Multi-stage combined rolling method for stainless steel resistant to corrosion of sulfate reducing bacteria

Abstract

The invention discloses a multi-stage combined rolling method for stainless steel resistant to corrosion of sulfate reducing bacteria. The multi-stage combined rolling method specifically comprises the steps that a Cu and Ce element synergistically doped stainless steel cast ingot prepared through a medium-frequency induction melting method is put into a heat treatment resistance furnace for heat preservation, water quenching treatment, grinding, cleaning and blow-drying; rolling the pretreated stainless steel cast ingot for the first time; rolling the stainless steel cast ingot rolled for the first time for the second time; carrying out third rolling on the stainless steel cast ingot subjected to the second rolling; putting the stainless steel cast ingot subjected to three-stage rolling into a furnace for heat preservation, and carrying out acid pickling and passivating treatment; and the stainless steel cast ingot subjected to passivation treatment is subjected to cold rolling and polishing, and the sulfate reducing bacteria corrosion resistant stainless steel is obtained. According to the method, the problems that the Cu and Ce-containing stainless steel is poor in hot working performance, easy to crack and easy to corrode when serving in an extreme environment are solved, and meanwhile, the tensile strength and the elongation of the stainless steel are synergistically improved.

Description

Technical Field

[0001] This invention belongs to the technical field of heat treatment and rolling forming of alloy plates, specifically relating to a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, and also relating to stainless steel resistant to sulfate-reducing bacteria corrosion. Background Technology

[0002] Stainless steel, due to its excellent corrosion resistance and mechanical properties, plays an irreplaceable role as a core protective material in marine resource development, energy security transportation, and environmental infrastructure construction. Among these, SRB-resistant stainless steel, which must withstand the sulfide corrosion produced by sulfate-reducing bacteria metabolism, is a key material for use in extreme conditions such as deep-sea oil and gas extraction and long-distance oil and gas transportation. SRB-induced microbial corrosion destroys the passivation film on the metal surface, leading to pitting corrosion, crevice corrosion, and even stress corrosion cracking, severely shortening equipment service life and increasing safety risks and maintenance costs.

[0003] Currently, corrosion-resistant pipeline steel is mainly produced using traditional electric arc furnace melting and conventional rolling processes. However, these processes have several drawbacks: First, traditional electric arc furnace melting leads to uneven internal composition of the material, and the low solid solubility of corrosion-resistant elements in the matrix easily results in local segregation, which is not only detrimental to improving corrosion resistance but also to subsequent hot working. Second, unreasonable setting of the single-pass pressure during rolling leads to a significant increase in internal stress concentration in stainless steel, making it prone to surface defects such as cracks and warping. All these technical defects result in excessively high corrosion rates of traditional stainless steel plates in SRB-containing media, far from meeting the long-term service requirements (over 15 years) of large equipment such as deep-sea equipment (requiring a corrosion rate ≤0.05 mm / year) and nuclear power plant circulating water systems (requiring a corrosion rate ≤0.08 mm / year). Summary of the Invention

[0004] The purpose of this invention is to provide a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which solves the problem of easy corrosion of Cu and Ce stainless steel when it is used in extreme environments.

[0005] The technical solution adopted in this invention is a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which is implemented according to the following steps:

[0006] Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace for heat preservation, water quenching, grinding, cleaning, and drying to obtain the pretreated stainless steel ingot. Step 2: Perform the first rolling on the pretreated stainless steel ingot; Step 3: Perform a second rolling process on the stainless steel ingot after the first rolling. Step 4: Perform a third rolling process on the stainless steel ingot after the second rolling. Step 5: Place the stainless steel ingots that have undergone three stages of rolling back into the furnace for heat preservation and pickling passivation treatment. Step 6: The passivated stainless steel ingot is cold rolled and polished to obtain stainless steel resistant to sulfate-reducing bacteria corrosion.

