阅读说明：本技术 一种含氮钢的冶炼方法 (Method for smelting nitrogen-containing steel ) 是由 高振波 龚志翔 李小虎 王尚 陶承岗 何云龙 于 2019-10-21 设计创作，主要内容包括：本发明公开了一种含氮钢的冶炼方法,含氮钢的氮含量为80～200ppm,其工艺路线为：电炉—LF精炼—RH—连铸；电炉采用转炉；连铸采用模铸。在RH的真空全过程中采用氮气作为提升气体,氮气压力为1.0～2.0MPa。采用上述技术方案,RH提升气体的流量可以精确控制,增氮效果易于控制；与钢水充分接触,形成有效的循环,钢水的流场更加稳定；钢水的平衡氮含量远远超过80ppm,真空过程中使用氮气作为提升气体,增氮与真空脱氮的平衡随着钢水氮含量的提高逐步平稳,30～300mbar的真空度下钢水氮含量无法超过钢种的判钢要求,避免了氮含量超标带来的损失。(The invention discloses a method for smelting nitrogen-containing steel, wherein the nitrogen content of the nitrogen-containing steel is 80-200 ppm, and the process route is as follows: electric furnace-LF refining-RH-continuous casting; the electric furnace adopts a converter; the continuous casting adopts die casting. And nitrogen is used as lifting gas in the whole RH vacuum process, and the pressure of the nitrogen is 1.0-2.0 MPa. By adopting the technical scheme, the flow of RH lifting gas can be accurately controlled, and the nitrogen increasing effect is easy to control; the molten steel is fully contacted with molten steel to form effective circulation, and the flow field of the molten steel is more stable; the balance nitrogen content of the molten steel is far more than 80ppm, nitrogen is used as lifting gas in the vacuum process, the balance of nitrogen increasing and vacuum denitrification is gradually and stably realized along with the improvement of the nitrogen content of the molten steel, the nitrogen content of the molten steel cannot exceed the steel judgment requirement of steel types under the vacuum degree of 30-300 mbar, and the loss caused by the excessive nitrogen content is avoided.)

1. A method for smelting nitrogen-containing steel, wherein the nitrogen content of the nitrogen-containing steel is 80-200 ppm, and the method is characterized by comprising the following steps: the process route of the smelting method is as follows: electric furnace-LF refining-RH-continuous casting; the electric furnace adopts a converter; the continuous casting adopts die casting.

2. The method for smelting nitrogen-containing steel according to claim 1, wherein: and nitrogen is used as lifting gas in the whole RH vacuum process, and the pressure of the nitrogen is 1.0-2.0 MPa.

3. A method of smelting a nitrogen-containing steel as claimed in claim 2, wherein: in the degassing process of the vacuum whole process, the nitrogen flow is 300-1800 normal liters/minute, the vacuum degree is kept for more than 5 minutes after reaching below 100Pa, and the content of [ H ] is ensured to be less than or equal to 1.5 ppm.

4. A method of smelting a nitrogen-containing steel as claimed in claim 2, wherein: in the degassing process of the vacuum whole process, the nitrogen flow is adjusted to 500-2200 standard liters per minute, the vacuum degree is adjusted to 30-300 mbar by adjusting the vacuum pump, and the vacuum is broken after the vacuum is maintained for 10-25 minutes.

5. The method for smelting nitrogen-containing steel according to claim 1, wherein: the smelting method is applied to a nitrogen control process of 38MNVS5 nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 10 minutes, the nitrogen flow is 800 liters/minute, and the hydrogen [ H ] is determined to be 0.9 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 150mbar, the flow rate of the lifting gas is kept at 1000 liters/minute, the keeping time is 18 minutes, and after RH vacuum breaking, an oxygen and nitrogen sample is taken for analysis, and the nitrogen content is 146 ppm.

6. The method for smelting nitrogen-containing steel according to claim 1, wherein: the smelting method is applied to a nitrogen control process of FM8T nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 12 minutes, the nitrogen flow rate is 1800 liters/minute, and the hydrogen [ H ] is determined to be 0.7 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 250mbar, the flow rate of the lifting gas is kept at 1600 liters/minute, the keeping time is 15 minutes, and after RH vacuum breaking, an oxygen and nitrogen sample is taken for analysis, and the nitrogen content is 159 ppm.

7. The method for smelting nitrogen-containing steel according to claim 1, wherein: the smelting method is applied to a nitrogen control process of 36MnVS4 nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 10 minutes, the nitrogen flow rate is 1800 liters/minute, and the hydrogen [ H ] is determined to be 0.8 ppm;

after the vacuum degree was adjusted, the vacuum degree was maintained at 200mbar, the lift gas flow was maintained at 1800 liters/min, the hold time was 20 minutes, and after the RH vacuum break, an oxygen/nitrogen sample was taken for analysis, and the nitrogen content was 171 ppm.

