阅读说明：本技术 一种提高低碳低硅含铌钢铌收得率的冶炼方法 (Smelting method for improving niobium yield of low-carbon low-silicon niobium-containing steel ) 是由 张大江 万国喜 黄重 欧阳瑜 郑飞 张苓志 田云生 刘艳玲 刘广超 何晓波 王翠 于 2020-12-10 设计创作，主要内容包括：本发明公开了一种提高低碳低硅含铌钢铌收得率的冶炼方法,包括以下步骤：顶底复吹转炉：工业氧化钼随废钢加入转炉,转炉出钢过程采用铝铁合金、硅铁合金或硅锰合金、低碳锰铁下料顺序依次加入料仓；出钢过程加顶渣料,出钢过程增大氩气流量,出钢结束后降低氩气流量保持钢水搅动；LF精炼：LF精炼确保过程Alt：0.020%～0.045%,保证钢水中Si≥0.05%,铌铁在脱硫目标完成后加入；板坯连铸：连铸过程保护浇注。本发明转炉出钢采用铝脱氧,同时加入一定量的硅铁或硅锰,降低钢中的氧含量；进入LF炉后,埋弧造渣,合理控制钢中硅含量0.05%～0.12%、发挥Si的辅助脱氧能力,通过造渣、控硅,进一步脱除渣－钢中的氧,减少铌铁的氧化、提高铌的吸收率。(The invention discloses a smelting method for improving the niobium yield of low-carbon low-silicon niobium-containing steel, which comprises the following steps: top-bottom combined blown converter: adding industrial molybdenum oxide into a converter along with scrap steel, and sequentially adding aluminum-iron alloy, ferrosilicon or silicomanganese alloy and low-carbon ferromanganese into a storage bin in the converter tapping process; adding top slag in the tapping process, increasing the argon flow in the tapping process, and reducing the argon flow after tapping to keep molten steel stirring; LF refining: LF refining ensures process Alt: 0.020-0.045%, Si in molten steel is guaranteed to be more than or equal to 0.05%, and ferrocolumbium is added after the desulfurization goal is finished; slab continuous casting: and the continuous casting process protects pouring. The converter tapping adopts aluminum deoxidation, and simultaneously a certain amount of ferrosilicon or silicomanganese is added to reduce the oxygen content in steel; after the steel enters an LF furnace, submerged arc slagging is performed, the silicon content in the steel is reasonably controlled to be 0.05-0.12%, the auxiliary deoxidation capability of Si is exerted, oxygen in slag-steel is further removed through slagging and silicon control, the oxidation of ferroniobium is reduced, and the niobium absorption rate is improved.)

1. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel is characterized by comprising the following steps of:

top-bottom combined blown converter: industrial molybdenum oxide is added into a converter along with waste steel, the adding amount is controlled according to a target middle limit, aluminum-iron alloy, silicon-iron alloy or silicon-manganese alloy and low-carbon ferromanganese are sequentially added into a storage bin in the converter tapping process, the molten steel deoxidizing effect is ensured, slag is added in the tapping process, the argon flow is increased in the tapping process, the argon flow is reduced after tapping is finished, molten steel is kept stirring, and the serious overturning of the steel liquid level is avoided;

LF refining: LF refining ensures process Alt: 0.020-0.045%, determining whether industrial molybdenum oxide needs to be added additionally according to the Mo content in the steel, adding lime properly after adding, stirring for 1-2min, performing silicon and manganese alloying fine adjustment to ensure that Si in the molten steel is more than or equal to 0.05%, and adding ferroniobium after the desulfurization target is finished;

slab continuous casting: and the continuous casting process protects pouring.

2. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel as claimed in claim 1, wherein the low-carbon low-silicon niobium-containing steel comprises the following components in percentage by weight: c is less than or equal to 0.10%, Si: 0.05-0.15%, Mn is less than or equal to 2.00%, P is less than or equal to 0.018%, S is less than or equal to 0.005%, Alt: 0.020 to 0.060%, Nb: 0.040-0.080%, Ti is less than or equal to 0.14%, V is less than or equal to 0.08%, Mo is more than or equal to 0.11% and less than or equal to 0.20%, N is less than or equal to 0.007%, and the balance of iron and inevitable trace impurities.

3. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel as claimed in claim 1, wherein the molten steel composition at the end point of the top-bottom combined blown converter is controlled as follows: less than or equal to 0.07 percent of C, less than or equal to 0.015 percent of P, less than or equal to 0.020 percent of S, and the content of molybdenum meets the target lower limit.

4. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel as claimed in claim 1, wherein the addition amount of top slag charge per ton of steel in the top-bottom combined blown converter is 1.8-2.2 kg.

5. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel as claimed in claim 1, wherein the converter tapping in the top-bottom combined blown converter strictly controls the slag discharge amount, and the P return amount is less than or equal to 0.002%.

6. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel as claimed in claim 1, wherein the LF refining station is firstly submerged arc slagging, and then a first sample for refining is taken, and the aluminum supplementing operation is carried out according to the test result of the first sample for refining, so as to ensure that the Alt is more than or equal to 0.020% and less than or equal to 0.045% in the refining process.

7. The smelting method for improving the niobium yield of the low-carbon low-silicon niobium-containing steel as claimed in claim 1, wherein Si in the LF refining is controlled to be 0.05-0.12%, and ferrocolumbium is added after S is less than or equal to 0.005%, and the ferrocolumbium is added according to the target Nb middle limit.

Technical Field

The invention relates to the technical field of steelmaking, in particular to a smelting method for improving the niobium yield of low-carbon low-silicon niobium-containing steel.

Background

Niobium is widely used in the fields of metallurgy, machinery, chemistry, electronic manufacturing, aerospace, biomedicine, superconducting material industry and the like. Niobium is added into steel as a microalloy element and can be combined with carbon and nitrogen in the steel to form stable niobium carbon compounds and carbon-nitrogen compounds, and the niobium mainly plays a role in grain refinement and dispersion strengthening in the steel. Niobium can realize the dispersion distribution of precipitates by inducing precipitation and controlling the cooling speed, and the toughness level of the steel can be adjusted in a wider range. Therefore, the niobium is added, so that the strength of the steel can be improved, the toughness, high-temperature oxidation resistance and corrosion resistance of the steel can be improved, the brittle transition temperature of the steel is reduced, and good welding performance and forming performance are obtained.

Niobium has a rather weak affinity with oxygen in steel, has a lower reduction than that of the common deoxidizing elements Al, Si and other microalloy elements Ti and V, and is even lower than that of Mn at high temperature. Generally, in the steelmaking production of aluminum killed steel, the absorption rate of niobium is relatively stable, and the yield is more than 95%, however, for low-carbon low-silicon steel, particularly, Si is less than or equal to 0.15%, even if Al is more than or equal to 0.02% in the steel, Mn: 1.50-2.00%, the niobium absorptivity still fluctuates to a certain extent, and the niobium yield is even lower than 70% under individual conditions.

Disclosure of Invention

Aiming at the problem of unstable niobium absorption rate of low-carbon low-silicon niobium-containing steel, the invention provides a smelting process for improving the niobium yield, wherein the converter tapping adopts aluminum deoxidation, and simultaneously a certain amount of ferrosilicon or silicomanganese is added to reduce the oxygen content in the steel; after the steel enters an LF furnace, submerged arc slagging is performed, the silicon content in the steel is reasonably controlled to be 0.05-0.12%, the auxiliary deoxidation capability of Si is exerted, oxygen in slag-steel is further removed through slagging and silicon control, the oxidation of ferroniobium is reduced, and the niobium absorption rate is improved.

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

a smelting method for improving the niobium yield of low-carbon low-silicon niobium-containing steel comprises the following steps:

top-bottom combined blown converter: industrial molybdenum oxide is added into a converter along with waste steel, the adding amount is controlled according to a target middle limit, aluminum-iron alloy, silicon-iron alloy or silicon-manganese alloy and low-carbon ferromanganese are sequentially added into a storage bin in the converter tapping process, the molten steel deoxidizing effect is ensured, slag is added in the tapping process, the argon flow is increased in the tapping process, the argon flow is reduced after tapping is finished, molten steel is kept stirring, and the serious overturning of the steel liquid level is avoided;

LF refining: LF refining ensures process Alt: 0.020-0.045%, determining whether industrial molybdenum oxide needs to be added additionally according to the Mo content in the steel, adding lime properly after adding, stirring for 1-2min, performing silicon and manganese alloying fine adjustment to ensure that Si in the molten steel is more than or equal to 0.05%, and adding ferroniobium after the desulfurization target is finished;

slab continuous casting: the protection pouring in the continuous casting process specifically comprises the following steps: the ladle is arranged with the long nozzle and the ladle is sealed with the sealing pad, and the matching of argon blowing ensures good sealing of the ladle and the long nozzle, the immersion nozzle and the tundish nozzle.

