US3575737A

US3575737A - Razor blades and other thin cutting edge tools and method of manufacture of such tools

Info

Publication number: US3575737A
Application number: US739831A
Authority: US
Inventors: Jan-Christer Henric Ove Carlen; Francis Edward Flaherty
Original assignee: Sandvik AB
Current assignee: Santrade Ltd
Priority date: 1968-06-25
Filing date: 1968-06-25
Publication date: 1971-04-20
Anticipated expiration: 1988-04-20

Abstract

A HOT ROLLED STEEL STRIP CONTAINING 14% CHROMIUM IS ANNEALED AT 825*C. FOR AT LEAST TWO HOURS AND THEN COOLED. THE ANNEALED STRIP IS THEN COLD ROLLED IN SEVERAL STEPS WITH INTERMEDIATE RECRYSTALLIZATION ANNEALINGS TO A THICKNESS OF ABOUT 0.2 MM. THEN THE STRIP IS AUSTENITIZED AT A TEMPERATURE OF 1140*C. FOR ABOUT 5 SECONDS AND THEN QUENCHED TO PRODUCE A MARTENSITE AND AUSTENITE MIXTURE WITH AN AUSTENITE CONTENT OF ABOUT 60%. THE STRIP IS THEN HEATED AT 710*C. FOR TWO HOURS PRODUCING A PRECIPITATION OF FINE CARBIDE GRAINS IN A MATRIX OF FERRITE. AFTER FURTHER COLD ROLLING WITH INTERMEDIATE RECRYSTALLIZATION ANNEALINGS TO THE FINAL THICKNESS OF 0.1 MM., THE STRIP IS HEATED TO A TEMPERATURE OF ABOUT 1100*C., QUENCHED TO -80*C., AND ANNEALED AT ABOUT 200*C.; AN EDGE OF THE STRIP IS GROUND TO PROVIDE A SHARPENED RAZOR EDGE; AND A LAYER TO IMPROVE THE SHAVING PROPERTIES IS APPLIED TO THE SHARPENED EDGE IN A PROCESS INVOLVING HEATING THE STEEL TO A TEMPERATURE BETWEEN 200 AND 400*C.

Description

April 29, 1971 JAN'CHRISTER- 1-1.0. CARLEN ETAL 3,575,737

HV 0.5 v

RAZOR BLADES AND OTHER THIN CUTTING EDGE TOOLS AND METHOD OF MANUFACTURE OF SUCH TOOLS Filed June 25, 1968 United States Patent 3,575,737 RAZOR BLADES AND OTHER THIN CUTTING EDGE TOOLS AND METHOD OF MANUFAC- TURE OF SUCH TOOLS Jan-Christel Heuric Ovesson Carlen, Sandviken, Sweden, and Francis Edward Flaherty, Canton, Mass., assignors to Sandvikens .Iernverks Aktiebolag, Sandviken, Sweden Filed June 25, 1968, Ser. No. 739,831 Int. Cl. (121d 9/18 U.S. Cl. 14812.4 16 Claims ABSTRACT OF THE DISCLOSURE A hot rolled steel strip containing 14% chromium is annealed at 825 C. for at least two hours and then cooled. The annealed strip is then cold rolled in several steps with intermediate recrystallization annealings to a thickness of about 0.2 mm. Then the strip is austenitized at a temperature of 1140 C. for about 5 seconds and then quenched to produce a martensite and austenite mixture with an austenite content of about 60%. The strip is then heated at 710 C. for two hours producing a precipitation of fine carbide grains in a matrix of ferrite. After further cold rolling with intermediate recrystallization annealings to the final thickness of 0.1 mm., the strip is heated to a temperature of about 1100 C., quenched to 80 C., and annealed at about 200 C.; an edge of the strip is ground to provide a sharpened razor edge; and a layer to improve the shaving properties is applied to the sharpened edge in a process involving heating the steel to a temperature between 200 and 400 C.

The present invention relates to a method for the manufacture of razor blades and similar thin cutting edge tools with high wear resistance and high hardness from hardenable chromium steels containing at least 8% chromium and which are cold worked to thin dimensions, preferably by cold rolling. The invention also comprises razor blades and other cutting edge tools made according to the method of manufacture.

