Quantitative detection method for delta ferrite in martensite precipitation strengthened stainless steel

Abstract

The invention discloses a quantitative detection method for delta ferrite in martensitic precipitation strengthened stainless steel, and relates to the technical field of stainless steel detection.The method comprises the steps that a sample is prepared from the martensitic precipitation strengthened stainless steel, and the surface, parallel to the axial face of the stainless steel, of the sample is marked as an observation face; placing the sample in an environment with the temperature of 1040 + / -10 DEG C, preserving heat for 30 + / -5 minutes, taking out the sample, and performing water cooling to room temperature; sequentially carrying out mechanical grinding, polishing, cleaning and drying treatment on the observation surface of the sample; a NaOH electrolyte with the concentration of 10-20 g / 100 ml is used, and the sample is subjected to electrolytic corrosion for 30-40 s under the voltage of 5-8 V; cleaning and drying the sample; observing the observation surface of the sample through an optical microscope, and selecting a typical field of view of delta ferrite for photographing; and calculating the area proportion of the delta ferrite in the picture, and determining the content of the delta ferrite. According to the method, the delta ferrite content in the martensite precipitation strengthened stainless steel can be accurately calculated.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel detection, and in particular to a quantitative detection method for delta ferrite in martensite precipitation strengthened stainless steel. Background Art

[0002] Martensite precipitation strengthened stainless steel is widely used in shaft components for oil mining, internal structures of nuclear reactors, aircraft structures and load-bearing parts due to its high strength, good wear resistance and corrosion resistance.

[0003] Martensite precipitation-strengthened stainless steel has extremely high strength after aging treatment, but its significant disadvantage is low impact toughness. In particular, when martensite precipitation-strengthened stainless steel contains a small amount of delta ferrite, its impact toughness, especially the transverse impact toughness value, decreases significantly. Therefore, when used in parts that are sensitive to impact toughness, such as aviation structural parts, there are also extremely high requirements for the delta ferrite content in martensite precipitation-strengthened stainless steel. Generally, for parts that are not sensitive to impact toughness, the delta ferrite content in martensite precipitation-strengthened stainless steel is usually only required to be ≤10% or ≤5%. However, for parts that are sensitive to impact toughness, such as aviation structural parts, the delta ferrite content in martensite precipitation-strengthened stainless steel is required to be ≤3% or even ≤1%.

[0004] Currently, the δ-ferrite content in stainless steel is typically detected using either a standard pattern comparison method or a grid method. However, the standard pattern comparison method can only provide an approximate δ-ferrite content, such as less than 2%, less than 5%, less than 8%, and can only provide a rough estimate when the content is between the two patterns. While the grid method is more accurate than the standard pattern comparison method, it is highly dependent on the fineness of the grid and manual judgment, cannot achieve precise detection, and is time-consuming and labor-intensive. In actual application, neither of the above two detection methods can meet the demand for accurate detection of δ-ferrite content in martensite precipitation-strengthened stainless steel for high-end applications. Summary of the Invention

[0005] In order to solve some or all of the technical problems existing in the above-mentioned prior art, the present invention provides a method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for quantitatively detecting delta ferrite in martensite precipitation-strengthened stainless steel is provided, comprising:

[0008] Step 1: Prepare a sample from the martensite precipitation-strengthened stainless steel to be tested, and mark the surface of the sample parallel to the axial plane of the martensite precipitation-strengthened stainless steel as an observation surface;

[0009] Step 2, after the sample is kept in a temperature environment of 1040±10℃ for 30±5min, the sample is taken out and water-cooled to room temperature;

[0010] Step 3, the observation surface of the sample is sequentially subjected to mechanical grinding, polishing, cleaning and drying treatment;

[0011] Step 4, the sample is electrolytic etched for 30-40s using NaOH electrolyte with a concentration of 10-20g / 100ml at a voltage of 5-8V;

[0012] Step 5, the sample after electrolytic etching is subjected to cleaning and drying treatment;

[0013] Step 6, the observation surface of the sample is observed by optical microscope, and a typical field of view of δ-ferrite is selected for photographing;

[0014] Step 7, the area ratio of δ-ferrite in the photograph is calculated to determine the content of δ-ferrite in the martensite precipitation strengthened stainless steel.

[0015] In some optional embodiments, in the step 2, the sample is kept in a muffle furnace at 1040±10℃ for 30±5min, and the sample is immersed in water for water cooling.

[0016] In some optional embodiments, in the step 3, the mechanical grinding comprises sequentially using 150#, 320#, 600#, 800# and 2000# sandpaper for step-by-step grinding of the sample.

[0017] In some optional embodiments, in the step 3, the sample is polished using silk cloth and diamond polishing agent.

