GB2109730A

GB2109730A - Composite wear resisting member and the method for producing the same

Info

Publication number: GB2109730A
Application number: GB08224689A
Authority: GB
Inventors: Masaya Miyake; Koutaro Hagiwara; Shouzo Kazumoto; Toshikazu Hirayama; Akio Hara
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1981-08-28
Filing date: 1982-08-27
Publication date: 1983-06-08
Also published as: JPS5838682A; DE3232018C2; DE3232018A1; GB2109730B

Abstract

The invention relates to a composite wear resisting member comprising a cemented carbide and a steel member for use in a variety of composite tools, hot rolling rolls, steel cutting slitters, side reamer drills, punches, bites, and hobs, and to a method for producing the same. A cemented carbide and steel member are brought into direct contact with each other, the cemented carbide and the steel member being welded by melting part or whole of the interface thereof through the radiation of a high energy beam in a non-oxidizing atmosphere or a vacuum, thereby producing a composite wear resisting member with rigid adhesion, high heat resistance and free from thermal stress suitable.

Description

SPECIFICATION Composite wear resisting member and the method for producing the same The invention relates to a composite wear resisting member comprising cemented carbide and steel or cast iron and to a method for producing the same.

Conventionally, cemented carbides represented by WC-Co, WC-TiC-Co, etc. have been extensively used in the field of cutting tools, wear resisting members, shock resisting tools, etc. Particularly when for use in hot rolling rolls, wire drawing dies, etc. as a wear resisting member, the safety coefficient was raised by liberally increasing the size of the cemented carbide solid since the toughness of cemented carbides was lower than that of steel. However, cemented carbides involved difficulties not only in respect of the high price of the principal components, i.e. WC, TiC and TaC, but also in respect of saving of resources.

In order to overcome the difficulties, cemented carbide was generally used exclusively in the part where wear resistance was especially required.

Such a compound member was produced as follows. Cast iron was bonded to the inside of a cemented carbide ring by direct casting, a steel ring being cold-fitted to the inside thereof, or Ag or the like as solder was interposed between the cemented carbide and steel member, the whole being heated at 600N9000C for welding.

However, the former method had a disadvantage in that direct casting deteriorated not only the processing efficiency but also the strength of the welded interface, while the latter method involved difficulties in that, since the whole was heated at a high temperature and the thermal expansion coefficient of the cemented carbide was about + of that of the steel, the thermal stress remaining in the soldered interface caused cracks during the use thereby making it difficult to produce a largesized part. The problem of the thermal stress was also applicable to the former method. In case of the soldering method, the soldered layer had poor fatigue resistance and was easy to be detached at high temperatures.

The invention has for an object to provide a composite wear resisting member free from the generation of said thermal stress and yet having high heat resistance by the improvement in the method of bonding cemented carbide and steel member and the method for producing the same at very low cost and enabling to produce a largesized part which was unproducible heretofore.

As a result of a series of tests, the inventors concerned have found that, in bonding a cemented carbide and steel member, direct and complete adhesion is obtainable by melting the interface by a width of 1-2 mm without the necessity of providing an intermediate layer thereon. The composite member thus obtained has been found to have improved properties over the conventional product.

As the method for melting the interface by a width of 1 N2 mm, there wasoknown a variety of processes, such as arc welding, TiG welding, etc.

It has been found, however, that by the use of high energy beam, such as electron beam, laser beam, etc., the interface on the side of the steel member can be preferentially melted due to its higher thermal conductivity, the interface on the side of cemented carbide being not perfectly melted.

The use of an electron beam and the like as the method for bonding metal has been known as is disclosed in Japanese Specification No. SHO-5645288. The disclosure is characterized in that the electron beam is applied to the interface on the side of the metal or the interface on both sides for fused bonding.

The method according to the invention is characterized in that, although a high energy beam is applied to the interface between cemented carbide and steel members, steel only is melted for bonding. A large amount of energy is necessitated if the interface on the side of cemented carbide is to be melted. Then cracks will be produced by thermal shock and breakage will arise due to tensile stress at the same time of welding.

On the other hand, when a high energy beam is applied to the interface on the side of steel member only, the temperature of the cemented carbide is not elevated. Thus bonding is not obtainable.

