CN110987991A - Method for counting ultra-fine ferrite phase in austenitic stainless steel welding seam - Google Patents
Method for counting ultra-fine ferrite phase in austenitic stainless steel welding seam Download PDFInfo
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- CN110987991A CN110987991A CN201911129141.2A CN201911129141A CN110987991A CN 110987991 A CN110987991 A CN 110987991A CN 201911129141 A CN201911129141 A CN 201911129141A CN 110987991 A CN110987991 A CN 110987991A
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Abstract
The invention belongs to the field of material tissue analysis, and particularly provides a method for counting an ultrafine ferrite phase in an austenitic stainless steel weld joint, which comprises the following steps: step 1, preparing a welding seam position sample without a deformation disturbance layer on the surface, soaking the sample in a corrosive liquid for 2-5 seconds after mechanical polishing, and then quickly washing and drying the sample by using alcohol, wherein the corrosive liquid comprises the following components: ferric chloride, nitric acid, hydrochloric acid and water; step 2, collecting welding seam tissue information by using an electronic back scattering diffraction method; and 3, analyzing the collected weld joint tissue information. The invention has the following beneficial effects: (1) the welding seam position sample without a deformation disturbance layer on the surface can be simply and rapidly prepared without adopting electrolytic polishing equipment, and corrosive liquid is easy to obtain; (2) the content and the size distribution rule of the superfine delta ferrite phase can be quantitatively counted; (3) the phase morphology, distribution and relative orientation relation of the ultrafine delta ferrite can be observed simultaneously; (4) the method solves the limitation of low resolution of the existing method and improves the detection accuracy.
Description
Technical Field
The invention belongs to the field of material tissue analysis, and particularly relates to a method for counting an ultra-fine ferrite phase in an austenitic stainless steel weld joint.
Background
Austenitic stainless steel has better corrosion resistance, heat resistance, low temperature resistance, good formability and excellent weldability, is an important class of stainless steel series materials, the yield of the austenitic stainless steel accounts for about 70 percent of the total yield of the stainless steel, the heating temperature is overhigh, and delta ferrite is formed under the reasons of overlong retention time in high temperature, chemical composition fluctuation and the like. The quantity and distribution form of delta ferrite are closely related to the impact toughness, and the steel has certain magnetism, thus seriously influencing the application of the steel in special fields such as instruments and the like.
The delta ferrite plays an extremely important role in austenitic stainless steel welds. A certain amount of ferrite is often required to be formed in an austenitic stainless steel welding seam so as to have good plasticity and toughness, prevent the welding seam from generating solidification cracks (hot cracks), remarkably improve the weldability and improve the safety degree of a welding structure; meanwhile, the appropriate content of delta ferrite and distribution form can improve the intergranular corrosion resistance and stress corrosion resistance of the welding joint. However, it is generally desirable to control the ferrite content in the weld to about 5%.
Meanwhile, delta ferrite has a certain negative effect in the weld: for the weldment needing heat treatment at the temperature of more than 600 ℃ after welding or the weldment working at the temperature of 600-850 ℃ for a long time, sigma phase is separated out from delta ferrite at the high temperature, so that weld metal is embrittled; the corrosion resistance of austenite is reduced due to the fact that the content of delta ferrite is too high, electrode potentials of ferrite and the electrode potentials of the austenite are different, and after the quantity of the ferrite exceeds a limit, the pitting corrosion tendency is increased; too high a content of delta ferrite also increases the tendency of hot working to crack. Because the content of delta ferrite has great influence on the welding seam performance of steel, the control requirement on the content of delta ferrite in steel grades is generally required. Therefore, it is important to grasp the measurement method of the δ ferrite content in austenitic stainless steel.
