US3929471A

US3929471A - High speed steel having high wear-resistance

Info

Publication number: US3929471A
Application number: US316897A
Authority: US
Inventors: Kimihiko Akahori; Masayuki Era
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1971-12-22
Filing date: 1972-12-20
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: JPS5124969B2; JPS4868414A

Abstract

A high speed steel having high wear-resistance having a ferrous matrix consisting essentially of iron and containing 0.2-0.6 wt.% combined carbon, in which said matrix has crystallized therein a carbide which is formed by the combination of 5-12 wt. % of vanadium and 3-10 wt. % of niobium with an amount of carbon just enough for combination therewith.

Description

United States Patent [1 1v Akahori et al.

[ Dec. 30, 1975 [54] HIGH SPEED STEEL HAVING HIGH WEAR-RESISTANCE [75] Inventors? Kimihiko Akahori, Katsuta;

Masayuki Era, Hitachi, both of Japan [73] Assignee: Hitachi, Ltd., Japan [22] Filed: Dec. 20, 1972 [21] Appl. No.: 316,897

[30] Foreign Application Priority Data Dec. 22, 1971 Japan 46-103687 [52] US. Cl 75/123 J; 75/123 K; 75/126 A; 75/126 C, 75/126 E; 75/128 D; 75/128 G; 148/31 [51] Int. Cl. C22C 38/12; C22C 38/24;

[58] Field of Search 75/126 E, 123 J, 123 K,

75/126 A, 126 C, 126 E, 126 F,126 H, 128 B, 128 D, 128 G, 128 V; 148/31 [56] References Cited UNITED STATES PATENTS 2,343,069 2/1944 Luerssen et a1 75/126 C OTHER PUBLICATIONS Tool Steels, Roberts et al., 1962, pp. 189-195 and 521-528.

Primary Examiner-C. Lovell Attorney, Agent, or FirmCraig & Antonelli [57] ABSTRACT A high speed steel having high wear-resistance having a ferrous matrix consisting essentially of iron and containing 0.2-O.6 wt.% combined carbon, in which said matrix has crystallized therein a carbide which is formed by the combination of 5-12 wt, of vanadium and 3-10 wt. of niobium with an amount of carbon just enough for combination therewith.

19 Claims, 7 Drawing Figures US. Patent Dec. 30, 1975 Sheet 2 of2 3,929,471

FIG. 3

FIG.

FIG. 5

FIG.

HIGH SPEED STEEL HAVING HIGH WEAR-RESISTANCE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a high speed steel having high wear-resistance and more specifically to such high speed steel which contains primary crystals of vanadium niobium carbide, and can be heat-treated.

2. Description of the Prior Art ltis known that a high speed steel containing vanadium carbide has high wear-resistance.

This high speed steel has vanadium carbide distributed in its ferrous matrix consisting essentially of iron and containing combined carbon. In the ferrous matrix are contained Cr, Ni, etc. to facilitate the heat-treatment of the steel or remain Mn, Si, etc. which are added in the process of production of the steel by melting method for the purpose of removing detrimental elements such as oxygen. However, even in such a case, iron occupies the major portion of the weight of the matrix.

Vanadium is incorporated in such an amount that it may combine with carbon to form vanadium carbide in its entire weight. Carbon is incorporated in a weight in excess of the weight required for the formation of vanadium carbide, so that it will contribute to hardening of the matrix.

This vanadium carbide-containing high speed steel is produced by the melting method or powder metallurgical' method. The melting method is employed only when it is desired to obtain high speed steels containing relatively small amounts of vanadium carbide, but the powder metallurgical method is employed irrespective of the amount of vanadium carbide to becontained in the product steels.

