Smelting method of ultralow-manganese industrial pure iron

Abstract

The invention discloses a smelting method of ultralow-manganese industrial pure iron, and belongs to the technical field of steel smelting. The process route of the method is as follows: LF refining and RH refining continuous casting of a desulfurized molten iron and molten iron pre-demanganizing converter; the method mainly comprises the steps of low-alkalinity pre-demanganization of desulfurized molten iron, high-oxygen-level deep demanganization at the end point of a converter decarburization procedure, and demanganization through steel ladle slag washing and strong stirring in the tapping and refining process, the alkalinity of the low-alkalinity pre-demanganization of the molten iron is controlled to be 1.0-1.5, oxygen at the end point of the converter decarburization procedure is 600 ppm or above, the content of FeO in LF refining slag is controlled to be 20-30 wt%, the alkalinity is controlled to be 2.8-3.8, and the content of the low-alkalinity pre-demanganization of the molten iron is and after deep decarburization of RH and aluminum deoxidation, continuous casting and pouring are carried out. According to the method, the content Mn of medium-high-manganese original molten iron can be smaller than or equal to 0.40 wt%, the content of Mn of a finished product is controlled to be 0.01 wt% or below, the purity of a casting blank is stably controlled to be 99.95 wt% or above, and the requirement for ultralow-manganese industrial pure iron special for magnetic materials can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking and relates to a method for smelting ultra-low manganese industrial pure iron. Background Art

[0002] Industrial pure iron is an important raw material for manufacturing magnetic materials, and is used in both hard magnetic materials and soft magnetic materials. These magnetic materials have extremely strict requirements on the manganese content in the raw materials, usually requiring the manganese content to be less than 0.02wt%, or even need to be controlled below 0.01wt%. The reason is that manganese will form non-magnetic oxide inclusions in ferromagnetic materials, reducing the magnetic susceptibility, resistivity and corrosion resistance of the material.

[0003] Since manganese is an inevitable accompanying element in the steelmaking process and is widely present in the molten iron, the raw material for steelmaking, and due to its similar chemical properties to iron, it is difficult to control the manganese content at a very low level in traditional steelmaking production processes. Although the general converter smelting process has a certain effect in removing impurities, when faced with raw molten iron with medium and high manganese content, the manganese content of the finished product is also difficult to control below 0.01wt%.

[0004] In order to meet these challenges, the present invention proposes a method for smelting ultra-low manganese, which effectively realizes the precise control of manganese content by optimizing the process flow and controlling key process parameters. It can not only remove manganese from molten steel to the maximum extent, but also has high production efficiency and economy, so as to meet the growing demand for high-quality magnetic material raw materials and increase product added value, which has important practical significance.

[0005] Chinese patent publication number CN110453032B discloses a method for smelting ultra-low manganese steel using high manganese molten iron, which uses a double slag smelting process to remove most of the manganese and other elements in the high manganese molten iron, and further removes manganese by using a converter low-temperature steelmaking and LF refining furnace deep demanganese process. Under the condition that the molten iron entering the furnace is a high manganese molten iron with a manganese content higher than 0.40%, the manganese content in the molten steel can be stably controlled to be below 0.02%. However, in order to ensure the final demanganese effect, the amount of material added in the refining process is too large and the cost is high, and the large amount of slag in the refining will affect the RH decarburization effect, resulting in a low purity of the finished carbon.

[0006] The Chinese patent with publication number CN111440916B discloses a method for producing ultra-low manganese steel using a high-manganese hot metal converter. The invention achieves low manganese control of the finished product by adjusting the amount of scrap steel according to the hot metal conditions, controlling the position of the converter process gun, the timing and amount of material addition, etc. However, this method is different from this patent. Due to the limitation of its process conditions, it cannot achieve the requirement of Mn≤0.01%.

