Austenitic stainless steel and preparation method and application thereof

Abstract

The invention discloses austenitic stainless steel and a preparation method and application thereof, and the austenitic stainless steel comprises the following chemical components in percentage by weight: 0.01%-0.07% of C, 16.0%-19.0% of Cr, 10.0%-14.0% of Ni, 2.0%-3.0% of Mo, 0.5%-2.5% of W and the balance of Fe. The austenitic stainless steel composed of 0.01%-0.07% of C, 16.0%-19.0% of Cr, 10.0%-14.0% of Ni, 2.0%-3.0% of Mo, 0.5%-2.5% of W and the balance Fe has the advantages of being high in abrasion resistance and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to an austenitic stainless steel and a preparation method and application thereof. BACKGROUND

[0002] At present, in the field of wear-resistant steel, high-carbon steel occupies a dominant position because it has high hardness and excellent wear resistance. However, high-carbon steel also has obvious shortcomings, that is, poor corrosion resistance.

[0003] The primary loop of nuclear power is in a high-temperature and high-pressure B-Li water environment, and the service conditions are extremely harsh, with a temperature of up to 320 ℃ and a pressure of 15.5 MPa. In this environment, in order to resist corrosion and aging, the currently selected materials are mostly stainless steel or nickel-based alloy. However, both of these materials have limitations: although the nickel-based alloy has excellent performance, it is high in cost; the wear resistance of the conventional grade of stainless steel is relatively poor in actual application, and the service life is relatively short, which is particularly prominent. In a major overhaul cycle, the wall thickness reduction of some severely worn areas is as high as 70%, which makes the equipment face the risk of leakage at any time during the later service process.

[0004] Therefore, it is urgent to develop a new type of stainless steel. The new type of stainless steel can significantly improve the wear resistance of the material while maintaining good corrosion resistance, and has lower cost compared with the nickel-based alloy, which has significant economic advantages and application value. SUMMARY

[0005] The present application aims to at least solve one of the problems in the prior art. To this end, the first aspect of the present application provides an austenitic stainless steel which exhibits excellent wear resistance and corrosion resistance under high-temperature and high-pressure water environment conditions.

[0006] The second aspect of the present application further provides a preparation method of the austenitic stainless steel.

[0007] The third aspect of the present application further provides an application of the austenitic stainless steel.

[0008] According to the first aspect of the present application, an austenitic stainless steel is provided, which comprises, by weight percentage, C 0.01 %~0.07 %, Cr 16.0 %~19.0 %, Ni 10.0 %~14.0 %, Mo 2.0 %~3.0 %, W 0.5 %~2.5 % and Fe balance.

[0009] According to a preferred embodiment of the present application, the chemical composition comprises, in percentage by weight: C 0.01 %~0.07 %, Cr 16.0 %~19.0 %, Ni 10.0 %~14.0 %, Mo 2.0 %~3.0 %, W 0.5 %~2.5 %, Si≤0.75 %, Mn≤2.0 %, P≤0.03 %, S≤0.015 % and Fe balance.

[0010] According to a preferred embodiment of the present application, the content of Cr comprises 16.0 %, 16.5 %, 17.0 %, 17.5 %, 18.0 %, 19.0 % or any sub-range consisting of any two of the aforementioned values.

[0011] According to a preferred embodiment of the present application, the content of Ni comprises 10.0 %, 10.5 %, 11.0 %, 11.5 %, 12.0 %, 13.0 %, 14.0 % or any sub-range consisting of any two of the aforementioned values.

[0012] According to a preferred embodiment of the present application, the content of Mo comprises 2.0 %, 2.1 %, 2.2 %, 2.3 %, 2.4 %, 2.5 %, 2.6 %, 2.7 %, 2.8 %, 3.0 % or any sub-range consisting of any two of the aforementioned values.

[0013] According to a preferred embodiment of the present application, the content of W comprises 0.5 %, 1.0 %, 1.5 %, 1.8 %, 2.0 %, 2.5 % or any sub-range consisting of any two of the aforementioned values.

[0014] According to a preferred embodiment of the present application, the austenitic stainless steel has an austenitic grain size index ≥ 2.

