US3595643A

US3595643A - Razor blade of a chromium containing steel

Info

Publication number: US3595643A
Application number: US556691A
Authority: US
Inventors: Joseph F Boyce; Axel Vilhelm Bernstein; Jan-Christer Henric Ove Carlen
Original assignee: Sandvik AB
Current assignee: Santrade Ltd
Priority date: 1965-10-18
Filing date: 1966-06-10
Publication date: 1971-07-27
Anticipated expiration: 1988-07-27
Also published as: NL6614492A; ES332349A1; NL6614639A; CH474337A; BE688415A; DE1533381B1; BE688416A; CH474338A; GB1108377A; DE1533380B1; GB1107233A

Abstract

A RAZOR BLADE MADE OF A CHROMIUM STAINLESS STEEL HAVING GOOD CORROSION RESISTANCE AND CUTTING PROPERTIES AND ALSO A METHOD FORMING SUCH AN ARTICLE IS DICLOSED. THE STEEL CONTAINS .30-45 CARBON, 11-16 CR, A MEMBER OF THE CLASS CONSISTING OF TUNGSTEN AND MOLYBDENUM WHEREIN THE AMOUNT OF MO MAY BE .5-2.5% AND W1.0-5%, SI MAX. 70, MN 1.5 MAX., 0-2% OF VA, TA, TI AND ZR AND 0-1% CO, NI, CU, AL, BE AND B. THE STELL MAY BE FORMED BY COLD ROLLING, HARDENING BY HEATING TO A RANGE OF 10001150*C. SUBSEQUENT TEMPERING MAY BE UTILIZED.

Description

.IuIy 27, 197T J. IF. mmmfi mm... 3595 643 RAZOR BLADE OF A CHROMIUM CONTAINING STEEL Filed June 10, 1966 STRESS CORROSION SENSITIVITY HIGH INTER MEDIATE LOW PERCENT CARBON 3,595,643 RAZOR BLADE OF A CHROMHUM CONTATNlNG STEEL Joseph F. Boyce, Braintree, Mass, and Axel Vilhelm Bernstein and Jan-Christen- Henric Uvesson (Iarln, Sandviken, Sweden, assignors to Sandvikens .llernverlm Aktiebolag, Sandviken, Sweden Filed June 10, 1966, Ser. No. 556,691 Int. Cl. CZZc 33/00 US. Cl. 75-126C 3 Claims ABSTRACT OF THE DISCLOSURE A razor blade made of a chromium stainless steel having good corrosion resistance and cutting properties and also a method forming such an article is disclosed. The steel contains .30.45 carbon, 11-16 Cr, a member of the class consisting of tungsten and molybdenum wherein the amount of Mo may be .52.5% and W 1.05%, Si max. 70, Mn 1.5 max., 02% of Va, Ta, Ti and Zr and 0-1% Co, Ni, Cu, Al, Be and B. The steel may be formed by cold rolling, hardening by heating to a range of 1000- 1150 C. Subsequent tempering may be utilized.

The present invention relates to razor blades especially in the form of thin ribbon-like razor blades, and similar thin elongated sharp edged blades having very good corrosion resistance and cutting properties and simultaneously being able to withstand stress corrosion or hydrogen induced failures when subjected to severe bending stresses. The ribbon-like razor blades are for instance used in a razor where a thin strip successively can be fed from one roll to another for changing the cutting edge. When used in this way the steel is subjected to high bending stresses and a simultaneous chemical attack of a relatively long duration, which requires a high resistance to stress corrosion to avoid ruptures. The steel must also provide very good cutting edges after grinding. Previously known steels have not had the desired combination of properties. The steel according to the invention has a composition which in combination with a suitable heat treatment provides the desired corrosion resistance and flexibility, at the same time having hardness satisfactorily high for obtaining a sufficient sharpness and wear resistance of the cutting edge.

The phenomenon which above has been referred to as stress corrosion is not wholly clarified. In certain cases the cause of rupture is considered to be what normally is called stress corrosion. In other cases it seems obvious that the ruptures are caused by hydrogen absorption and embrittlement. In the following we refer to the actual rupture phenomenon as stress corrosion without regard to which of the said explanations is correct.

Previously known steels of the type containing 18% chromium and 8% nickel, cold worked and heat treated to a high hardness (as for instance described in UK Pat. No. 979,512) have shown a low sensitivity to stress corrosion, but they contain a high percentage of residual austenite which causes difficulties in finishing the cutting edge or edges. In order to avoid said and other difiiculties and drawbacks of the previous steel alloys used for the purpose mentioned, the present invention provides razor blades and similar thin elongated sharp edged blades made of a stainless martensitic chromium steel having, for a razor blade steel, a very low content of carbon and containing molybdenum and/or tungsten which have been found necessary to improve the important properties, such as corrosion resistance and stress corrosion resistance.

