RU2536711C1 - Plate from non-textured electrical steel, and method for its manufacture - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel contains the following, wt %: C: 0.008 or more and 0.040 or less, Si: 5.0 or less, Mn: 2.0 or less; Al: 2.0 or less; P: 0.05 or less; N: 0.003 or less, Ti: 0.04 or less; Fe and inevitable impurities are the rest. Contents of components included in steel meet expressions (1) and (2): $$300\le 85[Si\%]+16[Mn\%]+40[Al\%]+490[P\%]\le 430(1)$$

, $$0,008\le Ti*<1,2[C\%](2)$$

, where Ti∗=Ti-3.4[N%].

EFFECT: steel has high magnetic and mechanical properties, low price and high quality of the manufactured steel plate.

6 cl, 3 dwg, 6 tbl, 2 ex

Description

FIELD OF THE INVENTION

The present invention relates to a non-textured electrical steel sheet and, in particular, to a non-textured electrical steel sheet with high strength and excellent fatigue properties and, in addition, excellent magnetic properties, which are respectively used in components that are subjected to high voltages, typically drive motors for turbo-generators, electric vehicles, and hybrid vehicles or rotors of high-speed rotating devices, such as servomotors Teli for robots, machine tools, etc. and to the method of its manufacture. In addition, the present invention relates to the above-described non-textured electrical steel sheet having a lower price in comparison with steel of the prior art.

Prior art

Recent advances in drive systems have made it possible to adjust the drive frequency of power supplies; more and more variable speed motors are offered, providing high speed at frequencies above the industrial frequency. In such engines, providing a high speed of rotation, the centrifugal force acting on the rotating bodies is proportional to the radius of rotation and increases in proportion to the square of the speed of rotation. Accordingly, in particular, rotor materials for medium- and large-sized high-speed engines require high strength.

In addition, in the IPM (internal permanent magnesium) type in direct current inverters of control motors, which have become more widely used as motors in hybrid vehicles, such as drive motors or compressor motors, the voltage is concentrated on the part between the grooves of the built-in rotor magnets and the external the circumference of the rotor, or on a narrow part of the bridge a few millimeters wide between the grooves for the built-in magnets. Since the size of engines can be reduced by increasing the speed of rotation, there is a growing need to increase the speed of rotation of the engine, for example, in drive motors for hybrid vehicles with limited space and weight. Thus, high-strength materials are mainly used as basic materials for use in rotors of high-speed engines.

On the other hand, since rotating equipment, such as motors and generators, uses electromagnetic phenomena, the basic materials of the iron cores of rotating equipment must also have excellent magnetic properties. In particular, for rotors of high-speed engines, low iron loss at high frequency is required; loss in iron at high frequency could lead to an increase in internal temperature due to the eddy current induced by high-frequency magnetic flux, which leads to thermal demagnetization of built-in permanent magnets, reducing motor efficiency, and so on. Thus, there is a need for such an electrotechnical sheet steel as a rotor material that has high strength and excellent magnetic properties.

Steel hardening mechanisms include solid solution hardening, dispersion hardening; grinding crystalline grains, strain hardening, and so on. To date, a number of high-strength, non-textured, electrotechnical sheet steels that meet the requirements of steels for rotors of high-speed engines have been reviewed and proposed.

As an example of the use of solid solution hardening, for example, JP 60-238421 A (PTL 1), a method is proposed for increasing the strength of steel by adding elements such as Ti, W, Mo, Mn, Ni, Co or Al to steel primarily to increase the Si content from 3.5% to 7.0% and, in addition, the achievement of solid solution hardening. In addition, in addition to the hardening methods described above, JP 62-112723 A (PTL 2) provides a method for improving magnetic properties by controlling the size of the crystal grain in the range from 0.01 mm to 5.0 mm by controlling the final annealing.

However, when these methods are used in industrial production, malfunctions can occur more often, such as a fracture of the sheet on the rolling line after hot rolling, which can lead to a decrease in output and the production line to stop if necessary. The occurrence of a fracture of the sheet can be reduced if cold rolling is carried out in warm conditions at a sheet temperature of several hundred degrees Celsius, in this case, however, process control will be difficult, for example, when setting up a plant for warm rolling, severe production restrictions, and so on.

In addition, as a method using the separation of carbonitrides, JP 06-330255 A (PTL 3) proposes a method that uses the effects of dispersion hardening and grinding of crystalline grains provided by carbonitrides in steel, steel with a Si content from 2.0% to 4, 0%, C in the range of 0.05% or less, and one or two of Nb, Zr, Ti and V in the range of 0.1 <(Nb + Zr) / 8 (C + N) <1.0 and 0, 4 <(Ti + V) / 4 (C + N) <4.0.

Similarly, JP 02-008346 A (PTL 4) proposes a method in which, in addition to the features described in PTL 3, Ni and Mn are added in a total amount of 0.3% to 10% to the solid solution hardening steel and additionally added to the steel Nb, Zr, Ti, and V in the same ratio as described in PTL 3, thereby providing a balance of high strength with magnetic properties.

However, if these methods are used to obtain high strength, problems arise that not only inevitably cause a deterioration in magnetic properties, but also make the resulting products susceptible to surface defects, such as captivity caused by precipitates, internal defects, etc., leading to a decrease product quality, and, in addition, the tendency to reduce product yield due to removal of defects and problems with kink in the production process of steel sheet, and as a result leads to an increase in cost. In addition, the method described in PTL 4 will lead to an even greater increase in cost because it involves the addition of expensive elements for solid solution hardening, such as Ni.

