Method for manufacturing yttrium-containing ultra-pure high-chromium ferritic stainless steel master alloy

Abstract

The application discloses a manufacturing method of yttrium-containing super-pure high-chromium ferrite stainless steel master alloy, and ingredients are prepared according to the component control requirements of the master alloy, the prepared raw materials are dried in a raw material baking furnace at 125 DEG C for more than 1 hour, and the raw materials are sequentially added in the order of Fe (50%), Cr (50%), W, Mo, Nb, Cr (50%), and Fe (50%); the raw materials are melted and sent under vacuum, the vacuum degree is less than 10 Pa; after the molten steel is melted and refined, the vacuum degree is less than 1 Pa, the refining temperature is 1570-1590 DEG C, the molten steel temperature is 1620 DEG C, and the mold group is prepared in a heat preservation state; argon is filled to 50000 Pa, pure iron skin is used to wrap metallic yttrium and manganese, and the metallic yttrium and manganese are added and stirred for 1.5 minutes after being added and then rapidly poured. The method can be suitable for automobile exhaust manifolds or turbochargers, and alloy elements of the produced low-carbon-nitrogen super-pure ferrite stainless steel can be accurately controlled.

Description

Technical Field

[0001] This invention relates to the field of stainless steel master alloy manufacturing technology, and in particular to a method for manufacturing yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy. Background Technology

[0002] Ferritic stainless steel typically refers to stainless steel with a chromium (Cr) content of 12% to 30% by mass. Based on the Cr content, it can be classified into three types: low-Cr, medium-Cr, and high-Cr. Generally, the corrosion resistance of ferritic stainless steel is related to the Cr content; the higher the Cr content, the stronger the corrosion resistance. To improve the overall performance of the material and avoid the adverse effects of Cr carbide and nitride precipitation on the mechanical properties and corrosion resistance of the steel, current development of ferritic stainless steel is towards lower C and N content. Ultra-pure ferritic stainless steel is a type of ferritic stainless steel with extremely low C and N content (the sum of C and N content does not exceed 0.010%) and a medium to high Cr content. Due to its good resistance to hot corrosion, thermal conductivity, shock resistance, and processing performance, it is widely used in the automotive industry and petrochemical fields.

[0003] The automotive industry requires hot-end components for car engine exhaust systems and turbochargers to possess excellent high-temperature resistance, formability, and weldability, while also meeting requirements for high-temperature oxidation, corrosion resistance, and fatigue resistance. In the 1970s, to improve catalytic efficiency and reduce emissions, engine exhaust temperatures were continuously increased, raising exhaust manifold operating temperatures from 750–800℃ to 900–950℃. Simultaneously, to improve fuel economy and reduce vehicle weight, exhaust temperatures have now risen to 950–1000℃, placing even higher demands on the materials used in exhaust manifolds. Domestically produced car exhaust systems primarily use austenitic stainless steel, mainly 1.4826, 1.4828, 1.4837, 1.4848, and 1.4849. While austenitic stainless steels possess excellent heat resistance and machinability, their high coefficient of thermal expansion makes them prone to thermal fatigue failure when used in components like exhaust manifolds that undergo repeated heating and cooling. On the other hand, compared to austenitic stainless steel, ferritic stainless steel exhibits superior thermal fatigue characteristics and resistance to oxide scale peeling due to its lower coefficient of thermal expansion. Furthermore, compared to austenitic stainless steel, it is less expensive due to the absence of nickel, leading to its widespread use. However, ferritic stainless steel suffers from lower high-temperature strength compared to austenitic stainless steel, prompting ongoing research into technologies to improve its high-temperature strength. Therefore, low-cost, high-temperature oxidation-resistant materials have become a trend in material alloying.

[0004] Pure ferritic stainless steel possesses excellent weldability and toughness, and exhibits superior corrosion resistance in various corrosive media, particularly against stress corrosion and intergranular corrosion. The realization of these properties hinges entirely on reducing impurities such as C, O, N, and S in the steel to ultra-pure levels. The development and cost-effectiveness of ultra-pure alloy smelting technology are crucial for the application of this alloy. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy, which can be applied to automotive exhaust manifolds or turbochargers, and the alloying elements of the produced low-carbon and nitrogen-containing ultrapure ferritic stainless steel can be precisely controlled.

[0006] A method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy according to a first aspect of the present invention includes:

[0007] Step 1: Preheat the vacuum induction furnace to 100-150℃. The furnace lining and refractory materials of the vacuum induction furnace are both made of alumina.

