Preparation method of high-magnetic-induction oriented silicon steel

Abstract

The invention discloses a preparation method of high-magnetic-induction oriented silicon steel, which comprises the following steps: sequentially heating, roughly rolling, finely rolling and coiling a plate blank obtained by continuously casting qualified molten steel to obtain a hot-rolled coil; the hot-rolled coil is sequentially subjected to normalizing treatment and cold rolling, and a cold-rolled sheet is obtained; the cold-rolled sheet is sequentially subjected to decarburization and nitriding, and the high-magnetic-induction oriented silicon steel is obtained; in the nitriding process, the nitriding temperature is 910-980 DEG C, and the dew point is 10-60 DEG C. A 910-980 DEG C high-temperature nitriding method is adopted, the diffusion efficiency of N atoms in the steel strip is improved, the uniformity of the N concentration in the thickness direction is improved, the secondary recrystallization quality and the thickness consistency of a magnesium silicate bottom layer can be improved, meanwhile, the heating rate can be properly increased during high-temperature annealing, and the high-temperature annealing time is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of production of oriented silicon steel, and in particular to a method for preparing high magnetic induction oriented silicon steel. Background Art

[0002] High magnetic induction oriented silicon steel (HiB) is an important ferrosilicon alloy used in transformer manufacturing industry. Its production methods can be summarized into three types according to the different ways of obtaining inhibitors and the different slab heating temperatures: inherent inhibitor high temperature method, inherent inhibitor medium temperature method and inhibitor acquisition low temperature method. The slab heating temperatures of the three methods are 1350-1400℃, 1250-1300℃ and 1100-1250℃ respectively. In recent years, global resources have gradually become scarce and environmental pollution has become increasingly serious. The disadvantages of using inherent inhibitor high temperature method and medium temperature method to produce oriented silicon steel have become more and more obvious. Its high energy consumption, high pollution and low efficiency production process are in urgent need of innovation. Reducing costs and improving production efficiency have become the most urgent needs. Therefore, under the premise of ensuring product quality, replacing traditional technology with energy-saving, environmentally friendly and economical production processes has become a research hotspot in the field of silicon steel production and manufacturing, among which the production of oriented silicon steel by low temperature method is an important development content.

[0003] In the production of oriented silicon steel by low temperature method, due to the low heating temperature of the slab, the amount of inhibitors precipitated during hot rolling and normalization is insufficient, and the steel strip is required to be treated with N in the subsequent treatment to improve the inhibitor strength. Among them, nitriding treatment is the key step in forming inhibitors. At present, a variety of schemes have been proposed for nitriding process, such as nitriding by nano-composite electrodeposition technology, nitriding by adding nitride to magnesium oxide separator, gas nitriding, etc. Gas nitriding is the mainstream nitriding method at present, among which using NH3 as nitriding medium is the most common gas nitriding method.

[0004] In the prior art, the temperature range of the low-temperature nitriding process is mostly about 500 to 830° C., and the production efficiency is low. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing high magnetic induction oriented silicon steel to solve the problem in the prior art that the nitriding efficiency is low, the secondary recrystallization quality is unstable, and the magnetic properties of the product are poor.

[0006] In order to achieve the above object, the present invention adopts the following technical solution.

[0007] The present invention provides a method for preparing high magnetic induction oriented silicon steel, the method comprising:

[0008] The slab obtained after secondary refining and continuous casting of molten steel is sequentially heated, rough rolled, finish rolled and coiled to obtain a hot rolled coil;

[0009] The hot-rolled coil is subjected to normalizing treatment and cold rolling in sequence to obtain a cold-rolled sheet;

[0010] The cold rolled sheet is sequentially decarburized and nitrided to obtain high magnetic induction oriented silicon steel; in the nitriding process, the nitriding temperature is 910-980°C and the dew point is 10-60°C.

[0011] Furthermore, the thickness of the slab is 110-250 mm, the thickness of the hot-rolled coil is 1.3-3.0 mm, and the thickness of the cold-rolled plate is 0.15-0.35 mm.

