DE2221875A1 - SURFACE-HARDENED AND Sintered CARBIDE SHAPED ARTICLE - Google Patents

Description

DR R. POSCHENRIEDER _{Dr B} ^

DR E. BOETTNEB _t . _dl ., ^

DIPL iNG.H.-J. MÜLLER ^ _{Ε11β 129} 6

Patent attorneys

MUNICH 80 '9 9? 187 ζ

T «cüe-Giabn-Strasse 3 *> Z £ Z I O / P

Telephone 475155

CHROMALLOY AMERIOAHr GOEPOHATIOIi, 4430 Director Drive San Antonio / Texas, "(V.St« A *)

Surface-bonded and sintered carbide molded article

The invention relates to a sintered refractory metal carbide shaped body and in particular a cemented carbide preparation, in which the grains from the refractory metal carbide are dispersed on the surface of the body by a borided layer of the matrix, which by the presence of an iron group metal boride such as iron boride is characterized.

Sintered composite metal molded articles are known from a powder mixture of a refractory metal carbide and metal powder by compressing the powder mixture in a standard to form a molded body of the desired shape and sintering the molded body at increased Temperature under non-oxidizing conditions, the compressed particles being sintered together / a dense Structure are brought to produce.

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. In the case of the use of refractory carbide hard metals, most of which are made of titanium, tungsten and / or carbides other refractory carbides are made by sintering Cemented into the matrix metal in the liquid phase, the favorable properties are largely revealed the rather high hardness peculiar to carbides in combination with the pestilence effects of the binding metal traced back. The term "primary carbide grains" denotes the grains or particles of refractory carbide immediately added to the preparation during its formation and which essentially retain their identity in the finished composition, compared to the secondary carbide grains that are formed by reaction during heat treatment.

In recent years, a machinable refractory carbide body has become the primary titanium carbide grains which are dispersed in a heat treatable steel matrix, the primary Hardening effects inherent in carbide with hardenability combined with the steel matrix. The machinable carbide body has over conventional sintered Carbides have an advantage, which consists in the fact that the matrix of a preparation which is about 50 volume »- $ titanium carbide and as Reat essentially contains steel, can be increased by tempering in such a way that the total hardness of the Preparation to:. For example 40 Ro can be lowered so that the body is mechanically converted into a desired Porm can be brought and thereafter up to about 72 Rc by quenching the alloy from elevated temperature similarly as is done with ventilated tool steel alloys, is hardened.

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In the manufacture of refractory carbide preparations of the type mentioned with a matrix consisting of a heat-treatable or non-heat treatable metal refractory carbide powder, such as titanium carbide, is mixed with finely divided steel-forming components and the mixture is then brought into the desired dimensions in a mold and the resulting compact ierte molded body sintering in the liquid phase by heating to a temperature above the lowest But subjected to the melting phase of the matrix metal below the melting point of the refractory carbide.

It has been found that the sintering takes place in the liquid phase is advantageous for its intended purposes, since dense products which are essentially non-porous can be obtained are. The above-described type of compound Metals has many different uses Found use, such as in molding tools, nozzle tips, abrasion-resistant parts, measuring gauges, machine parts and the same.

When using such refractory carbide preparations in the manufacture of various tools or machine parts, it is sometimes useful to the metallurgical properties of the matrix metal modify it to meet the specific requirements intended for a particular tool Intended use are given · If for example a composition which is to .45 volume * - ^ from Titanium carbide in a matrix made of stainless steel

the composition is dispersed, the 55 volumrfS / ausmaohii, a ± s part of a If a pump is used which is exposed to sliding friction at elevated temperature, preferential wear occurs in the matrix metal between the carbide grains

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on »This composition has an average hardness near about 45 Rc. Since stainless steel is the Grade 18/8 is essentially not heat-treatable, lies in the hardness peculiar to the steel significantly below the actual hardness of the carbide. Therefore, if a machine part made of this material is a Is exposed to sliding friction at elevated temperature, the soft matrix material is preferably all around the carbide grains are removed. The primary carbide grains create wear resistance themselves, but only do so if they are firmly in the matrix metal are embedded and anchored. However, as the matrix metal wears away selectively around the grains or is for-eroded, the grains tend to loosen and fall out. Such a preferred one Wear and tear has its drawbacks because it can lead to a surface indentation effect occurs, which lowers the strength of the metal against impact ^ stress. It would therefore be desirable when the matrix is to retain a high degree of hardness on the surface of the machine part, to avoid the difficulties mentioned.

