A method for producing 308L high alloy steel by adopting AOD converter secondary smelting

Abstract

The application discloses a method for producing 308L high alloy steel by adopting AOD converter secondary smelting, which comprises a primary smelting main decarburization stage, a primary smelting alloy smelting stage, a primary smelting reduction stage, a tapping and slagging operation, a secondary smelting oxidation stage, a secondary smelting reduction stage and a desulfurization tapping operation. The method adopts the mode of AOD converter twice smelting, the primary smelting utilizes the condition of AOD converter top side combined blowing, completes the alloying of metal materials, controls the C content of molten steel to be less than or equal to 0.2%, and the temperature is 1650-1700 DEG C, and then the molten steel is tapped and slagged. Before the secondary smelting, the required alloy materials are placed on the bottom of the AOD converter according to the tapping composition of the primary smelting, the molten steel after slagging is poured into the AOD converter to re-smelt and perform secondary smelting, the alloy components Ni and Cr are accurately controlled, and the yield of the alloy components Ni and Cr is improved. Meanwhile, under the effective control of the smelting process temperature, the erosion of the converter lining is obviously reduced, and the C content of the AOD converter tapping can be controlled to be within 0.005%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high alloy stainless steel smelting, in particular to a method for producing 308L high alloy steel by adopting AOD converter secondary smelting. BACKGROUND

[0002] The 308L high alloy steel has excellent corrosion resistance and high temperature resistance, but due to its high alloy content, there are problems such as difficulty in decarburization, high smelting process temperature, and inability to accurately control alloy composition during AOD converter smelting, which not only causes serious erosion to the AOD converter lining, but also increases the processing time of the LF refining furnace and the amount of alloy added, ultimately affecting the control of C, Ni, and Cr element content in the finished product. Therefore, how to control the composition and temperature of the AOD converter tapping directly determines the success or failure of high alloy steel smelting. SUMMARY

[0003] The present application aims to solve the above technical problems existing in the existing smelting method of 308L high alloy steel, and provides a method for producing 308L high alloy steel by adopting AOD converter secondary smelting. Specifically:

[0004] The AOD converter is used for twice smelting, that is, the first smelting utilizes the condition of AOD converter top side combined blowing to complete the alloying of metal materials, and at the same time, the C content is controlled within 0.2%, and the temperature is controlled within 1650-1700℃, then the steel is tapped and slag is removed. Before the second smelting, the required alloy materials are placed on the bottom of the AOD converter according to the tapping composition of the first smelting, and then the molten steel after slag removal is poured into the AOD converter for secondary smelting, so that the alloy components Ni and Cr are accurately controlled, and the yield of alloy components Ni and Cr is improved. At the same time, under the effective control of the smelting process temperature, the erosion of the converter lining can be significantly reduced, and the C content of the AOD converter tapping can be controlled within 0.005%.

[0005] To achieve the purpose, the present application adopts the following technical scheme:

[0006] A method for producing 308L high alloy steel by adopting AOD converter secondary smelting, comprising the following steps:

[0007] (1) Main decarburization of the first smelting: the mixed molten iron of intermediate frequency furnace and three decarburization is poured into the AOD converter, 1-3t of lime and 2-3t of dolomite are added, and then 300Nm of oxygen is blown from the side to take a sample of molten iron, and then O2:N2=7:1 top side combined blowing is adopted for oxygen supply, and the final carbon content is ≤0.2%; 3

[0008] (2) Alloy smelting of the first smelting: calculate the amount of high-carbon chromium iron, nickel alloy, and electrolytic manganese to be added, and add lime to control the slag binary basicity R≤3.0;​

[0009] (3) primary smelting reduction;

[0010] (4) tapping and slagging;

[0011] (5) secondary smelting oxidation: according to the composition of the primary smelting reduction, the amount of high-carbon chromium iron and crude nickel required is calculated, then the high-carbon chromium iron and crude nickel are laid on the bottom of the AOD converter, and then the molten steel after slagging is mixed into the AOD converter for secondary smelting, and the slag binary basicity R is controlled to be less than or equal to 3.0;

