A non-oriented electrical steel and a method of manufacturing non-oriented electrical steel thereof

Abstract

A non-oriented electrical steel sheet having a thickness from 0.2mm to 0.4mm and having a composition comprising of the following elements, 0.0001% ≤ Carbon ≤ 0.007 %,0.2% ≤ Manganese ≤ 0.5%,3% ≤ Silicon ≤ 3.6%,0.5% ≤ Aluminum ≤ 0.96 %,0.001%≤ Nickel ≤ 0.1%,Phosphorus ≤ 0.15 %,Sulfur ≤ 0.006 %,Nitrogen ≤ 0.09% with 4% ≤ Si+Al+Mn ≤ 5.5%, Titanium ≤ 0.1%,Niobium ≤ 0.1%,Vanadium ≤ 0.1%, Chromium ≤ 1%, Molybdenum ≤ 0.5%,Tungsten≤ 0.1%,Cobalt ≤ 1%,Arsenic ≤ 0.05%,Calcium ≤ 0.01%,Copper ≤ 1%,Boron ≤ 0.05%,Lead ≤ 0.2%,Tin≤ 0.2%, Antimony ≤ 0.2%,the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet being made of ferrite and comprising in area fraction, 70% to 100% recrystallized microstructure, 0% to 30% non-recrystallized microstructure wherein the average grain size of recrystallized microstructure is from 95 microns to 250 microns and having a percentage of eddy current losses in total iron losses, measured at 1.5 T and 400 Hz according to standard 60404-2, of less than 15% when calculated in accordance with Bertotti method.

Description

[0001] A NON-ORIENTED ELECTRICAL STEEL AND A METHOD OF MANUFACTURING NON-ORIENTED ELECTRICAL STEEL THEREOF

[0002]

[0001] The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the present invention relates to a nonoriented electrical steel sheet and a manufacturing method thereof that have low iron losses specifically a low eddy current loss while having good mechanical properties.

[0003]

[0002] Therefore, intense research and development endeavors are put in higher performance properties have been required for a non-oriented electrical steel sheet to be used as an iron core material of a electrical machine due to a worldwide increase in achievement of energy saving of an electrical apparatus. Recently in particular, as a motor to be used for an Hydro, wind and turbo motors or the like as well as Industry high power motors and generators, a demand for a small-sized high-power motor has been high. Such an electric motor has been designed to make high-speed rotation possible to thereby obtain high torque while having lowest possible losses. This requires light and highly efficient non oriented electrical steels which have low losses as their key property. Finding the balance between losses, permeability, polarisation, thermal conductivity, tensile strength and yield strength, is vital for non-oriented electrical steels.

[0004]

[0003] The lower the iron losses in the electric machine, the higher its efficiency, hence to reduce the quantity of the iron losses in an electrical machine the manufacturers of the electrical machines have several options, whereby their principal options are to reduce either the hysteresis losses or the eddy current losses to improve the efficiency of their electrical machine. Advances are frequently achieved by a combination of the two approaches. This invention relates to the second option, namely the reduction of eddy current losses for an electrical machine, there is two-track alternatives to reduce the eddy current losses:

[0005]

[0004] The first track consists of reducing the thicknesses of the steel sheets used in the electrical machines such as to have the thickness of the steel sheet from 0.35mm to 0.8mm. Unfortunately, this solution has its limits on account of a reduction in the stacking factor which decreases the torque achievable for a given machine height and further a prohibitive decrease in the rigidity of certain parts and the appearance of acoustical problems.

[0006]

[0005] The second track consists of optimizing the elemental composition of the steel sheet such as by increase the amount of alloying elements to restrict the eddy current losses. Among these alloying elements such as, the Aluminum and Manganese ones have attractive mechanical and magnetic properties while making it possible to significantly reduce the eddy current losses. However, addition of alloying elements can be done up to a limit because after a certain percentage presence alloying elements will impacts the hysteresis losses and the magnetic polarization.