After a series of tests of high strength bonding of cemented carbide and steel members without the occurrence of cracks, the following conclusions have been reached.

The diameter of high energy beam is known to be 0.3 mm, for example, in case of an electron beam. Since the temperature is known to be elevated above 25000C within the range of 0.3 mm, the steel melting range is about 0.5 mm around the beam center. Thus within the range of 0.5 mm from the interface between cemented carbide and steel member, the surface temperature of the cemented carbide can be elevated above 13000C at which liquid phase is produced thereby enabling to bond cemented carbide and steel member. It has been found that, by applying an electron beam within the range of 0.5 mm of the interface, a cemented carbide and steel member can be completely bonded through melting of the steel and generation of a liquid phase on the cemented carbide.

In case of a cemented carbide and steel member, however, the application of electron beam to the interface on the side of the cemented carbide only will result in incomplete melting, while radiation beyond the range of 0.5 mm of the interface on the side of the steel member will broaden the melting width thereby greatly reducing the bonding strength for lack heating on the interface on the side of cemented carbide.

According to the invention, it is necessary that a high energy beam, for example, electron beam, is applied within the range of 0.5 mm of the interface between the steel and cemented carbide thereby enabling to obtain a heating effect on the interface on the side of the cemented carbide and a suitable melting width on the interface on the side of the steel member resulting in high strength bonding between the cemented carbide and the steel member. It is needless to mention that the abutting faces to be radiated should be brought into pressure contact with each other by means of hot-fitting, cold-fitting, pressing and the like.

The composite member according to the invention is characterized in that firstly it is free from deformation and breakage while in use since the whole of the composite member is not subjected to a high temperature and accordingly no stress is generated from the difference of thermal expansion rates; secondly it has high resistance to fatigue and high compression strength since the cemented carbide and steel members are directly bonded to each other; and thirdly it is free the generation of a deteriorated layer (Fe3W3C) due to the reaction between cemented carbide and steel (Fe) since the melted layer arises exclusively on the steel member, while cemented carbide is never completely melted though only liquid phase is produced thereon.

The method for welding steel and cemented carbide has not been put to practical use though the test has been repeated heretofore. Practical bonding has been unobtainable for the reason that cemented carbide has poor resistance to tensile strength though highly resisting to compression, cracks being produced by the tensile stress arising at the time of welding. In order to obviate the occurrence of cracks, there has been introduced a method of placing a thin metal sheet of Ni, Co, etc. over the interface between steel and cemented carbide. This method, however, has a disadvantage in that sufficient strength is unobtainable since uniform welding is prevented by the difference of thermal conductivity.After a series of tests, the inventors concerned have invented a solid bonded composite wear resisting member completely free from cracks arising between the cemented carbide and steel member.

The composite wear resisting member according to the invention and the method for producing the same will hereinafter be described in detail with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of a composite member comprising a cemented carbide body and a steel body for describing the principle of the invention; Fig. 2 is a sectional view of a compound roll showing an embodiment of the invention; Fig. 3(A) is a perspective view of a steel ring showing an embodiment of the invention, (B) being a fragmentary sectional view thereof; Fig. 4 is a top view of a side slitter showing another embodiment of the invention; Fig. 5 is an elevational sectional view of the same; and Figs. 6 and 7 are sectional view of hot rolling rolls showing still further embodiments of the invention.

When cemented carbide and steel members are relatively small in size, i.e. when the interface between them is relatively small, they are bonded by melting the whole interface on the side of the steel member by a width of 1~2 mm. It has been found as a result of a series of tests that, in the case of a large-sized wear resisting part, e.g. a hot rolling roll (Morgan roll, etc.), it is sufficient if the interface thereof is melted by a depth less than 20 mm. Usually, its welding face suffices in 5-1 5 mm.Fig. 2 is a sectional view showing an embodiment of a hot rolling roll, in which a ring 6 of SCM2 1 steel or the like is cold-fitted to the inside of a cemented carbide ring 5, electron beam 3 being applied to the end of the interface between the steel and cemented carbide, melted layers 7 being formed on the interface on the side of the steel thereby enabling to bond the cemented carbide and the steel members to each other. Thus the cemented carbide and steel members are directly bonded in the center which is mostly subjected to stress, the bonded layer being free from the occurrence of cracks and having high fatigue resistance as a whole.

