DE2840608C2 - Process to improve the solderability of hard metals - Google Patents

Description

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The invention relates to a method for improving the solderability of hard metals by reducing them the carbide content in the surface of the hard metals, which consists of at least one of the binding metals iron, Cobalt or nickel, in particular cobalt, as well as one or more carbides and / or nitrides of the Elements consist of titanium, zirconium, chromium, molybdenum, hafnium, vanadium, niobium, tantalum or tungsten.

Hard metal parts are used for many purposes in cutting and non-cutting shaping Non-hard metals, d. H. usually with steels, connected by soldering with different solders. As examples be carbide teeth for saws, carbide plates for drills, turning, milling, planing, cutting, punching and Shear tools as well as guide and deflection elements called.

In the manufacture of the mentioned tools or tool parts by soldering, the bad has an effect The wettability of the carbide content contained in the hard metal is a problem. There are also different ones Surface conditions of the hard metals that have arisen as a result of the sintering process. To overcome these difficulties have gone over to electrolytically nickel-plating or to the parts to be soldered cobalt. This achieves better wettability of the hard metal body. Same purpose as Nickel and cobalt also perform well as binders in cemented carbide as well as all others solderable metals. According to DE-AS 25 02 275, the metal should be electrodeposited from a Sulphamate bath of the corresponding metal, by vapor deposition using electron beam methods or by Deposition can be applied from a solvent.

However, the methods outlined have several disadvantages. In addition to the sometimes very high production costs, that arise during electroplating or vapor deposition using electron beam processes, the different surface conditions resulting from sintering have a detrimental effect on application a binder. Not to be forgotten are the health hazards that result from the evaporation of There is a risk of nickel, be it through the vapor pressure above the nickel bath or through the development of steam during the process Soldering.

The invention is based on the object of creating a method which has the disadvantages outlined does not have and increases the solderability of hard metals

The object is achieved in that the hard metal is subjected to an electrolytic treatment in an alkaline solution before deip soldering. The electrolytic treatment at anodic potential is expediently carried out in a commercially available galvanizing drum. Potassium hydroxide is preferably used as the lye, since the degradation products formed dissolve easily in it. But other alkaline solutions (e.g. NaOH, Na ₂ CO ₃ , K ₂ CO ₃ ) and / or complex-forming substances are also suitable. The applied voltage or current strength must be adapted to the hard metal to be treated. The method is advantageously applied so that the thickness of the carbide-free surface layer is 0.1 to 10 μm.

The advantage of the method according to the invention over the previously used is that different surface conditions as an unavoidable consequence of the sintering process, no negative effects and a health hazard from carcinogenic substances is excluded. Farther this process can be carried out extremely inexpensively, since it consumes expensive metals not applicable.

The greater wettability of the hard metal surface is achieved when using the method according to the invention not by intermediate layers of z. B. nickel or cobalt, i.e. a metal enrichment of the surface, but achieved in that the surface carbide content is reduced. By removing the Carbide phase, the surface available for adhesion is increased. Surprisingly does not lose the exposed auxiliary metal layer of the hard metal despite the reduction in the carbide content Bond to the hard metal. The "tearing off" of the surface layers does not occur with mechanical Load. The explanation for this is likely to include in the surface enlargement of the material that occurs lie. For example, there were ten carbide drill bits according to DIN 8010 according to the invention in a 4N potassium hydroxide solution at about 20 ° C in an electrolytic solution Treated and soldered and compared with ten more specimens obtained after the one so far known processes had been nickel-plated and soldered. Those from each of the ten samples in 6 test series Measured shear strengths - which can be found in the following table - show a clear

Rehearse. from 10 samples) Nickel-plated Invention I.
Ψ, Starting according to
procedure was standing 285 338 Shear strength in N / mm ² 202 219 287 I. (Average _ 253 308 y Attempt 245 323 395 line _ 223 272 1 _ 176 272 2 3 4th 5 6th

Claims (3)

Patent claims: 1. A method for improving the solderability of hard metal from at least one of the binder metals Iron, cobalt or nickel and one or more carbide (s) and / or nitriles) of the elements Titanium, zirconium, hafnium, vanadium, niobium, molybdenum, chromium, tantalum, tungsten through reduction of the carbide content in the hard metal surface, characterized in that the hard metal treated electrolytically at anodic potential in an alkaline solution prior to soldering will. 2. The method according to claim 1, characterized in that that a suitable alkaline and / or complex-forming solution is used. 3. The method according to claims 1 to 2, characterized in that a carbide-free layer with a thickness of 0.1 to 10 μπι is produced. 15th