RU2637437C2 - Method of forming fibrous composite coating - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: application of coating based on industrial powder PR-10 P6M5 by electron-beam or plasma-powder method. The fused surface is subjected to grinding and discrete melting by means of pulse laser or pulse electron-beam with beam diameter on coating surfaces of 0.25÷2 mm and pulse duration 5÷20 milliseconds focused on a line or point.

EFFECT: reduction of wear intensity in friction pair.

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Description

The invention relates to the field of surface treatment of coatings based on high speed steel by energy flows to improve the operational characteristics of products.

A known method of processing products in which the impact on structural (rail) steel is carried out by a pulsed laser beam (Zheng-yang Li, Xu-hui Xing, Ming-jiang Yang, Bing Yang, Zhi-yuan Ren, Hua-qiang Lin Investigation on rolling sliding wear behavior of wheel steel by laser dispersed treatment // Wear 314 (2014) P. 236-240). The remelting zone has a martensitic-austenitic (90: 10%) structure with a hardness of 550HV, a heat affected zone with a hardness of 850 HV, and then a base metal with a ferrite-pearlite structure with a hardness of 300 HV. The resulting structure allows to increase the wear resistance of the material under the conditions of the rolling-slip wear scheme twice.

The disadvantages of the method are:

- a large coefficient of surface treatment with a laser beam (80%), which creates significant thermal stresses and, as a consequence, a high probability of cracking from the side of the heat affected zone having high hardness;

- the method is unacceptable in the conditions of processing the pre-welded surface with a composite material that initially has high hardness.

The closest is the method taken as a prototype - a method for processing products from high-carbon alloyed alloys (RU 2494154 CI, IPC C21D 1/09 (2006.01), publ. 09/27/2613), including exposure to the product by a pulsed concentrated energy flow. The product is locally affected by a focused pulsed electron beam with a power density of 10 ^{4 ÷} l0 ⁵ W / cm ² , a beam diameter of 0.5 ÷ 2 mm and a pulse duration of 1 ÷ 30 ms with a discrete point distribution, forming modified zones of a given geometry on the surface of the product. Then the product is subjected to heat treatment at a temperature of 600 ÷ 1100 ° C and a holding time of 30 ÷ 60 minutes The disadvantages of the method are:

- additional heat treatment of products for which the combined operation of surfacing and melting is the finishing treatment;

- a focused point-like pulsed electron beam does not allow creating modified zones of a given geometry (except for a point one) without overlapping individual points (for example, with a strip unidirectional distribution), and creating a homogeneous structural-phase composition of the modified zones and their properties. This is important when the products do not work with purely abrasive wear, but in a pair of friction.

The objective is to create a method for processing coatings based on high-speed steel with concentrated energy flows, which ensure a decrease in the wear rate in the friction pair.

The method of forming a fibrous composite coating, as in the prototype, consists in exposing the product to a pulsed electron beam with a power density of 10 ⁴ ÷ 10 ⁵ W / cm ² .

According to the invention, low- or medium-carbon structural steel is coated on the basis of industrial powder PR-10R6M5 by electron beam or plasma-powder method, then the deposited surface is subjected to grinding and discrete fusion using a pulsed laser or pulsed electron beam with a beam diameter on the coating surface 0 , 25 ÷ 2 mm and a pulse duration of 5 ÷ 20 milliseconds, focused in a line or point, increasing the microhardness in part of the volume of the fiber located between the viscous layers Oykami melted zone and the main coating.

In FIG. Figure 1 shows the scheme of discrete fusion of a composite coating by a pulsed laser or electron beam turned to a point (the fiber axis is perpendicular to the deposited surface), where 1 is the base metal, 2 is the surfacing, 3 is the discrete hardened zone (fiber), 4 is the fiber axis, 5 is reflow depth (in the context).

In FIG. Figure 2 shows a discrete melting scheme of a composite coating by a pulsed laser or electron beam deployed in a line (the fiber axis is parallel to the deposited surface).

In FIG. Figure 3 shows the microstructure of the cross section of the cast core of coatings based on high-speed steel after laser fusion with increasing, where a) is the cast core and the heat affected zone - HAZ; b) - zone B and HAZ (zone C); c) - zone A and zone B.

In FIG. Figure 4 shows the distribution of average microhardness values over the zones of the cast core (zone A, zone B and zone C of the base metal) irradiated by a pulsed laser of coatings based on high-speed steel.

The fused zones or fibers in FIG. 1 and FIG. 2 consist of two structures — zone A and zone B (FIG. 3) and differ in the level of microhardness, as shown in FIG. 4. The solid part of the fiber — zone B, located between the viscous layers of fiber of zone A and zone B of the base metal of the coating in FIG. 3 and FIG. 4 carry the main load in tribocontact. Viscous layers - fibers of zone A and zone B provide stress relaxation and braking in the development of cracks. Depending on the stress state of the friction pair, the fiber axis is formed perpendicular (Fig. 1) or parallel (Fig. 2) to the working surface of the main coating.

