RU2727740C2 - Cast iron production method - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, particularly, to foundry production, particularly, to production of wear resistant cast iron. Wear-resistant cast iron characterized by uniform distribution of cubic titanium carbide is obtained by direct reduction by electroslag method. Chemical composition of initial oxides is: iron oxide 66.25 %, vanadium oxide 5.5 %, titanium oxide 1.63 %, manganese oxide 2.25 %, chromium oxide 0.2 %, molybdenum oxide 1.86 %, cerium oxide 1.5 %, aluminium oxide 11.6 % and silicon oxide 9.2 %, impurities of calcium, magnesium and phosphorus oxides 0.01 %. Initial oxides are mixed in a solid phase, metal aluminium is added, based on stoichiometry of reduction of titanium oxide and vanadium oxide, and additionally over stoichiometry by 10–15 % coke is added for reduction of iron oxide. Prepared mixture is fed into electroslag kiln crucible in portions equal to 0.01 part of total weight, with interval determined by termination of smoke extraction, melting is carried out at voltage 30 V and current 2000–2500 A.EFFECT: technical result is production of cast iron with high heat resistance, microhardness and wear resistance.1 cl, 4 dwg, 3 tbl, 2 ex

Description

The invention relates to metallurgy, in particular, to foundry, namely, to technologies for producing wear-resistant cast iron.

Known alloyed nodular cast iron. High-strength nodular cast irons (VChShG) compare favorably with steel in good casting properties (high fluidity, low tendency to hot cracking, less shrinkage, etc.), relative simplicity of the smelting process and lower cost. They are obtained by modification with magnesium, cerium, which are introduced into liquid iron in an amount of 0.02-0.08%. (Kolokoltsev VM, Nazarov OA, Korotchenko VV and others. Wear-resistant cast irons for casting parts of shot-blast chambers // Foundry, 1992. No. 7. P. 11-12) (Voinov BA. Wear-resistant alloys and coatings (Moscow: Mashinostroenie, 1980. 126 p.) [2].

As you know, in cast iron, the shape of the graphite grain has a decisive effect on the strength characteristics of the material. In high-strength cast iron (VChShG), graphite inclusions have a spherical shape. As a result, ductile iron is significantly superior in mechanical properties to gray cast iron and successfully competes with steel. Spheroidal graphite is also called spheroidal or globular graphite.

Ductile nodular cast iron is a material of construction. High-strength cast irons are used to make rolling rolls, forging equipment, steam turbine housings, crankshafts and other critical parts operating under high cyclic loads and under wear conditions.

High-strength cast irons (GOST 7293) can have ferritic (VCh 35), ferrite-pearlite (VCh45) and pearlitic (VCh 80) metal bases These cast irons are obtained from gray ones, as a result of modification with magnesium or cerium (0.02-0.08% is added . from the mass of the casting). Compared to gray cast irons, the mechanical properties are improved, this is due to the absence of uneven stress distribution due to the spheroidal shape of the graphite.

Cast irons with a pearlitic metal base have high strength values with a lower ductility value. The ratio of plasticity and strength of ferritic cast irons is the opposite.

Cast iron with vermicular (compact) graphite (CGG) allows obtaining the desired mechanical and physical properties, provided that the historically existing difficulties in the production of castings from CGG are eliminated (especially in terms of such an indicator as sensitivity to the thickness of the casting wall).

For many years, CWG has been successfully used in the production of cast iron molds, slag, siphons and siphon plates, but all these castings have thick sections and simple configuration. Today, the use of this material is gradually becoming more popular in the production of brake discs and drums, cylinder heads, various components of hydraulic systems and even piston rings.

The disadvantage of the standard technology for the manufacture of cast iron is the introduction into the melt of a sample of a modifier of the FSMg type, which is insufficient for complete spheroidization of graphite; the isolated free graphite has a low hardness, which leads to a decrease in the microhardness and wear resistance of this cast iron. In addition, the resulting primary structure of cast iron is not retained during secondary remelting, which leads to inoculation at each remelting.

The closest solution is the work of G.V. Petrochenko, E.V. Shekunov. Development of a new composition of chromium-titanium cast iron for work under conditions of abrasive wear at elevated temperatures // Bulletin of the Chelyabinsk Scientific Center, 2006. 4 (34) .Art. 48-52.) [3].

The study of new chromium-titanium cast irons was carried out with a change in the content of elements: carbon - 2.0, 2.5%; chromium - 10.0, 14.0%; titanium - 0.3, 0.6%.

The metallographic analysis of the microstructure of chromium-titanium cast irons made it possible to determine that all the compositions under study were eutectic.

During crystallization of chromium-titanium cast irons, titanium carbides are released first. The volume fraction of titanium carbides is 0.3-1.5%, the average size is 0.4 ... 3.9 microns.

The microstructure of chromium-titanium cast iron (microsection without etching) is shown in Fig. 13].

As a result of laboratory tests, it was determined that the hardness of chrome-titanium cast irons is 46.3 ... 62.5 HRC. Unit Wear resistance during wear with electrocorundum - 4.0 ... 6.9 units.

