US3929518A

US3929518A - High speed steel having high wear resistance

Info

Publication number: US3929518A
Application number: US435952A
Authority: US
Inventors: Kimihiko Akahori; Masayuki Era
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1973-01-24
Filing date: 1974-01-23
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: JPS5411767B2; JPS4997718A

Abstract

A high speed steel having high wear resistance consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, and the balance substantially iron, wherein all of vanadium and niobium reacts with carbon, 1.4 to 3.6% by weight of carbon forms cementite and 0.1 to 0.6% by weight of carbon dissolves in a ferrous matrix as hardened.

Description

United States Patent Akahori et a1.

HIGH SPEED STEEL HAVING HIGH WEAR RESISTANCE inventors: Kimihiko Akahori, Katsuta;

Masayuki Era, Hitachi, both of Japan Assignee: Hitachi, Ltd., Japan Filed: Jan. 23, 1974 Appl. No.: 435,952

Foreign Application Priority Data Jan. 24, 1973. Japan 48-9543 US. Cl 148/31; 75/123 J; 75/126 A; 75/126 E; 75/126 F; 75/128 D Int. Cl. C22C 38/12; C22C 38/36 Field of Search 75/123 R, 123 J, 126 A, 75/128 D, 128 13,128 V; 148/31 References Cited UNITED STATES PATENTS 11/1951 Giles 75/126 A OTHER PUBLICATIONS Tool Steels, Roberts et al., 1962, pp. 521-524.

Primary Examiner-C. Lovell Attorney, Agent, or Firm-Craig & Antonelli [5 7] ABSTRACT A high speed steel having high wear resistance consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, and the balance substantially iron, wherein all of vanadium and niobium reacts with carbon, 1.4 to

I 3.6% by weight of carbon forms cementite and 0.1 to

0.6% by weightof carbon dissolves in a ferrous matrix as hardened.

11 Claims, 8 Drawing Figures US. Patent ABRASION QUANTITY (9) Dec. 30, 1975 Sheet10f4 3,929,518

FIG. I

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bk 3 5 I0- I) (I.

l23456789|0ll ALLOYNUMBER ABNASION QUONTITY (9L atst Dec. 30, 1975 Sheet 3 of 4 F l G. 5

E T 7 T IO- E 0 l2 l3 l4 ALLOY NUMBER F l G. 6

0.0|O- 0.005- H H 0 l2 l3 l4 ALLOY NUMBER US. Patent Dec. 30, 1975 Sheet4 01-4 3,929,518

6 @8755: wmxoom IICD HARDENING TEMPERATURE (C) FIG.8

TEMPERING TEMPERATURE HIGHSPEED STEEL HAVING HIGH WEAR RESISTANCE BACKGROUND OF THE INVENTION 1. Field of the Invention r This invention relates to a high speed steel having high wear resistance, and more particularly to a high speed steel, wherein carbides of vanadium and niobium and cementite (Fe C) are crystallized in a ferrous matrix.

2. Description of the Prior Art The wear resistance of a steel, in general, increases with the increase in the amount of MC type carbides. It is accordingly a common practice to add to a steel elements which form MC type carbides, for improving wear resistance. However, the increase in the amount of the elements which form MC type carbides, gives rise to a problemassociated with a melting operation, with the resultant difficulties in production of steels, or it may be even impossible to produce such a steel. Among typical high speed steels which have improved wear resistance due to the presence of MC type carbides, there is a steel which contains vanadium as acarbide forming element. This high speed steel essentially contains Fe and has VC dispersed in the ferrous matrix containing a carbon solid solution therein. In the interest of facilitating heat treatment, this type of high speed steel contains Cr,.Ni or the like, or the elements such as Mn, Si or the like remaining therein which is added for the purpose of removing adverse elements such as oxygen. The amount of vanadium to be added is such that the entire amount thereof combines with C to form VC. Furthermore, the amount of carbon is such as exceeding the amount required for the formation of VC, in an attempt to assist in hardening of matrix. However, such a high speed steel has tobe encountered with difficulties in melting, in the case of the amount of vanadium exceeding 7% by weight, which forms carbide. This is because, in the melting of a high speed steel containing VC which is dispersed in a ferrous matrix, vanadium of an amount exceeding a certain level follows a different type of crystallization which accompanies local aggregation of VC. More specifically, VC crystallizes as eutectic crystals in a case where V is not more than 7% by weight, while in the case of V of an amount exceeding 7% by weight, the part of V exceeding said 7% crystallizes as primary crystals. The density of VC is as low as 5.6 g/cm, as compared with the density of iron of 7.87 g/cm. However, VC crystallized as eutectic crystalls has a narrow solidifying temperature range, such that most of VC will not float to the top surface of a melt and thus remains solidified therein in a manner to disperse in an ingot uniformly, thereby presenting high wear resistance. In addition, the crystal grains thereof are substantially fine, thus presenting high mechanical strength. In contrast thereto, VC crystallizing as pri- 2 parts of the ingot, thus failing to present uniform wear resistance and mechanical strength throughout the ingot. For such reasons, it"has been considered that the content of-V of no less than 7% by weight gives harm to high speed steels.

