IE52094B1 - Steel-hard carbide macrostructured tools,compositions and methods of forming - Google Patents

Abstract

Composition of matter composed of 33 to 80 weight per cent of a carbide material having a particle size greater than 400 mesh, and 23 to 70 weight per cent of a metallic matrix material, the carbide material which may be a cemented composite (30), being embedded in and bonded to said metallic matrix material (25) by powder metallurgical techniques of compaction and high temperature and high pressure diffusion bonding; and tools having a cemented carbide wear or cutting element (30), these tools also being formed by powder metallurgy techniques.

Description

Since 1940, wear-resistant parts for wear-prone tools and equipment have been made of cemented carbide alloys consisting of a finely-dispersed hard-carbide phase based on metals chosen from Groups IVB, VB AND VIB of the Periodic Table, cemented by cobalt or nickel or both.

Produced by compacting finely-milled powders followed by liquid-phase sintering to achieve consolidation, cemented carbide alloys possess micro-structures characterized by hard carbide grains generally in the 1 to 15 micron range.

The use of iron or steel as binder materials has proven difficult because the finely-divided state and high specific surface of the dispersed hard phases promote the ........ formation of comparatively brittle binary interstitial Etlloys of tungsten and iron with carbon, thus reducing the free binder volume fraction and embrittling the sintered body, more or less, depending on the precision maintained ' in- the formulation and sintering parameters and on the free carbon additions made to satisfy the affinity between iron and carbon.

Unlike cobalt and nickel, iron forms a stable carbide, ΡββΟ, and has a greater tendency to form brittle binary carbides than cobalt or nickel binder materials. Carbon transfer from the hard carbide phase or phases to iron is promoted by the presence of the liquid or plastic state of an iron or steel binder during liquid-stage sintering, carried out at temperatures near to, at, or above the melting point of the binder.

More recently, useful wear parts have been made by casting a liquid steel or cast iron melt into a prepared bed of comparatively coarse particulate, e.g. 3.175 to 4.763 mm sintered, cemented carbide.

CH-A-215 453 discloses a composition of matter comprising at least 80% of a carbide material selected from the group consisting of tungsten carbide and mixtures 10 of tungsten carbide with other carbides such as titanium carbide, tantalum carbide, niobium carbide or vanadium carbide, and 20% maximum of an auxiliary metal such as cobalt, nickel and/or iron. Besides, said reference is concerned with cemented carbide tools consisting of a base I-5 of sintered alloy such as nickel-iron, iron-chromiumtungsten alloy or molybdenum alloy.

GB-A-530 639 teaches a process of producing tools having supporting bodies provided with insets of hard metal with the insets being molded from a powdered mixture 20 of carbides, borides, nitrides, and the like of a metal of the tungsten group, and of a binding metal which preferably consists of the same metal of which the supporting body is made, namely iron, steel, and other metals of the iron group.

The present invention may be distinguished from the molten-steel casting method of Charles S. Baum, US-A-Nos. 4,024,902 and 4,140,170 and the molten-cast iron method of Sven Karl Gustav Ekemar in OS-A-4,119,459 by two main factors: (1) a powder compact of steel or iron and graphite containing dispersed particulates or sintered, cemented carbide, or a number of pieces of dimensioned sintered cemented carbide, or primary, unmilled macrocrystalline carbide crystals is sintered at a temperature below the melting temperature of steel or cast iron, and (2) in place of the use of matrix-alloy melting temperatures to achieve alloy densifieation, high compaction unit pressures, both before and after sintering, are used, thereby avoiding degradation of the dispersed hard phase particle surfaces by decompostion, melting or carbon diffusion reactions.

Foundry methods, also, lack the well-known economic advantages inherent in powder metallurgy methods, notably, when a multiplicity of wear parts either small or of thin section are to be made. Also, because of the necessarily relatively high processing temperatures and liquidity, excessive amounts of unwanted binary carbides may form despite the use of comparatively coarse, low-surface area carbide particles.

Since both the conventional powder metallurgy method S2084 of pressing and sintering finely-milled steel-cemented carbide powders and methods involving casting liquid steel or liquid cast iron into particulate cemented carbide prearranged in molds result in problems hereinbefore described, it is the primary objective of this invention to develop a method by which a steel-cemented hard carbide alloy can be fabricated essentially free of binary interstitial alloys of iron and tungsten with carbon and in which the dispersed hard carbide phase is free of boundary-area decomposition, melting or thermal cracking and is firmly bound in a steel matrix essentially free of macroporosity.

