Yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel and preparation method thereof

Abstract

The present invention belongs to the field of metal material technology, specifically relating to a yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel and a preparation method thereof. The yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel comprises the following components, calculated by mass fraction: carbon: ≤0.030%, silicon: 0.30-1.00%, manganese: 0.60-1.00%, phosphorus: ≤0.040%, sulfur: ≤0.030%, chromium: 17.0-19.0%, nickel: 0.20-0.50%, nitrogen: ≤0.0150%, and the remainder being titanium, yttrium, magnesium, iron, and unavoidable impurities. The present invention utilizes a yttrium-magnesium composite treatment to reduce the size of inclusions in the steel to below 2.0 μm, significantly refining TiN, which helps to improve nozzle nodule formation during continuous casting. The average equiaxed grain size is reduced to 2.180 mm, and the equiaxed grain ratio is increased to 100%, which can resolve wrinkling during the forming process and improve the performance of the steel. Furthermore, the production process is simple and controllable.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to yttrium-magnesium composite treated titanium-stabilized ferrite stainless steel and a preparation method thereof. Background Art

[0002] Ferritic stainless steel is widely used in the manufacture of various mechanical equipment due to its strong magnetic properties, high thermal conductivity, low specific resistance and expansion coefficient, insensitivity to chloride stress corrosion cracking, good resistance to pitting and crevice corrosion, and relatively low price. However, ferritic stainless steel also has some disadvantages, such as low impact toughness of welded joints and a tendency to brittleness, which greatly restrict its application in some fields such as household appliances and automobiles. In recent years, to further expand the application of ferritic stainless steel, new ultra-pure ferritic stainless steel materials have been developed by adding stabilizing elements such as Nb and Ti to ordinary ferritic stainless steel to further reduce the C+N content. Due to its superior corrosion resistance, formability, and weldability, ultra-pure ferritic stainless steel has gradually replaced 304 austenitic stainless steel in industries such as elevator panels.

[0003] The composition, morphology, and size of inclusions in steel have a significant impact on the microstructure and properties of steel. The traditional inclusion control concept is to remove inclusions from steel to the maximum extent possible and minimize their harmful effects. However, with the development of clean steelmaking technology, the cleanliness of steel has been greatly improved, and the cost of this control method has increased significantly. Based on this, a new inclusion control method has been proposed, which classifies inclusions into three categories based on size: large inclusions of 10-100 μm are harmful and require development of extreme removal technology; inclusions of 0.5-10 μm are between harmful and beneficial types, and new inclusion modification technologies are necessary to reduce the crack sensitivity of harmful inclusions in steel while enhancing their role in promoting microstructural transformation; and tiny inclusions of 50-500 nm can play a role in second-phase strengthening and improving the mechanical properties of the material. Therefore, priority should be given to developing inclusion miniaturization control technologies to promote the formation of a large number of fine, dispersed inclusions in steel, thereby enhancing steel quality.

[0004] According to the second phase theory and lattice mismatch theory in steel: tiny inclusion points can effectively pin grain boundaries, hinder further grain growth, and refine grains; a large number of small, dispersed, stable inclusions with a small planar two-dimensional lattice mismatch with the steel matrix can serve as heterogeneous nucleation cores during the solidification of molten steel, promote the formation of equiaxed crystals, refine the solidification structure of steel, maintain the heritability of the solidification structure in the subsequent rolling process, and improve the performance of steel.

[0005] Methods for refining metal solidification structures primarily include: 1. Increasing the solidification rate of the ingot; 2. Applying electromagnetic stirring during the solidification process; and 3. Adding inoculants or refiners to the steel. Currently, inoculants for ferritic stainless steel include CeO2, Ce2O3, CeS, Al2O3, NbN, NbC, ZrO2, W2C, and SiC. However, these inoculants are relatively large in size and poorly dispersed within the steel, necessitating the search for more optimal inoculants for grain refinement.