As has been described, the wear resistance of a high speed steel primarily depends on the amount of MC type carbides formed, and the wear resistance increases with, the increase'in the amount of carbides. It follows that the ,utility of the high speed steel will be even highly evaluated, if an increased amount of VC is dispersed in an ingot and yet the crystal grains of VC which crystalizes as primary crystals are rendered finer. Meanwhile, the aforesaid high speed steel finds its application as a Sendzimir work roll which is principally used for rolling a bright annealed stainless strip. On the other hand, a limitation as to the length is imposed on a'stri'p which is rolled by the high speed steel Sendzimir work rolls without its brightness being impaired. In other words, the length of a rolled strip having uniform brightness is limited up to 750 m, and in case the strip is longer than that, then the rolls'catch on their surfaces the strip powder produced during the rolling operation, thereby causing roughened surfaces in a strip due to seizure of powder to roll surfaces. The inventors discovered that such surface roughening phenomenon may be improved with the increase in amount of carmary crystals has a wide solidifying temperature range,

bides formed.

As is already clear, the improvement in wear resistance of a high speed steel dictates the distribution of a relatively great amount of MC type carbides, and in addition, the achievement of long lasting capability of the rolls of such high speed steel to present good surface condition for the rolled strip requires uniform distribution of a relatively great amount of carbides in an ingot.

Under such circumstances, the inventors first examined the possibility of uniform distribution in an ingot, of VC which crystallizes as primary crystals. To this end, the inventors added elements which formed solid solutions with VC, whereby the density of the carbides is increased. Included by the elements which form solid solutions with VC are Ti, Nb and Ta.'Those elements form carbides of MC type by combining with or bonding to carbon, such that they can not'only prevent the More particularly, the-density of the titanium carbide is as low as 4.9 g/cm, as compared with that of vanadium carbide, thereby failing-to prevent vanadium carbide from floating in a melt. On the other hand, the density of carbide of tantalum is too great to cause the resultant solid solution of vanadium carbide and tantalum to sink to the lower part of an ingot. In contrast to this, the density of the carbide of niobium is 7.8 g/cm which approximates that of iron, such that the carbide of vanadium forming a solid solution with niobium gives a danger of neitherfloating nor sinking in a melt. Thus, niobium has proved to be effective for preventing the floating of vanadium carbide. The continued experiment, however, further reveals that carbide'of vanadium forming a solid solution with niobiumv crystallizes at a temperature higher than that of the crystallization of vanadium carbide, and as a result, the addition of niobium presents a greater amount of carbide, as compared with the mereaddition of vanadium.

In view that niobium forms carbide and the crystallization temperature is higher than that of vanadium, the addition of niobium alone was also tried. However, the primary crystals of NbC gave a large grain size, with the attendant extremely lowered toughness.

Under such circumstances, there has come to the fore the development ofa high speed steel which prevents the primary crystals of VC from floating, due to the addition of Nb, and which contains as great amount crystallized as ternary-component eutectic crystals consisting of'carbides of vanadium and niobium, 'yFe of carbides of the primary crystals of VC and Nb as a possible, as far as such carbides ;are present in the form of fine particles.

