Surface inclusion removing treatment method for super 13Cr martensitic stainless steel

Abstract

The invention discloses a super 13Cr martensitic stainless steel surface inclusion removal treatment method which comprises the following steps: polishing a super 13Cr stainless steel sample by using abrasive paper, carrying out ultrasonic cleaning to obtain a pretreated sample, soaking the pretreated sample in an inclusion removal solution to remove surface inclusions, and removing impurities on the surface of the sample on the premise of not damaging a matrix. And the pitting potential of the surface of the super 13Cr martensitic stainless steel is improved, so that the corrosion resistance of the material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel surface treatment, and in particular relates to a method for removing inclusions from the surface of a super 13Cr martensitic stainless steel. Background Art

[0002] In the drilling and development of deep and ultra-deep wells, extreme temperatures, pressures and complex chemical environments place higher demands on the performance of materials. General materials often find it difficult to meet the application requirements under these harsh conditions, especially in terms of corrosion resistance and mechanical strength. Super 13Cr martensitic stainless steel has excellent corrosion resistance and cost-effectiveness, making it the material of choice in the development of deep and ultra-deep wells. It has become indispensable in the oil industry. However, super 13Cr stainless steel is not completely immune to corrosion failure, especially when exposed to corrosive environments. Among them, pitting, as a common form of localized corrosion, frequently occurs on the surface of stainless steel.

[0003] Inclusions in super 13Cr stainless steel are inevitable metallurgical defects in steel, which often induce the initiation of localized corrosion, thus having a significant impact on the corrosion resistance of the material. The chemical composition, size and shape of inclusions are key factors in inducing localized corrosion, but there is little research on this in the existing technology. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for removing inclusions from the surface of a super 13Cr martensitic stainless steel.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] Super 13Cr stainless steel was processed into a standard sample, which was rinsed with water and air-dried to obtain sample I;

[0009] After sample I was rinsed with distilled water, it was ultrasonically cleaned with anhydrous ethanol and acetone in sequence for the first surface treatment, and then dried to obtain sample II;

[0010] After grinding sample II with sandpaper, ultrasonic cleaning with anhydrous ethanol and acetone was performed in sequence, and the surface was treated for the second time, and then dried to obtain sample III;

[0011] Sample III was immersed in a de-inclusion solution, cleaned and dried to achieve de-inclusion treatment on the surface of super 13Cr martensitic stainless steel;

[0012] The de-impurity solution is a citric acid solution, and the pH of the citric acid solution is adjusted to 3-4 by sodium citrate and sodium phosphate.

[0013] As a preferred solution of the method for removing inclusions from the surface of super 13Cr martensitic stainless steel of the present invention, the concentration of the citric acid solution is 15-25wt%.

[0014] As a preferred solution of the method for removing inclusions from the surface of super 13Cr martensitic stainless steel of the present invention, the concentration of the citric acid solution is 20wt%.

[0015] As a preferred solution of the surface removal treatment method of super 13Cr martensitic stainless steel described in the present invention, the grinding is performed using sandpaper with granularity of 150#, 500#, 1000#, 1500# and 2000# in sequence.

[0016] As a preferred solution of the surface de-inclusion treatment method of the super 13Cr martensitic stainless steel of the present invention, wherein: the ultrasonic cleaning is performed by anhydrous ethanol and acetone in sequence, wherein the time of the anhydrous ethanol ultrasonic cleaning is 4 to 5 minutes.

[0017] As a preferred solution of the surface inclusion removal treatment method of the super 13Cr martensitic stainless steel of the present invention, the time of the acetone ultrasonic cleaning is 5 to 6 minutes.

[0018] As a preferred solution of the surface inclusion removal treatment method of the super 13Cr martensitic stainless steel of the present invention, the immersion temperature of the sample III in the inclusion removal solution is 60-65°C.

[0019] As a preferred solution of the surface inclusion removal treatment method of the super 13Cr martensitic stainless steel of the present invention, the immersion time of the sample III in the inclusion removal solution is 15 to 25 minutes.

[0020] Another object of the present invention is to overcome the deficiencies in the prior art and provide a super 13Cr martensitic stainless steel surface obtained by treating the surface of the super 13Cr martensitic stainless steel with a method for removing inclusions from the surface.

[0021] As a preferred solution of the surface of the super 13Cr martensitic stainless steel of the present invention, the content of Al in the inclusions on the surface of the super 13Cr martensitic stainless steel is 2.38-2.41 at%, and the content of Mg is 1.0-1.1 at%.

[0022] As a preferred solution of the super 13Cr martensitic stainless steel surface of the present invention, the pitting potential of the super 13Cr martensitic stainless steel surface is 0.47-0.57V.

