CA1238802A - Al-killed cold-rolled steel sheet with excellent demagnetization characteristics and process for producing the same, and shadow mask and color television using the same - Google Patents

Al-killed cold-rolled steel sheet with excellent demagnetization characteristics and process for producing the same, and shadow mask and color television using the same

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Publication number
CA1238802A
CA1238802A CA000475237A CA475237A CA1238802A CA 1238802 A CA1238802 A CA 1238802A CA 000475237 A CA000475237 A CA 000475237A CA 475237 A CA475237 A CA 475237A CA 1238802 A CA1238802 A CA 1238802A
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CA
Canada
Prior art keywords
less
cold
rolled steel
sol
steel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000475237A
Other languages
French (fr)
Inventor
Morinori Kamio
Susumu Kawauchi
Masahiro Tsuji
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Engineering Corp
Nippon Mining Holdings Inc
Original Assignee
Nippon Mining Co Ltd
Nippon Kokan Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Mining Co Ltd, Nippon Kokan Ltd filed Critical Nippon Mining Co Ltd
Application granted granted Critical
Publication of CA1238802A publication Critical patent/CA1238802A/en
Expired legal-status Critical Current

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  • Electrodes For Cathode-Ray Tubes (AREA)

Abstract

Abstract An Al-killed cold-rolled steel sheet with excellent demagnetization characteristics is provided which is sub-stantially consisted of 0.005% or less C; from 0.05 to 0.50%
Mn; 0.010% or less S; from 0.01 to 0.08% Sol.Al; 0.0050% or less N; wherein Mn%/S% 27 and (Sol.Al% - 0.003%)/N% ?6;
and the remainder iron and inevitable impurities. A shadow mask made of such Al-killed cold-rolled steel sheet and a color television receiver using the same exhibit a very excellent function. A preferred process for producing such an Al-killed cold-rolled steel is also provided, said process being characterized in first obtaining a steel or a specific composition by the use of a vacuum degassing apparatus and then subjecting the steel to sequential steps of hot rolling, cold rolling, decarburization-annealing, and cold rolling.

