Process method for producing low-alloy steel by using high-titanium molten iron

Abstract

The invention belongs to the technical field of ferrous metallurgy, and relates to a process method for producing low-alloy steel by using high-titanium molten iron, which comprises the following steps of: measuring temperature and sampling after converter smelting is finished, stopping slag by adopting a slag stopping cone after a tapping condition is met, and controlling the slag discharge quantity to be lower than a first set value; after 30 seconds of tapping, aluminum blocks are added for deoxidation, so that the content of Al in the molten steel is larger than 0.01 wt% when tapping is finished; manganese-iron alloy is added, so that the content of Mn in the molten steel is 0.2-0.5 wt%; the clearance of the molten steel is guaranteed to be larger than 800 mm, and preparation is made for adding the high-titanium molten iron; the adding amount of the high-titanium molten iron is X; and ferrotitanium is supplemented, so that the content of Ti in the molten steel is 0.035-0.045 wt%, and the components of the molten steel meet the control target. The method has the beneficial effects that a proper amount of high-titanium molten iron is supplemented after converter tapping, the burden of converter smelting is not increased, the components of the molten iron are fully utilized to carry out low-alloy steel deoxidation and microalloying operation, the purposes of reducing the titanium preparation cost and the deoxidation cost are achieved, recycling of carbon, silicon, manganese and titanium elements is increased, and the purposes of reducing the cost and improving the efficiency are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a process for producing low alloy steel by utilizing high-titanium molten iron. Background Art

[0002] Low-alloy high-strength steel (referred to as "low-alloy steel") refers to low-alloy engineering structural steel that adds a small amount of alloying elements to low-carbon steel so that the yield strength in the rolled or normalized state exceeds 275MPa. In the national standard for low-alloy high-strength steel GB / T1591-2018, the significant difference compared to the original standard is that the mandatory requirement for the lower limit of the Mn element content has been cancelled. Steel companies have begun to use trace amounts of alloying elements such as Nb, V, Ti, and Al, using as few alloying elements as possible to obtain the highest possible comprehensive mechanical properties while reducing production costs. Compared with other trace elements, the cost of adding aluminum and titanium elements is more economical, and has gradually become the mainstream alloy addition mode. Titanium-iron alloys are conventionally added to the target titanium composition.

[0003] In the process of blast furnace ironmaking, when the furnace condition fluctuates greatly, the blast furnace needs to be specially added with vanadium-titanium ore to protect the furnace. At this time, the titanium content in the molten iron of the blast furnace is greater than 0.1%, which is called high-titanium molten iron. The conventional operation is to load the high-titanium molten iron into the converter of the next process for oxygen blowing. The increase in the titanium content of the molten iron has many adverse effects on the operation of the steelmaking process, resulting in great difficulty in converter smelting, blowing loss of elements such as carbon (C), silicon (Si), manganese (Mn), and titanium (Ti), large slag consumption, and splashing losses, which not only increase the difficulty of production, but also cause waste of raw material elements. Therefore, a process method for producing high-quality steel using high-titanium molten iron is needed to solve the above technical problems. Summary of the invention

[0004] In order to solve the above-mentioned technical problems, the present invention provides a process method for producing low-alloy steel by using high-titanium molten iron. High-titanium molten iron is added after steelmaking. On the one hand, it does not increase the burden on the converter. At the same time, low-alloy steel needs to be added with elements such as titanium, carbon, silicon, and manganese to improve its strength. When producing low-alloy steel, the components of high-titanium molten iron are used for deoxidation and micro-alloying, so as to achieve the purpose of reducing the titanium matching cost and deoxidation cost of low-alloy steel. On the other hand, the recycling of carbon (C), silicon (Si), manganese (Mn), and titanium (Ti) elements is increased, so as to achieve the purpose of reducing costs and increasing efficiency.

[0005] The technical solution adopted in the embodiment of the present invention is: a process for producing low alloy steel using high-titanium molten iron, characterized in that it includes a converter process and a LF refining process: the processes of each process are as follows:

[0006] (1) Converter process: temperature measurement and sampling, after meeting the conditions for steel tapping, slag blocking is performed using a slag blocking cone, and the amount of slag is controlled to be lower than a first set value; 30 seconds after steel tapping, aluminum blocks are added for deoxidation, so that the Alt content in the molten steel is greater than 0.01wt% at the end of steel tapping; ferromanganese alloy is added to make the Mn content in the molten steel 0.2-0.5wt%; at the end of steel tapping, the molten steel clearance is ensured to be greater than 800mm, in preparation for adding high-titanium molten iron; the high-titanium molten iron is added in an amount of △X;

[0007] (2) LF refining process: titanium iron is added to make the Ti content in the molten steel 0.035-0.045wt%, so that the composition of the molten steel meets the control target.

