1.What is the chemical composition of inconel 718?
Nickel (Ni): The base metal, accounting for the largest proportion, approximately 50% - 55%. Nickel provides excellent corrosion resistance and serves as the matrix for the alloy's microstructure.
Chromium (Cr): Present in the range of 17% - 21%. Chromium enhances the alloy's oxidation resistance and provides additional corrosion protection, especially in high - temperature and acidic environments.
Iron (Fe): Usually around 18% - 21%. Iron is added to increase the alloy's strength and toughness.
Molybdenum (Mo): About 2.8% - 3.3%. Molybdenum improves the alloy's resistance to pitting and crevice corrosion in aggressive environments and also contributes to its high - temperature strength.
Niobium (Nb): Typically 4.75% - 5.50%. Niobium forms precipitates that strengthen the alloy, improving its creep and stress - rupture properties at high temperatures.
Cobalt (Co): Usually less than 1.0%. Cobalt is added in small amounts to enhance the alloy's high - temperature performance and strength.
Titanium (Ti): Around 0.65% - 1.15%. Titanium forms intermetallic compounds with nickel, which contribute to the alloy's strength and improve its resistance to stress - corrosion cracking.
Aluminum (Al): About 0.20% - 0.80%. Aluminum, like titanium, forms precipitates that strengthen the alloy and also improves its oxidation resistance.
Carbon (C): Typically limited to 0.08% maximum. Excessive carbon can form carbides, which may affect the alloy's corrosion resistance and mechanical properties.
Silicon (Si): Usually less than 0.35%. Silicon is a deoxidizer and can improve the alloy's fluidity during casting.
Manganese (Mn): Generally less than 0.35%. Manganese helps to improve the alloy's strength and hardness.
2.What is the ASTM grade of Inconel 718?
Inconel 718 corresponds to several ASTM grades, mainly ASTM B 637 and ASTM B 670
ASTM B 637
: It is the standard specification for precipitation - hardening and cold - worked nickel - alloy bars, forgings, and forging stock used in moderate or high - temperature service. Inconel 718 round bars, forgings, etc. usually comply with this standard.
ASTM B 670
: This is the standard specification for nickel - alloy sheets, strips, and plates. Inconel 718 sheets, coils, and plates typically meet the requirements of this standard.
3.Can Inconel 718 be welded?
Welding Challenges
High strength and hardness: Inconel 718 has high strength and hardness, which can lead to increased welding stress. This may cause cracking in the weld zone if not properly addressed.
Formation of intermetallic phases: During welding, there is a tendency for the formation of intermetallic phases, such as sigma phase. The presence of these phases can degrade the mechanical properties and corrosion resistance of the weld.
Sensitivity to heat input: The alloy is sensitive to heat input. Excessive heat can cause grain growth in the heat - affected zone, reducing the material's toughness and fatigue resistance.
4.What is Inconel 718 used for?
Aerospace industry
Automotive industry
Energy industry
Chemical processing industry
Marine industry
5.What are the mechanical properties of inconel 718?
Room - temperature properties
Tensile strength: The minimum tensile strength is about 1240 MPa. In fact, the actual tensile strength of Inconel 718 products often exceeds this value, usually reaching 1300 - 1400 MPa or higher, depending on the specific heat treatment and processing conditions.
Yield strength: The yield strength is typically around 1035 MPa. It represents the stress at which the material begins to deform plastically.
Elongation: The elongation is usually 12% - 20%. This indicates the material's ability to deform before fracture, reflecting its ductility. Inconel 718 has good ductility, which allows it to be formed and processed into various shapes.
Hardness: The hardness of Inconel 718 is usually in the range of 36 - 42 HRC (Rockwell hardness). This relatively high hardness provides good wear resistance and indentation resistance.
High - temperature properties
Creep resistance: Inconel 718 exhibits excellent creep resistance at high temperatures. For example, at 650°C, it can maintain a certain level of strength and resist slow, progressive deformation under long - term loading. It can withstand stresses of around 500 - 600 MPa for extended periods without significant creep deformation.
Stress - rupture strength: The alloy also has high stress - rupture strength at elevated temperatures. At 700°C, it can withstand stresses of approximately 300 - 400 MPa for a considerable time before rupturing. This property is crucial for applications in high - temperature and high - stress environments, such as in gas turbines.
Tensile strength retention: Even at high temperatures, Inconel 718 can retain a significant portion of its room - temperature tensile strength. At 650°C, the tensile strength is still around 900 - 1000 MPa, which is much higher than that of many other alloys.