When the melting methodand the powder metallurgical method are compared with each other, the former is preferable over the latter, because the latter method inevitably involves the steps of mixing a previously powderized carbide with previously powderized steelforming constituents and sintering the mixture under non-oxidizing conditions, and hence is quite complicated in production process, and also because it is not adapted for the production of large articles. Nevertheless, high speed steels containing large amounts of vanadium carbide or, more practically, containing 7 or more wt. of vanadium and carbon, are not being produced by the melting method. This is because of the following reason:

Namely, in the production of a high speed steel hav- 7 vanadium carbide, that is 5.6 g/cm, is extremely smaller than that of iron, that is 7.87 g/cm", the vanadium carbide crystallized in the form of eutectic solidi- -fies without substantially floating, since its solidification temperature range is narrow, and is distributed uniformly in the ingot; Further, sincethe grain size of in the form of primary crystal. Though the density of Y the vanadium carbide is very small, the vanadium carbide disperses finely in the ingot, imparting high wearresistance to the product steel. As contrasted, the vanadium carbidecrystallizing in the form of primary crystal is so wide in its solidification temperature range that it floats before it solidifies, subsequent to crystallization, and aggromerates at the upper portion of the ingot. In addition, because of the large grain size, the vanadium carbide cannot impart a sufficient wearresistance to the product steel. Further, the vanadium carbide tends to separate from the matrix.

It will be understood that when vanadium carbide crystallizes in the form of primary crystal, the structure of the cast steel varies between the upper and lower portions, and as a result, constant mechanical properties and wear-resistance cannot be obtained.

For the foregoing reason, it has been believed rather detrimental to contain 7 wt. or more of vanadium in a vanadium carbide-containing high speed steel when said steel is produced by the melting method, and the high speed steels containing 7 wt. or more of vanadium have not been produced by the melting method.

The wear-resistance of high speed steel is determined essentially by the amount of carbides formed therein and, as a matter of course, becomes greater with the amount of carbides. Therefore, should it be possible to distribute vanadium carbide uniformly in an ingot and yet to reduce the grain size of vanadium carbide which crystallizes in the form of primary crystal, even when the amount of the vanadium carbide is increased, it would be natural that the utility value of the ingot is substantially increased.

With this idea in mind, the present inventors first conducted a study with a view to distributing over the entire region of an ingot vanadium carbide which will crystallize in the form of primary crystal and, as a practical measure, attempted to add elements which will form solid solutions with vanadium carbide.

The elements which form solid solutions with vanadium carbide, include titanium, niobium and tantalum, and these elements themselves form carbides, namely titanium carbide, niobium carbide and tantalum carbide respectively. Therefore, should it be possible to prevent floating of the primary crystal of vanadium carbide, the wear-resistance of the produced steel could be further enhanced, not only by the effect of vanadium carbide but also by the effects of the carbides of said elements.

However, in the experiments conducted by the present inventors, a satisfactory result could not be obtained from these elements, except for niobium. Namely, the experiments revealed that titanium does not have the effect of preventing floating of vanadium carbide because the density of its carbide, that is, 4.9

g/cm", is smaller than that of vanadium carbide, whilst tantalum when formed an all proportional solid solution with vanadium carbide let said solid solution fall to the bottom of the steel ingot because its carbide is too large in density, but in case of niobium, since the den sity of its carbide is 7.8 g/cm and substantially close to that of iron, the crystal of the carbide formed by the solid solution of vanadium and niobium does not float nor precipitate in any case.

Thus, it was decided to add niobium for the purpose of preventing floating of vanadium carbide. in the subsequent study, it was found that when niobium is added, a greater amount of carbide can be formed than when vanadium only is added, since the solid solution 3 of niobium and vanadium carbides crystallizes at a temperature higher than the temperature at which vanadium carbide crystallizes and, therefore, an additional amount of vanadium which can be contained in the solid solution is added in the steel.

Niobium also forms a carbide and the crystallization temperature of said carbide is higher than that of vanadium carbide. In this view, the present inventors also attempted to add only niobium. Such attempt, however, met with an unsuccessful result in which the primary crystals of niobium carbide precipitated in the form of coarse grains and the product steel was degraded extremely in respect of toughness.

Thus, it became an important subject to develop a high speed steel in which the floating of the primary vanadium carbide crystal is suppressed by the addition of niobium.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high speed steel in which primary crystals of compound carbide formed by the combination of vanadium and niobium with carbon are distributed in its ferrous matrix.

Another object of the invention is to provide a high speed steel which has primary crystals of vanadium niobium carbide distributed therein in the form of fine grains.

Still another object of the invention is to provide a high speed steel which is capable of secondary hardening by quenching and tempering.

The high speed steel of the invention is characterized in that the carbide formed by the combination of 5-l2 wt. of vanadium and 3-l0 wt. of niobium with an amount of carbon just enough for the combination therewith is crystallized in its ferrous matrix comprising iron and 0.2-0.6 wt. of combined carbon.

