RU2366741C1 - Modifier - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, to foundry engineering and to machine building and can be implemented at production of casts out of grey cast hypoeutectic iron operating under conditions of excess wear, for example railroad car brake blocks, big tooth gears, parts of windlass and cylinder cartridge. As a zirconium containing additive the modifier contains zirconium dioxide (ZrO₂), as silicon containing additive it contains silicon dioxide (SiO₂), as a bubbling additive - foam plastic crumb and as a reducer - aluminium at following ratio of components, wt %: SiO₂ 35.0-45.0; ZrO₂ 35.0-45.0; Al 10.0-19.0; foam plastic crumb up to 1.0.

EFFECT: upgraded operational properties of iron casts: wear resistance is increased at 8-10%, and leak tightness - 1,5-2 times.

7 ex, 3 tbl

Description

The invention relates to metallurgy, foundry and mechanical engineering and can be used in the manufacture of castings of gray - pre-eutectic iron, working in conditions of increased wear, for example, car brake pads, large gears, parts of a windlass, cylinder liner (along with rare-earth metals), etc. .

The use of well-known zirconium modifiers makes it possible to obtain gray cast iron with improved mechanical characteristics (tensile strength, deflection arrow and wear resistance), which is mainly achieved by grinding the structure.

However, in some cases, in the manufacture of parts subject to intense wear, a special combination of wear resistance and tightness (absence of pores) of the material with limited hardness is required. Thus, an increase in the wear resistance of castings along with a decrease in the number of pores with a limited hardness of the material becomes the main problem in the modification of gray hypereutectic cast irons with zirconium.

Known modifier [Pat. 2184491 RF, IPC ⁷ C22C 35/00, Ligature. / V.M. Grigoriev, T.V. Belous (RF); KHTU (RF). Publ. 07/10/2002, Bull. No. 19], including silicon, manganese, tungsten, aluminum, magnesium, calcium and zirconium. The components are contained in an amount (wt.%):

Si 27.0-35.0;

Zr - 19.0-38.0;

W - 0.3-2.8;

Al - 3.0-6.0;

Mg 2.0-5.0;

Ca - 0-0.2.

The modifier is introduced in an amount of 0.05% by weight of gray cast iron in the ladle.

In the known modifier, the zirconium content in the ligature is increased, which provides a significant number of centers of crystallization of graphite, its grinding and a decrease in the concentration of stresses in the material.

Zirconium additive is easily soluble in molten iron.

The advantage of this modifier is to increase the wear resistance by 20.0%, as well as the tensile strength by 10.0-20.0% and the deflection boom by 2.0-5.0% compared with unmodified cast iron. This is due to an increase in the zirconium content in the ligature, which leads to the formation of additional centers of graphite crystallization. In turn, an increase in this number leads to grinding of graphite and, accordingly, a decrease in the concentration of stresses in the material, which increases the wear resistance.

However, even the increased wear resistance of gray cast iron by such a ligature remains insufficient for parts subjected to intensive wear. This is due to the fact that an increase in the zirconium content and the presence of tungsten leads to interparticle repulsion and increases the distances between iron atoms (ions) and, as a result, to an increase in the specific volume of the liquid phase (melt). This leads to an increase in volumetric shrinkage of the modified alloy. In turn, significant shrinkage increases the number of pores in gray pre-eutectic cast iron, which reduces wear resistance.

в чугуне.Another disadvantage of the known modifier, reducing wear resistance by increasing the porosity of cast iron, is its gas saturation. This is due to the fact that in the production process of the ligature itself, it is intensively saturated with atmospheric gases, which leads to an increase in the hydrogen content to

in cast iron.

Closest to the claimed combination of essential features and the achieved result is a modifier [Pat. 2316608 RF, IPC С22С 35/00 (2006.01), Modifier. / V.M. Makienko, E.M. Baranov, N.A. Andreiuk, D.V. Stroitelev, I.O. Romanov (RF); DVGUPS (RF). Publ. 02/10/2008, Bull. No. 4], including silicon, zirconium-containing additives and aluminum. As a silicon-containing additive selected silicon dioxide (SiO ₂ ), zirconium-containing additives - zirconium dioxide (ZrO ₂ ) in the following ratio of components (wt.%):

SiO ₂ - 35.0-5.0;

ZrO ₂ - 35.0-5.0;

Al - 10.0-20.0.

The modifier is introduced in an amount of 0.02% by weight of gray cast iron in the ladle.

During the interaction of the modifier with molten iron, a metallothermic reaction occurs during which zirconium is reduced from the dioxide and dissolved in the melt. The reaction constant determining the yield of zirconium is small due to the relatively low temperature of gray cast iron discharged from the cupola. A small amount of zirconium in gray cast iron (not more than 0.005 wt.%) Causes a sufficient number of centers of crystallization of graphite, which leads to its grinding and a decrease in stress concentration in the material.

