JPH11140601A - High-strength cold-rolled steel sheet and high-strength plated steel sheet with good geomagnetic shielding properties and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the geomagnetic shield characteristics, that is, to improve the geomagnetic shield characteristics.
A high-strength cold-rolled steel sheet and a high-strength plated steel sheet having a large relative magnetic permeability in a DC magnetic field before and after 3 Oersteds, and a method of manufacturing the same. SOLUTION: Ti and S are added to a steel of ultra low carbon of 0.0040% or less, which is solid solution hardened by Si and Mn, regardless of precipitation strengthening, and is taken out of a heating furnace at less than 1150 ° C. This allows C, S and N to be converted to Ti ₄ C ₂ S
₂ , fixed as TiN, finishing temperature 800 ° C ~ 980
After hot rolling at a temperature of 700 ° C or more and a winding temperature of 700 ° C or higher, 75 in continuous annealing equipment or continuous hot-dip galvanizing equipment of an in-line annealing type.
By annealing at a temperature range of 0 ° C. or more and an Ac ₃ point or less, the ferrite crystal grain size in the metal structure becomes 10 to 10.
Make it 30 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength cold-rolled steel sheet and a high-strength plated steel sheet having good geomagnetic shielding properties and a method of manufacturing the same.

[0002]

2. Description of the Related Art When a thin steel sheet is used for home electric appliances, automobiles, furniture, construction, etc., it is a typical characteristic that requires strength, rust prevention, etc. Parts such as a band and a support frame are required to shield the influence of terrestrial magnetism so that the electron beam does not deflect when passing through the space defined by the parts. Here, good geomagnetic shielding means that the relative magnetic permeability in a DC magnetic field around 0.3 Oersted, which is equivalent to terrestrial magnetism, is large. Therefore, there is a possibility that malfunction of the device can be suppressed.

[0003] Improving the terrestrial magnetism shielding property can be easily realized by using a non-oriented electrical steel sheet as generally specified in JIS C2552. 0.3 It is only to increase the relative magnetic permeability in a DC magnetic field before and after the Oersted, and does not require the characteristics in a high magnetic field such as a rotating machine, and can be manufactured if it can be manufactured with the same equipment as a thin steel sheet for press working. The thickness range is wide and the manufacturing cost can be reduced. In order to increase the relative magnetic permeability in a DC magnetic field of about 0.3 Oe, which corresponds to terrestrial magnetism, it is necessary to reduce the fine precipitates present in the steel and to coarsen the ferrite grains to facilitate the movement of the domain wall. For example, Japanese Patent Application Laid-Open No. 3-61330 discloses a method of coarsening crystal grains by open coil decarburizing annealing using a low Al killed steel. In JP-A-8-6134 and JP-A-8-27520, C is 0.01%.
In the following, a method of coarsening crystal grains by continuously annealing steel with reduced impurities is described, but it is estimated that the yield point of the steel sheet according to the invention is only 250 MPa at most.

On the other hand, in order to reduce the amount of steel used in terms of weight reduction and life cycle assessment (LCA), a high yield point of, for example, 250 to 300 MPa or more is required, and solid solution strengthening, fine grain strengthening, It is necessary to increase the yield point by combining one or more means of precipitation strengthening and processing strengthening, but in any case, the geomagnetic shield characteristics deteriorate rapidly with the increase of the yield point and achieve the purpose. Could not.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-strength cold-rolled steel sheet and a high-strength plated steel sheet having good geomagnetic shielding properties and a method of manufacturing the same. Here, the cold rolled steel sheet and the plated steel sheet are used for home electric appliances such as an explosion-proof band and a support frame of a TV cathode-ray tube, automobiles, furniture, construction, and the like. Rolled steel sheets, electroplated steel sheets plated with alloys such as Zn and Zn-Ni for rust prevention, galvanized steel sheets, galvannealed steel sheets, and further improved press formability and rust prevention For this reason, it refers to those that include a surface-treated steel sheet that has been subjected to alloying of the plating layer or an organic film treatment on the upper layer.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have typified by increasing the relative permeability in a DC magnetic field of about 0.3 Oersted corresponding to terrestrial magnetism and by a breakdown point. In order to achieve both high strength and low strength, it is important to use solid ultra-low carbon steel with a C content of 0.0050% or less and solid solution strengthening without refining ferrite grains without using precipitation strengthening. As a result of intensive studies, Ti and S were added,
i, Mn strengthens the solid solution and controls the temperature during hot rolling so that the ferrite crystal grain size is 10 to 30 μm.
It was found that the relative magnetic permeability in a DC field of 0.3 Oersted became 500 or more, and that the geomagnetic shield characteristics could be improved. That is, the present invention is a completely new steel plate, which has not been hitherto constructed, based on such new knowledge, and the gist thereof is as follows.

