KR20220035339A - Polar steel smelting method to control inclusions - Google Patents

Abstract

A polar steel smelting method that controls inclusions, the method forms and grows MnS on finely distributed Zr-Ti composite oxide core particles first formed in the solidification step through Zr-Ti deoxidized high-strength low-alloy steel. Accordingly, the formed MnS covers the fine spherical oxides and is distributed uniformly within the steel, and this structure improves the toughness of the steel. At the same time, a manganese depletion zone is created around MnS, which promotes the formation of needle-shaped ferrite and further improves the toughness of the steel through fine grain reinforcement. In addition, a large amount of finely and uniformly dispersed oxide is advantageous in uniformizing the structure of steel and increasing strength. Compared with conventional Al deoxidation, the malleability and toughness of the steel sheet are improved correspondingly, the corrosion current density is lower than 6mA/cm ² , the corrosion active inclusions are reduced by half, and the local corrosion rate of the steel sheet is lowered. This ensures the service life of the steel plate and satisfies the demand for 36 kg steel for polar use.

Description

Polar steel smelting method to control inclusions

The present invention belongs to the field of steelmaking technology, and specifically relates to a method of smelting polar steel to control inclusions.

Currently, there is a lack of research in the polar field in Korea, and we do not yet have the ability to design polar icebreakers. The deck steel of the Sherung was imported from Ukraine, and the Sherung 2 was designed in Finland. Polar icebreakers have poor commissioning conditions, so steel plates are required to have characteristics such as high toughness, high corrosion resistance, high wear resistance, and easy welding. Particularly high demands are placed on resisting seawater corrosion, requiring extremely demanding control measures and capabilities for inclusions, precipitates, texture and microscopic defects. Inclusions are distributed inside and on the surface of steel, and if the outer coating layer of an icebreaker is broken, it becomes a major cause of corrosion in poor service environments. The key to ensuring that steel base materials and weld joints can withstand seawater corrosion is technology to control corrosion-active inclusions in steel. The local corrosion rate of a steel sheet is determined by the content of corrosion-active non-metallic impurities in the steel. If the corrosion-active inclusions in the steel are lower than 2/mm ² , the local corrosion rate of the steel sheet can be effectively lowered to ensure the service life of the steel sheet.

To overcome the deficiencies of the prior art, the present invention provides a method for smelting polar steel with controlled inclusions. This smelting method effectively controls the corrosion active inclusions in the steel and reduces the local corrosion rate of the steel sheet, thereby ensuring the service life of the steel sheet and meeting the demand for 36 kg steel for polar use.

In the polar steel smelting method for controlling inclusions according to the present invention, the process route for smelting molten steel includes KR molten iron pretreatment → BOF upper and lower composite blowing converter → LF refining furnace → RH refining furnace,

It includes the following steps:

(1) If the mass percentage content of non-ferrous metal in molten iron is selected as Sn≤0.010%, Pb≤0.005%, As≤0.020, Sb≤0.010, Zn≤0.010, trial production is performed. During molten iron pretreatment, molten iron flowing into the blast furnace is guaranteed to have S≤0.0020% and slag removal of over 90%.

(2) Test production is carried out in a situation where the converter bottom smell and blast furnace conditions are good, the converter is subjected to slag formation work several times using activated lime, and the end points P and S are all controlled to less than 0.008%. The free oxygen in tap steel is controlled to 400 to 600 ppm, and the final carbon mass percentage content is controlled to 0.04 to 0.06%.

(3) When tapping steel in a converter, primary deoxygenation and alloying are performed using silicon iron and uncarboned manganese iron or silicon iron and manganese.

(4) After reaching the LF refining furnace, the [O] content in the steel is measured and recorded, and the oxygen content in the molten steel is controlled and maintained at 20 to 60 ppm. Then, low-aluminum Fe-Ti alloy and Fe-Zr alloy are added and deoxidation and alloying are performed.

(5) Low-aluminum Fe-Ti alloy and Fe-Zr alloy are refined for more than 3 minutes after deoxidation and alloying. Measure and record the [O] content in the steel, and if more than 10 ppm of free oxygen exists in the steel, add 10 to 20 kg of Si-Ca-Ba alloy and supplement deoxygenation.

(6) Proceed with the deS process. The addition of aluminum wire is prohibited during the deS process. When the deS process is completed, Al line is added according to the target component.

(7) In the RH refining furnace, inclusions are removed, degassed, and vacuum chamber oxygen blown. It is carried out with a holding time ≥ 20 min under the conditions of an oxygen intake amount of 50 m ³ and a vacuum level of ≤ 5.0 mbar. Once the RH degassing treatment is completed, calcium treatment is performed according to the target ingredient 3 minutes before exit.

Here, in the converter smelting process, pure molten iron operation is selected or waste steel whose non-ferrous metal components meet the requirements is selected to be used as the blast furnace inlet material.

