阅读说明：本技术 一种控制钢中氮含量的炼钢方法 (Steelmaking method for controlling nitrogen content in steel ) 是由 李建朝 赵国昌 李�杰 龙杰 赵晓辉 董亚楠 高雅 付冬阳 刘丹 袁平 付振坡 于 2021-08-17 设计创作，主要内容包括：一种控制钢中氮含量的炼钢方法,其特征在于,在LF精炼过程,钢液温度升至1630～1650℃,然后进行脱氧,渣白后添加合金。本发明应用范围广,所有要求控制氮含量的钢种均可使用。本发明操作方法简单,易于过程控制。本发明控制效果稳定有效,浇注毕氮含量可稳定控制在25-35ppm。(A steel-making method for controlling the nitrogen content in steel is characterized in that in the LF refining process, the temperature of molten steel is increased to 1630-1650 ℃, then deoxidation is carried out, and alloy is added after white slag is obtained. The invention has wide application range, and all steel grades which require to control the nitrogen content can be used. The method is simple in operation and easy for process control. The invention has stable and effective control effect, and the nitrogen content can be stably controlled to be 25-35ppm after the pouring is finished.)

1. A steel-making method for controlling the nitrogen content in steel is characterized in that in the LF refining process, the temperature of molten steel is increased to 1630-1650 ℃, then deoxidation is carried out, and alloy is added after white slag is obtained.

2. A steel making method capable of controlling the nitrogen content in steel as claimed in claim 1, wherein the deoxidation and aluminium feeding line amount is 500-1000 m.

3. A steelmaking method for controlling the nitrogen content in steel as claimed in claim 1, characterised in that after deoxidation, 100-200 kg of lime is added during argon blowing for desulphurisation.

4. The steelmaking method for controlling the nitrogen content in the steel as claimed in claim 1, wherein before the LF refining, the molten steel is primarily refined through an EAF furnace, the proportion of the molten iron in the EAF furnace is up to 65% -80% in the primary refining process, and the power transmission time is controlled within 14-18 min.

5. The steelmaking method for controlling the nitrogen content in steel according to claim 1, characterized in that after LF refining, VD furnace refining is performed, VD furnace refining process is performed, first vacuum is maintained for 6-8 min, ferrotitanium is added after breaking the space to perform Ti alloying, then secondary vacuum treatment is performed, vacuum is maintained for 11-15 min, and ferroboron and aluminum particles are added to perform boron alloying after vacuum is completed.

6. A steelmaking method as claimed in any one of claims 1 to 5 in which the molten steel is refined and then die cast, the gap between the nozzle and the nozzle of the central nozzle during die casting is sealed by means of an argon shield, the argon shield is a telescopic argon shield, and the telescopic cover is made of fibres of high temperature resistant material.

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a steelmaking method for controlling nitrogen content in steel.

Background

The boron is added as an alloy element, so that the performance of the wide and thick plate can be effectively improved, a large amount of noble metal alloy is replaced, and the cost is saved. The solubility of boron in steel is very low, the affinity with oxygen and nitrogen is very strong, boron nitride or boron oxide is directly generated under smelting conditions, and the recovery rate of boron is reduced; boron and nitrogen in steel easily form boron nitride precipitates at prior austenite grain boundaries, thereby causing grain boundary embrittlement and weakening the strengthening effect of boron. In order to make boron play a positive role, solid solution boron must be obtained, the recovery rate of boron is improved, and the generation of boron nitride is reduced, so that the control of the nitrogen content in the smelting process is the key for improving the performance qualification rate of boron-added steel.

Disclosure of Invention

Based on the reasons, the invention provides a steelmaking method for controlling the nitrogen content in steel, which can reduce the nitrogen increase of molten steel and reduce the nitrogen content in steel.

The technical scheme of the invention is as follows: a steel-making method for controlling the content of nitrogen in steel comprises the steps of heating molten steel to 1630-1650 ℃ in an LF refining process, then deoxidizing, adding alloy after white slag.

Further, the wire amount of the aluminum feeding is 500-1000 m in the deoxidation process.

Further, after deoxidation, 100-200 kg of lime is added during argon blowing desulfurization.

Further, before LF refining, molten steel is primarily refined through an EAF furnace, in the primary refining process of the EAF furnace, the ratio of the molten iron reaches 65-80%, and the power transmission time is controlled to be 14-18 min.

