The effect of microstructure anisotropy on low temperature fracture of ultrafine-grained iron

This papers deals with the character on low (−180 °C) temperature fracture of iron. Microcrystalline and ultrafine-grained (UFG) iron rods were investigated. To obtain UFG material 20 mm in diameter iron rod was hydrostatically extruded (HE) in two steps: from 20 to 12 mm and from 12 to 8 mm. Because of microstructure anisotropy caused by HE mini-disc and mini-beam samples were cut off from perpendicular and longitudinal cross-section of the rods. Microcrystalline rod fractured in brittle manner at low temperature for both cross-sections, but in UFG iron fracture character depended on grain's shape. For samples were crack propagates parallel to the grain's elongation axis intercrystalline fracture occurred. For mini-beams were crack propagates crosswise to the grain elongation axis transcrystalline fracture occurred and force deflection curve was similar to those obtained for room temperature.