At present, most of patents related to austenitic stainless steel welding relate to welding process methods, and few patents are provided for detection methods of weld structures. The pending patent, "a method for analyzing and detecting the ratio of two phases in a cast structure of duplex stainless steel", application No. 201711137137.1, is applied to the determination of the content of ferrite and austenite phases in the cast structure of duplex stainless steel, generally, the ferrite phase in the cast structure is relatively coarse, non-ultra-fine structure, and is different from the weld structure, and the main right item of the method is mainly described in the step of electrolytic polishing, and the remaining patents related to the analysis of the weld structure or austenite-ferrite phase are the displaying methods under a metallographic microscope such as corrosive, dyeing and the like. In patent 'display method of metallographic structure of austenitic and ferritic dissimilar steel joint' with application number 201610457652.7, it is also mentioned that an electrolytic polishing method is needed when a welded joint structure is observed and a sample is prepared, the electrolytic polishing method needs a specific power supply and search of voltage and current parameters, the controllability of actual operation is poor, and personal safety is threatened when electrolytic voltage is too high.
The method for measuring the ferrite content in the welding line can find 1 relevant standard, namely GB/T1954-2008 'method for measuring the ferrite content of the chromium-nickel austenitic stainless steel welding line', wherein the magnetic method and the metallographic method are mentioned for measurement: by utilizing the magnetic property of ferrite, the content of delta-phase ferrite in austenitic steel is in direct proportion to the ferromagnetism of steel, and a special magnetic measuring instrument can be used for directly measuring and reading the ferrite content; metallographic examination method: the relative amount of the cut by the dividing ruler on the micrometer eyepiece with 100 scales or the 100-dividing eyepiece piece is determined by the secant method under the condition that the microscope magnification is not less than 500 times, and the obtained numerical value is the relative content of the ferrite in the view field or the distribution condition and the occupied area ratio of the delta ferrite in the austenite observed under a metallographic microscope or compared with a standard metallographic picture to detect the approximate content of the delta ferrite.
The existing magnetic method has the defects that the distribution form of delta ferrite cannot be known, and the influence of the delta ferrite on the corrosion resistance and the like cannot be estimated; the existing metallographic detection method refers to a contrast method, the content is roughly determined, and the method depends on the resolution of a metallographic microscope, and at present, the highest resolution of the metallographic microscope is about 400nm, so that the ultra-fine delta ferrite phase which is less than or equal to 300nm in a welding line cannot be clearly observed.
In order to realize quantitative analysis of the ultrafine delta ferrite phase in the weld joint and assist in controlling the process adjustment of the ferrite content, the development of a research on a method for counting the ultrafine ferrite phase in the austenitic stainless steel weld joint is very critical and necessary. At present, no technical report of the similar ultra-fine ferrite phase in the austenitic stainless steel welding seam is found.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam.
The technical scheme of the invention is as follows:
a method for counting the ultra-fine ferrite phase in an austenitic stainless steel welding seam comprises the following steps:
step 1, preparing a welding seam position sample with no deformation disturbance layer on the surface;
step 2, collecting welding seam tissue information by using an electronic back scattering diffraction method;
and 3, analyzing the collected weld joint tissue information.
Preferably, step 1 comprises:
step 1.1, cutting a sample at the position of a welding seam;
step 1.2, grinding a sample: sequentially performing coarse grinding and fine grinding on sandpaper with different granularities of No. 150, No. 300, No. 600 and No. 1200, and cleaning and blow-drying by using alcohol after each piece of sandpaper is ground;
step 1.3, mechanically polishing the sample: polishing the surface to be observed by using a diamond polishing agent with the particle size of 1.5 mu m, cleaning and blow-drying by using alcohol, polishing by using a silicon oxide suspension with the particle size of 30nm for 10-20min, and cleaning and blow-drying by using alcohol;
and step 1.4, soaking the sample in the corrosive liquid for 2-5s, and then quickly washing and drying the sample by using alcohol.
