RU2048649C1 - Method for strengthening surface of slide bearing of drilling bit - Google Patents

Abstract

FIELD: drilling bits. SUBSTANCE: borating is carried out in two stages: first at 840-860 C, then the temperature is increased to 900-920 C for a preset period. This forms a multilayer structure of the coating wherein iron hemoboride and boron cementite with relatively penetrating teeth are positioned on the cemented layer. Borating is carried out with a mixture composed of, wt. -% boron carbide, 40-70; modifying mixture, 10-30; the balance consists of equal parts of graphite or aluminium oxide, or aluminium oxide and iron powder, or iron powder and graphite. EFFECT: high hardness and wear resistance of strong and plastic base. 2 cl, 5 dwg

Description

 The invention relates to methods for processing metal surfaces, in particular supporting surfaces of drill bits requiring high hardness and wear resistance, in the presence of a strong plastic base.

 The sliding bearings of the cone drill bit are known to perceive high cyclic loads and require high wear resistance of the supporting surface.

A method is known boronizing of steel parts, comprising the heating to the saturation temperature, maintaining a saturating medium with additional exposure to the same medium at a saturating temperature 40-70 ^{° C} below the conversion start temperature of pearlite to austenite.

 The disadvantage of this method is to obtain a single-layer boride coating on a soft basis, which excludes its use at high loads.

 The closest in technical essence, the achieved result and application is the boronation method, including cementing the supporting surface of the drill bit, boring, quenching and tempering. A single-layer structure of a boride coating lying on a layer of high-carbon martensite is obtained. A significant difference in the volumes of these phases and KTP leads to the occurrence of undesirable microstresses in the coating during the XTO process, and, therefore, there is a high probability of layer cracking under external loading, which affects the performance of the product.

 The purpose of the invention is the preparation of a hard wear-resistant coating with a damping structure.

This goal is achieved by the fact that in the method of hardening the surface of the sliding support, we include surface cementation, boring, hardening and tempering. Boriding process is conducted in two stages: first at a temperature of 840-860 ^{° C,} then the temperature was raised to 900-920 ^{° C} and held there. As a result, a multilayer structure of a hard wear-resistant coating is formed, in which iron hemoboride and boron cementite with interpenetrating teeth are located on the cemented layer.

To implement the proposed method, it is necessary to carry out the following operations in the above sequence. Cementation is carried out in an oven at a temperature of 920-940 ^C. endogas atmosphere having a carbon potential of 1.30-1.40% for 6 hours. This gives the cemented layer depth of about 2 mm with a carbon content at the surface of about 1 boriding is conducted in an oven for carburizing first at a temperature ^of 840-860 C and held at this temperature for at least 2 hours. The temperature was then raised to 900-920 ^C and kept at this temperature for 2-3 hours. boriding process is performed in endothermic gas atmosphere with a carbon potential of 1 Total boration time is 4-6 h

 When boron use a mixture of the following composition, wt. boron carbide 40-70; modifying mixture, consisting, for example, of niobium pentoxide 1-3, zirconium dioxide 25-30, titanium dioxide 3-6, cryolite up to 30, kaolin 10-30, graphite the rest. Instead of graphite, alumina, or alumina and iron powder, or iron powder and graphite can be used in at least equal proportions in both cases.

The need for boration in two stages is due to the following. At a temperature of 840-860 ^{° C} due to low diffusion mobility of atoms of boron in the high-boron steel is formed on the surface of the product phase. Carbon displaced from borides does not dissolve in austenite, because directly under the boride coating, its concentration exceeds 1 and forms secondary cementite with iron. Raising the temperature then to 900-920 ^{° C} leads to an increased mobility of boron diffusion and formation of the toothed structure of the coating. In this case, the carbon is displaced away from the teeth of the borides while maintaining the compound Fe ₃ (C, B) in the tooth bases (Fig. 1). The following method steps are hardening and tempering of a cemented, boronated and cleaned steel surface. Hardening is carried out in an atmosphere of cementation or reduction, which prevents decarburization or oxidation of the boron layer. Quenching temperature of 820 ^C. The tempering temperature of 180-200 ° ^C. This gives a cemented layer ductility without significantly reducing its strength in order to obtain martensite.

 Performing all operations in the indicated sequence according to the proposed method allows to obtain solid wear-resistant surfaces of sliding bearings of a cone drill bit, the service life of which is 1.5-2 times higher than, for example, the service life of the surface of sliding bearings using a cobalt-based carbide coating series "Stellit."

PRI me R. Boroning is carried out on samples of steel grade 15H3MA or 14XH3MA. To implement the method, a boron composition is used, prepared as follows: boron carbide, a modifying mixture (MS) and graphite are weighed in such an amount as to obtain the composition, wt. boron carbide 60; MS 30; graphite 10. Then the components are mixed in the mixer for 2 hours. A layer of the obtained mixture of sufficient thickness (at least 10 mm) is poured onto the bottom of the container made of heat-resistant steel, pre-cemented samples are placed at a distance of 10 mm from each other and filled with the remaining mixture. The container is placed in a carburizing furnace. Create an endothermic atmosphere with a carbon potential of the gas 1% and heated to 850 ° ^C held there for 2 hours, then heated to a temperature of 910 ^{° C} and held for 3 hours. The thickness of the boride layer is 80 microns. Next, cool the container to room temperature. Samples are taken out, mechanically cleaned and heat treated. Oil quenching from a temperature ^of 820 C, at a tempering temperature of 200 ^C. The quality and thickness of the boride layer metallographically checked using a microscope.

 Since the structure of cementite is more similar to the structure of martensite than boride, the physicomechanical properties of the multilayer coating are higher than the two-layer: boride-martensite. This is indicated by the formation of cracks in coatings with different structures upon indentation. The ratio of the load created by the indicator to the sum of the lengths of cracks originating from the fingerprint can serve as an indicator of the crack resistance of the coating. Figure 2 shows the P / e dependences for two coatings obtained by the proposed method (dependence 1) and traditional (dependence 2) having the structure of a single layer boride (Fig. 3). It is seen that the fracture toughness (crack resistance) is higher for the coating obtained by the proposed method. In friction tests, a multilayer coating also performed significantly better. Figures 4 and 5 show traces of friction on samples with the proposed (figure 4) and traditional (figure 5) coating. It can be seen that the single-layer boride coating (Fig. 5) is brittle, while the coating obtained by the proposed method does not collapse under the same test conditions (Fig. 4).

Claims (2)

1. SURFACE HARDENING METHOD OF A DRILL BIT SLIDING SUPPORT, including surface cementation, boronation, hardening and tempering, characterized in that, in order to obtain a hard wear-resistant coating with a damping structure, boroning is carried out in two stages: first at 840-860 ^o C, then increase the temperature to 900 920 ^o C and maintain it, while forming a multilayer coating structure in which iron hemoboride Fe ₂ B and boron cementite with interpenetrating teeth are located on the cemented layer.  2. The method according to claim 1, characterized in that the boron is produced by a mixture of the following composition, wt. Boron carbide 40 70
Modifying mixture 10-30
the rest is graphite or aluminum oxide, or aluminum oxide and iron powder, or iron and graphite powder in equal proportions in both cases.

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