[0007] The invention is further characterized in that, In step 1, the heat preservation temperature is 800℃-1200℃ and the heat preservation time is 1 h-2 h; after the heat preservation is completed, the stainless steel ingot is placed in water at 10℃-20℃ for water quenching treatment.

[0008] Step 2 specifically involves: The pretreated stainless steel ingot is heated to 800℃-1200℃ and fed into a rolling mill for rolling. The single-pass rolling pressure is controlled to be 17%-19% of the initial total thickness of the stainless steel ingot. After each rolling pass, it is necessary to hold it in a furnace at 800℃-1200℃ for 25min-40min. The rolling-holding process is repeated alternately until the remaining thickness of the stainless steel ingot is less than 62%-65% of the initial total thickness.

[0009] Step 3 specifically involves: The stainless steel ingot after the first rolling is rolled a second time, and the single-pass reduction is controlled to be 8%-10% of the initial total thickness of the stainless steel ingot. After each rolling pass, the stainless steel ingot needs to be placed back into the preset furnace temperature of 800℃-1200℃ and held for 25min-40min. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 43%-46% of the initial total thickness.

[0010] Step 4 specifically involves: Entering the third rolling stage, the stainless steel ingot after the second rolling is rolled for the third time. The single-pass reduction is 2%-4% of the initial total thickness of the stainless steel ingot. The above-mentioned furnace holding operation at 800℃-1200℃ for 25 min-40 min after each rolling is used alternately and repeated until the remaining thickness of the stainless steel ingot is less than 5%-8% of the initial total thickness.

[0011] Step 5 specifically involves: The stainless steel ingots, after undergoing three stages of rolling, are placed back into a furnace at 800℃-1200℃ and held for 25-40 minutes. After holding, they are removed and subjected to pickling and passivation treatment. The pickling and passivation treatment is as follows: First, the stainless steel ingots are immersed in NaOH solution for 5-20 minutes, then rinsed with water for 2-8 minutes. Next, they are immersed in a mixed acid solution of HNO3 and HF for 5-20 minutes, then rinsed a second time. Then, the stainless steel ingots are immersed in sodium carbonate solution for 3-12 minutes until the surface pH reaches 7-9, then rinsed again. Finally, they are immersed in nitric acid solution for 5-20 minutes, then air-dried to complete the passivation treatment.

[0012] Step 6 specifically involves: The passivated stainless steel ingot is cold rolled, with the single-pass rolling pressure controlled at 1%-2% of the initial total thickness of the ingot. The rolling is repeated until the remaining thickness of the stainless steel ingot is less than 4% of the initial total thickness. The rolled product is then polished to obtain stainless steel resistant to sulfate-reducing bacteria corrosion.

[0013] Another technical solution adopted in this invention is stainless steel obtained by a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion.

[0014] The beneficial effects of this invention are as follows: It addresses the technical difficulties of poor hot working performance of existing Cu and Ce co-doped stainless steel plates, where segregation during rolling becomes the source of crack initiation, easily leading to cracking. Cu-rich and Ce-rich phases are the main causes of cracking in stainless steel, deteriorating hot working performance, and corrosion resistance. Therefore, this invention proposes a homogenized annealing-multi-stage annealing hot rolling combined process, solving problems such as segregation inside castings, uneven microstructure distribution, and cracking along grain boundaries during rolling in conventional rolling processes. This improves the hot working performance of stainless steel, resulting in stainless steel ingots with no surface cracks, no obvious core defects, and uniform composition. Secondly, Cu... 2+ It possesses strong oxidizing properties, can penetrate the cell membrane and cell wall of SRB, destroy the enzyme structure within, and hinder the reduction process of SRB, thereby inhibiting the reproduction of SRB. 3+ It can promote Cu production by altering cell membrane permeability and increasing cell membrane porosity. 2+ They enter the interior of SRB cells. The synergistic effect of the two can amplify the destructive effect on the intracellular enzyme structure, more effectively block the reduction and energy metabolism processes of SRB, cause SRB reproduction to stop or even apoptosis, and thus improve the SRB corrosion resistance of stainless steel. Attached Figure Description

