CN107002196A - Magnetic pole is with hot rolled steel plate and its manufacture method and hydroelectric generation rim component - Google Patents

Abstract

The present invention provides a hot-rolled steel sheet for magnetic poles having high strength and excellent weldability and magnetic properties, a method for producing the same, and a rim member for hydroelectric power generation. Contains C: 0.02% to 0.12%, Si: 0.1% to 0.7%, Mn: 0.8% to 1.6%, P: 0.03% or less, S: 0.005% or less, Al: 0.08% or less, N : not more than 0.006%, Nb: not less than 0.06% and not more than 0.20%, and the balance is composed of Fe and unavoidable impurities. The area ratio of the ferrite phase is 98% or more, the amount of precipitated Fe is 0.22% by mass or less relative to the amount of Fe contained in the steel, and the amount of precipitated Nb is 80% by mass or more relative to the amount of Nb contained in the steel. The average particle size of the Nb-containing carbides is 6nm or less, the yield strength in the rolling direction is 500MPa or more, the magnetic flux density B ₅₀ is 1.4T or more, the magnetic flux density B ₁₀₀ is 1.5T or more, and the dimension of the welding heat-affected zone is The minimum value of the Vickers hardness is (the average value of the Vickers hardness of the base material -30) or more.

Description

Hot-rolled steel sheet for magnetic pole, manufacturing method thereof, and rim member for hydroelectric power generation

technical field

The present invention relates to a hot-rolled steel sheet for a magnetic pole suitable for a rim member for hydroelectric power generation, a manufacturing method thereof, and a rim member for hydroelectric power generation.

Background technique

In recent years, global warming has been regarded as a problem from the viewpoint of preservation of the global environment, and the demand for natural energy that does not emit carbon dioxide gas has increased. In addition, from the viewpoint of suppressing such global warming, recently, hydroelectric power generation as a clean energy is expected. A generator such as a hydroelectric generator includes a rotor and a stator, and the rotor is composed of a pole core functioning as a core and a rim supporting the pole core. In order to obtain power generation capacity, it is necessary to rotate the rotor at high speed. Therefore, the rim is required to maintain high strength in order to withstand the centrifugal force of high-speed rotation. In addition, at the same time, the steel plate for the rim (rim member) is required to maintain excellent magnetic properties. In addition, steel sheets are joined by welding, but the strength of the welded portion tends to fluctuate, so excellent weldability is also required.

To meet the above-mentioned demands, various technologies have been proposed so far for hot-rolled steel sheets focusing on magnetic properties and weldability.

For example, in Patent Document 1, by having a ferrite phase (ferrite phase) with an area ratio of 95% or more and in the crystal grains (crystal grains) of the ferrite phase, Ti-containing ferrite with an average grain size of less than 10 nm is precipitated. and V precipitates (precipitate) structure and the average grain size of the ferrite phase is set within the range of 2 μm or more and less than 10 μm, and the strength and magnetic properties with a yield strength of 700 MPa or more in the rolling direction can be obtained. A steel sheet having electromagnetic properties with a flux density _B50 of 1.5T or higher and a _B100 of 1.6T or higher.

In Patent Document 2, a steel plate containing C: 0.05% to 0.15%, Si: 0.5% or less, Mn: 0.70% to 2.00%, Ti: 0.10% to 0.30%, and B: 0.0015% to 0.0050% is hot rolled. Afterwards, coiling is carried out at 500°C or lower, thereby obtaining a high-tensile hot-rolled steel sheet with a high magnetic flux density.

Patent Document 3 discloses a high-formability, high-strength hot-rolled steel sheet for a rotator core, which contains C≤0.10%, Ti: 0.02-0.2%, and further contains Mo≤0.7%, W≤ In at least one of 1.5%, carbides smaller than 10 nm including Ti and at least one of Mo and W are substantially dispersed in the ferrite structure, and have a strength of 590 MPa or higher.

prior art literature

patent documents

Patent Document 1: International Publication No. 2013/115205

Patent Document 2: Japanese Patent Application Laid-Open No. 63-166931

Patent Document 3: Japanese Patent Application Laid-Open No. 2003-268509

Contents of the invention

The problem to be solved by the invention

However, in the technique proposed in Patent Document 1, since solid solution V (solute V) is contained, it is very difficult to control the amount of coarsely precipitated cementite (cementite), and furthermore, the weldability deteriorates.

