High-nitrogen anti-seismic HRB600E reinforcing steel bar and preparation method thereof

Abstract

The invention provides a high-nitrogen anti-seismic HRB600E reinforcing steel bar and a preparation method thereof, and the reinforcing steel bar comprises the following components in percentage by mass: the balance of iron and inevitable impurity elements, and Ceq is less than or equal to 0.58%. When the high-nitrogen anti-seismic HRB600E reinforcing steel bar is prepared, N2 is blown from the bottom of a converter in the whole converter smelting process, a specific vanadium-nitrogen alloy is added in the converter tapping process, the adding time and speed of the vanadium-nitrogen alloy are controlled, the N2 blowing flow is ingeniously controlled at different stages in the refining process of a refining furnace, and N2 overturning and escaping are controlled through refining slag submerged arc operation. The HRB600E reinforcing steel bar with excellent comprehensive properties such as shock resistance and the like and with low V content and high stable N content is prepared with high qualified rate, the production cost is reduced, and the economic benefits of enterprises are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of threaded steel production process, in particular to a high-nitrogen anti-seismic HRB600E steel bar and a preparation method thereof. BACKGROUND

[0002] In the new standard of threaded steel (Steel for Reinforced Concrete Part 2: Hot Rolled Ribbed Steel Bar GB / T1499.2-2018), there is only one 600MPa steel grade: HRB600, which has no anti-seismic performance requirements. With the expansion of the application of high-strength steel bars, especially in the earthquake-prone areas of the country, there is a strong demand for the anti-seismic performance of steel bars. The present application is invented to meet the demand for such anti-seismic performance.

[0003] In the new standard of threaded steel (GB / T 1499.2-2018), the content of N element is clearly specified: “7.2.3 The nitrogen content of the steel shall not be greater than 0.012wt%, and the supplier may not analyze it if it can be guaranteed. There are enough nitrogen-binding elements in the steel, and the limitation of nitrogen content can be appropriately relaxed”. That is, by adding V, Nb, Ti, Al and other strong nitrogen-binding elements to the steel, the nitrogen content of the steel can be greater than 0.012wt%.

[0004] At present, many enterprises control V in HRB600 threaded steel at 0.10-0.15wt%, and N: 120-200ppm. This design does not conform to the best match of VN precipitation strengthening, and the production cost is also high.

[0005] In the smelting process, N2 is directly blown into the molten steel to increase the N content of the molten steel, especially for steel with ultra-high N content (N: 0.021-0.032wt%, i.e. 210-320ppm), which is the most economical production process with low cost. However, since N2 is directly blown into the high-temperature molten steel, there are certain dangers, instability, uncontrollable N content and other factors, so the method of directly blowing N2 into the molten steel to increase the N content of the molten steel is generally used as an auxiliary nitrogen-increasing process, which needs to be combined with the subsequent stable nitrogen control process.

[0006] The dissolution of nitrogen-containing alloy in steel is affected by various factors such as thermodynamics and kinetics of molten steel, and the nitrogen element yield fluctuates greatly, especially in the high-nitrogen content range, so it is difficult to accurately control the nitrogen content in the steel. To increase the nitrogen content in the steel, the conventional process operation is to add nitrogen-containing alloy (such as vanadium-nitrogen alloy, high-nitrogen vanadium iron, manganese nitride, silicon nitride, etc.) to the steel after tapping, which has low yield, unstable N and high cost.

[0007] Through the retrieval of domestic related database and network information, it is found that the articles such as “Research on Nitrogen Blowing Process Technology in Converter Bottom Blowing Whole Process” (Wu Wei et al. China Steel Annual Conference Album, 2011), “Analysis of Nitrogen Content in Nitriding Alloy” (Fu Yudong. [C] South Metal, December 2018, No. 225: 18-20, 30) and “HRB600E Vanadium-containing High-strength Hot-rolled Anti-seismic Steel Bar and Production Method”, Chinese Patent CN106636917A (Jin Gang Qiao Guoping et al.), “Production Method of HRB600 Hot-rolled Ribbed Steel Bar”, Chinese Patent CN102534407A (Yang Maolin Liu Yonglin et al.), “Method for Producing HRB600 Hot-rolled Ribbed Steel Bar with Chromium-vanadium Micro-alloying”, Chinese Patent CN111575587A (Tan Biao Gao Xudong et al.), “HRB600E Hot-rolled Ribbed Steel Bar with Yield Ratio Greater than 1.26”, Chinese Patent CN114836686A (Qian Xuehai Li Zongqiang et al.) have carried out researches on related fields.

[0008] The above articles describe the nitrogen content range of each process in the smelting process of 600 MPa grade threaded steel, and even the process parameters such as nitrogen blowing pressure and flow, but do not describe how N is obtained in the steel and process control measures. The patent “HRB600E Vanadium-containing High-strength Hot-rolled Anti-seismic Steel Bar and Production Method” mainly describes the steel composition design, in which the N content is 0.015-0.025wt%. In addition, the secondary refining process only has “ensure the soft argon blowing time ≥8 min after refining is completed”. The patent “Production Method of HRB600 Hot-rolled Ribbed Steel Bar” mainly describes the method for strengthening Cr, Nb and VN micro-alloy composite strengthening in the production process of HRB600, the alloy addition sequence in the tapping process and the refining bottom argon blowing process, and does not involve N content and its control technology. The patent “Method for Producing HRB600 High-strength Hot-rolled Ribbed Steel Bar with Chromium-vanadium Micro-alloying” mainly describes the design of HRB600 steel composition system, V: 0.12-0.18wt%, Cr: 0.30-0.40wt%, N: 0.012-0.018wt%; silicon-nitrogen alloy is added in the converter tapping; vanadium-iron alloy is added in the refining, and N2 is blown at the same time, and the nitrogen content of the molten steel is controlled to be 8-15 ppm / min. The patent “HRB600E Hot-rolled Ribbed Steel Bar with Yield Ratio Greater than 1.26” only mentions that N is in the range of 0.020-0.035wt%, without any N addition and control technology measures.