[0012] Furthermore, in the heating step, the heating temperature is 1100-1250°C.

[0013] Furthermore, the normalizing treatment includes a first normalizing treatment and a second normalizing treatment. In the first normalizing treatment, the normalizing temperature is 1050-1150° C. and the holding time is 30-60 seconds. In the second normalizing treatment, the normalizing temperature is 900-1000° C. and the holding time is 1-5 minutes.

[0014] Furthermore, in the decarburization process, decarburization is carried out in a mixed gas atmosphere of water vapor, N2 and H2, the volume ratio of water vapor, N2 and H2 is 3-5:10:40, the heating rate is 20-50°C / s, the decarburization temperature is 750-850°C, and the dew point is 30-80°C.

[0015] Furthermore, in the nitriding process, the nitriding medium is NH3, the nitriding atmosphere is a mixed gas atmosphere of NH3, N2 and H2, the volume percentage of NH3 in the mixed gas is 12-30%, and the nitriding time is 10-40s.

[0016] Furthermore, the decarburizing and nitriding of the cold-rolled sheet in sequence comprises:

[0017] The cold rolled sheet is sequentially subjected to decarburization, nitriding, coating with a separator, drying and high temperature annealing.

[0018] Furthermore, in the drying process, the drying temperature is 160 to 260° C. and the heat preservation time is 2 to 10 minutes.

[0019] Furthermore, in the high temperature annealing process,

[0020] The heating rate in the temperature range of 700-1100°C is 30-50°C / h, and the heating rate in the temperature range of 1100-1250°C is 3-15°C / h;

[0021] In the temperature range of 700-1150° C., the annealing atmosphere is a mixed gas atmosphere of H2 and N2, and the volume ratio of the H2 to the N2 is (1-9):1; in the temperature range of 1150-1250° C., the annealing atmosphere is a H2 atmosphere;

[0022] The insulation time is 5 to 10 hours.

[0023] Furthermore, the chemical components and mass fractions of the chemical components of the high magnetic induction oriented silicon steel are: C: 0.04-0.08%, Si: 2.9-3.8%, Mn: 0.05-0.20%, S: 0.003-0.01%, Al: 0.02-0.04%, N: 0.003-0.01%, Sn: 0.05-0.15%, Cu: 0.003-0.20, and the rest are Fe and unavoidable impurities.

[0024] The beneficial effects of the present invention include at least:

[0025] The present invention provides a method for preparing high magnetic induction oriented silicon steel, wherein the slab obtained after secondary refining and continuous casting of molten steel is sequentially heated, rough rolled, finished rolled and coiled to obtain a hot rolled coil; the hot rolled coil is sequentially normalized and cold rolled to obtain a cold rolled plate; the cold rolled plate is sequentially decarburized and nitrided to obtain high magnetic induction oriented silicon steel; in the nitriding, the nitriding temperature is 910-980°C and the dew point is 10-60°C. The steel plate after molten steel smelting, hot rolling, normalizing, cold rolling and decarburization is subjected to a high temperature nitriding treatment of 910-980°C, which can increase the diffusion rate of N in the steel grade, and the N atoms can penetrate deeper and combine with the internal Al to precipitate new alumina inhibitors in the form of fine dispersion, which can obtain a more uniform nitriding effect under the premise of ensuring the nitriding amount, improve the change of the secondary recrystallization orientation, and thus increase the magnetic induction and reduce the iron loss. Since the nitriding effect is more uniform, the heating rate of the high-temperature annealing stage can be increased, the holding time can be reduced, the annealing time of oriented silicon steel can be shortened, the production efficiency can be improved, resources can be saved, and costs can be greatly saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 A process diagram of a method for preparing high magnetic induction oriented silicon steel according to an embodiment of the present invention;

[0028] Figure 2The EPMA test results of the nitriding effect of Example 2 and Comparative Example 3 of the present invention;

[0029] Figure 3 The calculation results of the distribution of nitriding AlN inhibitors in Example 2 of the present invention and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The embodiment of the present invention provides a method for preparing high magnetic induction oriented silicon steel, the core of which is to prepare high magnetic induction oriented silicon steel by high temperature nitriding process. Figure 1 A method for preparing high magnetic induction oriented silicon steel according to an embodiment of the present invention is combined with Figure 1 , the method comprising,

[0032] S1, the slab obtained by continuous casting of qualified molten steel is heated, rough rolled, finish rolled and coiled in sequence to obtain a hot rolled coil.

