Inconel 718 bolts are not ordinary fasteners. They are often called the “King of Superalloys”. These bolts are very expensive because they can do things regular steel cannot. They are special fasteners made for extremely hot or harsh environments. What makes them so powerful? The secret is in their materials and how they are made. We will break down what Inconel 718 is, why it is so strong, and where the world’s toughest industries use it.
1. Why Inconel 718 Bolts Stand Out?
Inconel 718 is a special kind of superalloy. It is a nickel-based alloy. It is mainly famous for keeping its strength and shape even when temperatures are extremely high. Regular steel gets soft and weak when it gets very hot. But Inconel 718 does not. It can handle temperatures up to 700°C (about 1292°F) and still be strong. It also fights corrosion very well. Because The key advantage is Its strength comes from a special heat treatment process called double aging. This process makes the metal incredibly hard and strong.
2. Inconel 718 Chemical Composition (What’s Inside the Alloy)
The strength of Inconel 718 comes from its exact mix of metals. The main ingredient is Nickel. Other key elements are added to give it special powers.
| Element | Approximate Percentage (by weight) | Function / Special Power |
| Nickel (Ni) | 50.0% – 55.0% | The main metal. Gives high temperature strength and corrosion resistance. |
| Chromium (Cr) | 17.0% – 21.0% | Gives excellent resistance to oxidation (rusting) and corrosion. |
| Iron (Fe) | Balance | A base metal, helps with manufacturing and cost. |
| Niobium (Nb) / Columbium (Cb) | 4.75% – 5.50% | The most important element. It forms the main strengthening phases ($\gamma”$). |
| Molybdenum (Mo) | 2.80% – 3.30% | Increases strength and improves resistance to pitting corrosion. |
| Titanium (Ti) | 0.65% – 1.15% | Helps Niobium in the hardening process. |
| Aluminum (Al) | 0.20% – 0.80% | Helps Niobium and Titanium in the hardening process. |
The special combination of Niobium, Titanium, and Aluminum is the key. They work together during heat treatment to form tiny, strong particles throughout the metal. These particles are what make the bolts so strong.
3. Precipitation Hardening – The Main Reason for Its Extreme Strength
Precipitation hardening is the most important step for Inconel 718. It is a heat treatment process. This process makes the alloy much stronger than it is naturally. When the metal is heated and then cooled slowly, new, very tiny metal structures form. These structures are called precipitates.In Inconel 718, the main strengthening precipitate is the Gamma Double Prime () phase. This phase is made of nickel, niobium, and iron ().These particles act like tiny roadblocks inside the metal structure. They stop the metal’s internal crystal layers from sliding past each other. This sliding is what makes metal bend or break under stress. Because the particles block movement, the material becomes much harder and much stronger. This is why an Inconel 718 bolt can handle massive forces.
4. High Temperature Resistance
Inconel 718 is designed to work in places where it is constantly hot. It is not just about keeping strength. It is also about fighting creep and oxidation.
Creep Resistance: Creep is when a material slowly changes shape under constant stress at high temperatures. Think of it as a very slow stretch. Inconel 718 has excellent creep resistance. It can keep its shape and size at temperatures up to 700°C for long periods. This is vital for parts that spin very fast, like turbine blades.
Oxidation Resistance: High heat usually causes metals to react with oxygen in the air. This forms scale or rust, which weakens the metal. The high content of Chromium in Inconel 718 creates a thin, stable protective oxide layer on the surface. This layer prevents further oxidation, protecting the bolt inside.
5. Exceptional Mechanical Strength (Provide Approx Values)
Because of the hardening process, Inconel 718 bolts show amazing strength. These values are just examples, and the exact strength depends on the final heat treatment.
| Mechanical Property | Approximate Value | What It Means |
| Ultimate Tensile Strength | 1280 MPa (185,000 psi) minimum | The maximum stress the bolt can handle before it breaks. It is very high. |
| Yield Strength | 1035 MPa (150,000 psi) minimum | The stress point where the bolt starts to stretch or deform permanently. |
| Hardness | 35-42 HRC | A measure of how much the bolt resists being dented or scratched. It is very hard. |
The bolt’s tensile strength can reach 1280 Megapascals (MPa) or more. This is an incredible amount of pulling force. This strength is why these bolts are used in the most critical, load-bearing parts of any machine.
6. Corrosion and Oxidation Resistance
Inconel 718 is not just strong; it is also highly protected against its environment.
Corrosion Resistance: The large amount of Nickel and Chromium makes the alloy very resistant to many corrosive chemicals. This includes acids, alkalis, and especially chloride-ion stress-corrosion cracking. This last point is very important for sea water and deep oil well drilling.
Oxidation Resistance: As mentioned before, the Chromium forms a strong, protective layer. This layer fights off reaction with oxygen even when the temperature is very high. This means the bolts will not rust or weaken quickly in hot air.
7. Cryogenic Performance (Another Advantage)
Most metals become brittle (easily snapped) when they get extremely cold. This is the opposite of what happens with heat. But Inconel 718 has a special ability: it gets stronger at very low temperatures.
Cryogenic Temperature: This means temperatures near absolute zero, like in space or liquid fuel storage. The special crystal structure of Inconel 718 gives it great ductility (the ability to bend without breaking) and strength in these freezing conditions. This is why NASA and other space agencies use Inconel 718 fasteners in rockets. These bolts hold the parts of the rocket that handle super-chilled liquid oxygen or liquid hydrogen fuel.
8. Heat Treatment – How It Boosts Strength
The heat treatment process is the key step that gives Inconel 718 its extreme properties. The process is complex and must be done exactly right. It often involves a double aging process:
1.Solution Annealing: First, the bolt is heated to a very high temperature (about to ). Then it is cooled quickly. This makes the alloy soft and prepares it for the next step.
2.Double Aging (Precipitation Hardening):
First Aging Step: The bolt is held at a temperature of around for a set time.
Second Aging Step: The temperature is then lowered to around and held there for a longer time.
These two aging steps are critical. They allow the strengthening precipitates () to form slowly and evenly throughout the metal structure. This gives the final, extreme strength and high-temperature performance. This precise, dual-temperature process is what makes the ultimate tensile strength reach the 1280 MPa mark.
What Industries Choose Inconel 718 Bolts?
Inconel 718 bolts are expensive. So, they are only used when failure is not allowed. These bolts control the most extreme environments.
Aerospace and Aviation:Jet Engines and Gas Turbines: Used to hold hot sections, combustors, and rotors where temperatures are highest.
Rocket Engines: Used for structural components and cryogenic fuel handling systems.
Oil and Gas:Down-Hole Tools: Used in deep, sour gas wells where high pressure, high temperature (HPHT), and corrosive hydrogen sulfide are a problem.
Power Generation:Nuclear Reactors: Used for internal components because of its long-term stability and corrosion resistance.
Marine and Chemical Processing: Used in equipment that handles harsh chemicals or hot seawater environments.
In summary, the strength of an Inconel 718 bolt is not due to just one thing. It is the result of a perfectly balanced formula. The high percentage of Nickel gives it stability. The Chromium fights corrosion and oxidation. Most importantly, the combination of Niobium, Titanium, and Aluminum allows for the crucial precipitation hardening process.
Inconel 718 bolts are extremely difficult to machine due to their high strength, work hardening behavior, and heat resistance. This is not a material that small or inexperienced factories can handle. When selecting an Inconel bolt supplier, it’s important to choose a manufacturer with advanced equipment, strict process control, and proven experience.