[0009] At present, the problems of HRB600E that each enterprise needs to solve are: ① how to stably prepare high N content of steel bar; ② ensure the performance of the steel bar, especially the anti-seismic performance; ③ reduce the production cost. SUMMARY

[0010] In view of the above problems, the present application provides a high-nitrogen anti-seismic HRB600E steel bar and a preparation method thereof.

[0011] In one aspect, the present application provides a high-nitrogen anti-vibration HRB600E steel bar, which has the following components in percentage by mass:

[0012]

[0013] V 0.100-0.120%

[0014] Nb 0.010-0.025%

[0015] N 0.021-0.032%

[0016] The balance is iron and inevitable impurity elements, and Ceq≤0.58%.

[0017] Optionally, the N content is 0.0215-0.030% by mass.

[0018] In another aspect, the present application provides a preparation method of a high-nitrogen anti-vibration HRB600E steel bar, which has the following components in percentage by mass:

[0019] C 0.23-0.28%

[0020] Si 0.65-0.80%

[0021] Mn 1.45-1.60%

[0022] P≤0.040%

[0023] S≤0.040%

[0024] V 0.100-0.120%

[0025] Nb 0.010-0.025%

[0026] N 0.021-0.032%

[0027] The balance is iron and inevitable impurity elements, and Ceq≤0.58%.

[0028] The preparation method of the high-nitrogen anti-vibration HRB600E steel bar comprises:

[0029] (1) converter smelting, full-process converter bottom blowing N2;

[0030] (2) tapping, N2 bottom blowing of the ladle during the process of the molten steel entering the ladle, and the flow rate is 1200-2000 m 3 / h;

[0031] (3) refining furnace refining, controlling the N2 flow rate in the following four stages:

[0032] Electrode heating stage 1000-1500 m 3 / h

[0033] White slag-sampling stage 200-1200 m 3 / h

[0034] Soft blowing stage 100-300 m 3 / h

[0035] Leaving the refining furnace blowing stage 100-600 m 3 / h

[0036] (4) The ladle leaves the refining furnace, and casting and rolling are carried out to obtain the high-nitrogen anti-vibration HRB600E steel bar.

[0037] Optionally, when step (3) is carried out, the N2 flow rate of the white slag-sampling stage is 800-1200 m 3 / h.

[0038] Optionally, when the converter smelting in step (1) is carried out, the bottom blowing N2 flow rate of several stages is controlled as follows:

[0039] Slag splashing 700-900 Nm 3 / h

[0040] Iron addition 300-400 Nm 3 / h

[0041] Blowing period 280-420 Nm 3 / h

[0042] Sublance sampling 200-300 Nm 3 / h

[0043] Point blowing 280-420 Nm 3 / h

[0044] Manual sampling 200-300 Nm 3 / h

[0045] Equal sample 200-300 Nm 3 / h.

[0046] Optionally, when the tapping in step (2) is carried out, a deoxidizer, a slag former, carbon powder, Si-Mn alloy and vanadium-nitrogen alloy are added;

[0047] The nitrogen content of the vanadium-nitrogen alloy is 10-35%, preferably 15-17% or 29-33%.

[0048] The vanadium-nitrogen alloy is added when the tapping in step (2) is carried out for greater than or equal to 1 min.

[0049] Optionally, during the tapping in step (2), the vanadium-nitrogen alloy is added according to the tapping hole usage as follows:

[0050] When the tapping hole is used for 1-20 heats, the vanadium-nitrogen alloy is added by bag at 1.5 min of tapping and completed at 2-2.5 min;

[0051] When the tapping hole is used for 21-50 heats, the vanadium-nitrogen alloy is added by bag at 1.25 min of tapping and completed at 1.5-2 min;

[0052] When the tapping hole is used for 51-130 heats, the vanadium-nitrogen alloy is added by bag at 1 min of tapping and completed at 1-1.5 min;

[0053] When the tapping hole is used for >130 heats, the vanadium-nitrogen alloy is added by bag at 1 min of tapping and completed at 0.5-1 min.

[0054] Optionally, during the refining in step (3):

[0055] The foamy slag thickness in the electrode heating stage is 200-250 mm, and the refining furnace pressure is 0--10 Pa;

[0056] The foamy slag thickness in the white slag-sampling stage and the isosample soft-blowing stage is 80-150 mm, preferably 80-135 mm.

[0057] Optionally, the nitrogen content of the molten steel increases by 10-18 ppm from the time the ladle leaves the refining furnace to the completion of the casting.

[0058] Optionally, according to the N content of the high-nitrogen anti-vibration HRB600E steel bar, the rolling of the threaded steel bar is performed as follows:

[0059] N 210-260 ppm, rolling diameter 6-14 mm steel bar;

[0060] N 240-300 ppm, rolling diameter 16-25 mm steel bar;

[0061] N 260-320 ppm, rolling diameter 28-40 mm steel bar;

[0062] Preferably, the rolling is performed as follows:

[0063] N 215-260 ppm, rolling diameter 6-14 mm steel bar;

[0064] N 240-280 ppm, rolling diameter 16-25 mm steel bar;

[0065] N 260-300 ppm, rolling diameter 28-40 mm steel bar.