[0007]

[0006] Earlier research and developments in the field of high strength non-oriented electrical steel have resulted in several methods for producing high strength nonoriented electrical steel, some of which are enumerated herein for conclusive appreciation of the present invention:

[0008]

[0007] WO2023 / 282197 is a high-strength non-oriented electromagnetic steel sheet having favorable fatigue characteristics suitable for a rotor core; and a nonoriented electromagnetic steel sheet having excellent magnetic characteristics suitable for a stator core. This non-oriented electromagnetic steel sheet has a component composition which contains, in terms of mass%, at most 0.01 % of C, 2.0-4.5% (exclusive of 4.5) of Si, 0.05-5.00% of Mn, at most 0.1 % of P, at most 0.01 % of S, at most 3.0% of Al, and at most 0.005% of N, with less than 4.5% of Si+AI and the remainder consisting of Fe and inevitable impurities, and is characterized in that crystal grains in the steel sheet have an average crystal grain diameter X1 of at most 50 pm, a standard deviation S1 of the crystal grain diameter distribution satisfying S1 / X1 <0.75, and a kurtosis K1 of the crystal grain diameter distribution of at most 20.0. WO2023 / 282197 does not demonstrate the total elongation and eddy current loss at all.

[0009]

[0008] The purpose of the present invention is to solve these problems by making non-oriented electrical steel sheets that have a percentage of eddy current losses in total iron losses, measured at 1 ,5T and 400 Hz, of less than 15% and preferably less than 13% and more preferably from 5% to 13%, when calculated in accordance with Bertotti method.

[0010]

[0009] In a preferred embodiment, the steel sheet according to the invention can have the following additional properties, taken in isolation or in combination:

[0011] - an ultimate tensile strength of 510MPa or more in both transversal direction as well as rolling direction and preferably more than 530MPa in both transversal direction as well as rolling direction

[0012] - a yield strength from 395MPa or more in both transversal direction as well as rolling direction and preferably from 410MPa or more in both transversal direction as well as rolling direction

[0013] - a total elongation of 10% or more in both transversal direction as well as rolling direction and preferably more than or equal to 13% in both transversal direction as well as rolling direction

[0014] - a magnetic polarization at 5000A / m (J50) from 1.550T to 1.6200T and preferably a magnetic polarization at 5000A / m (J50) from 1.570T to 1.615T.

[0015] - total iron losses from 2.0 to 2.6W / kg when measured at 1.5T and 400Hz and preferably from 2.2 to 2.5 W / kg when measured at 1 ,5T and 400Hz.

[0016]

[0010] Preferably, such steel can also have a good suitability for rolling with good punchability and coatability.

[0017]

[0011] Preferably, a hardness greater than or equal to 185HV and preferably hardness greater than or equal to 195HV.

[0018]

[0012] Another object of the present invention is also to make available a method for the manufacturing of these sheets that is compatible with conventional industrial applications while being robust towards manufacturing parameters shifts.

[0019]

[0013] The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention.

[0020]

[0014] The chemical composition of the non-oriented electrical steel comprises of the following elements:

[0015] Carbon is present in the steel of present invention from 0.0001 % to 0.007%. Carbon is a precipitate forming element that is why detrimental for the magnetic properties of the present steel. Hence the presence of Carbon in the present steel is from 0.0001 % to 0.007%. Since the Carbon promotes magnetic aging the preferred content of Carbon according to the present invention is from 0.001 % to 0.006% and more preferably from 0.001 % to 0.005%.

[0021]

[0016] Manganese content of the steel of present invention is from 0.2% to 0.5%. Manganese provides solid solution strengthening and reducing the lower eddy- current loss by increasing the specific resistance of the steel sheet. When the addition of manganese amount is above 0.5%, the magnetic flux density and permeability decreases, and recrystallization of the steel will be hindered during annealing. The preferred limit for the presence of Manganese is from 0.21 % to 0.4% and more preferably from 0.22% to 0.3%.

