JP5119710B2 - High strength non-oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a high-strength non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a high-strength non-oriented electrical steel sheet having a low high-frequency iron loss and a manufacturing method suitable for use in a rotor and a stator core of a high-speed rotating machine. is there.

  In recent years, motor drive control systems have been developed, and frequency control of drive power supply has become possible, and therefore, high-speed motors used in variable speed operation and commercial frequency ranges have increased. The centrifugal force acting on the rotating body is proportional to the radius of rotation and increases in proportion to the square of the rotational speed. Therefore, the electrical steel sheet used for the rotor material of such a high-speed rotating motor, in particular, a medium or large-sized motor that rotates at high speed, needs to have high strength.

  Further, in recent years, in an embedded magnet type DC inverter control motor, which is increasingly used in a drive motor, a compressor motor, and the like of a hybrid vehicle, a magnet is embedded by providing a slit in a rotor portion. For this reason, when the motor rotates, stress concentrates on a narrow bridge portion (between the outer periphery of the rotor and the slit), so that the core material used for the rotor is required to have high strength.

  Furthermore, since rotating devices such as motors and generators use electromagnetic phenomena, the material of the core (core) is naturally required to have excellent magnetic properties. In particular, in a motor that rotates at high speed, an eddy current is generated by high-frequency magnetic flux, which causes a reduction in motor efficiency.

  For the rotor core of a motor, a laminate of non-oriented electrical steel sheets that have been punched and pressed is usually used.If the steel sheet strength does not meet the mechanical strength required for a motor that rotates at high speed, a higher strength is required. A cast steel rotor must be used. However, since the cast rotor is a single piece, the eddy current loss generated is significantly higher than that of a rotor in which electromagnetic steel sheets are laminated. Accordingly, it is desired to develop a magnetic steel sheet having excellent magnetic properties and high strength as a rotor material that rotates at high speed.

  In order to meet the above requirements, several high-strength non-oriented electrical steel sheets have been studied and proposed to date. For example, in Patent Document 1, the Si content is increased to 3.5 to 7.0 mass%, and further strengthened by adding Ti, W, Mo, Mn, Ni, Co, Al, etc. as solid solution strengthening elements. A method for achieving this has been proposed. Patent Document 2 proposes a method for improving magnetic properties by setting the average crystal grain size to 0.01 to 5.0 mm by devising finish annealing conditions in addition to the strengthening method.

  However, when these methods are applied to the actual production of electromagnetic steel sheets, troubles such as sheet breakage are likely to occur in the production line after hot rolling, resulting in lower yields and lower line productivity. There was a problem such as inviting. For this problem, for example, in the case of cold rolling, it is possible to reduce the plate breakage by warming the plate temperature to several hundred degrees C. There are also many problems such as the need for such equipment and the large restrictions on manufacturing.

  Patent Document 3 discloses a method of solid solution strengthening by adding Mn and Ni to a steel containing 2.0 mass% or more and less than 4.0 mass% of Si, and Patent Document 4 discloses 2.0 mass of Si. % To less than 4.0 mass%, Mn and Ni are added to strengthen the solution, and carbonitride-forming elements such as Nb, Zr, Ti, and V are added to achieve high strength and magnetic properties. Techniques for achieving both have been proposed. However, the method of Patent Document 3 cannot obtain a sufficient strength, and the method of Patent Document 4 has a problem that although the strength is high, the magnetic property is greatly deteriorated.

