A method for treating inclusions in modified steel using rare earth lanthanum during refining

Abstract

The invention discloses a method for treating inclusions in modified steel with rare earth lanthanum during refining, which belongs to the technical field of iron and steel metallurgy and solves the technical problem that the effect of modified inclusions treated with calcium in existing steelmaking and refining is unstable. A method for treating inclusions in modified steel with rare earth lanthanum during refining comprises the following steps: step S1, converter or electric furnace smelting; step S2, aluminum deoxidation alloying operation in the ladle when the converter or electric furnace is tapped; step S3, LF furnace or LF furnace → RH furnace refining, rare earth lanthanum treatment is performed in the last step of refining; step S4, continuous casting or mold casting after refining. The recovery rate of rare earth La element in the steel of the invention is above 30%, which is much higher than the recovery rate of 5-15% of calcium. The rare earth La treatment method of the invention enables the spherical rate of inclusions in the steel to reach above 90%, and the corrosion resistance of the steel is reduced by more than 10% compared with the relative corrosion rate of calcium-treated steel.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for treating inclusions in modified steel by using rare earth lanthanum during refining. Background Art

[0002] Common MnS and Al in steel 2 O 3 Stable inclusions will cause pitting and reduce fatigue life, thus reducing the application of steel. At present, calcium treatment is usually carried out in steelmaking and refining. Calcium treatment technology is the most common, direct and effective method to modify non-metallic inclusions in steel. After calcium treatment, Al 2 O 3 Low melting point calcium aluminate inclusions will be formed, and MnS will be transformed into a single uniform spherical CaS inclusion, thereby reducing Al 2 O 3 The influence of MnS inclusions on steel properties. However, due to the active chemical properties and low boiling point of calcium metal itself, under smelting conditions, Ca will volatilize into Ca vapor, resulting in the empirical feeding of calcium in the calcium treatment process of steelmaking and refining, large fluctuations in the calcium alloy yield, and a low yield of about 5-15%, which makes the effect of modified inclusions unstable. Therefore, how to improve the effect of inclusion modification during refining has become a difficult problem for the development of the industry. Summary of the invention

[0003] In view of the above analysis, in view of the difficulties in the prior art, the present invention aims to provide a method for treating inclusions in modified steel with rare earth lanthanum during refining, so as to solve one of the technical problems in the existing steelmaking and refining calcium treatment, that is, the empirical calcium feeding amount, large fluctuations in the calcium alloy yield, and low yield, which make the modified inclusion effect unstable.

[0004] The purpose of the present invention is mainly achieved through the following technical solutions:

[0005] The present invention provides a method for treating inclusions in modified steel using rare earth lanthanum during refining, comprising the following steps:

[0006] Step S1, smelting in a converter or electric furnace;

[0007] Step S2: when the converter or electric furnace is tapping steel, aluminum deoxidation and alloying operation is performed in the ladle;

[0008] Step S3, LF furnace or LF furnace → RH furnace refining, rare earth lanthanum treatment is performed in the last step of refining;

[0009] Step S4, continuous casting or mold casting after refining.

[0010] Furthermore, in step S1, the steel type to be smelted is a steel type that usually requires calcium treatment during refining.

[0011] Furthermore, the steel types are pipeline steel, titanium-containing stainless steel, gear steel, heavy rail steel, electrical steel, non-quenched and tempered steel, deep drawing steel, structural steel, corrosion-resistant steel, wear-resistant steel, and 10# high-quality carbon steel.

[0012] Furthermore, in step 2, aluminum deoxidation is performed using aluminum blocks or aluminum particles, the purity of the aluminum blocks or aluminum particles reaches more than 99%, and the equivalent diameter is not greater than 12 mm.

[0013] Furthermore, in step 3, during the white slag operation in the LF furnace refining, the slag thickness is controlled to be 130-150 mm, the white slag duration is greater than 20 min, and argon is soft-blown before leaving the station.

[0014] Furthermore, the white slag composition is calculated by mass percentage as follows: CaO: 55-65%, SiO 2 : 5~8%, MgO: 11~15%, Al 2 O 3 : 15~24%, FeO+MnO<0.5%, CaO / SiO 2 :8.0~11.

[0015] Furthermore, in step 3, before rare earth lanthanum treatment, the mass percentage of Alt in the steel is controlled to be 0.02%≤Alt<1.00%, the mass percentage of total oxygen TO is below 0.01%, and the mass percentage of sulfur S is below 0.05%.

[0016] Furthermore, in step 3, rare earth La treatment is performed in the last step of refining as follows: when only LF furnace refining is performed, rare earth lanthanum is added 4 minutes before leaving the station; when refining from LF furnace to RH furnace, rare earth lanthanum is added 4 minutes before breaking vacuum in the RH furnace.

[0017] Furthermore, the rare earth lanthanum is added in the form of lanthanum-iron alloy, and the rare earth element content in the lanthanum-iron alloy is 30%.

[0018] Furthermore, in step S3, when rare earth lanthanum treatment is performed, the contents of La, Alt and S in the steel have the following relationship:

[0019] When total oxygen TO≤5ppm and S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0020] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2]2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] );

[0021] When total oxygen TO≤5ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0022] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [1.0034×lg(S％)+0.508] );

[0023] When 5ppm<TO≤10ppm, S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0024] max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] );

[0025] When 5ppm<TO≤10ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0026] max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [1.0034×lg(S％)+0.508]);

[0027] When 10ppm<TO≤20ppm, S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0028] max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] );

[0029] When 10ppm<TO≤20ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0030] max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [1.0034×lg(S％)+0.508] );

[0031] When 20ppm<TO≤50ppm and sulfur S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0032] max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] );

[0033] When 20ppm<TO≤50ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0034] max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] );

[0035] When 50ppm<TO≤100ppm and sulfur S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0036] max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] );

[0037] When 50ppm<TO≤100ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0038] max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ).

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) Since the boiling point of the rare earth La element is relatively high, the element will not volatilize. The yield of the rare earth La element in the steel of the present invention is above 30%, which is much higher than the yield of calcium of 5-15%.

[0041] (2) The method of the present invention is used to treat the steel with rare earth La, so that the spherical rate of inclusions in the steel can reach more than 90%, and the number of long strip-shaped MnS inclusions and non-deformable Al 2 O 3 Inclusions deteriorate the properties of steel.