Further, the low-carbon low-silicon niobium-containing steel comprises the following components in percentage by weight: c is less than or equal to 0.10%, Si: 0.05-0.15%, Mn is less than or equal to 2.00%, P is less than or equal to 0.018%, S is less than or equal to 0.005%, Alt: 0.020 to 0.060%, Nb: 0.040-0.080%, Ti is less than or equal to 0.14%, V is less than or equal to 0.08%, Mo is more than or equal to 0.11% and less than or equal to 0.20%, N is less than or equal to 0.007%, and the balance of iron and inevitable trace impurities.

Further, controlling the components of the molten steel at the end point of the top-bottom combined blown converter: less than or equal to 0.07 percent of C, less than or equal to 0.015 percent of P, less than or equal to 0.020 percent of S, and the content of molybdenum meets the target lower limit.

Further, the adding amount of top slag charge per ton of steel in the top-bottom combined blown converter is 1.8-2.2 kg.

Further, the slag discharge amount of the transfer furnace steel tapping of the top-bottom combined blown converter is strictly controlled, and the P return amount is less than or equal to 0.002%.

Further, the LF refining station is firstly submerged arc slagging, then a first refining sample is taken, and aluminum supplementing operation is carried out according to the test result of the first refining sample, so that Alt is more than or equal to 0.020% and less than or equal to 0.045% in the refining process.

Further, Si in the LF refining is controlled according to 0.05-0.12%, and ferrocolumbium is added after S is less than or equal to 0.005%, and is added according to the target middle limit of Nb.

Further, the continuous casting process of the plate blank keeps the drawing speed stable.

Compared with the prior art, the invention has the beneficial effects that:

1. the smelting process of the invention defines the charging sequence of the converter tapping alloy and ensures the deoxidation and alloying effects of the molten steel. The aluminum-iron alloy is added in the tapping process, so that the oxygen content in steel can be effectively reduced, and Al is promoted₂O₃Floating of impurities, and high Si and Mn absorptionThe alloy consumption is reduced, especially when the addition of the tapping alloy is more, if the aluminum-iron alloy is added at last, after tapping is finished, in order to reduce the nitrogen increase of the bare molten steel, the argon station generally reduces the flow of bottom blowing argon, at the moment, most of the aluminum-iron alloy floats on the top of the molten steel, not only can the effective deoxidation be realized, but also a large amount of aluminum loss is caused, and the increase of inclusions in the steel is caused.

2. In the low-carbon low-silicon niobium-containing aluminum killed steel, the Si content of more than 0.05 percent needs to be kept besides a certain aluminum content is controlled, so as to assist deoxidation and reduce the oxidation probability of niobium.

3. The yield of niobium element is improved, the niobium content in steel is stabilized, and the consumption of niobium-iron alloy is reduced.

4. The low-cost industrial molybdenum oxide is adopted to replace molybdenum ore, so that the cost is reduced, and meanwhile, the oxidation of molten steel is avoided.

Detailed Description

The technical solutions and effects of the present invention will be further described with reference to specific examples, but the scope of the present invention is not limited thereto.

Example 1

This example further illustrates the present invention by taking the process of smelting automobile beam steel as an example.

The smelting equipment in the embodiment is a 150-ton converter. In LF refining, the ferrocolumbium is in a barrel, the weight of each barrel is 10kg, and the ferrocolumbium contains 66 percent of niobium.

The automobile girder steel of the embodiment is prepared from the following components in percentage by weight: c: 0.07%, Si: 0.09%, Mn: 1.65%, P: 0.014%, S: 0.003%, Alt: 0.039%, Nb: 0.046%, Ti: 0.115%, Mo: 0.129%, N: 0.004%, and the balance of Fe and inevitable impurities.

