CN105803156B - Oxide control method for improving magnesium yield - Google Patents

Abstract

The invention discloses an oxide control method for increasing magnesium yield, which belongs to the technical field of steelmaking. In the method of the present invention, Ti-Fe alloy cored wire is fed into the ladle at the RH station to add alloy element Ti, after the ladle is hoisted to the turntable, the free oxygen content in the molten steel is controlled within the range of 10-18ppm, and the molten steel The degree of superheat is 20-30°C. Ni-Mg alloy cored wire is fed into the ladle at the continuous casting station to add the alloying element Mg, and the pressure is 0.4MPa and softly stirred for 3 minutes. With this method, the yield of the alloying element Mg can be stabilized at 15-30%. The oxides in the prepared slab are mainly Mg-Ti series composite oxides, and the oxides with a size of ≤2.0 μm account for all the above-mentioned oxides. The proportion of oxides reaches 83% and above, and the volume density of oxides with a size ≤ 2.0 μm reaches 3.7×10 ⁵ /mm ³ and above.

Description

A kind of oxide control method that improves magnesium yield

technical field

The invention belongs to the technical field of steelmaking production, and in particular relates to an oxide control method for adding titanium and magnesium during steelmaking to increase the yield of magnesium.

Background technique

At present, steel plates for high heat input welding have been widely used in many fields such as ships, buildings, pressure vessels, pipelines, and offshore platforms. According to estimates, using the high heat input welding method can even increase the welding efficiency by 5 times or more, greatly reduce the manufacturing hours, and greatly reduce the cost.

Oxide metallurgy technology is an effective method for manufacturing large heat input welded steel plates. This method mainly requires oxides to be kept below a certain size, and fine oxides are used to induce intragranular acicular ferrite nucleation and indirectly refine the original austenite grains. Grain size, so as to obtain high low temperature toughness of welding heat affected zone. Among them, the small-sized and dispersed Mg oxide particles can fully ensure the effect of oxide metallurgy and improve the performance of high-heat input steel plates, and the oxide control technology in the smelting process is in a key position.

Patents CN 102373371 A, CN 102191356 A, and CN 102296147 A all use the method of adding Ni-Mg alloy at the bottom of the ingot mold to add Mg alloy, which is only suitable for small-batch die-casting production, and the production efficiency is low, and it is not suitable for industrialized large-batch continuous casting.

Patent CN 103215507 A proposes to sequentially add Ti-Fe wire, Al wire, Ni-Mg wire, and Ca wire at the RH station for deoxidation and alloying. On the one hand, the continuous addition of a large amount of deoxidized alloy makes it difficult to control the splashing of molten steel. On the other hand, the timing of addition is too early, the Mg alloy burns more, the yield is low, and the Mg content in the steel plate cannot be effectively guaranteed.

Patent CN 103938065 A adopts the way of feeding wire to the tundish to add Ti and Mg for alloying. First of all, this method does not mention whether the wire feeding process is carried out at the same time as the pouring process. If it is carried out at the same time, it is difficult to ensure the uniformity of Ti and Mg alloys in the tundish molten steel, and the uniformity of oxides is poor. If it is not carried out at the same time, this method cannot A large number of steel plates are produced by continuous casting; secondly, this method uses alloy wires with Ti mass percentage ≥ 95% and Mg-Y-Ni alloy wires, and the cost is relatively high; finally, this method adds two easily oxidizable elements at the same time, requiring The steelmaking equipment is relatively complicated, which is not conducive to the operation and control of molten steel splashing, and the final magnesium recovery rate is only 8-15%.

Patent CN 103757178 A uses a steelmaking additive to improve the performance of large heat input for Ti and Mg composite alloying. In this method, raw materials are mixed according to a certain ratio, smelted in a vacuum smelting furnace and cast into ingots, and then the ingots are crushed into alloy powders and made into cored wires. The operation process of this method is cumbersome, the cost is high, and the operation process of adding alloy is not given in detail.

Contents of the invention

The object of the present invention is to provide a method for controlling oxides to increase the yield of magnesium, which is suitable for on-site converter or electric furnace primary smelting, ladle refining, and continuous casting processes. The method is used to feed Ti and Mg during steelmaking. Alloying can ensure a stable yield of the alloying element Mg, and can form a large number of fine Mg-Ti type composite oxides in the slab to ensure the metallurgical effect of the oxide.

