Alloy 601 / Inconel® 601 / 2.4851 / UNS N06601 / Nicrofer® 6023 H – nickel alloy NiCr23Fe
Alloy 601 (UNS N06601, 2.4851, NiCr23Fe, NiCr23Fe15Al, Inconel ® 601, VDM ® Alloy 601, Nicrofer ® 6023 H, BS NA49, JIS NCF601) is a heat-resistant nickel-chromium-iron alloy containing approximately 58–63% nickel, 21–25% chromium, and 1,0–1,7% aluminum. It combines high oxidation resistance, even after repeated heating and cooling, with good formability and weldability. It is used in industrial furnaces, chemical equipment, combustion systems, and the power generation industry.
Materials available at Alfa-Tech – Alloy 601 / Inconel 601 / 2.4851 / UNS N06601
Alloy 601 / Inconel 601 / 2.4851 / UNS N06601 bars – round and hexagonal, rolled / peeled / drawn Alloy 601 / Inconel 601 / 2.4851 / NiCr23Fe flat bars Alloy 601 / Inconel 601 / 2.4851 forged bars – round / square Alloy 601 / Inconel 601 / 2.4851 forgings – shafts, cubes, open-die forgings Alloy 601 / Inconel 601 / 2.4851 tubes – seamless and welded according to the required standard Alloy 601 / Inconel 601 / 2.4851 sheets – sheets, plates, hot- and cold-rolled sheets
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Chemical composition of Alloy 601 – comparison of standards, designations UNS N06601, 2.4851, Inconel 600, NW6601, NA49, NCF601
| Chemical composition – values in mass percentage | |||||||||||
| Alloy grade | Norma | Ni | Cr | Fe | Al | Mn | Cu | Si | C | S | Other |
| Alloy 601 / UNS N06601 | ASTM / UNS | 58,0–63,0 | 21,0–25,0 | rest | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P not specified |
| Inconel® 601 | Special Metals | 58,0–63,0 | 21,0–25,0 | rest | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P no separate limit on the card |
| 2.4851 / NiCr23Fe | EN 10095 | 58,0–63,0 | 21,0–25,0 | max. 18,0 | 1,0–1,7 | max. 1,0 | max. 0,5 | max. 0,5 | 0,03–0,10 | max. 0,015 | P max 0,020; Co max 1,5; Ti max 0,5; B max. 0,006 |
| NW6601 / Ni6601 | ISO (designation) | 58,0–63,0 | 21,0–25,0 | the rest / according to spec. | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P max 0,030; Co max. 1,0 |
| NiCr23Fe15Al | ISO 9722 | 58,0–63,0 | 21,0–25,0 | rest | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P according to the standard; Co max. 1,5 |
| NA49 | BS 2901 | 58,0–63,0 | 21,0–25,0 | rest | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P max 0,030; Co max. 1,0 |
| NCF601 | JIS G 4901 / 4902 | 58,0–63,0 | 21,0–25,0 | rest | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P max. 0,030 |
| H06601 / HNS3103 / NS3103 | GB/T – catalog designations | 58,0–63,0 | 21,0–25,0 | rest | 1,0–1,7 | max. 1,0 | max. 1,0 | max. 0,5 | max. 0,10 | max. 0,015 | P max 0,030; Co according to GB/T |
| VDM® Alloy 601 / Nicrofer 6023 H | VDM Metals | 58,0–63,0 | 21,0–25,0 | max. 18,0 | 1,0–1,7 | max. 1,0 | max. 0,5 | max. 0,5 | 0,03–0,10 (EN) | max. 0,015 | P max 0,020; Co max 1,5; Ti max 0,5; B max. 0,006 |
Comparison note: Special Metals and VDM values are based on manufacturer data sheets, while EN values are based on composition list 2.4851. The ISO/BS/JIS/GB/T lines provide a comparison of designations and limits found in catalog lists; they do not replace the text of the specific standard, its edition, or the inspection certificate. The "balance" sign indicates the iron content resulting from the composition balance. In EN, cobalt content may be included in nickel within the limits established for a given product.
Alloy 601 / Inconel 601 – material characteristics
Alloy 601 is a nickel-based alloy with a stable austenitic structure (face-centered cubic, FCC). Nickel stabilizes the structure and provides good properties over a wide temperature range. Chromium supports the formation of a protective oxide layer, while aluminum increases its adhesion and durability, which is particularly important during cyclic heating and cooling.