[0066] Advantages:

[0067] When the high-nitrogen anti-vibration HRB600E steel bar is prepared, N2 is blown at the bottom of the converter throughout the converter smelting process, a specific vanadium-nitrogen alloy is added when the converter is tapped, and the timing and speed of adding the vanadium-nitrogen alloy are controlled, the N2 flow rate during different stages of the refining furnace refining process is skillfully controlled, the N2 turbulence escape is controlled by the submerged arc operation of the refining slag, and a series of integrated technologies are used to prepare the HRB600E steel bar with excellent comprehensive performance such as anti-vibration, V content in a lower range, and stable N content in a higher range, while reducing the production cost and improving the economic benefit of the enterprise. DETAILED DESCRIPTION

[0068] The application will be further described in detail by examples. Through these descriptions, the features and advantages of the application will become more apparent.

[0069] The special word "exemplary" here means "serving as an example, embodiment, or illustration". Any embodiment described as "exemplary" here is not necessarily to be construed as superior or better than other embodiments.

[0070] In the present application, the term "LF furnace", "refining LF" or "LF" means a refining furnace;

[0071] In the present application, the term "Φ" means diameter;

[0072] In the present application, the term "Ceq" means carbon equivalent.

[0073] In addition, the technical features involved in different embodiments of the application described below can be combined with each other as long as there is no conflict.

[0074] In one aspect, the present application provides a high-nitrogen anti-vibration HRB600E steel bar, the components of which are as follows in mass percentage:

[0075]

[0076] Nb 0.010-0.025%

[0077] N 0.021-0.032%

[0078] The balance is iron and unavoidable impurity elements, and Ceq≤0.58%.

[0079] It should be noted that the N content of 0.021-0.032% corresponds to 210-320 ppm. If the V content in the 600 MPa grade threaded steel is set to 0.10-0.12 wt%, according to the V / N ratio of 3.64, the N theoretically required to match is 275-330 ppm. If the V content is increased to V: 0.13-0.15 wt%, the corresponding N required is 357-412 ppm. N of 350-400 ppm is very unstable in molten steel, even if it is added, after rolling, a certain amount of V is in solid solution state (Ti, Al and other elements inevitably exist in the steel), that is, the expensive V is in excess. The present inventors unexpectedly found through years of research and experiments that when the V content is low, 0.10-0.12 t%, the N content is high, 0.021-0.032%, and other ingredients are controlled as above, the strength, ductility, and shock resistance of HRB600E steel are all optimal.

[0080] In one embodiment of the above high-nitrogen shock-resistant HRB600E steel rod of the present application, the N content is 0.0215-0.030% by mass percentage.

[0081] It should be noted that the N content of 0.0215-0.030% corresponds to 215-300 ppm, the N content can also be 220-310 ppm, and the N content can also be 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, etc. Further optimization of the N content can further improve the performance of the shock-resistant HRB600E steel rod.

[0082] On the other hand, the present application also provides a preparation method of high-nitrogen shock-resistant HRB600E steel rod, the composition of the high-nitrogen shock-resistant HRB600E steel rod is as follows by mass percentage:

[0083] C 0.23-0.28%

[0084] Si 0.65-0.80%

[0085] Mn 1.45-1.60%

[0086] P≤0.040%

[0087] S≤0.040%

[0088] V 0.100-0.120%

[0089] Nb 0.010-0.025%

[0090] N 0.021-0.032%

[0091] Balance is iron and inevitable impurity elements, Ceq≤0.58%;

[0092] The preparation method of the high-nitrogen anti-vibration HRB600E reinforcing bar comprises the following steps:

[0093] (1) converter smelting, full process converter bottom blowing N2;

[0094] (2) tapping, the ladle bottom blowing N2 and the flow is 1200-2000m 3 / h during the process of the molten steel entering the ladle;

[0095] (3) refining furnace refining, controlling the blowing N2 flow in the following four stages:

[0096] electrode heating stage 1000-1500m 3 / h

[0097] white slag-sampling stage 200-1200m 3 / h

[0098] soft blowing stage 100-300m 3 / h

[0099] leaving the refining furnace supplement blowing stage 100-600m 3 / h

[0100] (4) the ladle leaving the refining furnace, carrying out casting and rolling to obtain the high-nitrogen anti-vibration HRB600E reinforcing bar.

[0101] The preparation method divides the refining furnace refining process into the electrode heating stage, the white slag-sampling stage, the soft blowing stage and the leaving the refining furnace supplement blowing stage, and blows N2 in the stages, and controls the blowing N2 flow in each stage, so that the N content is stably improved, and the high-nitrogen anti-vibration HRB600E reinforcing bar with high N content and excellent performance is finally prepared.

[0102] In step (1), the pressure of the full process converter bottom blowing N2 is greater than or equal to 1.2 MPa, and the N2 purity is greater than or equal to 99.99%. In step (2), the ladle bottom blowing N2 with large flow is beneficial to quickly forming new slag and alloy homogenization, and further improving the performance of the prepared reinforcing bar. In step (3), during the ladle refining in the refining furnace, in the electrode heating stage, the N2 is blown with a medium flow to accelerate the formation of slag and alloy into the molten steel, and the blowing N2 flow is controlled as above; the soft blowing stage needs to avoid the oxidation of the molten steel; the blowing N2 flow is controlled as above in the leaving the refining furnace supplement blowing stage, which is beneficial to stably preparing the reinforcing bar with high N content and excellent performance. The converter smelting in the above preparation method can be carried out in a 80-200t converter.

[0103] In one embodiment of the above-mentioned preparation method of the present application, when the refining is performed in step (3), the N2 blowing flow rate in the white slag-sampling stage is 800-1200 m 3 / h.

[0104] By further optimizing the N2 blowing flow rate in the white slag-sampling stage, the high nitrogen content can be better stabilized, and the performance of the prepared HRB600E reinforcing steel bar can be improved.