[0015] Figure 1 This is a microstructure image of the stainless steel sample obtained in Example 2; Figure 2 This is a microstructure image of the stainless steel sample obtained in Example 3; Figure 3 The image shows the microstructure of the stainless steel sample obtained in Example 2 after 14 days of immersion corrosion. Figure 4 The image shows the microstructure of the stainless steel sample obtained in Example 3 after 14 days of immersion corrosion. Figure 5 These are stress-strain curves of the stainless steel samples obtained in Examples 1-4. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0017] The present invention discloses a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which is implemented according to the following steps: Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace and hold it at 800℃-1200℃ for 1 h-2 h. After holding, quench the stainless steel ingot in water at 10℃-20℃. Then polish its surface and clean and dry it with gasoline to obtain the pretreated stainless steel ingot. High-purity chromium granules, high-purity nickel plates, pure silicon blocks, pure manganese blocks, pure Cu rods, pure iron blocks, and Cu-20Ce alloy were completely melted using medium-frequency induction melting. After holding at a certain temperature, the molten metal was poured into an alumina crucible, and after cooling, a stainless steel ingot with Cu and Ce co-doped elements was obtained. The mass percentage of Cu element was 0.1wt%-4.0wt%, and the mass percentage of Ce element was 0.1wt%-0.5wt%. Medium-frequency induction melting can effectively eliminate component segregation and inclusion aggregation inside the molten pool during the preparation process, while also eliminating bubbles in the molten pool and reducing the generation of porosity and shrinkage defects.

[0018] Step 2: Perform the first rolling on the pretreated stainless steel ingot; The pretreated stainless steel ingot is heated to 800℃-1200℃ and fed into a rolling mill for rolling. The single-pass reduction is controlled to be 17%-19% of the initial total thickness of the stainless steel ingot. After each rolling pass, it is necessary to hold it in a furnace at 800℃-1200℃ for 25 min-40 min. This rolling-holding process is repeated alternately until the remaining thickness of the stainless steel ingot is less than 62%-65% of the initial total thickness. Step 3: Proceed to the second rolling stage. The stainless steel ingot, after the first rolling, undergoes a second rolling process. The reduction in pressure per pass is controlled to be 8%-10% of the initial total thickness of the stainless steel ingot. After each rolling pass, the stainless steel ingot is returned to the preset furnace temperature of 800℃-1200℃ and held for 25-40 minutes. After holding, the next rolling pass is performed. This rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 43%-46% of the initial total thickness. Step 4: Enter the third rolling stage. The stainless steel ingot after the second rolling is rolled for the third time. The reduction in a single pass is 2%-4% of the initial total thickness of the stainless steel ingot. The process of reheating at 800℃-1200℃ for 25min-40min after each rolling pass is repeated alternately until the remaining thickness of the stainless steel ingot is less than 5%-8% of the initial total thickness. Step 5: Place the stainless steel ingots that have undergone three stages of rolling back into the furnace at 800℃-1200℃ and hold for 25 min-40 min. After holding, take them out and perform pickling and passivation treatment. The pickling and passivation treatment is as follows: First, immerse the stainless steel ingot in a 10% NaOH solution at 60℃ for 5-20 minutes, then rinse with clean water for 2-8 minutes. Next, immerse it in a mixed acid solution (10% HNO3 and 3% HF) at 30℃ for 5-20 minutes, then rinse it with water a second time. Then, immerse the stainless steel ingot in a 5% sodium carbonate solution for 3-12 minutes, and rinse it with water again when the surface pH reaches 7-9. Finally, immerse it in a 20% nitric acid solution at 50℃ for 5-20 minutes, then let it air dry naturally to complete the passivation treatment.

