GB441775A - Improvements in and relating to the production of sheets, bands and objects of metal for electrical purposes - Google Patents

Abstract

Metal sheet or wire is treated to obtain large crystal grains of 1/2 to 10 sq. cms. and improved electrical properties, e.g. small power loss, high magnetic induction and high maximum permeability by a series of hot or cold deformation by forging, rolling, pressing or drawing with interposed annealing, then by critical internal straining, and by a final recrystallizing heat treatment at a critical temperature, the silicon content of the metal, ,5-5 per cent determining in inverse ratio the degree of deformation which varies from 35 to 5 per cent and also determining the final straining reduction 12 to ,3 per cent and also determining the recrystallizing temperature treatment at from 900-1250 DEG C. all in accordance with the tables set out. The heating between the deformations is from 800-850 DEG C. After each intermediate heating and/or after the recrystallizing heating the steel may be quenched in water or other suitable cooling liquid and then again heated to 500-800 DEG C. Prior to the final critical straining, the normalizing heat treatment may be above or near the A3 point to 900-1250 DEG C., depending on the silicon content, between ,5 and 5 DEG . The critical straining, particularly with high silicon content metal, may be brought about by heating above 900 DEG C. and quenching in water at 0 DEG C., or in a cooling liquid at below 0 DEG C. After the recrystallizing heat treatment it may be held at 700-850 DEG C. for e.g. 10 hours to increase the permeability.