In conventional manufacture of razor blades from hardenable steels, the steel is subjected to a succession of annealing and cold working operations. Thus, the hotworked raw material is annealed so that the hotworked structure is transformed into a structure more suitable for coldworking consisting of ferrite and carbides whereby the material at the same time becomes soft enough to be coldworked. In coldworking the hardness increases, but by annealing the material after coldworking to a certain degree a recrystallization is achieved by which the material again becomes soft enough for continued coldworking. By alternating coldworking and recrystallization annealing the material is given a desired thin dimension. The structure achieved after the final coldworking will be dependent on how the annealing of the hotworked material was done as well as the annealing operations between the diiferent steps of coldworking. Longer time of annealing and/or higher annealing temperature gives a coarse grained carbide structure while short time and/ or low temperature gives a finegrained carbide structure. As to the properties of the materials after the final hardening, a finegrained carbide structure in many cases would be preferred. However, materials with a finegrained carbide structure are expensive and difiicult to coldwork as they are harder and brittler than materials with coarse carbides and have considerably worsened coldworking properties.

The purpose of the present invention is to produce razor blades and other thin cutting edge tools with high wear resistance and high hardness from hardenable chromium steels containing at least 8% chromium by giving the steel such a finegrained carbide structure that the hardening properties are greatly improved without in any appreciable degree worsening the coldworking properties.

The steels for use in making the razor blades or cutting edge tools according to the invention are of the type that contains at least 20% and preferably at least 40% residual austenite after complete or practically complete carbide dissolution of austenitizing and a subsequent cooling to room temperature or less. The residual austenite is usually also so stable that it will not disintegrate to any great extent in conventional tempering operations (max. 450 C.).

The method according to the invention is substantially characterized in that the steel after coldworking, i.e., coldrolling, is austenitized at such a high temperature that practically all of the carbide grains in it are completely dissolved, the steel thereafter being so rapidly cooled that a mixture of austenite and martensite is obtained, then the steel is heat treated at a temperaure under the temperature for austenitizing but above 600 C. and thereafter is hardened preferably after additional coldworking such as cold-rolling.

The coldworking before the austenitizing is usually done in several steps between which the steel is recrystallization annealed. Also, the coldworking between the previously mentioned heat treatment and the hardening is usually carried out in two or more steps with recrystallization annealings in between. The hardening temperature is dependent on the composition of the steel. It is usually chosen between 8501l50 C. and often within the narrower interval l000ll50 C. In hardening, the steel is cooled from hardening temperature to room temperature or less, i.e., within the range between -20 C. and C. Normally, the hardening is followed by a tempering between l00275 C. The cutting edge is preferably formed after this tempering by grinding or similar methods. Then another tempering can be made, i.e., in connection with application of a coating to the cutting edges to improve the shaving properties. The last-mentioned tempering occurs usually in a limited time period at a temperature exceeding C., i.e., between 150- 250 C., and in certain cases up to 400 C. Immediately before the hardening the strip steel is often shaped, i.e., by stamping.

