EA019270B1 - Abrasion-resistant cast iron - Google Patents

Abstract

The present invention relates to the metallurgic engineering, in particular to the iron compositions, used for manufacture of pieces, operating under the impact abrasive wear conditions, for example, tumbling bodies (balls, cylpebses, etc.) of the ball mills in the cement, construction, mining and another fields industry. The abrasion-resistant cast iron is provided, comprising, in percent by weight: carbon 2.6-3.1; silicon 0.6-1.3; manganese 0.5-1.5; nickel 0.2-0.5; titanium 0.1-0.2; sulphur 0.03-0.12;0.06-0.1; chrome 1.0-12.0; ferrum - the rest, the chrome content being in inverse proportion to the casting cooling rate, determined by the casting weight value. The provided abrasion-resistant cast iron ensures high hardness casting at the controlled hardness distribution throughout the casting cross section for the different weight castings (in particular, of 0.013 to 5.7 kg).

Description

The invention relates to metallurgy, in particular to the compositions of cast irons used for the manufacture of parts operating in conditions of impact-abrasive wear, for example grinding bodies (balls, tsilpebs, etc.) of ball mills in cement, construction, mining and other industries.

A fairly large number of cast iron compositions are known, the wear resistance of which increases due to the introduction and the correct selection of the input amounts of various alloying additives, in particular chromium, manganese, nickel, etc. [1-5]. All these and other known compositions of cast irons, as a rule, are developed for specific production conditions and specific applications (in particular, a specific casting mass) and, when the conditions change, may exhibit disadvantages associated with non-compliance with the requirements for a number of physical and mechanical characteristics.

In particular, wear-resistant cast iron [6] is known with the following chemical composition, wt.%: Carbon 2.6-3.1, silicon 0.6-1.3, manganese 0.5-1.5, chromium 0.07- 0.2, titanium 0.1-0.2, molybdenum 0.01-0.02, vanadium 0.07-0.015, nickel 0.02-0.04, copper 0.03-0.04, tungsten 0, 01-0.02, aluminum 0.03-0.05, sulfur 0.08-0.13, phosphorus 0.06-0.08, iron - the rest. The disadvantage of this cast iron is still insufficient wear and tear resistance associated with the insufficient content of carbide-forming elements (the total content is 0.4-0.8 wt.%), Which, in connection with this, do not provide the required amount and hardness in cast iron cementitious carbides that increase the wear resistance of castings of grinding media.

The closest in essence and the technical result achieved to the claimed wear-resistant cast iron is cast iron [7] of the following chemical composition, wt.%: Carbon 2.0-2.5, silicon 0.3-0.5, manganese 1.7-2 6, chrome 15-18, titanium 0.05-0.1, nickel 0.4-0.8, iron - the rest. The disadvantage of such cast iron is the difficulty of its production during smelting, since it, in fact, is synthetic, obtained only in electric furnaces by carburizing steel scrap and using chromium ferroalloys. Due to the low carbon content, such cast iron has an increased tendency to form shrink shells and porosity in castings, which reduces its advantages in terms of strength, wear resistance and impact resistance.

It is known that the formation of the structure of cast iron occurs during the solidification of the casting, and the main factors affecting the structure formation of cast iron are its chemical composition and the cooling rate of the casting in the form, which, in turn, is determined by the mass of the casting. Thus, in order to expand the possible areas of application of wear-resistant cast iron of a certain composition, it would be desirable that the quality of castings obtained by their cast iron of this composition does not depend, in particular, on the mass of castings.

The objective of the invention is to develop a composition of economically alloyed wear-resistant cast iron, which would provide high hardness of the casting with a uniform distribution of hardness throughout the cross section. The composition should provide the ability to obtain castings of various weights (in particular, from 0.013 to 5.7 kg) with equally high values of hardness and uniformity of distribution of hardness over the cross section of the casting.