In addition, as a method of using strain hardening, JP 2005-113185 A (PTL 5) proposes a method for increasing the strength of steel with a Si content in the range from 0.2% to 3.5%, allowing the imparted microstructure to remain in the steel material. In particular, PTL 5 discloses means that prevent heat treatment after cold rolling, or, if carried out, withstand the steel material at 750 ° C for no more than 30 seconds, preferably at 700 ° C or lower, more preferably at 650 ° C or lower, 600 ° C or lower, 550 ° C or lower, and 500 ° C or lower. PTL 5 discloses actual results indicating that the fraction of the attached microstructure is 5% with annealing at 750 ° C for 30 seconds, 20% with annealing at 700 ° C for 30 seconds, and 50% with annealing at 600 ° C for 30 seconds. In this case, there is a problem that such low annealing temperatures lead to insufficient shape correction of the rolled strip. The problem of the irregular shape of the steel sheets is that it can lead to a lower fill factor of the burnt core package in the manufacture of a packaged motor core, a non-uniform distribution of stresses in the rotor at high speed, and so on. There is another problem, namely, that the ratio of treated grain to recrystallized grain varies significantly depending on the composition of the steel and the annealing temperature, which makes it difficult to obtain stable properties. In addition, non-textured electrical steel sheet is usually subjected to final annealing using a continuous annealing furnace, which typically maintains an atmosphere containing at least several percent hydrogen to reduce oxidation of the surface of the steel sheet. When carrying out low-temperature annealing at temperatures below 700 ° C, in such a continuous annealing device there will be significant operational limitations, such as the need for long-term changes in the furnace temperature setting, replacing the atmosphere in the furnace to prevent a hydrogen explosion, and so on.

In light of the aforementioned prior art, the inventors of the present invention proposed in JP 2007-186790 A (PTL 6) high-strength electrical steel sheet with a balance in the ability to correct the shape of a steel sheet with the possibility of hardening the unrecrystallized microstructure during the final annealing, which is obtained by sufficient and excessive addition of Ti by relative to C and N in silicon steel with a low content of C and N and thereby increasing the temperature of recrystallization of silicon steel. The problem of this method is that it can increase the cost of the alloy due to the relatively high Ti content, leading to a change in mechanical properties due to the remaining recrystallized microstructure and so on.

List of cited literature

Patent Literature

PTL 1: JP 60-238421 A

PTL 2: JP 62-112723 A

PTL 3: JP 6-330255 A

PTL 4: JP 2-008346 A

PTL 5: JP 2005-113185 A

PTL 6: JP 2007-186790 A

Summary of the invention

Technical Problem Solved by the Invention

As described above, some suggestions were made to create high-strength, non-textured electrical steel sheet. However, in the proposals that exist today, there is no possibility of manufacturing electrical steel sheet in a stable manner on an industrial scale with good yield and low cost using conventional means for producing, for example, high-strength non-textured electrical steel sheet, which has good magnetic properties in addition to high tensile strength and high fatigue strength and, in addition, satisfying the requirements for the quality of steel one such as those relating to surface defects, internal defects, a sheet form or the like. In particular, high-strength electrical steel sheets, which until now have been used for rotors of high-speed engines, lead to a situation where the resulting rotors will inevitably generate heat due to their magnetic properties, that is, they have high losses in iron at a high frequency, which creates limitations of technical standards when designing engines.

Thus, the aim of the present invention is to provide a high-strength non-textured electrical steel sheet at a low price with excellent magnetic properties and quality of the steel sheet and the method of its manufacture. In particular, it is an object of the present invention to provide a method for manufacturing such a non-textured electrical steel sheet in a stable manner on an industrial scale, and also at a low price, tensile strength of which is 650 MPa or more, preferably 700 MPa or more, and with good low losses in iron at a high frequency such that, for example, a steel material with a sheet thickness of 0.35 mm has a value of W _10/400 of 40 W / kg or less, preferably 35 W / kg or less.

Ways to solve the problem

The authors of the present invention conducted intensive research with high-strength electrical sheet steel, which can achieve the above goals and methods for its manufacture. As a result, the inventors of the present invention showed that the amount and ratio of Ti and C that are added to the steel is related to a balance between the strength properties and magnetic properties of the electrical steel sheet, and that high strength electrical steel sheet with excellent properties can be manufactured in a stable manner and at low cost by optimizing the amount of Ti carbide precipitation.

That is, the present invention is based on the following data:

(A) The growth of crystalline grain of electrical steel sheet during the final annealing can be inhibited by the presence of a relatively small amount of titanium carbides, and hardening can be achieved by reducing the size of the crystalline grain.

(B) the presence of an excess of Ti carbides does not contribute to effective inhibition of crystalline grain growth, but rather has side effects, such as the appearance of a greater number of surface and internal defects, deterioration in the quality of sheet steel, contributing to fracture, and so on. In this sense, surface defects such as captivity and internal defects are significantly reduced by controlling the amount of Ti added to the steel in an appropriate range.

On the other hand, Ti nitrides are formed at higher temperatures than Ti carbides. Thus, they are less effective for inhibiting the growth of crystalline grains and are not suitable for controlling a decrease in the size of crystalline grains, which is the aim of the present invention. Thus, to inhibit the growth of crystalline grain by controlling the amount of Ti carbides, it is desirable to stably reduce the content of N. This is completely different from conventional approaches using dispersion hardening, where there is a similar effect of C and N.

(C) In sheet steel with a reduced crystalline grain, solution C not only increases the tensile strength, but also improves the fatigue properties essential for the material of the rotor rotating at high speed.

(D) The main components of the alloy, which is usually added in order to reduce iron loss by increasing the electrical resistance of the electrical steel sheet, are Si, Al and Mn. These three replacement alloy elements also have the effect of solid-solution hardening of steel. Accordingly, the balance between high strength and low losses in iron is effectively ensured on the basis of solid solution hardening by these elements. However, there is a restriction on the addition of these elements, since excessive addition leads to embrittlement of the steel and creates difficulties in the manufacture of steel. Si-based additives are desirable to meet the requirements of solid solution hardening, reducing iron loss and productivity in the most efficient way.