In the technique proposed in Patent Document 2, coiling needs to be performed in a difficult-to-control temperature range where the coiling temperature is 500° C. or lower, and variation in characteristics between coils and within coils becomes a problem. In addition, the low-temperature transformation phase is not suitable as a member for rims due to the deterioration of the plate shape caused by the non-uniformity of the transformation strain.

In the technique proposed in Patent Document 3, not only weldability but also the influence of coarse cementite are not taken into consideration, and thus stable magnetic properties cannot be obtained.

In view of the above circumstances, an object of the present invention is to provide a hot-rolled steel sheet for magnetic poles having a yield strength of 500 MPa or more in the rolling direction and excellent weldability and magnetic properties, a method of manufacturing the same, and a rim member for hydroelectric power generation.

method used to solve the problem

In-depth studies have been conducted on the conditions for high-strength steel sheets with good weldability and good magnetic properties. It was found that the decrease in hardness in the heat-affected zone of welding is affected by carbides containing V with high solubility. The influence of the dissolution (re-solution) is greater. And it was found that in order to suppress the softening in the weld heat-affected zone, it is effective to contain Si as a solid solution strengthening element (solute strengthening element) without adding V or controlling the content of V. On the other hand, the magnetic properties in a high magnetic field are degraded by the content of Si. Therefore, studies to improve magnetic properties have been carried out, and it has been clarified that it is important to suppress the formation of coarse cementite to the limit and to make carbide precipitation with a good coherent relation with the base material (matrix). Consider the conditions of high strength and good magnetic properties.

This invention was completed based on the said knowledge, and makes the following content into summary.

[1] A hot-rolled steel sheet for a magnetic pole, wherein the component composition contains C: 0.02% to 0.12% in mass %, Si: 0.1% to 0.7% inclusive, Mn: 0.8% to 1.6% inclusive, P: 0.03% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.006% or less, Nb: 0.06% or more and 0.20% or less, and the balance is composed of Fe and unavoidable impurities (incidental impurities),

The area ratio of the ferrite phase in the structure is 98% or more, the amount of precipitated Fe is 0.22% by mass or less relative to the amount of Fe contained in the steel, and the amount of precipitated Nb is 80% by mass or more relative to the amount of Nb contained in the steel , The average particle size of the precipitated Nb-containing carbides is 6nm or less,

The yield strength in the rolling direction (rolling direction) is 500MPa or more, the magnetic flux density B ₅₀ is 1.4T or more, the magnetic flux density B ₁₀₀ is 1.5T or more, and the minimum value of the Vickers hardness in the welding heat-affected zone is (base metal The average value of Vickers hardness -30) or more.

[2] The hot-rolled steel sheet for a magnetic pole according to the above [1], which further satisfies the following formula (1).

Among them, %C, %Nb, %V, and %Ti represent the content of each element. In addition, it is set to 0 when not included.

[3] The hot-rolled steel sheet for a magnetic pole according to the above [1] or [2], which contains, in mass %, V: 0.01% to less than 0.05%, and Ti: 0.01 in addition to the above composition. % or more and less than 0.05% or more.

[4] A method for producing a hot-rolled steel sheet for a magnetic pole, wherein a raw steel material having the composition described in any one of [1] to [3] above is subjected to a temperature of 1100° C. to 1350° C. After heating, hot rolling is performed at a temperature of 1100°C or higher to complete rough rolling and the finishing rolling temperature is set to 840°C or higher, and within 3 seconds after the finish rolling is completed, the rolling is carried out at 30°C. Cooling is performed at an average cooling rate per second or more, and then coiling (coil) is performed at a temperature of 550° C. or more and 700° C. or less.

[5] The method for producing a hot-rolled steel sheet for a magnetic pole according to [4] above, wherein the surface of the steel sheet is further subjected to a plating treatment.