The presence of zirconium and aluminum in the melt leads to the simultaneous deoxidation, desulfurization, and hydride nitride formation.

In addition, the presence of zirconium in the melt provides an intensive dissolution of silicon and manganese in a solid solution (austenite), leading to an increase in the percentage of perlite (wear-resistant component of the microstructure).

The advantage of the modifier described above is an increase in wear resistance compared to the analogue by 10.0-15.0% at a low temperature of modification of castings from gray pre-eutectic cast iron, operating under conditions of intensive wear, and while maintaining a high level of mechanical characteristics. This is due to the small amount of zirconium in gray cast iron (not more than 0.005 wt.%), Which leads to sufficient grinding of graphite and a decrease in stress concentration in the material, a simultaneous increase in the percentage of perlite (wear-resistant component of the microstructure) and, as a result, to increase wear resistance of cast iron.

In addition, the presence of oxygen in the modifier leads to a sharp decrease in the specific gravity of the modifier due to the increase in periods (interplanar distances) in the crystal lattices of oxides. A decrease in the specific gravity of the modifier causes it to emerge (flotation effect) with the simultaneous assimilation of dissolved gases, which provides additional degassing of gray cast iron, along with the refining and degassing effect of reduced zirconium. Degassing leads to a sharp reduction in the number of pores in gray cast iron, which creates an additional, tangible increase in wear resistance.

However, at an elevated temperature of modification (1460-1480 ° C), for example, when smelting cast iron in a large-capacity induction furnace or gas cupola, the viscosity of cast iron decreases sharply, which leads to an increase in the ascent rate of the modifier. An increased ascent rate leads, in turn, to a decrease in the constant of the metallothermal reaction (the amount of reduced zirconium decreases), as well as to insufficient completeness of degassing, and, accordingly, to an increase in porosity. This reduces the wear resistance of the modified material at elevated temperature modification.

The basis of the invention is the task of developing a gray cast iron modifier with high wear resistance at an elevated temperature of modification and increased tightness of cast iron castings due to the intensification of the metallothermal reaction by bubbling the modifier components in the melt.

To solve the problem, a modifier containing silicon-containing and zirconium-containing additives and aluminum, while silicon dioxide (SiO ₂ ) was selected as a silicon-containing additive, zirconia (ZrO ₂ ) was added as a zirconium-containing additive, was additionally introduced

polystyrene foam as a bubbling additive in the following ratio of components (wt.%):

SiO ₂ - 35.0-5.0;

ZrO ₂ 35.0-45.0;

Al - 10.0-19.0;

polystyrene crumb - up to 1.

The introduction of polystyrene chips as a bubbling additive distinguishes the claimed solution from the prototype, which indicates the compliance of the proposed solution to the patentability criterion of "novelty."

Due to the introduction of polystyrene foam into the modifier as a bubbling additive, it increases the wear resistance of gray cast iron at a high temperature of modification. This is due to the fact that during the interaction of the foam with molten iron, it undergoes destruction with the release of a large volume of gases. The emitted gas mixes the modifier, contributing to an increase in the reaction surface and a sharp increase in the constant of the metallothermic reaction. The intensification of the reaction increases the amount of zirconium passing into the melt. This, in turn, increases the amount of perlite in the structure and grinds graphite, which sharply increases the wear resistance, as well as other mechanical characteristics of the material.

The causal relationship "Introduction to the modifier of foam chips leads to the intensification of the metallothermic reaction" clearly follows from the prior art.

At the same time, the introduction of polystyrene foam into the modifier leads to the release of a large amount of gas during the destruction of the foam, which contributes to the cooling of the melt, leading to a sharp decrease in gas-shrinkage porosity and, as a result, to increase the tightness of cast iron castings.

The causal relationship "Introduction to the modifier of polystyrene foam leads to an increase in the tightness of cast iron castings" does not explicitly follow from the prior art, which indicates that the proposed solution meets the patentability criterion of "inventive step".

The modifier includes silicon- and zirconium-containing additives, aluminum and polystyrene crumb as a bubbling additive. Silicon dioxide (SiO ₂ ) was chosen as a silicon-containing additive, zirconia (ZrO ₂ ) was chosen as a zirconium-containing additive. Components selected in the amount (wt.%):

SiO ₂ - 35.0-45.0;

ZrO ₂ - 35.0-5.0;

Al - 10.0-19.0;

polystyrene crumb - up to 1.

To prepare the modifier use zirconium ore (baddeleyite), for example, Algaminsk deposits (Khabarovsk Territory) or deposits of the northern Urals and Ukraine. The mineralogical composition of baddeleyite from the Algaminskoye field is shown in table 1.