[0033] Furthermore, the slab has a thickness of 110 to 250 mm.

[0034] Furthermore, the heating temperature is 1100-1250°C.

[0035] The above heating temperature can ensure the uniform temperature of oriented silicon steel and save energy. If the temperature is too high, it will cause the slab to be overburned, increase iron loss and waste energy. If the heating temperature is too low, it will lead to low slab temperature and uniform internal structure.

[0036] Furthermore, the thickness of the hot-rolled coil is 1.3 to 3.0 mm.

[0037] S2, performing normalizing treatment and cold rolling on the hot-rolled coil in sequence to obtain a cold-rolled sheet.

[0038] Furthermore, the normalizing treatment includes a first normalizing treatment and a second normalizing treatment. In the first normalizing treatment, the normalizing temperature is 1050-1150°C and the holding time is 30-60S; in the second normalizing treatment, the normalizing temperature is 900-1000°C and the holding time is 1-5min. Through the first normalizing treatment and the second normalizing treatment, the material structure can be homogenized, and the AlN precipitated by hot rolling can be dissolved and re-precipitated in a fine and uniform manner through austenitization. If the normalizing temperature is too high and the holding time is too long, it will cause energy waste. If the normalizing temperature is too low and the holding time is too short, the unevenness of the material structure may increase. In addition, the size and quantity of the precipitated AlN do not match the grain size of the subsequent ferrite structure.

[0039] Furthermore, the thickness of the cold-rolled sheet is 0.15-0.35 mm.

[0040] S3, sequentially decarburizing, nitriding, coating with a release agent, drying and high-temperature annealing the cold-rolled sheet to obtain high magnetic induction oriented silicon steel.

[0041] Furthermore, in the decarburization, decarburization is carried out in a mixed gas atmosphere of water vapor, N2 and H2, the volume ratio of water vapor, N2 and H2 is 3-5:10:40, the heating rate is 20-50°C / s, the decarburization temperature is 750-850°C, and the dew point is 30-80°C.

[0042] Through the above-mentioned temperature and atmosphere, the surface cold-rolled plate can be decarburized, the austenite phase region can be removed, the influence of the Gaussian texture and other orientation texture ratio changes caused by the austenite phase transformation in the subsequent high-temperature annealing can be eliminated, and a reasonable grain size can be obtained at the same time.

[0043] Furthermore, in the nitriding process, the nitriding temperature is 910-980°C, for example, 920°C, 925°C, 935°C, 940°C, 945°C, 950°C, 960°C, 970 or 9750°C, and the dew point is 10-60°C, for example, 20°C, 25°C, 27°C, 32°C, 36°C, 40°C, 55°C or 58°C.

[0044] Furthermore, the nitriding medium is NH3, the nitriding atmosphere is a mixed gas atmosphere of NH3, N2 and H2, the volume percentage of NH3 in the mixed gas is 12 to 30%, for example, 15%, 18%, 22%, 25% or 28%, and the nitriding time is 10 to 40s, for example, 12s, 15s, 18s, 22s, 28s, 32s, 35s or 38s.

[0045] This step uses a high-temperature nitriding process to improve the diffusion efficiency of N in the steel strip. N atoms can penetrate deeper and combine with the internal Al to precipitate new aluminum nitride inhibitors in the form of fine dispersion; under the premise of ensuring the nitriding amount, a more uniform nitriding effect is obtained, thereby changing the secondary recrystallization orientation, thereby improving the magnetic induction and reducing iron loss. At the same time, it can also increase the heating rate in the 700-1100℃ heating range in the subsequent high-temperature annealing process, saving processing time, reducing energy consumption, and improving production efficiency.