In step (3), during the first deoxygenation and alloying, silicon iron is mixed at 0.10 to 0.18% of Si, and uncarboned manganese iron or metal manganese is mixed at 0.93 to 0.98% of Mn.

In step (4), the method of controlling and maintaining the oxygen content in the molten steel at 20 to 60 ppm is as follows. If the oxygen content in the molten steel is more than 60 ppm, ferrosilicon is added and deoxygenation is performed until the oxygen content in the molten steel reaches 20 to 60 ppm, depending on the estimate.

In step (4), a total of 10 to 70 kg of low aluminum Fe-Ti alloy and Fe-Zr alloy are added and deoxidation and alloying are performed.

In step (4), the low aluminum Fe-Ti alloy and the Fe-Zr alloy are added together, and when the amount of both added is converted according to the target composition and alloy content, the conversion coefficient for the Zr content is 60%.

In step (6), during the desulfurization process, an appropriate amount of Al powder is uniformly sprinkled on the slag surface and diffusion deoxygenation is performed. When adding Al powder, argon gas is controlled according to the static stirring method.

In the above smelting method, MnS is formed and grown on finely distributed Zr-Ti composite oxide core particles first formed in the solidification step through Zr-Ti deoxidized high-strength low-alloy steel. Therefore, the formed MnS covers the fine spherical oxide and is distributed uniformly within the steel, and this structure improves the toughness of the steel. In addition, MnS is formed on Zr-Ti oxide, which creates a manganese-depleted zone around it, promoting the formation of needle-shaped ferrite, which further improves the toughness of steel through fine particle strengthening. In addition, a large amount of finely and uniformly dispersed oxide is advantageous in uniformizing the structure of steel and increasing strength. Compared with conventional Al deoxidation, the ductility and toughness of Zr-Ti deoxidation steel sheet were improved correspondingly, the corrosion current density was lower than 6mA/cm ² , and the corrosion active inclusions were reduced by half. Accordingly, by lowering the local corrosion rate of the steel plate, the service life of the steel plate can be guaranteed and the demand for 36kg steel for polar use can be satisfied.

1 is an external view of an inclusion.
Figure 2 is a distribution chart of inclusion sizes.
Figure 3 is a component energy spectrum analysis diagram of inclusions according to an example.

Hereinafter, the present invention will be described in more detail, taking as an example a special deck produced by the method described in the present invention.

The process sequence for producing the special deck includes KR molten iron pretreatment → BOF upper and lower composite blowing converter → LF refining furnace → RH refining furnace → continuous casting machine.

The specific steps are as follows.

(1) Test production is conducted when the mass percentage content of non-ferrous metals Sn, Pb, As, Bi, Sb, and Zn in molten iron is low. Here, Sn ≤ 0.010%, Pb ≤ 0.005%, As ≤ 0.020, Sb ≤ 0.010, Zn ≤ 0.010, S ≤ 0.0020% of molten iron flowing into the blast furnace during molten iron pretreatment, and slag removal of over 90% are guaranteed.

(2) In order to reduce various impurity elements in the raw materials, choose to work with pure molten iron or choose to use high-quality waste steel whose non-ferrous metal components meet the requirements as the blast furnace inlet material. Test production is carried out in a situation where the converter bottom smell and blast furnace conditions are good, and the converter uses activated lime to form slag several times, and the end points P and S are all controlled to less than 0.008%. The free oxygen in tap steel is controlled to 400 to 600 ppm, and the final carbon mass percentage content is controlled to 0.04 to 0.06%.

(3) When tapping steel in a converter, primary deoxygenation and alloying are performed using silicon iron and uncarboned manganese iron or silicon iron and manganese. Si is mixed with 0.10 to 0.18% of silicon iron, and Mn is mixed with 0.93 to 0.98% of uncarboned manganese iron or metal manganese. In addition, deoxidation and alloying are performed without using Al-containing materials.

(4) After reaching the LF refining furnace, the [O] content in the steel is measured and recorded using a rapid oxygen measuring probe, and the oxygen content in the molten steel is controlled and maintained at 20 to 60 ppm. If the oxygen content in the molten steel is more than 60 ppm, ferrosilicon is added and deoxygenation is performed until the oxygen content in the molten steel reaches 20 to 60 ppm, depending on the estimate. Then, 10 to 70 kg of low aluminum Fe-Ti alloy and Fe-Zr alloy are added and deoxidation and alloying are performed. Low-aluminum Fe-Ti alloy and Fe-Zr alloy are added together, and when the addition amount of both is converted according to the target composition and alloy content, the conversion coefficient for Zr content is 60%.

(5) Low-aluminum Fe-Ti alloy and Fe-Zr alloy are refined for more than 3 minutes after deoxidation and alloying. Measure and record the [O] content in the steel using a rapid oxygen measuring probe. If more than 10 ppm of free oxygen exists in the steel, add 10 to 20 kg of Si-Ca-Ba alloy and supplement deoxidation.

