Design of novel Fe–Mn–Ni cryogenic steel: microstructure-property relationship during simulated welding

Abstract

We describe here the microstructural evolution during simulation of welding thermal cycles in novel Fe-Mn-Ni cryogenic steel and elucidate the mechanism of cryogenic toughness. The original microstructure was tempered martensite and ∼ 10% retained austenite. Electron backscattered diffraction indicated that the frequency of large-angle boundaries with misorientation > 15°was similar at peak temperatures of 1320, 870 and 760°C. The volume fraction of retained austenite determined by X-ray diffraction was ∼ 11% at 760°C, 9% at 870°C and 1% at 1320°C. Retained austenite was film-like near the bainite lath, and it was enriched with Mn and Ni at peak temperatures of 760 and 870°C. The enrichment with Mn and Ni stabilised the austenite and softened the bainitic matrix. The higher volume fraction of stable retained austenite was the dominant factor responsible for superior cryogenic toughness at the peak temperature of 760°C.

Optimization of Mechanical Properties of High-Manganese Steel for LNG Storage Tanks: A Comprehensive Review of Alloying Element Effects

“…As the Mn content increased, a twinning-induced mechanism became apparent, which enhanced the low-temperature toughness of the 24Mn and 26Mn steels in comparison to the 22Mn steel. Sohn et al [90] investigated the mechanical properties of four high-manganese steels, Fe- (19,22) Mn and Fe- (19,22) Mn-2Al, at both room and low temperatures. Their findings indicated that with a decrease in the testing temperature, the impact absorption energy of the 19Mn and 22Mn steels diminished significantly.…”

“…Thanks to its face-centered cubic (FCC) crystal structure, high-manganese steel maintains its ductility without undergoing a ductile-to-brittle transition across a broad temperature spectrum, from room temperature (RT) down to liquid nitrogen temperature (LNT, −196 • C) [18,19]. This inherent characteristic ensures the material's cryogenic toughness to a considerable degree.…”

“…Figure13. A comparison of the yield strength increase in Fe-(18)(19)(20)(21)(22)Mn-(0.6-0.9)C cold strips as a function of microalloying additions. Reproduced with permission from ref [128]…”

Evolution of inclusions in novel cryogenic high-Mn austenitic steel weld metal with cerium addition

“…Recently, novel cryogenic high-Mn austenitic steels have been developed with their excellent cryogenic toughness and remarkable economic advantages for replacing traditional 9% nickel cryogenic steels, austenitic stainless steels and invar alloys for the manufacture of liquefied natural gas (LNG) tanks [1,2]. The high-Mn cryogenic steel in the fabrication of LNG tanks should be connected by welding, and submerged arc welding is one of the most widely used welding methods in high-Mn cryogenic steel [3].…”