Low-carbon chromium-containing steel for chromium charging in converter

Abstract

This invention belongs to the field of iron and steel metallurgy technology, specifically relating to molten steel for chromium addition in a converter for low-carbon chromium steel production. In conventional alloy steel smelting processes using high-carbon ferrochrome for alloying, the carbon content in the molten steel obtained after secondary slag formation easily exceeds the upper limit, making it difficult to obtain low-carbon chromium steel with a carbon content below 0.15% after subsequent alloying processes. To address this problem, this invention provides molten steel for chromium addition in a converter for low-carbon chromium steel production. To improve the chromium recovery rate in low-carbon chromium steel and prevent the carbon content in the molten steel obtained after secondary slag formation from exceeding the upper limit, this invention adds a small amount of chromium concentrate during the secondary slag formation process and continuously blows oxygen from the top during the secondary slag formation process. This significantly reduces the carbon content in the molten steel obtained after secondary slag formation while simultaneously improving the chromium recovery rate.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and specifically relates to a low-carbon chromium-containing steel converter for chromium-containing molten steel. Background Technology

[0002] Low-carbon chromium steel requires a chromium content of 1.4-1.6% and a carbon content of 0.09-0.15% in the finished steel. Conventional smelting processes generally use low-carbon ferrochrome for alloying, which ensures that the chromium content in the molten steel after secondary slag formation meets the requirements while keeping the carbon content within the upper limit. However, low-carbon ferrochrome is expensive, resulting in high production costs. Using relatively cheaper high-carbon ferrochrome for alloying, on the other hand, easily leads to a carbon content in the molten steel after secondary slag formation that exceeds the upper limit, thus affecting subsequent low-carbon chromium steel alloying processes and making it difficult to obtain low-carbon chromium steel with a carbon content below 0.15%. While high-intensity oxygen blowing decarburization in a converter can ensure that the carbon content in the molten steel meets the requirements, the chromium recovery rate will decrease, generally to around 50%.

[0003] To address the aforementioned problems, this invention optimizes the smelting process by using relatively low-cost high-carbon ferrochrome for alloying. A small amount of chromium concentrate is added in the later stages of smelting, and the reversible reaction between chromium and oxygen is utilized to reverse the reaction, significantly reducing the oxidation of chromium in the molten steel obtained after secondary slag formation. This achieves the technical effect of a chromium recovery rate of over 90% in the molten steel obtained after secondary slag formation while ensuring that the carbon content does not exceed the upper limit. Summary of the Invention

[0004] The problem with existing technologies is that in conventional alloy steel smelting processes using high-carbon ferrochrome for alloying, the carbon content in the molten steel obtained after secondary slag formation easily exceeds the upper limit, making it difficult to obtain low-carbon chromium steel with a carbon content below 0.15% after subsequent alloying processes. To address these problems, this invention provides molten steel for chromium addition in a converter for low-carbon chromium steel production, comprising the following process steps:

[0005] (1) Scrap steel and molten iron are added to the converter in sequence. The weight ratio of scrap steel to molten iron is 80-90:10-20. The weight percentage of carbon in the molten iron is 3.5-4.5%, the weight percentage of silicon in the molten iron is 0.2-0.6%, and the weight percentage of phosphorus in the molten iron is 0.10-0.14%. The total weight of scrap steel and molten iron is called the total loading amount.

[0006] (2) After the first slag formation, light-burned dolomite, quicklime and iron-based slag-forming agent are added to the converter in sequence after top oxygen blowing. The amount of light-burned dolomite added is 13.5-16.5 kg / t of total charge, the amount of quicklime added is 27.5-38.5 kg / t of total charge, and the amount of iron-based slag-forming agent added is 13-37 kg / t of total charge. Oxygen blowing is continued until the furnace temperature rises to 1650-1700℃. The first blowing is then stopped. After the first blowing is completed, the slag is poured off. The amount of slag poured off in one go is 80-92%.

