RU2137849C1 - Process for production of anisotropic electric steel - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: process includes smelting, hot rolling, decarbonization, double cold rolling, retarded heating during primary recrystallization period, and final high- temperature annealing. To increase magnetic properties and stabilize secondary recrystallization of steel, heating temperature of hot rolling (T) is set in dependence of aluminum content in steel expressed by relationship: T = 1190 + 4x10% Al ± 10^{3 °}C . Coiling is accomplished at 520- 570 C. Retarded heating is effected (i) after final cold rolling with rate 5- 15 C/hr over a temperature range of 400 to 700 C with probability of decarbonization in smelting stage or (ii) after heat treatment of strip plate with initial, intermediate, or final thickness and probability of addition of 0.2-0.7% of copper to steel. EFFECT: enhanced process efficiency. 3 cl, 2 tbl

Description

 The invention relates to ferrous metallurgy, in particular to the production of sheet electrotechnical steel. According to operating conditions in the transformer, this steel requires high magnetic induction and low power losses during magnetization reversal (specific losses). A necessary condition for obtaining the required level of magnetic properties is the presence of a perfect rib texture in steel, which is formed during slow heating during high-temperature annealing (WTO) under conditions when normal grain growth is inhibited by the so-called inhibitory phase. The role of the inhibitory phase can be played by dispersed particles of AlN, MnS, BN, etc.

Depending on the type of phase, technological schemes for steel production also differ. So, for steel with sulfide inhibition, a distinctive feature of the technology is the high-temperature (> 1400 ^o C) heating of the slabs before hot rolling in order to dissolve MnS and its subsequent isolation in the form of dispersed particles [1]. The indicated operation is extremely low-tech, requires special equipment and leads to increased metal consumption.

 Steel with nitride inhibition in this respect is more preferable, since it does not require high heating temperatures before hot rolling [2]. However, in the presence of only one inhibitor (for example, AlN), these steels exhibit instability of secondary recrystallization and, as a result, a significant dispersion of magnetic properties between individual melts and a lower yield of higher grades of steel. It was found that the deficiency of the inhibitory phase in such steels does not allow obtaining, during primary recrystallization, a sufficient amount of {111} <112> texture, which is necessary for the successful growth of rib grains during the subsequent secondary recrystallization. Meanwhile, it is known that copper is an effective inhibitor that enhances the orientations of {554} <225> and {110} <001> in the texture of primary recrystallization. The addition of copper in the amount of 0.24 - 0.75% in steel with sulfide inhibition is recommended by the patent [3].

However, experiments have shown that on steels with nitride inhibition (high Al content and low S) processed by conventional technology with decarburization annealing (OO) in the final thickness, the effect of Cu on the texture and magnetic properties did not appear. In mild steel, an improvement in the texture under the influence of copper is observed only upon slow heating or holding in the primary recrystallization interval [4], with the largest development of a favorable orientation {111} <112> (or {554} <225>) corresponding to the release of particles with a size of 20-30 mm at a density of 3 • 10 ¹⁴ cm ^-3 .

Slowing down the heating during primary recrystallization is proposed in the method [5] (patent prototype), according to which the electrical steel with the addition of Se or S before decarburization annealing (OO) is heated for 0.5-10 minutes at 600-650 ^o C. However, experiments have shown that on steel with AlN as an inhibitor, the use of this technique alone does not make it possible to improve magnetic properties.

In the present invention, the goal is to obtain high magnetic properties and stable secondary recrystallization by strengthening the orientation {111} <112> in steel with nitride inhibition (without copper or with the addition of 0.3-0.7% Cu) is achieved by changing the technological parameters of the entire redistribution. To obtain a sufficient amount of phase-forming impurities — Al and N in the solid solution — the temperature of heating the slabs before hot rolling Tn is set depending on the Al content: Tn = 1190 + 4 • 10 ³ % Al ( ^o C), and the temperature of the winding after hot rolling decreases up to 520-570 ^o C. The separation of dispersed nitrides responsible for the formation of the {111} <112> texture is carried out before the initial recrystallization begins, during slow (5-15 ^o / h) heating in the range of 400-700 ^o C of the cold-rolled metal of the final thickness at the WTO. Decarburization is carried out by evacuation of molten steel, or by heat treatment of the tackle in the initial, intermediate or final thickness (after aging).

Thus, the hallmarks of the proposed technical solution are:
1. The regulated temperature for heating slabs before hot rolling, depending on the aluminum content in the steel.

2. Low temperature of the winding (520-570 ^o C).

3. Slow (5-15 ^o / h) heating of the cold-deformed metal in the range of 400-700 ^o C during the WTO for the allocation of dispersed AlN before primary recrystallization.

 4. Decarburization of steel in a liquid state or in a roll of the initial, intermediate or final thickness.

 5. Additive to steel 0.4-0.7% Cu.

 The invention extends to steels with 2.8-3.5% Si; 0.030-0.045% C; 0.10-0.30% Mn; 0.003-0.020% S; 0.008-0.028% Al; 0.03-0.7% Cu. Two swimming trunks of the specified composition were selected to verify the proposed method (see tab. 1).

Continuously cast slabs were heated to a temperature Tn, selected depending on the Al content, and rolled into strips 2.5 mm thick with a winding temperature in the range of 520-570 ^o C. Various methods of decarburization were tested: in a liquid state, in a roll of the initial and intermediate thickness. Both steels were rolled to a thickness of 0.30 mm with intermediate annealing. The dispersed AlN particles, the regulators of texture formation, were isolated during the slow (5–15 ^o / h) heating of cold-rolled steel of finite thickness at the WTO. The processing parameters and the obtained magnetic properties are shown below in table 2. For comparison, the selected steels were processed according to the prototype method (without regulation of the hot rolling and winding modes, with the deceleration of heating in the OO process in the final thickness), as well as for modes slightly different from the modes the proposed method. As can be seen from the table, in the steels of both melts a stable high level of magnetic properties is achieved only by combining the specified modes of hot rolling and heating during primary recrystallization. Deviation of one of these parameters leads to a deterioration in the quality of steel. Mass testing of the invention in an industrial environment confirmed its high efficiency.

Claims (3)

1. Method for the production of anisotropic electrical steel containing 0.008-0.028% Al with high magnetic induction and low specific losses, including smelting, hot rolling, decarburization, double cold rolling, high temperature annealing with delayed heating in the primary recrystallization interval, characterized in that the temperature heating for hot rolling is set depending on the Al content in the steel according to the ratio T _n = 1190 + 4 x 10 ³ % Al ± 10 ^o C, after hot rolling, winding at 520 - 570 ^o C, and slow The heating is carried out after the final cold rolling at a speed of 5 - 15 ^o s / h in the temperature range 400 - 700 ^o C.  2. The method according to any one of claims 1 and 2, characterized in that decarburization is carried out at the smelting stage or at the rolling stage in the initial, intermediate or final thickness.  3. The method according to any one of claims 1 to 3, characterized in that 0.4 to 0.7% Cu is added to the steel.

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