A Comprehensive Guide to Pure Nickel: Nickel 200 (UNS N02200)/Nickel 201 (UNS N02201)

What is Nickel 200 (UNS N02200)?

Designated as UNS N02200 & W.Nr. 2.4060 & 2.4066, Nickel 200 is solid solution strengthened and commercially pure wrought nickel. It has good mechanical properties and excellent resistance to many corrosive environments. Nickel 200 is primarily used in food processing industry due to its corrosion resistance. It can also be used in applications involving reducing chemicals, caustic alkalies, distilled and natural waters, alkaline salt solutions, dry fluorine, and synthetic fibers. Depending on the specific product form, Nickel 200 may be furnished with different heat treatment and delivery conditions which result in different mechanical properties (tensile strength, yield strength, elongation, reduction of area, hardness, etc).

Nickel 200 is industrial grade, with good mechanical properties and excellent corrosion resistance to alkali (such as sodium hydroxide). It also has good electrical, thermal and magnetostrictive properties.
The nickel 200 is also known as the phywell 200.

Nickel 200 (UNS N02200) is widely used in many fields such as marine engineering, chemical and hydrocarbon processing equipment, valves, pumps, shafts, flanges, fittings, fasteners, and heat exchangers.

Chemical Composition of Nickel 200 (UNS N02200)

Physical Properties of Nickel 200 (UNS N02200)

Product Forms & Standards of Nickel 200 (UNS N02200)

Key characteristics of Nickel 200 (UNS N02200)

• Industrial grade nickel.
• Resistant to various reducing chemicals and caustic.
• Good magnetostrictive properties.
• High conductivity and thermal conductivity.
• Good ductility and low work hardening rate.
• Good welding characteristics.

What is Nickel 201 (UNS N02201)?

Designated as UNS N02201 or W.Nr. 2.4061 & 2.4068, Nickel 201 is has almost identical chemical composition as Nickel 200 except the lower-carbon content. Nickel 201 is typically applied in caustic evaporators, combustion boats, plater bars, as well as electronic components. Compared to Nickel 200, Nickel 201 has much lower base hardness and lower work-hardening rate hence is particularly suited for spinning and cold forming. According to ASME Boiler and Pressure Vessel Code Section VIII-Division 1, Nickel 201 is approved for construction of pressure vessels for service up to 1250°F. Its mechanical properties also vary depending on the manufacture process and heat treatment conditions.

Chemical Composition of Nickel 201 (UNS N02201)

Physical Properties of Nickel 201 (UNS N02201)

The above tensile strength is typical. If you need a different value, ask for details.

Key characteristics of Nickel 201 (UNS N02201)

• Low carbon version of nickel 200.
• Prior to nickel 200 in applications requiring exposure above 315 ° C (600 ° f).
• Resistant to various reducing chemicals and caustic.
• Good magnetostrictive properties.
• High conductivity and thermal conductivity.
• Good ductility and low work hardening rate.
• Good welding characteristics.

Product Forms and Standards of Nickel 201 (UNS N02201)

What’s the difference between nickel-200 and nickel-201?

Nickel is available in two variants, Nickel 200, and a low-carbon Nickel 201, both of which have excellent resistance to caustic soda, even as the hot anhydrous form. Except for silver, nickel is the most resistant metal for high caustic concentrations at the elevated temperatures which generally prevail. At concentrations up to 73% caustic, the corrosion rate is generally less than 0.025 mm/y (1 mpy). The rates increase slightly above 73%, as shown.
Nickel 200 contains up to 0.10% carbon, which can precipitate as graphitic carbon on heating above 425°C (800°F), which reduces the ductility of the alloy. This may
also occur upon prolonged heating at temperatures as low as 315°C (600°F). Above 300°C (570°F), e.g., in molten anhydrous caustic, the low-carbon Nickel 201 should be used to avoid graphite formation and attendant embrittlement and intergranular attack.
In most caustic applications Nickel 200 and Nickel 201 are very resistant to caustic SCC at all concentrations and temperatures up to about 290°C (550°F). Though Nickel 200 or 201 are usually most resistant, Alloy 400 and 600 are often used for higher strength.
Nickel 200 is subject to cracking in mercury and a few cases of cracking have been attributed to mercury contamination of the caustic process feed.

