A smelting process for a low-carbon high-strength alloy steel base blank

Abstract

The present application relates to the technical field of steelmaking, and particularly relates to a smelting process of low-carbon high-strength alloy steel base material. The smelting process mainly comprises the following steps: smelting by using a medium-frequency electric furnace, optimizing selection of furnace lining material, controlling temperature and chemical composition of molten steel in the smelting process, ensuring uniform dissolution of alloy elements, and covering the following processes in the process flow: phased addition of refining agent, multiple deoxidation treatment of molten steel, preheating and one-time addition of alloy elements, and introduction of micro-alloy elements such as chromium iron nitride at a suitable temperature. The smelting process can prepare the low-carbon high-strength alloy steel base material with excellent process weldability and use weldability. The base material does not need preheating and tempering treatment when making composite layer surfacing. The smelting process is simple and efficient, the steel material has excellent performance, and has important industrial application prospect.

Description

[Technical Field]

[0001] This invention relates to the field of steelmaking technology, specifically to a smelting process for low-carbon, high-strength alloy steel matrix billets. [Background Technology]

[0002] Modern steel production technology primarily involves rolling, and the billets for rolled steel (such as slabs and billets) are produced using continuous casting (also known as continuous casting). The continuous casting rolls used in slab continuous casting processes serve the stage from when the steel billet is slowly pulled out of the crystallizer until the billet cross-section is completely crystallized and solidified, then cooled to a certain temperature for cutting or before entering continuous rolling (also known as continuous rolling). Slab continuous casting rolls, however, are used in slab continuous casting.

[0003] Industry insiders know that the continuous casting rolls used in the slab casting process operate under harsh conditions. The surface of the slab immediately after exiting the crystallizer is a thin, newly solidified shell, while the interior remains molten steel. The surface temperature of this shell is approximately 1300℃. This quasi-slab, with a thin shell on the outside and molten steel inside, is supported by the surface of the continuous casting roll sleeve after being pulled from the crystallizer. The rotation of the continuous casting roll moves the slab, and during this movement, it is continuously cooled by the spray of cooling water until the entire cross-section solidifies, before entering the shearing or rolling process. As equipment for slab continuous casting, the slab continuous casting roll surface is subjected to heat conduction and radiation from the high-temperature slab (1300℃~1100℃), the extrusion of the steel billet (sometimes artificially pressurized to make the interior of the billet denser), and the spray of cooling water, resulting in alternating compressive stress (1.5~5 times / min) and alternating thermal stress on the roll surface. When two alternating stresses exceed the yield limit of the material, fatigue occurs on the roller surface, resulting in fatigue cracks, and in severe cases, cracks, delamination, and peeling.

[0004] To improve the service life of the roll surface, a composite technology is typically used. A 1-2mm transition layer is deposited onto the base material of the roll sleeve using submerged arc welding, followed by a 4-5mm alloy working layer that is resistant to high temperatures, oxidation, and thermal fatigue. During continuous casting roll service, fatigue cracks appearing in the composite layer will affect the surface quality of the slab. Generally, without considering other factors affecting slab quality, the presence of a certain number of fatigue cracks on the roll surface signifies the end of the roll's service life. Therefore, the fatigue resistance of the composite layer on the roll sleeve surface is a key factor determining the roll's lifespan.

[0005] The lifespan of the roller sleeve composite layer depends on the manufacturing process technology of the roller sleeve. Current roller sleeve production technology involves using special welding wire (usually flux-cored wire) to deposit a certain thickness of alloy layer onto the surface of a steel (carbon steel, alloy steel) base material. Therefore, it can be seen that the main factors affecting the lifespan of the roller sleeve composite layer are: the chemical composition of the roller sleeve base material, the smelting process technology, and the roller sleeve manufacturing process technology.

[0006] There's a saying in the industry: "Steelmaking is slag making." This saying highlights the relationship between slag and steel quality during the steelmaking process. Therefore, besides the critical composition of the billet, the smelting process of the billet also significantly impacts the performance of the processed low-carbon high-strength alloy steel matrix billet. The low-carbon high-strength alloy steel matrix billet developed by our company differs from commonly used billets, and traditional processes are unsuitable for it. Therefore, there is an urgent need to develop a new smelting process suitable for low-carbon high-strength alloy steel matrix billets. [Summary of the Invention]

[0007] The purpose of this invention is to address the problems in the prior art by providing a smelting process for low-carbon high-strength alloy steel matrix billets. The aim is to develop a suitable smelting process for low-carbon high-strength alloy steel billets. The low-carbon high-strength alloy steel matrix billets prepared by this process have excellent weldability and high strength and strong tempering resistance in the quenched and tempered state.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A smelting process for a low-carbon, high-strength alloy steel matrix billet, comprising the following steps:

[0010] (a) Select a medium-frequency electric furnace as the base billet for melting. The electric furnace uses a neutral to slightly alkaline furnace lining material. Start the electric furnace and add furnace charge after the furnace starts normally.