[6] The method for producing a hot-rolled steel sheet for a magnetic pole according to the above [5], wherein the coating treatment is hot-dip galvanizing, hot-dip galvannealing, or hot-dip galvanizing. ) treatment and electrogalvanized plating treatment.

[7] The method for producing a hot-rolled steel sheet for a magnetic pole according to the above [5] or [6], wherein the composition of the coating layer formed in the coating treatment contains Zn, Si, Al, Ni, Mg, one or more of two.

[8] A rim member for hydroelectric power generation comprising the hot-rolled steel sheet for a magnetic pole according to any one of the above [1] to [3].

It should be noted that, in the present invention, the hot-rolled steel sheet for magnetic poles is a steel sheet (hot-rolled steel sheet) that has not been galvanized, a steel sheet (GI) that has been galvanized, and is further galvanized after galvanizing. Any one of the alloyed steel sheet (GA) and the electrogalvanized steel sheet (EG) was used as the object.

Invention effect

According to the present invention, a hot-rolled steel sheet for magnetic poles having a yield strength of 500 MPa or more in the rolling direction and excellent weldability and magnetic properties can be obtained. The hot-rolled steel sheet for magnetic poles of the present invention is suitable for rim members for hydroelectric power generation and the like. By using the hot-rolled steel sheet for a magnetic pole of the present invention for a rim member for hydroelectric power generation, it is possible to increase the efficiency of hydroelectric power generation and improve the life of equipment, and the effect is remarkable.

detailed description

Hereinafter, the present invention will be described in detail. In addition, unless otherwise stated, the following % means mass %.

First, the structure that is an important condition of the steel sheet of the present invention will be described.

Area ratio of ferrite phase: 98% or more (including 100%)

In a state where the dislocation density (dislocation density) is high, the magnetic flux density decreases remarkably. Therefore, it is necessary to form a structure that does not include low-temperature transformation phases (dislocation density) such as bainite phase and martensite phase that contain a large dislocation density. In the present invention, in order to satisfy desired magnetic properties, the area ratio of the ferrite phase is set to 98% or more. The balance includes bainite phase, martensite phase and pearlite.

Precipitated Fe is 0.22% or less relative to the amount of Fe contained in the steel

Fe as a precipitate originates from cementite. Coarse cementite reduces the magnetic flux density, so it is preferable to reduce it as much as possible. In order to reduce cementite and obtain the magnetic flux density required in the present invention, it is necessary to set the ratio of "the amount of precipitated Fe" to the "amount of Fe contained in the steel" (hereinafter, sometimes referred to as the amount of Fe precipitation) 0.22% or less. Preferably it is 0.20% or less. In addition, the Fe precipitation amount can be measured according to the method described in the Example mentioned later.

In order to suppress the formation of cementite, it is preferable that the contained amount of C be precipitated as carbides containing Nb as much as possible. Therefore, it is preferable to satisfy the following formula (1).

Among them, %C, %Nb, %V, and %Ti represent the content of each element. In addition, it is set to 0 when not included.

The above formula (1) shows that under appropriate manufacturing conditions, C is combined with Nb, V, and/or Ti to precipitate in the form of fine carbides and reduce cementite from the viewpoint of chemical composition. Formula, by setting it to 0.040 or less, the precipitation amount of cementite is in the range that does not lower the magnetic flux density. Particularly excellent magnetic properties in which the magnetic flux density _B50 is 1.5T or more and the magnetic flux density _B100 is 1.6T or more are obtained by setting the formula (1) to 0.03 or less. On the other hand, C forms fine carbides, so the formula (1) is preferably -0.005 or more.

In addition, C that is not combined with Nb, V, and Ti is precipitated as Fe carbides. In order to precipitate almost all of the contained C in the form of fine carbides containing Nb, V, and Ti, it is preferable to complete the rough rolling before finish rolling at 1100° C. or higher.

