Material Characteristics

N4 Pure Nickel Rod is a metal bar product based on commercially pure nickel, with a nickel plus cobalt content of no less than 99.4% and a carbon content strictly controlled at ≤0.02%. In the Chinese national standard system, grade N4 corresponds to the internationally recognized Nickel 201 (UNS N02201), widely known as "low-carbon pure nickel." Compared to ordinary pure nickel materials, the most critical difference of N4 lies in its extremely low carbon content, a microchemical distinction that gives it an irreplaceable position in specific high-end industrial applications.

N4 pure nickel rods are manufactured using electrolytic nickel as raw material, processed by vacuum melting, hot rolling, hot forging, or cold drawing, and can be supplied in various surface conditions such as black scale, turned, or polished. N4 is not a complex multi-element alloy but a single metal material based on high-purity nickel, whose performance advantages derive from the inherent physicochemical properties of nickel and the microstructure purity resulting from extremely low impurities. Within the range from room temperature to approximately 360°C, N4 maintains a stable face-centered cubic lattice structure, which endows the material with excellent ductility and processability.

The market positioning of N4 pure nickel rods lies in filling the gap that ordinary pure nickel cannot address in high-temperature-sensitive applications. When the service temperature exceeds 315°C, graphitic carbides begin to precipitate at the grain boundaries of ordinary pure nickel (such as N6), causing "intermediate-temperature embrittlement" that renders the material engineering-unusable. N4, with its low-carbon design, fundamentally avoids this failure mechanism, raising the maximum recommended service temperature to about 600°C. This differentiated performance makes N4 the preferred pure nickel solution for applications in the temperature range above 315°C.

Products Parameters

Product Name	N4 Pure Nickel Rod
Purity	Ni+Co≥99.5%
Thickness	Φ6 mm – Φ150 mm/customized
Length	500 mm – 6000 mm/customized
Surface State	Black leather state/car glossy state/polished state
Tolerance	+-0.05mm
Delivery Status	Hot working state (R)/cold working state (Y)/annealed state (M)
Density	8.89 g/cm³
Melting point	1440 - 1460 ℃
Thermal conductivity	82 W/(m·K)
Resistivity (20℃)	0.086 μΩ·m
Linear expansion coefficient	13.3 × 10⁻⁶ /K
Curie point	360°C
Modulus of elasticity	200 GPa
Tensile strength	≥380 MPa
Yield strength	≥100 MPa
Elongation	≥ 40%
Hardness	70 - 100HBW

Products Advantages

High-Temperature Stability – Core Advantage of Low Carbon Design

The most outstanding characteristic of the N4 pure nickel rod is its exceptional high-temperature stability. When ordinary pure nickel materials are in long-term service in the range of 315°C to 600°C, the precipitation of graphitic carbides at grain boundaries causes severe "intermediate-temperature embrittlement," leading to a sharp drop in toughness or even brittle fracture. Thanks to its carbon content being strictly limited to ≤0.02%, N4 fundamentally eliminates the possibility of carbide precipitation at grain boundaries, thereby maintaining stable mechanical properties within this critical temperature range. This enhanced temperature tolerance allows N4 to achieve a maximum recommended service temperature of 600°C-50–100°C higher than N6-and even higher in inert or dry atmospheres.

Corrosion Resistance in Strong Alkaline Environments

N4 pure nickel ranks second only to silver among metallic materials for resistance to alkaline corrosion. In high-temperature, high-concentration caustic soda solutions, N4 rapidly forms a dense oxide film on its surface without suffering from caustic embrittlement (stress corrosion cracking), making it the preferred material for evaporator agitators, concentrator tanks, and similar equipment in the chlor-alkali industry. At room temperature, N4 is also highly stable in seawater, salt solutions, and organic media, and is extremely insensitive to chloride-induced stress corrosion cracking-in stark contrast to austenitic stainless steels (e.g., 304, 316), which are prone to pitting and stress corrosion cracking in seawater. Additionally, N4 exhibits good corrosion resistance in anhydrous halogens, medium-concentration sulfuric acid, hydrochloric acid, and other non-oxidizing acids.

Excellent Workability and Weldability

N4 pure nickel rod offers a "strong yet tough" mechanical profile. In the annealed condition, it has a tensile strength of approximately 380–450 MPa, a yield strength of about 100–200 MPa, and an elongation of up to 40% or more. This means it can withstand severe cold forming processes such as deep drawing and bending without cracking. The weldability of N4 is equally excellent, with a low tendency for cracks or defects during welding and a wide welding temperature range. It can be processed using TIG, MIG, submerged arc welding, and other techniques. Matching pure nickel filler wire (ERNi-1) is typically used, and welded joints achieve over 96% of the base metal's strength with a ductile fracture mode. It should be noted that N4 is extremely sensitive to sulfur; heating in a sulfur-containing atmosphere can cause "sulfur embrittlement," so atmospheric conditions must be strictly controlled during hot working and heat treatment.

