A method for preparing austenitic stainless steel replacing 304

Abstract

The present invention discloses a method for preparing austenitic stainless steel that can replace 304 stainless steel, and relates to the technical field of stainless steel preparation. The method comprises the following steps: step 1: charging molten steel into an AOD furnace for slag desulfurization; step 2: pouring the desulfurized molten steel into a ladle for nitrogen blowing; step 3: casting steel billets from the ladle; step 4: heating the steel billets; step 5: rolling and coiling the steel billets into steel coils; step 6: annealing the steel coils; and step 7: pickling the steel coils. The austenitic stainless steel preparation method provided by the present invention ensures that the prepared austenitic stainless steel has no pores or thermal cracks on the surface, has mechanical properties that are not significantly different from those of 304 stainless steel, and has better work hardening curves and pitting corrosion resistance than 304 stainless steel. Furthermore, the processing cost is lower than that of 304 stainless steel, making it a viable alternative to 304 stainless steel.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel preparation, and in particular to a method for preparing austenitic stainless steel that can replace 304. Background Art

[0002] 304 stainless steel is currently the most widely used stainless steel on the market. Its strength, formability, corrosion resistance, and weldability are excellent, making it widely used in surface decoration, equipment, and machinery manufacturing. However, with increasingly fierce competition in the industry, cost savings are crucial. Therefore, reducing material costs while maintaining the same performance and quality is a key research direction in the stainless steel industry.

[0003] In the existing technology, austenitic stainless steel is a kind of alternative to 304 stainless steel. In order to make austenitic stainless steel achieve the same corrosion resistance as 304 stainless steel, the elements for preparing austenitic stainless steel materials are rationally distributed and optimized. The method of reducing nickel and increasing carbon and nitrogen is adopted. While reducing costs, the same corrosion resistance as 304 is guaranteed, and the same processing and forming performance can also be achieved.

[0004] However, in the process of preparing austenitic stainless steel today, due to the presence of high carbon and nitrogen in the elements of the material, austenitic stainless steel is difficult to manufacture. During the manufacturing process, problems such as surface pores, surface cracks and high material strength are prone to occur. The existence of these problems directly affects the quality and difficulty of austenitic stainless steel preparation, and easily leads to an increase in the manufacturing cost of austenitic stainless steel. In order to solve these problems, a method for preparing austenitic stainless steel that replaces 304 is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing austenitic stainless steel that replaces 304, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing austenitic stainless steel that replaces 304, comprising:

[0007] Step 1: The molten steel obtained after steelmaking is charged into an AOD furnace for oxygen blowing decarburization. After the oxygen blowing decarburization is completed, ferrosilicon is added for deoxidation, and then slag desulfurization is carried out. After the desulfurization is completed, the next step is entered;

[0008] Step 2: Pour the molten steel after desulfurization in the AOD furnace into a ladle and send it to the ladle treatment station for treatment. Nitrogen is connected to the bottom of the ladle for nitrogen blowing to adjust the nitrogen composition in the molten steel. The ladle is then sent to the continuous casting platform for the next step;

[0009] Step 3: After the ladle is placed on the continuous casting platform, it is sent to the continuous casting machine for pouring. After cooling and solidification in the crystallizer on the continuous casting machine, the steel billet is obtained and enters the next step;

[0010] Step 4: directly sending the steel billet to the hot rolling heating furnace, where the steel billet is heated;

[0011] Step 5: After the steel billet is heated in step 4, it is extracted and sent to a roughing mill, and after rough rolling in the roughing mill, it is sent to a continuous rolling mill for continuous rolling and then coiled into a steel coil;

[0012] Step 6: Send the steel coil to the annealing equipment for annealing;

[0013] Step 7: The annealed steel coils are sent to the pickling tank for pickling, and then packed after being pickled into white skin, and finally put into storage for registration;

[0014] Wherein, in the step 3, during the pouring process of the ladle in the continuous casting machine, the baking requirement for the tundish is to preheat it with a low fire, then bake it with a medium fire, and finally bake it with a high fire;

[0015] Wherein, in said step 3, the water temperature at the inlet of the crystallizer on the continuous casting machine is controlled within the range of less than 30°C-50°C;

[0016] Among them, in the step 4, the hot rolling heating furnace is divided into a preheating zone, a heating zone and a soaking zone, and the heating rate of the preheating zone of the hot rolling heating furnace is 2°C-4°C / minute, and the heating rate of the heating section is 3°C-5°C / minute.

