EP0164002B1 - Method for manufacturing wear-resistant articles - Google Patents

Abstract

1. Method for the manufacture of wear-resistant composite articles (1) from a metallic base material with a highly wear-resistant area (2) in which particles of hard material are incorporated within the base material, characterized in that the base material, in the form of at least one electrode (3, 33, 43), is continuously remelted by the electrode-slag remelting process in an arrangement of moulds (4 ; 23, 24) under a layer of liquid slag (9) forming a solidified ingot growing from the bottom of the mould arrangement, during which process a pool of molten metal (10 ; 28) forms under the slag layer, and that hard meterial particles (11) with a grain size of 0.1...20 mm are added to the pool (10) for at least one period of time for embedding in the base material, with the period of time or the sum of all time periods being shorter than the total electrode (3) remelting time.

Description

The invention relates to a method for producing wear-resistant composite bodies made of a metallic base material with a highly wear-resistant area in which hard material particles are embedded within the base material, hard material and / or hard metal particles being summarized below and in the patent claims under the name “hard material particles”. The term "base material" also stands for the terms base or matrix material.

It is known to produce wear-resistant composite bodies by welding, a melting electrode being used with a tube consisting of a metal alloy, in which hard material particles are contained. The metal alloy of the pipe can consist of the same material as the base material on which the highly wear-resistant zone is welded. The disadvantage of this method is that only relatively thin wear layers can be applied satisfactorily.

From DE-C 2919477 a composite body with a highly wear-resistant area is known, which is produced by pouring the base material into a mold and by adding hard material particles. The base material of this known composite body can only be welded with considerable effort and can only be machined with difficulty.

When the known composite body is produced by casting, the melted base material is poured into a mold, which preferably consists of molding sand. The hard material particles need a certain minimum time to sink into the area intended for them. Since the mold has no energy supply device, the cooling time (this is the time in which the base material has cooled from the casting temperature to its liquidus temperature) must be greater than the minimum time for the hard material particles to sink. With regard to the temperature resistance of the mold or a corresponding crucible, the casting temperature cannot be chosen as high as desired. However, in order to maintain the temperature difference required for a certain minimum time for the hard material particles to sink, the liquidus temperature of the base material must be set accordingly low. This limits the known casting process to the use of base materials whose liquidus temperature is not higher than about 1400 ° C.

Is deviated from the DE-A 2063181 is known, workpieces of a hochverschleissbeständigen composite _f produce lm and these workpieces together with a less verschleissbeständigen, tough basic or main body in a further step by the Elektroschlakkeumschmelzverfahren with the addition of hard-material particles with a grain size of at most 6 assemble a wear-resistant composite body. The hard material particles to be added are embedded in a master alloy, which is arranged on the outside or inside of the electrode to be remelted with the base material or is melted as a separate electrode. In addition to the fact that a composite body can only be finished in a further process step by joining separately manufactured individual parts, another disadvantage is that the small grain size, at least in the case of hard metal particles, increases the risk of the particles dissolving in the base material and thus embrittlement of the composite material contains what can manifest itself in particular in a bursting under impact stress.

Finally, it is also known from GB-A 2036617 to use the electroslag remelting process for producing a composite body with areas of different chemical compositions, all areas having a different base material.

Based on the prior art according to DE-C 2919477, which forms the basis for the preamble of claim 1, the invention is based on the object of specifying a method for producing highly wear-resistant composite bodies which avoids the aforementioned disadvantages and which allows the use of any Base materials, in particular also those materials permitted, whose liquidus temperature is above 1400 ° C.

This object is achieved by the features characterized in claim 1. The electrode is melted down by the resistance heating of the slag in accordance with the processes in the electroslag remelting process (ESR process). Melting temperatures of up to 1900 ° C are reached. A microfilm of the liquid base material first forms on the end face of the electrode, which is immersed in the liquid slag, from which a drop stream then forms, which travels through the slag layer, with intensive reactions occurring between the base material and the slag, in which the metal drops largely differ unwanted impurities are freed. The drops of the base material cleaned in this way collect in a metal or melt sump at the bottom of the mold, and the block is continuously built up from the electrode material with a corresponding increase in the melt sump.

Due to the high achievable melting temperatures, the choice of base materials that can be used is increased considerably, so that in particular materials with higher melting temperatures can also be used.

The high temperature that can be achieved with the method according to the invention is also significant Liche decrease in the viscosity of the melt, so that the sinking and dissolving of the hard material particles through the base material or in the base material also takes place without problems with those materials whose liquidus temperature is above 1400 ° C. The hot slag pre-heats the hard material particles, which promotes their dissolving in the base material. Due to the low viscosity of the hot slag and the high density differences in the hard material particles and the slag, the hard material particles migrate through the slag layer in a very short time.