The corrosive liquid comprises the following components: ferric chloride, nitric acid, hydrochloric acid and water, wherein the volume ratio of the nitric acid to the hydrochloric acid to the water is as follows: (3-10): (25-50): (100-150), the mass percent concentration of the ferric chloride is (0.01-0.07) g/ml, and the preparation steps of the corrosive liquid are as follows: mixing nitric acid, hydrochloric acid and water, and adding ferric chloride into the mixed solution.
Preferably, the corrosive liquid comprises the following components: 2-8g of ferric chloride, 3-10ml of nitric acid, 25-50ml of hydrochloric acid and 150ml of water.
Preferably, step 2 comprises:
step 2.1, adhering the sample on a sample support by using conductive adhesive, and fixing the sample support on a pre-tilting table of 70 degrees according to requirements after determining each direction of the sample;
step 2.2, putting the pre-tilt sample stage with the angle of 70 degrees and the sample into a scanning electron microscope;
step 2.3, selecting 10-25KV of accelerating voltage, selecting 5-7 light spot size and selecting 5-20 mm of working distance;
step 2.4, selecting a position for focusing after finding the position of the welding seam;
step 2.5, enabling the electron back scattering diffraction probe to be close to the position of a weld joint to be observed;
step 2.6, selecting fcc (space group 225) austenite phase and bcc (space group 229) ferrite phase in the steel in the crystallography database;
and 2.7, setting unequal step lengths of 20nm-200nm and collecting tissue information in each area.
Preferably, step 3 comprises:
step 3.1, exporting data acquired by electron backscatter diffraction into a Channel 5 processable format ". cpr" file;
3.2, opening a weld joint organization file by Channel 5 software, reducing noise of the data and removing incorrect analysis data points;
step 3.3, establishing a diffraction zone contrast + bcc ferrite phase + phase boundary working area, and forming a bcc ferrite phase distribution diagram based on a specific scanning step length;
step 3.4, clicking a statistics subdirectory under a view directory in software to obtain proportional data of a bcc ferrite phase and an fcc austenite phase based on a specific scanning step length;
step 3.5, clicking a crystal grain detection button, setting a critical angle to be 15 degrees, and obtaining the information characteristics of each crystal grain;
and 3.6, clicking statistical data of the crystal grains, and selecting a bcc ferrite phase to obtain a distribution diagram of the area and percentage of the crystal grains of the bcc ferrite phase based on a specific scanning step length.
Compared with the prior art, the invention has the following beneficial effects:
(1) the welding seam position sample without deformation disturbance layer on the surface can be simply and rapidly prepared without adopting electrolytic polishing equipment, and the corrosive liquid is easy to obtain.
(2) The content and the size distribution rule of the superfine delta ferrite phase can be quantitatively counted;
(3) the phase morphology, distribution and relative orientation relation of the ultrafine delta ferrite can be observed simultaneously;
(4) the problem of low resolution ratio of the existing method is solved, and the detection accuracy is improved.
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Other characteristic objects and advantages of the invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following figures.
FIG. 1 is a schematic layout of an electron back-scattering diffraction analysis system according to the present invention.
FIG. 2 is a distribution diagram of the ultra-fine δ ferrite phase in the weld under 100nm step scanning obtained in example 1 of the present invention.
FIG. 3 is a table showing the ratio of two-phase structures in the weld joint according to the statistics of embodiment 1 of the present invention.
FIG. 4 is a graph showing the size and distribution of the delta ferrite phase in the weld obtained in example 1 of the present invention.
FIG. 5 is an orientation diagram of the delta ferrite phase grains in the weld of example 1 of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam can simultaneously observe and count the form, distribution and content of the ultra-fine ferrite.