The production process of the automobile beam steel comprises top-bottom combined blown converter, LF refining and slab continuous casting; wherein the content of the first and second substances,

top-bottom combined blown converter: 440kg of industrial molybdenum oxide is added in the converter, and the molten steel at the end point of the converter comprises the following components: c: 0.05%, P: 0.013%, S: 0.017 percent of steel core aluminum, 453kg of silicon-manganese alloy and 1957kg of low-carbon manganese are added during steel tapping, and the steel core aluminum, the silicon-manganese alloy and the low-carbon manganese are sequentially added into a steel ladle according to the alloy adding sequence; after the alloy is completely added, 300kg of top slag is added, the flow of argon blown from the bottom of the ladle is 800 NL/min in the tapping process, and the flow of the argon is reduced to 400 NL/min after the alloying is finished; the weight of molten steel in an argon station is 153.21 t; in the process, the carbon content of the low-carbon manganese is 0.4 percent;

in the step, attention needs to be paid to adding the alloy in batches if the converter bin cannot be simultaneously filled with the aluminum iron, the silicon iron or the silicon manganese and the low-carbon ferromanganese, but the aluminum iron, the silicon iron or the silicon manganese needs to be added in the first batch;

LF refining: refining submerged arc slagging, wherein the Al content is more than 0.020%, supplementing 240kg of silicon-manganese alloy, the Si content is 0.07%, the S content is 0.002%, adding 110kg of ferrocolumbium, adding 585kg of 30 ferrotitanium, supplementing 100m of aluminum wire, feeding 150m of pure calcium wire after stirring for 2min, and feeding steel after soft stirring for more than or equal to 8 min;

slab continuous casting: the continuous casting section is 230 multiplied by 1530mm, the superheat degree of a tundish is 10-20 ℃, a weak cold water meter is adopted for secondary cooling, the casting speed is 0.95-1.05 m/min, the fluctuation of the liquid level of a crystallizer is not more than +/-5 mm, and the continuous casting is well protected.

The absorptance of niobium obtained in this example was 97.76%, respectively.

In the example, because molybdenum oxide has strong oxidizability, molten steel is oxidized when being added in the refining process, the content of Al and Si in the steel is reduced, and the stable absorption of niobium is influenced. Therefore, the industrial molybdenum oxide is generally added together with the scrap steel by a scrap steel hopper in front of the converter, and the addition amount is generally controlled at the middle limit of the Mo content of the finished product, so that refining and supplementing are avoided.

The tapping of the converter is added according to the sequence of aluminum-iron alloy, ferrosilicon or silicon-manganese alloy and low-carbon ferromanganese, so that the content of O in the steel is reduced, and simultaneously, a certain content of Si in the steel is ensured to assist deoxidation.

In the refining process, the Al content is controlled to be more than or equal to 0.020%, the lower dissolved oxygen content of the molten steel is kept, when the refined Si content is less than 0.05%, the silicomanganese alloy is supplemented according to the target middle limit of the finished Si content, the Si content is ensured to be more than or equal to 0.05%, and the ferrocolumbium is added after the S content reaches the target upper limit, so that even if part of Nb is oxidized and enters slag, when the Al content is more than 0.020% and the Si content is more than or equal to 0.05%, the oxide of the niobium can still be reduced by the Al and the Si and enters the molten steel, and the stability of.

Example 2

This example further illustrates the present invention by taking the process of this company for producing high-strength pipe-making steel AG750YT as an example.

The smelting equipment in the embodiment is a 150-ton converter. In LF refining, the ferrocolumbium is in a barrel, the weight of each barrel is 10kg, and the ferrocolumbium contains 66 percent of niobium.

The steel AG750YT for high-strength pipe making in the embodiment is prepared from the following components in percentage by weight: c: 0.06%, Si: 0.06%, Mn: 1.92%, P: 0.012%, S: 0.002%, Alt: 0.046%, Mo: 0.115%, Nb: 0.069%, Ti: 0.12%, N: 0.004%, and the balance of Fe and inevitable impurities.

