Process for heat treating an electrical steel sheet

摘要

Heat treatment method for steel strip comprises continuous annealing followed by cooling in three stages. In the first stage the strip is cooled to a temperature 50[deg]C above the Curie temperature. In the second stage it is cooled to 80[deg]C below the Curie temperature and in the final stage with a cooling gradient up to 85[deg]C/s. Heat treatment method is used for steel strip with an Si and Al content (wt%) given by the relationship: 0.9=Si + 2 x Al =1.8, an Mn content up to 2.5 wt%, up to 1 wt% of each of P, Cr and Ni and up to 0.1 wt% of each of C, N and S. The method comprises continuous annealing followed by cooling in three stages. In the first stage the strip is cooled to a temperature 50[deg]C above the Curie temperature with a cooling gradient of -38[deg] to -1[deg]C/s. In the second stage it is cooled to 80[deg]C below the Curie temperature. The cooling gradient has an upper limit (CR2MAX) given by: CR2MAX = pi (cos(2(TBAND - TC)pi /26>((TBAND - TC)(pi /26>)2> + 1)) - 1) - pi . Its lower limit (CR2MIN) is given by: (CR2MIN) = 3pi (cos(2(TBAND - TC)pi /26>((TBAND - TC)(pi /26>)2> + 1)) - 1) - pi . In the final stage the cooling gradient is up to 85[deg]C/s.