Composition of Hastelloy
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What are the components of Hastelloy, and what is its main component? I would appreciate the advice from all the experts!
Hastelloy alloy is a type of nickel-based alloy. It is currently classified into three series: B, C, and G. It is primarily used in environments with highly corrosive conditions where iron-based Cr-Ni or Cr-Ni-Mo stainless steels and non-metallic materials cannot be used. Abroad, it is widely applied in various fields such as petroleum, chemicals, and environmental protection. Hastelloy alloy: I. Currently, it is mainly divided into three series: B, C, and G. It is primarily used in environments with highly corrosive media where iron-based Cr-Ni or Cr-Ni-Mo stainless steels and non-metallic materials cannot be used. Hastelloy grades: To improve the corrosion resistance and machinability of Hastelloy, it has undergone three major improvements over time; the development process is as follows:
B series: B → B-2 (00Ni70Mo28) → B-3
C series: C → C-276 (00Cr16Mo16W4) → C-4 (00Cr16Mo16) → C-22 (00Cr22Mo13W3) → C-2000 (00Cr20Mo16)
G series: G → G-3 (00Cr22Ni48Mo7Cu) → G-30 (00Cr30Ni48Mo7Cu)
The most widely used materials today are the second-generation ones: N10665 (B-2), N10276 (C-276), N06022 (C-22), N06455 (C-4), and N06985 (G-3). II. Typical Chemical Composition of Hastelloy Alloys
Chemical composition of the material:
Ni, Cr, Mo, Fe, C, Si, Co, Mn, P, S, W, V, Cu, Nb+Ta
N10665 (B-2) base: ≤1.0, 26.0–30, ≤2.0, ≤0.02, ≤0.10, ≤1.0, ≤1.0, ≤0.04, ≤0.03
N10276 (C-276) base: 14.5–16.5, 15.0–17.0, 4.0–7.0, ≤0.01, ≤0.08, ≤2.5, ≤1.0, ≤0.04, ≤0.03; 3.0–4.5, ≤0.035
N06007 (G-3) base: 21.0–23.5, 6.0–8.0, 18.0–21, ≤0.015, ≤1.0, ≤5.0, ≤1.0, ≤0.04, ≤0.03, ≤1.5; 1.5–2.5, ≤0.50
III. Mechanical Properties
Hastelloy alloys possess excellent mechanical properties, featuring high strength and high toughness. As a result, they are somewhat difficult to machine. Moreover, they exhibit a strong tendency to strain harden; when the degree of deformation reaches 15%, it is approximately twice that of 18-8 stainless steel. Hastelloy also has a medium-temperature sensitization zone, whose sensitization tendency increases with the increase in strain rate. At higher temperatures, Hastelloy is prone to absorbing harmful elements, which reduces its mechanical properties and corrosion resistance. Mechanical properties of materials IV. Commonly used Hastelloy alloys 1: Hastelloy B-2 alloy I. Corrosion resistance Hastelloy B-2 is a Ni-Mo alloy with extremely low carbon and silicon contents; this low content reduces the precipitation of carbides and other phases in the welds and heat-affected zones, thereby ensuring good corrosion resistance even in welded states. It is well known that Hastelloy B-2 exhibits excellent corrosion resistance in various reducing media, and can withstand the corrosion of hydrochloric acid at any temperature and concentration under normal pressure. It exhibits excellent corrosion resistance in non-oxidizing sulfuric acid at moderate concentrations without inflation, phosphoric acids of various concentrations, high-temperature acetic acid, organic acids such as formic acid, bromic acid, and hydrogen chloride gas; simultaneously, it is also resistant to corrosion by halogen catalysts. Therefore, Hastelloy B-2 alloy is commonly used in various demanding petroleum and chemical processes, such as the distillation and concentration of hydrochloric acid ； In production processes such as the alkylation of ethylbenzene and low-pressure carbonylation to produce acetic acid. However, years of industrial use of Hastelloy B-2 have revealed that: (1) there are two sensitization zones in Hastelloy B-2 that have a significant impact on its resistance to intergranular corrosion: a high-temperature zone of 1200–1300°C and a medium-temperature zone of 550–900°C ； (2) The weld metal and heat-affected zone of Hastelloy B-2 are highly susceptible to intergranular corrosion due to dendritic segregation, with intermetallic phases and carbides precipitating along the grain boundaries ； (3) Hastelloy B-2 alloy has poor medium-temperature thermal stability. When the iron content in Hastelloy B-2 alloy drops below 2%, the alloy becomes sensitive to the transformation of the β phase (i.e., the Ni4Mo phase, an ordered intermetallic compound). When the alloy is held at a temperature in the range of 650–750°C for a slightly longer period, the β phase is formed instantaneously. The presence of the β phase reduces the toughness of Hastelloy B-2, making it susceptible to stress corrosion; this can even lead to cracking in Hastelloy B-2 during raw material production (such as in the hot rolling process), during