SUMMARY or THE INVENTION Object-of the Invention It is accordinglyan object of the invention to provide a novel high speed steel, in which the primary crystals of VC are uniformly dispersed throughout an ingot and which fine particles of carbides otherrthan VC are present in a great amount. v 7

It is another object of the invention to provide a high speedsteel which permits the secondary hardening due to hardening andtempering g Itis a further object of the invention to provide ahigh speed steel which may be used for Sendzimir workrolls for rolling a bright annealed stainless strip and assures the capability to maintain a smooth surface condition in rolling stripsfor a period of time twice that of the conventional rolls of this type.

r Statement of the Invention According to the present invention, there is provided a high speed'steel having high wear resistance, consisting essentially of 3.1 to 6.3% by weight of carbon, to 1.2% by weight of vanadium, 3 to 10% by weight of niobium, and the balance substantially iron, wherein all of ,vanadium and niobium reacts with carbon, 1.4 to 3 .6% by weight of carbon forms cementite and 0.1 to 0.6% by weight of carbon dissolves in a ferrous matrix ashardened.

The present invention is based on discoveries that an ingot ofia high speed steel may be produced by melting, in-which ingot there are uniformly dispersed carbides of vanadium and niobium, if 5 to 12% by weight of vanadium and 3 to 1.0% by weight of niobium are coexistent for forming carbides with carbon. More particularly, the present invention contemplates to present a relatively great amount of carbides of niobium and vanadium, thereby improving wear resistance and the capability of presenting good surface condition for a rolled strip for long period of time, when used as a roll, whiledesired mechanical strength is retained.

The highspeed steel of the present invention contains not only carbides of vanadium and niobium but also cementite (Fe c) of 1.4 to 3.6% by weightwhich consists of carbon and. iron, in a uniformly dispersed manner in an ingot. The grain size of the cementite (Fe,C) is extremely fine, whereby even if the amount of carbides is increased, there will result no appreciable decrease in mechanical strength. lt-is known in the field of various types of cast iron thatthe formation of Fe C improves the wear resistance of a steel. However, in the conventional cast iron, Fe; C ispresent in the form of binary-component eutectic crystals, having an ex-' and Fe C, and thus Fe C appearing as such ternarycomponent eutectic crystals is prevented from its grain growth due to the presence of vanadium and niobium, with the result that it remains'uniformly in a steel, with the grain size thereof being maintained in the form of fine particles. The reason why the grain size of Fe C crystals is fine is that the formation of carbides of vanadium and niobium takes place prior to the formation of Fe' -,C, and this fact has been discovered by the inventors.

With the melting production of a high speed steel according to the present invention, carbides consisting essentially ofrNb crystallizes inthe form that they dissolves asmall amount of vanadium therein. Then, carbides consisting essentially of vanadium will crystallize in the form that they dissolves asmall amount of niobiumtherein, followed by crystallization of Fe c. The carbide consisting essentially of vanadium and dissolving a small amount of niobiumtherein is lessin density than that of matrix, and hence it tends to float in a melt. However, the floating of such carbides are prevented by the carbides consisting essentially of niobium which has crystallized beforehand,such that the aforesaid carbides willbe uniformly dispersed in a matrix. The'portion of the melt, from which the carbides have crystallized, remains in the form of 'yFe, which in turn is precipitated as aFe and Fe C in the course of cooling. After solidification, ingot is heated for hardening matrix to an austenizing temperature,-followed by quenching to give the matrix of a martensite structure.

However, in the course of heating, Fe Cwhich has been precipitated from :yFe is decomposed to be dissolved in 'yFe again. The amount of carbon which has been decomposed from Fe' C- and dissolved into 'yFe increases with the increase in heating temperature.

Besthardening may be achieved, if the high speed steel of .the invention is heated to a temperature of 800 to 1,000C, preferably 900C, followed by hardening. The

amount of carbon dissolved into 'yFe, in this state, is 0.1

to 0.6% by weight. After hardening, the ductility of matrix of a martensite is raised by tempering. However, the hardnessof a high speed steel islowered by this tempering treatment, such that the tempering temperature should be-below 200C, preferably in the neighborhood. of C.

