RU2516323C1 - Method to produce highly permeable anisotropic electric steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel is smelted, poured to produce a slab, the slab is heated, rough and finishing rolling is carried out, then cooling, etching, double-stage cold rolling with intermediate decarbonising annealing, application of a magnesia coating onto a strip, high-temperature and straightening annealing is carried out, at the same time steel is smelted at the following ratio of components, wt %: C 0.018-0.035, Mn 0.10-0.40, Si 3.0-3.50, Al 0.010-0.035, N₂ 0.008-0.015, Cu 0.4-0.6, balance - iron and unavoidable admixtures, meeting the ratio between carbon and silicon so that the share of austenite during finishing hot rolling in the temperature range of 1150-1050°C makes 2-10%, prior to finishing hot rolling temperature of rolling is maintained in the range 1180-1280°C, and rolling is carried out with total extent of deformation 80-95% and with temperature of rolling end 970-1030°C, strips are cooled after rolling during the time not exceeding two seconds, and heating for high-temperature annealing in the range of temperatures 400-700°C is carried out with speed of 20-25°C/hour.

EFFECT: provision of high magnetic permeability of steel and evenness of magnetic properties of steel.

3 cl, 2 tbl, 3 dwg, 2 ex

Description

The invention relates to the field of ferrous metallurgy and can be used in the production of anisotropic electrical steel used in the manufacture of magnetic cores of power transformers.

Depending on the purpose of the transformers, anisotropic steel is divided into steel with limited (B ₈ ≤ 1.85 T), high (B ₈ = 1.86-1.89 T) and high (B ₈ = 1.90-1.95 T ) permeability. The first group is used for the manufacture of distribution transformers. The second is partly distribution and partly power transformers, and the third group is mainly used in power transformer construction. The share of the metal of the third group is estimated at 35-45%, and in the future it can be increased to 45-50%.

, во многом определяются степенью совершенства ребровой текстуры ({110}<001>), которая формируется в процессе вторичной рекристаллизации. Для металла первой группы характерно среднее отклонение зерен с ребровой текстурой от идеальной ориентировки на 7-8 градусов, для второй группы отклонение на 4-6 градусов и для третьей группы на 3-4 градуса.The magnetic properties of steel, and in particular, the value of induction B $${}_8$$

, are largely determined by the degree of perfection of the rib texture ({110} <001>), which is formed in the process of secondary recrystallization. The metal of the first group is characterized by an average deviation of grains with a rib texture from an ideal orientation of 7-8 degrees, for the second group, a deviation of 4-6 degrees and for the third group by 3-4 degrees.

To create a perfect texture, the following basic conditions must be observed:

- the formation in the primary recrystallization matrix of a pronounced octahedral ({111} <112>) component of the texture (absorbed component) and grains with a sharp rib texture (absorbing component), the severity of which is limited;

- restriction of grain growth at the stages preceding secondary recrystallization, which is realized by controlling an impurity system in the form of dissolved surface-active impurities and non-metallic inclusions.

Steel with limited permeability (B ₈ = 1.82-1.85 T), the share of which has decreased from 65 to 20% in the last decade, is produced using technology with sulfide inhibition of the structure according to the redistribution scheme with double cold rolling and recrystallization annealing in the intermediate thickness [one].

Steel with increased permeability, is also produced according to the scheme with double cold rolling. A variant of the Kawasaki company (now JFE) provides for the improvement of properties due to the exacerbation of the rib component in the subsurface zone of hot-rolled strips [2], which is then reproduced in the finished metal by the mechanism of texture heredity [3]. However, due to the insufficient severity of the octahedral texture, the induction of B _{8 is} limited to 1.86-1.89 T. Approximately the same level of induction B _{8 is} typical for steel with nitride inhibition of the structure [4], practiced in Russia, China and Eastern Europe, and this option is characterized by sufficient severity of the absorbed texture. At the same time, the more dispersed rib component of the texture of the hot-rolled steel does not allow increasing the B ₈ value to 1.90 T or more.

