RU2637734C1 - Iron-based powder for plasma surfacing of parts of agricultural machined in compressed air medium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: iron-based powder for plasma surfacing of parts of agricultural machines in compressed air medium contains, wt %: carbon 3.3-4.5, chromium 25-28, silicon 1.0-2.0, manganese 1.0-1.5, nickel, 1.5-2.0; tungsten, 0.2-0.4; molybdenum, 0.08-0.015; sulfur, no more than 0.07, phosphorus not more than 0.06, aluminium 0.1-0.15, titanium carbide 0.2-0.25, the rest is iron.

EFFECT: reduced likelihood of quench crack formation, reduced deformations and carrier when hardening thin-wall hardened surfacing parts by applying additional components in the powder composition while providing required wear resistance of parts of agricultural machines.

1 tbl, 1 ex

Description

The invention relates to agricultural machinery and can be used to protect parts operating in a soil-grassy environment.

Powders are known for protecting parts against abrasive and fatigue wear (for example, for protecting knives grinding the silage mass or cutting segments of combine harvester headers), in particular powders AP LPS NPO Tulachermet PN55T45 type. Such powders are applied by plasma or flame spraying, where the thickness of the hardened layer is 0.5 ... 1.5 mm. Parts hardened in this way have good sharpness with a total thickness of the part not exceeding 2 ... 4 mm.

A disadvantage of the known powders is the rapid abrasion of the hardened layer, leading to frequent change of cutting elements.

Known powder for surfacing, adopted as a prototype, PR - C27 / Volovik E.L. Handbook for restoration of parts // Moscow: Kolos. 1981. 274 p. / containing iron base, carbon, manganese, chromium, silicon, molybdenum and tungsten. One of the significant advantages of the known powder is its low cost for agricultural machinery. Moreover, parts hardened by a known powder far exceed the wear resistance of parts hardened by spraying.

A disadvantage of the known powder is the formation of quenching cracks, large deformations and leashes when quenching thin-walled parts less than 2 ... 2.5 mm, for example knives for grinding grass mass.

The technical result of the invention is to reduce the likelihood of hardening cracks, to reduce deformations and leashes during hardening of thin-walled hardened surfacing parts due to the use of additional components in the composition of the powder while ensuring specified wear resistance of parts of agricultural machines.

The technical result is achieved in that the iron-based powder for plasma surfacing of agricultural machinery parts in a compressed air environment contains carbon, manganese, chromium, silicon, molybdenum, tungsten and iron additionally contains aluminum and titanium carbide in the following ratio of components, wt.%:

carbon 3.3-4.5 chromium 25-28 silicon 1.0-2.0 manganese 1.0-1.5 nickel 1.5-2.0 tungsten 0.2-0.4 molybdenum 0.08-0.015 sulfur no more 0,07 phosphorus no more 0.06 aluminum 0.1-0.15 titanium carbide 0.2-0.25 iron rest.

It is known (Steel at the turn of the century. / Under the editorship of Yu.S. Karabasov. M .: MISiS. 2001. 664 p.) That the introduction of aluminum into the composition of alloys based on iron-based alloys makes it possible to stabilize grain size due to the formation of AlN particles high degree of dispersion. And in sheet production, in order to make the “hereditary” grain even smaller, the nanoparticles are dissolved during heating for rolling and their subsequent “reprecipitation” during hot rolling is the most important way to control the current and final “hereditary” grain size.

However, within the framework of the proposed solution, the use of small aluminum additives in iron-based hard alloys is not limited only to the effect on the grain size. In particular, use of the fact that aluminum in small amounts in the iron aluminide alloys reduces hardening module, which has a minimum 108 GN / m (in steel - in the range of 160 ... 220 GN / m ²⁾ (Special Steel Gudremon E. T. 1. 2. M.: Moscow, 1966.). Small additives of aluminum reduce the twinning stress (Kopeckii C.V. Structure and properties of refractory metals. - M .: Metallurgy, 1974. -202 p.), Which leads to softening, including due to the influence of aluminum in small quantities on the high Peierls bond on the “corrugated” sliding surface (Stremel M.A. Strength of alloys. Part II. Deformation. M: MISiS. 1997. - 527 p.). By attracting the dislocation, an aluminum impurity helps it to eject into the next valley of the potential relief (Ahmadich A., Mitchell J., Dorn JE // Trans. Met. Soc. AIME. 1965. V. 233, N 6, P. 1130).

In general, this can be used for stress relaxation during cooling of hard alloys during quenching and, as a result, to reduce the risk of formation of quenching cracks (as a rule, due to the concentration of internal stresses during heat treatment). At the same time, it remains possible to obtain an additive effect from grain refinement (similarly to a decrease in the sensitivity of metal to crack formation during welding from stress due to grain refinement [for example, Goodremont E. Special steels. Vol. 1, 2. M .: Moscow, 1966.]).

It is also known (Glazer N., Morris JW // Phil. Mag. Letters, 1990, V. 62, N 1, P. 33) that the presence of dispersed particles in steels and alloys, the lattice of which is very different from the matrix and arbitrarily oriented, is an obstacle accumulating dislocations. This fact is widely used in the practice of heat treatment in the appointment of tempering of steels and alloys of a wide purpose in order to separate dispersed particles from a solid solution, for example carbides, in order to increase the strength of steels.