[0012] (6) secondary smelting reduction: in the secondary smelting reduction stage, 500-800 Nm 3 / min of Ar is blown at a rate of 300 Nm 3 / min to remove nitrogen, according to the oxygen consumption of the side blowing in the smelting process and the target silicon content of the molten steel, the amount of ultra-low-carbon silicon iron and fluorite is added, the amount of ultra-low-carbon silicon iron added = oxygen consumption of side blowing * 1.66 + molten steel volume * target molten steel silicon content / 0.75 (1.25 Kg of Si is required for 1 standard of oxygen, and the silicon content in silicon iron is 0.75%, so 1.25 Kg of Si is converted to 1.66 Kg of silicon iron), the amount of fluorite is added according to 17-20% of the amount of lime, and the slag binary basicity R is controlled to be 1.9;

[0013] (7) desulfurization tapping.

[0014] As a further preferred technical solution of the present application, in step (1), the initial carbon content of the mixed molten iron of the three depletions is greater than 4.0%, the silicon content is greater than 0.4%, and the initial temperature is less than or equal to 1400℃, to ensure that the temperature control in the primary smelting process of the AOD converter is within the range of 1650-1700℃.

[0015] Further, in step (3), after calculating the oxidation amount of Cr element according to the oxygen consumption in the smelting process, the reduction silicon iron is added to make the chromium in the slag fully reduced into the molten steel, and the slag binary basicity R is controlled to be 1.9, and then the molten steel is tapped and slagged.

[0016] Further, in step (5), in the secondary smelting oxidation stage, the main decarburization AOD converter adopts O2:N2=1:2 side blowing oxygen supply, and the oxygen blowing amount is calculated according to the target values of carbon and oxygen content in the target composition of the molten steel, and 3-5 t of lime is added; dynamic decarburization adopts O2:N2=1:3 side blowing oxygen supply, and the terminal carbon content is less than or equal to 0.005%.

[0017] Further, in step (7), according to the reduction S content, the desulfurization tapping stage is carried out, and the slag binary basicity R is controlled to be 2.0.

[0018] The beneficial effects of the present application are:

[0019] The present application significantly reduces the erosion of the AOD converter lining by adopting the mode of twice smelting high alloy steel 308L in the AOD converter, the AOD converter can not only accurately control the alloy composition, but also effectively control the content of C and N in the AOD converter, and ensure that the content of C, N and Cr, Ni in the finished product is within the target range, so that the LF refining can be carried out smoothly, and the required 308L high alloy steel is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The process flow chart of the method for smelting high alloy steel 308L in the AOD converter according to the present application.

[0021] Figure 2 The 308L steel slab microstructure diagram obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0022] The present application will be described in detail below in combination with the drawings and specific examples.

[0023] Example 1

[0024] Step one: iron charging. When smelting in the AOD converter, mixed iron water of three dephosphorization and medium frequency furnace is used, the composition of the iron water is C: 4.02%, Si: 0.485%, Mn: 0.118%, P: 0.0098%, S: 0.088%, Cr: 10.936%, Ni: 8.85%, the iron charging amount is 93.5t, and the temperature of the furnace is 1398℃.

[0025] Step two: twice smelting process in the AOD converter:

[0026] a. Primary smelting main decarburization stage: after the mixed iron water of medium frequency furnace and three dephosphorization is charged into the AOD converter, 1.5t of lime and 3t of dolomite are added, and then 300Nm 3 of oxygen is blown from the side to take the iron water sample. Then O2:N2=7:1 top and side combined blowing is used to supply oxygen, and the final carbon content is controlled to be 0.1%.

[0027] b. Primary smelting alloy smelting stage: through the smelting model, the addition amount of high-carbon chromium iron and nickel alloy is calculated, the slag basicity is controlled according to R≤3.0, the lime is added in three batches, the cumulative addition amount of high-carbon chromium iron is 18.7t, the addition amount of nickel alloy is 4.5t, the addition amount of crude nickel is 2t, the addition amount of electrolytic manganese is 2t, and the addition amount of lime is 11t.

[0028] c. Primary smelting reduction stage: according to the oxygen consumption in the smelting process (the oxygen consumption in the oxidation stage of the molten steel, 6460Nm 3), the oxidation amount of Cr element was calculated, and then 2105 Kg of reduced ferrosilicon was added, the reduction basicity R = 1.9, and the reduction composition was C: 0.1661%, Si: 0.585%, Mn: 0.139%, P: 0.0142%, S: 0.001%, Cr: 20.810%, and Ni: 9.756%;

[0029] d. Tapping and slagging.

