RU2247791C1 - Low-carbon high-purity ferrotitanium - Google Patents

Abstract

FIELD: steelmaking and foundry industry, addition alloy manufacturing, in particular ferrotinatium.

SUBSTANCE: invention relates to low-carbon high-purity ferrotitanium, containing (mass %): titanium 20.0-75.0; aluminum 0.05-0.30; silicon 0.10-0.30; manganese 0.10-0.30; carbon 0.005-0.07; molybdenum 0.02-0.10; chromium 0.02-0.10; vanadium 0.02-0.10; copper 0.02-0.10; nickel 0.02-0.10; zirconium 0.02-0.10; nitrogen 0.005-0.04; calcium 0.005-0.05; oxygen 0.01-0.15; and balance: iron and impurities, such as lead <=0.001; antimony <=0.002; bismuth <=0.002; tin <=0.002; arsenic <=0.001; zinc <=0.002; sulfur <=0.015, and phosphorus <=0.015, wherein total content of lead, tin, antimony, arsenic, bismuth, and zinc is not more than 0.008 mass %. Alloy of present invention is useful in manufacturing of welding and fluxing materials to obtain weld seam of refractory steel and alloy with high long-term strength at >600⁰C.

EFFECT: high-purity ferrotitanium for weld seam with high long-term strength, corrosion resistance and autocrack resistance during welding and rolling.

3 cl, 3 tbl, 1 ex

Description

The invention relates to the field of production of ligatures, namely ferrotitanium for alloying high-quality steels and alloys of high purity, the production of welding materials and fluxes, and can be used in the steel and foundry industries.

The known compositions of ferrotitanium used for these purposes in the relevant industries (AS No. 1705386, grade FTi30, FTi70S05 in accordance with GOST 4761-91, table No. 1a, page 3; brand FeTi70 according to international ISO No. 5445-80, reference “Ferroalloys” Mizin V.G., Chirkov N.A. et al., Moscow, Metallurgy, 1992, p. 406, table 1; brands of ferrotitanium FeTi40A16, FeTi70 according to the Swedish standard SS146662-79, p. 50, “Alloying alloys and steels with titanium” N.P. Lyakishev, Yu.L. Pliner, S.I. Lappo, Moscow, “Metallurgy”, 1985; brands of ferrotitanium FeTi30, FeTi70VB no. To German standard DIN 17566, table No. 17, p. 50 in the same place).

The closest to the claimed composition of ferrotitanium for the purpose and composition of the components and taken as a prototype is a ferroalloy grade FTi70, “Ferroalloys” directory, Mizin V.G., Chirkov N.A., Ignatiev BC, Akhmanaev S.I., Povolotsky V. D., Moscow, “Metallurgy”, 1992, Table 5.121, p. 325), containing in wt.%:

Titanium 65-72

Aluminum 0.85-5.0

Silicon 0.10-0.50

Carbon 0.09-0.15

Molybdenum 0.19-2.12

Vanadium 0.12-0.26

Copper 0.03-0.40

Zirconium 0.03-1.30

Iron and impurities - the rest

The main disadvantage of the known composition of ferrotitanium is that it does not provide the base metal and weld metal of heat-resistant steels and alloys smelted with its use, high long-term strength at temperatures above 600 ° C, corrosion resistance, as well as resistance to hot cracks during welding due to the high content of sulfur, phosphorus and non-ferrous metals of copper, aluminum and tin, as well as the presence of an unregulated content of impurities with a low melting point of lead, zinc, tin, antimony, bismuth and arsenic.

The technical result of the invention is the creation of a composition of high purity low-carbon ferrotitanium, which provides the base metal and metal welds of heat-resistant steels and alloys of higher long-term strength at temperatures above 600 ° C, corrosion resistance, and resistance to hot cracks during welding.

