The most comprehensive introduction to various varieties of Hastelloy alloys
Hastelloy alloy
I. Introduction
Hastelloy is a type of nickel-based alloy. It is currently divided into three series: B, C, and G. It is mainly used for strong corrosion that cannot be used in iron-based Cr-Ni or Cr-Ni-Mo stainless steel, non-metallic materials, etc. It has been widely used in petroleum, chemical industry, environmental protection and many other fields abroad. Its grades and typical usage situations are shown in the table below.
Hastelloy grades
In order to improve the corrosion resistance and cold and hot working properties of Hastelloy, Hastelloy has made three major improvements. The development process is as follows: Reference:
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 at present are N10665 (B-2), N10276 (C-276), N06022 (C-22), N06455 (C-4) and N06985 (G-3). The third generation materials N10675 (B-3), N10629 (B-4), and N06059 (C-59) are in the promotion stage. Due to the advancement of metallurgical technology, multiple brands of so-called "super stainless steel" containing ~6% Mo have appeared in recent years, replacing G series alloys, causing a rapid decline in the production and use of G series alloys.
2. Typical chemical composition of Hastelloy alloy
chemical composition of material
Ni Cr Mo Fe C Si Co Mn P S W V Cu Nb+T
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
3. Mechanical properties reference:
The mechanical properties of Hastelloy are very outstanding. It has the characteristics of high strength and high toughness, so it is difficult to machine. Moreover, its strain hardening tendency is extremely strong. When the deformation rate reaches 15%, it is about 18-8 Twice that of stainless steel. Hastelloy also has a medium-temperature sensitization zone, and its sensitization tendency increases with the increase in deformation rate. When the temperature is high, Hastelloy easily absorbs harmful elements, causing its mechanical properties and corrosion resistance to decrease.
4. Commonly used Hastelloy alloys
1: Hastelloy B-2 alloy (Hastelloy B-2 alloy)
1. Corrosion resistance
Hastelloy B-2 alloy is a Ni-Mo alloy with extremely low carbon and silicon content. It reduces the precipitation of carbides and other phases in the weld and heat-affected zone, thereby ensuring that even under welding conditions Also has good corrosion resistance.
As we all know, Hastelloy B-2 alloy has excellent corrosion resistance in various reducing media and can withstand corrosion at any temperature and concentration of hydrochloric acid under normal pressure. It has excellent corrosion resistance in non-aerated medium-concentration non-oxidizing sulfuric acid, various concentrations of phosphoric acid, high-temperature acetic acid, formic acid and other organic acids, bromic acid and hydrogen chloride gases. At the same time, it is also resistant to corrosion by halogen catalysts. Therefore, Hastelloy B-2 alloy is usually used in a variety of harsh petroleum and chemical processes, such as the distillation and concentration of hydrochloric acid; the alkylation of ethylbenzene and low-pressure oxo synthesis of acetic acid and other production processes.
However, in the industrial application of Hastelloy B-2 alloy for many years, it has been found that: (1) Hastelloy B-2 alloy has two sensitization zones that have a considerable impact on the resistance to intergranular corrosion: the high temperature zone of 1200~1300°C and the 550°C sensitization zone. ~900℃ medium temperature zone; (2) Due to dendrite segregation in the weld metal and heat-affected zone of Hastelloy B-2 alloy, intermetallic phases and carbides precipitate along the grain boundaries, making them more sensitive to intergranular corrosion ; (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 is sensitive to the transformation of the beta phase (ie, Ni4Mo phase, an ordered intermetallic compound). When the alloy stays in the temperature range of 650~750℃ for a slightly longer time, the β phase is generated instantly. The existence of β phase reduces the toughness of Hastelloy B-2 alloy, making it sensitive to stress corrosion, and even causes Hastelloy B-2 alloy to be damaged during raw material production (such as hot rolling process) and equipment manufacturing process (such as Hastelloy B-2 alloy equipment post-weld overall heat treatment) and Hastelloy B-2 alloy equipment cracks in the service environment. Nowadays, the standard test method designated by my country and other countries around the world for the intergranular corrosion resistance of Hastelloy B-2 alloy is the normal pressure boiling hydrochloric acid method, and the evaluation method is the weight loss method. Since Hastelloy B-2 alloy is an alloy resistant to hydrochloric acid corrosion, the normal pressure boiling hydrochloric acid method is quite insensitive to test the intergranular corrosion tendency of Hastelloy B-2 alloy. Domestic scientific research institutions used high-temperature hydrochloric acid method to study Hastelloy B-2 alloy and found that the corrosion resistance of Hastelloy B-2 alloy not only depends on its chemical composition, but also depends on its thermal processing control process. When the thermal processing process is improperly controlled, the grains of Hastelloy B-2 alloy not only grow, but also the high Mo σ phase precipitates between the grains. At this time, the resistance to intergranular corrosion of Hastelloy B-2 alloy decreases significantly. , in the high-temperature hydrochloric acid test, the grain boundary etching depth of the coarse-grained plate and the normal plate differed by about twice.