[0007] (3) Secondary slag formation: Chromium concentrate, high-carbon ferrochrome and quicklime are added to the converter in sequence. The amount of chromium concentrate added is 1-1.5 kg / t of total charge, the amount of high-carbon ferrochrome added is 25-28 kg / t of total charge, and the amount of quicklime added is 2-5 kg / t of total charge. Then, top oxygen blowing is started and oxygen blowing is continued until the furnace temperature rises to 1680-1730℃. Steel is then tapped to obtain molten steel for chromium-containing converter of low-carbon chromium steel.

[0008] Preferably, the iron-based slag-reducing agent is added in three stages: the first stage adds 60-70% of the total amount, the second stage adds 15-20% of the total amount, and the third stage adds 15-20% of the total amount. The timing of each addition is when the oxygen blowing time reaches 1.5-2.5 min, 5-6 min, and 6-7 min, respectively.

[0009] Preferably, the iron-based slag-reducing agent comprises, by mass percentage, the following components:

[0010]

[0011] Preferably, the high-carbon ferrochrome comprises, by weight percentage, the following components:

[0012] C 7-8%;

[0013] Cr 52-54%;

[0014] Fe balance, and unavoidable impurities.

[0015] Preferably, the chromium concentrate comprises, by mass percentage, the following components:

[0016] CaO 10-20%;

[0017] SiO2 10-20%;

[0018] The balance is Cr2O3, and there are unavoidable impurities.

[0019] Preferably, the top-blown oxygen supply intensity during a single slag-forming process is controlled at 35,000-38,000 Nm. 3 / h, gun position controlled at 1.5-2.0m.

[0020] Preferably, the top-blown oxygen supply intensity during the secondary slag formation process is controlled at 40,000-42,000 Nm. 3 / h, gun position controlled at 1.3-1.6m.

[0021] Preferably, the scrap steel, by mass percentage, comprises the following components:

[0022] C 0.05-0.50%;

[0023] Si 0.1-0.5%;

[0024] Mn 0.10-0.50%;

[0025] P≤0.05%;

[0026] S≤0.05%;

[0027] Fe balance, and unavoidable impurities.

[0028] The present invention has the following beneficial effects:

[0029] (1) The present invention adds an iron-based slag-forming agent during the primary slag-forming process, which greatly improves the slag-forming effect and enhances the dephosphorization efficiency, and is very beneficial to improving the chromium recovery rate of the molten steel obtained after secondary slag-forming.

[0030] (2) After the first slag formation, the present invention removes more than 80% of the slag, which can effectively ensure the phosphorus content requirements of the molten steel at high temperature during the secondary blowing process. After the first slag formation, the P content in the molten steel obtained is less than 0.015%.

[0031] (3) After the slag formation is completed, high-iron ferrochrome is added to the converter. The high-temperature environment with less slag in the converter can reduce the oxidation of chromium and increase the chromium yield in low-carbon chromium steel.

[0032] (4) After adding high-carbon ferrochrome during the secondary slag formation process of the present invention, the carbon content of the molten steel exceeds the upper limit. By performing a secondary oxygen blowing operation, the carbon content requirements of the molten steel obtained after the secondary slag formation can be met.

[0033] (5) In order to further improve the chromium yield in the molten steel obtained after secondary slag formation, a small amount of chromium concentrate was added during the secondary slag formation process. The addition of chromium concentrate will increase the chromium oxide content in the slag. The oxidation reaction of chromium is a reversible reaction. The high temperature environment and the increase in the chromium oxide content in the slag are conducive to the reverse reaction of chromium oxidation in the converter. Therefore, the chromium yield in the molten steel obtained after secondary slag formation is significantly improved. Detailed implementation method:

[0034] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0035] Example 1

[0036] The process steps for preparing chromium-containing molten steel for a low-carbon chromium steel converter are as follows:

[0037] (1) 26t of scrap steel and 104t of molten iron are added to the converter in sequence. The weight ratio of scrap steel to molten iron is 20:80. The weight percentage of carbon in the molten iron is 4.5%, the weight percentage of silicon in the molten iron is 0.6%, and the weight percentage of phosphorus in the molten iron is 0.14%.