In the case of a preparation that can be treated with heat, for example a preparation consisting of about 50 volume ^ titanium carbide and the remainder 50 volume ^ steel with composed of low chromium and low molybdenum content it may be desirable to have said composition of a hardness of about 70 Rc to bring a hardness of about 50 - 55 Rc by tempering, for example in the case of a drawing tool. It would However, it is essential to ensure that there is a hard, abrasion-resistant surface on the neck or opening of the tool

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Surface is ensured, especially between the hard grains of primary carbide that are in the matrix are embedded. It would therefore be desirable to have a hardened surface between the carbide grains to create to anchor these grains in place to prevent preferential erosion occurs away from the matrix and prevent displacement of carbide particles.

The hardened surface should be such that it has the lowest possible coefficient of friction has while it is supposed to have an optimal hardness in addition to anchoring the primary grains from the refractory metal carbides.

The process of surface hardening, however, should be such that is able not only to harden Stahloberfläohe but also other alloys of matrix metals from the iron group _t as matrix metals on the Baeis of liokel and cobalt. For example, it would be useful to create a preparation of tungsten carbide and cobalt in which the cobalt metal matrix is surface hardened to improve its abrasion resistance in applications where sliding friction occurs.

It is therefore the aim of the invention to provide a sintered preparation of refractory carbides, in which the surface of the matrix metal is borided to a hardened surface with low To create coefficient of friction.

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Another object of the invention is to provide a steel bonded carbide in which the Surface of the matrix surrounding the carbide grains, boridier-t is to increase the erosion resistance improve while having a hard surface low coefficient of friction is created, which is particularly suitable for applications, where there is a sliding contact with a metal surface occurs

These and other objects of the invention are further explained in the following description.

In the broadest sense, the invention creates one Standard article made from a surface-hardened sintered material Refractory metal carbide, which consists essentially of about 20 - 80 volume * - $ primary grains from a hard Refractory metal carbide, which are distributed in a metal matrix, which consists essentially of one Metal of the iron group is composed, for example a matrix alloy, on at least one Iron group based metal, the surface hardened cemented carbide by a microstructure adjacent to their surface is characterized, which consists mainly of erimary grains of refractory metal carbide consists, which are dispersed in a boridized layer of the metal matrix and the boridized Layer contains an iron group metal boride such as iron boride, cobalt boride and nickel boride.

The primary grains of the refractory metal carbides include those selected from the group consisting of carbides of chromium, tungsten, molybdenum,

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Titanium, zirconium, hafnium, mob, tantalum and vanadium; While the amount of carbide in the composition from about 20 - 80 volume ^ can be a Range of about $ 30- $ 70 in volume may be preferred.

The invention is particularly applicable to sintered steel-bonded carbides of the type shown in FIGS U.S.A. patents Mr. 2 828 202, 3 053 706, 3 183 127, 3 369 891, 3 369 892 and 3 416 976 mentioned is.

Examples of matrix steel compositions that can be borided are SAE 1010 bis steels SAE 1080 and such other steels as 0.8 $ Cr, 0.2 $ Mo, 0.3 $ C, the remainder essentially iron, 5 $ Cr, 1.4 $ Mo, 1.4 $ W, 0.45 $ V, 0.35 $ D, remainder essentially iron, 8 $ Mo, 4 $ Cr, 2 $ V, 0.8 $ C, remainder im essential iron and 18 $ W, 4 $ Or, 1 $ V, 0.75 $ C, the remainder being essentially iron.

A preferred composition of the steel matrix for boriding is one which is about 1-6% by weight Cr, about 0.3-6 weight- $ Mo, about 0.3-0.8 weight- $ C, the remainder essentially contains iron.

Another preferred composition of the steel matrix for boriding is one that is about 6 or 7-12 weight- $ Cr, about 0.6 to 1.2 weight- $ C, about 0.5-5 weight- $ Mo, up to about 5 weight- $ W, up to about 2 weight- $ V, up to about 3 weight- $ Ni, up to about 5 weight- $ cobalt, remainder essentially contains iron.

