RU2345160C1 - White wear-resistant cast iron - Google Patents

Abstract

FIELD: metallurgy industry.

SUBSTANCE: invention refers to ferrous metallurgy, and namely to white wear-resistant cast iron compounds, and can be used for manufacturing working assemblies of ore-dressing equipment, which are affected by abrasive hydraulic mixture being transported. Cast iron contains, wt %: carbon 2.4-2.6; silicon 0.5-0.6; manganese 0.8-1.8; chrome 25-26; nickel not more than 0.5; tungsten 0.1-0.15; molybdenum 0.3-0.5; titanium 0.5-0.7; vanadium 0.1-0.15; cuprum 1.8-2.0 and iron - the rest.

EFFECT: improving mechanical processing of cast iron parts, and maintaining wear-and-tear resistance.

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Description

The claimed invention relates to metallurgy, in particular to cast irons, intended for the manufacture of wear-resistant working units of mining and processing equipment, most exposed to the damaging effects of abrasive transported hydraulic mixtures.

White cast iron, designed for these parts, must have high wear resistance and increased mechanical properties. Wear resistance is determined by the structure and hardness of the alloy. In white cast iron, carbon is in the form of graphite and in the form of carbide - compounds with metals and nonmetals, i.e. most of the carbon is in a bound state, which determines the properties of white cast irons: high hardness and brittleness. The latter property creates difficulties in machinability in the manufacture of parts from well-known brands of white cast iron.

For many years, the efforts of the developers are aimed at obtaining such alloys of white wear-resistant cast iron, which would combine both high wear resistance and acceptable mechanical workability.

Known for white wear-resistant cast iron of the IChKh28N2 brand (see. Handbook of iron castings. / Ed. By Doctor of Technical Sciences N.G. Girshovich. - 3rd ed., Revised and additional - L .: Engineering. Leningrad. Department, 1978, p.101, Table 1.39, p.105, Table 1.43), containing components in the following ratio, wt.%:

carbon 2.7-3.0 manganese 0.8 silicon 0.7-1.4 chromium 28-30 nickel 1.5-3.0 iron rest

Table 1.43 shows HB Brinell hardness equal to 480-600 for a known alloy. Moreover, HRC - Rockwell hardness is 49-62, based on the ratio that it is 9.7 times less than HB. As practice shows, with high wear resistance of parts obtained from well-known white cast iron, the alloy is quite brittle, as a result of which chips and breaks occur during machining. The low mechanical properties are the disadvantage of the well-known white wear-resistant cast iron.

The closest in technical essence, the achieved effect and selected as a prototype is white wear-resistant cast iron, intended for the manufacture of working parts of hydraulic pumps operating in the mining and chemical industries (see USSR author's certificate No. 309971 "Abrasive-wear-resistant cast iron", IPC С22С 37 / 00, claimed 08.05.1969). It contains components in the following ratio, wt.%:

carbon 2.4-2.8 manganese 0.5-0.8 silicon 1.5-2.0 chromium 30-34 nickel 1.5-2.0 molybdenum 1.5-2.0 titanium 0.4-0.6 iron rest

When comparing the components of cast iron brand ICHKH28N2 and ed. USSR No. 309971, the compositions of which are very close to each other, it is evident that titanium is introduced into the latter, which positively affects the increase in wear resistance. This is due to two factors:

1 - titanium modifies the alloy due to the formation of refractory, thermodynamically stable carbides, nitrides and titanium oxides, which are crystallization centers in the liquid metal and contribute to the refinement of the cast iron structure;

2 - titanium carbides with the highest microhardness among carbides form an independent phase, increasing wear resistance.

However, according to copyright certificate No. 309971, white cast iron alloy has the same drawback as the previous analogue, namely, the difficulty of machining.

The objective of the present invention is to improve the machinability of parts made from the inventive alloy, while maintaining a high value of wear resistance.

The technical result obtained by the implementation of the invention is to increase the viscosity and plastic characteristics of the alloy.

