RU2255994C1 - Method of production of bimetallic ingot (versions) - Google Patents

Abstract

FIELD: special-purpose electro-metallurgy; production of bimetallic ingots by use of electro-slag technology.

SUBSTANCE: proposed method is adaptable for production of ingots having main layer made from carbon low-alloy or alloy steel and welded-on (cladding) layer made from corrosion-resistant steel; these ingots are subjected to rolling in bimetallic strips and sheets. Alloy steel used for making the main layer has the following composition, mass-%: carbon, 0.05-0.25; silicon, 0.01-0.50; manganese, 0.20-0.60; phosphorus, no more than 0.025; sulfur, no more than 0.020; chromium, 0.7-2.5; molybdenum, 0.2-1.0; iron and unavoidable admixtures, arsenic inclusive being the remainder. Melting the consumable electrodes at content of arsenic in steel lesser than 0.005% is performed at current of 9.0-10.0 kA and at content of arsenic no less than 0.005% melting is performed at current set in accordance with expression I≥9.5+100(As), where I is magnitude of current at each consumable electrode; kA, (As) is content of arsenic in steel, mass-%. Bimetallic ingot is then subjected to slow cooling to ensure rate of cooling on cladding layer surface not exceeding 50°C/h at temperature of 500°C. According to another version, main layer is made from low-alloy steel at the following composition, mass-%: silicon, 0.01-0.80; carbon, 0.05-0.25; manganese, 0.20-1.60; phosphorus, no more than 0.025; sulfur, no more than 0.020; iron and unavoidable admixture, arsenic inclusive being the remainder. Melting the consumable electrodes at content of arsenic in steel of main layer lesser than 0.005% is performed at magnitude of current of 8.0-10.0 kA and at content of arsenic no less than 0.005% melting is performed at magnitude of current determined in the following expression I≥9.0+100 (As), where I is magnitude of current at each consumable electrode, kA, (As) is content of arsenic in steel, mass-%.

EFFECT: enhanced strength and continuity of connection of layers; smooth thick, corrosion resistance and improved quality of cladding layer.

3 cl, 1 tbl, 1 ex

Description

The invention relates to metallurgy, and more specifically to the field of special electrometallurgy, namely to the production using electroslag technology of bimetallic ingots consisting of a base layer of carbon, low alloy or alloy steel and a deposited (cladding) layer of corrosion-resistant steel, intended for subsequent rolling on bimetallic stripes and sheets. Important requirements for such ingots are high strength and guaranteed continuity of the connection of the layers, uniformity of the thickness of the deposited layer and its high corrosion resistance with satisfactory surface quality, as well as certain geometric dimensions - relatively low values of the thickness of the ingot and high values of its width, which facilitates the subsequent rolling of ingots on sheets of a certain size, that is, improves manufacturability and leads to lower costs.

A known method for producing a bimetallic ingot with a cladding layer of corrosion-resistant steel, comprising placing in the mold with a gap from one of its walls a metal billet, which is one of the layers of the bimetallic ingot, installing a consumable electrode in this gap, guiding the slag bath in the gap and remelting it in consumable electrode with the formation of a deposited layer of a bimetallic ingot with a speed set depending on the size of the gap (H ₁ ) and the thickness of the workpiece (H ₂ ) mathematically the expression V _f = 3.6 (1-0.3H ₁ / H ₂ ) ± 0.3, kg / min, with the electrical resistance of the slag bath, determined from the mathematical dependence R = 2.5B ₁ B ₂ ± 0.2, where R is the electrical resistance of the slag bath, mOhm; B ₁ - the width of the electrode, mm; In ₂ - the width of the workpiece, mm (RF Patent No. 2087561, IPC С 22 В 9/18, publ. 08/20/1997). The method provides uniformity of thickness and chemical composition of the deposited layer with satisfactory surface quality during surfacing of workpieces with a thickness of more than 350 mm and a width of less than 1000 mm. However, its use to obtain bimetallic billets with a thickness of less than 350 mm and a width of more than 1000 mm, more technologically advanced in the production of bimetallic sheets, does not provide the required quality of the connection of the layers: there are delays or zones with low adhesion layers. Subsequent rolling of such ingots onto sheets may result in the formation of a significant area of delamination of the clad layer.