Example 1
A method for counting the ultra-fine ferrite phase in an austenitic stainless steel welding seam comprises the following steps:
step 1, preparing a weld joint position sample with a surface without a deformation disturbance layer:
(1) cutting a sample at the position of the welding seam;
(2) grinding a sample: sequentially performing coarse grinding and fine grinding on sandpaper with different granularities of No. 150, No. 300, No. 600 and No. 1200, and cleaning and blow-drying by using alcohol after each piece of sandpaper is ground;
(3) mechanically polishing the sample: polishing the surface to be observed by using a diamond polishing agent with the particle size of 1.5 mu m, cleaning the surface by using alcohol, and blow-drying the surface, polishing the surface by using a silicon oxide suspension with the particle size of 30nm for 10min, and cleaning the surface by using the alcohol and blow-drying the surface;
(4) the sample is soaked in the corrosive liquid for 5s and then is quickly washed by alcohol and dried by blowing, and the corrosive liquid comprises the following components: 5g of ferric chloride, 3ml of nitric acid, 40ml of hydrochloric acid and 150ml of water, and the preparation steps of the corrosive liquid are as follows: mixing nitric acid, hydrochloric acid and water, and adding ferric chloride into the mixed solution.
Step 2, collecting the welding seam tissue information by using an electron back scattering diffraction method:
(1) adhering a sample on a sample support by conductive adhesive, and fixing the sample support on a 70-degree pre-tilting table according to requirements after determining each direction of the sample;
(2) putting a pre-tilt sample stage with the angle of 70 degrees and a sample into a scanning electron microscope;
(3) the accelerating voltage is 20KV, the size of a light spot is 6, and the working distance is 10 mm;
(4) after the position of the welding seam is found, selecting a position for focusing;
(5) the electron back scattering diffraction probe is close to the position of a welding seam to be observed;
(6) selecting fcc (space group 225) austenite phase and bcc (space group 229) ferrite phase in the steel from the crystallographic database;
(7) setting the step length to be 100nm and collecting the tissue information in each area.
Step 3, analyzing the collected weld joint tissue information:
(1) deriving data collected by electron backscatter diffraction into a Channel 5 processable format ". cpr" file;
(2) opening a weld joint organization file by Channel 5 software, reducing noise of data and removing incorrect analysis data points;
(3) establishing a diffraction zone contrast + bcc ferrite phase + phase boundary working area, and forming a bcc ferrite phase distribution diagram based on a specific scanning step length;
(4) clicking a statistics subdirectory under a view directory in software to obtain proportion data of a bcc ferrite phase and an fcc austenite phase based on a specific scanning step;
(5) clicking a grain detection button, setting a critical angle to be 15 degrees, and obtaining the information characteristics of each grain;
(6) and clicking the statistical data of the crystal grains, and selecting the bcc ferrite phase to obtain a distribution diagram of the area and percentage of the crystal grains of the bcc ferrite phase based on a specific scanning step length.
Example 2
A method for counting the ultra-fine ferrite phase in an austenitic stainless steel welding seam comprises the following steps:
step 1, preparing a welding seam position sample with no deformation disturbance layer on the surface;
(1) cutting a sample at the position of the welding seam;
(2) grinding a sample: sequentially performing coarse grinding and fine grinding on sandpaper with different granularities of No. 150, No. 300, No. 600 and No. 1200, and cleaning and blow-drying by using alcohol after each piece of sandpaper is ground;
(3) mechanically polishing the sample: polishing the surface to be observed by using a diamond polishing agent with the particle size of 1.5um, cleaning and blow-drying by using alcohol, polishing by using a silicon oxide suspension with the particle size of 30nm for 20min, and cleaning and blow-drying by using alcohol;
(4) the sample is soaked in the corrosive liquid for 2s and then is quickly washed by alcohol for blow-drying, and the corrosive liquid comprises the following components: 2g of ferric chloride, 5ml of nitric acid, 25ml of hydrochloric acid and 120ml of water, and the preparation steps of the corrosive liquid are as follows: mixing nitric acid, hydrochloric acid and water, and adding ferric chloride into the mixed solution.