This problem is solved due to the fact that in the well-known white wear-resistant cast iron, including carbon, silicon, manganese, chromium, nickel, molybdenum, titanium, according to the invention, tungsten, vanadium and copper are additionally introduced in the following ratio of components, wt.%:

carbon 2.4-2.6 silicon 0.5-0.6 manganese 0.8-1.8 chromium 25-26 nickel no more than 0.5 tungsten 0.1-0.15 molybdenum 0.3-0.5 titanium 0.5-0.7 vanadium 0.1-0.15 copper 1.8-2.0 iron rest

Studies conducted on the sources of patent and scientific and technical information have shown that the claimed white wear-resistant cast iron is unknown and does not follow explicitly from the studied prior art, i.e. meets the criteria of "novelty" and "inventive step".

The inventive white wear-resistant cast iron can be obtained in the conditions of metallurgical production, because this requires well-known technologies, materials and standard domestic or imported equipment. It can be widely used in enterprises manufacturing mining and processing equipment for pumping waterjet mixtures, such as soil pumps.

The main components that determine the properties of white wear-resistant cast irons and their structural components, the ratio of carbides and metal base, are carbon and chromium.

To obtain the best wear-resistant properties of the alloy, it is necessary that the amount of carbides is determined by the ratio K = 12.23 (% C) +0.55 (% Cr) -12.3. On average, K ranges from 10 to 33. In addition, it was experimentally found that the highest results of wear resistance are achieved with another ratio, namely% C /% Cr = 10. A greater number of carbides leads to a decrease in the plastic characteristics of the alloy and a deterioration in its machinability. In the inventive alloy, carbides are formed by combining carbon with chromium, molybdenum, vanadium, titanium and iron, while the Charpy principle is observed, the hardest structural components lie in the form of inclusions isolated from each other, and the most viscous form a continuous matrix, which is best provide high wear-resistant properties, as well as strength, toughness and resistance in the conditions of heat exchange.

The combined presence of titanium and vanadium in the alloy in the claimed amounts, obtained experimentally, allows you to effectively control the crystallization of cast iron.

Titanium is a strong carbide forming element, microalloying and modifying cast iron. Titanium carbides (carbonitrides) formed in molten iron are highly dispersed and hard. Being centers of crystallization, they also contribute to a significant refinement of the cast structure of the alloy and a uniform distribution of the carbide phase in the metal matrix. Being, in addition, in a cementite eutectic and along the boundaries of the dendrites of former austenite, titanium carbides contribute to an increase in microhardness. Aligning the crystallization rates of cementite and austenite, titanium increases the amount of the latter, which increases the viscosity of cast iron. The combination of all these factors provides an increase in the wear resistance of the resulting alloy.

Vanadium, like titanium, has a high affinity for carbon and forms special dispersed monocarbides with it with high hardness and wear resistance. Alloying vanadium with nickel, chromium, copper and manganese is very effective for improving the mechanical properties and obtaining wear-resistant castings. Copper, hardening the austenic structure, improves machinability while maintaining high alloy hardness.

Complex alloying of white cast iron gives, along with high initial hardness, hardening without exposure to abrasive particles, which ensures high wear resistance.

The preparation of white cast iron of the claimed composition was carried out as follows. The chemical composition of cast iron: sample 1, sample 4 are shown in Table 1.

Table 1 Component No. sample FROM Si Mn Cr Ni W Mo Ti V Cu The inventive composition one 2,4 0.6 1.8 24 0.5 0.12 0.4 0.7 0.14 2.0 2 2.6 0.5 1.4 26 0.3 0.1 0.35 0.56 0.1 1.9 3 2.45 0.6 1,5 24.5 0.5 0.14 0.5 0.6 0.11 1.8 four 2,55 0.5 1.7 25.5 0.4 0.15 0.4 0.7 0.13 2.0 prototype one 2,4 1.55 0.5 30.5 1,5 - 1,6 0.5 - - 2 2.5 1.55 0.6 31 1,6 - 1.8 0.6 - - 3 2.6 1,6 0.7 32 1.7 - 2.0 0.6 - - four 2,8 1.7 0.8 thirty 1.8 - 1,6 0.4 - -