[0105] In another embodiment of the above-mentioned preparation method of the present application, when the converter smelting in step (1) is performed, the bottom N2 flow rate in several stages is controlled as follows:

[0106] Splashing slag 700-900 Nm 3 / h

[0107] Iron mixing 300-400 Nm 3 / h

[0108] Blowing period 280-420 Nm 3 / h

[0109] Sublance sampling 200-300 Nm 3 / h

[0110] Point blowing 280-420 Nm 3 / h

[0111] Manual sampling 200-300 Nm 3 / h

[0112] Sampling 200-300 Nm 3 / h.

[0113] It should be noted that the bottom N2 flow rate in the splashing slag stage can be 750 Nm 3 / h, 800 Nm 3 / h, 850 Nm 3 / h, etc., and the bottom N2 flow rate in the iron mixing stage can be 320 Nm 3 / h, 340 Nm 3 / h, 360 Nm 3 / h, 380 Nm 3 / h, etc. When the converter smelting is performed, the N2 flow rate in the above-mentioned several stages is controlled as above, and then the N2 flow rate in the several stages during the refining of the refining furnace is cleverly controlled as above, and the synergistic effect between multiple steps is achieved, so that the high nitrogen content can be better stabilized, and the HRB600E reinforcing steel bar with excellent comprehensive performance can be prepared with a high pass rate.

[0114] In one embodiment of the above-mentioned preparation method of the present application, when the converter smelting in step (1) is performed, the bottom N2 flow rate in several stages is controlled as follows:

[0115] The nitrogen content of the vanadium-nitrogen alloy is 10-35%, preferably 15-17% or 29-33%;

[0116] The vanadium-nitrogen alloy is added when the tapping is performed for greater than or equal to 1 min in step (2).

[0117] It should be noted that when the tapping is performed in step (2), the amount of vanadium-nitrogen alloy used can be appropriately reduced to control the V content in the final high-nitrogen anti-vibration HRB600E steel bar, i.e., to control the V content to be relatively low. The vanadium-nitrogen alloy added when the tapping is performed in step (2) is preferably a vanadium-nitrogen alloy with a nitrogen content of 15-17% or a high-nitrogen vanadium alloy (specific type of vanadium-nitrogen alloy) with a nitrogen content of 29-33%. The vanadium-iron alloy can also be added when the above-mentioned additives and vanadium-nitrogen alloy are added during the tapping.

[0118] The addition of the vanadium-nitrogen alloy when the tapping is performed for greater than or equal to 1 min in step (2) can increase the N content to some extent and improve the nitrogen yield. The 600 MPa grade high-nitrogen anti-vibration threaded steel bar HRB600E is prepared at low cost, and the nitrogen content in the anti-vibration steel bar is comprehensively designed in terms of process source, material cost budget, and nitrogen content control technology during the whole smelting process.

[0119] In another embodiment of the above-mentioned preparation method of the present application, when the tapping is performed in step (2), the vanadium-nitrogen alloy is added according to the number of times of use of the tapping hole as follows:

[0120] When the tapping hole is used for 1-20 heats, the vanadium-nitrogen alloy is added in bags starting at 1.5 min of tapping and is completely added at 2-2.5 min;

[0121] When the tapping hole is used for 21-50 heats, the vanadium-nitrogen alloy is added in bags starting at 1.25 min of tapping and is completely added at 1.5-2 min;

[0122] When the tapping hole is used for 51-130 heats, the vanadium-nitrogen alloy is added in bags starting at 1 min of tapping and is completely added at 1-1.5 min;

[0123] When the tapping hole is used for >130 heats, the vanadium-nitrogen alloy is added in bags starting at 1 min of tapping and is completely added at 0.5-1 min.

[0124] As described above, as the number of times of use of the tapping hole increases, the speed of adding the vanadium-nitrogen alloy gradually increases, and when the tapping hole is used for >130 heats, the vanadium-nitrogen alloy needs to be completely added at 0.5-1 min. At this time, 1-2 or 2-3 people can simultaneously add the vanadium-nitrogen alloy to ensure the speed of adding the vanadium-nitrogen alloy.

[0125] The preparation method of the present application can further stabilize the high N content of the steel bar and prepare the high nitrogen anti-vibration HRB600E steel bar with better comprehensive performance at a higher qualified rate. When adding multiple alloys, the sequence of adding the alloys after the refining is controlled, and the preferred sequence is high nitrogen vanadium iron-vanadium-nitrogen alloy-vanadium iron, which can further improve the performance of the prepared steel bar.

[0126] In an embodiment of the above preparation method of the present application, the refining in step (3) is performed as follows:

[0127] The foam slag thickness in the electrode heating stage is 200-250 mm, and the furnace pressure of the refining furnace is 0--10 Pa.

[0128] The foam slag thickness in the white slag-sampling stage and the isometric soft blowing stage is 80-150 mm, preferably 80-135 mm.

[0129] It should be noted that the high temperature of 3500°C during the electrode discharge of the LF furnace ionizes the nitrogen in the air, causing the nitrogen to become ions and enter the molten steel. The refining submerged arc slag can prevent fresh air from entering the ionization area, and the submerged arc slag layer thickness is controlled to hinder the N ions in the molten steel from escaping as nitrogen gas, thereby increasing the N content in the molten steel. The submerged arc slag must have foaming components, so it is also called foam slag and contains CO bubbles. After the formation of the foam slag, the slag layer thickness increases. After the CO in the slag is released, the slag layer thickness becomes thin.

[0130] In the above preparation method of the present application, foam slag is formed at the initial stage of refining, and carbon powder, silicon carbide powder, and ferrosilicon powder can be used to control the foam slag thickness at different stages. In the electrode heating stage, the molten steel is strictly prohibited from being exposed to N2 escape, and the micro-negative pressure in the LF furnace is controlled, the furnace cover is tight, and the foam slag is formed outside the furnace to prevent N2 escape, so that the N content in the steel bar is stably increased.