Based on the results, the authors of the present invention found that the correctly balanced use of solid-solution hardening using replacement alloy elements consisting mainly of Si, a decrease in crystalline grain by Ti carbides and solid-solution hardening by intermediate element C, can give a non-textured electrical steel sheet, which has high strength excellent fatigue properties under conditions of use, and, in addition, excellent magnetic properties you and quality sheet steel, essentially without additional restrictions on manufacturing the steel sheet, or additional steps in the conventional method of manufacturing a non-oriented electrical steel sheet, and also found a process necessary for the manufacture thereof. As a result, the inventors have completed the present invention.

With this in mind, the main features of the present invention are as follows.

(i) Non-textured electrical steel sheet, including, in% of the mass:

Si: 5.0% or less;

Mn: 2.0% or less;

Al: 2.0% or less; and

P: 0.05% or less

in the range satisfying the formula (1), and a steel sheet, further including, in% of the mass:

C: 0.008% or more, but 0.040% or less;

N: 0.003% or less; and

Ti: 0.04% or less

in the range satisfying formula (2), the rest is Fe and random impurities:

where Ti ∗ = Ti-3.4 [N%], and

[Si%], [Mn%], [Al%], [P%], [C%] and [N%] represent the content (% wt.) Of these elements, respectively.

(ii) Non-textured electrical steel sheet in accordance with the above (i), in which the content of Si, Mn, Al and P is, in% by weight:

Si: more than 3.5%, but not more than 5.0%,

Mn: 0.3% or less

Al: 0.1% or less, and

P: 0.05% or less.

(iii) Non-textured electrical steel sheet in accordance with the above (i) or (ii), further comprising, in% by weight, at least one of the following:

Sb: 0.0005% or more, but 0.1% or less;

Sn: 0.0005% or more, but 0.1% or less;

B: 0.0005% or more, but 0.01% or less;

Ca: 0.001% or more, but 0.01% or less;

REM: 0.001% or more, but 0.01% or less;

Co: 0.05% or more, but 5% or less;

Ni: 0.05% or more, but 5% or less; and

Cu: 0.2% or more, but 4% or less.

(iv) A method of manufacturing a non-textured electrical steel sheet, including:

exposure of the steel slab at a temperature of 1000 ° C-1200 ° C, and the steel slab includes, in% of the mass:

Si: 5.0% or less

Mn: 2.0% or less

Al: 2.0% or less, and

P: 0.05% or less

in the range satisfying the formula (1), and further includes, in% of the mass .:

C: 0.008% or more, but 0.040% or less,

N: 0.003% or less, and

Ti: 0.04% or less

in the range satisfying the formula (2);

subsequent hot rolling of the steel slab to obtain hot rolled steel material;

then cold rolling or warm rolling of the steel material in one or two, or more passes with intermediate annealing between them, to a final sheet thickness; and

the final annealing of the steel material, and before the final annealing, the steel material is subjected to at least one heat treatment in which the steel material is held at a temperature of 800 ° C or higher and 950 ° C or lower for 30 seconds or more, and then the final annealing at 700 ° C or higher 850 ° C or lower, where formulas (1) and (2):

where Ti ∗ = Ti-3.4 [N%].

(v) A method of manufacturing a non-textured electrical steel sheet in accordance with the above (iv), where the content of Si, Mn, Al and P is, in% by weight:

Si: more than 3.5%, but not more than 5.0%,

Mn: 0.3% or less

Al: 0.1% or less, and

P: 0.05% or less.

(vi) A method of manufacturing a non-textured electrical steel sheet in accordance with the above (iv) or (v), wherein the steel slab further comprises, in% by weight, at least one of the following:

Sb: 0.0005% or more, but 0.1% or less;

Sn: 0.0005% or more, but 0.1% or less;

B: 0.0005% or more, but 0.01% or less;

Ca: 0.001% or more, but 0.01% or less;

REM: 0.001% or more, but 0.01% or less;

Co: 0.05% or more, but 5% or less;

Ni: 0.05% or more, but 5% or less; and

Cu: 0.2% or more, but 4% or less.

The positive effect of the invention

In accordance with the present invention, non-textured electrical steel sheet can be manufactured with excellent mechanical and magnetic properties required for the rotor material of a high speed motor, and with excellent quality of the steel sheet in terms of foam, sheet shape and so on. The present invention also provides for the stable production of such a non-textured electrical steel sheet with a high yield, without significantly increasing the cost or introducing severe manufacturing restrictions or the need for additional steps compared to the conventional production of non-textured electrical steel sheet. Thus, the present invention is applicable in the field of engines, such as drive motors of electric vehicles and hybrid vehicles or servomotors of robots and machine tools, where the demand for higher speeds will increase in the future. Thus, the present invention has high industrial value and makes a significant contribution to the industry.

Brief Description of the Drawings

The present invention will be further described below with reference to the accompanying drawings, in which:

1 is a graph illustrating the relationship between the Ti content and tensile strength;

2 is a graph illustrating the relationship between the Ti content and iron loss; and

3 is a graph illustrating the relationship between the Ti content and the fraction of surface defects.

The implementation of the invention

The experimental results underlying the present invention will be described in detail below.

The authors of the present invention investigated in detail how Ti, which is the main element that forms carbonitrides, affects the quality of the steel sheet with respect to hardening, recrystallization, grain growth behavior, captivity, and so on. As a result, it was found that Ti has different effects, in particular when added, so that as a result the Ti content is equal to or less than the total carbon and nitrogen content in atomic fractions, and has an optimal addition range to meet the requirements of a high level of high strength, as well as the magnetic properties and quality of the steel sheet. The main experimental results will be described below. The percentage ″% ″ of each steel component represents ″% mass ″ unless otherwise indicated.

