Cutlery – Blades – Razor blade
Reexamination Certificate
2002-01-24
2004-07-20
Payer, Hwei-Siu (Department: 3724)
Cutlery
Blades
Razor blade
C030S346530, C148S325000, C148S326000
Reexamination Certificate
active
06763593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a razor blade material having excellent mechanical and chemical properties, and to a razor blade made of the material. The razor blade material is characterized by that a razor blade made of the material has a cutting blade portion with high hardness, a good blade edge form accuracy, excellent sharpness, and excellent corrosion and wear resistances.
2. Brief Description of the Related Art
A conventional razor blade is made of a crystalline metal, such as carbon steel or stainless steel, which is coated with a resin. However, a carbon steel razor has problems that are lacking in enough sharpness because of extremely deteriorated hardness due to inadequate resistance to softening by tempering heat treatment, coarse carbides, and deteriorated durability due to inferior corrosion resistance.
A stainless steel razor blade has been made from, for example, a 1% C-13% Cr steel or a 0.65% C-13% Cr steel through a melting-casting process. The former can be of high hardness because of high carbon and high chromium contents, but it is liable to have an alloy structure containing coarse carbides. Therefore, in recent years, the latter of 0.65% C-13% Cr steel has been preferably used. However, while the latter contains a very small amount of coarse carbides which deteriorates the steel in corrosion resistance, it has a problem that a high hardness is not expectable because of a low carbon content.
On the other hand, the usual razor blade is coated with a resin at a temperature of 300 to 400° C. in order to improve a shaving feel. Thus, the razor blade has a problem that a cutting edge portion of the razor blade is deteriorated in hardness down to HV600 to 650 due to heating when resin-coating the razor blade. If strength of the blade edge is inadequate, it is bent during shaving resulting in deteriorated durability. Taking this into consideration, if the carbon amount of the razor blade steel is increased in order to improve the blade edge strength so as to have high hardness, a lot of carbides (which are mainly Cr-containing carbides such as M
7
C
3
and M
23
C
6
) each having a diameter of about not less than 0.1 &mgr;m is generated, resulting in deteriorated corrosion resistance, becoming brittle and/or defects such as a break in some using manners.
Therefore, in order to produce a razor blade material from the above materials, it is necessary for those to adjust some material factors including a size and hardness by a combination of heat treatment, hot-rolling and cold-rolling resulting in increased production process steps.
In order to solve the above problems, there has been proposed a material made of an amorphous metal. Since the amorphous metal material can have remarkably improved hardness, strength and corrosion resistance, an alloy component design, which enables the alloys to become amorphous, was intensively examined in a broad range of chemical compositions at the earliest in the 1970s, as can be seen from, for example, JP-A-51-4019. There has been a trial to apply the amorphous metal for a blade material. For example, according to JP-A-54-31023, there is proposed a material being provided with an amorphous structure by adding 2 to 40 wt % of at least one nonmetal element selected from the group of P, C, B, Si, etc. to the material.
SUMMARY OF THE INVENTION
The proposed amorphous metal blade material is effective as means for improving properties of hardness, strength and corrosion resistance. However, it is required for the alloy design to be subjected to quenching solidification at least at a critical cooling rate of about 10
7
K/second in order to make the alloy amorphous to obtain the improvement effects. Thus, a materials thickness for production is limited to a very small value, so that it is considerably difficult to produce a material having a thickness of about 30 &mgr;m.
Further, according to a result that the present inventors examined an amorphous metal on the basis of the above mentioned chemical composition in various points of view, the material having a thickness of about not less than 30 &mgr;m did not become completely amorphous, and there occurred deterioration of corrosion resistance and brittleness because a lot of precipitates, each of which had a diameter of about not less than 0.1 &mgr;m and which were carbides, borides, etc., was generated in the metal structure. The precipitates were mainly carbides including M
7
C
3
and M
23
C
6
and borides including Fe
3
B, Fe
2
B, Cr
3
b and Cr
2
B.
An object of the present invention is to provide a razor blade material which has excellent corrosion and wear resistances and contains a reduced amount of precipitates, and which can ensures a cutting edge form of a razor blade made thereof to have a good accuracy and excellent sharpness. More particularly, the object is to provide the razor blade material which is made to an amorphous metal structure containing a reduced amount of precipitates and which can have a large thickness and a high hardness of a cutting edge portion. Another object of the present invention is to provide a razor blade made of the razor blade material.
The present inventors intensively studied chemical compositions and microstructures of some variances of the razor blade material. As a result, it has been found that there is a state of precipitates effective for improvement of corrosion resistance and inhibiting brittleness, and that there is a chemical composition range in which alloying elements of C, Cr and Mo are adjusted to have optimized contents, respectively, so as to inhibit formation of precipitates. Further, some alloying elements have been identified, and it has been found also that an appropriate amount of B and Si can be effectively added into the material. The inventors examined also an amorphous structure advantageous for inhibiting formation of precipitates. As a result, the present invention has been achieved.
According to a first aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy comprising, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, wherein precipitates, which can be observed at an optional cross section of the razor blade material, have a diameter of less than 0.1 &mgr;m, respectively.
According to a second aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy consisting essentially of, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, B and/or Si in an amount as defined by the equation of 0<B+Si≦8.0%, and the balance of Fe and unavoidable impurities, wherein precipitates, which can be observed at an optional cross section of the razor blade material, have a diameter of less than 0.1 &mgr;m, respectively. The razor blade material has high hardness, high strength and good corrosion resistance.
According to a third aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy comprising, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, wherein no precipitate can be observed at an optional cross section of the razor blade material.
According to a fourth aspect of the present invention, there is provided a razor blade material made of an Fe-base alloy consisting essentially of, by mass %, not less than 0.5% carbon, 9.0 to 14.0% Cr and from more than zero to 8.0% Mo, B and/or Si in an amount as defined by the equation of 0<B+Si≦8.0%, and the balance of Fe and unavoidable impurities, wherein no precipitate can be observed at an optional cross section of the razor blade material.
Preferably, a metal structure of the razor blade material includes an amorphous structure in a volume fraction of not less than 30 volume %. Thereby, the corrosion resistance and mechanical properties are greatly improved. Herein, the term of “amorphous structure” may include also a grain boundary layer which is a kind of amorphous structur
Nakatsu Hideshi
Tamura Yasushi
Hitachi Metals Ltd.
Payer Hwei-Siu
Sughrue & Mion, PLLC
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