NICKEL ALLOY

ALLOY 20 / CARPENTER 20 / N08020

ASTM A 265, B 366, B 463
B 464, B 471, B 472, B 473
B 474, B 475
NACE MR0175

   

Other common names: Carpenter 20, 20Cb-3®, Incoloy® alloy 20Alloy 20, also known as Carpenter 20, is a nickel-iron-chromium austenitic alloy that was developed for maximum resistance to acid attack, specifically sulfuric acid. This superalloy has excellent resistance to general corrosion, pitting, and crevice corrosion in chemicals containing chlorides and sulfuric, phosphoric, and nitric acids. It also contains niobium for stabilization against sensitization and resultant intergranular corrosion. Carpenter 20 combines excellent corrosion resistance with elevated mechanical properties and relatively easy fabrication. Although originally designed for use in sulfuric acid related industries, Alloy 20 is now a popular choice for a wide variety of industries including the chemical, food, pharmaceutical, and plastics industries. In addition, this superalloy is used in heat exchangers, mixing tanks, metal cleaning and pickling equipment, and piping.

There has long been a debate on whether Carpenter 20 is a stainless steel or a nickel alloy because the nickel content is right on the border of defining it as one way or the other. So, depending on who you talk to this alloy may be referred to as alloy 20 Stainless Steel or as a nickel alloy. Either way it is still great for corrosion resistance.

ASTM Specifications

Pipe Smls	Pipe Welded	Tube Smls	Tube Welded	Sheet/Plate	Bar	Forging	Fitting
B729	B464	B729	B468	B463	B473	B462	B366

Availability :
Alloy 20 is available as round / flat / sheet / hexagonal / plate/ square / coil / pipe & fittings.

   

Chemical Composition, %

Ni	Fe	Cr	Cu	Mo	Nb
32.00-38.00	Balance	19.0-21.0	3.0-4.0	2.0-3.0	8xC-1.0max

   

C	Mn	P	S	Si
.07max	2.0max	.045max	.035max	1.0max

   

Oxidation Resistance

The introduction of small amounts (<7%) of chromium to nickel increase the sensitivity of the alloy to oxidation. This is because the diffusion rate of oxygen in the scale is increased. This trend reverses after addition levels increase above 7% chromium and increases up to an addition level of approximately 30%. Above this level, there is little change.

Oxidation resistance can be attributed to the formation of a highly adherent protective scale. The adherence and coherence of the scale can be improved by the addition of small amounts of other reactive elements such as zirconium, silicon, cerium, calcium or similar. The scale thus formed is a mixture of nickel and chrome oxides (NiO and Cr₂O₃). These combine to form nickel chromite (NiCr₂O₄), which has a spinel-type structure.

   

In what forms is Alloy 20 Available at SAGAR STEELS?

• Sheet
• Plate
• Bar
• Pipe & Tube (welded & seamless)
• Fittings (i.e. flanges, slip-ons, blinds, weld-necks, lapjoints, long welding necks, socket welds, elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples)
• Wire

While the compositional changes have a negligible effect on mechanical properties, higher additions of reactive elements tend to prevent flaking of the scale during cyclic heating and cooling. This effect is less of an issue with continuously operating heating elements, so addition levels do not need to be as high.

The binary 90/10 Ni/Cr alloy is also used for heating elements, and has a maximum operating temperature of 1100°C. Other uses for this alloy are thermocouples.

Thermocouples

The 90/10 Ni/Cr alloy is commonly used in thermocouples, in conjunction with a 95/5 Ni/Al alloy. This combination is called chromel-alumel, and similar to heating elements has a maximum operating temperature of 1100°C. This couple becomes susceptible to drift in the region of 1000°C due to preferential oxidation after prolonged usage. The addition of silicon has been found to overcome this effect. Commercial grades include Nicrosil (containing 14% Cr and 1.5% Si) and Nisil (containing 4.5% Si and 0.1% Mg).

Wear Resistant Alloys

Wear mechanisms are complex, but high hardness and good corrosion resistance contribute to good wear resistance. Ni/Cr alloys provide an economical alternative to materials such as weld deposited cobalt-chrome alloys with additions of carbon and tungsten which are commonly used wear resistant applications. An example of a Ni/Cr alloy for this type of application is 8-12% Cr, 0.3-1.0% C, 3-4% Si, 1.5-2.5% B, 1-4% Fe and the balance Ni. A coating of this material deposited by inert gas shielded arc techniques would be in the range 40-50 Rockwell C.

High Temperature Corrosion Resistant Alloys

The 80/20 Ni/Cr alloy is often used for wrought and cast parts for high temperature applications, as it has better oxidation and hot corrosion resistance compared to cheaper iron-nickel-chromium alloys. This alloy is highly suited to applications that are subject to oxidation.

In applications where fuel ashes, and/or deposits such as alkali metal salts such as sulphates are encountered, higher chromium content alloys are more suitable. This is because fuel ashes react with the oxide scale. Ashes containing vanadium are particularly aggressive in the respect and have a fluxing effect on the scale, increasing the susceptibility of the alloy to attack by oxidation.

