The banded structure of ASTM A573 Gr 70 steel plate

ASTM A573 Gr 70 steel plate contains many alloying elements such as Cr, Mn, Si, etc. The segregation of alloying elements is the main reason for the formation of banded structure. The banded structure consists of primary banded structure and secondary banded structure. The primary band structure is the original band structure, which is caused by the primary dendrite segregation during the nucleation of the micro-structure of continuous casting billet; the secondary band structure is the structure formed by the stacking of the pre-eutectoid ferrite band and pearlite band along the rolling direction of ASTM A573 Gr 70 steel after rolling or heat treatment on the basis of the primary band structure.

Secondary banded structure can be reduced or eliminated by optimizing the heat treatment process of ASTM A573 Gr 70 steel plate, while primary banded structure can hardly be eliminated by conventional means. It can be improved and eliminated by electroslag remelting, improving the purity of A573 Gr 70steel, electromagnetic stirring, increasing the superheat of steelmaking and soft reduction. Serious ribbon structure will affect the homogeneity of steel structure, which will greatly reduce the mechanical properties of ASTM A573 Gr 70 steel.

The composition segregation band in the core of A573 Gr 70 steel after rolling and heat treatment is secondary band structure, which destroys the uniformity of microstructure and reduces the mechanical properties of the ASTM A573 Gr 70 steel plate. Normalizing heat treatment can make alloy elements fully soluble in the grain interior, rather than enriched in the grain boundary, greatly alleviate the formation of segregation and improve the strength and toughness matching of ASTM A573 Gr 70 steel plate.