On the other hand, the inventors have made separate studies for improving the workability of high-Si steel. As a result, as disclosed in Patent Document 5, the workability (workability of the Fe—Si alloy or Fe—Si—Al alloy, which is the basic composition of the non-oriented electrical steel sheet, can be evaluated almost by toughness. It is effective to sufficiently purify the steel itself, reduce the total amount of C and N in the steel to 100 massppm or less, and then add a certain amount or more of Cr. I found out. In addition, with regard to magnetic properties, the simultaneous inclusion of Cr and Si or Al produces a synergistic effect in increasing electrical resistance. As a result, eddy current loss is reduced, and iron loss particularly in the high frequency region is reduced. It has been found that it can be remarkably reduced as compared with Fe-Si alloys, Fe-Al alloys, and Fe-Si-Al alloys not containing Cr.
JP 60-238421 A JP-A-62-112723 Japanese Patent Laid-Open No. 02-022442 Japanese Patent Laid-Open No. 02-008346 Japanese Patent No. 3758425

  According to the technique disclosed in Patent Document 5, an electromagnetic steel sheet having high strength and excellent magnetic properties can be stably manufactured by increasing the Si concentration in the steel. However, this technique requires the high purity of the steel as an essential requirement, and in particular, C and N in the steel need to be 0.01 mass% or less in total amount.

  However, when melting Cr-added steel, the added Cr source (ferrochrome or metallic Cr) contains a large amount of C as an impurity, so the amount of mixed C is higher than that of a normal Fe-Si based electromagnetic steel sheet. Will increase. Moreover, since Cr is a strong oxide-forming element, 2 such as RH (Ruhrstahl-Hausen) vacuum degassing equipment and LF (Laddle Furnace), which are used for mass production of high-purity steel at the present integrated steelworks. In the next refining equipment, there is a problem that it is difficult to decarburize to an extremely low carbon region while preventing oxidation loss of Cr after addition of Cr. For example, when RH is used as a secondary refining device, the purity obtained with 2-5 mass% Cr-added steel is about 0.005-0.01 mass% for C and about 0.002-0.005 mass% for N. In addition, it is difficult to stably achieve 0.01 mass% or less in the total amount of C and N.

  In order to advance the preferential decarburization of carbon in the presence of Cr, it is effective to lower the partial pressure of carbon monoxide in the refining atmosphere. For that purpose, the VOD furnace (used for the production of stainless steel ( Since a long-time refining is required using special degassing refining equipment such as Vacuum Oxygen Decarburization) and AOD furnace (ArgoNo. Xygen Decarburization), the production equipment is limited and the productivity is inferior. There is a problem of rising.

  As mentioned above, although several proposals regarding high-strength non-oriented electrical steel sheets have been made, at present, electromagnetic steel sheets that ensure the high strength and magnetic properties required for high-speed rotating equipment are used as ordinary steel sheets. Actually, it has not been possible to achieve industrially stable production using production equipment.

  Accordingly, an object of the present invention is to provide a Cr-added high-Si non-oriented electrical steel sheet that is suitable for use as a rotor material of a high-speed rotating device and has a high strength and a low high-frequency iron loss. Without the need for long-time processing in special secondary refining equipment used in the industry, using ordinary secondary refining equipment such as RH and LF, industrially stable and high productivity And to propose a method of manufacturing.

  In order to solve the above-mentioned problems, the inventors conducted various experiments and repeated studies on a method for producing Cr-added high-Si steel. As a result, if a certain amount of Ti is added together with Cr addition, the workability (toughness) can be imparted so that the subsequent steel plate production can be stably performed even with the purity of C and N that can be reduced by ordinary RH degassing equipment. In order to achieve both high strength and excellent magnetic properties, it has been found that solid solution strengthening is effective, and in particular, solid solution strengthening by adding Si is effective. And by using the said technique, it is possible to manufacture stably the high Si steel exceeding 4 mass% which was difficult to manufacture stably by the conventional technique using the manufacturing equipment of a normal non-oriented electrical steel sheet. As a result, the present invention has been developed.

That is, the present invention is C: more than 0.0050 mass% 0.020 mass% or less, N: 0.01 mass% or less, (C + N): 0.030 mass% or less, Si: more than 4.0 mass%, 10.0 mass% or less, Cr: 2.0-10.0 mass%, P: 0.04 mass% or less is contained, and further Ti is represented by the following formula (1);
−0.02 ≦ Ti-4 (C + N) ≦ 0.04 (1)
Is a high-strength non-oriented electrical steel sheet that contains and balances Fe and unavoidable impurities.