[0011] (b) 5-8 minutes before the furnace charge is melted and cleared, put the alkaline material refining agent preheated to not less than 250°C into the furnace for the first time. The amount of the refining agent put in for the first time shall not exceed one-third of the total amount used.

[0012] (c) Once the furnace charge is completely melted, stir the slag and add no more than one-third of the total amount of alkaline refining agent; simultaneously, deoxidize the material.

[0013] (d) After deoxidation is completed, put in the preheated nickel plate, high carbon ferrochrome, and ferrosilicon all at once, and then put in the remaining amount of alkaline refining agent.

[0014] (e) When the liquid temperature in the furnace reaches 1700-1710℃, add preheated ferrochrome nitride and tilt the furnace to drain the water;

[0015] (f) Hoist the molten steel ladle preheated to not less than 500°C to the front of the furnace, place the preheated ferrovanadium and rare earth alloy into the bottom of the ladle, and collect the molten steel.

[0016] A further preferred embodiment, by weight percentage, comprises the following materials in the furnace lining material of step (a): 83 parts sintered tabular corundum, 1.3 parts fused white corundum micro powder, 15 parts fused magnesia, and 0.7 parts borax.

[0017] In a further preferred embodiment, the electric furnace startup in step (a) includes cold furnace startup and hot furnace startup. For cold furnace startup, a portion of the raw material is placed in the furnace first, and the remaining raw material is added after the furnace starts up normally. For hot furnace startup, a portion of the raw material in the state of molten steel is reserved in the furnace to facilitate rapid melting by increasing the power of the electric furnace. The remaining raw material is added after the furnace starts up normally.

[0018] In a further preferred embodiment, the deoxidation in step (b) is carried out in three stages, as follows: ferromanganese is added at once for the first deoxidation. After the first deoxidation reaction stabilizes, ferrosilicon is added at once for the second deoxidation. After the second deoxidation reaction stabilizes, aluminum wire is inserted into the furnace for the third deoxidation.

[0019] In a further preferred embodiment, the ferrochrome nitride in step (e) is preheated to a temperature not lower than 300°C, and the ferrochrome nitride has a diameter of 50-100 mm to promote its rapid dissolution in molten steel.

[0020] In a further preferred embodiment, the ferrovanadium and rare earth alloy described in step (f) are preheated to a temperature of not less than 400°C before being placed into the molten steel ladle to ensure that they are fully dissolved and react with the molten steel when it is received.

[0021] In a further preferred embodiment, the matrix blank comprises the following chemical composition by weight percentage: C: 0.14–0.18%, N: 0.08–0.1%, Ni: 1.3–1.7%, Si: 0.6–0.8%, Mn: 0.9–1.1%, Cr: 0.6–0.8%, Mo: 0.15–0.25%, V: 0.05–0.1%, Ti: 0.15–0.25%, with the balance being iron and unavoidable impurities.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] The smelting process of this invention utilizes a medium-frequency electric furnace and selects specific furnace lining materials to reduce the reaction between molten steel and the furnace lining, thereby increasing the purity of the molten steel and reducing non-metallic inclusions and gas content in the alloy steel. This high-purity molten steel provides a good base material for subsequent surfacing welding of roller sleeves, ensuring excellent weldability. This invention effectively reduces the phase transformation stress and welding stress in the heat-affected zone generated during surfacing welding, reducing the risk of welding deformation and cracking, and enabling direct surfacing welding without preheating.

[0024] The phased addition of refining agents and the implementation of phased deoxidation treatment effectively controlled the residual oxygen content in the molten steel, thereby reducing the thermal stress and welding stress generated during welding, reducing the preheating and subsequent heat treatment steps in the welding process, improving production efficiency and reducing energy consumption.