[0006] In summary, there are currently two major problems in the production of ultra-pure ferritic stainless steel: ultra-pure ferritic stainless steel has well-developed columnar crystals, and grains with the same orientation after rolling and annealing are easily segregated to form grain clusters, causing wrinkling during the forming process; TiN in molten steel production is coarse, causing nozzle nodules during the continuous casting process, seriously hindering smooth production and reducing production efficiency. Summary of the Invention

[0007] The present invention aims to solve the above problems and provides a yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel and a preparation method thereof. The yttrium-magnesium inoculant composite treatment is used to modify Al2O3 inclusions, refine TiN, refine grains, and increase the equiaxed crystal ratio of the titanium-stabilized ferritic stainless steel, thereby preparing ferritic stainless steel with excellent performance.

[0008] According to the technical solution of the present invention, the yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel comprises the following components by mass fraction (mass percentage): carbon: ≤0.030%, silicon: 0.30-1.00%, manganese: 0.60-1.00%, phosphorus: ≤0.040%, sulfur: ≤0.030%, chromium: 17.0-19.0%, nickel: 0.20-0.50%, nitrogen: ≤0.0150%, titanium: 0.15×(0.20+4×[%C]+ 4×[%N])~0.80×(0.20+4×[%C]+4×[%N])%,yttrium: 0.0030×(0.20+4×[%C]+4×[%N])~0.016×(0.20+4×[%C]+4×[%N])%,magnesium: 0.0006×(0.20+4×[%C]+4×[%N])~0.0032×(0.20+4×[%C]+4×[%N])%, the balance being iron and unavoidable impurities;

[0009] Wherein, [%C] and [%N] are the mass fractions of carbon and nitrogen, respectively, in %.

[0010] Another aspect of the present invention provides a method for preparing the above-mentioned yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel, comprising the following steps:

[0011] S1: preparing a molten steel I containing 17.0-19.0% chromium, and decarburizing the molten steel I to below 0.030 wt% to obtain a molten steel II;

[0012] S2: slagging and deep deoxidation of aluminum on the molten steel II to obtain molten steel III;

[0013] The smelting slag system used in the slag making includes basic slag system and TiO2 and Y2O3;

[0014] S3: performing yttrium-magnesium composite treatment and titanium micro-alloying on the molten steel III to obtain yttrium-magnesium composite treated titanium stabilized ferritic stainless steel liquid;

[0015] The yttrium-magnesium composite treatment is achieved by feeding Mg-Y-Fe cored wire into the molten steel III, wherein the Mg-Y-Fe cored wire comprises, by mass fraction, 10.00-30.00% magnesium, 4.00-13.00% yttrium, less than 1.00% impurities, and the remainder iron.

[0016] S4: liquid-casting the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel into a slab to obtain the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel.

[0017] Furthermore, in step S1, scrap steel and high carbon ferrochrome are used as raw materials to prepare molten steel I containing 17.0-19.0 wt% chromium; the preparation process can be carried out in an electric arc furnace (EAF).

[0018] Specifically, the molten steel I includes, by mass fraction, carbon ≤ 0.10%, silicon 0.30-1.00%, manganese 0.60-1.00%, phosphorus ≤ 0.040%, sulfur ≤ 0.10%, chromium 17.0-19.0%, and nickel 0.20-0.50%.

[0019] Furthermore, in step S1, the specific operation of decarburizing the molten steel I to below 0.030wt% includes: performing slag desulfurization and argon oxygen decarburization to the molten steel I in an AOD furnace (argon oxygen refining furnace) to reduce the carbon content to 0.050-0.10wt%; and then entering the VOD furnace (vacuum decarburization furnace) to perform vacuum oxygen deep decarburization to obtain a molten steel II with a carbon content of ≤0.030wt%.

[0020] Specifically, the slagging desulfurization, argon-oxygen decarburization to preserve chromium, and vacuum oxygen deep decarburization are carried out using conventional industry methods.