[0022]

[0017] Silicon content of the steel of present invention is from 3% to 3.6%. Silicon is an element that contributes to increasing the strength by solid solution strengthening and is a key element to reduce eddy current loss of iron loss by increasing specific resistance of steel. The mentioned effects require a minimum Silicon content of at least 3%. However, when silicon content is in an amount exceeding 3.6% cause decrease in permeability and flux density. The preferred limit for the presence of Silicon is from 3.1 % to 3.5% and more preferably from 3.2% to 3.4%.

[0023]

[0018] The content of the Aluminum is from 0.5% to 0.96%. Aluminum increases the electrical resistivity of the material and can effectively reduce the iron loss of steel. A minimum of 0.7% of Aluminum is required to have desired iron losses as well as to elevating permeability and enhancing electrical resistivity. When the content of Aluminum is present more than 0.96%, fine AIN tends to precipitate to increase iron loss. Since reducing Al improves texture and enhances magnetic flux density, the preferred limit for the presence of Aluminium is from 0.7% and 0.96% and more preferably from 0.8% to 0.96%.

[0024]

[0019] Nickel is an essential element and is present in an amount of 0.001 % to 0.1 % to increase the strength of the steel present invention specifically to reach the tensile strength more than or equal to 51 OMPa and also to improve its strength and elongation. However, when its content is above 0.1 %, Nickel causes ductility deterioration. The preferred limit for the presence of Nickel is from 0.005% and 0.09% and more preferably from 0.008% to 0.06%.

[0025]

[0020] Phosphorus constituent of the Steel of present invention is up to 0.15%, Phosphorus reduces the hot and cold ductility, particularly due to its tendency to segregate at the grain boundaries or co-segregate with Manganese. For these reasons, its content is limited to 0.15% and preferably lower than 0.09%.

[0026]

[0021] Sulfur is not an essential element but may be contained as an impurity in steel and from point of view of the present invention the Sulfur content is preferably as low as possible but 0.006% or less from the viewpoint of manufacturing cost. Further if higher Sulfur is present in steel it combines to form Sulfides which are detrimental for the magnetic properties of the present invention.

[0027]

[0022] Nitrogen is limited to 0.09% to minimize the precipitation of Aluminum nitrides during solidification which are detrimental for magnetic properties of the steel.

[0028]

[0023] Titanium is an optional element and the content of the titanium is up to 0.1 %. It forms Titanium-Carbo-Sulphides or Titanium-Carbo-nitrides appearing during or cooling after hot tolling of the steel of present invention to enhance the mechanical properties without impairing the magnetic properties. The amount of Titanium is so limited to 0.1 % to avoid the formation of Titanium-nitrides detrimental for magnetic properties of the steel of present invention. The preferred limit for the presence of Titanium is from 0% and 0.09% and more preferably from 0 to 0.05%.

[0029]

[0024] Niobium is an optional element in the Steel of present invention up to 0.1 % and suitable for forming carbo-nitrides to increase strength of the Steel of present invention by precipitation hardening. Niobium will also impact the size of microstructural components through its precipitation as carbo-nitrides. However, Niobium content above 0.1 % is not economically interesting as a saturation effect.

[0025] Vanadium is an optional element in the Steel of present invention up to 0.1 % and is effective in enhancing the strength of steel by forming carbides or carbonitrides and the upper limit is 0.1 % from economic points of view.

[0030]

[0026] Chromium is an optional element for the steel of present invention up to 1 %. Chromium provide strength to the steel by solid solution strengthening but when used above 1 % impairs surface finish of steel.

[0031]

[0027] Molybdenum is an optional element up to 0.5% of the Steel of present invention. Mo has an effect of coarsening carbide and thus reducing the iron loss. When it exceeds 0.5%, the effect of improving the iron loss is saturated.