[0046] Furthermore, in the drying, the drying temperature is 160 to 260°C, such as 180°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, and the holding time is 2 to 10 minutes;

[0047] Furthermore, in the high temperature annealing,

[0048] The heating rate in the temperature range of 700-1100°C is 30-50°C / h, such as 33°C / h, 35°C / h, 38°C / h, 40°C / h, 43°C / h, 45°C / h, 47°C / h or 49°C / h, etc. The heating rate in the temperature range of 3100-1250°C is 3-15°C / h, such as 4°C / h, 5°C / h, 7°C / h, 9°C / h, 11°C / h or 13°C / h, etc.;

[0049] In the temperature range of 700-1150° C., the annealing atmosphere is a mixed gas atmosphere of H2 and N2, and the volume ratio of the H2 to the N2 is (1-9):1; in the temperature range of 1150-1250° C., the annealing atmosphere is a H2 atmosphere;

[0050] The insulation time is 5 to 10 hours.

[0051] Since the present application adopts high-temperature nitriding, the penetration rate of N is fast, so the penetration depth of nitrogen is deep, and the penetrated nitrogen is more uniform in the thickness direction, and the crystal structure is more reasonable. The heating rate at the beginning of conventional high-temperature annealing is about 15°C / s, and the heating rate is low. The purpose is to make the N in the steel more uniform by sufficient time. The high-temperature nitriding of the present application is fast and uniform. Therefore, the heating rate can be increased in the early stage of high-temperature annealing, thereby improving the efficiency of high-temperature annealing, and can also achieve the effect of inhibitor homogenization and organizational transformation.

[0052] Furthermore, the chemical components and mass fractions of the chemical components of the high magnetic induction oriented silicon steel are: C: 0.04-0.08%, Si: 2.9-3.8%, Mn: 0.05-0.20%, S: 0.003-0.01%, Al: 0.02-0.04%, N: 0.003-0.01%, Sn: 0.05-0.15%, Cu: 0.003-0.20, and the rest are Fe and unavoidable impurities.

[0053] In the prior art, a low-temperature nitriding process is adopted, and the nitriding temperature range is mostly about 500-830°C. After this low-temperature nitriding treatment, the N content is unevenly distributed on the steel strip, specifically, N is concentrated in the surface area, and a slower heating rate is required during high-temperature annealing to dissolve the silicon nitride precipitate phase on the surface, and the released N diffuses inward into the plate to form a new AlN inhibitor. However, this method makes it easy for the N on the surface to return to the atmosphere, which reduces the nitriding efficiency. At the same time, it causes the internal inhibitor to be insufficiently inhibited, and prematurely ripens and solid-solubilizes during the high-temperature annealing stage, resulting in the quality of secondary recrystallization being affected and unstable, and ultimately affecting the magnetic properties of the product. The present invention provides a preparation method for high magnetic induction oriented silicon steel, which adopts a higher nitriding temperature to improve the diffusion efficiency of N in the steel strip, so that N atoms can penetrate deeper and combine with the internal Al to precipitate new aluminum nitride inhibitors in the form of fine dispersion; the nitriding atmosphere is adjusted to obtain a more uniform nitriding effect under the premise of ensuring the nitriding amount, and the secondary recrystallization quality and the consistency of the thickness of the magnesium silicate bottom layer can also be improved. At the same time, the high temperature annealing heating rate can be increased during high temperature annealing, the high temperature annealing time can be shortened, and the production efficiency can be improved.

[0054] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0055] Embodiments 1 to 4 provide a method for preparing high magnetic induction oriented silicon steel, combining Figure 1 , the method comprising,

[0056] S1, heating, rough rolling, finish rolling and coiling are performed on the slab obtained after continuous casting of qualified molten steel in sequence to obtain a hot rolled coil.

[0057] S2, performing normalizing treatment and cold rolling on the hot-rolled coil in sequence to obtain a cold-rolled sheet.