8. The method for smelting nitrogen-containing steel according to claim 1, wherein: the smelting method is applied to a nitrogen control process of 18CrNiMo7-6 nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 10 minutes, the nitrogen flow rate is 1400L/min, and the hydrogen [ H ] is determined to be 0.8 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 80mbar, the flow rate of the lifting gas is kept at 800 liters/minute, the keeping time is 15 minutes, and after RH vacuum breaking, an oxygen and nitrogen sample is taken for analysis, and the nitrogen content is 105 ppm.

Technical Field

The invention belongs to a smelting method of nitrogen-containing steel, in particular to a smelting method for realizing rapid and accurate nitrogen control through an RH refining process, which is suitable for steel grades with the nitrogen content requirement of 80-200 ppm.

Background

In the steel market, especially in the fields of automotive steels and high-grade tube blank steels, many steel grades have strict requirements on the nitrogen content of finished steel products, such as: the nitrogen content of the steel 38MnVS5 for the automobile crankshaft is required to be 130-170 ppm; the nitrogen content of the non-quenched and tempered steel 36MnVS4 for the expansion-broken connecting rod is required to be 150-200 ppm; the nitrogen content of the gear steel ZF7B is required to be more than or equal to 120 ppm.

For the mainstream production process of the steel products at present, the nitrogen content of molten steel is reduced to be below 80ppm after vacuum degassing, then nitrogen-containing alloy (vanadium-nitrogen alloy, manganese nitride, high-nitrogen ferrochrome and the like) is added after vacuum treatment, or a nitrogen line is fed after vacuum is finished, or the nitrogen content is controlled by blowing nitrogen from the bottom of a steel ladle, or the nitrogen content of the steel is controlled by matching of three methods, so that the control of the nitrogen content of the steel can be basically realized, but the following problems exist:

1. the purity of the molten steel is higher after vacuum, and the nitrogen increasing material is additionally added, so that the risk of secondary oxidation pollution to the molten steel is increased, and the fluctuation of the product quality is caused;

2. the cost is high, taking nitrogen control by using nitrogen and the nitrogen content of the molten steel is 150ppm as an example, the nitrogen content of the molten steel after vacuum degassing is 50ppm, 1.5kg/t steel of nitrogen line is needed for increasing 100ppm of nitrogen, and the cost of steel per ton is increased by 20 yuan calculated according to the market price of 13000 yuan/ton;

3. the steel ladle is used for blowing nitrogen gas in a low way, so that the stable control of nitrogen content is difficult to realize, the treatment period is long, the steel-making efficiency is influenced, and the stable and smooth operation of production is not facilitated.

For controlling the nitrogen content of molten steel in the steelmaking process, a series of researches and achievements exist at present, such as:

1. the Chinese invention patent (CN201510366458) discloses a method for smelting nitrogen-containing steel, nitrogen-containing steel with the nitrogen content of 0.010-0.030% can be produced by bottom blowing nitrogen in a VD vacuum process and bottom blowing nitrogen in a soft blowing process, and the effect of bottom blowing nitrogen is fluctuated by the VD process;

2. the Chinese invention patent (CN200810243439) discloses a nitrogen increasing method in a nitrogen-containing gear steel production process, which realizes the accurate control of nitrogen content by bottom blowing nitrogen and timing sampling detection, and the method needs nitrogen-containing alloy for preliminary adjustment, has higher cost, and simultaneously performs timing sampling analysis on the nitrogen content, has long inspection period and slow production rhythm;

3. the Chinese invention patent (CN201310230261) discloses a method for controlling carbon and oxygen in the production of an automobile panel by a vacuum circulation degassing furnace, wherein the nitrogen is increased in vacuum by adopting nitrogen as a circulation gas in RH, so that the nitrogen content of steel for the automobile panel can be controlled to be about 0.0030 percent, and the method is not suitable for producing molten steel with the content of more than 80-200 ppm;

4. in the saddle steel technology, 6 th year 2014, the article "smelting vanadium-nitrogen microalloyed steel by a gas nitrogen-adding method" introduces that RH lifting gas uses nitrogen, RH vacuum degree is controlled to 5KPa, nitrogen is blown from the bottom of a rotary kiln before RH feeding, the nitrogen content of the vanadium-nitrogen microalloyed steel can be adjusted to 118ppm, but only aiming at one steel type with the vanadium content of 0.03-0.05%, the patent has no requirement on molten steel components, and is completely different from the patent in key parameters such as vacuum degree control, flow control and the like, on the other hand, the patent has no requirement on the nitrogen content of the molten steel before RH processing and is different from the above-mentioned paper;