[0021] Furthermore, in step S2, the yttrium and titanium contents in the steel are precisely controlled to meet the composition requirements through the slag-metal reaction balance;

[0022] Specifically, in the smelting slag system, the basic slag system includes, by mass fraction: CaO: 50-55%; CaF2: 10-13%; SiO2: 10-15%; MgO: 8-10%; Al2O3: 20-25%;

[0023] The thermodynamic equilibrium reaction formulas of TiO2 and Y2O3 with liquid steel II are shown in formulas (1) and (3), respectively:

[0024] [Si]+(TiO2)=[Ti]+(SiO2) (1)

[0025] 3[Si]+2(Y2O3)=4[Y]+3(SiO2) (3)

[0026] The addition of TiO2 and Y2O3 is calculated by formula (2) and (4) respectively:

[0027]

[0028] In formulas (2) and (4), are the mass fractions of SiO2, TiO2 and Y2O3 in the basic slag system, respectively, in %;

[0029] [%Ti], [%Si], [%Y] are the mass fractions of Ti, Si, and Y in the liquid steel III, respectively, in %;

[0030] C1 and C2 are activity coefficient terms, with values ​​of 1.527 and 1.745, respectively;

[0031] T is the slag-gold reaction temperature, in °C.

[0032] Furthermore, in step S2, the aluminum deep deoxidation is specifically performed by adding pure aluminum blocks to the slag-treated molten steel II for deep deoxidation, and controlling the aluminum content in the molten steel (molten steel III) to be ≤ 0.1%. Specifically, the aluminum deep deoxidation can be performed in an LF furnace, and the amount of pure aluminum blocks added is 100-150g / t of steel.

[0033] Furthermore, in the Mg-Y-Fe cored wire, the magnesium to yttrium ratio is 2.33.

[0034] Furthermore, the core weight of the Mg-Y-Fe cored wire is 150-400 g / m.

[0035] Furthermore, in step S3, the feeding speed of the Mg-Y-Fe cored wire is 2.5-3.0 m / s.

[0036] Furthermore, in step S3, the amount of Mg-Y-Fe cored wire fed per ton of molten steel III is calculated according to formula (5):

[0037]

[0038] In formula (5), L Mg-Y-Fe is the feed rate of Mg-Y-Fe cored wire, in m / t steel;

[0039] [% Y] total is the mass fraction of yttrium in the yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel liquid, in %;

[0040] Y Y The yttrium recovery rate in titanium-stabilized ferritic stainless steel treated with yttrium-magnesium composite treatment is 75%;

[0041] W Y is the mass fraction of yttrium in the Mg-Y-Fe cored wire, in %;

[0042] m Mg-Y-Fe It is the core weight of Mg-Y-Fe cored wire per unit length, in g / m.

[0043] Furthermore, by substituting relevant data into the calculation, it is found that the feeding amount of Mg-Y-Fe cored wire is 2.5-3.0 m / t steel.

[0044] Furthermore, in the step S3, the yttrium-magnesium ratio in the yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel liquid is controlled by the magnesium-yttrium ratio in the Mg-Y-Fe cored wire to be 4.80-5.20.

[0045] Specifically, through yttrium-magnesium composite treatment, the yttrium content in the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel liquid is 0.0030×(0.20+4×[%C]+4×[%N]) to 0.016×(0.20+4×[%C]+4×[%N])%, and the magnesium content is 0.0006×(0.20+4×[%C]+4×[%N]) to 0.0032×(0.20+4×[%C]+4×[%N])%; wherein [%C] and [%N] are the mass fractions of carbon and nitrogen in the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel liquid (i.e., yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel), respectively, and the unit is %.

[0046] Furthermore, in step S3, titanium microalloying is to add microalloying element titanium to the molten steel so that the titanium content in the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel liquid is 0.15×(0.20+4×[%C]+4×[%N])~0.80×(0.20+4×[%C]+4×[%N])%, wherein [%C] and [%N] are the mass fractions of carbon and nitrogen in the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel liquid, respectively, and the unit is %.

[0047] Furthermore, steps S2 and S3 are performed in a LF furnace (ladle refining furnace).