[0058] S3, sequentially decarburizing, nitriding, applying a separator, drying and high-temperature annealing the cold-rolled sheet to obtain high magnetic induction oriented silicon steel. The nitriding is performed in a mixed gas atmosphere of NH3, N2 and H2.

[0059] The chemical compositions of the high magnetic induction oriented silicon steels prepared in Examples 1 to 4 are shown in Table 1, and the process control of the preparation process is detailed in Tables 2, 3, 4 and 5.

[0060] Comparative Examples 1 to 3 provide a method for preparing high magnetic induction oriented silicon steel, wherein the slab with a composition as shown in Table 1 is subjected to hot rolling, normalizing treatment, cold rolling, decarburization, nitriding, drying and annealing to obtain high magnetic induction oriented silicon steel, wherein the decarburization, drying and annealing processes are shown in Tables 4, 5 and 6, and the nitriding temperature is 840°C.

[0061] Table 1

[0062]

[0063] Table 2

[0064]

[0065] Table 3

[0066]

[0067] Table 4

[0068]

[0069] Table 5

[0070]

[0071] Table 6

[0072]

[0073] Table 7

[0074]

[0075] Note: The above embodiments are only the best examples and are not intended to limit the implementation of the present invention.

[0076] Table 7 shows the test results of the iron loss and magnetic steel of the non-oriented silicon steel prepared in Examples 1 to 4 of the present invention and Comparative Examples 1 to 3. As can be seen from Table 7, the nitriding temperatures of Examples 1 to 4 are 930°C, 930°C, 950°C and 950°C, and the iron loss P of the oriented silicon steel prepared therefrom is 0.1437 W / m2 after sampling and testing. 1.7 / 50 The magnetic induction is 0.0767~0.0790w / kg, the iron loss range in the coil length direction is 0.01~0.03, and the magnetic induction B 800 is 1.922~1.931T; the nitriding temperature used in Comparative Examples 1 to 3 is 840℃, and the iron loss P 1.7 / 50 The magnetic induction is 0.821~0.956w / kg, the iron loss range in the coil length direction is 0.07~0.73, and the magnetic induction B 800 It is 1.767~1.908T.

[0077] Compared with Comparative Examples 1 to 3, the oriented silicon steel prepared in Examples 1 to 4 has a lower iron loss P 1.7 / 50 At least 0.031w / kg was increased, the extreme difference of iron loss in the coil length direction was reduced by 0.05w / kg, and the magnetic induction B 800 It has increased by at least 0.014 T. It can be seen that the high-temperature nitriding process has significantly improved the iron loss and magnetic induction properties of high magnetic induction oriented silicon steel compared with the low-temperature nitriding process.

[0078] In Example 2 and Example 3, the high temperature annealing process is adjusted on the basis of Example 1, and the heating rate in the heating stage of 700-1100°C is increased and the holding time in the holding stage is reduced, respectively, as shown in Table 5. Compared with Example 1, the performance of the oriented silicon steel products prepared in Example 2 and Example 3 is not deteriorated, and is even slightly improved. It can be seen that the high temperature nitriding process of the present invention can significantly increase the heating rate (30-50°C / h) in the initial stage (700-1100°C) of the heating stage of high temperature annealing, and reduce the holding time, while improving the steel loss and magnetic induction properties of high magnetic induction oriented silicon steel. The heating rate is 2-3 times higher than that of the conventional annealing process, which greatly shortens the annealing treatment time of oriented silicon steel, saves resources, and greatly saves costs.

[0079] Figure 2 The EPMA test results of the nitriding effect of the oriented silicon steel prepared in Example 2 and Comparative Example 3 are as follows. Figure 2 It can be seen that compared with the comparative example 3 of the conventional temperature nitriding at 840°C, the N content of the surface area of ​​the sample of the embodiment 2 of the high temperature nitriding at 950°C is lower, while the N content inside is high. The penetration distance of the embodiment of the present invention is larger and the distribution is more uniform (see Figure 3 ). At the same time, the distribution of AlN inhibitors was calculated using a numerical model. The calculation results show that after the nitriding process is completed, the conventional nitriding process at a temperature of 840°C precipitates more AlN near the surface of the steel strip, and very little AlN is inside the steel strip. The high-temperature nitriding process generates more AlN inhibitors inside the steel strip (see Figure 3 ).