(6) Proceed with the deS process. During the deS process, the addition of aluminum wire is prohibited, and an appropriate amount of Al powder can be evenly sprinkled on the slag surface to perform diffusion deoxygenation. When adding Al powder, argon gas is controlled according to the static stirring method.

When the deS process is completed, Al line is added according to the target component.

(7) In the RH refining furnace, inclusions are removed, degassed, and vacuum chamber oxygen blown. It is carried out with a holding time ≥ 20 min under the conditions of an oxygen intake amount of 50 m ³ and a vacuum level of ≤ 5.0 mbar. Once the RH degassing treatment is completed, calcium treatment is performed according to the target ingredient 3 minutes before exit.

Looking at the steel sheet impact performance, after the process improvement, the steel sheet impact performance has been significantly improved to -120 degree steel sheet impact≥200J, the average tensile strength of the steel sheet is 605Mpa, which has a large margin, and the steel sheet tensile requirement is 490~620Mpa, so the tensile strength is close to the upper limit. .

Combining Figures 1 to 3, the number of corrosion-active inclusions in the steel is 1.87/mm ² and the average current density is 5.78 mA/cm ² , which can effectively lower the local corrosion rate of the steel sheet and ensure the service life of the steel sheet.

Claims (7)

In the polar steel smelting method for controlling inclusions,
The process route for smelting molten steel includes KR molten iron pretreatment → BOF upper and lower complex blowing converter → LF refining furnace → RH refining furnace,
The following steps,
(1) If the mass percentage content of non-ferrous metal in molten iron is selected as Sn≤0.010%, Pb≤0.005%, As≤0.020, Sb≤0.010, Zn≤0.010, trial production is performed; In the molten iron pretreatment, ensuring that the molten iron flowing into the blast furnace has S≤0.0020% and slag removal of 90% or more;
(2) Proceed with test production in a situation where the converter bottom and blast furnace conditions are good, the converter uses activated lime to form slag several times, and the end points P and S are all controlled to 0.008% or less; Controlling the tapping free oxygen to 400 to 600 ppm and controlling the final carbon mass percentage content to 0.04 to 0.06%;
(3) performing primary deoxygenation and alloying using silicon iron and uncarboned manganese iron or silicon iron and manganese when tapping steel in a converter;
(4) After reaching the LF refining furnace, measure and record the [O] content in the steel, and control and maintain the oxygen content in the molten steel at 20 to 60 ppm; Then, adding low-aluminum Fe-Ti alloy and Fe-Zr alloy and proceeding with deoxidation and alloying;
(5) low-aluminum Fe-Ti alloy and Fe-Zr alloy are deoxidized and alloyed and then refined for more than 3 minutes; Measure and record the [O] content in the steel, and if more than 10 ppm of free oxygen exists in the steel, add 10 to 20 kg of Si-Ca-Ba alloy and supplement deoxygenation;
(6) Proceed with the deS process work. During the deS process, the addition of aluminum wire is prohibited; When the deS process is completed, adding Al line according to the target component;
(7) In the RH refining furnace, inclusion removal and degassing treatment and vacuum chamber oxygen blowing are carried out, and the holding time is ≥ 20 min under the conditions of oxygen blowing amount of 50 m ³ and vacuum degree ≤ 5.0 mbar; A polar steel smelting method for controlling inclusions, comprising the step of performing calcium treatment according to the target composition 3 minutes before release when the RH degassing treatment is completed. According to paragraph 1,
A polar steel smelting method for controlling inclusions, characterized in that in the converter smelting process, pure molten iron operation is selected or waste steel whose non-ferrous metal content satisfies the requirements is selected to be used as a blast furnace inlet material. According to paragraph 1,
In step (3), during the first deoxidation and alloying, silicon iron is mixed at 0.10 to 0.18% of Si, and uncarboned manganese iron or metal manganese is mixed at 0.93 to 0.98% of Mn. Polar steel smelting method to control inclusions. According to paragraph 1,
In the above step (4), the method of controlling and maintaining the oxygen content in the molten steel at 20 to 60 ppm is that, if the oxygen content in the molten steel is more than 60 ppm, ferrosilicon is added until the oxygen content in the molten steel reaches 20 to 60 ppm according to the estimate. A polar steel smelting method for controlling inclusions, characterized by adding and deoxidizing them. According to clause 4,
In step (4), a polar steel smelting method for controlling inclusions, characterized in that a total of 10 to 70 kg of low aluminum Fe-Ti alloy and Fe-Zr alloy are added and deoxidation and alloying are performed. According to clause 5,
In step (4), the low aluminum Fe-Ti alloy and the Fe-Zr alloy are added together, and when the addition amount of both is converted according to the target composition and alloy content, the conversion coefficient for the Zr content is 60%. Polar steel smelting method to control inclusions. According to paragraph 1,
In step (6), during the desulfurization process, an appropriate amount of Al powder is uniformly sprinkled on the slag surface and diffusion deoxygenation is performed; A polar steel smelting method for controlling inclusions, characterized in that when adding Al powder, argon gas is controlled according to a static stirring method.