[0048] Furthermore, in step S4, continuous casting is used to cast the billet, and the obtained yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel is a slab, a square billet, a rectangular billet or a round billet.

[0049] Specifically, in the method of the present invention, a large number of finely dispersed MgAl2O4 and Y2O3 oxide particles are formed during the solidification process of the molten steel. The chain nucleation mechanism of obtaining finely dispersed oxides by yttrium-magnesium composite treatment, inducing the dispersion and precipitation of fine TiN precipitates, and then inducing the nucleation of ferrite by fine TiN refines TiN, refines grains, and improves the equiaxed crystal ratio of the titanium-stabilized ferritic stainless steel.

[0050] The technical solution of the present invention has the following advantages over the prior art:

[0051] (1) After the titanium-stabilized ferritic stainless steel of the present invention is treated with yttrium-magnesium composite, the type of inclusions in the steel is transformed from pure TiN to MgAl2O4 / Y2O3+TiN, and the inclusion size is reduced from more than 5.0 μm to less than 2.0 μm. The significant refinement of TiN helps to improve the nozzle nodule problem in the continuous casting process and improve production efficiency.

[0052] (2) After the titanium-stabilized ferritic stainless steel of the present invention is treated with yttrium-magnesium composite, the average grain size of the equiaxed crystal is reduced from 3.252 mm to 2.180 mm, the grain size of the steel solidification structure is significantly refined, and the equiaxed crystal ratio is increased from 39% to 100%. This is of great significance for maintaining the heritability of the solidification structure in the subsequent rolling process, solving the wrinkling problem during the forming process, and improving the performance of the steel;

[0053] (3) The production process of the present invention is simple and controllable, the addition of Mg-Y-Fe cored wire is stable, and the metal yttrium yield is high (Y Y =75%), and the iron-containing part as the core wire weight will not affect the composition of the molten steel;

[0054] (4) The novel smelting slag with added TiO2 and Y2O3 of the present invention realizes the precise control of the titanium and yttrium contents in the steel during the LF furnace smelting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Schematic diagram of δ-Fe heterogeneous nucleation during the solidification process of titanium-stabilized ferritic stainless steel.

[0056] Figure 2 This is the inclusion detection diagram of the titanium-stabilized ferritic stainless steel treated with yttrium-magnesium composite in Example 1.

[0057] Figure 3 This is the macroscopic cross-sectional structure of the titanium-stabilized ferritic stainless steel clip in Example 1.

[0058] Figure 4 This is the inclusion detection diagram of the titanium stabilized ferritic stainless steel in Comparative Example 1.

[0059] Figure 5This is the cross-sectional macrostructure of the titanium-stabilized ferritic stainless steel clip in Comparative Example 1. DETAILED DESCRIPTION

[0060] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0061] The present invention provides a yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel, the preparation method of which comprises the following steps:

[0062] Step 1) smelting scrap steel, high carbon ferrochrome and the like in an electric arc furnace to obtain qualified molten steel containing 17.0-19.0% chromium; decarburizing the molten steel to 0.050-0.10% in an AOD furnace, and then decarburizing the molten steel to below 0.030% in a VOD furnace;

[0063] Step 2) The molten steel is fed into an LF furnace and sequentially subjected to slag formation, aluminum deep deoxidation, yttrium-magnesium composite treatment, and titanium microalloying. The titanium and yttrium contents in the molten steel are precisely controlled according to the slag-metal reaction to meet the composition design requirements. Finally, qualified molten steel is cast into an ingot, i.e., yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel.