[0015] The austenitic stainless steel according to the embodiments of the present application has at least the following beneficial effects: The austenitic stainless steel according to the embodiments of the present application has at least the following beneficial effects:

[0016] This is because the tungsten of the present application mainly enhances the wear resistance in stainless steel through solid solution strengthening and carbide precipitation synergy. Tungsten has a large atomic radius, and when it is dissolved into the iron matrix, it will produce strong lattice distortion, hinder dislocation movement, and directly improve the strength and hardness of the matrix. The addition of 0.5%-2.5% tungsten in austenitic stainless steel can increase the hardness of the matrix from 160-180 HV to 200-240 HV, significantly enhancing the material's ability to resist plastic deformation. At the same time, tungsten has a strong affinity for carbon and can form hard carbides such as W2C, WC, or (W, Cr)2C with carbon and chromium. These carbides have a hardness of 1200-2000 HV and better chemical stability than Cr 23 C6, which can be uniformly distributed in the matrix or grain boundary, resists the plowing and cutting of abrasive particles through the dual effects of "dispersion strengthening + hard phase support", and reduces material loss during wear.

[0017] Further, based on this characteristic, the material has the feasibility of being applied to the finger sleeve of the primary loop of a nuclear power plant for neutron detection. In actual application scenarios, it can effectively address and solve the key problem of short service life caused by the synergistic effect of multiple complex factors such as neutron irradiation, high temperature, high pressure, corrosive medium, and vibration on the material of the finger sleeve, providing reliable material support for the stable operation of the primary loop system of the nuclear power plant.

[0018] According to a second aspect of the present application, a method for preparing the austenitic stainless steel according to the first aspect of the present application is provided, comprising the following steps: Fe powder, Cr powder, Mo powder, Ni powder, and W powder are mixed, heated and melted under vacuum conditions, refined by temperature rising, cast into shape, forged, and cooled to obtain the austenitic stainless steel.

[0019] According to a preferred embodiment of the present application, the refining temperature is 1500-1700℃. For example, the refining temperature includes 1500℃, 1520℃, 1550℃, 1600℃, 1650℃, 1670℃, 1700℃, or a sub-range consisting of any two of the above values.

[0020] According to a preferred embodiment of the present application, the refining time is 8-15 min. For example, the refining time includes 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, or a sub-range consisting of any two of the above values.

[0021] According to a preferred embodiment of the present application, the forging temperature is 1150-1350℃. For example, the forging temperature includes 1150℃, 1200℃, 1250℃, 1280℃, 1300℃, 1350℃, or a sub-range consisting of any two of the above values.

[0022] According to a preferred embodiment of the present application, the forging ratio of the forging is ≥ 3. The "forging ratio" refers to the cross-sectional area ratio before and after deformation during forging.

[0023] According to a preferred embodiment of the present application, the cooling method comprises air cooling and / or water cooling.

[0024] According to a preferred embodiment of the present application, the vacuum degree of the vacuum condition is ≤ 2 Pa.

[0025] The third aspect of the present application provides an application of the austenitic stainless steel in the detection of the finger sleeve pipe of a nuclear power plant.

[0026] Other features and advantages of the present application will be set forth in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which: Figure 1 is a grain size distribution diagram of the austenitic grains of the austenitic stainless steel of Example 1 of the present application; Figure 2 is an SEM diagram of Example 1 of the present application; Figure 3 is an XRD diagram of the austenitic stainless steel of Examples 1-3 of the present application; Figure 4 is a physical diagram of a Bruker UMT-TriboLab type friction and wear tester of the present application; Figure 5 is a wear form diagram of the wear resistance test of the present application; Figure 6 is a wear morphology diagram of the austenitic stainless steel prepared in Examples 1-3 of the present application; Figure 7 is a physical diagram of an electrochemical workstation for corrosion resistance test of the present application; Figure 8 is an equivalent circuit diagram when the electrochemical impedance test of the present application is performed; Figure 9 is an electrochemical impedance test diagram of Examples 1-3 of the present application; Figure 10 is a potential polarization curve diagram of Examples 1-3 of the present application. DETAILED DESCRIPTION

[0028] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in combination with the embodiments, but the present application is not limited to these embodiments.

[0029] The reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field unless otherwise specified.

[0030] In some embodiments of the present application, an austenitic stainless steel is provided, which has a chemical composition including, in terms of percentage by weight: C 0.01 %~0.07 %, Cr 16.0 %~19.0 %, Ni 10.0 %~14.0 %, Mo 2.0 %~3.0 %, W 0.5 %~2.5 %, and Fe balance.