<Experiment 1>

Samples of steel with a steel composition mainly composed of silicon (Si): 4.0% to 4.1%, manganese (Mn): 0.03% to 0.05%, aluminum (Al): 0.001% or less phosphorus (P): 0.007% to 0.009% and sulfur (S): 0.001% to 0.002%, including a substantially constant amount of carbon (C): 0.024% to 0.026% and nitrogen (N): 0.001 % to 0.002% and various amounts of titanium (Ti) in the range from 0.001% to 0.36% were obtained by melting steel in a vacuum melting furnace. These steel samples were heated to 1100 ° C and then hot rolled to a thickness of 2.1 mm, respectively. Then, the steel samples were annealed in the hot zone at 900 ° C for 90 seconds and then cold rolled to a thickness of 0.35 mm, after which the presence of surface defects of the steel sheet was determined (the share of captivity per unit area). Next, the steel samples are finally annealed at 800 ° C for 30 seconds and their mechanical properties (using JIS No. 5 on tensile test specimens cut parallel to the rolling direction) and magnetic properties (using Epstein test specimens cut in the direction) are evaluated rolling and in the transverse direction, by measuring the loss in iron W _10/400 with a magnetic flux density of 1.0 T and a frequency of 400 Hz). The results of the study of tensile strength, magnetic properties and the appearance of surface defects are presented in figures 1, 2 and 3 depending on the content of Ti, respectively.

First, as shown in FIG. 1, the tensile strength increases with the addition of Ti. However, it was found that this effect is less pronounced in the Ti content range indicated by ″ A ″ (range A) in FIG. 1, where the Ti content is lower, while a steady improvement in strength is observed in the Ti content range indicated by ″ B ″ ( Range B) in the figure. In addition, even further improvement in strength is achieved in the range indicated by “C” (range C) in the figure, where the Ti content is higher. When studying the structure of steel in these ranges, it was found that in range B the steel structure includes a homogeneous microstructure with a crystal grain size of 10 μm or less, while in range A it includes the growth of crystalline grain to a value greater than in range B, in particular mixed grain size of the microstructure with partial grain growth. On the other hand, in range C, the steel structure becomes multiphase, consisting of unrecrystallized grain and recrystallized grain.

Figure 2 illustrates the relationship between the content of Ti and W _10/400 losses in iron. Although good iron loss properties were obtained in range A with the lowest iron loss, as shown in FIG. 1, range A shows a lower level of strength. On the other hand, although high-strength materials are obtained in ranges C and D in FIG. 2, iron losses are also high in these ranges. In contrast, range B offers materials that have iron losses that are almost as good as those in range A, while yield results are comparable to those obtained in range C.

On the other hand, as shown in FIG. 3, the proportion of surface defects begins to increase when the Ti content exceeds 0.04%, and continues to grow to about the point where the ratio of the equivalents of the elements Ti to C and N is 1, where substantially achieved constant percentage of surface defects. Assuming that the content of C and N is constant, the amount of titanium carbonitride precipitates continues to increase to approximately the point at which this ratio of element equivalents is 1, and then remains constant. Thus, it is believed that the amount of titanium carbonitride precipitates is related to the number of surface defects. These results showed that by adjusting the Ti content in range B, a balance of high strength and low losses in iron is possible, while reducing surface defects that could lead to a decrease in yield and a fracture problem and are directly associated with an increase in production costs. That is, it is preferable that Ti is contained in an amount of 0.04% or less from the point of view of reducing surface defects, provided that it is sufficient to form a certain amount of Ti carbonitrides.

In addition, as a result of further studies carried out with the same components, with the exception of the steel described above and the nitrogen content and with a varying N content, it was also found that the lower limit of the Ti content at which high strength can be obtained increases with increasing N content However, further studies have shown that it is necessary to comply with the relation 0.008≤Ti ∗ (where Ti ∗ = Ti-3.4 [N%]). Based on this, it is believed that since Ti carbides contribute a lot to increasing strength, while Ti nitrides are less involved, controlling the content of Ti carbides is more important.

These results showed that by adjusting the Ti content at the level of range B, it becomes possible to balance high strength and low losses in iron, while reducing surface defects, which could lead to a decrease in yield and the problem of fracture of the sheet and are directly associated with an increase in production costs.

<Experiment 2>

Then, in order to study the details of the effect of Ti carbonitrides, steel samples with the composition shown in Table 1 were obtained by smelting steel in a vacuum melting furnace to produce steel sheets, each of which has a thickness of 0.35 mm, according to the same procedure as in experiment 1. The content of C and N in steel samples was changed using a steel sample ″ a ″ with a low content of carbon and nitrogen for comparison. Samples of steel ″ c ″ and ″ d ″ include C and N, so that their total content is within a given range. The fraction of surface defects, loss in iron, and tensile strength of the obtained samples are shown in Table 2. Whereas steel samples ″ b ″, ″ c ″ and ″ d ″ show an increase in strength with respect to the steel sample ″ a ″ when comparing steel samples ″ C ″ and ″ d ″, with essentially the same total carbon and nitrogen, to evaluate the effects of additions of C and N, it can be seen that the sample of steel ″ c ″ with a lower N content has greater strength. When studying the microstructure, it was found that steel samples, listed in decreasing order of crystalline grain size a> d> b> c, also represent the order in which tensile strength decreases.

Table 1 (% wt.) Steel Si Mn Al P C N Ti a 4.33 0,07 0,0005 0.010 0.0019 0.0021 0,0302

b 4.32 0.05 0.0010 0.010 0.0240 0,0009 0,0295 c 4.29 0,03 0,0007 0.010 0,0293 0,0009 0,0298 d 4.25 0.08 0.0018 0,020 0,0249 0.0052 0,0301

table 2 Steel W_10/400, (W / kg) Tensile Strength TS, (MPa) Fatigue Strength FS, (MPa) Strength Factor FS / TS The proportion of surface defects, (m / m ² ) a 26.9 641 535 0.83 0,000 b 33.0 722 630 0.87 0.003 c 32,5 730 665 0.91 0.003 d 31,0 676 540 0.80 0.004