The amount of precipitated Nb is 80% by mass or more relative to the amount of Nb contained in the steel

In the present invention, high strength with a proof stress of 500 MPa or more can be obtained by dispersing fine Nb-containing carbides. When the ratio of "the amount of precipitated Nb" to the "amount of Nb contained in the steel" (sometimes referred to as the amount of Nb precipitation or the ratio of Nb precipitation) is less than 80%, the desired strength cannot be obtained, and furthermore, due to solid solution of Nb The effect of this makes the magnetic flux density decrease. From the above viewpoint, the Nb precipitation amount is set to 80% or more. Preferably it is 85% or more. In addition, the Nb precipitation amount can be measured according to the method described in the Example mentioned later.

The average grain size of precipitated Nb-containing carbides is 6nm or less

The amount of strength increase by dispersing Nb-containing carbides increases as the carbide particle size decreases. In order to obtain a high strength with a yield strength of 500 MPa or more, it is necessary to set the average particle diameter of the precipitated Nb-containing carbides to 6 nm or less. In addition, the average particle diameter of carbide can be measured according to the method described in the Example mentioned later.

Next, the reason for limitation of the component composition of this invention is demonstrated.

C: 0.02% to 0.12%

C is an element that combines with Nb to form fine carbides containing Nb, thereby contributing to high strength of the steel sheet. In order to obtain a yield strength of 500 MPa or more, it is necessary to contain at least 0.02% or more of C. Preferably it is 0.03% or more. On the other hand, if the content exceeds 0.12%, cementite will be formed and the magnetic flux density will decrease. Therefore, the upper limit of C is set at 0.12%. Preferably it is 0.10% or less.

Si: 0.1% to 0.7%

Si is a heat-stable solid-solution strengthening element, and has an effect of suppressing softening of the welding heat-affected zone. In addition, Si has the effect of making cementite finer and suppressing the adverse effect of reduction in magnetic flux density due to cementite precipitation. Thus, Si is an important condition in the present invention. The lower limit of Si for obtaining these effects is 0.1%. Preferably it is 0.2% or more, More preferably, it is 0.35% or more. On the other hand, if the Si content exceeds 0.7%, the adverse effect of the reduction of the magnetic flux density due to the Si content becomes significant, and red scale occurs on the surface of the steel sheet, impairing the appearance, or degrading the platability. Therefore, the upper limit of Si is set at 0.7%. Preferably it is 0.6% or less.

Mn: 0.8% to 1.6%

Carbide containing Nb becomes finer as the transformation temperature from austenite to ferrite decreases. Mn has an effect of lowering the transformation temperature from austenite to ferrite, and therefore, by containing Mn, carbides containing Nb are made finer and stronger. In order to obtain a yield strength of 500 MPa or more, Mn needs to be 0.8% or more. On the other hand, if it exceeds 1.6%, a bainite phase is likely to be formed, resulting in a decrease in strength and a variation in magnetic flux density due to the formation of coarse cementite. Therefore, the range of the Mn content is set to 0.8% or more and 1.6% or less. Preferably it is 0.9% or more and 1.5% or less.

P: less than 0.03%

P is an element that segregates at grain boundaries and significantly deteriorates the toughness of welded parts. Therefore, it is preferable to reduce P as much as possible. In the present invention, in order to avoid the above problems, the P content is set to 0.03% or less. Preferably it is 0.02% or less.

S: 0.005% or less

S exists in the form of inclusions (inclusions) such as MnS in steel. The inclusions are coarse, and therefore cause a decrease in magnetic flux density. Therefore, in the present invention, it is preferable to reduce the S content as much as possible, and set it to 0.005% or less. Preferably it is 0.003% or less.

Al: less than 0.08%

When Al is contained as a deoxidizer at the stage of steelmaking, it is contained in an amount of 0.02% or more. On the other hand, when the Al content exceeds 0.08%, the magnetic flux density decreases due to coarse inclusions such as alumina. Therefore, the Al content is set to 0.08% or less. Preferably it is 0.07% or less.

N: 0.006% or less

N combines with Nb to form coarse nitrides, thereby reducing the magnetic flux density. In addition, since the amount of precipitation of fine carbides containing Nb that contribute to strengthening is reduced, the strength is also lowered. Therefore, it is preferable to reduce the N content as much as possible, and set the upper limit to 0.006%. Preferably it is 0.005% or less.