As pure nickel, nickel 200 and nickel 201 have good mechanical properties and corrosion resistance.
At the application temperature higher than 300 ° C (572 ° f), nickel 201 is superior to nickel 200 because of its low carbon content, which greatly reduces the strength and work hardening rate, thus improving the ductility. These two materials are widely used in automobile manufacturing and chemical industry.
Excellent corrosion resistance
Nickel 200 and nickel 201 have excellent corrosion resistance to a variety of corrosive media, especially hydrofluoric acid and alkali. It not only shows outstanding corrosion resistance under reduction condition, but also has good corrosion resistance in oxidation medium once passivation oxide layer is formed. In addition, due to their high nickel content, the corrosion resistance of the two materials is still excellent in the environment of high concentration alkaline solution and salt bath.
As the carbon content of nickel 201 decreases, intergranular corrosion can be almost completely avoided even in high temperature environment above 315 ° C (599 ° f). However, in alkaline solutions, the chlorate concentration must be kept at a low level, because it is susceptible to corrosion through the formation of chlorides.
The corrosion resistance of nickel 200 and nickel 201 to inorganic acid will change with temperature, solution concentration and ventilation. For example, the corrosion resistance of the two materials is stronger in the acid environment without ventilation; the two materials have good corrosion resistance in the acid, alkali and neutral salt solution (except for the oxidizing salt solution); the two materials have good dry gas resistance at room temperature. Nickel 201 can be used in dry chlorine and hydrogen chloride at temperatures up to 550 ° C (1022 ° f).
Nickel 201 is a pure nickel with a carbon limit of no more than 0.02%. It should be used instead of nickel 200 when the temperature is higher than 315 ℃ (600 ℉). The material has been certified for use in pressure vessels operating at temperatures between – 10 ° C and 600 ° C (14 ° F and 1112 ° f).
At the application temperature higher than 300 ° C (572 ° f), nickel 201 is superior to nickel 200 because of its low carbon content, which greatly reduces the strength and work hardening rate, thus improving the ductility.

Nickel 200 Welding Neck Flanges

Recently, we have supplied several pieces of Nickel 200 welding neck flanges to a Polish customer which are manufactured from ASTM B160 grade N02200 bars. The flanges dimensions are in accordance with EN 1092-1 Type 11 DN32 (welding neck, raised face).

Annealing process of N6 pure nickel sheet after cold rolling

Pure nickel has excellent corrosion resistance, excellent welding performance and processing performance, high electrical vacuum performance and electromagnetic control performance. It is widely used in chemical, mechanical and electronic, as well as the preparation of electronic, magnetic thin films, high-purity reagents, standards, etc. in integrated circuits. It is an indispensable and important material in modern industry and plays an extremely important role in the national economy, national defense construction, modernization, and information society. Pure nickel N6 is the most widely used pure nickel material in the industry. At present, the main methods for producing N6 pure nickel are using vacuum induction furnaces and vacuum consumable arc furnaces. However, the production process is complex, requires multiple remelting and refining treatments, and consumes much energy, resulting in many defects in the product.
The use of an electron beams cold bed furnace for melting only requires one melting, shortening the process flow and improving production capacity. Suppose we can find the electron beam cold bed furnace for melting N6 nickel ingots and its rolling process, as well as the heat treatment process after cold rolling. In that case, it will reduce production costs and have important significance for industrial production.
This article uses pure nickel N6 (Nickel 200/UNS N02200) cold rolled sheet melted in an electron beam cold bed furnace as the experimental material. By studying the changes in microstructure and mechanical properties of the material after heat treatment at different temperatures, the optimal heat treatment process for the N6 sheet after cold rolling is explored.

1. Experimental Materials and Plan

The experimental material is pure nickel N6 (Nickel 200/UNS N02200) plate melted in an electron beam cold bed furnace and subjected to 50% cold rolling deformation. Its chemical composition is shown in Table 1.
Table.1 Chemical Composition of Pure Nickel N6 Plate (Mass Fraction, %)

The raw material specification used in the experiment is 300mm × 20mm × 1.5mm N6 slab. Conduct microstructure observation and tensile strength and hardness testing on the original material. Because pure nickel is prone to oxidation at high temperatures, this experiment conducted vacuum annealing treatment in an SG-GL1400K vacuum heat treatment furnace. The annealing temperatures were 350, 400, 450, 500, and 550 ℃, respectively, and the holding time was 1 hour. The cooling method was to cool the furnace to 150 ℃ and then air-cool it to room temperature. Conduct microstructure observation and performance testing on the annealed sheet. Cut a small amount of samples for metallographic and microstructural observation. Inlay the cut samples, perform rough grinding, fine grinding, and polishing on a water mill, and then corrode the polished samples. Observe the microstructure using an optical microscope (OM). Measure the microhardness using a full Rockwell hardness tester and load 5 times at different parts of the sample during the test. Read the average value as the microhardness value. Perform room temperature tensile performance test using an electronic universal testing machine and take the average of three specimens for tensile data.

