A Comprehensive Guide to Nickel-based Alloy: Hastelloy C-2000 (UNS N06200)

What is Hastelloy C-2000?

Hastelloy C-2000, named UNS N06200, is a nickel base alloy composed of nickel, molybdenum, chromium and other elements, with a nickel content of about 55%. Adding a certain amount of copper into sulfuric acid, hydrofluoric acid and dilute hydrochloric acid can improve its temperature performance. The high chromium content allows it to maximize resistance to oxidizing chemicals and process streams contaminated by iron ions and dissolved oxygen. The alloy has excellent chloride corrosion resistance and corrosion resistance. UNS N06200 alloy is widely used in chemical reactor, heat exchanger, petrochemical pipeline, pharmaceutical industry and gas desulfurization system.
Hastelloy C-2000 Hastelloy alloy, as an optimized alloy developed to expand the application range of materials, started with the conceptual idea of adding copper to the established Ni Cr Mo alloy. Since it entered the market at the end of 1995, it has been constantly recognized by the market, thanks to its inherent versatility. The technical innovation not only improves the resistance of alloy to water corrosion, but also expands the application range of Ni Cr Mo family alloys. The new material is designed to resist more corrosive chemicals, including sulfuric acid, hydrochloric acid and hydrofluoric acid. Compared with the previously optimized Ni Cr Mo alloy which can only resist oxidation or reducing acid, C-2000 Hastelloy has corrosion resistance in both environments. The combined action of molybdenum and copper (at 16% and 1.6% levels respectively) makes the alloy have excellent resistance to reducing medium corrosion, and the high chromium content (23% wt) ensures the resistance to corrosion in oxidizing media.
From the engineering point of view, C-2000 Hastelloy provides a great potential to improve production. When used in the original Ni Cr Mo alloy, its enhanced corrosion resistance can obtain longer equipment life under the same material thickness and higher safety factor under worse conditions. The improvement of corrosion resistance in various aspects enables the equipment to be used for multiple purposes (reactor, heat exchanger, valve, pump, etc.) so as to receive a greater return on investment. For example, one reactor can adapt to another working condition of hydrochloric acid mixture and then convert into nitric acid based mixture. Because of its various abilities, C-2000 Hastelloy is the best nickel base alloy material which can adapt to various processes. The corrosion resistance of ni-2000 alloy in various environments is excellent. The excellent performance of C-2000 makes a breakthrough in the application of chemical industry equipment.
High chromium content is used to resist corrosion in oxidizing media such as iron, copper and dissolved oxygen. Reducing media, such as dilute hydrochloric acid or sulfuric acid, require high molybdenum and tungsten content. The limitation of metallurgical stability makes it impossible to optimize both at the same time. Hastelloy C-2000 alloy solves the design dilemma of this alloy.
High chromium content combined with molybdenum and copper gives excellent resistance to reductive environmental corrosion without sacrificing metallurgical stability. C-2000 alloy shows better pitting and crevice corrosion resistance than C-276 alloy, which is the industrial standard. Its forming, welding and machining properties are similar to those of C-276. C-2000 alloy has various shapes of products: plate, sheet, forging billet, bar, wire rod, welding rod and pipe. The forged products are delivered by final solution heat treatment, unless the customer has special needs. The alloy has been listed in ASTM B562-564, B564-B, 564-B, and B566-B. The DIN standard number is NO.2.4675, and nicr23mo16cu. The unified number of C-2000 alloy UNS is N06200, but there are more strict composition control to improve the performance.

ASME B16.47 Series A Hastelloy C-2000 weld neck flanges

Characteristics of Hastelloy C-2000 (UNS N06200)

• Excellent oxidation resistance at high temperature(>1200℃)).
• Good high-temperature strength.
• Good formability and weldability.
• Good resistance to stress corrosion cracking.

Hastelloy C-2000 Forged Elbow 1″ 3000#

Types of Hastelloy

• Hastelloy B-3 nickel molybdenum alloy has excellent corrosion resistance in reducing environment.
• The upgraded version of Hastelloy B-3: B-3 has excellent corrosion resistance to hydrochloric acid at any temperature and concentration.
• Hastelloy C-4: good thermal stability, good toughness and corrosion resistance at 650-1040 ℃.
• Hastelloy C-22: has better uniform corrosion resistance than C-4 and C-276 in oxidizing medium and excellent local corrosion resistance.
• Hastelloy C-276: good resistance to oxidizing and moderate reducing corrosion, excellent resistance to stress corrosion.
• Hastelloy C-2000: the most comprehensive corrosion resistant alloy with excellent uniform corrosion resistance in oxidation and reduction environments.
• Hastelloy G-35: the upgraded product of G-30 has better corrosion resistance and thermal stability, and has excellent performance in phosphoric acid and other strong oxidizing mixed acid media with high chromium content.
• Hastelloy X: combined with the characteristics of high strength, oxidation resistance and easy processing, each of the above grades has its own specific chemical composition, mechanical properties and strong points, so we can’t generalize the characteristics of Hastelloy.