[0018] In some optional embodiments, the NaOH electrolyte uses deionized water as solvent.

[0019] In some optional embodiments, the cleaning and drying treatment comprises using flowing water for flushing, using anhydrous ethanol for wiping after flushing, and using a hair dryer for blowing dry after wiping.

[0020] In some optional embodiments, the area ratio of δ-ferrite in the photograph is calculated using image analysis software.

[0021] In some optional embodiments, the sample is a square sample with a side length of 20-25mm.

[0022] In some optional embodiments, the sample is prepared from the martensite precipitation strengthened stainless steel by sawing or wire cutting.

[0023] In some optional embodiments, the martensite precipitation strengthened stainless steel has the following composition:

[0024] C: 0.0001-0.1%, Si: 0-2.0%, Mn: 0-1.0%, P: 0-0.03%, S: 0-0.01%, Cr: 12.0-17.0%, Ni: 3.0-11.0%, Cu: 0-5.0%, Nb: 0-0.5%, Mo: 0-1.5%, Ti: 0-2.0%.

[0025] The main advantages of the technical scheme of the present application are as follows:

[0026] The quantitative detection method of the delta ferrite in the martensite precipitation strengthened stainless steel provided by the present application can accurately calculate the content of the delta ferrite in the martensite precipitation strengthened stainless steel by performing solid solution treatment on the martensite precipitation strengthened stainless steel, performing grinding, polishing and other treatments on the martensite precipitation strengthened stainless steel after the solid solution treatment, performing electrolytic corrosion on the martensite precipitation strengthened stainless steel by using an alkaline solution, and observing and calculating the area ratio of the delta ferrite by using an optical microscope. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are included to provide a further understanding of the embodiments of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and serve to explain the present application. In the drawings:

[0028] Figure 1 The flow chart of the quantitative detection method of the delta ferrite in the martensite precipitation strengthened stainless steel provided by the present application is shown in FIG. 1. DETAILED DESCRIPTION

[0029] To make the objectives, technical schemes and advantages of the present application clearer, the technical scheme of the present application will be described below in detail with reference to the embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0030] The technical scheme provided by the embodiments of the present application will be described in detail below with reference to the drawings.

[0031] Reference Figure 1 The quantitative detection method of the delta ferrite in the martensite precipitation strengthened stainless steel provided by the embodiments of the present application includes the following steps:

[0032] Step 1: Prepare a sample from the martensite precipitation strengthened stainless steel to be detected, and mark the surface of the sample parallel to the axial surface of the martensite precipitation strengthened stainless steel as an observation surface;

[0033] Step 2: After being kept at a temperature of 1040±10℃ for 30±5 min, the sample is taken out and water-cooled to room temperature;

[0034] Step 3, sequentially performing mechanical grinding, polishing, cleaning and drying treatment on the observation surface of the sample;

[0035] Step 4, using NaOH electrolyte with a concentration of 10-20 g / 100 ml to electrolytic corrosion the sample at a voltage of 5-8 V for 30-40 s;

[0036] Step 5, cleaning and drying the sample after electrolytic corrosion;

[0037] Step 6, observing the observation surface of the sample by optical microscope and selecting a typical field of view of the δ ferrite to take a photo;

[0038] Step 7, calculating the area ratio of the δ ferrite in the photo to determine the content of the δ ferrite in the martensite precipitation strengthened stainless steel.

[0039] In the embodiment of the present application, the typical field of view of the δ ferrite represents the most serious region of the δ ferrite distribution under the visual angle of the optical microscope.

[0040] The martensite precipitation strengthened stainless steel forging material is generally in annealed state or aged state, and the metallographic structure in the two states is annealed martensite (or tempered martensite) + δ ferrite. Since the corrosion resistance of the annealed martensite and the tempered martensite is close to that of the δ ferrite, when the martensite precipitation strengthened stainless steel is treated by the conventional metallographic corrosion method, the annealed martensite (or tempered martensite) and the δ ferrite will be displayed, and at this time, it is difficult to calculate the area ratio of the δ ferrite by optical microscope observation to determine the content of the δ ferrite in the martensite precipitation strengthened stainless steel.

[0041] Therefore, in the embodiment of the present application, the martensite precipitation strengthened stainless steel is first treated by solid solution to convert the annealed martensite or the tempered martensite in the martensite precipitation strengthened stainless steel into quenched martensite. Since the corrosion resistance of the quenched martensite and the δ ferrite is different, after the solid solution treated martensite precipitation strengthened stainless steel is treated by grinding, polishing and other treatments, the base structure of the martensite precipitation strengthened stainless steel is not corroded to present a pure white background color, and the δ ferrite is corroded to present other colors, so that the area ratio of the δ ferrite can be easily calculated to determine the content of the δ ferrite in the martensite precipitation strengthened stainless steel.