Nb: 0.06% to 0.20%

Nb is an element that forms fine carbides and contributes to high strength of the steel sheet. In order to obtain a yield strength of 500 MPa or more, it is necessary to contain Nb in an amount of 0.06% or more. On the other hand, if it exceeds 0.20%, the coarse Nb-containing carbide cannot be dissolved when the slab is heated before hot rolling, and the contribution to the increase in strength is saturated, and the magnetic flux density decreases. Therefore, the range of the Nb content is set to 0.06% or more and 0.20% or less. Preferably it is 0.08% or more and 0.18% or less. The preferable range for obtaining the yield strength in the rolling direction of 550 MPa or more is 0.10% or more and 0.18% or less.

The balance is Fe and unavoidable impurities.

The above is the component composition in the present invention, and in addition to the above component composition, one or more of V: 0.01% to less than 0.05%, Ti: 0.01% to less than 0.05% may be further contained according to the following purposes .

V and Ti are elements that combine with C to contribute to further strengthening. In order to obtain this effect, it is preferable that both V and Ti are contained in an amount of 0.01% or more. On the other hand, when V is contained in an amount of 0.05% or more, the influence of softening due to the dissolution of V-containing carbides in the weld heat-affected zone becomes significant, and weldability decreases. When Ti is contained in an amount of 0.05% or more, coarse Ti-containing carbides remain in the slab heating step before hot rolling, resulting in a decrease in magnetic flux density. Therefore, when contained, V: 0.01% to less than 0.05%, and Ti: 0.01% to less than 0.05% are set. V: 0.01% to 0.04% and Ti: 0.01% to 0.03% are preferable.

Next, reasons for limiting the characteristics of the hot-rolled steel sheet for magnetic poles of the present invention will be described.

The yield strength in the rolling direction is 500MPa or more

When used for a rim member for hydroelectric power generation, etc., strength is required. When the yield strength in the rolling direction is 500 MPa or more, the sheet thickness can be reduced and applied to a high-efficiency hydroelectric power generation rim member. In this case, since the yield strength based on the tensile test in the direction parallel to the rolling direction becomes important, the yield strength in the rolling direction is specified. Steel sheets with a yield strength of less than 700 MPa are particularly suitable for the present invention.

The magnetic flux density B ₅₀ is 1.4T or more, and the magnetic flux density B ₁₀₀ is 1.5T or more

When the magnetic flux density _B50 is 1.4T or more and the magnetic flux density _B100 is 1.5T or more, when it is used for the rim member for hydroelectric power generation, high efficiency of hydroelectric power generation can be achieved.

The minimum value of the Vickers hardness of the welding heat-affected zone is (the average value of the Vickers hardness of the base metal - 30) or more

The flange members for hydroelectric power generation are often joined by welding. By setting the Vickers hardness of the welded heat-affected zone to (the average value of the Vickers hardness of the base material-30) or more, defects and defects in the welded portion can be suppressed. The welding conditions at this time may be the same as those described in Examples.

Next, the method of manufacturing the hot-rolled steel sheet for magnetic poles of the present invention will be described.

The hot-rolled steel sheet for magnetic poles of the present invention can be produced by heating a raw steel material (steel billet) having the above composition at a temperature of 1100° C. to 1350° C., and then performing rough rolling at a temperature of 1100° C. Hot rolling with the finish rolling temperature set at 840°C or higher, cooling at an average cooling rate of 30°C/s or higher within 3 seconds after finish rolling, and then coiling at 550°C to 700°C.

In the present invention, the steel melting method is not particularly limited, and known melting methods such as a converter (converter) and an electric furnace can be used. In addition, secondary refining (secondary refining) can be performed using a vacuum degassing furnace. Then, from the viewpoint of productivity and quality, it is preferable to form a slab (steel raw material) by continuous casting, but it may also be produced by ingot casting and blooming, thin slab continuous casting, etc. Known casting methods produce slabs.

