What is Hastelloy C4?

Describe

HASTELLOY C4 alloy (UNS N06455) is the most (microstructurally) stable of the widely used nickel-chromium-molybdenum materials, which are well known for their resistance to many aggressive chemicals, in particular hydrochloric acid, sulfuric acid, and chlorides. This stability means that the alloy can be welded without fear of sensitization, i.e. the nucleation and growth of deleterious, second phase precipitates in the grain boundaries of the weld heat-affected zone (HAZ).

Hastelloy C4 alloy is a nickel-chromium-molybdenum alloy with outstanding high-temperature stability as evidenced by high ductility and corrosion resistance even after aging in the 1200 to 1900ºF (649 to 1038ºC) range. Hastelloy C4 alloy can be forged, hot-upset and impact extruded. Although the alloy tends to work-harden, it can be succesfully deep-drawn, spun, press formed or punched. Wrought forms of C4 alloy are furnished in the solution heat-treated condition unless otherwise specified. C4 alloy is solution heat-treated at 1950ºF (1066ºC) and rapid quenched.

Like other nickel alloys, Hastelloy C4 is ductile, easy to form and weld, and possesses exceptional resistance to stress corrosion cracking in chloride-bearing solutions (a form of degradation to which the austenitic stainless steels are prone). With its high chromium and molybdenum contents, it is able to withstand both oxidizing and non-oxidizing acids, and is resistant to pitting and crevice attack in the presence of chlorides and other halides. This Nickel-Chromium-Molybdenum alloy tolerates high temperatures and gives a design freedom in areas where weld geometry makes excessive heat build-up unavoidable. Resistance to general and localised corrosion and stress corrosion cracking is generally similar to Hastelloy C-276.

Hastelloy C4 Chemical Composition

Hastelloy C4 is a tungsten-free, low-carbon, low-silicon ternary alloy of nickel, chromium, and molybdenum with addition of titanium to stabilize residual carbon. It has an outstanding high-temperature stability, excellent resistance to aggresive aqueous environments and good weldability. It can be seen as a more stable and better weldable variant of Alloy C276.Thermal stability and weldability - Hastelloy C4 displays good ductility and corrosion resistance after long-time aging at 650 to 1040°C.

Hastelloy C4 (N06455) Hastelloy is an austenitic low carbon nickel-molybdenum-chromium alloy. The main difference between Nicrofer6616hMo and other earlier developed alloys of similar chemical composition is the low carbon, silicon, iron, and tungsten content. Such a chemical composition enables it to exhibit excellent stability at 650-1040°C, improve resistance to intergranular corrosion, and avoid edge-line corrosion susceptibility and weld heat-affected zone corrosion under appropriate manufacturing conditions. It resists formation of grain-boundary precipitates in weld heat-affected zones, and is apt for most chemical process applications without any additional post-welding heat treatment. It has excellent resistance to stress-corrosion cracking and to oxidizing atmospheres up to 1040°C. The chemical composition of Hastelloy(r) C-4 is outlined in the following table.

Hastelloy C4 Mechanical Properties

Hastelloy C4 has exceptional resistance to a variety of chemical process environments, including hot contaminated mineral acids, solvents, chlorine, and chlorine-contaminated media (organic and inorganic, dry chlorine, formic and acetic acids, acetic anhydride, seawater, and brine). The general corrosion resistance of Alloy C276 and Alloy C4 was essentially the same in many corrosive environments, except that in strongly reducing media like hydrochloric acid, Alloy C276 was better; but in highly oxidizing media, the opposite was true, that is, Alloy C4 was better. Alloy C4 offers good corrosion resistance to a wide variety of media including organic acids and acid chloride solutions.

Forging: Hastelloy C4 can be processed by hot forging and cold forging. The temperature range of hot forging is 1150-950℃, and the temperature range of cold forging is 760-870℃.

Heat treatment: Hastelloy C4 can be heat treated by solution treatment and aging treatment. The solid solution treatment temperature is 1150-900℃ and the aging treatment temperature is 760℃. Hastelloy C4 requires careful heat treatment to achieve optimal mechanical properties. The alloy is annealed at 1025°C-1125°C followed by rapid cooling through water or air quenching. The material is then age-hardened by heating to 870°C- 980°C for one hour, followed by water or air quenching.

Cold working: Hastelloy C4 in the work-hardened state of tensile strength and yield strength are high, so it is suitable for cold working, such as cold rolling, cold drawing and so on.

Corrosion resistance: Hastelloy C4 has excellent corrosion resistance in acids, alkalis, salts and other media, especially in chlorine-containing media corrosion resistance is more prominent. Hastelloy C4 is a highly corrosion-resistant material, standing up well to several corrosive environments, including oxidizing and reducing acid environments. It has superior resistance to pitting, crevice corrosion, and stress cracking. In addition to its resistance to acid and highly corrosive environments, Hastelloy C4 also resists intergranular cracking in welding.

Mechanical properties: Hastelloy C4 has a high yield strength and tensile strength, other mechanical property indicators including elongation, impact toughness. Hastelloy C4 is classified as a difficult-to-machine alloy due to its high elasticity modulus and work hardening. Therefore, special care must be taken when machining Hastelloy C4. Carbide-cutting tools are recommended to minimize tool wear and prolong tool life. High-speed steel tools are not recommended since they wear quickly.

Performance: Hastelloy C4's main advantage is its excellent corrosion resistance and resistance to thermal oxidation, but also has good mechanical properties and processability.

Welding: Hastelloy Welding material grades for Hastelloy C4 include ERNiCrMo-7 and ENiMo-7. Careful attention needs to be given when welding Hastelloy C4. The alloy can be readily welded, but the filler material selection is crucial to obtain optimal mechanical properties. TIG welding is the most common method of fusing Hastelloy C4 due to its low-heat input, allowing for successful welding without cracking. Moreover, post-welding heat treatment is required for Hastelloy C4 to reduce residual welding stress and restore mechanical properties.

Hastelloy C4 Applications

Hastelloy C4 has become a top choice among industries requiring high-performance alloys due to its unique mechanical and physical properties, exceptional corrosion resistance, and versatility. We have learned how Hastelloy C4 stands out in various applications, from its composition to its mechanical and physical properties. Whether operating in the chemical processing, aerospace, or pharmaceutical industry, Hastelloy C4 offers excellent corrosion resistance to help your equipment last longer and perform better.

Hastelloy C4 is used in various industries, including chemical processing, aerospace, power generation, petrochemical, pharmaceuticals, and marine applications. This alloy suits sulfuric acid, hydrochloric acid, and acetic acid applications. It is commonly used in chemical reactors, heat exchangers, furnace components, and catalyst support grids.