Hastelloy is a class of high-performance corrosion-resistant alloys based on nickel (Ni). Due to its excellent acid and alkali resistance and high-temperature oxidation resistance, it is widely used in extreme corrosive environments. Its chemical composition is based on Ni, combined with key elements such as chromium (Cr), molybdenum (Mo), iron (Fe), and silicon (Si). Depending on the elemental ratio, it is mainly divided into three series: Ni-Mo series, Ni-Cr-Mo series, and Ni-Si series. The Ni-Mo series, with nickel and molybdenum as the core components, focuses on resistance to reductive corrosion; the Ni-Cr-Mo series balances nickel, chromium, and molybdenum, providing corrosion resistance in both oxidizing and reducing environments; the Ni-Si series contains a specific proportion of silicon, combining corrosion resistance with heat resistance.
In the chemical composition of Hastelloy alloys, there are several key elements that play a decisive role in their properties. The first is the main alloying element, which accounts for a high proportion and directly determines the core properties of the alloy. Among them, nickel (Ni) serves as the “matrix skeleton” of the alloy, typically accounting for more than 50% (with slight variations across different series). It not only provides the alloy with basic corrosion resistance and high-temperature oxidation resistance but also ensures the alloy’s ductility and processability. In reducing media (such as hydrochloric acid and hydrofluoric acid), it can inhibit intergranular corrosion of the alloy, enhancing long-term service stability. Chromium (Cr) is the core “anti-oxidation element”, which can form a dense Cr₂O₃ oxide film on the alloy surface, effectively isolating it from corrosive media such as oxygen and acidic gases. This greatly improves the alloy’s corrosion resistance in oxidizing environments (such as nitric acid and concentrated sulfuric acid). When combined with molybdenum, it further enhances the alloy’s resistance to composite acids. Molybdenum (Mo), as the “key element for resisting localized corrosion”, can significantly improve the alloy’s resistance to pitting and crevice corrosion (especially in chlorine-containing media). It can also reduce the corrosion rate of the alloy in reducing acids (such as hydrochloric acid and phosphoric acid). It is the core performance-supporting element in Ni-Mo and Ni-Cr-Mo alloys. Iron (Fe) mainly plays a role in “structural support and cost optimization”. In some series (such as G series and X series), the iron content can reach 15%-25%, enhancing the mechanical strength of the alloy. However, the iron content needs to be strictly controlled, as too high a content may reduce corrosion resistance, while too low a content may increase material costs. Different series adjust the iron content according to the application scenario.
In addition to the main alloying elements, Hastelloy alloys also contain some auxiliary elements, which are mostly added in trace amounts to optimize the balance of properties. For example, tungsten (W) is only added in specific grades (such as C-276, C-2000), typically at a content of 3%-4%, which enhances the alloy’s high-temperature strength and resistance to intergranular corrosion, making it particularly suitable for high-temperature acidic environments. Cobalt (Co) is a trace impurity in most grades (content ≤1%), and is added in small amounts (≤5%) in some customized alloys. Its main function is to improve the alloy’s high-temperature creep resistance, rather than as a core corrosion-resistant element. Silicon (Si), manganese (Mn), and carbon (C) are all “strictly controlled elements”. The silicon content is usually ≤1% (to avoid reducing ductility), the manganese content is ≤1.5% (to prevent the formation of harmful carbides), and the carbon content is ≤0.08% (to reduce the risk of intergranular corrosion). These three elements need to be precisely controlled to ensure that they do not damage the alloy’s corrosion resistance and processing properties, while also assisting in improving the alloy’s welding stability
Different series of Hastelloy alloys exhibit significant differences in composition and properties. The representative models of the Ni-Mo series include B-2 and B-3, with core chemical compositions (mass fraction) of Ni: 65%-70%, Mo: 26%-30%, and Fe≤2%. They exhibit excellent corrosion resistance to reducing acids such as hydrochloric acid, hydrogen chloride, and acetic acid, but are not resistant to oxidizing media. The representative models of the Ni-Cr-Mo series, such as C-276 and C-2000, have core chemical compositions (mass fraction) of Ni: 50%-60%, Cr: 15%-20%, Mo: 10%-18%, and W: 3%-5%. They are suitable for both oxidizing and reducing environments, demonstrate excellent resistance to pitting and crevice corrosion, and are suitable for mixed acid environments. The representative model of the Ni-Cr-Fe series (G series), G-35, has core chemical compositions (mass fraction) of Ni: 45%-50%, Cr: 20%-25%, and Fe: 15%-20%. It is a dedicated material for strongly oxidizing environments (such as concentrated nitric acid and phosphoric acid) and exhibits outstanding resistance to localized corrosion. The representative model of the X series, Hastelloy X, has core chemical compositions (mass fraction) of Ni: 47%, Cr: 22%, Mo: 9%, and Fe: 18%. It combines high strength and oxidation resistance, is easy to weld and process, and is suitable for high-temperature structural components (such as aeroengine combustion chambers).
Based on its corrosion resistance characteristics across different series, Hastelloy alloy finds its application primarily in extreme corrosion and high-temperature environments. In the chemical and petrochemical industries, it serves as a core material for manufacturing equipment such as reactors, heat exchangers, and transmission pipelines, which often come into contact with corrosive media like sulfuric acid, nitric acid, strong alkalis, and chlorine compounds (such as chlorine gas in PVC production). In the field of environmental pollution control, it can be used in absorption towers and spray pipes of wet flue gas desulfurization (FGD) systems, effectively resisting corrosion from sulfuric acid and chlorides in flue gas. In the petroleum exploration and development sector, it is suitable for casings and wellhead devices in acidic oil and gas wells (containing H₂S and CO₂), particularly excelling in acidizing treatments (hydrochloric acid injection operations) of oil wells. Furthermore, it has wide applications in high-end manufacturing, such as high-temperature components in the aerospace industry (like rocket engine nozzles), bleaching equipment in the paper industry, and catalyst carriers in flue gas denitrification (SCR) systems.
The performance of Hastelloy alloys is directly determined by their chemical composition. Therefore, when selecting the type, the principle of “environmental matching” should be followed. If the application environment is a pure reducing acid environment (such as a hydrochloric acid storage tank), the Ni-Mo series (B-2, B-3) should be preferred. If it is an oxidizing/reducing mixed acid environment (such as a chemical mixing reactor), the Ni-Cr-Mo series (C-276, C-2000) should be the first choice. If both high temperature and strength are required (such as high-temperature structural components), the X series (Hastelloy X) can be selected. At the same time, parameters such as medium concentration, temperature, and pressure should also be considered during selection. If necessary, corrosion tests should be conducted to verify the material’s suitability to ensure that the selected alloy meets the actual usage requirements.