[0031] In some embodiments of the present application, the chemical composition includes, in terms of percentage by weight: C 0.01 %~0.07 %, Cr 16.0 %~19.0 %, Ni 10.0 %~14.0 %, Mo 2.0 %~3.0 %, W 0.5 %~2.5 %, Si≤0.75 %, Mn≤2.0 %, P≤0.03 %, S≤0.015 %, and Fe balance.

[0032] In some embodiments of the present application, the content of Cr includes 16.0 %, 16.5 %, 17.0 %, 17.5 %, 18.0 %, 19.0 %, or a sub-range consisting of any two of the above-mentioned values.

[0033] In some embodiments of the present application, the content of Ni includes 10.0 %, 10.5 %, 11.0 %, 11.5 %, 12.0 %, 13.0 %, 14.0 %, or a sub-range consisting of any two of the above-mentioned values.

[0034] In some embodiments of the present application, the content of Mo includes 2.0 %, 2.1 %, 2.2 %, 2.3 %, 2.4 %, 2.5 %, 2.6 %, 2.7 %, 2.8 %, 3.0 %, or a sub-range consisting of any two of the above-mentioned values.

[0035] In some embodiments of the present application, the content of W includes 0.5 %, 1.0 %, 1.5 %, 1.8 %, 2.0 %, 2.5 %, or a sub-range consisting of any two of the above-mentioned values.

[0036] In some embodiments of the present application, the austenitic grain size index of the austenitic stainless steel is ≥2.

[0037] In some embodiments of the present application, the austenitic stainless steel consisting of C 0.01 %~0.07 %, Cr 16.0 %~19.0 %, Ni 10.0 %~14.0 %, Mo 2.0 %~3.0 %, W 0.5 %~2.5 % and Fe balance has high wear resistance and corrosion resistance.

[0038] Further, this is because the tungsten of the present application mainly enhances the wear resistance in the stainless steel through solid solution strengthening and carbide precipitation synergy. The atomic radius of tungsten is large, and after being dissolved into the iron matrix, it will produce strong lattice distortion, hinder dislocation movement, and directly improve the strength and hardness of the matrix. The addition of 0.5%-2.5% tungsten in the austenitic stainless steel can increase the hardness of the matrix from 160-180 HV to 200-240 HV, significantly enhancing the material's ability to resist plastic deformation. At the same time, tungsten has strong affinity with carbon and will form hard carbides such as W2C, WC or (W, Cr)2C with carbon, chromium and other elements. The hardness of these carbides is as high as 1200-2000 HV, and the chemical stability is better than Cr 23 C6, which can be uniformly distributed in the matrix or grain boundary, resists the plowing and cutting of abrasive particles through the dual effects of "dispersion strengthening + hard phase support", and reduces material loss during wear.

[0039] Further, based on this characteristic, the material has the feasibility of being applied to the finger sleeve of the primary loop of the nuclear power plant for neutron detection. In actual application scenarios, it can effectively deal with and solve the key problem that the service life of the finger sleeve material is too short due to the synergistic effect of multiple complex factors such as neutron irradiation, high temperature, high pressure, corrosive medium and vibration, and provide reliable material guarantee for the stable operation of the primary loop system of the nuclear power plant.

[0040] In some embodiments of the present application, a method for preparing the austenitic stainless steel as described in the first aspect of the present application is provided, comprising the following steps: The Fe powder, Cr powder, Mo powder, Ni powder and W powder are mixed, heated and melted under vacuum conditions, refined by temperature rising, cast into shape, forged and cooled to obtain.

[0041] In some embodiments of the present application, the refining temperature is 1500~1700℃. For example, the refining temperature includes 1500℃, 1520℃, 1550℃, 1600℃, 1650℃, 1670℃, 1700℃ or a sub-range consisting of any two of the above values.

[0042] In some embodiments of the present application, the refining time is 8-15 min. For example, the refining time includes 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min or a sub-range consisting of any two of the above values.

[0043] In some embodiments of the present application, the forging temperature is 1150-1350°C. For example, the forging temperature includes 1150°C, 1200°C, 1250°C, 1280°C, 1300°C, 1350°C or a sub-range consisting of any two of the above values.

[0044] In some embodiments of the present application, the forging ratio of the forging is ≥3.

[0045] In some embodiments of the present application, the cooling method includes air cooling and / or water cooling.

[0046] In some embodiments of the present application, the vacuum degree of the vacuum condition is ≤2 Pa.