The high strength non-oriented electrical steel sheet according to claim 1, wherein the electrical steel sheet of the present invention further contains at least one component of the following groups A to C in addition to the above component composition. .
Group A: Any one or two of Sb and Sn in total 0.1 mass% or less,
Group B: Any one or more of Al, Mn, Cu, Mo, Ni and Co in a total of 5.0 mass% or less,
Group C: 0.01 mass% or less of one or more of Ca, rare earth elements (REM) and B in total

Further, the present invention is C: more than 0.0050 mass%, 0.020 mass% or less, N: 0.01 mass% or less, (C + N): 0.030 mass% or less, Si: more than 4.0 mass%, 10.0 mass% or less, Cr: 2.0-10.0 mass%, P: 0.04 mass% or less is contained, and further Ti is represented by the following formula (1);
−0.02 ≦ Ti-4 (C + N) ≦ 0.04 (1)
The slab containing Fe and the inevitable impurities is hot-rolled, pickled after or without hot-rolled sheet annealing, and sandwiched by one cold rolling or intermediate annealing. Cold-rolled twice or more, the following formula (2);
T _min (° C.) = 3000 × (C + N) +750 (2)
In represented by T _min ° C. or higher, we propose a method of producing a high strength non-oriented electrical steel sheet characterized by annealing finishing at 1050 ° C. or lower.

In addition to the above component composition, the production method of the present invention further includes at least one component of the following groups A to C.
Group A: Any one or two of Sb and Sn in total 0.1 mass% or less,
Group B: Any one or more of Al, Mn, Cu, Mo, Ni and Co in a total of 5.0 mass% or less,
Group C: 0.01 mass% or less of one or more of Ca, rare earth elements (REM) and B in total

  According to the present invention, a non-oriented electrical steel sheet having high strength that can withstand high-speed rotation of a rotor and excellent magnetic properties can be obtained at a normal electrical steel sheet manufacturing facility, for example, an integrated steelworks such as RH and LF. Producing industrially stable and highly productive using general secondary refining equipment used for mass production of pure steel, and without using special rolling equipment such as warm rolling. Can do.

First, an experiment that triggered the development of the present invention will be described.
Various steels each containing 5 mass% of Si and Cr, the balance being substantially made of Fe, and the total content of C and N being varied in the range of 0.003 to 0.04 mass% are experimentally used. These steel ingots were hot-rolled into hot rolled sheets having a plate thickness of 2.0 mm and annealed at 1000 ° C. Next, a test piece having a thickness of 2 mm, a width of 30 mm, and a length of 100 mm was cut out from the rolling direction of the hot-rolled sheet, and a repeated bending test was performed at room temperature (25 ° C.) with a bending radius of 15 mm and a bending angle of 90 degrees. The toughness of the hot-rolled sheet was evaluated by obtaining the number of bendings until the occurrence of the crack. In addition, in the case of a material in which the number of times of repeated bending is less than 10, it is known that the frequency of fracture on the production line is high.

  FIG. 1 shows the result of the above measurement as a relationship between the total amount of C and N and the number of repeated bendings until breakage. From FIG. 1, the toughness of the hot-rolled sheet has a clear correlation with the (C + N) amount, and the toughness rapidly decreases with an increase in the (C + N) amount, but if (C + N) ≦ 0.01 mass%, It can be seen that the number of bending times is 20 times or more, and that the toughness is sufficient.

  Therefore, the cause of this improvement in toughness is considered to be due to the presence of C and N, and the toughness was inferior to the sample having a good (T + N) amount of 0.0056 mass% ( With respect to the sample having an amount of C + N) of 0.0138 mass%, the structure was observed using an electron microscope. As a result, it was confirmed that in the sample having poor toughness, more Cr carbonitride precipitates exist on the grain boundaries than in the sample having good toughness. From this result, although Cr is an element that improves the workability of high-Si steel, if the reduction of C and N in the steel is insufficient, it forms Cr-based carbonitrides at the grain boundaries and precipitates. It was estimated that this would be the starting point for fracture during bending deformation.