[0008] Further, △X=(GA)×B / η / w, wherein G is the target titanium content of the molten steel, A is the actual titanium content of the molten steel, B is the amount of molten steel, η is the titanium recovery rate of high-titanium iron water, and w is the titanium content of high-titanium iron water.

[0009] Furthermore, the target of controlling the composition of the molten steel is C 0.15-0.20wt%, Si≤0.05wt%, Mn 0.30-0.35wt%, P≤0.035wt%, S≤0.025wt%, Alt>0.025wt%, Ti 0.035-0.045wt%.

[0010] Furthermore, the steel tapping conditions are: end point C 0.05-0.08wt%, end point P < 0.018%, and end point temperature T > 1620°C.

[0011] Furthermore, the Al content in the aluminum block is ≥99wt%.

[0012] Furthermore, when the steel is tapped for 3 to 4 minutes, the ferromanganese alloy having a manganese content of ≥ 65 wt % is added.

[0013] Furthermore, the first set value is 5kg / t.

[0014] Furthermore, the titanium content in the ferrotitanium is ≥30wt%.

[0015] Furthermore, in the rolling process after the refining process, the starting temperature of the rough rolling is 1080-1160°C, the finishing temperature of the fine rolling is 850-870°C, the threading speed is 7-9 m / s, and the coiling temperature is 580-600°C.

[0016] The advantages and positive effects of the present invention are as follows: in the process of producing low alloy steel, high-titanium molten iron is added after steel is tapped from the converter, and violent titanium-oxygen and carbon-oxygen reactions no longer occur, and the risk of metal splashing is greatly reduced, i.e., the burden on converter smelting is not increased, and at the same time, various components of high-titanium molten iron are fully utilized for deoxidation and micro-alloying, thereby achieving the purpose of reducing titanium matching cost and deoxidation cost, and fully utilizing existing resources for the production of low-alloy steel, thereby achieving the purpose of reducing cost and increasing efficiency, increasing the recycling of carbon (C), silicon (Si), manganese (Mn), and titanium (Ti) elements, making up for the defects of high-titanium molten iron in smelting, and being able to produce low-alloy steel with performance indicators meeting standards, thus achieving multiple goals at one stroke. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart provided by the present invention;

[0018] Figure 2 This is the process flow of the embodiment provided by the present invention during use. DETAILED DESCRIPTION

[0019] The embodiment of the present invention provides a process for producing low alloy steel using high titanium molten iron, which is described below in conjunction with the accompanying drawings. In this technical solution, the molten steel clearance refers to the height of the molten steel level from the upper edge of the ladle.

[0020] like Figure 2 As shown, molten iron and scrap steel are loaded into the converter for oxygen blowing and slag making. After the converter taps out steel, deoxidation and alloying are carried out, and then LF refining process, continuous casting, rolling and product testing are carried out. Molten iron can use ordinary molten iron or high-titanium molten iron produced in the blast furnace ironmaking process. Adding high-titanium molten iron to the converter will make the converter smelting difficult, and the blowing loss of carbon (C), silicon (Si), manganese (Mn), titanium (Ti) and other elements, the slag consumption is large, and there are also losses such as splashing, which not only increases the difficulty of production, but also causes waste of raw materials.

[0021] Reference Figure 1 As shown, a process for producing low alloy steel using high titanium molten iron is characterized by comprising a converter process and a LF refining process. The processes of each process are as follows:

[0022] (1) Converter process: temperature measurement and sampling, after meeting the conditions for steel tapping, slag blocking is performed using a slag blocking cone, and the amount of slag is controlled to be lower than a first set value; 30 seconds after steel tapping, aluminum blocks are added for deoxidation, so that the Alt content in the molten steel is greater than 0.01wt% at the end of steel tapping; ferromanganese alloy is added, so that the Mn content in the molten steel is 0.2-0.5wt%; at the end of steel tapping, the clearance of the molten steel is ensured to be greater than 800mm, in preparation for adding high-titanium molten iron; the amount of high-titanium molten iron added is △X;

[0023] (2) LF refining process: titanium iron is added to make the Ti content in the molten steel 0.035-0.045wt%, so that the composition of the molten steel meets the control target.