As seen from Fig. 1: firstly, titanium carbide occupies an insignificant share in the volume of cast iron. Most of the volume is free of titanium carbide. Secondly, it did not become centers of crystallization for the alloy. This weight leads to the fact that such cast iron will have low toughness and hardness.

The problem solved by the invention is to create a method for producing cast iron, characterized by a uniform distribution of cubic titanium carbide throughout the entire volume of cast iron, with properties similar to nodular cast iron and vermicular, but having a higher micro-hardness, ensured by a uniform distribution throughout the volume of cast iron carbide titanium, which has the highest hardness of all metal carbides [1].

The technical result is that the proposed technology makes it possible to produce cast iron with high physical and mechanical properties: high heat resistance, microhardness and wear resistance; in strength and fluidity, it is almost 2 times higher than these parameters for vermicular cast irons, and in terms of viscosity it exceeds both vermicular cast irons and cast irons with spherical graphite. These properties are retained after melting.

The task is achieved by the fact that a method for producing cast iron has been developed, in which cubic titanium carbide is evenly distributed over the entire volume of the melt when the initial components are melted. Cast iron is obtained by direct reduction by the electroslag method, for this, the initial oxides are mixed in the solid phase: iron oxide 66.25%, vanadium oxide 5.5%, titanium oxide 1.63%, manganese oxide 2.25%, chromium oxide 0.2% , molybdenum oxide 1.86%, cerium oxide 1.5%, aluminum oxide 11.6% and silicon oxide 9.2%, impurities of calcium, magnesium and phosphorus oxides 0.01%, metallic aluminum is added, based on the stoichiometry of the reduction of the oxide titanium and vanadium oxide, and additionally above the stoichiometry by 10-15%, add coke based on the reduction of iron oxide, the prepared mixture is fed into the crucible of the electroslag plant in portions of 0.01 part of the total weight, with an interval as the previous portion is completely restored and homogenization of the melt in terms of density.

The raw material for use as starting oxides can be a spent cerium catalyst having a composition (wt%): FeO - 75, Mo - 2, CeO ₂ - 3, Al ₂ O ₃ - _- 20 and metallurgical slag of the composition: V ₂ O ₅ - 20.51, MnO - 11, SiO ₂ - 8, CaO - 2, TiO ₂ - 8.5, MgO - 0.2, - 49.29, Cr ₂ O ₃ - 0.3, P - 0.2, which are mixed in the solid phase in a ratio of 3/1

Examples of making cast iron.

Example 1. Mix in the solid phase: 53 kg of iron oxide, 1.5 kg of molybdenum oxide, 1.2 kg of cerium oxide, 9.3 kg of aluminum oxide, 4.4 kg of vanadium oxide, 1.3 kg of titanium oxide, 1, 8 kg of manganese oxide, 0.16 kg of chromium oxide and 7.34 kg of silicon oxide.

Metal aluminum is added, based on the stoichiometry of the reduction of titanium oxide and vanadium oxide, this is 3.83 kg,

Metallic aluminum is added in excess of the stoichiometry of 10-15%. This makes it possible to obtain an excess of aluminum in the metal by 1.5-2%.

Add coke based on the reduction of iron oxide is 7 kg. As a result, 80 kg of oxides and plus 10.83 kg of a reducing agent are obtained. (3.83 kg of metallic aluminum and 7 kg of coke)

Admissible ingress of uncontrolled amount of oxides of calcium, magnesium and phosphorus 0.01%

Mix the components again.

The method of direct reduction of oxides by electroslag method is used.

Ceramic crucible with bottom bottom water-cooled graphite electrode. Calculate the volume of the crucible for 100 kg of the mixture. Upper non-consumable copper-steel electrode (RF patent 2661322) [4]. The “hard start” process is started on CaF ₂ slags weighing 0.5 kg. Upon receipt of the liquid state of the slag, they begin to fill in the mixture. The mixture is poured in portions of 0.5 kg - 1 kg. As soon as the reducing agent has worked (the exit of smoke from the crucible stops) add the next portion. The voltage at the electrode is 30 V, the melting current is 2000..2500 A. After the entire mixture has melted, it is poured into a metal chill mold. After cooling, take out the resulting ingot, separate the slag from the metal.

Example 2.

1. Take a spent catalyst of the following chemical composition - table 1.

2. Take the metallurgical slag of the Nizhniy Tagil Metallurgical Plant - table 2.

3. Mix the spent catalyst and metallurgical slag in a 3/1 ratio.

4. Aluminum is added at the rate of complete recovery of vanadium and giant - this is 3.83 kg.

Metallic aluminum is added above the stoichiometry by 10-15%. This makes it possible to obtain an excess of aluminum in the metal by 1.5-2%.

5. Coke is added at the rate of 100% iron reduction - this is 7 kg. This mixture is mixed well with aluminum. Pig iron is smelted according to example 1

The microstructure of the obtained white cast iron × 1000 with titanium carbide is shown in Fig. 2.

When comparing this structure with the structure in Fig. 1 [3], it can be seen that there are several orders of magnitude more TiC nuclei with the same Ti percentage (0.412%).