[0019] Step 6: Cold roll the passivated stainless steel ingot, controlling the single-pass rolling pressure to 1%-2% of the initial total thickness of the ingot, and alternately roll until the remaining thickness of the stainless steel ingot is less than 4% of the initial total thickness; then further polish the rolled product to remove excess impurities and defects on the surface, and stainless steel resistant to sulfate-reducing bacteria corrosion can be obtained.

[0020] This invention relates to a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion. Through a combination of medium-frequency induction melting, homogenization annealing, and multi-stage annealing hot rolling processes, it achieves synergistic optimization of high corrosion resistance and excellent mechanical properties of stainless steel in SRB-containing media. It is applicable to key fields such as marine engineering equipment, oil and gas pipelines, and nuclear power circulating water systems.

[0021] Example 1 The present invention discloses a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which is implemented according to the following steps: Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace, heat it to 800℃ and hold it for 1 h. After the holding period, quickly immerse it in water for water quenching. After water quenching, grind and polish the surface of the ingot until the surface oxide scale is completely removed. Step 2: Reheat the pretreated ingot to 800°C and send it into the rolling mill for rolling. The single-pass rolling pressure is controlled to be 17% of the initial total thickness of the ingot. After each rolling pass, the ingot needs to be placed back into the furnace at 800°C and held for 25 minutes. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 62% of the initial total thickness.

[0022] Step 3: The ingot after the first rolling is hot rolled again (heated to 800℃). The single pass reduction is 8% of the initial total thickness of the ingot. After each rolling pass, the ingot is placed in an 800℃ furnace and held for 25 minutes. After the holding period, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 43% of the initial total thickness (second rolling stage).

[0023] Step 4: Enter the third rolling stage. The stainless steel ingot after the second rolling is rolled for the third time. The single pass reduction is 2% of the initial total thickness of the ingot. After each rolling pass, the temperature is maintained at 800℃ for 25 minutes. This process is repeated alternately until the remaining thickness of the ingot is less than 5% of the initial total thickness.

[0024] Step 5: Place the ingot, which has undergone three stages of rolling, back into the furnace at 800℃ and hold for 25 minutes. After holding, remove it and perform pickling and passivation treatment: First, immerse the ingot in a 60℃, 10% NaOH solution for 5 minutes, then rinse it with water for 2 minutes; then immerse it in a 30℃ HNO3+HF mixed solution for 5 minutes, then rinse it with water a second time; then immerse it in a 5% sodium carbonate solution at room temperature for 3 minutes, and rinse it with water again when the surface pH reaches 7.1; finally, immerse it in a 50℃, 20% nitric acid solution for 5 minutes, then remove it and air dry it naturally to complete the passivation treatment.

[0025] Step 6: The passivated ingot is cold-rolled, with the single-pass rolling pressure controlled at 1% of the initial total thickness of the ingot. Rolling is repeated alternately until the remaining thickness of the ingot is less than 2% of the initial total thickness. The rolled product is then ground to remove excess impurities and defects from the surface. Testing shows that the product has a yield strength of 700.55 MPa and an elongation of 140.4%, meeting the minimum mechanical property requirements for this series of pipeline steels.

[0026] Example 2 The present invention discloses a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which is implemented according to the following steps: Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace, heat it to 1000℃ and hold it for 1.5 h. After the holding period, quickly immerse it in water for water quenching. After water quenching, grind and polish the surface of the ingot until the surface oxide scale is completely removed. Step 2: Reheat the pretreated ingot to 1000℃ and send it into the rolling mill for rolling. The single-pass rolling pressure is controlled to be 18% of the initial total thickness of the ingot. After each rolling pass, the ingot needs to be placed back into the furnace at 1000℃ and held for 30 minutes. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 63% of the initial total thickness.

[0027] Step 3: After the first rolling, the ingot is hot rolled again (heated to 1000℃). The single pass reduction is 9% of the initial total thickness of the ingot. After each rolling pass, the ingot is placed in a furnace at 1000℃ and held for 30 minutes. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 44% of the initial total thickness.