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Another composition of the steel matrix is a heat treatable, low carbon composition containing about 10-30 weight- ^ Ni, 0.2-9 weight- ^ Ti, up to 5 weight $ Al, the sum of titanium and aluminum being about Does not exceed 9 weight- ^, up to about 25 weight- ^ Go, up to about 10 weight- ^ Mo, remainder of the matrix essentially = »at least about 50 weight- ^ contains iron and the metals of which the matrix preparation consists, are measured such that when the nickel content is about 10-22% by weight, the sum of aluminum and titanium is less than 1.5% by weight, the contents of cobalt and molybdenum are each less than about 2% by weight and such that when the nickel content is about 18-30% by weight and the molybdenum content is less than 2% by weight, the sum of aluminum and titanium exceeds 1.5% by weight. This matrix alloy forms a soft martensite when they made a solution temperature of about 760-1165 ⁰ C (about HOO - 2150 ⁰ P) is quenched and is subjected to age hardening when stored at a temperature of about 260 - 65O ⁰ C (500-1200 ⁰ P) is heated for about 3 hours.

Examples of matrix metals other than steel are the metals nickel, cobalt and nickel-based alloys and iron group cobalt base. These metals can be borided to form Nickel boride and cobalt boride.

Cobalt is a well-known matrix metal or binder metal used to make sintered tungsten

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Carbide for use in cutting tools, drill bits, etc. is used.

The abovementioned sintered carbides are produced by powder metallurgy. In the case of a steel-bound Carbide can, for example, be a composition of primary grains of titanium carbide, which are in a steel · Composition with low chromium and low molybdenum are dispersed, the composition consists of 40 weight $ titanium carbide and 60 weight $ steel, can be manufactured as follows:

An amount of 1,000 g of titanium carbide powder with a size of about 5-7 μm is used with an addition of 150 g of a steel-forming mixture that is calculated to form a matrix steel that contains about 1.25 $ chromium, 2.5 $ Molybdenum, 0.4 $ carbon, the remainder carbonyl iron powder of about 20 μm in size, mixed. The powdered ingredients contained in the mixture so that a gram of paraffin wax per 100 g of components D · s _a mixing is carried out about 40 hours in a steel mixer which is half filled with steel balls, using hexane as a carrier.

After complete mixing, the mixture is removed and dried in vacuo. A portion of the mixed product is pressed in a mold at a pressure of 23.5 kg / mm (15 tons / sqdnch) to form a nozzle tip of the desired size. The nozzle tip is then approximately about / more sintered in the liquid phase at a temperature of about 1435 ⁰ C ..- (about 2615 ⁰ F) for half an hour under a vacuum corresponding to 20 to Hg or.

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After complete sintering, the whole thing is cooled and then ^{tempered by heating to 900 0} C (about 1165 ^{0 F) for 2 hours and then cooled to about 10O 0} G (212 ⁰ P) at a rate of about 15 ° C / hour, with one annealed microstructure is formed which contains spherical cementite. After tempering, the nozzle tip is machined to the desired size. The tip is then cleaned and borided. After the tip has been borided, it is hardened by ^{converting it into austenite at 954 0} G (175O ⁰ P) and then setting it in an oil bath.

When performing the boridation step, a Cementing process applied in powder packs. A stainless steel retort is used, the lid of which is tightly closed with the splash of the retort The lid and the splash of the retort have been machine-smoothed before each approach to ensure a gas-tight seal. With each approach, there is between the splash and the Cover of the retort a new 0-ring made of nickel-plated stainless steel AISI 321 brought.

A typical powder pack is a mixture of about 5 weight ^ boron and about 95 weight ^ alumina, 0.75 weight ^ of a halide exciter (e.g. Ammonium bifluoride and potassium fluoride). The boron powder used is amorphous and has the size of a particle of about 5 µm and has a purity of about 90-92 #. The main impurities are $ 6.2 Mg,

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0.1 $ Pe and 2.2 $ 0 · The aluminum oxide has a particle size corresponding to a sieve size below 0.043 mm (-325 mesh) · ■

The powder pack can contain about 1-50 weight- ^ boron, a small but effective amount of a halide exciter (e.g. t> is about 2 $), the remainder an inert diluent such as alumina. Examples of inert diluents are: TiO ₂ , ZrO ₂ , GaO, SrO, BaO, MgO and other refractory oxides. A "preferred range of boron content is 3-25% by weight. Representative examples of halides are ET, HaF, IHJ?, HH.01 and other halides of the alkali metals.