Step 2, collecting the welding seam tissue information by using an electron back scattering diffraction method:
(1) adhering a sample on a sample support by conductive adhesive, and fixing the sample support on a 70-degree pre-tilting table according to requirements after determining each direction of the sample;
(2) putting a pre-tilt sample stage with the angle of 70 degrees and a sample into a scanning electron microscope;
(3) the accelerating voltage is 10KV, the size of a light spot is 7, and the working distance is 5 mm;
(4) after the position of the welding seam is found, selecting a position for focusing;
(5) the electron back scattering diffraction probe is close to the position of a welding seam to be observed;
(6) selecting fcc (space group 225) austenite phase and bcc (space group 229) ferrite phase in the steel from the crystallographic database;
(7) setting the step length to be 20nm and collecting the tissue information in each area.
Step 3, analyzing the collected weld joint tissue information:
(1) deriving data collected by electron backscatter diffraction into a Channel 5 processable format ". cpr" file;
(2) opening a weld joint organization file by Channel 5 software, reducing noise of data and removing incorrect analysis data points;
(3) establishing a diffraction zone contrast + bcc ferrite phase + phase boundary working area, and forming a bcc ferrite phase distribution diagram based on a specific scanning step length;
(4) clicking a statistics subdirectory under a view directory in software to obtain proportion data of a bcc ferrite phase and an fcc austenite phase based on a specific scanning step;
(5) clicking a grain detection button, setting a critical angle to be 15 degrees, and obtaining the information characteristics of each grain;
(6) and clicking the statistical data of the crystal grains, and selecting the bcc ferrite phase to obtain a distribution diagram of the area and percentage of the crystal grains of the bcc ferrite phase based on a specific scanning step length.
Example 3
A method for counting the ultra-fine ferrite phase in an austenitic stainless steel welding seam comprises the following steps:
step 1, preparing a welding seam position sample with no deformation disturbance layer on the surface;
(1) cutting a sample at the position of the welding seam;
(2) grinding a sample: sequentially performing coarse grinding and fine grinding on sandpaper with different granularities of No. 150, No. 300, No. 600 and No. 1200, and cleaning and blow-drying by using alcohol after each piece of sandpaper is ground;
(3) mechanically polishing the sample: polishing the surface to be observed by using a diamond polishing agent with the particle size of 1.5um, cleaning and blow-drying by using alcohol, polishing by using a silicon oxide suspension with the particle size of 30nm for 15min, and cleaning and blow-drying by using alcohol;
(4) the sample is soaked in the corrosive liquid for 4s and then is quickly washed by alcohol for blow-drying, and the corrosive liquid comprises the following components: 8g of ferric chloride, 10ml of nitric acid, 50ml of hydrochloric acid and 150ml of water, and the preparation steps of the corrosive liquid are as follows: mixing nitric acid, hydrochloric acid and water, and adding ferric chloride into the mixed solution.
Step 2, collecting the welding seam tissue information by using an electron back scattering diffraction method:
(1) adhering a sample on a sample support by conductive adhesive, and fixing the sample support on a 70-degree pre-tilting table according to requirements after determining each direction of the sample;
(2) putting a pre-tilt sample stage with the angle of 70 degrees and a sample into a scanning electron microscope;
(3) the accelerating voltage is 25KV, the light spot size is 5, and the working distance is 20 mm;
(4) after the position of the welding seam is found, selecting a position for focusing;
(5) the electron back scattering diffraction probe is close to the position of a welding seam to be observed;
(6) selecting fcc (space group 225) austenite phase and bcc (space group 229) ferrite phase in the steel from the crystallographic database;
(7) setting the step length to be 200nm and collecting the tissue information in each area.