In order to achieve uniformity of the distribution of carbides during tempering of steels, their dispersion (as well as the completeness of the martensitic transformation in the product) during the aging of the steel, when quenched, the problems associated with the dissolution of existing carbides and the homogenization of the solid solution as a whole are traditionally solved.

If these particles have a high resistance to transition to a solid solution when heated, for example, under quenching, as in the proposed solution for titanium carbide particles, then upon subsequent cooling they should provide increased resistance to deformation. The strength of the particles themselves is indifferent, it can only occur with very large deformations, when the chip (or detachment) of the particle stops the accumulation of dislocation loops on it (and soon leads to macrodestruction) (Martin J. W. Micromechanisms of the dispersion hardening of alloys: Transl. From English .-M.: Metallurgy, 1983 .-- 168 p.).

Thus, the proposed introduction to the composition of the powder for hardening parts of agricultural machinery of aluminum allows for stress relaxation during cooling during the hardening of thin-walled, less than 2 ... 2.5 mm, parts of agricultural machinery. As a result, the number of cracks and chips during hardening will also decrease. Introduction to the composition of the powder for hardening these parts of titanium carbide, the solubility temperature of which in a solid solution is, for example, when the carbon content in austenite is 1.2% wt. and titanium content of 0.02% wt. ~ 1250 ° С (Kiparisov S.S., Levinsky Yu.V., Petrov A.P. Titanium carbide: preparation, properties, application, M., 1987) - increase the rigidity of the hardened part, which will lead to a decrease in deformations and hardening during hardening .

The specified amount of aluminum and titanium carbide: aluminum in an amount of 0.1 ... 0.15% wt., And titanium carbide in an amount of 0.20 ... 0.25% wt. is optimal. If the aluminum content is less than 0.10 wt.%, The ductility will decrease and the number of cracks during hardening will increase, which will entail chipping of fragments of the hardened part, if more than 0.15% by weight, its wear resistance will decrease. If the titanium carbide content is less than 0.20% by weight, deformations and leads of the hardened part will increase, if more than 0.25% by weight, its brittleness will increase (resistance to impact loads will decrease).

An example of the implementation of the proposed approach (plasma surfacing).

Aluminum and titanium carbide were mixed with the main powder used, in this example, with PR-C20 in a special cylindrical container in the mass proportions in which they are specified. Mixing was carried out for 30 minutes.

The surfacing technology involved the use of a narrow copper hole through which a plasma-forming gas (argon) flows. When creating a sufficient strong electric field, the gas loses its insulating properties, its temperature rises, the number of ions and electrons increases, and when their concentration exceeds 10 ⁹ per 1 cm ³ , the resulting substance can be called plasma. Powder was fed into the resulting arc by protective and conveying gas and deposited on the part.

Usually, relatively expensive argon is used as a transporting and shielding gas in plasma surfacing in our country and abroad. Our studies have shown that for hardening relatively cheap soil-cutting working bodies, hardening by plasma surfacing in an argon medium is economically inefficient and is inferior in economic indicators to induction surfacing.

Therefore, a technology was developed (plasmatron, powders, modes, etc.) for plasma surfacing of working bodies of tillage machines in a compressed air environment. In contrast to surfacing in argon, surfacing in compressed air is 1.5 ... 1.7 times more productive, 30 ... 40% less energy intensive. Argon consumption is reduced by 8 ... 9 times (argon is used only for plasma formation). In general, the cost of the surfacing process when using compressed air instead of argon as a transport and protective gas is reduced to two times. And although the coating during surfacing in a compressed air environment is somewhat less qualitative (not so smooth, individual pores are possible) in comparison with surfacing in an argon medium, these differences have practically no effect upon operation in a soil mass.

According to our data, a slight increase in the wear resistance of blades of working bodies hardened by plasma surfacing, in comparison with the wear resistance of blades hardened by other surfacing methods (induction, etc.), is explained by the following metallurgical features:

- the absence of overheating of the base metal during plasma surfacing, in contrast to the induction and, accordingly, the best structure of the base metal;

- more uniform coating according to physico-mechanical and geometric criteria in plasma surfacing;

- a higher penetration depth in plasma surfacing, a decrease in the likelihood of "grinding" and chipping of the deposited layer and, accordingly, a slightly larger thickness of the hardened layer with equal sharpness of the blade.

* when tested for wear resistance on a friction machine IM-01. Laboratory test conditions: abrasive - electrocorundum granulation 40-80 microns; load on the roller - 200 g; test cycle - 30 min; repetition - 3 times.

As a result of the invention, the risk of formation of quenching cracks will be reduced, deformations and leashes during hardening of thin-walled surfaced hardened parts of agricultural machines will decrease.

Claims (4)

Iron-based powder for plasma surfacing of agricultural machinery parts in a compressed air environment containing carbon, manganese, chromium, silicon, molybdenum, tungsten and iron, characterized in that it additionally contains aluminum and titanium carbide in the following ratio, wt.%: carbon 3.3-4.5 chromium 25-28 silicon 1.0-2.0 manganese 1.0-1.5 nickel 1.5-2.0 tungsten 0.2-0.4 molybdenum 0.08-0.015 sulfur no more than 0,07 phosphorus no more than 0,06 aluminum 0.1-0.15 titanium carbide 0.2-0.25 iron rest