Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Reexamination Certificate
2000-07-03
2002-05-21
Yee, Deborah (Department: 1742)
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
C420S054000, C148S327000
Reexamination Certificate
active
06391254
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an Fe—Cr—Ni alloy which is required to be nonmagnetic and is used in electron gun electrodes, and specifically relates to an alloy with improved press forming properties for drawing.
In general, electron gun electrodes used in color picture tubes and the like are produced by drawing a nonmagnetic Fe—Cr—Ni stainless steel material with a thickness of 0.05 to 0.5 mm into a predetermined shape using press forming. In order to improve the formability for drawing, in particular, to facilitate burring (working in which a circular hole is formed and the circumference thereof is projected like a cylinder), improvement in degree of rolling reduction and annealing conditions has been proposed in Japanese Patent Application, First Publication, No. 257253/94. Japanese Patent Application, First Publication, No. 205453/96 proposes a method in which press forming properties are improved by limiting center line average height and maximum height of surface roughness in press forming using a low viscosity lubricating oil, which is easy to degrease and has been used to increase production efficiency. Japanese Patent Application No. 283039/97 demonstrates that burrs remaining in press punching a through hole relates to cracks in burring, and proposes a method in which burring properties are improved by suitable amounts of S being contained to improve punching properties and minute amounts of the elements are controlled to improve the formability for drawing.
According to the rapid advances of finer and brighter picture tubes for computers in recent years, requirements on focusing characteristics of the electron guns has become more severe. Therefore, the requirement on materials is necessary to have not only high precision formability for the large lens diameter electrodes but also good formability for high speed press forming. As a result, the prior art alloys have not been adequate since cracks occur on drawing surfaces.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to complete the above situation. An object of the invention is to provide an Fe—Cr—Ni alloy for electron gun electrodes, having superior formability for drawing, which has been more severe in recent years, in particular, having superior surface qualities after drawing.
The inventors have extensively studied the surface conditions of materials to complete the problems. As a result, the inventors have found that the formability for drawing is influenced by the degree of sharpness of projections in surface profile. In particular, the inventors have found that the formability for drawing is inferior and surface cracks in drawing readily occur when the ends of the projections are sharp and the intermediate portion (valley) between the projections is deep and steep. In particular, it has been estimated that cracks would surely occur when the valley is deep and steep and when foreign particles such as inclusions are present at the bottom of the valley. The inventors have made the invention by representing the degree of the sharpness of the projections by kurtosis Kr and analyzing the relationship between the kurtosis Kr and the formability for drawing. The kurtosis Kr is represented by the following formula (1).
Kr=&Sgr;(Y
i
/R
q
)
4
/N (1)
Wherein y
i
is roughness profile, R
q
is root mean square roughness, and N is number of samples.
This invention provides an Fe—Cr—Ni alloy for electron gun electrodes comprising: 15 to 20% Cr; 9 to 15% Ni; 0.12% or less C; 0.005 to 1.0% Si; 0.005% to 2.5% Mn; 0.03% or less P; 0.0003 to 0.0100% S; 2.0% or less Mo; 0.001 to 0.2% Al; 0.003% or less O; 0.1% or less N; 0.1% or less Ti; 0.1% or less Nb; 0.1% or less V; 0.1% or less Zr; 0.05% or less Ca; 0.02% or less Mg; and the balance Fe and inevitable impurities by weight, and the alloy having a surface roughness satisfying the following formula (2) when kurtosis in the rolling direction and kurtosis in the transverse direction to the rolling direction in surface roughness of the alloy are respectively defined as Kr
0
and Kr
90
.
Kr
0
≦4, Kr
90
≦4 (2)
The reasons for the above limitations in the surface roughness and the alloy composition in the Fe—Cr—Ni alloy for electron gun electrodes will be explained together with the effects of the present invention. In the following explanation, “%” means “weight %”.
(Kr
0
, Kr
90
): The above-mentioned kurtosis range has been found by the inventors performing quantity analysis. According to the research by the inventors, if Kr
0
and Kr
90
are more than 4, a large number of high ridges and deep valleys with very sharp shapes exist in the surface roughness profile, and as a result, cracks occur on the drawn surface. Therefore, Kr
0
and Kr
90
are restricted to 4 or less.
(Cr): Electron gun electrodes are essentially required to be nonmagnetic. Normally, permeability is required to be 1.005 or less for them to be nonmagnetic. In order to meet the requirement, the content of Cr is restricted to within the range of 15 to 20%. A more preferable range for the Cr content is from 15 to 17%.
(Ni): If the Ni content is less than 9%, magnetic characteristics increase. If the Ni content exceeds 15%, the material cost increases too much. Hence, the Ni content is restricted to within the range of 9 to 15%.
(C): If the C content exceeds 0.12%, a large amount of carbide is formed, thereby the formability for drawing is inferior, and hence, the C content is restricted to 0.12% or less.
(Si): Si is added for deoxidation. If the Si content is less than 0.005%, the effect as a deoxidizer cannot be obtained. On the other hand, if the Si content exceeds 1.0%, the formability is inferior. Hence, the Si content is restricted to within the range of 0.005 to 1.0%.
(Mn): Mn is added for deoxidation and formation of MnS. If the Mn content is less than 0.005%, these effects are not expected. If the Mn content exceeds 2.5%, the hardness of the alloy increases, thereby the formability for drawing is inferior. Hence, the Mn content is restricted to within the range of 0.005 to 2.5%.
(P): If the P content exceeds 0.03%, the formability for drawing is inferior. Hence, the P content is restricted to 0.03% or less.
(S): When S is contained in an appropriate amount, S forms MnS together with Mn, so that the forming of burrs is inhibited in press punching a hole and cracks in burring is inhibited. If the S content is less than 0.0003%, such effects are not expected. If the S content exceeds 0.0100%, coarse MnS is formed, thereby the formability for drawing is inferior. Hence, the S content is restricted to within the range of 0.0003 to 0.0100%.
(Mo): Since Mo improves corrosion resistance, Mo can be advantageously added when special corrosion resistance is required. However, if the Mo content exceeds 2.0%, the formability for drawing is inferior. Hence, the Mo content is restricted to 2.0% or less.
(Al): Al is added for deoxidation, which is effective with an Al content of 0.001% or more. If the Al content exceeds 0.2%, the formability for drawing is inferior. Hence, the Al content is restricted to within the range of 0.001 to 0.2%.
(O): When an exceeding large amount O is contained, the amount of oxide-type inclusions increase, thereby the formability for drawing is inferior. Hence, the O content is restricted to 0.003% or less.
(N): When the N content exceeds 0.1%, the formability is inferior. Hence, the N content is restricted to 0.1% or less.
(Ti): Ti forms carbides, sulfides, oxides and nitrides, thereby the formability for drawing is inferior. Hence, the Ti content is restricted to 0.1% or less. A more preferable range for the Ti content is 0.02% or less.
(Nb): Nb forms carbides, sulfides, oxides and nitrides, thereby the formability for drawing is inferior. Hence, the Nb content is restricted to 0.1% or less. More preferable range of the Nb content is 0.02% or less.
(V): V forms carbides and nitrides, thereby the formability for drawing is inferior. Hence, the V content is restricted to 0.1% or less. A more preferable range for the
Arent Fox Kintner & Plotkin & Kahn, PLLC
Nippon Mining & Metals Co., Ltd.
Yee Deborah
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