The invention relates to the technical field of steel for
liquid ammonia storage tanks, in particular to 5Ni steel for a
liquid ammonia storage tank and a manufacturing method of the 5Ni steel. The invention discloses a high-strength and high-
toughness steel which is composed of the following chemical components in percentage by weight: 0.01%-0.12% of C, 0.10%-0.30% of Si, 0.30%-0.80% of Mn, 4.75%-4.99% of Ni, 0.01%-0.10% of Mo, less than or equal to 0.005% of S, less than or equal to 0.008% of P and the balance of Fe and inevitable impurities. Converter + LF + VD refining is adopted for
smelting, and accurate control over steel components and the gas content in steel is guaranteed;
casting and slab
slow cooling are protected in the whole
continuous casting process, and the
internal quality of a
casting blank is guaranteed; refining of an initial structure is guaranteed through controlled rolling; and after-rolling heat treatment adopts a process of offline
quenching, two-phase region
quenching and
tempering, so that the low-temperature
toughness of the steel plate is improved, and the
yield ratio is effectively reduced. The yield strength is larger than or equal to 390 MPa, the tensile strength is 530-710 MPa, the-120 DEG C V-type
impact energy is larger than or equal to 100 J, and the side expansion is larger than or equal to 1.0. The
nickel-saving type design is adopted, the Ni content is smaller than 5%, the requirement for stress
corrosion prevention of the
liquid ammonia storage tank is met, and various mechanical properties are excellent.