A method for producing high-purity SPA-H molten steel

Abstract

This invention discloses a method for producing high-purity SPA-H molten steel, belonging to the field of iron and steel smelting. The water composition is controlled as follows by mass percentage: C: 0.07%–0.10%, Si: 0.35%–0.45%, Mn: 0.43%–0.53%, P: 0.075%–0.100%, S≤0.010%, Cr: 0.30%–0.36%, Cu: 0.25%–0.31%, Ni: 0.05%–0.09%, Alt: 0.015%–0.050%, with the balance being iron and trace amounts of unavoidable impurities. The production method includes molten iron → converter smelting → LF refining: the LF refining step involves two Si addition operations; the bottom argon soft blowing calming of the ladle uses a single soft blowing, without calcium feeding wire treatment. Compared with existing technologies, this method can improve the cleanliness of molten steel, and is characterized by environmental control, cost reduction, and efficiency improvement.

Description

TECHNICAL FIELD

[0001] The application is a divisional application of the invention patent "Method for improving the purity of weathering steel smelting" (2022108941741), and relates to a steel smelting process, in particular, a high-purity SPA-H molten steel production method. BACKGROUND

[0002] The current production process of weathering steel (high Si and low Mn) generally adopts the following steps: molten iron, oxygen top and bottom combined blowing converter, LF refining, argon soft blowing at the bottom of the ladle, calcium treatment, argon soft blowing at the bottom of the ladle, thin slab continuous casting and rolling. The calcium treatment process is used to change the high-melting-point spinel inclusions and calcium sulfide in the aluminum deoxidized steel into low-melting-point calcium aluminate (12CaO·7Al2O3, 3CaO·Al2O3) to solve the problem of nozzle clogging. The industry commonly uses seamless calcium wire, silicon-calcium wire and calcium-iron wire for calcium treatment. Due to the low solubility of Ca in steel, part of the metallic Ca cannot be absorbed by the molten steel during the upward process and is gasified to form calcium bubbles. When the calcium bubbles leave the molten steel, they react violently with oxygen in the air and oxygen in the slag, forming spatters and causing secondary oxidation of the molten steel, which not only contaminates the molten steel and destroys the cleanliness of the molten steel, but also adversely affects the on-site environment.

[0003] Because the quantity, shape and size of inclusions in steel determine the steel grade and product use, the control of molten steel cleanliness has always been the goal pursued by steelmaking personnel.

[0004] The "Calcium-free treatment and static clean steel production process" (CN2018100948303) of the company eliminates the calcium treatment process and avoids the problem of easy flocculation of high-melting-point aluminate, improving the forming performance of the steel plate. However, this technology promotes the floating of Al2O3 inclusions by soft blowing for 20-30 min, and does not perform modification treatment on the Al2O3 inclusions remaining in the molten steel, still existing the problem of flocculation during casting. In addition, the process requires pretreatment of molten iron, and the process route is complex. Furthermore, this process cannot be applied to the production of Cr-containing weathering steel, and cannot meet the castability requirements of weathering steel.

[0005] Therefore, there is an urgent need for a new process to control the secondary oxidation of weathering steel molten steel, which can reduce the production process of molten steel oxidation during the conventional calcium treatment process under the premise of stable molten steel quality, so as to improve the cleanliness of molten steel, control environmental protection, and reduce costs and increase efficiency. SUMMARY

[0006] The technical task of the present application is to provide a high-purity SPA-H molten steel production method to solve the above problems in the prior art.

[0007] The technical solution of the present application for solving the technical problem is: a high-purity SPA-H molten steel production method, characterized in that the mass percentage of the molten steel composition is controlled as follows: C: 0.07%-0.10%, Si: 0.35%-0.45%, Mn: 0.43%-0.53%, P: 0.075%-0.100%, S≤0.010%, Cr: 0.30%-0.36%, Cu: 0.25%-0.31%, Ni: 0.05%-0.09%, Alt: 0.015%-0.050%, and the balance is iron and trace amounts of unavoidable impurities; the production method comprises the following steps of molten iron→converter smelting→LF refining:

[0008] S1, molten iron: no S removal pretreatment is needed;

[0009] S2, converter smelting: oxygen top and bottom combined blowing converter;

[0010] S3, LF refining:

[0011] (1) No Si and Mn alloying is performed during the converter tapping process, and only Cr alloying is performed according to the end point [C];