[0017] Preferably, in step 1, the steel used for chemical steelmaking is smelted according to the following chemical composition in weight percentage: carbon 0.08%, silicon 0.5%, manganese 1.3%, sulfur ≤ 0.003%, nickel 7.5%-8.0%, chromium 18%-19%, nitrogen 0.2%-0.3%, a trace amount of rhenium, and the balance is iron and other inevitable impurity elements.

[0018] Preferably, in the step 1, the sulfur content in the molten steel charged into the AOD furnace needs to be controlled within 0.08%;

[0019] After adding ferrosilicon for deoxidation, the basicity in the AOD furnace is controlled between 2.3-2.5;

[0020] After desulfurization, the sulfur content in molten steel is less than or equal to 15ppm;

[0021] Nitrogen stirring was used during the deoxidation reduction reaction in the AOD furnace;

[0022] Preferably, in step 2, the target nitrogen content in the ladle is 0.21%.

[0023] The method for preparing austenitic stainless steel that replaces 304 according to claim 1, characterized in that, in the step 3, the ladle is allowed to stand on the continuous casting platform for 15-30 minutes, and the low-fire preheating time of the tundish is 25-35 minutes, the medium-fire baking time is 45-55 minutes, and the high-fire baking time is 55-65 minutes. The superheat range of the continuously cast molten steel is controlled between 15°C and 20°C. In addition, the stirring mode in the crystallizer is electromagnetic stirring, the stirring current is 200-300A, and the stirring frequency is 5-6Hz.

[0024] Preferably, in step three, the crystallizer adopts a strong cooling mode, the water flow rate on the wide side is 4000L / min, the water flow rate on the narrow side is 600L / min, and the secondary cooling of the continuous casting sector is equipped with dynamic secondary cooling water according to the straightening section temperature of 900℃-950℃.

[0025] Preferably, in step four, the temperature of the steel billet entering the hot rolling heating furnace needs to be controlled between 600°C and 800°C, the steel billet needs to be heated to 900°C in the preheating zone of the hot rolling heating furnace before it can be sent to the heating zone of the hot rolling heating furnace, and at the same time, the steel billet needs to be heated to 1200°C in the heating zone of the hot rolling heating furnace before it can be sent to the soaking zone of the hot rolling heating furnace, and the insulation time of the steel billet in the soaking zone of the hot rolling heating furnace is 30 minutes.

[0026] Preferably, in step 4, the flame lengths on both sides of the hot rolling heating furnace range from 30cm to 40cm, the width range from 12cm to 15cm, and the height range from ±5cm, and the fuel of the hot rolling heating furnace is natural gas, the sulfur content in the gas is <0.08%, and the moisture content is <0.09%.

[0027] Preferably, in step five, the downward pressing amplitude of the first rough rolling pass of the rough rolling mill is 11%-14%, and the rough rolling is a reversible rolling mill that rolls the steel billet from 220 mm to 28 mm through five passes, and the thickness of the steel billet after rolling by the rough rolling mill is required to be 3.0-6.0 mm after continuous rolling in the continuous rolling mill.

[0028] Preferably, in step six, the annealing temperature of the steel coil is controlled within 1200° C.-1300° C., and the annealing speed of the steel coil is 10-30 mpm.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The austenitic stainless steel preparation method provided by the present invention can effectively eliminate the problem of nitrogen pores that are easily generated during the preparation of traditional austenitic stainless steel. At the same time, the problem of thermal crack defects that occur during the forging process of the steel billet can be effectively avoided by combining with the improvement of the heating and hot rolling processes. The surface of the prepared austenitic stainless steel is free of pores and thermal cracks, and the mechanical properties are not significantly different from those of 304 stainless steel. The work hardening curve and pitting corrosion resistance are both better than those of 304 stainless steel. At the same time, the processing cost is lower than that of 304 stainless steel, and 304 stainless steel can be replaced by the prepared austenitic stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the preparation method of the present invention. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] The present invention provides Figure 1 A method for preparing austenitic stainless steel that replaces 304 is shown, comprising:

[0034] Step 1. In step 1, the steel used for steelmaking is smelted according to the following chemical composition in weight percentage: carbon 0.08%, silicon 0.5%, manganese 1.3%, sulfur ≤ 0.003%, nickel 7.5%-8.0%, chromium 18%-19%, nitrogen 0.2%-0.3%, a trace of rhenium, and the balance is iron and other inevitable impurity elements. The molten steel obtained after steelmaking is charged into an AOD furnace for oxygen blowing and decarburization. The sulfur content in the molten steel charged into the AOD furnace needs to be controlled within 0.08%. After the oxygen blowing and decarburization is completed, ferrosilicon is added into the AOD furnace for deoxidation. It should be noted that during the deoxidation reduction reaction, not only the target alkalinity of the molten steel in the AOD furnace should be maintained between 2.3 and 2.5, and the target alkalinity is preferably maintained at 2.4, but also gas stirring is performed by introducing nitrogen, which can not only utilize the target alkalinity of the molten steel to be between 2.3 and 2.5, but also the target alkalinity is preferably maintained at 2.4. 2.4 Achieve efficient desulfurization and control the sulfur content at a lower level to avoid the problem of hot-rolled surface thermal cracks. At the same time, by stirring with nitrogen, the purpose of adding nitrogen in advance and stirring is achieved, which is beneficial to improving the rate of deoxidation and reduction reaction. The superheat range of continuous casting molten steel is controlled between 15℃ and 20℃, with the best being 18℃. This can effectively prevent the generation of nitrogen pore defects and improve the quality of product preparation. After oxygen blowing and decarburization are completed, ferrosilicon deoxidation is added, and then slag desulfurization is carried out to control the sulfur content in the molten steel within 15ppm and then stop. The sulfur content in the molten steel can be measured by sampling and testing. It should be noted that the sulfur content in the molten steel is measured by spectroscopy or carbon-sulfur instrument. If the sampling test finds that the sulfur content does not meet the standard, the AOD furnace can be tilted to remove part of the slag, and then slag desulfurization is continued until the sulfur content in the molten steel reaches the target value, and then the next step can be entered.

[0035] Step 2: Pour the molten steel after desulfurization in the AOD furnace into a ladle and send it to the ladle treatment station (LT) for treatment. Nitrogen is connected to the bottom of the ladle for nitrogen blowing to adjust the nitrogen content of the molten steel to the target composition. The target nitrogen content in the ladle is 0.21% (the target composition is within the range of 304 material replacement, see Table 1 below). The ladle is then sent to the continuous casting platform for the next step;

[0036] Step 3. After the ladle has been left standing on the continuous casting platform for a period of time, it is sent to the continuous casting machine for pouring. The ladle is left standing on the continuous casting platform for 15-30 minutes, with the best being 22 minutes. This allows excess nitrogen bubbles in the ladle to escape in time, and in order to avoid nitrogen precipitation caused by excessive temperature drop in the tundish when the ladle is poured on the continuous casting machine, the tundish is required to be preheated on low heat for 30 minutes, baked on medium heat for 50 minutes, and baked on high heat for 60 minutes. It should be noted that low heat means that all outer flames are extinguished, leaving only the inner flame, the flame is small and high or low, the flame is blue-orange, the width is darker and the heat is lower, and the temperature is generally controlled at 40°C-50°C; medium heat means that the outer flame becomes smaller than the inner flame, the flame is lower and unstable, the flame is blue-red, the brightness is bright, and the temperature is generally between 60°C-80°C; A big fire means that both the outer and inner flames are very large, the flame column is high and stable, the flame is blue-white, and the temperature is generally not less than 100 degrees Celsius. The billet is obtained after being cooled into a solid state through the crystallizer on the continuous casting machine. The electromagnetic stirring process is adopted on the crystallizer, the stirring current is 200-300A, and the stirring frequency is 5-6Hz, which can speed up the crystallization efficiency and quality. In addition, the crystallizer on the continuous casting machine adopts a strong cooling mode, the wide surface water flow is 4000L / min, and the narrow surface water flow is 600L / min, so that the water temperature at the crystallizer inlet is controlled within the range of less than 40°C. These operations can further prevent the problem of nitrogen pore defects, and the secondary cooling of the continuous casting sector is equipped with dynamic secondary cooling water according to the temperature of the straightening section of 900°C-950°C, which can prevent cracks on the steel surface and then proceed to the next step;