  Therefore, it was studied to suppress grain boundary precipitation of Cr-based carbonitrides by fixing C and N with elements other than Cr. The amount of (C + N) is in the range of 0.01 to 0.02 mass%, which is a level that enables large-scale and highly efficient production by secondary refining with an RH vacuum degassing device, and the amount of Ti added is changed. The steel was melted in the laboratory, hot-rolled sheets were produced in the same manner as the above experiment, repeated bending tests were performed, and toughness was evaluated.

FIG. 2 shows the results of the bending test in relation to Ti and the amount of C and N. From this figure, the range where Ti-4 (C + N) is −0.02 to 0.04 mass%. It can be seen that the toughness is greatly improved. In addition, by observation of the structure with an electron microscope, it was confirmed that, in the range where toughness was improved, mainly Ti-based carbonitrides were precipitated in the crystal grains, and Cr-based grain boundary precipitates were greatly reduced. It was done. In addition, in the sample in which Ti was added excessively from the above range, improvement in toughness was not observed despite the small amount of Cr precipitates on the grain boundaries. The reason for this is not clear, but it is considered that the excessive Ti dissolved in the solid solution lowered the toughness.
From the above results, it was found that the productivity of Cr-added high-Si steel can be greatly improved even at a high purity level that can be produced by commonly used RH.

Next, the reason why the component composition of the electrical steel sheet of the present invention is limited to the above range will be described.
C: more than 0.0050 mass% and 0.020 mass% or less, N: 0.01 mass% or less Since C and N are components that deteriorate the toughness of Cr-added high Si steel, it is preferable to reduce as much as possible. In terms of technology, there were restrictions in terms of refining facilities and operability for high purity. However, as described above, in the present invention, by adding an appropriate amount of Ti, it can be melted by using a secondary refining facility that is usually used for mass production of high-purity steel at integrated steelworks such as RH and LF. Even levels of C and N content are acceptable.

  The purpose of the present invention is to stably produce the toughness of Cr-added high-Si steel using ordinary steelmaking equipment, but when RH is used as a secondary refining device, the decarburization capacity under normal operating conditions is There is a limit, and the lower decarburization lower limit of 2-5 mass% Cr added steel is about 0.005 mass%. Therefore, in the present invention, the allowable range of C is set to more than 0.005 mass% and 0.020 mass% or less that can be sufficiently achieved even by RH. Similarly, the N content is set to 0.01 mass% or less that can be sufficiently achieved by RH.

(C + N): 0.030 mass% or less Manufacturability typified by bendability (toughness) of a hot-rolled sheet depends on the total amount of C and N, and the amount of Ti added as the amount of (C + N) increases. Is also undesirable. Therefore, the amount of (C + N) is 0.030 mass% or less, preferably 0.02 mass% or less, more preferably 0.015 mass% or less. In addition, although the high-purification capability by a normal steelmaking facility largely depends on the purity of the Cr source to be added, C is about 0.008 mass%, N is about 0.005 mass%, and therefore (C + N): 0. If it is up to about .013 mass%, it is possible to manufacture without problems even in the RH type degassing refining equipment usually used for the manufacture of electrical steel sheets.

Si: more than 4.0 mass% and less than 10.0 mass% Si is added as a deoxidizer and has the effect of reducing the iron loss by increasing the electrical resistance of steel, so it is important to constitute a non-oriented electrical steel sheet Element. In addition, Si is an element having a high solid solution strengthening ability, and has higher strength and fatigue resistance than other solid solution strengthening elements such as Mn, Al, and Ni added to non-oriented electrical steel sheets. It is an element that can achieve the balance between improvement of iron and reduction of iron loss in the most balanced manner. Therefore, in the present invention, Si is positively added exceeding 4.0 mass%. On the other hand, if it exceeds 10 mass%, sufficient toughness capable of rolling cannot be ensured even if Cr is added. Therefore, in the present invention, the range of Si is set to 4.0 mass% and 10.0 mass% or less. The Si content is preferably in the range of 4.2 to 7.0 mass%, more preferably in the range of 4.5 to 6.5 mass%, from the viewpoint of achieving both strength and magnetic property improvement effects and manufacturability. It is.