Unlike materials designed primarily for resistance to aqueous corrosion, Alloy 601 stands out primarily for its resistance to high-temperature oxidation, carburization, and changes in the furnace's operating atmosphere. However, it's important to distinguish between heat resistance and creep resistance: good preservation of the protective layer does not guarantee durability under long-term loading.
Alloy 601 is composed primarily of nickel, chromium, and iron, but the controlled addition of aluminum distinguishes it from Alloy 600 and is largely responsible for the scale's behavior under temperature fluctuations. During furnace operation, it is not only the metal's resistance to reaction with oxygen that matters, but also the adhesion of the formed oxides and their ability to survive multiple heating cycles.
When selecting an alloy, it's important to consider four criteria: metal temperature, atmospheric composition, mechanical stress, and expected service life. A material that resists oxidation very well may not necessarily be the most resistant to sulfurization, corrosion in aqueous environments, or prolonged creep under load.
- High oxidation resistance: in appropriately selected atmospheres even at temperatures close to 1200°C.
- Resistance to thermal cycles: limited tendency for the oxide layer to flake off upon repeated heating and cooling.
- Carburization resistance: suitability for furnace components and process atmospheres with carbon activity.
- Good technological suitability: possibility of rolling, forging, bending, welding and machining, taking into account the appropriate parameters.
- Metallurgical stability: preservation of the austenitic matrix, with possible carbide precipitation after certain thermal exposures.
Alloy 601 – Industrial Applications
Industrial furnaces and heat treatment installations
Alloy 601 is used for charging baskets, trays, retorts, muffles, radiant tubes, flame shields, supports, burners, conveyor meshes, and furnace fittings for annealing , carburizing , carbonitriding , and nitriding . The material is valued in equipment operating in heating and cooling cycles and in applications requiring reduced scale flaking.
Petrochemical and chemical industry
The alloy is used in gas heaters, ammonia reformer components, insulation shields, catalyst regeneration, and assemblies utilizing high-temperature process gases. In nitric acid production plants, it is used for catalytic grid supports and combustion chamber components, among other applications; however, the actual process atmosphere determines the choice.
Energy, combustion installations and environmental protection
In the energy industry, Alloy 601 is used for superheater tube supports, furnace fittings, ash removal components, and parts of energy recovery installations. In flue gas treatment systems and waste incineration plants, it can be used for selected components of combustion chambers and thermal reactors after analysis of sulfur and halogen content.
Automotive and aviation
Example applications include sensor and exhaust system covers, burner components, aircraft engine igniters, and selected turbine combustion chamber parts. This does not mean that Alloy 601 replaces specialized turbine superalloys in the most demanding blade applications.
Alloy 601 – physical properties
The values summarized below help predict component mass, heating during furnace operation, heat conduction, and dimensional growth during startup and cooling. When designing high-temperature systems, it's important to use properties that correspond to the actual material temperature, not just data at 20°C.
| Basic Physical Properties of Alloy 601 | ||
| Parameter and physical property | Indicative value | Measurement conditions and explanation for the designer |
| Density | 8,11 g / cm³ | The volumetric weight of the alloy at room temperature; Special Metals quotes 8,11 g/cm³ and VDM around 8,05 g/cm³ for its version of the material. |
| Melting range | 1360-1411 ° C | The interval between the start and end of melting of the alloy; Special Metals: 1360–1411°C, while in the VDM data it occurs around 1330–1370°C. |
| Specific heat | 448 J/(kg K) | Data for ambient temperature, approximately 20–21°C; a parameter needed when calculating the heating and cooling energy of components. |
| Thermal conductivity | 11,2 W/(m K) | Data at 20°C; the parameter determines the rate of heat flow through the material and is important when analyzing temperature gradients. |
| Electrical resistivity | 1,180 µΩ m | Data at 20°C; a parameter important for components heated by electricity and the assessment of energy losses in electrical devices. |
| Young's modulus E | 206,5 GPa | Dynamic value at 20°C; defines elastic stiffness in tension and bending. At high temperatures, it decreases significantly. |
| Relative magnetic permeability | approx. 1,003 | Approximately 1,003 at about 24°C; the material exhibits very weak magnetic properties at room temperature. |
| Curie temperature | below -196°C | No typical ferromagnetic transition is observed for the alloy under normal operating conditions; the approximate value is given in the manufacturer's data sheet. |
| How to interpret the table: Properties are given for specific material states, most often at room temperature. For mass, heat flow, and deformation calculations, data corresponding to the supplied material and operating temperature should be used. | ||
The values describe a specific material and test method; differences between catalogues result from, among other things, melt composition, heat treatment and measurement methods.