In manufacturing the razor blades and the cutting edge tools according to the invention, a hardenable chromium (steel is used which, as mentioned earlier, contains at least 8% chromium and which preferably has been formed into a strip by hot-rolling. The hot-rolled strip is annealed, depending on the composition of the steel, at such a temperature, i.e., between 775875 C., that it obtains a coarse grained structure which is especially suitable for the subsequent coldworking. The coldworking which is usually done by cold-rolling is carried out in several steps with recrystallization annealings in between. When the steel strip is coldworked to a dimension at or near the desired thin final dimension, i.e., a thickness between 0.1- 0.4 mm. preferably 0.15-0.33 mm., a heat treatment is made characterized in that the steel strip is austenitized at such a high temperature, i.e., more than 1000 C. and preferably above 1100 C., that practically all occuring carbide grains are totally dissolved and thereafter the steel strip is cooled preferably to room temperature of eventually to lower temperatures. As a result, the steel strip has a structure consisting of matensite and austenite in which the austenite content usually lies between 20-l00% and in most cases between 4080%. By heat treating the steel strip after this at a compaartively low temperature, that is a temperature below the temperature for austenitizing but above 600 C., a finely dispersed precipitation of carbides in a matrix of ferrite is obtained. Thereafter, the strip can be finished in cold condition preferably by cold-rolling in one or more steps to the intended final dimension, i.e., a thickness about 0.1 mm. One or more recrystallization annealings can also be made during this coldworking. By the above-mentioned heat treatment, the material obtains a structure which is especially suitable for the following hardening whereby a considerably higher hardness can be achieved at the hardening than has earlier been possible in conventionally produced steels of the corresponding composition. To achieve maximum hardness after the hardening, the material, according to the invention, should normally be deep cooled to a temperature between and 120 C. and tempered to a temperature between 100-275 C. in which the higher tempering temperature is used at short tempering times and the lower at long times, i.e., at least 15 minutes. As a result of the structure and high hardness obtained through the invention, the shaping of the cutting edge by grinding or similar methods is facilitated. When the cutting edge is shaped it is often coated with a layer which improves the shaving properties and this requires heating to a temperature above 150 C. Even if the hardness is somewhat decreased at such a heating, the razor blades and cutting edge tools according to the invention will have a higher final hardness than conventionally manufactured razor blades and cutting edge tools of the same chemical composition.

The reason for the favorable results with the method according to the invention will probably be explained by the following.

In hardening a high alloyed chromium steel, the structure is transformed from ferrite with carbides to martensite and depneding on the basic structure and the hardening conditions to a certain amount of residual austenite. Often the carbides are incompletely dissolved in the hardening heating so a certain amount of residual carbides are to be found in the hardened material. In austenitizing, whereby the carbides are dissolved, the degree of carbide dissolution is determined partly by the temperature and time and partly by the carbide structure of the basic material. The carbides are rich in carbide forming elements such as chromium, tungsten and vanadium and this causes that the matrix close to the carbides to become rich in these elements upon carbide dissolution in austenitizing. In austenitizing, a certain equalization of the percentages of the carbide forming elements between the area which surrounds the carbides and the rest of the matrix is obtained by diffusion. However, this equalization advances at normal austenitizing times only to a limited extent thus causing the composition of the matrix to vary. As almost all alloying elements decrease the temperature at which martensite begins to form, the areas rich in alloying elements form martensite at a lower temperature and thus after hardening contain a higher percentage of residual austenite than the remaining steel. This phenomenon is accentuated by the fact that the carbide forming alloying elements also decrease the carbon activity causing the carbon in said areas to be also enriched and to strongly contribute to increasing the percentage of residual austenite in these areas.

In steels with finely dispersed precipitated carbides, the carbide dissolution in austenitizing occurs rapidly compared to a material with coarse grained carbides. Moreover, the diffusion distances are reduced in steels with many and small carbides as compared to a steel with few and big carbides and, as a result, the variations in composition in the steel are reduced. A steel with finely dispersed precipitated carbides thus can be hardened more rapidly to a high hardness and the necessary hardening time is shorted. Also, by having better homogenity in the composition, a final product with considerably higher hardness is obtained after hardening than if a conventionally manufactured material with a coarse carbide structure has been used.

The method according to the invention can be applied to a plurality of suitable hardenable chromium steels with at least 8% chromium. It is characteristic of the steels that when austenitized at such high temperatures that practically all occurring carbides are dissolved and that the steel in the subsequent cooling to room temperature or lower has a structure of at least 20% and preferably at least 40% or more residual austenite and that this residual austenite is so stable that it will not disintegrate to any considerable exent in conventional tempering at temperatures up to 450 C.

In the heat treatment following the austenitizing, the steel shall be heated to a temperature below the temperature for austenitizing, i.e., below 850 C. but above 600 C., and often above 700 C., and thereafter preferably be cold-rolled to final thickness. However, normally the temperature range for said heat treatment is chosen between 650 to 735 C.

As examples of steel analyses suitable for the invention, the following may be given.

Percent C 0.3-1.0 Si 0-2 Mn 0-2 Cr 8-17 Mo 0-2 W 0-4 Additionally, V, Ti, Ta, Nb and Zr in sum totals altogether of 02% and Co, Cu, Ni, Be, Al and B in sum totals altogether of 0-3% and preferably 02% can be included.

