Austenitic stainless steel pipe for heat exchanger and preparation method and application thereof

Abstract

The invention belongs to the technical field of austenitic stainless steel pipes, and particularly relates to an austenitic stainless steel pipe for a heat exchanger and a preparation method and application thereof. The austenitic stainless steel pipe for the heat exchanger comprises the following components in percentage by mass: less than or equal to 0.03% of C, less than or equal to 0.75% of Si, 3-6% of Mn, less than or equal to 0.04% of P, less than or equal to 0.03% of S, 16-19% of Cr, 4-7% of Ni, 2-4% of Mo, 1-3% of Cu, 0.3-0.6% of Hf, 0.2-0.5% of Ti, 0.1-0.3% of Co and the balance of Fe and inevitable impurities. The austenitic stainless steel pipe for the heat exchanger has excellent mechanical performance and is resistant to chloride ions and microbial corrosion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of austenitic stainless steel pipes, and particularly relates to an austenitic stainless steel pipe for a heat exchanger and a preparation method and application thereof. BACKGROUND

[0002] The austenitic stainless steel pipe is widely applied to the petroleum, chemical, pharmaceutical, food and other industries due to good heat resistance, corrosion resistance and mechanical properties. Different application scenarios have different performance requirements for the austenitic stainless steel pipe.

[0003] The heat exchanger is one of the indispensable devices in the operation process of a nuclear power station, which uses high-pressure water to take away heat energy, and the performance and operation reliability of the heat exchanger directly affect the operation of the nuclear power station. Since the nuclear power station is mostly established in coastal areas, seawater is often used as the cooling medium for the heat exchanger. The seawater contains high salt content, microorganisms and a large number of sand particles, so there are not only the problems of high chlorine ion content and easy corrosion of the heat exchanger, but also the problems of microbial corrosion and particle erosion, which result in low heat exchange efficiency of the heat exchange pipe. In addition, the service environment of the heat exchanger used in the nuclear power station is usually a high-temperature and high-pressure water environment. High-temperature and high-pressure water will form bubbles under high-speed flow and pressure change, which will cause cavitation.

[0004] A ferritic stainless steel and a manufacturing process thereof are disclosed in a Chinese patent with the publication number CN105063496A. The ferritic stainless steel includes Fe elements and modified chemical elements, and the modified chemical elements include elements in the following weight percentages: 0≤C≤0.02%, 0≤Si≤0.55%, 0≤P≤0.025%, 0≤S≤0.006%, 0≤Ni≤0.40%, 0≤Cu≤0.06%, 0≤Al≤0.04%, 0≤N≤0.02%, and further includes Cr, Mn, Mo and Ti elements. The ferritic stainless steel of the technical solution is corrosion-resistant and erosion-resistant, and the manufacturing process can adjust the hardness of the ferritic stainless steel, so that the ferritic stainless steel can be applied to the heat exchanger of the nuclear power station.

[0005] A Chinese patent with the publication number CN109504916B discloses a copper-titanium-containing high-strength and high-corrosion-resistant austenitic stainless steel and a preparation method thereof. The alloy element content is as follows: C≤0.08, Ni=10.0~14.0, Cr=16.0~18.5, Mo=2.0~3.0, Ti≤0.32, Cu=0.2~0.8, Mn≤2.0, Si≤1.0, P≤0.035, S≤0.030, wherein 3.98×(C-0.01)≤Ti≤3.98×C, and the balance is Fe. After alloy smelting, hot deformation breakdown and cold deformation are performed to fully break and disperse TiC, and coarse austenitic grains are obtained through high-temperature solid solution treatment. Under the condition of hydrogen, 80℃ contains 5×10 -6 F- The alloy corrosion current in 0.5 mol / L H2SO4 electrolyte is 6.9-9.8 mu A / cm 2 Compared with 316 stainless steel, the corrosion rate is greatly reduced, and the mechanical property is slightly better than that of 316 stainless steel.

[0006] However, the mechanical property of the above technical solution needs to be improved, and the microbial corrosion resistance is not concerned. SUMMARY

[0007] 1. Problems to be solved In view of the problems that the mechanical property of the heat exchanger used in the nuclear power plant needs to be improved and the microbial corrosion resistance is not concerned in the prior art, the application provides an austenitic stainless steel tube for heat exchanger and a preparation method and application thereof. The austenitic stainless steel tube for heat exchanger with excellent mechanical property and resistance to chloride ions and microbial corrosion is obtained by optimizing the raw material formula.