To achieve the above object, the present invention adopts the following technical solutions:

An oxide control method to increase the yield of magnesium, LF refining stage: the range of free oxygen in the molten steel is 20-30ppm when tapping; RH stage: the net cycle time is 5-10min, and the superheat of the molten steel is 55 -75°C, feed Ti-Fe alloy cored wire into the ladle, then use 0.4-0.6MPa pressure to bottom blow argon to softly stir the molten steel, time ≥ 5min; continuous casting stage: the ladle is hoisted to the turntable, The range of free oxygen in the molten steel is 10-18ppm; the superheat of the molten steel is 20-30°C. Before continuous casting, Ni-Mg alloy cored wire is fed into the ladle, and the pressure of 0.4MPa is used for soft stirring for 3 minutes. Injection flow in tundish.

Further, in the oxide control method for increasing the yield of magnesium, the feeding speed of the Ti-Fe alloy cored wire is 4-6m/s, and the Ti alloy content in the core powder is 25%; the Ni-Mg alloy cored wire The wire feeding speed is 7-10m/s, the core powder particle size of the cored wire is 0.5-2.0mm, and the alloy core powder contains Mg alloy with a weight ratio of 2-18%.

1) In the LF refining stage, after deoxidation control, the free oxygen content of molten steel is guaranteed to be 20-30ppm, and the free oxygen content of molten steel is guaranteed to be 10-18ppm.

2) In the RH refining stage, after 5-10 minutes of net circulation, the N ₂ , H ₂ and other gases in the molten steel are removed, and the large particles of inclusions are promoted to float up to purify the molten steel.

3) In the RH refining stage, control the superheat of the molten steel to 55-75°C after it breaks through the void, and ensure that the temperature of the molten steel is 20-30°C after the ladle enters the rotary table and before continuous casting, while avoiding excessive temperature and waste of electric energy. The yield rate is low, and the follow-up production rhythm is difficult to adjust.

4) In the RH refining stage, Ti-Fe alloy cored wire is fed, and the alloying element Ti can combine with O and N in the molten steel to form fine TiO _x and TiN particles, achieving the effect of partial oxide metallurgy. In addition, the binding ability of Ti and O is less than that of Mg and O. Ti and oxygen in molten steel combine to compete for part of the oxygen in molten steel in advance to prevent the oxygen content in molten steel from being too high when Mg alloy wire is subsequently fed, which is Mg-containing. The formation of oxides provides favorable conditions to reduce the burning loss of alloying element Mg.

5) In the RH refining stage, stir with a pressure of 0.4-0.6MPa for more than 5 minutes, and the large particle inclusions in the molten steel will float up to ensure the purity of the molten steel, and then add a liquid surface covering agent to keep the molten steel warm.

4) In the continuous casting stage, if the oxygen content of the molten steel is higher than 18ppm before entering the continuous casting station, after adding the Ni-Mg alloy cored wire, some oxides with larger particle sizes will be formed in the molten steel. Being able to float up will cause the yield of Mg to be too low. If this part of the oxide remains in the molten steel because it cannot fully float up, it will inevitably affect the cleanliness of the molten steel and deteriorate the mechanical properties of the steel. If the oxygen content in the molten steel is lower than 10ppm, it is unfavorable to generate a sufficient number of fine Mg-Ti composite oxide particles in the molten steel, which affects the metallurgical effect of using a large number of fine oxides.

5) In the continuous casting stage, when the superheat of the molten steel is between 20-30°C, feed the line quickly at a speed of 7-10m/s, so as to avoid problems such as the floating of oxides and the easy burning of Mg in the steel due to long-term waiting; Secondly, the grain size of the cored wire is kept at 0.5-2.0mm, and the alloy particles smaller than 0.5mm have a high burning loss rate, and the alloy particles larger than 2.0mm tend to form aggregated and large-sized oxide particles; thirdly, the Mg alloy in the core powder The content is between 2-18%, to prevent the problems of low yield and splashing of molten steel caused by high Mg alloy content ratio. The combination ability of Mg element and O element is strong, and a large number of fine Mg-Ti series composite oxides can be formed in molten steel.

6) In the continuous casting stage, if the Ni-Mg alloy cored wire is added to the RH station, the superheat of the molten steel will be high. In addition, due to the influence of long-term residence, Mg is prone to burning loss or large particle size in the molten steel. Oxide, the yield will be greatly reduced. In addition, during steelmaking, a variety of deoxidizing and alloying elements need to be added in the RH stage, and the possibility of molten steel splashing is relatively high. In order to improve the yield of Mg and the safety of operation, the present invention adopts feeding Ni-Mg alloy cored wire into the ladle at the continuous casting station.

7) In the continuous casting stage, the pressure of 0.4MPa is used for soft stirring for 3 minutes to ensure the uniformity of Mg in the molten steel. The Mg-Ti series composite oxides formed through the above process flow into the tundish and crystallizer in sequence as the casting process progresses. , a large number of fine Mg-Ti series composite oxides are retained in the solid slab.