[0042] The method for quantitatively detecting the delta ferrite in the martensite precipitation strengthened stainless steel provided by the embodiment of the application can accurately calculate the content of the delta ferrite in the martensite precipitation strengthened stainless steel by the following steps: performing solid solution treatment on the martensite precipitation strengthened stainless steel, performing grinding, polishing and other treatments on the martensite precipitation strengthened stainless steel after the solid solution treatment, performing electrolytic corrosion on the martensite precipitation strengthened stainless steel by using an alkaline solution, and observing and calculating the area ratio of the delta ferrite by using an optical microscope.

[0043] Further, in the embodiment of the application, in step 2, the sample is placed in a muffle furnace at 1040±10℃ for 30±5min, and then the sample is immersed in water for water cooling.

[0044] Further, in the embodiment of the application, in step 3, the mechanical grinding comprises: sequentially using 150#, 320#, 600#, 800# and 2000# sandpaper to perform step-by-step grinding on the sample.

[0045] By performing step-by-step grinding, the damage layer can be eliminated.

[0046] In each step of grinding, the grinding direction is rotated by 90° relative to the grinding direction of the previous step to ensure that the scratches generated in the previous step are completely removed.

[0047] Further, in the embodiment of the application, in step 3, the sample is polished by using silk cloth and diamond polishing agent.

[0048] By polishing the sample by using silk cloth and diamond polishing agent, a mirror surface can be ensured.

[0049] Further, in the embodiment of the application, the NaOH electrolyte uses deionized water as a solvent.

[0050] By using deionized water as a solvent, the introduction of impurity ions can be avoided to cause adverse effects.

[0051] Further, in the embodiment of the application, in steps 3 and 5, the cleaning and drying treatment comprises: using flowing water for flushing, using anhydrous ethanol for wiping after flushing, and using a hair dryer for blowing dry after wiping.

[0052] Further, in the embodiment of the application, the image analysis software is used to calculate the area ratio of the delta ferrite in the photos.

[0053] Specifically, the image analysis software is used to calculate the area ratio of the delta ferrite by using a gray threshold segmentation method.

[0054] Further, in the embodiment of the application, in order to facilitate the above-mentioned treatment and observation, the sample is a square sample with a side length of 20-25mm.

[0055] Optionally, the sample is prepared from the martensite precipitation strengthening stainless steel by sawing or wire cutting.

[0056] Further, in the embodiment of the present application, the martensite precipitation strengthening stainless steel used in the method has the following composition:

[0057] C≤0.07%, Si≤2.0%, Mn≤1.0%, P≤0.03%, S≤0.01%, Cr: 12.0-17.0%, Ni: 3.0-11.0%, Cu: 0-5.0%, Nb: 0-0.5%, Mo: 0-1.5%, Ti: 0-2.0%.

[0058] To make the above technical solutions of the present application clearer, the technical solutions of the present application will be described clearly and completely in combination with the specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments.

[0059] Example 1

[0060] This embodiment 1 is directed to the content detection of δ ferrite in a martensite precipitation strengthening stainless steel forged round steel with a diameter of 180 mm and the following chemical composition:

[0061] C: 0.05%, Si: 0.51%, Mn: 0.63%, P: 0.025%, S: 0.001%, Cr: 15.23%, Ni: 4.85%, Cu: 3.51%, Mo: 0.18%, Nb: 0.23%.

[0062] Step 1, a square sample with a side length of 20 mm is prepared from the forged round steel by wire cutting, and the surface parallel to the axial surface of the forged round steel is marked as the observation surface;

[0063] Step 2, the sample is placed into a muffle furnace heated to 1037℃ and kept for 30 min, then taken out and cooled in a quenching water tank for 20 min, and then taken out;

[0064] Step 3, after the observation surface of the sample is ground step by step using 150#, 320#, 600#, 800# and 2000# sandpaper, the observation surface of the sample is polished using silk cloth and diamond polishing agent, and after polishing, the sample is rinsed using running water, then wiped using anhydrous ethanol, and then dried using a hair dryer;

[0065] Step 4, the dried sample is electrolytic etched using a NaOH electrolyte with a concentration of 14g / 100ml and deionized water as the solvent at a voltage of 6.8V for 35s, and then taken out;

[0066] Step 5, rinse the sample with running water, then wipe with anhydrous ethanol, and finally dry with a hair dryer;

[0067] Step 6, transfer the dried sample to an optical microscope for observation, and select a typical field of view of δ ferrite for photography;

[0068] Step 7, use image analysis software to calculate the area ratio of δ ferrite in the photograph by gray threshold segmentation method, and obtain the content of δ ferrite in the martensite precipitation strengthened stainless steel forged round bar.