The closest analogue of the claimed invention is a method for producing a bimetallic ingot, comprising placing a metal billet, which is the main layer of a bimetallic ingot, with a gap from the mold wall, installing a sacrificial electrode made of corrosion-resistant steel in this gap, guiding the slag bath and remelting the sacrificial electrode with forming the deposited layer with that in the blank the basic layer thickness of 150-300 mm (H _o) and a width of 1000-1600 mm form the alloy layer, the thickness koto th is 5-30% of the total thickness of the ingot at a rate assignable in accordance with the relation

V _n = (1150-2000D) ± 200, kg / h,

where V _n - the speed of formation of the deposited layer, kg / h,

D is the thickness of the deposited layer,% of the total thickness of the ingot,

when the value of the electrical resistance of the slag bath in the range of 3.5-5.0 mOhm, under the slag containing, wt.%

20-30 Cao

10-30 SiO ₂

2-15 Al ₂ O ₃

and 2-5 MgO

the rest is CaF ₂ and impurities, and the basicity of the slag calculated by the equation: O = (1.5 <(0.018CaO + 0.015MgO + 0.006CaF ₂ ) / (0.017SiO ₂ + 0.005Al ₂ O ₃ ), corresponds to the condition: 1, 5 <O <3.0.

(RF patent No. 2193071, IPC ⁷ C 22 V 9/20, publ. November 20, 2002, description - prototype).

The method is aimed at increasing the corrosion resistance of the deposited layer of bimetallic ingots and their manufacturability when rolling into sheets, as well as reducing the cost of converting ingots into sheet metal while maintaining the strength and continuity of the connection of the layers, uniform thickness of the layers and satisfactory surface quality of the deposited layer. However, in the presence of arsenic in the steel of the base layer in an amount of 0.005% or more, a sharp decrease in the quality of the connection of the layers is possible. In addition, when using low alloy and alloy steels as the main layer, which is required to increase the strength characteristics of bimetallic rolled products at normal and elevated temperatures, an increase in the heat capacity and heat of fusion of the steel of the main layer can lead to insufficient heat during surfacing to ensure high-quality bonding of the layers.

The problem solved by this invention is to provide high quality bimetallic ingots, including those intended for subsequent rolling onto sheets: high strength and guaranteed continuity of the connection of the layers, uniform thickness, high corrosion resistance, strength characteristics, including at elevated temperatures , and satisfactory surface quality of the clad layer.

The technical result of this invention is to increase the strength and continuity of the connection layers, the strength characteristics of bimetallic steel at normal and elevated temperatures while maintaining manufacturability, uniform thickness, corrosion resistance and satisfactory surface quality of the clad layer.

The technical result is achieved by the fact that in the known method for producing a bimetallic ingot with a cladding layer of corrosion-resistant steel, including the placement of a steel billet, which is the main layer of the bimetallic ingot, with a gap from the mold wall, installation of consumable electrodes made of corrosion-resistant steel in this gap, guidance of the slag bath and remelting of the consumable electrodes in it with the formation of a cladding layer, the thickness of which is 5-30% of the total thickness of the bimetallic ingot with Barrier-slag bath resistivity in the range of 3.5-5.0 milliohms, then cooling the ingot, according to the invention the main layer is made of an alloy steel containing, wt.%:

carbon - 0.05-0.25

silicon - 0.01-0.50

Manganese - 0.20-0.60

phosphorus - not more than 0.025

sulfur - not more than 0,020

chrome - 0.7-2.5

molybdenum - 0.2-1.0

iron and unavoidable impurities, including arsenic - the rest, remelting of consumable electrodes when the arsenic content in the steel of the base layer is less than 0.005% is carried out at a current value of 9.0-10.0 kA, and with an arsenic content of at least 0.005% - at a current value assigned in accordance with the expression

where I is the magnitude of the current at each consumable electrode, kA,

(As) - arsenic content in steel, wt.%,

and the cooling of the bimetallic ingot is carried out slowly to ensure the cooling rate on the surface of the cladding layer at temperatures below 500 ° C not more than 50 ° C per hour;

as an option, the main layer is made of low alloy steel containing, wt.%:

carbon - 0.05-0.25

silicon - 0.01-0.80

Manganese - 0.20-1.60

phosphorus - not more than 0.025

sulfur - not more than 0,020

iron and inevitable impurities, including arsenic - the rest,

remelting of consumable electrodes when the arsenic content in the steel of the base layer is less than 0.005% is carried out at a current value of 8.0-10.0 kA, and when the arsenic content is not less than 0.005%, at a current value assigned in accordance with the expression

where I is the magnitude of the current at each consumable electrode, kA,

(As) - arsenic content in steel, wt.%,

The essence of the proposal is as follows.

The specific chemical composition of the steel of the base layer plays a decisive role in ensuring the mechanical properties of two-layer steel and its products - strength, including at elevated temperatures, toughness, and weldability.

Alloy steel containing 0.7-2.5% chromium and 0.2-1.0% molybdenum has high strength at elevated temperatures up to 500 ° C, which determines the possibility of high-temperature operation of products from two-layer steel with the corresponding clad layer. The content of carbon, silicon and manganese in alloy steel within the proposed range allows to obtain the required level of strength without reducing weldability.

