Effect of intercritical quenching soaking time on cryogenic toughness and internal friction characterization of 9Ni steel

Quenching, intercritical quenching and high-temperature tempering of 9Ni steel is widely used in large-size and high-capacity liquefied natural gas storage tanks due to its excellent mechanical properties at low temperatures. This paper studied the microstructure, internal friction and mechanical properties of different intercritical quenching heat soaking times on the cryogenic toughness of 9Ni steel. The effect of martensitic strip thickness change on thermal stability and morphology of reversed austenite after intercritical quenching heat soaking time of 9Ni steel was revealed. The findings show that the thickness of the martensitic slats increases by 4.5μm when the intercritical quenching of steel is conducted for 50 min, and the maximum concentration of Ni and Mn reaches 13.5% and 10.25%, respectively. The volume fraction of thin film reversed austenite is about 5%. Different frequency under the condition of isothermal Snoek-Kê-Köster peak changes shows there will be a loss of mechanical energy in the process of phase transition. They are important factors for the maximum volume fraction of 9Ni steel film reversed austenite and the significant improvement of cryogenic toughness.