[0028] Step 4: Enter the third rolling stage. The stainless steel ingot after the second rolling is rolled for the third time. The single pass reduction is 3% of the initial total thickness of the ingot. After each rolling pass, the temperature is maintained at 1000℃ for 30 minutes. This process is repeated alternately until the remaining thickness of the ingot is less than 6% of the initial total thickness.

[0029] Step 5: Place the ingot, which has undergone three stages of rolling, back into the furnace at 800℃ and hold for 25 minutes. After holding, remove it and perform pickling and passivation treatment: First, immerse the ingot in a 10% NaOH solution at 60℃ for 10 minutes, then rinse it with water for 4 minutes; then immerse it in a mixed HNO3+HF solution (10% HNO3 and 3% HF) at 30℃ for 10 minutes, then rinse it with water a second time; then immerse it in a 5% sodium carbonate solution at room temperature for 6 minutes, and rinse it with water again when the surface pH reaches 7.6; finally, immerse it in a 20% nitric acid solution at 50℃ for 10 minutes, then air dry it naturally to complete the passivation treatment.

[0030] Step 6: The passivated ingot is cold-rolled, with the single-pass rolling pressure controlled at 1.5% of the initial total thickness of the ingot. Rolling is repeated alternately until the remaining thickness of the ingot is less than 3% of the initial total thickness. The rolled product is then ground to remove excess impurities and defects from the surface. Testing shows that the product has a yield strength of 566.55 MPa and an elongation of 100.15%, meeting the minimum mechanical property requirements for this series of pipeline steels.

[0031] Example 3 The present invention discloses a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which is implemented according to the following steps: Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace, heat it to 1100℃ and hold it for 1.75 h. After the holding period, quickly immerse it in water for water quenching. After water quenching, grind and polish the surface of the ingot until the surface oxide scale is completely removed. Step 2: Reheat the pretreated ingot to 1100℃ and send it into the rolling mill for rolling. The single-pass rolling pressure is controlled to be 18.5% of the initial total thickness of the ingot. After each rolling pass, the ingot needs to be placed back into the furnace at 1100℃ and held for 35 minutes. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 64% of the initial total thickness.

[0032] Step 3: After the first rolling, the ingot is hot rolled again (heated to 1100℃). The single pass reduction is 9.5% of the initial total thickness of the ingot. After each rolling pass, the ingot is placed in a furnace at 1100℃ and held for 35 minutes. After the holding period, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 45% of the initial total thickness (second rolling stage).

[0033] Step 4: Enter the third rolling stage. The stainless steel ingot after the second rolling is rolled for the third time. The single pass reduction is 3.5% of the initial total thickness of the ingot. After each rolling pass, the temperature is maintained at 1100℃ for 35 minutes. This process is repeated alternately until the remaining thickness of the ingot is less than 7% of the initial total thickness.

[0034] Step 5: Place the ingot, which has undergone three stages of rolling, back into the furnace at 800℃ and hold for 25 minutes. After holding, remove it and perform pickling and passivation treatment: First, immerse the ingot in a 10% NaOH solution at 60℃ for 15 minutes, then rinse it with clean water for 6 minutes; then immerse it in a mixed HNO3+HF solution at 30℃ for 15 minutes, then rinse it with water a second time; then immerse it in a 5% sodium carbonate solution at room temperature for 9 minutes, and rinse it with water again when the surface pH reaches 8.2; finally, immerse it in a 20% nitric acid solution at 50℃ for 15 minutes, then air dry it naturally to complete the passivation treatment.

[0035] Step 6: The passivated ingot is cold-rolled, with the single-pass rolling pressure controlled at 1.75% of the initial total thickness of the ingot. Rolling is repeated alternately until the remaining thickness of the ingot is less than 4% of the initial total thickness. The rolled product is then ground to remove excess impurities and defects from the surface. Testing shows that the product has a yield strength of 511.18 MPa and an elongation of 108.2%, meeting the minimum mechanical property requirements for this series of pipeline steels.