The high speed steel of the invention has crystallized in its ferrous matrix niobium-vanadium carbides in the form of primary crystals, which consist essentially of niobium and containing a small amount of vanadium in the form of solid solution, and when the amount of vanadium'exceeds 7 wt. has crystallized in its ferrous matrix said niobium-vanadium carbides plus vanadium-niobium carbides which consists essentially of vanadium and containing a small amount of niobium in the form of solid solution. It also has in its ferrous matrix a carbide in the form of eutectic, which consists essentially of vanadium and containing a small amount of niobium.

Niobium carbide forms coarse grains when crystallized singly, but forms fine grains when crystallized with vanadium contained therein in the form of solid solution, and, therefore, the wear-resistance of the product steel can be increased. Thus, it will be understood that it is not always necessary to combine 7 wt. or more of vanadium with carbon.

In the process of production of the high speed steel of the invention by the melting method, niobium first tends to precipitate in the form of primary crystal of niobium carbide. In this case, however, niobium does not singly combine with carbon but combines with carbon, in the form having a small amount of vanadium present therein in the form of solid solution. As may be understood from the fact that the density of niobium carbide is 7.8 glcm this niobium-vanadium carbide has a density close to that of iron and hence, is distributed over the entire region of the ingot. Then, in the event when vanadium is contained in excess of 7 wt. the excess vanadium combines with carbon in the form consisting essentially of vanadium and containing a small amount of niobium in the form of solid solution, and precipitates in the form of primary crystal of vanadium-niobium carbide. This vanadium-niobium carbide is also distributed over the entire region of the ingot because floating thereof is suppressed by the niobium-vanadium carbide consisting essentially of niobium. After the primary crystals of carbides have precipitated, vanadium carbide precipitates as an eutectic in the form containing therein in the form of solid solution the small amount of niobium which has not precipitated as primary crystal.

The present inventors found in the subsequent study that, if vanadium is contained in an amount of 5 wt. or more in the event when the amount of niobium consumed by the combination with carbon is 3-10 wt the niobium-vanadium carbide in which niobium is predominant will not become large in grain size and contribute sufficiently to the improvement in wearresistance of the steel. In the event when the amount of niobium was in excess of 10 wt. it was impossible to reduce the grain size of the niobium-vanadium carbide primary crystal.

In the present invention, carbon is necessary for forming carbides and for hardening the matrix in which said carbides are contained in the form of solid solution.

0.13 wt. of carbon per 1 wt. of niobium is necessary for the formation of niobium carbide and 0.24 wt. of carbon per 1 wt. of vanadium for the formation of vanadium carbide. Therefore, a total of 1.59 wt. of carbon is required for the combination with the minimum 3 wt. niobium and minimum 5 wt. of vanadium. The maximum amount of niobium is 10 wt.

and that of vanadium is 12 wt. and therefore, a total of 4.18 wt. of carbon is required for the combination therewith. On other hand, a certain amount of additional carbon is required for hardening the matrix, and according to the study conducted by the present inventors, 0.2-0.6 wt. of additional carbon is required for such purpose. Consequently, the total amount of carbon which is required is from 1.79 to 4.78 wt.

Niobium is substantially entirely consumed for the formation of carbide. The minimum amount of niobium, which is the amount required for causing the niobium-vanadium carbide in which niobium is predominant and a small amount of vanadium is contained in the form of solid solution, to precipitate as primary crystal and thereby for increasing the wear-resistance of the product steel, is 3 wt. However, the amount of niobium should not exceed 10 wt. because if the amount is larger than l0 wt. the primary niobiumvanadium carbide crystal will become too large in grain size, resulting in a strength reduction of the matrix and separation of the carbide from the matrix.

Vanadium is the source element for the formation of vanadium carbide which increases the wear-resistance of the matrix. The minimum amount of vanadium is 5 wt. which is the amount required for preventing the primary crystals of the niobium-rich carbide from be coming large in grain size, whilst the maximum amount thereof is 12 wt. which is the amount necessary for the primary crystal of the vanadium-rich carbide, precipitating subsequent to the precipitation of the primary crystal of niobium-rich carbide, to be restrained against floating by said primary crystal of niobium-rich carbide, in the process of production of the desired steel by the melting method. An amount in excess of 12 wt. will result in the formation of a too large amount of vanadium-rich carbide and floating of said carbide.