Description

i23~8~2 Al-killed cold-rolled steel sheet with excellent demagnetization characteristics and process for producing the same, and shadow mask and color television using the same Field of the Invention This invention relates to an Al-killed cold-rolled steel sheet with excellent demagnetization characteristics and a process for producing the same and also relates to a shadow mask and a color television using the same.
Background of the Invention As materials of shadow masks to be used in cathode-ray tubes for color television and color display, low-carbon, rimmed, cold-rolled steel sheets have hitherto been employed.
However, such low-carbon, rimmed, cold-rolled steel sheets have disadvantages, for example, in that nonmetallic inclusions or carbides in the steel can cause unregulated contours of the mask holes when they are made by photoetch:ing and in that low-temperature annealing performed inevitably to prevent adhesion of flat masks to each other in the final annealing will make the crystal grain size so small that levelling prior to press forming will not thoroughly strain the sheet and stretcher strains tend to develop due to yield point elongation caused by solid-soluted C and N during the press work. Development of these stretcher strains, which i ~
1 -- . _ i238802 deform the hole contours and uneven color development, must be avoided to satisfactorily function the shadow mask.
Another problem with rimmed steels is that annealing at elevated temperatures coarsens the crystal grains, thus again deforming the contours of the mask holes on press working of the shadow masks. To overcome these difficulties, variations of steel compositions and final annealing conditions must be strictly controlled.
In an effort to lessen these disadvantages, low-carbon Al-killed cold-rolled steel sheets with a C content of 0.005%
or below are recently coming to use.
Problems of the Prior Art The shadow mask not only controls the electron beams for color reproduction but also serves as a magnetic shield inside a cathode-ray tube to keep the paths of electron beams from being undesirably deflected by external magnetic fields such as of the earth magnetism. It thus avoids reduction of color purity or uneven color reproduction due to mislanding, a phenomenon in which the electron beam paths in the color cathode-ray tube are distorted by variations in the horizontal component of the earth magnetism, making it no longer possible for the electron beam spots on the phosphor screen and the phosphor locations on the screen to maintain precise alignment~
Thus, in an ordinary color cathode-ray tube, the drift spaces of the electron beams are isolated from external magnetic 1;~38~302 influences by the magnetic shield, and the demagnetization characteristics of the shadow mask itself also are important.
In respect of the demagnetization characteristics, the low-carbon, Al-killed cold-rolled steel sheet is inferior to the low-carbon, rimmed cold-rolled steel sheet. Problems arise from its use in forming a shadow mask, such as the necessity of a special circuit to improve the landing characteristics in the cathode-ray tube.
Thus, it is essential that the shadow mask itself has excellent demagnetization characteristics. The existing low-carbon, Al-killed cold-rolled steel sheets are unsatis-factory for the application, and a steel sheet of this type with greater demagnetization characteristics than usual has been desired.
The Object of the Invention The object of this invention is to provide a low-carbon Al-kflled cold~rolled steel sheet with excellent demagneti-zation characteristics which meets the demand described above.
Further, this invention has an object of establishing a process effective to produce such low-carbon Al-killed cold-rolled steel sheet.
Explanation of the Invention The present inventors have made diversified investigations in view of the foregoing and have now found..that excellent demagnetization characteristics are accomplished in an 123E~8~2 Al-killed cold-rolled steel sheet substantially consisted of (all percentages herein being by weight) 0.004% or less C;
from 0.05 to 0.50~, preferably 0.1 to 0.50%, Mn; 0.010% or less S; from 0.01 to 0.08%, preferably 0.02 to 0.08% Sol.Al (acid-soluble Al); 0.0040% or less N; wherein Mn%/S% 2 7 and ( Sol.
Al% - 0~. 003% ~/N~ 2 6; the remainder iron and inevitable impurities, said sheet having a coercive force not more than 1.30 Oe.
Accordingly, a shadow mask fabricated from such Al-killed cold-rolled steel sheet and a cathode-ray tube for a color television, color display, etc. using such shadow mask exhibit a very excellent function.
In another embodiment the present invention provides a process for producing an Al-killed cold-rolled steel sheet with enhanced demagnetization characteristics for shadow masks characterized in comprising the steps of preparing a molten steel with the use of a vacuum degassing apparatus which con-sists essentially of 0.008% or less C; from 0.05 to 0.50% Mn;
0.010% or less S; from 0.01 to 0.08% Sol. Al; 0.0040% or less N; wherein Mn%/S% ~ 7 and ( Sol. Al~ - 0.003% )/N% 2 6; the remainder iron and ~nevitable impurities; making the melt with ordinary ingot casting or continuous casting into a steel piece;
hot-rolling the steel piece and then cold-rolling it; decarburizing and annealing the cold-rolled steel to a C content of 0.004%
or less in a decarburization-annealing furnace and again cold-rolling the steel into a sheet of 0.2 mm or less in thickness.