[0069] In this embodiment 1, the final calculated content of δ ferrite is 2.09%.

[0070] Example 2

[0071] This embodiment 2 is aimed at detecting the content of δ ferrite in a martensite precipitation strengthened stainless steel forged round bar with a diameter of 120 mm and the following chemical composition:

[0072] C: 0.005%, Si: 0.02%, Mn: 0.02%, P: 0.008%, S: 0.001%, Cr: 12.57%, Ni: 10.74%, Mo: 1.25%, Ti: 1.75%.

[0073] Step 1, use sawing method to prepare a square sample with a side length of 20 mm from the forged round bar, and mark the surface parallel to the axial surface of the forged round bar as the observation surface;

[0074] Step 2, place the sample in a muffle furnace heated to 1042℃ for 31 min, then take it out and cool it in tap water for 15 min, and then take it out;

[0075] Step 3, use 150#, 320#, 600#, 800# and 2000# sandpaper to grind the observation surface of the sample step by step, then use silk cloth and diamond polishing agent to polish the observation surface of the sample, then rinse with running water, wipe with anhydrous ethanol, and finally dry with a hair dryer;

[0076] Step 4, use NaOH electrolyte with a concentration of 14g / 100ml and deionized water as solvent to electrolytic etch the dried sample at a voltage of 7.6V for 40s, and then take it out;

[0077] Step 5, rinse the sample with running water, then wipe with anhydrous ethanol, and finally dry with a hair dryer;

[0078] Step 6, transfer the dried sample to an optical microscope for observation, and select a typical field of view of δ ferrite for photography;

[0079] Step 7, the content of the delta ferrite in the martensite precipitation strengthened stainless steel round bar is calculated by using the image analysis software through the gray threshold segmentation method.

[0080] In this embodiment 2, the final calculated content of the delta ferrite is 0.29%.

[0081] It can be seen that the quantitative detection method of the delta ferrite in the martensite precipitation strengthened stainless steel provided by the embodiment of the present application can accurately calculate the content of the delta ferrite in the martensite precipitation strengthened stainless steel.

[0082] It should be noted that in this paper, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. In addition, "before", "after", "left", "right", "up", "down" in this paper are referred to the placement state shown in the drawings.

[0083] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel, characterized in that: include: Step 1: Prepare a sample from the martensite precipitation-strengthened stainless steel to be tested, and mark the surface of the sample parallel to the axial plane of the martensite precipitation-strengthened stainless steel as an observation surface; Step 2: Place the sample in a 1040±10°C temperature environment for 30±5 minutes, then remove and cool to room temperature. Step 3, mechanically grinding, polishing, cleaning and drying the observation surface of the sample in sequence; Step 4: using a NaOH electrolyte with a concentration of 10 to 20 g / 100 ml, electrolytically corrode the sample at a voltage of 5 to 8 V for 30 to 40 seconds; Step 5, cleaning and drying the sample after electrolytic corrosion; Step 6: Observe the observation surface of the sample through an optical microscope and select a typical field of view of delta ferrite to take a picture; Step 7: Calculate the area ratio of delta ferrite in the photo to determine the content of delta ferrite in the martensite precipitation strengthened stainless steel.

2. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: In step 2, the sample is placed in a muffle furnace at 1040±10° C. for 30±5 minutes, and then immersed in water for water cooling.

3. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: In step 3, the mechanical grinding includes: grinding the sample step by step using 150#, 320#, 600#, 800# and 2000# sandpaper in sequence.

4. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: In step 3, the sample is polished using velvet cloth and diamond polishing agent.

5. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: The NaOH electrolyte uses deionized water as solvent.

6. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: The cleaning and drying process includes: rinsing with running water, wiping with anhydrous ethanol after rinsing, and drying with a hair dryer after wiping.

7. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: Image analysis software was used to calculate the area ratio of delta ferrite in the photographs.

8. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: The sample is a square sample with a side length of 20 to 25 mm.

9. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to claim 1, characterized in that: The specimens were prepared from martensite precipitation strengthened stainless steel by saw cutting or wire cutting.

10. The method for quantitatively detecting delta ferrite in martensite precipitation strengthened stainless steel according to any one of claims 1 to 9, characterized in that: The composition of martensite precipitation strengthened stainless steel is as follows: C≤0.07%, Si≤2.0%, Mn≤1.0%, P≤0.03%, S≤0.01%, Cr: 12.0~17.0%, Ni: 3.0~11.0%, Cu: 0~5.0%, Nb: 0~0.5%, Mo: 0~1.5%, Ti: 0~2.0%.

Images