[0032]

[0028] Tungsten is an optional element up to 0.1 % of the Steel of present invention. Tungsten has an effect of coarsening carbide and reducing the iron loss, like Mo. However, when the addition amount is less than 0.001 mass%, the above effect cannot be obtained sufficiently, while when it exceeds 0.1 wt.%, the effect of improving the iron loss is saturated.

[0033]

[0029] Cobalt is an optional element up to 1 % of the Steel of present invention. Cobalt is an element increasing the magnetic moment of Fe alloy and has an effect of increasing a magnetic flux density and reducing the iron loss. However, when the addition amount is less than 0.01 wt.%, the above effects cannot be obtained sufficiently, while when it exceeds 1 wt.%, the raw material cost is largely increased.

[0034]

[0030] Arsenic is an optional element up to 0.05% of the Steel of present invention. As is a grain boundary segregation element and has an effect of improving the texture and thus reducing the iron loss. The above effect is obtained by the addition of not less than 0.001 wt.%. However, As is an element causing grain boundary embrittlement, and this adverse effect becomes particularly remarkable when it is added by more than 0.05 wt.%. Therefore, As is preferable to be added within the range of 0.001 to 0.05 wt.%

[0035]

[0031] Copper may be added as an optional element in an amount up to 1 % to increase the strength and elongation of the of Steel of present invention. However, when its content is above 1 %, it can degrade the surface aspects.

[0032] Boron is an optional element for the steel of present invention and may be present up to 0.05%. Boron forms boro-nitirides and impart additional strength to steel of present invention when added in an amount of at least 0.0001 %.

[0036]

[0033] Calcium may be present in the steel of present invention optionally up to 0.01 % and may preferably be from 0.001 % to 0.01 %%. Calcium contributes towards the refining of the Steel by binding the detrimental Sulfur content in globular form thereby retarding the harmful effect of Sulfur.

[0037]

[0034] Other elements such as Sn , Pb or Sb can be added individually or in combination in the following proportions: Sn < 0.2%, Pb < 0.2% and Sb < 0.2%. Up to the maximum content levels indicated, these elements make it possible to refine the grain during solidification. The remainder of the composition of the steel consists of iron and inevitable impurities resulting from processing.

[0038]

[0035] 4% < Si + Al +Mn < 5.5%

[0039]

[0036] The non-oriented electrical steel sheet according to the invention mandatorily contains Silicon, Manganese and Aluminum such that the total content is from 4% to 5.5%. When the total content of Si, Mn and Al is less than 4%, it is not possible to achieve the mechanical properties with the magnetic properties. However, when the total content of Si , Mn and Al exceeds 5.5%, steel is hardened and the rolling becomes difficult. The preferred limit for the presence of Si, Mn and Al is from 4.1 % to 5.2% and more preferably from 4.2% to 4.9%.

[0040]

[0037] The microstructure of the non-oriented electrical steel will now be described in detail, all percentages being in area fraction.

[0041]

[0038] The microstructure is made of ferrite. The steel of present invention has a recrystallized microstructural region from at least 70% to 100% in area fraction with grains having an average grain size from 95 microns to 250 microns. The recrystallized structure with a high degree of recrystallization is due to the homogenous Silicon enrichment which improves magnetic properties of the steel of present invention. A controlled grain size ensures the mechanical properties in both transverse and rolling direction. The preferred degree of recrystallization is from 80% to 100% and more preferably from 85% to 100% or even better of 100%. The preferred average grain size for the present invention is from 100microns to 220microns and more preferably from 105 microns to 180 microns.

[0042]

[0039] The steel of present invention may have a non-recrystallized microstructural region from 0% to 20% in area fraction and the preferred degree of nonrecrystallization is from 0% to 30% and more preferably from 0% to 20% or even better equal to 0%.

[0043]

[0040] In addition to the above-mentioned microstructure, the microstructure of the non-oriented electrical steel is free from microstructural components such as martensite, bainite, pearlite and cementite.