equipment manufacturing (such as after welding Hastelloy B-2 equipment and during overall heat treatment), and while the equipment is in service. Currently, the standard test methods specified in our country and around the world for evaluating the intergranular corrosion resistance of Hastelloy B-2 are all the atmospheric-pressure boiling hydrochloric acid method, with the evaluation being carried out using the weight loss method. Since Hastelloy B-2 is an alloy resistant to hydrochloric acid corrosion, the atmospheric-pressure boiling hydrochloric acid test for assessing the intergranular corrosion tendency of Hastelloy B-2 is quite insensitive. Research conducted by domestic scientific institutions using the high-temperature hydrochloric acid method on Hastelloy B-2 has shown that the corrosion resistance of this alloy depends not only on its chemical composition but also on the control processes involved in its heat treatment. When the hot working process is not properly controlled, in Hastelloy B-2 not only do the grains grow larger, but a σ phase rich in Mo also precipitates at the grain boundaries. As a result, the intergranular corrosion resistance of Hastelloy B-2 decreases significantly; in high-temperature hydrochloric acid tests, the erosion depth at the grain boundaries of plates with coarse grains is approximately twice that of normal plates. II. Physical Properties Density: 9.2 g/cm3, Melting point: 1330–1380°C, Magnetic permeability: (°C, RT) ≤ 1.001 III. Chemical Composition Elements: Ni, Cr, Fe, C, Mn, Si, Cu, Mo, Co, P, S Minimum allowable amounts: 0.4, 1.6, 26.0 Maximum allowable amounts: 1.0, 2.0, 0.01, 1.0, 0.08, 0.5, 30.0, 1.0, 0.02, 0.010 V. Manufacturing and Heat Treatment 1: Heating For Hastelloy B-2 alloy, it is very important to keep the surface clean and free from contaminants before and during heating. If Hastelloy B-2 alloy is heated in an environment contaminated with sulfur, phosphorus, lead, or other low-melting-point metals, it becomes brittle; the sources of these contaminants include marker pen marks, temperature-indicating paints, greases and liquids, and smoke. This flue gas must have low sulfur content ； For example: natural gas and liquefied petroleum gas are considered acceptable if their sulfur content is no more than 0.1%, urban air has a sulfur content of no more than 0.25 g/m3, and fuel oil is acceptable if its sulfur content is no more than 0.5%. The gas environment required for the heating furnace is a neutral or slightly reducing environment, and it must not fluctuate between oxidizing and reducing conditions. The flame in the furnace must not directly impact Hastelloy B-2 alloy. At the same time, the material must be heated to the desired temperature at the fastest possible rate; this means that the temperature of the heating furnace must first be raised to the required level before the material is placed in the furnace for heating. 2: Hot working Hastelloy B-2 can be hot-worked in the temperature range of 900–1160°C, and it should be quenched in water after processing. To ensure the best corrosion resistance, annealing should be performed after hot working. 3: Cold working Hastelloy B-2 alloy subjected to cold working must undergo solution treatment; due to its much higher work hardening rate compared to austenitic stainless steels, special consideration must be given to the forming equipment. If cold forming is performed, inter-stage annealing is necessary. When the cold working deformation exceeds 15%, solution treatment is required before use. 4: Heat treatment The temperature for solution heat treatment should be maintained between 1060~1080°C; thereafter, water quenching should be carried out, or rapid air cooling can be used when the material thickness is 1.5 mm or more, in order to achieve the best corrosion resistance. During any heating process, preventive measures must be taken to keep the surface of the material clean. When heat-treating Hastelloy materials or equipment components, the following points should be taken into consideration: To prevent deformation of the components during heat treatment, stainless steel reinforcement rings should be used ； The charging temperature, as well as the heating and cooling times, must be strictly controlled ； Before loading into the furnace, pre-treat the heat-treated parts to prevent the formation of thermal cracks ； After heat treatment, 100% PT of the heat-treated parts ； If thermal cracks occur during heat treatment and need to be repaired by welding after grinding, a specialized welding process must be employed. 