[0036] Example 4 The present invention discloses a multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, which is implemented according to the following steps: Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace, heat it to 1200℃ and hold it for 2 hours. After the holding period, quickly immerse it in water for water quenching. After water quenching, grind and polish the surface of the ingot until the surface oxide scale is completely removed. Step 2: Reheat the pretreated ingot to 1200℃ and send it into the rolling mill for rolling. The single-pass rolling pressure is controlled to be 19% of the initial total thickness of the ingot. After each rolling pass, the ingot needs to be placed back into the furnace at 1200℃ and held for 40 minutes. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 65% of the initial total thickness.

[0037] Step 3: After the first rolling, the ingot is hot rolled again (heated to 1200℃). The reduction in a single pass is 10% of the initial total thickness of the ingot. After each rolling pass, the ingot is placed in a furnace at 1200℃ and held for 40 minutes. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 46% of the initial total thickness.

[0038] Step 4: Enter the third rolling stage. The stainless steel ingot after the second rolling is rolled for the third time. The single pass reduction is 2% of the initial total thickness of the ingot. After each rolling pass, the temperature is maintained at 1200℃ for 40 minutes. This process is repeated alternately until the remaining thickness of the ingot is less than 8% of the initial total thickness.

[0039] Step 5: Place the ingot, which has undergone three stages of rolling, back into the furnace at 800℃ and hold for 25 minutes. After holding, remove it and perform pickling and passivation treatment: First, immerse the ingot in a 60℃, 10% NaOH solution for 20 minutes, then rinse with clean water for 8 minutes; then immerse it in a 30℃ HNO3+HF mixed solution (10% HNO3 and 3% HF) for 20 minutes, then rinse it a second time; then immerse it in a 5% sodium carbonate solution at room temperature for 12 minutes, and rinse it again when the surface pH reaches 8.7; finally, immerse it in a 50℃, 20% nitric acid solution for 20 minutes, then air dry it naturally to complete the passivation treatment.

[0040] Step 6: The passivated ingot is cold-rolled, with the single-pass rolling pressure controlled at 2% of the initial total thickness of the ingot. Rolling is repeated alternately until the remaining thickness of the ingot is less than 5% of the initial total thickness. The rolled product is then ground to remove excess impurities and defects from the surface. Testing shows that the product has a yield strength of 450.45 MPa and an elongation of 101.58%, meeting the minimum mechanical property requirements for this series of pipeline steels.

[0041] Example 5 Depend on Figure 1 , Figure 2 It can be seen that the stainless steel plate prepared by Example 3 has finer grains, more uniform distribution, no Cu and Ce element segregation phases, and fine carbide particles are dispersed at the grain boundaries. Depend on Figure 3 , Figure 4 It can be seen that after immersing the prepared stainless steel samples in an SRB-containing solution for 14 days for corrosion, the microstructure of the samples after corrosion was observed, and it was found that the number of corrosion pits in the stainless steel plates prepared in Examples 2 and 3 was relatively small; Figure 5 It can be seen that the stainless steel plates prepared in Examples 2 and 3 have high plasticity and excellent comprehensive mechanical properties; In summary, after rolling the stainless steel sample using the multi-stage combined rolling method proposed in this invention, there is no Cu or Ce element segregation phase present, and the comprehensive mechanical properties and corrosion resistance are greatly improved. Moreover, the stainless steel plate prepared by Example 3 has the best overall corrosion resistance and plasticity.

[0042] Example 6 The method of the present invention performs homogenization annealing on Cu and Ce co-doped stainless steel ingots prepared by medium frequency induction melting, followed by multi-stage annealing and hot rolling. This solves the problems of poor hot working performance, easy cracking, and easy corrosion of Cu and Ce stainless steel when it is used in extreme environments. At the same time, it achieves a synergistic improvement in the tensile strength and elongation of stainless steel.