(1) C: 0.0008-0.
0050%, Si: 0.3 to 1.8%, Mn: 0.5 to
1.8%, P: 0.12% or less, S: 0.002-0.
020%, Al: 0.020-0.060%, Ti:
0.01 to 0.06%, N: 0.0030% or less, the balance being Fe and unavoidable impurities, and the metal structure thereof has a ferrite crystal grain size of 10 to 30 μm. A high-strength cold-rolled steel sheet having good geomagnetic shielding properties with a relative magnetic permeability of 500 or more in a DC field of 3 Oersted. (2) A high-strength plated steel sheet having good geomagnetic shielding properties having a relative magnetic permeability of 500 or more in a DC field of 0.3 Oersted according to (1).

(3) A slab composed of the chemical component described in (1) is taken out of the heating furnace at a temperature lower than 1150 ° C., hot-rolled at a finishing temperature of 800 ° C. to 980 ° C., and wound at a temperature of 700 ° C. or more. Thereafter, the steel sheet is subjected to cold rolling of 60 to 90%, and then annealed in a continuous annealing facility or a continuous hot-dip galvanizing facility of an in-line annealing type in a temperature range of 750 ° C. or more and Ac ₃ points or less. Diameter 10
A method for producing a high-strength cold-rolled steel sheet having good geomagnetic shielding properties, having a relative magnetic permeability of 500 or more in a 0.3 Oersted DC magnetic field, characterized in that the thickness of the cold-rolled steel sheet is about 30 μm.

(4) The slab comprising the chemical component described in (2) is taken out of the heating furnace at a temperature lower than 1150 ° C., hot-rolled at a finishing temperature of 800 ° C. to 980 ° C., and wound at a temperature of 700 ° C. or more. Thereafter, the steel sheet is subjected to cold rolling of 60 to 90%, and then annealed in a continuous annealing facility or a continuous hot-dip galvanizing facility of an in-line annealing type in a temperature range of 750 ° C. or more and Ac ₃ points or less. Diameter 10
It is a method for producing a high-strength plated steel sheet having good geomagnetic shielding properties, having a relative magnetic permeability of 500 or more in a DC magnetic field of 0.3 Oersted, characterized by having a diameter of about 30 μm.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the reasons for limiting C, Si, Mn, P, S, Al, Ti, and N will be described. C is a very important element that increases the yield point by solid solution strengthening or precipitation strengthening.
If the content exceeds 0.0050%, C remaining without being fixed by Ti is aged and precipitated as fine carbides, so that the geomagnetic shield characteristics deteriorate. On the other hand, C is 0.0008%
It is not preferable to set the content to be less than a long time for vacuum degassing, which is not preferable because the production cost is remarkably increased. It does not become coarse and the geomagnetic shielding properties cannot be improved.

[0011] Si does not significantly change the ferrite crystal grain size, and dissolves in the crystal to replace Fe atoms, thereby distorting the crystal lattice, thereby increasing the yield point. On the other hand, since the adverse effect on the geomagnetic shield characteristics is small, 0.3% or more is added for the purpose of increasing the yield point. However, if the addition amount exceeds 1.8%, an internal oxide layer is formed on the surface layer of the steel sheet,
This causes a surface defect, and when hot-dip galvanizing is performed, a coating of SiO ₂ is formed on the surface layer, so that the adhesion of the plating is deteriorated.

Mn, like Si, does not greatly change the ferrite crystal grain size, but dissolves in the crystal to replace Fe atoms and distorts the crystal lattice, thereby increasing the yield point. On the other hand, since the adverse effect on the geomagnetic shield characteristics is small, 0.5% or more is added for the purpose of increasing the yield point. However, when the addition amount exceeds 1.8%, the ferrite crystal grains are remarkably refined, and not only the geomagnetic shield characteristics are significantly deteriorated, but also extremely high cost is required to make the C content within the range of the present invention. Becomes

P is for refining ferrite crystal grains.
It has a greater adverse effect on geomagnetic shielding than Si and Mn, which are the same solid solution strengthening elements. However, when it is necessary to increase the yield point strength, geomagnetic shielding deteriorates more than precipitation strengthening or processing strengthening. Is acceptable,
It can be added up to 0.12%. If the amount exceeds 0.12%, the refinement of the ferrite crystal grains becomes remarkable, and not only the geomagnetic shield properties deteriorate significantly, but also the center segregation is remarkable, so that the cold rolling property deteriorates and secondary work embrittlement occurs. .