[0025] By controlling the temperature of molten steel and preheating it before adding key alloying elements such as nickel, chromium, and vanadium, this invention ensures the uniform distribution and full reaction of these elements in the molten steel. Such uniformity contributes to the high strength and tempering resistance of the matrix material in the quenched and tempered state, enabling it to provide stable service for extended periods even under high temperatures, heavy loads, alternating thermal stress, and alternating extrusion stress.

[0026] The targeted alloy design and smelting process of this invention delays the formation of a fatigue layer in the composite roll sleeve prepared from a low-carbon, high-strength alloy steel matrix billet during actual use, and prevents the fatigue layer from extending into the matrix, thus greatly improving the weldability and reliability of the continuous casting roll sleeve.

[0027] Overall, the smelting process of the low-carbon high-strength alloy steel matrix billet of the present invention effectively solves the process and performance requirements of the low-carbon high-strength alloy steel matrix billet required for the production of continuous casting roll sleeves, and provides a matrix billet with simple process and excellent performance.

Detailed Implementation Methods

[0028] The present invention will be further described below with reference to the embodiments.

[0029] Example 1

[0030] A smelting process for a low-carbon, high-strength alloy steel matrix billet, comprising the following steps:

[0031] (a) Select a medium-frequency electric furnace as the base billet for the smelting furnace. The electric furnace adopts a neutral to slightly alkaline furnace lining material. Start the electric furnace and add furnace charge after the furnace starts normally. The furnace lining material consists of the following materials in parts by weight: 83 parts of sintered tabular corundum, 1.3 parts of fused white corundum powder, 15 parts of fused magnesia, and 0.7 parts of borax.

[0032] In this embodiment, when starting the electric furnace and the color-cooled furnace, first put one-fifth of the total amount of furnace charge into the furnace, and then add the remaining furnace charge after the furnace starts up normally.

[0033] (b) 5-8 minutes before the furnace charge is melted and cleared, the alkaline material refining agent preheated to not less than 250°C is put into the furnace for the first time. The amount of the refining agent put in for the first time is one-third of the total amount. Deoxidation is carried out in three stages, as follows: ferromanganese is put in at once for the first deoxidation. After the first deoxidation reaction is stable, ferrosilicon is put in at once for the second deoxidation. After the second deoxidation reaction is stable, aluminum wire is inserted into the furnace for the third deoxidation.

[0034] (c) When the furnace charge is melted and cleared, stir the slag and add one-third of the total amount of alkaline refining agent; at the same time, deoxidize and preheat the ferrochrome nitride to not less than 300°C. The ferrochrome nitride has a size of 50-100mm to promote its rapid dissolution in the molten steel.

[0035] (d) After deoxidation is completed, put in the preheated nickel plate, high carbon ferrochrome, and ferrosilicon all at once, and then put in the remaining amount of alkaline refining agent.

[0036] (e) When the liquid temperature in the furnace reaches 1700-1710℃, add preheated ferrochrome nitride and tilt the furnace to drain the water;

[0037] (f) Hoist the molten steel ladle, preheated to not less than 500°C, to the front of the furnace, place the preheated ferrovanadium and rare earth alloys at the bottom of the ladle, and receive the molten steel. The ferrovanadium and rare earth alloys are preheated to not less than 400°C before being placed into the molten steel ladle to ensure that they fully dissolve and react with the molten steel when it is received.

[0038] The matrix blank obtained by the above method includes the following chemical composition by weight percentage: C: 0.14%, N: 0.08%, Ni: 1.3%, Si: 0.6%, Mn: 0.9%, Cr: 0.6%, Mo: 0.15%, V: 0.05%, Ti: 0.15%, S: 0.014%, P: 0.09%, with the balance being iron and unavoidable impurities.

[0039] Example 2

[0040] A smelting process for a low-carbon, high-strength alloy steel matrix billet, comprising the following steps:

[0041] (a) Select a medium-frequency electric furnace as the base billet for the smelting furnace. The electric furnace adopts a neutral to slightly alkaline furnace lining material. Start the electric furnace and add furnace charge after the furnace starts normally. The furnace lining material consists of the following materials in parts by weight: 83 parts of sintered tabular corundum, 1.3 parts of fused white corundum powder, 15 parts of fused magnesia, and 0.7 parts of borax.

[0042] In this embodiment, a hot furnace is started. When the furnace is started, about 20% of the total charge in the furnace is in the form of molten steel, which is conducive to the rapid melting of the electric furnace by increasing the power. After the furnace is started normally, the remaining charge is added.