[0012] (2) The Si and Mn are added according to the composition of the argon station to make the Mn content reach the lower limit of the target internal control minus 0.02-0.07%; the Si iron is added to make the Si content reach 0.15-0.20%; after stirring for 2-3 min, the aluminum wire is fed to add aluminum to make the Als content reach the target value;

[0013] (3) The Mn is added to the target value during the slagging process of the refining furnace, and no Si is added;

[0014] (4) After the molten steel temperature is heated to 1590-1600℃, the Si iron is added 0.5-1 min before the end of the desulfurization stirring to add Si to the target composition for the second time;

[0015] (5) The argon soft blowing for the ladle bottom argon soft blowing and setting is performed once, the soft blowing time is ≥12 min, and no calcium wire calcium treatment is performed.

[0016] Further, in the converter smelting step, the end point temperature of the converter is controlled to be greater than or equal to 1620 DEG C, and [O] is 250-450 ppm.

[0017] Further, in the converter tapping Cr alloying, if the tapping C is 0.09%-0.10%, the high-carbon chromium iron is added in an amount of 2.0-2.5 kg / ton of steel; if the tapping C is less than or equal to 0.09%, the high-carbon chromium iron is added in an amount of 3.5-4.4 kg / ton of steel.

[0018] Further, in the LF refining, before the silicon iron is added, the sulfur is ensured to be removed to an internal control value of less than or equal to 0.010%.

[0019] Compared with the prior art, the present application has the following outstanding beneficial effects:

[0020] 1. By the present application, the calcium feeding line process of weathering steel is cancelled, the cleanliness and castability of molten steel are effectively improved, the inclusion floating and adsorption effect are obvious, and the product composition qualification rate reaches 100%;

[0021] 2. The calcium treatment cost is saved, the cost per ton of steel is reduced by 4 yuan / t, and the annual cost reduction amount is several million yuan;

[0022] 3. There are also improvements and improvements in aspects such as on-site smoke control and customer use. DETAILED DESCRIPTION

[0023] The present application will be further described below in conjunction with specific embodiments.

[0024] For the purposes of the following detailed description, it is to be understood that the application can assume various alternative variations and step sequences, except where expressly indicated to the contrary. Moreover, other than in any operation examples or where otherwise indicated, all numbers expressing, for example, quantities of components in the specification and claims are to be understood as being modified in all instances by the term "about". At least, and unless otherwise indicated, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0025] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0026] It should also be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges, for example, 1 to 6.1, 5.1 to 10, etc., as implicitly disclosed additional to the exact numerical boundaries.

[0027] In this application, the use of the singular includes the plural and the plural encompasses the singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and / or" unless specifically stated otherwise, even though "and / or" can be explicitly used in certain instances. Further, in this application, the use of "one" or "a" means "at least one" unless specifically stated otherwise. For example, "a" first material, "a" coating composition, and the like refer to one or more items in any of these items.

[0028] The present application provides a method for improving the smelting cleanliness of weathering-resistant steel, which cancels the process of conventional calcium wire calcium treatment by adopting a new process of alloy calcium treatment on weathering-resistant steel, reduces the oxidation of molten steel, and provides molten steel with higher cleanliness, thereby providing more high-quality products for the weathering-resistant steel market.

[0029] To achieve the above-mentioned purpose, the technical scheme of the present application is: molten iron → converter smelting → LF refining → continuous casting.

[0030] S1, molten iron:

[0031] There is no special requirement, and there is no need for S removal pretreatment.

[0032] S2, converter smelting:

[0033] The molten iron is initially smelted in the converter, and the oxygen top and bottom combined blowing converter is used. The control terminal temperature of the converter is ≥1620℃, and [O] is 250-450ppm.

[0034] S3, LF refining:

[0035] (1) Si and Mn alloying is not performed during the converter tapping process, and only Cr alloying is performed according to the terminal [C]. Specifically, if the tapping C is 0.09%-0.10%, the high-carbon chromium iron addition amount is 2.0-2.5kg / ton of steel; if the tapping C is ≤0.09%, the high-carbon chromium iron addition amount is 3.5-4.4kg / ton of steel.