Step 3, analyzing the collected weld joint tissue information:
(1) deriving data collected by electron backscatter diffraction into a Channel 5 processable format ". cpr" file;
(2) opening a weld joint organization file by Channel 5 software, reducing noise of data and removing incorrect analysis data points;
(3) establishing a diffraction zone contrast + bcc ferrite phase + phase boundary working area, and forming a bcc ferrite phase distribution diagram based on a specific scanning step length;
(4) clicking a statistics subdirectory under a view directory in software to obtain proportion data of a bcc ferrite phase and an fcc austenite phase based on a specific scanning step;
(5) clicking a grain detection button, setting a critical angle to be 15 degrees, and obtaining the information characteristics of each grain;
(6) and clicking the statistical data of the crystal grains, and selecting the bcc ferrite phase to obtain a distribution diagram of the area and percentage of the crystal grains of the bcc ferrite phase based on a specific scanning step length.
The basic principle of the electron backscattering diffraction analysis method in the scanning electron microscope related to the method is as follows: the basic layout of the analysis system is shown in fig. 1. The sample in the sample chamber is typically tilted 65-70 deg., and the absorption signal is reduced by reducing the path of the backscattered electrons out of the surface to obtain a sufficiently strong backscattered diffraction signal. Incident electron beams act on the surface of a sample, when the incident electron beams enter a certain crystal face and meet Bragg diffraction conditions, Bragg diffraction is generated to generate a chrysanthemum cell band, a three-dimensional pattern consisting of diffraction cones is projected onto a low-light-intensity phosphor screen, the chrysanthemum cell band pattern which is mutually crossed is cut on a two-dimensional screen, the pattern is received by a back CCD camera, processed by an image processor (such as signal amplification, addition and averaging, back-bottom subtraction and the like), collected into a computer by a capture image card, the computer automatically determines the position, the width, the intensity and the inter-band included angle of the chrysanthemum cell band through hough transformation, compares the position, the width, the intensity and the inter-band included angle with theoretical values in a corresponding crystallography library, marks out a corresponding crystal face index and a crystal band axis, and calculates the orientation of a measured crystal grain crystal coordinate system relative to a sample coordinate system.
The shape and the property of the electron back scattering diffraction pattern are related to the crystal structure of a tested sample, each pair of chrysanthemum pool lines corresponds to a group of crystal faces in the crystal, the intersection of the chrysanthemum pool lines represents a crystallographic direction, and the chrysanthemum pool lines formed by different crystal faces form an electron back scattering pattern. Each crystal has its specific structural parameters and can react in an electron back-scattered diffraction pattern, with different materials producing different diffraction patterns. It is therefore possible to distinguish between phases of similar chemical composition, such as the austenite phase (fcc structure) and the ferrite phase (bcc structure) in steel.
The method according to the invention is implemented to obtain the form and distribution map of the ultra-fine ferrite in the weld seam under the scanning step length of 100nm, wherein the ferrite is sketched by a coil, as shown in figure 2. Most of the ferrite phase is distributed along the grain boundaries, and according to literature reports, this distribution will improve the intergranular corrosion resistance of austenitic stainless steels, since the intergranular ferrite blocks the grain boundary channels and extends the total channel length. The ferrite phase in the crystal is small in relative size, and is even up to the nanometer level.
Data analysis is performed on a single observation area, and the two-phase ratio of the ferrite phase and the austenite phase in a local area in the welding seam is obtained, and is shown in figure 3. Since the ferrite size is small, the overall occupation ratio is small even if the distribution range is large. After the average content is obtained in a plurality of areas, the process adjustment and design of ferrite content control can be guided.
FIG. 4 shows the size and distribution of ferrite phases in a weld bead at a scanning step of 100nm obtained after the method according to the present invention has been carried out. It can be seen that most of the ferrite phase in the weld has a grain area of less than 1 μm2Belongs to ultra-fine ferrite, and also has some ferrite phases with grain area larger than 4 μm.
Fig. 5 is a schematic illustration of the grain orientation of a single ferrite phase obtained after the method according to the invention has been carried out. The method can not only count the content of the ferrite, but also count the orientation distribution condition of the ferrite crystal grains, and analyze the texture composition of the ferrite phase by measuring the orientation of single ferrite crystal grains and adding volume weight according to the principle.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (7)
1. A method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam is characterized in that: the method comprises the following steps:
step 1, preparing a welding seam position sample with no deformation disturbance layer on the surface;
step 2, collecting welding seam tissue information by using an electronic back scattering diffraction method;
and 3, analyzing the collected weld joint tissue information.