5: Descaling The oxides on the surface of Hastelloy B-2 alloy, as well as any stains in the area around welds, must be removed thoroughly using fine grinding wheels or similar tools. Since Hastelloy B-2 is sensitive to oxidizing media, a large amount of nitrogen-containing gases are generated during the pickling process. 6: Machining Hastelloy B-2 alloy should be machined in its annealed state, and it is necessary to be aware of its work hardening property. For example, a slower surface cutting speed should be used compared to standard austenitic stainless steels; a larger feed rate should be employed for the hardened surface layer, and the tool should remain in a continuous working condition. 7: Welding The weld metal and heat-affected zone of Hastelloy B-2 are deficient in Mo due to the easy precipitation of the β phase, which makes them susceptible to intergranular corrosion. Therefore, the welding process for Hastelloy B-2 must be carefully planned and strictly controlled. The general welding process is as follows: ERNi-Mo7 is used as the welding material ； Welding method GTAW ； Keep the temperature between layers at no more than 120℃ ； Wire diameter φ2.4, φ3.2 ； Welding current: 90~150A. At the same time, before welding, the welding wire, the groove of the workpiece to be welded, and adjacent areas should be cleaned and degreased. The thermal conductivity of Hastelloy B-2 is much lower than that of steel; therefore, if a single V-groove is used, the groove angle should be around 70°, along with a lower heat input. Post-weld heat treatment can eliminate residual stresses and improve resistance to stress corrosion cracking. 2: Hastelloy C-276 alloy I. Corrosion resistance Hastelloy C-276 belongs to the nickel-based alloy family composed of nickel, molybdenum, chromium, iron, and tungsten. It is the most corrosion-resistant among modern metal materials. It is primarily resistant to moisture, various oxidizing chlorides, chloride salt solutions, sulfuric acid, and oxidizing salts, and exhibits excellent corrosion resistance in both low-temperature and medium-temperature hydrochloric acids. Therefore, over the past three decades, it has found wide application in harsh corrosive environments across various industrial sectors such as chemicals, petrochemicals, flue gas desulfurization, pulp and paper, and environmental protection. The various corrosion data for Hastelloy C-276 are typical, but they cannot be used as a standard; especially in unknown environments, testing is necessary before selecting this material. Hastelloy C-276 does not contain enough Cr to resist corrosion in highly oxidizing environments, such as hot concentrated nitric acid. This alloy was developed primarily for use in chemical processing environments, especially those with mixed acids, such as the discharge pipes of flue gas desulfurization systems. The table below shows the comparative corrosion test results of the four alloys in different environments. (All welding specimens were prepared using self-fluxing tungsten inert gas welding.) Corrosion comparison tests of four metals in different environments. Test environment: Boiling; Corrosion rate: mm/. Typical metals: 316, AL-6XN, Inconel 625, C-276. Basic metal specimens, welded specimens, basic metal specimens, welded specimens, basic metal specimens, welded specimens. 20% acetic acid: 0.003, 0.003, 0.0036, 0.0018, 0.0076, 0.013, 0.006. 45% formic acid: 0.277, 0.262, 0.116, 0.142, 0.13, 0.07, 0.049. 10% oxalic acid: 1.02, 0.991, 0.277, 0.274, 0.15, 0.29, 0.259. 20% phosphoric acid: 0.177, 0.155, 0.007, 0.006, 0.001, 0.001, 0.0006. 10% sulfamic acid: 1.62, 1.58, 0.751, 0.381, 0.12, 0.07, 0.061. 10% sulfuric acid: 9.44, 9.44, 2.14, 2.34, 0.64, 0.35, 0.503. 10% sodium bicarbonate: 1.06, 1.06, 0.609, 0.344, 0.10, 0.07, 0.055. Hastelloy C-276 can be used as components for flue gas desulfurization in coal-fired systems; in such environments, it is the most corrosion-resistant material. The table below shows the comparative corrosion test results of C-276 alloy and typical 316 in the \"Green Death\" solution of the flue gas simulation system. “Corrosion comparison test in the “Green Death” solution \"Green Death\" solution (boiling) – Corrosion rate (mm/a) Typical 316 C-276 7% sulfuric acid: Damage level of 0.67 3% hydrochloric acid 1% CuCl2 1% FeCl3 As can be seen from the table above, the C-276 alloy exhibits excellent corrosion resistance to mixed acid and salt solutions containing chloride ions. The addition of Cr, Mo, and W to Hastelloy C-276 **improves** the alloy’s resistance to pitting and crevice corrosion. C-276 alloy is considered inert in seawater environments, which is why it is widely used in marine, saline, and high-chloride environments, even under conditions of strong acids and low pH levels. The table below shows a comparison of crevice corrosion of four metals in a 6% FeCl3 