[0023] Beneficial effects of the present invention:

[0024] The present invention analyzes the inclusion type and dissolves the inclusions, thereby improving the corrosion resistance of super 13Cr stainless steel. Aiming at the pitting damage behavior of super 13Cr martensitic stainless steel, the corrosion resistance of super 13Cr martensitic stainless steel is improved without damaging the matrix. The surface of super 13Cr martensitic stainless steel obtained by the treatment method has a significantly improved pitting potential compared to the matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0026] Figure 1 This is a flow chart of the method for removing inclusions in Example 1 of the present invention;

[0027] Figure 2 This is a mechanism diagram of the de-inclusion treatment of Example 1 of the present invention;

[0028] Figure 3 The pitting potential diagrams of the samples after the removal of inclusions in Examples 1 to 2 of the present invention and Comparative Examples 1 to 5 are shown. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] Electrochemical performance test: In order to examine the effect of removal of inclusions on the corrosion resistance of super 13Cr stainless steel, electrochemical tests were carried out on the sample surface and the data were fitted and analyzed using ZSimpWin software.

[0033] The raw materials used in the present invention are commercially available unless otherwise specified.

[0034] Example 1

[0035] This embodiment provides a method for removing inclusions from the surface of super 13Cr martensitic stainless steel, specifically:

[0036] 1) Sample preparation: Super 13Cr stainless steel was processed into a standard sample with a size of 10 mm × 10 mm × 3 mm, rinsed with clean water and air-dried to obtain sample I;

[0037] 2) Surface cleaning: Sample I was rinsed with distilled water, then ultrasonically cleaned with anhydrous ethanol for 4 min and then ultrasonically cleaned with acetone for 5 min to perform the first surface treatment, and then dried to obtain sample II;

[0038] 3) Grinding treatment: Sample II was polished with 150#, 500#, 1000#, 1500#, and 2000# sandpaper in sequence, and then ultrasonically cleaned with anhydrous ethanol for 4 minutes and acetone for 5 minutes for secondary surface treatment, and then dried to obtain sample III;

[0039] 4) De-inclusion treatment: Sample III was immersed in a 20 wt % citric acid solution at 65° C. for 15 min, and then washed and dried to obtain the final sample, wherein the pH of the citric acid solution was adjusted to 3 with sodium citrate and sodium phosphate.

[0040] Comparative Example 1

[0041] The difference between this comparative example and Example 1 is that the step (4) of removing inclusions is not performed, and the rest of the preparation process is the same as that of Example 1.

[0042] Comparative Example 2

[0043] The difference between this comparative example and Example 1 is that the concentration of the citric acid solution in step (4) is adjusted to 15 wt %, and the rest of the preparation process is the same as that of Example 1.

[0044] Comparative Example 3

[0045] The difference between this comparative example and Example 1 is that the concentration of the citric acid solution in step (4) is adjusted to 25 wt %, and the rest of the preparation process is the same as that of Example 1.

[0046] The components and contents of the surface of the super 13Cr stainless steel before and after the inclusion removal treatment of Example 1 and Comparative Examples 1 to 3 were analyzed, and the results are shown in Table 1.

[0047] Table 1 Composition and content (At%) of surface inclusions on super 13Cr martensitic stainless steel before and after removal of inclusions

[0048]

[0049] As can be seen from Table 1, by comparing the components and contents of the surface of super 13Cr stainless steel treated with different citric acid solution concentrations when the treatment time is 15min, it can be seen that when the concentration of the citric acid solution is 20wt%, the inclusions Al and Mg content on the surface of super 13Cr martensitic stainless steel are low, indicating that this concentration can effectively dissolve inclusions. At the same time, the content of Fe and Cr in the matrix of super 13Cr martensitic stainless steel is still high, indicating that the matrix is ​​almost not damaged at this time. When the concentration of the citric acid solution increases to 25wt%, the inclusions Al and Mg content continue to decrease, and the matrix also begins to be damaged.

[0050] Electrochemical tests were performed on the surface of super 13Cr martensitic stainless steel in Example 1 and Comparative Examples 1 to 3. The results are shown in Table 2 and Figure 3 shown.

[0051] Table 2 Surface electrochemical properties of super 13Cr martensitic stainless steel after removal of inclusions

[0052]

[0053] As can be seen from Table 2, the pitting potential of the super 13Cr stainless steel surface after de-inclusion treatment in a 20wt% citric acid solution concentration is the highest, reaching 0.57V, which is significantly increased by about 3 times compared with the surface without de-inclusion treatment, indicating that the corrosion resistance of the super 13Cr stainless steel surface after treatment is the best.

[0054] Example 2

[0055] This embodiment provides a method for removing inclusions from the surface of super 13Cr martensitic stainless steel, specifically:

[0056] 1) Sample preparation: Super 13Cr stainless steel was processed into a standard sample with a size of 10 mm × 10 mm × 3 mm, rinsed with clean water and air-dried to obtain sample I;

[0057] 2) Surface cleaning: Sample I was rinsed with distilled water, then ultrasonically cleaned with anhydrous ethanol for 5 min and then ultrasonically cleaned with acetone for 6 min to perform the first surface treatment, and then dried to obtain sample II;

[0058] 3) Grinding treatment: Sample II was polished with 150#, 500#, 1000#, 1500#, and 2000# sandpaper in sequence, and then ultrasonically cleaned with anhydrous ethanol for 5 minutes and acetone for 6 minutes, and then the surface was treated for the second time, and dried to obtain sample III;

[0059] 4) Inclusion removal treatment: Sample III was immersed in a 15 wt % citric acid solution at 65° C. for 20 min, and then washed and dried to obtain the final sample, wherein the pH of the citric acid solution was adjusted to 4 using sodium citrate and sodium phosphate.

