Nickel-based super alloy: Inconel 718 (Alloy 718/UNS N07718)

What is Inconel 718?

Inconel 718 alloy is a nickel base superalloy strengthened by body centered tetragonal γ” and FCC γ′ phase precipitation. It has good comprehensive properties in the temperature range from – 253 ℃ to 700 ℃. The yield strength below 650 ℃ is the first among the deformed superalloys, and has good fatigue resistance, radiation resistance, oxidation resistance and corrosion resistance, And good processability, weldability and long-term structure stability, can manufacture various shape complex parts, in aerospace, nuclear energy, petroleum industry, in the above temperature range has been widely used.
Another characteristic of the alloy is that the alloy structure is particularly sensitive to the hot working process. Mastering the law of precipitation and dissolution of phases in the alloy and the relationship between the structure, process and properties, reasonable and feasible process procedures can be formulated according to different use requirements, and various parts that can meet different strength levels and service requirements can be obtained. The products we supply are Inconel 718 BLRF Flange, incoloy 718 forging, incoloy 718 bar, incoloy 718 flange, incoloy 718 pipe fitting, incoloy 718 ring, incoloy 718 plate, incoloy 718 strip, incoloy 718 wire, incoloy 718 pipe, Inconel 718 Seamless 90 Degree Long Radius Elbow, etc. It can be made into incoloy 718 disc, incoloy 718 ring, incoloy 718 blade, incoloy 718 shaft, incoloy 718 fastener and elastic element, plate structure, casing and other parts, which can be used in aviation for a long time.
Designated as UNS N07718 or W.Nr. 2.4668, Inconel 718, also known as “Alloy 718”, is a precipitation-hardenable nickel-chromium alloy containing significant amount of iron, niobium, and molybdenum along with lesser amounts of aluminum and titanium. The titanium and niobium are added to overcome strain-age cracking problems during welding and weld repair. Inconel Alloy 718 combines corrosion resistance and high strength with outstanding weldability, including resistance to postweld cracking. The alloy has excellent creep-rupture strength at temperatures up to 1300°F [700°C]. The Inconel 718 is fabricated for gas turbines, rocket motors, spacecraft, nuclear reactors, pumps and other piping tools. Most commonly, it is used for fasteners and springs.

Characteristics of Inconel 718 (Alloy 718/UNS N06718)

Inconel718 precipitation sclerosis type of molybdenum alloy containing niobium, nichrome, has high strength at 700 ℃, good toughness and good corrosion resistance in high and low temperature environment.Delivery status can be a solid solution treatment or precipitation hardening state.

  • Easy processing;
  • High tensile strength, fatigue strength, creep strength and rupture strength at 700 ℃;
  • The oxidation resistance at 1000 ℃;
  • Stable chemical properties at low temperature ;
  • The characteristics of good welding performance.

No matter in the high temperature or low temperature environment, 718 alloy has excellent resistance to stress corrosion cracking and pitting. 718 alloy has particularly outstanding oxidation resistance at high temperature.

Corrosion resistance of Inconel 718 (Alloy 718/UNS N06718):

The chemical composition of the alloy can be divided into three categories: standard component, high quality component and high purity component. The high quality components can reduce carbon and increase niobium on the basis of standard composition, so as to reduce the amount of niobium carbide, reduce the fatigue source and increase the number of strengthening phase, and improve the fatigue resistance and material strength. At the same time, reduce the content of harmful impurities and gases. High purity component is to reduce the content of sulfur and harmful impurities on the basis of high quality standards, and improve the purity and comprehensive properties of materials.
The boron content of Inconel 718 alloy for nuclear energy application needs to be controlled (other elements remain unchanged), and the specific content shall be determined by both parties through negotiation. When ω (b) ≤ 0.002%, it is different from Inconel 718 alloy used in aerospace industry, and the alloy grade is inconel 718A.