[0042] (3) Through corrosion resistance tests, it was found that, using the method of the present invention, rare earth La treatment reduces the corrosion resistance of steel by more than 10% compared with the relative corrosion rate of calcium-treated steel.

[0043] (4) The technical solution of the present invention opens up new avenues for the application of rare earth in steel and provides a model for the modification of inclusions in steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is the La-Al-O-Fe equilibrium phase diagram in steel at 1873K;

[0045] Figure 2 This is the La-Mn-SO-Fe equilibrium phase diagram in steel at 1273K. DETAILED DESCRIPTION

[0046] The following is a further detailed description of a method for treating inclusions in modified steel with rare earth lanthanum during refining in conjunction with specific examples. These examples are only for the purpose of explanation, and the present invention is not limited to these examples. It should be noted that the component contents in the present invention are all mass percentages.

[0047] In recent years, research has found that rare earth elements also have modified Al 2 O 3 The ability of rare earth La to remove MnS, the properties of rare earth La are similar to those of Ca, and it has the characteristics of high activity. At the same time, La has a high boiling point and is not easy to volatilize during the smelting process, so the yield is higher than that of Ca. In addition, the extraction process of La element has gradually matured, and the high abundance of La element in rare earth ore determines its low application cost in steel. Therefore, it is very appropriate to use La element with similar properties to Ca element to replace Ca for the modification treatment of some stable inclusions, that is, the use of rare earth La treatment in refining has good application value.

[0048] The present invention provides a method for treating inclusions in modified steel using rare earth lanthanum during refining, comprising the following steps:

[0049] Step S1, smelting in a converter or electric furnace;

[0050] Step S2: when the converter or electric furnace is tapping steel, aluminum deoxidation and alloying operation is performed in the ladle;

[0051] Step S3, LF furnace or LF furnace → RH furnace refining, rare earth lanthanum treatment is performed in the last step of refining;

[0052] Step S4, continuous casting or mold casting after refining.

[0053] Specifically, in step S1, the steel type smelted is the steel type that usually needs to be treated with calcium during refining, such as pipeline steel, titanium-containing stainless steel, gear steel, heavy rail steel, electrical steel, non-quenched and tempered steel, deep drawing steel, structural steel, corrosion-resistant steel, wear-resistant steel, 10# high-quality carbon steel and other steel types.

[0054] Specifically, in step 2, aluminum blocks or aluminum particles are used for aluminum deoxidation operation, the purity of the aluminum blocks or aluminum particles reaches more than 99%, and the equivalent diameter is not greater than 12 mm.

[0055] In step S3, rare earth La treatment is performed in the last step of refining, that is, when only LF furnace refining is performed, rare earth treatment is performed before the LF furnace leaves the station; when refining from LF furnace to RH furnace, rare earth treatment is performed in the RH furnace.

[0056] Specifically, when only LF furnace is used for refining, white slag is operated during refining, the slag thickness is controlled to be 130-150mm, the white slag duration is greater than 20min, argon is soft-blown before leaving the station, and rare earth lanthanum is added 4min before leaving the station; the composition of the ladle top slag in LF furnace refining is CaO: 55-65% by mass, SiO 2 : 5~8%, MgO: 11~15%, Al 2 O 3 : 15~24%, FeO+MnO<0.5%, CaO / SiO 2 : 8.0~11, high basicity top slag is used to ensure the recovery rate of rare earth elements is above 30%.

[0057] During the refining process from LF furnace to RH furnace, the slag thickness is controlled to be 130-150mm, the duration of white slag is greater than 20min, and argon is blown softly before leaving the station; the composition of white slag is CaO: 55-65%, SiO 2 : 5~8%, MgO: 11~15%, Al 2 O 3 : 15~24%, FeO+MnO<0.5%, CaO / SiO 2 : 8.0~11. After the LF furnace is refined out of the station, it is vacuum cycled and degassed in the RH furnace. Rare earth lanthanum is added 4 minutes before the RH furnace breaks the vacuum. After the vacuum is broken, argon is softly blown. High basicity top slag is used to ensure that the recovery rate of rare earth elements is above 30%.

[0058] Specifically, before the rare earth lanthanum treatment, the mass percentage of Alt in the steel is controlled to be 0.02%≤Alt<1.00%, the mass percentage of total oxygen TO is below 0.01%, and the mass percentage of sulfur S in the steel is below 0.05%; the rare earth lanthanum is added in the form of lanthanum-iron alloy, and the rare earth element content in the lanthanum-iron alloy is 30%.

[0059] Specifically, when rare earth lanthanum treatment is performed, the contents of La, Alt and S in the steel have the following relationship:

[0060] When total oxygen TO≤5ppm and S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0061] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ) (1)

[0062] When total oxygen TO≤5ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0063] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [1.0034 ×lg(S％)+0 . 508] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [1.0034×lg(S％)+0.508] ) (2)

[0064] When 5ppm<TO≤10ppm, S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0065] max(-10 -3 ×{3.133×[lg(Alt%)-2] 2+14.96×[lg(Alt%)-2]+10.04},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ) (3)

[0066] When 5ppm<TO≤10ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0067] max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [1.0034×lg(S％)+0.508] ) (4)

[0068] When 10ppm<TO≤20ppm, S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0069] max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ) (5)

[0070] When 10ppm<TO≤20ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0071] max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [1.0034 ×lg(S％)+0.508])<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [1.0034×lg(S％)+0.508] ) (6)

[0072] When 20ppm<TO≤50ppm and sulfur S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0073] max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ) (7)

[0074] When 20ppm<TO≤50ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0075] max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ) (8)

[0076] When 50ppm<TO≤100ppm and sulfur S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0077] max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2+9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ) (9)

[0078] When 50ppm<TO≤100ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows:

[0079] max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ) (10)

[0080] It should be noted that, in the above formula, La%, Alt% and S% in steel represent the values ​​before the percentage sign %, that is, if La=0.02%, then La%=0.02; if Alt=0.05%, then Alt%=0.05; if S=500ppm=0.05%, then S%=0.05.

