A calcium treatment process for improving castability of steel

Abstract

The present invention relates to a calcium treatment process for improving the castability of steel, belonging to the technical field of steelmaking processes. The treatment process includes: after the LF molten steel temperature rises to a predetermined temperature, argon is blown from the bottom of the ladle for refining, and CaSi wire is fed according to the sulfur content at the LF tapping; after wire feeding, soft argon blowing is carried out; after RH vacuum treatment, CaSi wire is fed according to the sulfur increase amount in RH, bottom argon blowing is maintained during the wire feeding process, and soft argon blowing is carried out after wire feeding. The present invention adopts calcium treatment after LF refining + calcium treatment after RH treatment, that is, denaturing treatment of Al2O3 and its high-melting-point complexes, realizes the treatment of class A inclusions, significantly improves the qualification rate of micro-carbon steel, the cleanliness of molten steel, and the castability of molten steel with high sulfur content, and its production process is stable, significantly improving its production control level and metallurgical effect.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking technology, and particularly relates to a calcium treatment process for improving the castability of steel. Background Art

[0002] When the sulfur content in steel is high, new problems are raised for its calcium treatment process. The traditional calcium treatment process feeds calcium wire into the molten steel. This is to prevent the existence of Al2O3 inclusions and secondary oxidation Al2O3 (2030℃ high melting point inclusions) in the steel from causing "nodulation". CaO generated by calcium and oxygen is combined with Al2O3 in the steel to form 12CaO·7Al2O3 with a low melting point of 1360℃, that is, Al2O3 is denatured. However, in actual production, there is still the phenomenon of molten steel sticking. Through the analysis of the nodules caused by molten steel sticking to the nozzle, it is found that the molten steel contains a large amount of CaS, that is, when the sulfur content in the molten steel is high, the traditional calcium treatment process of feeding calcium wire into the molten steel cannot eliminate the "nodulation" phenomenon, and cannot meet the castability of the steel, especially the castability of gear steel with high sulfur content. Summary of the invention

[0003] In view of the above problems, the present invention provides a calcium treatment process for improving the castability of steel, which adopts a segmented calcium treatment process, that is, calcium treatment is performed after the LF (ladle refining) and RH (molten steel vacuum treatment) treatments. The calcium treatment after the LF refining is mainly to denature Al2O3 and its high melting point complexes, and a small amount of argon blowing is implemented; after the RH vacuum treatment is completed, different amounts of Ca-Si wire are fed according to the sulfur increase amount for calcium treatment to reduce the level of Class A inclusions, and a small amount of argon blowing is performed after the wire is fed.

[0004] The first object of the present invention is to provide a calcium treatment process for improving the castability of steel, the treatment process comprising:

[0005] After the LF molten steel temperature rises to the predetermined temperature, argon is blown from the bottom of the ladle for refining, and the CaSi wire is fed according to the sulfur content of the LF outlet, and argon is soft-blown after the wire is fed;

[0006] After RH vacuum treatment, the CaSi wire is fed according to the RH sulfur increase amount. During the wire feeding process, argon is blown at the bottom, and argon is soft-blown after wire feeding.

[0007] Furthermore, the predetermined temperature is 1640°C to 1660°C.

[0008] Furthermore, the amount of argon blowing in the argon blowing refining is 0 to 100 Nl / min.

[0009] Furthermore, the CaSi line is fed according to the sulfur content of the LF outbound station, as shown below:

[0010] The sulfur content of LF outgoing station is <0.005%, and the CaSi line feeding is 400m per furnace;

[0011] The sulfur content of LF outgoing station is <0.005~0.011%, and the CaSi feeding line is 450m per furnace;

[0012] The sulfur content of LF outgoing station is <0.011~0.016%, and the CaSi feeding line is 500m per furnace;

[0013] The sulfur content of LF outgoing station is <0.016~0.021%, and the CaSi feeding line is 550m per furnace;

[0014] The sulfur content of LF outgoing station is <0.021~0.026%, and the CaSi feeding line is 600m per furnace;

[0015] Among them, the sulfur content of LF outgoing station is the percentage of sulfur weight in the ladle.

[0016] Furthermore, the CaSi line is fed according to the sulfur content of the LF outgoing station, and when soft argon is blown after the line is fed, the argon blowing time is 4-7 minutes.

[0017] Furthermore, the CaSi line is fed according to the sulfur content of the LF outgoing station, and when soft argon is blown after the line is fed, the blowing speed is 0-100Nl / min.

[0018] Furthermore, the RH sulfur increase amount is fed to the CaSi line as follows:

[0019] The RH sulfur increase is <0.001%, and the CaSi feed line is 400m per furnace;

[0020] The RH sulfur increase is <0.001-0.005%, and the CaSi feed line is 450m per furnace;

[0021] The RH sulfur increase is <0.005-0.010%, and the CaSi feed line is 500m per furnace;

[0022] The RH sulfur increase is <0.010~0.015%, and the CaSi feed line is 550m per furnace;

[0023] The RH sulfur increase is <0.015-0.020%, and the CaSi feed line is 600m per furnace;

[0024] Among them, RH sulfur gain is the percentage of sulfur weight increase in molten steel.