In the high speed steel of the invention may be contained Mn and Si which are added in the process of production for the purpose of removing detrimental elements, such as oxygen, and remain in the ferrous matrix of the steel without being removed. However, the amounts of these elements each should not be larger than 2 wt.

The high speed steel of the invention has a structure in which carbide is distributed in the ferrous matrix, in an amount of 12-30 with respect to area ratio. It will be seen that the area ratio of carbide in the steel of the invention is much larger than that in the conventional high speed steel having vanadium carbide singly contained in its matrix.

The high speed steel of the invention having the primary crystal of carbide finely distributed in the matrix thereof can be used without subjecting it to a heat treatment. However, it is desirable to subject the steelto quenching for imparting a higher wear-resistance thereto, or to tempering for imparting ductility thereto.

In order to enhance the quenching effect, at least one element selected from the group consisting of nickel, chromium, molybdenum, tungsten and coblat may be incorporated in the steel. In this case, nickel should be incorporated not more-than 2 wt. chromium in the range of 26 wt. molybdenum in the range of l-6 wt. tungsten in the range of 1-6 wt. and cobalt not more than wt. The amount to be incorporated of these elements are specified as above for the following reasons: namely, nickel forms a solid solution in the matrix and has the effect of improving the quenching property of the steel, but the incorporation of 2 wt. or more of nickel is rather detrimental and results in softening of the matrix. Chromium also forms a solid solution in the matrix at the time of quenching and facilitates the quenching, but the incorporation of chromium in excess of 6 wt. renders the structure of cast steel coarse. Molybdenum when added is partially incorporated in the matrix and has the effect of improving the quenching property of the steel and concurrently enhancing the secondary hardening property by tempering and the temper softening-resistance of the steel. However, the incorporation of not more than 1 wt. is ineffective, whilst the incorporation of more than 6 wt. provides a cause of machinability degradation of the steel. Tungsten has substantially the same effect as molybdenum and may be incorporated in substitution for molybdenum. This element similar to molybdenum is added preferably in the range of l-6 wt. The only difference from molybdenum is that 5 temper-resistance, which can be obtained when the amount of cobalt is not more than 10 wt.

In the process of further study on the high speed steel of the invention, the present inventors found that chromium, molybdenum and tungsten, when incorporated 10 concurrently, will bring about a synergistic effect.

Namely, it was found that, when the three elements, i.e. chromium, molybdenum and tungsten, are incorporated concurrently respectively in the ranges specified above, the secondary hardening of the steel can be achieved by tempering.

It was also acknowledged that, when the weight ratio of niobium in the range of 3-10 wt. to vanadium in the range of 5-12 wt. i.e., Nb/V, is from 0.6 to 1, the grains of the niobium-rich niobiumvanadium carbide,

precipitating as primary crystal, become finest.

It will be understood from the foregoing that the steel of the invention has the heat properties when the niobium to vanadium weight ratio is selected in the range specified above and further chromium, molybdenum and tungsten are incorporated respectively in the ranges also specified above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphic representation showing the result of an abrasion test conducted on a high speed steel, in

terms of relationship between the amount of wear and the carbide area ratio;

FIGS. 2 and 3 are microphotographic pictures respectively showing the structures of examples of the high speed steel according to the invention;

FIGS. 4 and 5 are microphotographic pictures respectively showing the structures of control high speed steels;

FIG. 6 is a graphic representation showing the quench hardness of the high speed steel of the invention relative to the quenching temperature; and

FIG. 7 is a graphic representation showing the temper hardenes of the steel of the invention after quenching, relative to the frequency of tempering.

DESCRIPTION OF THE PREFERRED EXAMPLES EXAMPLES In Table 1 given below are shown the chemical compositions of high vanadium series high speed steels which have heretofore been most excellent in wearresistance, the compositions of high speed steels according to the invention which contain niobium and vanadium as the main constituents, and the heat-treatment hardnesses and carbide area ratios of these steels.