It is also an object of this invention to produce a composite wear resistant body having dispersed hard carbide material firmly and adherently bonded in a metallic matrix by powder metallurgical techniques of compaction and high temperature and high pressure diffusion bonding as well as to provide a method for manufacturing said composite wear resistant body.

It is a further object of this invention to manufacture tools having hard carbide wear or cutting inserts embedded in and bonded to a consolidated steel powder matrix or composite wear resistant body according to this invention.

It is a further object of this invention to manufacture parts being substantially nonmachinable and of sufficient impact resistance to make them suitable for use as security plates and padlock components.

This invention provides a solid-state sintered steel 5 hard carbide composite wear resistant body comprising: to 80 weight percent of a carbide material having a size greater than 37 pm; said carbide material selected from the group of hard carbides consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their mixtures, their solid solutions, and their cemented composites; 20 to 70 weight percent of a matrix material selected from the group consisting of steel, steel and iron, steel and copper, and steel and nickel; said carbide material embedded in and bonded to said matrix; and an interface between said carbide material and said matrix no greater than 50 microns in thickness, said interface being essentially free of brittle double carbides.

In a preferred embodiment of the invention, the said carbide material additionally has a metallic coating forming a tough and adherent bond between said carbide material and said matrix.

The method of the present invention for manufacturing 52084 the said composite wear resistant body involves blending and mixing sintered, cemented tungsten carbide particles or primarily unmilled macrocrystalline (i.e., greater than 37 um) tungsten carbide crystals with a matrix of iron and graphite powders or steel powder, cold isostatically pressing the composite in a preform mold to a desired shape, then solid-state sintering at a comparatively low temperature, specifically, at a temperature below the melting temperature of the steel, preferably, between 1038°C and 1232°C, then hot isostatically solid-state pressing (HIP) the sintered-body at a temperature well below the melting point of steel to achieve final densification. A diffusion body is formed between the hard carbide particles and the surrounding steel powder, which holds the wear-resistant hard carbide particles in place.

Furthermore, the present invention is concerned with a tool made by the same method according to the invention comprising: a working end having a hard wear resistant cemented carbide insert; a body having steel; a bond region joining said insert to said body; wherein said bond region comprises an alloy having iron and cobalt and being essentially free of brittle double carbides of iron and tungsten.

And finally, this invention is concerned with the use - 8 of said method for forming said cemented carbide tool comprising embedding a predimensioned cobalt cemented carbide insert in a predetermined location in a blend of steel forming powder; consolidating said powder around said insert to form a preform; and interdiffusing cobalt from said insert with iron from said consolidated steel forming powder adjacent the insert at a high temperature below the temperature at which the steel is at least partially liquid and, simultaneously at a high pressure, to form a metallurgical bond between said insert and said steel.

A critical factor of the present invention is highpressure densification, both cold and hot, to avoid process temperatures which produce liquidity of the steel binder phase and, thus, promote the aforementioend undesirable reactions between the steel binder material and hard dispersed phase. The technique is reinforced in this respect by the use of a hard dispersed particle or particles of low specific surface. The method also provides a significant advance in production capability for the manufacture of steel-carbide wear parts of comparatively small size or of thin section or intricate design, as compared with methods as disclosed in United States patents hereinbefore enumerated in which molten steel or molten cast iron are poured into a mold preloaded with particles or cemented carbide.

Further, both chemical control of and compositional flexibility of the matrix alloy are superior to moltenmetal casting methods. The avoidance of high processing temperatures required to melt and pour steel or cast iron provides better economy of molds, which may be reused, and matrix metals, which are not subject to pouring loss and recycle cost. The method of the present invention is well suited for the formation of parts that must withstand highly abrasive wear forces as well as impact forces. The process is ideally suited to form wear-resistant parts and cutting tools for equipment for agriculture, road and highway construction and maintenance, crushing, comminuting, excavation, and processing. Since the wear resistance of the products produced by this process is so high, so as to make them practically nonmachinable, they are also ideally suited for use as security plates in safes. This wear resistance in combination with the impact resistance of these compositions makes them also suitable for use in padlocks.

The exact nature of the present invention will become more clearly apparent upon reference to the following detailed specification taken in connection with the accompanying drawings in which: Figure 1 is a photomicrograph at 1500 magnification - 10 showing a cemented carbide particle having a cobalt binder embedded in and bonded to a consolidated steel powder matrix.