Unique Physical Properties

N4 is ferromagnetic at room temperature, with a Curie point around 360°C; above this temperature, it becomes paramagnetic. This property offers unique value in applications such as electromagnetic shielding and sensor housings. Thermal conductivity is approximately 82 W/(m·K), and electrical resistivity is about 0.086 μΩ·m (20°C), combining good thermal conductivity and moderate electrical conductivity. Density is 8.89 g/cm³, melting point approximately 1440–1460°C, thermal expansion coefficient 13.3×10⁻⁶/K (20–100°C), and elastic modulus about 200 GPa.

Products Applications

Chlor-Alkali and Soda Ash Industry – The Core Market for N4

N4 pure nickel rod occupies a dominant position in the chlor-alkali industry. In the ion-exchange membrane caustic soda process, equipment is exposed to severe conditions of high temperature (>150°C) and high-concentration caustic soda (NaOH ~50%). Carbon steel suffers severe corrosion, stainless steel undergoes caustic embrittlement, and only nickel materials can provide long-term, reliable service. N4 is particularly suitable for critical moving parts such as evaporator agitator shafts, concentrator valve stems, and pump shafts, where its low-carbon nature ensures it does not prematurely fail due to grain boundary carbide precipitation under high-temperature conditions. Moreover, N4 is stable in hydrogen fluoride, hydrogen chloride, and organochlorine, phenol, and other chemical environments, and is widely used for corrosion-resistant structural components in fluorochemicals and refrigerant production equipment.

Electronics, Electrical, and New Energy

The high-value applications of the N4 pure nickel rod in the electronics and electrical fields are concentrated in vacuum electronic devices and high-performance battery equipment. As structural materials and lead wires in vacuum electronic tubes, N4 is irreplaceable due to its low contact resistance, suitable coefficient of thermal expansion, excellent electrical conductivity, and thermal stability. In the new energy sector, N4 pure nickel is used for coating machine dies and rollers in lithium battery manufacturing equipment-applications that demand extremely high surface finish and purity, which the clean chemistry of N4 satisfies. N4 rods can also be machined into electrode materials for spark plug electrodes, alkaline battery tabs, and other conductive components.

Aerospace and Marine Engineering

In aerospace, the N4 pure nickel rod is used for rocket engine valve components and structural parts in high-temperature environments. Its stable operating temperature range spans -200°C to 600°C, allowing it to withstand severe thermal cycling. In marine engineering, N4 is highly insensitive to chloride-induced stress corrosion cracking, making it suitable for heat exchanger tubes in desalination plants, corrosion-resistant fasteners on naval vessels, and instrumentation parts. Its extremely high corrosion resistance in seawater splash zones makes it an ideal material selection for weather-resistant components in offshore engineering.

Product Packaging

Carton Package

Wooden Box Package

Advantages of N4 Over N6 Pure Nickel

1. Carbon Content Difference – Fundamental Compositional Distinction

The core difference between N4 and N6 lies in the control level of carbon content: N6 has a maximum carbon content of 0.10%, while N4 is strictly controlled at ≤0.02%. This seemingly small 0.08% difference in carbon determines the fate of the two materials in different temperature ranges. Carbon has limited solubility in nickel; during high-temperature service, it precipitates as graphite at grain boundaries, which is the root cause of "intermediate-temperature embrittlement" in pure nickel materials.

2. High-Temperature Service Range – The Core Competitiveness of N4

N6 (corresponding to Ni200) has a maximum recommended service temperature of approximately 315°C. Above this critical temperature, carbides begin to precipitate significantly at the grain boundaries of N6, leading to a sharp reduction in toughness or even brittle fracture. Owing to its extremely low carbon content, N4 fundamentally avoids this issue, achieving a maximum recommended service temperature of 600°C-about 50–100°C higher than N6. This enhanced temperature tolerance makes N4 the only choice for pure nickel applications above 315°C.

3. Intergranular Corrosion Susceptibility – An Unignorable Engineering Gap

The low-carbon design of N4 makes it less prone to intergranular corrosion, whereas N6 carries a risk of intergranular corrosion in certain environments. When N6 is exposed to certain corrosive media, carbides at grain boundaries become preferential "weak paths" for corrosion attack, leading to intergranular failure. Because N4 has no carbide precipitation at grain boundaries, it does not easily trigger this failure mode even in the same environment.

4. Industry Status of Corresponding International Grades

N6 corresponds to the international grade Nickel 200 (UNS N02200), positioned as a general-purpose industrial pure nickel. N4 corresponds to Nickel 201 (UNS N02201), positioned as a higher-specification low-carbon pure nickel. In international high-end engineering projects, when the technical specification sheet explicitly requires "low-carbon pure nickel," N4 (Nickel 201) is the only grade that meets the requirement.

5. Material Selection Principle

The decision logic in material selection should follow the "temperature-first" principle: when the service temperature is below 315°C, and there are no special intergranular corrosion requirements, N6, with its higher strength (achievable via cold working) and more mature market supply, is a cost-effective choice. When the service temperature is in the range of 315°C to 600°C, or when there is a risk of intergranular corrosion, or under conditions sensitive to carbide precipitation, N4 is the indispensable core material.

In short, N4 is the "high-temperature enhanced version" of pure nickel, providing a reliable engineering solution in the temperature range where N6 cannot safely serve.