Method for increasing residual manganese content in deoxidized molten steel for threaded steel

Abstract

The present application belongs to the technical field of steel metallurgy, and particularly relates to a method for increasing residual manganese content in primary refining molten steel of screw thread steel, which adjusts the adding time of scrap steel from before converter blowing to the end of converter blowing, controls the molten steel temperature at the adding time of scrap steel and after that to be above 1600 DEG C, and the reducing property of C is stronger than that of Mn at high temperature, so the oxidation loss rate of Mn in scrap steel is low, in addition, after adding scrap steel, oxygen blowing is continued to decarburize and maintain the molten steel temperature in the range of 1600-1670 DEG C, and the oxygen blowing time is 3-5 min, which is beneficial to the reduction of MnO in slag into molten steel, and improves the recovery rate of Mn element in slag. Moreover, the scrap steel is added after being pressed into a block, the volume and density of the scrap steel are controlled to make it melt in 3-5 min, and the density of the scrap steel is greater than that of molten steel, so in 3-5 min, the scrap steel needs to go through two links of melting into molten steel and diffusion mixing with molten steel, which greatly reduces the contact probability of molten steel formed by melting of scrap steel and oxygen, and improves the recovery rate of Mn element in scrap steel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel metallurgy, and particularly relates to a method for increasing the residual manganese content in the initial molten steel of deformed steel. BACKGROUND

[0002] Hot-rolled deformed steel is the most widely used building steel at present, and the annual consumption is about 200 million tons. If the residual manganese content in the initial molten steel of deformed steel is increased by 0.1% through optimization of the converter steelmaking process, the economic benefit of 2 billion yuan per year nationwide can be increased according to the price of manganese alloy, and the economic benefit is huge.

[0003] According to the common sense of converter steelmaking, the oxidation order of alloy elements in molten iron and scrap steel at different temperatures is: when t<1400℃, the oxidation order of elements is: Si, V, Mn, C, P, Fe; when 1400

[0004] At present, the method of adding scrap steel into the converter before starting smelting is generally used, specifically: first, shake the furnace to a certain angle so that the furnace door is directed to the side of adding scrap steel, then use the crane to add the scrap steel in the scrap steel bucket into the converter through the furnace door, then add molten iron, and then lower the oxygen lance to perform oxygen blowing smelting operation in the converter. In this mode, since the scrap steel is added into the converter before the converter starts blowing, at the initial stage of converter smelting, Mn is rapidly oxidized to form MnO which enters the slag. In the later period, although part of the MnO is reduced to form Mn, due to the short time of the high temperature stage in the later period of converter smelting and the temperature t>1600℃ for only about 1-2 min, only about 20-30% of the MnO is reduced, and the recovery rate of Mn elements in molten iron and scrap steel is still low. A large amount of beneficial metal elements are oxidized and lost into the slag, and the recovery rate of beneficial alloy elements is low.

[0005] Chinese patent document CN105543440A (201511009302.6) discloses a high manganese iron molten decarburization and manganese preservation converter smelting method, including iron molten scrap ratio, initial silicon equivalent control, slag basicity control and free manganese oxide (MnO) reduction, manganese metal in the end point reduction free manganese oxide. The principle of the above patent is mainly to smelt with high manganese iron molten and increase the Mn content in the scrap steel, control the FeO content in the slag at 8-15% at the end point, control the carbon content in the slag greater than or equal to 0.07%, increase the end point temperature at 1679-1965℃, control the steel slag interface reaction (MnO) +

Fe

Mn

C

Mn

[0006] The above patents promote the reduction of MnO by increasing the converter blowing end point temperature and controlling the total iron mass percentage content of the slag, but the technology disclosed in the above patents all add scrap steel before the converter blowing. Since the scrap steel is cold charge, adding scrap steel before the converter blowing will lead to slow heating speed in the early stage of the converter smelting (low temperature stage, Mn in the molten iron is rapidly oxidized, and a large amount of heat is released), and the duration time of the high temperature stage of the molten steel in the late stage of the converter smelting (C can reduce MnO in the slag to elemental Mn in the late stage of the converter smelting) is short, which is not conducive to promoting the reduction of free manganese oxide in the slag into the molten steel in thermodynamics. SUMMARY

[0007] The present application aims at the above problems, and provides a method for increasing the residual manganese content in the primary refining molten steel of screw thread steel, mainly including adjusting and controlling the type, adding time and converter molten steel temperature of scrap steel, increasing the duration of the high temperature stage of molten steel in the converter smelting process, so as to remove the C element in the molten steel to protect the Mn element in the molten steel from being oxidized, and shortening the oxygen blowing time of the molten steel after the scrap steel is melted in the converter, so as to reduce the opportunity of the molten steel formed by the melting of the scrap steel to contact with oxygen at the top of the converter, and reduce the oxidation loss rate of the Mn element in the scrap steel.

