US3837931A

US3837931A - Composite iron-base metal product

Info

Publication number: US3837931A
Application number: US00128738A
Authority: US
Inventors: T Nemoto; K Kuniya; T Tamamura
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1970-03-27
Filing date: 1971-03-29
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24
Also published as: JPS5411257B1; GB1326494A; DE2114852A1; DE2114852B2; FR2083615A1; FR2083615B1; DE2114852C3

Abstract

A composite iron-base metal product comprising an iron-base metal in which a martensitic structure having a high mechanical strength is formed in a particular portion of the base metal in such a manner that the tensile strength and rupture strength in the direction of orientation of the martensitic structure are improved. The resulting composite product has a tensile strength which approximates the theoretical strength thereof.

Description

United States Patent 119 1 Nemoto et al.

COMPOSITE IRON-BASE METAL PRODUCT Inventors: Tadashi Nemoto, Tokyo; Keiichi Kuniya; Takeo Tamamura, both of Hitachi, all of Japan Assignee: Hitachi, Ltd., Tokyo, Japan Filed: Mar. 29, 1971 Appl. No.: 128,738

Foreign Application Priority Data Mar. 27, 1970 Japan 45-25277 US. Cl 148/12.4, 29/l9l.4, 29/196.1,

Int. Cl. lain/90 Field of Search 148/1 1.5, 12, 12.4, 34, 148/3l.5, 39, 127, 134, 143, 144; 29/l96.1, 191.4, 197.5, 191.6; 75/135, DIG. 1

References Cited UNITED STATES PATENTS l/l888 Marshall 29/I91.6 X

5/1903 Falk 148/39 7/1951 Kinnear 29/196.1 X 7/1963 Micks 29/l83.5 9/1965 V0rdahl l48/ll.5 X 11/1965 Allen et al. 29/191.4

[ Sept. 24, 1974 3,314,825 4/1967 Forsyth et al 148/11.5 A

3,419,952 1/1969 Carlson 29/197.5 X

3,450,510 6/1969 Calow 75/D1G. 1

3,466,166 9/1969 Levinstein et al. 75/135 3,489,534 l/l970 Levinstein 29/l91.6

3,686,081 8/1972 Butter et al 29/l9l.6 OTHER PUBLICATIONS DMIC Memorandum 243, May 1969, Metal-Matrix Composites, pp. l-6.

Blackburn et al., Filament-Matrix Interactions in Metal Matrix Composites, Strengthening Mechanisms, Metals and Ceramic Proceedings of the 12th Sagamore Army Materials Conference, Aug. 1965, Syracuse Univ. Press, 1966 pp. 447-475.

Primary ExaminerCharles N. Lovell Attorney, Agent, or Firm-Craig & Antonelli [5 7] ABSTRACT 13 Claims, 10 Drawing Figures PAIENIEUSEPZMHN 3.837. 931 m1 '2 Br 4 FIG.Y3

3L ZOEQOZO E m w m ZOO 400 600 TEMPERATURE OF TEMPERlNG ("m INVENTORS TADRSHI NEMOTO, KEHCHI KUNIYA BY AND TAKED TAMAMURA Craig Anlbneui, Stewa t- ATTOR NEIS COMPOSITE IRON-BASE METAL PRODUCT BACKGROUND OF THE INVENTION This invention relates to a new composite metal produce and a method for producing the same in which grains different from the base metal are present in clusters therein. More particularly, it relates to a composite iron-base metal product comprising an iron-base metal in which a martensitic structure having a high mechanical strength is formed in a particular portion of the base metal whereby the tensile strength and rupture strength in the direction of orientation of the martensitic structure are improved.

The development of reinforced plastic, in which fiber glass is utilized to improve defects such as poor strength and poor elasticity of the plastic or synthetic resin, has now reached the stage where it occupies an established position as an industrial material. However, fiber-reinforced plastics have poor heat resistance, so that the upper threshold temperature applicable thereto is usually limited to as low as about 300C.

On the other hand, there has recently been a strong demand for the development of fiber-reinforced composite metal materials using a metal as a base, and the trend in the industry today is directed toward this new product. The aim of developing such fiber-reinforced composite metal materials is the obtainment of improved mechanical strength and a striking enhancement of heat resistance, as compared with fiberreinforced plastics (synthetic resins). The key factors in the development of such fiber-reinforced composite metal materials are the establishment of techniques of industrially producing metallic fibers and the provision of methods of producing composite metal materials using such fibers. It is doubtless that the successful attainment of a manufacturing system, which is industrially acceptable with regard to the above points, will pave the way for a bright future for fiber-reinforced composite metal materials.