Low alloy steel is designed to operate at lower temperatures than alloy steel. The required set of mechanical characteristics of two-layer sheets with a base layer of low alloy steel is provided by the content of the main alloying elements - carbon, silicon and manganese within the proposed range.

With a lower content of the main alloying elements, the necessary level of strength may not be provided, with a higher content of them, a decrease in viscosity and weldability is possible.

Limiting the content of phosphorus and sulfur in both alloyed and low alloy steel is also associated with the need to provide a certain level of viscosity and weldability.

Ensuring uniform thickness, chemical composition and high strength and continuity of the connection of the layers in the bimetallic ingot is achieved by providing a certain and uniform penetration depth, mainly from 3 to 10 mm. An important parameter of electroslag remelting, which determines the penetration depth of the billet of the base layer and its uniformity, is the electrical resistance of the slag bath, which should be within the limits defined by the claims of 3.5-5.0 mOhm. In addition, the input power and, consequently, the amount of heat that is supplied to melt the corrosion-resistant steel and to partially melt the steel of the base layer determines the value of the current on the electrodes.

The minimum current value when using alloy steel as the main layer should be higher than when using low alloy steel, respectively, 9.0 and 8.0 kA (with arsenic content less than 0.005%), which is associated with higher values of heat capacity and heat of fusion, and , therefore, with the need for greater heat input during remelting.

With an increase in the arsenic content in the steel of the base layer with a constant mode of remelting, a decrease in the quality of the connection of the layers is possible for the following reasons. Arsenic, being a surface-active impurity, can accumulate on the interface between the layers, impairing their adhesion. In addition, during the transition of arsenic to slag in a certain amount, it may accumulate on the interface between the slag and metal baths, which changes the properties of the slag and the heat distribution in the slag bath, which becomes uneven. Moreover, in the coldest areas, the penetration of the main layer is not provided and high-quality connection of the layers does not occur. Therefore, when the arsenic content in the steel of the base layer is from 0.005% or more, adjustment of the remelting regimes is necessary, in particular, an increase in the current value on the electrodes in accordance with equations (1) and (2) for alloyed and low alloy steels, respectively. This allows you to ensure the receipt of the required amount of heat during remelting, its uniform distribution, and therefore, high-quality connection of the layers.

Slow cooling of bimetallic ingots is necessary in order to avoid significant temperature differences over the cross section of the ingot, especially in the temperature range below 500 ° C, when the ductility of the components of the bimetallic ingot and especially the boundary zone with a variable chemical composition decreases. With rapid cooling, increased stresses appear in the boundary zone, which can lead to cracking and, consequently, reduce the quality of the connection of the layers.

An example of a specific implementation of the method

To obtain a bimetallic ingot, the surfacing of the blanks of the main layer of alloy steel and low alloy steel with a thickness of 200 mm and a width of 1280 mm with a given thickness of the deposited layer of 10-15% of the total thickness of the workpiece was carried out on inclined type installations specially designed for electroslag surfacing.

ANF-29 grade slag was poured into the cavity between the surface of the preform of the base layer and the mold and electroslag remelting of consumable electrodes made of 08Kh18N10B steel in the form of separate plates 30–50 mm thick covering at least 80% of the preform width was formed in the resulting slag bath. (cladding) layer with different values of the current at the electrodes and with the values of the electrical resistance of the slag bath 3.9-4.3 mOhm. After surfacing and cooling until the surface of the deposited layer reaches a temperature of 500 ° C, the bimetallic ingots were placed in a thermostat, where they were cooled to room temperature with a cooling rate of the surface of the deposited layer of about 30 ° C per hour (options 1-6). One of the ingots was cooled in air (option 7). Moreover, the cooling rate of the surface of the deposited layer in the temperature range 500-300 ° C was about 90 ° C per hour.

After cooling the bimetallic ingots, they were hot rolled in a 2800 mill to 18 mm thick sheets. After normalization, the bimetallic sheets passed certification in accordance with GOST 10885 with the determination of mechanical characteristics, resistance to inter-crystalline corrosion of MKK, continuity and strength of the connection of layers, etc.

The chemical composition of the steel of the main layer, the current values during electroslag remelting of consumable electrodes and the formation of a deposited layer, the cooling rate of the surface of the deposited layer in the temperature range 500-300 ° C are given in table. 1. The quality of the connection of the layers in bimetallic sheets according to the results of ultrasonic testing (the fraction of the area of the sheets having delamination,%), shear resistance σ _cf (adhesion of the layers during shear tests of the clad layer in accordance with GOST 10885), as well as the strength characteristics of the steel of the base layer at room temperature (yield strength and tensile strength) and at a temperature of 500 ° C (yield strength), determined in accordance with GOST 5520, are also given in table. 1. All other technical characteristics of the obtained sheets, including resistance to MKK, uniformity of layer thickness, surface quality of the deposited layer and others, met the requirements of GOST 10885.