[0081] Figure 1 is the La-Al-O-Fe equilibrium phase diagram in steel at 1873K. Figure 1 As can be seen, the following chemical reactions occur:

[0082] 1 / 2S+La+[O]=1 / 2La 2 O 2 S (11)

[0083] 2 / 3Al+[O]=1 / 3Al 2 O 3 (12)

[0084] 1 / 2S+La+1 / 3Al 2 O 3 =1 / 2La 2 O 2 S+2 / 3Al (13)

[0085] Adding equation (11) to equation (13) yields the following equation:

[0086] S+2La+[O]+1 / 3Al 2 O 3 =La 2 O 2S+2 / 3Al (14)

[0087] from Figure 1 It can be seen that there are iso-oxygen lines of TO = 5ppm, 10ppm, 20ppm, and 50ppm. The iso-oxygen lines represent the total oxygen content and the equilibrium line of the chemical reaction of formula (14) at 1873K. The point values ​​on the iso-oxygen lines represent the critical contents of La and Alt corresponding to the equilibrium of the chemical reaction. The lower right range surrounded by each iso-oxygen line indicates that the chemical reaction of formula (14) has a tendency to proceed spontaneously from right to left. Al 2 O 3 The amount gradually increases as the reaction proceeds, and as the La content decreases and / or the Alt content increases, the tendency of spontaneous reaction from right to left becomes stronger and stronger; on the contrary, outside this range, the chemical reaction of formula (14) tends to proceed spontaneously from left to right, and Al 2 O 3 The number of inclusions decreases as the reaction proceeds, and as the La content increases and / or the Alt content decreases, the tendency of spontaneous reaction from left to right becomes stronger and stronger. The technical effect pursued by the modified inclusions of the present invention is to minimize the Al content in steel. 2 O 3 Therefore, under a certain Alt content, it is the inherent meaning of the present invention to control the La content in the steel to not be lower than the critical content at the reaction equilibrium.

[0088] The present invention is achieved by fitting Figure 1 The equilibrium line of the chemical reaction of formula (14) under different isoxic lines is obtained to obtain the critical content formula of La. The obtained critical content of La is used as the lower limit of La content control in steel, and 1.2 times of the obtained critical content of La is used as the upper limit of La content control in steel.

[0089] Specifically, when the total oxygen TO in the steel is ≤5ppm, the La and Alt in the steel have the following relationship:

[0090] -10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377}<La%≤-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377} (15)

[0091] When 5ppm<TO≤10ppm in steel, the relationship between La and Alt in steel is as follows:

[0092] -10 -3×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04}<La%≤-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04} (16)

[0093] When 10ppm<TO≤20ppm in steel, La and Alt in steel have the following relationship:

[0094] -10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78}<La%≤-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78} (17)

[0095] When 20ppm<TO≤50ppm in steel, La and Alt in steel have the following relationship:

[0096] -10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187}<La%≤-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187} (18)

[0097] It should be noted that the control level of total oxygen TO in the current steelmaking process is generally within 50ppm. Figure 1It can be seen that with the increase of total oxygen TO content, the La critical content corresponding to the chemical reaction equilibrium of formula (14) gradually approaches the same under different Alt contents in steel, that is, with the increase of total oxygen TO content, the chemical reaction equilibrium is less and less affected by the change of Alt content, but depends on a certain critical value of La content. When TO = 50ppm, this phenomenon is particularly obvious, and the La content converges to 195-197ppm. Therefore, when TO>50ppm in steel and reaches 100ppm, for different Alt contents, the La content must also converge to a certain critical value. In addition, it can be seen from formula (14) that when the Alt content is within a certain range and the total oxygen TO content is high enough, the balance of the chemical reaction in formula (14) depends more on the proportional relationship between the La content and the total oxygen TO content. Therefore, when TO increases from 50 ppm to 100 ppm, if the same reaction balance as when TO = 50 ppm is to be maintained, according to the proportional principle of chemical reaction, the critical content of La must at least be increased by 1 times compared to the critical value corresponding to when TO = 50 ppm. Therefore, when 50 ppm < TO ≤ 100 ppm in steel, La and Alt in steel have the following relationship:

[0098] -2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187}<La%≤-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187} (19)

[0099] Similarly, another technical effect pursued by the modified inclusions of the present invention is to reduce the generation of MnS. Since MnS in steel is more easily precipitated in steel below 1873K, but the precipitation temperature of MnS is higher than 1273K, it is necessary to establish the La-Mn-SO-Fe equilibrium phase diagram in steel at 1273K as a research object. Figure 2 is the La-Mn-SO-Fe equilibrium phase diagram in steel at 1273K. Figure 2 It can be seen that when S≤55ppm, the following chemical reactions will occur:

[0100] Mn+S=MnS (20)

[0101] La+[O]+MnS=1 / 2La 2 O 2 S+Mn+1 / 2S (21)

[0102] Figure 2The vertical line at the lower right is the equilibrium line of the chemical reaction of formula (21). The point values ​​on the equilibrium line represent the critical contents of La and S corresponding to the chemical reaction equilibrium. The right area of ​​the equilibrium line represents that the chemical reaction of formula (21) has a tendency to proceed spontaneously from right to left, and the amount of MnS gradually increases as the reaction proceeds. Moreover, as the La content decreases and / or the S content increases, this tendency of spontaneous reaction from right to left becomes stronger and stronger. The left area of ​​the equilibrium line represents that the chemical reaction of formula (21) has a tendency to proceed spontaneously from left to right, and the amount of MnS gradually decreases as the reaction proceeds. Moreover, as the La content increases and / or the S content decreases, this tendency of spontaneous reaction from left to right becomes stronger and stronger. The technical effect pursued by the modified inclusions of the present invention is to minimize the amount of MnS generated in the steel. Therefore, under a certain S content, it is the inherent meaning of the present invention to control the La content in the steel to be not lower than the critical content at the reaction equilibrium.