Currently, high-permeability steel is produced according to two technological options developed by the Nippon Steel concern. The general condition of these technologies is a single cold rolling with a high degree of deformation, which ensures both an increase in the representation of the octahedral component and an exacerbation of the rib component. The difference between the options is in the control methods of impurity systems. The first classical technology [5, 6], practiced first in the 70s, provides for the formation of the required impurity system during hot rolling, and the second, introduced in the mid-90s [7, 8], is based on the introduction of the main modifying element - nitrogen at chemical-thermal treatment in the final thickness.

The main disadvantage of the first direction is the need for high-temperature heating of slabs, accompanied by abundant slag formation, the removal of which is very time-consuming and requires additional material costs.

The second direction, firstly, significantly limits the performance of decarburization annealing furnaces and, secondly, involves the use of environmentally unfavorable ammonia technology.

The disadvantages of both technologies include:

- the need to introduce into the technological cycle the operation of high-temperature (T-1150 ° C) heat treatment of hot-rolled steel;

- increased consumption of material (by 10-13%), energy (by 20-25%) and labor (by 15-20%) resources.

The objective of the proposed invention is the creation of a new technology for the production of highly permeable anisotropic electrical steel, devoid of the above disadvantages, which is based on a combination of the advantages of technological options practiced by the Japanese company "Kawasaki" (JFE) and the Russian company NLMK.

The technical result of the invention is the provision of high magnetic permeability of steel.

To achieve the specified technical result, a method for producing highly permeable anisotropic electrical steel, including steel smelting, casting to obtain a slab, heating a slab, rough and finish hot rolling, cooling, etching, double cold rolling with intermediate decarburizing annealing, applying a magnesian coating to the strip, and high temperature rectifying annealing, steel is melted in the following ratio of components, wt.%: C 0.018-0.035, Mn 0.10-0.40, Si 3.0-3.50, Al 0.010-0.035, N ₂ 0.008-0.015, Si 0 , 4-0.6, the rest is iron and unavoidable impurities, when the ratio between carbon and silicon is chosen so that the fraction of austenite during finish hot rolling in the temperature range 1150-1050 ° C is 2-10%, and the temperature before final hot rolling the roll support in the range of 1180-1280 ° C and then carry out rolling with a total degree of deformation of 80-95% and with a temperature of the end of rolling of 970-103 0 ° C, cooling of the strips after rolling is carried out for a time not exceeding two seconds, and heating at high temperature annealing in ntervale temperatures are 400-700 ° C at a rate 20-25 ° C / hour. Casting into thin slabs and rolling is carried out on casting and rolling modules. Before finishing rolling, the reels are heated to 1180-1280 ° C in flame or induction furnaces.

This technology conceptually differs from the existing ones in that high permeability is achieved during redistribution according to the scheme with double cold rolling. The effectiveness of the proposed technology consists in a significant reduction in the cost of redistribution, as well as the exclusion of labor-intensive and environmentally unfavorable operations from the technological cycle (high-temperature heating of slabs, nitriding, etc.).

The differences between the known [5-8] and the proposed technology for the redistribution of highly permeable steel follow from a comparison of the schemes shown in figures 1-3.

Preservation of the structure and textures of hot-rolled steel, characteristic of a deformed state (with minimal development of recrystallization), in which a zone with a sharp rib texture is formed in the subsurface layer (1 / 10-1 / 7 in thickness), which is achieved by:

- increase the deformation temperature in the finishing group of stands to (970-1030 ° C), at which dynamic return limits the possibility of recrystallization;

- minimize the volume of phase recrystallization, which also limits the possibility of recrystallization;

- time limits between completion of rolling and forced cooling of hot rolled strips.

An increase in the temperature of rolling completion is possible due to:

- increasing the heating temperature of the slabs and increasing the thickness of the intermediate roll;

- increase in rolling speed;

- heating the roll before finishing rolling;

- production of rolled metal on casting and rolling modules.

A decrease in the volume of phase recrystallization is achieved as a result of a rational choice of the ratio between the concentrations of carbon and silicon.

The formation of a pronounced octahedral texture in the primary recrystallization matrix is achieved as a result of:

- exceptions of the operation of high-speed heating of the strips in the final thickness;

- restrictions on the rate of metal heating during high-temperature annealing (20–25 ° C / h) in the range of return and recrystallization temperatures (400–700 ° C) [9];

- preservation of part of nitrogen in a solid solution up to the stage of softening during high-temperature annealing;

- metal modification with copper (0.4-0.6%).