[0007] Chinese patent publication number CN113774277B discloses an ultra-low carbon and ultra-low manganese industrial pure iron and a preparation method. The invention achieves the requirements of C≤0.002% and Mn≤0.035% for the finished product through molten iron pretreatment KR desulfurization → converter double slag → ladle heating → vacuum furnace → continuous casting. However, compared with this patent, this method lacks the pretreatment demanganeseization link, resulting in excessively high residual Mn content in the slag, and the manganese content of the final product cannot reach the ≤0.01% level requirement. Summary of the invention

[0008] Aiming at the technical problem that it is difficult to effectively remove manganese from molten iron in the traditional converter steelmaking process, this paper invented a smelting method of ultra-low manganese industrial pure iron, which overcomes the insufficient steelmaking manganese removal effect of medium-high manganese (Mn≤0.30wt%) molten iron and can stably control the manganese content of the finished product to below 0.01wt%.

[0009] To achieve the above purpose, the technical solution of the present invention is:

[0010] A method for smelting ultra-low manganese industrial pure iron comprises the following steps:

[0011] (1) Dephosphorization furnace process: After the hot metal is desulfurized, the dephosphorization furnace is pre-demanganized, and the scrap steel ratio is controlled to be 8-10wt%. After the blowing is started, slag-making agents such as lime and iron ore are added during the process. The oxygen supply intensity and bottom blowing intensity are well controlled during the process. The oxygen blowing time is 8-10 minutes. After the slag inhibitor 1.5-2kg / t is added at the end point, the furnace is quickly turned over to tap the steel. During the tapping process, a slide plate is used to block the slag and prevent the slag from falling. Ferrosilicon is added during the process to supplement the silicon content of the semi-steel.

[0012] (2) Decarburization in the converter: During decarburization, the scrap ratio is controlled at 4-6wt%, and lime, light-burned dolomite and part of the ore are added to make slag. The tapping process uses a slide plate to block slag and a double slag block. Lime, fluorite and wollastonite are added to pre-slag during the process. The ladle bottom blowing and strong stirring are turned on during the tapping process;

[0013] (3) LF heating: The molten steel is heated in the LF furnace with oxygen and the slag is reformed. Fluorite, wollastonite and special slag for refining are added during the slag adjustment process. During the process, the ladle is stirred to remove Mn.

[0014] (4) RH decarburization and deoxidation: After entering the station, the RH is decarburized using oxygen in the steel. After decarburization, the residual oxygen is deoxidized using aluminum particles. The amount of aluminum particles used is 0.5-1.5 kg / t. The molten steel is subjected to pure circulation degassing treatment before leaving the station;

[0015] (5) continuous casting machine casting: the molten steel obtained in the above steps is cast to obtain a casting billet, the purity of which is above 99.90wt%, wherein Mn≤0.01wt%;

[0016] Furthermore, in the step (1), the main components of the desulfurized molten iron used are as follows in percentage by mass: Mn≤0.30%, Si: 0.20-0.50%, P≤0.120%, S≤0.002%.

[0017] Furthermore, in the step (1), the scrap steel is small-sized scrap steel such as light and thin scrap steel, and the scrap steel ratio is controlled to be 8-10wt%. The amount of lime added in the process is slag-making agent lime, and the amount added is controlled according to the target basicity of 1.0 with reference to the silicon content of molten iron. The T.Fe content of the iron ore is controlled to be ≥60wt%. The process oxygen supply intensity is controlled at 0.96-1.15Nm / (t*min), the bottom blowing intensity is 0.15-0.20Nm / (t*min), the oxygen blowing time is 8-10 minutes, and the terminal temperature is controlled at 1330-1360°C.

[0018] Furthermore, in the step (1), a slide plate is used to block slag during the steel tapping process to prevent slag from falling, and 2 kg / t of ferrosilicon is added during the steel tapping process to supplement the silicon content of the semi-steel, and the Si content of the ferrosilicon is controlled to be: 73-78 wt%;

[0019] Furthermore, in the step (1), the main components after the semi-steel is produced are calculated by mass percentage as follows: C: 3.5-3.8%, Si≤0.01%, Mn≤0.03%, S≤0.003%, P≤0.040%;

[0020] Furthermore, in the step (2), the scrap steel ratio is controlled at 4-6wt% during decarbonization, 17-20kg / t of lime, 8-10kg / t of light-burned dolomite and part of the ore are added for slag making, the terminal temperature is controlled at 1590-1610°C, and the terminal oxygen level is ≥600ppm.