The technical result is achieved due to the fact that the composition of ferrotitanium, containing titanium, iron, carbon aluminum, silicon, molybdenum, vanadium, zirconium and copper, additionally contains calcium, nitrogen, manganese, nickel, chromium and oxygen with the following components, wt. %:

Titanium 20.0-75.0

Aluminum 0.05-0.30

Silicon 0.10-0.30

Manganese 0.10-0.30

Carbon 0.005-0.07

Molybdenum 0.02-0.10

Chrome 0.02-0.10

Vanadium 0.02-0.10

Copper 0.02-0.10

Nickel 0.02-0.10

Zirconium 0.02-0.10

Nitrogen 0.005-0.04

Calcium 0.005-0.05

Oxygen 0.01-0.15

Iron and impurities - the rest,

while in the quality of impurities it contains sulfur, phosphorus, lead, tin, arsenic, antimony, bismuth and zinc at their content, wt.%:

Sulfur ≤0.015

Phosphorus ≤0.015

Lead ≤0.001

Tin ≤0.002

Arsenic ≤0.001

Antimony ≤0.002

Bismuth ≤0.002

Zinc ≤0.002,

and the total content of impurities of lead, tin, arsenic, antimony, bismuth and zinc should be less than or equal to 0.008% (Σ Pb + Zn + Sn + Sb + As + Bi≤0.008%).

Titanium in the inventive composition of ferrotitanium is contained in the range from 20 to 75%.

Ferrotitanium with a titanium content of less than 20% is excessively depleted in the main alloying element and contains an increased amount of aluminum and especially silicon, which leads to an increase in the content of non-metallic inclusions during alloying of steels and alloys, the production of welding ceramic fluxes, worsening their properties.

When the titanium content is more than 75%, the melting point of ferrotitanium sharply increases, which leads to a significant increase in energy consumption during its smelting and saturation with gases (O, N, H), the level of which can reach 1% O, 0.6-0.8% N, 30-50 cm ³ N in 100 g of alloy. In addition, when the titanium content is more than 75%, its assimilation sharply decreases when alloying it with steels.

Carbon in the proposed composition of ferrotitanium is contained at a level of from 0.005 to 0.07%.

When the carbon content in ferrotitanium is more than 0.07%, alloying of corrosion-resistant austenitic steels and alloys decreases their resistance to intergranular corrosion and weldability.

When the carbon content in ferrotitanium is less than 0.005%, the strength properties and heat resistance of steels and alloys alloyed by it sharply decrease due to the reduction of carbides.

Oxygen in the proposed composition of ferrotitanium is contained in the range from 0.01-0.15%.

When the content of oxygen in ferrotitanium is more than 0.15% in alloyed steels and alloys, an increased amount of oxide inclusions is formed, which reduces the strength properties at elevated temperatures. In addition, oxygen in an amount of more than 0.15% together with nitrogen during welding contributes to the formation of porosity in the welds.

A decrease in oxygen content of less than 0.01% increases the cost of its production and does not give a noticeable technical effect.

Nitrogen forms non-metallic inclusions in ferrotitanium - nitrides, which, when alloyed, transform steel and alloys into metal, impairing its quality.

The nitrogen content in the ferrotitanium of the proposed composition should be in the range of 0.005-0.04%, which allows to obtain stable properties of the metal alloyed steels and welding materials.

When the nitrogen content is more than 0.04% in ferrotitanium, the ductility and corrosion resistance of austenitic corrosion-resistant steels and alloys decrease, and the porosity in the welds during their welding also increases.

A nitrogen content of less than 0.005% leads to an increase in energy costs in the production of ferrotitanium and does not give a noticeable technical effect.

Sulfur and phosphorus are harmful impurities in the proposed composition of ferrotitanium and should not be more than 0.015%.

With an increase in sulfur content in ferrotitanium of more than 0.015% in alloyed steels and alloys, resistance to hot cracks sharply decreases during welding and hot plastic processing.

When the phosphorus content in ferrotitanium is more than 0.015%, the ductility of alloyed steels and alloys decreases and its cold brittleness increases.

In the proposed composition of ferrotitanium, the aluminum content is regulated in the range of 0.05-0.3% and manganese 0.1-0.3%, which significantly reduces the number of non-metallic inclusions in alloyed alloys and welds and leads to an increase in their mechanical properties and ductility.

In the proposed composition of ferrotitanium, the content of refractory metals of molybdenum, vanadium, chromium is regulated within the range of 0.02-0.1% of each separately, which expands the possibilities of using ferrotitanium as a ligature for alloying heat-resistant steels and alloys with a low content of molybdenum and vanadium. In addition, a chromium content of more than 0.1% leads to the formation of an increased amount of non-metallic inclusions of the type FeO · Cr ₂ O ₃ .

In the claimed composition of ferrotitanium, copper, nickel and zirconium are contained in the range of 0.02-0.10%, because at a higher content in alloy steels and alloys, fusible eutectics are formed, which cause crystallization cracks. In addition, copper and zirconium are the source of the formation of nonmetallic inclusions of the Cu ₂ O type, as well as zirconium nitrides and carbonitrides.