The production process of the high-strength pipe-making steel AG750YT of the embodiment comprises molten iron pretreatment, top-bottom combined blown converter, LF refining, RH vacuum refining and slab continuous casting; wherein the content of the first and second substances,

pretreating molten iron: the content of molten iron entering the pretreatment procedure S is 0.03 percent, the content of molten iron exiting the pretreatment procedure S is 0.003 percent, and the slag raking amount is 2.3 t;

top-bottom combined blown converter: 400kg of industrial molybdenum oxide is loaded in front of the converter, and molten steel at the end point of the converter comprises the following components: c: 0.039%, P: 0.010%, S: 0.014%, adding 3442kg of low-carbon manganese, 493kg of steel core aluminum and 100kg of ferrosilicon into converter tapping, and sequentially adding the steel core aluminum, the ferrosilicon and the low-carbon manganese into a steel ladle according to the alloy adding sequence; after the alloy is completely added, 300Kg of top slag material is added, the flow of argon blown to the bottom of the ladle is 1000 NL/min in the tapping process, and the flow of argon is as low as 400 NL/min after the alloying is finished; the weight of molten steel in an argon station is 162.70 t; in the process, the carbon content of the low-carbon manganese is 0.4 percent;

in the step, attention needs to be paid to the fact that if steel core aluminum, ferrosilicon or silicomanganese and low-carbon ferromanganese cannot be simultaneously loaded into a converter bin, the alloy can be added in batches, but the steel core aluminum, the ferrosilicon or the silicomanganese need to be added in the first batch;

LF refining: refining submerged arc slagging, wherein the Al content is more than 0.020 percent in the process, 30kg of industrial molybdenum oxide is supplemented, 50kg of lime is added, after stirring for 1min, 223kg of high carbon manganese and 30kg of ferrosilicon are supplemented, the Si content is 0.05 percent and the S content is 0.004 percent in the refining process, 175kg of ferrocolumbium is added, and the LF outlet molten steel temperature is 1645 ℃; the carbon content of the high-carbon manganese used in the process is 6 percent;

RH vacuum refining: RH adopts this processing mode, promotes argon gas control: 80-100 m in the first 3min³H; in the process: 120m³H, keeping the vacuum degree below 2mbar, carrying out vacuum treatment for 25min, keeping the vacuum for 20min, and carrying out vacuum net circulation for 8 min; 290kg of high-titanium iron (the Ti content is 68 percent) is added after aluminum control, a 150m pure calcium wire is fed after air breaking, and a low-carbon covering agent is added before steel feeding;

slab continuous casting: the continuous casting section is 210 multiplied by 1240mm, the superheat degree of a tundish is 15-25 ℃, a weak cold water meter is adopted for secondary cooling, the drawing speed is 1.1-1.2 m/min, the fluctuation of the liquid level of a crystallizer is not more than +/-5 mm, and the continuous casting protection casting is good.

The niobium absorption rate obtained in this example was 97.73%.

In the embodiment, 4035kg of low-carbon manganese, steel-cored aluminum and ferrosilicon alloy are added in total during converter tapping, the addition amount is large, in order to avoid blockage of a storage bin, the alloy is added in two batches, the first batch of alloy is added with all the steel-cored aluminum and the ferrosilicon alloy, part of the low-carbon manganese is added, and the second batch of the low-carbon manganese is added with the rest; therefore, the steel core aluminum and the ferrosilicon can be prevented from floating on the top of the molten steel, good deoxidation of the molten steel is ensured, and the absorption rate of the alloy is improved;

the LF refining is entered into a station and is firstly submerged arc slagging is firstly carried out, then a first refining sample is taken, aluminum supplementing operation is carried out according to the testing result of the first refining sample, the refining process is ensured to be more than or equal to 0.020% and less than or equal to 0.045%, then industrial molybdenum oxide is supplemented according to the content of Mo, a small amount of lime needs to be properly added due to strong oxidizability of the molybdenum oxide, and after stirring for 1-2min, silicon and manganese alloying fine adjustment is carried out to prevent unstable component control caused by alloy oxidation, in addition, when the refined alloy is fine adjusted, the [ Si ] in the molten steel is ensured to be more than or equal to 0.05%, the auxiliary deoxidation effect of the Si is exerted, and the absorption rate of the.