[0103] The present invention is achieved by fitting Figure 2 The equilibrium line of the chemical reaction in formula (21) is used to obtain the critical content formula of La. The obtained critical content of La is used as the lower limit of the La content in steel, and 1.2 times of the obtained critical content of La is used as the upper limit of the La content in steel. Specifically, when S in steel is ≤55ppm, the relationship between La and S in steel is as follows:

[0104] 10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] <La%≤1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] (twenty two)

[0105] When 55ppm<S≤500ppm, from Figure 2 As can be seen, the following chemical reactions occur:

[0106] Mn+S=MnS (20)

[0107] 3S+2La=La 2 S 3 (twenty three)

[0108] (x-2)La+La 2 S 3 +zMnS=La x S y +zMn+(z+3-y)S (24)

[0109] Figure 2The oblique line in the upper right corner is the equilibrium line of the chemical reaction of formula (24). The point values ​​on the equilibrium line represent the critical contents of La and S corresponding to the chemical reaction equilibrium. The right area of ​​the equilibrium line represents that the chemical reaction of formula (24) has a tendency to proceed spontaneously from right to left, and the amount of MnS gradually increases as the reaction proceeds. Moreover, as the La content decreases and / or the S content increases, this tendency of spontaneous reaction from right to left becomes stronger and stronger. The left area of ​​the equilibrium line represents that the chemical reaction of formula (24) has a tendency to proceed spontaneously from left to right, and the amount of MnS gradually decreases as the reaction proceeds. Moreover, as the La content increases and / or the S content decreases, this tendency of spontaneous reaction from left to right becomes stronger and stronger. The technical effect pursued by the modified inclusions of the present invention is to minimize the amount of MnS generated in the steel. Therefore, under a certain S content, it is the inherent meaning of the present invention to control the La content in the steel to be not lower than the critical content at the reaction equilibrium.

[0110] The present invention is achieved by fitting Figure 2 The equilibrium line of the chemical reaction in formula (24) is used to obtain the critical content formula of La. The obtained critical content of La is used as the lower limit of the La content in steel, and 1.2 times of the obtained critical content of La is used as the upper limit of the La content in steel. Specifically, when 55ppm<S≤500ppm in steel, La and S in steel have the following relationship:

[0111] 10 [1.0034×lg(S％)+0.508] <La%≤1.2×10 [1.0034×lg(S％)+0.508] (25)

[0112] Since the present invention needs to limit Al 2 O 3 And the amount of MnS generated, so the five regions with different total oxygen TO contents, namely, formulas (15) to (19), and the two regions with different S contents, namely, formulas (22) and (25), are combined to obtain the corresponding 10 La relationship equations, namely formulas (1) to (10).

[0113] When the La% calculated by formula (1) to (10) is less than 0, it is calculated as 0. The La content determined by the above formula is the La content in the steel. When adding lanthanum-iron alloy to the refined ingredients, it is necessary to consider the rare earth yield in the steel and the lanthanum content in the lanthanum-iron alloy to calculate the amount of lanthanum-iron alloy added. In the present invention, the rare earth yield is calculated as a minimum of 30%, and the lanthanum content in the lanthanum-iron alloy is 30%, so the amount of lanthanum-iron alloy added in the present invention is La / 0.09.

[0114] Comparative Example

[0115] Step S1, smelting gear steel 20CrMnTi in a converter;

[0116] Step S2: when the converter is tapping steel, aluminum deoxidation and alloying operation is performed in the ladle, and the mass of molten steel is 260t;

[0117] Step S3, LF furnace → RH furnace refining;

[0118] S1: LF refining temperature is 1569℃, white slag is made for deoxidation and desulfurization, the S content of molten steel is controlled to be less than 0.0030%, the Alt content is within the range of 0.05%, the TO content of molten steel is less than 20ppm, and the temperature is adjusted. The white slag duration is 22min. After feeding 23.2kg of calcium wire, the [Ca] content in the molten steel is controlled within the range of 0.0008~0.0038%, and the measured value is 0.0010%. The white slag composition is CaO: 52.58%, SiO 2 : 11.78%, Al 2 O 3 : 28.11%, MgO: 7.02%, TFeO: 0.334%, MnO: 0.18%, basicity CaO / SiO 2 The argon blowing time is 6 minutes and the argon blowing volume is 0.008 Nm 3 / (t·min). The temperature of LF leaving the station is 1591℃, and the chemical composition for RH refining is shown in Table 1.

[0119] Table 1 Chemical composition (wt%) of LF off-station in comparative examples of the present invention

[0120] Test No. C Si Mn P S Als Ca Cr Ni Cu Comparative Example 0.21 0.25 0.90 0.011 0.003 0.05 0.0010 1.2 0.30 0.25

[0121] The calcium recovery rate was calculated to be 11.2%.

[0122] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1589℃. The vacuum cycle degassing is carried out in the RH1 furnace. The vacuum degree is 160Pa and the holding time is 18min. After breaking the vacuum, argon is soft-blown for 10min and the soft-blowing amount is 0.007Nm 3 / (t·min), RH departure temperature 1565℃.

[0123] Step S4, continuous casting after refining.

[0124] After testing, the inclusions in the finished product are CaS and 12CaO·7Al 2 O 3 , spherical inclusions account for 84.4%.

[0125] Example 1

[0126] Step S1, smelting corrosion-resistant steel Q450NQR1 in a converter;

[0127] Step S2: when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99%, the maximum equivalent diameter is 9 mm, and the mass of the molten steel is 260 t;

[0128] Step S3, LF furnace → RH furnace refining;

[0129] S1: LF refining in-situ temperature is 1563℃, LF furnace refining white slag operation, slag thickness is controlled to be 132mm, white slag duration is 22min, white slag composition is calculated by mass percentage as CaO: 55%, SiO 2 :6%,MgO:15%,Al 2 O 3 :23.6%, FeO+MnO:0.4%, CaO / SiO 2 : 9.1, soft blowing argon before leaving the station, soft blowing argon time is 6min, soft blowing argon volume is 0.008Nm 3 / (t·min), LF departure temperature is 1592℃.

[0130] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1589℃. The vacuum cycle degassing is carried out in the RH1 furnace. The vacuum degree is 160Pa and the holding time is 18min. 4min before breaking the vacuum, 32.4kg of lanthanum-iron alloy is added. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel is 0.05%, the mass percentage of total oxygen TO is 5ppm, and the mass percentage of sulfur S in the steel is 0.0030%. After breaking the vacuum, argon is soft-blown for 10min and the soft-blowing amount is 0.007Nm 3 / (t·min), RH departure temperature 1565℃.

[0131] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0132] (1) Calculate the La content to be retained in the steel

[0133] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ), we get: max(9.3×10 -4 , 2.6×10 -6 )<La%≤max(1.12×10 -3, 3.12×10 -6 ), take the upper limit La% = 1.12 × 10 -3 ;

[0134] (2) Calculate the amount of lanthanum-iron alloy added

[0135] The recovery rate of La is calculated as 30%, and the content of lanthanum in the ferro-lanthanum alloy is calculated as 30%. (260t×1.12×10 -3 % / 0.09) / (1-1.12×10 -3 % / 0.09)=32.4kg.