[0008] The technical problem to be solved by the present application is solved by the following technical scheme: a method for increasing the residual manganese content in the primary refining molten steel of screw thread steel, comprising the following steps:

[0009] S1, the scrap steel is pressed into blocks, the volume and density of the scrap steel are controlled so that the scrap steel is melted in the molten steel within 3-5 min, and the density of the scrap steel is greater than the density of the molten steel;

[0010] S2, the adding time of the scrap steel is adjusted, the scrap steel is not added before the converter is blown, the scrap steel is added into the converter at the end of the converter blowing, the temperature of the molten steel in the converter is 1600-1650 DEG C before the scrap steel is added, the mass percentage concentration of the C element in the molten steel is controlled within the range of 1.1-1.6%, the mass percentage concentration of MnO in the slag is controlled within the range of 4-6%, the mass percentage concentration of the C element in the molten steel and the mass percentage concentration of MnO in the slag are controlled, the C+MnO→CO+Mn reaction is made to proceed in the positive direction, so as to promote the reduction of MnO in the slag;

[0011] S3, after the scrap steel is added, oxygen blowing and decarburization are continued, so that the temperature of the molten steel is always within the range of 1600-1670 DEG C, and the duration is 3-5 min.

[0012] The technical scheme of the present application further has: in step S1, the scrap steel used is scrap steel bar. The type of the scrap steel added by the present application is adjusted, the type of the scrap steel added into the converter is adjusted to be a steel bar block, the steel bar block is pressed from scrap steel bar, the composition system of the scrap steel bar is basically the same as the target composition system of the molten steel, the alloy elements contained in the scrap steel bar are all needed by the screw thread steel, can be matched with the target composition of the molten steel to the maximum extent, the Mn content in most of the scrap steel bar is 1.2-1.5%, can increase the total amount of the manganese element added into the converter, and the part of the manganese element exists in the form of unoxidized manganese element.

[0013] The technical scheme of the present application further has: in step S1, the scrap steel bar is pressed into a square block, the specification range of the steel bar is Φ12-28 mm, the density of the steel bar block is 2-4 g / cm 3The length, width and height of the steel bar briquetting are all 400-500mm. By controlling the density, size of the steel bar briquetting and the specification of the steel bar, the steel bar briquetting of the size and porosity can be completely melted in 1600 DEG C molten steel for 3-5 minutes, wherein the smaller the volume of the single steel bar briquetting is, the faster the melting speed is, but the cost of the scrap steel processing is increased.

[0014] The technical scheme of the present application further has that the waste steel bar comprises one or more of HRB335, HRB400E, HRB500E and HRB600. Since the Mn content in the waste steel bar is high, and the waste steel bar is melted at the bottom of the molten steel, the Mn element in the molten steel has less chance of being oxidized, the recovery rate of the Mn element in the waste steel bar reaches more than 80%, and the recovery rate of the metal elements such as Nb and V in the waste steel bar is greater than 50%.

[0015] The technical scheme of the present application further has that in step S2, the method for controlling the mass percentage concentration of C element in the molten steel to be 1.1-1.6% and the molten steel temperature to be 1600-1650 DEG C is that: no scrap steel is added before the converter is blown, the total amount of lime added is controlled to be 20-25 kg / ton of steel·furnace, the total amount of dolomite added is controlled to be 7-9 kg / ton of steel·furnace, the total amount of sinter added is controlled to be 8-10 kg / ton of steel·furnace, no other cold charge is added, all the above steelmaking accessories are added before the scrap steel is added, the mass percentage concentration of Si element in the molten iron charged into the furnace is controlled to be in the range of 0.3-0.45%, the mass percentage concentration of Mn element in the molten iron charged into the furnace is controlled to be in the range of 0.3-0.45%, and the total amount of oxygen supplied before the scrap steel is added is controlled to be 110-140 m 3 / ton of steel.

