Metallurgical Investigation of Flying Shear Blades at Hot Rolling Rebar Mills.

Divide shear assembly in a rebar rolling mill performs the function of cutting rebars into 72 m length. It uses two shear blades mounted on rotating arms, which rotate in directions opposite to each other and cut the rebars passing in between. These blades hit the rebars at a location from two opposite sides for cutting, and their cutting edges gradually become blunt after cutting of approximately 4000–5000 tons of rebars. Replacing the blunt blades results in interruption in operation leading to increased down time and resulting decreased productivity. A thorough metallurgical root cause analysis was carried out to improve the service life of shear blades. Damages on shear cutting blades were analyzed after trimming of 4000–5000T on thermo-mechanically treated rebars. Chemical analysis revealed that the material of the shear blade was AISI D2, which is a widely used material for cutting of rebars in cold conditions. AISI D2 is a high carbon grade with high Cr content. Microstructural examination revealed large fraction of coarse carbides in tempered martensitic matrix. However, excessive number of coarse carbides imparts brittleness which can limit its applications under severe conditions. The used blade exhibited chipping off materials at the cutting edge in brittle manner. The damaged blades and subsurface damage were examined using Profilometer, SEM, XRD and other metallography techniques. After detailed metallurgical investigation new material was developed to improve the (performance) of the cold shear blades. [ABSTRACT FROM AUTHOR]