Heating temperature of steel raw materials: above 1100°C and below 1350°C

Before hot rolling, the steel material needs to be heated to form a substantially homogeneous austenite phase. When the heating temperature is lower than 1100°C, coarse carbides containing Nb and Ti cannot be dissolved, and the strength and magnetic flux density decrease. On the other hand, when the heating temperature exceeds 1350° C., the amount of scale (scale) generated increases, the scale is bitten during hot rolling, and the surface properties of the hot-rolled steel sheet deteriorate. Therefore, the heating temperature of the steel material is set to 1100°C or higher and 1350°C or lower. Preferably, it is 1150°C or more and 1300°C or less. However, when hot-rolling a raw steel material, when the cast steel raw material is in a temperature range of 1100° C. to 1350° C. or when carbides of the steel raw material are dissolved, direct rolling may be performed. The steel raw material is not heated.

Hot rolling that completes rough rolling at a temperature of 1100°C or higher and sets the finish rolling temperature to 840°C or higher

C that is not combined with Nb, V, and Ti is precipitated in the form of Fe carbides. In order to precipitate almost all of the contained C in the form of fine carbides containing Nb, V, and Ti, it is necessary to complete the rough rolling before finish rolling at 1100° C. or higher. This is because, when the rough rolling is completed at lower than 1100°C, the strain introduced in the rough rolling is used as the driving force, and the carbides containing Nb, V, and Ti are coarsely precipitated in the austenite due to the subsequent long-term holding. matter, which makes the adverse effects on strength and flux density become significant. When the finish rolling temperature is lower than 840° C., ferrite transformation starts during finish rolling to form a structure in which ferrite grains expand. A large number of dislocations are introduced into the elongated ferrite grains, resulting in a decrease in magnetic flux density. Therefore, the finish rolling temperature is set at 840°C or higher. Preferably it is 860°C or higher. In addition, the temperature in the finish rolling is lower than 1100 degreeC, but the continuous rolling in the finish rolling does not have time for precipitation and growth compared with rough rolling, Therefore, the adverse influence of the said rough rolling is not remarkable.

Cool at an average cooling rate of 30°C/sec or more within 3 seconds after finishing rolling

Carbide containing Nb becomes finer as the transformation temperature from austenite to ferrite decreases. In order to obtain carbides with an average grain size of 6 nm or less, it is necessary to set the transformation temperature from austenite to ferrite to 700° C. or less. For this reason, it is necessary to cool at an average cooling rate of 30° C./sec or more within 3 seconds after finish rolling. In addition, the average cooling rate is the average cooling rate from finish rolling temperature to 700 degreeC.

Coiling temperature: above 550°C and below 700°C

When the coiling temperature exceeds 700°C, the carbides are coarsened, and desired strength and magnetic properties cannot be obtained. On the other hand, when the temperature is lower than 550° C., a bainite phase is formed, thereby deteriorating the magnetic properties. Therefore, the range of the coiling temperature is set to 550°C or higher and 700°C or lower. Preferably, it is 580°C or more and 680°C or less.

The hot-rolled steel sheet for a magnetic pole of the present invention is manufactured by the above method. It should be noted that even if the hot-rolled steel sheet for a magnetic pole of the present invention is passed through a continuous hot-dip coating line with an annealing temperature of 720° C. or lower, the quality is not affected. Therefore, a plating treatment can be further performed on the surface of the steel sheet to have a plating layer on the surface of the steel sheet. In addition, since the plating treatment and the composition of the plating bath do not affect the material, any of hot-dip galvanizing treatment, alloying hot-dip galvanizing treatment, and electro-galvanizing treatment can be applied as the plating treatment. In addition, the composition of the plating bath may contain one or two or more of Zn, Si, Al, Ni, and Mg. That is, the composition of the plated layer formed in the plating process may contain one or two or more of Zn, Si, Al, Ni, and Mg.

The hot-rolled steel sheet for magnetic poles of the present invention obtained by the method described above is suitable for parts requiring high magnetic poles, and is particularly suitable for use as a rim member for hydroelectric power generation. For example, the hot-rolled steel sheet of the present invention is cut into a predetermined shape by shearing, punching, laser cutting, etc., and laminated to be used as an electromagnetic member facing a rim or a core (pole core, etc.). In particular, the hot-rolled steel sheet of the present invention can be suitably used for a generator rim that requires both high strength and good magnetic properties. When stacking steel plates, it is preferable to electrically insulate the stacked steel plates by insulating the steel plates or interposing an insulating material between the steel plates.