[0064] The basic slag system for slag making includes, by mass fraction, CaO: 50-55%; CaF2: 10-13%; SiO2: 10-15%; MgO: 8-10%; Al2O3: 20-25%;

[0065] Add TiO2 and Y2O3 to the basic slag system to obtain a smelting slag system;

[0066] The thermodynamic equilibrium reaction formulas of TiO2 and Y2O3 with liquid steel II are shown in formulas (1) and (3), respectively:

[0067] [Si]+(TiO2)=[Ti]+(SiO2) (1)

[0068] 3[Si]+2(Y2O3)=4[Y]+3(SiO2) (3)

[0069] The addition of TiO2 and Y2O3 is calculated by formula (2) and (4) respectively:

[0070]

[0071] In formulas (2) and (4), are the mass fractions of SiO2, TiO2 and Y2O3 in the basic slag system, respectively, in %;

[0072] [%Ti], [%Si], [%Y] are the mass fractions of Ti, Si, and Y in the liquid steel III, respectively, in %;

[0073] C1 and C2 are activity coefficient terms, with values ​​of 1.527 and 1.745, respectively;

[0074] T is the slag-gold reaction temperature, in °C.

[0075] Yttrium-magnesium composite treatment is achieved by feeding Mg-Y-Fe cored wire into the molten steel. The Mg-Y-Fe cored wire includes, by mass fraction, magnesium: 10.00-30.00%, yttrium: 4.00-13.00%, impurities <1.00%, and the remainder is iron; the core weight of the Mg-Y-Fe cored wire is 150-400 g / m.

[0076] In some preferred embodiments, the feeding speed of the Mg-Y-Fe cored wire is 2.5-3.0 m / s, and the amount of the Mg-Y-Fe cored wire fed per ton of molten steel III is calculated according to formula (5):

[0077]

[0078] In formula (5), L Mg-Y-Fe is the feed rate of Mg-Y-Fe cored wire, in m / t steel;

[0079] %Y] total is the mass fraction of yttrium in molten steel III, in %;

[0080] Y Y The yttrium recovery rate in titanium-stabilized ferritic stainless steel treated with yttrium-magnesium composite treatment is 75%;

[0081] W Y is the mass fraction of yttrium in the Mg-Y-Fe cored wire, in %;

[0082] m Mg-Y-Fe is the mass of Mg-Y-Fe cored wire per unit length, in g / m.

[0083] like Figure 1 As shown in the figure, the inclusions in the molten steel without Y-Mg composite treatment (upper part, represented by initial state) are only TiN. After Y-Mg composite treatment (lower part, represented by Mg-Y in the figure), the type of inclusions in the molten steel (liquid phase) changes from pure TiN to MgAl2O4 / Y2O3+TiN. During the solidification process (solid phase + liquid phase), MgAl2O4 and Y2O3 induce the dispersion and precipitation of TiN fine precipitates. The fine TiN then induces the chain nucleation mechanism of ferrite nucleation, refining TiN, refining grain size, and increasing the equiaxed grain ratio of the titanium-stabilized ferritic stainless steel.

[0084] In the above method, the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel is cast into billets by continuous casting, and the obtained yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel is in the form of slabs, square billets, rectangular billets or round billets. At present, the continuous casting billets (titanium-stabilized ferritic stainless steel that has not been treated with yttrium-magnesium composite) are subjected to thermal stresses and mechanical stresses such as cooling, bending, straightening, drawing, clamping and static pressure head of the molten steel during the casting and solidification process, which easily produce various crack defects, and the solidification characteristics of the continuous casting billets are that they are prone to internal defects such as central segregation and looseness. The present invention does not change the existing continuous casting billet process. After the vacuum oxygen decarburization in the VOD furnace is completed, Mg-Y-Fe cored wire is fed into the molten steel. The obtained yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel has significantly refined TiN and grains, and a greatly improved equiaxed crystal ratio.

[0085] The obtained yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel includes the following components by mass fraction: carbon: ≤0.030%, silicon: 0.30-1.00%, manganese: 0.60-1.00%, phosphorus: ≤0.040%, sulfur: ≤0.030%, chromium: 17.0-19.0%, nickel: 0.20-0.50%, nitrogen: ≤0.0150%, titanium: 0.15×(0.20+4×[%C]+4×[%N])-0 0.80×(0.20+4×[%C]+4×[%N])%,yttrium: 0.0030×(0.20+4×[%C]+4×[%N])~0.016×(0.20+4×[%C]+4×[%N])%,magnesium: 0.0006×(0.20+4×[%C]+4×[%N])~0.0032×(0.20+4×[%C]+4×[%N])%,balance being iron and unavoidable impurities;

[0086] Wherein, [%C] and [%N] are the mass fractions of carbon and nitrogen, respectively, in %.