The content of vanadium according to a high speed steel of the invention should range from 5 to 12% by weight. The vanadium in this range forms VC, presenting hi'gh wear resistance. Vanadium of an amount of less than.5% by weight fails to presentdesired wear resistance. i

The formation of Fe C of a great amount leads to extremely lowered toughness. On the other hand, vanadium of an amount more than 12% by weight fails to prevent the floating of the primary crystals of carbides consisting essentially of vanadium, while most of niobium forms carbides. Although niobium is added for the dual purposes of increasing the amount of carbides and preventing the floating of the primary crystals of VC, it also serves to prevent the decrease in toughness of a steel by presentingternary-component eutectic crystals of a fine grain size. If niobium is no more than 3% by weight in amounts, niobium will not crystallize as the primary crystals, thus failing to prevent floating of VC. In case niobium is more than 10% by weight'in amounts, the grain size ofv the primary crystals of carbides consisting essentially of niobium is increased, thereby lowering the toughness of a steel. There is present an optimum ratio, in amount, of vanadium to niobium. According to experiments, the optimum ratio Nb wt% V wt% 0.5 to 1.0. Thus, as far as the ratio is maintained in this range, the primary carbide crystals will not grow, but will be dispersed in the matrix uniformly.

The weight ratio of Nb to V of no more than 0.5 still presents carbides of a finer grain size, while presenting a tendency of floating of the primary carbide crystals in a melt. On the other hand, if the ratio is no less than 1 then the grain size of the primary carbide crystals will become larger.

Carbon is added for the dual reasons, i.e., for forming carbides and for hardening matirx. For formation of VC containing l% by weight of vanadium, the addition of 0.24% by weight of carbon is required, while for the formation of NbC containing 1% by weight of niobium, the addition of 0.13% by weight of carbon is required. It follows then that for bonding carbon to the entire amount of vanadium and niobium, the addition of 1.6 to 4.2% by weight of carbon is required in total. Meanwhile, according to the present invention, the amount of cabides may be increased without impairing the mechanical strength of a steel by crystallizing eutectic crystals, Fe C, in a fine grain form. In this respect, the eutectic crystals, Fe C, should crystallize as ternarycomponent eutectic crystals, and for this purpose, carbon of an amount of no less than 1.4% is required. The area ratio of Fe;, C thus obtained is 20%. On the other hand, the amount of Fe C should be limited to a certain level, because if the amount of Fe C is excessive, the brittleness of a steel will increase, even if Fe C is present in the form of a fine grain size. Specifically, the amount of Fe C should be maintained below 50% in terms of area ratio. For this reason, the amount of carbon required for the formation of Fe C should be below 3.6% by weight, inclusive. Accordingly, the total amount of carbon required for formation of carbides will be 3.0 to 7.8% by weight. On the other hand, since 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrix in a hardened condition, the total amount of carbon required will be further increased. However, if the amount of carbon is excessive and hence the excessive amount of carbides is formed, then there will result difficulties with the melting operation, such that an ordinary type high frequency induction furnace no longer finds its application in melting such materials. Experiments reveal that for heating and melting according to a high frequency induction furnace, the amount of carbon should be no more than 6.3% by weight. The carbides of vanadium of 5 to 12% by weight occupies 8.2 to 19.7% in terms of area ratio, while the carbides of niobium of 3 to by weight occupies about 3.4 to l 1.4% in terms of area ratio. As the amount of MC type carbides increases, the wear resistance of a steel increases, and as a result, the excellent wear resistance may be obtained at an area ratio of over 15%. On the other hand, in case the area ratio of Fe C is over and yet in case the sum of the area ratio of Fe C and that of the aforesaid MC type carbides is over then the capability of maintaining good surface condition of a strip will be materially enhanced.