Cr: 2.0-10.0 mass%
Cr is an element effective for improving the workability of high-Si steel, and further, by synergistic effects with Si and / or Al, the electric resistance is greatly improved and the iron loss in the high frequency region is reduced. In addition, it is a basic alloy component having an effect of improving the corrosion resistance. Therefore, in the steel of the present invention containing 4 mass% or more of Si, it is necessary to add 2.0 mass% or more of Cr. On the other hand, if it exceeds 10 mass%, the effect of improving toughness is saturated and only the cost is increased. Therefore, the Cr content is in the range of 2.0 to 10 mass%, preferably 3.0 to 7.0 mass%.

P: 0.04 mass% or less P is an element that increases the electrical resistance of steel, but is also an element that segregates at the grain boundaries and embrittles the steel, and is therefore 0.04 mass% or less, preferably 0.03 mass%. The following.

Ti-4 (C + N): -0.02 to 0.04 mass%
Ti fixes solute C and N present in the steel, suppresses precipitation of Cr carbonitrides at grain boundaries, and has an effect of improving the productivity (toughness) of the Cr-added high-Si steel. In order to develop this effect, Ti-4 (C + N) needs to be set to −0.02 mass% or more in relation to C and N. Furthermore, the supersaturated component that is not consumed for fixing C and N also acts as a solid solution strengthening element, contributing to an increase in strength. However, if Ti becomes excessive, the toughness of the steel is reduced, so the upper limit of Ti-4 (C + N) is set to 0.04 mass%.

In addition to the above component composition, the electrical steel sheet of the present invention may further contain one or more components selected from the following group.
Sn, Sb: 0.1 mass% or less in total Sb and Sn both have the effect of improving the texture and contribute to the improvement of the high-frequency iron loss characteristics. However, Sb and Sn segregate in the grain boundaries and surface layers of steel and have the effect of embrittlement of the grain boundaries. In particular, when the amount of Sb and Sn added exceeds 0.1 mass%, the material becomes brittle and heat Reduce the toughness of the rolled sheet. Therefore, the addition amount of Sb and Sn is preferably 0.1 mass% or less in total of one or two of them. In addition, although the minimum of the addition amount of Sb and Sn is not specifically limited, in order to express the characteristic improvement effect by Sb and Sn addition mentioned above, it is preferable to add 0.01 mass% or more.

Al, Mn, Cu, Mo, Ni, Co: 5.0 mass% or less in total Al, like Si, is effective in increasing the electrical resistance by the synergistic effect with Cr and reducing iron loss in the high frequency range Is an essential ingredient. Mn is an element that improves the hot workability of steel and has the effect of improving the iron loss in the high frequency range by increasing the electrical resistance of the steel. Cu and Mo also have the effect of improving iron loss by increasing the electrical resistance of steel. Ni and Co have the effect of increasing the saturation magnetic flux density of steel while increasing the electrical resistance to improve the iron loss. However, all of these elements have a small effect of increasing the strength compared to Si, and if the addition amount is excessive, the toughness of the hot-rolled sheet is reduced. It is more effective to increase it. Further, in the present invention, in order to obtain high strength, the Si content is set to 4.0 mass% or more. Therefore, if the above elements are added in total exceeding 5.0 mass%, sufficient heat can be contained even if Cr or Ti is contained. The toughness of the rolled sheet may not be ensured. Accordingly, the total content of Al, Mn, Cu, Mo, Ni, and Co is preferably 5.0 mass% or less.

Ca, rare earth elements (REM), B: 0.01 mass% or less in total Ca, rare earth elements (REM) are segregated at grain boundaries by fixing S, which is an impurity in steel. It is an element that has the effect of improving the workability of steel by strengthening the grain boundaries. However, if these elements are added excessively, they remain in the steel as oxides and nitrides, deteriorating the magnetic properties. Therefore, in this invention, it is preferable to add these elements in 0.01 mass% or less in total.