Claims

1. A multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion, characterized in that, The specific steps are as follows: Step 1: Place the Cu and Ce co-doped stainless steel ingot prepared by medium frequency induction melting into a heat treatment resistance furnace for heat preservation, water quenching, grinding, cleaning, and drying to obtain the pretreated stainless steel ingot. Step 2: Perform the first rolling on the pretreated stainless steel ingot; Step 3: Perform a second rolling process on the stainless steel ingot after the first rolling. Step 4: Perform a third rolling process on the stainless steel ingot after the second rolling. Step 5: Place the stainless steel ingots that have undergone three stages of rolling back into the furnace for heat preservation and pickling passivation treatment. Step 6: The passivated stainless steel ingot is cold rolled and polished to obtain stainless steel resistant to sulfate-reducing bacteria corrosion.

2. The multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in claim 1, characterized in that, In step 1, the heat preservation temperature is 800℃-1200℃ and the heat preservation time is 1 h-2 h; after the heat preservation is completed, the stainless steel ingot is placed in water at 10℃-20℃ for water quenching treatment.

3. The multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in claim 1, characterized in that, Step 2 specifically involves: The pretreated stainless steel ingot is heated to 800℃-1200℃ and fed into a rolling mill for rolling. The single-pass rolling pressure is controlled to be 17%-19% of the initial total thickness of the stainless steel ingot. After each rolling pass, it is necessary to hold it in a furnace at 800℃-1200℃ for 25min-40min. The rolling-holding process is repeated alternately until the remaining thickness of the stainless steel ingot is less than 62%-65% of the initial total thickness.

4. The multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in claim 3, characterized in that, Step 3 specifically involves: The stainless steel ingot after the first rolling is rolled a second time, and the single-pass reduction is controlled to be 8%-10% of the initial total thickness of the stainless steel ingot. After each rolling pass, the stainless steel ingot needs to be placed back into the preset furnace temperature of 800℃-1200℃ and held for 25 min-40 min. After the holding is completed, the next rolling pass is carried out. The rolling-holding process is repeated alternately until the remaining thickness of the ingot is less than 43%-46% of the initial total thickness.

5. The multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in claim 4, characterized in that, Step 4 specifically involves: Entering the third rolling stage, the stainless steel ingot after the second rolling is rolled for the third time. The single-pass reduction is 2%-4% of the initial total thickness of the stainless steel ingot. The above-mentioned furnace holding operation at 800℃-1200℃ for 25 min-40 min after each rolling is used. The process is repeated alternately until the remaining thickness of the stainless steel ingot is less than 5%-8% of the initial total thickness.

6. The multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in claim 5, characterized in that, Step 5 specifically involves: The stainless steel ingots, after undergoing three stages of rolling, are placed back into a furnace at 800℃-1200℃ and held for 25-40 minutes. After holding, they are removed and subjected to pickling and passivation treatment. The pickling and passivation treatment is as follows: First, the stainless steel ingots are immersed in NaOH solution for 5-20 minutes, then rinsed with clean water for 2-8 minutes; then, they are immersed in a mixed acid solution of HNO3 and HF for 5-20 minutes, then rinsed a second time; next, the stainless steel ingots are immersed in sodium carbonate solution for 3-12 minutes, and rinsed again when the surface pH reaches 7-9; finally, they are immersed in nitric acid solution for 5-20 minutes, then air-dried to complete the passivation treatment.

7. The multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in claim 6, characterized in that, Step 6 specifically involves: The passivated stainless steel ingot is cold rolled, with the single-pass rolling pressure controlled at 1%-2% of the initial total thickness of the ingot. The rolling is repeated until the remaining thickness of the stainless steel ingot is less than 4% of the initial total thickness. The rolled product is then polished to obtain stainless steel resistant to sulfate-reducing bacteria corrosion.

8. Stainless steel obtained by the multi-stage combined rolling method for stainless steel resistant to sulfate-reducing bacteria corrosion as described in any one of claims 1-7.

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