In the method according to the invention, the liquid metal sump solidifies into a solid block growing from the bottom of the mold arrangement. In contrast to the known casting processes for the production of wearing parts, only a limited, flat area of the base material - the melting or metal sump - is always molten, so that the hard material particles are only a relatively short way from their storage in or to their anchoring have to travel in the base material. Despite the high slag temperatures customary in electro-slag remelting and a corresponding preheating of the hard material particles, the short time in which the hard material particles can sink through the flat melting sump does not cause the hard material particles to melt and dissolve. Rather, it has surprisingly been found that the hard material particles are only loosened at their edge zones, as a result of which there is a good prerequisite for their anchoring in the base material.

It is possible to place the wear-resistant zone in the middle of a composite or wear body if the electrode is first melted without the addition of hard material particles and the hard material particles are only added at a later point in time and the supply is stopped again before the melting process has ended .

A composite body with a wear zone located between the ends can also be achieved according to claims 3 and 4 if the hard material particles are assigned to the electrode over a corresponding area of their length.

• Fig. 1 ein zylindrisches Einsteckwerkzeug für ein Schlagwerkzeug mit einem am unteren Ende befindlichen hochverschleissbeständigen Bereich,
• Fig. 2 eine Anlage zur Herstellung des Einsteckwerkzeuges nach Fig. 1 während des Abschmelzens der Elektrode in schematischer Darstellung,
• Fig. 3 ein ringförmiges Rohrstück zur Bildung eines verschleiss- und korrosionsbeständigen Rohres,
• Fig. 4 eine Anlage zur Herstellung des Rohrstücks nach Fig. 3 in einem schematisierten Querschnitt,
• Fig. 5 eine an ihrer Oberfläche teilweise mit Hartstoffteilchen beschichtete Elektrode in einer Seitenansicht und
• Fig. 6 eine Elektrode, die auf einem Teil ihrer Länge Hartstoffteilchen enthält, in einem Längsschnitt.

Embodiments of the subject of the invention are shown in the drawing and are described in more detail below. Show it:

• 1 shows a cylindrical insertion tool for an impact tool with a highly wear-resistant area located at the lower end,
• 2 shows a system for producing the insertion tool according to FIG. 1 during the melting of the electrode in a schematic representation,
• 3 shows an annular piece of pipe for forming a wear-resistant and corrosion-resistant pipe,
• 4 shows a plant for the production of the pipe section according to FIG. 3 in a schematic cross section,
• 5 shows an electrode partially coated on its surface with hard material particles in a side view and
• Fig. 6 shows an electrode which contains hard material particles over part of its length, in a longitudinal section.

The insertion tool 1 intended for a hydraulic hammer with a diameter D _I of 75 mm and a length L _I of 800 mm has at its lower end a highly wear-resistant area 2 which extends over a length L ₂ of approximately 100 mm. The insertion tool 1 has the material 42CrMo4 (material number 1.7225) as the base material. In the highly wear-resistant area, tungsten carbide particles are embedded in the base material.

To manufacture this tool, an electrode 3 made of the base material with a diameter D ₃ of 50 mm and a length of 1800 mm is remelted in a copper mold 4 with an inner diameter d ₄ of 80 mm (Figure 2). The copper mold 4, which stands on a copper or base plate 5, is water-cooled and has a water inlet 6, a water outlet 7 and a cavity 8 for the water to flow through.

After the ignition of the electrode 3, the slag 9 entered in powder form is liquefied. The slag powder consists of 60% fluorspar, 20% crystal lime and 20% aluminum oxide (the% data mean mass%). The metal drops 3 ″ formed on the bottom or front side 3 ′ of the electrode 3 migrate through the liquid slag 9 and form a liquid metal sump 10. By solidifying the metal sump 10, a starting block with a height of approximately 10 mm is first built up on the base plate After this starting block has been built up, hard metal particles 11 made of tungsten carbide (WC) are added, 50% of which have a grain size of 1 ... 1.6 mm and 50% of which have a grain size of 0.8 ... 1.2 mm In one test carried out, the base material 42CrMo4 was melted with a line of 0.65 kg / min. During a period of 6 minutes after formation of the starting block, the hard metal particles 11 were melted with a mass flow of 0.52 kg / min using a (not ) dosing device is added, so that the hard material particles 11 make up a proportion of approximately 44.5% in the highly wear-resistant area 2. The volume proportion of the highly wear-resistant area 2 of the entire insertion tool 1 is approximately 12.5%.