When forming the powder pack, the powders are mixed together in the appropriate amounts and incorporated into a rotary mixer containing stainless steel balls, mixed for 1-2 hours.

The samples to be borided are thoroughly degreased in trichlorethylene vapors and then with semolina made of aluminum oxide of a size accordingly the screen mesh size below 0.03 mm (- 4-00 mesh) peeled off. The withdrawn samples are then packed in the retort, which is the powder pack for boriding contains. The retort is tightly filled with the powder pack so that on top no empty space remains, and the lid is then closed with the retort flange as described above.

The filled retort is heated in an oven to 843 ⁰ C (155O ⁰ P) or in the range of 732 - 926 ⁰ C (1350 -

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170O ⁰ F) and held at this temperature for about 10 hours, for example 24 hours. During this period of time, boron is deposited on the surface of the sintered molded body via boron halide vapors formed by the packing then diffuses into the surface to form iron boride. At the end of the 24 hour period, the betorte is removed from the furnace and allowed to cool, the retort is then opened and the packing is removed.

The surface-hardened samples are either cleaned in an ultrasonic cleaner or by being drawn off in liquid cleaned to remove any remaining powder.

The composition of the samples was as follows:

Table I.

No. Vol. $ Carbide

VoI · Ji matrix

45 TiC

45 TiC

45

55 (Matrix contains in wt .- $ 2.87 $ Cr $ 2.87 Mo, $ 0.65 C, remainder Fe)

55 (Matrix contains, in wt .- $ 10 $ Cr $ 3.0 Mo, $ 0.8 C, remainder Fe)

55 (matrix contains in wt .- $ 20 $ Cr 0.8 $ C remainder Fe)

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Mr. YoI. <Fo Carbide Vol. $ Matrix

4 45 TiO 55 (matrix contains in wt .- $ 18 $ ITi,

8.5 $ Go, 4.75 $ Mo, 1 $ Ti, remainder le)

5 50 TiO 50 (matrix contains in weight $ 18 $

$ 8.5 $ 00.4.75 Mon, $ 1 Ti, remainder le)

6 55 TiC 45 (matrix contains in wt .- $ 18 $ Hi,

$ 8.5 Oo, $ 4.75 Mo, $ 1 Ti, remainder each)

7 45 TiO 55 (matrix contains in wt .- $ 14 $ Cr,

6 $ Hi, 5 $ Co, 1.5 $ Ti, remainder Pe)

8 45 TiO 55 (matrix contains in wt .- $ 71 $

18 $ Cr, '8 $ le, 2 $ Ti, 1 $ Al)

The samples were made according to their respective composition hardened as follows:

Composition Mr. 1: deterred by 954 ^ 0 (175O ^u l)

using an inert gas stream, to the chi ies s end it annealing "at 190.5 ⁰ C (375 ⁰ I) 1 hr.

Composition Mr. 2: deterred by 1093 ⁰ O (2000 ⁰ I)

with a Inertgaastrom, anschiiessendes annealing 2 at 524 ⁰ C (975 ⁰ I) 1-hr.

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Composition Mr. 3 *

Composition No. 4 "Composition Mr" 5 p Composition Kr. 6:

Composition No. 7x Quenched of 1024 ° 0 (1875 ⁰ F) in an inert atmosphere and then Annealed 204-426 ⁰ C. (400-800 ⁰ F).

Treated in solution at 815 ⁰ G (1500 ⁰ I) and aged 3 Sta at 482 ⁰ C (900 ⁰ F) and then cooled in the air.

Treated in solution at 815 ⁰ C (150O ⁰ I ¹ ) and aged for 3 hours at 482 ⁰ C (900 ⁰ F) and then cooled in the air.

Treated in solution at 815 ⁰ O (150 ⁰ F) and aged for 3 hours at 482 ⁰ C (90 ⁰ F) and then cooled in the air.

Bi solution at 982 ⁰ C (1800 ⁰ F) annealed and cured for 10 hrs at 482 ⁰ C (90O ⁰ F) and then cooled in air.

Composition Ur. In 8t solution by pacing in a nieht-oxidizing atmosphere of about 1065 ⁰ C (195o F ⁰⁾ annealed and then 8 h at 871 ⁰ C (160o F ⁰⁾ ■ and then 4 hr. At 76o ⁰ C (HOO ⁰ F ) aged.