The high speed steel according to the present invention may contain Mn, Si, P and S as impurities. The

amounts ofMn and Si of below 2% by weight, respectively, are allowable, because they serve as deoxidizers, while the amounts of P and S of below 0.020% by weight, respectively, are allowable. Furthermore, the high speed steel of the invention may contain Ni, Cr, Mo, W and Co, for improving hardenability and tempering resistance. The content of Ni should be no more than 2% by weight, Crshould range from 2 to 6% by weight, Mo from 1 to 6% by weight, W from 1 to 6% by weight and Co below 10% by weight. The aforesaid ranges of these elements are based on the following:

Nickel may dissolve into a matrix to improve the harnenability of a steel. However, Ni of an amount of over 2% by weight softens the matrix. Chromium may dissolve in a matrix upon hardening treatment to improve hardenability, but loses such effect, unless the amount thereof exceeds 2% by weight. If the amount of chromium exceeds 6% by weight, it presents a large grain size of casting structure. Part of molybdenum dissolves into a matrix to better hardenability, while enhancing the secondary hardening characteristic due to tempering, and tempering resistance. For this purpose, the amount of molybdenum should be no less than 1% by weight. Molybdenum of an amount exceeding 6% by weight lowers toughness. Tungsten serves a function similar to that of molybdenum, such that it may be used in place of molybdenum. The amount of tungsten to be added is likewise from 1 to 6% by weight. The only difference of tungstenfrom molybdenum is that the former widens an optimum hardening and tempering temperature ranges. Accordingly, the both elements should be combines in the practical application. Cobalt enhances the tempering resistance, and it should be contained in an amount of below 10% by weight. The further continued experiments made by the inventors reveal the advantage of the combined use of three types of elements of Cr, Mo and W asalloy elements. More specifically, when the aforesaid three types of elements are contained in a high speed steel of the invention in the aforesaid ranges, there will be achieved the secondary hardening, when tempered at a temperature of 450 to 550C. Another discovery is that, upon rolling of a bright annealed stainless strip by using Sendzimir work rolls, the carbides of an area ratio of over 35% may present the capability of maintaining smooth surface condition for a period of time twice that of the conventional roll.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing wear amounts of high speed steel samples used for wear tests according to experiments of the invention;

FIG. 2 is a graph showing rupture loads measured in bending tests;

FIG. 3 is a plot illustrating the relationship of hardness and hardening temperature for high speed steel samples;

FIG 4 is a plot showing the relationship of hardness and tempering temperature;

FIG. 5 is a graph showing rupture loads measured in bending tests for high speed steel samples according to another type of embodiment;

FIG. 6 is a graph showing results of wear tests;

FIG. 7 is a plot showing the relationship of hardness and hardening temperature; and

FIG. 8 is a plot showing the relationship of hardness and tempering temperature.

' EXAMPLES Table 1 shows chemical compositions of high speed steels used in the various experiments of the invention, coupled with area ratios of carbides calculatedv from the aforesaid chemical compositions plus hardness obtained when subjected to hardening treatment including oil quenching from 900C, followed by-tempering at 150C. Among samples, No. 1 designates a conventional high speed steel, Nos. 2 and 3 and Nos. and 1 1 represent those presented for comparison purpose with samples of steels of the invention, and Nos. 4 to 9 represent high speed steels according to the present invention. Those steels were prepared by melting in air atmosphere in a high frequency induction furnace, after which'they were cast in metallic molds having 60 mm d). Then, various samples were cut from the center portions of ingots, respectively.

In passing, the amounts of P and S fall in a range from 0.010 to 0.020% byweight, respectively.

Table 1 Chemical composition (wt%) Area ratio of carbide wear resistance and mechanical strength, but suffered from a danger of causing surface roughness, because of smaller area ratio of Fe C. The relationship of temperature to hardness in hardening treatment was obtained as to Nos. 5, 8 and 10. FIG. 3 shows the results thereof, presenting Rockwell hardness (I-I C) as an ordinate and hardening temperature as abscissa. In either sample, a high hardness was obtained at the hardening temperature of 800 to 1,000C. Particularly, there was obtained the highest hardness at 900C. FIG. 4 shows the relationship of the tempering temperature to hardness, by using samples'which were tempered, after oil quenching from a temperature of 900C. In either sample, the hardness decreases with the increase in tempering temperature.