Table l Chemical composition (wt. Heat- Carbide treatment area No C Cr Mo W V Nb Co hardness ratio (7:)

(HRC) No. l is a representative conventional high vanadium series high speed steel; No. 2 is a high speed steel having niobium singly incorporated therein; Nos. 3-7 are high speed steels according to the invention; and No. 8 is a high speed steel having more than 10 wt. of niobium incorporated therein.

The heat-treatment hardness is the highest hardness measured when each high speed steel was oil-cooled from a suitable temperature above 1,000C. The hardnesses measured of all high speed steels of Nos. l-8 were 65 or higher in terms of the Rockwell hardness (H C) and satisfactory.

Then, each steel was subjected to an abrasion test. The abrasion test was conducted by depressing a test piece (18 mm in diameter) of each of Nos. 1-8 steels under a load of 800 g against an emery paper adhered to a 20 cm diameter turntable rotating at the rate of 600 r.p.m., for 2 minutes and 20 seconds, and measuring the amount of wear of the test piece. FIG. 1 shows the amounts of wear of the respective test pieces in relation with the carbide area ratio. It will be understood from FIG. 1 that the amount of wear decreases with the carbide area ratio increasing, and that the rate of decrease is large when the carbide area ratio is not larger than 20 and is small when the same is larger than 20 Namely, this means that the steel is substantially not subjected to wear when the carbide area ratio exceeds 20%.

FIGS. 2 and 3 are microphotographic pictures showing the cast structures of Nos. 6 and 7 high speed steels according to the invention, and FIGS. 4 and 5 are microphotographic pictures showing the cast structures of Nos. 2 and 8 control high speed steels, respectively at the magnification of 100 times. It will be seen that Nos. 6 and 7 steels of the invention have fine carbide grains uniformly dispersed in their materixes, but No. 2 steel having niobium singly incorporated therein and No. 8 steel rich in niobium have large primary crystals of carbide grown therein. This tells that Nos. 6 and 7 steels have excellent toughness but Nos. 7 and 8 steels are poor in toughness and susceptible to rupture by low stresses. In view of the fact that the incorporation of an excessively large amount of niobium or non-incorporation of vanadium results in excessive growth the carbide primary crystals, rendering the cast structure of the product steel coarse, the present inventors conducted a further study with a view to determining the optimum amount ratio of niobium and vanadium, and found that the carbide primary crystals are prevented from growing and finely distributed in the matrix when the niobium and vanadium incorporated are at the weight ratio of 0.6-1.

Table 2 given below shows the chemical compositions of super-wear-resistant steels with the three elements, i.e. chromium, molybdenum and tungsten, incorporated therein.

Table 2 Chemical composition (wt. No. C Cr 0 W V Nb vanadium series high speed steel, that is, No. 1 steel in Table l is also shown for comparison. It will be understood from FIG. 6 that No. 1 steel increases in quench hardness with the quenching temperature increasing, and the optimum quenching temperature is 1,200C. or higher, but Nos. 9 and 10 steels according to the invention shown the maximum hardness at quenching temperatures between 1,050 and I,100C. This is extremely advantageous in increasing the efficiency of heat-treatment, and is advantageous also in that the distortion by heat-treatment can be minimized.

FIG. 7 shows the hardnesses of the steels after oilquenching from l,150C. and tempering at 550C. for 1 hour, in relation with the frequency of tempering. It will be seen that the hardness of the conventional high vanadium series high speed steel No. I is now lowered by tempering, owing to the chromium, molybdenum and tungsten incorporated therein for enhancing the quenching effect, but on the other hand, is not increased by secondary hardening. As contrasted, Nos. 9 and I0 steels of the invention had the secondary hardening induced therein by tempering and their wearresistances are further improved.

As will be understood from the foregoing description of the examples, according to the present invention steels can be obtained which have a large amount of fine carbide dispersed in its matrix and which, therefore, have wear-resistance much higher than that of the conventional high vanadium series high speed steels.

The high speed steel of the invention was used for the working rolls of a Senzimir rolling mill for the rolling of stainless steel sheets. The working rolls made of the steel of the invention were capable of rolling at 2,000 meter long stainless steel sheet and the rolled stainless steel sheet had a gloss.

We claim:

1. A high speed steel having wearresistance consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, and the balance essentially iron, wherein substantially all of vanadium and niobium are present in carbide form, wherein 0.2 to 0.6% by weight of carbon is contained in a ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to 1, and wherein the area ratio of the carbide particles is 12 to 30%.

