Comprehensive Guide to Nickel-Based Alloys: Hastelloy G3 (UNS N06985)
What is Hastelloy G3?
Hastelloy G3 (also known as "Alloy G3"), designated UNS N06985 or DIN 2.4619, is a nickel-chromium-iron alloy with additions of molybdenum and copper. It has good weldability and resistance to intergranular corrosion in welded conditions. The low carbon content helps prevent sensitization and subsequent intergranular corrosion in the weld heat-affected zone. Hastelloy G3 is commonly used in flue gas scrubbers and processing reducing acids such as phosphoric acid and sulfuric acid.
Hastelloy G3 is a nickel-based high-temperature alloy composed of nickel, chromium, molybdenum, cobalt and other elements, with a nickel content of about 44%. Hastelloy G3 alloy, referred to as G3, is a superior nickel-based corrosion-resistant alloy. It belongs to the Ni-Cr-Fe series containing Mo and Cu. It has excellent resistance to oxidation, atmospheric corrosion and stress corrosion cracking, and has high resistance to localized corrosion (pitting, crevice corrosion). Due to the high Fe content in this alloy, it has the characteristics of low cost compared with other nickel-based corrosion-resistant alloys. G3 alloy is often used in flue gas desulfurization systems, papermaking, phosphoric acid production steam generators and heat exchangers. The oil well pipe made of this alloy has excellent resistance to H2S, CO2, Cl- corrosion and is the best material for oil well pipes in acidic gas fields.
Characteristics of Hastelloy G3 (UNS N06985)
1. Good resistance to heat affected zone (HAZ) corrosion and welding performance;
2. Excellent corrosion resistance to oxidizing chemicals and atmosphere;
3. Good resistance to reducing chemicals;
4. Excellent resistance to stress corrosion cracking in chloride-containing environments;
5. Good resistance to pitting and crevice corrosion.
6. Good resistance to intergranular corrosion.
Hastelloy G3 alloy is a nickel-based corrosion-resistant alloy with superior performance. Among the cold-worked strengthened nickel-based corrosion-resistant alloys, Hastelloy G3 alloy has better corrosion resistance than 825 and 028 alloys. The temperature of Hastelloy G3 alloy is 220℃, pH=3.3, and Cl ion concentration is 15.175%. H2S and CO: It still shows good corrosion resistance in a corrosive environment with a partial pressure of 2.1MPa.
In addition, the grain size of G-3 alloy affects its corrosion resistance in a simulated acid solution in the Gulf of Mexico (25%NaCl+1.03 MPa H2S+1.03 MPa CO2, temperature is 218℃). The results of slow strain rate corrosion test show that the cross-sectional shrinkage and elongation of G-3 alloy are both greater than 92%, and no secondary cracks occur. G-3 alloy shows good resistance to stress corrosion cracking. When the grain size changes from 6-7.5 to 4-5.5, it has little effect on its resistance to stress corrosion cracking. Intergranular corrosion test shows that the corrosion rate of G-3 alloy is about 0.27-0.36 mm/a, which is significantly lower than the maximum allowable corrosion rate (0.61 mm/a) in the chemical process, and the grain size has almost no change. Effect on intergranular corrosion. , Thompson et al. used the cyclic potential scanning method to study the pitting behavior of G-3 alloy in an acidic solution with a Cl ion concentration of 100 g/L and a temperature of 50 ℃. The results showed that the pitting potential of G-3 alloy was 0.59 V. When the potential exceeded this value, the corrosion current increased rapidly and the corrosion resistance was greatly reduced.
Types of Hastelloy Alloys
Hastelloy B-3 Nickel-molybdenum alloy with excellent corrosion resistance in reducing environments
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: Better uniform corrosion resistance and excellent local corrosion resistance than C-4 and C-276 in oxidizing media
Hastelloy C-276: Good resistance to oxidation and moderate reductive corrosion, excellent resistance to stress corrosion
Hastelloy C-2000: The most comprehensive corrosion-resistant alloy with excellent uniform corrosion resistance in oxidizing and reducing environments
Hastelloy G-35: An upgraded product of G-30, with better corrosion resistance and thermal stability, and excellent performance in highly oxidizing mixed acid media with high chromium content such as phosphoric acid
Hastelloy X.: Combining the characteristics of high strength, oxidation resistance and easy processing, each of the above grades has its specific chemical composition, mechanical properties and advantages, so we cannot generalize the characteristics of Hastelloy.
Hastelloy is mainly divided into three series: B, C, and G, and is mainly used in iron-based CrNi or CrNiMo stainless steel, non-metallic materials and other highly corrosive media.
In order to improve the corrosion resistance and hot and cold processing performance of Hastelloy alloy, three major improvements have been made to Hastelloy alloy:
B series: B → B-3 (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 are N06985 (B-3), N10276 (C-276), N06985 (C-22), N06455 (C-4) and N06985 (G-3)