Compared with the prior art, the present invention has at least the following beneficial effects:

In the refining and continuous casting stages, the invention completes the alloying of Ti and Mg elements by precisely controlling the oxygen content and the superheat of molten steel, accurately grasping the timing of wire feeding, and rationally controlling the wire feeding process, so as to ensure the stable yield of alloying element Mg At 17-21%, the alloy utilization rate is improved, the alloy cost is reduced, and the Mg-Ti series composite oxides with a size of 2.0 μm and below in the slab account for 83% and above of all oxides, and the Mg-Ti series with a size of 2.0 μm and below -The volume density of the Ti series composite oxide reaches 3.7×10 ⁵ pieces/mm ² , ensuring the effect of oxide metallurgy.

detailed description

Below in conjunction with embodiment the present invention is further described in detail.

Example 1

When the LF refining station taps the steel, the oxygen content of the molten steel is 21ppm. After the molten steel is vacuum degassed and alloyed at the RH station, the net circulation is 5 minutes. The superheat of the molten steel is 72°C after the vacuum is broken, and the Ti-Fe alloy cored wire is fed at a speed of 5m/s. The Ti alloy in the core powder The content is 25%; the bottom blowing pressure of 0.6MPa is softly stirred for 6 minutes, and before the ladle is hoisted away from the RH station, ultra-low carbon carbonized rice husk is added to the liquid surface to keep it warm. Entering the continuous casting station, the superheated degree of molten steel is 28°C, the content of free oxygen is 10ppm, and 425m of Ni-Mg alloy cored wire is fed at a speed of 7m/s, and the particle size of the cored wire core powder is 0.5-2.0mm. The alloy core powder contains 2-18% Mg by weight, and is softly stirred at a pressure of 0.4 MPa for 3 minutes, and then the ladle is poured into the tundish to enter the continuous casting process.

Example 2

When the steel is tapped at the LF refining station, the oxygen content of the molten steel is 26ppm. After the molten steel is vacuum degassed and alloyed at the RH station, the net circulation is 7 minutes. After the vacuum is broken, the superheat of the molten steel is 68 ° C. The Ti-Fe alloy cored wire is fed at a speed of 5 m/s. The Ti alloy in the core powder The content is 25%; the bottom blowing pressure of 0.5MPa is softly stirred for 7 minutes, and before the ladle is hoisted away from the RH station, ultra-low carbon carbonized rice husk is added to the liquid surface to keep it warm. Entering the continuous casting station, the superheated degree of molten steel is 26°C, the free oxygen content is 17ppm, and 409m of Ni-Mg alloy cored wire is fed at a speed of 9m/s, and the particle size of the cored wire core powder is 0.5-2.0mm. The alloy core powder contains 2-18% Mg by weight, and is softly stirred at a pressure of 0.4 MPa for 3 minutes, and then the ladle is poured into the tundish to enter the continuous casting process.

Example 3

When the steel is tapped at the LF refining station, the oxygen content of the molten steel is 29ppm. After the molten steel is vacuum degassed and alloyed at the RH station, the net circulation is 8 minutes. The superheat of the molten steel is 57°C after the vacuum is broken, and the Ti-Fe alloy cored wire is fed at a speed of 5m/s. The Ti alloy in the core powder The content is 25%; the bottom blowing pressure of 0.4MPa is softly stirred for 9 minutes, and before the ladle is hoisted away from the RH station, ultra-low carbon carbonized rice husk is added to the liquid surface to keep it warm. Entering the continuous casting station, the superheated degree of molten steel is 21°C, the free oxygen content is 20ppm, and 412m of Ni-Mg alloy cored wire is fed at a speed of 10m/s, and the particle size of the cored wire core powder is 0.5-2.0mm. The alloy core powder contains 2-18% Mg by weight, and is softly stirred at a pressure of 0.4 MPa for 3 minutes, and then the ladle is poured into the tundish to enter the continuous casting process.

Comparative Example 1

When the steel is tapped at the LF refining station, the oxygen content of the molten steel is 48ppm. After the molten steel is vacuum degassed and alloyed at the RH station, the net circulation is 5 minutes, and the superheat of the molten steel is 73°C after the void is broken. Feed Ti-Fe alloy cored wire at a speed of 5m/s, and the content of Ti alloy in the core powder is 25%; softly stir for 5min with a bottom blowing pressure of 0.6MPa. Before the ladle is hoisted away from the RH station, ultra-low carbon carbonized rice husk is added to the liquid surface to keep it warm. Entering the continuous casting station, the superheated degree of molten steel is 26°C, the free oxygen content is 26ppm, and 407m of Ni-Mg alloy cored wire is fed at a speed of 7m/s, and the particle size of the cored wire core powder is 0.5-2.0mm. The alloy core powder contains 2-18% Mg by weight, and is softly stirred at a pressure of 0.4 MPa for 3 minutes, and then the ladle is poured into the tundish to enter the continuous casting process.