As has been described earlier, the-addition of an element selected from Cr, Mo, W, Co and Ni to the high speed steel of the invention presents better hardenability. The effect of the elements added is particularly prominent, when Cr, Mo and W are added in Hardness after Special type heat treatment No. C Si Mn V Nb carbide Fe,C Total (H C) 1 3.98 0.17 0.63 6.34 10 32 42 67.0 2 4.89 0.16 0.71 2.83 5.67 11 47 58 67.5 3 3.57 0.20 0.55 7.50 5.78 18 10 28 67.5 4 3.65 0.19 0.58 5.04 5.12 l4 22 37 I 67.0 5 5.07 0.19 0.50 5.25 5.31 15 42 57 68.0 6 4.67 0.19 0.74 7.32 5.41 18 28 46 68.0 7 5.48 0.17 0.70 7.31 5.75 19 39 58 69.0 8 .4.74 0.20' 0.64 9.51 5.39 22 21 43 70.0 9 5.81 0.l8 0.61 9.65 9.26 26 29 70.5 10 5.27 0.19 s 0.70 10.58 9.00 28 17 45 70.5 11 4.40 0.18 0.68 11.34 8.94 29 3 32 69.0

combination. This .presents thesecondary hardening due to tempering treatment. For thistest, high speed steel samples having compositions as shown in FIG. 2 were prepared in the same manner as has been described, and tested for rupture loads in bending tests and wear amounts and for the relationship of hardening and tempering temperature to, hardness. In passing, the amountsof S and P in the respective sample ranged from 0.010 to 0.020% by weight,.respectively.

Table 2 Area Chemical composition (wt%) ratio of v entire carbides No. Mn Cr Mo Nb lent wear resistance. This test reveals that the wear resistance increases with the increase in the area ratio of MC type carbides which consist of V, Nb and C.

This test was then followed by bending tests for measuring ru'ptureloads. The bending test was carried out by placing bar shaped samples of 2 mm X 22 mm on tools spaced 12 mm apart from each other. Then, loads were applied from above on the bar shaped samples for bending same until they were broken. FIG. 2 shows rupture loads of the samples used. The high speed steels according to the present invention presented high rupture loads, despite a greater total amount of carbides, presenting excellent high wear resistance and mechanical strength. Nos. 10 and 11 showed excellent FIG. 5 shows rupture loads obtained in bending tests which were carried out in the same manner as has been described. The rupture loads were increased by about 30 lcg/mm due to the addition of Cr, Mo, W. These values are apparently higher than any one of values given in Table 1. FIG. 6 shows the wear amounts obtained in the wear tests, while FIG. 7 shows the rela-.

optimum hardening temperature is proved to be in the range from 800 to 1,000C, preferably 900C. FIG. 8 shows the relationship of tempering temperature to hardness of the samples which were subjected to tempering after oil quenching from 1,000C. It should be noted by referring to FIG. 8 that there takes place the secondary hardening by using tempering at 450 to 550C.

As is apparent from the foregoing description, the high speed steels according to the present invention present extremely high wear resistance and excellent mechanical strength.

The high speed steels according to the present invention are adapted for use in a Sendzimir work rolls for rolling bright annealed stainless strip. In this respect, the length of strip which can be continuously rolled without causing surface roughness was"1,500 m. This value corresponds to about twice the length of conventional high speed steel containing less than 7% by weight of vanadium.

We claim:

1. A high speed steel having high wear resistance consisting essentially of 3.1 to 6.3% by weight of carbon, to 12% by weight of vanadium, 3 to 10% by weight of niobium, and the balance essentially iron, wherein all of vanadium and niobium is combined with carbon, 1.4 to 3.6% by weight of carbon forms cementite in the form of ternary-component eutectic crystals of carbides of vanadium and niobium, 'yFe and Fe C and 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from 0.5 to 1.

2. A high speed steel according to claim 1, wherein the area ratio of carbides of vanadium and niobium and cementite is more than 35%.

3. A high speed steel according to claim 1, wherein said ferrous matrix is a martensite matrix.

4. A high speed steel according to claim 3, wherein the area ratio of carbides of vanadium and niobium and cementite is more than 35%.

5. A high speed steel which consists essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, 2 to 6% by weight of chromium, 1 to 6% by weight of molybde' num, l to 6% by weight of tungsten, and the balance essentially iron, substantially all of vanadium and niobium being combined with carbon, 1.4 to 3.6% by weight of carbon forming cementite in the form of ternary -component eutectic crystals of carbides of vanadium and niobium, 'yFe and Fe C and 0.1 to 0.6% by weight of carbon being dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from 0.5 to l.