Iron was smelted in an induction crucible. After overheating of the melt to 1450 °, the chemical composition was adjusted according to the main and alloying elements. Used: ferrochrome FK 400-650 (68%), ferromanganese FMn78 (86%), ferrotitanium Fti68, ferrosilicon FS45 (45%), anodic copper AN-1, nickel H1, ferrovanadium FVd35A, ferromolybdenum FMo60. Finished by chemical composition, the melt was poured into sand form with a diameter of 25 mm and a length of 55 mm. The metal samples were subsequently subjected to heat treatment in an electric heating furnace at a heating rate of 80 ° C / h. Three different types of heat treatment were selected:

1. Recrystallization annealing with a temperature of 500 ° C, holding - 2 hours cooling with the oven turned off.

2. Normalization annealing from a temperature of 800 ° C and 900 ° C, holding for 2 hours.

3. Quenching from a temperature of 950 ° C and 1100 ° C, holding - 2 hours, cooling in air.

After heat treatment, hardness was measured on a Rockwell hardness tester. HRC ranged from 47 to 55.

The study of abrasion resistance was carried out on a test bench.

Samples with a diameter of 25 mm and a length of 55 mm were carefully weighed to an accuracy of 0.01 g and, under a pressure of 5 kg, they were pressed against a corundum circle rotating at a speed of 360 rpm for 2 min. Then the sample was weighed. The difference in the two weighings was used to determine the weight loss and calculate the relative abrasive wear resistance (And rel.) By the formula

where: M experience. - weight loss of the test sample, M etal. - loss of mass of the standard steel specimen CT20.

The formula shows that the greater the value And rel., The lower the wear resistance of the sample.

Given that the working bodies of the pumps operate in different environments, we determined the relative hydroabrasive wear resistance of the studied samples of white cast iron on a test bench.

The test samples previously weighed with a clean surface were fixed in the socket of the plan washer driven into rotation from the machine spindle. Hydroabrasive wear resistance was determined by weight loss after 40 hours of rotation in a mixture of electrocorundum (50%) and water. The steel sample CT20 is taken as a reference.

The results of the study patentable white wear-resistant cast iron are shown in table 2.

table 2 Alloy sample no. Relative abrasion resistance Relative waterjet abrasion resistance Recrystallization Normalization Quenching Recrystallization Normalization Quenching 500 ° C 900 ° C 950 ° C 500 ° C 900 ° C 950 ° C claimed cast iron one 0.15 0.14 0.12 0.11 0.09 0,07 2 0.14 0.11 0.09 0.10 0,07 0.05 3 0.15 0.14 0.10 0.11 0.08 0,07 four 0.15 0.13 0.10 0.12 0.09 0.08 prototype one 0.21 0.16 0.14 0.13 0.12 0.11 2 0.19 0.15 0.13 0.12 0.10 0.09 3 0.18 0.15 0.13 0.12 0.10 0.09 four 0.20 0.14 0.14 0.13 0.12 0.10

Then tests were carried out for processing with cutters with VK6M plates. The cutting speed of the prototype samples did not exceed 25 mm / min with a cutting depth of 4-5 mm and a feed of 0.3-0.4 mm / rev for roughing and 0.5-0.6 mm / rev for finishing. Three samples 1, 2, and 4 showed cracks and chips.

The cutting speed of the samples of the claimed was 32.5 m / min, i.e. increased by approximately 30%. In this case, no mechanical damage to the samples (chips, cracks, etc.) was observed.

Claims (1)

White wear-resistant cast iron containing carbon, silicon, manganese, chromium, nickel, molybdenum, titanium and iron, characterized in that it additionally contains tungsten, vanadium and copper in the following ratio, wt.%:
carbon 2.4-2.6 silicon 0.5-0.6 manganese 0.8-1.8 chromium 25-26 nickel no more than 0.5 tungsten 0.1-0.15 molybdenum 0.3-0.5 titanium 0.5-0.7 vanadium 0.1-0.15 copper 1.8-2.0 iron rest