[0044]

[0041] The steel according to the invention can be manufactured by any suitable methods. It is however preferable to use the method according to the invention that will be detailed, as a non-limitative example.

[0045]

[0042] Such preferred method consists in providing a semi-finished casting of steel with a chemical composition of the steel according to the invention. The casting can be done either into ingots or continuously in form of thin slabs or thin strips, i.e. with a thickness ranging from approximately 240mm for slabs up to several tens of millimeters for thin strip.

[0046]

[0043] For example, the cast in form of a slab is casted with the chemical composition according to the invention and then it is reheated, the Slab Reheating Temperature lying from 1050°C to 1280°C until the temperature is homogeneous through the whole slab. Below 1050°C, rolling becomes difficult and forces on the mill will be too high. Above 1280°C, high silicon grades become very soft and might show some sagging and thus become difficult to handle. Preferably, the slab reheating temperature is from 1080°C to 1260°C and more preferably from 1100°C to 1200°C

[0047]

[0044] Subjecting the reheated slab to hot rolling wherein the hot rolling finishing temperature plays a role on the final hot rolled microstructure and takes place from 800°C to 950°C. When the Finishing Rolling Temperature is below 800°C, recrystallization is limited and the microstructure is highly deformed. Above 950°C would mean more impurities in solid solution and possible consequent precipitation and deterioration of magnetic properties as well. Preferably, the Finishing Rolling Temperature is from 820°C to 920°C and more preferably from 850°C to 890°C.

[0048]

[0045] The hot rolled steel sheet obtained in this manner is then cooled immediately at a cooling rate of at least 10°C / s to the Coiling Temperature of the hot rolled steel sheet which also plays a role on the hot rolled steel sheet; it takes place from 480°C to 580°C. Coiling at temperatures below 480°C would not allow sufficient recovery to take place while this metallurgical step is necessary for magnetic properties. Above 580°C, a thick oxide layer would appear, and it will cause difficulties for subsequent processing steps such as cold rolling and / or pickling. Preferably, the cooling rate will be less than or equal to 200° C / s. Preferably, the Coiling Temperature is from 500°C to 570°C and more preferably from 525°C to 555°C.

[0049]

[0046] The coiled hot rolled steel sheet is then cooled down to room temperature before subjecting it to optional hot band annealing.

[0050]

[0047] The hot rolled steel sheet may be subjected to an optional scale removal step to remove the scale formed during the hot rolling before optional hot band annealing. The hot rolled sheet then be subjected to an optional hot band annealing such hot band annealing is performed at temperatures from 650°C to 1100°C, preferably for at least 10 seconds and not more than 96 hours, the temperature preferably remaining from 700°C to 1070°C and more preferably from 780°C to 1000°C. Thereafter, an optional scale removal step of this hot rolled steel sheet may be performed through, for example, pickling of such sheet.

[0051]

[0048] This hot rolled steel sheet is then subjected to cold rolling to obtain a cold rolled steel sheet with a thickness reduction from 50 to 95%. Preferably, the thickness reduction from 60% to 95% and more preferably from 75% to 95%.

[0052]

[0049] Thereafter the cold rolled steel sheet is being heat treated which will impart the steel of present invention with requisite mechanical properties and microstructure.

[0053]

[0050] The cold rolled steel sheet is then heated wherein the heating starts from room temperature, the cold rolled steel sheet being heated, at a heating rate HR1 of at least 1 °C / s, to an annealing temperature Tsoak which is from 800°C to 1100°C, preferably from 825°C to 1080°C and more preferably from 850°C to 1060°C. In a preferred embodiment, the heating rate HR1 for heating is at least 2°C / s and more preferably at least 5°C / s.

[0054]

[0051] The cold rolled steel sheet is held at Tsoak during 10 seconds to 5000 seconds to ensure a recrystallization of minimum 70%.