So far, success in connection with the artificial production of whiskers and high strength fine metal fibers has provided a blueprint of a fair prospect of the industrialization of the fibers, and now efforts are being made toward establishing a commercially acceptable method for producing composite metal materials using these metallic fibers. According to the literature published to date concerning fiber-reinforced composite metal materials, many and various attempts have been made on this subject by utilizing, for example, an infiltration method, a powder method, a diffusion bonding method or an electrodeposition method. Most popularly used among these known methods are the infiltration method, in which a tube filled with fibers is immersed in a metal bath and molten metal is sucked into the vacuumized top portion of the tube, and the diffusion bonding method, wherein metallic fibers are inserted between the metal plates and are then subjected to pressure bonding under heating. The fiberreinforced composite metal material thus produced has advantages over fiber-reinforced plastics in that the poor strength and poor elasticity of the base metal are sufficiently covered up and overcome by the fibers and a far higher heat resistance than that of fiber-reinforced plastic material is obtained.

It is, therefore, a natural consequence that the development of such fiber-reinforced composite metal materials will represent a breakthrough in a new field which is of a completely different nature from the conventional property-improving methods based on the alloying of metals. in this connection. it is also inevitable that some difficult problems are encountered. For example, a fiber-reinforced composite metal material is subject to restriction by the differences in adhesion and coefficient of thermal expansion between the base metal and the fibers, so that practical uses thereof are confined to the scope of specific combinations. Also, the property of the resultant material cannot be better than what may result from a combination of the properties of the respective components. The fact should also not be ignored that the artificially produced whiskers or high strength fine fibers are extremely expensive.

These facts dictate that success in varying the properties of metallic fibers in combinations of base metal and fibers will result in an appreciably widened scope of application of the material. Also, if a method involving no need of using expensively produced whiskers or high strength fine fibers should be devised, it will open up a way for developing a completely new type of composite metal material which is beyond the scope of fiberreinforced composite metal materials.

The present invention is intended to meet all of these factors, and, therefore, the primary object of this invention is to provide a novel composite iron-base metal product in which the properties of the elements included in the base metal are varied.

Another object of the invention is to provide a method for producing such composite metal products.

tion and claims, taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION Essentially, the composite iron-base metal products of the present invention can be obtained by giving a certain directionality to the grains produced by the reaction between the base metal and the elements reactable therewith.

The method of producing such composite metal products according to the present invention comprises, essentially, the steps of incorporating in an iron-base metal the elements reactable therewith in such a manner that they are kept safe from the influence of oxygen,- and reacting them by a heat treatment at a temperature lower than the melting point of the base metal.

Although iron and steel materials have the broadest scope of utilization in present day industrial circles, few experimental attempts have been conducted to date for improving fiber-reinforced composite metal materials because of the failure to find out fibers which are effectively utilizable for the reinforcement of iron and steel. Therefore, the strengthening of such materials has heretofore relied upon the selection of alloying elements and of heat treatment conditions. The application of the present invention to iron-type composite metal products is characterized by employing the concept of a transformation of the structure. It is a typical embodiment of the present invention to form a martensite structure with a certain directionality in an iron base having high strength, thereby maintaining the strength of the product with the presence of martensite and to compensate for the brittleness of martensite with the tenacious nature of base iron.

In order to embody this principle and concept into the fiber-reinforced composite metal materials which are now being developed, a first consideration is paid to the modification of brittle martensite into the form of a fiber. To this end, finely pulverized pieces or powder of carbon, foil, paper or the like may be utilized in the present invention. The fibers employed in this connection do not necessarily have to be whiskers or strong fine metal fibers. The fibers employed may be weak in and of themselves.