[0047] In some embodiments of the present application, the application of the austenitic stainless steel described above in the detection of the guide tube of the nuclear power plant is provided.

[0048] Example 1 This example provides an austenitic stainless steel #1, the raw material usage amount of which is shown in Table 1, the chemical composition of which is shown in Table 2, and the preparation method of which is as follows: The smelting is performed by a vacuum induction (medium frequency) furnace, the principle of which is to realize the heating function by using the principle of coil induction. High-purity Fe, Cr, Mo and Ni powders are accurately weighed and placed in a magnesia crucible (the weight of each element is accurate to 0.1 g), and then vacuumizing is carried out. When the vacuum composite pressure display shows that the air pressure is below 2 Pa, heating is started. After all the furnace raw materials are completely melted, argon protection is started, and electromagnetic stirring is carried out at the same time to promote the uniform distribution of the melt. Then, the temperature is raised for refining, the refining temperature is 1650°C, the refining time is 10 minutes, and after refining, the temperature is lowered to 1550°C. Finally, pouring and shaping are performed under argon protection. Then, forging is performed at a temperature of 1250°C, the total forging ratio of the base material is 3, and air cooling is used after forging. The grain size distribution of the austenitic stainless steel of the present application is shown in Figure 1 The austenitic grain size index of the finished product measured after forging is at least 2.

[0049] Examples 2-3 Examples 2-3 provide an austenitic stainless steel #2 and an austenitic stainless steel #3, the preparation method of which is the same as that of Example 1, the raw material usage amount of which is shown in Table 1, and the chemical composition of which is shown in Table 2.

[0050] Table 1

[0051] Table 2 (wt. %)

[0052] Performance test Figure 2 The SEM image of the sample with tungsten content of 0.5% (No. 1 of Example 1) is shown. In this sample, it can be observed that the sample is a typical equiaxed austenite crystal, accompanied by partial twinning. In addition, some granular substances are uniformly dispersed at the grain boundaries, which are hard carbides such as W2C, WC or (W, Cr)2C formed by the combination of tungsten with carbon, chromium and other elements. They are uniformly distributed in the matrix or grain boundaries, which can effectively resist the plowing and cutting action of abrasive particles, thereby reducing the loss of material during wear.

[0053] At the same time, X-ray diffraction experiments (XRD) were performed on the above-mentioned Nos. 1, 2 and 3, and the experimental results are shown in Figure 3 . Comparing the peak values of the results with the standard spectrum, the results show that the spectrum presents typical austenite diffraction peak characteristics, and no other redundant peaks are observed. This fully indicates that only austenite phase exists in the series of samples, and no other phase structure is detected, so it can be determined that all the samples are pure austenite phase.

[0054] 1. Wear resistance test The friction and wear test of the sample was carried out by using a Bruker UMT-TriboLab type friction and wear tester (as shown in Figure 4 ), and the wear sample was a 20*30*4 mm plate sample. Before the wear test, the sample was polished to 5000 mesh with sandpaper, and then polished with grinding paste. After polishing, the sample was cleaned with 75% ethanol for 15 min. The grinding pair was a 10 mm diameter Si3N4 ceramic ball with a hardness of 1600-1800 HV, and the contact was point contact. The wear form is shown in Figure 5 , the wear track is 15 mm, the applied load is 5 N, the experimental time is 60 min, and the wear environment is boron-lithium water environment (the test water solution is prepared by using deionized water, the content of H3BO3 is 1500 ppm, the content of LiOH is 2.3 ppm, and the conductivity is 0.08 μS / cm. High-purity nitrogen (99.99%) is continuously bubbled into the water environment to make the dissolved oxygen less than 5 ppb), and the friction force in the test process is recorded in real time by the data acquisition system of the system.

[0055] The three-dimensional morphology of the wear scar was measured by a three-dimensional white light interferometer (Bruker Contour GT-K1) (as shown in Figure 6(a), the two-dimensional profile of the wear scar (e.g. Figure 6 (b) the wear depth and other information. The wear volume was calculated using the dimensions of the wear scar obtained from the three-dimensional profilometer. The wear volume is shown in Table 3.