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 2 is that the immersion time of sample III in the citric acid solution in step (4) is adjusted to 15 minutes, and the rest of the preparation process is the same as that of Example 2.

[0062] Comparative Example 5

[0063] The difference between this comparative example and Example 2 is that the immersion time of sample III in the citric acid solution in step (4) is adjusted to 25 minutes, and the rest of the preparation process is the same as that of Example 2.

[0064] The components and contents of the surface of the super 13Cr stainless steel before and after the inclusion removal treatment of Example 2 and Comparative Examples 4-5 were analyzed. The results are shown in Table 3.

[0065] Table 3 Composition and content (At%) of surface inclusions of super 13Cr martensitic stainless steel before and after removal of inclusions

[0066]

[0067] As can be seen from Table 2, when the concentration of the citric acid solution is 15wt% and the immersion time is 20min, the inclusions Al and Mg content on the surface of the super 13Cr martensitic stainless steel are also low, and the inclusions are removed to a certain extent, and the matrix is ​​basically not damaged. However, when the time is further extended to 25min, the matrix begins to be damaged.

[0068] Electrochemical tests were performed on the surfaces of the super 13Cr martensitic stainless steels of Example 2 and Comparative Examples 4-5. The results are shown in Tables 4 and Figure 3 shown.

[0069] Table 4 Surface electrochemical properties of super 13Cr martensitic stainless steel after de-inclusion treatment at different times

[0070]

[0071] It can be seen from Table 4 that when the concentration of the citric acid solution is 15wt%, the pitting potential of the surface of the super 13Cr martensitic stainless steel after immersion for 20min is higher. Although further extending the immersion time removes more inclusions, it also leads to a decrease in the corrosion resistance of the stainless steel surface.

[0072] In summary, the present invention improves the corrosion resistance of super 13Cr martensitic stainless steel by ultrasonic cleaning, polishing, and immersing the surface of super 13Cr stainless steel in a de-inclusion solution without damaging the substrate. With respect to the pitting corrosion damage behavior of super 13Cr martensitic stainless steel, the surface of super 13Cr martensitic stainless steel obtained by the treatment method has a higher pitting potential and a slower corrosion rate than the substrate.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for removing inclusions from the surface of super 13Cr martensitic stainless steel, characterized in that: include, Super 13Cr stainless steel was processed into a standard sample, which was rinsed with water and air-dried to obtain sample I; After sample I was rinsed with distilled water, it was ultrasonically cleaned with anhydrous ethanol and acetone in sequence for the first surface treatment, and then dried to obtain sample II; After grinding sample II with sandpaper, ultrasonic cleaning with anhydrous ethanol and acetone was performed in sequence, and the surface was treated for the second time, and then dried to obtain sample III; Sample III was immersed in a de-inclusion solution, cleaned and dried to achieve de-inclusion treatment on the surface of super 13Cr martensitic stainless steel; The de-impurity solution is a citric acid solution, and the pH of the citric acid solution is adjusted to 3-4 by sodium citrate and sodium phosphate.

2. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel as claimed in claim 1, characterized in that the concentration of the citric acid solution is 15-25wt%.

3. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel according to claim 2, characterized in that: The concentration of the citric acid solution is 20 wt %.

4. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel according to claim 1, characterized in that: The grinding is performed using sandpaper with granularity of 150#, 500#, 1000#, 1500# and 2000# in sequence.

5. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel according to claim 1, characterized in that: The ultrasonic cleaning is performed by anhydrous ethanol and acetone in sequence, wherein the time of the ultrasonic cleaning by anhydrous ethanol is 4 to 5 minutes.

6. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel according to claim 5, characterized in that: The acetone ultrasonic cleaning time is 5 to 6 minutes.

7. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel according to claim 1, characterized in that: The immersion temperature of the sample III in the de-inclusion solution is 60-65°C.

8. The method for removing inclusions from the surface of super 13Cr martensitic stainless steel according to claim 7, characterized in that: The sample III is immersed in the de-inclusion solution for 15 to 25 minutes.

9. A super 13Cr martensitic stainless steel surface obtained by the de-inclusion treatment method according to any one of claims 1 to 8, characterized in that: The inclusions on the surface of the super 13Cr martensitic stainless steel have an Al content of 2.38-2.41 at %, and a Mg content of 1.0-1.1 at %.

10. The super 13Cr martensitic stainless steel surface according to claim 9, characterized in that: The pitting potential on the surface of the super 13Cr martensitic stainless steel is 0.47-0.57V.

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