Good results were obtainable when the steel member was soft for better adhesion with the cemented carbide and easy absorption of distortion; the steel member preferably contained carbon below 0.5 weight %; wear resistance was raised by increasing the hardness through carbonizing and quenching except the interface, particularly in the case of rolling rolls.

The reasons are as follows. Rapid cooling enables to raise the hardness and prevent the deterioration of the interface, while the hardness can be controlled to HRc50~60 where wear resistance is required when used as a tool.

Suppose that the carbon content of the steel on the interface between the steel and cemented carbide is difficult to control. In such a case, it is preferable that a pure metal, such as Ni, Co, Cu, etc., is placed exclusively on the welding interface between the steel and cemented carbide, welding being executed twice, i.e. between the cemented carbide and the pure metal and then between the pure metal and the steel, thereby controlling the carbon amount of the steel abutting the cemented carbide below 0.5%. This enables to obviate the occurrence of plastic deformation when the steel is cooled despite the generation of tensile stress by the welding of the steel and cemented carbide.

When the welding interface is partially and continuously melted by applying high energy beam thereto, carbon and oxygen in the melted steel usually react to generate gas. Degassing grooves preliminarily provided on the steel can effectively remove blow holes in the welding layer. Fig. 3(A) is a perspective view of the steel member in the case of said rolling roll, (B) being a fragmentary sectional view, on a magnified scale, of the same. The numeral 8 designates a groove located at the forward end of the welding beam 9, 9' designating degassing grooves for discharging the gas generated in the melted layer.

The invention is also effective in composing a cemented carbide with a plurality of steel members.

In case of rolling rolls and slitters, there is frequently required a composite member comprising a steel ring and a cemented carbide ring with a steel ring of a different kind or a cast iron ring interposed therebetween. In one example, steel having a thermal expansion coefficient of 3-10x10-6 cm/ C up to 3000C is welded to the inside of a cemented carbide ring, further to the inside thereof being welded a steel ring having a greater wear resistance than that of the intermediate steel ring. In another example, to the inside of a cemented carbide ring is welded a cast iron ring or a pure metal ring relatively soft, capable of absorbing thermal expansion and having an elasticity limit of 50 kg/mm2, a steel ring being welded to the inside of said cast iron or pure metal ring.In both cases, the method according to the invention was applied to the welding of the intermediate rings of steel, cast iron and pure metal respectively to obtain rolls of longer useful life compared with the three-layer compound rolls and slitters according to the conventional method. The specific material of said thermal expansion coefficient may comprise Ni, Co alloy, Fe-Ni alloy or kovar. They are useful particularssy in conditions of use susceptible to heat.

When a plurality of members are welded, it is preferable that the cemented carbide and the steel ring are directly welded, the stress generated through welding being caused to be absorbed by the difference of thermal expansion due to deformation of the intermediate member, then a third intermediate member being welded to the steel ring. Rapid adhesion is obtainable by placing a thin metal sheet between the steel and the cemented carbide. In some of the embodiments according to the invention, low carbon alloy may be used exclusively in the part to which high energy beam is applied. Thus a composite member having great strength and high wear resistance is obtainable by carbonizing and quenching the unwelded part.

Electron beam and laser beam are preferable for their welding precision, while a non-oxidizing atmosphere or a vacuum is indispensable for the prevention of oxidization of the steel member and cemented carbide, a vacuum being particularly preferable in respect degassing.

The invention will now be described in more detail in reference to the following examples.

Example 1 In a Morgan roll 159 mmf in outside diameter, 87 mmf in inside diameter and 70 mm in thickness as shown in Fig. 2, cemented carbide having 85% WC was produced into a ring 159 mmf in outside diameter and 123 mm in inside diameter, while steel (SCM21) having 0.15% carbon was produced into a ring 123 mm# in outside diameter and 87 mmf in inside diameter.