solution (per ASTM standard G-48). Occurrence of crevice corrosion Alloy Temperature at which crevice corrosion occurs °F °C Typical 316 27 2.5 AL-6XN 113 45 Inconel 625 113 45 C-276 140 60 The high content of Ni and Mo in the C-276 alloy gives it strong resistance to stress corrosion cracking caused by chloride ions. The table below shows the results of stress corrosion cracking tests for these four metals in different chloride-containing solutions. Chloride stress corrosion cracking test results: Test solution, bent U-shaped specimen, test time (hours), and test outcomes. Typical materials include 316, AL-6XN, Inconel 625, and C-276. For 42% MgCl2 (boiling): failure after 24 hours; mixed results after 1000 hours; resistance after 1000 hours; resistance after 1000 hours. For 33% LiCl (boiling): failure after 100 hours; resistance after 1000 hours; resistance after 1000 hours; resistance after 1000 hours. For 26% NaCl (boiling): failure after 300 hours; resistance after 1000 hours; resistance after 1000 hours; resistance after 1000 hours. II. Physical properties: Density: 8.90 g/cm3; specific heat: 425 J/kg/K; elastic modulus: 205 GPa (at 21°C). III. Mechanical properties: The tensile test results for the typical C-276 alloy are shown in the table below. This material was annealed at 1150°C and then rapidly cooled in water. Mechanical property test values Temperature (°C) Yield strength σ0.2 (Mpa) Tensile strength σb (Mpa) Elongation δ5 (%) -196 565 965 45 -101 480 895 50 21 415 790 50 93 380 725 50 204 345 710 50 316 315 675 55 427 290 655 60 538 270 640 60 Cold working of the C-276 alloy increases its strength. When subjected to impact testing, V-groove impact specimens are made from 10 mm thick sheets (which have been annealed); if the specimens are welded, they exhibit a certain degree of flexibility within the same temperature range, due to the welds. The results of the plate impact test are shown in the table below. Test temperature (°C) Impact energy of V-groove specimen (J) -196 245 21 325 200 325 The C-276 alloy and conventional austenitic stainless steel have similar formability. However, because its strength is greater than that of ordinary austenitic stainless steels, higher stresses are generated during cold forming processes. Furthermore, this material hardens much faster than ordinary stainless steel; therefore, intermediate annealing treatments are required during extensive cold forming processes. IV. Welding and Heat Treatment The weldability of C-276 alloy is similar to that of conventional austenitic stainless steels. Before using any welding method to weld C-276, measures must be taken to minimize the reduction in the corrosion resistance of the weld zone and the heat-affected area; methods such as Gas Tungsten Arc Welding (GTAW), Gas Metal Arc Welding (GMAW), Submerged Arc Welding, or other welding techniques that help to minimize such a reduction in corrosion resistance are suitable for this purpose. However, welding methods such as oxy-acetylene welding, which may increase the carbon or silicon content in the weld and heat-affected zone of the material, are not suitable for use. Regarding the selection of weld joint configurations, the successful experience with C-276 weld joints as outlined in the ASME Boiler and Pressure Vessel Code can be referenced. Mechanical processing is the preferred method for preparing welding grooves, but this process causes work hardening; therefore, it is necessary to grind the mechanically processed grooves before welding them. An appropriate heat input rate should be used during welding to prevent the formation of hot cracks. In the vast majority of corrosive environments, C-276 can be used in welded form. However, in extremely harsh environments, the C-276 material and its welded components must undergo solution heat treatment to achieve the best corrosion resistance. For welding C-276 alloy, it can be used either as the welding material or as a filler metal. If it is required to add certain elements to the welds of C-276, such as other nickel-based alloys or stainless steels, and these welds are to be exposed to corrosive environments, then the electrodes or wires used for welding must possess corrosion resistance comparable to that of the base metal. The solution heat treatment of Hastelloy C-276 alloy material involves two processes: (1) heating at 1040°C to 1150°C ； (2) Rapidly cool to a black state (around 400°C) within two minutes; materials treated in this way exhibit excellent corrosion resistance. Therefore, stress-relief heat treatment alone on Hastelloy C-276 alloy is ineffective. Before heat treatment, the oil and other contaminants on the alloy’s surface, as well as any impurities that could produce carbon during the heat treatment process, must be removed. During welding or heat treatment, oxides form on the surface of C-276 alloy, which reduces the Cr content in the alloy and affects its corrosion resistance; therefore, surface cleaning is necessary. A stainless steel wire brush or grinding wheel can be used, followed by pickling in a mixture of nitric acid and hydrofluoric acid in the appropriate proportions, and finally rinsing thoroughly with clean water