[0008] 2. Technical solutions In order to solve the above problems, the technical solutions adopted by the application are as follows: In the first aspect, the application provides an austenitic stainless steel tube for heat exchanger, which comprises the following components in percentage by mass: C: ≤0.03%, Si: ≤0.75%, Mn: 3-6%, P: ≤0.04%, S: ≤0.03%, Cr: 16-19%, Ni: 4-7%, Mo: 2-4%, Cu: 1-3%, Hf: 0.3-0.6%, Ti: 0.2-0.5%, Co: 0.1-0.3%, and the balance of Fe and inevitable impurities.

[0009] Further, the austenitic stainless steel tube for heat exchanger comprises the following components in percentage by mass: C: ≤0.03%, Si: ≤0.75%, Mn: 4-5%, P: ≤0.04%, S: ≤0.03%, Cr: 17-19%, Ni: 5-6%, Mo: 2-3%, Cu: 1.5-2.5%, Hf: 0.4-0.6%, Ti: 0.3-0.5%, Co: 0.15-0.3%, and the balance of Fe and inevitable impurities.

[0010] Further, the mass ratio of Cu, Hf, Ti and Co is 8-12: 1.5-3: 1.5-2.5: 1.

[0011] Further, the mass ratio of Cu, Hf, Ti and Co is 10-11: 1.5-3: 1.5-2.5: 1.

[0012] Further, the austenitic stainless steel pipe for heat exchanger comprises the following components in percentage by mass: C: 0.024%, Si: 0.37%, Mn: 5%, P: 0.04%, S: 0.007%, Cr: 19%, Ni: 5%, Mo: 2.01%, Cu: 2.5%, Hf: 0.4%, Ti: 0.5%, Co: 0.25%, and the balance of Fe and inevitable impurities.

[0013] The application can make the austenitic stainless steel have excellent mechanical properties, excellent resistance to chloride ion corrosion and excellent resistance to microbial corrosion by adding Cu, Hf, Ti and Co in a specific ratio and optimizing the mass percentage of the composition, and the specific action principle is as follows: C: High C content will cause corrosion sensitivity to increase, so the C content is controlled to be less than or equal to 0.03% in the application. Si: Si can improve the strength of the austenitic stainless steel.

[0014] Mn: Mn is a forming element of the austenitic stainless steel, and appropriate content can improve the strength of the austenitic stainless steel and improve the resistance to chloride ion corrosion.

[0015] P and S: The existence of P and S will reduce the plasticity and toughness of the austenitic stainless steel, so the P content is controlled to be less than or equal to 0.04% and the S content is controlled to be less than or equal to 0.03% in the application.

[0016] Cr: Cr is easy to contact with oxygen to form a dense oxide film, which improves the resistance to chloride ion corrosion of the austenitic stainless steel and has an inhibitory effect on microbial activity.

[0017] Ni: Ni is an austenite forming element, which improves the plasticity and toughness of the austenitic stainless steel and improves the resistance to chloride ion corrosion of the austenitic stainless steel.

[0018] Mo: Mo improves the strength of the austenitic stainless steel pipe and improves the density of the passivation film.

[0019] Cu: Cu can not only improve the plasticity and toughness of the austenitic stainless steel pipe, but also inhibit microbial activity by dissolving Cu ions on the surface of the austenitic stainless steel pipe during use, thereby improving the microbial corrosion resistance of the austenitic stainless steel pipe.

[0020] Hf and Ti: Hf and Ti can not only combine with C to improve the resistance to chloride ion corrosion and microbial corrosion of the austenitic stainless steel, but also improve the strength of the austenitic stainless steel.

[0021] Co: Co can stabilize the austenitic structure, improve the resistance to chloride ion corrosion of the austenitic stainless steel, and improve the toughness.

[0022] The application can obtain the austenitic stainless steel pipe with the pitting potential higher than 850 mV, the maximum pitting depth less than 2 µm, the tensile strength greater than or equal to 450 MPa, the tensile strength greater than 650 MPa and the elongation greater than or equal to 46%, which can be used as the heat exchanger of the nuclear power plant.

[0023] In the second aspect, the application provides a preparation method of the austenitic stainless steel pipe for the heat exchanger, which comprises the following steps: (1) melting, mold casting and hot forging forming the pipe blank in a vacuum induction melting furnace according to the formula; (2) the pipe blank is subjected to hot extrusion and cold rolling to obtain the austenitic stainless steel pipe for the heat exchanger.

[0024] Further, the temperature of the hot extrusion is 1100-1250 ℃, and the extrusion ratio is 12-15:1.