[0136] Table 2 Chemical composition (wt%) of RH off-station in Example 1 of the present invention

[0137] Test No. C Si Mn P S Als Cr Ni Cu La 1 0.05 0.08 1.30 0.011 0.003 0.05 0.73 0.30 0.38 0.0014

[0138] The actual yield of La was calculated to be 35%.

[0139] Step S4, continuous casting after refining.

[0140] After testing, the main types of inclusions in the finished product are La 2 O 2 S, spherical inclusions account for more than 92.1%, no MnS and Al 2 O 3 Inclusions.

[0141] Example 2

[0142] Step S1, smelting wear-resistant steel NM400 in a converter;

[0143] Step S2: when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99.2%, the maximum equivalent diameter is 12 mm, and the mass of the molten steel is 260 t;

[0144] Step S3, LF furnace refining;

[0145] The LF refining temperature is 1565℃. The LF furnace refining white slag operation is carried out. The slag thickness is controlled to be 139mm. The white slag duration is 22min. The white slag composition is calculated by mass percentage as CaO: 65%, SiO 2 : 5.91%, MgO: 11%, Al 2 O 3 :17.6%, FeO+MnO:0.49%, CaO / SiO 2: 11, 1149kg lanthanum-iron alloy was added 4min before leaving the station. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel was measured to be 0.02%, the mass percentage of total oxygen TO was 80ppm, and the mass percentage of sulfur S in the steel was 80ppm; argon was soft-blown before leaving the station, the soft blowing time was 6min, the soft blowing amount of argon was 0.008Nm3 / (t·min), and the LF leaving station temperature was 1592℃.

[0146] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0147] (1) Calculate the La content to be retained in the steel

[0148] max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ), calculated as follows: max(0.0391, 0.0253)<La%≤max(0.0470, 0.0304), take La%=0.04;

[0149] (2) Calculate the amount of lanthanum-iron alloy added

[0150] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.04% / 0.09] / (1-0.04% / 0.09)=1149kg.

[0151] Table 3 Chemical composition (wt%) of LF off-station in Example 2 of the present invention

[0152] Test No. C Si Mn P S Als Cr Ni Mo La 2 0.30 0.70 1.60 0.025 0.0080 0.02 1.0 0.70 0.5 0.0401

[0153] The actual yield of lanthanum was calculated to be 30%.

[0154] Step S4, continuous casting after refining.

[0155] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 98%, no MnS and Al 2 O 3 Inclusions.

[0156] Example 3

[0157] Step S1, smelting 10# high-quality carbon steel in a converter;

[0158] Step S2, when the converter is tapped, aluminum deoxidation and alloying operation is performed in the ladle, the purity of the aluminum block is 99.5%, the maximum equivalent diameter is 10 mm, and the mass of the molten steel is 260 t;

[0159] Step S3, LF furnace refining;

[0160] The LF refining temperature is 1563℃. The LF furnace refining white slag operation controls the slag thickness to 140mm. The white slag duration is 21min. The white slag composition is calculated by mass percentage as CaO: 55%, SiO 2 : 5.6%, MgO: 15%, Al 2 O 3 :24%, FeO+MnO:0.4%, CaO / SiO 2 : 9.82, 710kg lanthanum-iron alloy was added 4min before leaving the station, and before adding lanthanum-iron alloy, the mass percentage of Alt in the steel was measured to be 0.05%, the mass percentage of total oxygen TO was 8ppm, and the mass percentage of sulfur S in the steel was 75ppm; argon was soft-blown before leaving the station, the soft-blowing time was 10min, and the soft-blowing amount of argon was 0.007Nm 3 / (t·min), LF departure temperature is 1598℃.

[0161] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0162] (1) Calculate the La content to be retained in the steel

[0163] max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [1.0034 ×lg(S％)+0 . 508] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [1.0034×lg(S％)+0.508] ), calculated as follows: max(0.0052, 0.0238)<La%≤max(0.0062, 0.0286), take La%=0.0245;

[0164] (2) Calculate the amount of lanthanum-iron alloy added

[0165] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.0245% / 0.09] / (1-0.0245% / 0.09)=710kg.

[0166] Table 4 Chemical composition (wt%) of LF off-station in Example 3 of the present invention

[0167] Test No. C Si Mn P S Als Cr Ni Cu La 3 0.076 0.21 0.496 0.008 0.0075 0.05 0.15 0.20 0.25 0.0254

[0168] The actual yield of lanthanum was calculated to be 31.1%.

[0169] Step S4, continuous casting after refining.

[0170] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 95%, no MnS and Al 2 O 3 Inclusions.

[0171] Example 4

[0172] Step S1, smelting gear steel 20CrMnTi in a converter;

[0173] Step S2, when the converter is tapped, aluminum deoxidation and alloying operation is performed in the ladle, the purity of the aluminum block is 99%, the maximum equivalent diameter is 11 mm, and the mass of the molten steel is 260 t;

[0174] Step S3, LF furnace refining;

[0175] The LF refining temperature is 1567℃. The LF furnace refining white slag operation controls the slag thickness to 140mm. The white slag duration is 23min. The white slag composition is CaO: 62.7%, SiO 2 :7%,MgO:15%,Al 2 O 3 :15%, FeO+MnO:0.3%, CaO / SiO 2 : 8.96, 376kg lanthanum iron alloy was added 4min before leaving the station, and before adding lanthanum iron alloy, the mass percentage of Alt in the steel was measured to be 0.03%, the mass percentage of total oxygen TO was 20ppm, and the mass percentage of sulfur S in the steel was 20ppm; before leaving the station, argon was soft-blown for 10min and the amount of argon was 0.007Nm 3 / (t·min), LF departure temperature is 1587℃.

[0176] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0177] (1) Calculate the La content to be retained in the steel

[0178] max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ); calculated: max(0.0122, 0.0000)<La%≤max(0.0146, 0.0000), take La%=0.0130;

[0179] (2) Calculate the amount of lanthanum-iron alloy added

[0180] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.013% / 0.09] / (1-0.013% / 0.09)=376kg.

[0181] Table 5 Chemical composition (wt%) of LF off-station in Example 4 of the present invention

[0182] Test No. C Si Mn P S Als Cr Ti Ni La 4 0.21 0.25 0.90 0.02 0.002 0.03 1.1 0.08 0.20 0.0137

[0183] The actual yield of lanthanum was calculated to be 31.6%.