[0087] Example 1

[0088] This embodiment provides a titanium-stabilized ferritic stainless steel treated with yttrium-magnesium composite. The composition range of the steel (untreated titanium-stabilized ferritic stainless steel) is shown in Table 1.

[0089] Table 1 Design composition range of titanium stabilized ferritic stainless steel (wt%)

[0090]

[0091]

[0092] The invention adopts a 100tEAF→AOD→VOD→LF smelting process, and the specific preparation method includes the following steps: first, scrap steel, high carbon ferrochrome and the like are used as raw materials to smelt in an electric arc furnace to obtain qualified molten steel (molten steel I) with a carbon content of ≤0.10%, 0.30-1.00% silicon, 0.60-1.00% manganese, ≤0.040% phosphorus, ≤0.10% sulfur, 17.0-19.0% chromium and 0.20-0.50% nickel; then, slag making and desulfurization and argon oxygen decarburization to preserve chromium are carried out in an AOD furnace; then, vacuum oxygen deep decarburization is carried out in a VOD furnace to obtain qualified molten steel (molten steel II) with a carbon content of ≤0.030%; and then, basic slag is added in the LF furnace, the components of which are, by weight, 50% CaO, 12% CaF2, 10% SiO2, 8% MgO and 20% Al2O3.

[0093] Before slag making in the LF furnace, samples were taken and the composition was determined. First, the target titanium and yttrium contents were determined based on the carbon and nitrogen contents. The slag-metal reaction temperature was the VOD furnace tapping temperature of 1590°C. Then, based on the target titanium and yttrium contents and formulas (2) and (4), the TiO2 and Y2O3 addition amounts in the basic slag were calculated to be 8% and 4%, respectively.

[0094] Subsequently, deep deoxidation and yttrium-magnesium composite treatment were carried out. According to the target yttrium content and formula (5), the feeding rate of Mg-Y-Fe cored wire was determined to be 2.8 m / t steel, and the feeding speed was 2.8 m / s. Then titanium microalloying was carried out, and finally the ingot was continuously cast to obtain yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel.

[0095] The composition of the titanium stabilized ferritic stainless steel ingot treated with yttrium-magnesium composite was tested, and the results are shown in Table 2.

[0096] Table 2 Composition of Y-Mg composite treated titanium stabilized ferritic stainless steel ingot (wt%)

[0097]

[0098] Take a sample at half the radius of the yttrium-magnesium composite treated titanium stabilized ferrite stainless steel ingot. Figure 2 As shown in the figure, the inclusions in the ingot are fine MgAl2O4 / Y2O3+TiN particles with a size of less than 2μm. The cross section of the ingot shows that the equiaxed crystal ratio is 100%. Figure 3 As shown in the figure, the average grain size of the equiaxed crystals is 2.180 mm. The ingot has good formability and can be rolled into high-quality rolled products.

[0099] Comparative Example 1

[0100] This comparative example provides a titanium-stabilized ferritic stainless steel, which adopts a 100tEAF→AOD→VOD→LF→CC smelting process. The steel type and main production steps are the same as those in Example 1, except that the yttrium-magnesium composite treatment in Example 1 is replaced with a conventional calcium treatment process. The specific steps and parameters are as follows: After deep deoxidation of aluminum in the LF furnace, sampling is taken and the composition is determined. According to the aluminum content, 5.6m / t of pure calcium wire is fed into the steel at a calcium-aluminum ratio of 1.20 to 1.30. The pure calcium wire core weight is 250 to 300g / m, and the feeding speed is 2.8m / s.

[0101] The composition test results of the obtained titanium stabilized ferritic stainless steel ingot are shown in Table 3.