B series: B → B-2 (00Ni70Mo28) → B-3
C series: C → C-276 (00Cr16Mo16W4) → C-4 (00Cr16Mo16) → C-22 (00Cr22Mo13W3) → C-2000 (00Cr20Mo16)
G series: G → G-3 (00Cr22Ni48Mo7Cu) → G-30 (00Cr30Ni48Mo7Cu)
The most widely used materials today are the second-generation ones: N10665 (B-2), N10276 (C-276), N06022 (C-22), N06455 (C-4), and N06985 (G-3). II. Typical Chemical Composition of Hastelloy Alloys
Chemical composition of the material:
Ni, Cr, Mo, Fe, C, Si, Co, Mn, P, S, W, V, Cu, Nb+Ta
N10665 (B-2) base: ≤1.0, 26.0–30, ≤2.0, ≤0.02, ≤0.10, ≤1.0, ≤1.0, ≤0.04, ≤0.03
N10276 (C-276) base: 14.5–16.5, 15.0–17.0, 4.0–7.0, ≤0.01, ≤0.08, ≤2.5, ≤1.0, ≤0.04, ≤0.03; 3.0–4.5, ≤0.035
N06007 (G-3) base: 21.0–23.5, 6.0–8.0, 18.0–21, ≤0.015, ≤1.0, ≤5.0, ≤1.0, ≤0.04, ≤0.03, ≤1.5; 1.5–2.5, ≤0.50
III. Mechanical Properties
Hastelloy alloys possess excellent mechanical properties, featuring high strength and high toughness. As a result, they are somewhat difficult to machine. Moreover, they exhibit a strong tendency to strain harden; when the degree of deformation reaches 15%, it is approximately twice that of 18-8 stainless steel. Hastelloy also has a medium-temperature sensitization zone, whose sensitization tendency increases with the increase in strain rate. At higher temperatures, Hastelloy is prone to absorbing harmful elements, which reduces its mechanical properties and corrosion resistance. Mechanical properties of materials IV. Commonly used Hastelloy alloys 1: Hastelloy B-2 alloy I. Corrosion resistance Hastelloy B-2 is a Ni-Mo alloy with extremely low carbon and silicon contents; this low content reduces the precipitation of carbides and other phases in the welds and heat-affected zones, thereby ensuring good corrosion resistance even in welded states. It is well known that Hastelloy B-2 exhibits excellent corrosion resistance in various reducing media, and can withstand the corrosion of hydrochloric acid at any temperature and concentration under normal pressure. It exhibits excellent corrosion resistance in non-oxidizing sulfuric acid at moderate concentrations without inflation, phosphoric acids of various concentrations, high-temperature acetic acid, organic acids such as formic acid, bromic acid, and hydrogen chloride gas; simultaneously, it is also resistant to corrosion by halogen catalysts. Therefore, Hastelloy B-2 alloy is commonly used in various demanding petroleum and chemical processes, such as the distillation and concentration of hydrochloric acid ； In production processes such as the alkylation of ethylbenzene and low-pressure carbonylation to produce acetic acid. However, years of industrial use of Hastelloy B-2 have revealed that: (1) there are two sensitization zones in Hastelloy B-2 that have a significant impact on its resistance to intergranular corrosion: a high-temperature zone of 1200–1300°C and a medium-temperature zone of 550–900°C ； (2) The weld metal and heat-affected zone of Hastelloy B-2 are highly susceptible to intergranular corrosion due to dendritic segregation, with intermetallic phases and carbides precipitating along the grain boundaries ； (3) Hastelloy B-2 alloy has poor medium-temperature thermal stability. When the iron content in Hastelloy B-2 alloy drops below 2%, the alloy becomes sensitive to the transformation of the β phase (i.e., the Ni4Mo phase, an ordered intermetallic compound). When the alloy is held at a temperature in the range of 650–750°C for a slightly longer period, the β phase is formed instantaneously. The presence of the β phase reduces the toughness of Hastelloy B-2, making it susceptible to stress corrosion; this can even lead to cracking in Hastelloy B-2 during raw material production (such as in the hot rolling process), during equipment manufacturing (such as after welding Hastelloy B-2 equipment and during overall heat treatment), and while the equipment is in service. Currently, the standard test methods specified in our country and around the world for evaluating the intergranular corrosion resistance of Hastelloy B-2 are all the atmospheric-pressure boiling hydrochloric acid method, with the evaluation being carried out using the weight loss method. Since Hastelloy B-2 is an alloy resistant to hydrochloric acid corrosion, the atmospheric-pressure