Comparative example 1

In the comparative example, the smelting equipment and the ferrocolumbium are the same as those in the example 1;

the production process of the automobile beam steel of the comparative example comprises top-bottom combined blown converter, LF refining and slab continuous casting; wherein the content of the first and second substances,

top-bottom combined blown converter: 440kg of industrial molybdenum oxide is added in the converter, and the molten steel at the end point of the converter comprises the following components: c: 0.06%, P: 0.010%, S: 0.015 percent, 461kg of steel core aluminum and 1968kg of low-carbon manganese are added in the converter tapping, and the steel core aluminum and the low-carbon manganese are sequentially added into a steel ladle according to the alloy adding sequence; after the alloy is completely added, 300Kg of top slag material is added, the flow of argon blown to the bottom of the ladle is 800 NL/min in the tapping process, and the flow of the argon is reduced to 400 NL/min after the alloying is finished; total amount of molten steel 153.04t in the argon station; in the process, the carbon content of the low-carbon manganese is 0.4 percent;

LF refining: refining submerged arc slagging, wherein in the refining process, when the content of Si is 0.012 percent, the content of Al is 0.026 percent and the content of S is 0.001 percent, 110kg of ferrocolumbium, 582kg of 30 ferrotitanium and 100m of aluminum supplement wire are added, a 150m pure calcium wire is fed after stirring for 2min, and steel is fed after soft stirring is more than or equal to 8 min;

slab continuous casting: the continuous casting section is 230 multiplied by 1530mm, the superheat degree of a tundish is 10-20 ℃, a weak cold water meter is adopted for secondary cooling, the casting speed is 0.95-1.05 m/min, the fluctuation of the liquid level of a crystallizer is not more than +/-5 mm, and the continuous casting is well protected.

The finished automobile beam steel product of the comparative example comprises the following components in percentage by weight: c: 0.07%, Si: 0.02%, Mn: 1.64%, P: 0.012%, S: 0.001%, Alt: 0.035%, Nb: 0.039%, Ti: 0.114%, Mo: 0.130%, N: 0.0045%, the balance being Fe and unavoidable impurities.

The comparative example is the same as example 1, except that ferrosilicon or silicomanganese is not added in both tapping and refining of the converter, and ferroniobium is added when the silicon content is 0.012% and the Al content is 0.026%.

The niobium absorption rate of comparative example 1 was 82.79%.

Comparative example 2

In the comparative example, the smelting equipment and the ferrocolumbium are the same as those in the example 1;

the production process of the automobile beam steel of the comparative example comprises top-bottom combined blown converter, LF refining and slab continuous casting; wherein the content of the first and second substances,

top-bottom combined blown converter: 440kg of industrial molybdenum oxide is added in the converter, and the molten steel at the end point of the converter comprises the following components: c: 0.05%, P: 0.013%, S: 0.019 percent, adding 448kg of steel core aluminum, 100kg of silicomanganese and 1941kg of low-carbon manganese into converter tapping, and sequentially adding the steel core aluminum, the silicomanganese and the low-carbon manganese into a steel ladle according to the alloy adding sequence; after the alloy is completely added, 300Kg of top slag material is added, the flow of argon blown to the bottom of the ladle is 800 NL/min in the tapping process, and the flow of the argon is reduced to 400 NL/min after the alloying is finished; the weight of the molten steel in the argon station is 151.96t, and in the process, the carbon content of the low-carbon manganese is 0.4%;

LF refining: refining submerged arc slagging, wherein in the refining process, when the Si content is 0.03 percent, the Al content is 0.032 percent and the S content is 0.002 percent, 110kg of ferrocolumbium, 573kg of 30 ferrotitanium and 100m of aluminum supplement wire are added, a 150m pure calcium wire is fed after stirring for 2min, and steel is fed after soft stirring is more than or equal to 8 min;

slab continuous casting: the continuous casting section is 230 multiplied by 1500mm, the superheat degree of a tundish is 10-20 ℃, a weak cold water meter is adopted for secondary cooling, the casting speed is 0.95-1.05 m/min, the fluctuation of the liquid level of a crystallizer is not more than +/-5 mm, and the continuous casting is well protected.

