JP2510640B2 - High tensile strength non-oriented electrical steel sheet manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high tensile strength non-oriented electrical steel sheet, and relates to a magnetic material having low iron loss and high strength for a high speed rotating machine and an electromagnetic switch. The present invention relates to a method for producing a suitable magnetic material having excellent wear resistance.

(Prior Art) Conventionally, the rotational speed required for rotating equipment is at most 100,000.
It is about rpm, and laminated electromagnetic steel sheets have been used as materials for rotors. Recently, ultra-high speed rotation of 200,000 to 300,000 rpm has been required, and the centrifugal force applied to the rotor may exceed the strength of electrical steel sheets.

Therefore, a solid rotor made of cast steel having sufficient strength is usually used for the ultra-high speed rotating machine instead of the electromagnetic steel plate. However, in this case, the cost is high because a complicated processing step of cutting out the rotor from the cast steel plate block is required, moreover, the eddy current loss is larger than that of the laminated type, and the efficiency of the motor is significantly reduced. There is.

In addition, since the contact surface of the electromagnetic switch wears as it is used, a magnetic material having excellent wear resistance as well as magnetic properties is desired.

In response to such needs, non-oriented electrical steel sheets having high tensile strength have recently been studied and some proposals have been made. For example, Japanese Patent Laid-Open No. 60-238421 discloses Si
Higher at 3.5-7.0%, Mn: 0.1-11.5%, Ni: 0.1-2
0.0%, Co: 0.5-20.0%, Ti: 0.05-3.0%, W: 0.05-3.0
%, Mo: 0.05 to 3.0%, Al: 0.5 to 13.0% of a solid solution strengthening component 1.0 to 20.0% slab is used as a raw material, and after hot rolling 100 to 600 This is a method for producing a high tensile strength non-oriented electrical steel sheet having a tensile strength of 50 kg / mm ² or more by repeating warm rolling at ℃ and rolling to a final thickness and annealing.

Since this is a high Si content that is difficult to roll, troublesome warm rolling is indispensable, but there is a possibility that plate breakage will occur during rolling, which leads to a decrease in productivity and a decrease in yield. There is room for

In JP-A-61-84360, Ni: 8-20%, Mo: 0.2-5.0
%, Al: 0.1 to 2.0%, Ti: 0.1 to 1.0%, Cr: 1.0 to 10.0%, a high tensile soft magnetic material for a high-speed rotating electric motor has been proposed. This is an extremely expensive material because it contains a large amount of Ni and Mo and Cr.

Further, JP-A-61-9520 discloses that Si: 2.5 to 7.0% and Ti:
0.05-3.0%, W: 0.05-3.0%, Mo: 0.05-3.0%, Ni: 0.1
~ 20.0%, Al: 0.5 ~ 13.0% 1 or 2 or more 1.0
A high tensile strength non-oriented electrical steel sheet is manufactured by a rapid solidification method from molten steel containing ~ 20.0%. Since this is a special process, it cannot be manufactured by ordinary manufacturing equipment for electromagnetic steel sheets, and it is considered difficult to industrially manufacture it.

(Problems to be Solved by the Invention) As described above, a proposal has been made for the production of a high tensile strength non-oriented electrical steel sheet, but it is industrially stably produced using ordinary electrical steel sheet production equipment. The reality is that it hasn't arrived yet.

Further, since the high tensile strength non-oriented electrical steel sheet is used as a material for ultra-high speed rotating electromagnetic equipment and electromagnetic switch as described above, it is necessary to have high tensile strength, low iron loss and excellent magnetic flux density. .

The present invention is suitable as a material for ultra-high speed rotating machines and electromagnetic switches, yield strength YP ≧ 55 kg / mm ² , tensile strength TS ≧ 60 kg / m 2.
High tensile strength non-oriented electrical steel sheet with m ² , hardness Hμv ≧ 150, high strength and wear resistance, and excellent magnetic characteristics with magnetic flux density B 50 ≧ 1.60T, is used for rolling and other process lines. The purpose of the present invention is to industrially stably produce a sheet without causing breakage during passage.