[0038] (2) After primary slag formation and top oxygen blowing, lightly calcined dolomite and quicklime are added sequentially to the converter. The top oxygen supply flow rate is 35,000 Nm³. 3 / h, the lance position is controlled at 1.5m. During the blowing process, an iron-based slag-forming agent is added. The iron-based slag-forming agent is added in three parts. The first addition is 70% of the total amount, and the second and third additions are 15% of the total amount. The timing of each addition is 1.5min, 5.0min, and 6.0min of the oxygen blowing time, respectively. The amount of lightly calcined dolomite added is 2145kg, the amount of active lime added is 5005kg, and the amount of iron-based slag-forming agent added is 4800kg. Oxygen blowing continues until the furnace temperature rises to 1650℃. Then, one blowing is stopped, and the slag is poured off. The amount of slag poured off in one go is 92%.

[0039] (3) Secondary slag formation: Chromium concentrate, high-carbon ferrochrome, and quicklime are added sequentially to the converter. The amount of chromium concentrate added is 120 kg, the amount of high-carbon ferrochrome added is 3360 kg, and the amount of quicklime added is 260 kg. Then, top oxygen blowing begins, and the top oxygen supply intensity is controlled at 40000 Nm. 3 / h, the lance position is controlled at 1.3m, oxygen is continuously blown until the furnace temperature rises to 1680℃, then the secondary blowing is stopped and the steel is tapped to obtain the chromium-coated molten steel for the converter.

[0040] The composition of the iron-based slag-reducing agent used, by mass percentage, is as follows:

[0041]

[0042]

[0043] The high-carbon ferrochrome used has the following composition by mass percentage:

[0044] C 7%;

[0045] Cr 52%;

[0046] Fe balance, and unavoidable impurities.

[0047] The composition of the chromium concentrate used, by mass percentage, is as follows:

[0048] CaO 10%;

[0049] SiO2 10%;

[0050] The balance is Cr2O3, and there are unavoidable impurities.

[0051] The composition of the scrap steel used, by mass percentage, is as follows:

[0052]

[0053] Fe balance, and unavoidable impurities.

[0054] Example 2

[0055] The process steps for preparing chromium-containing molten steel for a low-carbon chromium steel converter are as follows:

[0056] (1) 13t of scrap steel and 117t of molten iron are added to the converter in sequence. The weight ratio of scrap steel to molten iron is 10:90. The weight percentage of silicon in the molten iron is 0.2%, the weight percentage of phosphorus in the molten iron is 0.10%, and the weight percentage of carbon in the molten iron is 3.5%.

[0057] (2) After the initial slag formation and top oxygen blowing, lightly calcined dolomite and quicklime are added sequentially to the converter. The top oxygen supply flow rate is 38,000 Nm³. 3 / h, the lance position is controlled at 1.8m. During the blowing process, an iron-based slag-forming agent is added. The iron-based slag-forming agent is added in three parts. The first addition is 60% of the total amount, and the second and third additions are each 20% of the total amount. The timing of each addition is 2.5min, 6.0min, and 7.0min of the oxygen blowing time, respectively. The amount of lightly calcined dolomite added is 1800kg, the amount of active lime added is 3600kg, and the amount of iron-based slag-forming agent added is 3000kg. Oxygen blowing continues until the furnace temperature rises to 1700℃. Then, one blowing is stopped, and the slag is dumped. The amount of slag dumped at one time is 80%.

[0058] (3) Secondary slag formation: Chromium concentrate, high-carbon ferrochrome, and quicklime are added sequentially to the converter. The amount of chromium concentrate added is 180 kg, the amount of high-carbon ferrochrome added is 3600 kg, and the amount of quicklime added is 600 kg. Then, top oxygen blowing begins, and the top oxygen supply intensity is controlled at 42000 Nm. 3 / h, with the lance position controlled at 1.6m, oxygen blowing continues until the furnace temperature rises to 1730℃, at which point secondary blowing is stopped and steel is tapped, thus obtaining molten steel for low-carbon chromium steel converter with chromium content.

[0059] The composition of the iron-based slag-reducing agent used, by mass percentage, is as follows:

[0060]

[0061] The high-carbon ferrochrome used has the following composition by mass percentage:

[0062] C 8%;

[0063] Cr 54%;

[0064] Fe balance, and unavoidable impurities.

[0065] The composition of the chromium concentrate used, by mass percentage, is as follows:

[0066] CaO 20%;

[0067] SiO2 20%;

[0068] The balance is Cr2O3, and there are unavoidable impurities.