In the matrix on Bisenbasis there is a tendency to form a eutectic mixture Fe-FepB, the (F 2100 ⁰⁾ melting at about 1149 ⁰ C. Therefore, the heat treatment for hardening should preferably be limited to a temperature below this temperature

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to protect the hardness assessment. In addition, boriding at very high temperatures can result in undesirable interactions with the alloying elements in the steel matrix and also with the dispersed carbide particles. Thus, in the case of the sample, Ur. 2 the! Temperature of the heat treatment are well below 1093 ⁰ C (2000 °! ').

The boride coating on the surface of the sample was identified by X-ray diffraction analysis and indicated the presence of IIFe ₂ B and PeB. Coatings of about 30.7-51 µm (1.5-2 mils) were obtained on all samples. The microhardness of the coating was measured by producing microhardness indentations according to Vickers using a load of 25 g in the surface of the matrix area in which no dispersed primary carbides were contained. The hardness determinations before and after boriding are given in Table II below.

Table II

Surface micro hardness (tickers)

Before coating after coating

2055; 2055 2285; 2055 2055; 2055 2285; 2285

1855; 1855

1 283; 282 2 237; 254 3 274; 405 4th 376; 413 5 376; 413

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Surface micro hardness (Vickers)

No Yor Coating Tray Coating

6th 332; 339 7th 319; 386 8th 405; 464

.2285; 2055 2285; 2285 1855; 2055

As can be seen from Table II, a borided Matrix with a hardness above 1855 Vickers can be obtained · Generally speaking, the hardness is the borided matrix are over 1500 yickers, regardless of whether the matrix is based on iron or nickel or cobalt as a base metal.

Generally speaking, the density of the borided Layer up to about 178 µm (7 mils).

The thickness range of the borided layer can depend on the hardness that is achieved in the substrate target. '"Since the substrate can generally be treated with heat after boriding, it is advisable to use a borided layer up to about 51 μm (2nd mils) in order to keep the cracking of the borided layer during quenching to a minimum.

On the other hand, in applications where a tempered substrate is preferred, such as thread gauges and the like or in the case of complex

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bodies having the borided layer in excess of 51 / µm (2 mils) up to about 178 / µm (7 mils) in thickness. It It can therefore be expedient to use a layer carrier made of tempered titanium carbide steel in the form of drilling tools and to use drawing tools, the borided surface having improved abrasion resistance gives and the tempered substrate better vibration damping properties results «

As an example of an additional embodiment / invention the following example of the manufacture of a thread gauge is shown

There is first prepared by compressing a rod of a mixture of titanium carbide and steel aue about 45 Volum- $ titanium carbide and the balance (about 55 Volum- $) a steel matrix of a composition consisting essentially of about 3 weight- ^ chromium, 3 weight- io molybdenum, 0.65 weight- ^ carbon, remainder iron.

The compacted rod is about sintered for half an hour in the liquid phase under vacuum at a temperature of about 1435 ⁰ C (about 2615 ⁰ I). After complete sintering, the rod is cooled to room temperature in the furnace in order to create a tempering hardness of about 47Rc. The tempered rod is machined to the desired diameter and the threads are cut with a precision tool along one rod length while the opposite length is knurled ο Then the threaded gauge is made as described above

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borided and the threads subsequently cleaned and Ground to the finished size. The borided thread gauge is used without solubilizing heat treatment to avoid volume size change and deformation that is usually caused by oil quenching. caused by high temperature. The surface hardness is generally over 1500 tickers

Similarly, borided drilling tools and drawing tools are made from the titanium carbide steel preparations of the type mentioned.

As mentioned above, one advantage of the borided layer is that it imparts low friction properties to the surface of the sintered refractory carbide material, while at the same time it imparts better abrasion resistance to the metal matrix surrounding the refractory carbide grains. If the matrix is heat treatable, especially a steel matrix, the coated sintered refractory carbide material can be hardened and tempered by the heat treatment commonly used for the uncoated matrix, provided that sufficient care is taken to ensure that the coating does not oxidize or otherwise is chemically changed. If the hardness is achieved by oil quenching of the steel bonded carbide of a relatively high temperature, for example from 954 ⁰ G (175O ⁰ P), it is thus preferred that cooling with a stream of inert gas to effect such as argon.