[0184] Step S4, continuous casting after refining.

[0185] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 96%, no MnS and Al 2 O 3 Inclusions.

[0186] Example 5

[0187] Step S1, smelting gear steel 20CrMnTi in a converter;

[0188] Step S2: when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99.1%, the maximum equivalent diameter is 9 mm, and the mass of the molten steel is 260 t;

[0189] Step S3, LF furnace refining → RH furnace refining;

[0190] S1: LF refining in-situ temperature is 1561℃, white slag operation is performed in LF furnace refining, slag thickness is controlled to be 150mm, white slag duration is 23min, and argon is softly blown before leaving the station; the composition of white slag is CaO: 58.15%, SiO 2 : 6.5%, MgO: 13%, Al 2 O 3 :22%, FeO+MnO=0.35%, CaO / SiO 2 :8.94. LF leaving station temperature 1590℃.

[0191] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1585℃. The RH furnace is vacuum cycled and degassed. The vacuum degree is 160Pa and the holding time is 18min. 1248kg of lanthanum-iron alloy is added 4min before the RH furnace breaks the vacuum. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel is 0.06%, the mass percentage of total oxygen TO is 60ppm, and the mass percentage of sulfur S in the steel is 10ppm. Argon is soft-blown before leaving the station. The soft blowing time is 10min and the soft blowing volume is 0.007Nm 3 / (t·min), RH departure temperature 1569℃.

[0192] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0193] (1) Calculate the La content to be retained in the steel

[0194] max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ), calculated as follows: max(0.0395, 0.0000)<La%≤max(0.0474, 0.0000), take La%=0.043;

[0195] (2) Calculate the amount of lanthanum-iron alloy added

[0196] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.043% / 0.09] / (1-0.043% / 0.09)=1248kg.

[0197] Table 6 Chemical composition (wt%) of LF off-station in Example 5 of the present invention

[0198] Test No. C Si Mn P S Als Cr Ni Ti La 5 0.19 0.30 0.97 0.009 0.001 0.06 1.2 0.19 0.07 0.045

[0199] The actual yield of lanthanum was calculated to be 31.4%.

[0200] Step S4, continuous casting after refining.

[0201] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 93%, no MnS and Al 2 O 3 Inclusions.

[0202] Example 6

[0203] Step S1, smelting heavy rail steel U75 in a converter;

[0204] Step S2, when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99.8%, the maximum equivalent diameter is 11.5 mm, and the mass of the molten steel is 260 t;

[0205] Step S3, LF furnace refining → RH furnace refining;

[0206] S1: LF refining in-situ temperature is 1554℃, white slag operation is performed in LF furnace refining, slag thickness is controlled to be 130mm, white slag duration is 23min, and argon is softly blown before leaving the station; the composition of white slag is CaO: 56%, SiO 2 :7%, MgO:13.8%, Al 2 O 3 :23%, FeO+MnO=0.2%, CaO / SiO 2 :8. LF departure temperature 1597℃.

[0207] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1588℃. The RH furnace is vacuum cycled and degassed. The vacuum degree is 160Pa and the holding time is 18min. 957kg of lanthanum-iron alloy is added 4min before the RH furnace breaks the vacuum. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel is 0.02%, the mass percentage of total oxygen TO is 30ppm, and the mass percentage of sulfur S in the steel is 100ppm. Argon is soft-blown before leaving the station. The soft blowing time is 10min and the soft blowing volume is 0.007Nm 3 / (t·min), RH departure temperature 1565℃.

[0208] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0209] (1) Calculate the La content to be retained in the steel

[0210] max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ), calculated as follows: max(0.0196, 0.0317)<La%≤max(0.0236, 0.0381), take La%=0.0330;

[0211] (2) Calculate the amount of lanthanum-iron alloy added

[0212] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.033% / 0.09] / (1-0.033% / 0.09)=957kg.

[0213] Table 7 Chemical composition (wt%) of LF off-station in Example 6 of the present invention

[0214] Test No. C Si Mn P S Als La 6 0.75 0.55 0.79 0.014 0.01 0.02 0.0330

[0215] The actual yield of lanthanum was calculated to be 30.0%.

[0216] Step S4, continuous casting after refining.

[0217] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 97%, no MnS and Al 2 O 3 Inclusions.

[0218] Example 7

[0219] Step S1, smelting heavy rail steel U75 in a converter;

[0220] Step S2, when the converter is tapped, aluminum deoxidation and alloying operation is performed in the ladle, the purity of the aluminum block is 99%, the maximum equivalent diameter is 10 mm, and the mass of the molten steel is 260 t;

[0221] Step S3, LF furnace refining;

[0222] The LF refining temperature is 1563℃. The LF furnace refining white slag operation controls the slag thickness to 140mm. The white slag duration is 23min. The white slag composition is CaO: 64%, SiO 2 : 6.4%, MgO: 13%, Al 2 O 3 :16.3%, FeO+MnO:0.3%, CaO / SiO 2 : 10, 159kg lanthanum-iron alloy was added 4min before leaving the station. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel was measured to be 0.05%, the mass percentage of total oxygen TO was 8ppm, and the mass percentage of sulfur S in the steel was 10ppm; argon was soft-blown before leaving the station, the soft-blowing time was 10min, and the soft-blowing amount of argon was 0.007Nm 3 / (t·min), LF departure temperature is 1587℃.

[0223] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0224] (1) Calculate the La content to be retained in the steel

[0225] max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ), calculated as follows: max(0.0052, 0.0000)<La%≤max(0.0063, 0.0000), take La%=0.0055;

[0226] (2) Calculate the amount of lanthanum-iron alloy added

[0227] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.0055% / 0.09] / (1-0.0055% / 0.09)=159kg.

[0228] Table 8 Chemical composition (wt%) of LF off-station in Example 7 of the present invention

[0229] Test No. C Si Mn P S Als La 7 0.76 0.70 0.92 0.019 0.001 0.05 0.0059

[0230] The actual yield of lanthanum was calculated to be 32.2%.

[0231] Step S4, refining and then die casting.

[0232] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 96%, no MnS and Al 2 O 3 Inclusions.