boiling hydrochloric acid test for assessing the intergranular corrosion tendency of Hastelloy B-2 is quite insensitive. Research conducted by domestic scientific institutions using the high-temperature hydrochloric acid method on Hastelloy B-2 has shown that the corrosion resistance of this alloy depends not only on its chemical composition but also on the control processes involved in its heat treatment. When the hot working process is not properly controlled, in Hastelloy B-2 not only do the grains grow larger, but a σ phase rich in Mo also precipitates at the grain boundaries. As a result, the intergranular corrosion resistance of Hastelloy B-2 decreases significantly; in high-temperature hydrochloric acid tests, the erosion depth at the grain boundaries of plates with coarse grains is approximately twice that of normal plates. II. Physical Properties Density: 9.2 g/cm3, Melting point: 1330–1380°C, Magnetic permeability: (°C, RT) ≤ 1.001 III. Chemical Composition Elements: Ni, Cr, Fe, C, Mn, Si, Cu, Mo, Co, P, S Minimum allowable amounts: 0.4, 1.6, 26.0 Maximum allowable amounts: 1.0, 2.0, 0.01, 1.0, 0.08, 0.5, 30.0, 1.0, 0.02, 0.010 V. Manufacturing and Heat Treatment 1: Heating For Hastelloy B-2 alloy, it is very important to keep the surface clean and free from contaminants before and during heating. If Hastelloy B-2 alloy is heated in an environment contaminated with sulfur, phosphorus, lead, or other low-melting-point metals, it becomes brittle; the sources of these contaminants include marker pen marks, temperature-indicating paints, greases and liquids, and smoke. This flue gas must have low sulfur content ； For example: natural gas and liquefied petroleum gas are considered acceptable if their sulfur content is no more than 0.1%, urban air has a sulfur content of no more than 0.25 g/m3, and fuel oil is acceptable if its sulfur content is no more than 0.5%. The gas environment required for the heating furnace is a neutral or slightly reducing environment, and it must not fluctuate between oxidizing and reducing conditions. The flame in the furnace must not directly impact Hastelloy B-2 alloy. At the same time, the material must be heated to the desired temperature at the fastest possible rate; this means that the temperature of the heating furnace must first be raised to the required level before the material is placed in the furnace for heating. 2: Hot working Hastelloy B-2 can be hot-worked in the temperature range of 900–1160°C, and it should be quenched in water after processing. To ensure the best corrosion resistance, annealing should be performed after hot working. 3: Cold working Hastelloy B-2 alloy subjected to cold working must undergo solution treatment; due to its much higher work hardening rate compared to austenitic stainless steels, special consideration must be given to the forming equipment. If cold forming is performed, inter-stage annealing is necessary. When the cold working deformation exceeds 15%, solution treatment is required before use. 4: Heat treatment The temperature for solution heat treatment should be maintained between 1060~1080°C; thereafter, water quenching should be carried out, or rapid air cooling can be used when the material thickness is 1.5 mm or more, in order to achieve the best corrosion resistance. During any heating process, preventive measures must be taken to keep the surface of the material clean. When heat-treating Hastelloy materials or equipment components, the following points should be taken into consideration: To prevent deformation of the components during heat treatment, stainless steel reinforcement rings should be used ； The charging temperature, as well as the heating and cooling times, must be strictly controlled ； Before loading into the furnace, pre-treat the heat-treated parts to prevent the formation of thermal cracks ； After heat treatment, 100% PT of the heat-treated parts ； If thermal cracks occur during heat treatment and need to be repaired by welding after grinding, a specialized welding process must be employed. 5: Descaling The oxides on the surface of Hastelloy B-2 alloy, as well as any stains in the area around welds, must be removed thoroughly using fine grinding wheels or similar tools. Since Hastelloy B-2 is sensitive to oxidizing media, a large amount of nitrogen-containing gases are generated during the pickling process. 6: Machining Hastelloy B-2 alloy should be machined in its annealed state, and it is necessary to be aware of its work hardening property. For example, a slower surface cutting speed should be used compared to standard austenitic stainless steels; a larger feed rate should be employed for the hardened surface layer, and the tool should remain in a continuous working condition. 