[0016] The technical scheme of the present application further has that in step S2, the method for controlling the mass concentration of MnO in the converter slag to be 4-6% is that: the mass percentage content of Mn element in the iron ore used by the blast furnace is controlled to be 0.2-0.3%, so as to achieve the purpose that the Mn content in the molten iron is 0.3-0.45%, and the total amount of the converter slag is controlled to be 40-66 kg / ton of steel. Through the above control, it can be ensured that more than 80% of the Mn element in the molten iron is oxidized into the converter slag in the early stage of the converter smelting.

[0017] The technical scheme of the present application further comprises the following steps: in step S3, the method for controlling the temperature of the molten steel in the range of 1600-1670 DEG C after adding the scrap steel is as follows: the carbon content at the end of the converter smelting is 0.1-0.2%, and the amount of the scrap steel added is 10-15% of the nominal tonnage of the converter. Since the carbon content at the end of the converter smelting is 0.1-0.2%, after adding the scrap steel, the oxygen blowing decarburization is continued, the carbon content in the molten steel is reduced from 1.1-1.6% to 0.1-0.2%, and the reduction range is 1.0-1.5%. According to the production experience, in the later stage of the converter smelting, the oxygen blowing can remove 1.0-1.5% of C, which can increase the temperature of the molten steel by 150-225 DEG C. According to the specific heat capacity of the scrap steel and the molten steel, the addition of 10-15% of the scrap steel of the nominal tonnage of the converter can reduce the temperature of the molten steel by 150-225 DEG C. Therefore, after adding the scrap steel and continuing the oxygen blowing decarburization, the heat absorption of the melting of the scrap steel and the heat release of the oxygen blowing decarburization reach a dynamic temperature balance, and the temperature of the molten steel is always in the range of 1600-1670 DEG C.

[0018] The technical scheme of the present application further comprises the following steps: in step S1, the water content in the scrap steel is controlled to be less than 1%, so as to reduce the content of the element [H] which is harmful to the performance of the steel.

[0019] The technical scheme of the present application further comprises the following steps: in step S2, the method for adding the scrap steel into the converter is as follows: first, the furnace is shaken to make the furnace door open towards the side where the scrap steel is added, and then the scrap steel briquettes in the scrap steel bucket are added into the converter through the furnace door by using the unmanned vehicle.

[0020] The inventive concept of the present application:

[0021] After the scrap steel briquettes are added into the molten steel, since the density of the scrap steel (about 7.8 g / cm 3 ) is greater than the density of the molten steel (about 7.0 / cm 3 ), the scrap steel sinks to the bottom of the converter. Within 3-5 min, the scrap steel needs to go through two links of melting into molten steel and diffusing and mixing with the molten steel. In such a short time, the molten steel formed by the melting of the scrap steel has a small probability of diffusing to the top of the converter, that is, the molten steel formed by the melting of the scrap steel has a small opportunity to contact with oxygen at the top of the converter, and the C element has a greater reducing property than the Mn element in the continuous high-temperature stage. Therefore, the Mn element in the molten steel formed by the melting of the scrap steel has a small opportunity to be oxidized, and the recovery rate of the Mn element in the scrap steel is more than 80%. In addition, the scrap steel is added into the converter at the end of the converter blowing, which shortens the oxygen blowing time after the melting of the scrap steel in the converter, further reduces the opportunity of the molten steel formed by the melting of the scrap steel to contact with oxygen at the top of the converter, and reduces the oxidation loss rate of the Mn element in the scrap steel. Moreover, the present application prolongs the duration of the high-temperature stage in the later stage of the converter smelting, which is beneficial to the reduction of MnO in the slag into the molten steel and helps to improve the recovery rate of the Mn element in the slag.

[0022] Compared with the prior art, the application has the following advantages:

[0023] 1、The application adjusts the adding time of scrap steel from before the converter blowing to the end of the converter blowing, and the temperature of the molten steel at the adding time of the scrap steel and after that is controlled above 1600℃, the reduction of C is obviously stronger than that of Mn at high temperature, according to the balance diagram of alloy elements and oxygen, the oxygen element in the molten steel reacts with the C element preferentially, so the oxidation loss rate of Mn in the scrap steel is low. In addition, the oxygen blowing decarburization is continued after the scrap steel is added to maintain the temperature of the molten steel in the range of 1600-1670℃, and the oxygen blowing time is 3-5min, which is beneficial to the reduction of MnO in the slag into the molten steel, thereby improving the recovery rate of Mn element in the slag.