[0080] The nitriding effect of high temperature nitriding allows N to penetrate deep into the sample instead of being confined to the surface area, and at the same time improves the distribution of the effective inhibitor AlN inside the steel strip, which can avoid the influence of high temperature annealing process fluctuations on performance, and is conducive to improving product performance. At the same time, due to the use of a higher nitriding temperature, the nitriding effect is more uniform, and the heating rate of the high temperature annealing heating stage (700-1100°C) can be increased to 30-50°C / h, which is 2-3 times higher than the conventional heating rate, shortening the processing time and greatly saving costs.

[0081] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing high magnetic induction oriented silicon steel, characterized in that: include: The slab obtained by continuous casting of qualified molten steel is sequentially heated, rough rolled, finish rolled and coiled to obtain a hot rolled coil; The hot-rolled coil is subjected to normalizing treatment and cold rolling in sequence to obtain a cold-rolled sheet; The cold rolled sheet is sequentially decarburized and nitrided to obtain high magnetic induction oriented silicon steel; in the nitriding process, the nitriding temperature is 910-980°C and the dew point is 10-60°C.

2. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: The thickness of the slab is 110-250 mm, the thickness of the hot-rolled coil is 1.3-3.0 mm, and the thickness of the cold-rolled plate is 0.15-0.35 mm.

3. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: In the heating step, the heating temperature is 1100-1250°C.

4. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: The normalizing treatment includes a first normalizing treatment and a second normalizing treatment. In the first normalizing treatment, the normalizing temperature is 1050-1150° C. and the holding time is 30-60 seconds. In the second normalizing treatment, the normalizing temperature is 900-1000° C. and the holding time is 1-5 minutes.

5. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: In the decarburization process, decarburization is carried out in a mixed gas atmosphere of water vapor, N2 and H2, the volume ratio of water vapor, N2 and H2 is 3-5:10:40, the heating rate is 20-50°C / s, the decarburization temperature is 750-850°C, and the dew point is 30-80°C.

6. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: In the nitriding process, the nitriding medium is NH3, the nitriding atmosphere is a mixed gas atmosphere of NH3, N2 and H2, the volume percentage of NH3 in the mixed gas is 12-30%, and the nitriding time is 10-40s.

7. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: The step of sequentially decarburizing and nitriding the cold-rolled sheet comprises: The cold rolled sheet is sequentially subjected to decarburization, nitriding, coating with a separator, drying and high temperature annealing.

8. The method for preparing high magnetic induction oriented silicon steel according to claim 7, characterized in that: In the drying process, the drying temperature is 160-260° C. and the heat preservation time is 2-10 minutes.

9. The method for preparing high magnetic induction oriented silicon steel according to claim 7, characterized in that: In the high temperature annealing process, the heating rate in the temperature range of 700-1100°C is 30-50°C / h, and the heating rate in the temperature range of 1100-1250°C is 3-15°C / h; In the temperature range of 700-1150° C., the annealing atmosphere is a mixed gas atmosphere of H2 and N2, the volume ratio of the H2 to the N2 is (1-9):1, and in the temperature range of 1150-1250° C., the annealing atmosphere is a H2 atmosphere; The insulation time is 5 to 10 hours.

10. The method for preparing high magnetic induction oriented silicon steel according to claim 1, characterized in that: The chemical components and mass fractions of the chemical components of the high magnetic induction oriented silicon steel are: C: 0.04-0.08%, Si: 2.9-3.8%, Mn: 0.05-0.20%, S: 0.003-0.01%, Al: 0.02-0.04%, N: 0.003-0.01%, Sn: 0.05-0.15%, Cu: 0.003-0.20, and the rest are Fe and unavoidable impurities.

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