Classification C Cr Ni Co Mo Al Ti Fe
Standard ≤0.08 17.0~21.0 50.0~55.0 ≤1.0 2.80~3.30 0.30~0.70 0.75~1.15 Balance
High quality 0.02~0.06 17.0~21.0 50.0~55.0 ≤1.0 2.80~3.30 0.30~0.70 0.75~1.15 Balance
High purity 0.02~0.06 17.0~21.0 50.0~55.0 ≤1.0 2.80~3.30 0.30~0.70 0.75~1.15 Balance
Classification Nb B Mg Mn Si P S Cu Ca
Standard 4.75~5.50 0.006 0.01 0.35 0.35 0.015 0.015 0.30 0.01
High quality 5.00~5.50 0.006 0.01 0.35 0.35 0.015 0.015 0.30 0.01
High purity 5.00~5.50 0.006 0.005 0.35 0.35 0.015 0.002 0.30 0.005
Classification Bi Sn Pb Ag Se Te Tl N O
 
Standard 0.0005 0.0003
High quality 0.001 0.005 0.001 0.001 0.0003 0.01 0.01
High purity 0.00003 0.005 0.001 0.001 0.0003 0.00005 0.0001 0.01 0.005

Mechanical Properties of Inconel 718 (Alloy 718/UNS N06718)

Density, lb/in3 Melting Range Specific Heat at 70°F, Btu/lb °F Curie Temperature, °F(°C) Permeability at 200 oersted and 70°F
Annealed Annealed and Aged °F °C at 21°C, J/kg °C) Annealed Material Annealed and Aged Material Annealed Material Annealed and Aged Material
0.296 0.297 2300-2437 1260-1336 0.104(435) <-320(<-196) -170(-112) 1.0013 1.0011

Physical Properties of Inconel 718 (Alloy 718/UNS N06718)

Density 
(g/cm3)

Elastic modulus
(GPa)

Melting point
(℃)

8.24 

204.9

1260~1320 

Thermal conductivity
(W(m•℃))

Hardness
(HBS)

 Thermal expansion coefficient( 21 – 93°C)
10-6×m/m °C

14.7

346-450

13.0 

Product Forms and Standards

Product Forms Standards
Rod, Bar & Wire ASTM B166
Plate, Sheet & Strip ASTM B168, ASTM B906
Seamless Pipe and Tube ASTM B167, ASTM B829
Welded Pipe ASTM B472
Welded Tube ASTM B564

Heat treatment system of nickel-based alloy incoloy 718:

The alloys have different heat treatment systems to control grain size, shape, distribution and quantity of δ phase, so as to obtain different mechanical properties. The heat treatment system of alloy can be divided into three types:

  • (1) (1010 ~ 1065) ℃± 10 ℃, 1 h, oil cooling, air cooling or water cooling + 720 ℃± 5 ℃, 8h, furnace cooling at 50 ℃ / h to 620 ℃± 5 ℃, 8h, air cooling. The results show that the grain size of the treated material is coarsened, there is no δ phase in the grain boundary and grain, and there is notch sensitivity, but it is beneficial to improve impact properties and resist low temperature hydrogen embrittlement.
  • (2) (950 ~ 980) ℃± 10 ℃, 1 h, oil cooling, air cooling or water cooling + 720 ℃± 5 ℃, 8h, furnace cooling at 50 ℃ / h to 620 ℃± 5 ℃, 8h, air cooling. It is the most commonly used heat treatment system, also known as the standard heat treatment system.
  • (3) It is cooled to 620 ℃± 5 ℃ for 8h at 50 ℃ / h and air cooled for 8h. After the treatment, the δ phase in the material is less, which can improve the strength and impact properties of the material. This system is also called direct aging heat treatment system.

Melting and casting process of Inconel718:

The smelting process of the alloy can be divided into three categories:

  • Vacuum induction plus electroslag remelting;
  • Vacuum induction plus vacuum arc remelting;
  • Vacuum induction plus electroslag remelting plus vacuum arc remelting.

According to the use requirements of parts, the smelting process can be selected to meet the application requirements.