5. the Chinese invention patent (201510682746.X) discloses an RH dehydrogenation nitrogen increasing process for nitrogen-containing steel, wherein the vacuum degree is 4-6 KPa, the nitrogen increasing rate is 2-3 ppm/min, and related parameters and effects of the process are completely different from those of the application patent, in fact, the nitrogen increasing efficiency of molten steel has a direct relation with component content, and according to the process and parameters of the process, the nitrogen increasing rate is more than 4ppm/min even for the steel which is most difficult to increase nitrogen.

In conclusion, the rapid and accurate control of the nitrogen content of the molten steel of the high-grade steel grade which contains 80-200 ppm of nitrogen and needs to be subjected to RH vacuum treatment is a great problem in the smelting process.

Disclosure of Invention

The invention provides a method for smelting nitrogen-containing steel, and aims to accurately control the nitrogen content of molten steel after RH refining of the nitrogen-containing steel.

In order to achieve the purpose, the invention adopts the technical scheme that:

the smelting method of the nitrogen-containing steel has the nitrogen content of 80-200 ppm, and the process route of the smelting method is as follows: electric furnace-LF refining-RH-continuous casting; the electric furnace adopts a converter; the continuous casting adopts die casting.

And nitrogen is used as lifting gas in the whole RH vacuum process, and the pressure of the nitrogen is 1.0-2.0 MPa.

In the degassing process of the vacuum whole process, the nitrogen flow is 300-1800 normal liters/minute, the vacuum degree is kept for more than 5 minutes after reaching below 100Pa, and the content of [ H ] is ensured to be less than or equal to 1.5 ppm.

In the degassing process of the vacuum whole process, the nitrogen flow is adjusted to 500-2200 standard liters per minute, the vacuum degree is adjusted to 30-300 mbar by adjusting the vacuum pump, and the vacuum is broken after the vacuum is maintained for 10-25 minutes.

The smelting method is applied to a nitrogen control process of 38MNVS5 nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 10 minutes, the nitrogen flow is 800 liters/minute, and the hydrogen [ H ] is determined to be 0.9 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 150mbar, the flow rate of the lifting gas is kept at 1000 liters/minute, the keeping time is 18 minutes, an oxygen and nitrogen sample is taken for analysis after RH vacuum breaking, the nitrogen content is 146ppm, and the internal control requirement of 130-170 ppm is met.

The smelting method is applied to a nitrogen control process of FM8T nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 12 minutes, the nitrogen flow rate is 1800 liters/minute, and the hydrogen [ H ] is determined to be 0.7 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 250mbar, the flow rate of the lifting gas is kept at 1600 liters/minute, the holding time is 15 minutes, an oxygen and nitrogen sample is taken for analysis after RH vacuum breaking, the nitrogen content is 159ppm, and the internal control requirement of being more than or equal to 120ppm is met.

The smelting method is applied to a nitrogen control process of 36MnVS4 nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 10 minutes, the nitrogen flow rate is 1800 liters/minute, and the hydrogen [ H ] is determined to be 0.8 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 200mbar, the flow rate of the lifting gas is kept at 1800 liters/minute, the keeping time is 20 minutes, an oxygen and nitrogen sample is taken for analysis after RH vacuum breaking, the nitrogen content is 171ppm, and the internal control requirement of 160-180 ppm is met.

The smelting method is applied to a nitrogen control process of 18CrNiMo7-6 nitrogen-containing steel:

nitrogen is used as lifting gas;

the vacuum cycle time below 100Pa is 10 minutes, the nitrogen flow rate is 1400L/min, and the hydrogen [ H ] is determined to be 0.8 ppm;

after the vacuum degree is adjusted, the vacuum degree is kept at 80mbar, the flow rate of the lifting gas is kept at 800 liters/minute, the keeping time is 15 minutes, an oxygen and nitrogen sample is taken for analysis after RH vacuum breaking, the nitrogen content is 105ppm, and the internal control requirement of 90-150 ppm is met.

By adopting the technical scheme, the flow of RH lifting gas can be accurately controlled, the pipeline is stable, the fluctuation caused by gas leakage of a pipeline joint and poor bottom blowing air brick effect is avoided, and the nitrogen increasing effect is easy to control; the molten steel is fully contacted with molten steel to form effective circulation, and the flow field of the molten steel is more stable; the balance nitrogen content of the molten steel is far more than 80ppm, nitrogen is used as lifting gas in the vacuum process, the balance of nitrogen increasing and vacuum denitrification is gradually and stably realized along with the improvement of the nitrogen content of the molten steel, the nitrogen content of the molten steel cannot exceed the steel judgment requirement of steel types under the vacuum degree of 30-300 mbar, and the loss caused by the excessive nitrogen content is avoided.