2. Physical performance reference
The physical properties of Hastelloy B-2 alloy are shown in the table below.
Density: 9.2g/cm3, melting point: 1330~1380℃, magnetic permeability: (℃, RT)≤1.001
Physical properties
Temperature (℃) Specific heat (J/kg-k) Thermal conductivity coefficient (W/m-k) Resistivity (μΩcm) Elastic modulus (Gpa) Thermal expansion coefficient from room temperature to T (10-6/K)
0 373 137 218
20 377 11.1 137 217
100 389 12.2 138 213 10.3
200 406 13.4 138 208 10.8
300 423 14.6 139 203 11.1
400 431 16.0 139 197 11.4
500 444 17.3 141 191 11.6
600 456 18.7 146 184 11.8
700 176
3. Chemical composition
chemical composition
Element Ni Cr Fe C Mn Si Cu Mo Co P S
Minimum margin 0.4 1.6 26.0
Maximum 1.0 2.0 0.01 1.0 0.08 0.5 30.0 1.0 0.02 0.010
4. Mechanical properties
The general mechanical properties of Hastelloy B-2 alloy are shown in the following two tables
Minimum mechanical property values at room temperature (refer to DIN/ASTM standards)
Product form Dimensions (mm) 0.2% Yield strength (Mpa) 1.0% Yield strength (Mpa) Tensile strength (Mpa) Elongation A5 % Brinell hardness HB Grain size (μm)
Cold rolled strip ≤5 340 380 755 40 250 127
Hot rolled plate 5~65 214
Rod 325 370 745 - -
Tube 340 360 755 - -
ASTM Standard 350 - 760 241 Same as above
Minimum mechanical property values at high temperatures
Product form 0.2% yield strength (Mpa) ℃ 1.0% yield strength (Mpa) ℃
100 200 300 400 100 200 300 400
Board 315 285 270 255 355 325 310 295
Tube
Rod 300 275 255 240 340 315 300 285
5. Manufacturing and heat treatment
1: Heating
For Hastelloy B-2 alloy, it is very important that the surface is kept clean and free of contaminants before and during heating. Hastelloy B-2 alloy will become brittle if heated in an environment containing sulfur, phosphorus, lead or other low melting point metal contaminants. The main sources of these contaminants include marker marks, temperature indicating paint, grease and liquids, smoke. This flue gas must contain low sulfur; for example: the sulfur content of natural gas and liquefied petroleum gas does not exceed 0.1%, the sulfur content of urban air does not exceed 0.25g/m3, and the sulfur content of fuel oil does not exceed 0.5% is qualified.
The gas environment of the heating furnace is required to be a neutral environment or a lightly reducing environment, and it cannot fluctuate between oxidizing and reducing. The flame in the furnace cannot directly impact Hastelloy B-2 alloy. At the same time, the material must be heated to the required temperature at the fastest heating speed, which means that the temperature of the heating furnace must first be raised to the required temperature, and then the material must be put into the furnace for heating.
2: Thermal processing
Hastelloy B-2 alloy can be hot processed in the range of 900~1160℃, and should be quenched with water after processing. In order to ensure the best corrosion resistance, annealing should be performed after hot working.
