Effect of final-annealing regimes on the magnetic properties of unalloyed electrical steel

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Anneallng temperature, "C
Time, mln
Fig. I. Hagnetic properties with different temperatures of final annealing and a holding time of 2 h (a) and with different holding times and an annealing temperature of 8300C (b).
0,59 2,08 1,98 0~84 2,46 0,75
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0,75 1,19 1,05 1,04 2,17 1,05 0,54 2,78 1,42 1,02 2,44 0,79 0,57 2,2~: 1,34 1,13 2,08 0,94
where lhk ~ is the integral intensity of the x-ray line. The level of the magnetic properties of the metal before the final annealing was as follows: from 1.52 to 1.57 T for magnetic induction; from 12.0 to 14.0 W/kg for core loss. After the final annealing, done according to specifications, magnetic induction had increased by 0.05-0.10 T and core loss had decreased by 6.0-8.0 W/kg. Magnetic induction did not change with a change in annealing temperature from 550 to 750~ but decreased by 0.03-0.05 T (Fig. la) with an increase in annealing temperature to 830~ The anisotropy of magnetic induction (~B25oo) increased by 0.003-0.005 T up to annealing temperatures of 650-700~ and then remained nearly constant. Core loss decreased by 3.1-4.4 W/kg with an increase in temperature to 750~ and then increased slightly by 0.2-0.8 W/kg. Results of study of the microstructure show that the greatest variation in grain size, from 4 to 9 points, is seen with annealing temperatures of 550-650~ and regions of unrecrystallized metal are present. A microstructure with a coarse 3-4-point grain, uniform through the thickness of the metallographic section, was obtained in the annealing temperature range 750-800~ The results of the x-ray diffraction analysis (Table i) show that the 200, 332, and, especially, 222 orientations have the maximum intensities at an annealing temperKaraganda Metallurgical Combine. 1984. 0026-0894/84/0102-0027508.50 9 1984 Plenum Publishing Corporation 27 Translated from Metallurg, No. I, pp. 26-28, January,
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75 JO q5 60 75 90 705 120 Time, m ~
Fig. 2. Anisotropy of magnetic induction with different holding times (lot 325) and annealing temperatures of 830~ (i) and 750~ (2). TABLE i. Dependence of the Parameter OhkZ on Annealing Temperature and Holding Time-
ROLLED PRODUCTS
EFFECT OF FINAL-ANNEALING REGIMES ON THE IiAGNETIC PROPERTIES OF UNALLOYED ELECTRICAL STEEL V. V. Medvedev, V. I. Sidorkin, P. M. Mikhalev, and B. A. Fel'dman UDC 621.771.237:621.785.3
The Karaganda Metallurgical Combine produces cold-rolled unalloyed isotropic electrical (dynamo) steel of grades 2011-2012. The steel is delivered to consumers in the form of sheet 0.5 mm thick and from I00 to 400 mm wide. The steel is delivered in the unannealed state, i n accordance with GOST 21427.2-75. In accordance with the specifications, the magnetic properties of the steel are determined on specimens which have received a final annealing in the regime: heating in a protective atmosphere to 830~ holding for 2 h, cooling to 600~ at a rate of 50 deg C/h followed by cooling in the furnace with the furnace turned off. With the existing technology, about 4% of the metal has a magnetic induction (B25oo) lower than 1.60 T after the final annealing, which does not meet the requirements of GOST 21427-2.75. Moreover, analysis of the results of tests of 362 lots of metal showed that more than 50% of the metal corresponds to grade 2012 with respect to core loss (P1.s/5o), while only about 30% corresponds to this grade with respect to magnetic induction. According to the available data, annealing the unalloyed isotropic steel at 830~ does not ensure an optimum combination of magnetic properties. We undertook a study of the effect of the regimes of final annealing on the formation of the magnetic properties of the finished metal. Tests were conducted on nine gross heats of steel containing 0.25-0.40% silicon. Eight to ten sets of specimens measuring 0.5 • 30 • 280 mm were taken from each heat along and across the rolling direction. The final annealing was done in a protective atmosphere (94-96% N2; 4-6% H2). The annealing temperature was changed from 550 to 830~ holding time was changed from 15 min to 2 h, and cooling was done by one of three variants: at rates of 50 or i00 deg C/h and with the turned-off furnace (uncontrolled cooling). The magnetic properties were determined on mixed specimens in a four-pole Epstein unit on a U-5033 device before and after annealing. The formation of the texture was studied on the test specimens by comparing integral intensities of x-ray lines. The method of fixed pulse-counting time was used on a DRON-2 diffractometer in molybdenum radiation. The fraction of preferred orientations in the rolling plane was determined about the perimeter ~ (the standard was carbonyl iron powder annealed at 750~ for i0 h): ~ = lhk~ for the specimen/lhk z for the standard,