Hastelloy alloy is mainly divided into three series B, C and G. it is mainly used in iron-based Cr Ni or Cr Ni Mo stainless steel, non-metallic materials and other occasions with strong corrosive medium.
In order to improve the corrosion resistance and cold and hot working properties of Hastelloy, three major improvements have been made to Hastelloy:

• Series B: B → B-3 (00ni70mo28) → B-3
• Series C: C → C-276 (00cr16mo16w4) → C-4 (00cr16mo16) → X (00cr22mo13w3) → C-2000 (00cr20mo16)
• G Series: G → G-3 (00cr22ni48mo7cu) → G-30 (00cr30ni48mo7cu)
• The most widely used materials are N06200 (B-3), N10276 (C-276), N06200 (X), N06455 (C-4) and N06985 (G-3)

Chemical Composition of Hastelloy C-2000 (UNS N06200)

C	≤0.01
Cr	22.0-23.0
Ni	Balance
Fe	≤3.0
Mo	15.0-17.0
W	3.0-4.5
Cu	1.3-1.9
Si	≤0.08
Mn	≤0.5
P	≤0.02
S	≤0.08

ASTM B574 Hastelloy C-2000 Round Bar

Equivalent Grades of Hastelloy C-2000 (UNS N06200)

Trademarks	GB	ASTM	UNS	DIN	W.Nr
Hastelloy C-2000	NS3405	Hastelloy C-2000	N06200	NiCr23Mo16Cu	2.4675

Physical Properties of Hastelloy C-2000 (UNS N06200)

Density		Specific Heat		Melting Range		Elastic modulus (GPa)	Thermal conductivity	Hardness	Coefficient of thermal expansion	Operating temperature
lb/in3	g/cm3	Btu/lb.°F	J/kg.°C	°F	°C		( W/(m•K)	(HRC)	(25-100℃)(μm/m°C)	(°C )
0.307	8.5	0.102	428	2422-2476	1328-1358	206	10.8	90	12.4	-200～+400

Product Forms and Standards of Hastelloy C-2000

Product From	Standard
Sheet, Plate & Strip	ASTM B575
Billet, Rod & Bar	ASTM B574, B472
Coated Electrodes	DIN 2.4699
Bare Welding Rods & Wire	DIN 2.4698
Seamless Pipe & Tube	ASTM B622
Welded Pipe & Tube	ASTM B619, B626
Fittings	ASTM B366, B462
Forgings	ASTM B564, B462

Application areas of nickel-based alloy Hastelloy C-2000 (UNS N06200)

An Alloy C-2000 90DEG Elbow 6″ SCH80S extruded from the UNS N06200 seamless pipe

Due to its corrosion resistance to all kinds of atmosphere at high temperatures,and excellent high-temperature strength, Hastelloy C-2000 has been widely used in various high temperature environment. Some of the more common uses of Hastelloy C-2000 include:

• Wire wound resistors.
• Bimetal contacts.
• Electric and electronic applications.
• Marine engineering.
• Chemical and hydrocarbon processing equipment.
• Gasoline and freshwater tanks.
• Crude petroleum stills.
• De-aerating heaters.
• Boiler feed water heaters and other heat exchangers.
• Pumps, shafts and fasteners.
• Industrial heat exchangers.
• Chlorinated solvents.
• Crude oil distillation towers.
• Meter and valve parts.
• Screw machine products.
• Oil refinery piping.
• Heat exchangers.
• Nuclear fuel production.
• Generator tubing.
• High temperature heating coils.
• Crude oil transfer piping.
• Propeller and pump shafts.
• Piping system.
• Heat exchange tubes.
• Pipe fittings.
• Flanges.
• Valves.

Variety specifications and supply status of Nickel-based super alloy: Hastelloy C-2000 (UNS N06200)

Variety classification:

Yaang Pipe Industry can produce various specifications of Hastelloy C-2000 seamless pipe, Hastelloy C-2000 steel plate, Hastelloy C-2000 round bar, Hastelloy C-2000 forgings, Hastelloy C-2000 flange, Hastelloy C-2000 pipe fittings, Hastelloy C-2000 welded pipe, Hastelloy C-2000 steel strip, Hastelloy C-2000 wire and supporting welding materials. 

