RU2262540C1 - Method of production of isotropic electrical steel with phosphorus - Google Patents

Abstract

FIELD: metallurgy; production of isotropic electrical steel used for manufacture of magnetic circuits for electrical equipment working in revolving magnetic field.

SUBSTANCE: proposed method includes melting, hot and cold rolling and annealing. After melting, steel contains 0.05-0.40% of phosphorus. After cold rolling, re-crystallization annealing is performed in continuous furnace followed by additional annealing performed in bell-type furnace. If necessary, straightening annealing may be performed in continuous furnace at application of insulating coat. Proposed method makes it possible to avoid increase of specific losses-finely dispersed phosphorus-containing phase.

EFFECT: enhanced efficiency; reduced losses of phosphorus-containing phase.

2 cl, 1 dwg, 2 tbl, 1 ex

Description

The present invention relates to metallurgy, specifically to the production of isotropic electrical steel used for the manufacture of magnetic circuits of electrical equipment operating in a rotating magnetic field.

The main criteria for assessing the quality of isotropic steel are magnetic and mechanical properties. This is the specific energy loss for magnetization reversal, magnetic induction and their anisotropy, the ratio of yield strength to ultimate strength. Specific losses and anisotropy should be minimal, magnetic induction should be maximum, and the ratio of the limits should be more than 0.85. The magnetic properties of steel depend on the parameters of the microstructure and texture, non-metallic inclusions. Specific losses and anisotropy decrease, and magnetic induction increases with the amount of component {100} <uvw> in the steel texture. Specific losses are reduced, and magnetic induction increases with increasing grain size and a decrease in the number of non-metallic inclusions. Magnetic properties also depend on the chemical composition of the steel, mainly on the silicon content. With an increase in silicon content (0.10 ÷ 3.25%), specific losses and magnetic induction decrease. For many years, silicon has been the main tool for influencing specific losses, although a decrease in induction was a negative fact. For engines and generators of low power, in which magnetic induction is more important, steel with a low silicon content was used, and for powerful equipment where specific losses are more important, steel with a high silicon content was used. The problem of obtaining steel with low specific losses and high magnetic induction was partially solved by replacing silicon with phosphorus. This replacement is also successful in terms of the mechanical properties of steel. The requirement for a certain value of the ratio of yield strength to strength is caused by the dependence of the formability of steel on this value. Currently, high-speed machines are used for stamping. If the steel is mild, stamping becomes impossible. Requirements for mechanical properties allowed to perform silicon. Typically, stamping difficulties occurred when the silicon content was reduced to less than 1%. Phosphorus is no less effective than silicon, allowed to obtain the necessary mechanical properties of steel.

Known methods for the production of isotropic steel, in which the improvement of magnetic properties is achieved by alloying steel with phosphorus and the regulation of the modes of technological operations. In a method for the production of isotropic electrical steel, including smelting, hot rolling, normalization, etching, cold rolling and decarburization-recrystallization annealing (RF patent No. 2223338, C1 7 C 21 D 8/12, 2004), the phosphorus concentration depends on the silicon content and is determined by the equation P = -0.004 [Si,%] ² -0.02 [Si,%] + 0.168 ± 0.02% when the carbon content in the steel after smelting is less than 0.015% and silicon in the range 1.4 ÷ 3.4 % In a method for the production of isotropic electrical steel, including smelting, hot rolling, normalization, pickling, cold rolling and decarburization-recrystallization annealing (RF patent No. 2215796, C1 7 C 21 D 8/12, 2003), the normalization temperature is selected taking into account the content silicon and phosphorus according to the equation t _n = 950-45 [Si,%] + 100 [P,%] ± 10 ° C with a change in the silicon content in the range of 1.60 ÷ 2.69%, phosphorus - 0.05 ÷ 0, fifteen%.

Closest to the proposed invention is a method for producing isotropic electrical steel, including smelting, hot and cold rolling, decarburization-recrystallization annealing (RF patent No. 2155234, C1 7 C 21 D 8/12, 2000). The method is characterized in that the temperature of the final recrystallization annealing after cold rolling is determined taking into account the content of silicon and phosphorus from the ratio T = (3.7 [Si,%] ^1/2 / [P,%]) + 880 ± 10 ° С with a change in the silicon content of 1.4 ÷ 2.6% and phosphorus 0.05 ÷ 0.15%. This method is selected as a prototype. The technical result of this method is the exclusion from the technology of the operation of normalizing hot rolled strips. This makes it possible to increase the ductility of steel and the phosphorus content to 0.15%, to obtain magnetic properties corresponding to grades 2411, and to reduce the cost of steel. The exclusion of the normalization operation necessitates determining the temperature of the decarburization-recrystallization annealing depending on the content of silicon and phosphorus. However, in the known method, all the features of the production of steel with a high phosphorus content are not taken into account. This does not significantly improve the magnetic properties of steel and is a disadvantage.