A sharp decrease in the content of molybdenum and copper allows the use of this ferrotitanium in the smelting of low-activated steels, since it is these elements that increase the induced radioactivity.

The introduction of calcium in ferrotitanium in an amount of 0.005-0.05% contributes to a decrease in the content of gases in the ferroalloy, primarily oxygen and non-metallic inclusions of the type SiO ₂ and Al ₂ O ₃ due to the high degree of chemical affinity of calcium to oxygen. In addition, calcium actively interacts with impurities and purifies steel of sulfur and phosphorus, forming intermetallic compounds like Ca ₂ S ₃ .

The elements responsible for the formation of hot cracks in alloy steels and alloys during hot deformation and welding are colored impurities with a low melting point (lead, tin, antimony, arsenic, bismuth and zinc), which reduce the weldability, hot ductility and heat resistance of steels and alloys. Calcium binds these low-melting non-ferrous metals to form Ca ₂ Pb type intermetallic compounds.

The introduction of calcium of more than 0.05% makes it difficult to dissolve it in the molten metal, as a result of which the number of brittle non-metallic inclusions of large size increases, the hardness of which exceeds 780 HB.

The introduction of calcium of less than 0.005% is not enough to reduce the oxygen content, non-metallic inclusions and low-melting non-ferrous non-ferrous metals in ferrotitanium.

The content of lead and arsenic in the claimed composition of ferrotitanium should be no more than 0.001%. When the content of lead and arsenic in ferrotitanium is more than 0.001% each, the ductility of alloyed heat-resistant steels and alloys during their hot deformation sharply deteriorates due to the formation of low-melting eutectic.

The content in the proposed composition of ferrotitanium bismuth, antimony, tin and zinc should be no more than 0.002%. When the content of these elements is more than 0.002%, embrittlement of alloyed alloys takes place at thermal exposures and a decrease in crack resistance of welds.

Moreover, the total content of low-melting colored impurities of lead, zinc, tin, antimony, arsenic and bismuth should not be less than or equal to 0.008% (Σ Рb + Zn + Sn + Sb + As + Bi≤0.008%).

When their total content in ferrotitanium exceeds 0.008%, hot ductility, weldability, and heat resistance of alloyed steels and alloys sharply decrease.

An example of a specific implementation: A set of laboratory and pilot industrial works was carried out at the Central Research Institute of CM “Prometey” for the smelting, forging, rolling and welding of steel metal and alloy grades 08Х18Н10Т, Х15Н35ВТ, ХН78Т alloyed with the proposed and well-known composition of ferrotitanium, and their properties were tested.

The experimental compositions of the proposed and known compositions of ferrotitanium were smelted in an open induction furnace IST-016 with a volume of 160 kg.

Ferrotitanium was obtained by the electric furnace method by remelting pure charge materials (Armco iron with technical titanium of grade VT 1-0) in an induction furnace without flux, since a protective film of titanium oxides was formed during melting. In order to reduce the loss of titanium, ferrotitanium was added to the steel bath in the final melting period.

Ferrotitanium was poured into cast iron molds at 1250-1350 ° C. The resulting ingots were cooled with water for 10-15 minutes to prepare for crushing. The burning of titanium did not exceed 5%. Rod samples for chemical analysis of ferrotitanium were taken from each heat, then they were crushed and crushed in a vibration eraser, and a complete chemical analysis of each sample was performed.

One of their quality characteristics of ferrotitanium is the appearance of its pieces (GOST 4761-91).

Pieces of ferrotitanium of known composition had a blue oxidized surface on the surface and in the fracture, contaminated with oxide inclusions, which indicates the low quality of the known brand of ferrotitanium.

Pieces of ferrotitanium of the proposed composition had a homogeneous structure. The surface was silver-yellow in color with no obvious signs of oxidation, which is one of the indicators of higher quality of the proposed composition of ferrotitanium compared to the known one.

Sampling for chemical and sieve analysis is carried out in accordance with the requirements of ISO 4552-1, ISO 4551.

The particle size range of ferrotitanium corresponded to particle size class 4 according to GOST 4761-91 and ranged from 10 to 50 mm.

A point sample for the chemical analysis of ferrotitanium was prepared as a laboratory one (GOST 26201-84). The size of the maximum particles in the sample was 0.5 mm. The weight of the laboratory sample was 0.2 kg.