6. A high speed steel according to claim 5, wherein the area ratio of carbides of vanadium and niobium and cementite is more than 35%.

7. A high speed steel according to claim 5, wherein said ferrous matrix is a martensite matrix.

8. A high speed steel consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, up to 2% by weight of silicon, up to 2% by weight of manganese, and the balance essentially iron, wherein all of vanadium and niobium is combined with carbon, 1.4 to 3.6% by weight of carbon forms cementite in the form of ternary -component eutectic crystals of carbides of vanadium and niobium, 'yFe and Fe C and 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from 0.5 to 1.

9. A high speed steel according to claim 8, wherein said ferrous matrix is a martensite matrix.

10. A high speed steel consisting essentially of 3.1 to 6.3% by weightof carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, up to 2% by weight of nickel, 2 to 6% by weight of chromium, 1 to 6% by weight of molybdenum, l to 6% by weight of tungsten, up to 10% by weight of cobalt, up to 2% by weight of silicon, up to 2% by weight of manganese, and tha balance essentially iron, wherein all of vanadium and niobium'is combined with carbon, 1.4 to 3.6% by weight of carbon forms cementite in the form of ternary-component eutectic crystals of carbides of vanadium and niobium, 71% and Fe C and 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from0.5 to l.

l l. A high speed steel according to claim 10, wherein said ferrous m'atrix'is a martensite matrix.

Claims

1. A HIGH SPEED STEEL HAVING HIGH WEAR RESISTANCE CONSISTING ESSENTIALLY OF 3.1 TO 6.3% BY WEIGHT OF CARBON, 5 TO 12% BY WEIGHT OF VANADIUM, 3 TO 10% BY WEIGHT OF NIOBIUM, AND THE BALANCE ESSENTIALLY IRON, WHEREIN ALL OF VANADIUM AND NIOBIUM IS COMBINED WITH CARBON, 1.4 TO 3.6% BY WEIGHT OF CARBON FORMS CEMENTITE IN THE FORM OF TERNARY-COMPONENT EUTECTIC CRYSTALS OF CARBIDES OF VANADIUM AND NIOBIUM, YFE AND FE3C AND 0.1 TO 0.6% BY WEIGHT OF CARBON IS DISSOLVED IN A FERROUS MATRIX AS HARDENED AND WHEREIN THE WEIGHT RATIO OF NIOBIUM TO VANADIUM IS FROM 0.5 TO 1.

5. A high speed steel which consists essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, 2 to 6% by weight of chromium, 1 to 6% by weight of molybdenum, 1 to 6% by weight of tungsten, and the balance essentially iron, substantially all of vanadium and niobium being combined with carbon, 1.4 to 3.6% by weight of carbon forming cementite in the form of ternary -component eutectic crystals of carbides of vanadium and niobium, gamma Fe and Fe3C and 0.1 to 0.6% by weight of carbon being dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from 0.5 to 1.

8. A high speed steel consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, up to 2% by weight of silicon, up to 2% by weight of manganese, and the balance essentially iron, wherein all of vanadium and niobium is combined with carbon, 1.4 to 3.6% by weight of carbon forms cementite in the form of ternary -component eutectic crystals of carbides of vanadium and niobium, gamma Fe and Fe3C and 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from 0.5 to 1.

10. A high speed steel consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, up to 2% by weight of nickel, 2 to 6% by weight of chromium, 1 to 6% by weight of molybdenum, 1 to 6% by weight of tungsten, up to 10% by weight of cobalt, up to 2% by weight of silicon, up to 2% by weight of manganese, and tha balance essentially iron, wherein all of vanadium and niobium is combined with carbon, 1.4 to 3.6% by weight of carbon forms cementite in the form of ternary-component eutectic crystals of carbides of vanadium and niobium, gamma Fe and Fe3C and 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrix as hardened and wherein the weight ratio of niobium to vanadium is from 0.5 to 1.

11. A high speed steel according to claim 10, wherein said ferrous matrix is a martensite matrix.