7: Welding The weld metal and heat-affected zone of Hastelloy B-2 are deficient in Mo due to the easy precipitation of the β phase, which makes them susceptible to intergranular corrosion. Therefore, the welding process for Hastelloy B-2 must be carefully planned and strictly controlled. The general welding process is as follows: ERNi-Mo7 is used as the welding material ； Welding method GTAW ； Keep the temperature between layers at no more than 120℃ ； Wire diameter φ2.4, φ3.2 ； Welding current: 90~150A. At the same time, before welding, the welding wire, the groove of the workpiece to be welded, and adjacent areas should be cleaned and degreased. The thermal conductivity of Hastelloy B-2 is much lower than that of steel; therefore, if a single V-groove is used, the groove angle should be around 70°, along with a lower heat input. Post-weld heat treatment can eliminate residual stresses and improve resistance to stress corrosion cracking. 2: Hastelloy C-276 alloy I. Corrosion resistance Hastelloy C-276 belongs to the nickel-based alloy family composed of nickel, molybdenum, chromium, iron, and tungsten. It is the most corrosion-resistant among modern metal materials. It is primarily resistant to moisture, various oxidizing chlorides, chloride salt solutions, sulfuric acid, and oxidizing salts, and exhibits excellent corrosion resistance in both low-temperature and medium-temperature hydrochloric acids. Therefore, over the past three decades, it has found wide application in harsh corrosive environments across various industrial sectors such as chemicals, petrochemicals, flue gas desulfurization, pulp and paper, and environmental protection. The various corrosion data for Hastelloy C-276 are typical, but they cannot be used as a standard; especially in unknown environments, testing is necessary before selecting this material. Hastelloy C-276 does not contain enough Cr to resist corrosion in highly oxidizing environments, such as hot concentrated nitric acid. This alloy was developed primarily for use in chemical processing environments, especially those with mixed acids, such as the discharge pipes of flue gas desulfurization systems. The table below shows the comparative corrosion test results of the four alloys in different environments. (All welding specimens were prepared using self-fluxing tungsten inert gas welding.) Corrosion comparison tests of four metals in different environments. Test environment: Boiling; Corrosion rate: mm/. Typical metals: 316, AL-6XN, Inconel 625, C-276. Basic metal specimens, welded specimens, basic metal specimens, welded specimens, basic metal specimens, welded specimens. 20% acetic acid: 0.003, 0.003, 0.0036, 0.0018, 0.0076, 0.013, 0.006. 45% formic acid: 0.277, 0.262, 0.116, 0.142, 0.13, 0.07, 0.049. 10% oxalic acid: 1.02, 0.991, 0.277, 0.274, 0.15, 0.29, 0.259. 20% phosphoric acid: 0.177, 0.155, 0.007, 0.006, 0.001, 0.001, 0.0006. 10% sulfamic acid: 1.62, 1.58, 0.751, 0.381, 0.12, 0.07, 0.061. 10% sulfuric acid: 9.44, 9.44, 2.14, 2.34, 0.64, 0.35, 0.503. 10% sodium bicarbonate: 1.06, 1.06, 0.609, 0.344, 0.10, 0.07, 0.055. Hastelloy C-276 can be used as components for flue gas desulfurization in coal-fired systems; in such environments, it is the most corrosion-resistant material. The table below shows the comparative corrosion test results of C-276 alloy and typical 316 in the \"Green Death\" solution of the flue gas simulation system. “Corrosion comparison test in the “Green Death” solution \"Green Death\" solution (boiling) – Corrosion rate (mm/a) Typical 316 C-276 7% sulfuric acid: Damage level of 0.67 3% hydrochloric acid 1% CuCl2 1% FeCl3 As can be seen from the table above, the C-276 alloy exhibits excellent corrosion resistance to mixed acid and salt solutions containing chloride ions. The addition of Cr, Mo, and W to Hastelloy C-276 **improves** the alloy’s resistance to pitting and crevice corrosion. C-276 alloy is considered inert in seawater environments, which is why it is widely used in marine, saline, and high-chloride environments, even under conditions of strong acids and low pH levels. The table below shows a comparison of crevice corrosion of four metals in a 6% FeCl3 solution (per ASTM standard G-48). Occurrence of crevice corrosion Alloy Temperature at which crevice corrosion occurs °F °C Typical 316 27 2.5 AL-6XN 113 45 Inconel 625 113 45 C-276 140 60 The high content of Ni and Mo in the C-276 alloy gives it strong resistance to stress corrosion cracking caused by chloride ions. The table below shows the results of stress corrosion cracking tests for these four metals in different chloride-containing solutions. Chloride stress corrosion cracking test results: Test solution, bent