The strength of martensite produced by the reaction of iron and carbon is not as low as that of ordinary alloyed steel, but actually approximates the intrinsic theoretical value. From this fact, it will be understood that the elements worked into a powder or foil can be effectively utilized in a manner to be more particularly described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is a graph showing the relationship between the tensile strength and carbon content of ordinary martensitic alloyed steel;

FIG. 2 is a graph showing the effect of carbon content on 0.6 percent proof stress of an iron-nickelcarbon alloyed steel;

FIG. 3 is a graph showing the relationship between tensile strength and elongation percentage and carbon content of martensitic carbon steel, and;

FIGS. 4, 5, 6, 7, 8, 9 and 10 are perspective views illustrating various embodiments of the composite metal products of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the tensile strength, in comparison with carbon content, of the martensite structure of alloyed steel for general use when it is tempered at 200C. Since these alloyed steel materials were produced by ignoring their elasticity, they have an extremely small elongation percentage. For the sake of comparison, similar data are also given for carbon steel, but these data are the presumed values which are considered to be intrinsically possessed by carbon steel. It will be understood from this figure that the tensile strength of martensite is improved proportionally to an increase of the carbon content.

FIG. 2 shows the results of experiments conducted with the iron-nickel-carbon alloyed steel as an example to show the proof stress of martensite steel. The 0.6 percent proof stress [the quotient obtained by dividing the load (kg), at which a permanent elongation of 0.6 percent takes place, by the original sectional area (mm of the parallel part in a tensile test or compression test] is given on the ordinate, and the carbon and nickel contents are shown on the abscissae.

In FIG. 2, curve (I) shows the compression proof stress observed in a compression test after an aging treatment for three hours at C., and curve (2) shows the tensile proof stress observed in a tensile test with no age treatment being conducted. It is to be noted from FIG. 2 that the tensile strength is steadily increased. until the carbon content reaches the 0.6 percent level. It has thus been found that the strength characteristic of martensite is improved proportionally to an increase in the carbon content until the latter reaches the 0.5 to 0.6 percent level, but above that level, no such improvement is observed.

This fact is evidently attested to by FIG. 3, wherein the tensile strength and elongation percentage of the three carbon steel martensite test pieces having different carbon contents from each other are shown in relation to tempering temperature. In FIG. 3, curves (3) and (3a) represent steel containing 0.34 percent of carbon and being oil-quenched starting from 850C curves (4) and (4a) represent steel containing 0.65 percent of carbon and being oil-quenched starting from 850C, and curves (5) and (50) represent steel containing 0.99 percent of carbon and being waterquenched from 750C. Curves (3), (4) and (5) show tensile strength, while curves (3a), (4a) and (5a) show elongation percentage.

The results of FIG. 3 reveal that the tensile strength of carbon steel is rather low when the carbon content is up to about 1 percent. However, in view of the fact that, intrinsically, strength and elongation are contradictory factors, a reasonable conclusion is that the true tensile strength of steel containing 0.99 percent carbon, which has the lowest elongation percentage, should be the highest among the curves (3), (4) and (5). Actually, however, it only exhibits a low tensile strength such as represented in the graph. This is attributable to the fact that too high of an increase of the carbon content invites premature rupture phenomenon, which makes it impossible to obtain a true tensile strength.

Owing to these reasons. in the field of iron alloys, it has not been possible to fully utilize the intrinsic strength of martensite containing a large amount of carbon, and even maraging steel, which is representative of high-strength martensite steel, had a tensile strength as low as below 200 kglmm However, in the composite metal products according to the present invention, even if local rupture would be caused due to brittleness of the martensite structure produced by reaction with the iron base, the destructive energy is absorbed by the tenacious iron base, so that such rupture does not extend over the entire composite metal material but is forced to advance in a stepby-step manner. It is thus possible to fully utilize the excellent strength characteristics of martensite, which contains carbon in abundance.

The present invention also overthrows the conventional conception of fiber-reinforced composite metal materials, which dictates that it is necessary to previously prepare the martensite fibers, which are very difficult to produce, since it is contemplated to utilize for reinforcement the particles of martensite produced by reaction between the iron base and carbon introduced therein. Hence, the technical difficulties in this respect are removed. Furthermore, the utilization of the reaction between the iron base and carbon brings about the advantage that the element incorporated may be, in itself, weak fibers or may be in the form of a powder or foil. It should, however, be kept in mind that, in the case of using a powder or foil, the martensite grains must be arranged with directionality.

Thus, one of the important features of the present invention is that the element incorporated in the metal base becomes a component of the base through reaction therewith and, as a result, a metal product presenting the same structure as that of an alloy product is obtained.

In a composite metal material where the fibers are arranged continuously in one direction, the average tensile strength 8 of this material, when a tensile force is acting in the fiber direction, is expressed by the following formula:

0 f I m m SIVI m( VI), wherein 6, stands for the tensile strength of the fiber, 8, represents the inherent tensile strength of the base metal, 8', is the stress of the base metal in regard to the rupture strain of the composite metal material, and V; and V,,, represent the volume ratios of fiber and base metal, respectively.

