RU2349432C2 - Cyanidation method of steel or titanic products - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns ferrous metallurgy field and mechanical engineering. Particularly it concerns cyanidation methods of steel or titanic products. Method includes application on working surface of product of diffusion layers containing carbon and nitrogen. Diffusion layers application is implemented by means of electroerosion alloying by graphite electrode, cooled by gaseous nitrogen.

EFFECT: increasing of microhardness and wear resistance of received layers.

1 tbl, 1 ex

Description

The present invention relates to the field of ferrous metallurgy and mechanical engineering, in particular to the hardening of parts and products by diffusion cyanide.

A known method of solid cyanide using a mixture of the following composition: 60-70% charcoal and 30-40% yellow blood salt. Intensive dissociation of cyanide salts begins in the solid state at 540-560 ° C (Geller Yu.A. Instrumental steels. M: Metallurgy, 1975, p. 489-490). The disadvantage of this process is the high cost of the nitrogen-containing component - yellow blood salt, as well as its toxicity.

A known method of cyanidation using a mixture of the following composition: 70% yellow blood salt, 20% carbon black, 5% chalk and 5% soda. Intensive dissociation of cyanide salts begins upon melting at a temperature of 650 ° C (Dolzhenkov VN Cyanization of improved steels in pastes. Kursk, State Technical University, 2001, 127 pp.). The disadvantage of this process is the high cost of the nitrogen-containing component - yellow blood salt, its toxicity, as well as the relatively high temperature of the process compared to other low-temperature processes.

A known method of hardening steel parts, including high-temperature nitrocarburizing with holding at the beginning at 800-900 ° C, and then at 940-960 ° C followed by tempering at 630 ± 10 ° C, and hardening and tempering according to the accepted regimes (Geller Yu.A. Tool steels. M.: Metallurgy, 1975, S. 493-514).

However, the known method is characterized by the duration of the nitrocementation process and the insufficient depth of the hardened layer. In addition, the application of the known method does not provide the required distribution of hardness.

A known composition of the coating for solid cyanide of steel products, including 50-55 parts by weight urea and 50-45 parts by weight soot (AS No. 2250930, class C23C 8/76, publ. 04/27/2005).

A known composition of water paste applied to the surface of cemented parts in the hardening method, containing carboxymethyl cellulose and urea (A.S. 1164290, class C21D 1/78, C23C 8/76, publ. 30.06.1985).

The disadvantages of the composition of these mixtures in the poor surface coverage, weak and unstable adhesion to the surface, high oxidizing ability and low technology in relation to parts of complex geometric shape and low properties of the surface layer.

Closest to the proposed technical solution is a method of chemical-thermal treatment of self-tapping, mainly finely threaded from carbon steels used to assemble refrigerators, including nitrocarburizing in a composition containing urea and volcanic perlite, quenching from the temperature of nitrocarburizing and tempering, according to the invention nitrocarburizing is carried out at 900 910 ° C in a composition additionally containing Trilon B and polyethylene when their ratio with urea and volcanic perlite is 1: 4: 10: 1, and tempering is tempered by hoists conducted in vacuum of 10 ^-1 mmHg for 45-60 minutes, while the polyethylene is used in the form of a bag for packing parts in the composition for nitrocarburizing (patent No. 2015198, C23C 8/32, publ. 30.06.1994).

A disadvantage of the known solution is the low depth of the diffusion hardening layer, as well as its insufficient hardness.

A common drawback of all known mixtures used in the method of cyanidation and nitrocarburizing of parts from alloy steels and titanium alloys is the high toxicity of the processes, the use of expensive components, the relatively high temperature of the process compared to other low-temperature processes (from 550 to 900 ° C), not high the depth of the hardened layer (0.05-0.17 mm), as well as the instability of the properties of the formed diffusion layers.

An object of the invention is the development of a new, more efficient, environmentally friendly and more productive process of cyanidation of steel parts and products.

The technical result of the proposed solution is to obtain reinforcing diffusion layers with high microhardness and wear resistance.

The technical result is achieved in that in the method of cyanidation of steel or titanium products, including applying to the working surface of the product diffusion layers containing carbon and nitrogen, according to the invention, the diffusion layers are applied by electroerosive alloying with a graphite electrode cooled by nitrogen.

To achieve a technical result on an industrial scale, methods of hardening by concentrated energy flows are proposed, including using electric discharges.

The simplest method is electroerosive alloying.

Electroerosive alloying is especially effective for increasing the wear resistance of products from expensive alloy steels and titanium alloys.

To implement the proposed technical solution, the workpiece is subjected to electrical discharge machining by known methods. Depending on the initial physicochemical properties of the treated surface, the treatment regimes and the type of alloying material — the electrode — are established (see Ivanov GP, Technology of electrospark hardening of tools and parts. Mashizdat. 1961).

