Metallurgical source of cryogenic intergranular fracture of Fe-38Mn austenitic alloy

• Published in: Journal of iron and steel research, international Vol. 7; no. 1; pp. 31 - 35
• Main Authors: Fu, R.-D.,--, Zheng, Y.-Z.,--, Li, S.-H.,--, Zhou, H.-H.,--
• Format: Journal Article
• Language: English
• Published: Yanshan University, Qinhuangdao 066004, China%Central Iron & Steel Research Institute, Beijing 100081, China%Tsinghua University, Beijing 100084, China 01.05.2000
• Subjects: rich Mnaustenitic alloy; cryogenic intergranular fracture; grain boundary segregation; electroslag remelting
• ISSN: 1006-706X

SEM and Field emitting TEM-EDAX were used to investigate the fracture surface of series impact specimens and the grain boundary chemistries of VIM (vacuum-induction-melted) Fe-38Mn austenitic alloy before and after ESR (electroslag remelting). The quantity and the size of inclusions were also examined. The results show that the VIM Fe-38Mn austenitinic alloy water-quenched from 1100 deg C undergoes an obvious ductile-to-brittle transition, and the impact work at ambient temperature is 242 J, the corresponding fracture surface exhibits a dimple character. However, the impact work at 77K of VIM alloy is only 25 J and the fracture mode is IGF (intergranular fracture). After ESR, the impact work at ambient temperature is 320 J and the fracture surface exhibits a character of "volcano lava" (meaning excellent toughness). The impact work at 77K is up to 300 J and the fracture mode is microvoid coalescence mixed with quasi-cleavage. The segregation of Mn is not found in all specimens, but the segregation of S is observed, and the S segregation is decreased after ESR. The examined results of inclusions show that ESR reduces the quantity and improves the morphology of inclusions. From the above results it can be seen that the cryogenic IGF of VIM Fe-38Mn austenitic alloy is related to the S segregation at grain boundary. After ESR the decrease in the quantity and size of inclusion results in the increase of the impact work at ambient temperature, while the restriction of IGF is related to the decrease in the total level, and hence in the grain boundary segregation of S.