2. A high speed steel which consists essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, and at least one of 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and l to 6% by weight tungsten, the balance being essentially iron, wherein substantially all of the vanadium and niobium are in carbide form, wherein 0.2 to 0.6% by weight of carbon is contained in a ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to l, and wherein the area ratio of the carbide particles is 12 to 30%.

3. A high speed steel according to claim 2, wherein said high speed steel contains 2 to 6% by weight chromium, l to 6% by weight molybdenum and l to 6% by weight tungsten.

4. A high speed steel consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and at least one of 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and 10 to 6% by weight tungsten, the balance being essentially iron, wherein substantially all of the vanadium and niobium are in carbide form, wherein 9 0.2 to 0.6% by weight carbon is contained in the ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to 1, and wherein the area ratio of the carbide particles is 12 to 30%.

5. A high speed steel according to claim 4, wherein said steel contains 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and l to 6% by weight tungsten.

6. A high speed steel consisting essentially of 1.79 to 4.78% by weightcarbon, to 12% by weight vanadium, 3 to by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and at least one of up to 2% by weight nickel, 2 to 6% by weight chromium, 1 to 6% by weight molybdenum, and 1 to 6% by weight tungsten, the balance being essentially iron, wherein all of the vanadium and niobium are in carbide form, wherein 0.2 to 0.6% by weight carbon is contained in a ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to l, and wherein the area ratio of the carbide particles is 12 to 30%.

7. A high speed steel according to claim 6, wherein said steel contains 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and l to 6% by weight tungsten.

8. A high speed steel having high wear resistance consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and at least one of 2 to 6% by weight chromium, l to 6% by weight molybdenum, 1 to 6% by weight tungsten, up to 2% by weight nickel and up to 10% by weight cobalt, the balance being essentially iron, said high speed steel composed of a ferrous matrix having 0.2 to 0.6% by weight combined carbon therein and carbide particles substantially uniformly distributed throughout the body of said high speed steel, substantially all of the vanadium and niobium in said high speed steel being in the form of primary carbide crystals, the weight ratio of niobium of vanadium (Nb/V) in said steel being 0.6 to 1 and the area ratio of the carbide particles in said steel being 12 to 30%.

9. A high speed steel according to claim 8, wherein said steel contains 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and 1 to 6% by weight tungsten.

10. The high speed steel of claim 8, wherein said carbide particles contain both vanadium and niobium.

11. The high speed steel of claim 10, wherein said carbide particles are composed of a mixture of niobium carbide and vanadium carbide, a portion of said carbide particles containing predominantly niobium carbide, and another portion of said carbide particles containing predominantly vanadium carbide.

12. The high speed steel of claim 8, containing 7 to 12% vanadium.

13. The high speed steel of claim 8, wherein the carbide area ratio of the steel is greater than 20%.

14. The high speed steel of claim 8, having sufficient wear resistance such that the wear on a test piece 18 mm in diameter under a load of 800 g against an emery paper adhered to a 20 cm diameter turntable rotating at a rate of 600 rpm for seconds in less than 0.02g.

15. The high speed steel of claim 14, wherein the wear resistance of the steel is such that the amount of wear is about 0.01g or less.

16. A high speed steel consisting essentially of 1.79 to 4.7 8% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and the balance essentially iron, wherein substantially all of the vanadium and niobium are in carbide form, wherein 0.2 to 0.6% by weight carbon is contained in the ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to 1, and wherein the area ratio of the carbide particles is 12 to 30%.

17. A high speed steel according to claim 16, wherein substantially all of the vanadium and niobium in said high speed steel are in the form of primary carbide crystals.

18. A high speed steel according to claim 17, wherein said carbide particles contain both vanadium and niobium.

19. A high speed steel according to claim 17, containing 7 to 12% vanadium.

Claims

1. A HIGH SPEED STEEL HAVING WEARRESISTANCE CONSISTING ESSENTIALLY OF 1.79 TO 4.78% BY WEIGHT CARBON, 5 TO 12% BY WEIGHT VANADIUM, 3 TO 10% BY WEIGHT NIOBIUM, AND THE BALANCE ESSENTIALLY IRON, WHEREIN SUBSTANTIALLY ALL OF VANDIUM AND NIOBIUM ARE PRESENT IN CARBIDE FORM, WHEREIN 0.2 TO 0.6% BY WEIGHT OF CARBON IS CONTAINED IN A FERROUS MATRIX, WHEREIN THE WEIGHT RATIO OF NIOBIUM TO VANADIUM (NB/V) IS FORM 0.6 TO 1, AND WHEREIN THE AREA RATIO OF THE CARBIDE PARTICLES IS 12 TO 30%.