Effect of temperature on thermal conductivity, resistivity, specific heat and expansion
As temperature increases, the alloy's thermal conductivity and specific heat increase, while the mean linear expansion coefficient depends on the measurement range used. Data for the material annealed according to Special Metals are given below.
| Alloy 601 / Inconel 601 – physical properties as a function of temperature | ||||
| Material temperature T [°C] | Specific heat cₚ [J/(kg K)] | Thermal conductivity λ [W/(m K)] | Electrical resistivity ρₑ [µΩ m] | Mean linear expansion α [µm/(m K)] |
| 20 | 448 | 11,2 | 1,18 | |
| 100 | 469 | 12,7 | 1,192 | 13,75 |
| 200 | 498 | 14,3 | 1,207 | 14,36 |
| 300 | 523 | 16,0 | 1,22 | 14,58 |
| 400 | 548 | 17,7 | 1,229 | 14,83 |
| 500 | 578 | 19,5 | 1,239 | 15,19 |
| 600 | 603 | 21,0 | 1,247 | 15,62 |
| 700 | 632 | 22,8 | 1,249 | 16,11 |
| 800 | 657 | 24,4 | 1,249 | 16,67 |
| 900 | 686 | 26,1 | 1,259 | 17,24 |
| 1000 | 712 | 27,8 | 1,262 | 17,82 |
| How to interpret the table: As the temperature increases from 20 to 1000°C, the thermal conductivity in this combination increases from 11,2 to 27,8 W/(m K), and the specific heat from 448 to 712 J/(kg K). The coefficient α denotes the average expansion over a given temperature range, not the instantaneous expansion at a single point. | ||||
α is the average coefficient of linear expansion from a reference temperature of approximately 27°C to the indicated temperature, not the local coefficient at a single temperature. λ by Special Metals was calculated from resistivity.
Modulus of elasticity E, Kirchhoff modulus G and Poisson's number ν
At elevated temperatures, Alloy 601 becomes less elastically stiff. For furnace, pipe, and fastener designs, the decrease in elastic modulus can have a significant impact on deflection, thermal stresses, and part stability.
| Alloy 601 / Inconel 601 – elastic parameters as a function of temperature | |||
| Test temperature T [°C] | Young's modulus E – longitudinal elasticity [GPa] | Kirchhoff's modulus G – transverse elasticity [GPa] | Poisson's number ν [–] |
| 20 | 206,5 | 81,2 | 0,272 |
| 100 | 202,4 | 79,2 | 0,278 |
| 200 | 196,8 | 76,5 | 0,286 |
| 300 | 191,2 | 73,8 | 0,296 |
| 400 | 184,8 | 71,2 | 0,299 |
| 500 | 178,2 | 68,1 | 0,308 |
| 600 | 170,8 | 64,3 | 0,327 |
| 700 | 161,3 | 60,2 | 0,340 |
| 800 | 150,2 | 55,6 | 0,350 |
| 900 | 137,9 | 50,3 | 0,370 |
| 1000 | 124,7 | 44,7 | 0,395 |
| How to interpret the table: At 20°C, the E value is 206,5 GPa, and at 1000°C it drops to 124,7 GPa. Therefore, when calculating deflections, thermal expansion compensation, and fixing stiffness, room parameters alone must not be used. | |||
Source: Special Metals. Poisson's ratio was determined based on elastic modulus values. Data describe dynamic testing, not guaranteed design characteristics.
Alloy 601 – mechanical properties
The typical strength of laboratory samples should not be confused with the guaranteed value for the ordered batch. The product's form, degree of deformation, heat treatment, and the specifications of the product standard are important factors when making a purchase.