[0030] e. Secondary smelting oxidation stage: according to the reduction composition of the primary smelting, 0.5 t of high-carbon chromium iron and 1.6 t of crude nickel were laid on the bottom of the AOD converter, and then the molten steel after slagging was charged into the AOD converter for secondary smelting. O2:N2=1:2 side blowing oxygen was used for main decarburization, and 3 t of lime was added.

[0031] f. Dynamic decarburization was carried out by using O2:N2=1:3 side blowing oxygen, and the target carbon content was controlled at 0.018%. Then the temperature was measured by turning the furnace, and the oxygen amount was supplemented according to the sampling results. The final carbon content was 0.0031%.

[0032] g. Secondary reduction stage: 500 Nm 3 / min of Ar was blown at a rate of 300 Nm 3 / min to remove nitrogen, 2100 Kg of ultra-low-carbon ferrosilicon and 350 Kg of fluorite were added according to the oxygen consumption during the smelting process and the target silicon content of the molten steel (oxygen consumption = the content of C and Si in the oxidation of the reduction composition + the content of C and Si in the oxidation of the secondary smelting supplemented high-carbon chromium iron), the reduction basicity R = 1.9, and the secondary reduction composition was C: 0.0035%, Si: 0.355%, Mn: 1.899%, P: 0.014%, S: 0.0024%, Cr: 20.100%, Ni: 10.626%, and N: 0.0692%.

[0033] h. Desulfurization and tapping: the composition of the finished product was C: 0.0042%, Si: 0.309%, Mn: 1.917%, P: 0.014%, S: 0.0013%, Cr: 20.073%, Ni: 10.827%, and N: 0.0340%.

[0034] The composition of the finished product is shown in Table 1.

[0035]

[0036] In this embodiment, the yield of nickel reached 93.55%, the yield of chromium reached 96.69%, and the C and N contents of the finished product were 0.0153% and 0.041% respectively, indicating that the AOD converter twice smelting process of 308L high alloy steel is feasible, and can significantly improve the yield of chromium and nickel and reduce the production cost.

[0037] In addition, from the quality feedback of the 308L continuous casting and rolling process, the slab quality is good, and no metallurgical defects are found Figure 2 , which has certain application value.

[0038] Example 2

[0039] Step one: iron. When AOD converter smelting is used with mixed iron of three-removal and intermediate frequency furnace, the composition of the molten iron is C: 4.03%, Si: 0.48%, Mn: 0.145%, P: 0.0124%, S: 0.0335%, Cr: 11.008%, Ni: 10.77%, the amount of iron is 98.5t, and the temperature of the furnace is 1381℃.

[0040] Step two: AOD converter two smelting process:

[0041] a. Primary smelting main decarburization stage: after the mixed iron of intermediate frequency furnace and three-removal is added into the AOD converter, 2t of lime and 3t of dolomite are added, and 300Nm 3 of oxygen is blown from the side, and then the molten iron sample is taken. Then O2:N2=7:1 top and side combined blowing is used to supply oxygen, and the terminal carbon content is controlled to be 0.06%.

[0042] b. Primary smelting alloy smelting stage: through the smelting model, the amount of high-carbon chromium iron and nickel alloy is calculated, the slag basicity is divided into three batches according to R≤3.0, the amount of lime is added, the cumulative amount of high-carbon chromium iron is 18.9t, the amount of nickel alloy is 1.9t, the amount of crude nickel is 2.2t, the amount of electrolytic manganese is 2t, and the amount of lime is 12.5t.

[0043] c. Primary smelting reduction stage: according to the oxygen consumption in the smelting process (oxygen consumption in the molten steel oxidation stage, 7405Nm 3 ), the oxidation amount of Cr element is calculated, and then 2500Kg of reducing ferrosilicon is added, the reduction basicity R=1.9, and the reduction composition is C: 0.062%, Si: 0.327%, Mn: 0.157%, P: 0.016%, S: 0.001%, Cr: 20.770%, Ni: 9.517%;

[0044] d. Tapping and slagging.