U-shaped specimen, test time (hours), and test outcomes. Typical materials include 316, AL-6XN, Inconel 625, and C-276. For 42% MgCl2 (boiling): failure after 24 hours; mixed results after 1000 hours; resistance after 1000 hours; resistance after 1000 hours. For 33% LiCl (boiling): failure after 100 hours; resistance after 1000 hours; resistance after 1000 hours; resistance after 1000 hours. For 26% NaCl (boiling): failure after 300 hours; resistance after 1000 hours; resistance after 1000 hours; resistance after 1000 hours. II. Physical properties: Density: 8.90 g/cm3; specific heat: 425 J/kg/K; elastic modulus: 205 GPa (at 21°C). III. Mechanical properties: The tensile test results for the typical C-276 alloy are shown in the table below. This material was annealed at 1150°C and then rapidly cooled in water. Mechanical property test values Temperature (°C) Yield strength σ0.2 (Mpa) Tensile strength σb (Mpa) Elongation δ5 (%) -196 565 965 45 -101 480 895 50 21 415 790 50 93 380 725 50 204 345 710 50 316 315 675 55 427 290 655 60 538 270 640 60 Cold working of the C-276 alloy increases its strength. When subjected to impact testing, V-groove impact specimens are made from 10 mm thick sheets (which have been annealed); if the specimens are welded, they exhibit a certain degree of flexibility within the same temperature range, due to the welds. The results of the plate impact test are shown in the table below. Test temperature (°C) Impact energy of V-groove specimen (J) -196 245 21 325 200 325 The C-276 alloy and conventional austenitic stainless steel have similar formability. However, because its strength is greater than that of ordinary austenitic stainless steels, higher stresses are generated during cold forming processes. Furthermore, this material hardens much faster than ordinary stainless steel; therefore, intermediate annealing treatments are required during extensive cold forming processes. IV. Welding and Heat Treatment The weldability of C-276 alloy is similar to that of conventional austenitic stainless steels. Before using any welding method to weld C-276, measures must be taken to minimize the reduction in the corrosion resistance of the weld zone and the heat-affected area; methods such as Gas Tungsten Arc Welding (GTAW), Gas Metal Arc Welding (GMAW), Submerged Arc Welding, or other welding techniques that help to minimize such a reduction in corrosion resistance are suitable for this purpose. However, welding methods such as oxy-acetylene welding, which may increase the carbon or silicon content in the weld and heat-affected zone of the material, are not suitable for use. Regarding the selection of weld joint configurations, the successful experience with C-276 weld joints as outlined in the ASME Boiler and Pressure Vessel Code can be referenced. Mechanical processing is the preferred method for preparing welding grooves, but this process causes work hardening; therefore, it is necessary to grind the mechanically processed grooves before welding them. An appropriate heat input rate should be used during welding to prevent the formation of hot cracks. In the vast majority of corrosive environments, C-276 can be used in welded form. However, in extremely harsh environments, the C-276 material and its welded components must undergo solution heat treatment to achieve the best corrosion resistance. For welding C-276 alloy, it can be used either as the welding material or as a filler metal. If it is required to add certain elements to the welds of C-276, such as other nickel-based alloys or stainless steels, and these welds are to be exposed to corrosive environments, then the electrodes or wires used for welding must possess corrosion resistance comparable to that of the base metal. The solution heat treatment of Hastelloy C-276 alloy material involves two processes: (1) heating at 1040°C to 1150°C ； (2) Rapidly cool to a black state (around 400°C) within two minutes; materials treated in this way exhibit excellent corrosion resistance. Therefore, stress-relief heat treatment alone on Hastelloy C-276 alloy is ineffective. Before heat treatment, the oil and other contaminants on the alloy’s surface, as well as any impurities that could produce carbon during the heat treatment process, must be removed. During welding or heat treatment, oxides form on the surface of C-276 alloy, which reduces the Cr content in the alloy and affects its corrosion resistance; therefore, surface cleaning is necessary. A stainless steel wire brush or grinding wheel can be used, followed by pickling in a mixture of nitric acid and hydrofluoric acid in the appropriate proportions, and finally rinsing thoroughly with clean water
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