RU2228242C1 - Method for strengthening parts by induction surfacing - Google Patents

Abstract

FIELD: restoration and strengthening of parts operating at conditions of abrasive wear and shock loads. SUBSTANCE: method comprises steps of making on restored surface recesses by plug welding of steel cleats normally relative to direction of abrasive mass flow acting upon part at operation process; preliminarily filing made recesses with thin layer of easy-to- melt charge and completely filling said recesses with metal-ceramic grit; applying onto prepared surface powder charge containing wear-resistant alloy and flux for forming matrix. EFFECT: enlarged assortment of strengthened parts with improved wear resistance. 4 cl, 6 dwg, 1 tbl

Description

The invention relates to mechanical engineering, in particular to an induction-metallurgical method for the restoration and hardening of parts in accordance with the nature of their wear, operating under conditions of abrasive wear and shock loads, for example, parts of track rubble-cleaning machines.

A known method of induction surfacing (see patent RU No. 2120363, IPC 6 23 K 12/02, publ. 20.10.98,) [1], providing for the cutting of grooves by mechanical means, followed by filling them with a wear-resistant alloy.

The disadvantages of this method are the high complexity of the process of cutting grooves and limited application, since surface hardening is possible only for parts having a sufficient thickness, and with a small thickness, the cut grooves weaken the section of the part.

A known method of hardening by induction surfacing of parts (see patent RU No. 2138377, IPC 6 V 23 K 13/01, B 22 D 19/00, publ. 04/21/98,) [2], which is the closest in technical essence to the claimed method and is taken as a prototype. In order to increase the service life of products operating under conditions of abrasive wear and shock loads, in the prototype method, depressions are applied to the working surface of the part, filled with reinforcing material, a powder mixture is applied to the entire surface of the part and melted under an inductor. The depressions are reinforced with a granular tungsten carbide alloy, and a mixture containing 80% cobalt alloy and 20% boron-containing flux is used as a powder mixture, the charge layer thickness being 2 ... 3 mm with a ratio of tungsten carbide alloy and powder mixture, wt.% : alloy of tungsten carbides 40-60, powder mixture 60-40.

Alloy PG-10K-02 is used as a cobalt alloy, P-1.5 M flux is used as a boron-containing flux, and Relit is used as a granular tungsten carbide alloy.

The disadvantages of the prototype are that the manufacture of recesses on the surface of the hardened part is possible only for parts of sufficient thickness and does not allow hardening of thin parts, such as lining of the working bodies of road-building machines.

The technical result of the invention is the expansion of the range of parts to be hardened with high wear resistance of hardened parts.

The technical result is achieved by the fact that in the known method of hardening by induction surfacing of parts operating under conditions of abrasive wear and shock loads, including the manufacture of recesses on the working surface, filling them with reinforcing metal grains, applying a powder mixture containing a wear-resistant alloy and flux forming on the surface of the part the matrix, followed by its melting by the inductor, according to the invention, the recesses on the working surface are made by welding with a cork seam laths that are perpendicular to the direction of flow of the abrasive mass acting on the part during operation, the resulting recesses are pre-filled with a thin layer of a charge, more easily melted than the charge forming the matrix, then the recesses are completely filled with cermet, and then applied to the resulting surface of the part said powder mixture containing a wear-resistant alloy and flux.

Another difference is that the composition 80% PG-Cp + 20% remelting (Na ₂ B ₄ O ₇ + H ₃ BO ₃ ) is used as a low-melting charge for filling the recesses. Another difference is that as a reinforcing cermet grains use alloys VK or TK granulation 2.5-4 mm, Another difference is that as the powder mixture forming the matrix, use the composition of 75% PG-USCH No.% + 10% PG-Ср2 + 15% flux П1 , 5M.

Another difference is that the layer of powder mixture forming the matrix is applied 3-4 mm thick above the planks.

Figure 1 is a diagram explaining the sequence of the method, where a is a top view, b is a cross section of a hardenable part with welded strips, c is a section of a part with filled recesses with a fusible mixture and a ceramic or VK grout, and d is a section of a part coated on the entire surface of the charge wear-resistant alloy. Figure 2 shows a photograph of the microstructure of the obtained wear-resistant alloy. Figure 3 shows a schematic drawing of a part with steel strips located perpendicular to the flow of the abrasive mass, where 1 is the hardened part, P is the trajectory of the abrasive mass.

The method of hardening by induction surfacing of parts is as follows.

On the surface of the part 1 place steel strips 2 with a thickness of 3-4 mm and a pitch of 15-20 mm (figa, b). Holes 3 are pre-drilled in steel strips with a diameter of 6 ... 7 mm and a pitch of 40 ... 50 mm, through which the strips are electrically welded with cork seams to the hardened part. Fixing holes 3 in the part to prevent their melting are filled with a molding mixture consisting of clay (80%) and quartz sand (20%).

The space between the slats (recesses) is covered with a fusible mixture of composition PG-Cr2 (80%) + remelted Na ₂ B ₄ O ₇ + H ₃ BO ₃ (20%), the thickness of the backfill layer is 1 mm (item 4 in Fig. 1c), on the surface of which reinforcing cermet granules of hard alloy of tungsten carbide (VK) or titanium carbide (TC) granulation of 2.5 ... 4.0 mm are poured until the grooves are completely filled (item 5 in Fig. 1c). A powder mixture of a wear-resistant alloy of the composition PG-USCH35 (75%) + PG-Cr2 (10%) + flux P1.5 (15%) is poured onto the entire surface of the part, the thickness of the filling is 3 ... 4 mm above the strips (item 6 on Fig.1d). After melting a charge and a charge of a wear-resistant alloy on the surface of a part under an inductor with a fusible material, a composite material is obtained in which the wear-resistant alloy matrix is reinforced with coarse hard alloy.