Delivery status:

• Seamless pipe: solid solution + acid white, length can be set;
• Plate: solid solution, pickling, trimming;
• Welded pipe: solid solution acid white + RT% flaw detection;
• Forging: annealing + car polish; Bars are forged and rolled, surface polished or car polished;
• Strips are delivered after cold rolling, solid solution soft state, and deoxidized;
• Wire rods are finely ground in solid solution pickled disk or straight strips, solid solution straight strips Delivery in light state.

Welding process of Hastelloy C2000

The corrosion resistance, chemical composition, and mechanical properties of Hastelloy C2000 were introduced. Through welding process evaluation, experimental research was conducted on the welding process of Hastelloy C2000, and the test results were successfully applied to engineering practice.
In engineering applications, C2000 provides excellent economic performance. Compared to other Ni Cr Mo alloys, their enhanced corrosion resistance can achieve longer equipment life under the same material thickness and higher safety factors under more severe conditions. The improvement of comprehensive corrosion resistance performance can enable the equipment to be used in various reactors, heat exchangers, etc. Due to the above advantages of C2000, it is the nickel based alloy material with the best corrosion resistance in the Hastelloy series of products.

1. Chemical composition and mechanical properties of C2000 alloy

The chemical composition of typical C2000 alloy is shown in Table 1, and the mechanical properties are shown in Table 2.
Table.1 Chemical composition of C2000 alloy

Chemical composition	Ni	Cr	Mo	Cu	C	Si
C2000	allowance	23	16	1.6	0.01	0.08
SB575 N06200	allowance	22.0-24.0	15.0-17.0	1.3-1.9	0.01	0.08

Table.2 Mechanical property of C2000 alloy

Tensile strength Rm/MPa	Yield strength Re/MPa	Elongation after fracture A/%
≥ 752	372	63

2. Welding of C2000 alloy

The weldability of C2000 alloy is similar to the welding requirements of other nickel based alloys and austenitic stainless steel. However, from the perspective of achieving good corrosion resistance of the weld metal in reducing or oxidizing media, it is necessary to conduct experimental research on welding method selection, filler material selection, joint type design, welding parameters, preheating and interlayer temperature, and finally obtain the best welding process specification.
2.1 Selection of welding methods
The welding of C2000 alloy generally adopts manual tungsten argon arc welding or electrode arc welding. It is not recommended to use submerged arc welding methods with large heat input. For thicker thicknesses and longer weld sizes that require submerged arc welding, finer ones should be used Φ 2.4mm welding wire or Φ 3.2mm welding wire and welding with smaller heat input; When the thickness of the weld seam is small, tungsten argon arc welding or electrode arc welding can be used. It is required that the argon arc welding machine should have high-frequency arc ignition and current attenuation devices, which can achieve early ventilation and delayed gas interruption after welding to achieve the protection effect of the weld seam.
If tungsten argon arc welding is used, large nozzles should be used as much as possible to achieve the best protection effect on the weld seam (Φ>10mm) welding gun should also have a gas diffusion screen to reduce abnormal disturbance of the protective gas. When welding on the front, argon gas should be used for continuous follow-up protection on the back, and the protection effect should be judged by the color of the weld seam. Silver white is the best protection effect. According to engineering experience, when the thickness of the protected weld metal exceeds 6mm, the heat generated by the front welding is insufficient to cause oxidation on the back of the weld, and gas protection on the back can be cancelled.
2.2 Selection of Welding Filler Materials
There are generally two methods for selecting welding materials for C2000 alloy, namely using matching welding materials with corrosion-resistant alloy elements close to the base metal, or selecting super matching welding materials with corrosion-resistant alloy elements higher than the welded base metal. For welding of different base materials, the principle of “high not low” should be adopted, and the alloy composition of the welding material should be consistent with the higher alloy composition of the base metal. The widely used filler welding material for Hastelloy C2000 is a welding filler material containing 23%Cr16%Mo and other components. In other words, AWS A5.14 ERNi Cr Mo17 welding wire or AWS A5.11 ENi Cr Mo17 welding rod can be used for welding between the same materials in C2000. This welding material is also suitable for welding C2000 alloy with other ferrite steels.
2.3 Groove preparation
The welding groove of C2000 alloy can be machined, hot cut, or polished, but the edges of hot cut must be polished bright to expose the metallic luster before welding. Before welding, the groove should undergo visual inspection or penetration inspection, and there should be no defects that affect the welding quality.
The surface of the base metal within at least 50mm of the groove and its two sides should be cleaned with clean solvents such as acetone or anhydrous alcohol. All grease, residual machining solution, marking pen marks, dust, oxides, etc. that affect the welding quality must be cleaned. If necessary, use a stainless steel wire brush to clean the groove and the area at the edge of the groove after cleaning.
2.4 Welding control points
Like other nickel based alloys, the biggest problem in the welding process of Hastelloy C2000 is to prevent the generation of hot cracks. The reason for the easy occurrence of hot cracks is that there are residual grain boundaries of low melting point metals and low melting point eutectic liquid films during the solidification of the weld, which cause cracking under the action of shrinkage stress. To prevent the occurrence of thermal cracks, from a process perspective, firstly, lower heat input should be used for welding; The second is to control the interlayer temperature well and accelerate the cooling of the weld seam. To reduce heat input during the welding process, narrow pass welding should be used, and swing welding should not be used. The maximum interlayer temperature should be limited to below 100 ℃. Due to the tendency of hot cracks in the arc crater, the starting and extinguishing points should be polished after welding. Cleaning and protection between passes are also very important, as impurities such as grease and rust can cause hot cracking. The passes must be cleaned thoroughly. If there are cracks, pores, and other defects during the welding process, they should be thoroughly eliminated by polishing or other mechanical means before depositing the next pass.