[0025] Furthermore, when the bottom blowing of argon is maintained during the wire feeding process, the blowing amount of argon is 0 to 100 Nl / min.

[0026] Furthermore, when soft argon blowing is performed after the wire feeding, the blowing time is 4-7 minutes.

[0027] Furthermore, when soft argon blowing is performed after the wire feeding, the blowing speed is 0 to 100 Nl / min.

[0028] Beneficial effects of the present invention:

[0029] The calcium treatment process for improving the castability of steel provided by the present invention adopts calcium treatment after LF refining and calcium treatment after RH treatment, that is, denaturation treatment of Al2O3 and its high melting point composites to achieve treatment of Class A inclusion level, significantly improves the qualified rate of micro-carbon steel, the cleanliness of molten steel, and the castability of molten steel with high sulfur content, and its production process is stable, which significantly improves its production control level and metallurgical effect.

[0030] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 A flow chart of a calcium treatment process for improving castability of steel according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, a calcium treatment process for improving castability of steel according to an embodiment of the present invention comprises:

[0035] Step 1: After the LF molten steel temperature reaches the predetermined temperature, argon is blown from the bottom of the ladle for refining, and the CaSi wire is fed according to the sulfur content of the LF outlet, and argon is soft-blown after the wire is fed;

[0036] Step 2: After RH vacuum treatment, feed the CaSi wire according to the RH sulfur increase amount, keep bottom blowing argon during the wire feeding process, and soft blow argon after wire feeding.

[0037] In step one, the amount of argon blown in the argon blowing refining is 0 to 100 Nl / min, and the specific value of the amount of argon blown in the argon blowing refining is any one of 10 Nl / min, 20 Nl / min, 30 Nl / min, 40 Nl / min, 50 Nl / min, 60 Nl / min, 70 Nl / min, 80 Nl / min, 90 Nl / min, and 100 Nl / min, or other values ​​in the range of 0 to 100 Nl / min, so as to ensure a small amount of argon blowing.

[0038] In step 1, the CaSi line is fed according to the LF outbound sulfur content, as shown in Table 1.

[0039] Table 1

[0040]

[0041] The sulfur content of LF outgoing is the percentage of sulfur weight in the ladle. In the embodiment of the present invention, the steelmaking capacity of each furnace is 131.5 tons.

[0042] In step 1, the predetermined temperature is 1640°C to 1660°C, and the predetermined temperature may be any one of 1640°C, 1645°C, 1650°C, 1655°C, and 1660°C.

[0043] In step 1, the CaSi wire is fed according to the sulfur content of the LF outgoing station, and when soft argon is blown after the wire feeding, the argon blowing time is 4-7 minutes, preferably the argon blowing time is 6 minutes, and the molten steel shall not be exposed during the argon blowing process.

[0044] In step one, the CaSi line is fed according to the sulfur content of the LF outlet. When soft argon is blown after the line is fed, the blowing speed is 0-100Nl / min, and the specific value of the blowing amount of argon is any one of 10Nl / min, 20Nl / min, 30Nl / min, 40Nl / min, 50Nl / min, 60Nl / min, 70Nl / min, 80Nl / min, 90Nl / min, 100Nl / min, or other values ​​in the range of 0-100Nl / min, so as to ensure that a small amount of argon is blown.

[0045] The purpose of step 1 is to perform calcium treatment at the end of LF refining mainly to denature Al2O3 and its high melting point complexes.

[0046] In step 2, the RH sulfur increase amount is fed to the CaSi line, as shown in Table 2.

[0047] Table 2

[0048]

[0049] The RH sulfur increase is the percentage of the weight increase of sulfur in the molten steel. In the embodiment of the present invention, the steelmaking capacity of each furnace is 131.5 tons.

[0050] In step 2, the amount of argon blown during bottom blowing is 0-100 Nl / min, and the specific value of the amount of argon blown during bottom blowing is any one of 10 Nl / min, 20 Nl / min, 30 Nl / min, 40 Nl / min, 50 Nl / min, 60 Nl / min, 70 Nl / min, 80 Nl / min, 90 Nl / min, 100 Nl / min, or other values ​​in the range of 0-100 Nl / min, so as to ensure that a small amount of argon is blown, and when the bottom blowing of argon is maintained during the wire feeding process, it is strictly forbidden to overturn the molten steel.

[0051] In step 2, the bottom argon blowing is maintained during the wire feeding process. When soft argon blowing is performed after the wire feeding, the argon blowing time is 4-7 minutes, preferably 6 minutes. The molten steel shall not be exposed during the argon blowing process.

[0052] In step 2, the wire feeding process maintains bottom blowing of argon. When soft blowing of argon is performed after wire feeding, the blowing speed is 0-100 Nl / min, and the specific value of the blowing amount of argon is any one of 10 Nl / min, 20 Nl / min, 30 Nl / min, 40 Nl / min, 50 Nl / min, 60 Nl / min, 70 Nl / min, 80 Nl / min, 90 Nl / min, and 100 Nl / min, or other values ​​in the range of 0-100 Nl / min, so as to ensure the blowing of a small amount of argon.