[0102] Table 3 Chemical composition of titanium stabilized ferritic stainless steel ingot (wt%)

[0103]

[0104] Take samples at half the radius of the titanium stabilized ferritic stainless steel ingot. Figure 4 As shown in the figure, the inclusions in the ingot are coarse TiN inclusions with a size greater than 5μm. The cross-section test results of the ingot show that its columnar crystals are well developed, such as Figure 5 As shown, the equiaxed grain ratio is 39% and the average grain size is 3.252 mm. This can easily lead to wrinkling during the forming process, resulting in significant defects in the rolled material. Furthermore, large TiN inclusions can cause nozzle nodules during continuous casting, interrupting casting and impacting production.

[0105] Comparative Example 2

[0106] This comparative example provides a titanium-stabilized ferritic stainless steel treated with a yttrium-magnesium composite. The steel grade and the 100tEAF→AOD→VOD→LF→CC smelting process are the same as those in Example 1, except that the feed rate of Mg-Y-Fe cored wire in the yttrium-magnesium composite treatment is reduced to 1.4 m / t steel; and the Y2O3 content in the base slag is 2.6%.

[0107] The composition test results of the obtained yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel ingot are shown in Table 4.

[0108] Table 4 Composition of Y-Mg composite treated titanium stabilized ferritic stainless steel ingot (wt%)

[0109]

[0110] Inspection revealed inclusions in the ingot as MgAl2O4 / Y2O3+TiN particles less than 5 μm in size. Cross-sectional examination of the ingot revealed increased columnar crystallinity, a decrease in the equiaxed fraction to 64%, and an average grain size of 2.857 mm. Compared to Example 1, the ingot quality declined.

[0111] Comparative Example 3

[0112] This comparative example provides a yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel. The steel grade and the 100tEAF→AOD→VOD→LF→CC smelting process are the same as those in Example 1. Since it is extremely difficult to increase the yttrium content in the steel through slag-metal balance, the addition amounts of Y2O3 and TiO2 in the basic slag remain unchanged, and the feed rate of Mg-Y-Fe cored wire is increased to 8.0 m / t steel to increase the yttrium content in the steel.

[0113] The composition test results of the obtained yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel ingot are shown in Table 5.

[0114] Table 5 Composition of Y-Mg composite treated titanium stabilized ferritic stainless steel ingot (wt%)

[0115]

[0116] Inspection revealed inclusions in the ingot consisting of MgAl2O4 / Y2O3+TiN particles less than 3 μm in size. A cross-section of the ingot revealed the development of columnar crystals, a decrease in the equiaxed fraction to 75%, and an average grain size of 2.436 mm. Compared to Example 1, the ingot quality was reduced.

[0117] Comparative Example 4

[0118] This comparative example provides a yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel, the steel type and the 100tEAF→AOD→VOD→LF→CC smelting process are the same as those in Example 1, except that TiO2 and Y2O3 are not added to the LF furnace smelting slag.

[0119] The composition test results of the obtained yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel ingot are shown in Table 6.

[0120] Table 6 Composition of Y-Mg composite treated titanium stabilized ferritic stainless steel ingot (wt%)

[0121]

[0122] Inspection revealed inclusions in the ingot as MgAl2O4 / Y2O3+TiN particles less than 2 μm in size. However, cross-sectional inspection of the ingot revealed a drop in equiaxed fraction to 55%, with an average grain size of 3.106 mm. Compared to Example 1, the ingot quality was reduced.

