a concern.
Many marine applications such as fasteners, pumps and some kinds of propeller shafts, valves, tanks and any device or marine fixture for sea water service. Mostly used in off shore structures, in desalination and chemical plants and in sour gas environments.
EG1 is not as susceptible to pitting and crevice corrosion in stagnant sea water as with typical austenitic grades. In any case this kind of corrosion is not so rapid in the propagation of deep pits. In addition, EG1 offers a good corrosion resistance in reducing environments and is immune to stress corrosion cracking in fresh and industrial water, but doesn’t offer the same resistance in oxidizing environments. Even though this grade has excellent stress corrosion cracking resistance, the stress relieving of a strain hardened structure reduces or avoids the risk of this kind of corrosion in certain very aggressive environments.
EG1 offers excellent cold forming properties thanks a low cold hardening factor, but the best results, in the case of a large amount of cold deformation, such as cold extrusion or heading, is when this alloy is soft annealed.
EG1 is classified as difficult when machining but has approximately the typical machinability of an austenitic structure with a low Sulphur content and some difficulties could happen in turning, threading and milling processes. Operators should know that EG1 requires more rigid and powerful machines in addition to the correct choice of tools, coating carbides and cutting fluids. This grade can be machined in the soft annealed condition but better results are obtained when machined in the work hardened or work hardened + stress relieved condition, such as cold drawn or cold deformed. However, machining parameters should avoid operations able to cause stresses of the structure and its work hardening level should be considered. A stress relieving should be done in case of distortions after machining.
EG1 surfaces to be welded must be free of any kind of contaminants. Welding procedures are substantially the same of those applied for Austenitic Stainless steels but joint design and a different weld penetration behavior should be evaluated. Using shielding gas is recommended. Neither preheating nor post-welding heat treatment are normally required but heat tint should be always be eliminated to maximize corrosion resistance.
EG1 has a good hot plasticity and is suitable for processing by drop forging, hot extrusion or by upsetting. Being softer than many austenitic grades, it is recommended to choose temperatures at the low end of the range of forging and to avoid a long-time soaking detrimental to its structure. Overheating must be always avoided. The choice of hot working temperature and process parameters must always evaluate both the strain rate and the consequent increasing of temperature that is reached after hot deformation. High strain rates and temperatures at the top of the range during the extrusion and forging process, could generate internal bursts, large grain size and structural permanent damage. EG1 could be used in the hot rolled or forged condition, in order to obtain an increasing of strength but an annealing after hot working could improve its corrosion resistance in certain environments. As with other Ni-alloys, the atmosphere of the furnace should be well monitored in order to avoid embrittlement and surface damage.
Typical heat treatments are soft annealing and stress relieving, but the choice depends on the final use of EG1 and the service environment. Surfaces of products must free of any contaminants and very clean before heat treatment. Stress reliving at low or medium temperatures are useful to avoid deformation before and/or after machining, while high temperatures should be chosen when a very soft structure is required. In this case, pay attention on soaking in order to avoid a rapid increasing of grain size. In the case of high strength requirements, a final heat treatment is not necessary and high values of strength are reached by a controlled hot working deformation with lower temperatures of forging or rolling processes.