[0069] The composition of the scrap steel used, by mass percentage, is as follows:

[0070]

[0071] Fe balance, and unavoidable impurities.

[0072] Example 3

[0073] The process steps for preparing chromium-containing molten steel for a low-carbon chromium steel converter are as follows:

[0074] (1) 19.5t of scrap steel and 110.5t of molten iron are added to the converter in sequence. The weight ratio of scrap steel to molten iron is 15:85. The weight percentage of carbon in the molten iron is 4.0%, the weight percentage of silicon in the molten iron is 0.38%, and the weight percentage of phosphorus in the molten iron is 0.12%.

[0075] (2) After the initial slag formation and top oxygen blowing, lightly calcined dolomite and quicklime are added sequentially to the converter. The top oxygen supply intensity is controlled at 36500 Nm. 3 / h, the lance position is controlled at 2.0m. During the blowing process, an iron-based slag-forming agent is added. The iron-based slag-forming agent is added in three parts. The first addition is 66% of the total amount, and the second and third additions are each 17% of the total amount. The timing of each addition is 2.0min, 5.5min, and 6.5min of the oxygen blowing time, respectively. The amount of lightly calcined dolomite added is 1900kg, the amount of active lime added is 4500kg, and the amount of iron-based slag-forming agent added is 3800kg. Oxygen blowing continues until the furnace temperature reaches 1672℃. Then, one blowing is stopped, and the slag is discarded. The amount of slag discarded in one go is 86%.

[0076] (3) Secondary slag formation: Chromium concentrate, high-carbon ferrochrome, and quicklime are added sequentially to the converter. The amount of chromium concentrate added is 160 kg, the amount of high-carbon ferrochrome added is 3500 kg, and the amount of quicklime added is 360 kg. Then, top oxygen blowing begins, and the top oxygen supply intensity is controlled at 41000 Nm. 3 / h, with the lance position controlled at 1.4m, oxygen blowing continues until the furnace temperature rises to 1700℃, at which point secondary blowing stops and steel is tapped, thus obtaining molten steel for low-carbon chromium-containing steel converter with chromium content.

[0077] The composition of the iron-based slag-reducing agent used, by mass percentage, is as follows:

[0078]

[0079] The high-carbon ferrochrome used has the following composition by mass percentage:

[0080] C 8%;

[0081] Cr 53%;

[0082] Fe balance, and unavoidable impurities.

[0083] The composition of the chromium concentrate used, by mass percentage, is as follows:

[0084] CaO 15%;

[0085] SiO2 15%;

[0086] The balance is Cr2O3, and there are unavoidable impurities.

[0087] The composition of the scrap steel used, by mass percentage, is as follows:

[0088]

[0089] Fe balance, and unavoidable impurities.

[0090] Comparative Example 1 is the same as Example 1, except that no iron-based slag-forming agent was added in Comparative Example 1.

[0091] Comparative Example 2 is the same as Example 1, except that the iron-based slag-forming agent in Comparative Example 2 was not added in batches but was added all at once during oxygen blowing for 1.5 minutes.

[0092] Comparative Example 3 is the same as Example 1, except that no chromium concentrate was added during the secondary slag formation process in Comparative Example 3.

[0093] Comparative Example 4 is the same as Example 1, except that in Comparative Example 4, only 70% of the slag was poured out after one slag-making process.

[0094] Comparative Example 5 is the same as Example 1, except that in Comparative Example 5, the iron-based slag-forming agent was added in three stages during a single slag-forming process: 17% of the total amount was added in the first stage, 17% in the second stage, and 66% in the third stage. The timing of each addition was at 2.0 min, 5.5 min, and 6.5 min of oxygen blowing time, respectively.

[0095] Performance testing

[0096] The elemental composition of the chromium-containing steel for converters of low-carbon chromium steel obtained after secondary slag formation in Examples 1-3 and Comparative Examples 1-5 of this invention, expressed as a percentage by mass, is shown in Table 1.

[0097] The formula for calculating the chromium recovery rate of the molten steel used in the converter for chromium addition in low-carbon chromium steelmaking after secondary slag formation is as follows:

[0098] The formula for calculating chromium recovery rate is: Chromium content in molten steel used for chromium addition in low-carbon chromium steel converter / Chromium content in high-carbon ferrochrome × 100%.