Next, the manufacturing method of the high intensity | strength non-oriented electrical steel sheet which concerns on this invention is demonstrated.
The melting of steel can be performed by a generally known method such as a converter method or an electric furnace method. Also, secondary refining is used for refining stainless steel and high-purity steel in the prior art because when producing high-Si CrSi steel, it was necessary to reduce C and N in the steel as much as possible. However, in the present invention, secondary refining equipment such as RH and LF, which are usually used for production of high-purity steel at an integrated steelworks, is used. be able to. Of course, it is possible to use a VOD furnace or an AOD furnace. In this case, efficient production with a shorter refining time than before can be achieved.

  The molten steel adjusted to the above-described component composition range by the above method is then made into a slab by a continuous casting method or an ingot-bundling rolling method. Moreover, you may manufacture a thin slab using a thin slab continuous casting method. The slab obtained as described above is then heated and held in a soaking furnace and then subjected to hot rolling, or, as in the CC-DR method and the HCR method, while maintaining the sensible heat during continuous casting. It can also be subjected to hot rolling without heating. Although there is no restriction | limiting in particular about hot rolling conditions, From a viewpoint of energy saving, it is desirable that slab heating temperature shall be 1200 degrees C or less.

  The hot-rolled sheet after hot rolling is subjected to hot-rolled sheet annealing as necessary. This hot-rolled sheet annealing improves the texture formed by hot rolling and improves the iron loss characteristics. Moreover, since a rolling raw material can be softened by performing hot-rolled sheet annealing, the cold rolling property performed subsequently can be improved. The conditions for hot-rolled sheet annealing can be appropriately determined in the range of 700 to 1100 ° C. and soaking time of 1 second to 2 hours. When the annealing temperature is higher than the above range or when the annealing time is long, the effect of improving the iron loss characteristics is saturated, which causes an increase in cost. On the other hand, when the annealing temperature is lower than the above range or when the annealing time is short, the effect of improving the iron loss characteristics is small.

  The hot-rolled sheet or hot-rolled annealed sheet is then stripped by pickling or shot blasting, and then the hot-rolled scale is removed, and then the final sheet thickness (product sheet thickness) is obtained by cold rolling at least once with intermediate annealing. And The intermediate annealing has an effect of improving the cold loss property and the warm rolling property as well as beneficially improving the iron loss property through the improvement of the texture of the cold rolled material. The conditions for the intermediate annealing may be appropriately determined, for example, in the range of a temperature of 600 to 1100 ° C. and a soaking time of 1 second to 10 minutes. When the annealing temperature is low or when the annealing time is short, the effect of improving the iron loss characteristics is small, while when the annealing temperature is high or when the annealing time is long, the effect of improving the iron loss by annealing is saturated and the cost is low. Increase factor. Of course, warm rolling may be performed instead of the cold rolling.

  The sheet thickness after cold rolling (product sheet thickness) greatly affects the high-frequency magnetic characteristics, the productivity of the steel sheet, and the processing man-hours of the electrical equipment. That is, in order to reduce the high-frequency iron loss, it is advantageous that the plate thickness is thin, and the plate thickness is 0.5 mm or less, preferably 0.30 mm or less. On the other hand, from the viewpoint of steel plate manufacturability and the number of man-hours for processing electrical equipment, it is preferable that the plate thickness is thicker. Since the cost increases, it is desirable that the plate thickness be 0.05 mm or more.