[0024] After the converter is tapped, high-titanium molten iron is added, and no oxidation reaction will occur, nor will splashing and other hazards occur, that is, it will not add burden to converter smelting, and at the same time, the various components of molten iron are fully utilized for deoxidation and micro-alloying, achieving the purpose of reducing the cost of titanium and deoxidation. There are two test results for aluminum in molten steel, Alt represents the total aluminum content in steel, and Als represents the acid-soluble aluminum content in steel. The cost control target of molten steel in this technical solution is Alt.

[0025] Preferably, the tapping conditions are: end point C 0.05-0.08wt%, end point P < 0.018%, end point T > 1620° C. If the end point carbon is too low, the molten steel will have strong oxidizability, and if the end point carbon is too high, the subsequent addition of high-titanium iron water will easily result in excessive components.

[0026] Preferably, the first set value is 5kg / t. Too much slag will cause strong oxidation of molten steel, P element is easy to exceed the standard, and large slag amount will reduce SiO2 in aluminum-killed slag, causing Si element to exceed the internal control standard (Si≤0.05%), affecting the plasticity of steel. Therefore, the slag amount per ton of molten steel should not exceed 5kg.

[0027] Preferably, the Al content in the aluminum block is ≥99wt%. In this embodiment, 30 seconds after the start of steel tapping, aluminum blocks are added for deoxidation, and 1.0kg / t is added based on the end point carbon of 0.08%. For every 0.01% decrease in the end point carbon, the amount of aluminum blocks added is increased by 0.2kg / t. 0.2kg / t is added in each batch, with an interval of 30 seconds, and the aluminum content of the aluminum blocks is ≥99wt%. At the end of steel tapping, Alt>0.01wt% is controlled to facilitate the realization of the process goal of adding aluminum to maintain titanium.

[0028] Preferably, when the steel is tapped for 3-4 minutes, a ferromanganese alloy with a manganese content of ≥65wt% is added. The added ferromanganese alloy contains ≥65wt% manganese, and the remaining elements are mainly iron, so that the Mn content in the molten steel is 0.2-0.5wt%.

[0029] Preferably, the amount of high-titanium molten iron added is △X, △X=(GA)×B / η / w, wherein G is the target titanium content in the molten steel, A is the actual titanium content in the molten steel, B is the amount of molten steel, η is the titanium recovery rate of high-titanium molten iron, and w is the titanium content of high-titanium molten iron.

[0030] Preferably, the titanium content in the ferrotitanium is ≥ 99 wt %.

[0031] Preferably, the cost control target of molten steel is C 0.15-0.20wt%, Si≤0.05wt%, Mn 0.30-0.35wt%, P≤0.035wt%, S≤0.025wt%, Alt>0.025wt%, Ti 0.035-0.045wt%.

[0032] Preferably, in the rolling process after the LF refining step, the rough rolling start temperature is 1080-1160°C, the fine rolling final rolling temperature is 850-870°C, the strip threading speed is 7-9 m / s, and the coiling temperature is 580-600°C.

[0033] Embodiment 1:

[0034] Taking the production of low alloy high strength steel Q355D in a 100-ton nominal converter as an example, the specific steps are as follows:

[0035] (1) After the converter smelting was completed, the first temperature measurement sampling was carried out, the steel tapping end point C was 0.07wt%, the end point P was 0.016%, and the end point temperature T was 1625℃.

[0036] (2) The slag cone is used to block the slag during steel tapping, and the slag discharge amount is 4 kg (calculated based on the phosphorus return data) in combination with the slag discharge detection system.

[0037] (3) 30 seconds after the start of steel tapping, aluminum blocks were added for deoxidation. The amount of aluminum blocks added was 120 kg. 20 kg / t was added in each batch with an interval of 30 seconds. The aluminum content of the molten steel was 0.018 wt% at the end of steel tapping.

[0038] (4) When the steel is tapped 2 / 3 of the time, add 200 kg of ferromanganese alloy with a manganese content of ≥ 65 wt%.

[0039] (5) After steel tapping is completed, the molten steel clearance is ensured to be 900 mm, and the ladle carrying the molten steel arrives at the argon blowing station.

[0040] (6) Using a crane to hoist high-titanium molten iron, the composition is C 4.5wt%, Si 0.32wt%, Mn 0.24wt%, P0.08wt%, S 0.022wt%, Ti 0.4wt%, and the titanium recovery rate is calculated as 85%. With the goal of increasing titanium by 0.015wt%, the ladle is tilted to add 4.17t of high-titanium molten iron into the ladle.

[0041] (7) The ladle is hoisted to LF for processing. The amount of aluminum wire fed is adjusted based on the composition of the molten steel. Titanium iron is added based on the Ti content of the molten steel sample.