(Means for Solving Problems) The present inventors have conducted various experiments and studies in order to achieve the above object. That is, the present invention further requires C: 0.01% or less, Si: 2.0% or more and 3.5% or less, Mn: 0.1% or more and 10.0% or less, P: 0.20% or less, Al: 0.10% or more and 1.50% or less, B: 0.008% or less According to the above, when a slab containing 6.0% or less of Ni and the balance of iron and unavoidable impurities is hot-rolled, it is represented by the following formula in relation to the hot-rolled sheet thickness (t; mm). Winding below the take-up temperature (CT; ° C), start cooling within 5 hours after winding, and cool up to 300 ° C at an average cooling rate of 100 ° C / hour or more, then leave it unannealed Alternatively, a hot-rolled sheet is annealed, cold-rolled, and annealed to produce a non-oriented electrical steel sheet having high tensile strength and magnetic properties.

CT (° C) ≤ -200 x t (mm) + 1000 where 0.5 ≤ t ≤ 2.5 First, the steel composition will be described.

C is a component that deteriorates magnetic properties, and if it is contained in excess of 0.01 (wt)%, iron loss increases, so the content is made 0.01% or less. Incidentally, C may be decarburized by a hot-rolled plate or a cold-rolled plate instead of being decarburized by steelmaking and put in the above range.

Si increases the specific resistance of steel, reduces eddy currents, reduces iron loss, and increases tensile strength, but the content is 2.0.
If it is less than%, the effect is small. Further, if it exceeds 3.5%, the steel becomes brittle and the magnetic flux density of the product is further lowered.
5% or less.

Mn not only increases the tensile strength of steel, but also increases the specific resistance and decreases the iron loss, but if it is less than 0.1%, the effect is small, preferably more than 1.0% to 5.0%. If it exceeds 10.0%, the magnetic flux density of the product will decrease, so it should be 0.1-10.0%.

P is an element with a remarkable effect of increasing the tensile strength, but 0.20
If it exceeds 0.1%, embrittlement becomes severe, and it becomes difficult to perform hot rolling, cold rolling, etc. on an industrial scale, so the upper limit is made 0.20%.

In addition, when the product is punched or used on the end face as it is sheared, if it is exposed to an atmosphere of 150 ° C or more for a long time, P0.03
If it exceeds%, there may be apparent elongation deterioration. It is considered that this is due to the fact that the fracture surface of the high tensile strength steel sheet relatively easily contains microcracks, and strain aging.

Therefore, if the elongation after aging becomes a problem for the application, the end face processing method that is smooth and does not leave distortion is adopted. It is effective to punch with sandpaper and remove the sheared surface layer. If the content of P is 0.03% or less, the above problem does not occur.

Al must be at least 0.10% as a deoxidizer,
Further, by containing Al, the strength is improved, and the iron loss is also reduced due to the increase in the specific resistance, but if it exceeds 1.50%, embrittlement becomes a problem, so the content is made 0.10 to 1.50%.

B segregates at the crystal grain boundaries and has the effect of suppressing the embrittlement due to the grain boundary segregation of P, but if it exceeds 0.008%, it becomes significantly embrittled, so the upper limit is made 0.008%.

Further, Ni is contained if necessary. Ni has little adverse effect on the magnetic properties and is effective in improving tensile strength, but if it exceeds 6.0%, the magnetic flux density is greatly reduced, so it is made 6.0% or less.

A steel slab containing the above components and the balance consisting of iron and unavoidable impurities is melted in a converter and manufactured by continuous casting or ingot-slab rolling.

The steel slab is heated in a known manner and then for example 0.5
Hot rolled to a plate thickness of ~ 3.5 mm. The relationship between the coiling temperature of hot rolling and the thickness of hot-rolled sheet and the cooling condition after winding are important for improving the rollability and workability of the steel sheet. Winding at a temperature below the winding temperature according to the thickness, start cooling within 5 hours after winding,
Up to an average cooling rate of 100 ° C / hour or more.

In hot rolling, the coiling temperature (CT) is determined by the hot rolled sheet thickness (t; m
The relational expression with m) CT (° C) ≤-200 x t (mm) + 1000 is taken up.