The remainder is substantially all iron and the normally occurring impurities in iron.

Percent Si -a 0.1-0.7

Percent Additionally, Mo and/or W is included; the sum of the percentage of M0 and half of the percentage of W being 0.5-1.5%. The percentage Mo will amount to at most 1.5% and the percentage W to at most 3%. The remainder is substantially all iron and the impuritiees normally occuring in iron.

The curves in FIGS. 1-4 show the hardness in Vickers (load 0.5 kg.) as function of the hardening temperature for steels treated conventionally (full lined/curves) and according to the invention (dash and dot liner curves) respectively.

The curves shown in FIGS. 1 and 2 refer to a stainless martensitic steel with the composition 0.57% C., 0.38% Si, 0.39% Mn, 14.1% Cr and the remainder Fe. The steel having been hardened as strip with a thickness of about 0.10 mm. from temperatures within the interval 100 C.- 1150 C. with a heating time of one minute and cooling to room temperature (curves 1 and 3) resp. to C. (curves 2 and 4).

The curves 1 and 2 show the hardnesses which are obtained in the earlier normal method of manufacture when a hot-rolled strip with a thickness of about 3 mm. after annealing was cold-rolled in several steps with intermediate recrystallization annealings to a final thickness of about 0.1 mm. and thereafter was hardened. All annealings were made within the interval 700-840 C.

Curves 3 and 4 show how a considerably higher hardness was achieved when a hot-rolled 3 mm. thick strip was treated according to the invention and then hardened.

The treatment characteristic of the invention, i.e., austenitizing at high temperature and a subsequent heat treatment at a lower temperature (about 710 C.) than the temperature for austenitizing was made when the thickness of the strip was about 0.2 mm.

When the steel strip was finished by rolling to a thickness of about 0.1 mm., the hardening was made. The profit in hardness in this case was more than 100 Vickers (load 0.5 kg).

The FIGS. 3 and 4 show curves from a corresponding trial with a steel having the composition C= .63%, Si=1.12%, Mn=0.36%, Cr=10.5%, Mo=1.04% and the remainder iron.

Curves 5 and 6 show the hardnesses according to the conventional way of manufacture and curves 7 and 8 according to the method of the invention. Further, curves 5 and 7 represent the hardness after cooling to room temperature and curves 6 and 8 after cooling to -70 C. Also, for this steel considerable improvement was achieved by applying the special heat treatment according to the invention. The profit in hardness was about 95 Vickers (HV 0.5 kg.).

As an example of the method according to the invention the following may be mentioned:

A hot rolled strip of a steel alloy containing in percent of weight 0.60% C; 0.35% Si; 0.35% Mn; 14.0% Cr; balance Fe, was annealed at 825 C. for at least two hours followed by a slow cooling, whereby a structure was obtained having coarse carbide grains. The annealed strip was cold-rolled in several steps with intermediate recrystallization annealings to a thickness of near the final thickness e.g. 0.2 mm. or alternatively to the final thickness of e.g. 0.1 mm. The strip was thereafter austenitized at 1140 C. for about 5 seconds and then quenched between blocks. Hereby the carbide grains were practically completely dissolved and a structure comprising a mixture of martensite and austenite obtained, e.g. with an austenite content of about 60%. By a heat treatment for about 2 hours at 710 C. a precipitation of fine carbide grains in a matrix of ferrite was obtained. When the strip was cold-rolled to a thickness near the final thickness the strip was finished after said heat treatment by cold-rolling in one or more steps, possibly with intermediate recrystallization annealings to the intended final thickness, e.g. 0.1 mm. By heating to a temperature of about -1l00 C. followed by quenching to e.g. 80 C. and a possible subsequent annealing to about 200 C., a maximal hardness of about Vickers 800 (load 0.5 kg.) is obtained, whereafter the edge or the edges are shaped by grinding or similar methods. Finally the edge or the edges may be coated with a layer improving the shaving properties, which requires a further heating to a temperature, e.g. between ZOO-400 C.