Further details of the invention appear from the follow ing specification and the appended drawing which shows, in the form of a diagram, resistance to stress corrosion in 3,95,643 Patented July 27, 1971 relation to hardness by steels according to the invention and a similar steel Without molybdenum.

The razor blades according to the present invention are characterized by very good cutting properties, high corrosion resistance and toughness and high resistance to ruptures at blending stresses exceeding 71,000 psi. under simultaneous chemical attack, e.g. of the type found in locations in which razors are used and/or stored. The blades are consequently made of a steel having the following analysis: 0.30-0.45% carbon; 11-16% chromium; 0.5-2.5% molybdenum, or 1.05.0% tungsten, or a mixture of molybdenum and tungsten in an amount such that the sum of molybdenum and one-half of the tungsten is 0.5-2.5%; 00.70% silicon; 0-1.5% manganese and the rest iron with incidental impurities. While very small amounts of additional carbide formers, such as vanadium, niobium, tantalum, titanium and/or zirconium may be tolerated, the total amount of these metals should in no event exceed 2% by weight, preferably 1%, and usually should be much less. Even smaller quantities of such elements as cobalt, nickel, copper, aluminum, beryllium, and/ or boron may 'be tolterated, the total in no event exceeding 1% by weight. Furthermore, the sum of the amounts of the carbide formers, chromium, molybdenum, vanadium, titanium and one-half of the amounts of tungsten, niobium, tantalum, and zirconium should be 12-165 preferably l316%. It is preferred that no other carbide formers be present in addition to chromium, molybdenum and tungsten. As a rule, the carbon content should be chosen within the narrower range 0.350.45%. Further the chromium content should normally be held within the range 12l5 preferably 13-14%, and the silicon content should normally be at most 06%, and the manganese content at most 1.2%.

The carbon content has been chosen sufficiently high so that the steel can attain a hardness of at least VPN 625 (test load 0.5 kg.) after hardening and subzero cooling and possibly low temperature tempering, and at the same time so low that the steel is highly resistant to stress corrosion failure. The content of chromium is so high that good corrosion resistance is obtained, but sufficiently low so that a satisfactory hardness can be attained after hardening. The content of molybdenum is usually chosen rather high to obtain good corrosion resistance, being from 0.5 to 2.0%, preferably from 0.8 to 1.5% when no tungsten is present. While theoretically twice as much tungsten is needed to obtain the same effect as molybdenum, it is usually advisable to avoid using the maxium quantity of tungsten and to confine its amount to 1.6 to 3.0% when no molybdenum is present. The sum of the amounts of molybdenum and one-half the tungsten, when both are present is 0.5 to 2.0%, preferably 0.8 to 1.5%.

The steel for the razor blades according to the invention should permit hardening to a high hardness in order to facilitate the grinding of the cutting edge or edges. Further the steel should be corrosion resistant and not liable to ruptures under the influence of chemical attack and simultaneous bending. In order to achieve these properties the steel according to the composition defined has to be subject to a heat treatment especially adapted for the purpose.

The steel according to the invention should be heat treated in such a way that absorption of nitrogen during the hardening is avoided, and for this purpose the procedure should preferably be performed in a suitable protective atmosphere, for instance pure hydrogen. In order to obtain the best possible combination of flexibility, corrosion resistance, stress corrosion resistance and hardness the steel should be tempered at a temperature between 250 and 450 C., preferably 300-400 C.

The heat treatment includes an initial heating to a temperature between 1000 and 1150 0, preferably l075 1100 C., followed by cooling to room temperature, usually between blocks cooled by water. This step may be followed by subzero cooling to a temperature between 20 and 120 0., usually 40 to -80 C., whereafter the steel preferably is tempered for a short time at a temperature between 100 and 450 C., in order to obtain a maximal hardness exceeding VPN 625 (load 0.5 kg.). After this heat treatment the cutting edge or edges are prepared e.g. by shaping as by grinding and then preferably a coating of the edge with a material for enhancing the shaving characteristics is applied and sintered to the steel at a temperature between 250 and 450 C., e.g. at about 350 C., resulting in a final hardness of about VPN 550 (load 0.5 kg).

The appended diagram comprises curves representing the susceptibility to said corrosion as a function of the carbon content for some different steel compositions, some of which are within and some without the scope of the invention. Curve .A represent steels containing 13.5% Cr, while the curves B and C show steels according to the in vention containing 13.5% Cr and 1.25% M0, the C steels having been melted in high vacuum. The steels in the form of thin cold-rolled strips have been heated at 1075" C. during 30 seconds and have then been cooled to room temperature and thereafter to 70 C. and have finally been tempered at 350 C. during 15 minutes. The diagram shows that for steels having about 13.5% chro mium and carbon contents Within the range 0.30-0.45 the sensitivity for stress corrosion is substantially lessened if molybdenum is added. The diagram also shows that high vacuum treatment further decreases the susceptibility to stress corrosion failures. It is thus advantageous to melt the steel in high vacuum, as this further lessens the risk for ruptures under the influence of stress corrosion conditions. However, this is not an absolute requirement. In the diagram the variation of hardness in relation to the content of carbon is also noted.