Now, by way of example, martensite grains having a 1 percent carbon content are produced in a ferrite base such that the amount of martensite takes 70 percent (in one embodiment) and 50 percent (in another embodiment) of the entire composite metal material. In this case, as mentioned above, when the carbon content in carbon steel martensite reaches a 1 percent level, a premature rupture phenomenon is caused and, therefore, a true tensile strength is not exhibited. However, as estimated from the tensile strength of martensite of low carbon content (0.1 to 0.6 percent), it may be considered that the tensile strength of martensite containing 1 percent carbon must be about 320 kg/mm when it is tempered at 200C. Likewise, the tensile strength of ferrite is estimated to be about 31 kglmm Also, the stress 6', of the base metal, that is, ferrite in this case, in rupture strain of the composite metal material may be estimated to be about 14 to 17 kg/mm Introducing these estimated values into the above formula, the following results are obtained:

In case the volume ratio of the martensite structure is 0.7,

8,. 320 X 0.7 X 0.3 228.5 kglmm In case the volume ratio of the martensite structure is 0.5,

8, 320 X 0.5 +15 X 0.5 167.5 kglmm These results indicate that even if the base iron is of low strength, the martensite structure will compensate for it and a high strength product can be obtained. As to the elastic property, such as elongation or contraction, this is well supplemented by the base iron, so that the product of such high strength is also provided with excellent elasticity and tenacity.

It will be understood from the examples described hereinbelow that tensile strength calculated in this manner substantially agrees with the actually measured tensile strength of the composite metal product and, thus, the intrinsic tensile strength of martensite is displayed in such a case.

Now, the essential means employed for producing the composite metal products according to the present invention will be described in detail.

Referring first to FIG. 4, which shows an embodiment of the present invention, it will be seen that grooves 2 are formed in a metal base 1 and that elements 3 reactable with the base metal are disposed in said grooves in a manner as shown in FIG. 5. Formation of grooves 2 in the metal base 1 may be accomplished by using any suitable conventional mechanical method, such as, for example, marking-off. It is also possible to employ photo-etching, which is popularly used in semiconductor devices. It is preferable not to make the depth of the grooves 2 too large. This is because if the groove depth is too large, the grooves will not vanish and will remain as voids even if subjected to rolling after or during the manufacture of the composite metal products. The presence of such voids causes a decline of strength.

The grooves are provided in sufficient number to satisfy the required volume ratio of the elements disposed therein. It is to be noted that if these grooves are pro vided in regular order in one direction alone, a variation of characteristic by reaction between the metal base and the elements appears conspicuously only in that direction, with substantially no effect appearing in the direction which crosses the above-said direction, so that, if necessary, similar grooves can be provided in the crossing direction also.

After providing a required number of grooves in the metal base in the above-described manner, the elements 3 reactable with the base metal are then placed in the grooves. It should be noted that if the elements thus placed in position are directly subjected to heating in an oxygen atmosphere, they will be oxidized to produce an oxide, such as, for example, CO or CD so that the desired results will not be obtained. It is therefore necessary to conduct a heating treatment after sealing the grooves 2 so as to keep them free from the influence of oxygen. One of the convenient measures for carrying out this treatment is to place a new metal base 1A in close contact with the surface of the metal base 1 where the grooves 2 are formed, as shown in FIG. 4. For industrial use, it is necessary to laminate the metal bases in many layers to produce one article, so that this measure proves extremely effective. Even in the case where the metal bases are laminated in many layers, it is desirable to seal the grooves at the end faces by means of welding or soldering.

In another embodiment, as shown in FIG. 6, holes 4 are provided in the metal base 11 and the element 3 reactable with the base metal are placed in said holes. These holes may be formed easily by the use of a drill or other like means. Since it is difficult to form small holes from the beginning, it is recommended to first form comparatively large holes and then to stretch the metal base 11 by rolling to thereby make the holes smaller. It is also practical to arrange, with a certain directionality, the elements 3 reactable with the base metal directly on the surface of a flat plate-shaped metal base 1, as shown in FIG. 7, and to let them react under this state. In this case, a prevention against oxidation of the elements 3 may be achieved by using new metal bases 1A, 1B and 11C in the same manner as in the case where the grooves 2 are provided in the metal bases are to be combined together integrally, they are first suitably bundled together as shown in the figure, with the contacting faces being welded together, and are then subjected to a rolling operation to remove the grooves into the form of a plate.