[0055]

[0052] The cold rolled steel sheet is then cooled wherein cooling starts from Tsoak, the cold rolled steel sheet being cooled down, at a cooling rate CR1 from 1 °C / s to 150°C / s, to a temperature T1 which is in a range from 20°C to 300°C. In a preferred embodiment, the cooling rate CR1 is from 3°C / s to 120°C / s. The preferred T1 temperature is from 20°C to 200°C.

[0056]

[0053] The cold rolled steel sheet thus obtained has a thickness from 0.2mm to 0.4mm and more preferably from 0.22 mm to 0.38 mm and even more preferably from 0.25mm to 0.37 mm.

[0057]

[0054] Then, the cold rolled steel sheet is cooled down to room temperature to obtain a non-oriented electrical steel sheet.

[0058]

[0055] The non-oriented electrical steel sheet of the present invention may optionally be coated with insulation, organic coating or inorganic coating or combination of to improve isolation.

[0059]

[0056] EXAMPLES

[0060]

[0057] The following tests, examples, figurative exemplification and tables which are presented herein are non-restricting in nature and must be considered for purposes of illustration only and will display the advantageous features of the present invention.

[0061]

[0058] Steel sheets made of steels with different compositions are gathered in Table 1 , where the steel sheets are produced according to process parameters as stipulated in Table 2, respectively. Thereafter, Table 3 gathers the result of evaluations of obtained properties.

[0062]

[0059] Table 2 gathers the hot rolling and annealing process parameters implemented on cold rolled steel sheets to impart the steels of table 1 with requisite mechanical and magnetic properties to become a non-oriented electrical steel. All the Inventive steels are cooled after hot rolling at cooling rate 15°C / s and after the coiling are subjected hot band annealing at 800°C for 12 hours. Further the heating rate HR1 to the annealing soaking temperature is 5°C / s. The T1 temperature for all the inventive examples is 25°C while the cooling rate CR1 is at 5°C / s.

[0063]

[0060] All steels produced according to table 2 parameters showed a 100% recrystallized microstructure with a grain size of 140pm plus or minus 2 microns and a thickness of 0.35mm.

[0064]

[0061] Table 1

[0065]

[0062] Table 2

[0066]

[0063] Table 3

[0067]

[0064] The results of the various mechanical tests conducted in accordance with the standards are gathered. The ultimate tensile strength, total elongation and yield strength are measured in accordance with NF EN ISO 6892-1 standards and the J50 magnetic properties and the iron total losses at 1.5T and 400Hz were measured in accordance with I EC 60404-2 standards. The Eddy current losses are calculated in accordance with the Bertotti Method published in the paper entitled as “General Properties of Power Losses in Soft Ferromagnetic Materials” by Giorgio Berttoti published in IEEE TRANSACTIONS ON MAGNETICS, Vol. 24, No.1 of January 1988. The Equation 2 identifies classical losses which is designated by (pclass) which for the purpose of this invention is referred to as Eddy current losses.

[0068]

[0065] The average grain size of the recrystallized microstructure is measured in accordance with ASTM E112 96(02) standards with linear intercept method.

Claims

CLAIMS1 . A non-oriented electrical steel sheet having a thickness from 0.2mm to 0.4mm and having a composition comprising of the following elements, expressed in percentage by weight:0.0001 % < Carbon < 0.007 %0.2% < Manganese < 0.5%3% < Silicon < 3.6%0.5% < Aluminum < 0.96 %0.001 %< Nickel < 0.1 %Phosphorus < 0.15 % Sulfur < 0.006 % Nitrogen < 0.09% with 4% < Si+AI+Mn < 5.5% and can contain one or more of the following optional elementsTitanium < 0.1 %Niobium < 0.1 %Vanadium < 0.1 %Chromium < 1 %Molybdenum < 0.5%Tungsten< 0.1 %Cobalt < 1 %Arsenic < 0.05%Calcium < 0.01 %Copper < 1 %Boron < 0.05%Lead < 0.2%Tin< 0.2%Antimony < 0.2%the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet being made of ferrite and comprising in area fraction, 70% to 100% recrystallized microstructure, 0% to 30% non-recrystallized microstructure wherein the average grain size of recrystallized microstructure is from 95 microns to 250 microns and having a percentage of eddy current losses in total iron losses, measured at 1.5 T and 400 Hz according to standard 60404-2, of less than 15% when calculated in accordance with Bertotti method.