In order further to increase the resistance to stress corrosion it is, as previously mentioned, desirable to have a low content of nitrogen. It is also essential that the contents of phosphorous and sulphur be low. A preferred range of analysis is the following: 0.35-0.45% carbon; 0.8-1.5 molybdenum or twice this amount of tungsten; up to 0.6% silicon; up to 1.2% manganese; 12.015.0% chromium; the balance being iron with insignificant amounts of impurities, e.g. 50.025% phosphorus;

0.020% sulphur and 0.06% nitrogen Possibly minor quantities of other constituents as vanadium, titanium, niobium, tantalum, zirconium, aluminum, beryllium, boron, nickel, cobalt and copper, the total of these being at the most 1% may be included.

As a preferred range of analysis for steels according to the present invention the following can be mentioned: carbon=0.370.43%; molybdenum=l.11.4% (or twice this amount of tungsten) the sum of the amounts of molybdenum and one-half the tungsten being from 1.1-1.4%; chromium:13.0-14.0%; silicon=0.20.5%; manganese- 0.2-05 phosphorus g0.025%; sulphur 50.020%; nitrogen 50.06%; the balance being substantially all iron.

As examples of alloys in percent of weight according to the invention the following may be mentioned:

Steel Si Mn Cr M0 P S NFe 0. 041 B alance. 0. 028 D 0.

4 final condition test pieces of the strip were subjected to a stress corrosion test by bending to yield a surface tensile stress of 90,000 p.s.i. and immersing in a 0.1% acetic acid solution at room temperature for 48 hours. No fractures occurred.

Steel 2 was treated in the same way but high vacuum remelted before rolling down to a strip with the thickness of 0.0015". With the same heat treatment as for steel No. 1 the hardness after the first tempering at 125 C. was VPN 690 and after the final tempering at 350 C. VPN 540. No fractures occurred at the stress corrosion test.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto but to include all of the variations and modifications which suggest themselves to a person skilled in the art.

What is claimed is:

1. Razor blades and similar thin elongated sharp edged blades having good cutting properties and high corrosion resistance and toughness characterized in that the blades are made from a steel consisting essentially of 0.35- 0.45% carbon; 12-15% chromium; a member of the class consisting of molybdenum, tungsten and mixtures thereof, the amount of molybdenum when present alone being 0.8-1.5%, the amount of tungsten when present alone being 1.63.0%, and the sum of the amounts of molybdenum and one-half the tungsten when both are present being 0.8-1.5% 00.6% silicon; 01.2% manganese; O1% each of a member of the class consisting of vanadium, niobium, tantalum, titanium and zirconium, the total of all the last said members being a maximum of 1%; and 01% each of a member of the class consisting of cobalt, nickel, copper, aluminum, beryllium,

' and boron, the total of all the last said members being a maximum of 1%; and the remainder being substantially all iron; and in which the sum of the amounts of chromium, molybdenum, vanadium, titanium and one-half of the amounts of tungsten, niobium, tantalum and zirconium is 13-16%.

2. Razor blades as claimed in claim 1 in which the total amount of all vanadium, niobium, tantalum, titan ium, zirconium, cobalt, nickel, copper, aluminum, beryllium and boron is 01%.

3. Razor blades having good cutting properties, high corrosion resistance, and toughness characterized in that the blades are made from a steel which in addition to iron with incidental impurities consists essentially of 0.37- 0.43% carbon; 1314% chromium; a member of the group consisting of molybdenum, tungsten and mixtures thereof, the amount of molybdenum when present alone being 1.1l.4%, the amount of tungsten when present alone being 2.22.8%, and the sum of the amounts of molybdenum and one-half the tungsten when both are present being 1.11.4%; 0.20.5% silicon; and 02-05% manganese.

References Cited UNITED STATES PATENTS 2,853,410 9/1958 Lula 14831 3,116,180 12/1963 Malzacher 14812.4 2,105,583 1/1938 Casselman 30-346.54 2,513,935 7/1950 Harris 126(C) 2,648,602 8/1953 Payson 75126(C) 2,905,577 9/1959 Harris 75126(C) 3,071,856 1/1963 Fischbein 30346.53 3,104,168 9/1963 Bedell 75126(C) 3,152,934 10/1964 Lula 75128.9

HYLAND BIZOT, Primary Examiner UJS. Cl. X.'R. 75126F