Chemical analysis of the proposed and known compositions of ferrotitanium was carried out according to ISO 7692. Their chemical composition is presented in table 1.

The results of the comparison of chemical compositions for interstitial impurities (P, S) and non-ferrous metal impurities (Pb, Zn, Sn, Sb, As, Bi) show that the proposed composition of ferrotitanium has a higher quality and significantly lower content of harmful impurities in comparison with the known composition.

The obtained ferrotitanium of the proposed and known compositions in accordance with table 1 was used for smelting 4 ingots of each composition of steel and alloy grades 08X18H10T, X15H35BT, XH78T weighing 16 kg. The chemical composition of the smelted metal corresponded to GOST 5632-72. From each ingot of smelted metal, 16 mm diameter rods, a 20 mm square profile and 400 × 100 × 10 mm plates were forged and rolled. Samples were made from the obtained blanks and tested the properties of the metal of smelted steel and alloys and their welded joints.

Samples of 20 × 80 × 3 mm in size with a weld in the middle part were tested for resistance to intergranular corrosion according to the method GOST 6032-84, method AM-24 and autoclave tests for corrosion cracking (CR) in a boiling 42% MgCl ₂ solution at a temperature 155 ° C, tensile stresses σ _p = 1.2σ _0.2 . The test results are shown in table 2.

On the AIMA-5 machine, tests were carried out for long-term strength on the basis of 10 ⁴ and 10 ⁵ hours of 5-fold samples of steel grade 08X18H10T and alloy grades X15H35BT and XH78T. The test data are presented in table 2.

At the LTP-6 installation, plates 40 × 60 × 3 mm in size were subjected to a test for technological strength by the method of MVTU im. N.E.Bauman by butt welding with simultaneous stretching of the weld zone at different speeds until the first hot cracks appear in the weld zone, thereby fixing the critical strain rate V _cr at which the first hot cracks appear. The test results for technological strength during welding are presented in table 2.

The welding and technological properties of the flux were determined by welding with wire of the Sv-10GNA grade of samples of size 400X100X10 mm using an ADS 1000-2 welding machine under the flux of grade 48AF-51 made with the addition of ferrotitanium of known and proposed compositions. The test results of the properties of the weld metal are shown in table 3.

Comparative data of mechanical, technological and corrosion tests showed the advantage of materials manufactured using the proposed composition of ferrotitanium.

The expected technical and economic effect of the use of the proposed composition of high-purity low-carbon ferrotitanium for alloying steels and alloys and the production of high-purity welding materials will be expressed in an increase in the service life of structures and parts used in various industries, including nuclear reactor vessels, parts of in-reactor equipment, and etc. in nuclear and power engineering, responsible main pipelines in the oil and gas industry and shipbuilding by improving the service characteristics of steels and alloys: corrosion resistance, heat resistance, long-term strength and ductility, as well as improving the purity and quality of welding and surfacing materials, electrode coatings and welding fluxing agents.

Claims (3)

1. Highly pure low-carbon ferrotitanium containing titanium, aluminum, silicon, carbon, molybdenum, vanadium, zirconium, copper, iron and impurities, characterized in that it additionally contains manganese, nickel, chromium, calcium, nitrogen and oxygen, in the following ratio components, wt.%: Titanium 20.0-75.0 Aluminum 0.05-0.30 Silicon 0.10-0.30 Manganese 0.10-0.30 Carbon 0.005-0.07 Molybdenum 0.02-0.10 Chrome 0.02-0.10 Vanadium 0.02-0.10 Copper 0.02-0.10 Nickel 0.02-0.10 Zirconium 0.02-0.10 Nitrogen 0.005-0.04 Calcium 0.005-0.05 Oxygen 0.01-0.15 Iron and impurities Else 2. Particularly pure low-carbon ferrotitanium according to claim 1, characterized in that it contains lead, tin, arsenic, antimony, bismuth, zinc, sulfur and phosphorus as impurities, with their content, wt.%: Lead ≤0.001, antimony ≤ 0.002, bismuth ≤0.002, tin ≤0.002, arsenic ≤0.001, zinc ≤0.002, sulfur ≤0.015 and phosphorus ≤0.015. 3. Particularly pure low-carbon ferrotitanium according to claim 2, characterized in that the total content of impurities - lead, tin, antimony, arsenic, bismuth and zinc should be less than or equal to 0.008 wt.% (ΣРb + Sn + Sb + As + Bi + Zn <0.008).