| Natural gas is a promising alternative energy source,and may well be the fastest-growing major fuel in coming decades;its resource base is vast and widely dispersed geographically,and its environmental advantages are widely recognized.Because of this,the storage and transportation of liquefied natural gas(LNG)is increasingly important,but technologically challenging.For LNG tank materials,aluminum alloys,austenitic stainless steels,9%Ni steel,Invar alloys,and others have been successfully used.But all of these materials have disadvantages,such as costly plate or welding consumables,low design strength,welding difficulties,and others.High-Mn alloys may offer an attractive alternative.Manganese and carbon are austenite stabilizers in steel,and austenitic Fe-Mn-C alloys that are stable at LNG storage temperatures can be made at relatively low cost.High-Mn alloys can combine high strength with excellent toughness at cryogenic temperature.If efficient welding consumables are developed for manganese-based alloys,the total construction costs of LNG tanks may be significantly reduced.Based on this,this paper made a preliminary theoretical study on the application of high manganese steel in cryogenic storage tanks and obtained the following results.(1)Based on the effect of alloying elements on the properties of high manganese steel and the influence of the stacking fault energy on the deformation mechanism,the alloy composition of the experimental steel was designed.The microstructure and the segregation of C and Mn in the experimental steel after forging were studied.The average grain size of forged steel was 32.8?m,and C is enriched at grain boundaries.(2)The thermal deformation behavior of the experimental steel was studied to know the recrystallization law and deformation resistance model for the experimental steel.(3)The microstructure and properties of the experimental steel were analyzed after hot rolling.The microstructure of the experimental steel rolled below the recrystallization temperature is deformation band organization,and the recrystallized structure is more uniform with an average grain size of 17.3?m.When the finishing rolling temperature is below the recrystallization temperature,the strength of the experimental steel is higher,the impact toughness at low temperature is poorer,and the experimental steel rolled above the recrystallization temperature is exactly the opposite.(4)The experimental steel with a finish rolling temperature above the recrystallization temperature has lower strength.Based on this,the aging treatment is set according to the phase diagram.The results show that the strength increases after aging treatment,the impact toughness decreases,and the grain size increases.After aging treatment,the C element changes from a banded distribution to a diffuse distribution with a small amount of enrichment at the grain boundary.The pinning effect of the C atom on the dislocation increases the strength,and the enrichment at the grain boundary decreases the impact toughness.Through the research of this article,the experimental steel meets the requirements of the steel for LNG storage tank in terms of impact toughness and is difficult to meet the needs of use in strength,and need to do further research on the rolling process and alloy composition. |
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