[0008] Step 2: Prepare the raw materials according to the composition control requirements of the master alloy, consisting of the following components by weight percentage: 0.2%≤Y≤0.3%, C≤0.006%, N≤0.002%, O≤0.002%, Si≤0.02%, P≤0.01%, S≤0.005%, Ni≤0.05%, 0.4%≤Mn≤1.0%, 22%≤Cr≤28%, 0.2%≤Nb≤0.5%, 0.05%≤Al≤0.2%, Ti≤0.02%, Cu≤0.02%, V≤0.02%, 1.0%≤W≤3.0%, 1.0%≤Mo≤3.0%, and the balance being iron;

[0009] Step 3: Use a raw material drying oven to dry the prepared raw materials at 100-150℃ for more than 1 hour;

[0010] Step 4: Add the materials in the following order: Fe (50%), Cr (50%), W, Mo, Nb, Cr (50%), Fe (50%);

[0011] Step 5: Melt under vacuum with electric current, vacuum degree less than 10 Pa;

[0012] Step 6: After the molten steel is melted and purified, it is heated and refined at a vacuum degree of less than 1 Pa and a refining temperature of 1570-1590℃.

[0013] Step 7: Cool down and add Al, stir, and then take a sample for analysis in front of the furnace;

[0014] Step 8: With the molten steel temperature at 1610-1630℃ and under heat preservation, prepare the module; purge with argon at 50000Pa, wrap yttrium metal (calculated and controlled according to 80% yield) and manganese (calculated and controlled according to 95% yield) in pure iron sheet, stir for 1-2 minutes and pour quickly.

[0015] According to an embodiment of the present invention, a method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy has at least the following beneficial effects: This method can cast a master alloy suitable for automotive exhaust manifolds or turbochargers. The alloying elements of the produced low-carbon, nitrogen-containing ultrapure ferritic stainless steel can be precisely controlled (yttrium element control is precise, with a control accuracy of 95%), resulting in pure material. Impurities C, O, N, and S in the steel are reduced to ultrapure limits. This invention, while ensuring that the composition of the smelted alloy fully meets the requirements of the foreign EB26-1 standard, ensures that the amount of C+N, which seriously affects the corrosion performance of the alloy, is less than 80 ppm, and C+N+O is less than 100 ppm. Simultaneously, it reduces the S content of the smelted alloy to below 30 ppm, ensuring good plasticity and excellent forging performance at high temperatures, and achieving a 100% yield rate for hot-penetrating alloy tubes.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0017] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0018] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0019] Example 1

[0020] A method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy includes:

[0021] Step 1: Preheat the vacuum induction furnace to 100℃. The furnace lining and refractory materials of the vacuum induction furnace are both made of alumina.

[0022] Step 2: Prepare the raw materials according to the composition control requirements of the master alloy, consisting of the following components by weight percentage: Y: 0.2%, C: 0.002%, N: 0.001%, O: 0.001%, Si: 0.01%, P: 0.01%, S: 0.005%, Ni: 0.05%, Mn: 0.4%, Cr: 22%, Nb: 0.2%, Al: 0.05%, Ti: 0.02%, Cu: 0.02%, V: 0.02%, W: 1.0%, Mo: 1.0%, and the balance being iron;

[0023] Step 3: Dry the prepared raw materials at 100℃ for more than 1 hour using a raw material drying oven;

[0024] Step 4: Add the materials in the following order: Fe (50%), Cr (50%), W, Mo, Nb, Cr (50%), Fe (50%);

[0025] Step 5: Melt under vacuum with electric current, vacuum degree less than 10 Pa;

[0026] Step 6: After the molten steel is melted and purified, it is heated and refined at a vacuum degree of less than 1 Pa and a refining temperature of 1570℃.

[0027] Step 7: Cool down and add Al, stir, and then take a sample for analysis in front of the furnace;

[0028] Step 8: With the molten steel temperature at 1610℃ and under heat preservation, prepare the module; purge with argon at 50000Pa, wrap yttrium metal (calculated and controlled according to an 80% yield) and manganese (calculated and controlled according to a 95% yield) in pure iron sheet, stir for 1 minute and pour quickly.

[0029] Example 2

[0030] A method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy includes:

[0031] Step 1: Preheat the vacuum induction furnace to 150℃. The furnace lining and refractory materials of the vacuum induction furnace are both made of alumina.

[0032] Step 2: Prepare the raw materials according to the composition control requirements of the master alloy, consisting of the following components by weight percentage: Y: 0.3%, C: 0.006%, N: 0.002%, O: 0.002%, Si: 0.02%, P: 0.01%, S: 0.005%, Ni: 0.05%, Mn: 1.0%, Cr: 28%, Nb: 0.5%, Al: 0.2%, Ti: 0.02%, Cu: 0.02%, V: 0.02%, W: 3.0%, Mo: 3.0%, and the balance being iron;

[0033] Step 3: Dry the prepared raw materials at 150℃ for more than 1 hour using a raw material baking oven;

[0034] Step 4: Add the materials in the following order: Fe (50%), Cr (50%), W, Mo, Nb, Cr (50%), Fe (50%);

[0035] Step 5: Melt under vacuum with electric current, vacuum degree less than 10 Pa;

[0036] Step 6: After the molten steel is melted and purified, it is heated and refined at a vacuum degree of less than 1 Pa and a refining temperature of 1590℃.