The process occurring during smelting proceeds according to the following scheme: centers of nuclei of a solid phase in the form of titanium carbide (TiC) are formed in the melt (melting temperature T _TiCn = 3260 ° C, and density, ρ _TiC = 4.93 g / cm ³ ) ^, on which vanadium carbide (VC) begins to precipitate (melting point T _VCn = 2770 ° C-2830 ° C, density ρ _VC = 5.77 g / cm ³ ), the next will be a transition zone, consisting mainly of vanadium carbide and molybdenum carbide (MoC) (T _MoCn = 2682 ° C, density ρ _MoC = 8.78 g / cm ³ ). Thus, the most refractory element (TiC) is the first to fall out of the liquid phase, together with vanadium carbide (VC). The density of these nuclei is still less than that of the melt. When the transition zone begins to form, where molybdenum carbide (MoC) is involved, the overall density of the nuclei increases significantly. As soon as the density of the nuclei of the mixture of titanium carbide, vanadium carbide and molybdenum carbide is equal to the density of the liquid melt, they will sink and will be evenly distributed throughout the volume of the melt. The temperature of the melt in the metal chill mold will decrease and, as soon as it reaches the crystallization temperature, iron crystals begin to grow on the centers of carbides.

This conclusion is confirmed by X-ray structural analysis of cast iron.

Spectrum 1.O-22.5, Al-12.83, Ca-2.49, Fe-1.6, Ce-62.24

Spectrum 2.Ti-20.49, V-47.63, Mo-12.4

Spectrum 3.Al-0.25, Si-0.94, Ti-46.67, V-14.32, Mn-0.22, Fe-13, Mo-5.43

Spectrum 4.Ti-33.64, V-33.73, Fe-1.15, Mo-13.25

Spectrum 5. Ti-4.18, V-60.78, Cr-0.99, Fe-2.16, Mo-14.3.

Spectrum 6.Al-2.02, Si-9.03, V-0.3, Cr-0.99, Mn-1.39, Fe-86.34, Mo-0.43

The microstructure of the alloy is shown in Fig 3. In the figure:

1 - the region of predominance of cerium and oxygen (spectrum 1),

2 - attached crystallization center (Ti-20.49, V-47.63, Mo-12.4) (spectrum 2)

3 - a nucleus of a cubic shape, characterized by spectrum 3, where the amount of Ti is 46.67%, which indicates that titanium carbide was the first to fall out.

4 - zone, characterized by spectrum 4, where the amount of gitan and vanadium is the same Ti-33.64, V-33.73,

5 - zone characterized by spectrum 5, where the amount of vanadium (60.78) and molybdenum (14.3) is decisive in relation to the density of the nucleus as a whole.

6 - main melt (spectrum 6)

As seen from Fig. 3, the crystallization center has the same structure as suggested on the basis of their thermodynamic properties. In fig. 3 it can be seen that the boundaries of the centers of crystallization are free of oxides, this was due to cerium, spectrum 1 Fig. 3 shows that all non-metallic inclusions are surrounded by cerium.

Figure 4, which shows the structure of the alloy after metal remelting, demonstrates the preservation of the uniform distribution of cubic titanium carbide after secondary remelting, which indicates the preservation of the physicochemical properties of cast iron (increased wear resistance, heat resistance and mechanical properties) given in Table 4, which also illustrates a comparison of cast iron with cubic titanium obtained by the proposed method with other types of cast iron.

In the table: σ _in - tensile strength N / mm ² ,

σ _0.2 - yield point N / mm ² ,

δ% - relative elongation.

Claims (2)

1. A method of producing wear-resistant cast iron with a uniform distribution of cubic titanium carbide, characterized by the fact that cast iron is obtained by direct reduction by electroslag melting, while the chemical composition of the initial oxides is: iron oxide 66.25%, vanadium oxide 5.5%, titanium oxide 1 , 63%, manganese oxide 2.25%, chromium oxide 0.2%, molybdenum oxide 1.86%, cerium oxide 1.5%, aluminum oxide 11.6% and silicon oxide 9.2%, impurities of calcium oxides, magnesium and phosphorus 0.01%, the initial oxides are mixed in the solid phase, metallic aluminum is added based on the stoichiometry of the reduction of titanium oxide and vanadium oxide, and additionally over stoichiometry, coke is added by 10-15% based on the reduction of iron oxide, the prepared mixture is fed into an electroslag crucible installation in portions of 0.01 part of the total weight, with an interval determined by the cessation of smoke emission, while the melting process is carried out at a voltage of 30 V and a current of 2000-2500 A. 2. The method according to claim 1, characterized in that a spent catalyst is used as the starting oxides having a composition (wt%): FeO - 75, Mo - 2, CeO ₂ - 3, Al ₂ O ₃ - 20 and metallurgical slag composition: V ₂ O ₅ - 20.51, MnO - 11, SiO ₂ - 8, CaO - 2, TiO ₂ - 8.5, MgO - 0.2, FeO - 49.29, Cr ₂ O ₃ - 0, 3, P - 0.2, which are mixed in the solid phase in a ratio of 3/1.

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