2. Experimental results and analysis

2.1 Microstructure of N6 Plate

Figure 1 shows the microstructure of cold rolled slabs with 50% deformation and N6 pure nickel plates annealed at different temperatures. Figure 1 (a) shows the microstructure of the original cold-rolled slab with a deformation of 50%. From the figure, it can be seen that after rolling, the grain orientation undergoes deformation in the same deformation direction, and the grain structure is fine. It is elongated and flattened along the rolling direction, resulting in severe distortion. This is because during the plastic deformation process of the sheet metal, the metal is subjected to shear stress, and the grains are refined by extrusion. Figure 1 (b) shows the microstructure of a cold rolled slab after being insulated at 350 ℃ for 1 hour. At 350 ℃, impurities begin to precipitate along grain boundaries, promoting grain nucleation and growth. At the same time, the fine grains after rolling also grow under the influence of temperature. Compared with the original state in Figure 1 (a), a large number of unevenly distributed small particles appeared between the heavily deformed grains. When the temperature rises to 400 ℃ (Figure 1 (c)), small particles gradually grow, and at 450 ℃, there are obvious precipitates, while impurity element aggregation occurs.
Figure 1 (e) shows the microstructure after annealing at 500 ℃ for 1 hour. It can be seen that as the temperature continues to rise, impurity elements diffuse back into the matrix material, and the plate undergoes complete recrystallization. The grains clearly grow and transform back into uniform equiaxed grains. The grain deformation caused by rolling has disappeared, and the grain boundaries have changed from large angle grain boundaries to small angle grain boundaries, which helps to eliminate deformation strengthening and residual stress. When the temperature reaches 550 ℃ (Figure 1 (f)), on the basis of recrystallization at 500 ℃, the grain boundaries between small grains fuse, and large grains engulf small grains, resulting in a significant increase in grain size.

Figure.1 Microstructure of N6 pure nickel after annealing at different temperatures for 1 hour × 100

2.2 Mechanical properties of N6 sheet at room temperature

The mechanical properties of N6 sheets in their original state and after annealing at different temperatures are shown in Table 2, and the data is organized as shown in Figure 2. From the table, it can be seen that after rolling with 50% deformation, the material is affected by mechanical work hardening. The hardness, tensile strength, and yield strength of the original state plate all reach their highest values, with low elongation and poor plasticity. As the annealing temperature increases, the Rockwell hardness of the material shows a decreasing trend. The tensile strength and yield strength show a fluctuating trend of first decreasing and then increasing before 500 ℃, and then continuing to decrease with the increase in temperature. The reason for the fluctuation is due to the beginning of the recrystallization process and the effect of precipitates around the grain boundaries. The elongation shows a trend of first increasing and then decreasing, reaching the highest value of 51% at 500 ℃. Based on the microstructure analysis in Figure 1, the highest elongation at 500 ℃ is related to a large number of uniformly distributed recrystallized particles. The uniformity of the recrystallized structure eliminates the work hardening phenomenon of the material and increases plasticity.
Table.2 Mechanical properties of cold-rolled pure nickel materials after annealing at different temperatures

Figure.2 Mechanical properties of cold-rolled N6 pure nickel after annealing at different temperatures
Considering the actual production needs of the factory, the heat treatment after cold rolling at excessively high annealing temperature or prolonged insulation time is detrimental to production costs and cycles. So, after rolling with 50% deformation, the plate is used at 500 ℃ × the comprehensive mechanical properties of the N6 sheet obtained by a 1-hour post-cold rolling heat treatment process are the best, making it the best post-cold rolling heat treatment process.

3. Conclusion

• (1) As the temperature increases, the elongation of the N6 cold rolled sheet first increases and then decreases, reaching its maximum value at 500 ℃.
• (2) After annealing at 350 ℃, a large number of unevenly distributed small particles appeared between the heavily deformed grains, and as the temperature increased to 450 ℃, there were obvious precipitates. At the same time, impurity element aggregation was generated. When recrystallization was completed at 500 ℃, the distribution became equiaxed, and the grain deformation caused by rolling disappeared.
• (3) N6 pure nickel cold rolled at 500 ℃ × After 1 hour of annealing, the work hardening phenomenon of the plate is eliminated, and the comprehensive mechanical properties reach the best.

Author: Wang Ding