Inconel 718 Density Inconel 718 Chemical Composition and Implementation Standards
Inconel 718
Inconel718 alloy is a precipitation hardening nickel-chromium iron alloy containing niobium and molybdenum. It has high strength, good toughness below 650°C, and corrosion resistance in high and low temperature environments. Its state can be solid solution treatment or precipitation hardening state.
Heat treatment and mechanical properties
For most uses, INCONEL 718 alloy requires annealing and hardening. INCONEL 718 alloy is hardened into a certain metal crystal array by two-stage quenching. Under heat treatment at 593~815℃, these nickels (aluminum, titanium, niobium) are changed. Due to the complete metallurgical reaction, those metal elements such as aluminum, titanium, and niobium are completely dissolved in the alloy phase matrix and diffused uniformly); if these elements are crystallized in other ways or composed in a certain way, it will not meet the requirements. strength. In order to achieve these functions, alloy materials must first undergo annealing heat treatment.
For INCONEL 718 alloy, two heat treatment methods are generally used:
Scheme 1: Heating to 926~1010℃, quickly cooling to room temperature in water, then raising the temperature to 718℃ to keep it
Furnace cooled to 621°C, maintained at 621°C for 18 hours as an aging treatment, and then cooled to room temperature in air.
Plan 2: Heating to 1037~1065℃, rapidly cooling to room temperature in water, then raising the temperature to 760℃ for 10 hours, furnace cooling to 648℃, holding at 649℃ for 20 hours as aging treatment, and then cooling to room temperature in the air.
If the material is to be machined, formed, or welded, the material purchased in the factory will usually
Treatment or stress relief treatment. Molding is performed at maximum elongation. After the molding process, heat treatment is performed according to the application requirements of each body.
This hardenable alloy has good plasticity and can even be processed into various complex parts; it has good welding characteristics, especially the ability to effectively suppress the occurrence of welding cracks, and the effect is relatively obvious.
Inconel718 alloy has good plasticity, ductility, fatigue properties, creep properties, and tensile strength, so it is widely used in various fields. Typical examples are formed sheet metal parts used in liquid rockets, columns, protective sleeves, various aircraft, ground gas turbine engines, and cryogenic storage tanks. Can also be used for fasteners and instrument parts.
Physical Constants and Thermal Properties
The physical constants, Young's modulus, torsion coefficient, etc. of Inconel718 are listed in Tables 3 and 4. The values in these tables of thermal characteristic coefficients may be slightly different due to differences in chemical content and testing environment. These are general parameters, not specific to a project.
Physical properties
Density Density ρ=8.24g/cm3
Melting temperature range Melting temperature range 1260～1320℃
Processing and heat treatment
Inconel718 alloy is a difficult-to-machine material in the field of machining.
preheat
The surface of the workpiece must be cleaned before and during the heating process to keep the surface clean. If the heating environment contains sulfur, phosphorus, lead or other low melting point metals, Inconel718 alloy will become brittle. Impurities come from paint, chalk, lubricating oil, water, fuel, etc. used for marking. The sulfur content of fuel should be low. For example, the impurity content of liquefied petroleum gas and natural gas should be less than 0.1%, the sulfur content of city gas should be less than 0.25g/m3, and the sulfur content of petroleum gas should be less than 0.5%.
The electric furnace for heating should have relatively accurate temperature control capabilities. The furnace gas must be neutral or weakly alkaline, and the composition of the furnace gas should be prevented from being unstable in oxidation and reduction.
Thermal processing
The suitable hot processing temperature for Inconel718 alloy is 1120-900°C. The cooling method can be water quenching or other rapid cooling methods. After hot processing, it should be annealed in time to ensure the best performance. During thermal processing, the material should be heated to the upper limit of the processing temperature. In order to ensure the plasticity during processing, the final processing temperature when the deformation reaches 20% should not be lower than 960°C.
Cold working
Cold working should be carried out after solid solution treatment. The work hardening rate of Inconel718 is greater than austenitic stainless steel, so the processing equipment should be adjusted accordingly, and there should be a central annealing process during the cold working process.
heat treatment
Different solution treatment and aging treatment processes will produce different material functions. Due to the low dispersion rate of the γ" phase, Inconel718 alloy can obtain optimal mechanical properties through long-term aging treatment.
polish
The oxides near the welds of Inconel718 workpieces are more difficult to remove than those of stainless steel. They need to be polished with a fine abrasive belt. Before pickling in a mixed acid of nitric acid and hydrofluoric acid, the oxides must also be removed with sandpaper or pre-salted in a salt bath. deal with.
machining
The machining of Inconel718 needs to be carried out after solution treatment, and the work hardening of the material must be taken into consideration. Unlike austenitic stainless steel, Inconel718 is suitable for low surface cutting speeds.