[0045] e. Secondary smelting oxidation stage: according to the reduction composition of the primary smelting, 0.7t of high-carbon chromium iron and 1.2t of crude nickel are calculated, which are laid on the bottom of the AOD converter, and then the molten steel after slagging is added into the AOD converter for secondary smelting, O2:N2=1:2 side blowing oxygen is used for main decarburization, and 3.5t of lime is added.

[0046] f. Dynamic decarburization adopts O2:N2=1:3 side blowing oxygen, the target carbon content is controlled to be 0.015%, then the furnace is inverted to measure the temperature and take the sample, according to the sampling result, the oxygen amount is supplemented, and the terminal carbon content is 0.0033%.

[0047] g. Secondary reduction stage: using 300Nm 3 Blowing in 500 Nm at a rate of / min 3 Ar was denitrified. Based on the side-blown oxygen consumption during the smelting process and the target silicon content of the molten steel (side-blown oxygen consumption = C and Si content in the primary oxidation-reduction composition + C and Si content in the high-carbon ferrochrome added during the secondary oxidation smelting), 1803 kg of ultra-low carbon ferrosilicon and 300 kg of fluorite were added. The reducing basicity R = 1.9, and the secondary reduction composition was C: 0.0031%, Si: 0.319%, Mn: 1.657%, P: 0.0159%, S: 0.0025%, Cr: 19.985%, Ni: 10.531%, and N: 0.0453%.

[0048] h. Desulfurization and tapping: The steel composition is C: 0.0066%, Si: 0.276%, Mn: 1.835%, P: 0.0159%, S: 0.0017%, Cr: 20.193%, Ni: 10.807%, N: 0.0375%.

[0049] The composition of the finished product is shown in Table 2.

[0050]

[0051] In this embodiment, the nickel yield reached 94.12%, the chromium yield reached 96.53%, and the C and N contents of the finished product were 0.0138% and 0.041%, respectively.

[0052] Example 3

[0053] Step 1: Iron Mixing. The AOD converter uses a mixture of molten iron from a three-stage desulfurization process and an intermediate frequency furnace. The molten iron composition is: C: 4.05%, Si: 0.42%, Mn: 0.117%, P: 0.0082%, S: 0.0125%, Cr: 10.793%, Ni: 11.352%. The amount of iron mixed is 96.6t, and the furnace temperature is 1392℃.

[0054] Step Two: Two-stage smelting process in the AOD converter:

[0055] c. Primary decarburization stage of smelting: After the mixed molten iron from the medium-frequency furnace and the three decarburization processes is added to the AOD converter, 2t of lime and 3t of dolomite are added, and 300Nm of side-blown gas is injected. 3 After oxygen was introduced, molten iron samples were taken. Then, oxygen was supplied by top-side reblowing using an O2:N2 ratio of 7:1, and the carbon content was controlled to be 0.06% at the endpoint.

[0056] d. Primary smelting alloy smelting stage: through the smelting model, the amount of high-carbon chromium iron, nickel alloy is calculated, the slag basicity is added according to R≤3.0 three batches of lime amount, the cumulative addition of high-carbon chromium iron is 18.1t, nickel alloy is 5t, electrolytic manganese is 1.9t, and lime is 12t.

[0057] c. Primary smelting reduction stage: according to the oxygen consumption of the smelting process, that is, the oxygen consumption of the molten steel oxidation stage (6800Nm 3 ), the oxidation amount of Cr element is calculated, and then 2620Kg of reduced ferrosilicon is added, the reduction basicity R=1.9, and the reduction composition is C:0.064%, Si:0.142%, Mn:0.139%, P:0.013%, S:0.002%, Cr:21.126%, and Ni:10.631%;

[0058] d. Tapping and slagging.

[0059] e. Secondary smelting oxidation stage: according to the reduction composition of the primary smelting, 0.5t of high-carbon chromium iron and 600Kg of crude nickel are calculated, which are laid on the bottom of the AOD converter, and then the molten steel after slagging is mixed into the AOD converter for secondary smelting, O2:N2=1:2 side blowing oxygen is used for main decarburization, and 3t of lime is added.

[0060] f. Dynamic decarburization adopts O2:N2=1:3 side blowing oxygen, and the target carbon content is controlled at 0.010%, then the furnace is reversed to measure the temperature and sample, and the oxygen amount is supplemented according to the sampling result, and the final carbon content is 0.0042%.