Strength parameters depend on the deformation state and heat treatment. Hot-rolled bar may exhibit a higher yield strength than solution-treated material, while cold-worked strips achieve high strength with lower elongation. The table summarizes approximate room-temperature ranges according to Special Metals.
| Mechanical properties of Alloy 601 products – approximate ranges | ||||
| Material form and processing state | Tensile strength Rm [MPa] | Yield strength Rp0,2 [MPa] | Elongation A [%] | HRB hardness |
| Hot rolled and finished bars, without leveling annealing | 585–825 | 240–690 | 15–60 | 65–95 |
| Annealed bars with increased plasticity | 550–790 | 205–415 | 40–70 | 60–80 |
| Thick plates after annealing, for further processing and structural applications | 550–690 | 205–310 | 45–65 | 60–75 |
| Cold-rolled and strain-hardened sheets | 790–1310 | 690–1205 | 2–20 | |
| Sheets after soft annealing | 585–690 | 205–345 | 35–55 | 65–80 |
| Tubes drawn and then annealed | 550–760 | 205–415 | 35–65 | 70–95 |
| Highly strengthened cold drawn wire | 825–1415 | 690–1345 | 3–20 | |
| Various product forms after solution heat treatment and cooling | 515–760 | 160–380 | 40–75 | 55–95 |
| How to interpret the table: The table illustrates the effect of product form and strain hardening on Rm, Rp0,2, and ductility. The ranges are derived from various products and should not be considered a guarantee of acceptance requirements for each delivery. | ||||
The ranges summarize various product dimensions and conditions and do not constitute automatic acceptance requirements. For products ordered according to EN 10095, requirements of Rp0,2 ≥ 205 MPa, Rm 550–750 MPa, A ≥ 30%, and HB ≤ 220 are met, depending on the form and condition of delivery.
Strength of the rod after annealing at 1090°C – influence of the test temperature
| Example of hot rolled bar, annealed to 1090°C | |||
| Testing temperature [°C] | Tensile strength Rm [MPa] | Conventional yield strength Rp0,2 [MPa] | Elongation after break A [%] |
| 20 | 741 | 290 | 47 |
| 100 | 701 | 250 | 44 |
| 200 | 687 | 236 | 43 |
| 300 | 674 | 221 | 46 |
| 400 | 654 | 219 | 45 |
| 500 | 640 | 203 | 45 |
| How to interpret the table: In the bar test shown, increasing the temperature from 20 to 500°C reduced Rm from 741 to 640 MPa and Rp0,2 from 290 to 203 MPa. The results are specific to the specific specimen and are not design limit values. | |||
Results from a single Special Metals test program (bar approximately 16 mm in diameter). They should not be considered guaranteed values for all dimensions.
Alloy 601 – Creep, Long-Term Strength and Fatigue
When a component supports the weight of a charge or acts as a support in a furnace, selecting solely based on Rm and Rp0,2 at room temperature can lead to erroneous conclusions. Creep describes slow deformation under constant stress over time, while fracture toughness describes the test result at a given temperature and time. These are two distinct types of data.
At temperatures above approximately 540–550°C, creep mechanisms and durability under sustained loading become increasingly important. In these applications, a supersaturated state with appropriately selected grain size can be advantageous. Short-term tensile strength Rm is not sufficient for design calculations; material data for a specific operating time and temperature are required.
Manufacturers' charts show the relationship between time to rupture and temperature and stress. The so-called 1000- or 10,000-hour rupture stress is not the same as the allowable design stress according to ASME or other pressure equipment codes.
Thermal stability and Charpy impact strength after annealing
Charpy tests conducted on solution heat-treated bars indicate that the alloy can retain significant ductility despite long-term exposure. However, this does not prove the absence of any structural changes under all conditions.
| Impact strength KV after high temperature exposure – measurement at room temperature | ||
| The temperature of the material prior to heating | Exposure time at this temperature | Charpy KV impact strength [J] after annealing |
| Reference sample – without prior annealing | 176 | |
| Heating at 540°C | 100 h | 117 |
| Heating at 540°C | 1000 h | 121 |
| Heating at 590°C | 1000 h | 126 |
| Heating at 650°C | 1000 h | 127 |
| Heating at 700°C | 100 h | 129 |
| Heating at 820°C | 159 h | 159 |
| Heating at 870°C | 103 h | 159 |
| How to interpret the table: The data refer to the fracture energy of samples previously heated and then tested at room temperature. They do not represent the results of a KV test conducted directly at the heating temperature. | ||
The values correspond to tests on a specific bar in the supersaturated condition; some of the exposure times in the original studies are not the same and therefore should not be presented as a single wear curve.