[0043] (b) 5-8 minutes before the furnace charge is melted and cleared, the alkaline material refining agent preheated to 260°C is added into the furnace for the first time. The amount of the refining agent added for the first time is no more than one-quarter of the total amount. Deoxidation is carried out in three stages, as follows: ferromanganese is added at once for the first deoxidation. After the first deoxidation reaction is stable, ferrosilicon is added at once for the second deoxidation. After the second deoxidation reaction is stable, aluminum wire is inserted into the furnace for the third deoxidation.

[0044] (c) When the furnace charge is melted and cleared, stir the slag and add one-third of the total amount of alkaline refining agent; at the same time, deoxidize and preheat the ferrochrome nitride to not less than 300°C. The ferrochrome nitride has a size of 50-100mm to promote its rapid dissolution in the molten steel.

[0045] (d) After deoxidation is completed, put in the preheated nickel plate, high carbon ferrochrome, and ferrosilicon all at once, and then put in the remaining amount of alkaline refining agent.

[0046] (e) When the liquid temperature in the furnace reaches 1700-1710℃, add preheated ferrochrome nitride and tilt the furnace to drain the water;

[0047] (f) The molten steel ladle, preheated to 600°C, is hoisted to the front of the furnace. The preheated ferrovanadium and rare earth alloys are placed at the bottom of the ladle, and the molten steel is then collected. The ferrovanadium and rare earth alloys are preheated before being placed in the ladle to ensure that they fully dissolve and react with the molten steel when collected.

[0048] The matrix blank obtained by the above method has the following chemical composition by weight percentage: C: 0.18%, N: 0.1%, Ni: 1.7%, Si: 0.8%, Mn: 1.1%, Cr: 0.8%, Mo: 0.25%, V: 0.1%, Ti: 0.25%, S: 0.009%, P: 0.007%, with the balance being iron and unavoidable impurities.

[0049] Example 3

[0050] A smelting process for a low-carbon, high-strength alloy steel matrix billet, comprising the following steps:

[0051] (a) Select a medium-frequency electric furnace as the base billet for the smelting furnace. The electric furnace adopts a neutral to slightly alkaline furnace lining material. Start the electric furnace and add furnace charge after the furnace starts normally. The furnace lining material consists of the following materials in parts by weight: 83 parts of sintered tabular corundum, 1.3 parts of fused white corundum powder, 15 parts of fused magnesia, and 0.7 parts of borax.

[0052] In this embodiment, a hot furnace is started. When the furnace is started, about 20% of the total charge in the furnace is in the form of molten steel, which is conducive to the rapid melting of the electric furnace by increasing the power. After the furnace is started normally, the remaining charge is added.

[0053] (b) 5-8 minutes before the furnace charge is melted and cleared, the alkaline material refining agent preheated to not less than 250°C is put into the furnace for the first time. The amount of the refining agent put in for the first time is not more than one-third of the total amount. Deoxidation is carried out in three stages, as follows: ferromanganese is put in at once for the first deoxidation. After the first deoxidation reaction is stable, ferrosilicon is put in at once for the second deoxidation. After the second deoxidation reaction is stable, aluminum wire is inserted into the furnace for the third deoxidation.

[0054] (c) When the furnace charge is melted and cleared, stir the slag and add no more than one-third of the total amount of alkaline refining agent; at the same time, deoxidize and preheat the ferrochrome nitride to no less than 300°C. The ferrochrome nitride has a size of 50-100mm to promote its rapid dissolution in the molten steel.

[0055] (d) After deoxidation is completed, put in the preheated nickel plate, high carbon ferrochrome, and ferrosilicon all at once, and then put in the remaining amount of alkaline refining agent.

[0056] (e) When the liquid temperature in the furnace reaches 1700-1710℃, add preheated ferrochrome nitride and tilt the furnace to drain the water;

[0057] (f) Hoist the molten steel ladle, preheated to not less than 500°C, to the front of the furnace, place the preheated ferrovanadium and rare earth alloys at the bottom of the ladle, and receive the molten steel. The ferrovanadium and rare earth alloys are preheated to not less than 400°C before being placed into the molten steel ladle to ensure that they fully dissolve and react with the molten steel when it is received.

[0058] The matrix blank obtained by the above method has the following chemical composition by weight percentage: C: 0.15%, N: 0.082%, Ni: 1.55%, Si: 0.63%, Mn: 0.97%, Cr: 0.7%, Mo: 0.22%, V: 0.058%, Ti: 0.17%, S: 0.008%, P: 0.009%, with the balance being iron and unavoidable impurities.