[0025] Further, the cold rolling is performed for 2-3 times, and the pipe is subjected to intermediate heat treatment and pickling after each cold rolling.

[0026] Further, the cold working deformation amount in the cold rolling process is controlled within 50%.

[0027] Further, the temperature of the intermediate heat treatment is 1000-1100 ℃, and the time is 30-60 min.

[0028] Further, the pickling is performed by using the nitric acid solution with the mass concentration of 4-5% for 30-60 min.

[0029] The cold rolling, the intermediate heat treatment and the pickling in the preparation method can be performed by using the conventional treatment conditions in the field.

[0030] In the third aspect, the application provides the application of the austenitic stainless steel pipe for the heat exchanger in the nuclear power plant.

[0031] 3. Advantages By adding Cu, Hf, Ti and Co in specific proportions and optimizing the mass percentage of the composition, the application can make the austenitic stainless steel have excellent mechanical properties, excellent resistance to chloride ion corrosion and excellent resistance to microbial corrosion through the synergistic effect of the elements, so that the obtained austenitic stainless steel pipe has the pitting potential higher than 850 mV, the maximum pitting depth less than 2 µm, the tensile strength greater than or equal to 450 MPa, the tensile strength greater than 650 MPa and the elongation greater than or equal to 46%, which can be used as the heat exchanger of the nuclear power plant. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1This is a physical image of the austenitic stainless steel tube used in the heat exchanger of Example 1. Detailed Implementation

[0033] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0034] Unless otherwise specified, the raw materials, reagents or apparatus used in the following examples and comparative examples are available from conventional commercial sources or can be obtained by existing known methods.

[0035] Example 1 An austenitic stainless steel tube for a heat exchanger, comprising the following components by weight percentage: C: 0.021%, Si: 0.62%, Mn: 4.5%, P: 0.03%, S: 0.005%, Cr: 18.5%, Ni: 6%, Mo: 2.09%, Cu: 2.2%, Hf: 0.58%, Ti: 0.4%, Co: 0.2%, and the balance being Fe and unavoidable impurities.

[0036] The method for preparing the austenitic stainless steel tube for the heat exchanger includes the following steps: (1) The tube blank is obtained by melting, casting and hot forging in a vacuum induction furnace according to the formula; (2) The tube blank is extruded and cold rolled at 1150℃ with a hot extrusion ratio of 14:1. The cold working deformation is controlled at 450%. It is then heat-treated at 1050℃ for 30 minutes and pickled with 5% nitric acid solution for 30 minutes. The above cold rolling-heat treatment-pickling is repeated twice to obtain the austenitic stainless steel tube for heat exchangers.

[0037] Example 2 An austenitic stainless steel tube for a heat exchanger, comprising the following components by weight percentage: C: 0.022%, Si: 0.45%, Mn: 4%, P: 0.03%, S: 0.005%, Cr: 17%, Ni: 5.5%, Mo: 2.06%, Cu: 1.8%, Hf: 0.5%, Ti: 0.3%, Co: 0.18%, and the balance being Fe and unavoidable impurities.

[0038] The method for preparing the austenitic stainless steel tube for the heat exchanger includes the following steps: (1) The tube blank is obtained by melting, casting and hot forging in a vacuum induction furnace according to the formula; (2) The tube blank is extruded and cold rolled at 1150℃ with a hot extrusion ratio of 14:1. The cold working deformation is controlled at 450%. It is then heat-treated at 1050℃ for 30 minutes and pickled with 5% nitric acid solution for 30 minutes. The above cold rolling-heat treatment-pickling is repeated twice to obtain the austenitic stainless steel tube for heat exchangers.

[0039] Example 3 An austenitic stainless steel tube for a heat exchanger, comprising the following components by weight percentage: C: 0.024%, Si: 0.37%, Mn: 5%, P: 0.04%, S: 0.007%, Cr: 19%, Ni: 5%, Mo: 2.01%, Cu: 2.5%, Hf: 0.4%, Ti: 0.5%, Co: 0.25%, and the balance being Fe and unavoidable impurities.

[0040] The method for preparing the austenitic stainless steel tube for the heat exchanger includes the following steps: (1) The tube blank is obtained by melting, casting and hot forging in a vacuum induction furnace according to the formula; (2) The tube blank is extruded and cold rolled at 1150℃ with a hot extrusion ratio of 14:1. The cold working deformation is controlled at 450%. It is then heat-treated at 1050℃ for 30 minutes and pickled with 5% nitric acid solution for 30 minutes. The above cold rolling-heat treatment-pickling is repeated twice to obtain the austenitic stainless steel tube for heat exchangers.