3. Welding process qualification test

A certain chemical project undertaken by the company has extremely strict requirements for equipment material selection due to the strong corrosiveness and toxicity of the medium. Considering corrosion resistance and economy, Hastelloy C2000 was ultimately chosen. Before product manufacturing, welding process qualification shall be conducted in accordance with JB4708 welding process qualification standard and with reference to ASME Section IX “Welding and Brazing Qualification”. The qualification test shall be conducted on C2000 alloy with a thickness of 6.35mm, using a combined welding method of manual argon arc welding as the backing and electrode arc welding as the filling.
Due to the relatively poor fluidity of nickel based alloys, in order to prevent the occurrence of defects such as lack of fusion and porosity, the welding groove angle is generally larger than that of carbon steel or stainless steel. For butt grooves of 3mm and below, welding can be carried out directly without opening the groove. For thicker materials, in order to reduce the amount of welding material filling, an X-shaped groove is generally used for double-sided welding; The thickness of this test plate is 6.35mm, and a single V-shaped groove can be opened. The welding groove type is shown in Figure 1, and the welding process parameters of the test plate are shown in Table 3.

Table.3 Welding parameters of WPQ

Welding sequence	Weld bead	Welding method	Welding Material		Power polarity	Welding current I/A	Positive protective air flow rate Q1/(L.min-1)	Back protection gas flow rate Q2/(L.min-1)
			Type	Spec /mm
1	1	Manual argon arc welding	ERNiCrMo-17	2.4	DC direct connection	90-120	10-15	15-18
2	1	Manual arc welding	ERNiCrMo-3	3.2	DC reverse connection	90-110	10-15	15-18
3	1	Manual arc welding	ERNiCrMo-3	4	DC reverse connection	110-130	10-15	15-18

Figure.1 Welding groove type
According to technical requirements, 100% PT testing was conducted on the test plate after welding, and it was qualified according to JB 4730I level; 100% RT testing was conducted on the weld seam of the test panel, and JB 4730 Grade II was qualified. Subsequently, destructive mechanical performance tests were conducted on the test panel, and the results are shown in Table 4.

Table.4 Mechanical property test results

Test plate thickness t/mm	Tensile strength Rm/MPa	Fracture location	Face bending and back bending test D=4a, α= 180 °	Hardness (HV10)
6.35	765,765	Weld seam	Qualified	Welding seam 208, 195, 200

Take corrosion samples and conduct corrosion tests using the ASTM G28A method. Take two corrosion samples with corrosion rates of 0.65 g/(m².h) respectively; 0.64 g/(m².h), the result meets the product technical requirements.

4. Conclusion

According to the welding process evaluation results, the manufacturing task of the product was successfully completed. Through the non-destructive testing results of the product welds and the physical and chemical performance test results of the product welding test plate, it was proven that the selected welding materials and welding process control were correct and fully met the design requirements. At present, products made of Hastelloy C2000 material have been in safe operation for many years and have received good feedback from users.
Author: Liu Qinghui