The steel sheet after rolling is subjected to finish annealing, and an insulating coating is formed as necessary to obtain a product. The recrystallization behavior of steel depends on its component composition. As a result of the inventors' investigation, in the case of a component system that satisfies the present invention conditions, the recrystallization behavior of steel mainly depends on the total amount of C and N, and soaking is generally used in the manufacture of electrical steel sheets. In order to complete recrystallization using a continuous annealing facility with a time of about 1 second to 2 minutes, the soaking temperature is expressed by the following equation (2):
T _min (° C.) = 3000 × (C + N) +750 (2)
It was found that it was necessary to make it _Tmin or more represented by On the other hand, if the annealing temperature exceeds 1050 ° C., the crystal grains are coarsened, which leads to a decrease in strength and deterioration of high-frequency iron loss characteristics.

  Steel having the component composition shown in Table 1 was melted in the laboratory to form an ingot, which was heated to 1100 ° C. and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm. From this hot-rolled sheet or a hot-rolled sheet subjected to hot-rolled sheet annealing under the conditions described in Table 2, a test piece having a thickness of 2.0 mm × width 30 mm × length 100 mm was cut out in parallel to the rolling direction. The toughness of the hot-rolled sheet was evaluated by repeatedly conducting a bending test at room temperature (25 ° C.) under the conditions of a bending radius of 15 mm and a bending angle of 90 degrees, and obtaining the number of bendings until the occurrence of cracks. Next, the hot-rolled sheet or the hot-rolled sheet after hot-rolled sheet annealing was pickled and cold-rolled to a final thickness of 0.20 mm. At this time, the occurrence of cracks and breaks was investigated, and the manufacturability was evaluated from the viewpoint of cold rollability. Further, the samples that could be cold-rolled to 0.20 mm were subjected to finish annealing under the conditions shown in Table 2.

  From the cold-rolled annealed plate obtained as described above, an Epstein test piece was collected and the iron loss value at a frequency of 1 kHz and a magnetic flux density of 1.0 T was measured. Further, a JIS No. 5 tensile test piece was taken in parallel with the rolling direction, and a tensile test was performed at a tensile speed of 10 mm / min. The measurement results are shown in Table 2.

Table 2 shows the following.
A conventional high Si non-oriented electrical steel sheet No. containing 3.11% by mass of Si. Steel plate No. 1 has a tensile strength (TS) of only 485 MPa, which is insufficient as a rotor material for high-speed rotation. In addition, Mn and Ni were added to 3.05 mass% Si for solid solution strengthening, and precipitation strengthening with Nb and Ti was further performed. No. 2 steel is No. 2. Although high strength was obtained as compared with Steel No. 1, the toughness of the hot-rolled sheet was lowered, and cracking occurred even in cold rolling. Also, the iron loss at 1 kHz exceeds 60 W / kg. No. 5 containing 5.1 mass% of Cr together with 5.1 mass% of Si and having a (C + N) content reduced to 0.0033 mass%. The steel plate No. 3 has a number of bendings of the hot-rolled annealed plate of 50 times or more and has a good cold rolling property, and further achieves high strength and low iron loss of 50 W / kg or less. Dedicated equipment and long-term refining are required to reduce the above to the above level in an industrially stable manner. No. No. 3 with a higher (C + N) amount than the No. 3 steel plate. In the steel plate No. 4, the toughness of the hot-rolled plate is greatly reduced. On the other hand, no. No. 4 of the present invention with the same amount of Si, Cr and (C + N) as the steel plate No. 4 but with an appropriate amount of Ti added. Steel plate No. 5 exhibits good hot-rolled sheet toughness and cold rollability, and also has high strength and low iron loss with respect to the properties after finish annealing. Furthermore, No. satisfying the conditions of the present invention. The same applies to 6, 8 to 10 and 13 to 16 steel plates. On the other hand, no. No. 7 steel sheet, No. in which Si addition amount exceeds 10 mass%. No. 11 steel, No. with excessive addition of Ti. All the 12 steel plates had low toughness of hot-rolled plates, and cracks occurred during cold rolling. In particular, no. In the steel plates 7 and 11, severe plate cracking occurred from the beginning of rolling, and rolling to collect a small sample was impossible.