The finished automobile beam steel product of the comparative example comprises the following components in percentage by weight: c: 0.07%, Si: 0.03%, Mn: 1.63%, P: 0.015%, S: 0.002%, Alt: 0.033%, Nb: 0.041%, Ti: 0.113%, Mo: 0.132%, N: 0.0042%, the balance being Fe and unavoidable impurities.

This comparative example was the same as example 1 except that ferroniobium was added at a refining time of 0.03% Si and 0.032% Al.

The niobium absorption rate of comparative example 1 was 86.42%.

Comparative example 3

In the comparative example, the smelting equipment and the ferrocolumbium are the same as those in the example 2;

the production process of the high-strength steel AG750YT for pipe making in the comparative example comprises molten iron pretreatment, top-bottom combined blown converter, LF refining, RH vacuum refining and slab continuous casting; wherein the content of the first and second substances,

pretreating molten iron: the content of the molten iron entering the pretreatment procedure S is 0.035%, the content of the molten iron exiting the pretreatment procedure S is 0.002%, and the slag raking amount is 2.5 t;

top-bottom combined blown converter: 400kg of industrial molybdenum oxide is loaded in front of the converter, and molten steel at the end point of the converter comprises the following components: c: 0.047%, P: 0.012%, S: 0.012 percent, adding the alloy into the converter tapping in two batches, wherein 3562kg of low-carbon ferromanganese, 100kg of ferrosilicon and 300kg of steel-cored aluminum are sequentially added into the first batch according to the sequence of low-carbon manganese, ferrosilicon and steel-cored aluminum, and 350kg of steel-cored aluminum is added into the second batch; after the alloy is completely added, 300Kg of top slag material is added, the flow of argon blown to the bottom of the ladle is 1000 NL/min in the tapping process, and the flow of argon is as low as 400 NL/min after the alloying is finished; tapping 163.16t from an argon station; in the process, the carbon content of the low-carbon manganese is 0.4%.

LF refining: refining submerged arc slagging, refining and supplementing 100kg of aluminum and iron, ensuring that the Al content is more than 0.020%, supplementing 45kg of industrial molybdenum oxide, adding 60kg of lime, stirring for 1min, supplementing 230kg of high carbon manganese and 52kg of ferrosilicon, wherein the refining process sample shows that the Si content is 0.05%, the S content is 0.003%, adding 175kg of ferrocolumbium, and the LF outlet molten steel temperature is 1645 ℃; the carbon content of the high carbon manganese used in the process was 6%.

RH vacuum refining: RH adopts this processing mode, promotes argon gas control: 80-100 m in the first 3min³H; in the process: 120m³H, keeping the vacuum degree below 2mbar, treating for 27min in vacuum, keeping for 22min in vacuum, and keeping the circulation time for 10min in vacuum; adding 285kg of high-titanium iron after controlling aluminum, feeding 150m of pure calcium wire after breaking empty, and adding a low-carbon covering agent before feeding steel;

slab continuous casting: the continuous casting section is 210 multiplied by 1240mm, the superheat degree of a tundish is 15-25 ℃, a weak cold water meter is adopted for secondary cooling, the drawing speed is 1.1-1.2 m/min, the fluctuation of the liquid level of a crystallizer is not more than +/-5 mm, and the continuous casting protection casting is good.

The finished product of the high-strength steel AG750YT for pipe making of the comparative example comprises the following components in percentage by weight: c: 0.07%, Si: 0.05%, Mn: 1.90%, P: 0.013%, S: 0.002%, Alt: 0.037%, Mo: 0.113%, Nb: 0.063%, Ti: 0.118%, N: 0.0065%, the balance of Fe and inevitable impurities.

The comparative example is the same as the example 2, except that the alloy is added into the converter steel tapping in two batches, and the steel core aluminum is added in the later period of the steel tapping process, so that part of the steel core aluminum floats on the upper layer of the molten steel and contacts with the steel slag surface, the burning loss is increased, the yield of the aluminum is reduced, the Alt content of the refining station is only 0.007 percent, the oxygen content of the molten steel is higher, the white slag is difficult to produce by refining, the refining time is prolonged, the alloy consumption is increased, and the low-cost and high-efficiency production is not facilitated.

The niobium absorption of this example was 92.37%.