The technical problem solved by the invention is to improve the magnetic properties of steel.

It is achieved by the fact that according to the proposed method, steel is smelted containing 0.05 ÷ 0.40% phosphorus, hot and cold rolling, decarburization-recrystallization annealing and additional annealing in a bell furnace. If necessary, normalize the hot-rolled strips.

The invention consists in the following. Our research has established that with a phosphorus content of more than 0.03 ÷ 0.05%, a finely dispersed phosphorus-containing phase is released in steel. Its amount in the finished steel can reach 10 ¹³ pcs / cm ³ . It is known that such phases inhibit the motion of domain walls during magnetization reversal of ferromagnetic material and increase the energy consumption for this process. This was the reason for the insufficient improvement of the magnetic properties of steel in the known method. The phase is formed during the final decarburization-recrystallization annealing. For uniform and sufficient decarburization, obtaining uniform parameters of the microstructure and texture along the length and width of the strips, the steel is annealed in continuous furnaces. Phosphorus-containing phase is released at temperatures of 850-900 ° C. The cooling modes used after annealing in a continuous furnace cannot provide coalescence and phase dissolution, since cooling rate is higher than required. This allows for the cooling of steel after annealing in a bell furnace. The drawing shows that annealing in a bell furnace can significantly reduce the specific energy loss for magnetization reversal. After annealing at 850 ° С, the value of P _{1.0 / 50} decreased by 20.4%, and P _{1.5 / 50} - by 18.7%. The higher the annealing temperature, the longer the steel is in conditions of more complete implementation of coalescence and dissolution of the phosphorus-containing phase, the more significant is the decrease in specific losses. In this case, the values of magnetic induction B ₁₀₀₀ increase by 0.03 T, B ₂₅₀₀ - by 0.01 T, and the anisotropy of specific losses and magnetic induction decreases.

It should be noted that the upper limit on the phosphorus content of 0.40 wt.% Was chosen based on the fact that steel with a high phosphorus content becomes non-technological, i.e. difficult to handle, especially during cold rolling. The lower limit of 0.05 wt.% Of phosphorus is due to the fact that the number of particles of the phosphorus-containing phase is reduced so that the effect of additional annealing becomes insignificant.

The search for the totality of the features of the proposed method in the Russian and foreign scientific and technical literature has not yielded results. We can assume that the invention meets the criterion of "Novelty."

An example implementation of the method.

Steel is smelted in a converter, and slabs are produced by continuous casting. The chemical composition of the steel is shown in table 1. Examples 1 and 6 go beyond the claimed parameters for the phosphorus content. The slabs are heated in a methodical furnace and hot rolled to a strip thickness of 2.2 mm. Normalization is carried out for steel with a silicon content of more than wt. 1.2% and less than 0.1 wt.%. Then the strips are subjected to etching, cold rolling to a strip thickness of 0.50 mm, decarburization-recrystallization annealing in a continuous furnace and additional annealing in a bell furnace. Table 2 shows the magnetic properties of steel before (Prototype method) and after additional annealing in a bell furnace (The inventive method). The results indicate that in all cases there is a decrease in specific losses.

The inventive method is universal, because in electrical steel with phosphorus after any technology eliminates one of the main reasons for the increase in specific losses - finely dispersed phosphorus-containing phase.

Table 1
The chemical composition of steel, wt.% Steel FROM Si Mn S R Al Cr Ni Cu Ti N ₂ 1* 0,03 0.08 0.18 0.011 0.010 0,03 0,03 0.01 0.02 0.004 0.006 2 0,03 0,07 0.17 0.012 0.190 0.04 0,03 0.01 0,03 0.005 0.007 3 0,03 0.49 0.20 0.005 0.131 0.8 0.04 0.02 0.06 0.006 0.006 4 0.05 1.25 0.20 0.005 0,120 0.39 0.04 0.02 0.06 0.010 0.004 5 0,03 2.00 0.17 0.004 0,065 0.39 0.06 0.04 0.06 0.007 0.005 6 * 0,03 3.00 0.21 0.005 0,038 0.39 0.05 0,03 0,07 0.010 0.004

table 2
Specific losses (P _15/50 , W / kg) and their difference in steel after decarburization-recrystallization (ANO) and additional annealing in a bell furnace (KP) Steel ANO KP Δ,% 1* 6.49 6.42 1,1 2 6.10 4.91 19.5 3 5.60 4,52 19.3 4 4.78 3.99 16.5 5 4.34 3.89 10,4 6 * 2.98 2.91 2,3

Claims (2)

1. Method for the production of isotropic electrical steel with phosphorus, including smelting, hot and cold rolling and decarburization-recrystallization annealing, characterized in that the steel is smelted containing 0.05 ÷ 0.40% phosphorus, and after decarburization-recrystallization annealing, an additional annealing is carried out in a bell furnace. 2. The method according to claim 1, characterized in that after hot rolling, normalization of the hot-rolled strips is carried out.