You can control Inconel 718 hardness by changing its material condition and heat treatment. The way you process this alloy changes its microstructure and the phases inside, which directly affects how hard or strong it becomes. For example, solution-annealed Inconel 718 usually has a hardness of 25–35 HRC, while precipitation-hardened material reaches 36–45 HRC:
| Material Condition | Hardness (HRC) |
|---|---|
| Solution-Annealed | 25–35 |
| Precipitation Hardened | 36–45 |
When you use aging treatments, fine γ′ and γ″ phases form and block dislocation movement, making the alloy much harder. Understanding these strengthening mechanisms helps you choose the right process for your application.
Key Takeaways
- Inconel 718 hardness varies with processing methods. Solution annealing yields 25–35 HRC, while aging increases it to 36–45 HRC.
- Heat treatment is crucial for optimizing Inconel 718 hardness. Aging forms strengthening phases that block dislocation movement, enhancing hardness.
- Higher hardness in Inconel 718 correlates with increased strength. Aged material can achieve yield strengths above 1,100 MPa, making it suitable for demanding applications.
- Microstructure significantly impacts hardness. Techniques like cold working and aging can fine-tune the alloy’s properties for specific engineering needs.
- Understanding the relationship between hardness and tensile strength helps in material selection. You can estimate tensile strength from hardness values for quick assessments.
Inconel 718 Hardness Overview
Typical Hardness Range of Inconel 718
You can find inconel 718 hardness values that change with different processing methods. The typical hardness range depends on whether you use solution annealing, aging, or cold working. When you look at the numbers, you see that solution-annealed inconel 718 usually measures around 20 HRC or 220 HV. If you age the alloy, the hardness increases to 36–44 HRC or 360–450 HV. Cold working and aging together push the maximum hardness even higher, reaching 45–50 HRC or 460–520 HV.
Here is a summary table showing how inconel 718 hardness varies with material condition:
| Material Condition | Rockwell Hardness (HRC) | Vickers Hardness (HV) |
|---|---|---|
| Solution Annealed | ~20 | ~220 |
| Aged Condition | 36–44 | 360–450 |
| Cold Worked + Aged | 45–50 | 460–520 |
You should remember that inconel 718 hardness also depends on how you process the alloy. For example, cast inconel can reach 408 HV, while laser powder bed fusion samples show values between 296 and 349 HV. If you use direct energy deposition, you may see even more variation.
Tip: You can optimize inconel 718 hardness by choosing the right heat treatment and manufacturing method.
Hardness vs. Strength
When you compare inconel 718 hardness to its strength, you notice a close relationship. Hardness measures how well the alloy resists indentation, while strength tells you how much force the material can handle before it breaks. If you increase the hardness by aging or cold working, you also boost the yield strength. For example, aged inconel 718 can reach yield strengths above 1,100 MPa.
Here is a table that shows how hardness and strength relate in inconel 718:
| Condition | Hardness (HV) | Yield Strength (MPa) |
|---|---|---|
| Solution Annealed | ~220 | 540 |
| Aged Condition | 360–450 | 1,147 |
You can see that higher hardness means higher strength. This connection helps you select the right inconel for your application. If you need parts that resist wear and deformation, you should choose a process that gives you higher inconel 718 hardness.
Other nickel-based superalloys, like inconel 625, show similar Brinell hardness values (175–240), but inconel 718 stands out because precipitation hardening gives it greater strength.
- Inconel 718 is a precipitation-strengthened nickel-based superalloy.
- The alloy keeps its mechanical properties stable up to 650 °C.
- You can optimize the microstructure and hardness through heat treatment and aging.
You should also know that factors like chip thickness and chamfer angle during machining can change surface hardness. Thin sections may not reach peak hardness, especially if they measure less than 2 mm.
If you understand the typical hardness range and how it connects to strength, you can make better choices for your engineering projects. You can select the right material condition to get the inconel 718 hardness and performance you need.
Material Condition Determines Microstructure
Microstructure Effects
You can change the microstructure of Inconel 718 by using different processing methods. Each method creates unique features inside the alloy, which affect its hardness and strength.
- When you anneal Inconel 718, you promote recrystallization. This process forms new grains and removes the effects of previous deformation. If you cold roll the alloy before annealing, you see a high fraction of recrystallized grains—up to 97%. These new grains help improve ductility and toughness.
- Cold working, such as rolling, changes the shape and distribution of precipitated phases. You especially affect the γ′′ variant, which boosts creep resistance. Cold working also increases dislocation density, making the alloy harder.