Nitrogen and copper, released from the supersaturated solution at the polygonization stage, increase the primary recrystallization temperature and provide more than twofold amplification of the octahedral component in the primary recrystallization matrix.

Thus, the proposed technology includes the following operations as the main ones:

1. Metal smelting of the following composition, wt.%: C 0.018-0.035, preferably 0.002-0.03, Mn 0.10-0.40, preferably 0.20-0.35, Si 3.0-3.50, preferably 3.15-3.40, Al 0.010-0.035, preferably 0.010-0.025, N ₂ 0.008-0.015, preferably 0.009-0.013, Cu 0.4-0.6, the rest is iron and unavoidable impurities;

2. Continuous casting into slabs, including thin slabs on casting and rolling modules;

3. Hot rolling to a thickness of 1.5-3.5 mm, with the completion of deformation at temperatures of 970-103 0 ° C and forced cooling of the strips in less than two seconds after completion of the deformation;

4. Cold rolling to an intermediate thickness of 0.55-0.90 mm;

5. Decarburization annealing in a humidified nitrogen-hydrogen mixture;

6. Cold rolling to a thickness of 0.15-0.35 mm;

7. Application of heat-resistant coating;

8. High-temperature annealing with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / h;

9. Rectifier annealing with electrical insulating coating.

Example 1. Steel was melted with a chemical composition, wt.%: C 0.018-0.035, Mn 0.1-0.4, Si 3.0-3.5, Al 0.01-0.035, N ₂ 0.08-0.015, Cu 0.4-0.6, the rest is iron and inevitable impurities. Steel was poured on continuous casting machines into 220 mm thick slabs. The slabs were heated to 1350-1400 ° C and rolled in a roughing stand of a broadband mill to a roll with a thickness of 50 mm with a rolling completion temperature of 1210-1230 ° C. Before the finish rolling, the roll was heated in a tunnel flame furnace to 1180-1280 ° C, preferably 1200-1250 ° C, which guarantees a deltaferritic structure, and finish rolling was carried out on a strip 2.5 mm thick. The temperature of the end of the finish rolling was changed in the range of 970-1030 ° C due to changes in the strain rate and the thickness of the intermediate roll. Further redistribution included etching, the first cold rolling to a thickness of 0.65 mm, decarburizing annealing, the second cold rolling to a thickness of 0.30 mm, applying a magnesia coating, high-temperature annealing with a limitation of the heating rate of the coils in the temperature range 400-700 ° С to 20- 25 ° C / hour, straightening annealing with the application of an electrical insulating coating. Table 1 shows the data characterizing the effect of the temperature of the completion of hot rolling on the magnetic properties of steel.

Table 1. The effect of the temperature of the end of rolling on the magnetic properties of steel. Sequence number №№ The temperature of the end of rolling, ° C Magnetic properties P _{1.7 / 50} W / kg B ₈₀₀ , T one 900 1.23 1.85 2 930 1.20 1.86 3 960 1.12 1.88 four 978 1,03 1.91 5 990 1.00 1.91 6 1003 1,02 1.90 7 1010 1.00 1.91 8 1030 1,02 1.91

From the table it follows that an increase in the rolling temperature makes it possible to achieve the level of magnetic properties characteristic of high-permeability steel, which is explained by the suppression of recrystallization processes during hot deformation both due to softening by the dynamic return mechanism and as a result of the limitation of phase recrystallization, determined by the rational ratio between ferrite-forming [Si] and austenite-forming [C] components.

Example 2. Smelted steel of the following chemical composition, wt.%: C 0.025-0.035, Mn 0.15-0.25, Si 3.15-3.17, Al 0.016-0.018, N ₂ 0.009-0.011, Cu 0, 4-0.6, the rest is iron and inevitable impurities, and the steel is poured on continuous casting machines into slabs 220 mm thick.

The slabs were heated in furnaces with walking beams to 1350-1400 ° C and rolled in a roughing stand of a broadband mill to a roll with a thickness of 50 mm. The rolling completion temperature was 1210-1230 ° C.

The roll was heated in a tunnel flame furnace to 1180-1200 ° C. The temperature before rolling in the first stand of the finishing group varied from a 2.2 mm thick strip. The reel was deformed in the finishing group of the stands into strips 2.2 mm thick. The rolling completion temperature was maintained in the range of 990-1010 ° C.