Machining

Machinability Ratings

Nickel & cobalt base corrosion, temperature and wear-resistant alloys, such as Inconel 718, are classified as moderate to difficult when machining, however, it should be emphasized that these alloys can be machined using conventional production methods at satisfactory rates. During machining these alloys work harden rapidly, generate high heat during cutting, weld to the cutting tool surface and offer high resistance to metal removal because of their high shear strengths. The following are key points which should be considered during machining operations:

  • Capacity – machine should be rigid and overpowered as much as possible.
  • Rigidity – work piece and tool should be held rigid. Minimize tool overhang.
  • Tool sharpness – make sure tools are sharp at all times. Change to sharpened tools at regular intervals rather than out of necessity. A 0.015 inch wear land is considered a dull tool.
  • Tools – use positive rake angle tools for most machining operations. Negative rake angle tools can be considered for intermittent cuts and heavy stock removal. Carbide-tipped tools are suggested for most applications. High speed tools can be used, with lower production rates, and are often recommended for intermittent cuts.
  • Positive cuts – use heavy, constant, feeds to maintain positive cutting action. If feed slows and the tool dwells in the cut, work hardening occurs, tool life deteriorates and close tolerances are impossible.

Thermal performance of Inconel718:

(1) The melting temperature range of Inconel718: 1260 ~ 1320 ℃.
(2) Thermal conductivity of Inconel718:

θ/℃ 11 100 200 300 400 500 600 700 800 900 1000
λ/(W/(m·℃)) 13.4 14.7 15.9 17.8 18.3 19.6 21.2 22.8 23.6 7.6 30.4

Specific heat capacity of Inconel718

θ/℃ 300 400 500 600 700 800 900 1000
c/(J/(kg·℃)) 481.4 493.9 514.8 539.0 573.4 615.4 657.2 707.4

Coefficient of linear expansion of Inconel718

θ/℃ 20-100 20-200 20-300 20-400 20-500 20-600 20-700 20-800 20-900 20-1000
α/10-6-1 11.8 13.0 13.5 14.1 14.4 14.8 15.4 17.0 18.4 18.7

Oxidation resistance of Inconel718:

The oxidation rate after 100 h in air medium is shown in the table.

θ/℃ 600 700 800 900 1000
Oxidation rate/(g/(m2·h)) 0.0176 0.0277 0.0351 0.0961 0.1620

Application areas of nickel-based alloy incoloy 718 (Alloy 718/UNS N06718):

  • Heat treatment factories with tray,basket and fixture.
  • Steel wire annealing and radiant tube, high-speed gas burner,the mesh belt furnace.
  • The ammonia reforming in the isolation tank and the catalytic support grid for production of nitric acid.
  • Heating pipes, containers, baskets and chains used in sulfuric acid pickling plants.
  • Exhaust system components.
  • Piping system.
  • The solid waste incinerator combustion chamber.
  • Pipe supports and ash handling part.
  • Exhaust detoxification system components.
  • Oxygen to the heater.
  • Heat exchange tubes.
  • Pipe fittings.
  • Flanges.
  • Valves.

Variety specifications and supply status of Nickel-based super alloy: Inconel 718 (Alloy 718/UNS N06718):

Variety classification:

Yaang Pipe Industry can produce various specifications of Inconel718 seamless pipe, Inconel718 steel plate, Inconel718 round bar, Inconel718 forgings, Inconel718 flangeInconel718 pipe fittings, Inconel718 welded pipe, Inconel718 steel strip, Inconel718 wire and supporting welding materials. 

Delivery status:

  • Seamless pipe: solid solution + acid white, length can be set;
  • Plate: solid solution, pickling, trimming;
  • Welded pipe: solid solution acid white + RT% flaw detection;
  • Forging: annealing + car polish; Bars are forged and rolled, surface polished or car polished;
  • Strips are delivered after cold rolling, solid solution soft state, and deoxidized;
  • Wire rods are finely ground in solid solution pickled disk or straight strips, solid solution straight strips Delivery in light state.

Source: China Inconel 718 Flanges Manufcturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Summary
nickel based super alloy incoloy 800 uns n08800 w nr 1 4876 - Nickel-based super alloy: Inconel 718 (Alloy 718/UNS N07718)
Article Name
Nickel-based super alloy: Inconel 718 (Alloy 718/UNS N07718)
Description
Inconel 718 alloy is a nickel base superalloy strengthened by body centered tetragonal γ" and FCC γ′ phase precipitation.
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