- Aging causes the precipitation of strengthening phases. You see the formation of γ′ and γ′′ particles, which block dislocation movement and increase hardness.
Note: The microstructure you create through processing controls how hard and strong your Inconel 718 becomes.
You can see how specific microstructural features influence hardness in the table below:
| Microstructural Feature — | Effect on Hardness — | | γ′ particles at 565 °C — | Slight increase in hardness — | | γ″ precipitation at 740 °C — | Peak hardness due to large precipitation — | | Coarsening of precipitates — | Decrease in hardness — | | δ phase precipitates — | Strengthening effect, recovery of hardness loss — | | Fine grain sizes — | Enhanced strength and plasticity according to Hall-Petch relationship — |
If you create fine grains, you boost both strength and plasticity. The Hall-Petch relationship shows that smaller grains make metals harder and stronger. When you control the size and distribution of precipitates, you can fine-tune the hardness for your needs.
Heat Treatment Impact
You can use heat treatment to change the microstructure and hardness of Inconel 718. Each process creates different phases and grain structures, which affect mechanical properties.
| Study — | Heat Treatment Process — | Effect on Microstructure — | Effect on Hardness — | | Zhai et al. — | Aging — | Precipitation of γ″ and γ′ phases — | Improved mechanical properties — | | Zhao et al. — | Homogenization at 1180 °C — | Eliminated residual stress, reconstructed microstructure — | Introduced isotropic tensile properties — | | Li et al. — | Solution treatment — | Formation of short-rod δ phases at grain boundaries — | Increased hardness due to grain boundary pinning — | | Sui et al. — | Heat treatment at 1050 °C + double aging — | Modified Laves phases from long chain-like to granular — | Enhanced high-temperature stress rupture performance — |
When you age Inconel 718, you increase the size and number of γ′ and γ′′ precipitates. These phases are essential for hardness and strength. If you use solution treatment, you form δ phases at grain boundaries. These phases pin the grains and prevent movement, which increases hardness. Homogenization removes residual stress and creates a more uniform microstructure, which helps the alloy perform better under stress.
Tip: You can adjust the heat treatment process to create the microstructure you need for your application. Aging at the right temperature leads to peak hardness by maximizing γ′ and γ′′ precipitation.
Precipitation hardening is the key mechanism that makes Inconel 718 so strong. When you age the alloy at around 718 °C, you see a sharp increase in hardness because of the growth of γ′ and γ′′ phases. If you control the heat treatment, you can balance hardness, ductility, and toughness for your engineering needs.
You have the power to design the microstructure of Inconel 718. By choosing the right combination of annealing, cold working, and aging, you can create an alloy with the hardness and strength required for demanding applications.
Strengthening Mechanisms
Precipitation Hardening
You can boost the hardness of Inconel 718 by using precipitation hardening. This strengthening mechanism relies on the formation of tiny particles called γ′ and γ″ phases. When you heat treat the alloy, these particles appear and block the movement of dislocations inside the metal. Dislocations are defects that allow metals to bend or stretch. By stopping them, you make the alloy much harder.
- Heat treatment can raise the hardness from about 20 HRC in the annealed state to 36–44 HRC after aging.
- The Lifshitz–Slyozov–Wagner theory helps explain how these particles grow and increase hardness.
- Aging treatment leads to the formation of γ′ and γ″ precipitates, which hinder dislocation movement.
- The size and number of these particles depend on how long and how hot you age the alloy.
You see the first signs of strengthening after just 10–15 minutes of aging. If you keep aging the alloy, the particles grow larger and stronger, giving you even more hardness. This process is key for applications that need high strength and wear resistance.
Tip: You can control the amount of strengthening by adjusting the aging time and temperature.
Dislocation Density
Cold working also plays a big role in strengthening Inconel 718. When you deform the alloy, you increase the number of dislocations. More dislocations mean the metal becomes harder because they get tangled and cannot move easily.
| Evidence Description — | Findings — | | Influence of cooling rate on dislocation density — | Higher cooling rates create more dislocations, which boost hardness. — | | Dislocation density calculation method — | The Williamson-Hall method shows that faster scanning speeds increase dislocation density. — | | Hardness measurement range — | Micro-hardness values range from 200 HV0.3 to 295 HV0.3, depending on cooling rate and microstructure. — |
Aging treatment adds another layer of strengthening. The γ′ and γ″ precipitates formed during aging block dislocation movement even more. You can see the effect in the increased hardness and strength. The combination of cold working and aging gives you a powerful way to fine-tune the properties of Inconel 718.