  By primary refining by a converter and secondary refining by RH degassing, C: 0.0096 mass%, N: 0.0036 mass%, (C + N): 0.0132 mass%, Si: 6.32 mass%, Cr: 4. 03 mass%, Mn: 0.007 mass%, P: 0.011 mass%, Al: 0.001 mass%, Ti: 0.042 mass%, Ti-4 (C + N): -0.0108 mass%, the balance being Fe and inevitable Steel made of impurities was melted and continuously cast into a steel slab. The slab was heated to 1100 ° C. and hot-rolled to obtain a hot-rolled sheet having a thickness of 1.5 mm. When this hot-rolled sheet was repeatedly subjected to a bending test in the same manner as in Example 1, the number of bendings until the occurrence of cracking was 37, indicating sufficient toughness.

  Next, the hot-rolled sheet is cold-rolled to form a cold-rolled sheet having a thickness of 0.15 mm or 0.35 mm, and after finishing annealing at the annealing temperature shown in Table 3 for 30 seconds, an insulating film is coated. The product (magnetic steel sheet). With respect to this electromagnetic steel sheet, magnetic properties and mechanical properties were evaluated under the same conditions as in Example 1.

  The results are shown in Table 3. No. with a final annealing temperature of 750 ° C. Although the steel plate No. 17 can obtain high strength, an unrecrystallized structure remains in part, and the iron loss is somewhat high. On the other hand, No. satisfying the production conditions of the present invention. The 18-20 steel plates are all excellent in manufacturability and have good iron loss and strength. In addition, the finish annealing temperature is as high as 1100 ° C. No. 21 steel plate is No. of the invention example. Although the iron loss is almost the same as that of 20 steel plates, the strength tends to decrease slightly.

It is a graph which shows the influence of the amount of (C + N) on the brittleness of Cr addition high Si hot-rolled sheet. It is a graph which shows the influence of Ti and (C + N) on the brittleness of Cr addition high Si hot-rolled sheet.

Claims (4)

C: more than 0.0050 mass%, 0.020 mass% or less, N: 0.01 mass% or less, (C + N): 0.030 mass% or less, Si: more than 4.0 mass%, 10.0 mass% or less, Cr: 2.0 to A high-strength non-oriented electrical steel sheet containing 10.0 mass%, P: 0.04 mass% or less, further containing Ti satisfying the following formula (1), and the balance being Fe and inevitable impurities.
−0.02 ≦ Ti-4 (C + N) ≦ 0.04 (1) The high-strength non-oriented electrical steel sheet according to claim 1, further comprising at least one component of the following group A to group C in addition to the component composition.
Group A: Any one or two of Sb and Sn in total 0.1 mass% or less,
Group B: Any one or more of Al, Mn, Cu, Mo, Ni and Co in a total of 5.0 mass% or less,
Group C: 0.01 mass% or less of one or more of Ca, rare earth elements (REM) and B in total C: more than 0.0050 mass%, 0.020 mass% or less, N: 0.01 mass% or less, (C + N): 0.030 mass% or less, Si: more than 4.0 mass%, 10.0 mass% or less, Cr: 2.0 to Hot rolled a slab containing 10.0 mass%, P: 0.04 mass% or less, further containing Ti satisfying the following formula (1), the balance being Fe and inevitable impurities, Pickling after or without annealing, and cold-rolling twice or more with one cold rolling or intermediate annealing, and T _min ° C or higher represented by the following formula (2): 1050 ° C A method for producing a high-strength non-oriented electrical steel sheet, characterized by performing finish annealing at the following temperature.
−0.02 ≦ Ti-4 (C + N) ≦ 0.04 (1)
T _min (° C.) = 3000 × (C + N) +750 (2) The method for producing a high-strength non-oriented electrical steel sheet according to claim 3, further comprising at least one component of the following groups A to C in addition to the component composition.
Group A: Any one or two of Sb and Sn in total 0.1 mass% or less,
Group B: Any one or more of Al, Mn, Cu, Mo, Ni and Co in a total of 5.0 mass% or less,
Group C: 0.01 mass% or less of one or more of Ca, rare earth elements (REM) and B in total

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