1238l302 Although the above Al-killed cold-rolled steel jheet may be produced by ordinary processes, the present invention is based on the discovery that one effective production process is to produce it by first obtaining a steel of a specific composition by the use of a vacuum degassing appara~us and then subjecting the steel to sequential steps of hot.rolling, cold rolling decarburization-annealing, and cold rolling.
In the above process, the composition of the steel produced by the use of a vacuum degassing apparatus is substantially consisted of, all by weigh, 0.008~ or less C; from 0.05 to O.S0% Mn; 0.010% or less S; from 0.010 to 0.080~ Sol.Al; 0.005% or less N, and the remainder iron and inevitable impurities, the ranges being so confined as to satisfy the relations Mn(%)/S(%) >7 and (Sol.Al(%) -- 4a -0.003)/N(~)2 6.
A molten steel having a composition of the range described above is cast by ordinary ingot casting or continuous casting into a steel piece, and the steel piece is subjected to a series of hot rolling, descaling, cold rolling, surface clean-ing and other treatments, and then decarburized in a decarbu-rizing-annealing furnace while avoiding nitrogen absorption until the C content decreases to no~ more than 0.005%, preferably not more than 0.004%. The steel is again cold rolled into a sheet of 0.2 mm or less in thickness.
Annealing this Al-killed cold-rolled steel sheet once or more before its fabrication into shadow masks will give pro-ducts with excellent demagnetization and picture characteris-tics.
This process differs markedly from the conventional methods in that after in its steel making and ingot making processes decarburization and cleaning treatment are effected with a vacuum degassing apparatus, decarburization treatment is again effected in its annealing process. The decarburi~
zation by the degassing apparatus is intended to eliminate the carbide (Fe3C) in the stage of hot rolling, to promote the growth of crystal grains to a larger size for improved demagnetization characteristics during the hot rolling and subsequent steps. The decarburization in the annealing furnace is aimed at minimizing the-C content in steel or ~2;~8802 reducing the solid-soluted C content before press forming to a percentage low enough to prevent the possible stretcher strain during the forming process.
As will be obvious from the foregoing, the addition of Nb, Ti or other element with the view to fixing the solid-soluted C is objectionable for the purposes of the invention, because they form fine carbide particle precipitates which deteriorate the demagnetization characteristics of the product.
The reasons for which the contents of the elements accord-ing to the invention are confined within the specified ranges will now be explained.
C:- As described above, too large a C content in cold-rolled steel would lead to iron carbide formation, which has deleterious effects upon the demagnetization characteristics, hindering reduction of the coercive force in particular. Also, t~ie solid-soluted C content must be low enough when the flat masks of the sheet are annealed after they have perforated for the manufacture of shadow masks; otherwise, uneven forming (development of stretcher strains) will result from the subsequent press forming. In order to meet the both requirements, the C content in the Al-killed cold-rolled steel sheet must have an upper limit of 0.005~, preferably 0.004%. When the C content is within this range, the solid-soluted C content is satisfactorily low and there is no possibility of a very small amount of C precipitating at the 1238~2 crystal grain boundaries on final annealing and thereby deterio-rating the demagnetization characteristics. On the other hand, the C content in the stage of steel making should be 0.008%
or below so as to adequately accelerate the grain growth during hot rolling and also during the early period of decarburization-annealing and to coarsen the particles of the precipitate.
For these reasons, the C content in the cold-rolled steel sheet is specified to be 0.005% or below, preferably 0.004~ or below and that in the steel before the hot rolling to be 0.008%
or below.
Mn:- In addition to achieving a deoxidation action, Mn helps to increase the strength of steel without affecting adversely the various characteristics of the resulting shadow mask. As another role, Mn plays is to combine with S in the steel to prevent red shortness of the steel. For these purposes at least 0.05 %, preferably at least 0.10% Mn is required. !In addition, with respect to the weight ratio of Mn to S, it is more suitable that a relation of Mn(%)/S(%)27 is satisfied. However, if the Mn content exceeds 0.50%, the resulting flat masks are too hard to form into shadow masks.
Therefore, Mn is specified to be in the range from 0.05 to 0.50~, preferably 0.10 to 0.50~, and Mn(~)/S(%)27.
S:- S in steel produces MnS inclusions, which hamper the growth of recrystallized grains in the cold-rolled steel.
These undergrown small grains and minute MnS particles 12388~2 themselves deteriorate the demagnetization characteristics.