In the present invention, S forms coarse Ti ₄ C ₂ S ₂ to inhibit the movement of the domain wall and the growth of ferrite crystal grains, so that the magnetic field shielding characteristics are not adversely affected. , When the amount exceeds 0.020%, M
Since nS is easily formed, the movement of the domain wall is inhibited, and the growth of ferrite crystal grains is suppressed.
The performance is deteriorated. On the other hand, if the content is less than 0.002%, the production cost becomes extremely high, which is not preferable.

Although Al is used for deoxidizing steel, in the present invention, since Ti is added to fix N as TiN, excess Al for capturing O becomes fine AlN.
Does not hinder the movement of the domain wall or suppress the growth of ferrite crystal grains, thereby deteriorating the geomagnetic shield characteristics. For this reason, it is added in an amount of 0.02% or more so as not to cause defects in surface properties. On the other hand, addition exceeding 0.06% is not preferable because it increases the cost.

Ti is a coarse Ti ₄ C ₂ S ₂ together with C.
And MnS is prevented from being precipitated, and N is fixed as TiN to suppress precipitation as fine AlN. It is hard to be hindered, and the geomagnetic shield property is improved. If the amount is less than 0.01%, the effect is not recognized. on the other hand,
Addition of more than 0.06% not only increases the cost, but also forms a fine compound with P, which hinders the movement of the domain wall, suppresses the growth of ferrite crystal grains, and deteriorates the geomagnetic shield characteristics. .

In the present invention, N is added to Ti and precipitated as TiN to suppress the deterioration of the geomagnetic seal characteristics. However, the remaining N becomes fine precipitates and hinders the movement of the domain wall. If the amount of TiN becomes excessive, the degree of hindrance to the movement of the domain wall becomes remarkable.
Nb, Cu, Sn, Zr, M
Although it contains unavoidable impurities such as o, W, Cr, Ni, and B, it is often unfavorable in order to achieve both the desired geomagnetic shield characteristics and high strength of the present invention. Is preferably less than 0.3%.

Next, the reasons for limiting the manufacturing conditions will be described. The slab to be subjected to hot rolling is not particularly limited. That is, any material manufactured by a continuous cast slab thin slab caster or the like may be used. Neither is the condition of hot rolling specified. Before starting hot rolling, most of C, S and N are fixed as Ti ₄ C ₂ S ₂ and TiN, and the temperature at which the slab is taken out of the heating furnace is 1150 ° C. in order to minimize the adverse effect on the geomagnetic shield characteristics. Less than The finishing temperature is 800 to 980 ° C. If the finishing temperature is lower than 800 ° C., a non-recrystallized structure remains, deteriorating the cold rolling property, and reducing the ferrite crystal grains after cold rolling and annealing to 10 μm.
m or more is not easy, and the geomagnetic shield characteristics are inferior. On the other hand, in order to finish hot rolling at a temperature exceeding 980 ° C., it is necessary to remarkably raise the heating temperature, which is not preferable. In particular, from the viewpoint of facilitating the growth of ferrite crystal grains after cold rolling and annealing, the temperature is preferably set to 800 ° C. or more and Ar ₃ points or less. The cooling method and the winding temperature after hot rolling are not particularly limited, but the remaining C and N are finely precipitated to inhibit domain wall movement, suppress the growth of ferrite crystal grains, and improve the geomagnetic shield characteristics. 7 not to deteriorate
It should be at least 00 ° C.

The cold rolling may be carried out under ordinary conditions. In order to efficiently pickle the scale efficiently, the rolling ratio is 60%.
Above. On the other hand, performing cold rolling at a rolling ratio exceeding 90% is not practical because a large cold rolling load is required. When annealing with continuous annealing equipment or continuous hot-dip galvanizing equipment of an in-line annealing type, the annealing temperature is 750 ° C. or more and Ac ₃ points or less. If the annealing temperature is lower than 750 ° C., recrystallization is insufficient and the processed structure remains, so that the geomagnetic shear
Remarkably deteriorates the characteristics. Although the geomagnetic shield characteristics improve with an increase in the annealing temperature and the growth of ferrite grains, they may decrease when annealing at a temperature exceeding the Ac ₃ point and a mixed grain structure due to transformation occurs. It is desirable to avoid.