[0053] In order to better illustrate the technical solution of the present invention, the molten steel in the embodiment of the present invention is gear steel, and the chemical composition of the gear steel is specifically shown in Table 3.

[0054] Table 3

[0055]

[0056] Example 1

[0057] The calcium treatment process provided by the embodiment of the present invention is carried out on the LF and RH of the above gear steel, specifically as follows:

[0058] Step 1: After the LF molten steel temperature rises to 1650°C, argon is blown at the bottom of the ladle for refining at 60Nl / min, and the CaSi wire is fed according to the sulfur content of the LF outlet. After the wire is fed, soft argon is blown for 6 minutes (argon blowing speed 30Nl / min). The molten steel shall not be exposed during the argon blowing process. The specific feeding of the CaSi wire according to the sulfur content of the LF outlet is carried out with reference to Table 1;

[0059] Step 2. After RH vacuum treatment, low melting point inclusions are more likely to escape from the molten steel, reducing their total number in the molten steel. The CaSi wire is fed according to the RH sulfur increase. During the wire feeding process, argon is blown at the bottom at 50Nl / min. It is strictly forbidden to turn over the molten steel. After wire feeding, soft argon is blown for 6 minutes (argon blowing speed 30Nl / min). The molten steel must not be exposed during the argon blowing process. Among them, the CaSi wire is fed according to the RH sulfur increase, and the specific implementation is shown in Table 2.

[0060] By comparing the effects of the conventional calcium treatment process (the calcium treatment process before the calcium treatment process in Example 1 of the present invention) and the treatment process (Example 1) provided by the present invention, it is found that:

[0061] In Example 1, the [Ca] / [Al] and [Ca] / [S] of the molten steel in the middle clad steel of different heats are controlled at about 0.10. After calcium treatment, the inclusions are mainly fine calcium aluminate inclusions, containing a small amount of sulfide inclusions, indicating that the inclusion modification effect is good.

[0062] Before and after the calcium treatment process of Example 1 is adopted, the flow rate of molten steel is reduced from 4.8% to 2.1%, and the number of continuous casting furnaces is increased from 5 to 8, which not only solves the problem of molten steel castability, but also improves the overall quality of gear steel.

[0063] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calcium treatment process for improving the castability of steel, characterized in that: include: After the LF molten steel temperature rises to the predetermined temperature, argon is blown from the bottom of the ladle for refining, and the CaSi wire is fed according to the sulfur content of the LF outlet, and argon is soft-blown after the wire is fed; After RH vacuum treatment, feed CaSi wire according to the RH sulfur increase amount, keep bottom blowing argon during wire feeding, and soft blow argon after wire feeding; The CaSi line is fed according to the sulfur content of the LF outbound station, as shown below: The sulfur content of LF outgoing is less than 0.005%, and the CaSi line feeding is 400m per furnace; The sulfur content of LF outgoing station is greater than or equal to 0.005% and less than 0.011%, and the CaSi feeding line is 450m per furnace; The sulfur content of LF outgoing is greater than or equal to 0.011% and less than 0.016%, and the CaSi feeding line is 500m per furnace; The sulfur content of LF outgoing station is greater than or equal to 0.016% and less than 0.021%, and the CaSi feeding line is 550m per furnace; The sulfur content of LF outgoing is greater than or equal to 0.021% and less than 0.026%, and the CaSi feeding line is 600m per furnace; Among them, the sulfur content of LF outgoing station is the percentage of sulfur weight in molten steel; The RH sulfur increase amount for feeding the CaSi line is as follows: The RH sulfur increase is less than 0.001%, and the CaSi feed line is 400m per furnace; RH sulfur increase is greater than or equal to 0.001% and less than 0.005%, and the CaSi feed line is 450m per furnace; RH sulfur increase is greater than or equal to 0.005% and less than 0.010%, and the CaSi feed line is 500m per furnace; RH sulfur increase is greater than or equal to 0.010% and less than 0.015%, and the CaSi feed line is 550m per furnace; The RH sulfur increase is greater than or equal to 0.015% and less than 0.020%, and the CaSi feed line is 600m per furnace; Among them, RH sulfur increase is the percentage of sulfur weight increase in molten steel; The CaSi line is fed according to the sulfur content of the LF outgoing station, and when soft argon is blown after the line is fed, the blowing time is 4-7 minutes, and the blowing speed is 0-100NL / min; When the bottom argon blowing is maintained during the wire feeding process, the blowing amount of argon is 0-100 NL / min; When the argon is soft blown after the wire feeding, the blowing time is 4-7 minutes, and the blowing speed is 0-100NL / min.

2. A calcium treatment process for improving castability of steel according to claim 1, characterized in that: The predetermined temperature is 1640°C to 1660°C.

3. A calcium treatment process for improving castability of steel according to claim 1, characterized in that: The argon blowing amount in the argon blowing refining is 0-100 NL / min.

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