When S is in excess of 0~010%, the demagnetization charac-teristics is poor regardless of the hot rolling, annealing and other conditions. The S content should therefore be confined to 0.010~ or downwards. It is to be noted that in ingot making by continuous casting, electromagnetic stirring has been found to be additionally beneficial in that it prevents segregation of MnS distribution in the center of the steel ingot.
Sol.A1:- An Al content in the form of Sol.A1 (acid-soluble Al) is necessary in order to fix solid-soluted N as AlN and prevent stretcher strains during press forming, aside from its main action to deoxidize the steel and lower its content of inclusions. An excessive content not only deteriorates the ductility but allows the steel to absorb N2 from the atmosphere during the annealing to-increase the absolute AlN content and thereby impair the demagnetization characteristics.
For the sake of deoxidation 0.010% or more, preferably 0.02~ or more Sol.Al is required but the upper limit is fixed to 0.080~ in consideration of the ductility and nitrogen absorption. Also, in order to coarsen the AlN
particles during annealing sufficiently to avoid deteriora-tion of the demagnetization characteristics with the formation of fine AlN particles, available Sol.Al in a percentage at ~238~302 least six times that of N is desirable. On conducting analysis, a certain amount of fine A12O3 and composite aluminum oxides are unavoidably included in the analyzed Sol.Al amount. It is appropriate, therefore, that the analytical value of Sol.Al minus 0.003% divided by the percentage of N equals 6 or more.
N:- As stated above, N combines with Sol.Al in steel to form AlN, the fine particles of which deteriorate the demagnetization characterist cs. Hence, the N content in the cold-rolled steel sheet is limited to 0.0050% or less, pre-ferably 0.0040% or less.
The molten steel of the foregoing composition is prepared in the following way. After tapping from a converter, the melt is decarburized by a degassing refining apparatus to a C content of 0.008% or less, and then Al or the like is added to prepare an Al-killed steel. At this time, refining outside the furnace is effective for enhancing the cleanness rate of the steel. While casting may be performed by the usual ingot making process, continuous casting with electro-magnetic stirring gives a steel of better quality. The reason therefore is that segregation of MnS distribution in the center of the ingot is prevented. After hot rolling under prescribed conditions, cold rolling is carried out, followed by open-coil decarburization-annealing. For this decarburization-annealing, care should be taken to limit the NH3 content in the ambien~ atmosphere to 15 ppm or less, ~2388(12 a level low enough to prevent nitrogen absorption by the steelO
Although the decarburized steel is desired to have the lowest possible C content, excessive decarburization must be avoided because the consequent internal oxidation of the grain boundaries has an adverse effect on the demagnetization characteristics. For satisfactory demagnetization charac-teristice 0.005% or less, preferably 0.004% or less C is adequate. When carburization is expected to result from the final pre-pressing annealing for the manufacture of shadow masks, it is advisable to allow for it and accordingly reduce the C content to a lower level.
After the decarburization-annealing, it is desirable to carry out skin-pass rolling or roller levelling before the steel is cold-rolled again. The secondary cold rolling gives a sheet of a thickness required by the shadow mask manu-facturer.
Final annealing-of the Al-killed cold-rolled steel sheet made in this way finishes it as a steel sheet with excellent demagnetization characteristics. Consequently, the shadow mask and the color television receiver using it both attain improved landing characteristics.
Example For the preparation of test pieces, low carbon steel was tapped from a 150-ton converter, refined through decarburi-zation by an RH degassing unit down to 0.005% C, and, i2-38~3~2 -following compositional adjustments with the addition of Fe-Mn and Al, cast by continuous casting into ingots. A total of seven charges were tapped. The c contents after the casting varied from 0.005 to ~.008% due to pickup from the composition-adjusting additives and casting powders.
The steel workpieces were passed through sequential steps of hot rolling, pickling, cold rolling, decarburization anneal-ing, skin-pass rolling, and another cold rolling to form thin sheets 0.15 mm in thickness.
The compositions of these cold-rolled steels are given in Table l.
The test pieces were annealed, in an atmosphere of 8% H2 and the balance N2 with a dew point of 0C, at 700C for 10 minutes. Following furnace cooling, their magnetic charac-teristics were determined. The demagnetization characteris-tics were represented by the coercive force, Hc.
As the coercive force, Hc, values also shown in Table l indicate, the steels I of the invention, test pieces A
through D having the Hc values ranging from 0.9 to l.l Oe, were superior in demagnetization characteristics to comparative steels E to G having the Hc values ranging from 1.4 to 1.5 Oe.
It is known from experience that lower Hc is more prefered, and an Hc value in excess of 1.4 Oe of a shadow mask has some adverse influence on the characteristics of the color cathode-ray tube incorporating the mask.