[0131] In another embodiment of the above preparation method of the present application, the ladle is removed from the refining furnace to complete the casting, and the nitrogen content of the molten steel is increased by 10-18 ppm.

[0132] It should be noted that during the process of lifting the ladle away from the LF furnace to the completion of casting, the high-temperature molten steel flows from the ladle to the tundish and then to the continuous casting crystallizer. During the flow process, the molten steel inevitably adsorbs air. According to the superheat of the molten steel, it is predicted that the nitrogen content of the molten steel is increased by 10-18 ppm.

[0133] In an embodiment of the above preparation method of the present application, according to the N content of the high nitrogen anti-vibration HRB600E steel bar, the rolling of the deformed steel bar is performed as follows:

[0134] N 210-260 ppm, rolled diameter 6-14 mm rebar;

[0135] N 240-300 ppm, rolled diameter 16-25 mm rebar;

[0136] N 260-320 ppm, rolled diameter 28-40 mm rebar;

[0137] Preferably, the following is performed:

[0138] N 215-260 ppm, rolled diameter 6-14 mm rebar;

[0139] N 240-280 ppm, rolled diameter 16-25 mm rebar;

[0140] N 260-300 ppm, rolled diameter 28-40 mm rebar.

[0141] According to the N content in the steel, different specifications of threaded steel bars are rolled respectively to make the final steel bar product have excellent anti-seismic performance.

[0142] The present application reduces the V content, adopts "converter bottom blowing N2 + ferrovanadium / vanadium-nitrogen / high-nitrogen vanadium alloy optimization selection", "precise control of vanadium-nitrogen alloy adding time", "refining slag submerged arc operation control N2 escape" and other technologies, solves the instability of ultra-high nitrogen content (N: 210-320 ppm) in 600 MPa grade steel bars, and improves the anti-seismic performance of the reinforced steel bars, while reducing the production cost and improving the economic benefit of enterprises.

[0143] Specifically, firstly, the preparation method of the present application can effectively reduce the production cost, for example, the cost of Ar per ton of steel is 1.87 yuan, the cost of N2 per ton of steel is 0.20 yuan, and the cost will be reduced by 1.67 yuan / t by changing the bottom blowing Ar to bottom blowing N2; at the same time, the converter bottom blowing N2 can increase the N content of high-nitrogen (N: 210-320 ppm) threaded steel HRB600E by 11-13%, which can save 0.1 kg / t of vanadium-nitrogen alloy (the current price of vanadium-nitrogen alloy is 150,000 yuan / t), and reduce the cost by 15 yuan / t.

[0144] Secondly, the designed V content is reduced from 0.10-0.15wt% to 0.10-0.12wt%, and according to the average reduction of V: 0.015wt%, 0.24 kg / t of ferrovanadium is saved, and the cost is reduced by 36 yuan / t;

[0145] Thirdly, according to the N content of the converter sample, low-cost vanadium, vanadium-nitrogen alloy, high-nitrogen vanadium alloy, silicon-nitrogen alloy and other alloys are selected, which can reduce the cost by 3 yuan / t;

[0146] Fourth, the nitrogen content of H RB600E is improved and stabilized. The nitrogen content of H RB600E is 100% by using the preparation method, and the nitrogen content of the steel is 215-280 ppm, and the qualified rate is 95.7%.

[0147] The application will be further described in detail by examples, but the application is not limited by the examples. In the following examples, the experimental instruments and raw materials involved are commercially available products.

[0148] Example 1

[0149] The 80t converter smelting, the tapping amount is about 97t, and the continuous casting billet section size is 165x165mm;

[0150] 1) The nitrogen N2 is bottom blown in the whole process of converter smelting, the N2 pressure is 1.32MPa, and the N2 purity is 99.995%.

[0151] 2) The converter bottom blowing N2 flow rate in each stage of smelting is controlled as follows:

[0152] Table 1

[0153]

[0154] 3) The sampling before the converter tapping, C: 0.09wt%, N: 46ppm, and the temperature: 1667℃. According to the low-cost V, N alloy model, the vanadium-nitrogen alloy (the nitrogen content of the alloy: 16%) is preferred.

[0155] 4) Tapping, adding deoxidizer, slag former, carbon powder, Si-Mn alloy, Nb alloy, vanadium-nitrogen alloy (nitrogen content 16%) and the like according to the operation procedure; the converter bottom blowing N2 flow rate is controlled to be 1500m 3 / h during the process of the molten steel entering the ladle. The large data of the furnace shows that the converter bottom blowing Ar tapping sample N is 26ppm, and the nitrogen content of the converter bottom blowing N2 in the embodiment is increased by N: 46-26=20ppm.

[0156] 5) According to the use of 16 heats of the tapping hole, the vanadium-nitrogen alloy (nitrogen content 16%) 85kg is uniformly added in bags for 1.5min, and is added completely at 2min29s.

[0157] 6) LF blowing N2 operation: ① electrode heating stage blowing N2 flow rate: 1200m 3 / h; ② white slag-sampling stage, the ladle 1 sample N: 207ppm, nitrogen yield: 92.3%, blowing N2 flow rate: 1000m 3 / h; ③ sample soft blowing stage, blowing N2 flow rate: 120m 3 / h; 4) ladle lifted off LF furnace stage, ladle 2 sample N: 216 ppm, N2 flow rate: 600 m 3 / h.

[0158] 7) LF furnace refining initial stage foaming slag, 1) LF furnace electrode heating stage using submerged arc operation, foaming slag thickness 245 mm, LF furnace pressure -8 Pa, LF furnace cover tight, temperature 1613 °C; 2) white slag sampling and sample soft blowing stage, refining slag thickness 120 mm.

