First, the meaning is different: the banded structure in metal is the structural defect produced in the process of casting, forging and rolling in iron and steel smelting. In fact, the distribution of alloying elements is uneven, and it is banded in a certain direction, and the segregation between alloying elements is serious.
2. Different microstructure: the mechanical properties of the material will be anisotropic, and the area shrinkage will be reduced, especially the transverse properties, transverse impact toughness and longitudinal impact toughness are twice different. Severe banded structure will lead to serious problems such as uneven hardness and insufficient plastic toughness of the final parts.
The fiber structure is generally common, and the alloy elements are distributed in the fiber along the rolling direction, and the mechanical properties in the transverse and longitudinal directions are different. It affects or reduces the material properties to a lesser extent than the segregation of banded distribution.
Causes of fibrous tissue formation
The fibrous structure caused by element segregation, including dendritic segregation and banded segregation, is a common defect of this steel and an important reason for the early failure of forging dies. The upper and lower sides of the picture are normal quenched structures, and the middle is a mixed structure of troostite (black) and martensite (gray needle). The hardness imprint shows that the hardness of the black region of troostite is lower than that of the gray martensite region. Element segregation zone leads to additional structural stress during quenching, which often cracks the die during quenching.