Further, after LF refining, VD furnace refining is carried out, the VD furnace refining process is carried out, the first vacuum maintaining time is 6-8 min, ferrotitanium is added for Ti alloying after the vacuum breaking, then the second vacuum treatment is carried out, the vacuum maintaining time is 11-15 min, and ferroboron and aluminum particles are added for boron alloying after the vacuum is finished.

Further, die casting is carried out after the molten steel is refined, and the clearance between die casting process mouth of a river and the well sprue adopts argon gas protection device to seal, argon gas protection device is scalable argon gas protection device, and its flexible cover comprises the fibre of high temperature resistant material.

The diameter of the aluminum wire is as follows: 11.5-12.8 mmm.

After the deoxidation, 100-200 kg of lime is added during argon blowing desulfurization, namely during LF refining, the temperature of molten steel is raised to 1630-1650 ℃, then a deoxidizer is added for deoxidation, and then 100-200 kg of lime is added during argon blowing desulfurization.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

1. the invention has wide application range, and all steel grades which require to control the nitrogen content can be used.

2. The method is simple in operation and easy for process control.

3. The invention has stable and effective control effect, and the nitrogen content can be stably controlled to be 25-35ppm after the pouring is finished.

Detailed Description

The reason for establishing the process parameters will be explained below.

In the LF refining process, the temperature of molten steel is increased to 1630-1650 ℃, then deoxidation is carried out, and alloy is added after white slag is obtained.

Further, the wire amount of the aluminum feeding is 500-1000 m in the deoxidation process.

Further, after deoxidation, 100-200 kg of lime is added during argon blowing desulfurization.

The invention is refined in an LF furnace, and deep deoxidation alloying operation is carried out in the stage of ladle slagging and heating to a high temperature. In the LF refining process, nitrogen mainly comes from electric arc decomposing furnace gas, air in contact with molten steel, added alloy, flux and the like. As the refining time is prolonged, the phenomenon of nitrogen absorption of molten steel is more and more serious. Because the surface activity of oxygen and sulfur can prevent molten steel from absorbing nitrogen, the nitrogen increase amount in the process can be reduced by adopting molten steel to be heated to high temperature and then carrying out deep deoxidation alloying in the refining process.

Before LF refining, molten steel is primarily refined through an EAF furnace, in the primary refining process of the EAF furnace, the molten iron proportion reaches 65% -80%, and the power transmission time is controlled to be 14-18 min.

The invention adopts the electric furnace smelting process to control the proportion of molten iron and the power transmission time, the electric furnace smelting process has both a nitrogen increasing process and a nitrogen removing process, high-voltage electric arc decomposes furnace gas, so that a large amount of nitrogen is absorbed by exposed molten steel, and simultaneously, bubbles are generated by carbon-oxygen reaction, so that part of nitrogen in the molten steel can be removed. The proportion of the molten iron is increased, the power transmission time can be reduced, the nitrogen absorption amount of the molten steel is reduced, the carbon distribution amount is increased, the carbon-oxygen reaction is enhanced, the discharge of nitrogen is promoted, and the nitrogen content is controlled at a lower level (N) from the source]＜80×10 ^-6) And the refining and vacuum nitrogen control pressure is reduced.

And after LF refining, carrying out VD furnace refining, wherein the VD furnace refining process is carried out, the first vacuum maintaining time is 6-8 min, ferrotitanium is added for Ti alloying after the vacuum is broken, then the second vacuum treatment is carried out, the vacuum maintaining time is 11-15 min, and after the vacuum is finished, ferroboron and aluminum particles are added for boron alloying.

The invention adds ferrotitanium and ferroboron by controlling temperature by stages in a VD process. The VD vacuum denitrification efficiency is limited due to the influence of factors such as nitrogen atom radius size, vacuum degree and process temperature drop, [ N ]]≤40×10 ^-6Then, VD has extremely low denitrification efficiency. Elements in steelThe deoxidation capacity of the elements is that Al is more than Ti, more than Si, more than B, more than Mn, more than C and more than Fe from large to small, the denitrification capacity is that Ti is more than B, more than Al from large to small, and after the first vacuum, ferrotitanium is effectively added under the condition of lower free nitrogen content for deep denitrification. The ferroboron and the aluminum particles are added in proportion, so that the boron is added under the condition of low free nitrogen content, and the recovery rate of the boron is ensured.