Note: You can use both precipitation hardening and cold working to achieve the exact hardness and strength you need for your project.
Approximate Relationship Between Hardness and Ultimate Tensile Strength (UTS)
| Rockwell Hardness (HRC) | UTS (MPa) | UTS (ksi) |
| 20 | ≈ 750 | ≈ 109 |
| 30 | ≈ 950 | ≈ 138 |
| 35 | ≈ 1100 | ≈ 160 |
| 40 | ≈ 1250 | ≈ 181 |
| 45 | ≈ 1400 | ≈ 203 |
| 50 | ≈ 1550 | ≈ 225 |
You might wonder how hardness connects to the strength of Inconel 718. When you measure hardness, you check how well the alloy resists being scratched or dented. Ultimate tensile strength tells you the maximum force the material can handle before it breaks. These two properties often rise together, so you can use one to estimate the other.
If you know the hardness of your Inconel 718 sample, you can estimate its ultimate tensile strength using conversion charts. These charts give you a quick way to predict strength without running a full tensile test. For example, a Vickers hardness of 400 HV usually means the alloy has an ultimate tensile strength of about 1,250 MPa.
Here is a simple table that shows the relationship between hardness and strength for Inconel 718:
| Vickers Hardness (HV) | Estimated UTS (MPa) |
|---|---|
| 220 | 540 |
| 360 | 1,100 |
| 400 | 1,250 |
| 450 | 1,350 |
Note: These values are approximate. You should always check with actual test data for critical applications.
You can use this relationship to make quick decisions during manufacturing or quality checks. If you see a drop in hardness, you may also see a drop in strength. This helps you spot problems early and keep your parts safe.
When you select Inconel 718 for a project, remember that hardness and ultimate tensile strength work together. By understanding this link, you can choose the right processing steps and heat treatments to get the performance you need.
Inconel 718 Heat Treatment Reference Values
You can improve the mechanical properties of Inconel 718 by choosing the right heat treatment. Each process changes the microstructure and affects hardness. You should know how different treatments work so you can select the best option for your application.
- Solution Annealed: HRC 18–22, tensile strength ~750–950 MPa
- Standard Aged (per ASTM B637): HRC 36–44, tensile strength ~1240–1380 MPa
- High Strength Condition (Cold Worked + Aged): HRC up to 50, tensile strength over 1500 MPa
You can see that solution heat treatment for three hours gives you a hardness of about 200 HV. If you use direct aging, you get a significant increase in mechanical properties. The STA9 process, which combines a nine-hour solution treatment with aging, gives you the highest hardness and the best mechanical properties. Shorter solution treatments like STA1 do not dissolve all defects, so you get lower hardness and weaker mechanical properties.
Tip: You should use a solution treatment longer than six hours at 1100 °C if you want a stress-free microstructure and stable mechanical properties.
When you select a heat treatment, you control the balance between hardness and other mechanical properties. You can adjust the process to match the needs of your part. For example, aerospace components often need maximum hardness and strength, so you should choose the STA9 process. If you need more ductility, you might select a shorter treatment.
You can use these reference values to guide your decisions. By understanding how heat treatment affects mechanical properties, you make sure your Inconel 718 parts perform well in demanding environments.
Applications Requiring High Hardness of Inconel 718
Aerospace Uses
You often find Inconel 718 in aerospace applications that demand high hardness and strength. This high-temperature alloy stands out because it keeps its properties even in extreme environments. You see it used in many jet engine components and other aerospace structural components where durability is critical.
Some key aerospace applications that require high hardness levels include:
- Jet engine components
- Turbine disks
- Compressor blades
- High-strength fasteners
- Next-generation propulsion systems
- Supersonic flight designs
The hardness of Inconel 718, usually between 30 to 35 HRC, helps these parts resist scratching and plastic deformation. This property is essential for durability and long service life in jet engines and turbine blades. When you select the right material condition, you make sure these parts perform well under high stress and temperature.