[0021] Furthermore, in the step (2), the steel tapping process adopts a slide plate slag blocking and a slag blocking mark double blocking, lime, fluorite and wollastonite are added in the process to pre-slag, and the ladle bottom blowing and strong stirring are turned on during the steel tapping process;

[0022] In the step (2), 2.7-3 kg / t of lime, 0.7-0.8 kg / t of fluorite and 2.5-2.7 kg / t of wollastonite are added for pre-slagging.

[0023] Furthermore, in the step (2), the main components after steel production are calculated by mass percentage as follows: C: 0.02-0.03%, Mn≤0.015%, S≤0.003%, P≤0.004%;

[0024] Furthermore, in the step (3), the molten steel is heated with oxygen and the slag is modified in the LF furnace. During the process, fluorite, wollastonite and low-sulfur refined slag are added to adjust the slag, and the slag basicity is controlled at 2.8-3.8, the FeO in the slag is 20-30wt%, and the refining temperature is controlled at: 1590-1610°C; the sulfur mass content in the low-sulfur refined slag is less than 0.52%.

[0025] Furthermore, in step (4), the Mn mass content of the finished ingot is ≤0.01% and the purity is above 99.90wt%.

[0026] Beneficial effects of the present invention:

[0027] The invention can achieve the content of Mn of the original medium-high manganese molten iron less than or equal to 0.40wt%, the Mn content of the finished product is controlled below 0.01wt%, and the purity of the ingot is stably controlled above 99.95wt%, which can meet the demand for ultra-low manganese industrial pure iron for magnetic materials. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with embodiments:

[0029] A method for smelting ultra-low manganese industrial pure iron comprises the following steps:

[0030] (1) Pre-manganese removal process: After the molten iron is desulfurized, the dephosphorization furnace is pre-manganese removed, and the scrap steel ratio is controlled to be 8-10wt%. After the blowing is started, slag-forming agents such as lime, wollastonite and iron ore are added during the process. The oxygen blowing time is 8-10 minutes. After the slag inhibitor 1.5-2kg / t is added at the end point, the furnace is poured out and the slag is prevented from falling during the steel-out process by using a slide plate to block the slag. Ferrosilicon is added during the process to supplement the silicon content of the semi-steel;

[0031] (2) Decarburization in a converter: During decarburization, the scrap steel ratio is controlled at 4-6wt%, lime, light-burned dolomite and part of the ore are added to make slag, the terminal temperature is controlled at 1590-1610°C, and the terminal oxygen level is ≥600ppm; the tapping process adopts a slide plate slag stop and a slag stop standard double stop, lime, fluorite and wollastonite are added to pre-slag during the process, and the ladle bottom blowing and strong stirring are turned on during the tapping process to remove Mn;

[0032] (3) LF heating: The molten steel is heated in the LF furnace with oxygen and the slag is modified. Fluorite, wollastonite and special slag conditioning agent for refining are added during the process. During this period, the ladle is stirred to remove Mn;

[0033] (4) RH decarburization and deoxidation: After RH enters the station, it uses oxygen in the steel to decarburize. After decarburization, 0.5-1.5kg / t aluminum particles are used to remove residual oxygen in the steel. The molten steel is subjected to pure circulation degassing treatment before leaving the station;

[0034] (5) Casting by continuous casting machine: The molten steel obtained in the above steps is cast into a cast billet.

[0035] Examples 1-5

[0036] The method of the present invention smelts industrial pure iron. Taking a converter with a capacity of 260t as an example, the smelting data of 5 furnaces of steel are statistically analyzed. The parameters of the furnace desulfurization molten iron are shown in Table 1, the smelting process control parameters are shown in Tables 2-7 below, and the composition and mass percentage of the ingots obtained in each embodiment are shown in Table 8.