Figure 2 is a cross sectionalized and perspective 5 view of a wear plate having cemented carbide inserts embedded in and bonded to a consolidated steel powder matrix.

Figure 3 is a cross section view of part of a cutting tool having cemented carbide button embedded in and bonded to a consolidated steel powder matrix.

Prealloyed steel matrix powder, or a mixture of iron powder and graphite powder, comprising 20 weight per cent (w/o) to 70 w/o of the final mixture is blended and mixed with 30 w/o to 80 w/o of hard carbide particles of W, Ti, Ta, Nb, or Zr, V, Hf, Mo, B, Si, Cr or a mixture of these, either as sintered cemented carbide particles or as primary, uncemented, unsintered, unmilled carbide crystals. About 3 percent of naphtha or other liquid hydrocarbon is added to the powder blend during mixing to prevent segregation of higher density carbide particles during mixing and mold filling, specifically when the dispersed hard phase is composed of hard carbide particles coarser than about 250 microns.

For dispersed hard phase particles finer than about 250 microns, paraffin wax or a solid lubricant such as - 11 zinc stearate may be used, because the possibility of component particle segregation during mixing is then diminished.

Next, the matrix powder containing the dispersed hard carbide phase is packed in a preform mold made of polyurethane or other elastomeric plastic. Steel powders of different chemical compositions (such as carbon, alloy or stainless steel powders) or elemental powders such as iron, copper or nickel, may also be packed in the same mold with the main composite steel powder carbide blend, in any desired location, adjacent to and in contact with the body containing the hard carbide dispersed phase, or surrounding such body, or enveloping a dimensioned, sintered cemented carbide insert. The packed mold with a suitable fitted cover is then sealed and placed in a rubber bag or balloon which is then evacuated, sealed and isostatically pressed, preferably at about 2,413.25·105 Pa, but not less than 689.5·1θ5 Pa.

The compacted powder preform is then removed from the mold and heated in vacuum or in a protective or reducing gas atmosphere, e.g., hydrogen, to a temperature below the melting temperature of the steel matrix, preferably between 1038°C and 1149°C, for between 20 and 90 minutes.

An alternative preforming method consists of packing - 12 the composite mixture containing preferably liquid hydrocarbon, e.g. naphtha, preferably 7 w/o and methyl cellulose, preferably 0.5 w/o, as pressing lubricant and green-state binder, respectively, in a steel preform mold.

The green preform is then air dried at room temperature, in the mold, then removed from the mold and placed in a rubber bag which is then evacuated and sealed, ready for cold isostatic compaction as hereinbefore described.

Compacts thus solid-state sintered retain some 10 porosity; shrinkage during sintering does not exceed 1 per cent. It has been found, however, that densification achieved by high-pressure isostatic compacting followed by sintering as herein described is sufficient to eliminate any inter-connected pore network and that the sintered bodies, therefore, qualify for effective final densification by known hot isostatic pressing (HIP) methods.

Hot isostatic pressing for the purpose of this invention is applied in an inert atmosphere, preferably at 871°C to 1260°C or at any temperature below the melting temperature of the steel for from 20 to 90 minutes at a minimum pressure of 689.5»10^Pa but, preferably at a pressure of about 1,034.25·1θ5 Pa for 60 minutes.

Equally important, an alloy layer is formed at the interfaces of cemented carbide particles and steel matrix. - 13 This interfacial alloy bond, which first forms during sintering and is later enhanced during hot isostatic pressing, consists of a thin border area between, for example, a 0.75 per cent carbon steel matrix and dispersed cobalt-cemented carbide particles in a 3.175 to 4.763 mm size range. The bond is typically less than 40 microns thick, and no greater than 50 microns thick. The interfacial bonding alloy under these conditions is composed of, principally, cobalt and iron. Bond formation becomes important especially when the hard dispersed phase is of comparatively coarse particles, because these are apt to pull out if not securely anchored in the matrix alloy.

