Material properties
The characteristics of commercial pure nickel or low alloy nickel are very useful in many fields, such as chemical processes and electronic industries. Nickel has some resistance to various reducing chemicals, and its resistance to caustic alkalis is irreplaceable. Compared with nickel-based alloys, commercial pure nickel has higher electrical and thermal conductivity, a higher Curie temperature, and good magnetostrictive properties. Annealed nickel has low hardness and good ductility and flexibility. These properties, combined with its good weldability, make the metal easy to work and shape. Nickel has a relatively slow work hardening rate, but it can be cold worked to achieve moderate strength levels and retain its ductility. Pure nickel is a silver-white metal. Due to its excellent corrosion resistance, high electric vacuum performance and electromagnetic control performance, it is widely used in chemical industry, mechanical electronics, food, etc. Pure nickel has excellent welding and processing properties. Nickel and nickel alloys can be processed into tubes, rods, wire sheets, strips and foil products. N6 is the most widely used material in industry. It has good mechanical properties and excellent corrosion resistance in many corrosive environments, especially corrosion by caustic soda. Table 1 grades and standards
| Material
grade |
Standard
series |
standard | |||||||
| chemical
composition |
pipes | plate | Rod | Strip | Welding wire | Forgings | |||
| Seamless tube | welded pipe | ||||||||
| National standard
N6 |
GB/T | 5235 | 2882 | / | 2054 | 4435 | 2072 | 26030 | |
| NB/T | 47019 | / | |||||||
| JB/T | 4748 | ||||||||
Table 2 Chemical composition
| element | C | Si | Mn | P | S | Ni+Co | Mo |
| N6 | ≤ 0.1 | ≤ 0.1 | ≤ 0.05 | ≤ 0.02 | ≤ 0.005 | ≥99.5 | — |
| element | Cr | Fe | Al | Ti | Mg | Cu | — |
| N6 | — | ≤ 0.1 | — | — | ≤ 0.1 | ≤ 0.1 | Impurities ≤ 0.5 |
Table 3 Physical Properties
| density | 8.89 g/cm³ |
| melting point | 1435 ~ 1450 ℃ |
Mechanical behavior
Table 6 Nominal mechanical properties
| state | thickness | Tensile strength
( MPa ) |
Yield strength 0.2%, ( MPa ) | Elongation ( 50mm )
( % ) |
hardness | |||
| Bruce | Rockwell B | |||||||
| Rod | ||||||||
| Y (hard state) | 3~20 | ≥ 590 | — | ≥ 5 | ||||
| ＞20~30 | ≥ 540 | — | ≥ 6 | |||||
| ＞30~65 | ≥510 | — | ≥ 9 | |||||
| M (annealed state) | 3~30 | ≥ 380 | — | ≥ 34 | ||||
| ＞30~65 | ≥ 345 | — | ≥ 34 | |||||
| R (hot processed state) | 32~60 | ≥ 515 | — | ≥ 15 | ||||
| ＞60~254 | ≥ 345 | — | ≥ 20 | |||||
| plate | ||||||||
| M (annealed state) | ≤ 1.5 | ≥ 380 | ≥ 100 | ≥ 35 | ||||
| ＞1.5 | ≥ 380 | ≥ 100 | ≥ 40 | |||||
| R (hot processed state) | ＞4 | ≥ 380 | ≥ 135 | ≥ 30 | ||||
| Y (hard state) | ≤ 1.5 | ≥ 540 | — | ≥ 2 | ||||
| ＞1.5 | ≥ 620 | ≥ 480 | ≥ 2 | 90-95 | ||||
| Y 2 (semi-hard state) | ＞1.5 | ≥ 490 | ≥ 290 | ≥ 20 | 79-85 | |||
| pipes | ||||||||
| M (annealed state) | ＜0.9 | ≥ 390 | — | ≥ 35 | — | — | ||
| ≥ 0.9 | ≥ 370 | — | A ≥ 35 | — | — | |||
| Y (hard state) | ＜0.9 | ≥ 540 | — | — | — | |||
| ≥ 0.9 | ≥ 520 | — | A ≥ 6 | — | — | |||
| Y2 (semi-hard state) | ≥ 0.9 | ≥ 420 | — | ≥ 12 | — | — | ||
| Y 0 (stress relief) | ≥ 0.9 | ≥ 460 | — | — | — | — | ||
| Strip | ||||||||
| M (soft state) | 0.25~1.2 | ≥ 392 | A ≥ 30 | |||||
| Y (hard state) | ≥ 539 | A ≥ 2 | ||||||
High temperature performance
The high temperature performance of nickel N6 can refer to the American standard N02200 material.
Metallographic structure
Nickel N6 is a solid solution alloy with a face-centered cubic structure. The microstructure typically shows a small amount of non-metallic inclusions, which are mainly oxides and do not change with annealing. Exposure times in the temperature range of 425-650 °C will produce graphite precipitates (see Figure 9 ). For this reason this alloy is not recommended for use in the temperature range 315-650 °C ; Nickel 201 or N5 should be used in this temperature range .
Corrosion Resistance:
For Nickel N6, corrosion data is recommended to reference ASTM standard N02200 (N7) material.