[0024] 2、Since the scrap steel is added after being briquetted, the volume and density of the scrap steel are controlled to make it melt in the molten steel within 3-5min, and the density of the scrap steel is greater than that of the molten steel, the oxygen blowing decarburization is carried out after the scrap steel is added to maintain the temperature of the molten steel in the range of 1600-1670℃, and the oxygen blowing time is 3-5min, since the oxygen blowing time is short, within the 3-5min, the scrap steel needs to go through two links of melting into molten steel and diffusing and mixing with the molten steel, within such a short time, the molten steel formed by the melting of the scrap steel has a small probability of diffusing to the top of the converter, and the molten steel formed by the melting of the scrap steel has a small opportunity of contacting with oxygen, the short oxygen blowing time can greatly reduce the contact probability of the molten steel formed by the melting of the scrap steel and oxygen, so the recovery rate of Mn element in the scrap steel is high, and the recovery rate of metal elements is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a balance diagram of Mn and C alloy elements and oxygen. DETAILED DESCRIPTION

[0026] The application will be further described below in combination with the embodiments.

[0027] Embodiment 1

[0028] A threaded steel enterprise wants to reduce the alloy cost, and studies how to "improve the residual manganese content in the molten steel of the converter", the enterprise first analyzes the chemical equation ① of reducing MnO in the C reduction slag as follows:

[0029] C+MnO→CO+Mn ①

[0030] According to the thermodynamic formula, the relationship among the element concentration, gas partial pressure and molten steel temperature at the reaction equilibrium of the above formula is as follows:

[0031] lg([a C ]*[a MnO ] / p co *[a Mn]) = -7.57 + 11600 / T

[0032] a in formula 2 C , a Mn are the mass percentage concentrations of C and Mn elements in the molten steel, respectively (%); [a MnO ] is the mass percentage concentration of (MnO) in the slag (%); p co is the partial pressure of CO in the converter gas (bar); and T is the temperature of the molten steel (K).

[0033] According to formula 2, when the value of [a MnO ] / p co remains unchanged, with the increase of the temperature T of the molten steel, the value of [a C ] / [a Mn ] decreases, that is, the reaction proceeds in the positive direction, and the residual manganese in the molten steel increases.

[0034] According to the analysis results of formula 1 and 2, the enterprise prolongs the duration of the high-temperature stage of the molten steel in the converter smelting process to achieve the purpose of protecting the Mn element in the molten steel from being oxidized by removing the C element in the molten steel; and shortens the oxygen blowing time after the scrap steel is melted in the converter to reduce the opportunity of the molten steel formed by the melting of the scrap steel to contact with oxygen at the top of the converter, and to reduce the oxidation loss rate of the Mn element in the scrap steel. Therefore, a method for increasing the residual manganese content in the preliminary molten steel of deformed steel bars is proposed, and the specific measures are as follows:

[0035] S1, the type of scrap steel added in the converter is adjusted to be a reinforcing bar briquette

[0036] The reinforcing bar briquette is a square block formed by pressing reinforcing bars with a diameter of Φ12-28mm, and the length, width and height of the reinforcing bar briquette are all 450mm. During pressing, 400-500kg of reinforcing bars are weighed in advance, and then pressed into a square mold with a length, width and height of 450mm. The density of the reinforcing bar briquette is calculated to be 4.4-5.5g / cm 3 , and the porosity of the reinforcing bar briquette is calculated to be 29-43% according to the density of the steel.

[0037] The melting time of the reinforcing bar briquette with the above size and porosity in the molten steel at 1600℃ is 3-5min.

[0038] The grade of the scrap reinforcing bar is one or more of HRB335, HRB400E, HRB500E and HRB600, and the component system of the scrap reinforcing bar is basically the same as the target component system of the molten steel, and the alloy elements contained therein are all required by the deformed steel bar and can be matched with the target component of the molten steel to the greatest extent. The Mn content in the scrap reinforcing bar with these grades is basically in the range of 1.2-1.5%.

[0039] S2, scrap steel addition time

[0040] Scrap steel is added into the converter at the time when the converter steel temperature is 1650℃, the C content in the steel is controlled at 1.1% before the addition of the scrap steel, and the MnO content in the slag is 5.6%.