The inner periphery, upper and lower faces of the steel ring were carbonized and quenched with its outer periphery protected against carbonization, so that the steel surface had a hardness of HRc55 The steel ring was preliminarily provided with degassing grooves prior to carbonization and quenching as shown in Fig. 3. The carbonized and quenched steel ring was cold-fitted into the cemented carbide ring with a fitting margin of 0.015 mm to obtain close contact between the two rings. Electron beam, 60 KV and 90 mA, was applied circumferentially along the end face of the interface (A) at a velocity of 800 mm/min in a vacuum in such manner that said beam is applied to the interface between the steel and the cemented carbide.On the side of the steel of the roll thus obtained was found a welding layer 1.ON1.5 mm in width and 15 mm in depth, and the two rings were completely welded with the interface on the side of the cemented carbide thoroughly free from melting. The annular compression strength of the roll was tested to obtain a result of 51.3 tons, which was about twice as high as that of the conventional roll, since the annular compression strength of the compound roll of the same size produced by the conventional soldering method was 27 tons.

As described hereinabove, the invention enabled the production of a wear resisting member having great bonding strength and free from stress after welding with high precision and economy.

Example 2 In the production of a side slitter for cutting steel plates comprising, as shown in Fig. 4, Fe 40% Ni alloy ring 12 (320 mmf in outside diameter, 280 mm# in inside diameter and 20 mm in thickness) fitted to the inside of cemented carbide ring 11(400 mmf in outside diameter, 320 mmf in inside diameter and 20 mm in thickness) consisting of 85 wt % WC and 15 wt % Co alloy, and SCM440 ring having 0.45% carbon 13 (280 mm# in outside diameter, 80 mmf in inside diameter and 20 mm in thickness) fitted further thereinside, each of the rings was coldfitted with a fitting margin of 0.03 mm to obtain close contact respectively.The end face of the interface (B) was welded by applying electron beam circumferentially thereof. The conditions of application of the electron beam were 1 50 KV, 10 mA, velocity 500 mm/min in a vacuum. Then the end face of the interface (C) was circumferentially welded under the same conditions. The side slitter thus obtained was completely welded. When a steel plate 2 mm in thickness was cut by this slitter, it was found to be far stronger than the conventional soldered cutter.

Example 3 In the Morgan roll of the same size as in Example 1, the cemented carbide (14 in Fig. 6) was produced as a ring 159 mme in outside diameter and 136 mmf in inside diameter, while steel (SCM445) was produced into a ring 126 mm in outside diameter and 87 mm in inside diameter. The steel ring 15 was quenched so as to have hardness of HRc44. Ni rings 16 (124 mmf in outside diameter, 106 mmf in inside diameter and 10 mm in thickness) were fitted round the upper and lower outer peripheries of the steel ring respectively as shown in Fig. 6. The interface (B) was machined so that the fitting margin was 0.03 mm, and the cemented carbide ring and the steel ring were integrated by cold-fitting.Electron beam 150 KV and 10 mA was radiated at a velocity of 500 m/min in a vacuum of 10-4 Torr in such manner that the Ni part only of the interface (B) was melted. Referring to Fig. 6, the cemented carbide and Ni ring were bonded by welding the part designated at 17, and then the Ni ring and steel ring were bonded by welding the part designated at 18. The compound roll thus obtained was finished into the predetermined size. When the roll was used as a wire rolling roll under the conditions of wire material temperature 9000C and wire velocity 60 m/sec, the roll exhibited a useful life of 500 Ton/KAL, which was same as that of the conventional cemented carbide solid roll. The roll could be used until its thickness of the cemented carbide was reduced to 5 mm after machining. Its breakage resistance was found to be superior to that of the cemented carbide solid roll.

Example 4 A cemented carbide ring and a steel ring were prepared the same as in Example 3, and an Fe40Ni ring 20 of small thermal expansion coefficient was fitted round the outer periphery of the steel ring. The Fe-40Ni ring 20 was 126 mmf in outside diameter, 106 mmf in inside diameter and 70 mm in width.

The cemented carbide ring 18, Fe-4ONi ring 20 and steel ring 19 were combined in three layers in the order mentioned as shown in Fig. 7.

