RU2704047C2 - Intrinsic safety copper-based alloy based on copper of high hardness and strength - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, in particular, to compositions of wear-resistant cast alloys based on copper, which can be used for production of parts operating under conditions of friction and wear in inflammable atmospheres, as well as for manufacture of intrinsically safe metalwork tool. Alloy on base of copper contains, wt%: nickel 6.0–9.0, chrome 1.0–2.0, silicon 1.0–1.5, aluminum 7.5–9.5, carbon 0.15–0.20, copper making the rest.EFFECT: invention is aimed at increasing friction-impact intrinsic safety and wear resistance of shaped cast billets.1 cl, 2 tbl

Description

The invention relates to metallurgy, in particular, to compositions of wear-resistant cast alloys based on copper, which can be used for the manufacture of parts operating under friction and wear in flammable atmospheres, as well as for the manufacture of intrinsically safe bench tools.

At present, an AKN intrinsically safe copper alloy is used, the chemical composition of which according to TU 1846-001-80569151-2009 is as follows: Ni (3.7-4.3%), Cr (0.5-0.1%), Si (0 , 6-1%), Σ (Sn, Pb, Zn, P, Fe, Al) <0.35%, the rest is copper Cu. The mechanical properties after heat treatment of HRC 30-35, σ _B (790-670) MPa are indicated for bronze intended for the manufacture of assembly bench tools (long wrenches) when working in explosive and fire hazardous rooms.

A significant drawback of this alloy is the absence in its composition of a balanced content of chemical elements, which during crystallization and cooling of the melt, as well as as a result of heat treatment, can form chemical compounds - heat-resistant intermetallic hardening phases that ensure the performance of parts at elevated temperatures under friction. In addition, AKN bronze belongs to the group of deformable ones and is not suitable for casting technological properties for the manufacture of shaped cast billets. It is mainly intended for the manufacture of metalwork intrinsically safe tools.

Known alloy based on copper, containing Nickel, aluminum, manganese, chromium, silicon in the following ratio of components, mass. %:

Nickel 18.0-23.0;

Aluminum 4.1-4.9;

Manganese 4.1-4.9;

Silicon 0.2-0.5;

Chrome 2.2-3.0;

Copper rest;

(see IPC С22С 9/00 description of the invention to copyright certificate No. 261697 publ. 01/13/1970).

The disadvantages of this alloy are:

• increased tendency of the alloy to gas saturation due to the high content of easily oxidized alloying elements (Ni + Cr + Al) ~ 30%;

• the silicon content in this alloy is clearly insufficient to ensure intrinsic safety and the formation of a strengthening phase of Ni ₂ Si, as the average ratio Si: Ni = 0.35: 20.5 = 0.017, (in the AKN alloy this ratio is 0.2) .

• The high degree of alloying of the alloy 36% leads to its high cost.

The closest technical solution for the chemical composition, mechanical properties and purpose is casting bronze BrА11Ж6Н9, used for the manufacture of antifriction parts operating at temperatures up to 500 ° C, containing aluminum, iron, nickel, copper in the following ratio of components, masses. %:

Aluminum 10.5-11.5;

Iron 5.0-6.5;

Nickel 5.0-6.5;

(see GOST 493-79)

The main disadvantages of this bronze are:

- high risk of sparks during operation of products from this alloy due to the absence of chemical elements such as silicon or beryllium in its composition, which ensure the intrinsic safety of the alloy by increasing thermal conductivity and electrical conductivity.

- insufficient bronze hardness HB = 250, which is due to the low nickel content, in relation to the aluminum content necessary for the formation of hardening phases Ni ₃ Al.

- according to the state diagram of Cu-Fe with an iron content of 6%, the liquidus temperature is 1210 ° C, and the crystallization temperature range is 116 ° C. Due to a significant increase in the temperature of the melt, compared with pure copper, this alloy is significantly more prone to absorption of gases and the formation of oxides (Al ₂ O ₃ ). A wide crystallization range of 116 ° C is the reason for the formation of shrinkage defects on castings.

Thus, according to the set of physicomechanical properties, casting bronze BrА11Ж6Н9 cannot be used as an intrinsically safe antifriction alloy.

The aim of the invention is to provide the required technical and operational characteristics of the material (hardness, wear resistance, intrinsic safety) in the manufacture of cast billets from it.