The reason for this is that if the coiling temperature is higher than the coiling temperature (CT) corresponding to the plate thickness (t) expressed by this formula, the coil becomes brittle and frequently breaks during rolling.

After winding, it takes a long time to start cooling, and if the cooling rate is slow, the steel becomes brittle. To prevent this, it is necessary to start cooling within 5 hours after winding.
The cooling rate needs to be an average cooling rate of 100 ° C./hour or more.

If this cooling end point is high, workability such as rollability deteriorates, so cooling is performed up to 300 ° C. at the average cooling rate. If it is necessary to carry out cold rolling without annealing after hot rolling or further improve magnetic properties, hot-rolled sheet annealing is performed at 500 to 1000 ° C. for 5 seconds to 15 minutes, and then, , Cold rolling.

It is 500 to perform hot-rolled sheet annealing within the above temperature and time range.
This is because if the temperature is lower than ℃ or shorter than 5 seconds, the annealing effect that further enhances the magnetic properties does not appear.
Alternatively, if it exceeds 15 minutes, the crystal grains become coarse, causing plate breakage in cold rolling, and reducing the strength of the final product.

After cold rolling, annealing is performed at 700 to 900 ° C for 5 seconds to 15 minutes. The reason is that if the temperature is less than 700 ° C. or less than 5 seconds, a sufficient annealing effect for reducing iron loss and improving magnetic flux density does not appear, and the rolling structure remains or the flatness remains unimproved. If the temperature exceeds 900 ° C or exceeds 15 minutes, the crystal grains become coarse and the strength decreases, and a high tensile strength steel sheet cannot be obtained.

In the annealing of this cold-rolled sheet, decarburization may be carried out in a decarburizing atmosphere if necessary.

(Example) Example 1 C: 0.0025%, Si: 3.05%, Mn: 1.40%, P: 0.010%, TA
l: 0.50%, B: 0.0025%, the balance is steel and a steel slab consisting of inevitable impurities is hot rolled at a hot rolled sheet thickness of 0.5 to 3.5 mm and a hot rolling coiling temperature of 200 to 1000 ° C. After taking, changing the time until the start of cooling from 0 to 6 hours, the average cooling rate 100
A repeated bending test was performed on the hot-rolled sheet cooled to 250 ° C at a rate of ° C / hour.

The results are shown in Fig. 1. From the figure, in the case of this component system, a clear correlation is observed between the hot rolled sheet thickness, the winding temperature, the time from the winding to the start of cooling at 100 ° C. per hour, and the brittleness of the hot rolled sheet. When the following formula is satisfied, the number of repeated bendings is ≧ 3.

CT (° C) ≤ -200 x t (mm) + 1000 However, 0.5 ≤ t ≤ 2.5 Furthermore, (time from winding to the start of cooling at 100 ° C or more per hour) ≤ 5 hours Following hot rolling, there is no hot-rolled sheet annealing, Alternatively, hot-rolled sheet annealing conditions are changed in the range of (400 to 1100) ° C × (5 to 900) seconds, and cold rolled to a sheet thickness of 0.5 mm, then (650 to 925) ° C × 30 seconds Was annealed, and the mechanical properties, iron loss of W15 / 50 and magnetic flux density of B50 were measured.

For the magnetic measurement, 30 mm × 320 mm Epstein test pieces (rolling direction, right-angle direction half amount) were used.

The results are shown in Table 1.

No. 1, 4, 5, 7, which could not be cold rolled due to brittle fracture
Of 8, 9, 11, 12, 14, 17, 18, 19, 20, 21, 22,
No. 12 has a high hot-rolled sheet annealing temperature, and all others have hot-rolled winding temperatures that do not satisfy the above-described relational expression between plate thickness and winding temperature, and the number of repeated bendings of the hot-rolled sheet is 2 or less. Is.

No. 2, 3, 6, 10, 13, 15, manufactured under the conditions of the present invention
No. 16 was rolled without causing plate breakage, and the yield strength YP was 55.
~68kg / mm ^2, the high tensile strength TS has high strength characteristics and 60~76kg / mm ^2, further iron loss W15 / 50, is also excellent and the magnetic flux density B50.