2. Non-oriented electrical steel sheet according to claim 1 , wherein the composition includes 3.1 % to 3.5% of Silicon.

3. Non-oriented electrical steel sheet according to claim 1 or 2, wherein the composition includes 0.001 % to 0.006% of Carbon.

4. Non-oriented electrical steel sheet according to claims 1 to 3, wherein the composition includes 0.8% to 0.96% of Aluminum.

5. Non-oriented electrical steel sheet according to anyone of claim 1 to 4, wherein the composition includes 0.21 % to 0.4% of Manganese.

6. Non-oriented electrical steel sheet according to anyone of claim 1 to 5, wherein the amount of non-recrystallized microstructure is from 0% to 20%7. Non-oriented electrical steel sheet to anyone of claim 1 to 6, wherein , wherein the amount of recrystallized microstructure is from 80% to 100%.

8. Non-oriented electrical steel sheet to anyone of claims 1 to 7, wherein said steel sheet has a tensile strength of at least 510 MPa in both transversal direction as well as rolling direction.

9. Non-oriented electrical steel sheet to anyone of claims 1 to 8, wherein said steel sheet has a total elongation of at least 10% in both transversal direction as well as rolling direction.

10. A method of production of a non-oriented electrical steel sheet comprising the following successive steps:- providing a steel composition according to anyone of claims 1 to 5;- reheating said semi-finished product to a temperature from 1050°C to 1280°C;- rolling the said semi-finished product wherein the hot rolling finishing temperature shall be from 800°C to 950°C to obtain a hot rolled steel sheet;- cooling the hot rolled sheet immediately after the finishing of hot rolling- then the hot rolled steel sheet is cooled from finishing of hot rolling to a coiling temperature range which is from 480°C to 580°C at a cooling rate of at least 10°C / s- thereafter coiling the hot rolled steel sheet in the coiling temperature range from 480°C to 580°C- optionally performing scale removal process on said hot rolled steel sheet;- optionally hot band annealing is performed on hot rolled steel sheet from 650°C to 1100°C during 10 seconds to 96 hours;- optionally performing scale removal process on said hot rolled steel sheet;- cold rolling the said hot rolled steel sheet with a reduction rate from 50% to 95% to obtain a cold rolled steel sheet having a thickness from 0.2mm to 0.4mm; thereafter annealing the said cold rolled steel sheet wherein the heating for annealing starts from room temperature to an annealing temperature range Tsoak which is from 800°C to 1100°C, with a heating rate HR1 of at least 1 °C / s,- then perform annealing at annealing temperature during 10 to 5000 seconds, then cooling the cold rolled steel sheet which starts from the annealing temperature to a temperature T1 from 300°C to 20°C, with a cooling rate CR1 from rC / s to 150°C / s- then cooling to room temperature to obtain a non-oriented electrical steel sheet .

11. A method according to claim 10, wherein the Tsoak temperature for annealing is from 925°C to 1080°C.

12. A method according to claim 10 or 11 , wherein temperature T1 is from 200°C to13. A method according to anyone of claims 10 to 12, wherein the cooling rate CR1 is from 3°C / s to 120°C / s.

14. Use of a steel sheet according to anyone of claims 1 to 9 or of a steel sheet produced according to the method of claims 10 to 13, for the manufacture of parts of electrical machines.

15. Electrical machine comprising a part obtained according to claim 14.

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