The problem is solved by the claimed wear-resistant cast iron, containing, wt.%:

carbon

2.6-3.1 silicon

0.6 - 1.3 manganese

0.5 - 1.5 nickel

0.2 - 0.5 titanium

0.1-0.2 sulfur

0.03-0.12 phosphorus

0.06 - 0.1 chrome iron

1.0-12.0 the rest, and the chromium content is inversely proportional to the cooling rate of the casting, determined by the weight of the casting.

When developing and testing the inventive (basic) composition of cast iron, the authors found that it is possible to maintain high values of the hardness of the casting and the uniformity of the distribution of hardness over the volume of the casting for different masses of castings by differentially changing the chromium content within the above ranges of values.

So, for forms of execution in which the inventive wear-resistant cast iron is intended for the manufacture of castings (grinding bodies) weighing less than 0.5 kg (respectively, the diameter of the balls is up to 40 mm), the chromium content is preferably 1.0-6.0 wt.% provided that the ratio (wt.% / wt.%) chromium / carbon = 0.35-2.1.

For forms of execution in which the inventive wear-resistant cast iron is intended for the manufacture of castings (grinding media) weighing from 0.5 to 5.7 kg (respectively, the diameter of the balls is from 40 to 110 mm), the chromium content is 6.0-12.0 wt. .% provided that the ratio (wt.% / wt.%)

- 1 019270 chromium / carbon = 2.1-4.2.

In preferred forms of implementation in the inventive wear-resistant cast iron, the total content of carbon and silicon is 3.2-4.4 wt.%.

The above ranges of chromium content and the ratios between the content of chromium and carbon were obtained by calculation and experimental methods. The initial data, calculated indicators and obtained characteristics of the hardness of the castings for some of the experiments are shown in the table below.

The dependence of the chromium content on the mass of castings in the basic composition of cast iron (wt.%: C = 2.6-3.1; 81 = 0.6-1.3; Μη = 0.5-1.5; Νΐ = 0.2 -0.5; Τί = 0.1-0.2; 8 = 0.03-0.12; P = 0.06-0.1; Cr = 1.0-12.0; D - rest)

The chromium content, wt.% Conditional diameter of casting, mm The estimated volume of the casting, cm ³ Estimated mass of the cast, kg The ratio of chromium / carbon (wt.% / Wt.%) Carbide types The microhardness of carbides, kgf / mm ² Surface hardness, HB 1,0 fifteen 1.76 0.013 0.35 Re ₃ C + (Re Cg) ₃ C 800-1000 380-415 2.0 twenty 4.18 0,030 0.7 3.0 25 8.18 0,060 1,0 4.0 thirty 16,4 0,120 1.41 (ReSg) ss 1000-1100 415-460 5,0 40 37,4 0.275 1.76 6.0 fifty 74 0.540 2.1 7.0 60 125 0.920 2.7 (ReSg) ₃ C + (ReSg) ₇ C _e 1100-1300 460 - 480 8.0 70 204 1,500 3.0 9.0 80 299 2,200 3.23 10.0 90 435 3,200 3.53 (ReSg) ₇ C ₃ 1300 - 1500 480 - 530 11.0 one hundred 589 4,330 3.89 12.0 but 776 5,700 4.20 18.0 6.0 (ReSg), C ₃ + (ReSg) ₂₃ C ₆ 1400 - 1500

Note: the estimated volume and estimated mass of the ball are calculated by the nominal diameter with a density of white cast iron 7.35 g / cm ³ .

The following conclusions can be drawn from the table.

At ratios (wt.% / Wt.%) Of chromium / carbon = 0.35-2.1, which corresponds to the chromium content in cast iron of 1.0-6.0 wt.%, Cementitious carbides of the type Re ₃ C prevail in the structure of cast iron and (FeCg) ₃ C, which have a hardness of 800-1000 kgf / mm ² [8]. Thus, the basic composition of the inventive wear-resistant cast iron with a ratio (wt.% / Wt.%) Chromium / carbon = 0.35-2.1, it is advisable to use to obtain small castings (balls, tsilpebs, etc.) weighing up to 0, 5 kg This ensures the necessary hardness of the castings both on their surface and throughout the volume without preliminary heat treatment.