Thereafter, if necessary, for example, Z
Even if a surface treatment such as n-plating or alloy plating such as Zn-Ni, and further an organic coating treatment is performed thereon, no influence on the geomagnetic shield characteristics characteristic of the present invention is observed. After annealing, the relative permeability in a DC magnetic field around 0.3 Oersted decreases with temper rolling, shearing of a steel sheet, and processing into a part shape, but the explosion-proof band and support frame of a TV cathode-ray tube are reduced. Since the system is compressed by thermal shrinkage when forcibly cooled from about 600 ° C., that is, used in a shrink-fit state, much of the strain applied during the process of reheating to 600 ° C. is released, and the geomagnetic shield is released. The characteristics of the magnetic field, that is, the relative magnetic permeability in a DC magnetic field around 0.3 Oe, are not significantly different from those immediately after annealing. That is, both good geomagnetic shield characteristics and high strength as represented by the yield point can be achieved.

[0021]

Next, the present invention will be described in more detail with reference to Examples. (Example 1) Steel having the composition shown in Table 1 was hot-rolled to a thickness of 3.0 mm to 6.0 mm under the conditions shown in Table 2, and after pickling, cold-rolled to 0.7 mm to 1. After forming a cold-rolled steel strip having a thickness of 6 mm, heat treatment under the conditions shown in Table 2 was performed using continuous annealing equipment, and temper rolling was performed at an elongation of 0.3%. A JIS No. 5 test piece was cut out from the steel strip thus manufactured in parallel to the rolling direction, and a tensile test was performed at room temperature to determine a yield strength (YP) and a tensile strength (TS). 30m cut from the same steel strip
Combination of mx 300mm sample, JIS C255
The relative magnetic permeability in a DC magnetic field of 0.3 Oersted was determined by a DC Epstein method based on 0. Further, after the cross section was corroded, the average grain size of the ferrite crystal grains was determined by observing with an optical microscope at a magnification of 100 times. Table 2 shows the results.

[0022]

[Table 1]

[0023]

[Table 2]

As is clear from this table, the ferrite has a chemical composition defined in the present invention and has a ferrite grain size of 10 to 3 mm.
Samples Nos. 2, 4, 6, 7, 13, 15, and 16 of 0 μm are high-strength cold-rolled steel sheets having a yield point of 300 MPa or more, and have a specific permeability of 500 or more in a 0.3-Oersted DC magnetic field. It has magnetic susceptibility and has excellent geomagnetic shield characteristics. On the other hand, sample Nos. 3, 5,
As described in 8, 9, and 14, even if it has the chemical composition specified in the present invention, the manufacturing conditions are inappropriate, the ferrite crystal grain size is not in the range of 10 to 30 μm, Is contained or when a mixed grain structure is formed
Rusted has a relative magnetic permeability of less than 500 in a DC magnetic field, and is inferior in geomagnetic shield characteristics.

In steels other than the chemical composition specified in the present invention, if the amount of addition of Si or Mn is small as shown in Samples Nos. 10 and 11, 50% at 0.3 Oersted DC magnetic field.
It is difficult to obtain a yield point of 300 MPa or more even with a relative magnetic permeability of 0 or more,
If Mn and P are excessively added as in Nos. 2 and 17 to 20, or if the added amounts of C, S and Ti are inappropriate, the ferrite crystal grain size is 1 even if the yield point is 300 MPa or more.
On the other hand, the sample N
When C exceeds 0.0040% as in O21, fine carbides tend to precipitate due to aging, and the relative magnetic permeability in a DC field of 0.3 Oe is less than 500, which is inferior in the geomagnetic shield characteristics. .