Comparative Example 2

When the LF refining station taps the steel, the oxygen content of the molten steel is 28ppm. After the molten steel is vacuum degassed and alloyed at the RH station, the net circulation is 5 minutes, and the superheat of the molten steel is 50°C after the void is broken. Feed Ti-Fe alloy cored wire at a speed of 5m/s, and the content of Ti alloy in the core powder is 25%; softly stir for 8min with a bottom blowing pressure of 0.5MPa. Before the ladle is hoisted away from the RH station, ultra-low carbon carbonized rice husk is added to the liquid surface to keep it warm. Entering the continuous casting station, the superheated degree of molten steel is 15°C, the content of free oxygen is 15ppm, and 410m of Ni-Mg alloy cored wire is fed at a speed of 9m/s, and the particle size of the cored wire core powder is 0.5-2.0mm. The alloy core powder contains 2-18% Mg by weight, and is softly stirred at a pressure of 0.4 MPa for 3 minutes, and then the ladle is poured into the tundish to enter the continuous casting process.

Comparative Example 3

When the steel is tapped at the LF refining station, the oxygen content of the molten steel is 29ppm. After the molten steel is vacuum degassed and alloyed at the RH station, the net circulation is 4 minutes, and the superheat of the molten steel is 63 °C after the void is broken. Feed the Ti-Fe alloy cored wire at a speed of 3m/s, and the Ti alloy content in the core powder is 25%; softly stir for 4min with a bottom blowing pressure of 0.3MPa. Before the ladle is hoisted away from the RH station, ultra-low carbon carbonized rice husk is added to the liquid surface to keep it warm. Entering the continuous casting station, the superheated degree of molten steel is 22°C, the free oxygen content is 18ppm, and 417m of Ni-Mg alloy cored wire is fed at a speed of 0.5m/s, and the particle size of the cored wire core powder is 0.5-2.0mm , the alloy core powder contains 2-18% Mg by weight. Then the ladle pours into the tundish and enters the continuous casting process.

The continuous casting process of Examples 1-3 and Comparative Examples 1-3 is used to produce medium-thick plate slabs.

Samples were taken from the steel plates of Examples 1-3 and Comparative Examples 1-3 respectively, and the chemical components were detected. The experimental results are shown in Table 1. The yield of the alloying element Mg in Example 1-3 is 17.3-28.5%, with an average of 21.7%, and the yield of the alloyed element Mg in Comparative Example 1-3 is only 7.1-10.2%, with an average of 8.4%.

Table 1 Example 1-3 and comparative example 1-3 chemical composition (wt, %) and yield (%) of Mg of the steel plate of comparative example 1-3

For Examples 1-3 and Comparative Examples 1-3, samples were taken from the slabs respectively, and statistical analysis of inclusions was carried out. The analysis results are shown in Table 2. In Examples 1-3, the proportion of oxides with a size of 2.0 μm and below is 83-87%, and the areal density of oxides with a size of 2.0 μm and below is 3.7×10 ⁵ /mm ³ and above. In Comparative Examples 1-3, the proportion of oxides with a size of 2.0 μm and below is 65-74%, and the areal density of oxides with a size of 2.0 μm and below is greater than 1.9×10 ⁵ /mm ² .

Oxide proportion and density in the slab of table 2 embodiment 1-3 and comparative example 1-3

Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that it can be described in terms of form and Various changes may be made in the details without departing from the scope of the invention defined by the claims.

Claims (2)

1. A kind of 1. oxide control method for improving magnesium recovery rate, it is characterised in that LF refining stage：During tapping in molten steel freely Oxygen scope is in 20-30ppm；The RH stages：Net circulation time 5-10min, the degree of superheat is 55-75 DEG C after molten steel breaks sky, into ladle Ti-Fe alloy core-spun yarn is fed, then uses the 0.4-0.6MPa soft stirring molten steel of pressure argon bottom-blowing, time >=5min；Even The casting stage：After ladle is hung to panoramic table, the free oxygen scope of molten steel is in 10-18ppm in ladle；Superheat of liquid steel is 20-30 DEG C, Ni-Mg alloy claded wires are fed before continuous casting into ladle, and with the soft stirring 3min of 0.4MPa pressure, subsequent ladle is to tundish Middle beam.
2. 2. the oxide control method according to claim 1 for improving magnesium recovery rate, it is characterised in that described Ti-Fe Alloy claded wire wire-feeding velocity is 4-6m/s, and Ti alloy contents are 25% in core powder；Ni-Mg alloy claded wires wire-feeding velocity is 7- 10m/s, cored core Powder Particle Size are 0.5-2.0mm, the Mg containing part by weight 2-18% in alloy core powder.