Detailed Description

The following examples are included to provide further detailed description of the present invention and to provide those skilled in the art with a more complete, concise, and exact understanding of the principles and spirit of the invention.

The invention relates to a steelmaking process for accurately controlling nitrogen of nitrogen-containing steel through RH refining. In order to overcome the defects of the prior art and realize the purpose of accurately controlling the nitrogen content of molten steel after RH refining of nitrogen-containing steel, the invention adopts the technical scheme that:

the method for smelting the nitrogen-containing steel adopted by the invention has the nitrogen content of 80-200 ppm, and the process route of the smelting method is as follows: electric furnace-LF refining-RH-continuous casting; the electric furnace adopts a converter; the continuous casting adopts die casting.

In order to accurately control the nitrogen content of molten steel after RH refining of nitrogen-containing steel, the nitrogen control process of nitrogen-containing steel disclosed by the invention can be used for quickly and accurately adjusting the nitrogen content of the molten steel in an RH treatment period for steel grades with the nitrogen content requirement of 80-200 ppm, a nitrogen increasing material is not required to be additionally added after vacuum, the nitrogen content can stably meet the product requirement, meanwhile, the risk of secondary oxidation pollution to the molten steel is reduced, and the production cost is extremely low.

And nitrogen is used as lifting gas in the whole RH vacuum process, and the pressure of the nitrogen is 1.0-2.0 MPa.

In the degassing process of the vacuum whole process, the nitrogen flow is 300-1800 normal liters/minute, the vacuum degree is kept for more than 5 minutes after reaching below 100Pa, and the content of [ H ] is ensured to be less than or equal to 1.5 ppm.

In the degassing process of the vacuum whole process, the nitrogen flow is adjusted to 500-2200 standard liters per minute, the vacuum degree is adjusted to 30-300 mbar by adjusting the vacuum pump, and the vacuum is broken after the vacuum is maintained for 10-25 minutes.

The technical scheme is determined by multiple tests, and the effects of the process requirements are as follows:

1. the nitrogen content of the molten steel is closely related to the initial nitrogen content of the molten steel, the nitrogen fixing capacity of molten steel components, the RH vacuum degree, the vacuum cycle time and the like;

2. for different steel grades, the components are different, the nitrogen fixing capacity is not completely the same, but the nitrogen content can be stably controlled between 80ppm and 200ppm by the method;

3. in the RH process, nitrogen is used as a lifting gas, so that the nitrogen removal balance left shift under vacuum circulation can be promoted, the nitrogen content in balance is improved, and the time for later nitrogen increase is shortened;

4. in order to ensure that the content of [ H ] meets the product requirement, certain vacuum deep processing time must be ensured, and generally, when the nitrogen flow is 300-1800 standard liters per minute, the RH vacuum degree is kept below 100Pa for more than 5 minutes, and then the content of [ H ] is less than or equal to 1.5 ppm; if the hydrogen is determined to be higher, the circulation time under the vacuum degree of below 100Pa needs to be prolonged;

5. the vacuum degree, the lift gas flow and the cycle time jointly determine the nitrogen content level of the molten steel. By adjusting the vacuum pump, the circulating vacuum degree of the molten steel can reach the required range (30-300 mbar), meanwhile, the flow of the nitrogen lifting gas is adjusted to 500-2200 standard liters per minute, and the holding time is 10-25 minutes, so that the stable control of the nitrogen content of the molten steel can be realized.

Adopt RH's lifting gas to control molten steel nitrogen content, there are following advantages: firstly, the flow of RH lifting gas can be accurately controlled, the pipeline is stable, the fluctuation caused by gas leakage of a pipeline joint and poor bottom blowing air brick effect is avoided, and the nitrogen increasing effect is easy to control; secondly, the molten steel is fully contacted with the molten steel to form effective circulation, and the flow field of the molten steel is more stable; and thirdly, through theoretical calculation, the balanced nitrogen content of the molten steel is far more than 80ppm, nitrogen is used as lifting gas in the vacuum process, the balance of nitrogen increase and vacuum denitrification is gradually and stably realized along with the improvement of the nitrogen content of the molten steel, the nitrogen content of the molten steel cannot exceed the steel judgment requirement of steel grade under the vacuum degree of 30-300 mbar, and the loss caused by the over-standard nitrogen content is avoided.