Example 1

Hot-rolled steel sheets were produced under the hot-rolling conditions shown in Table 2 for raw steel materials having a thickness of 250 mm having the composition shown in Table 1. Some of the hot-rolled steel sheets were further subjected to galvanizing treatment. Alloying hot-dip galvanizing treatment An annealing temperature of 700°C or less, a molten bath composition of Zn-0.13% by mass Al, a bath temperature of 460°C, and an alloying temperature of 530°C are continuous hot-dip galvanizing lines Production was carried out, and the coating weight was set at 45 to 65 g/m ² per one side.

Test pieces were cut from the hot-rolled steel sheets or galvanized steel sheets obtained by the above method with a thickness of 1.6 mm to 3.2 mm, and the structures were observed and performances were evaluated by the following methods.

(i) Organization Observation

The area ratio of each phase was evaluated by the following method. Cut a hot-rolled steel sheet or an alloyed galvanized steel sheet so that the section parallel to the rolling direction is the observation surface, and use 3% nital solution (nital) to corrode (etching) the metal at the center of the sheet thickness The tissue was magnified to 400 times with a scanning optical microscope, and 10 fields of view were photographed. The ferrite phase is a structure in which no corrosion marks or cementite are observed in the crystal grains. These were separated into bainite phase, martensite phase, pearlite (pearlite) and the like other than the ferrite phase by image analysis, and calculated using the area ratio with respect to the observation field of view. When calculating the area, the ferrite grain boundaries are included as part of the ferrite phase.

The average particle size of the precipitated Nb-containing carbides was observed with a transmission electron microscope at a magnification of 135,000 or more, and the average particle size of the carbides at 100 points or more was obtained to obtain the equivalent circle diameter as the particle size of each carbide. .

Regarding the amount of Fe precipitation, about 0.2 g was subjected to constant current electrolysis at a current density of 20 mA/cm ² in a 10% AA-based electrolyte solution (10 vol % acetylacetone-1 mass % tetramethylammonium chloride-methanol). , capture the precipitate from the electrolyte by filtration, use the ICP-MS method to find the amount of Fe contained in the precipitate, and find the ratio to the mass of the steel base after electrolysis by constant current electrolysis, thereby obtaining Fe Precipitation amount.

Regarding the Nb precipitation amount (Nb precipitation ratio), galvanostatic electrolysis was performed in the same procedure as the method for measuring the Fe precipitation amount, and the Nb amount contained in the electrolytic solution was measured by the ICP-MS method. The amount of Nb contained in the electrolytic solution is the amount of Nb in a solid solution state, and the amount of Nb precipitated is obtained by subtracting the amount of Nb in a solid solution state from the Nb content.

(ii) Tensile test

From a hot-rolled steel sheet or an alloyed hot-dip galvanized steel sheet, a JIS No. 5 tensile test piece is prepared in a direction parallel to the rolling direction, and the tensile test according to JIS Z 2241 (2011) is performed five times, and the average value is obtained. Yield strength (YS), tensile strength (TS), total elongation (El). The crosshead speed for the tensile test was set at 10 mm/min.

(iii) Measurement of magnetic flux density

A sample of 30 mm x 280 mm was cut from a hot-rolled steel sheet or an alloyed hot-dip galvanized steel sheet, and the magnetic flux density B ₅₀ and the magnetic flux density B ₁₀₀ were obtained by measurement based on JIS C 2555 using a DC magnetic characteristic measuring device. B ₅₀ and B ₁₀₀ represent the magnetic flux density under the magnetizing force of 5000A/m and 10000A/m, respectively.

