RU2003734C1 - Method of chemical and thermal treatment of steel articles - Google Patents

Description

The invention relates to metallurgy, in particular to chemical-thermal treatment of steel products, in particular to chromium plating methods, and can be used in mechanical engineering and other industries to increase the operational stability of machine parts operating under conditions of intense mechanical and thermal loads.

There are known methods of diffusion chromium plating from the gas phase by a contact method, in which the products are placed in a container with a saturating mixture, after which they are heated to a saturation temperature, isothermal exposure for 4-10 hours and cooling. (G. Dubinin. Diffusion chromium plating of alloys. M: Mechanical Engineering, 1964, p. 451). The disadvantages of this method are the long duration of the process and the shallow depth of the layer consisting of chromium carbides in the processing of sredneglerodny alloyed and stamped steels.

The closest in technical essence and the achieved effect is a method of chemical-thermal treatment, including the preparation of a saturating mixture containing 53.2 wt.% Chromium oxide, and 13.3 wt.% Aluminum, 4.7 wt.% Fluorine - aluminum (activator), 28.8 wt.% alumina (inert diluent), loading into a container, heating to 900-1200 ° С, holding and cooling (L. L. Lkhovich and others. Application of metallothermy method for chemical heat treatment.In Sat. Protective coatings on metals, issue 9, 1975. S. 17-24).

When chromizing media of non-carbon and die steels of known composition in the SHS ignition mode, the thickness of the surface layer is insufficient. In addition, when tested for heat resistance under conditions of abrupt temperature changes, cracking and crack formation of a diffusion layer, consisting mainly of chromium carbides, are observed.

The aim of the invention is to intensify the process, increase the heat resistance of the layer on the inner surface of the product due to the formation of a diffusion layer with an inner zone consisting of solid chromium in a-Fe, and the efficiency of the process.

This goal is achieved by the preparation of saturated mixtures of 2 compositions containing, as an inert diluent, the reaction product of chromium oxide with aluminum, aluminum chloride crystalline hydrate as an activator, and chromium oxide and aluminum are taken

in a molar ratio of 1: 2 in the following ratio of components in the composition No. 1, wt.%:

A mixture of chromium oxide and aluminum about molar

ratio 1: 233.5-64.5

Chemical product

oxide interactions

chrome and aluminum 35.0-45.0

0 Crystal hydrate

aluminum chloride 0.5-1.5 and in the composition No. 2, wt.%:

Chromium oxide mixture

and aluminum in a molar 5 ratio of 1: 228.0-47.6

Chemical product

oxide interactions

chromium and aluminum 47.6-71.1

Crystalline Hydrate 0 Aluminum Chloride 0.9-4.8

the products are loaded into the reactor in the following order: first, the product channel is filled with a saturating mixture of composition Mg 1, then the products are placed vertically in re-5 acor, and then the reactor is filled with a saturating mixture of composition N; 2 when the mass ratio of the mixtures and the processed products per unit of their length is within 1: (1-2). heating is carried out at a speed of 0-10-20 deg / min until the saturating mixture of composition No. 2 self-ignites, and exposure at the saturation temperature is carried out for 30-90 minutes.

The use of a saturating mixture of composition No. 2 makes it possible to achieve process efficiency due to the higher content of inert diluent. In this case, composition No. 2 provides the conditions for self-ignition of a saturating mixture of composition No. 1, with a Q ratio of components taken up within the declared limits.

An inert solvent in both compositions of saturating mixtures, which is used as the product of chemical interaction of chromium oxide and aluminum, prevents sintering of mixtures and their adhesion to the surface of products. The use of aluminum chloride crystalline hydrate as an activator enhances the process as a result of accelerated delivery of active chromium atoms to the surface of workpieces. In addition, the activator captures the initial moment of ignition.

5 Chromium oxide and aluminum are taken in a molar ratio of 1: 2, i.e. in stoichiometry to produce pure chromium and alumina. Deviation from stoichiometry, for example, in the case of excess chromium oxide and a lack of aluminum as a result of the reaction

reduction in a mixture along with chromium and alumina there will be an excess of chromium oxide and the object of the invention will not be achieved. In the case of a lack of chromium oxide and an excess of aluminum upon saturation, along with diffusion of chromium, aluminum diffusion will also be observed, which will negatively affect the heat resistance.

When the content of the mixture of chromium oxide and aluminum in composition No. 2 is lower than the claimed self-ignition, the mixture of composition No. 1 does not occur, and if the content is higher than the claimed heating of the inner surface of the products from the mixture of composition No. 1, it will exceed the melting temperature of the material of the products. When the content of an inert diluent in a mixture of composition N 2 below the claimed high temperatures arise on the surface of the channel of the products, and when the content is higher than the claimed, self-ignition of composition No. 1 does not occur.

If the content of the activator in the mixture of composition No. 2 is lower than the declared value, the ignition temperature and the time before it begins to increase, which leads to a deterioration in the efficiency of the process and degeneration of the process in the internal channel. Exceeding the declared limit leads to a decrease in the total heat release during autoignition.

The content of the components in the mixture of composition No. 1b of the stated limits ensures thermal stability due to the formation of a surface layer on the inner surface of the product of the required phase composition with an inner zone consisting of a solid solution of chromium in a-Fe. The outer zone of the layer consists of chromium carbides.