[0037] Step 4: The steel billet produced from the crystallizer in the previous step is directly sent to the hot rolling heating furnace after leaving the continuous casting machine. The temperature of the steel billet entering the hot rolling heating furnace needs to be controlled between 600℃ and 800℃, with the optimal temperature being 750℃. It is heated to 1200℃ in the hot rolling heating furnace.

[0038] Step 5. After the heating in step 4 is completed, the steel billet is extracted and sent to the roughing mill. To avoid thermal cracks, the first pass of the roughing mill has a downward pressure of 11%-14% (the first pass should normally be pressed to 15%. To prevent thermal cracks, the downward pressure should be smaller than the normal pressure, with a downward pressure of 13% being the best). The rolling speed is controlled at 10000 rpm. The roughing mill is a reversible rolling mill that rolls the steel billet from 220 mm to 28 mm in five passes. After the roughing mill is rough-rolled, the steel billet is sent to the continuous rolling mill for continuous rolling to a certain thickness and then coiled into a steel coil. After continuous rolling to a thickness of 3.0-6.0 mm in the continuous rolling mill, in some embodiments, the continuous rolling thickness of the steel billet is generally 4.5 mm as the best, and then coiled into a steel coil.

[0039] Step 6: Send the steel coil to the annealing equipment for annealing. Since the steel coil contains higher carbon and nitrogen elements, its strength is higher than that of 304 stainless steel, but its elongation is lower than that of 304 stainless steel. Therefore, during the annealing process, the annealing temperature of the steel coil needs to be controlled within 1200℃-1300℃, with 1250℃ as the standard value, and the annealing speed of the steel coil is controlled between 10-30mpm, with 20mpm as the implementation standard. In this way, the steel coil can achieve the same mechanical properties as 304 stainless steel. The annealing temperature is higher than that of 304 stainless steel. The normal annealing temperature of 304 is only 1100℃. By adopting a higher annealing temperature than normal, the strength of the steel coil is reduced, and the strength will not be too high than that of 304 stainless steel, avoiding the problem of easy cracking due to too high strength, so that the prepared austenitic stainless steel is superior to 304 stainless steel in this performance.

[0040] Step 7: The annealed steel coils are sent to the pickling tank for pickling, and are packaged after being pickled into white skin. Finally, they are put into storage for registration, thereby obtaining austenitic stainless steel that can replace 304 stainless steel.

[0041] It should be noted that in step 4, the hot rolling heating furnace is divided into a preheating zone, a heating zone and a soaking zone, and the heating rate of the preheating zone of the hot rolling heating furnace is 3°C / minute, and the heating rate of the heating section is 4°C / minute. Different heating rates are used in the three zones in the hot rolling heating furnace, which can effectively eliminate the defect problem of thermal cracks on the surface of the steel coil after hot rolling; moreover, the steel billet needs to be heated to 900°C in the preheating zone of the hot rolling heating furnace before it can be fed into the heating zone of the hot rolling heating furnace, and the steel billet needs to be heated to 1200°C in the heating zone of the hot rolling heating furnace before it can be fed into the soaking zone of the hot rolling heating furnace, and the insulation time of the steel billet in the soaking zone of the hot rolling heating furnace is 30 minutes. By allowing the steel billet to enter the corresponding zone at a precise temperature in the hot rolling heating furnace, the heating effect of the steel billet can be guaranteed, thereby effectively avoiding the defect problem of thermal cracks on the surface of the steel billet after hot rolling, which helps to improve the quality of subsequent austenitic stainless steel.