Cemented tungsten carbide particle sizes comprising the dispersed hard phase are selected from within the general size range of 8 mm to 0.149 mm (2.5 mesh to 100 mesh in the U.S. sieve series), preferred size ranges being of from 0.84 to 1.53 mm (+20 to -12 mesh), from 1.53 to 3.36 mm (+12 to -6 mesh), and from 3.36 to 4.76 mm (+6 to -4 mesh). Specific selected size ranges may be prepared by known methods of crushing and sizing sintered, cemented carbide tool components, and which alloys are more commonly of a cobalt or nickel-cemented tungsten carbide (WC) base, sometimes containing also Tie, TaC or NbC or combinations of these hard carbides. - 14 10 An additional useful aspect in the process of the present invention is to apply a coating of an alloy or metal, preferably Corson bronze or nickel, on the surfaces of a dimensioned sintered cemented tungsten carbide insert of selected shape and size, or a number of such inserts, which are then embedded in a steel or iron-graphite matrix powder at selected locations within a preform mold before the filled mold is isostatically compacted. The corson bronze coating used may be either of the two nominal compositions shown in Table 1.

TABLE 1 Corson Bronze Compositions A 2.5 w/o Ni 0.6 w/o Si 0.25 w/o Mn Balance Cu D w/o Mn 4 w/o Co w/o Cu Following cold isostatic compaction and during subsequent sintering and hot isostatic pressing of the carbide steel compact, the coating on the cemented carbide body autogenously forms a diffusion bond, to increase the bonding strength with which dimensioned cemented carbide bodies are held in the matrix. By this method, a cemented carbide body, or a number of them, of specific shape and size may replace a dispersed hard carbide phase of - 15 particulate nature, and thereby form a wear-resistant body or a tool for cutting or drilling metal or rook.

It is recognized that the comparatively low processing temperatures employed in the process of this invention may, in cases in which steel matrix powder compositions are used which do not bond well to particles of a dispersed hard carbide phase, result in inadequate bond strength at the matrix-carbide particle interface.

In such cases, for example when alloy steel powders are used which are known to be less sinterable at the comparatively low solid-state sintering temperatures described in the process of this invention, it has been found beneficial to precoat the hard carbide particles with nickel or copper, for example, by known processes such as electroless metal coating or by vacuum vapor-phase coating. Nickel coatings thus applied to the hard carbide dispersed fraction, prior to blending, have been found to improve carbide particle bonding strength. Such precoating of the hard carbide particles would also be beneficial when stainless steel powders are being used.

A further and useful part of the foregoing method is the incorporation of a dispersed hard carbide phase in a steel or iron-graphite powder compact consisting of unmilled macrocrystalline carbide crystals in size range fractions between 0.037 and 0.250 mm (between 400 and 60 53094 - 16 mesh) and in preferred size ranges of e.g. from 0.149 to 0.250 mm (+100 to -60 mesh), from 0.074 to 0.177 mm (+200 to -80), or from 0.044 to 0.099 mm (+325 to -150 mesh), instead of and in place of particles of cemented carbide.

The method of the present invention for formulating and forming macrostructured cemented carbide compositions is exactly as heretobefore described.

The relatively low processing temperature practiced results in a macrostructure essentially free of brittle double carbides of iron and tungsten (eta phase) and gross porosity. The tendency for liquid-phase sintered, microstructured, cemented tungsten carbide alloys employing a steel binder, for example, in place of the usual cobalt binder, to develop brittle eta-type phases is well known. It is believed that the avoidance of liquid phase sintering and consequently the avoidance of carbontransfer that such practice encourages, as well as the uniquely low specific surface of the unmilled macrocrystalline carbide particles comprising the dispersed hard phase are essential for the successful formation of the two-phase, steel-carbide macrostructures produced by this method. It should be understood that liquid phase sintering as referred to herein means sintering at a temperature at which the steel binder is at least partially liquid. The prohibition of liquid phase - 17 sintering in this invention, therefore, does not apply to any lower melting point metals or alloys (e.g., copper or corson bronze) which may be added as a powder or coating to promote bonding or densifieation, and may intentionally become liquid during sintering or hot isostatic pressing.

The use of unmilled macrocrystalline hard carbide crystals as a dispersed hard phase is a preferred embodiment of the method of this invention, as an efficient means of maintaining a hard phase possessing low specific surface. It is recognized, however, that essentially binderless, hard aggregates of finer or milled hard carbides may be so used.

An important aspect of the aforementioned macrostructured bodies is the avoidance of ball milling or other comminution of the matrix-carbide powder mixtures, or of either of these two materials separately, prior to cold isostatic compaction, sintering and HIP. The former practice, widely considered essential to sound commercial cemented carbide structures, leads to enhanced reaction between carbides and iron-base matrix powders with resultant formation of brittle double carbides. Avoidance of powder milling also reduces cost.