Comparative example 4

In the comparative example, the smelting equipment and the ferrocolumbium are the same as those in the example 2;

the production process of the high-strength steel AG750YT for pipe making in the comparative example comprises molten iron pretreatment, top-bottom combined blown converter, LF refining, RH vacuum refining and slab continuous casting; wherein the content of the first and second substances,

pretreating molten iron: the content of molten iron entering the pretreatment process S is 0.028%, the content of molten iron exiting the pretreatment process S is 0.002%, and the slag raking amount is 2.2 t;

top-bottom combined blown converter: 400kg of industrial molybdenum oxide is loaded in front of the converter, and molten steel at the end point of the converter comprises the following components: c: 0.042%, P: 0.013%, S: 0.015 percent, adding 3426kg of low-carbon manganese, 471kg of steel core aluminum and 100kg of ferrosilicon into converter tapping, and sequentially adding the steel core aluminum, the ferrosilicon and the low-carbon manganese into a steel ladle according to the alloy adding sequence; after the alloy is completely added, 300Kg of top slag material is added, the flow of argon blown to the bottom of the ladle is 1000 NL/min in the tapping process, and the flow of argon is as low as 400 NL/min after the alloying is finished; the weight of molten steel in an argon station is 161.39 t; in the process, the carbon content of the low-carbon manganese is 0.4%.

LF refining: refining submerged arc slagging, wherein the Al content is more than 0.020%, 30kg of industrial molybdenum oxide is supplemented, 223kg of high carbon manganese and 30kg of ferrosilicon are supplemented, the Si content is 0.04% and the S content is 0.003% in a sample in the refining process, 170kg of ferroniobium is added, and the LF outlet molten steel temperature is 1645 ℃; the carbon content of the high carbon manganese used in the process was 6%.

RH vacuum refining: RH adopts this processing mode, promotes argon gas control: 80-100 m3/h within the first 3 min; in the process: 120m3/h, the vacuum degree is kept below 2mbar, the vacuum treatment time is 26min, the vacuum keeping time is 21min, and the vacuum net circulation time is 8 min; adding 280kg of high-titanium iron after controlling aluminum, feeding 150m of pure calcium wire after breaking empty, and adding a low-carbon covering agent before feeding steel;

slab continuous casting: the continuous casting section is 210 multiplied by 1240mm, the superheat degree of a tundish is 15-25 ℃, a weak cold water meter is adopted for secondary cooling, the drawing speed is 1.1-1.2 m/min, the fluctuation of the liquid level of a crystallizer is not more than +/-5 mm, and the continuous casting protection casting is good.

The finished product of the high-strength steel AG750YT for pipe making of the comparative example comprises the following components in percentage by weight: c: 0.06%, Si: 0.04%, Mn: 1.90%, P: 0.014%, S: 0.002%, Alt: 0.040%, Mo: 0.116%, Nb: 0.061%, Ti: 0.116%, N: 0.0043%, the balance being Fe and unavoidable impurities.

The comparative example is the same as example 2, except that after LF refining molybdenum oxide supplement, lime is not added for stirring, high carbon manganese and silicon iron are directly added, so that the silicon absorption rate is reduced, and when the Si content is 0.04% and the Al content is 0.030%, ferrocolumbium is added.

The niobium absorption of this example was 88.22%.

TABLE 1 chemical composition (wt%) of finished product and yield (% of Nb) of examples 1-2 and comparative examples 1-4

Case(s)	C	Si	Mn	P	S	Alt	Mo	Ti	Nb	Yield of Nb
											Example 1	0.07	0.09	1.65	0.014	0.003	0.039	0.129	0.115	0.046	97.76
Example 2	0.06	0.06	1.92	0.012	0.002	0.046	0.115	0.120	0.069	97.73
											Comparative example 1	0.07	0.02	1.64	0.012	0.001	0.035	0.130	0.114	0.039	82.79
Comparative example 2	0.07	0.03	1.63	0.015	0.002	0.033	0.132	0.113	0.041	86.42
											Comparative example 3	0.07	0.05	1.90	0.013	0.002	0.037	0.113	0.118	0.063	92.37
Comparative example 4	0.06	0.04	1.90	0.014	0.002	0.040	0.116	0.116	0.061	88.22

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.