In sulphur containing environments, chromium sulphide (Cr₂S₃, melting point 1550°C) is formed preferentially to nickel sulphide. Formation of nickel sulphide is preferred as this hinders the formation of the nickel/nickel-sulphide eutectic which has a low melting point. Eventually, local chromium supplies can be exhausted, leaving sulphur to react with nickel to form the low melting point eutectic compound, leading to liquid phase attack. Alloys that have suffered this form of attack have wart-like growths on their surface. Due to the preferential formation of chromium sulphides, it follows that higher chromium containing alloys are more resistant to this type of attack.

Nickel/chromium alloys containing more than 30% chromium have a two phase structure which consists of α-chromium and γ-nickel. The α-chromium phase brittle and hence the alloy decreases in ductility with increasing chromium content. Properties for some binary alloys are given in table 2. The addition of about 1.5% niobium induces improved strength and ductility, while at the same time reducing embrittlement after high temperature exposure provided impurities such as carbon, nitrogen and silicon are controlled.

Tensile and ductility properties for some Ni/Cr alloys at room temperature.

Alloys with chromium contents up to approximately 35% are suitable for hot working. Above this level, they are generally only suited to casting. Some ductility gains can be achieved by the addition of zirconium or titanium. Inconel 671, (containing 48% Cr and 0.35% Ti is such an alloy and is used in applications including duplex tubing for coal-fired superheating tubing.

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NICKEL 200 / 201 UNS N02200 / N02201

Nickel 200 and Nickel 201 are solid solution strengthened, commercially pure wrought materials with good mechanical properties over a wide range of temperatures and excellent resistance to many corrosives, in particular hydroxides. Nickel 201 was a modification of 200 to control carbon (.02 max) which keeps it from being embrittled by intergranular precipitates at temperatures of 600° F to 1400° F in many processes. Typically, the elemental restrictions of both, nickel 200 and nickel 201, are combined into one, dual-certified chemistry resulting in a single alloy with the desired characteristics of both alloys, Nickel 200/201.

 

Nickel 200/201 ASTM Specifications

 

Other Designations

Other designations that are equivalent to nickel 200 alloy include the following:

• ASME SB-160 - SB-163
• DIN 17740
• DIN 17750-17754
• BS 3072-3076
• ASTM B 160 - B 163
• ASTM B 725
• ASTM B 730

Availability :
Alloy 200/201 is available as round / flat / sheet / hexagonal / plate/ square / coil / pipe & fittings.

 

Chemical Composition

The chemical composition Nickel 200 alloy is outlined in the following table.

Element	Content (%)
Nickel, Ni	≥ 99
Iron, Fe	≤ 0.40
Manganese, Mn	≤ 0.35
Silicon, Si	≤ 0.35
Copper, Cu	≤ 0.25
Carbon, C	≤ 0.15
Sulfur, S	≤ 0.010

Physical Properties

The following table shows the physical properties of Nickel 200 alloy.

Properties	Metric	Imperial
Density	8.89 g/cm3	0.321 lb/in3
Melting point	1435-1446°C	2615-2635°F

Mechanical Properties
Room Temperature properties of Various Products

 

Electrical Electronic Nickel Properties

 

Electrical Electronic Nickel Physical Properties
Nickel Grade		Nickel 200	Nickel 201	Nickel 205	Nickel 233
Density	lb/cu in	0.321	0.321	0.321	0.321
Specific Gravity		8.89	8.89	8.89	8.89
Curie Temp	°F	680	680	680	680
	°C	360	360	360	360
Melting Point	°F	2624	2624	2624	2624
	°C	1440	1440	1440	1440
Electrical Resistivity	Micro-ohm-cm	8.5	8.5	9.5	7.7
	ohm-cir mil/ft	51	51	57	46
Thermal Conductivity	W/cm °C	0.79	0.79	0.75	0.81
	BTU-in/sq. ft-hr-	550	550	520	565
Specific Heat	Cal/g- °C	0.108	0.108	0.108	0.108
	BTU/lbm- °F	0.108	0.108	0.108	0.108
Thermal Expansion	ppm / °F (212°F)	7.2	7.2	7.2	7.2
	ppm / °C (100°C)	13	13	13	13

 

 

Thermal Properties

The thermal properties of Nickel 200 alloy are given in the following table

Properties	Metric	Imperial
Thermal expansion co-efficient (@20-100°C/68-212°F)	13.3 µm/m°C	7.39 µin/in°F
Thermal conductivity	70.2 W/mK	487 BTU.in/hrft².°F

Fabrication and Heat Treatment

Nickel 200 alloy can be shaped through all hot working and cold working practices. The alloy can be hot worked between 649°C (1200°F) and 1232°C (2250°F), with heavy forming carried out at temperatures above 871°C (1600°F). Annealing is performed at temperature between 704°C (1300°F) and 871°C (1600°F).

Applications

The following are the list of applications of nickel 200 alloy:

• Synthetic fibers
• Food processing equipment
• Drums to transport chemicals
• Rocket motors
• Piping and equipment used in conjunction with alkalis
• Handling of foods
• Aerospace and missile components