Effect of cooling rate on bending behavior of 6.5 wt.% Si electrical steel thin sheets fabricated by strip casting and rolling

Thin sheets of 6.5 wt.% Si electrical steel with the thickness of 0.35 mm were fabricated by strip casting and rolling. Influences of different cooling processes after annealing, including air cooling, water quenching, brine quenching and brine ice quenching, on the bending behavior at room temperature were systematically investigated. The results showed that with increase of the cooling rate, the room-temperature bending properties could be much improved, the fracture deflection values of the air cooled, water quenched, brine quenched and brine ice quenched specimens were measured to be 2.82 mm, 3.36 mm, 4.17 mm and 5.85 mm, respectively, moreover, obvious plastic deformation could be observed in the brine ice quenched specimen. The fracture modes of the air cooled and water quenched specimens were trans-granular cleavage fracture, while for the brine and brine ice quenched specimens, because the phosphorus segregation at grain boundary during high temperature could be preserved to room temperature by rapid quenching, the fracture modes were inter-granular fracture. The ordered phases in all specimens were observed and analyzed by TEM. The average sizes of B2 ordered domains in the air cooled, water quenched, brine quenched and brine ice quenched specimens were measured to be 107 nm, 2.7 nm, 1.6 nm, and 12 nm, respectively, and the DO3 ordered domain with the average size of 2 nm could only be detected in the air cooled specimen. Therefore, the reduction of the order degree caused by fast cooling was believed to be mainly responsible for the improvement of bending properties, which might have led to significant decrease of the order-strengthening effect. (C) 2015 Elsevier Inc. All rights reserved.