[0159] 8) ladle lifted off LF furnace for casting, LF 3# sample N: 229 ppm, tundish finished product sample N: 243 ppm, ladle from refining furnace to complete casting liquid N2 absorption: 14 ppm (due to high temperature liquid steel from ladle to tundish, from tundish to continuous casting crystallizer, the flowing process of liquid steel inevitably adsorbs air, leading to nitrogen increase in steel). Tundish finished product sample V: 0.107wt%.

[0160] 9) According to the N content in steel: 243 ppm, arrange Φ8 mm HRB600E coil for rolling.

[0161] The composition of the Φ8 mm HRB600E coil prepared in Example 1 is as follows in mass percent:

[0162] C 0.26%, Si 0.76%, Mn 1.53%, P 0.023%, S 0.005%, V 0.107%, Nb 0.023%, N 0.0243%, the balance being iron and unavoidable impurity elements, Ceq 0.53%.

[0163] Example 2:

[0164] The 150 t converter smelting, tapping amount is about 172 t, continuous casting billet cross-sectional size is: 165x165 mm;

[0165] 1) Bottom blowing nitrogen gas N2 throughout the converter smelting, N2 pressure: 1.22 MPa, N2 purity: 99.995%.

[0166] 2) Converter bottom blowing N2 flow rate control at each stage as follows:

[0167] Table 2

[0168]

[0169] 3) Sampling before converter tapping, C: 0.13wt%, N: 36 ppm, temperature: 1663 °C. According to the low-cost V, N alloy model, high nitrogen vanadium alloy is preferred (the nitrogen content of this alloy is 31.5%).

[0170] 4) Tapping, adding deoxidizer, slag forming agent, carbon powder, Si-Mn alloy, Nb alloy, high-nitrogen vanadium alloy (nitrogen content 31.5%) according to the operation procedure; the N2 flow rate of the bottom blowing of the ladle during the process of the molten steel entering the ladle is controlled to be 2000 m 3 / h. The large data of the furnace shows that the N content of the converter bottom blowing Ar tapping sample is 24 ppm, and the nitrogen content of the present embodiment is increased by N: 36-24 = 12 ppm.

[0171] 5) According to the use of 261 heats of the tapping hole, 155 kg of high-nitrogen vanadium alloy (nitrogen content 31.5%) is added uniformly in bags at the beginning of tapping for 1 min, and is added completely at 51 s.

[0172] 6) N2 blowing operation of refining LF: ① Electrode heating stage blowing N2 flow rate: 1350 m 3 / h; ② White slag-sampling stage, ladle 1 sample N: 245 ppm, nitrogen yield: 81.9%, blowing N2 flow rate: 1100 m 3 / h; ③ Isosample soft blowing stage, blowing N2 flow rate: 110 m 3 / h; ④ LF furnace lifting stage, ladle 2 sample N: 262 ppm, blowing N2 flow rate: 100 m 3 / h.

[0173] 7) LF furnace refining initial stage bubble forming slag, ① LF furnace electrode heating stage adopts submerged arc operation, bubble forming slag thickness 223 mm, LF furnace pressure 0 Pa, LF furnace cover slightly leaks, temperature 1594℃; ② White slag sampling and isosample soft blowing stage, refining slag thickness 80 mm

[0174] 8) Ladle lifting from LF furnace for casting, LF 3# sample N: 279 ppm, tundish finished product sample N: 297 ppm, ladle leaving the refining furnace to complete the casting of the molten steel absorbing N2: 18 ppm (due to the high temperature molten steel flowing from the ladle to the tundish, from the tundish to the continuous casting crystallizer, the molten steel inevitably absorbs air, resulting in the increase of nitrogen in the molten steel). Tundish finished product sample V: 0.118wt%.

[0175] 9) According to the N content in the steel: 297 ppm, arrange Φ32 mm HRB600E rolling.

[0176] The composition of the Φ32 mm HRB600E prepared in Example 2 is in mass percentage:

[0177] C 0.28%, Si 0.75%, Mn 1.57%, P 0.020%, S 0.007%, V 0.118%, Nb 0.022%, N 0.0297%, the balance being iron and inevitable impurity elements, Ceq 0.57%.

[0178] Example 3:

[0179] The converter smelting is 200t, and the tapping quantity is about 235t. The continuous casting billet section size is 165x165mm;

[0180] 1) The nitrogen N2 is bottom blown in the whole process of converter smelting. The N2 pressure is 1.37MPa, and the N2 purity is 99.995%.

[0181] 2) The converter bottom blowing N2 flow rate in each smelting stage is controlled as follows:

[0182] Table 3

[0183]

[0184] 3) Sampling before converter tapping, C: 0.10wt%, N: 61ppm, temperature: 1683℃, according to the low-cost V, N alloy model, preferably vanadium iron + vanadium-nitrogen alloy (the nitrogen content of vanadium iron is 0, and the nitrogen content of vanadium-nitrogen alloy is 16%).

[0185] 4) Tapping, adding deoxidizer, slag former, carbon powder, Si-Mn alloy, Nb alloy, vanadium iron alloy and vanadium-nitrogen alloy (nitrogen content: 16%) according to the operation procedure; the converter bottom blowing N2 flow rate is controlled to be 1200m 3 / h during the process of the molten steel entering the ladle. The large data of this furnace shows that the converter bottom blowing Ar tapping sample N is 29ppm, and the nitrogen content of this embodiment is increased by N: 61-29=32ppm.

[0186] 5) According to the use of 85 heats of the tapping hole, 255kg of vanadium-nitrogen alloy (nitrogen content: 16%) is uniformly added in bags for 1min, and is added completely at 1min27s.