In the case of including the reactable elements in the metal base, it is also possible to include other kinds of elements along with the mentioned reactable elements. An example of such a situation is illustrated in FIG. 10, where the

elements

3 and 3A are disposed in the grooves 2 formed in the metal base 1. Both

elements

3 and 3A may be elements which react with the base metal or with each other. Of course, the element 3A may be an element which does not react either with the base metal or with the element 3. in this case, high strength fine fibers are preferred.

In the case that different kinds of elements are arranged with each other as mentioned above, if the elements 3A are capable of reacting with base metal 1 or with the elements 3, it is possible to control excess diffusion of the elements 3 into the metal base.

In the case of having martensite particles existing in an iron base, an iron-carbon alloy base is previously prepared and pure iron is distrubuted therein with a certain directionality, the structure then being subjected to heat treatment. The amount of included pure iron, which is reacted with carbon in the base, is extremely small, so that it is reduced into ferrite while the base metal is turned into martensite.

When pure iron is distributed with a certain directionality in, for example, an 18 percent chromium-8 percent nickel steel base having a stable austenite structure, and this base is subjected to heat treatment, the nickel and chromium in the base at the part in the vicinity of pure iron are diluted and turned into a martensitic structure area, while the part remote from pure iron remains as austenite.

The proper range of heat treatment temperature and heating time may vary according to the thickness and composition of the metal base and the amount of elements included in the base, but, basically, the purpose can be obtained if such temperature is above the lower threshold temperature at which the base metal and the elements are reacted. For instance, in the case of generating martensite containing 1 percent carbon by reacting pure iron and carbon, the heat treatment is preferably conducted within the temperature range of from 770 to 850C. A rise of the heat treatment temperature promotes diffusion of the elements into the base, so that when it is desired to further raise the heat treatment temperature, the heating time can be shortened correspondingly.

EXAMPLES OF THE INVENTION The following examples are given merely as illustrative of the present invention and are not to be considered as limiting.

EXAMPLE 1 Grooves about 0.1 mm. in depth and width were formed at intervals of about 2 mm., by marking-off, on the surface of a pure iron plate having a thickness of mm., a width of 100 mm. and a length of 200 mm. Carbon fibers were then distributed therein. The carbon fibers used were not high strength fine fibers, but weak fibers in and of themselves, and they were arranged continuously with no breaks throughout. The amount of the carbon fibers was selected such that martensite containing 1 percent carbon will be present in an amount of 50 percent by volume ratio.

Then, a metal plate having the same size as said pure iron plate was placed on the surface of the latter where the grooves were formed, and after sealing the periphery by tungsten inert gas welding (referred to herein as TlG welding), the assembly was subjected to hot rolling. The hot rolling procedure flattened the plate assembly to a thickness of about 5 mm. After rolling the assembly was heated at 800C. to cause reaction between the pure iron base and the carbon fibers and was maintained at that temperature for 30 minutes and thereafter immersed in water to effect cooling. Then, the assembly was further subjected to a tempering treatment at 200C. to improve the toughness of the pure iron plate and the generated martensite.

Thereafter, specimens for a tensile strength test were collected from the obtained composite metal product and were subjected to tests to determine their tensile strength and elongation percentage. The specimens were collected in such a way as to allow a determination of the strength in the direction where the martensite grains are arranged continuously. The tensile strength was 150 kg/mm and the elongation percentage was l5 percent.

These results agree well with the calculated values obtained from the formula for calculating the average tensile strength of a composite metal material having fibers arranged continuously in one direction in the case where a tensile force is applied therein in the direction of the fibers.

EXAMPLE 2 Holes having a diameter of 2 mm. were formed by a drill centrally (of the thicknesswise direction) in a pure iron plate having a thickness of 10 mm., a width of 100 mm. and a length of 200 mm. Twenty of such holes were formed equidistantly along the longitudinal length of the plate.

Then, the same carbon fibers as used in Example 1 were inserted into these holes, and the plate was then subjected to cold rolling in an argon atmosphere to flatten the plate to a thickness of about 7 mm. The amount of carbon fibers was adjusted such that martensite containing 1 percent carbon will be present in an amount of percent by volume ratio. Then, three pieces of similar composite metal plates produced in the same manner were placed thereon in layers, and after sealing the periphery by TlG welding, the entire assembly was subjected to hot rolling in an argon atmosphere to reduce the total thickness to 5 mm. The resultant composite metal product was heated at 800C. for 30 minutes and then cooled in water in the same manner as in Example 1. Thereafter, the product was further sub jected to a tempering treatment at 200C. The tensile strength and elongation percentage in the longitudinal direction of the product were 205 kg/mm and 14 percent, respectively.