Table 1. The mineralogical composition of baddeleyite Component SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ ZrO ₂ Wo ₃ CaO MgO Wt% 46.0-52.0 0.35-0.47 up to 0.16 45.0-48.0 up to 2 rest

To prepare the modifier, the ingredients are selected in the following ranges (wt.%):

- baddeleyite (zirconium ore) - 70.0-90.0; which corresponds to 35.0-45.0 ZrO ₂ and 35.0-45.0 SiO ₂ ;

- SiO ₂ - 13.0-15.0;

- aluminum shavings - 10.0-19.0;

- foam crumb - up to 1.0.

Aluminum shavings are a waste of cutting the profile of building structures. Quartz sand is taken from the Kichiginsky quarry.

Modification of cast iron is carried out in a ladle, pouring the modifier with superheated cupola iron. Mixing occurs on its own when the modifier emerges and sparges. After surfacing, they give a five-minute exposure, after which the slag is removed and molds are filled.

Example 1. To prepare the modifier, take 150.0 kg of baddeleyite (which corresponds to 45.0% ZrO ₂ and 33.0% SiO ₂ ), grind in a ball mill, then in a screw mixer, mix with 34.0 kg of aluminum shavings (19 , 0%) with the addition of 4.5 kg of silica sand SiO ₂ (2.5%). The resulting mixture was calcined for 5 hours at a temperature of 350 ° C, followed by cooling and packaging. In the packaging process add 1.0 kg (0.5%) of polystyrene foam.

The modifier is introduced in an amount of 350.0 g per 180.0 kg of metal in the bucket (0.02% of 180.0 kg). A plastic bag with a modifier is placed on the bottom of the bucket, then 180.0 kg of gray cast iron is poured from the gas cupola into the bucket. Mixing occurs on its own when the modifier emerges and sparges. After surfacing, they give a five-minute exposure, after which the slag is removed and molds are filled.

Examples 2-3. Gray cast iron is modified as described in example 1. To obtain a modifier in these examples, take 150.0 kg of baddeleyite and 34.0 kg of aluminum shavings, changing the composition of the remaining components, as shown in table 2.

Example 4. Gray cast iron is modified as described in example 1. To obtain a modifier in these examples, 130 kg of baddeleyite and 34 kg of aluminum shavings are taken, changing the composition of the remaining components, as shown in table 2.

Example 5. Gray cast iron is modified as described in example 1. To obtain a modifier in these examples, take 150 kg of baddeleyite and 15 kg of aluminum shavings, changing the composition of the remaining components, as shown in table 2.

Example 6. Gray cast iron is obtained by modification without foam crumb.

Example 7. Gray cast iron is modified as described in example 1. To obtain a modifier in these examples, take 150 kg of baddeleyite and 34 kg of aluminum shavings, changing the composition of the remaining components, as shown in table 2, while the amount of foam crumb is outside the stated interval.

Table 2. Modifier Composition The content of the component, wt.% SiO ₂ ZrO ₂ Al Styrofoam Example 1 35.5 45.0 19.0 0.5 Example 2 35.25 45.0 19.0 0.75 Example 3 35.0 45.0 19.0 1,0 Example 4 45.0 35.0 19.0 1,0 Example 5 44.0 45.0 10.0 1,0 Example 6 35.5 45.5 19.0 - Example 7 34.5 45.0 19.0 1,5

Then, standard tribometric tests were performed on the MI-401 tribometric machine of the Moscow Experimental Plant. Cast samples of the samples were broken and the number of pores per square centimeter of fracture was determined.

The results of physical and technical indicators of modified gray cast iron are shown in table 3.

Table 3. Physical and technical indicators of cast iron Cast iron specifications The number of pores per square centimeter Wear resistance (loss of weight loss),% Example 1 12.0 40,0 Example 2 10.0 42.0 Example 3 8.0 46.0 Example 4 15.0 38,0 Example 5 15.0 36.0 Example 6 22.0 45.0 Example 7 7.0 45.0

Tests of modified cast iron show that the wear resistance of cast iron in comparison with the prototype increases by 8-10%, and the tightness of cast iron increases by 1.5-2 times, which ensures high performance castings.

Claims (1)

A modifier containing silicon-containing and zirconium-containing additives and aluminum, while silicon dioxide (SiO ₂ ) is selected as a silicon-containing additive, zirconium dioxide (ZrO ₂ ) is selected as a zirconium-containing additive, characterized in that it additionally contains polystyrene foam as a bubbling additive the following ratio of components, wt.%:
silicon dioxide (SiO ₂ ) 35.0-45.0 zirconium dioxide (ZrO ₂ ) 35.0-45.0 aluminum 10.0-19.0 polystyrene crumb up to 1.0