[0041] The method for controlling the C content in the steel at 1.1% and the steel temperature at 1650℃ is as follows: the weight of the molten iron entering the converter is 145 tons, the mass percentage concentration of the Si element in the molten iron entering the converter is controlled within the range of 0.37%, and the mass percentage concentration of the Mn element in the molten iron entering the converter is controlled within the range of 0.35%. No scrap steel is added before the converter is blown, the total amount of lime added is controlled at 22 kg / ton of steel·furnace, the total amount of dolomite added is controlled at 7.8 kg / ton of steel·furnace, the total amount of sinter added is controlled at 8.6 kg / ton of steel·furnace, no other cold charge is added, all the above steelmaking accessories are added completely before the addition of the scrap steel, the total amount of oxygen supplied before the addition of the scrap steel is controlled at 118 m 3 / ton of steel, at the time when the converter is blown for 8 minutes, the temperature is measured by sampling through the sub-lance, the C content in the steel is 1.1%, and the steel temperature is 1650℃.

[0042] The method for controlling the mass concentration of the MnO in the converter slag at 5.6% is as follows: the mass percentage content of the Mn element in the iron ore used by the blast furnace is 0.22% so as to achieve the purpose that the Mn content in the molten iron is 0.37%, and the total amount of the converter slag is controlled at 54 kg / ton of steel. In the early stage of the converter smelting, more than 80% of the Mn element in the molten iron is oxidized into the converter slag.

[0043] The method for adding the scrap steel into the converter is as follows: the converter is shaken to a certain angle of inclination at the furnace door, the converter body is directed to the side of the scrap steel, then the reinforcement briquettes in the scrap steel bucket are added into the converter through the furnace door by using the unmanned vehicle, and the water content in the reinforcement briquettes is controlled at less than 1%.

[0044] The amount of the scrap steel added is 15% of the nominal tonnage of the converter, the nominal tonnage of the converter is 150 tons, and the amount of the scrap steel added is 22.5 tons,

[0045] S3, converter steel temperature control method

[0046] As described above, no scrap steel is added before the converter is blown, the steel is rapidly heated, at the time when the temperature is heated to 1650℃, the C content in the steel is controlled at 1.1%, the scrap steel is added at this time, and the oxygen decarburization is continued, due to the heat absorption of the melting of the scrap steel and the heat release of the oxygen decarburization, the dynamic temperature balance is achieved, the steel temperature is always within the range of 1620-1670℃, the oxygen decarburization is continued for 4 minutes, the converter is tapped, at the time when the converter smelting is completed, the steel temperature is 1653℃, the C content in the steel is 0.16%, the MnO content in the slag is 2.7%, and the CO partial pressure in the converter gas is 0.33 bar.

[0047] Substitute the steel temperature, C content, MnO content in the slag, and CO partial pressure in the converter gas at the end of the converter smelting process into both sides of equation ② to calculate the Mn content at equilibrium of reaction equation ①:

[0048] lg(0.16*0.027 / 0.33*[a Mn = -7.57 + 11600 / (273 + 1653)

[0049] Solution: lg(0.0131 / [a Mn ])=-1.547

[0050] 0.0131 / [a Mn ] = 0.0284

[0051] [a Mn ] = 0.461%

[0052] From the above calculations, it can be seen that the Mn content in the molten steel at equilibrium with the converter smelting endpoint conditions is 0.461%. Based on the actual manganese content in the scrap steel added during steelmaking being 1.2-1.5%, and the manganese content in the molten iron being 0.35%, and the scrap steel addition being 15% of the nominal tonnage of the converter, the maximum Mn content in the molten steel calculated using the weighted average method is: (0.15*1.5+0.96*0.35-2.7*54 / 1000)=0.415%. The above calculation method is existing technology and will not be elaborated here. Since the "maximum Mn content in the molten steel" is less than the "Mn content in the molten steel at equilibrium with the converter smelting endpoint conditions," reaction ① proceeds in the positive direction under the converter smelting endpoint conditions, achieving the purpose of "protecting the Mn element in the molten steel from oxidation by removing the C element."

[0053] After the converter blowing process was completed, a sample of the molten steel was taken and tested. The manganese content in the molten steel was 0.31%, indicating a high residual manganese content.

[0054] Example 2

[0055] The company used the above technology to smelt 5 more batches of rebar. The technical parameters involved are shown in Table 1. Other technical contents are the same as in Example 1.

[0056] Table 1. Technical parameters of five furnaces of rebar smelting in Example 2

[0057]

[0058]

[0059] As can be seen from Table 1, after using the method described in this application to increase the residual manganese content in the initial rebar smelting molten steel, the manganese content in the final molten steel of the converter smelting is 0.29-0.33%, with an average of 0.302%.