Alloy 601 – high temperature corrosion resistance
The same temperature does not necessarily mean the same corrosive atmosphere. Air, combustion gas mixtures, ammonia, chlorine, and environments with high carbon activity affect the alloy through different mechanisms. Therefore, the test values in the tables refer only to the specified conditions.
Oxidation and scale removal
The most important characteristic of Alloy 601 is its high oxidation resistance. Chromium and aluminum form an adhesive protective layer that limits the transport of oxygen to the substrate. In many applications, this advantage is particularly noticeable during sudden and repeated temperature changes, when less stable oxides can crack and flake off.
Special Metals presents cyclic oxidation testing at 1095°C, 1150°C, and 1200°C. Alloy 601 can operate in oxidizing atmospheres at temperatures approaching 1200°C, but product durability depends on exposure time, loading, and the presence of aggressive gas components. Therefore, 1200°C should not be used as a universal allowable design temperature.
| Alloy 601 / Inconel 601 – Long-Term Static Oxidation Results | ||
| Test temperature [°C] | Exposure time [h] | Average depth of the affected area [mm] |
| 980 | 1008 | 0,033 |
| 1095 | 1008 | 0,067 |
| 1150 | 1008 | 0,135 |
| 1205 | 1008 | 0,190 |
| Data interpretation: The results of a specific static test after 1008 hours of exposure are given. The depth of attack is not the same as the thickness loss due to scale flaking alone; the comparison is only meaningful under similar test conditions. | ||
Carburizing and carbonitriding
The alloy exhibits good resistance in many carburizing atmospheres, hence its use in baskets, trays, and furnace fittings. However, in atmospheres containing carbon and nitrogen, the interaction of the components can affect the surface layer and the precipitate phases.
| Example test results in an atmosphere of 2% CH₄ and 98% H₂ | ||
| Sample temperature [°C] | Gas mixture operating time [h] | Recorded sample mass increase [mg/cm²] |
| 925 | 100 | 2,72 |
| 980 | 100 | 4,32 |
| 1095 | 25 | 3,67 |
| How to interpret the table: The results given are for the 2% CH₄ + 98% H₂ mixture and the indicated exposure times only. Mass gain is not a direct measure of the allowable carburization rate of each furnace component. | ||
Data from comparative experiments by Special Metals. Mass gain describes a specific test and is not a universal carburization rate across all furnaces.
Nitriding and the effects of ammonia
Alloy 601 demonstrates resistance to many industrial atmospheres containing nitrogen or ammonia. However, at high temperatures, nitrogen diffusion and the formation of nitrides, including aluminum and titanium nitrides, are possible. Particularly in ammonia systems, good resistance in a single test should not be equated with complete absence of chemical attack.
| Alloy 601 / Inconel 601 – Comparison of nitriding results in different atmospheres | |||
| Atmosphere affecting the alloy | Test temperature [°C] | Exposure time [h] | Penetration depth [mm] |
| Ammonia (NH₃) | 650 | 168 | 0,03 |
| Ammonia (NH₃) | 980 | 168 | 0,17 |
| Ammonia (NH₃) | 1090 | 168 | over 0,58 |
| Pure nitrogen (N₂) | 980 | 168 | 1,55 |
| Pure nitrogen (N₂) | 1090 | 168 | 2,79 |
| Pure nitrogen (N₂) | 1204 | 168 | 3,81 |
| Data interpretation: The numbers refer only to the indicated material tests. Nitriding resistance should not be assessed without also taking into account nitrogen activity, atmosphere, and temperature. | |||
Sulphidation, chlorine and hydrogen chloride
Sulfiding environments are potentially hazardous to high-nickel alloys: reducing atmospheres with active sulfur, in particular, can accelerate degradation. The presence of oxygen, hydrogen, water vapor, and active halogens can significantly alter the material's behavior. Data from tests in chloride or HCl always refer to strictly defined conditions; a separate corrosion assessment is required for exhaust gases containing chlorine and sulfur.
| Alloy 601 / Inconel 601 – an example of resistance in a mixture of argon and chlorine | |||
| Chlorinating atmosphere | Temperature [° C] | Time [h] | Sample weight loss [mg/cm²] |
| Ar + 30% Cl₂ | 400 | 500 | 0,3 |
| Ar + 30% Cl₂ | 500 | 500 | 3 |
| Ar + 30% Cl₂ | 600 | 500 | 85–200 |
| Ar + 30% Cl₂ | 705 | 500 | 215 |
| Data interpretation: Mass loss increases rapidly as temperature increases. The results show that the chlorine resistance rating cannot be transferred from 400–500°C to significantly higher temperatures without additional verification. | |||
Water corrosion and stress cracking
Alloy 601 exhibits good resistance to a range of aqueous environments and some stress corrosion cracking mechanisms, but was primarily designed for high-temperature service. For prolonged exposure to aggressive seawater or chloride environments, a molybdenum-containing material, such as Alloy 625, may be a better choice if design conditions support this.