While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. Method for the manufacture of razor blades and similar thin cutting edge tools with high wear resistance and high hardness from a hardenable chromium steel having a chromium content of at least 8%, Comprising the steps of austenitizing the steel after cold working at such a high temperature that practically all carbide grains occurring therein are dissolved, rapidly cooling the steel to obtain a mixed structure of austenite and martensite and then heat treating the steel at a temperature below the temperature for austenitizing, but above 600 C.

2. Method as claimed in claim 1 wherein said cold working before the austenitizing is done in several steps, said steel being subjected to recrystallization annealing between said cold working steps.

3. Method as claimed in claim 1 further including the step subsequent to said heat treating step of hardening the steel by heating to a temperature within the range of 850-1150 C. followed by a quenching step.

4. Method as claimed in claim 3 wherein said steel is quenched to a temperature between 20 and C.

5. Method as claimed in claim 3 wherein said hardening step is followed by a tempering step at 100-275 C. whereafter a cutting edge is formed.

6. Method as claimed in claim 5 and further including the step of tempering the steel after forming of the cutting edge at a temperature of more than C.

7. Method as claimed in claim 1, characterized in that said steel has the following composition: 0.3-1.0% carbon, 0-2% silicon, 02% manganese, 817% chromium, 02% molybdenum, 0 4% tungsten, 02% altogether of vanadium, titanium, tantalum, niobium and zirconium, 0-2% altogether of cobalt, copper, nickel, beryllium, aluminum, and boron and the remainder consisting substantially of iron.

8. Razor blades and other cutting edge tools, manufactured as claimed in claim 1.

9. Method for the manufacture of razor blades and similar thin cutting edge tools with high resistance and high hardness from a hardenable chromium steel having a chromium content of at least 8% comprising the steps of austenitizing the steel to dissolve practically all the carbide grains, rapidly quenching the steel strip to obtain a mixed structure of austenite and martensite, the austenite content being at least 20%,

and heat treating the steel strip of temperature above 600 C. but below the austenitizing temperature to obtain a precipitation of fine carbide grains in a matrix of ferrite.

10. Method as claimed in claim 9 wherein said austenitizing temperature is at least 1000 C.

11. Method as claimed in claim 9 and further including the steps of subjecting said steel strip to a first cold working operation before austenitizing and a second cold working operation after heat treating, then hardening said steel strip by heating said strip to a temperature within the range of 850-1150 C.; and forming a cutting edge on said steel strip.

12. Method as claimed in claim 11 and further including the step of subjecting said steel strip to a mechanical shaping operation between the second cold working step and the hardening step.

13. Method as claimed in claim 11 further including a first tempering step of heating said strip to a temperature of 100275 C. before forming said cutting edge and a second tempering step of heating said steel strip to a temperature in excess of 150 C. after forming said cutting edge.

14. Method as claimed in claim 11 wherein at least one of said cold working operations is done in a series of steps, said steel strip being subjected to recrystallization annealing between said cold working steps.

15. Method as claimed in claim 14, characterized in that said steel is within the following range of compositions: OJ-1.0% carbon; 02% silicon; 02% manganese; 817% chromium; 0-2% molybdenum; 0-4% tungsten; 02% altogether of vanadium, titanium, tantalum, niobium and zirconium; 0-2% altogether of cobalt, copper, nickel, beryllium, aluminum and boron; and the remainder consisting substantially of iron.

8 16. Method as claimed in claim 15 wherein said 3,340,048 9/1967 Floreen 148-12.3 austenitizing temperature is at least 1100 C. and said heat 3,437,477 4/ 1969 McCune III 148-12.3 treating temperature is in the range of 650-735 C. 3,469,972 9/1969 Carlen et a1. 75-126 3,473,973 10/1969 Maekawa et a1 148-123 References 22 s 5 L. DEWAYNE RUTLEDGE, Primary Examiner UNITED STATES ENT W. W. STALLARD, Assistant Examiner 2,999,039 9/1961 Lula et a1. 148-123 3,152,934 10/1964 Lula et a1 148-12.4 US. Cl. X.R.

3,336,168 8/1967 Morita ct a1. 148-12.3 10 148143