~2388~2 Among the comparative steels I, the test pieces E and F
showed high Hc values by virtue of the large S content and S
and N contents, respectively, whereas test piece G had a larger N content due to nitrogen adsorption during annealing.
Two charges of steels II, H and I according to the invention, were likewise tapped from a converter but directly cast continuously without subjection to the RH degassing treatment. The C contents of the hot-rolled plates were 0.04%
and 0.06~, respectively. From the casting stage onward, ~he two steels were passed through the same sequential steps. It will be seen that the omission of the degassing-decarburization treatment kept their Hc values high. But, their Hc values of 1.3 are allowable.

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Claims

What is claimed is:
(1) An Al-killed cold-rolled steel sheet with enhanced demagnetization characteristics consisting essentially of 0.004% or less C; from 0.05 to 0.50% Mn; 0.010% or less S; from 0.01 to 0.08% Sol. Al; 0.0040% or less N; wherein Mn%/S% ?
7 and ( Sol. Al% - 0.003% )/N% ? 6; the remainder iron and inevitable impurities, said sheet having a coercive force not more than 1.30 Oe.
(2) A shadow mask using an Al-killed cold-rolled steel sheet with enhanced demagnetization characteristics consisting essentially of 0.004% or less C; from 0.05 to 0.50% Mn; 0.010%
or less S; from 0.01 to 0.08% Sol. Al; 0.0040% or less N;
wherein Mn%/S% ? 7 and ( Sol. Al% - 0.003% )/N% ?
6; the remainder iron and inevitable impurities, said sheet having a coercive force not more than 1.30 Oe.
(3) A process for producing an Al-killed cold-rolled steel sheet with enhanced demagnetization characteristics for shadow masks characterized in comprising the steps of:
preparing a molten steel with the use of a vacuum degassing apparatus which consists essentially of 0.008% or less C; from 0.05 to 0.50% Mn; 0.010% or less S; from 0.01 to 0.08% Sol. Al; 0.0040% or less N; wherein Mn%/S% ? 7 and ( Sol. Al% - 0.003% )/N% ? 6; the remainder iron and inevitable impurities, making the melt with ordinary ingot casting or con-tinuous casting into a steel piece, hot-rolling the steel piece and then cold-rolling it, decarburizing and annealing the cold-rolled steel to a C content of 0.004% or less in a decarburization-annealing furnace, and again cold-rolling the steel into a sheet of 0.2 mm or less in thickness.
CA000475237A 1984-02-28 1985-02-27 Al-killed cold-rolled steel sheet with excellent demagnetization characteristics and process for producing the same, and shadow mask and color television using the same Expired CA1238802A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP3532884A JPS60181252A (en) 1984-02-28 1984-02-28 Cold rolled al killed steel sheet having superior demagnetizing characteristic, its manufacture, and shadow mask and color television using it
JP35328/1984 1984-02-28

Publications (1)

Publication Number Publication Date
CA1238802A true CA1238802A (en) 1988-07-05

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ID=12438753

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Application Number Title Priority Date Filing Date
CA000475237A Expired CA1238802A (en) 1984-02-28 1985-02-27 Al-killed cold-rolled steel sheet with excellent demagnetization characteristics and process for producing the same, and shadow mask and color television using the same

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CA (1) CA1238802A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114959426A (en) * 2022-05-09 2022-08-30 包头钢铁(集团)有限责任公司 Preparation method of metal material for automobile brake cable

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2548133B2 (en) * 1986-04-21 1996-10-30 ソニー株式会社 Cathode ray tube color selection mechanism
JPH0644920A (en) * 1992-07-22 1994-02-18 Nkk Corp Sheet metal for shadow mask and manufacture thereof

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5825432A (en) * 1981-08-05 1983-02-15 Nippon Kokan Kk <Nkk> Manufacture of cold rolling steel plate

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114959426A (en) * 2022-05-09 2022-08-30 包头钢铁(集团)有限责任公司 Preparation method of metal material for automobile brake cable

Also Published As

Publication number Publication date
JPS60181252A (en) 1985-09-14

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