[0041] Comparative Example 1 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 6.5%, P: 0.03%, S: 0.005%, Cr: 16.5%, Ni: 3.5%, Mo: 2.09%, Cu: 2.7%, Hf: 1.58%, Ti: 1.4%, Co: 0.2% and the balance Fe and unavoidable impurities; all others are the same.

[0042] Comparative Example 2 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 2.0%, P: 0.03%, S: 0.005%, Cr: 19.5%, Ni: 6.7%, Mo: 2.09%, Cu: 3.2%, Hf: 0.28%, Ti: 0.4%, Co: 0.2% and the balance Fe and unavoidable impurities; all others are the same.

[0043] Comparative Example 3 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 4.5%, P: 0.03%, S: 0.005%, Cr: 18.5%, Ni: 6%, Mo: 2.09%, Cu: 2.38%, Hf: 0.4%, Ti: 0.3%, Co: 0.3%, and the balance being Fe and unavoidable impurities; all other components are the same.

[0044] Comparative Example 4 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 4.5%, P: 0.03%, S: 0.005%, Cr: 18.5%, Ni: 6%, Mo: 2.09%, Cu: 1.7%, Hf: 0.8%, Ti: 0.18%, Co: 0.25%, and the balance being Fe and unavoidable impurities; all other components are the same.

[0045] Comparative Example 5 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 4.5%, P: 0.03%, S: 0.005%, Cr: 18.5%, Ni: 6%, Mo: 2.09%, Cu: 2.2%, La: 0.98%, Ti: 0%, Co: 0.2% and the balance Fe and unavoidable impurities; all others are the same.

[0046] Comparative Example 6 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 4.5%, P: 0.03%, S: 0.005%, Cr: 18.5%, Ni: 6%, Mo: 2.09%, Cu: 2.2%, Hf: 0.58%, Ga: 0.6%, Co: 0%, and the balance being Fe and unavoidable impurities; all other components are the same.

[0047] Comparative Example 7 The only difference from Example 1 is that the heat exchanger uses austenitic stainless steel tubing, which, by mass percentage, comprises the following components: C: 0.021%, Si: 0.62%, Mn: 4.5%, P: 0.03%, S: 0.005%, Cr: 18.5%, Ni: 6%, Mo: 2.09%, Cu: 2.2%, Nb: 0.58%, Ti: 0.4%, Co: 0.2% and the balance Fe and unavoidable impurities; all others are the same.

[0048] I. Performance Testing Performance Test 1: Corrosion Resistance (1) The pitting potential was tested according to GB / T17899-2023 standard, and the results are shown in Table 1.

[0049] (2) The maximum pitting depth was detected after co-culturing with sulfate-reducing bacteria (25,000 CFU / mL) in the culture medium for 14 days. The results are shown in Table 1 below.

[0050] Performance Test 2 Tensile Test The elongation strength, tensile strength and elongation after fracture were tested according to GB / T228.1-2021, and the results are shown in Table 1.

[0051] Performance Test 3 (1) The austenitic stainless steel tubes for heat exchangers prepared in Example 1 were sent to external testing for appearance quality, tensile test, flattening test, flaring test, hydraulic test, air tightness test, intergranular corrosion test and salt spray test. The results are shown in Table 2.

[0052] (2) The austenitic stainless steel tubes for heat exchangers prepared in Example 2 were sent to external testing for appearance quality, tensile test, flattening test, flaring test, hydraulic test, air tightness test, intergranular corrosion test and salt spray test. The results are shown in Table 3.

[0053] (3) The austenitic stainless steel tubes for heat exchangers prepared in Example 3 were sent to external testing for appearance quality, tensile test, flattening test, flaring test, hydraulic test, air tightness test, intergranular corrosion test and salt spray test. The results are shown in Table 4.

