This work demonstrated the viability of friction stir welding for the welding of medium-Mn steels when used as cryogenic vessel materials for liquefied gas storage.We used an intercritically annealed Fe-7Mn-0.2C-3Al(wt.％)steel with a dual-phase(α'martensite and γR retained austenite)nanolaminate structure as a base material and systematically compared its microstructure and impact toughness after friction stir and tungsten inert gas welding.The friction stir welded specimen exhibited a large amount of γR phase owing to a relatively low temperature during welding,whereas the tungsten inert gas welded specimen comprised only the α'phase.Furthermore,the friction stir welded steel exhibited a tuned morphology of nanoscale globular microstructure at the weld zone and did not exhibit any prior austenite grain bound-ary due to active recrystallization caused by deformation during welding.The preserved fraction of γR and morphological tuning in the weldment improved the impact toughness of the friction stir welded steel at low temperatures.In the steel processed by tungsten inert gas welding,the notch crack propa-gated rapidly along the prior austenite grain boundaries-weakened by Mn and P segregations-resulting in poor impact toughness.However,the friction stir welded steel exhibited a higher resistance against notch crack propagation due to the slow crack propagation along the ultrafine ferrite/ferrite(α/α)inter-faces,damage tolerance by the active transformation-induced plasticity from the large amount of γR,and enhanced boundary cohesion by suppressed Mn and P segregations.

Mun Sik Jeong;Tak Min Park;Dong-Il Kim;Hidetoshi Fujii;Hye Ji Im;Pyuck-Pa Choi;Seung-Joon Lee;Jeongho Han

Division of Materials Science and Engineering,Hanyang University,Seoul 04763,Republic of Korea;Department of Advanced Materials Engineering,Korea Polytechnic University,Siheung 15073,Republic of Korea;Joining and Welding Research Institute,Osaka University,Osaka 567-0047,Japan;Department of Materials Science and Engineering,Northwestern University,Evanston,IL 60208,USA;Department of Materials Science and Engineering,Korea Advanced Institute of Science and Technology,Daejeon 34141,Republic of Korea

材料科学技术（英文版）

[1]Mun Sik Jeong;Tak Min Park;Dong-Il Kim;Hidetoshi Fujii;Hye Ji Im;Pyuck-Pa Choi;Seung-Joon Lee;Jeongho Han-.Improving toughness of medium-Mn steels after friction stir welding through grain morphology tuning)[J].材料科学技术（英文版）,2022(23):243-254

intercritically,weldment

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