The technical result that can be obtained using the inventive alloy is to ensure trouble-free operation of parts under friction and wear in flammable atmospheres. An additional technical result is the possibility of using industrial alloys in the preparation of the alloy instead of specially prepared alloys or pure metals.

The goal set in the application is achieved, in contrast to previously known solution methods, by changing the ratio of alloying elements and introducing copper, containing chromium, nickel, silicon, additionally aluminum and carbon, into a copper-based alloy. Estimated alloy contains (% mass):

Nickel 6.0-9.0

Chrome 1.0-2.0

Silicon 1.0-1.5

Aluminum 7.5-9.5

Carbon 0.15-0.20

Copper is the rest.

The influence of the ingredients of the proposed alloy to achieve a new technical result is as follows.

Chrome has a positive effect on the mechanical properties of the inventive alloy due to solid-solution hardening together with nickel and due to the formation of carbides Cr ₃ C ₂ . No less important is the positive effect of chromium on the main casting property of bronze - fluidity, since at a chromium content of 1.25% in the Cu-Cr system, a eutectic with a melting point of ° C is formed, which ensures good fluidity.

When the chromium content is less than 1%, it is not enough, firstly, for the formation of a eutectic, and secondly, for the formation of carbides Cr ₃ C ₂ . A chromium content of more than 2% is impractical, since due to the formation of a hypereutectoid structure, the thermal conductivity and intrinsic safety of bronze are reduced.

Nickel dissolves unlimitedly in copper, and as a result of the interaction of nickel and chromium, a complex solid solution of Cu (Ni, Cr) is formed, the mechanical properties of which increase by 20-25%. The main reason for the need for sufficient nickel in this alloying complex is the formation of intermetallic compounds NiAl, NiAl ₃ , which mainly provide the hardness and wear resistance of the alloy.

Based on the analysis of the Ni-Al state diagram, it was found that when the nickel content is less than 6%, a sufficient number of strengthening phases Ni ₃ Al and Ni ₂ Si in the alloy structure is not provided, and, therefore, the required hardness is not provided. When Ni content> 9%, an excessive content of hardening phases is formed, which leads to excessive hardness and brittleness.

Aluminum is limitedly soluble in copper. Moreover, during cooling, the solubility of aluminum increases from 7.4% to 9%, which leads to the formation of intermetallic compounds Cu ₃ Al, Cu ₇ Al - hardening phases. In the presence of a sufficient amount of nickel, Ni ₃ Al, NiAl intermetallides are formed, which provide the most effective dispersion hardening. Given the high thermal conductivity of aluminum, we can assume that it not only provides high strength and hardness of bronze, as well as intrinsic safety. The positive effect of aluminum is also manifested in the fact that at a content of 8.5% a eutectic with a melting point of 1035 ° C is formed, which, together with a “chromic” eutectic (1074 ° C), provides a sufficiently high level of the main technological property of cast bronzes - fluidity.

When the aluminum content is less than 7.5%, that is, less than the minimum solubility of aluminum in copper, the formation of hardening phases Cu ₃ Al, Cu ₇ Al, Ni ₃ Al is impossible, which will not allow to obtain the required hardness and wear resistance.

When the aluminum content is more than 9%, a significant increase in hardness and strength of the alloy does not occur. However, due to excess free aluminum, the propensity of the alloy for gas saturation increases significantly, which reduces the quality of the alloy and significantly complicates the technology of its melting. Therefore, the aluminum content in the proposed alloy should not exceed 9%.

Silicon is one of the main elements ensuring the intrinsic safety of copper alloys; therefore, its content is extremely necessary. In addition, silicon has a significant effect on the increase in hardness due to the formation of nickel silicide Ni ₂ Si. Given the stoichiometric composition and residual nickel content (2-2.5%) after the formation of a solid solution of Cu (NiCr) and the hardening phase Ni ₃ Al, it is advisable to have a silicon content in the alloy in the range of 1.0-1.5%.

Obviously, with a silicon content of less than 1%, the formation of Ni ₂ Si is practically impossible. When the silicon content is more than 1.5%, an excess of silicon and a phase of Ni ₂ Si. Increases the brittleness of the alloy and the tendency to form cold cracks.