Additionally investigate the fatigue properties of these samples. The tests were performed in the voltage-to-voltage mode with a voltage cycle asymmetry coefficient of 0.1 at a frequency of 20 Hz, where the fatigue strength is defined as the voltage that allows the sample to withstand 10 million cycles of voltage amplitude. These results are also shown in Table 2. Although there is a tendency that materials with a higher tensile strength TS have a higher fatigue strength FS, the FS / TS coefficient is different for different materials. In this case, the steel ″ c ″ sample gives the best result. On the other hand, the ″ d ″ steel sample does not so much improve the fatigue strength with its high tensile strength. Given these circumstances and as a result of detailed studies of the microstructure of the ″ d ″ steel sample, it was found that a significant part of the precipitates, presumably TiN precipitates with a grain size of more than 5 μm, are distributed in the microstructure and these precipitates are involved in fatigue fracture. It should be noted that nitrogen reacts with titanium at relatively high temperatures from 1100 ° C or higher and tends to precipitate apparently in the form of TiN. Thus, it is assumed that TiN contributes to fatigue failure and is less effective than Ti carbides in inhibiting crystalline grain growth, which is one of the objectives of the present invention.

On the other hand, when comparing steel samples ″ b ″ and ″ c ″, it was also found that the steel sample ″ c ″ gives better results in tensile strength and fatigue strength and, in particular, is characterized by a relatively high fatigue strength and high strength factor FS / TS. Since the contents of Ti and N in the steel samples ″ b ″ and ″ c ″ are essentially the same, they have similar behavior in the precipitation of Ti nitrides and Ti carbides. Thus, it is believed that the difference between them is due to the difference in the amount of dissolved carbon. Accordingly, it is believed that the presence of dissolved carbon reduces the occurrence and propagation of cracks and increases the fatigue strength by blocking dislocations caused by repeated stress cycles, such as those present in fatigue tests. Thus, it is also important to ensure the formation of dissolved carbon.

Based on the above experimental results, the present inventors performed further studies on how these factors, including Ti carbides, Ti nitrides and dissolved carbon, when a relatively small amount of Ti is added, affect the steel structure, surface quality of the steel sheet, and mechanical properties and magnetic properties of steel sheets. As a result, the inventors have determined the rules that are fully applicable to these factors, and completed the present invention.

The present invention will be described in detail below with respect to each of the requirements. Firstly, the reasons for limiting the main components of steel are described. The steel according to the present invention includes Si: 5.0% or less, Mn: 2.0% or less, Al: 2.0% or less, P: 0.05% or less in the range satisfying formula (I):

The aim of the present invention is to provide electrical steel sheet with high strength and excellent magnetic properties at low cost. For this, it is necessary to achieve solid solution hardening above a certain level by means of the above four main components of the alloy. Thus, it is important to determine the content of the four main components of the alloy, as described below, and add these components to the steel so that the total amount of these alloy components is within the range satisfying the above formula (1), taking into account the individual contribution to the solid solution hardening. That is, if formula (1) gives a result of less than 300, the strength of the obtained material is insufficient, and if formula (1) results in more than 430, there are more problems with cracking of the sheet during the manufacture of the steel sheet, which leads to poor performance and significant increase in manufacturing costs.

The following describes the basis for limiting the content of each of the four main components of the alloy.

Si≤5.0%

Silicon (Si) is commonly used as a deoxidizing agent and one of the main elements included in non-textured electrical steel sheet, which increase the electrical resistance of steel to reduce losses in iron. In addition, Si has a high ability to solid solution hardening. That is, Si is an element that is necessarily added to non-textured electrical steel sheet, since it is able to provide a high tensile strength, high fatigue strength and low iron loss in the most balanced way compared to other elements that cause solid solution hardening, such as Mn, Al or Ni, which are added to non-textured electrical steel sheet. For this, the predominant Si content in the steel is 3.0% or more, more preferably more than 3.5%. However, above 5.0%, the impact strength deterioration becomes pronounced, which requires complex control during sheet sinking and rolling process, which leads to a decrease in productivity. Therefore, the upper limit of the Si content should be 5.0% or less.

Mn≤2.0%

Manganese (Mn) is effective for improving the properties of red brittleness and also increases the electrical resistance of steel to reduce losses in iron and increase the strength of steel by solid-hardening. Thus, the Mn content in the steel is preferably 0.01% or more. However, the addition of Mn is less effective for increasing the strength of steel compared to Si and its excessive addition leads to embrittlement of the obtained steel. Thus, the Mn content is 2.0% or less.

Al≤2.0%

Aluminum (Al) is an element that is commonly used as a strong deoxidizer to improve steel. In addition, as in the case of Si and Mn, Al also increases the electrical resistance of steel to reduce losses in iron and increase the strength of steel by solid-hardening. Thus, the content in Al steel is preferably 0.0001% or more. However, the addition of Al is less effective for increasing the strength of steel compared to Si, and its excessive addition leads to embrittlement of the obtained steel. Therefore, the Al content is 2.0% or less.

P≤0.05%

Phosphorus (P) is extremely effective for increasing the strength of steel, since it has a high ability of solid solution hardening even when added in relatively small quantities. Thus, the content in steel P is preferably 0.005% or more. However, excessive addition of P leads to embrittlement of the steel due to segregation, which leads to intergranular cracks or to a decrease in rolling ability. Therefore, the P content is limited to 0.05% or less.

In addition, among these basic elements of the alloy of Si, Mn, Al and P, the development of a Si-based alloy is advantageous for the balance of solid solution hardening / low loss in iron and the most efficient performance. That is, preferably, the Si content in the steel is more than 3.5% to optimize the balance of the properties of the non-textured electrical steel sheet, the content of the remaining three elements being preferably controlled as follows: Mn: 0.3% or less, Al: 0.1% or less, P: 0.05% or less. The reasons for limiting the upper limit are described above.