[0056] Table 3

[0057] As can be seen from Table 3, compared with the base material (RCC-M3304), when the tungsten addition amount is 0.5% (i.e. Sample #1), the wear amount is reduced from 16282800 μm 3 to 12755038 μm 3 , the wear resistance is increased by about 21%; when the tungsten content is further increased to 1.5% (i.e. Sample #2), the wear amount is significantly reduced to 7149767 μm 3 , in which case the wear amount reaches a minimum value, and the wear resistance is increased by about 56%; and when the tungsten content is further increased to 2.5% (i.e. Sample #3), the wear amount is very close to that of Sample #2, being 6494311 μm 3 , and the wear resistance is increased by about 60%.

[0058] 2. Corrosion resistance test The corrosion resistance of the austenitic stainless steel material prepared in Example 1~# of the present application was verified by electrochemical testing. The EchemLab XM electrochemical workstation produced by AMETEK was used for the experiment (as shown in Figure 7 ), the working electrode in the three-electrode system was the experimental material with a test area of 1 cm 2 , the saturated calomel electrode was the reference electrode, and the platinum sheet was the counter electrode. A 3.5 wt.% NaCl solution was used as the solution. All experiments were carried out after one hour of open circuit testing to stabilize; the alternating current impedance spectrum under the open circuit potential was measured, a 10 mV perturbation potential was applied, and the frequency was from 100k-0.01 Hz; the potentiodynamic polarization curve was scanned up and down from -0.8 V to 0.6 V at a scan rate of 0.333 mV / s.

[0059] The impedance fitting used an Rs(Q1R1)(Q2R2) equivalent circuit (as shown in Figure 8 ), Rs represents the solution resistance, Q1R1 represents the passivation film capacitance and resistance, Q2R2 represents the double-layer capacitance and charge transfer resistance, and the fitting data is shown in Figure 9 and Table 4, and the passivation film impedance performance of the doped material is significantly improved. The charge transfer resistance R2 can directly reflect the element dissolution of the material, and the higher the resistance value, the better the corrosion resistance.

[0060] Table 4 Impedance values after fitting

[0061] By comparison, it is found that the R2 values of the doped materials are all increased by several times compared with the base material, and the No.1 is the most obvious, the Nos.2 and 3 are lower than the No.1, but are all higher than the RCC-3304 material.

[0062] Further, it is known from the analysis of the potentiodynamic polarization curves (as shown in Figure 10 The curves of the doped materials and the base material have no great change, the self-corrosion potential is slightly increased, the No.1 material is the most, the corrosion current of the Nos.1, 2 and 3 materials is slightly reduced compared with the base material, the current density of the four materials in the passivation region has little difference, and the passivity breakdown potential of the three doped materials is slightly increased. In summary, the corrosion resistance of the No.1 material is more significantly improved, and when the tungsten addition amount is 1.5% and 2.5%, the corrosion resistance of the material is slightly reduced, but is stronger than the RCC-M3304 material.

[0063] The above is the detailed description combined with the embodiments of the present application, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge range of the ordinary skilled in the art without departing from the purpose of the present application.

Claims

1. An austenitic stainless steel, characterized in that, Its chemical composition, by weight percentage, includes: C 0.01%~0.07%, Cr 16.0%~19.0%, Ni 10.0%~14.0%, Mo 2.0%~3.0%, W 0.5%~2.5%, and Fe balance.

2. An austenitic stainless steel, characterized in that, Its chemical composition, by weight percentage, includes: C 0.01%~0.07%, Cr 16.0%~19.0%, Ni 10.0%~14.0%, Mo 2.0%~3.0%, W 0.5%~2.5%, Si≤0.75%, Mn≤2.0%, P≤0.03%, S≤0.015%, and Fe balance.

3. A method for preparing austenitic stainless steel as described in claim 1 or 2, characterized in that, Includes the following steps: Fe powder, Cr powder, Mo powder, Ni powder and W powder are mixed, heated and melted under vacuum, refined by heating, cast into shape, forged and cooled to obtain the final product.

4. The preparation method according to claim 3, characterized in that, The refining temperature is 1500~1700℃.

5. The preparation method according to claim 3, characterized in that, The refining time is 8-15 minutes.

6. The preparation method according to claim 3, characterized in that, The forging temperature is 1150~1350℃.

7. The preparation method according to claim 3, characterized in that, The forging ratio of the forging is ≥3.

8. The preparation method according to claim 3, characterized in that, The cooling method includes air cooling.

9. The preparation method according to claim 3, characterized in that, The vacuum level of the vacuum condition is ≤2 Pa.

10. The application of the austenitic stainless steel according to claim 1 or 2 in the testing finger sleeve of a nuclear power plant.

Images