SU1764968A1 - Process of restoring cylindrical long parts - Google Patents

Abstract

Usage: mechanical engineering and turbine construction, in particular the manufacture and restoration of used parts of turbines made of pearlitic steel. SUMMARY OF THE INVENTION: To increase wear resistance and corrosion resistance of products operating at temperatures above 400 ° C, prior to electric spark doping, preliminary annealing is performed to relieve stresses and stabilize the structure and to grind to remove the defective layer, after which the worn out layer is increased to the required dimensions, and then heated and rolled. 1 dw., 2 tab.

Description

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The invention relates to the engineering and the repair of agricultural machinery, in particular, to methods of restoring cylindrical length-dimensional products from pearlite steel.

A known method of repairing machine parts consists in applying a material with an electric-spark doping on the surface being repaired, in which, to improve the quality and accuracy of the surfaces being repaired, carbides of refractory metals of a given size and continuity are applied, then subjected to electromechanical treatment with carbide rollers; em 500-550 MPa.

This method involves the restoration of the surface of the part with the formation of a multitude of refractory particles on the surface after they are pressed into the base metal, followed by rollers.

The disadvantage of this method is the heating of the surface layer under the electrocontact exposure up to 700-1000 ° C, which leads to a change in the properties of the core and loss of stability when operating a long-length rod-type part. In addition, hard alloys are expensive and scarce to repair parts in repair production conditions.

Another method of surface restoration, closer in technical essence to the proposed one, is a prototype and consists of electrospark doping followed by surface plastic deformation. In accordance with this method, after the electromotive alloying of the surface of the parts (shafts, axles, etc.), they are processed with a steel ball under a load of 345 N in order to increase

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length-dimensional products doped by the electrospray method. Surface plastic deformation increases the hardness and wear resistance of products.

The disadvantage of this method is that during operation of products in the temperature range of 400-550 ° C, a softening process occurs due to the recrystallization of the hardened layer, which contributes to a decrease in hardness, wear resistance and corrosion resistance of the surface. Reduced wear resistance and corrosion resistance of products during operation leads to scuffing, metal welds and loss of shape. As a result, there is a jamming of parts during operation.

The aim of the invention is to increase the wear resistance and corrosion resistance of products operating at temperatures above 400 ° C.

This is achieved by the fact that when lengthy products made of pearlite steel are restored, electric annealing is performed prior to electrospark alloying to relieve stresses and stabilize the structure, grind to remove the defective layer, then build up the worn out layer to the required size, and then heat run in. The temperature of the stabilizing annealing is chosen in accordance with the expression

toTx tn pn - K 49,

and the preheating of the products before the run-in is carried out to a temperature exceeding the operating temperature but lower than the temperature of the technological holiday.

The restoration of cylindrical lengthy articles of pearlitic steel is carried out according to the following technology: stabilizing annealing at a temperature

1tzh tn pn - K Ho, 49;

grinding to remove fodder and rust;

build-up of the worn layer to the required dimensions by electro-spark doping;

heated to a temperature above the temperature of operation, but below the temperature of the technological holiday;

subsequent surface rolling on the proposed method.

Example. Testing of the proposed method for the recovery of steel products was carried out (see test report).

For comparison, the reduced layer was studied on steel products obtained by processing in two different ways.

The first method (prototype method) is to restore the layer with an electric spark alloying of steel products according to the mode: the discharge energy is 0.1 J, the pulse repetition rate is 100 Hz (the alloying electrode is 0 steel 40x13), the ball is run-in with a force of 345 N.

The second method (proposed) is annealing at a temperature of L h tH.n.n. - К-Нр, 49 520 ° С, mechanical processing (grinding),

5 electric alloy alloying of steel products according to the mode; the energy of the discharge is 0.1 J, the pulse frequency is 100 Hz (the alloying electrode is steel 40x13), heated in a furnace to a temperature of 500 ° C, tested with a ball with a force of 345 N. For the test, samples of cylindrical 251 MF and 20XIMIOTP steels were used, imitating the steam distribution node of the turbine of the type K-300-240 and K-500-240.

