06Ni9DR

06Ni9DR is a high-performance nickel-alloy structural steel specifically designed for ultra-low-temperature service. The designation carries precise technical meaning: "06" indicates an average carbon content of approximately 0.06%, classifying it as a low-carbon steel, which enhances weldability and toughness; "Ni9D" signifies a nickel (Ni) content of about 9%, with "D" standing for "low temperature" application, indicating excellent resistance to brittleness; and "R" stands for "Rongqi" (vessel), denoting its dedicated use in pressure vessel manufacturing. Therefore, 06Ni9DR refers to a 9% nickel-containing steel plate intended for cryogenic pressure vessel applications.

This steel plate is primarily used in the fabrication of large-scale welded pressure vessels operating at extremely low temperatures down to -192°C (liquid nitrogen temperature) or even approaching -196°C. Typical applications include inner tanks of full-containment liquefied natural gas (LNG) storage tanks, liquid hydrogen storage and transportation systems, cryogenic heat exchangers in air separation units, and experimental equipment in scientific research facilities. Under such extreme conditions, most steels lose ductility and are prone to brittle fracture. In contrast, 06Ni9DR, due to its high nickel content, significantly lowers the ductile-to-brittle transition temperature, enabling the steel to maintain good plasticity and impact toughness even at liquid nitrogen or liquid hydrogen temperatures. It is one of the most widely used high-toughness materials in ambient-pressure cryogenic vessels.

Key characteristics of 06Ni9DR include exceptional low-temperature impact toughness (ensuring an average Charpy V-notch impact energy of ≥27 J at -192°C), good weldability (requiring specialized welding consumables and procedures), excellent cold-forming capability, and moderate strength. Its microstructure consists of a stable austenite-ferrite duplex phase, providing superior crack resistance and fatigue performance. Manufacturing requires clean steelmaking, precise controlled rolling, and normalizing heat treatment to ensure uniform and stable mechanical properties.

The current national standard for 06Ni9DR is GB/T 3531-2023 "Steel Plates for Low-Temperature Pressure Vessels", released in 2023, replacing the previous GB/T 3531-2014 edition. This updated standard formally includes 06Ni9DR for the first time, establishing systematic requirements for chemical composition, mechanical properties, impact testing at -192°C, ultrasonic inspection, and heat treatment conditions.