[0233] Example 8

[0234] Step S1, smelting Q355 structural steel in a converter;

[0235] Step S2: when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99.9%, the maximum equivalent diameter is 9 mm, and the mass of the molten steel is 260 t;

[0236] Step S3, LF furnace refining → RH furnace refining;

[0237] S1: LF refining in-situ temperature is 1564℃, white slag operation is performed in LF furnace refining, slag thickness is controlled to be 145mm, white slag duration is 23min, and argon is softly blown before leaving the station; the composition of white slag is CaO: 58%, SiO 2 :6%,MgO:12%,Al 2 O 3 :23.6%, FeO+MnO=0.4%, CaO / SiO 2 :9.7. LF departure temperature 1599℃.

[0238] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1589℃. The RH furnace is vacuum cycled for degassing with a vacuum degree of 160Pa for 18min. 1015kg of lanthanum-iron alloy is added 4min before the RH furnace breaks the vacuum. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel is 0.04%, the mass percentage of total oxygen TO is 4ppm, and the mass percentage of sulfur S in the steel is 100ppm. Argon is soft-blown before leaving the station for 10min and the amount of argon is 0.007Nm 3 / (t·min), RH leaving station temperature 1568℃.

[0239] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0240] (1) Calculate the La content to be retained in the steel

[0241] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10[1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [1.0034×lg(S％)+0.508] ), calculated as follows: max(0.0005, 0.0317)<La%≤max(0.0006, 0.038), take La%=0.035;

[0242] (2) Calculate the amount of lanthanum-iron alloy added

[0243] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.035% / 0.09] / (1-0.035% / 0.09)=1015kg.

[0244] Table 9 Chemical composition (wt%) of LF off-station in Example 8 of the present invention

[0245]

[0246]

[0247] The actual yield of lanthanum was calculated to be 34.3%.

[0248] Step S4, continuous casting after refining.

[0249] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 93%, no MnS and Al 2 O 3 Inclusions.

[0250] Example 9

[0251] Step S1, smelting Q355 structural steel in a converter;

[0252] Step S2: when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99.4%, the maximum equivalent diameter is 10 mm, and the mass of the molten steel is 260 t;

[0253] Step S3, LF furnace refining;

[0254] The LF refining temperature is 1565℃. The LF furnace refining white slag operation controls the slag thickness to 135mm. The white slag duration is 23min. The white slag composition is calculated by mass percentage as CaO: 58%, SiO 2 :6.2%, MgO: 13.7%, Al 2 O3 :22%, FeO+MnO:0.1%, CaO / SiO 2 : 9.4, 2921kg lanthanum iron alloy was added 4min before leaving the station. Before adding the lanthanum iron alloy, the mass percentage of Alt in the steel was measured to be 0.05%, the mass percentage of total oxygen TO was 15ppm, and the mass percentage of sulfur S in the steel was 300ppm; argon was soft-blown before leaving the station, the soft-blowing time was 10min, and the soft-blowing amount of argon was 0.007Nm 3 / (t·min), LF departure temperature is 1589℃.

[0255] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0256] (1) Calculate the La content to be retained in the steel

[0257] max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]},1.2×10 [1.0034×lg(S％)+0.508] ), calculated as follows: max(0.0141, 0.0955)<La%≤max(0.0169, 0.1146), take La%=0.1;

[0258] (2) Calculate the amount of lanthanum-iron alloy added

[0259] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.1% / 0.09] / (1-0.1% / 0.09)=2921kg.

[0260] Table 10 Chemical composition (wt%) of LF off-station in Example 9 of the present invention

[0261] Test No. C Si Mn P S Als Cr Ni Cu La 9 0.24 0.55 1.50 0.004 0.003 0.05 0.3 0.3 0.4 0.1

[0262] The actual yield of lanthanum was calculated to be 30%.

[0263] Step S4, continuous casting after refining.

[0264] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 93%, no MnS and Al 2 O3 Inclusions.

[0265] Example 10

[0266] Step S1, smelting Q450NQR1 in a converter;

[0267] Step S2: when the converter is tapped, aluminum deoxidation and alloying operations are performed in the ladle, the purity of the aluminum block is 99%, the maximum equivalent diameter is 9 mm, and the mass of the molten steel is 260 t;

[0268] Step S3, LF furnace refining → RH furnace refining;

[0269] S1: LF refining in-situ temperature is 1561℃, white slag operation is performed in LF furnace refining, slag thickness is controlled to be 133mm, white slag duration is 23min, and argon is softly blown before leaving the station; the composition of white slag is CaO: 56%, SiO 2 :7%,MgO:13%,Al 2 O 3 :23.52%, FeO+MnO=0.48%, CaO / SiO 2 :8. LF leaving station temperature 1590℃.

[0270] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1585℃. The RH1 furnace is vacuum cycled and degassed with a vacuum degree of 160Pa for 18min. 579kg of lanthanum-iron alloy is added 4min before the RH furnace breaks the vacuum. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel is 0.06%, the mass percentage of total oxygen TO is 30ppm, and the mass percentage of sulfur S in the steel is 55ppm. Argon is soft-blown before leaving the station. The soft-blowing time is 10min and the soft-blowing volume is 0.007Nm 3 / (t·min), RH leaving station temperature 1564℃.

[0271] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0272] (1) Calculate the La content to be retained in the steel

[0273] max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474]), calculated as follows: max(0.0198, 0.0174)<La%≤max(0.0238, 0.0209), take La%=0.0200;

[0274] (2) Calculate the amount of lanthanum-iron alloy added

[0275] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, [260t×0.02% / 0.09] / (1-0.02% / 0.09)=579kg.

[0276] Table 11 Chemical composition (wt%) of LF off-station in Example 10 of the present invention

[0277] Test No. C Si Mn P S Als Cr Ni Cu La 10 0.70 0.74 1.39 0.005 0.0055 0.06 1.0 0.5 0.30 0.0210

[0278] The actual yield of lanthanum was calculated to be 31.5%.

[0279] Step S4, continuous casting after refining.

[0280] After testing, the type of inclusions in the finished product is La 2 O 2 S, spherical inclusions account for more than 93%, no MnS and Al 2 O 3 Inclusions.