[0042] (8) Final molten steel composition: C: 0.19wt%, Si: 0.04wt%, Mn: 0.302wt%, P: 0.029wt%, S: 0.01wt%, Alt 0.0382wt%, Ti: 0.042wt%.

[0043] (9) The specifications of the rolled strip steel are 2.5×495 mm. The main process parameters of the rolling process are: the starting temperature of the rough rolling is 1090°C, the final rolling temperature of the fine rolling is 858°C, the threading speed is 8.0 m / s, and the coiling temperature is 590°C.

[0044] (10) The performance of the strip steel was tested, and the yield strength was 497Mpa, the tensile strength was 540Mpa, and the elongation after fracture was 29%. The product performance met the standard requirements, the average impact energy at -20℃ reached 135J, the low-temperature toughness was excellent, and the plasticity met the requirements for use.

[0045] The advantages and positive effects of the present invention are as follows: in the process of producing low alloy steel, high-titanium molten iron is added after steel is tapped from the converter, and violent titanium-oxygen and carbon-oxygen reactions no longer occur, and the risk of metal splashing is greatly reduced, i.e., the burden on converter smelting is not increased, and at the same time, various components of high-titanium molten iron are fully utilized for deoxidation and micro-alloying, thereby achieving the purpose of reducing titanium matching cost and deoxidation cost, and fully utilizing existing resources for the production of low-alloy steel, thereby achieving the purpose of reducing cost and increasing efficiency, increasing the recycling of carbon (C), silicon (Si), manganese (Mn), and titanium (Ti) elements, making up for the defects of high-titanium molten iron in smelting, and being able to produce low-alloy steel with performance indicators meeting standards, thus achieving multiple goals at one stroke.

[0046] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A process for producing low alloy steel using high titanium molten iron, characterized in that: Including converter process and LF refining process: the process of each process is as follows: (1) Converter process: temperature measurement and sampling, after meeting the conditions for steel tapping, slag blocking is performed using a slag blocking cone, and the amount of slag is controlled to be lower than a first set value; 30 seconds after steel tapping, aluminum blocks are added for deoxidation, so that the Alt content in the molten steel is greater than 0.01wt% at the end of steel tapping; ferromanganese alloy is added to make the Mn content in the molten steel 0.2-0.5wt%; at the end of steel tapping, the molten steel clearance is ensured to be greater than 800mm, in preparation for adding high-titanium molten iron; the high-titanium molten iron is added in an amount of △X; (2) LF refining process: titanium iron is added to make the Ti content in the molten steel 0.035-0.045wt%, so that the composition of the molten steel meets the control target.

2. The process for producing low alloy steel using high titanium molten iron according to claim 1, characterized in that: △X=(GA)×B / η / w, where G is the target titanium content of molten steel, A is the actual titanium content of molten steel, B is the amount of molten steel, η is the titanium recovery rate of high-titanium iron water, and w is the titanium content of high-titanium iron water.

3. The process for producing low alloy steel using high titanium molten iron according to claim 2, characterized in that: The target of controlling the composition of the molten steel is C 0.15-0.20wt%, Si≤0.05wt%, Mn0.30-0.35wt%, P≤0.035wt%, S≤0.025wt%, Alt>0.025wt%, Ti 0.035-0.045wt%.

4. The process for producing low alloy steel using high titanium molten iron according to any one of claims 1 to 3, characterized in that: The steel tapping conditions are: end point C 0.05-0.08wt%, end point P < 0.018%, and end point temperature T > 1620°C.

5. The process for producing low alloy steel using high titanium molten iron according to claim 4, characterized in that: The Al content in the aluminum block is ≥99wt%.

6. The process for producing low alloy steel using high titanium molten iron according to claim 4, characterized in that: When the steel is tapped for 3 to 4 minutes, the ferromanganese alloy having a manganese content of ≥65wt% is added.

7. The process for producing low alloy steel by using high titanium molten iron according to any one of claims 1 to 3, 5 and 6, characterized in that: The first set value is 5kg / t.

8. The process for producing low alloy steel using high titanium molten iron according to claim 7, characterized in that: The titanium content in the ferrotitanium is ≥30wt%.

9. The process for producing low alloy steel using high titanium molten iron according to claim 8, characterized in that: In the rolling process after the refining process, the starting temperature of rough rolling is 1080-1160°C, the final rolling temperature of fine rolling is 850-870°C, the threading speed is 7-9 m / s, and the coiling temperature is 580-600°C.

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