5 Samples processed according to the first and

the second method was tested in a MP-2UM type laboratory muffle furnace at a temperature of 550 ° C (corresponding to the operating temperature of the steam distribution components in

0 K-300-240 and K-500-240 type turbines for 1000 hours).

The hardness and depth of the hardened layer were measured on the samples before and after testing. We also conducted wear tests.

5 and corrosion resistance. Test data are given in table. one.

Tests have shown that the hardness and wear resistance of specimens recovered by a known method are reduced in the course of operation, there is a gain and traces of corrosion are found. The hardness and wear resistance of the samples, restored by the proposed method, after 1000 hours of testing remained on

5, the level of corrosion and weight gain of the samples was not observed. Consequently, the reduced layer on steel products obtained by processing according to the claimed method, i.e. with the use of stabilizing annealing at a temperature calculated by the proposed formula and equal to 520 ° C (tH p n. 660 ° C and K 0.35), grinding, electrofusion doping, followed by heating to 500 ° C and running. After a long exposure at a temperature of 550 ° C, a constant hardness is ensured, the wear resistance and the corrosion resistance of the surface of the products are high due to the formation of oriented stable carbide and carbonitride phases. This treatment maintains a stable structure of the core of the stem, which ensures its elastic properties in operation.

The drawing shows the structure of the restored layer obtained by the known and claimed methods.

Test results

The increase in corrosion resistance of products restored by the proposed method is due to the fact that the run-in of products previously heated to a temperature above 400 ° C, but lower than the operating temperature (550 ° C), as compared to running on a cold surface or surface heated in the process of concomitant heating with an electric doping alloy (150-250 ° C), ensures the formation of the most dense structure without defects (pores, microcracks).

It is statically established that the number of defects without preheating reaches 9-14k pcs./cm2, and with heating it is practically absent, does not exceed 1-2 pcs./cm.

Conducting a preliminary stabilizing annealing, taking into account the state of the working surface, the level of its hardness, as well as the preservation of the properties of the core, provide the necessary level of quality of the growing layer when restoring long parts.

Optimal quality indicators that provide for stress relief and structure stabilization are achieved with a differentiated approach to the choice of a coefficient characterizing the temperature correction, taking into account the effect of hardness. It is established that the coefficient K for the hardness level NLD49 is in the range of 0.15-0.85 ° C / unit. hardness

In tab. Table 2 gives K values for different levels of hardness, which vary with the degree of wear of the hardened layer.

Example. The temperature of the preliminary annealing of the restored parts made of steel 20XIMIOTP with a surface hardness after decommissioning equal to Nf ° -49 400, will be

Тстж 660 - 0,35-400 520 ° С.

At this annealing temperature, when building, it provides high quality transition layer, there are no defects (pores, cracks, etc.). The level of achievable properties in tests for hardness stability and corrosion resistance are given in Table 1.

The technical advantages of the inventive method are as follows:

restoration of used products;

ensuring stable wear resistance and corrosion resistance of reconditioned products operating at temperatures above 400 ° C for the entire period of operation;

- increase the service life of recovered products.

The economic effect from the implementation of the claimed method is 118.8 thousand rubles per year per K-500-240 turbine.

Claims (1)

Invention Formula A method of restoring cylindrical lengthy products, including electric-spark doping and running in a surface, characterized in that, in order to increase the wear resistance and corrosion resistance of products operating at temperatures above 400 ° C, a preliminary annealing is performed to remove heat and stabilization of the structure and grinding to remove the defective layer, and before the run-in, the products are heated to a temperature below the tempering temperature, while the temperature the aura of the above mentioned pre-annealing is chosen according to the expression   tn.n.n. - K, 49, where gotzh - temperature of preliminary annealing, ° С; tH.n.n. temperature of onset of falling hardness; H, o, 49 microhardness of the worn surface; K - temperature correction, taking into account the effect of hardness, ° C / unit. hardness  The wear resistance of the samples before the test (at 550 ° С - 1000 h) was taken as 1. Temperature correction (K) for various microhardness values but Table 1 table 2 five