[0187] 6) N2 blowing operation of refining LF: ① Electrode heating stage blowing N2 flow rate: 1500m 3 / h; ② White slag-sampling stage, ladle 1 sample N: 242ppm, nitrogen yield: 83.5%, blowing N2 flow rate: 1200m 3 / h; ③ Iso-sample soft blowing stage, blowing N2 flow rate: 300m 3 / h; ④ LF furnace lifting stage, ladle 2 sample N: 251ppm, blowing N2 flow rate: 500m 3 / h.

[0188] 7) LF furnace refining initial stage bubble forming slag, ① LF furnace electrode heating stage adopts submerged arc operation, bubble forming slag thickness 202mm, LF furnace pressure-10Pa, temperature 1594℃; ② White slag sampling and isosample soft blowing stage, refining slag thickness 95mm

[0189] 8) ladle is lifted away from the LF furnace for casting, LF3 sample: N: 257 ppm, tundish finished product sample N: 269 ppm, the ladle leaves the refining furnace to complete the casting of the liquid steel absorbs N2: 12 ppm (because the high temperature liquid steel flows from the ladle to the tundish, from the tundish to the continuous casting crystallizer, the liquid steel inevitably adsorbs air during the flow process, resulting in an increase in nitrogen content of the liquid steel). The tundish finished product sample V: 0.112wt%.

[0190] 9) According to the N content in the steel: 269 ppm, arrange to roll Φ25mm HRB600E.

[0191] The composition in mass percent of the Φ25mm HRB600E prepared in Example 3:

[0192] C 0.27%, Si 0.73%, Mn 1.51%, P 0.027%, S 0.004%, V 0.112%, Nb 0.024%, N 0.0269%, the balance being iron and unavoidable impurity elements, Ceq 0.55%.

[0193] Example 4:

[0194] The 100t converter smelting, tapping amount is about 117t, the continuous casting billet section size is: 165x165mm;

[0195] 1) The converter smelting is bottom blown with nitrogen gas N2 throughout the process, N2 pressure: 1.38MPa, N2 purity: 99.995%.

[0196] 2) The converter bottom blowing N2 flow rate is controlled as follows in each stage of smelting:

[0197] Table 4

[0198]

[0199] 3) Sampling before converter tapping, C: 0.05%, N: 48ppm, temperature: 1683℃, according to the low-cost V, N alloy model, the vanadium-nitrogen alloy (nitrogen content: 15.8%) is preferred.

[0200] 4) Tapping, according to the operating procedures, add deoxidizers, slag formers, carbon powder, Si-Mn alloy, Nb alloy, vanadium-nitrogen alloy (nitrogen content: 15.8%) and the like; the ladle bottom blowing N2 flow rate is controlled at 1700m 3 / h during the process of the liquid steel entering the ladle. The large data of this furnace shows that the converter bottom blowing Ar tapping sample N: 32ppm, the nitrogen content of this embodiment increases: N: 48-32=16ppm.

[0201] 5) According to the tapping port, 41 heats were used, and the vanadium-nitrogen alloy (nitrogen content: 15.8%) 100 kg was added uniformly in bags starting from 1 min 15 s of tapping, and was added completely at 1 min 45 s.

[0202] 6) LF refining N2 blowing operation: ① electrode heating stage blowing N2 flow: 1000 m 3 / h; ② white slag-sampling stage, ladle 1 sample [N]: 193 ppm, nitrogen yield: 81%, blowing N2 flow: 800 m 3 / h; ③ isometric soft blowing stage, blowing N2 flow: 150 m 3 / h; ④ LF furnace lifting stage, ladle 2 sample N: 204 ppm, blowing N2 flow: 200 m 3 / h.

[0203] 7) LF furnace refining initial stage bubble forming slag, ① LF furnace electrode heating stage adopts submerged arc operation, bubble forming slag thickness 240 mm, LF furnace pressure -6 Pa, temperature 1614℃; ② white slag sampling and isometric soft blowing stage, refining slag thickness 135 mm.

[0204] 8) Ladle lifting from LF furnace for casting, LF 3# sample [N]: 245 ppm, tundish finished product sample N: 261 ppm, ladle leaving refining furnace to complete casting liquid N2 absorption: 16 ppm. Tundish finished product sample V: 0.101%.

[0205] 9) According to the N content in the steel: 261 ppm, arrange Φ20 mm HRB600E rolling.

[0206] The composition of the Φ20 mm HRB600E prepared in Example 4 in mass percent:

[0207] C 0.25%, Si 0.76%, Mn 1.55%, P 0.019%, S 0.006%, V 0.101%, Nb 0.021%, N 0.0261%, the balance being iron and inevitable impurity elements, Ceq 0.54%.

[0208] Test Example

[0209] The performance of the reinforcing bars prepared in the above examples was tested, wherein the reinforcing bar of Example 1 was Φ8 mm spiral reinforcing bar, and the reinforcing bars of Examples 2-4 were straight reinforcing bars.

[0210] “Rel” is the yield strength;

[0211] “Rm” is the tensile strength;

[0212] “A” is the elongation after fracture, which is the seismic index parameter of the deformed steel bar;

[0213] “Agt "Rm / Rel" is the tensile strength to yield strength ratio, and is a seismic index parameter of the threaded steel;

[0214] "Rm / Rel" is the tensile strength to yield strength ratio, and is a seismic index parameter of the threaded steel;

[0215] "Rel / Rel standard" is the measured yield strength to standard required yield strength ratio, and is a seismic index parameter of the threaded steel;

[0216] "Bending" means: the steel bars with E should be subjected to reverse bending test, and the steel bars are qualified if no cracks are generated on the surface of the bending part after the reverse bending test.