[0060] Example 3

[0061] The enterprise continues to smelt 5 furnaces of threaded steel using the above technology, and the technical parameters involved are shown in Table 2. The difference from Example 1 is that the scrap steel is a social scrap steel briquette, and the other technical contents are the same as those of Example 1.

[0062] Table 2, technical parameters of smelting five furnaces of threaded steel in Example 3

[0063]

[0064]

[0065] As can be seen from Table 2, using social scrap steel and using the original scrap steel composition, only compression is performed, and after using the method for increasing the residual manganese content in the primary molten steel of threaded steel described in the present application, the manganese content in the molten steel at the end of the converter smelting is 0.23-0.26%, with an average of 0.244%.

[0066] Comparative Example 1

[0067] A threaded steel enterprise smelts threaded steel using a traditional process, and the specific process is as follows:

[0068] 1. Add scrap steel before the converter starts blowing, and the scrap steel addition amount is 10-15% of the nominal tonnage of the converter. First, shake the furnace to a certain angle so that the furnace door is directed to the side where the scrap steel is added, and then use the crane to add the reinforcement briquettes in the scrap steel bucket through the furnace door into the converter. The type of scrap steel is not limited, the volume of scrap steel is not more than 0.125m 3 , the length is not more than 1.5m, and the single weight is not more than 1500kg. After adding the scrap steel, add molten iron, and the molten iron addition amount is 95-100% of the nominal tonnage of the converter. The Si content in the molten iron is 0.2-0.4%, and the Mn content is 0.2-0.5%.

[0069] 2. After the converter starts blowing, use the normal oxygen supply process system for decarburization. The oxygen consumption during the entire smelting process is 170-190m 3 / ton of steel, the entire blowing process lasts for 12-13min, and the total amount of auxiliary materials added during the entire smelting process is controlled as follows: the total amount of lime added is controlled at 20-25kg / ton of steel·furnace, the total amount of dolomite added is controlled at 7-9kg / ton of steel·furnace, and the total amount of sinter added is controlled at 8-10kg / ton of steel·furnace. No other cold materials are added. The carbon content at the end of the converter smelting is controlled in the range of 0.14-0.20%, and the molten steel temperature at the end of the converter smelting is controlled in the range of 1600-1670℃.

[0070] The above process is used to smelt 5 furnaces of steel, and the specific process parameters of the 5 furnaces of steel are shown in Table 3:

[0071] Table 3. Technical parameters for smelting five batches of rebar using existing traditional technology

[0072]

[0073]

[0074] As can be seen from Table 3, in comparison with Example 1, which uses existing conventional technology to smelt rebar, the manganese content in the molten steel at the end of the converter smelting was 0.13-0.17%, with an average of 0.15%.

[0075] Comparing Tables 1 and 3, there are almost no differences in the process parameters of molten iron composition, molten iron quantity, scrap steel addition amount, converter steelmaking auxiliary material addition amount, converter oxygen supply, converter smelting endpoint temperature, and converter smelting endpoint carbon content. However, there are significant differences in the scrap steel addition type, scrap steel addition timing, converter smelting endpoint manganese content, and converter smelting endpoint slag MnO content between Tables 1 and 3.

[0076] After using the method described in this application to increase the residual manganese content in the initial refining molten steel of rebar in Examples 1 and 2, the manganese content in the final molten steel of the converter smelting was 0.29-0.33%, with an average of 0.31%. The residual manganese content in the initial refining molten steel of the converter in Examples 1 and 2 was significantly higher than that in Comparative Example 1. The reasons for this include the following three points:

[0077] (1) The scrap steel in Examples 1 and 2 is scrap steel bar briquettes. The scrap steel bars have a high manganese content, and the Mn content in the scrap steel bars is basically in the range of 1.2-1.5%. However, there are no requirements for the composition of scrap steel in Comparative Example 1. Currently, most of the scrap steel in society is ordinary carbon steel with a manganese content of less than 0.6%. Therefore, its manganese content is low. After being added to the converter, the total amount of original manganese elements brought into the molten steel of the converter is low, which affects the manganese content at the end of the converter.

[0078] (2) In Examples 1 and 2, the timing of scrap steel addition was adjusted from before converter blowing to the end of converter blowing. The temperature of the molten steel after adding scrap steel was controlled above 1600℃. At high temperatures, the reducing power of C is significantly stronger than that of Mn. Figure 1 The diagram showing the equilibrium relationship between Mn, C alloying elements and oxygen (Steel Metallurgy, by F. Otts, Metallurgical Industry Press, June 1997, p. 66) shows that the CO line is below the MnO line. Therefore, less C reacts with the same amount of [O] to reach equilibrium than Mn, meaning that C is more easily oxidized than Mn. In other words, oxygen in the molten steel preferentially reacts with C, resulting in a lower oxidation loss rate of Mn. C also reduces some of the MnO in the slag. The final stage of converter smelting has a high manganese content in the molten steel and a low MnO content in the slag.

