The Engineer's Data Handbook: Inconel 625 Density, Melting Point & Key Physical Properties

Your Quick-Reference Guide

Inconel 625, designated as UNS N06625, is a top nickel-chromium-molybdenum superalloy. It was made for great performance in the world's toughest settings.

This material gives a special mix of high strength, excellent fabricability, and top corrosion resistance. It works well from very cold levels to high temps up to 980°C (1800°F).

For quick reference, here are the most important data points for engineers and designers.

Property	Value (Metric)	Value (Imperial)
Inconel 625 Density	8.44 g/cm³	0.305 lb/in³
Inconel 625 Melting Point	1290 - 1350 °C	2350 - 2460 °F

This handbook is a complete data-driven resource. We will look at the detailed physical, mechanical, and chemical properties that show how this alloy performs.

Knowing these basic traits is the first step in good material selection and design. For engineers and designers who want to get this high-performance material, various forms of Inconel 625 are ready to meet specific project needs.

In-Depth Physical Properties

The physical properties of a material are basic to engineering analysis. These values show how a part will act under heat and electrical loads, and how much it will weigh.

For Inconel 625, these values are key for simulations, manufacturing design, and predicting how it will work in high-temp service. The data here shows typical values for annealed material at room temperature unless stated otherwise.

This table gives a one-stop data source for these vital calculations.

Physical Property	Value at Room Temperature (unless specified)	Significance in Application
Density	8.44 g/cm³ (0.305 lb/in³)	The inconel 625 density is key for weight calculations in aerospace, marine, and mobile uses where mass matters a lot.
Melting Range (Solidus-Liquidus)	1290 - 1350 °C (2350 - 2460 °F)	This range shows its fit for high-temp service and sets key factors for welding and casting.
Specific Heat Capacity	410 J/kg·K (0.098 BTU/lb·°F)	This value affects how much heat energy is needed to change its temp, impacting heat models and analysis.
Inconel Thermal Conductivity	9.8 W/m·K at 21°C (68°F)	Low thermal conductivity means poor heat flow. This matters for machining, where heat can build up in the tool and work piece.
Coefficient of Thermal Expansion	12.8 µm/m·°C (7.1 µin/in·°F) from 20-100°C	This shows how much the material grows when heated, a key factor for designing joints, seals, and tight-fit parts.
Electrical Resistivity	1.29 µΩ·m at 21°C	High resistivity makes it good for some heating uses but must be noted in other electrical designs.

The inconel 625 melting temperature is not one point but a range. The solidus (1290°C) is where melting starts, and the liquidus (1350°C) is where it becomes fully liquid. How it acts during this change is complex and is studied in recent non-equilibrium solidification studies.

A material's traits are not fixed; they change with temperature. For an alloy used in heat settings, knowing this is a must.

The inconel thermal conductivity, for example, goes up with temperature. At 200°C (392°F), it rises to about 11.5 W/m·K, and by 600°C (1112°F), it reaches around 16.9 W/m·K. This affects heat transfer math in parts like heat exchangers or exhaust systems.

In the same way, the mean coefficient of thermal expansion increases as the temp range widens. For a range from 20°C to 400°C, the coefficient is about 14.1 µm/m·°C, and up to 600°C, it is about 15.0 µm/m·°C. This data is vital for predicting size changes and managing heat stresses in use.

Key Mechanical Properties

While physical properties define thermal and mass traits, mechanical properties show how a material responds to physical forces. For structural parts, these are the most vital data points.

The inconel 625 material properties in the mechanical sense are defined by its strength, ductility, and hardness. These are usually given for the solution-annealed state, which is the most common supply form, offering a good balance of performance.

This table shows the typical mechanical properties of Inconel 625 at room temperature.

Mechanical Property	Typical Value (Annealed Condition)
Ultimate Tensile Strength	827 - 1034 MPa (120 - 150 ksi)
Inconel 625 Yield Strength (0.2% Offset)	414 - 760 MPa (60 - 110 ksi)
Elongation at Break	30 - 50%
Hardness	~95 HRB / ~220 HV

Ultimate Tensile Strength (UTS) is the max stress a material can take while being pulled before necking begins.

The inconel 625 yield strength is often the most crucial value for structural design. It shows the stress at which the material starts to deform. Components are usually designed to work well below this limit.

Elongation at break measures the material's ductility. The high elongation of Inconel 625 (30-50%) shows excellent formability and toughness, meaning it can deform a lot before breaking.

These properties are not just typical values; they follow international standards to ensure reliability across suppliers and uses. For instance, these mechanical requirements are set in standards such as ASTM B446 for bar and rod. This gives engineers a guarantee of performance.

High and Low Temperatures

A key difference for superalloys is how they work at extreme temps. Inconel 625 does very well in this area.

At high temps, it keeps much of its strength. At 540°C (1000°F), it can maintain a yield strength well over 350 MPa (50 ksi). Even at 870°C (1600°F), it still shows useful strength, which comes from the solid-solution strengthening from its molybdenum and niobium content.

This high-temp strength, plus its great oxidation resistance, makes it a top choice for exhaust systems, flare stacks, and furnace parts.

At very cold temps, Inconel 625 shows excellent toughness. Unlike many carbon steels that get brittle when cold, this alloy keeps its ductility and strength, avoiding brittle breaks. This makes it good for cryogenic storage tanks, transfer lines, and parts in liquefied natural gas (LNG) processing.