[0036] (2) The Si and Mn are added according to the composition of the argon station to make the Mn content reach the lower limit of the target internal control minus 0.02-0.07%; the Si iron is added to make the Si content reach 0.15-0.20%. After stirring for 2-3min, the aluminum wire is fed to add aluminum, so that the Als content reaches the target value.

[0037] (3) The Mn is added to the target value during the slagging process of the refining furnace, and the Si is not added.

[0038] (4) After the temperature of the molten steel is heated to 1590-1600 °C, ferrosilicon is added 0.5-1 min before the end of desulfurization stirring, and secondary Si is added to the target composition (0.35-0.45%).

[0039] (5) The argon soft blowing and settling at the bottom of the ladle is performed by one-time soft blowing, and the soft blowing time is ≥12 min, and no calcium wire calcium treatment is performed.

[0040] The molten steel is obtained, and the subsequent continuous casting process is performed.

[0041] The part not mentioned in the technical solution is the prior art, and the process and parameters of the prior art are used.

[0042] The "secondary Si addition method" of the application: the first Si addition is performed to 0.15-0.20% at the station of the refining furnace, and the second Si addition is performed to the target composition 0.35-0.45% after the completion of slagging. The process of ferrosilicon smelting is to produce CO by coke combustion, and to reduce SiO2 in silica at high temperature. Since CaO is associated in silica, a certain amount of metal Ca is contained in ferrosilicon. By controlling the adding time and amount, the metal Ca in the alloy is used to realize calcium treatment, so as to achieve the purpose of inclusion modification. However, in actual production, the Ca content of each batch is not stable and consistent, and is generally between 1.0% and 2.0%, and the "secondary Si addition method" of the application not only ensures the alloy melting effect, but also ensures the stability of the Ca in the tundish.

[0043] Taking the production process of the SPA-H steel as an example, the mass percentage of the composition of the molten steel is controlled as follows: C: 0.07-0.10%, Si: 0.35-0.45%, Mn: 0.43-0.53%, P: 0.075-0.100%, S≤0.010%, Cr: 0.30-0.36%, Cu: 0.25-0.31%, Ni: 0.05-0.09%, Alt: 0.015-0.050%, and the balance is iron and trace amounts of unavoidable impurities.

[0044] In the LF refining process of examples 1-4:

[0045] (1) The [C] at the end point is used for Cr alloying during the converter tapping process; if the tapping C is 0.09-0.10%, the high-carbon chromium iron is added at 2.0-2.5 kg / ton of steel; if the tapping C is ≤0.09%, the high-carbon chromium iron is added at 3.5-4.4 kg / ton of steel.

[0046] (2) LF to station according to argon station composition, add silicon manganese to Mn to target internal control lower limit minus 0.05%~0.08%, example group is 0.038%~0.041%, add silicon iron to Si to 0.15%~0.20%, after stirring 2min~3min, feed aluminum wire, add aluminum to Als to 0.010%~0.020%.

[0047] (3) Refining furnace slagging process, add Mn to target value (0.43%~0.53%).

[0048] (4) After the molten steel temperature is heated to 1590℃~1600℃, add silicon iron 1min before the end of desulfurization stirring, carry out secondary Si addition to 0.35%~0.45%, ensure that the sulfur is removed to S≤0.010% before adding silicon iron, ensure that the silicon iron is completely melted, and take a sample for composition analysis.

[0049] Comparative Example 1: the existing process.

[0050] (1) During the converter tapping process, add Mn to 0.39%~0.41%, add Si to 0.28%~0.31%, and add Cr to the target value;

[0051] (2) LF to station according to argon station composition, before desulfurization, add silicon manganese, silicon iron and other alloys, and the refining off-site composition meets the steel grade requirements.

[0052] (3) Feed calcium line calcium treatment, wherein the calcium line usage is 50-60m / furnace (70-100m / furnace for open pouring furnace), and secondary soft blowing is adopted (soft blowing≥5min before calcium treatment, and soft blowing time≥7min after calcium treatment).

[0053] Comparative Example 2: simply remove the calcium treatment step, change to one-time soft blowing≥12min; other process step parameters are the same as those of Comparative Example 1.

[0054] Other process parameters are the same as those of Examples 1-4 and Comparative Example.

