Microstructural investigations of 0.2% carbon content steel Sajjad Tollabimazraehno JKU – Johannes Kepler University Linz, Austria Christian Doppler Laboratory for Microscopic and Spectroscopic Material Characterisation

Samples 0.2% Carbon, hypoeutectoid composition Consider a composition to the left of the utectoid, between 0.022 and 0.76 wt% C Cooling an alloy of this composition vertical line

Sample 1 (S1): Martensite, 0.2% RA Sample 2 (S2): temp. Martensite,0.3% RA Sample 3 (S3): Bainite, 16.6% RA Sample 4 (S4): 50% M, 50% B, 11.1% RA Sample 5 (S5): 65%T.M, 5%B, 20%M, 8.2%RA Sample 6 (S6): 65%T.M, 20%B, 5%M, 8.4% RA

Nano Indentation Hardness : S1 > S2 > S6 > S4 > S3 >S5 Sample 1 (S1): Martensite Sample 2 (S2): temp. Martensite Sample 3 (S3): Bainite Sample 4 (S4): 50% M, 50% B Sample 5 (S5): 65%T.M, 5%B, 20%M Sample 6 (S6): 65%T.M, 20%B, 5%M Hardness : S1 > S2 > S6 > S4 > S3 >S5

Electron Backscatter Diffraction: Grain Size 50 µm S3 S4 S5 S6

Phases S1 S2 S3 S4 S5 S6

Misorientation Angle Distribution Kurdjomov-Sachs <111>α || <110>ɣ S5 S6 Nishiyama-Wassermann <110>α || <211>ɣ A.-F. Gourgues, H. M. Flower, and T. C. Lindley Materials Science and Technology Jan. 2000 Vol. 16

Grain boundaries S1 S2 S3 S4 S6 S5 Most boundaries have MA 47°-60° Inside the grains with low MA MA 60° related to twin relation

Conclusions EBSD is very accurate to measure the grain size, even for fine microstrucutures like temp. martensite and provides information about larger areas than TEM The hardness of samples is influenced by the grain size The martensite variants were frequently twin related and formed from the same {111}ɣ. The misorientation relationship in lower bainite and martensite were consistent with near Kurdjomov-Sachs orientation relationship.