Inconel 625 vs. 718

Engineers often must choose between Inconel 625 and Inconel 718, the two main nickel superalloys. The choice depends on the specific needs of the use, as each alloy is made for different performance traits. A data-driven comparison helps make the right choice.

The basic difference is in how they gain strength. This metallurgical difference drives every performance variance between them.

The following table breaks down the key differences to guide an engineering decision.

Feature	Inconel 625	Inconel 718	Engineering Takeaway
Primary Strengthening	Solid Solution (Mo, Nb)	Precipitation Hardening (Nb, Ti, Al)	718 can be age-hardened to get much higher strength. 625's strength is built-in and stable without complex heat treatment.
Melting Temperature	1290-1350°C	1260-1336°C	The slightly higher inconel 625 melting point gives a small thermal edge, but 718's better high-temp strength is often the key factor for structural parts.
Inconel Density	inconel 625 density: 8.44 g/cm³	inconel 718 density: 8.19 g/cm³	718 is a bit lighter, a small but maybe relevant factor in aerospace weight math where every gram counts.
Max Service Temp.	~980°C (1800°F)	~700°C (1300°F) for strength	625 is better in corrosion and oxidation resistance at higher temps. 718 is better in pure strength up to its aging temp limit of ~700°C.
Yield Strength (Aged)	~414 MPa	~1034 MPa	Choose 718 for uses needing max strength and creep resistance, such as turbine disks, high-strength bolts, and downhole oil tools.
Corrosion Resistance	Superior	Good	Choose 625 for better resistance to more corrosive media, especially in chemical processing, marine settings, and acidic conditions.
Weldability	Excellent	Good (can crack after welding if not properly heat-treated)	625 is generally seen as more forgiving and easier to weld, making it ideal for complex fabricated structures without needing immediate post-weld heat treatment.

The inconel 718 melting point is slightly lower than that of 625. But the critical factor for high-temp structural use is not the melting temperature of inconel, but rather the temp at which it keeps its strength. Inconel 718's strength drops off sharply above its aging temp of about 700°C.

In contrast, Inconel 625, while having a lower base strength, maintains its properties better at even higher temps, changing from a strength-based role to a corrosion/oxidation-resistance role.

The performance differences in harsh settings are well-documented. The higher chromium and molybdenum content in Inconel 625 gives it a clear advantage. This is measurable, as shown in detailed corrosion and wear resistance studies that compare its behavior to other alloys in harsh conditions.

The choice is clear: for highest strength below 700°C, choose 718. For better weldability and corrosion resistance, especially at temps above 700°C, choose 625.

Chemical Composition Analysis

The exceptional inconel 625 material properties don't happen by chance. They come directly from a carefully engineered chemical makeup, where each alloying element plays a specific and synergistic role.

Understanding this link between composition and performance moves an engineer from simply using data to truly knowing the material. It explains the "why" behind the numbers.

Decoding the Formula

The nominal composition of Inconel 625 is a masterclass in metallurgical design.

• Nickel (Ni ≥ 58%): Nickel forms the austenitic matrix, which is the alloy's backbone. It provides inherent toughness, ductility, and, most importantly, exceptional resistance to chloride-ion stress-corrosion cracking—a common failure mode for stainless steels in marine or chemical environments.

• Chromium (Cr 20-23%): Chromium is the main element for oxidation and corrosion resistance at high temps. It forms a passive, adherent, and self-healing chromium oxide (Cr2O3) layer on the material's surface, protecting the underlying metal from attack.

• Molybdenum (Mo 8-10%): Molybdenum is a powerhouse element. It provides significant solid-solution strengthening, which adds to the alloy's high strength without needing heat treatment. Critically, it is the key to resistance against pitting and crevice corrosion, particularly in chloride-rich environments and non-oxidizing acids.

• Niobium (Nb 3.15-4.15%): This is the secret sauce of Inconel 625. Niobium works with molybdenum to stiffen the alloy's matrix, providing powerful solid-solution strengthening. It also stabilizes the alloy during welding by forming niobium carbides, which prevents the formation of other harmful phases at the grain boundaries. This stabilization is a major reason for the alloy's outstanding weldability.

The balance of these elements creates a whole that is far greater than the sum of its parts. The synergy between nickel, chromium, and molybdenum delivers a level of corrosion resistance that few other commercial alloys can match across such a wide range of aggressive media, both oxidizing and reducing.

Engineering Summary

Inconel 625 (UNS N06625) is more than just a set of data points; it is a problem-solving material for extreme engineering challenges.

Its profile is defined by a unique trio of capabilities: high strength and toughness from cryogenic to elevated temperatures, outstanding fabricability and weldability, and world-class corrosion resistance in many aggressive media.

From the high inconel 625 density that must be factored into aerospace designs to the low inconel thermal conductivity that challenges machinists, every property has a direct impact on its use. The inconel 625 melting temperature dictates its use in hot sections of engines and furnaces, while the high inconel 625 yield strength provides structural integrity under immense pressure.

This alloy finds its home where lesser materials fail. It is used for reactor cores and control rods in nuclear power, for flexible flowlines and risers in subsea oil and gas extraction, for exhaust nozzles and combustion systems in aerospace, and for reaction vessels and heat exchangers in chemical processing plants.

Choosing Inconel 625 is a decision to prioritize reliability, longevity, and safety in environments where failure is not an option. By understanding the core data presented in this handbook, engineers can confidently specify, design, and implement this exceptional superalloy to push the boundaries of performance.