SU1526942A1 - Composition of thermit mixture - Google Patents

Abstract

FIELD OF THE INVENTION The invention relates to surfacing materials used for wear-resistant surfacing of steel parts. The purpose of the invention is to increase the wear resistance and quality of the weld metal. In a thermite mixture containing iron oxide, aluminum powder, graphite, and cryolite, calcium carbide, boric anhydride, and carbide powder of UMSCh-30 are additionally introduced. The termite mixture is composed of aluminum and iron oxide. The introduction of a solid alloy in the amount of 5-8 wt.% Provides, in combination with 0.5-1.5 wt.% Graphite and 1-6 wt.% Boric anhydride, the optimum doping of the weld metal. Calcium carbide reduces the tendency to form hot cracks, and the calcium included in it has a beneficial effect on the refining of the weld metal. 3 tab.

Description

The invention relates to the field of surfacing materials used for the repair and restoration of worn surfaces by the method of thermite welding, in particular for steel parts of railway rolling stock.

The composition of thermite sludge is known on the basis of iron oxide and alumina powder.

The aim of the invention is to improve the wear resistance and quality of the metal deposited on the supporting surfaces of steel parts.

When choosing the composition of the thermite mixture, it is taken into account that in the process of exothermic and carbon thermal reactions the temperature of the molten metal should be not lower than 1900-2200 K in order to provide the required heat input for melting the contact surface

details and optimum doping. Taking into account that 0.10–0.60 wt.% A1 passes into thermite steel, the composition of thermite mixture is optimized by the level of chemical composition of the weld metal corresponding to 45X3 medium carbon chromium steel, which has high mechanical properties within the specified aluminum insertion limits. In addition, this chemical composition of the steel provides the optimal combination of wear resistance and friction coefficient in accordance with the requirements imposed on the bearing surfaces of the supporting parts of railway rolling stock.

Optimal alloying of the deposited metal is achieved by introducing into the thermite mixture a hard alloy of PG, MSH-30, in an amount of 5-8 wt.%, Which contains,%: C, 5; MP 2-2.5; L1o 1.5-1,8; C 45-50;

SP GchE

O5 QD

to

Ni 2-4; Sb 0.2-0.3. The granulometric composition of this powder is determined by the size of the 1.25 sieve, which ensures its uniform distribution in the charge and, ultimately, in the weld metal during the fast-flowing process of surfacing. The presence of high carbon content in the hard alloy prevents the oxidation of the entrance of chromium and molybdenum into it.

To eliminate the cracking of the deposited metal in the temperature range for the formation of hot cracks, calcium carbide is introduced into the thermite mixture. This helps prevent hydrogen absorption of the molten metal as a result of the transfer of moisture contained in hygroscopic iron oxides to a volatile hydrocarbon at the beginning of the thermite reaction. In addition, calcium reduces the solubility of sulfur in liquid iron, contributing to the formation of sulfide inclusions at high temperatures and transfer them to slag. Calcium also has a beneficial effect on the refining of the grain boundaries of the metal and the formation of non-bulky non-metallic inclusions.

To improve the flux of the best properties of the deposited metal and increase the strength of its compound with the base metal, dehydrated boric anhydride is introduced into the thermite mixture, which, partially entering into the carbon-thermal reaction, forms boron carbides. As is known, boron carbides, which are evenly distributed in the metal, effectively reduce its wear resistance.

The materiality of the proposed 1 limits of the content of the components of the thermite mixture is confirmed by the results of studies of the compositions presented in Table. 1. The results of mechanical tests of samples cut from the deposited metal of the indicated compositions are given in table. 2. They indicate a high level of mechanical properties of the deposited metal on the proposed formulations (options 1-9), satisfying the requirements of RTL1 32 CV 201-78: LAPa, Ua, KCi-25 J / cm-, J / cm. Compounds 10 and 13 do not satisfy the requirements for strength properties, and compounds 11 and 12 do not have impact strength.

The wear tests were carried out on dry sliding friction of a specimen in the form of a roller 5 mm thick and 40 mm in diameter, machined from the weld metal, relative to the counterbody in steel 20L in the form of a block. The test mode is determined by the value of the normal load of 500 N and by the 5000 m of fatigue passed. The requirements for wear resistance of the deposited metal are governed by a wear value of 1.5 g. Compositions 10 and 13 do not satisfy this requirement.

The compositions of the thermite mixture are also compared to the complex index of the quality of the deposited metal K, expressed in terms of the product of the relative indices of the individual properties:

(o; - K (n) -Klg.

0

(0).

where Kj, f 7-g- is relative, (o F

K ML

 (N) f

to -A

-Af, content content

oxygen; - relative hydrogen;

the relative content of residual aluminum;

(O) | p, (H) F, A1F - the actual content in the weld metal of oxygen, hydrogen, residual aluminum;

(0), 10%; (H), 7,

Uoh

0

five

0

five

0

five

0

five

May 20

% are respectively the nominal values of oxygen, hydrogen and aluminum in the deposited metal.

The calculated values of the quality indicators are given in Table. 3. They show that composition 1-9, corresponding to the proposed limits for the composition of the thermite mixture, is superior to composition 10-14 by the value of the complex quality indicator K.

Example. The proposed composition of thermite mixture is used for surfacing of the rubbing surfaces of the wedges of the vibration damper of the trolley of a freight car made of 20L steel. The wall thickness is 15 mm and the deposited layer is 10 mm. Before surfacing, the wedge is heated to 950 K, and a copper conductor is placed along the contour of a copper conductor to form a layer of the required dimensions. A thermite mixture of optimum composition (composition 3) is used. The termite reaction is carried out in a 10 dm crucible lined with a refractory compound. After completion of the thermite reaction, an exposure is made for 1 minute, which is necessary for the separation of its products into metal and slag. Molten metal is poured by scanning the crucible outlet orifice against the weld surface to fill the conductor cavity. The temperature of the metal during casting is controlled by an optical pyrometer. In the concrete example, the temperature of thermite steel is 2150 K. During the metallographic examination of the weld metal, the quality indicators corresponded to the requirements of RTM 32 CV 201-78.

Comparative analysis of the obtained data on the proposed technical solution with a known material shows the complete absence of cracks and pores in the weld metal, good continuity of the metal in the transition layer (weld metal - base metal), high wear resistance of the weld metal, compliance of the properties with operational requirements for the coefficient of friction and low the cost of thermite mixture.

Claims (1)

The economic effect of using the proposed technical solution is due to the manufacture of the thermite mixture directly under the conditions of production of the parts, since its basis is made up of its own waste in the form of iron scale. An additional economic effect is created in operation by increasing the durability of parts by 1.2 times. Invention Formula The composition of thermite mixture containing aluminum, iron oxide graphite and cryo five 0 Liter, characterized in that, in order to increase the wear resistance and quality of the deposited metal when using the mixture for thermite surfacing, the mixture additionally contains calcium carbide, boric anhydride and hard iron-chromium alloy PG USCh-30, with the following ratio of mixture components, wt%: Aluminum 20-26 Graphite0.5-1.5 Cryolit0,4-1,0 Calcium carbide 0,2-1,2 Boric anhydride1-6 Hard iron-chromium alloy PG USCH-305-8 Iron oxide Else 23 23 23 26 20 23 23 20 26 23 23 23 23 23 Table 1 5.0 5.0 6.5 6.5 6.5 6.5 6.5 5.0 8.0 6.5 6.5 8.2, E 6.5 63.1 66 62 67 61.9 67.3 72.9 56.3 68.0 61.1 60,8 68.2 65.2 Table 2 Table}