The technical result in the implementation of the proposed method is achieved due to the formation of periodic fibers on the coating surface (the distance between the fiber axes is 2 ÷ 3 fiber diameters) by a focused pulsed laser or pulsed electron beam (power density 10 ⁴ ÷ 10 ⁵ W / cm ² and pulse duration 5 ÷ 20 milliseconds) of spot or linear fusion. Two structures are formed inside the fiber based on an austenitic-martensitic matrix with carbide inclusions, which differ in the level of dispersion of martensitic needles and carbides and, therefore, in the level of microhardness. Zone A, due to the larger size of carbide precipitates, has a high etchability (Fig. 3c). Zone B, due to the more dispersed structure of both martensite and carbides, has less etchability (Fig. 3b). On the surface of the surfacing, fibers are formed with a perpendicular or parallel arrangement of the fiber axis relative to the surface of the hardened layer. The distance between the axes of the fibers is 2 ÷ 3 fiber diameters.

The proposed method is as follows: on the samples of the base metal 1 of low- or medium-carbon structural steel, a composite coating 2 is applied on the basis of powder of high-speed steel PR-10R6M5 by multipass electron beam welding in vacuum or by plasma powder surfacing. Then, the formed coating is subjected to grinding and pulsed laser or pulsed electron beam fusion of a surface of a certain geometric shape 3 (Fig. 1, Fig. 2) with a given step. The penetration depth of surface 5 (0.25-1.5 mm) is controlled by the parameters of a pulsed laser or pulsed electron beam with a power density of 10 ⁴ ÷ 10 ⁵ W / cm ² , a pulse duration of 5 ÷ 20 milliseconds, a beam diameter on the coating surface of 0.25 ÷ 2 mm. The direction of formation of the axis of the fiber 4 is selected depending on the stress state of the friction pair, which can be perpendicular (Fig. 1) or parallel (Fig. 2) to the surface to be treated.

The indicated ranges of parameters of pulsed laser or pulsed electron beam processing are due to the following:

- the power density less than 10 ⁴ W / cm ^{2 is} insufficient for melting the coating, and the power density above 10 ⁵ W / cm ² leads to boiling of the coating material and the formation of defects on its surface in the form of pores and craters;

- the diameter of the electron beam less than 0.25 mm leads to a decrease in the productivity of surface treatment, and the diameter of more than 2 mm leads to the formation of cracks at the interface between the modified zone and the main material, due to the increase in the area of the interface;

- a pulse duration of less than 5 milliseconds leads to a decrease in the depth of the modified zone, and a pulse duration of more than 20 milliseconds leads to boiling of the material in the area of the beam.

Tests of the samples of the fibrous composite coating for friction paired with heat-treated steel ШХ15 were carried out on a SMT-20 friction machine using the “wheel - two flat pads” scheme at a speed of 1.2 m / s and load N (20, 40, 60, 80 and 100 N) under friction without lubrication, showed the following results:

- the wear rate of only the deposited coatings in the range of these loads increases linearly from 0.4 ± 0.1 to 0.5 ± 0.1 mm ³ / km;

- the wear rate of the fibrous composite coating with the axis of the fiber located perpendicular to the hardened surface was 0.2 ± 0.05 mm ³ / km, and with the axis of the fiber parallel to the hardened surface 0.15 ± 0.04 mm ³ / km, and does not depend on the load.

Thus, the wear rate of the fibrous composite coating based on 10P6M5 steel is halved. It is known that due to the waviness and roughness of the surface, contacting of real solids in friction pairs is carried out at separate sites. The sum of these small areas is the actual contact area of the bodies, which is the main pressure applied to the friction pair. As a result of this effect, surface irregularities and underlying volumes of body materials are deformed, distorted, and destroyed. Friction pair wear occurs.

Claims (1)

A method of forming a fibrous composite coating on a product of low- or medium-carbon structural steel, comprising applying a coating of a powder material to a product and treating the coating by pulsed radiation, characterized in that the electron beam or plasma method is coated using powder of high-speed steel PR -10Р6М5, then the deposited surface is subjected to grinding and coating treatment by pulsed-beam exposure with a power density of 10 ⁴ ÷ 10 ⁵ W / cm ² by di sinter fusion by a pulsed laser or electron beam with a diameter of 0.25 ÷ 2 mm and a pulse duration of 5 ÷ 10 milliseconds, deployed to a point with the formation of fibers perpendicular to the deposited surface of the coating, or - in line with the formation of fibers parallel to the deposited surface of the coating.

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