A further redistribution of the metal corresponded to that described in example 1. The intermediate thickness was 0.60 mm, the final one was 0.30 mm. Table 2 illustrates the results.

A further redistribution of metal corresponded to Example 1: etching, cold rolling, decarburizing annealing, cold rolling, applying a magnesia coating, high temperature, straightening annealing with applying an insulating coating.

Table 2. The effect of chemical and phase composition on magnetic properties. The concentration of elements that determine the phase composition,% The proportion of austenite at temperatures of 1150-1050 ° C,% * Magnetic properties C Si P _{1.7 / 50} , W / kg B ₈₀₀ , T 0.012 3.15 0 1.88 1.73 0.015 3.15 one 1.35 1.80 0,020 3.15 3 1,07 1.91 0.024 3.17 7 1,02 1.93 0,028 3.17 9 1.05 1.90 0,030 3.17 eleven 1,07 1.89 0,035 3.17 fifteen 1.12 1.87 0,041 3.17 22 1.19 1.86

The austenite fraction was calculated based on the Fe-Si-C diagram in accordance with the expression: Vγ = 694 [C] -23 [Si] +64.8;

where: Vγ is the austenite fraction, [C] and [Si] are the weight concentration of carbon and silicon. From the data of table 2 it follows: - with a typical silicon content (the main ferrite-forming element), the best magnetic properties that meet the requirements for highly permeable steel are obtained at a carbon concentration of 0.020-0.028 wt.%; - at a carbon concentration of 0.018 wt.% or less, secondary recrystallization is not fully realized, which is due to the release of aluminum nitrides in the early stages of hot rolling;

- at an increased carbon concentration of ≥0.030 wt.%, the magnesium properties gradually deteriorate due to degradation of the texture in the surface layers of the tack due to phase recrystallization.

An increase in carbon content in excess of 0.030% is possible and probably desirable provided that the silicon concentration is equivalently increased so that during the hot rolling in the temperature range 1100–1150 ° C, the volume fraction of austenite is maintained within 2–10%.

Information sources

1. B.V. Molotilov, A.K. Petrov, V.M. Borevsky, Sulfur in electrical steel, Metallurgizdat, 1973

2. Kokoku V. Patent Jpn. No. 51-13469.

3. V.Ya. Holstein, Abstract of a Ph.D. thesis, 1968

4. V.P. Baryatinsky, Abstract of a candidate dissertation, 1989

5. Taguchi S., Sakakura A., US Patent No. 3159511.

6. Taguchi S., Sakakura A., Takashima H., US Patent No. 3287183.

7. Kobayashi H., Kuroki K, US Patent No. 4979996.

8. Minkuchi M., Kondo Y., US Patent No. 5,266,129.

9.M.B. Tsyrlin, G.P. Sukhakov, F.A. Radin, Copyright Certificate No. 824679.

Claims (3)

1. A method of manufacturing a highly permeable anisotropic electrical steel, including steel smelting, casting to obtain a slab, heating a slab, rough and finish hot rolling, cooling, etching, double cold rolling with intermediate decarburization annealing, applying a magnesia coating to the strip, high temperature annealing and high temperature annealing characterized in that steel is smelted in the following ratio of components, wt.%: C 0.018-0.035, Mn 0.10-0.40, Si 3.0-3.50, Al 0.010-0.035, N ₂ 0.008-0.015, Cu 0.4-0.6, the rest is iron and inevitable si, while the ratio between carbon and silicon is chosen so that the fraction of austenite during the final hot rolling in the temperature range 1150-1050 ° C is 2-10%, and before the final hot rolling, the temperature of the roll is maintained in the range of 1180-1280 ° C and carry out rolling with a total degree of deformation of 80-95% and with a temperature of the end of rolling of 970-1030 ° C, cooling of the strips after rolling is carried out for a time not exceeding two seconds, and heating under high-temperature annealing in the temperature range 400-700 ° C is carried out with speed 20-25 ° C / hour. 2. The method according to claim 1, characterized in that the casting into thin slabs and rolling is carried out on casting and rolling modules. 3. The method according to claim 1, characterized in that before finishing rolling, the roll is heated in the range of 1180-1280 ° C in flame or induction furnaces.

Images