[0099] Table 1

[0100] Example 1 0.043 1.38 0.010 margin 95 Example 2 0.052 1.56 0.011 margin 96 Example 3 0.050 1.48 0.009 margin 96 Comparative Example 1 0.062 1.32 0.020 margin 91 Comparative Example 2 0.060 1.31 0.018 margin 90 Comparative Example 3 0.045 1.09 0.010 margin 75 Comparative Example 4 0.062 1.16 0.013 margin 80 Comparative Example 5 0.045 1.32 0.017 margin 91

[0101] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A type of chromium-containing molten steel for a low-carbon chromium steel converter, characterized in that, The process includes the following steps: (1) Scrap steel and molten iron are added to the converter in sequence. The weight ratio of scrap steel to molten iron is 80-90:10-20. The weight percentage of carbon in the molten iron is 3.5-4.5%, the weight percentage of silicon in the molten iron is 0.2-0.6%, and the weight percentage of phosphorus in the molten iron is 0.10-0.14%. The total weight of scrap steel and molten iron is called the total loading amount. (2) After the first slag formation, light-burned dolomite, quicklime and iron-based slag-forming agent are added to the converter in sequence after top oxygen blowing. The amount of light-burned dolomite added is 13.5-16.5 kg / t of total charge, the amount of quicklime added is 27.5-38.5 kg / t of total charge, and the amount of iron-based slag-forming agent added is 13-37 kg / t of total charge. Oxygen blowing is continued until the furnace temperature rises to 1650-1700℃. The first blowing is then stopped. After the first blowing is completed, the slag is poured off. The amount of slag poured off in one go is 80-92%. (3) Secondary slag formation: Chromium concentrate, high-carbon ferrochrome and quicklime are added to the converter in sequence. The amount of chromium concentrate added is 1-1.5 kg / t of total charge, the amount of high-carbon ferrochrome added is 25-28 kg / t of total charge, and the amount of quicklime added is 2-5 kg / t of total charge. Then, top oxygen blowing is started and oxygen blowing is continued until the furnace temperature rises to 1680-1730℃. Steel is then tapped to obtain molten steel for low-carbon chromium steel converter with chromium content. The iron-based slag-forming agent is added in three stages: the first stage adds 60-70% of the total amount, the second stage adds 15-20% of the total amount, and the third stage adds 15-20% of the total amount. The timing of each addition is when the oxygen blowing time reaches 1.5-2.5 min, 5-6 min, and 6-7 min, respectively. The chromium concentrate, by mass percentage, comprises the following components: CaO 10-20%; SiO2 10-20%; The balance is Cr2O3, and there are unavoidable impurities.

2. The chromium-containing molten steel for a low-carbon chromium steel converter according to claim 1, characterized in that, The iron-based slag-reducing agent comprises, by mass percentage, the following components: CaO 10-20%; SiO2 5-10%; Al2O 35-10%; The balance is Fe2O3, and unavoidable impurities.

3. The chromium-containing molten steel for a low-carbon chromium steel converter according to claim 1, characterized in that, The high-carbon ferrochrome, by mass percentage, comprises the following components: C 7-8%； Cr 52-54%； Fe balance, and unavoidable impurities.

4. The chromium-containing molten steel for a low-carbon chromium steel converter according to claim 1, characterized in that, During a single slag-making process, the top-blown oxygen supply intensity is controlled at 35,000-38,000 Nm. 3 / h, gun position controlled at 1.5-2.0m.

5. The chromium-containing molten steel for a low-carbon chromium steel converter according to claim 1, characterized in that, During the secondary slag formation process, the top-blown oxygen supply intensity is controlled at 40,000-42,000 Nm. 3 / h, gun position controlled at 1.3-1.6m.

6. The chromium-containing molten steel for a low-carbon chromium steel converter according to claim 1, characterized in that, The scrap steel, by mass percentage, comprises the following components: C 0.05-0.50%； Si 0.1-0.5%; Mn 0.10-0.50%; P≤0.05%； S≤0.05%； Fe balance, and unavoidable impurities.

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