Examples of other compositions according to the invention can be borided are the following:

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Table III

Ho. VoI · - # VoI · - # Matrix

carbide

9 20 TiC 80 (3 wt .- $ Gr ', 3 wt .- $ Mo, 0.5 G-ew .- ^ C,

Rest mainly Pe)

10 30 VC 70 (6 wt .- $ Pe, 15 wt .- ^ Or, 2.5 wt .- ^ Al,

2.5% by weight Ti, remainder mainly Ni)

11 45 WC 55 (matrix essentially Co)

12 50 TiC 50 (8 wt .- $ Cr, 3 wt .- jS Mo, 1 wt .-? S V,

0.9 Gew «> - $ C, - remainder mainly Ie)

13 60 HbC 40 (5 wt .- $ Cr, 1.4 wt .- # Mo, 1.4 wt .- ^ W,

0.45 wt .-% Y, 0.35 wt .- $ C, remainder mainly 3? E)

14 70 TiC 30 (10 wt .- ^ Cr, 2 wt .- ^ Mo, 2 wt .- $ ¥,

1 wt. Fo C, remainder mainly i "e)

15 55 TiC 45 (60 wt .- $ Hi, 15 wt .- $ Co, 20 wt .- $ Cr

and 5 wt .- ^ Fe)

16 25 ZrC 75 (80 wt .- ^ Hi - 20 wt .- $ Cr)

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The matrix metals used to sinter and bond the refractory carbide preferably contain. at least 50% by weight of at least one metal from the iron group, namely iron, nickel and cobalt, and the amount of refractory metal carbia is from about $ 20-80 by volume, with the matrix metal essentially making up the remainder.

In a preferred manner, the invention is applicable to steel-bound Carbides, and particularly on titanium carbide tool steels, are the primary grains of refractory Contain carbide, like titanium carbide, in an amount of about 20-80 yolum- $ dispersed in the following Steel matrices, which essentially make up the rest:

(A.) The matrix containing about 1-6 wt. $ Chromium, about 0.3

- 6 wt .- $ molybdenum, about 0.3-0.8 wt .-% carbon, The rest mainly contains iron,

(B) the matrix containing about 6-12 wt. $ Chromium, about 0.5

- 5 wt .- ^ molybdenum, about 0.6-1.2 wt .- $ carbon, up to about 5 wt .- ^ tungsten, up to about 2 wt .- ^ Vanadium, up to about 3 wt .- $ nickel, up to about 5 wt .- $ cobalt, the remainder mainly iron 'contains and

(C) the matrix comprising a high nickel alloy and about 10-30 wt% nickel, about 0.2-9 Weight% titanium, up to about 5 weight% aluminum, where the sum of the content of tifen and aluminum about 9 Weight does not exceed ^ and about 0.15% by weight Carbon, up to about 25 wt .- ^ cobalt, up to

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about 10 wt .- $ molybdenum, remainder of the matrix essentially contains at least about 50% by weight of iron, the metals which make up the matrix preparation are dimensioned in such a way that if the Mckel content is about 10 to 22% by weight reached and the sum of aluminum and titanium is below about 1.5 wt .- $, the content of molybdenum and cobalt is at least about 2 wt. that if the Mckel content is about 18-30% by weight and the molybdenum content is below 2% by weight, the The sum of aluminum and titanium exceeds 1.5 wt .- ^.

The matrix steels mentioned are characterized by the presence of martensite in the heat-treated state. With regard to the matrix steel (A), the tool steel produced therefrom, made of refractory carbide, is ^{heat-treated by heating above the temperature of the austenite formation, for example to 954 0} O (175O ⁰ I ¹ ) and then quenched, with the formation of hard martensite. When the refractory carbide tool steel is borided, it is preferred that the quenching be carried out by a flow of inert gas in order to avoid chipping of the borided layer. After quenching the steel, by heating over the temperature range of from about "121 to 287 ⁰ C (250 - 55O ⁰ P) are annealed up to about 5 hours.