The essence of the proposed method consists in the use of graphite as an alloying electrode, cooled by a cooler in the form of gaseous nitrogen.

In this case, the surface of the product is saturated with carbon by mass transfer from the anode (electrode) to the cathode (product), and N ₂ - 2N ⁺ ionization occurs in a stream of nitrogen in the spark zone, atomic nitrogen dissolves in the surface layer of the metal.

Since a high temperature (up to 3000 ° С) is created in the zone of contact of the graphite electrode with the metal, before cooling (due to the removal into the metal), both carbon and nitrogen atoms diffuse to a depth of 0.1 mm, forming a layer of increased hardness due to carbonitride hardening.

At the moment of contact of the electrode with the part, large short-circuit currents occur and the electrode begins to heat up, and if cooling is not performed, the electrode may become hot and droplets of the electrode material will stick to the surface to be treated.

In addition, the heated electrode is oxidized due to interaction with oxygen in the air, which leads to rapid electrode wear.

To eliminate this drawback, it is proposed to produce cooling of the electrode with a cooler. Nitrogen is used as a cooler, which is supplied to the electrode through a special nozzle.

Example

Studies of the modes of electroerosive alloying were carried out on a cutting tool made of high-speed steel grades using carbide electrodes of the VK6, VK8, VK15, T15K6 type, as well as Cr, Ni, Sormite, and graphite.

Experimental testing of hardened parts showed that the best hardening effect of the cutting tool in terms of surface cleanliness and hardness achieved was achieved by applying a hardening coating with a graphite electrode with nitrogen cooling the electrode.

Spark alloying of the cutting tool was carried out with the following parameters:

- technological current, A - one hundred - open circuit voltage, V - 120 is the capacitance of the capacitors, microfarads. - 950 - electrode cooling - nitrogen - hardness of tool material, HRC - 48 - hardness of the material of the 1st layer, HRC - 56 - hardness of the material of the 2nd layer, HRC - 65 - thickness of a 2-layer coating, mm - 0.20

Durable tests of the cutting tool were carried out with the longitudinal turning of blanks made of 30KhGSA steel on a lathe. Cutting inserts were installed and fixed in holders. The cutting conditions were as follows: cutting speed V = 60 m / min, feed S = 0.3 mm / rev, cutting depth t = 0.75 mm. A 5% aqueous solution of emulsol Ukrinol - 1M was used as coolant. For the wear criterion, the value of the chamfer of wear along the rear surface h = 0.4 mm The efficiency of the cutting tool was determined by the value of the coefficient of increase in resistance, defined as the ratio of the resistance of the coated tool to the resistance of the coated tool according to the method of the prototype and to the tool life without hardening. When hardening coatings were applied, nitrogen gas was supplied into the zone of contact between the electrode and the tool through a special nozzle.

Microstudies found that the entire surface had a uniform electrical discharge coating, between the individual sections of the gaps were not observed.

Data on wear resistance is given in the table.

Hardening method Alloying material Tool operating time, min. Wear coefficient 2-layer electroerosive graphite electrode with gaseous N ₂ 325 2.16 2-layer electroerosive VK6 - top layer,
Ni-Cr - lower layer (airflow - nitrogen gas) 340 2.26 coating for cementation (prototype) the mixture specified in the prototype, including graphite and urea 210 1.40 single layer electroerosive coating VK6 240 1,60 control without hardening - 150 1.00

As can be seen from the data in the table, the coefficient of wear resistance of the tool processed according to the proposed technical solution is 2.16-2.26 times higher in comparison with a conventional thermally quenched tool and 1.5-1.6 times higher than that processed by the prototype method.

As a result of electric discharge machining, a wear-resistant diffusion carbonitride layer was formed on the working surface of the products.

The proposed technical solution can significantly increase the wear resistance and heat resistance of products from expensive alloy steels and titanium alloys, which significantly increases the efficiency of the use of products from these materials.

Thus, the claimed technical solution fully fulfills the task.

The advantage of this technical solution is:

- high adhesion strength of the applied electrode material to the instrumental base due to mutual diffusion mechanical mixing;

- the possibility of local coating without special protection of the remaining surface;

- the absence of changes in the physico-mechanical properties of parts;

- the possibility of using instead of the traditional energy-consuming chemical-thermal cyanidation process;

- environmental cleanliness compared to chemical-thermal cyanidation.

Claims (1)

A method of cyanidation of steel or titanium products, comprising applying to the working surface of the product diffusion layers containing carbon and nitrogen, characterized in that the application of diffusion layers is carried out by electroerosive alloying with a graphite electrode cooled by gaseous nitrogen.