The part designated at 21 was welded by electron beam, and then the part designated at 22 was welded. There was no sign of cracks arising from welding. The roll was used as a hot rolling roll, and it was found to have a longer useful life and greater breakage resistance compared with the cemented carbide solid roll in Examples 1 and 3.

The foregoing are examples of the composite wear resisting member according to the invention and of the method for producing the same. The range of utility of the invention covers all the composite tools obtained by welding cemented carbide with a steel or cast iron member, for example, hot rolling roll, steel cutting slitter, drill, punch, bite, hob, etc.

Claims

1. Composite wear resisting member comprising a cemented carbide and a steel member characterized in that the cemented carbide and the steel member directly abut each other, part or whole of the interface on the side of the steel melted slit-wise by a high energy beam being welded to the interface on the side of the cemented carbide.

2. Composite wear resisting member as claimed in claim 1, wherein said composite wear resisting member is a hot rolling roll comprising a cemented carbide ring with a steel ring abutting the inside thereof, the abutting face of the steel ring below 20 mm at both ends in the direction of the thickness thereof being melted slit-wise by a high energy beam and welded to the interface on the side of the cemented carbide.

3. Composite wear resisting member as claimed in claim 1 or 2, wherein the cemented carbide principally consists of WC with a bonding metal above 10 weight %, the steel member containing carbon below 0.5 weight %, the steel member except its abutting face being carbonized and quenched thereby to impart high hardness and wear resistance thereto.

4. Composite wear resisting member for use in hot rolling rolls or slitters wherein a steel ring having a thermal expansion coefficient of 3N10X10-6 cm/ C up to 3000C, or a cast iron ring having an elasticity limit below 50 kg/mm2, or a ring of pure metal, such as Cu, Ni, Co, is disposed in a cemented carbide ring so as to directly abut the inside thereof, a steel ring having greater wear resistance than said ring being disposed in said steel ring or cast iron ring so as to directly abut the inside thereof, the cemented carbide and the first steel ring being welded by melting slit-wise part or whole of the interface on the side of said steel ring by high energy beam, the first and second rings being also welded by melting the interface thereof by high energy beam.

5. Composite wear resisting member as claimed in claim 1 or 4, wherein degassing grooves are provided on the interface between the steel member and cemented carbide, the interface being welded by applying a high energy beam thereto.

6. Composite wear resisting member as claimed in claim 1 or 4, wherein the high energy beam is an electron beam or laser beam.

7. The method for producing a composite wear resisting member consisting of cemented carbide and steel member, wherein the cemented carbide and the steel member are brought into direct adhesion by fitting and the like, a high energy beam being radiated in a non-oxidizing atmosphere or a vacuum in such manner that it is applied to both the cemented carbide and steel member at the end of the interface thereof or at least within 0.5 mm on the side of the steel member, part or whole of the interface on the side of the steel member being melted slit-wise thereby enabling to weld the cemented carbide and steel member.

8. The method for producing a composite wear resisting member wherein a steel ring having a thermal expansion coefficient of 3~10x 10-6 cm/ C up to 3000C, a cast iron ring having an elasticity limit below 50 kg/mm2, or a Cu, Ni, Co ring is brought into close contact with the inside of the cemented carbide ring, a high energy beam being radiated in a non-oxidizing atmosphere or a vacuum in such manner that it is applied to both the cemented carbide and steel member at the end of the interface thereof, part or whole of the interface on the side of the steel ring being melted thereby enabling to weld the cemented carbide and the steel member, another steel ring having high hardness and great wear resistance being brought into contact with the inside of the said steel ring, the interface thereof being welded by means of the high energy beam.

9. The method for producing a composite wear resisting member as claimed in claim 7 or 8, wherein degassing grooves are preliminarily provided on the interface between the steel member and the cemented carbide, the interface being welded by applying a high energy beam thereto while removing gas generated therein.

10. The method for producing composite wear resisting member as claimed in claim 7 or 8, wherein the high energy beam is an electron beam or laser beam.

11. Composite wear resisting members substantially as hereinbefore described with reference to the accompanying drawings.

12. The methods of producing composite wear resisting members substantially as hereinbefore described with reference to the accompanying drawings.