Carbon is introduced into the alloy as a microalloying element in order to grind the grains due to the formation of the refractory compound Cr ₃ C ₂ in the alloy. Given the weight content of carbon C = 13% in chromium carbide Cr ₃ C ₂ and the residual chromium content Cr = 0.8-1.2% for the formation of carbide, the required carbon content is 0.15-0.20%.

Based on the calculations and assumptions, the following composition of the wear-resistant intrinsically safe thermally hardened bronze is recommended:

Nickel 6-9%

Chrome 1-2%

Aluminum 7.5-9.5%

Silicon 1-1.5%

Carbon 0.15-0.20%

Copper is the rest.

An analysis of the proposed chemical composition shows that the ratio of nickel to chromium is Ni: Cr = 7.5: 1.5 = 5. Therefore, instead of pure metals or special alloys, you can use nichrome X20H80, the melting point of which is 1360 ° C. For comparison, the melting point of nickel is 1455 C, and chromium is 1860 C. Given the ratio of aluminum and silicon in bronze Al: Cr = 8.5: 1.25 = 6.8, it is advisable to use AK12 alloy instead of pure aluminum and silicon metals, in which the ratio Al: Si = 88: 12 = 7.3

The proposed bronze differs from the prototypes (bronze AKN and A.S. 261697) in the following essential features: 1) the chromium content corresponds to the eutectic composition (that is, more than in AKN, but less than in A.S. 261697), which is one of the conditions ensuring the manufacturability of cast alloys; 2) unlike AKN, aluminum was introduced into the composition of the proposed bronze, the content of which (7.5–9.5%) according to the calculations should ensure the formation of strengthening phases NiAl, Ni ₃ Al, Cu ₃ Al, Cu ₇ Al ₃ . Therefore, its content is taken 2 times more than in A.S. 261697. 3) for the possibility of forming a hardening phase of Ni ₂ Si, the silicon content is increased to 1.0-1.5% compared to the prototypes, which exceeds the ultimate solubility of silicon in copper (1.8%). 4) taking into account the possibility of the formation of the necessary fraction of strengthening phases in the structure of bronze - aluminum and silicon nitrides, as well as doped Cu (Cr, Nl) solid solution, the balanced nickel content is 6–9%, which is significantly higher than in AKN and 2– 3 times less than in A.S. 261697.5) alloying elements chromium, nickel, aluminum, silicon when melting the alleged bronze are recommended to be introduced not in the form of pure metals or specially prepared alloys, but in the form of industrial alloys X20H80 and AK12. This greatly simplifies the technology of smelting, increases the digestibility of alloying elements and reduce the technical and economic costs for the production of bronze. Thus, the proposed solution meets the criterion of "novelty."

For practical confirmation of the proposed chemical composition, melts were carried out, the chemical composition of which is presented in table 1.

Melting was carried out in induction furnaces in graphite-chamotte crucibles under a layer of protective flux. Cast samples were obtained by pouring the alloy into sandy clay dry forms. Four melts were made in each heat. On all samples in the molded state, the mechanical properties of σ _in and σ _{0.2 were} determined during tensile testing according to GOST 1497-73, HRC hardness according to GOST 9013-59, thermal conductivity λ.

To assess the manufacturability of bronze, fluidity (L) was determined by a spiral test according to GOST 16438-81. The average values of the test results for 4 samples are shown in table 2.

As can be seen from table 2, the alloy of the expected chemical composition (heat No. 1) has the best indicators of physico-mechanical and technological properties compared to the heat of No. 2 and 3, the chemical composition of which goes beyond the expected chemical composition.

The use of an alloy based on copper of the expected chemical composition will ensure frictional-shock intrinsic safety and wear resistance of shaped cast billets.

Information sources

1. Technical specifications for the alloy AKN TU 1846-001-80569151-2009. Copper alloy rods AKN.

2. Description of the invention to copyright certificate 261697 from 01/13/1970

3. GOST 493-79. Cast bronze tinless.

4. Double state diagrams of Cu-Cr, Cu-Al, Cu-Ni, Cu-Si, Ni-Cr, Ni-Al, Ni-Si alloys.

Claims (2)

A copper-based alloy containing chromium, nickel and silicon, characterized in that it additionally contains aluminum in the following components, wt.%: Nickel     6.0-9.0 Chromium                 1.0-2.0 Silicon     1.0-1.5 Aluminum     7.5-9.5 Carbon 0.15-0.20 Copper           rest