[0061] g. Secondary reduction stage: 500Nm 3 of Ar is blown at a rate of 300Nm 3 / min for denitrification, according to the side blowing oxygen consumption of the smelting process and the target molten steel silicon content (side blowing oxygen consumption=oxidation of C and Si content in the reduction composition+oxidation of C and Si content in the added high-carbon chromium iron in the secondary smelting), 1953Kg of ultra-low-carbon ferrosilicon and 350Kg of fluorite are added, the reduction basicity R=1.9, and the secondary reduction composition is C:0.0048%, Si:0.294%, Mn:1.723%, P:0.013%, S:0.002%, Cr:20.550%, Ni:10.637%, and N:0.048%.

[0062] h. Desulfurization and tapping: the composition of the tapping is C:0.0063%, Si:0.352%, Mn:1.813%, P:0.0135%, S:0.0011%, Cr:20.320%, Ni:10.736%, and N:0.0356%.

[0063] The finished product composition is shown in Table 3.

[0064]

[0065] In this embodiment, the yield of nickel reached 94.22%, the yield of chromium reached 95.58%, and the contents of C and N in the finished product were 0.0179% and 0.043%, respectively.

Claims

1. A method for producing 308L high alloy steel by secondary smelting with an AOD converter, characterized in that, It comprises the following steps: (1) One-time smelting main decarburization: the intermediate frequency furnace and the mixed molten iron of three decarburization are mixed into the AOD converter, 1-3 tons of lime and 2-3 tons of dolomite are added, 300 Nm 3 of oxygen is blown from the side, then O2:N2=7:1 top and side combined blowing is used, and the final carbon content is ≤0.2%; (2) Alloy smelting: the amount of high-carbon ferrochrome, nickel alloy and electrolytic manganese is calculated, and lime is added to control the slag binary basicity R≤3.0; (3) Primary smelting reduction; (4) Tapping and slagging; (5) Secondary smelting oxidation: the amount of high-carbon ferrochrome and crude nickel is calculated according to the composition of primary smelting reduction, then the high-carbon ferrochrome and crude nickel are laid on the bottom of the AOD converter, and then the molten steel after slagging is mixed into the AOD converter for secondary smelting, and the slag binary basicity R≤3.0 is controlled; (6) Secondary smelting reduction: the secondary smelting reduction stage is denitrified by blowing 500-800 Nm 3 of Ar at a rate of 300 Nm 3 / min, and according to the oxygen consumption of the side blowing and the target silicon content of the molten steel in the smelting process, super-low-carbon ferrosilicon and fluorite are added, the addition amount of the super-low-carbon ferrosilicon = oxygen consumption of side blowing x 1.66 + molten steel amount x target molten steel silicon content / 0.75, the addition amount of fluorite is added according to 17-20% of the amount of lime, and the binary basicity R of the slag is controlled to be 1.

9. (7) Desulfurization tapping.

2. A method of producing 308L high alloy steel by secondary refining using an AOD converter according to claim 1, characterized in that, In step (1), the initial carbon content of the mixed molten iron of three desulfurization is >4.0%, the silicon content is >0.4%, and the initial temperature is ≤1400℃.

3. A method of producing 308L high alloy steel by secondary refining using an AOD converter according to claim 1, characterized in that, In step (3), the amount of Cr element oxidation is calculated according to the oxygen consumption of the smelting process, then the reduced ferrosilicon is added, the slag binary basicity R=1.9 is controlled, and then the molten steel is tapped and slagged.

4. The method of producing 308L high alloy steel by secondary refining with AOD converter according to claim 1, wherein, In step (5), the main decarburization AOD converter adopts O2:N2=1:2 side blowing oxygen supply in the secondary smelting oxidation stage, the oxygen blowing amount is calculated according to the target values of carbon and oxygen content in the target composition of the molten steel, 3-5t of lime is added; dynamic decarburization adopts O2:N2=1:3 side blowing oxygen supply, and the terminal carbon content is ≤0.005%.

5. The method of producing 308L high alloy steel by secondary refining with AOD converter according to claim 1, wherein, In step (7), the desulfurization tapping stage is carried out according to the reduced S content, the slag basicity is controlled to be binary basicity R=2.0.

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