[0123] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel, characterized in that: By mass fraction, stainless steel includes the following components: Carbon: ≤0.030%, Silicon: 0.30~1.00%, Manganese: 0.60~1.00%, Phosphorus: ≤0.040%, Sulfur: ≤0.030%, Chromium: 17.0~19.0%, Nickel: 0.20~0.50%, Nitrogen: ≤0.0150%, Titanium: 0.15×(0.20+4×[%C]+4×[%N])~0.80×(0.20+4×[%C]+4×[%N])%,Yttrium: 0.0 0.030×(0.20+4×[%C]+4×[%N])~0.016×(0.20+4×[%C]+4×[%N])%, magnesium: 0.0006×(0.20+4×[%C]+4×[%N])~0.0032×(0.20+4×[%C]+4×[%N])%, the remainder being iron and unavoidable impurities; wherein [%C] and [%N] are the mass fractions of carbon and nitrogen, respectively, in %; The preparation method comprises the following steps, S1: preparing a molten steel I containing 17.0-19.0 wt% chromium, and decarburizing the molten steel I to below 0.030 wt% to obtain a molten steel II; S2: slagging and deep deoxidation of aluminum on the molten steel II to obtain molten steel III; The smelting slag system used in the slag making includes basic slag system and TiO2 and Y2O3; S3: performing yttrium-magnesium composite treatment and titanium microalloying on the molten steel III to obtain yttrium-magnesium composite treated titanium stabilized ferritic stainless steel liquid; The yttrium-magnesium composite treatment is achieved by feeding Mg-Y-Fe cored wire into the molten steel III, wherein the Mg-Y-Fe cored wire comprises, by mass fraction, 10.00-30.00% magnesium, 4.00-13.00% yttrium, less than 1.00% impurities, and the remainder iron; S4: liquid-casting the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel into a slab to obtain the yttrium-magnesium composite-treated titanium-stabilized ferritic stainless steel.

2. The preparation method according to claim 1, wherein In the step S1, scrap steel and high carbon ferrochrome are used as raw materials to prepare molten steel I containing 17.0-19.0 wt% of chromium.

3. The preparation method according to claim 1, wherein In the step S1, the specific operation of decarburizing the molten steel I to below 0.030 wt% includes: performing slag desulfurization and argon oxygen decarburization to the molten steel I to retain chromium, so that the carbon content is reduced to 0.050-0.10 wt%; and then performing vacuum oxygen deep decarburization to obtain a molten steel II with a carbon content of ≤0.030 wt%.

4. The preparation method according to claim 1, wherein In the smelting slag system, The basic slag system is calculated by mass fraction as follows: CaO: 50%, CaF2: 12%, SiO2: 10%, MgO: 8%, Al2O3: 20%; The addition of TiO2 and Y2O3 is calculated by formula (2) and (4) respectively: In formulas (2) and (4), are the mass fractions of SiO2, TiO2 and Y2O3 in the basic slag system, respectively, in %; [%Ti], [%Si], and [%Y] are the mass fractions of Ti, Si, and Y in the liquid steel III, respectively, in %; C1 and C2 are activity coefficient terms, with values ​​of 1.527 and 1.745, respectively; T is the slag-gold reaction temperature, in °C.

5. The preparation method according to claim 1, wherein In the Mg-Y-Fe cored wire, the mass ratio of magnesium to yttrium is 2.

33.

6. The preparation method according to claim 1, wherein The core weight of the Mg-Y-Fe cored wire is 150-400 g / m.

7. The preparation method according to claim 1, wherein In step S3, the feeding speed of the Mg-Y-Fe cored wire is 2.5-3.0 m / s.

8. The preparation method according to claim 1 or 7, wherein In step S3, the amount of Mg-Y-Fe cored wire fed per ton of molten steel III is calculated according to formula (5): In formula (5), L Mg-Y-Fe is the feed rate of Mg-Y-Fe cored wire, in m / t steel; [% Y] total is the mass fraction of yttrium in the yttrium-magnesium composite treated titanium-stabilized ferritic stainless steel liquid, in %; Y Y The yttrium recovery rate in titanium-stabilized ferritic stainless steel treated with yttrium-magnesium composite treatment is 75%; W Y is the mass fraction of yttrium in the Mg-Y-Fe cored wire, in %; m Mg-Y-Fe It is the core weight of Mg-Y-Fe cored wire per unit length, in g / m.

9. The preparation method according to claim 1, wherein In the step S4, continuous casting is used to cast the billet.

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