[0217] The results are shown in the following table:

[0218] Table 5 Performance of high-nitrogen seismic HRB600E (diameter: Φ8mm-Φ32mm)

[0219]

[0220]

[0221] Before the converter tapping, the oxygen content in the molten steel is very high, such as 300-1000ppm, and some alloying elements in the molten steel cannot be oxidized, such as Nb, V, Mo, Cu, etc. First, the amount of the charge is calculated, and then it is directly added after the furnace. Si, Mn, Al, Ti and other elements that are easily oxidized can be calculated by the conventional method in the art to determine the amount of the charge, and these elements are also deoxidizing elements (or deoxidizers). The method for controlling the C content in the steel bar can use the conventional method in the art, such as the delivery standard C content = C content of the molten steel at tapping + C content brought in by the addition of alloy + C content increased by the carbon additive; the LF furnace electrode heating in the refining process also increases C. P and S in the steel bar can be removed by adding lime. The steel bar smelting process includes: first, removing C, P, S in the molten iron (oxidation reaction), then removing oxygen in the molten steel (reduction reaction), and finally making the composition meet the standard requirements.

[0222] The above describes the present application in combination with preferred embodiments, but these embodiments are only exemplary and serve only to illustrate. On this basis, various substitutions and improvements can be made to the present application, and these all fall within the protection scope of the present application.

Claims

1. A high-nitrogen, earthquake-resistant HRB600E steel bar, characterized in that, The ingredients, expressed as a percentage by weight, are as follows: The balance consists of iron and unavoidable impurity elements, Ceq≤0.58%.

2. The high-nitrogen seismic-resistant HRB600E steel bar according to claim 1, characterized in that, The nitrogen content, expressed as a percentage by mass, is 0.0215–0.030%.

3. A method for preparing high-nitrogen seismic-resistant HRB600E steel reinforcement, characterized in that, The composition of the high-nitrogen seismic-resistant HRB600E steel reinforcement, by mass percentage, is as follows: The balance consists of iron and unavoidable impurity elements, Ceq≤0.58%; The preparation method of the high-nitrogen seismic-resistant HRB600E steel reinforcement includes: (1) Converter smelting, with N2 blown from the bottom of the converter throughout the entire process; (2) During tapping, as the molten steel enters the ladle, N2 is blown from the bottom of the ladle at a flow rate of 1200–2000 m³ / h. 3 / h; (3) Refining in a refining furnace, controlling the N2 blowing flow rate in the following four stages: White slag - Sampling stage 200-1200m 3 / h Soft blowing stage (100-300m) 3 / h 100-600m after leaving the refining furnace blowing stage 3 / h (4) The ladle leaves the refining furnace and is cast and rolled to obtain the high-nitrogen earthquake-resistant HRB600E steel bars.

4. The preparation method according to claim 3, characterized in that, During the refining process in step (3), the N2 flow rate during the white slag-sampling stage is 800-1200 m³ / h. 3 / h.

5. The preparation method according to claim 3, characterized in that, When performing the converter smelting described in step (1), the bottom-blown N2 flow rate is controlled in several stages as follows: Slag splash 700-900 Nm 3 / h Add 300-400 Nm of iron 3 / h Refining period 280~420Nm 3 / h Secondary gun sampling 200-300 Nm 3 / h 280-420 Nm 3 / h Manual sampling 200-300 Nm 3 / h Equal sample 200-300 Nm 3 / h.

6. The preparation method according to claim 3, characterized in that, During the tapping process described in step (2), deoxidizer, slag-forming agent, carbon powder, Si-Mn alloy and vanadium-nitrogen alloy are added. The nitrogen content of the vanadium-nitrogen alloy is 10-35%, preferably 15-17% or 29-33%; The vanadium-nitrogen alloy is added when the steel tapping time is greater than or equal to 1 minute in step (2).

7. The preparation method according to claim 6, characterized in that, In step (2), when tapping the steel, the vanadium-nitrogen alloy is added according to the number of times the tapping port is used: The tapping outlet is used for 1 to 20 heats. Vanadium-nitrogen alloy is added bag by bag starting 1.5 minutes after tapping and is completed within 2 to 2.5 minutes. The tapping outlet is used for 21 to 50 heats. Vanadium-nitrogen alloy is added bag by bag starting 1.25 minutes after tapping and is completed in 1.5 to 2 minutes. The steel tapping outlet is used for 51 to 130 heats. Vanadium-nitrogen alloy is added bag by bag starting 1 minute after tapping and is completed in 1 to 1.5 minutes. For steel tapping, after more than 130 heats, vanadium-nitrogen alloy is added bag by bag starting 1 minute after tapping and is completed within 0.5 to 1 minute.

8. The preparation method according to claim 3, characterized in that, When performing the refining process described in step (3): The thickness of the foam slag during the electrode heating stage is 200-250 mm, and the furnace pressure of the refining furnace is 0 to -10 Pa. The thickness of the foam residue in the white residue-sampling stage and the equal sample soft blowing stage is 80-150 mm, preferably 80-135 mm.

9. The preparation method according to claim 3, characterized in that, From the time the ladle leaves the refining furnace until the casting is completed, the molten steel is enriched with nitrogen by 10 to 18 ppm.

10. The preparation method according to any one of claims 3 to 9, characterized in that, Based on the nitrogen content of the high-nitrogen seismic-resistant HRB600E steel bar, the threaded steel bars are rolled as follows: N 210~260ppm, for steel bars with a rolling diameter of 6~14mm; N 240~300ppm, for steel bars with a rolling diameter of 16~25mm; N 260~320ppm, for steel bars with a rolling diameter of 28~40mm; The preferred method is as follows: N 215~260ppm, for steel bars with a rolling diameter of 6~14mm; N 240~280ppm, for steel bars with a rolling diameter of 16~25mm; N 260~300ppm, for steel bars with a rolling diameter of 28~40mm.

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