Nickel 200 vs Nickel 201: Low Carbon Content and High-Temperature Service

Nickel 200 and Nickel 201 are both commercially pure (99.6% min.) wrought nickel, but a small difference in carbon content - well under one percent - determines whether a component stays ductile or becomes brittle at elevated temperature. This guide explains exactly what that difference means for material selection, fabrication, and service life.

What Is the Core Difference Between Nickel 200 and Nickel 201?

Nickel 200 (UNS N02200) and Nickel 201 (UNS N02201) are both commercially pure wrought nickel alloys with the same base composition, but Nickel 201 has a much lower maximum carbon content - 0.02% versus 0.15% for Nickel 200 - which prevents graphite embrittlement at high temperature and makes Nickel 201 the required choice for continuous service above 600°F (315°C).

Both grades are at least 99.0% nickel (commonly 99.6% or higher in commercial product), with small, tightly controlled additions of manganese, iron, and copper. Carbon is the one element deliberately limited far below its normal level in Nickel 201, because at high temperature carbon behaves very differently in these two grades - with real consequences for strength and toughness.

Table 1. Chemical composition limits per ASTM B160 / B162 (values are weight percent).

What Is Nickel 200 Best Used For?

Nickel 200 is best suited for room- and moderate-temperature applications that demand excellent corrosion resistance, high thermal and electrical conductivity, and ease of fabrication - including caustic soda handling, food processing, and electronic and electrical components.

Nickel 200's higher allowable carbon content is not a defect - it simply means the grade was never intended for prolonged high-temperature use. Below roughly 600°F (315°C), the carbon content has no meaningful effect on mechanical behavior, so Nickel 200 performs excellently and typically costs less to produce than the tighter-controlled Nickel 201.

Typical Nickel 200 Applications

• Caustic soda (sodium hydroxide) and alkali handling equipment
• Food-processing equipment requiring low metallic contamination
• Electrical and electronic components (lead wires, connectors, shielding)
• Chemical shipping drums and totes for high-purity products
• Marine and freshwater components below 600°F (315°C)

What Is Nickel 201 and Why Is It Used at High Temperatures?

Nickel 201 is the low-carbon version of commercially pure nickel, produced specifically to resist graphitization and embrittlement above 600°F (315°C), making it the standard grade for furnace parts, high-temperature process equipment, and any nickel component that will see sustained heat in service.

At temperatures above roughly 600°F (315°C), carbon in Nickel 200 can precipitate out of solid solution as graphite, concentrating at grain boundaries.

This graphitic carbon does not strengthen the metal the way carbides strengthen steel - instead, it forms a network of weak points that sharply reduces ductility and impact toughness, a failure mode commonly called high-temperature embrittlement. Because Nickel 201's carbon content is capped at 0.02%, there is not enough carbon present to form a damaging graphite network, so the alloy retains its ductility and toughness even after extended high-temperature exposure.

Typical Nickel 201 Applications

• Furnace components and heat-treating fixtures
• Caustic evaporators and high-temperature alkali service
• Electron tube and vacuum-furnace hardware
• Chemical processing equipment operating above 600°F (315°C)
• Welded assemblies that will see post-weld or in-service heat above 600°F (315°C)

How Does Carbon Content Cause High-Temperature Embrittlement?

Carbon content controls embrittlement risk because nickel has very low solid solubility for carbon at high temperature; excess carbon precipitates as graphite along grain boundaries, and the more carbon present, the denser and more damaging that graphite network becomes.

This is a solubility problem, not a strength problem. Unlike in steel, where carbon forms hard, strengthening carbides, carbon in nickel simply exceeds what the metal can hold in solution as temperature rises and then falls out as soft, weak graphite. The practical consequences for grade selection are direct:

Nickel 201 (0.02% C max): Carbon stays low enough that little or no graphite forms, even after prolonged exposure above 600°F (315°C). Ductility and toughness are preserved.

Nickel 200 (0.15% C max): Carbon content is high enough that graphite precipitation becomes likely above 600°F (315°C), especially with slow cooling or long dwell times, resulting in a measurable loss of impact toughness and ductility.

This is why the 600°F (315°C) threshold is treated as a hard boundary in specification and design practice, rather than a rough guideline: below it, either grade performs reliably; above it, only Nickel 201 is recommended for sustained service.

What Are the Mechanical and Physical Property Differences Between Nickel 200 and Nickel 201?

At room temperature, Nickel 200 and Nickel 201 have essentially identical mechanical and physical properties; the difference only becomes significant after extended exposure above 600°F (315°C), where Nickel 200 loses ductility and toughness while Nickel 201 retains both.

Table 2. Representative mechanical and physical properties per ASTM B160 / B161 / B162.

Which Grade Should You Choose for Your Application?

Choose Nickel 200 for cost-effective, room- to moderate-temperature service in corrosive or high-conductivity applications; choose Nickel 201 for any component operating continuously above 600°F (315°C), or for weldments that will experience sustained heat afterward.

Table 3. Quick-reference grade selection guide.

When a design falls near the 600°F (315°C) threshold, or when a component will be both welded and heated in service, the safer and standard practice is to specify Nickel 201 rather than risk graphitization in Nickel 200. The modest cost difference between the two grades is minor compared to the cost of an in-service brittle failure.

Frequently Asked Questions

Brief, occasional excursions above 600°F (315°C) are generally tolerated, since graphitization is a time- and temperature-dependent process. However, Nickel 200 is not recommended for continuous or repeated service above this threshold, where cumulative exposure increases embrittlement risk.

Is Nickel 201 more expensive than Nickel 200?

Nickel 201 typically carries a modest price premium over Nickel 200, reflecting the additional refining required to hold carbon at or below 0.02%. In high-temperature applications, this premium is minor compared to the cost of premature failure from graphite embrittlement.

Do Nickel 200 and Nickel 201 have the same corrosion resistance?

Yes. Corrosion resistance in both grades comes from the nickel matrix itself, not from carbon content, so Nickel 200 and Nickel 201 perform equivalently in caustic, neutral salt, and many organic and food-processing environments.

Can Nickel 201 be welded without special precautions?

Nickel 201 welds using standard nickel welding practices and filler metals, and its low carbon content actually reduces the risk of heat-affected-zone embrittlement compared to welding Nickel 200. Standard cleanliness and shielding precautions for pure nickel still apply.

How is graphitization in Nickel 200 detected or prevented?

Graphitization is typically identified through metallographic examination or a loss of impact toughness in mechanical testing after high-temperature exposure. The most reliable prevention is not a heat treatment but a material substitution: specifying Nickel 201 wherever sustained service temperature will exceed 600°F (315°C).