The method of the invention may employ any of the macrocrystalline carbides, or combinations or solid solutions of them, specifically WC, Tic, TaC or NbC, all - 18 exhibiting the low specific surface and angular, blocky shapes typifying these coarsely-crystalline mono and binary carbides. Xt is known that primary macrocrystalline carbide materials may be finely milled, together with cobalt or nickel, to form cemented carbide microstructures by liquid-phase sintering in the temperature range 1316°C to 1538°C, in which the resultant dispersed hard carbide phases are typically between one micron and about ten microns. The method of the invention, in contrast, results in dispersed, single macrocrystalline carbide grains in size ranges selected from within the much coarser extremes of 250 microns to about 40 microns.

This invention is further explained by the following examples: Example No. 1 Wear resistant cutting tips were fabricated for rotary sugar cane shredding machines. A uniformly blended mixture composed of approximately 55 w/o 3.175 to 4.763 mm cobalt cemented tungsten carbide granules, approximately 44.67 w/o to less than 0.149 mm atomized iron powder and 0.33 w/o of smaller than 0.044 mm graphite powder was prepared. During blending 5 w/o of naphtha was added to minimize segregation of the higher-density cemented carbide particles. The sample mixture was manually SS094 - 19 compacted into an elastomeric polyurethane mold cavity of the desired tool shape, dimensioned to allow for cold isostatic powder compaction plus one per cent sintering shrinkage. Following cold isostatic compaction at 2,413.25·1θ5 Pa, the compacted preform was removed from the mold and vacuum sintered at 1093°C for 60 minutes following which the sintered body was isostatically pressed at 1232°Cfor 60 minutes at 1,034.25*105 Pa under helium.

Metallographic examination disclosed a matrix structure composed of mostly pearlite and a little ferrite typical of conventional slow-cooled 0.75 per cent carbon steel of low porosity. The cemented carbide-matrix interfaces were occupied by bands of a width of about 5 microns of an alloy believed to be composed of iron and cobalt, principally. The cemented carbide dispersed particles appeared unimpaired by thermal cracking and no evidence of dissolution, melting or decomposition of the dispersed carbide phase existed at or near the interfacial boundaries, such boundaries being sharp except for the aforementioned iron-cobalt alloy diffusion zone. No potentially harmful concentrations of eta phase were observed. Test bodies were manually bent over a mandrel by hammering at room temperature and found to have a high 25 resistance to impact loading and to be essentially free of - 20 brittle fracture.

Figure 1 is a photomicrograph of a typical area in a composite produced according to Example 1, except that sintering was done at 1149°C. A cobalt cemented tungsten carbide granule 40 is shown metallurgically bonded to a plain carbon steel having a mostly pearlitic structure 50 by a diffusion zone 45 containing iron and cobalt. The diffusion zone 45 is approximately 3 microns thick.

Example No. 2 A wear-resistant, 12.9 cm2 by 0.95 cm thick plate was fabricated consisting of 60 w/o of unmilled macrocrystalline WC having a particle size of from 0.149 to 0.250 m (+100 to -60 mesh) and being cemented by 40 w/o of 0.75 per cent C steel containing 2 w/o Cu. A uniformly dry blended mixture of macrocrystalline WC crystals having a particle size of form 0.149 to 0.250 mm (+100 to -60 mesh), graphite powder having a particle size of less than 0.044 mm (-325 mesh), iron powder of less than 0.149 mm (-100 mesh), and copper powder of less than 0.044 mm (-325 mesh) were dry blended, unmilled, to a uniform mixture, then dampended by blending with liquid naphtha and methyl cellulose equal, respectively, to 7 per cent and 0.5 w/o of the dry mixture, and then packed into a steel preform mold to a firm, green, plate shape of - 21 dimensions equal to approximately 102 per cent of the desired final dimension.

Following air drying in the mold at room temperature, the compact was removed from the mold, placed in a rubber 5 bag and further processed by cold isostatic compaction, sintering and HIP as described in Example No. 1. Metallographic examination revealed a macrostructure of macrocrystalline WC evenly dispersed throughout a steel matrix. A 5 micron thick bond layer of unknown composition was observed at WC-steel interfaces.

These interfaces were free of brittle binary carbide phases and cracks.