In addition, in the present invention, C, N and Ti are also important elements. This is due to their importance for inhibiting the growth of crystalline grain during the annealing of a steel sheet using an appropriate amount of finely divided titanium carbides and gaining the ability to enhance grinding of crystalline grains. This requires a content of C: from 0.008% or more to 0.040% or less, N: 0.003% or less, and Ti: 0.04% or less in steel in the range satisfying formula (2):

where Ti ∗ = Ti-3.4 [N%].

0.008% ≤С≤0.040%

Carbon (C) must be present in the steel in an amount of 0.008% or more. A carbon content of less than 0.008% makes it difficult to provide stable precipitation of finely divided Ti carbides and leads to an insufficient amount of dissolved C, in which case further improvement in fatigue strength is impossible. On the other hand, excessive addition of C leads to a deterioration in magnetic properties, while it becomes a factor responsible for the increase in cost, due to more pronounced strain hardening during cold rolling and damage to the sheet, increasing the rolling cycle due to an increase in load during rolling, and so on. Therefore, the upper limit of C is limited to 0.04%.

N≤0.003%

Nitrogen (N) forms Ti nitrides, which, however, are formed at higher temperatures than titanium carbides. Thus, N is less effective for inhibiting the growth of crystalline grains, but not very effective for grinding crystalline grains. On the contrary, N sometimes causes side effects, such as the occurrence of fatigue failure. Thus, the N content is limited to 0.003% or less. In addition, without limitation, the lower limit is preferably about 0.0005% to provide degassability in steelmaking and to avoid degradation in productivity due to the length of processing.

Ti≤0.04%

The control of titanium carbides (Ti) is of great importance in the present invention. Ti at high temperatures tends to form nitrides rather than carbides. Thus, it is necessary to control the amount of Ti carbides formed. If the amount of Ti that carbides can form is denoted by Ti ∗, then Ti ∗ represents the content of Ti minus the atomic equivalent of N, namely:

Ti ∗ = Ti-3.4 [N%]

In order for added Ti to precipitate in the form of titanium carbides to increase the strength of steel, along with inhibiting the growth of crystalline grains to prevent an increase in iron loss, it is necessary to use an appropriate amount of C and correspond to Ti * ≥0.008. On the other hand, if the Ti content increases with respect to the C content, the amount of dissolved C decreases, in which case further improvement in fatigue strength is no longer possible. Thus, the correspondence Ti ∗ <1.2 [C%] is also necessary at the same time.

In addition, if the Ti content exceeds 0.04%, as described above with reference to FIG. 3, more surface defects will occur and the quality of the steel sheet and yield will be reduced, resulting in an increase in cost. Therefore, the upper limit of the Ti content is 0.04%.

The present invention may also include elements other than the above elements without prejudice to the effect of the present invention. For example, the present invention may include: antimony (Sb) and tin (Sn), each of which has the effect of improving the magnetic properties of steel, in the range of 0.0005% -0.1%; boron (B), which has the effect of increasing the strength of the grain boundaries of steel in the range of 0.0005% -0.01%; Ca and REM, each of which has the effect of controlling the forms of oxides and sulfides and improving the magnetic properties of steel in the range of 0.001% -0.01%, Co and Ni, each of which has the effect of improving the magnetic flux density of steel in the range of 0.05% - 5% and Cu, which is believed to provide dispersion hardening in the range of 0.2% -4%.

The reasons for limiting the manufacturing method according to the present invention will be described below.

In the present invention, the manufacturing process from steelmaking to cold rolling can be carried out by appropriate methods, typically used for the manufacture of conventional non-textured electrical steel sheet. For example, steel made by steelmaking and improvements with the help of predetermined components in a converter or an electric furnace can be continuously cast or bloomed after casting an ingot to produce steel slabs, which in turn can be subjected to process steps, including hot rolling, optional annealing in the hot zone, cold rolling, final annealing, applying an insulating coating and annealing and so on for the manufacture of steel sheets. At these stages, the conditions for proper monitoring of the condition of the secretions will be described below. It should be noted that annealing in the hot zone can optionally be carried out after hot rolling, and that cold rolling can be performed in one or two or more passes with intermediate annealing between them.

Steel slabs consisting of the above chemical compositions must be hot rolled at a slab heating temperature of 1000 ° C-1200 ° C. That is, if the slab heating temperature is below 1000 ° C, then it is not possible to achieve the effect of inhibiting the growth of crystalline grain during the final annealing, due to the precipitation and growth of Ti carbides during the heating of the slab. In addition, the temperature of heating the slab above 1200 ° C is not only disadvantageous in terms of cost, but also leads to deformation of the slab due to the decrease in strength at high temperature, which prevents, for example, the removal of the steel slab from the heating furnace, which leads to a decrease in performance . Therefore, the slab heating temperature should be between 1000 ° C-1200 ° C. In addition, hot rolling is not limited to a specific type and can be performed under conditions, for example, hot rolling with a final temperature in the range of 700 ° C - 950 ° C and a winding temperature of 750 ° C or lower.

Then, the obtained hot-rolled steel materials are subjected to optional annealing in the hot zone and cold rolling or warm rolling in one or two or more passes with intermediate annealing between them to reach the final sheet thickness before final annealing. Before final annealing, it is important to heat-treat the steel materials at least once, in which the steel materials are held at 800 ° C or higher and 950 ° C or lower for 30 seconds or more. This heat treatment can ensure the release of titanium carbides in the microstructures before the final annealing and thereby inhibit the growth of crystalline grain during the final annealing

If the above heat treatment is carried out at a temperature below 800 ° C, the precipitation may be insufficient as a result, while above 950 ° C, the effect of inhibiting the growth of crystalline grain during the final annealing will be insufficient due to the growth of precipitation.

In addition, the above heat treatment is preferably carried out in combination with annealing in the hot zone or with intermediate annealing before final annealing.