In Pail of a tool steel made of a refractory carbide using steel (B) as a matrix, the matrix in a similar way is heat treated by quenching from above the required for austenite formation temperature in the range of about 926 1121 ⁰ C (1700-2050 ⁰ F), for example of 954 ° C

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F). The annealing, however, is carried out at a higher temperature, for example from about 482 565 ⁰ C (900-1050 ⁰ F), such as 537 ⁰ C (1000 ⁰ F), for about 1 - 2 hours, with secondary hardening effects due to the formation can be achieved by secondary carbides

In the case of steel matrix (0) are steel preparations with refractory carbide that are made therefrom internally of the steel to a solution treatment by cooling (for example, air cooling) from a solution temperature of about 760-1100 ⁰ C (HOO - 195Q ⁰ F) _β

was subjected to a microstructure in the matrix / marked by the presence of soft martensite. 65O ⁰ C - Danaoh the matrix surrounding the grains of the carbide, to age hardening by heating the refractory Karbidstahls to a temperature of about 260 (500 to 1200 ⁰ F) is subjected to over about 3 hours. A typical temperature for age hardening is 483 ^° C (900 ^° F).

One of the advantages of the invention is that the matrix is kept in a relatively soft state can to make them tough, while with the help of the boridized layer a very hard surface is created will.

The Boridschiohten allow the production of Refractory carbide objects such as molds, tools, sandblasting nozzles, rollers, etc. Such Articles tend to contact hard particulates in use, which are usually selective

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remove the matrix surrounding the primary carbide grains. One of the advantages of the steel matrix ordered in that it can be tempered for machining sintered refractories To allow carbide material that is subsequently coated can be. The dimensional changes during the boridization are negligibly small, since the coating is essentially due to diffusion from boron to the inside.

Sandblasting nozzles were made from tempered titanium carbide tool steel produced and borided according to the invention. The composition corresponded 45 volumetric titanium carbide, the remainder containing a matrix steel 2.87 wt .- ^ chromium, 2.87 wt .- $ molybdenum, 0.65 wt .- # carbon, remainder iron, laughs at boriding the nozzles were heat treated to achieve a substrate hardness of 68-70 Rc. The lifespan the nozzles has been significantly improved. The rate of wear and tear and erosion was considerably lower than that used for nozzles made of ceramic hardened tool steels, Boron carbide and the aforementioned titanium-carbide tool steel was found in a hardened, but not borided state

Although the invention has been described in connection with preferred embodiments, modifications are possible and changes can be made without departing from the spirit of the invention, as would be apparent to those skilled in the art can be seen. Such modifications and changes

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changes are within the scope of the invention.

- patent claims -

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Claims (1)