Processing:
Heating and Pickling: Nickel N6 can be annealed over a wide temperature range above its recrystallization temperature. For heavily cold-worked materials, temperatures can be as low as 595°C to 650°C, but typically range from above 705°C to 925°C for practical purposes. Due to the lack of residual elements and second phases that suppress grain growth in more complex alloys, grain growth in Nickel 200 occurs very rapidly at higher temperatures. The influence of various annealing temperatures on grain size is shown in Figure 10. At higher temperatures, the exposure time must be strictly monitored to control excessive grain growth. In batch box furnaces, kettles, or open furnaces, the typical annealing temperature range is 705°C to 815°C, with annealing times ranging from 30 minutes to 3 hours depending on the part thickness and the amount of cold working involved. Nickel 200 has a relatively high thermal conductivity, so heating rates are relatively high. Cooling rate requirements are not strict; quenching is unnecessary unless to reduce the time of heat treatment cycles or to minimize oxidation of surfaces during heating and cooling in oxidative atmospheres. Reduced oxidation can be achieved by quenching in water containing 2% alcohol. A loose oxide may form, but can be removed by standard pickling solutions. In continuous annealing processes such as pusher, roller hearth, and conveyor belt furnaces, the temperature range is typically 790°C to 955°C with a time in the heat zone of 15 to 45 minutes. Coils and wires can be annealed in bundles, with temperatures ranging from 870°C to 1040°C and times in the heat zone ranging from 5 to 10 minutes down to a few seconds.
Manufacturers should establish specialized heat treatment procedures based on experience, selecting appropriate temperature ranges and treatment methods to provide the desired grain size and performance. Fine to medium grain size is necessary to maintain smooth surfaces during forming processes, with grain sizes ranging from 0.025 to 0.10mm, corresponding to ASME grain sizes of 7-1/2 to 3-1/2. Annealing at 925°C for 1 hour or longer will result in a hardness of approximately Rockwell B 20 to 40. This treatment, known as annealing to the softest condition, is used only in special applications such as rupture disks due to its low mechanical properties and coarse grain structure. Annealing should be conducted in a reducing atmosphere to maintain a bright surface, commonly using dry hydrogen and dissociated ammonia; however, more economical atmospheres such as partially combusted natural gas can also provide adequate brightness. Heating in highly oxidizing atmospheres at high temperatures should be avoided due to the risk of intergranular oxidation. Nickel 200 is very sensitive to intergranular attack by sulfur and low-melting metals such as lead, tin, zinc, and bismuth. All lubricants, markings, shop dust, etc., should be carefully removed prior to heating for practical use.
Cold and Hot Forming:
Hot Forming: Nickel 200 can be readily hot-formed into various shapes. The appropriate temperature for forming is the most critical factor for achieving hot ductility. The recommended temperature range for hot forming is 650°-1230°C. All forging involving large deformation should be carried out at temperatures above 870°C, as the material rapidly hardens below this temperature. However, slight forging at this temperature produces higher mechanical properties. Laboratory experiments on forged disc specimens have shown that 50% deformation at 650°C can enhance tensile properties at 650°C. The optimal temperature range for hot bending is 870°- 1230°C. Care should be taken in all operations to avoid heating Nickel 200 above 2250°F (1230°C).
The furnace used to heat Nickel 200 should be designed to burn gas before contacting the metal. It is preferable to use gas and fuel oil with low sulfur content. With proper measures, low sulfur content fuel oil (below 0.5%) can yield satisfactory results. The total sulfur content of the gas used to heat Nickel 200 must not exceed 30/100 cubic feet of gas (0.68 grams per cubic meter), preferably not exceeding 15/100 cubic feet of gas (0.34 grams per cubic meter). A reducing atmosphere is necessary to avoid oxidation. The metal should be loaded into preheated furnaces and removed as quickly as possible after reaching the required temperature for rapid processing. Steel rails or other supports should be provided to prevent contact between the metal and the bottom or sides of the furnace. Sometimes it is necessary to prevent contamination of the metal by furnace roof debris.
Cold Forming:
Nickel 200 can be processed using any existing cold forming method. Overall, except for requiring greater force due to its higher yield strength, its behavior is similar to low carbon steels during forming. Therefore, manual operations such as spinning and hand hammering are limited to simple shapes. Extensive manual forming can only be achieved by frequent annealing for softening. Drawing and deep drawing dies are made of gray iron, cold hard iron, and cast alloys. Chrome-hardened steel, tungsten carbide, and diamond dies are used for wire drawing dies. All die surfaces should be highly polished.
Animal fats, soap, sulfur-based oils, lard-refined lubricants, and similar medium lubricants are used in operations related to cold working. Cold-rolled sheets and strips can be bent to very large angles on bending axes perpendicular to the rolling direction. Nickel 200 condenser tubes, whether annealed or stress relieved, can be conveniently expanded into tube sheets of heat exchangers. Using annealed or stress-relieved materials in cold drawing or heavy deformation operations will generally yield satisfactory results. Cold rolling (non-ductile leveling) and annealed thin plates provide the best conditions for spinning and other manual processing.