[0037] Step 7: Cool down and add Al, stir, and then take a sample for analysis in front of the furnace;

[0038] Step 8: With the molten steel temperature at 1630℃ and under heat preservation, prepare the module; purge with argon at 50000Pa, wrap yttrium metal (calculated and controlled according to an 80% yield) and manganese (calculated and controlled according to a 95% yield) in pure iron sheet, stir for 2 minutes and pour quickly.

[0039] Example 3

[0040] A method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy includes:

[0041] Step 1: Preheat the vacuum induction furnace to 125℃. The furnace lining and refractory materials of the vacuum induction furnace are both made of alumina.

[0042] Step 2: Prepare the raw materials according to the composition control requirements of the master alloy, consisting of the following components by weight percentage: Y: 0.25%, C: 0.004%, N: 0.0015%, O: 0.0015%, Si: 0.015%, P: 0.01%, S: 0.005%, Ni: 0.05%, Mn: 0.7%, Cr: 25%, Nb: 0.35%, Al: 0.125%, Ti: 0.02%, Cu: 0.02%, V: 0.02%, W: 2.0%, Mo: 2.0%, and the balance being iron;

[0043] Step 3: Dry the prepared raw materials at 125℃ for more than 1 hour using a raw material baking oven;

[0044] Step 4: Add the materials in the following order: Fe (50%), Cr (50%), W, Mo, Nb, Cr (50%), Fe (50%);

[0045] Step 5: Melt under vacuum with electric current, vacuum degree less than 10 Pa;

[0046] Step 6: After the molten steel is melted and purified, it is heated and refined at a vacuum degree of less than 1 Pa and a refining temperature of 1570-1590℃.

[0047] Step 7: Cool down and add Al, stir, and then take a sample for analysis in front of the furnace;

[0048] Step 8: With the molten steel temperature at 1620℃ and under heat preservation, prepare the module; purge with argon at 50000Pa, wrap yttrium metal (calculated and controlled according to an 80% yield) and manganese (calculated and controlled according to a 95% yield) in pure iron sheet, stir for 1.5 minutes and pour quickly.

[0049] This invention discloses a method for manufacturing a yttrium-containing ultra-pure high-chromium ferritic stainless steel master alloy. The master alloy can be cast and is suitable for automotive exhaust manifolds or turbochargers. The produced low-carbon, ultra-pure ferritic stainless steel alloying elements can be precisely controlled (yttrium element control is precise, with a control accuracy of 95%), resulting in pure material. Impurities in the steel, such as C, O, N, and S, are reduced to ultra-pure limits. This invention ensures that the composition of the smelted alloy fully meets the requirements of the international EB26-1 standard, while achieving a C+N content of less than 80 ppm and a C+N+O content of less than 100 ppm in the alloy, which severely affects the alloy's corrosion performance. Simultaneously, the S content of the smelted alloy is reduced to below 30 ppm, ensuring good plasticity at high temperatures, excellent forging properties, and a 100% yield rate for hot-penetration tubes.

[0050] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for manufacturing a yttrium-containing ultrapure high-chromium ferritic stainless steel master alloy, characterized in that, include: Step 1: Preheat the vacuum induction furnace to 100-150℃. The furnace lining and refractory materials of the vacuum induction furnace are both made of alumina. Step 2: Prepare the raw materials according to the composition control requirements of the master alloy, consisting of the following components by weight percentage: 0.2%≤Y≤0.3%, C≤0.006%, N≤0.002%, O≤0.002%, Si≤0.02%, P≤0.01%, S≤0.005%, Ni≤0.05%, 0.4%≤Mn≤1.0%, 22%≤Cr≤28%, 0.2%≤Nb≤0.5%, 0.05%≤Al≤0.2%, Ti≤0.02%, Cu≤0.02%, V≤0.02%, 1.0%≤W≤3.0%, 1.0%≤Mo≤3.0%, and the balance being iron; Step 3: Use a raw material drying oven to dry the prepared raw materials at 100-150℃ for more than 1 hour; Step 4: Add the materials in the following order: 50% Fe, 50% Cr, W, Mo, Nb, 50% Cr, 50% Fe; Step 5: Melt under vacuum with electric current, vacuum degree less than 10 Pa; Step 6: After the molten steel is melted and purified, it is heated and refined at a vacuum degree of less than 1 Pa and a refining temperature of 1570-1590℃. Step 7: Cool down and add Al, stir, and then take a sample for analysis in front of the furnace; Step 8: With the molten steel temperature at 1610-1630℃ and under heat preservation conditions, prepare the module; purge with argon at 50000Pa, wrap yttrium in pure iron sheet and add it according to an 80% yield calculation, and add manganese according to a 95% yield calculation. After adding, stir for 1-2 minutes and pour quickly.