Patent claims 1. Surface hardened cemented carbide molded article. consisting mainly of about 20 - 80 Yolvtm-fo primary grains of a hard refractory carbide selected from the group consisting of primary carbides of chromium, tungsten, molybdenum, titanium, zirconium, hafnium, job, tantalum and vanadium, which are distributed in a metal matrix which contains at least 50% by weight of an iron group metal substantially constituting the remainder, characterized in that the surface-hardened cemented carbide has a microstructure at least adjacent to the surface thereof which is composed of primary grains of the refractory metal carbide, which in a borided layer of the metal matrix are anchored and dispersed therein, the borided layer being characterized by the presence of a boride of a metal from the iron group, 2. Surface hardened cemented carbide molded article according to claim 1, characterized in that the metal of the iron group in the matrix is iron is. - 3. Surface hardened cemented carbide molded article iiaoh claim 2, characterized _ 26 303838/0798 that the metal matrix made of steel beatent and the borided layer contains iron boride. Surface hardened cemented carbide molded article according to claim 3 »characterized in that the refractory carbide is essentially titanium carbide is. Surface-hardened, sintered carbide-shaped article according to claim 4, characterized in that the steel matrix is selected from the group consisting of (A) about 1-6 wt .- # chromium, about 0.3-6 wt .- $ molybdenum, about 0 , 3-0.8% by weight carbon, the remainder mainly iron, (B) about 6-12% by weight > chromium, about 0.5 to 5% by weight molybdenum, about 0.6-1.2 Wt .- ^ carbon, up to about wt .-% tungsten, up to about 2 wt .- # vanadium, up to about 3 wt .-% nickel, up to about 5 wt .- $ cobalt, the remainder mainly iron and ( C) a steel alloy with a high nickel content comprising about 10-30 wt .- $ nickel, about 0.2-9 wt .-% titanium, up to about 5 wt .-% aluminum, the sum of titanium and aluminum being about 9 wt .- ^ does not exceed, up to about 25 wt .- ^ cobalt, up to about 10 wt. -fo molybdenum, the rest of the matrix is substantially at least about 50 wt. -f> iron, with the proviso that the metals, which make up the composition of the matrix, are present in such amounts that if, the lii oil content of about 10-22 wt .- $ and the sum of aluminum and titanium - 27 - 309838/0798 -p 22 21 875.3 Ohromalloy American Corp, / T - 27 - is less than about 1.5 wt%, the content of Molybdenum and cobalt are each at least about 2 wt. # And such that if the hicke! Content is about 18-30 wt. -56 and the molybdenum content less than 2 Wt .- ^, the sum of aluminum and titanium exceeds 1.5 wt .- #, the matrix made from compositions (A), (B) and (G) being metallographic is characterized by the presence of martensite and iron boride. 6. Surface-hardened sintered carbide molded article consisting mainly of about 20-80 Yo .- $ of primary grains of a hard refractory carbide of essentially titanium carbide, which are distributed in a steel matrix, characterized in that the steel matrix consists of about 1 - 6 wt .- ^ chromium, about 0.3-6 wt. -4> molybdenum, about 0.3-0.8 wt .- ^ carbon, the remainder, mainly iron, consists that the surface-hardened cemented carbide by a microstructure at least adjacent to the surface of which contains primary grains of titanium carbide which are anchored and dispersed in a borided layer of the metal matrix and the borided layer is metallographically characterized by the presence of iron boride. 7. Surface hardened cemented carbide molded article according to claim 6, characterized in that - 28 309838/0798 that the steel matrix is in the tempered state. 8. Surface hardened cemented carbide molded article according to claim 6, characterized in that the steel matrix is in the hardened state, and also metallographic, characterized by the presence of martensite. 9. Surface-hardened sintered carbide Pormartikel, which consists mainly of about 20-80 YoI, - ^ of primary grains of a hard refractory carbide of essentially titanium carbide, which are distributed in a steel matrix, characterized in that the steel matrix up to about 5 G-CUV .- ^ tungsten, up to about 2 wt. -i "Yanadium, up to about 3 weight 7 $ ITickel, up to about 5 wt ¹ ^ cobalt, the remainder mainly. Contains iron, the surface of which contains primary grains of titanium carbide which are anchored and dispersed in a borided layer of the metal matrix and the borided layer is characterized metallographically by the presence of iron boride. 10. Surface hardened cemented carbide molded article according to claim. 9 »characterized in that the Stahlmetrix is in the tempered state. 11. Surface-hardened cemented carbide according to claim 9, characterized in that the - 29 - 309838/0798 Steel matrix is present in the hardened state and also metallographic by the presence characterized by martensite. 12. Surface-hardened sintered carbide shaped article consisting mainly of about 20-80% of primary grains of a hard refractory carbide of essentially titanium carbide, which are distributed in a steel matrix, characterized in that the steel matrix is mainly consists of a steel alloy with a high disgust content and about 10-30 .Qew.-fo nickel, about 0.2-9 wt .- ^ titanium, up to about 5 wt .- $ aluminum, the sum of titanium and aluminum does not exceed about 9% by weight, up to about 25% by weight cobalt, up to about 10% by weight molybdenum, the remainder of the matrix essentially contains at least about 50% by weight iron, the metals making up the matrix is composed, are present in such amounts that if the nickel content is about 10-22 wt .- ^ and the sum of aluminum and titanium is less than about 1.5 wt .- ^, the contents of molybdenum and Cobalt each at least about 2 wt. and in such a way that if the ITi cke content is about 13-30% by weight and the molybdenum content is below 2% by weight, the sum of aluminum and titanium exceeds 1.5% by weight and where the surface-hardened cemented carbide is characterized by a microstructure at least adjacent to its surface, which consists of primary grains of titanium - 30 - 309838/0798 carbides, which are anchored and dispersed in a borided layer of the metal matrix and the borided layer is metallographically characterized by the presence of iron boride 13 (Surface-Hardened Sintered Carbide-iOrm ~ Article according to Claim 12, characterized in that the steel matrix is in the tempered state. 14 · Surface-hardened sintered carbide according to claim 12, characterized in that the Steel matrix is present in the hardened state and metallographisoh due to the presence of martensite is marked. 309838/0798