[0079] The adding time of the scrap steel in Comparative Example 1 is before the converter is blown, and in the initial stage of the converter smelting, Mn is rapidly oxidized to form MnO and enter the slag. In the later stage, although part of the MnO is reduced to form Mn element, due to the short time of the high temperature stage in the later stage of the converter smelting and the time of the temperature t>1600℃ is only about 1-2 min, only about 20-30% of the MnO is reduced, the recovery rate of the Mn element in the molten iron and the scrap steel is still low, the content of MnO in the slag is high, and a large amount of beneficial metal elements are oxidized and lost into the slag, and the recovery rate of the beneficial alloy elements is low.

[0080] (3) The blowing time of the oxygen after the scrap steel is added in Example 1 and 2 is only 3-5 min, and in the 3-5 min, the scrap steel needs to go through two links of melting into the molten steel and diffusing and mixing with the molten steel. In such a short time, the molten steel formed by the melting of the scrap steel has a small probability of diffusing to the top of the converter, and the molten steel formed by the melting of the scrap steel has a small opportunity of contacting with the oxygen. The short blowing time can greatly reduce the contact probability of the molten steel formed after the melting of the scrap steel and the oxygen, so the recovery rate of the Mn element in the scrap steel is high, and the recovery rate of the metal element is improved.

[0081] The adding time of the scrap steel in Comparative Example 1 is before the converter is blown, and the blowing time of the oxygen after the scrap steel is added is 12-13 min. Generally, the scrap steel is melted after 5 min of the blowing of the converter, and the blowing of the oxygen is still performed for 7-8 min after the melting of the scrap steel. The molten steel after the melting of the scrap steel is in contact with the oxygen jet or the oxidizing slag for a long time, and the long oxidation time inevitably leads to a high oxidation loss rate of the manganese element, so the recovery rate of the Mn element in the scrap steel is low.

[0082] The scrap steel used in Example 3 is social scrap steel, and only the composition of the original scrap steel is compressed. After the method for improving the residual manganese content in the initial molten steel of the deformed steel bar is used, the manganese content in the molten steel at the end of the converter smelting is 0.23-0.26%, and the average value is 0.244%. The average value of the manganese content is lower than that in Example 2 but higher than that in Comparative Example 1, and the reason is that: (1) the scrap steel in Example 3 is a social scrap steel briquette, and most of the current social scrap steel is plain carbon steel with a manganese content lower than 0.6%, so the manganese content is low, the total amount of the original manganese element brought into the molten steel in the converter is low after the scrap steel is added into the converter, and the manganese content at the end of the converter smelting is affected, so the manganese content in the molten steel at the end of the converter smelting is lower than that in Example 2. (2) the adding time of the scrap steel in Example 3 is changed to the end of the blowing of the converter according to the method of the application, the adding time of the scrap steel and the temperature of the molten steel after the adding time are controlled to be higher than 1600℃, the duration of the high temperature stage of the molten steel reaches 3-5 min, part of the MnO in the slag is reduced by C at the high temperature, the manganese content in the molten steel at the end of the converter smelting is high, the content of MnO in the slag at the end of the converter smelting is low, and therefore the manganese content in the molten steel at the end of the converter smelting is higher than that in Comparative Example 1.

[0083] Comparing Example 1, 2 and Comparative Example 1, the residual manganese content in the thread steel initial molten steel is increased from 0.15% to 0.31% by using the technology described in the application, the residual manganese content is increased by 0.16%, and the benefit calculated at the price of high-carbon ferromanganese alloy is:

[0084] The price of high-carbon ferromanganese is 6400 yuan / ton, the high-carbon ferromanganese contains 68% manganese, and the manganese recovery rate after adding high-carbon ferromanganese into the molten steel is 96%. The calculated alloy cost required to increase 0.16% Mn in the molten steel is: 6400*0.16 / (100*0.68*0.96) = 15.68 yuan / ton of steel.