[0042] Furthermore, the flames on both sides of the hot rolling heating furnace have a length range of 30cm-40cm, a width range of 12cm-15cm, and a height range of ±5cm. By controlling the length, width, and height of the flames in the hot rolling heating furnace, the outer wall of the steel billet can be heated more evenly, thereby avoiding the occurrence of thermal cracks due to local overburning or underburning during the hot rolling process, thereby further improving the ability to avoid the occurrence of thermal crack defects. The fuel of the hot rolling heating furnace is natural gas, and the sulfur content in the gas is less than 0.08%, and the moisture content is less than 0.09%. By controlling the type of fuel in the hot rolling heating furnace and the sulfur and moisture content in the fuel, the sensitivity of the steel billet to thermal cracks during the hot rolling process can be reduced.

[0043] Table 1 is a material comparison table of 304 stainless steel and austenitic stainless steel prepared in this embodiment

[0044] element C carbon Si Mn S-sulfur Nickel Cr Nitrogen RE rhenium 304 Range ≤0.07 ≤0.75 ≤2.0 ≤0.03 8-10.5 17.5-19.5 ≤0.1 304 level 0.04 0.5 0.9 0.0080 8.01 18 0.05 Alternative 304 material range ≤0.08 ≤0.5 ≤1.3 ≤0.003 7.5-8.0 18-19 0.2～0.3 Add to Alternative 304 material level 0.06 0.4 0.8 0.0028 7.6 18.1 0.21 Add to

[0045] As can be seen from Table 1, the C and N contents of the austenitic stainless steel replacing 304 material prepared in this embodiment are significantly improved compared to those of 304, and the Ni content is reduced by about 0.4 compared to 304. Therefore, the decarburization and denitrification costs of steelmaking are reduced, and the cost of the alloying element Ni is also reduced. Therefore, the manufacturing cost of austenitic stainless steel is lower than that of stainless steel. Since the Cr and N elements of the 304 replacing material are relatively high, the pitting corrosion resistance equivalent of the material is higher than that of 304 stainless steel, and therefore the pitting corrosion resistance is superior to and can replace 304 stainless steel. However, considering that the higher C and N contents may lead to the precipitation of Cr, a trace amount of Re is added to the 304 replacing material. Moreover, since the higher C and N contents of the material can effectively reduce the work hardening of the material, the work hardening of the 304 replacing material is less than that of ordinary 304, so its process formability is superior to and can replace 304, and therefore it can replace 304 stainless steel in terms of corrosion resistance and mechanical properties.

[0046] Table 2 is the material substitution verification data table

[0047]

[0048] Table 3 is the verification data of bubble improvement by different processes

[0049]

[0050] Table 4 is the verification data of different processes for improving surface thermal cracks

[0051]

[0052] Table 5 is the verification data of different annealing effects on material mechanics

[0053]

[0054] In combination with Tables 2 to 5 above, it can be seen that the preparation of austenitic stainless steel by the preparation method provided in this embodiment can effectively improve the quality of austenitic stainless steel, and effectively reduce the problems of surface bubble defects, thermal crack defects, and defects that cannot meet the requirements of material mechanics on the surface of austenitic stainless steel. Therefore, it can more effectively replace 304 stainless steel, and at the same time, it can have a lower manufacturing cost and higher product quality than 304 stainless steel.