In the case of a hardness of the hard material particles 11 of 1100 HV 30, the highly wear-resistant region 2 has the hard material particles 11 of the insert tool 1 produced according to the described method has a hardness of approximately 550 HV 30 and the hardness-free region has a hardness of approximately 400 HV 30.

The pipe section 21 with an outer diameter D ₂₁ and an inner diameter d ₂₁ according to FIG. 3 is provided to form a wear and corrosion-resistant pipe 22 for conveying hot coarse-grained bulk material. This piece of pipe is subjected to thermal and abrasive stress.

The system for producing the pipe section 21 is shown in FIG. 4. Within the water-cooled mold 23 with an inner diameter d _z3 , which - apart from manufacturing-related deviations - corresponds to the _outer diameter D _{21 of} the pipe section 21 or the pipe 22, a likewise water-cooled, centrally arranged copper insert 24 is provided, the outer diameter D _{24 of which} is essentially the same Inner diameter d _{21 of} the pipe section 21 to be produced corresponds. On a common electrode holder 25, a plurality of electrodes 26 are arranged — evenly distributed around the circumference — which are inserted into the cylindrical annular gap 27 between the mold 23 and the copper insert 24. The lateral spacing of the individual electrodes 26 must be chosen so close that the liquid metal sumps 28 formed by the melting are connected to one another in a ring.

To produce the pipe section 21, electrodes made of the material X130CrSi29 (material number 1.4777) are melted off as the base material. After the formation of a starting block of approximately 10 mm in height, tungsten carbide particles are uniformly introduced into the annular gap 27 over the entire melting time. The proportion of tungsten carbide particles in the pipe section 21 can make up 20%. The slag used in powder form consists of one third each of fluorspar, crystal lime and aluminum oxide.

5, like the electrode 3, consists of the base material of the composite body 1 to be produced. On its surface 34, the electrode 33 has a coating 35 of hard material particles 11 over a length L ₃₅ . From the end face 36 to the coating 35, the surface 34 is free of hard material over a length L ₃₆ . The use of such an electrode makes the separate addition of hard material particles unnecessary and thus simplifies the process for producing a composite body. By restricting the coating 35 to a part of the total length L _{33 of} the electrode 33, a composite body can be produced, the highly wear-resistant area 2 of which has a position in the composite body that corresponds to the coating 35. Such a composite body - like the electrode 33 - likewise consists exclusively of the base material and has the highly wear-resistant area 2 between its ends.

FIG. 6 shows a further exemplary embodiment of an electrode, which eliminates the need to separately add hard material particles. The electrode 43 has a pipe section 44 made of the basic material to be used, which is filled in its cavity 45 with hard material particles 11. At its lower end, the electrode 43 is closed off with an end plate 46 made of the base material. At its upper end, the electrode 43 has a solid piece 47 made of the base material.

While the end plate 46, which holds the hard material particles 11 located within the pipe section 44, serves to form the starting block described, the pipe section 44 and the hard material particles 11 contained therein are used to form the highly wear-resistant area 2 and the electrode piece 47 to form the hard material-free area Composite body provided. The packing density of the metal particles 11 within the cavity 45 and the ratio of the volume of the cavity 45 to the total volume of the pipe section 44 allows the proportion of the hard material particles 11 in the highly wear-resistant area 2 of the composite body to be set.

Claims (6)

1. Method for the manufacture of wear-resistant composite articles (1) from a metallic base material with a highly wear-resistant area (2) in which particles of hard material are incorporated within the base material, characterized in that the base material, in the form of at least one electrode (3, 33, 43), is continuously remelted by the electrode-slag remelting process in an arrangement of moulds (4; 23, 24) under a layer of liquid slag (9) forming a solidified ingot growing from the bottom of the mould arrangement, during which process a pool of molten metal (10; 28) forms under the slag layer, and that hard material particles (11) with a grain size of 0.1...20 mm are added to the pool (10) for at least one period of time for embedding in the base material, with the period of time or the sum of all time periods being shorter than the total electrode (3) remelting time.

2. Method according to claim 1, characterized in that the hard material particles (11) are fed separately into the pool (10).

3. Method according to claim 1, characterized in that the surface (34) of the electrode used (33) is coated along part of its length with hard material particles (11).

4. Method according to claim 1, characterized in that the electrode used (43) contains hard material particles along part of its length.

5. Method according to any one of claims 1 to 4, characterized in that the mass per unit time of the hard material particles (11) added during the formation of the highly wear-resistant area (2) amounts to 15-95% of the mass per unit time of the remelted base material.

6. Method according to claim 1, characterized in that the added hard material particles (11) exhibit a grain size of 0.1...5 mm.

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