Alloy 601 – plastic, heat and machining processing
Alloy 601 is an austenitic alloy with high resistance to deformation at elevated temperatures. During forging and rolling, it requires appropriate selection of the deformation temperature, and during machining, consideration must be given to the hardening of the processed layer and the possibility of accelerated tool wear.
Hot working – forging and rolling
According to Special Metals, the typical hot working range is approximately 870–1230°C, with large deformations typically performed at 1040–1230°C. In the range of approximately 650–870°C, the material has limited ductility and intensive deformation is not recommended. The temperature selection depends on the cross-section, forging speed, tool temperature, and the degree of deformation.
After hot working, it is recommended to cool the material sufficiently through a temperature range that promotes undesirable precipitation. Before heating, remove any contaminants and use a low-sulfur fuel and atmosphere.
Annealing and solution heat treatment
Alloy 601 is not a typical precipitation-hardening alloy. The material's temper can be shaped by cold deformation followed by annealing. For components where lower-temperature strength properties dominate, annealing in the range of approximately 1000–1100°C is used. For long-term applications where creep resistance is critical, the solution heat treatment is used, typically in the range of approximately 1100–1200°C. The exact cycle should be selected based on the standard requirements, dimensions, and final properties.
| Example technological ranges – approximate data | ||
| Technological procedure and scope of the process | Process temperature or recommendation | Technological importance and limitations |
| Hot rolling and forging | 870-1230 ° C | A wider range of plastic working is permissible; substantial, larger deformations are usually carried out in the upper part of this range (approximately 1040–1230°C). |
| Limited plasticity range | approx. 650–870°C | In this range, intense deformation should be limited because the plasticity of the material may be lower than at the temperatures of the actual forging. |
| Annealing | approx. 1000–1100°C | It is used for recrystallization and adjustment of properties after plastic forming; the cycle parameters depend on the cross-section and the desired final state. |
| Oversaturation | approx. 1100–1200°C | It allows for the appropriate shaping of the microstructure and grain size, which is important for long-term operation at high temperatures. |
| Cooling | according to the procedure | The cooling rate is selected according to the cross-section, technological requirements and the limitation of undesirable precipitation. |
| How to interpret the table: Before using these temperatures in production, it is important to verify the product geometry, input material condition, allowable microstructural changes, and cooling method. These ranges do not constitute a universal heat treatment cycle. | ||
Cold working
The material can be bent, rolled, and cold-drawn. As deformation increases, strength increases, but ductility decreases. At significant work hardening rates, intermediate annealing may be necessary; components with small bend radii should be inspected for cracks and the required delivery condition.
Machining
Compared to unalloyed steels, machining Alloy 601 is more demanding due to material hardening in the cutting layer, strength at elevated temperatures, and tool wear. Rigid clamping, sharp tools, controlled chip evacuation, and appropriate cutting fluid are recommended. Cutting parameters should be based on the insert grade, tool geometry, machine rigidity, and material condition; a single turning speed should not be applied to all parts.
Alloy 601 – welding and additional materials
When welding furnace components, not only the properties of the joint after welding are important, but also the resistance of the metal to oxidation during subsequent operation. This is one reason why the choice of wire or electrode depends on the operating temperature and atmosphere.