[0037] Table 1. Desulfurized hot metal parameters

[0038]

[0039]

[0040] Table 2. Process parameters of hot metal pre-demanganeseization process

[0041]

[0042] Table 3. End point parameters of hot metal pre-demanganeseization

[0043]

[0044] Table 4. Converter process parameters

[0045]

[0046]

[0047] Table 5. Converter endpoint parameters

[0048]

[0049] Table 6. LF refining process parameters

[0050]

[0051] Table 7. Composition and mass percentage of each heat of ingot

[0052]

[0053]

[0054] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for smelting ultra-low manganese industrial pure iron, characterized in that: The following steps are involved: (1) Pre-manganese removal process: After the hot metal is desulfurized, pre-manganese removal is carried out in the dephosphorization furnace. The scrap steel ratio is controlled at 8-10wt%. After the blowing is started, slag-forming agents such as lime, wollastonite and iron ore are added. The oxygen blowing time is 8-10 minutes. After the slag inhibitor 1.5-2kg / t is added at the end, the furnace is poured out and the slag is prevented from falling during the steel-out process. Ferrosilicon is added during the process to supplement the silicon content of the semi-steel. (2) Decarburization in the converter: During decarburization, the scrap steel ratio is controlled at 4-6wt%, and lime and light-burned dolomite are added to make slag. During the steel-tapping process, the slide plate slag stop and the slag stop standard double stop are used. During the process, lime, fluorite and wollastonite are added to make pre-slag. During the steel-tapping process, the ladle bottom blowing and strong stirring are turned on to remove Mn. (3) LF heating: The molten steel is heated and slag modified in the LF furnace with oxygen. Fluorite, wollastonite and special slag conditioning agent for refining are added during the process. During the process, the ladle is stirred to remove Mn. (4) RH decarburization and deoxidation: After RH enters the station, it uses oxygen in the steel to decarburize. After decarburization, aluminum particles are used to remove residual oxygen in the steel. The amount of aluminum particles used is 0.5-1.5kg / t. The molten steel is subjected to pure circulation degassing treatment before leaving the station; (5) Casting by continuous casting machine: The molten steel obtained according to the above steps is poured to obtain a cast ingot.

2. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (1), the components of the desulfurized molten iron used are as follows: C ≥ 4.0%, Mn ≤ 0.35%, Si: 0.20-0.50%, P ≤ 0.120%, S ≤ 0.002% by mass percentage.

3. The smelting method of ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (1), the amount of slag-forming agent lime, wollastonite and iron ore added is controlled according to the silicon content of molten iron, and the target alkalinity is 1.0-1.

5. The process oxygen supply intensity is controlled at 0.96-1.15Nm / (t*min), the bottom blowing intensity is 0.15-0.20Nm / (t*min), the oxygen blowing time is 8-10 minutes, and the terminal temperature is controlled at 1330-1370°C.

4. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (1), 2 kg / t of ferrosilicon is added during the steel-making process, and the Si mass content of the ferrosilicon is controlled to be 72-80 wt%.

5. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (1), the composition of the semi-steel after production is calculated by mass percentage as follows: C: 3.3-3.8%, Si≤0.02%, Mn≤0.04%, S≤0.002%, P≤0.050%.

6. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (2), 17-20 kg / t of lime and 8-10 kg / t of light-burned dolomite are added to form slag during decarbonization, the final temperature is controlled at 1590-1610° C., and the final oxygen level is ≥600 ppm.

7. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (2), 2.7-3 kg / t of lime, 0.7-0.8 kg / t of fluorite and 2.5-2.7 kg / t of wollastonite are added for pre-slagging.

8. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (2), the composition of the steel after tapping is calculated by mass percentage as follows: C: 0.02-0.03%, Mn≤0.015%, S≤0.003%, P≤0.005%.

9. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (3), 1.1-1.6 kg / t of fluorite, 1.1-1.3 kg / t of wollastonite and 2.1-2.3 kg / t of low-sulfur refined slag are added, and the slag basicity is controlled in the range of 2.8-3.8 during the process, the FeO in the slag is 20-30 wt%, and the refining temperature is controlled at 1590-1610°C.

10. The method for smelting ultra-low manganese industrial pure iron according to claim 1, characterized in that: In the step (5), the Mn mass content of the finished ingot is ≤0.01wt%, and the purity of the ingot is stably controlled to be above 99.95wt%.

Images