The vertical arrangement of the products in the reactor provides uniform diffuser layers along the entire length and reduces lateral deformations.

The claimed ratio of the masses of the mixtures to the mass of the products makes it possible to provide ignition conditions for the saturating mixtures of compositions No. 1 and No. 2, which leads to an intensification of the process and an increase in heat resistance.

A heating rate of 10-20 deg / min until the moment of self-ignition provides self-ignition conditions and uniform heating of the contents of the reactor. At a heating rate lower than the claimed one, degeneration of the self-ignition process is observed, and at a heating rate higher than the claimed in the reactor large temperature gradients are observed over the cross section.

The exposure time at a saturation temperature in the specified range ensures the efficiency of the process and the achievement of the desired properties of the surface layer in the product channel. A time below 30 minutes is not enough, and above 90 minutes is not economical and does not improve the achieved characteristics of the surface layer.

0 Example. Chromium plating of samples and parts made of medium-carbon (50RA, ZOKHN2MFA) and die (25KhZNZM6CA), is carried out in non-rusting steel reactors. The products are loaded into the reactor in the following order: first, the internal hole of the products is filled with a saturating mixture of composition No. 1, then the product is placed vertically in a reactor, to the bottom of which a layer of saturating mixture No. 2 is pre-filled with a thickness of 20-30 mm. Products in the reactor positioned so that the distance to the walls of the reactor was not less than 15-20 mm, and the distance between the articles should be

5 is equal to their thickness. The articles are filled with saturating mixture No. 2. The distance from the top edge of the article to the edge of the reactor should be at least 40 microns. A stainless tube is placed on top of the reactor

0 steel through which argon is supplied to the mixture. Prepared for saturation, the reactor is placed in the furnace and heated with it to 600 ° C at a speed of 15 deg / min, after which the formation of coatings is carried out with thermal self-ignition of mixture No. 1 in the product channel for 30-90 min at 950-1050 ° WITH. After the end of the process, the reactor is removed from the furnace and cooled in air, after chegb

0 mixture with processed products is poured onto a pallet.

The thermal stability was evaluated by heating the samples in a gas flame

5 burners at a temperature above Асз for 6с with sharp cooling into water. The criterion of heat resistance was the number of heating-cooling cycles until microcracks appeared.

0 The intensification of the process was evaluated by the depth of the layer by the metallographic method.

The table provides comparative data on the intensification of the process,

5 heat resistance and chipping and cracking.

Summarizing the results presented in the table, it can be stated that the processing of long, hollow, cylindrical products with a channel diameter of 5-10 mm by the proposed method makes it possible to intensify the saturation process and increase the thermal stability by 2 times. The increase in heat resistance is associated with the formation of a surface Christmas tree with an inner zone consisting of a solid solution of chromium in Ci-Fe; moreover, during tests for heat resistance, near cracking is not observed. The formation of a surface layer is not observed.

Thus, the presented information also indicates the achievement of the object of the invention.

(56) Protective coatings on metals. Kiev: Naukova Dumka, vol. Kb 9, 1975, p. 17-24.

 - a product of eeimodelstayl oxidol rsme and alu-aipp 4 - crystalline hydrate of apuyu chloride Н.1Ч

Claims (1)

The claims METHOD OF CHI M AND CO. - T M AND C AND AND PROCESSING OF STEEL PRODUCTS,. predominantly long, hollow, cylindrical with an internal diameter of 5-10 mm, made of medium-carbon alloyed and stamped steels, including the preparation of a saturating mixture containing a mixture of chromium oxide and aluminum, an inert diluent and activator, loading the product and a reactor with a saturating mixture, heating holding at saturation temperature and cooling, characterized in that, in order to intensify the process, increase the heat resistance of the surface layer of the product by forming a diffusion layer inner zone consisting of a solid solution of chromium in a- Fe-, and economical process proaod m saturating preparation of mixtures of two formulations containing a diluent kachestae pnertio- of the reaction product of chromium oxide and aluminum, as activator - crystalline hydrate of aluminum chloride, and chromium oxide and aluminum are taken in a 40 molar ratio of 1: 2 in the following ratio of components in composition No. 1, wt%: . Mixture of chromium oxide and aluminum in a molar ratio of 45 1: 233.5-64.5 The product of the interaction of chromium oxide and aluminum 35.0-45.0 Crystalline hydrate of aluminum chloride 0.5 -1.5 50 in the composition, wt.%: A mixture of chromium oxide and aluminum about a molar ratio of 1: 228-47.6 The product of the interaction about to - g5 of chromium soda and aluminum 47,6-71,1 Aluminum chloride crystalline hydrate 0.9-4.8 and the loading of products is carried out as follows: first fill the product channel with a saturated mixture of composition N1, then 9200373410 the products are placed vertically in the reactor, heating is carried out at a rate of 10-20 and then the reactor is filled with saturating, deg / miX until the moment of self-igniting mixture of composition N2 at a ratio of saturating mixture of composition N2, and the holding time of the mixtures and processed products is saturation temperature is carried out per unit of their length within 1: 1 - 2L naked 5 for 30 - 90 minutes.