Alloy 601 is characterized by good weldability using TIG, MIG, and coated electrode methods, as well as selected automated processes. Prior to welding, surfaces must be clean, free of oil, sulfur, paint, and processing products. Limiting the influx of contaminants, appropriate heat input, and selecting the filler metal appropriate to the operating temperature also determine the success of the joint.
| Examples of selecting additional materials | ||
| Welding method and intended use of the joint | Example of filler metal or electrode type | Conditions of use and matters to be checked |
| TIG / MIG – filler metal compatible with alloy 601 | ERNiCrFe-11 / Inconel Filler Metal 601 | Preferred where chemical compatibility and elevated temperatures are required |
| TIG / MIG – typical conditions | ERNiCr-3 / Filler Metal 82 | Application after checking the connector requirements |
| Coated electrodes | ENiCrFe-3 / Electrode 182; Electrode 117 | The selection depends on the temperature and environment |
| Selected high-temperature conditions | Filler Metal 617 | Consider after verifying long-term durability requirements |
| How to interpret the table: The selection of a binder must take into account the operating conditions of the joint: temperature, atmosphere, stresses, susceptibility to cracking, and the required WPS/WPQR documentation. The list does not imply absolute interchangeability of all binders listed. | ||
Filler materials are not automatically interchangeable: Special Metals distinguishes filler materials for applications below and above approximately 980°C, and for atmospheres containing H₂S or SO₂. For critical applications, a WPS and process qualification are required.
Alloy 601 / 2.4851 – material and manufacturing standards
The UNS N06601 designation identifies the alloy's composition, while the product standards describe requirements for specific products, delivery conditions, testing, and tolerances. Both the grade and the product specification must be specified in the offer.
| Examples of standards and corresponding products | |
| Product standard or document designation | Type of product and practical scope of application of the standard |
| ASTM B166 / ASME SB-166 | Round bars, other bar products, and wire. When ordering, please specify the diameter, surface finish, and delivery condition. |
| ASTM B168 / ASME SB-168 | Nickel alloy plates, sheets and strips with thickness and property requirements. |
| ASTM B167 / ASME SB-167 | Seamless pipes; dimensions, tolerances, delivery condition and scope of required testing are important. |
| ASTM B163 / ASME SB-163 | Selected seamless tubes for heat exchangers and condensers; the scope of application of the relevant edition of the standard should be checked. |
| ASTM B564 / ASME SB-564 | Forgings and semi-finished forged products made of nickel alloys, intended for further mechanical processing. |
| DIN 17750 / 17752 / 17753 / 17754 | Historic DIN standards for flat materials, bars, wires and forgings, respectively; their status requires checking. |
| EN 10095 | Flat and long products made of heat-resistant steels and nickel alloys; condition and requirements should be referred to the relevant provisions. |
| ISO 6207 / ISO 6208 | ISO standards for nickel alloy pipes and flat products, respectively. |
| ISO 9723 / 9724 / 9725 | ISO standards for nickel alloy bars, wires and forgings, applicable depending on the form ordered. |
| AMS 5715 / AMS 5870 | Specifications used in the aerospace industry; check that they cover the product ordered and its condition. |
| How to interpret the table: The product standard specifies the material form and acceptance requirements. The UNS N06601 symbol alone identifies the alloy, but it does not replace the standard definition, processing condition, and quality control requirements. | |
The required current edition of the standard must be confirmed when ordering. Historical DIN designations do not always correspond to currently applicable documents. ASTM numbers alone should not be considered as substitutes for grade names.
Alloy 601 – Trade Names, Alternatives and International Designations
| Confirmed Alloy 601 Designations | |
| Name, symbol or material number | The meaning of the designation and its origin |
| Alloy 601 / Inconel® 601 | The alloy name and protected trademark Inconel® 601 used by Special Metals; it is not a separate product standard. |
| UNS N06601 | The UNS uniform material number is the basic designation of the chemical class of the alloy. |
| 2.4851 / NiCr23Fe | European material number 2.4851 and short name NiCr23Fe. |
| NiCr23Fe15Al | A component designation found in the ISO system; it indicates nickel, chromium, iron and aluminum. |
| NW6601 | The alloy designation in the ISO numbering system is an identifier, not a certificate of product properties. |
| NA49 | Historic British species designation BS NA49. |
| NCF601 | Japanese alloy designation class N06601 as found in JIS documentation. |
| NC23FeA | Historic French alloy designation for Alloy 601. |
| VDM® Alloy 601 / Nicrofer® 6023 H | Trade name VDM Metals and former designation Nicrofer® 6023 H. |
| GL5 | Trademark found in Valbruna manufacturer's catalogues. |
| How to interpret the table: Trade names, national systems and material numbers refer to Alloy 601 grade, but the specific specification, composition tolerances and product condition must be verified upon delivery. | |
Older catalogs also include the names EMVAC 601, VAT 601, NY 601, Nicrimphy 601, Coralloy 601, and NRX 601. However, each of these should not be considered an automatically verified trade name for an identical specification. When selecting a replacement, the confirmed UNS N06601 composition, delivery condition, standard requirements, and inspection certificate are more important than the name.