At ratios (wt.% / Wt.%) Chromium / carbon = 2.7-3.2, which corresponds to the chromium content in cast iron of 7.0-9.0 wt.%, In the structure of cast iron along with carbides (FeCg) ₃ The number of carbides (FeCg) ₇ C ₃ with a microhardness of up to 1300 kgf / mm ^{2 is} constantly increasing, which ensures satisfactory hardness of castings of grinding media of a larger mass, in particular from 1.0 to 2.2 kg (respectively, diameter from 60 to 80 mm) both on the surface and at a distance of 1/2 the radius of the ball.

At ratios (wt.% / Wt.%) Chromium / carbon = 3.2-4.2, which corresponds to the chromium content in cast iron 10.0-12.0 wt.%, Carbides (FeCg) ₇ С prevail in the structure of cast iron ₃ , the microhardness of which is 1300-1500 kgf / mm ² and which allow to obtain more massive balls weighing up to 5.7 kg (respectively, with a diameter of up to 110 mm).

With a further increase in the ratio (wt.% / Wt.%) Of chromium / carbon to more than 6–9 and chromium concentration of more than 18–20 wt.%, Cast irons also acquire corrosion resistance, since in addition to M ₇ C ₃ carbides, the number of M ₂₃ C ₆ carbide inclusions increases significantly [8, 9].

Wear-resistant cast iron of the proposed composition can be smelted both in a cupola and in an acidic furnace. When smelting cast iron in a cupola, the chromium content in cast iron should not exceed 6 wt.%. Cast iron with a higher chromium content (up to 12 wt.%) Is more advisable to melt in an electric furnace.

Reducing cast iron PL-2, scrap and waste products of corrosion-resistant and heat-resistant chromium steels containing, wt.%: Chromium 16-18, titanium no more than 0.8, nickel no more than 0.6 can be used as charge materials. Impurities of titanium and nickel in scrap are the main source of these useful elements in the composition of cast iron. To obtain a higher chromium content (7-12 wt.% Or more), carbon ferrochrome must be added to the electric furnace.

Thus, the creation of economically alloyed wear-resistant cast iron with differentiated chromium content depending on the cooling rate of the casting, determined by the mass of the casting, ensures the hardness and, therefore, wear resistance of the castings of grinding media without preliminary heat treatment.

Information sources.

1. Patent KI No. 2332507 C1, publ. 08/27/2008.

2. Patent No. 11609 C1, publ. 02/27/2009.

- 2 019270

3. Patent KI No. 2345160 C1, publ. 01/27/2009.

4. Patent 1P No. 3268238 B2, publ. 02.16.1999.

5. Patent EP No. 0525932 B1, publ. 02/03/1993.

6. Patent No. 10946 C1, publ. 05/12/2006.

7. Patent ΚΖ No. 11737 A, publ. 07/15/2002.

8. Poddubny A.N., Romanov L.M. Wear-resistant castings from white cast iron for metallurgy and mechanical engineering. - Bryansk: Pridesenie, 1999, p. 14-20.

9. Garber M.E. Castings made of white wear-resistant cast irons. - M.: Mechanical Engineering, 1972, p. 16-35.

Claims (4)

CLAIM 1. Wear-resistant cast iron containing, by weight.%: carbon silicon 0.6-1.3 manganese nickel 0.2 - 0.5 titanium 0.1 -0.2 sulfur 0.03-0.12 phosphorus 0.06-0.1 chromium iron is the rest, and the chromium content is inversely proportional to the cooling rate of the casting, determined by the value of the mass of the casting. 2. Cast iron according to claim 1, characterized in that the chromium content is 1.0-6.0 wt.%, Provided that the ratio (wt.% / Wt.%) Chromium / carbon = 0.35-2.1 with a mass of castings up to 0.5 kg. 3. Cast iron according to claim 1, characterized in that the chromium content is 6.0-12.0 wt.%, Provided that the ratio (wt.% / Wt.%) Chromium / carbon = 2.7-4.2 with a mass of castings from 0.5 to 5.7 kg. 4. Cast iron according to any one of claims 1 to 3, characterized in that the total content of carbon and silicon is 3.2-4.4 wt.%.