Subsequent final annealing can be carried out at 700 ° C or higher and 850 ° C or lower so as to control the microstructure of the recrystallized grain in a uniform and finely divided state, with the formation of sheet electrical steel with high strength and excellent magnetic properties. If the final annealing is carried out at a temperature below 700 ° C, the recrystallization obtained is insufficient, while at a temperature above 850 ° C, the crystalline grain tends to grow even when using the features of the present invention, resulting in a decrease in the strength of the products. After this final annealing, the steel materials are subjected to the processes of applying an insulating coating to them and annealing to obtain the final product.

Example 1

Steel samples, with the composition shown in table 3, are obtained by smelting steel in a vacuum melting furnace heated to 1100 ° C, and then subjected to hot rolling to a thickness of 2.1 mm The samples are then annealed in the hot zone at 900 ° C for 90 seconds and then cold rolled, which must be completed at a thickness of 0.35 mm. At this point, an assessment is made of the occurrence of surface defects of the steel sheet using the size of the foam per unit area for comparison. Then the samples are subjected to final annealing for 30 seconds under two different conditions of 750 ° C and 800 ° C, respectively. Then, samples are cut from sheet steel obtained in this way parallel to the rolling direction for tensile testing and fatigue testing. In addition, magnetic properties are estimated based on losses in iron with a magnetic flux density of 1.0 T and a frequency of 400 Hz by the Epstein test for samples that are cut in the rolling direction and in the transverse direction, respectively. The evaluation results are shown in table 4.

Table 3 (% wt.) Steel Si Mn Al P C N Ti Formula 1) Ti * Note one 4.08 0.08 0.0010 0.012 0.0250 0.0015 0.0010 354 -0.0041 Comparison example 2 4.10 0.05 0.0010 0.010 0,0247 0.0013 0.0189 354 0.0145 An example of the invention 3 4.05 0.04 0,0004 0.018 0,0251 0.0016 0,0349 354 0,0295 An example of the invention four 4.08 0.05 0.0015 0.011 0,0245 0.0012 0,0641 353 0,0600 Comparison example 5 4.02 0.04 0.0020 0.017 0,0258 0.0017 0.1164 351 0,1106 Comparison example 6 4.07 0.08 0.0019 0.014 0.0260 0.0019 0.1630 354 0.1565 Comparison example

Table 4 Steel The level of surface imperfection, (m / m ² ) 800 ° C Annealing 750 ° C Annealing Notes W _10/400 , (W / kg) Tensile Strength TS, (MPa) Fatigue Strength FS, (MPa) Strength Factor FS / TS W_10/400, (W / kg) Tensile Strength TS, (MPa) Fatigue Strength FS, (MPa) Strength Factor FS / TS one 0,000 27.4 634 540 0.85 33,4 707 570 0.81 Comparison example 2 0,000 31.5 710 635 0.89 33.9 727 650 0.89 An example of the invention 3 0.005 33.7 715 650 0.91 34.6 731 665 0.91 An example of the invention four 0.159 42.7 722 600 0.83 44,4 737 620 0.84 Comparison example 5 0.189 46.5 726 560 0.77 48.3 744 575 0.77 Comparison example 6 0.211 48.0 734 565 0.77 51.0 750 580 0.77 Comparison example

From table 4 it is seen that the sample of steel No. 1, the value of Ti * which is not included in the scope of claims of the present invention, the properties depend significantly on the temperature of the final annealing, which is a problem from the point of view of quality control. On the other hand, in steel samples containing an appropriate amount of Ti, the difference in properties depending on the temperature of the final annealing is less, which stably gives a high tensile strength. However, compared with steel samples No. 2 and 3 with a steel composition within the range defined by the present invention, steel samples No. 4, 5 and 6, with a Ti content, in each case beyond the scope of the present invention, exhibit a not very high fatigue strength for their high tensile strength and with poor magnetic properties and the amount of captivity.

Example 2

Steel samples with the compositions shown in table 5 are obtained by smelting steel in a vacuum melting furnace heated to 1050 ° C, and then subjected to hot rolling to a thickness of 2.1 mm The samples are then annealed in the hot region at 850 ° C for 120 seconds and then cold rolled to a final thickness of 0.35 mm. At this point, assess the presence of defects in the surface of the steel sheet using the size of the foam per unit area for comparison. Then the steel samples are subjected to final annealing at 800 ° C for 30 seconds. Then, samples are cut from sheet steel obtained in this way parallel to the rolling direction for tensile testing and fatigue testing. In addition, magnetic properties are estimated based on losses in iron with a magnetic flux density of 1.0 T and a frequency of 400 Hz by the Epstein test for samples that are cut in the rolling direction and in the transverse direction, respectively. The results are shown in table 6. In addition, the steel sample No. 18, which does not satisfy the ratio of formula (1) presented in the present invention, undergoes kink during cold rolling, therefore, it is not further evaluated.