[0054] II. Performance Test Results Table 1 As can be seen from Table 1, the austenitic stainless steel tubes for heat exchangers prepared in Examples 1-3 have high pitting potential, low maximum pitting depth, and high elongation, tensile strength and elongation after fracture. The mass percentage of the components in Comparative Example 1 is not within the scope of protection of this invention. The pitting potential of the prepared austenitic stainless steel tube for heat exchangers is significantly reduced, the maximum pitting depth is significantly increased, the elongation strength and tensile strength are improved, and the elongation after fracture is reduced. The mass percentage of the components in Comparative Example 2 is not within the scope of protection of this invention. The pitting potential of the prepared austenitic stainless steel tube for heat exchangers has decreased, the maximum pitting depth has not changed much, the elongation strength has decreased, the tensile strength has not changed much, and the elongation after fracture has decreased. The mass ratio of Cu, Hf, Ti and Co in Comparative Examples 3 and 4 is not within the scope of protection of this invention. The pitting potential of the prepared austenitic stainless steel tubes for heat exchangers has decreased, the maximum pitting depth has increased slightly, the elongation strength and tensile strength have not changed much, and the elongation after fracture has decreased. In Comparative Examples 4-7, the composition of Cu, Hf, Ti and Co was changed, and the pitting potential of the prepared austenitic stainless steel tubes for heat exchangers decreased significantly, the maximum pitting depth increased significantly, the elongation strength decreased, the tensile strength did not change much, and the elongation after fracture decreased. Table 1 shows that the austenitic stainless steel tubes for heat exchangers provided by this invention have excellent resistance to chloride ion corrosion, resistance to microbial corrosion, and excellent mechanical properties, and have broad application prospects in nuclear power plant heat exchangers.

[0055] Table 2 Table 3 Table 4 As can be seen from Tables 2-4, the austenitic stainless steel tubes for heat exchangers provided in Embodiments 1-3 of the present invention all meet the technical requirements.

[0056] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. An austenitic stainless steel tube for a heat exchanger, characterized in that, By weight percentage, it includes the following components: C: ≤0.03%, Si: ≤0.75%, Mn: 3-6%, P: ≤0.04%, S: ≤0.03%, Cr: 16-19%, Ni: 4-7%, Mo: 2-4%, Cu: 1-3%, Hf: 0.3-0.6%, Ti: 0.2-0.5%, Co: 0.1-0.3%, and the balance being Fe and unavoidable impurities.

2. The austenitic stainless steel tube for heat exchangers according to claim 1, characterized in that, The heat exchanger uses austenitic stainless steel tubes, which, by mass percentage, comprise the following components: C: ≤0.03%, Si: ≤0.75%, Mn: 4-5%, P: ≤0.04%, S: ≤0.03%, Cr: 17-19%, Ni: 5-6%, Mo: 2-3%, Cu: 1.5-2.5%, Hf: 0.4-0.6%, Ti: 0.3-0.5%, Co: 0.15-0.3%, and the balance being Fe and unavoidable impurities.

3. The austenitic stainless steel tube for heat exchangers according to claim 2, characterized in that, The mass ratio of Cu, Hf, Ti, and Co is 8-12: 1.5-3：1.5-2.5：1。 4. The austenitic stainless steel tube for heat exchangers according to claim 3, characterized in that, The mass ratio of Cu, Hf, Ti, and Co is 10-11: 1.5-3：1.5-2.5：1。 5. The austenitic stainless steel tube for heat exchangers according to claim 4, characterized in that, The heat exchanger uses austenitic stainless steel tubes, which, by mass percentage, comprise the following components: C: 0.024%, Si: 0.37%, Mn: 5%, P: 0.04%, S: 0.007%, Cr: 19%, Ni: 5%, Mo: 2.01%, Cu: 2.5%, Hf: 0.4%, Ti: 0.5%, Co: 0.25%, and the balance being Fe and unavoidable impurities.

6. The austenitic stainless steel tube for heat exchangers according to claim 5, characterized in that, The austenitic stainless steel tube has an elongation strength greater than or equal to 450 MPa, a tensile strength greater than 650 MPa, and an elongation after fracture greater than or equal to 46%.

7. The austenitic stainless steel tube for heat exchangers according to claim 6, characterized in that, The austenitic stainless steel tube was tested for 14 days in an environment with a sulfate-reducing bacteria concentration of 25,000 / mL, and the maximum pitting depth was less than 2 μm.

8. The method for preparing austenitic stainless steel tubes for heat exchangers according to any one of claims 1-7, characterized in that, Includes the following steps: (1) The tube blank is obtained by melting, casting and hot forging in a vacuum induction furnace according to the formula; (2) The tube blank is hot extruded and cold rolled to obtain austenitic stainless steel tubes for heat exchangers.

9. The method for preparing austenitic stainless steel tubes for heat exchangers according to claim 8, characterized in that, The cold rolling process is repeated 2-3 times, and the pipe is subjected to intermediate heat treatment and pickling after each cold rolling.

10. The application of the austenitic stainless steel tube for heat exchangers according to any one of claims 1-7 in nuclear power plants.

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