2. The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam according to claim 1, wherein the method comprises the following steps: the step 1 comprises the following steps:
step 1.1, cutting a sample at the position of a welding seam;
step 1.2, grinding a sample: sequentially performing coarse grinding and fine grinding on sandpaper with different granularities of No. 150, No. 300, No. 600 and No. 1200, and cleaning and blow-drying by using alcohol after each piece of sandpaper is ground;
step 1.3, mechanically polishing the sample: polishing the surface to be observed by using a diamond polishing agent with the particle size of 1.5 mu m, cleaning and blow-drying by using alcohol, polishing by using a silicon oxide suspension with the particle size of 30nm for 10-20min, and cleaning and blow-drying by using alcohol;
and step 1.4, soaking the sample in the corrosive liquid for 2-5s, and then quickly washing and drying the sample by using alcohol.
3. The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam according to claim 2, wherein the method comprises the following steps: the corrosive liquid comprises the following components: ferric chloride, nitric acid, hydrochloric acid and water, wherein the volume ratio of the nitric acid to the hydrochloric acid to the water is as follows: (3-10): (25-50): (100-150), the mass percent concentration of the ferric chloride is (0.01-0.07) g/ml.
4. The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam according to claim 3, wherein the method comprises the following steps: the corrosive liquid comprises the following components: 2-8g of ferric chloride, 3-10ml of nitric acid, 25-50ml of hydrochloric acid and 150ml of water.
5. The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam according to the claim 3 or 4, characterized in that: the preparation steps of the corrosive liquid are as follows: mixing nitric acid, hydrochloric acid and water, and adding ferric chloride into the mixed solution.
6. The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam according to claim 1, wherein the method comprises the following steps: the step 2 comprises the following steps:
step 2.1, adhering the sample on a sample support by using conductive adhesive, and fixing the sample support on a pre-tilting table of 70 degrees according to requirements after determining each direction of the sample;
step 2.2, putting the pre-tilt sample stage with the angle of 70 degrees and the sample into a scanning electron microscope;
step 2.3, selecting 10-25KV of accelerating voltage, selecting 5-7 light spot size and selecting 5-20 mm of working distance;
step 2.4, selecting a position for focusing after finding the position of the welding seam;
step 2.5, enabling the electron back scattering diffraction probe to be close to the position of a weld joint to be observed;
step 2.6, selecting fcc austenite phase and bcc ferrite phase in the steel from the crystallography database;
and 2.7, setting unequal step lengths of 20nm-200nm and collecting tissue information in each area.
7. The method for counting the ultra-fine ferrite phase in the austenitic stainless steel welding seam according to claim 1, wherein the method comprises the following steps: the step 3 comprises the following steps:
step 3.1, exporting data acquired by electron backscatter diffraction into a Channel 5 processable format ". cpr" file;
3.2, opening a weld joint organization file by Channel 5 software, reducing noise of the data and removing incorrect analysis data points;
step 3.3, establishing a diffraction zone contrast + bcc ferrite phase + phase boundary working area, and forming a bcc ferrite phase distribution diagram based on a specific scanning step length;
step 3.4, clicking a statistics subdirectory under a view directory in software to obtain proportional data of a bcc ferrite phase and an fcc austenite phase based on a specific scanning step length;
step 3.5, clicking a crystal grain detection button, setting a critical angle to be 15 degrees, and obtaining the information characteristics of each crystal grain;
and 3.6, clicking statistical data of the crystal grains, and selecting a bcc ferrite phase to obtain a distribution diagram of the area and percentage of the crystal grains of the bcc ferrite phase based on a specific scanning step length.
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