Example No. 3 A composite 38.1 mm cubic wear-resistant body of 15 steel enclosing a dimensioned plate of sintered, cemented w/o cobalt-tungsten carbide was fabricated, purposefully embedding the dimensioned plate of sintered, cemented carbide in the green powder prior to iso-compaction so that its outer surface was flush with the outer surface of the steel cube. A dry unmilled blend comprised of 97.25 w/o to less than 0,149 mm (-100 mesh) atomized iron powder, 2 w/o less than 0.044 mm (-325 mesh) Cu powder and 0.75 w/o graphite was made, then blended with naphtha and methyl cellulose equal to, respectively, 5 w/o and 0.3 w/o of the dry blend. This was then packed into an 53094 - 22 elastomeric mold following which a 25.4 mm square by 6.35 mm thick plate of sintered cemented carbide was pressed down into the iron powder mix so that the outer surfaces were congruent, The mold, after sealing, was placed in a rubber bag, evacuated, sealed and at this point was isostatically compacted, removed from the mold, sintered and hot isostatically compacted as in Example No. 1.

Metallographic examination revealed that the prepositioned sintered carbide plate was bonded by a 5 micron interfacial bond phase to the steel matrix surrounding it on three sides and that the entire structure appeared sound and free of cracks.

Figure 2 presents a description of a wear plate 20 manufactured in the manner described in this example, except that three rather than one cemented carbide inserts 30 are embedded in the plate 20 such that a surface 45 of each insert 30 is substantially flush with the working end 40 of the tool 20. It will be noted that the interfacial bond 35 forms a tough and adherent bond between the cemented carbide and the consolidated carbon steel and copper matrix 25.

In certain wear applications, depending on the corrosion nature of the environment in which the wear plate will be used, stainless steel or alloy steel powders - 23 may be advantageously substituted for the iron, carbon and copper powders utilized in this example.

Figure 3 provides a cross sectional view of another embodiment of a tool according to the present invention.

This tool 1 can be manufactured substantially as described in Example 3, except that the cemented carbide insert 5 is allowed to have its working end 2 extend outward and beyond the steel body 10 of tool 1. As shown in this figure, the insert 5 bonded to the steel body 10 by a diffusion zone 15 which was formed by the interdiffusion of cobalt from the insert 5 and iron from the steel body 10 during high temperature and high pressure sintering operations.

Modifications may be made within the scope of the appended claims.

Claims (20)

1. A solid-state sintered steel hard carbide composite wear resistant body comprising: 30 to 80 weight percent of a carbide material having a size greater than 37 tim;

2. Body according to Claim 1 wherein said interface has a thickness of 0 to 40 um. 20

3. Body according to Claim 1 wherein said carbide material is a cemented composite having a cobalt binder; and said interface has iron and cobalt and a thickness of 0 to 40 um.

4. Body according to Claim 3 wherein said cemented 25 composite contains tungsten carbide. 53094 - 25 5. Body according to Claim 1 wherein said hard carbide is tungsten carbide.

5. 70 weight percent of a matrix material selected from the group consisting of steel, steel and iron, steel and copper, and steel and nickel; consolidating said steel forming powder around said predimensioned insert to form a preform, solid-state sintering said preform at a 5 free of brittle double carbides of iron and tungsten. 5 comprising: a working end having a hard wear resistant cobalt cemented carbide insert; a body having steel; said insert powder metallurgically bonded to said body by a diffusion zone formed during high temperature solidstate sintering below the melting point of said steel; and 5 carbide, silicon carbide, their mixtures, their solid solutions and their cemented composites; cold pressing said mixture to produce a compacted preform; and solidstate densifying said compacted preform via a high temperature and high pressure diffusion bonding and 5 selected from the group of hard carbides consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their mixtures, their 5 said carbide material selected from the group of hard carbides consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their