(iv) Weldability evaluation

As a welding test, carbon dioxide arc welding using a wire with a diameter of 1.2 mm was performed for evaluation. The welding conditions were butt welding with a welding speed of 80 cm/min, a welding current of 220 A, a welding voltage of 25 V, and a gap of 1 mm. After welding, a cross-section of the welded portion was cut out, and a Vickers hardness test with a test load of 0.49N was performed at intervals of 0.5mm in the center of the thickness of the cross-section relative to the direction across the welded portion. On the other hand, the hardness of the base material was set as an average value obtained by measuring 5 points at positions 30 mm or more from the welded part with a test load of 0.49N. Table 3 shows the difference between the hardness of the base metal (the average value of the hardness of the base metal) and the minimum hardness in the heat-affected zone (the lowest value of the hardness of the welded heat-affected zone).

Table 3 shows the results obtained as described above.

It can be seen that in the examples of the present invention, the yield strength YS in the rolling direction is 500 MPa or more, and the minimum value of the Vickers hardness in the welded heat-affected zone is (the average value of the Vickers hardness of the base material - 30) or more. Weldability, Furthermore, the magnetic flux density _B50 is 1.4T or more, and the magnetic flux density _B100 is 1.5T or more is a hot-rolled steel sheet (galvanized steel sheet) having excellent magnetic properties. On the other hand, in the comparative example outside the range of the present invention, one or more of yield strength, weldability, and magnetic properties were inferior.

Claims (8)

1. a kind of magnetic pole hot rolled steel plate, wherein, composition composition contains C in terms of quality %：More than 0.02% and less than 0.12%, Si：More than 0.1% and less than 0.7%, Mn：More than 0.8% and less than 1.6%, P：Less than 0.03%, S：Less than 0.005%, Al：Less than 0.08%, N：Less than 0.006%, Nb：More than 0.06% and less than 0.20%, surplus by Fe and inevitably it is miscellaneous Texture into,

The ferritic phase of tissue is calculated as more than 98% with area occupation ratio,

The Fe of precipitation is below 0.22 mass % relative to Fe amounts contained in steel, the Nb of precipitation is relative to Nb amounts contained in steel Average grain diameter for more than 80 mass %, the carbide containing Nb separated out is below 6nm,

The yield strength of rolling direction is more than 500MPa, magnetic flux density B₅₀For more than 1.4T, magnetic flux density B₁₀₀For 1.5T with On, the minimum of the Vickers hardness of welding heat affected zone is more than (average value -30 of the Vickers hardness of mother metal).

2. magnetic pole hot rolled steel plate as claimed in claim 1, it is characterised in that further meet following formula (1),

$\[\%C\]-12(\frac{\[\%Nb\]}{93}+\frac{\[\%V\]}{51}+\frac{\[\%Ti\]}{48})\≤\mathrm{0.04...}\left(1\right)$

Wherein, %C, %Nb, %V, %Ti represent the content of each element, in addition, being set as 0 when not containing.

3. magnetic pole hot rolled steel plate as claimed in claim 1 or 2, wherein, on the basis of composition composition, with quality % Meter contains V：0.01% less than 0.05%, Ti：0.01% less than one or more of 0.05%.

4. a kind of manufacture method of magnetic pole hot rolled steel plate, wherein, there will be composition according to any one of claims 1 to 3 The steel former material of composition is heated more than 1100 DEG C and at less than 1350 DEG C of temperature, then, implements the temperature more than 1100 DEG C The lower hot rolling for completing roughing and final rolling temperature being set as to more than 840 DEG C, with more than 30 DEG C/sec within after finish rolling terminates 3 seconds Average cooling rate cooled down, then, batched more than 550 DEG C and at less than 700 DEG C of temperature.

5. the manufacture method of magnetic pole hot rolled steel plate as claimed in claim 4, it is characterised in that to the further reality of surface of steel plate Apply plating.

6. the manufacture method of magnetic pole hot rolled steel plate as claimed in claim 5, it is characterised in that the plating is hot dip Any of zinc processing, alloyed zinc hot dip galvanized processing, electrogalvanizing processing.

7. the manufacture method of the magnetic pole hot rolled steel plate as described in claim 5 or 6, it is characterised in that in the plating The composition of the coating of middle formation contains more than one or both of Zn, Si, Al, Ni, Mg.

8. a kind of hydroelectric generation rim component, it is by magnetic pole according to any one of claims 1 to 3 hot rolled steel plate structure Into.