Comparison of Alloy 601 with Alloy 600, Alloy 617, and Alloy 625
| Preliminary selection of nickel alloys – significant differences | ||
| Material grade and designation | The most important elements and composition differences | Primary use or technical advantage |
| Alloy 600 / 2.4816 | Ni–Cr–Fe; Cr approx. 14–17% | Used in select chemical environments and at elevated temperatures; not equivalent to 601 in every furnace. |
| Alloy 601 / 2.4851 | Ni–Cr–Fe–Al; Cr 21–25%, Al 1,0–1,7% | High resistance to oxidation and cyclical temperature changes, especially important when equipping industrial furnaces. |
| Alloy 617 / 2.4663 | Ni–Cr–Co–Mo–Al | Designed for operation under load at high temperatures where strength and creep resistance are important. |
| Alloy 625 / 2.4856 | Ni–Cr–Mo–Nb | High resistance to numerous aggressive chemical environments, especially to local corrosion in the presence of chlorides. |
| How to interpret the table: This preliminary comparison does not imply that alloys are interchangeable. Oxidation resistance, aqueous corrosion resistance, and creep strength are distinct design criteria. | ||
This comparison is used for initial material selection. In the actual design, temperature, time, stress, atmosphere, and availability of the required product form must be considered.
Frequently Asked Questions – Alloy 601 / Inconel 601
Are Alloy 601 and Inconel 601 the same material?
Yes. Alloy 601 refers to alloy grade UNS N06601 / 2.4851, while Inconel® 601 is a trademark of Special Metals. However, always check the condition and standard of the product before purchasing.
Is Alloy 601 stainless steel?
No. It is a nickel-based alloy, not an iron-based alloy, even though it contains a significant proportion of iron and has good corrosion resistance.
Up to what temperature can Alloy 601 be used?
In suitable oxidizing atmospheres, the material exhibits high oxidation resistance up to approximately 1200°C. However, the permissible temperature of the loaded component depends on stresses, operating time, and environmental conditions.
Does Alloy 601 contain aluminum?
Yes. It typically contains 1,0–1,7% Al. This addition increases the durability of the protective oxide layer and improves high-temperature performance.
What is the density of Alloy 601?
According to Special Metals, it's approximately 8,11 g/cm³. VDM Metals specifies approximately 8,05 g/cm³ for its own variety. For precise mass calculations, the value should be taken from the manufacturer's specifications for the specific material.
What is the hardness of Alloy 601?
In the annealed condition, typical values for many products are around 60–95 HRB, while some EN specifications specify a maximum hardness of 220 HB. Hardness depends on the condition and form of the product.
Can Alloy 601 be welded?
Yes. The alloy is easily weldable. ERNiCrFe-11 or ERNiCr-3 wires are used, but the choice of filler metal depends on the operating temperature and environmental composition.
Can Alloy 601 be hardened and tempered?
Not in the manner typical of heat-treated steels. Annealing, solution heat-treating, and cold working are used. This is not a typical precipitation-hardening alloy.
What is the difference between Alloy 601 and Alloy 600?
Alloy 601 contains more chromium and a controlled addition of aluminum, so it typically performs better in applications requiring resistance to high-temperature oxidation and thermal cycling.
What is the difference between Alloy 601 and Alloy 625?
Alloy 601 is often chosen for use in oxidizing furnace atmospheres. Alloy 625, thanks to its molybdenum and niobium content, provides superior resistance to many corrosive environments, particularly those conducive to localized corrosion.
Is Alloy 601 suitable for carburizing furnace components?
Yes, it is one of the materials used for baskets and fittings in furnaces operating in carburizing atmospheres. Durability is determined by gas concentration, temperature, cycle count, and mechanical load.
Alloy 601 / Inconel 601 / 2.4851 – Alfa-Tech inquiry
Need Alloy 601 in the form of bar, flat bar, forging, pipe or sheet?
Provide dimensions, quantity, desired standard, delivery status, and application conditions. Alfa-Tech will help verify the correct material and its availability. Availability and lead times are confirmed individually.