[0055] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing austenitic stainless steel that replaces 304, characterized in that: include: Step 1: The molten steel obtained after steelmaking is charged into an AOD furnace for oxygen blowing decarburization. After the oxygen blowing decarburization is completed, ferrosilicon is added for deoxidation, and then slag desulfurization is carried out. After the desulfurization is completed, the next step is entered; Step 2: Pour the molten steel after desulfurization in the AOD furnace into a ladle and send it to the ladle treatment station for treatment. Nitrogen is connected to the bottom of the ladle for nitrogen blowing to adjust the nitrogen composition in the molten steel. The ladle is then sent to the continuous casting platform for the next step; Step 3: After the ladle is placed on the continuous casting platform, it is sent to the continuous casting machine for pouring. After cooling and solidification in the crystallizer on the continuous casting machine, the steel billet is obtained and enters the next step; Step 4: directly sending the steel billet to the hot rolling heating furnace, where the steel billet is heated; Step 5: After the steel billet is heated in step 4, it is extracted and sent to a roughing mill, and after rough rolling in the roughing mill, it is sent to a continuous rolling mill for continuous rolling and then coiled into a steel coil; Step 6: Send the steel coil to the annealing equipment for annealing; Step 7: The annealed steel coils are sent to the pickling tank for pickling, and then packed after being pickled into white skin, and finally put into storage for registration; Wherein, in the step 3, during the pouring process of the ladle in the continuous casting machine, the baking requirement for the tundish is to preheat it with a low fire, then bake it with a medium fire, and finally bake it with a high fire; Wherein, in said step 3, the water temperature at the inlet of the crystallizer on the continuous casting machine is controlled within the range of less than 30°C-50°C; Wherein, in said step 4, the hot rolling heating furnace is divided into a preheating zone, a heating zone and a soaking zone, and the heating rate of the preheating zone of said hot rolling heating furnace is 2°C-4°C / minute, and the heating rate of the heating zone is 3°C-5°C / minute; In the step 1, the sulfur content in the molten steel charged into the AOD furnace needs to be controlled within 0.08%, the basicity in the AOD furnace after ferrosilicon deoxidation is controlled between 2.3-2.5, the sulfur content in the molten steel after desulfurization is completed is less than or equal to 15 ppm, and nitrogen is used for stirring during the deoxidation reduction reaction in the AOD furnace; In the step 3, the ladle is left standing on the continuous casting platform for 15-30 minutes, the tundish is preheated on a low heat for 25-35 minutes, the medium heat for 45-55 minutes, and the high heat for 55-65 minutes. The superheat range of the continuously cast molten steel is controlled between 15°C and 20°C. In addition, the stirring mode in the crystallizer is electromagnetic stirring, the stirring current is 200-300A, and the stirring frequency is 5-6Hz. In step 4, the temperature of the steel billet entering the hot rolling heating furnace needs to be controlled between 600°C and 800°C. The steel billet needs to be heated to 900°C in the preheating zone of the hot rolling heating furnace before it can be sent to the heating zone of the hot rolling heating furnace. At the same time, the steel billet needs to be heated to 1200°C in the heating zone of the hot rolling heating furnace before it can be sent to the soaking zone of the hot rolling heating furnace. The steel billet is kept warm in the soaking zone of the hot rolling heating furnace for 30 minutes. In step six, the annealing temperature of the steel coil is controlled within 1200° C.-1300° C., and the annealing speed of the steel coil is 10-30 mpm.

2. The method for preparing austenitic stainless steel replacing 304 according to claim 1, characterized in that: In step 1, the steel used for chemical steelmaking is smelted according to the following chemical composition in weight percentage: carbon 0.08%, silicon 0.5%, manganese 1.3%, sulfur ≤0.003%, nickel 7.5%-8.0%, chromium 18%-19%, nitrogen 0.2%-0.3%, a trace amount of rhenium, and the balance is iron and other inevitable impurity elements.

3. The method for preparing austenitic stainless steel replacing 304 according to claim 1, characterized in that: In step 2, the target nitrogen content in the ladle is 0.21%.

4. The method for preparing austenitic stainless steel replacing 304 according to claim 1, characterized in that: In step three, the crystallizer adopts a strong cooling mode, the water flow rate on the wide side is 4000L / min, the water flow rate on the narrow side is 600L / min, and the secondary cooling water of the continuous casting sector is equipped with dynamic secondary cooling water according to the straightening section temperature of 900℃-950℃.

5. The method for preparing austenitic stainless steel replacing 304 according to claim 1, characterized in that: In step 4, the flame lengths on both sides of the hot rolling heating furnace are in the range of 30cm-40cm, the width is in the range of 12cm-15cm, and the height is in the range of ±5cm. The fuel of the hot rolling heating furnace is natural gas, and the sulfur content in the gas is <0.08%, and the moisture content is <0.09%.

6. The method for preparing austenitic stainless steel replacing 304 according to claim 1, characterized in that: In step five, the first pass of the rough rolling mill has a downward pressing amplitude of 11%-14%. The rough rolling is a reversible rolling mill that rolls the steel billet from 220 mm to 28 mm through five passes. The thickness of the steel billet after rolling by the rough rolling mill is required to be 3.0-6.0 mm after continuous rolling in the continuous rolling mill.

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