[0059] The continuous casting roll sleeve blanks produced using this invention employ 0Cr17Ni2TiRe flux-cored welding wire (developed by our company) and a submerged arc welding process to deposit a 1-2mm transition layer; 0Cr13Ni4MoNTiRe flux-cored welding wire (developed by our company) is also used, employing a submerged arc welding process to deposit a 5-6mm layer. This produces composite roll sleeves. The roll sleeve blanks do not require preheating before welding; when the interpass temperature rises during welding, the inner hole can be cooled by water. No tempering treatment is required after welding; they can be directly assembled and used after precision machining. Excellent welding performance greatly improves production efficiency, improves the production environment, and saves production costs.

[0060] The composite roller sleeves made from the roller sleeve blanks produced using the technology of this invention, when assembled on the continuous casting rolls in the horizontal section, can handle 1.2-1.5 million tons of steel; when assembled on the continuous casting rolls in the straightening section, they can handle 1 million-1.2 million tons of steel; and when assembled on the continuous casting rolls in the arc section, they can handle 700,000-1 million tons of steel.

[0061] During the rework process of continuous casting rolls produced by this technology after service, the dissection and inspection of the fatigue layer revealed that the fatigue layer was 1-3mm thick, and no cracks appeared in the heat-affected zone of the transition layer weld. This reduced the amount of repair work, made recycling safe and reliable, and provided excellent welding performance.

[0062] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A smelting process for a low-carbon, high-strength alloy steel matrix billet, characterized in that, The process includes the following steps: (a) Select a medium-frequency electric furnace as the base billet for the smelting furnace. The electric furnace adopts a neutral to slightly alkaline furnace lining material. Start the electric furnace and add furnace charge after the furnace starts normally. The furnace lining material consists of the following materials in parts by weight: 83 parts of sintered tabular corundum, 1.3 parts of fused white corundum powder, 15 parts of fused magnesia, and 0.7 parts of borax. (b) 5-8 minutes before the furnace charge is melted and cleared, put the alkaline material refining agent preheated to not less than 250°C into the furnace for the first time. The amount of the refining agent put in for the first time shall not exceed one-third of the total amount used. (c) When the furnace charge is melted and cleared, stir the slag and add no more than one-third of the total amount of alkaline refining agent; at the same time, deoxidation is carried out in three stages, as follows: ferromanganese is added at once for the first deoxidation. After the first deoxidation reaction is stable, ferrosilicon is added at once for the second deoxidation. After the second deoxidation reaction is stable, aluminum wire is inserted into the furnace for the third deoxidation. (d) After deoxidation is completed, put in the preheated nickel plate, high carbon ferrochrome, and ferrosilicon all at once, and then put in the remaining amount of alkaline refining agent. (e) When the liquid temperature in the furnace reaches 1700-1710℃, add preheated ferrochrome nitride and tilt the furnace to drain the water; (f) Hoist the molten steel ladle preheated to not less than 500°C to the front of the furnace, place the preheated ferrovanadium and rare earth alloy into the bottom of the ladle, and collect the molten steel.

2. The smelting process according to claim 1, characterized in that, The start-up of the electric furnace in step (a) includes cold furnace start-up and hot furnace start-up. For cold furnace start-up, a portion of the furnace charge is placed in the furnace first, and the remaining charge is added after the furnace starts up normally. For hot furnace start-up, a portion of the furnace charge in the state of molten steel is reserved in the furnace to facilitate rapid melting by increasing the power of the electric furnace. The remaining charge is added after the furnace starts up normally.

3. The smelting process according to claim 1, characterized in that, The ferrochrome nitride described in step (e) is preheated to not less than 300°C, and the ferrochrome nitride has a diameter of 50-100 mm to promote its rapid dissolution in molten steel.

4. The smelting process according to claim 1, characterized in that, The ferrovanadium and rare earth alloy described in step (f) are preheated to no less than 400°C before being placed into the molten steel ladle to ensure that they fully dissolve and react with the molten steel when it is received.

5. The smelting process according to claim 1, characterized in that, The base blank comprises the following chemical composition by weight percentage: C: 0.14–0.18%, N: 0.08–0.1%, Ni: 1.3–1.7%, Si: 0.6–0.8%, Mn: 0.9–1.1%, Cr: 0.6–0.8%, Mo: 0.15–0.25%, V: 0.05–0.1%, Ti: 0.15–0.25%, with the balance being iron and unavoidable impurities.