[0085] After using the technology described in the application, the residual manganese content in the thread steel initial molten steel can be increased by 0.16%, and the amount of ferromanganese added can be correspondingly reduced, and the alloy cost can be reduced by 15.68 yuan / ton of steel. Based on the annual production of 3 million tons of domestic large steel, the alloy cost can be reduced by 300 million tons of steel * 15.68 yuan / ton of steel = 4704 million yuan per year. If it is popularized to the whole country, the alloy cost can be reduced by several billion yuan per year, and the economic benefit is significant.

Claims

1. A method for increasing the residual manganese amount in the hot metal of a thread steel, characterized in that, The method comprises the following steps: S1, the scrap steel is briquetted, the volume and density of the scrap steel are controlled so that the scrap steel melts in 3-5 minutes in the molten steel, and the density of the scrap steel is greater than the density of the molten steel; S2, the adding time of the scrap steel is adjusted, no scrap steel is added before the converter is blown, the scrap steel is added into the converter at the end of the converter blowing, the temperature of the molten steel in the converter is 1600-1650 DEG C before the scrap steel is added, the mass percentage concentration of C element in the molten steel is controlled in the range of 1.1-1.6%, and the mass percentage concentration of MnO in the slag is controlled in the range of 4-6%; S3, after the scrap steel is added, oxygen blowing is continued to decarburize, so that the temperature of the molten steel is always in the range of 1600-1670 DEG C, and the process lasts for 3-5 minutes.

2. The method for increasing the residual manganese amount in the hot metal of a thread steel according to claim 1, characterized in that: In step S1, the scrap steel used is scrap steel bar.

3. The method for increasing the residual manganese amount in the initial steel melt of a threaded steel according to claim 2, characterized in that: In step S1, the waste steel bars are pressed into cubic blocks, the steel bars have a diameter of Φ12-28mm, the density of the steel bar blocks is 2-4g / cm 3 , and the length, width and height of the steel bar blocks are all 400-500mm.

4. The method for increasing the residual manganese amount in the initial steel melt of a threaded steel according to claim 2, characterized in that: The scrap steel bar comprises one or more of HRB335, HRB400E, HRB500E and HRB600.

5. The method for increasing the residual manganese amount in the hot metal of a thread steel according to claim 1, characterized in that: In step S2, the method for controlling the mass percentage concentration of C element in the molten steel to be 1.1-1.6% and the temperature of the molten steel to be 1600-1650°C is as follows: no scrap steel is added before the converter is blown, the total amount of lime added is controlled to be 20-25 kg / ton of steel·furnace, the total amount of dolomite added is controlled to be 7-9 kg / ton of steel·furnace, the total amount of sinter added is controlled to be 8-10 kg / ton of steel·furnace, no other cold charge is added, all the above steelmaking accessories are added before the scrap steel is added, the mass percentage concentration of Si element in the molten iron charged into the furnace is controlled to be in the range of 0.3-0.45%, the mass percentage concentration of Mn element in the molten iron charged into the furnace is controlled to be in the range of 0.3-0.45%, and the total amount of oxygen supplied before the scrap steel is added is controlled to be 110-140 m 3 / ton of steel.

6. The method of increasing the residual manganese content of the hot metal of the steel grade for threaded bars according to claim 1, characterized in that: In step S2, the method for controlling the mass concentration of MnO in the converter slag to be 4-6% is as follows: the mass percentage content of Mn element in the iron ore used in the blast furnace is controlled to be 0.2-0.3%, so that the content of Mn in the molten iron is 0.3-0.45%, and the total amount of the converter slag is controlled to be 40-66 kg / ton of steel.

7. The method of increasing the residual manganese content of the hot metal of the steel grade for threaded bars according to claim 1, characterized in that: In step S3, after the scrap steel is added, the method for controlling the temperature of the molten steel to be always in the range of 1600-1670 DEG C is as follows: the carbon content at the end of the converter smelting is 0.1-0.2%, and the amount of the scrap steel added is 10-15% of the nominal tonnage of the converter.

8. The method of increasing the residual manganese content of the hot metal of the steel grade for threaded bars according to claim 1, characterized in that: In step S1, the water content in the scrap steel is controlled to be less than 1%.

9. The method of increasing the residual manganese content of the hot metal of the steel grade for threaded bars according to claim 1, characterized in that: In step S2, the method for adding the scrap steel into the converter is as follows: the converter is shaken until the converter body is inclined so that the furnace door is directed to the side where the scrap steel is added, and then the scrap steel briquetted in the scrap steel bucket is added into the converter through the furnace door by using the unmanned vehicle.

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