| 摘要 |
<p>The present invention provides a steel bar with an excellent brittle crack spreading stopping performance and a manufacturing method thereof. When the metal tissue is observed with an electric back scattering diffraction analysis method (EBSP method) at an area of a position between t/8 and t/4 in the depth of the steel bar, a formula (1) and a formula (2) are satisfied. In the formula (1), D represents an average equivalent circle diameter (mu m) of the grains which are surrounded by a large angle crystal boundary with a crystal azimuth difference that is larger than 15 DEG, wherein the azimuth difference is between adjacent crystals and is measured through the EBSP method. R represents the proportion of a random crystal boundary in the large angle crystal boundary (area%). Formulae: D is smaller than or equal with 8 mu m (1), and R is larger than or equal with 50 area% (2).</p> |