2. A HIGH SPEED STEEL WHICH CONSISTS ESSENTIALLY OF 1.79 TO 4,78% BY WEIGHT CARBON, 5 TO 12% BY WEIGHT VANADIUM, 3 TO 10% BY WEIGHT NIOBIUM, AND AT LEAST ONE OF 2 TO 6% BY WEIGHT CHROMIUM, 1 TO 6% BY WEIGHT MOLYBDENUM AND 1 TO 6% BY WEIGHT TUNGSTEN, THE BALANCE BEING ESSENTIALLY IRON, WHEREIN SUBSTANTIALLY ALL OF THE VANADIUM AND NIOBIUM ARE IN CARBIDE FORM, WHEREIN 0.2 TO 0.6% BY WEIGHT OF CARBON IS CONTAINED IN A FERROUS MATRIX, WHEREIN THE WEIGHT RATIO OF NIOBIUM TO VANADIUM (NB/V) IS FROM 0.6 TO 1, AND WHEREIN THE AREA RATIO OF THE CARBIDE PARTICLES IS 12 TO 30%.

3. A high speed steel according to claim 2, wherein said high speed steel contains 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and 1 to 6% by weight tungsten.

4. A high speed steel consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and at least one of 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and 10 to 6% by weight tungsten, the balance being essentially iron, wherein substantially all of the vanadium and niobium are in carbide form, wherein 0.2 to 0.6% by weight carbon is contained in the ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to 1, and wherein the area ratio of the carbide particles is 12 to 30%.

5. A high speed steel according to claim 4, wherein said steel contains 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and 1 to 6% by weight tungsten.

6. A high speed steel consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and at least one of up to 2% by weight nickel, 2 to 6% by weight chromium, 1 to 6% by weight molybdenum, and 1 to 6% by weight tungsten, the balance being essentially iron, wherein all of the vanadium and niobium are in carbide form, wherein 0.2 to 0.6% by weight carbon is contained in a ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to 1, and wherein the area ratio of the carbide particles is 12 to 30%.

7. A high speed steel according to claim 6, wherein said steel contains 2 to 6% by weight chromium, 1 to 6% by weight molybdenum and 1 to 6% by weight tungsten.

8. A high speed steel having high wear resistance consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and at least one of 2 to 6% by weight chromium, 1 to 6% by weight molybdenum, 1 to 6% by weight tungsten, up to 2% by weight nickel and up to 10% by weight cobalt, the balance being essentially iron, said high speed steel composed of a ferrous matrix having 0.2 to 0.6% by weight combined carbon therein and carbide particles substantially uniformly distributed throughout the body of said high speed steel, substantially all of the vanadium and niobium in said high speed steel being in the form of primary carbide crystals, the weight ratio of niobium of vanadium (Nb/V) in said steel being 0.6 to 1 and the area ratio of the carbide particles in said steel being 12 to 30%.

12. The high speed steel of claim 8, containing 7 to 12% vanadium.

14. The high speed steel of claim 8, having sufficient wear resistance such that the wear on a test piece 18 mm in diameter under a load of 800 g against an emery paper adhered to a 20 cm diameter turntable rotating at a rate of 600 rpm for 140 seconds in less than 0.02g.

16. A high speed steel consisting essentially of 1.79 to 4.78% by weight carbon, 5 to 12% by weight vanadium, 3 to 10% by weight niobium, up to 2% by weight silicon, up to 2% by weight manganese, and the balance essentially iron, wherein substantially all of the vanadium and niobium are in carbide form, wherein 0.2 to 0.6% by weight carbon is contained in the ferrous matrix, wherein the weight ratio of niobium to vanadium (Nb/V) is from 0.6 to 1, and wherein the area ratio of the carbide particles is 12 to 30%.

19. A high speed steel according to claim 17, containing 7 to 12% vanadium.