[0281] Embodiment 11

[0282] Step S1, smelting high aluminum steel 38CrMoAl in an electric furnace;

[0283] Step S2: When the electric furnace is tapping steel, aluminum is added along with the steel flow, and aluminum deoxidation and alloying operations are performed in the ladle. The purity of the aluminum block is 99%, the maximum equivalent diameter is 9 mm, and the mass of the molten steel is 100 t;

[0284] Step S3, LF furnace → RH furnace refining;

[0285] S1: LF refining in-situ temperature is 1563℃, LF furnace refining white slag operation, slag thickness is controlled to be 132mm, white slag duration is 22min, white slag composition is CaO: 64%, SiO 2 :8%,MgO:12%,Al 2 O 3 :15.6%, FeO+MnO:0.4%, CaO / SiO 2 : 8, soft blowing argon before leaving the station, soft blowing argon time is 6min, soft blowing argon volume is 0.008Nm 3 / (t·min), LF departure temperature is 1592℃.

[0286] S2: After the LF furnace is refined, it is transferred to the RH furnace. The RH refining temperature is 1589℃. The vacuum cycle degassing is carried out in the RH1 furnace. The vacuum degree is 160Pa and the holding time is 18min. The vacuum degree is 160Pa and the holding time is 18min. 4min before breaking the vacuum, 37.8kg of lanthanum-iron alloy is added. Before adding the lanthanum-iron alloy, the mass percentage of Alt in the steel is 0.95%, the mass percentage of total oxygen TO is 5ppm, and the mass percentage of sulfur S in the steel is 0.0030%. After breaking the vacuum, argon is soft-blown for 10min and the amount of argon is 0.007Nm 3 / (t·min), RH departure temperature 1565℃.

[0287] The amount of lanthanum-iron alloy added is calculated according to the following steps:

[0288] (1) Calculate the La content to be retained in the steel

[0289] max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ), we get: max(0.003, 2.6×10 -6 )<La%≤max(0.0036, 3.12×10 -6 ), take La%=0.0034;

[0290] (2) Calculate the amount of lanthanum-iron alloy added

[0291] The yield of La is calculated as 30%, and the content of lanthanum in the lanthanum-iron alloy is calculated as 30%, (100t×0.0034% / 0.09) / (1-0.0034% / 0.09)=37.8kg.

[0292] Table 12 Chemical composition (wt%) of RH off-station in Example 11 of the present invention

[0293] Test No. C Si Mn P S Als Cr Mo La 11 0.40 0.30 0.50 0.011 0.003 0.95 1.5 0.20 0.0034

[0294] The actual yield of La was calculated to be 30%.

[0295] Step S4, refining and then die casting.

[0296] After testing, the main types of inclusions in the finished product are La2 O 2 S, spherical inclusions account for more than 91%, no MnS and Al 2 O 3 Inclusions.

[0297] The steel of the above 10 embodiments was subjected to a cyclic immersion corrosion test, and the corrosive solution was NaHSO 3 , time 75h, compared with the same type of calcium-treated steel, the relative corrosion rate of the embodiments is less than 90%.

Claims

1. A method for treating inclusions in modified steel using rare earth lanthanum during refining, characterized in that: The method comprises the following steps: Step S1, smelting in a converter or electric furnace; Step S2: when the converter or electric furnace is tapping steel, aluminum deoxidation and alloying operation is performed in the ladle; Step S3, LF furnace or LF furnace → RH furnace refining, rare earth lanthanum treatment is performed in the last step of refining; Step S4, continuous casting or mold casting after refining; In the step 3, before the rare earth lanthanum treatment, the mass percentage of Alt in the steel is controlled to be 0.02%≤Alt<1.00%, the mass percentage of total oxygen TO is below 0.01%, and the mass percentage of S is below 0.05%; In step S3, when rare earth lanthanum treatment is performed, the contents of La, Alt and S in the steel have the following relationship: When total oxygen TO≤5ppm and S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ); When total oxygen TO≤5ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{2.12×[lg(Alt%)-2] 2 +9.655×[lg(Alt%)-2]+7.8377},1.2×10 [1.0034×lg(S％)+0.508] ); When 5ppm<TO≤10ppm, S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ); When 5ppm<TO≤10ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{3.133×[lg(Alt%)-2] 2 +14.96×[lg(Alt%)-2]+10.04},1.2×10 [1.0034×lg(S％)+0.508] ); When 10ppm<TO≤20ppm, S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ); When 10ppm<TO≤20ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -3 ×{4.869×[lg(Alt%)-2] 2 +24.82×[lg(Alt%)-2]+14.78},1.2×10 [1.0034×lg(S％)+0.508] ); When 20ppm<TO≤50ppm and sulfur S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ); When 20ppm<TO≤50ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-1.2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ); When 50ppm<TO≤100ppm and sulfur S≤55ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [-46.223×lg(S％)×lg(S％)-206.55×lg(S％)-232.474] ); When 50ppm<TO≤100ppm, 55ppm<S≤500ppm in steel, the relationship between La, Alt and S in steel is as follows: max(-2×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},10 [1.0034 ×lg(S％)+0.508] )<La%≤max(-2.4×10 -4 ×{2.048×[lg(Alt%)-2] 2 +9.887×[lg(Alt%)-2]-187},1.2×10 [1.0034×lg(S％)+0.508] ); When the La%, Alt% and S% parameters in the above formula are substituted into the calculation formula, the values ​​before the mass percentage of La, Alt and S in the steel are directly substituted without converting them into decimals.

2. The method according to claim 1, characterized in that: In the step 2, the aluminum deoxidation is performed by using aluminum blocks or aluminum particles, the purity of the aluminum blocks or aluminum particles reaches more than 99%, and the equivalent diameter is not greater than 12 mm.

3. The method according to claim 1, characterized in that: In step 3, during the white slag refining in the LF furnace, the slag thickness is controlled to be 130-150 mm, the white slag duration is greater than 20 min, and argon is soft-blown before leaving the station.

4. The method according to claim 3, characterized in that: The components of the white slag are, by mass percentage, CaO: 55-65%, SiO2: 5-8%, MgO: 11-15%, Al2O3: 15-24%, FeO+MnO<0.5%, and CaO / SiO2: 8.0-11.

5. The method according to claim 1, characterized in that: In step 3, the rare earth La treatment is performed in the last step of refining as follows: when only LF furnace is used for refining, rare earth lanthanum is added 4 minutes before leaving the station; when refining from LF furnace to RH furnace, rare earth lanthanum is added 4 minutes before breaking vacuum in the RH furnace.

6. The method according to claim 5, characterized in that: The rare earth lanthanum is added in the form of lanthanum-iron alloy, and the rare earth element content in the lanthanum-iron alloy is 30%.

Images