High-Temperature Components
You also see Inconel 718 used in high-temperature components outside of aerospace. Its hardness and stability at elevated temperatures make it a top choice for many demanding applications. The table below shows some common uses:
| Component Type | Description |
|---|---|
| Jet Engine Parts | Used for components like wheels and buckets. |
| High-Speed Airframe Parts | Includes spacers and high-temperature bolts and fasteners. |
Selecting the correct material condition is critical for performance. The table below explains why:
| Property | Description |
|---|---|
| Strength | Exceptional strength and durability, particularly in high-stress environments. |
| Corrosion Resistance | High resistance to corrosion, making it suitable for extreme environments. |
| Stability at High Temp | Retains structural integrity at elevated temperatures up to approximately 700°C (1,300°F). |
| Heat Treatment Process | Precipitation-hardening process enhances mechanical properties through heat treatment. |
You need to match the material condition to the demands of your application. If you choose the right heat treatment, you get the best balance of hardness, strength, and stability. This approach ensures your high-temperature alloy parts last longer and perform better in service.
Tip: Always consider the specific requirements of your applications when selecting Inconel 718. The right combination of hardness and microstructure will help you achieve the best results.
Additional Info: Hardness Conversion Chart (Approximate Values)
You often need to compare different hardness scales when you work with Inconel 718. Each scale uses a different method to measure how resistant a material is to indentation. You might see values listed in Rockwell, Vickers, or Brinell scales. If you want to convert between these scales, you can use a conversion chart. This helps you understand test results from different sources.
Here is a simple table that shows approximate conversions between common hardness scales:
| Rockwell C (HRC) | Vickers (HV) | Brinell (HB) | Rockwell B (HRB) |
| 20 | ≈ 220 | ≈ 215 | 96 |
| 25 | ≈ 245 | ≈ 240 | — |
| 30 | ≈ 270 | ≈ 265 | — |
| 35 | ≈ 310 | ≈ 300 | — |
| 40 | ≈ 370 | ≈ 340 | — |
| 45 | ≈ 430 | ≈ 390 | — |
| 50 | ≈ 500 | ≈ 450 | — |
Tip: You should use these values as a guide. Actual hardness readings can change based on the test method and the sample’s surface condition.
You can use this chart to check if your Inconel 718 part meets the required hardness for your application. If you see a value in one scale, you can quickly estimate what it would be in another. This makes it easier to compare specifications or quality control results.
- You should always confirm critical hardness values with direct testing.
- You can ask your supplier for the specific scale used in their reports.
- You might notice small differences between conversion charts from different sources.
If you understand how to use a hardness conversion chart, you make better decisions during material selection and inspection. You can avoid confusion and ensure your parts meet the right standards.
You can control the hardness of Inconel 718 by choosing the right material condition and heat treatment. The processing route shapes the microstructure, which directly affects performance. If you select an unsuitable method, you risk poor plasticity and weak mechanical performance. When you understand how microstructure changes, you make smarter choices for your projects.
| Treatment Duration | Microstructural Effects | Mechanical Properties Impact |
|---|---|---|
| 1 hour at 1080 °C | Laves phases and elemental segregation not completely dissolved | Minimal effect on hardness |
| 4 hours at 1080 °C | Complete recrystallization and stress-relieved equiaxed grains | Improved mechanical properties |
| 7 hours at 1080 °C | Coarser carbides observed | Potential negative impact on strength and ductility |
You use knowledge of hardness and microstructure to match the alloy’s performance to your needs. This approach helps you achieve reliable performance in demanding environments and ensures your engineering decisions lead to optimal performance.
FAQ
What is the typical hardness range for Inconel 718?
You usually see Inconel 718 hardness between 25–35 HRC in the solution-annealed state. Aging increases hardness to 36–45 HRC. Cold working and aging together can push hardness up to 50 HRC.
| Condition | Hardness (HRC) |
|---|---|
| Solution Annealed | 25–35 |
| Aged | 36–45 |
| Cold Worked + Aged | 45–50 |
How does heat treatment affect Inconel 718 hardness?
You change hardness by adjusting heat treatment. Aging forms γ′ and γ″ phases, which block dislocations and increase hardness. Solution treatment creates a softer microstructure. You select the process based on your application needs.
Tip: Aging at the right temperature gives you peak hardness.
Can you estimate tensile strength from hardness?
You can estimate tensile strength using hardness values. For example, a Vickers hardness of 400 HV usually means an ultimate tensile strength of about 1,250 MPa.
| Vickers Hardness (HV) | Estimated UTS (MPa) |
|---|---|
| 400 | 1,250 |
Why do aerospace parts need high hardness Inconel 718?
You need high hardness for aerospace parts to resist wear, deformation, and high temperatures. This property helps jet engine components and turbine blades last longer and perform better.
- Jet engine disks
- Compressor blades
- High-strength fasteners
