Nickel 200 and Nickel 201: One Element Apart
Nickel 200 (UNS N02200) and Nickel 201 (UNS N02201) are commercially pure wrought nickels with a nominal nickel content of 99 % or more. Their chemistry, mechanical behaviour, corrosion resistance and fabrication characteristics are almost identical, and in most room-temperature applications the two grades can be used interchangeably. The single meaningful difference is carbon: Nickel 200 is the standard low-carbon grade, while Nickel 201 is the extra-low-carbon version, and that difference governs what happens above about 315 °C.
Because the two designations look almost the same, they are frequently confused in purchase orders and material certificates. The distinction matters most in elevated-temperature service, in welded assemblies that will be stress relieved, and in caustic handling equipment where intergranular attack is a concern.
Chemical Composition Compared
The composition limits below are typical of ASTM B160 rod and bar, ASTM B161 seamless pipe and tube, and ASTM B162 plate, sheet and strip. Nickel 201 is normally referred to as LC nickel because its carbon maximum is roughly seven times lower than that of Nickel 200.
| Element, % | Nickel 200 (UNS N02200) | Nickel 201 (UNS N02201) |
|---|---|---|
| Nickel, Ni | ≥99.0 | ≥99.0 |
| Carbon, C | ≤0.15 | ≤0.02 |
| Iron, Fe | ≤0.40 | ≤0.40 |
| Copper, Cu | ≤0.25 | ≤0.25 |
| Manganese, Mn | ≤0.35 | ≤0.35 |
| Silicon, Si | ≤0.35 | ≤0.35 |
| Sulphur, S | ≤0.010 | ≤0.010 |
It is worth noting that carbon content in Nickel 201 is lower than in Nickel 200, not higher, and that this is the whole point of the grade. The remaining elements are residuals rather than deliberate additions, and cobalt is not specified as an alloying element in either grade.
Why Carbon Content Matters: Graphitisation and Service Temperature
In plain nickel, carbon is essentially insoluble in the matrix at moderate temperature and tends to precipitate as graphite along grain boundaries. This graphitisation reaction becomes measurable above roughly 315 °C (600 °F), and it progressively embrittles the material and weakens welded joints, particularly in the heat-affected zone. Reducing the carbon from a 0.15 % maximum to a 0.02 % maximum removes most of the graphite-forming potential, which is why Nickel 201 is the specified grade for service above 315 °C.
Nickel 200: recommended for service up to about 315 °C, where it offers slightly higher annealed strength and good ductility.
Nickel 201: recommended for continuous service above 315 °C and up to about 600 °C, where resistance to graphitisation is the controlling property.
Caustic service: both grades resist concentrated sodium hydroxide, but Nickel 201 is preferred for hot, concentrated caustic where intergranular attack is a risk.
Welded fabrications: Nickel 201 tolerates post-weld stress relieving at 540–650 °C without losing ductility; Nickel 200 can suffer graphitisation under the same treatment if the temperature exceeds about 315 °C.
Mechanical and Physical Properties
Nickel 201 is slightly softer and more ductile than Nickel 200 in the annealed condition, because the lower carbon content suppresses solid-solution strengthening and carbide precipitation. Typical room-temperature values for annealed material are shown below; cold working raises strength in both grades, and a 20 % reduction in thickness roughly doubles the yield strength of either.
| Property, annealed | Nickel 200 (UNS N02200) | Nickel 201 (UNS N02201) |
|---|---|---|
| Tensile strength | About 460 MPa | About 400 MPa |
| 0.2 % yield strength | About 150 MPa | About 105 MPa |
| Elongation | About 45 % | About 50 % |
| Hardness | About 65 HRB | About 55 HRB |
| Density | 8.89 g/cm³ | 8.89 g/cm³ |
| Melting range | About 1435–1446 °C | About 1435–1446 °C |
| Thermal conductivity at 20 °C | About 70 W/(m·K) | About 70 W/(m·K) |
Both grades are ferromagnetic at room temperature with similar magnetic characteristics, both retain excellent toughness at cryogenic temperatures, and both are readily hot worked, cold formed, machined and welded. Because they work-harden quickly, heavy cold-forming operations may need intermediate annealing at roughly 700–800 °C, followed by rapid cooling.
Corrosion Behaviour and Typical Applications
Caustic alkalies: both grades are among the few materials that handle concentrated sodium hydroxide and potassium hydroxide without stress corrosion cracking, and Nickel 201 is the preferred grade for hot concentrated liquors.
Chlor-alkali and chlorate plants: used for evaporators, caustic transfer lines, reactor vessels and heat exchanger tubing.
Chemical processing: vessels, piping and valves handling fatty acids, neutral and alkaline salt solutions and mineral acids in the reducing condition.
Electronics and electrical: Nickel 200 is widely used for electrodes, anodes, cathodes, transistor housings, magnetostrictive components and battery terminals, where its conductivity and magnetic response matter as much as its corrosion resistance.
Food and beverage: food processing equipment, handling of sodium hydroxide cleaning solutions and corrosion resistant utensils.
Aerospace and energy: rocket motor cases, heat shields, spark electrodes and components exposed to hot caustic or fluoride salt environments.
A practical selection summary: specify Nickel 200 for room-temperature and mildly elevated service where the highest possible annealed strength is wanted, and specify Nickel 201 whenever the metal temperature can exceed 315 °C, whenever welded assemblies are stress relieved, or when hot caustic service is involved.
Frequently Asked Questions
Q: What is the main difference between Nickel 200 and Nickel 201?
Carbon content. Nickel 200 permits up to 0.15 % carbon, while Nickel 201 is limited to 0.02 % maximum, which makes Nickel 201 resistant to graphitisation above 315 °C.
Q: Does Nickel 201 have higher carbon than Nickel 200?
No, the opposite is true. Nickel 201 is the low-carbon grade. Its maximum carbon is about seven times lower than that of Nickel 200, and its nickel content and all other element limits are the same.
Q: When should Nickel 201 be used instead of Nickel 200?
Use Nickel 201 when the service temperature exceeds about 315 °C, when welded joints will be stress relieved above that temperature, or when the equipment handles hot concentrated caustic solutions where intergranular attack is a risk.
Q: Are Nickel 200 and Nickel 201 interchangeable at room temperature?
For most ambient and mildly elevated applications, yes. Both grades have similar corrosion resistance, magnetic behaviour and fabrication characteristics, and Nickel 200 offers slightly higher annealed strength.
Q: What standards cover these two grades?
Rod and bar are covered by ASTM B160, seamless pipe and tube by ASTM B161, and plate, sheet and strip by ASTM B162. Werkstoff numbers 2.4060 and 2.4061 identify Nickel 200 and Nickel 201 respectively.
Q: How are Nickel 200 and Nickel 201 welded?
Both are welded with matching nickel filler metals using gas tungsten arc, gas metal arc or shielded metal arc processes. Low heat input, clean surfaces and, for Nickel 201, a stress relief at about 540–650 °C are the usual precautions.