Carrying out die casting after the molten steel is refined, sealing a gap between a water gap and a pouring gate of a middle injection pipe in the die casting process by adopting an argon protection device, wherein the argon protection device is a telescopic argon protection device, and a telescopic cover of the argon protection device is composed of fibers made of high-temperature-resistant materials.

The invention uses argon protection device to cast steel. After VD, the oxygen and sulfur contents in the molten steel reach extremely low levels, the nitrogen absorption of the molten steel is not hindered, and the oxygen and nitrogen can be absorbed as long as the molten steel is in contact with air. The argon protection device is scalable argon protection device, and scalable cover is by the fibre constitution of high temperature resistant material, and the pouring process does not have damaged phenomenon, and the effectual clearance of having sealed between mouth of a river and the well notes pipe runner, and then form stable protective atmosphere, reached the anticipated effect of argon protection pouring.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The chemical components and the weight percentage of the steel grades produced in the embodiments 1-6 are shown in table 1, pcm is a cold crack sensitivity index, ceq is carbon equivalent, and the cold crack sensitivity index pcm is a method for indirectly judging the weldability of the steel, and mainly used for judging the cold crack tendency of the steel. The larger the cold crack sensitivity index is, the more the steel tends to crack during welding, and the weldability is poor.

The smelting process comprises the working procedures of electric furnace refining, LF refining, VD refining and die casting, and the specific process steps are as follows:

(1) the primary smelting process of the EAF furnace comprises the following steps: the amount of molten iron added, the proportion of the molten iron added and the power transmission time are shown in table 2, the nitrogen content of the molten steel during tapping is shown in table 3, the tapping ladle sample C is less than or equal to 0.04wt%, the P is less than or equal to 0.007 wt%, and the ladle temperature is more than or equal to 1600 ℃.

(2) And (3) refining in an LF furnace: and (3) submerged arc heating is carried out by adding lime fluorite into the ladle, the manganese is adjusted to be about 1.0wt% in the process, when the temperature is increased to T, an aluminum wire is fed, the temperature T and the feeding amount of the aluminum wire are shown in the table 2, after slag is white, bucket-loaded alloy is added, the total refined ash amount is more than or equal to 1200 kg/furnace, the time of white slag is more than or equal to 20min, submerged arc power transmission operation is strictly forbidden after aluminum feeding, molten steel exposure is controlled by adding lime during argon blowing desulfurization, the lime adding amount is shown in the table 2, and water slag and thick slag are forbidden under the condition of ladle slag suspension. The liquid nitrogen content of the LF refined finished steel is shown in Table 3.

(3) VD vacuum treatment process: controlling the temperature and components in the vacuum process stage, finely adjusting the alloy according to a target value before vacuum, and feeding no aluminum before vacuum; the first hold time is shown in table 2, after hold argon flow: 100 plus 150L/min, breaking the blank, sampling, adding 0.015-0.020% Ti iron, and taking the first breaking temperature of 1625 ℃ as the target. Opening double argon to be more than or equal to 300L/min when adding ferrotitanium, setting the diameter of an argon blowing opening to be more than or equal to 300mm, pumping back again, keeping the time as shown in table 2, setting the total pumping time by taking 1580 ℃ of secondary vacuum breaking as a target value, adding ferroboron of 0.0005-0.0015% at the position of the argon blowing opening after the secondary vacuum breaking, mixing and adding ferroboron and aluminum particles according to a proportion, opening double argon to be more than or equal to 300L/min when adding ferroboron, setting the diameter of the argon blowing opening to be more than or equal to 300mm, pumping back argon for 5min of 20-50L/min after adding ferroboron, breaking and sampling again, and finishing VD refining, wherein the nitrogen content is shown in table 3.

(4) Die casting pouring procedure: the body is poured for 16min, the riser is poured for 4min, a gap between a water gap and a pouring gate of the middle injection pipe in the pouring process is sealed by adopting an argon protection device, the argon protection device is a telescopic argon protection device, and a telescopic cover of the argon protection device is made of fibers made of high-temperature-resistant materials. The argon protection device does not damage the cast steel, and the nitrogen content after the casting is shown in table 3.

TABLE 1

TABLE 2

TABLE 3

Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.