EXAMPLE 3 Carbon fibers were arranged in 20 rows equidistantly on a pure iron plate having a thickness of 0.2 mm., a width of mm. and a length of 200 mm. Then, another pure iron plate of the same dimension was placed on said rows of carbon fibers, and on this position were arranged an additional 20 rows of carbon fibers, on

which another such plate was placed. in this manner, a lamination of 30 layers in all was formed (each layer consisting of a pure iron plate and 20 rows of carbon fibers lodged thereon). Finally, the surface of the topmost rows of carbon fibers was covered with a pure iron plate, and the assembly was subjected to hot rolling in a vacuum atmosphere to reduce the total thickness thereof to 2 mm.

Thereafter, the assembly was subjected to quenching and tempering treatments under the same conditions as in Examples 1 and 2. The amount of carbon fibers becomes adjusted such that martensite containing 1 percent carbon will occupy 70 percent by volume of the entire structure.

The resultant composite metal product has a tensile strength of 208 kg/mm and an elongation percentage of 15 percent.

EXAMPLE 4 A cloth of carbon fibers woven in lattice shape (with a spacing of 5 mm.) was placed on the surface of a pure iron base having a thickness of 3 mm., a width of 100 mm. and a length of 200 mm., to thereby form a unitary structure, and the resulting structures were placed one on the other in layers. Finally, the topmost surface was covered with a pure iron plate, and the entire assembly was subjected to hot rolling in an argon atmosphere to make a total thickness of 8 mm.

The amount of the carbon cloth becomes adjusted such that martensite containing 1 percent carbon takes 50 percent by volume of the entire structure. Thereafter, quenching and tempering treatments starting at 800C. were conducted in the same manner as in the previous examples. A

The tensile test results showed that the obtained product had a tensile strength of 120 kg/mm and an elongation percentage of 14 percent.

EXAMPLE 5 Japanese paper was placed on the surface of a pure iron plate having a thickness of 3 mm., a width of 100 mm. and a length of 200 mm., and 5 groups of this combination were laminated in layers, with the topmost surface being covered with a pure iron plate. Then, the entire assembly was subjected to pressure welding under heating in an argon atmosphere to reduce the total thickness therof to 7 mm. Considering that about 50 percent of the paper contributes as carbon, the amount of paper was adjusted such that martensite containing 1 percent carbon will exist in an amount of 50 percent by volume ratio. After heating at 800C. for 30 minutes, the assembly was subjected to water quenching and tempering treatments.

The obtained product had a tensile strength of 125 kg/mm and an elongation percentage of 14 percent.

EXAMPLE 6 Then, seven pieces of the resulting composite metaltubes were assembled into a bundle, with the contacting faces being welded together by TlG welding, and then the bundle was subjected to hot rolling to flatten it into the form of a plate having a total thickness of about 1 mm.

The composite metal product thus obtained had a tensile strength of l5l kg/mm and an elongation percentage of 14.4 percent.

EXAMPLE 7 Grooves having a depth and width of about 0.1 mm. were formed, by marking-off, at intervals of about 2 mm. along the longitudinal length of a base plate formed from an iron alloy containing 5.4 percent of nickel-having a thickness of 5 mm., a width of 100 mm. and a length of 200 mm. Then, carbon fibers were placed in the grooves. The amount of carbon fibers was such that martensite including 1 percent carbon would be obtained in an amount of 70 percent by volume ratio. Then, a plate of the same composition and same dimension as the base plate was disposed on the surface of the latter where the grooves were formed, and after performing TIG welding around the periphery, the assembly was subjected to hot rolling. The plate thickness was lessened to 5 mm. by rolling. Thereafter, the structure was heated at 850C, maintained at that temperature for 30 minutes, immersed in water to effect cooling, and then further subjected to a tempering treatment at 200C.

The resulting composite metal product had a tensile strength of about 215 kg/mm and an elongation percentage of l 1.6 percent.