Example 2 C: 0.0015 to 0.0045% by weight%, Si: 2.8 to 3.23%, Mn:
0.04% to 3.05%, P: 0.005 to 0.50%, Al: 0.50 to 2.00%,
B: 0.000 to 0.0100%, Ni: 0.75 to 1.80%, steel slab specimen with balance of iron and unavoidable impurities was hot-rolled to a plate thickness of 2.0 mm, hot rolling temperature 400 After coiling at ℃, the time until the start of cooling (average cooling rate 100 ℃ / hour) is processed in 30 minutes, and hot-rolled sheet annealing is performed at 800 ℃ × 30 seconds, then cold rolled to a plate thickness of 0.5 mm. The mechanical and magnetic properties of the steel sheet annealed at 750 ℃ for 30 seconds were measured.

Regarding the magnetic properties, an Epstein test piece of 30 mm × 320 mm was sheared by half each in the rolling direction and the right angle direction, and the iron loss of W15 / 50 and the magnetic flux density of B50 were measured.

 The results are shown in Table 2.

As is clear from the results shown in Table 2, Samples 1 to 9 produced under the conditions of the present invention were rolled without causing plate breakage, yield strength YP was 63 to 72 kg / mm ² , tensile strength TS. Is 71 ~
It has high strength characteristics at 82 kg / mm ² , and also has excellent iron loss W15 / 50 and magnetic flux density B50.

(Effects of the Invention) As described above, according to the present invention, a non-oriented electrical steel sheet excellent in high strength and magnetic properties, which is suitable as a material for an ultrahigh-speed rotating electric motor and an electromagnetic switch, is broken during rolling. Stable manufacturing without any trouble.

[Brief description of drawings]

FIG. 1 is a table showing the results of an examination of the winding temperature and the hot rolled sheet thickness that affect the number of times the hot rolled sheet is repeatedly bent in one embodiment of the present invention.

Claims (2)

(57) [Claims] [Claim 1] C: 0.01% or less by weight% Si: 2.0% or more and 3.5% or less Mn: 0.1% or more and 10.0% or less P: 0.20% or less Al: 0.10% or more and 1.50% or less B: 0.008% or less When hot-rolling a slab whose balance consists of iron and unavoidable impurities, after rolling at a coiling temperature (CT; ° C) or less, the relationship with the hot-rolled sheet thickness (t; mm) is expressed by the following equation. , Start cooling within 5 hours after winding, 30
Cool down to 0 ℃ so that the average cooling rate is 100 ℃ or more per hour, anneal without annealing or at a temperature of 500 ℃ or more and 1000 ℃ or less for 5 seconds or more and 15 minutes or less, and cold-roll it, and further 700
A method for producing a high tensile strength non-oriented electrical steel sheet, which comprises performing annealing for 5 seconds or more and 15 minutes or less at a temperature of ℃ to 900 ℃. CT (° C) ≤ -200 x t (mm) + 1000 However, 0.5 ≤ t ≤ 2.5 2. In% by weight C: 0.01% or less Si: 2.0% or more and 3.5% or less Mn: 0.1% or more and 10.0% or less P: 0.20% or less Al: 0.10% or more and 1.50% or less B: 0.008% or less Ni: 6.0 % Or less, with the balance being iron and unavoidable impurities when hot rolling, the relationship with the hot-rolled sheet thickness (t; mm) is less than the coiling temperature (CT; ° C) shown by the following equation. After winding, start cooling within 5 hours after winding,
It is cooled up to ℃ so that the average cooling rate is 100 ℃ or more per hour, and it is annealed without annealing or at a temperature of 500 ℃ or more and 1000 ℃ or less for 5 seconds or more and 15 minutes or less, and cold rolled.
A method for producing a high tensile strength non-oriented electrical steel sheet, which comprises annealing at a temperature of 0 ° C to 900 ° C for 5 seconds to 15 minutes. CT (° C) ≤ -200 x t (mm) + 1000 However, 0.5 ≤ t ≤ 2.5