3: Cold processing
Cold-worked Hastelloy B-2 alloy must undergo solution treatment. Since it has a much higher work hardening rate than austenitic stainless steel, the forming equipment must be carefully considered. If a cold forming process is performed, interstage annealing is necessary.
When the cold working deformation exceeds 15%, solution treatment is required before use.
4: Heat treatment
The solution heat treatment temperature should be controlled between 1060 and 1080°C, followed by water cooling quenching or rapid air cooling when the material thickness is above 1.5mm to obtain the best corrosion resistance. During any heating operation, precautions must be taken to clean the surface of the material. The following issues should be paid attention to when heat treatment of Hastelloy materials or equipment parts: In order to prevent heat treatment deformation of equipment parts, stainless steel reinforcing rings should be used; the furnace loading temperature, heating and cooling time should be strictly controlled; before loading the furnace, heat treatment parts Pre-treatment is carried out to prevent the occurrence of thermal cracks; after heat treatment, the heat-treated parts are 100% PT; if thermal cracks occur during the heat treatment process and need to be repaired after being polished and eliminated, a special repair welding process must be used.
5: Descaling
The oxides on the surface of Hastelloy B-2 alloy and the stains near the welds must be polished away with fine grinding wheels.
Since Hastelloy B-2 alloy is relatively sensitive to oxidizing media, more nitrogen-containing gases will be produced during the pickling process.
6: Machining
Hastelloy B-2 alloy must be machined in the annealed state, and a clear understanding of its work hardening must be adopted. For example, compared with standard austenitic stainless steel, a slower surface cutting speed must be used, and the hardened layer on the surface must be used. Larger feed amount and keeping the tool in continuous working condition.
The weld metal and heat-affected zone of Hastelloy B-2 alloy are Mo-poor due to the easy precipitation of β phase, which is prone to intergranular corrosion. Therefore, the welding process of Hastelloy B-2 alloy should be carefully formulated and strictly controlled. The general welding process is as follows: the welding material is ERNiMo-7; the welding method is GTAW; the interlayer temperature is controlled to be no more than 120°C; the welding wire diameter is φ2.4, φ3.2; the welding current is 90~150A. At the same time, before welding, the welding wire, the groove of the welded parts and adjacent parts should be decontaminated and degreased.
The thermal conductivity of Hastelloy B-2 alloy is much smaller than that of steel. If a single V-shaped groove is selected, the groove angle should be about 70°, and a lower heat input should be used.
Post-weld heat treatment can eliminate residual stress and improve stress corrosion cracking resistance.
2: Hastelloy C-276
1. Corrosion resistance
Hastelloy C-276 metal is a nickel-molybdenum-chromium-iron-tungsten nickel-based alloy. It is one of the most corrosion-resistant modern metal materials. Mainly resistant to wet chlorine, various oxidizing chlorides, chloride salt solutions, sulfuric acid and oxidizing salts, and has good corrosion resistance in low and medium temperature hydrochloric acid. Therefore, in the past thirty years, it has been widely used in harsh corrosive environments, such as chemical industry, petrochemical industry, flue gas desulfurization, pulp and paper making, environmental protection and other industrial fields.
The various corrosion data of Hastelloy C-27 nickel-based alloy are typical, but they cannot be used as specifications, especially in unknown environments, and materials must be selected after testing. There is not enough Cr in Hastelloy C-27 nickel-based alloy to resist corrosion in strong oxidizing environments, such as hot concentrated nitric acid. The production of this alloy is mainly for chemical process environments, especially in the presence of mixed acids, such as the discharge pipe of flue gas desulfurization systems. The following table shows the corrosion comparison of four alloys in different environments.
test situation. (All welding samples adopt autogenous tungsten arc welding)
Comparative corrosion test of four metals in different environments
Test environment (boiling) Corrosion rate (mm/)
Typical 316 AL-6XN Inconel625 C-276
Basic metal specimen Welding specimen Basic metal specimen Welding specimen Basic metal specimen Basic metal specimen Welding specimen
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