As can be seen from the foregoing examples, the composite metal material prepared by distributing carbon in an iron base and reacting the same by heat treatment such that martensite grains exist therein with a certain directionality has a higher tensile strength and toughness than ordinary carbon steel or alloyed steel, since the strength characteristic is provided by martensite, while toughness is provided by the iron base. It

i is also apparent that these effects are not obtained by the simple inclusion of carbon fibers in the iron base; rather, the characterizing properties stem from the generation of grains having different characteristics, that is, martensite grains, by reaction between such carbon fibers and the iron base.

The modes of embodiments of the present invention are exemplified as follows:

1. A composite metal product comprising a metal base and the elements reactable therewith, said elements being present in continuation in a given direction and reacted with the base metal adjacent thereto by heat treatment at a temperature lower than the melting point thereof to thereby form the grains.

2. A composite metal product comprising a metal base and a plurality of different kinds of elements, at least one of which is reactable with the base metal, said elements being present in continuation in a given direction and being reacted with the base metal adjacent thereto by heat treatment at a temperature lower than the melting point thereof to thereby form more than one grain cluster.

3. A composite metal product comprising a metal base and elements reactable therewith, said elements being enclosed in the grooves are in said metal base condition free from the influence of oxygen to thereby form a cluster of grains.

4. A composite metal product comprising a metal base and the elements reactable therewith, said elements being enclosed in holes provided in said metal base with a certain directionality and being reacted with the base metal adjacent thereto by heat treatment under a condition free from the influence of oxygen to thereby form a cluster of grains 5. A composite metal product comprising a lamination of plural metal bases and elements reactable therewith, said elements being laminated alternately with said metal bases in layers and being reacted with the base metal adjacent thereto by heat treatment under a condition free from the influence of oxygen to thereby form a cluster of grains.

6. A method of producing a composite metal product comprising the steps of placing in a metal base the elements reactable therewith in a continuous arrangement in a certain given direction and, after sealing said elements so as to remain free from the influence of oxygen, reacting said base metal and elements by heat treatment at a temperature lower than the melting point thereof.

7. A method of producing a composite metal product comprising the steps of placing in a metal base a plurality of different kinds of elements, at least one of which is reactable with said base metal, in a continuous arrangement in a certain given direction and, after sealing said elements so as to remain free from the influence of oxygen, reacting said base metal and elements by heat treatment at a temperature lower than the melting point therof.

8. A method of producing a composite metal product comprising the steps of placing in grooves provided in a metal base with a certain directionality the elements reactable with said metal base and, after sealing said elements so as to remain free from the influence of oxygen, reacting said base metal and elements by heat treatment at a temperature lower than the melting point thereof.

9. A method of producing a composite metal product comprising the steps of placing in holes provided in a metal base with a certain directionality the elements reactable with saidmetal base and, after sealing said holes so as to keep the elements free from the influence of oxygen, reacting said base metal and elements by heat treatment at a temperature lower than the melting point thereof.

10. A method of producing a composite metal product comprising the steps of placing on the surface of a metal base the elements reactable therewith in a continuous arrangement in a certain given direction, laminating said metal bases and elements alternately in many layers, and after sealing said elements to keep them free from the influence of oxygen, reacting said elements with the base metal by heat treatment at a temperature lower than the melting point thereof.

Although in the above description, carbon has been exemplified as being utilized with the composite ironbase metal products for improving or modifying the characteristics of the iron-base metal, it has been found that elements having a mutual solid solubility with the iron-base metal and being capable of producing the y a transformation when the iron-base metal is subjected to cooling can be suitably employed.

As such elements, there may be mentioned W, Cr, Si, V, Mo, Ti, Be, Cu, P, S, Ni and various mixtures thereof. Of these elements, P and S may be used for improving the workability of the iron-base metal. and W, Cr, Si, V, Mo, Nb and Ti may be used for improving the mechanical characteristics of the iron-base metal. For example, several pipes made of Fe 5% Ni, wherein the holes are filled with a powder of W, are tightly bundled and are twisted to make the pipes into an assembly, followed by heat treatment under such a condition that the W atoms are diffused into the iron-base metal. instead of the W powder, fine wires or fibers of W or Mo, which are widely used in the field of conventional composite materials, can also be employed.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included herein.