[0055] The Si, Mn, Alt alloying conditions of Examples 1-4 and Comparative Example are as follows:

[0056]

[0057]

[0058] 1, the final product steel composition comparison is as follows:

[0059]

[0060] From the above table, it can be seen that the molten steel components of Examples 1-4 and Comparative Example 1 are stable and meet the product requirements. In Comparative Example 2, the Al2O3 inclusions do not change, are flocculated in the molten steel, are difficult to float, easily gather in the nozzle, and cause serious flocculation flow during continuous casting, which cannot continue production.

[0061] Through the implementation of the process of the present application, the molten steel of Examples 1-4 has a Ca content equivalent to that of Comparative Example 1, which is treated with a seamless calcium line, and has good castability, and no flocculation flow occurs during continuous casting of the molten steel.

[0062] Each example group cancels calcium treatment with a seamless calcium line, and the ladle oxygen is 5-15 Ppm lower than that of Comparative Example 1 (prior art), which avoids secondary oxidation of the molten steel caused by splashing of the molten steel in the calcium-free line process, and significantly improves cleanliness.

[0063] 2. Cost comparison of each group

[0064] Aluminium consumption t Acetylene t Calcium wire t Temperature in °C at the inlet Temperature in °C at the outlet Heating time in min Electricity consumption in kwh Example 1 0.128 0.075 0.000 1565.0 1583.1 12.1 3527.7 Example 2 0.126 0.070 0.000 1558.0 1582.3 14.1 4227.7 Example 3 0.125 0.070 0.000 1560.0 1581.5 13.1 3927.7 Example 4 0.112 0.072 0.000 1567.0 1580.7 12.1 3427.7 Comparative Example 1 0.133 0.083 0.0229 1559.0 1581.9 16.7 4724.5 Comparative Example 2 0.130 0.076 0.000 1562.0 1580.2 13.9 4027.7

[0065] The calcium-free line cost of each example group, and the reduction of calcium carbide and aluminum product consumption, and the reduction of temperature drop caused by molten steel splashing, have certain advantages in temperature control, so the power consumption is lower, and the present application has a cost advantage over the prior art (Comparative Example 1), and is clean and energy-saving.

[0066] It should be noted that the specific embodiments of the present application have been described in detail, and various obvious modifications made by those skilled in the art without departing from the spirit and scope of the present application are within the scope of protection of the present application.

Claims

1. A method for producing high purity SPA-H steel water, characterized by: The mass percentage of molten steel composition is controlled as follows: C: 0.07%-0.10%, Si: 0.35%-0.45%, Mn: 0.43%-0.53%, P: 0.075%-0.100%, S≤0.010%, Cr: 0.30%-0.36%, Cu: 0.25%-0.31%, Ni: 0.05%-0.09%, Alt: 0.015%-0.050%, and the balance is iron and trace amounts of unavoidable impurities; the production method comprises the following steps: molten iron→converter smelting→LF refining: S1, molten iron: no S removal pretreatment is needed; S2, converter smelting: oxygen top and bottom combined blowing converter; S3, LF refining: (1) no Si and Mn alloying is performed during the converter tapping process, and only Cr alloying is performed according to the end point [C]; during the Cr alloying in the converter tapping process, if the tapping C is 0.09%-0.10%, the high-carbon chromium iron is added at an amount of 2.0-2.5 kg / ton of steel; if the tapping C is less than 0.09%, the high-carbon chromium iron is added at an amount of 3.5-4.4 kg / ton of steel; (2) the Si and Mn are added according to the composition of the argon station, so that the Mn content reaches the lower limit of the target internal control minus 0.02-0.07%; the Si iron is added, so that the Si content reaches 0.15-0.20%; after stirring for 2-3 min, the aluminum wire is fed to add aluminum, so that the Als content reaches the target value; (3) the Mn is added during the slagging process of the refining furnace to reach the target value, and no Si is added; (4) after the molten steel temperature is heated to 1590-1600 ℃, the Si iron is added 0.5-1 min before the end of the desulfurization stirring, so that the Si is added for the second time to reach the target composition; before the Si iron is added, the sulfur is ensured to be removed to the internal control value of ≤0.010%; (5) the argon soft blowing and settling at the bottom of the ladle is performed by one-time soft blowing, and the soft blowing time is ≥12 min, and no calcium wire feeding and calcium treatment is performed.

2. The high-purity SPA-H steel water production method according to claim 1, characterized by: In the converter smelting step, the converter end point temperature is controlled to be ≥1620 ℃, and the [O] is 250-450 ppm.

Images