Abstract
Based on pure melting, multi-type and fine-microstructure design, a ferritic steel with an outstanding combination of cryogenic impact toughness and strength was fabricated. The microstructure was characterized by means of optical microscopy, electron back-scattered diffraction and transmission electron microscopy. The steels with different final cooling temperatures of 663 °C and 560 °C show ferrite and perlite microstructure, and ferrite grain size can be refined from 3.15 µm to 2.67 µm by lowering the final cooling temperature from 663 °C to 560 °C. Moreover, a higher volume fraction of acicular ferrite and polygonal ferrite can be obtained for a lower final cooling temperature of 560 °C. Hence, the cryogenic impact toughness can be enhanced, and the brittle failure can be suppressed, even at –110 °C, showing a higher impact toughness compared with other ferritic steels.
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