From the table. 1 it follows that for options 1, 3, corresponding to claim 1 of the claims, high continuity and bond strength of the layers in bimetallic sheets, as well as high strength characteristics of the base layer, including at elevated temperatures, are ensured. Option 2 does not comply with claim 1, since in accordance with equation (1) when the arsenic content in the steel of the base layer is 0.015%, the current value on the electrodes during electroslag surfacing must be at least 11 kA, while in this case it was 9.5 kA. This led to the low quality of the connection of the layers - a significant area of the delaminations, reduced compared with other options, the value of the shear resistance is 290 N / mm ² .

For options 4 and 6, corresponding to paragraph 2 of the claims, also obtained a high quality connection of the layers, as well as high values of strength characteristics, although the yield strength at 500 ° C for these options is lower than when using alloy steel. Option 5 does not comply with claim 2, since in accordance with equation (2) when the arsenic content in the steel of the base layer is 0.010%, the current value on the electrodes during electroslag surfacing should be at least 10 kA, while in this case it amounted to 9.0 kA. This led to the appearance of delaminations and to some reduction in shear resistance - up to 320 N / mm ² .

Option 7 does not comply with the claims because of the increased rate of cooling of the surface of the deposited layer in the temperature range 500-300 ° C - 90 ° C per hour instead of 30 ° C per hour. This also led to a decrease in the quality of the connection of the layers — the appearance of delaminations and to some reduction in shear resistance — to 310 N / mm.

Thus, the use of this proposal significantly improves the quality of the connection layers, strength characteristics, including at elevated temperatures while maintaining manufacturability, uniform thickness, corrosion resistance and satisfactory surface quality of the deposited layer.

Claims (2)

1. A method of producing a bimetallic ingot with a cladding layer of corrosion-resistant steel, comprising placing a steel billet, which is the main layer of a bimetallic ingot, with a gap from the mold wall, installing consumable electrodes from corrosion-resistant steel in this gap, pointing the slag bath and remelting of consumable electrodes with the formation of a cladding layer, the thickness of which is 5-30% of the total thickness of the bimetallic ingot, with values of the electrical resistance of the slag bath in the range of 3 , 5-5.0 mOhm, subsequent cooling of the ingot, characterized in that the main layer is made of alloy steel, containing, wt.%: Carbon 0.05-0.25 Silicon 0.01-0.50 Manganese 0.20-0.60 Phosphorus Not more than 0,025 Sulfur Not more than 0,020 Chrome 0.7-2.5 Molybdenum 0.2-1.0 Iron and inevitable impurities, including arsenic remelting of consumable electrodes when the arsenic content in the steel of the base layer is less than 0.005% is carried out at a current value of 9.0-10.0 kA, and when the arsenic content is not less than 0.005%, at a current value assigned in accordance with the expression I≥9.5 + 100 (As), where I is the magnitude of the current at each consumable electrode, kA; (As) - arsenic content in steel, wt.%, and the cooling of the bimetallic ingot is carried out slowly to ensure the cooling rate on the surface of the cladding layer at temperatures below 500 ° C not more than 50 ° C per hour. 2. A method of obtaining a bimetallic ingot with a cladding layer of corrosion-resistant steel, comprising placing a steel billet, which is the main layer of a bimetallic ingot, with a gap from the mold wall, installing consumable electrodes from corrosion-resistant steel in this gap, guiding the slag bath and remelting consumable electrodes with the formation of a clad layer, the thickness of which is 5-30% of the total thickness of the bimetallic ingot, with the values of the electrical resistance of the slag bath in the range of 3.5-5, 0 mOhm, subsequent cooling of the ingot, characterized in that the main layer is made of low alloy steel containing, wt.%: Carbon 0.05-0.25 Silicon 0.01-0.80 Manganese 0.20-1.60 Phosphorus Not more than 0,025 Sulfur Not more than 0,020 Iron and inevitable impurities, including arsenic remelting of consumable electrodes when the arsenic content in the steel of the base layer is less than 0.005% is carried out at a current value of 8.0-10.0 kA, and when the arsenic content is not less than 0.005%, at a current value assigned in accordance with the expression I≥9.0 + 100 (As), where I is the magnitude of the current at each consumable electrode, kA; (As) - arsenic content in steel, wt.%, and the cooling of the bimetallic ingot is carried out slowly to ensure the cooling rate on the surface of the cladding layer at temperatures below 500 ° C not more than 50 ° C per hour.