The chemical composition and characteristics of surfacing materials are presented in the table, see in [3, 4].

To ensure reliable fastening of the strips on the hardened surface, in addition to their welding with cork seams, they are brazed with PG-Cr2 alloy (80%) using Na ₂ B ₄ O ₇ + H ₃ BO ₃ remelting (20%) as a flux. The PG-Cp2 alloy has a melting point 150 ... 200 ° C below the melting temperature of the matrix. The amount of flux is determined experimentally and ensures maximum spreading and penetration of the alloy into the gap between the bar and the hardened surface.

The introduction of a wear-resistant alloy (granular powder, grade PG-USCH-35.TU U 332-19-007-97) and surfacing powder PG-Cr2 in the indicated quantitative content of components (see table) reduces the total carbon content in the matrix by 8% and increases the nickel content up to 10%, which reduces the viscosity of the melt, reduces its melting point by 80 ... 100 ° C, and also eliminates the formation of a carbide phase around the particles of the hard alloy and improves their wettability. The introduction of flux P1.5 (15%) contributes to better wetting of cermets.

After cooling in air, self-separation of slag occurs.

In an electromagnetic field of high frequency, due to edge effects, the bar is heated unevenly, the largest amount of heat is generated in the area adjacent to the perimeter of the bar. The melting of the PG-Cr2 charge (80%) + remelting of Na ₂ B ₄ O ₇ + H ₃ BO ₃ (20%) begins in the region of the bars with a sharp increase in thermal conductivity due to the formation of a liquid phase. The melt spreads over the surface of the part and penetrates into the gap between the bar and the hardened surface. Flux (remelting Na ₂ B ₄ O ₇ + H ₃ BO ₃ ) cleans the surfaces of the slats and parts and reduces the fluidity of the alloy. Then the charge of the wear-resistant alloy is melted and the grains are wetted by the wear-resistant alloy (alloy composition PG-USCH35 (75%) + PG-Ср2 (10%) + flux П1.5 (15%)).

The resulting composite material has a hardness of wear-resistant alloy - matrix HRC 49-59, hardness of reinforcing particles 2200 ... 2400 kg / mm ² and relative wear resistance when working in an abrasive medium 8-12 times greater than normalized steel 40.

With discrete hardening of large surfaces operating under shock loads in an abrasive medium, the need to have a given thickness of the hardening layer and a special orientation of the hardened sections is experimentally substantiated.

It was established that surfaces working in contact with granite gravel with a particle size of up to 80 mm should have a width of hardened sections of 18 ... 20 mm, the distance between these sections should be no more than 25 mm, and the thickness of the hardening layer should be 3 .. .4 mm. Induction-metallurgical method allows such a layer thickness to be obtained only when surfacing in a groove.

The greatest wear on the surface of the part, using the example of the liner of the lining of the rubble-cleaning machine SV-601, occurs in the zone perpendicular to the direction of the acting flow of the abrasive mass. When studying the influence of the angle of inclination of the strips, it was found that the location of the strips at an angle of 45 ° to the direction of movement of the abrasive mass allows you to increase the lining resource up to 9 km At the same time, the lining fails due to intensive wear of the base metal between the reinforcing bars, while the reinforcing surfaces remain almost worn out. The location of the strips at an angle of 90 ° to the direction of movement of the abrasive mass (figure 3) allowed to increase the lining life up to 12 km. At the same time, the lining failed due to the complete wear of the reinforcing layer.

Thus, the high wear resistance of the parts is ensured by the surfacing process and the arrangement of steel strips perpendicular to the flow of the abrasive mass. The exclusion of milling of grooves makes it possible to harden thin parts on which induction surfacing is impossible, and thereby expand the range of hardened parts.

Sources of information

1. Patent RU No. 2120363, IPC 6 V 23 K 12/02, publ. 10.20.98 g.

2. Patent RU No. 2138377, IPC 6 V 23 K 13/01, B 22 D 19/00, publ. 04/21/98 - a prototype.

3. Granular powder of the grade PG-USCH-35.TU U 332-19-007-97.

4. Catalog. Surfacing materials of the CMEA member countries. ICSTI. Kiev-Moscow, 1979, p. 471.

Claims (5)

1. The method of hardening by induction surfacing of parts operating under conditions of abrasive wear and shock loads, including the manufacture of recesses on the working surface, filling them with reinforcing cermet grains, applying a powder mixture containing a wear-resistant alloy and flux forming the matrix onto the surface of the part, followed by its melting inductor, characterized in that the recesses on the working surface are made by welding with a cork seam of steel strips that are perpendicular the direction of the flow of abrasive mass acting on the part during operation, the resulting recesses are pre-filled with a thin layer of the mixture, more easily melted than the charge forming the matrix, then the recesses are completely filled with cermet, and then the above powder mixture containing wear-resistant is applied to the surface of the part alloy and flux. 2. The method of hardening by induction surfacing of parts according to claim 1, characterized in that the composition of 80% PG-SR2 + 20% remelting (Na ₂ B ₄ O ₇ + H ₃ VO ₃ ) is used as a low-melting charge to fill the recesses. 3. The method of hardening by induction surfacing of parts according to claim 1 or 2, characterized in that alloys of VK or TK granulation of 2.5-4 mm are used as reinforcing cermets. 4. The method of hardening by induction surfacing of parts according to any one of claims 1 to 3, characterized in that the composition of the powder mixture forming the matrix is 75% PG-USCH35 + 10% PG-SR2 + 15% flux P1.5M. 5. The method of hardening by induction surfacing of parts according to any one of claims 1 to 4, characterized in that the layer of powder mixture forming the matrix is applied 3-4 mm thick above the strips.

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