6. Body according to Claim 1 wherein said body is ductile at room temperature.

7. Body according to Claims 1, 3 or 5 wherein said steel is an alloy steel.

8. Body according to Claims 1, 3 or 5 wherein said steel is a stainless steel.

9. A solid-state sintered steel hard carbide composite wear resistant body comprising: 30 to 80 weight percent of a carbide material having a size greater than 37 um and having a metallic coating: said carbide material selected from the group of hard carbides consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their mixtures, their solid solutions, and their cemented composites; 20 to 70 weight percent of a matrix material selected from the group consisting of steel, steel and iron, steel and copper, and steel and nickel; and said metallic coating forming a tough and adherent bond between said carbide materials and said matrix. 10. Temperature in the range of from 1038 to 1232°C and simultaneously at a pressure above 689.5·1θ5 pa to form a metallurgical bond between said insert and said steel. 10 steel forming powder; consolidating said powder around said insert to form a preform; and interdiffiising cobalt from said insert with iron from said consolidated steel forming powder adjacent the insert at a high temperature below the temperature at which the steel is at least 10 said diffusion zone having iron and cobalt and being essentially free of brittle double carbides of iron and tungsten. 10 sintering process comprising solid-state sintering said compacted preform at a temperature above 1038°C and below the solidus temperature of said steel to minimize interconnected porosity in the preform and then hot isostatically solid-state pressing said preform at a 10 solid solutions, and their cemented composites; 20 to 70 weight percent of a matrix material selected from the group consisting of steel, steel and iron, steel and copper, and steel and nickel; wherein said carbide material is embedded in and bonded to said matrix by

10. Body according to Claim 9 wherein said steel is selected from the group consisting of alloy steels and - 26 stainless steels. 10 mixtures, their solid solutions, and their cemented composites? 20 to 70 weight percent of a matrix material selected from the group consisting of steel, steel and iron, steel and copper, and steel and nickel; said carbide material embedded in and bonded to said matrix;

11. A body according to any one of claims 1 to 10 comprising: 30 to 80 weight percent of a carbide material having a size greater than 37 |im; said carbide material

12. A method for manufacturing the steel hard carbide composite wear resistant bodies according to any one of claims 1 to 8 and 11 comprising: blending 20 and 70 20 weight percent of steel forming powders with 30 to 80 weight per cent of hard carbide particles having a t particle size between 8 mm and 37 p,m to produce a mixture; said steel forming powders selected from the group consisting of iron and graphite, alloy steels and 25 stainless steels; said hard carbide particles selected - 27 from the group of hard carbide consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron

13. A method according to claim 12 for manufacturing the steel hard carbide composite wear resistant bodies according to any one of claims 9 to 11 comprising coating 20 said hard carbide particles with a metallic coating prior to said blending with said steel forming powders.

14. A tool made by the method of claim 12 or 13 comprising: a working end having a hard wear resistant cemented carbide insert; a body having steel; a bond 25 region joining said insert to said body; wherein said - 28 bond region comprises an alloy having iron and cobalt and being essentially free of brittle double carbides or iron and tungsten. 15. 20. A wear resistant body substantially as described with reference to Figure 1 and Figure 2 of the accompanying drawings. 21. A tool, according to Claims 14 to 16, substantially as described with reference to Figure 3 of the 15 partially liquid and, simultaneously at a high pressure, to form a metallurgical bond between said insert and said steel. 15 cemented carbide insert; said insert comprising 30 to 80 weight percent of a carbide material selected from the group of hard carbides consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, 20 molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their mixtures, their solid solutions and their cemented composites, and 20 to 70 weight percent of a matrix material selected from the group consisting of steel, steel and iron, steel and copper, and steel and 25 nickel; a body having steel; said insert powder 53094 - 29 metallurgically bonded to said body by a diffusion zone formed during high temperature solid-state sintering below the temperature at which the steel binder is at least partially liquid; said diffusion zone being essentially

15. A tool made by the method of claim 12 or 13 15 pressure above 689.5 ·1θ5 Pa and a temperature between 871°C and the melting temperature of the steel. 15 powder metallurgical techniques of compaction and solid state diffusion bonding. 15 and an interface between said carbide material and said matrix no greater than 50 um in thickness, said interface being essentially free of brittle double carbides.

16. A tool made by the method of claim 12 or 13 comprising: a working end having a hard wear resistant

17. Use of the method of claim 12 or 13 for forming the cemented carbide tool according to claim 14 or 15 comprising embedding a predimensioned cobalt cemented carbide insert in a predetermined location in a blend of

18. Use of the method of claim 12 or 13 for forming the cemented carbide tool and claim 16 comprising: embedding 20 a predimensioned cemented carbide insert in a predetermined location in a blend of steel forming powder; said predimensioned cemented carbide insert comprising 30 to 80 weight percent of a carbide material selected from the group of hard carbides consisting of 25 tungsten carbide, titanium carbide, tantalum carbide, S2094 - 30 niobium carbide, zirconium carbide, vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their mixtures, their solid solutions and their cemented composites, and 20 to

19. A method of manufacturing a wear resistant body, substantially as described with reference to the Examples.

20. Accompanying drawings.