We claim:

1. A method for producing a composite metal product comprising the steps of:

orienting at least one elongated carbon element in an metal base selected from group consisting of iron and iron alloys such that said element extends in at least one predetermined direction with respect to the metal base;

sealing said element within said metal base such that said element is protected from an oxidizing atmosphere; heating the resulting composite of metal base and oriented element at a temperature of from about 770C to about 850C for a period of time determined such that substantially all of the carbon of said element reacts with the iron in said metal base which is substantially in the region adjacent said oriented element, thereby forming an oriented portion in said metal base having a 'y structure; and

quenching the thus heated resulting composite to cause said oriented portion to have a martensitic structure said structure being different from that of the metal base.

2. The method of claim 1, wherein a plurality of said elongated carbon elements are oriented in said metal base, and a plurality of oriented portions having the martensitic structure are formed in said resulting composite during said quenching.

3. The method of claim 1, further comprising the step of tempering said resulting composite at a temperature of 200C following said quenching step.

4. The method of claim 2, wherein the metal base is formed of a sheet, and the step of orienting includes forming a plurality of grooves in said predetermined direction on one surface of said sheet and disposing said plurality of elongated elements into said grooves.

5. The method of claim 4, wherein said step of sealing includes laminating a second metal sheet of material substantially the same as said metal base on said one surface and sealing edges of the laminated sheets by welding.

6. The method of claim 5, further comprising, after the step of sealing, hot rolling said laminated sheets to compress said laminated sheets whereby said grooves are completely filled by said elongated elements.

7. The method of claim 6, wherein said laminated sheets are heated at a temperature of 800C for a period of 30 minutes, and quenched in water.

8. The method of claim 5, further comprising the steps of providing a plurality of said laminated sheets in a stack, laminating said plurality of sheets to one another, and hot rolling said laminated stack to decrease the thickness of said laminated stack prior to the step of reacting.

9. The method of claim 8, wherein said laminated stack is heated at a temperature of 800C for a period of 30 minutes, and quenched in water.

10. The method of claim 2, wherein said metal base is formed of a plate, and the step of orienting includes drilling a plurality of holes in a central thickness direction of said plate and filling said holes with said plurality of elongated elements.

11. The method of claim 10, wherein the step of sealing includes cold rolling said filled plate to compress the thickness of said plate, thereby completely filling said holes by said elongated elements and sealing the ends of said plate having holes formed therein by welding.

12. The method of claim 11, wherein said filled plate is heated at a temperature of 800C for a period of 30 minutes, and quenched in water.

13. The method of claim 1, wherein said carbon elements are selected from a material consisting of carbon fibers, elements formed of carbon powder, carbon cloth, carbon foils and carbon paper,

Claims

2. The method of claim 1, wherein a plurality of said elongated carbon elements are oriented in said metal base, and a plurality of oriented portions having the martensitic structure are formed in said resulting composite during said quenching.
3. The method of claim 1, further comprising the step of tempering said resulting composite at a temperature of 200*C following said quenching step.
4. The method of claim 2, wherein the metal base is formed of a sheet, and the step of orienting includes forming a plurality of grooves in said predetermined direction on one surface of said sheet and disposing said plurality of elongated elements into said grooves.
5. The method of claim 4, wherein said step of sealing includes laminating a second metal sheet of material substantially the same as said metal base on said one surface and sealing edges of the laminated sheets by welding.
6. The method of claim 5, further comprising, after the step of sealing, hot rolling said laminated sheets to compress said laminated sheets whereby said grooves are completely filled by said elongated elements.
7. The method of claim 6, wherein said laminated sheets are heated at a temperature of 800*C for a period of 30 minutes, and quenched in water.
8. The method of claim 5, further comprising the steps of providing a plurality of said laminated sheets in a stack, laminating said plurality of sheets to one another, and hot rolling said laminated stack to decrease the thickness of said laminated stack prior to the step of reacting.
9. The method of claim 8, wherein said laminated stack is heated at a temperature of 800*C for a period of 30 minutes, and quenched in water.
10. The method of claim 2, wherein said metal base is formed of a plate, and the step of orienting includes drilling a plurality of holes in a central thickness direction of said plate and filling said holes with said plurality of elongated elements.
11. The method of claim 10, wherein the step of sealing includes cold rolling said filled plate to compress the thickness of said plate, thereby completely filling said holes by said elongated elements and sealing the ends of said plate having holes formed therein by welding.
12. The method of claim 11, wherein said filled plate is heated at a temperature of 800*C for a period of 30 minutes, and quenched in water.
13. The Method of claim 1, wherein said carbon elements are selected from a material consisting of carbon fibers, elements formed of carbon powder, carbon cloth, carbon foils and carbon paper.