Table 5 (% wt.) Steel Si Mn Al P C N Ti Other Formula 1) Ti ∗ Note 7 3.05 0.15 0.3500 0.018 0.0165 0.0014 0.0174 - 284 0.0126 Comparison example 8 3.75 0.08 0.0010 0.019 0.0043 0.0015 0.0172 - 329 0.0121 Comparison example 9 3.78 0.05 0,0008 0.014 0.0159 0.0017 0.0166 - 329 0.0108 An example of the invention 10 4.01 0.04 0.0001 0.015 0.0135 0.0013 0.0154 - 349 0,0109 An example of the invention eleven 4.01 0.04 0,0004 0.015 0,0320 0.0016 0.0148 - 349 0.0093 An example of the invention 12 4.05 0.05 0,0004 0.013 0,0572 0.0016 0.0166 - 351 0.0111 Comparison example 13 4.03 0.01 0,0004 0.001 0.0175 0.0041 0.0168 - 343 0.0027 Comparison example fourteen 4.82 0.04 1,0300 0.018 0.0158 0.0016 0.0188 - 419 0.0133 An example of the invention fifteen 3.02 0.88 0.7000 0.010 0,0289 0.0016 0,0333 - 317 0,0278 An example of the invention 16 3,55 0.59 1,2100 0.010 0,0294 0.0021 0,0328 - 344 0,0256 An example of the invention 17 4.30 0.11 0.1800 0.012 0.0285 0.0025 0,0322 - 380 0,0236 An example of the invention eighteen 4.60 0.59 1,2100 0.010 0,0296 0.0011 0,0311 - 454 0,0293 Comparison example 19 4.03 0.15 0,0005 0.010 0.0144 0,0009 0,0244 Sb: 0.015 350 0.0213 An example of the invention twenty 4.11 0.08 0,0009 0.011 0.0167 0.0021 0,0217 Sn: 0,043 356 0.0145 An example of the invention 21 4.30 0.18 0.2530 0.007 0.0145 0,0009 0.0191 B: 0.003 382 0.0160 An example of the invention 22 4.25 0.09 0.2310 0.018 0.0181 0.0011 0.0155 Ca: 0.003 381 0.0117 An example of the invention 23 4.22 0.15 0.0830 0.015 0,0226 0.0016 0.0185 REM: 0.004 372 0.0130 An example of the invention 24 3.98 0.25 0.2250 0.013 0,0284 0.0018 0,0355 Co: 0.25 358 0,0293 An example of the invention 25 4.05 0.20 0.2840 0.016 0.0133 0.0015 0.0211 Ni: 0.15 367 0.0160 An example of the invention 26 3.87 0.18 0.2760 0.011 0,0336 0.0013 0,0347 Cu: 0.22 348 0,0302 An example of the invention

Table 6 Steel The level of surface imperfection, (m / m ² ) W_10/400, (W / kg) Tensile Strength TS, (MPa) Fatigue Strength FS, (MPa) Strength Factor FS / TS Note 7 0.001 28.6 625 510 0.82 Comparison example 8 0,000 32,7 673 535 0.79 Comparison example 9 0.001 34.5 685 624 0.91 An example of the invention 10 0.005 32,2 708 631 0.89 An example of the invention eleven 0.005 31,2 705 650 0.92 An example of the invention 12 0.230 38.7 694 575 0.93 Comparison example 13 0,110 36.8 701 540 0.77 Comparison example fourteen 0.005 28.8 779 715 0.92 An example of the invention fifteen 0,035 34.5 668 607 0.91 An example of the invention 16 0,026 33.3 703 645 0.92 An example of the invention 17 0,039 33.5 735 680 0.93 An example of the invention eighteen - - - - - Comparison example 19 0.003 31.9 701 620 0.88 An example of the invention twenty 0.004 31,2 707 635 0.90 An example of the invention 21 0.006 33,4 733 640 0.87 An example of the invention 22 0.003 31.6 729 640 0.88 An example of the invention 23 0.003 32,0 721 633 0.88 An example of the invention 24 0.007 33.3 723 645 0.89 An example of the invention 25 0.005 34.1 718 625 0.87 An example of the invention 26 0.008 33.5 706 608 0.86 An example of the invention

As can be seen from table 6, each of the steel sheets according to the present invention has fewer films, good iron loss and a high tensile strength, as well as a high fatigue strength.

Claims (6)

1. Non-textured electrical steel sheet containing, in wt.%:
Si: 5.0 or less
Mn: 2.0 or less
Al: 2.0 or less and
P: 0.05 or less
in the range satisfying the expression (1):

and further including, in wt.%:
C: 0.008 - 0.040
N: 0.003 or less and
Ti: 0.04 or less
in the range satisfying the expression (2),

,
where Ti * = Ti-3.4 [N%],
Fe and random impurities are the rest. 2. Non-textured electrical steel sheet according to claim 1, in which the content of Si, Mn, Al and P is, in wt.%:
Si: more than 3.5 and not more than 5.0
Mn: 0.3 or less
Al: 0.1 or less and
P: 0.05 or less. 3. Non-textured electrical steel sheet according to claim 1 or 2, which further comprises at least one element, in wt.%:
Sb: 0.0005 - 0.1
Sn: 0.0005 - 0.1
B: 0.0005 - 0.01
Ca: 0.001 - 0.01
REM: 0.001 - 0.01
Co: 0.05 - 5
Ni: 0.05 - 5 and
Cu: 0.2-4. 4. A method of manufacturing a non-textured electrical steel sheet, comprising holding a steel slab at a temperature of 1000 ° C-1200 ° C, and the steel slab contains, in wt.%:
Si: 5.0 or less
Mn: 2.0 or less
Al: 2.0 or less and
P: 0.05 or less
in the range satisfying the expression (1):

and further comprises, in wt.%:
C: 0.008 - 0.040
N: 0.003 or less and
Ti: 0.04 or less
in the range satisfying the expression (2):

,
where Ti * = Ti-3.4 [N%];
and subsequent hot rolling of the steel slab to produce hot rolled steel material;
then cold rolling of the steel material or warm rolling in one or two or more passes with intermediate annealing between them to a final sheet thickness; and
the final annealing of the steel material at 700 ° C or higher and 850 ° C or lower, while before the final annealing, the steel material is subjected to heat treatment, at least once, in which the steel material is maintained at a temperature of 800 ° C or higher and 950 ° C or lower for 30 seconds or more. 5. A method of manufacturing a non-textured electrical steel sheet according to claim 4, in which the content of Si, Mn, Al and P in the steel is, in wt.%:
Si: more than 3.5 but not more than 5.0
Mn: 0.3 or less
Al: 0.1 or less and
P: 0.05 or less. 6. A method of manufacturing a non-textured electrical steel sheet according to claim 4 or 5, in which the steel slab further comprises at least one element, in wt.%:
Sb: 0.0005 - 0.1
Sn: 0.0005 - 0.1
B: 0.0005 - 0.01
Ca: 0.001 - 0.01
REM: 0.001 - 0.01
Co: 0.05 - 5
Ni: 0.05 - 5 and
Cu: 0.2-4.

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