(Example 2) Steel C having the composition shown in Table 1
Is hot-rolled to a thickness of 3.5 to 6.0 mm under the conditions shown in Table 3, pickled, cold-rolled to a thickness of 0.8 to 1.6 mm, and then subjected to an in-line annealing continuous hot-dip galvanizing facility. While performing a heat treatment under the conditions shown in Table 3 by using the steel strip, the elongation percentage is further increased by 0.3%
Temper rolling. A JIS No. 5 test piece was cut out from the steel strip thus manufactured in parallel to the rolling direction, and a tensile test was performed at room temperature to determine a yield strength (YP) and a tensile strength (TS). In addition, a sample of 30 mm x 300 mm cut out from the same steel strip was combined, and JIS
0.3 according to the DC Epstein method based on C2550
The relative magnetic permeability of the Oersted in a DC magnetic field was determined.
Further, after the cross section was corroded, the ferrite crystal grain size was determined by observing with an optical microscope at a magnification of 100 times. Table 3 shows the results
Shown in

[0027]

[Table 3]

As is clear from this table, the ferrite has a chemical composition specified in the present invention and has a ferrite crystal grain size of 10 to 30.
Sample Nos. 1 and 2 which are μm are high-strength cold-rolled steel sheets with a yield point of 300 MPa or more, and have a relative magnetic permeability of 500 or more in a DC magnetic field of 0.3 Oersted,
It has excellent geomagnetic shield characteristics. On the other hand, even if it has the chemical composition specified in the present invention as in Sample Nos. 3 to 5, the production conditions are inappropriate and the ferrite crystal grain size is not in the range of 10 to 30 μm, and especially the Or a mixed grain structure, the relative magnetic permeability in a 0.3 Oersted DC magnetic field is less than 500, which is inferior in the geomagnetic shield characteristics.

[0029]

As described in detail above, the present invention has a high relative magnetic permeability in a DC magnetic field of about 0.3 Oe, which is equivalent to terrestrial magnetism, and has good geomagnetic shield characteristics and a yield point. High-strength cold-rolled steel sheet and high-strength plated steel sheet and a method for producing the same, both of which have high strength as described above, and the same continuous annealing as that in which a thin steel sheet for press working is produced. Since it can be easily manufactured using continuous galvanizing equipment of equipment or in-line annealing type, not only thin steel plates such as household electric products, automobiles, furniture and construction are used, as well as explosion-proof bands and support frames for TV cathode ray tubes. It can be applied to a wide range of applications, and has an extremely large industrial effect.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/14 C22C 38/14 (72) Inventor Jun Itami 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Works

Claims (4)

[Claims] 1. In weight%, C: 0.0008 to 0.0050%, Si: 0.3 to 1.8%, Mn: 0.5 to 1.8%, P: 0.12% or less, S: 0.002 to 0.020%, Al: 0.020 to 0.060%, Ti: 0.01 to 0.06%, N: 0.0030% or less, balance Fe and unavoidable impurities Characterized by having a ferrite crystal grain size of 10 to 30 μm in its metal structure.
The relative permeability in a DC field of 3 Oersted is 500
High-strength cold-rolled steel sheets with good geomagnetic shielding properties. 2. A high-strength plated steel sheet according to claim 1, having a relative magnetic permeability of 500 or more in a DC magnetic field of 0.3 Oersted and having good geomagnetic shield properties. 3. A slab consisting of the chemical component according to claim 1 is taken out of the heating furnace at a temperature lower than 1150 ° C., and the slab is subjected to a finishing temperature of 8.
After hot rolling at 00 ° C to 980 ° C, winding at a temperature of 700 ° C or more, cold rolling of 60 to 90% is performed, and then 750 using a continuous annealing facility or an in-line continuous hot-dip galvanizing facility. Annealing in the temperature range of not less than ₃ ° C and not more than Ac
In the metal structure, the ferrite grain size is 10 to 30.
A method for producing a high-strength cold-rolled steel sheet having good geomagnetic shielding properties, having a relative magnetic permeability of 500 or more in a DC magnetic field of 0.3 Oersted, characterized by having a diameter of 0.3 μm. 4. A slab consisting of the chemical component according to claim 2 is taken out of the heating furnace at a temperature lower than 1150 ° C., and the slab is subjected to a finishing temperature of 8.
After hot rolling at 00 ° C to 980 ° C, winding at a temperature of 700 ° C or more, cold rolling of 60 to 90% is performed, and then 750 using a continuous annealing facility or an in-line continuous hot-dip galvanizing facility. Anneal in the temperature range of not less than ₃ ° C and not more than Ac
In the metal structure, the ferrite grain size is 10 to 30.
A method for producing a high-strength plated steel sheet having a good magnetic permeability and a relative permeability of 500 or more in a DC magnetic field of 0.3 Oersted, characterized by having a diameter of 0.3 μm.