CS199184B1 - Forming smooth surfaces from metal carbides and nitriles - Google Patents

Description

The invention relates to a process for forming smooth coatings of metal carbides and nitrides. In particular, Ti, Zr, Hf, V, Nb, Ta, Si or Gr, Mo, W, respectively, intended to form guide surfaces for guiding low moving moving parts and for surface treatment of tools.

The frictional and guiding surfaces of the components should have a surface formed in such a way. to minimize abrasion. To a large extent, Kaka is often required not to wear the counterpart. In technical practice, these requirements are routinely solved by appropriate selection of friction pairs of unequal materials. In more complex cases, these methods are not sufficient and the solution is sought in the use of soft liners filled with harder particles or in the use of hard coatings with low surface roughness. For this purpose, hard surface layers are relatively laboriously treated. In the case of thin surface layers, mechanical treatment is practically not feasible, as the continuity of such a layer is damaged and thus its wear resistance decreases considerably. The wear resistance of the guide parts is also favorably influenced by the compressive stress in the surface layer, but does not have a favorable effect on the wear behavior of the guided parts. Therefore, these surface treatments, which increase the compressive stress of the surface layers, are suitable for surface treatment of all tools. requires an extension of the service life.

Nitride or carbide double slags of Ti, Zr, Hf, Y, Nb, Ta, Si and Gr, respectively. The MO, W, used for the production of guide surfaces, has so far been formed on alloys of aluminum.

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Genides of these metals in a hydrogen or inert atmosphere with an admixture of a reaction-capable component such as nitrogen; methane, at elevated temperature. In this case, the metal diffuses and the reaction-capable components into the steel and the reaction product, i.e. the nitrides or carbides, is formed. The reaction product is deposited under commonly known technological conditions, such as a uniform alloy layer, relatively evenly covering the treated surface of the steel or cast iron parts. The surface roughness of this coating depends on both the initial roughness of the steel or cast iron surface and the thickness of the coating. As the thickness of the cover layer increases, the surface roughness of the cover layer always increases. The increase in roughness adversely affects the mechanical properties of the coating, making it more brittle, brittle and less abrasion resistant. Due to its unfavorable properties, in particular the formation of abrasive dust, it increases the abrasion even in moving counter parts. In cutting and other tools, part of the cutting edges or other functional surfaces of the tool are damaged.

One known solution by which the cover layers are obtained on a thin layer of decarburized backing material to form the guide surfaces of the parts is that the cover layers are formed by the outer part of the hard layer, the thickness of which corresponds to up to 30 '.

- multiple of the surface roughness of the guide surface. The hard layer is based on the soft interlayer resulting from the decarburization of the material. The thickness of the intermediate layer is up to 50 times the surface roughness of the guide surface, the hardness of the hard layer exceeding the hardness of the material guided by it.

Technological treatment of the coating layers is formed in such a way that the component to be formed is placed in a reactive atmosphere at a barometric pressure of about 1150 ° C with a Hg content in the range of 50% to 99.5% by volume. 49% to 0.45% by weight of N, and 0.0.001% to 0.1% by weight of halides Ti, Zr, Hf, V, NB, Ta, Si and Cr, Mo, W. The hard layer formation is then facilitated by depressurization and insertion of the component to an ionizing voltage above 250 V or the corresponding coronary discharge. The component is connected to the cathode of the device.

It has been shown that one of the disadvantages of these processes is the formation of tensile stress coatings. Tensile stresses occur in the surface layers of materials processed at temperatures of 400 to 1500 ° C, depending on the content of alloying additives.

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This phenomenon limits the use of ledeburitic and especially high speed steels for the aforementioned purposes and is the reason why especially the surface roughness increases especially in these types of steels.

The above-mentioned disadvantages of existing solutions and technological processes and further improvements are provided by the method of forming smooth coatings of carbides and metal nitrides according to the invention, which consists in that they further act on the smoothed carbide and metal nitride coating, e.g. a composition of 35% by weight of potassium chloride, 35% by weight of sodium carbonate and 30% by weight of sodium cyanide at 800 to 1050 ° C or a carburizing atmosphere with a starting composition of 2λ> methane by volume and 98% by volume hydrogen at 1000 ° C.

By adjusting the surface according to the invention, not only the roughness of the surface to be treated is simultaneously reduced, while the original tensile stress is changed to slightly compressive. The coating thus provides a surface layer with more favorable properties on a substrate material in which, after heat treatment, all soft and intolerable interlayers disappear from the previously functional decarburized layers. In addition, the corrosion resistance is improved, or part of the titanium nitrides turns into titanium carbide. The method according to the invention makes it possible, inter alia, to process a number of tool and construction steels.

In carrying out the process, a coating of Ti, Zr,

Hf, V, Nb, Ta, Si or Cr, Moj W. In this treatment, the surface density is increased. By mechanical pressing, for example by rolling, calibrating, the surface is smoothed again. By smoothing, the hard substances are squeezed into the soft, carbon-lined layer below the nitride layer. This smoothing proyede with movement in one direction, thereby creating unidirectional seeds for further crystal growth. To this end, in order to significantly improve the technical properties, the treated surface is treated with a carburizing medium at reaction temperatures. As a result, the soft and low-bearing surface portions containing the decarburized base material under the titanium nitride solidify without increasing the density. In this case, it is possible to exchange nitrogen for carbon in the surface layer by exchange reactions, for example, to change titanium nitride to titanium carbide, which results in a marked increase in the hardness of the surface to be treated.

Example:

The surface treatment of parts made of carbon steel containing 0.60% carbon at 800 to 1100 ° C in an atmosphere composed of 99.5% by weight of hydrogen and 0.5% by weight, duéíku blended with 0.1% by weight of TiCl ₄ · Six After 3 hours, a TiN layer having a thickness of 3 to 25 µm was formed and an carbon-lined layer having a thickness of 100 µπι. The surface Digiost increases from the original 0.4 HRa for layers thicker than 10 µm in thickness to values exceeding 6 HRa. By pushing the unevennesses so formed into the soft undercoat of steel, the roughness is gradually reduced to 0.8 HRa. The treated surface is carburized for 8 hours in a salt water bath containing 35% by weight of KCl, 35% by weight of NagCO3 and 30% by weight of NaCN at 900 DEG C. or in a carburizing atmosphere of 2% by volume CH3, 98% volume Hg at 1000 ° C.

Claims (1)

DRAWING THE INVENTION Process for forming smooth coatings of metal carbide and nitride layers, in particular titanium, zirconium, hafnium, vanadium, niobium, tanial, silicon, possibly chromium, molybdenum, tungsten, formed on a decarburized steel or cast iron surface and subsequently treated by smoothing, e.g. pressure-smoothing, characterized in that the smoothed carbide and metal nitride coating is further treated with a carburizing medium, for example a salt bath of 35% by weight of potassium chloride, 35% by weight of sodium carbonate and 30% by weight of sodium cyanide at 800 to 1050 ° C or a carburizing atmosphere with an initial composition of 2% by volume methane and 98% by volume hydrogen at 1000 ° C.