CN112129755B - Method for detecting martensite content in high-strength dual-phase steel - Google Patents
Method for detecting martensite content in high-strength dual-phase steel Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/32—Polishing; Etching
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- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
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- G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
- G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
- G01N23/2252—Measuring emitted X-rays, e.g. electron probe microanalysis [EPMA]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
- G01N2001/2866—Grinding or homogeneising
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N2021/8477—Investigating crystals, e.g. liquid crystals
Abstract
The invention discloses a method for detecting the martensite content in high-strength dual-phase steel, and belongs to the technical field of physical analysis of steel materials. It comprises the following steps: 1) taking a sample to be analyzed and carrying out low-temperature tempering heat treatment; 2) preparing a metallographic sample: preparing a metallographic sample from the sample prepared in the step 1) according to a corresponding standard, and then grinding, thinning and polishing until a polished surface has no stress; 3) erosion of the sample: placing the sample prepared in the step 2) into an etchant for processing until the martensite island structure boundary and the ferrite grain boundary in the sample are displayed; 4) image acquisition and processing: acquiring different view field pictures of the sample prepared in the step 3) by adopting a metallographic microscope, further carrying out binary segmentation processing and analysis on the pictures to obtain the martensite content value in the sample, and analyzing the distribution of martensite island elements by using an electronic probe. The detection method realizes quantitative analysis of the martensite content in the high-strength-level dual-phase steel on the premise of not using a Lepera reagent.
Description
The invention relates to detection of a tissue structure in bidirectional steel, belongs to the technical field of physical analysis of steel materials, and particularly relates to a method for detecting the martensite content in high-strength dual-phase steel.
Background
The dual phase steel is abbreviated as DP steel and refers to a steel material composed of a ferrite and martensite two-phase structure. Martensite in steel is a main influence factor for improving the strength of the steel, and the martensite is distributed in an island shape in a steel matrix; because of the existence of the dual-phase structure, the dual-phase steel has low bending strength ratio and good strength and plasticity, the martensite content is one of important indexes for measuring the quality of the steel, and factors such as the form, the size, the distribution and the like of the martensite content have specific influence on the performance of the dual-phase steel.
With the progress of production technology and the improvement of market demand, the strength grade of the dual-phase steel gradually transits from the original 450MPa (DP450) grade and 590MPa (DP590) grade to the high strength grade such as 780MPa (DP780) grade and 980MPa (DP980) grade, and the DP1180 with the strength grade of more than 1000MPa also gradually starts to be applied commercially; the strength level is improved, so that the size levels of phase-ferrite and martensite islands in the dual-phase steel structure are reduced, and the size of the martensite island is reduced from about 5 mu m of 450MPa level to about 1-2 mu m of 780MPa level; the traditional method for measuring the martensite content in the dual-phase steel adopts a coloring erosion method, the method has better resolution ratio on a martensite island with larger size, but for the dual-phase steel with high strength grade, the effect of the coloring method is not ideal because the martensite size is smaller, and simultaneously, the influence of a grain boundary factor caused by the reduction of the martensite size is more prominent. How to utilize the existing analytical equipment to carry out quantitative determination on the martensite island content in the high-strength-level dual-phase steel quickly and accurately becomes the main point of the patent.
Patent application No. CN200910062704.0 discloses a quantitative determination method of martensite in dual-phase steel. The method comprises the following steps: preparing aqueous solution A with the concentration of 1.5-3% by mass by using sodium metabisulfite and water; preparing picric acid and alcohol into a solution B with the concentration of 2-3.8% in percentage by mass; mixing the aqueous solution A and the solution B according to the volume ratio of 1:1 and uniformly stirring; placing the dual-phase steel sample into the prepared etching agent, taking out the dual-phase steel sample after the surface of the sample is blue, wherein the etching environment temperature is 10-30 ℃; observing under a metallographic microscope provided with a color camera; and (4) performing determination by using metallographic quantitative analysis software. The invention is characterized in that each phase structure in the dual-phase steel presents different colors, the outline is clear, the level is clear, and the identification is easy; the method can effectively perform qualitative and quantitative analysis on the tissues of each phase, has high accuracy of quantitative results, and plays an important role in production inspection and basic research. However, the Lepera reagent, namely a mixed solution of a sodium metabisulfite solution and a picric acid solution, is prepared by mixing a 10g/L sodium metabisulfite solution and a 40g/L picric acid ethanol solution according to a ratio of 1:1, and the erosion time is 1-30 seconds. After reasonable erosion by the Lepera reagent, the martensite islands are white, the ferrite is black, and the martensite islands and the ferrite can be effectively distinguished and calculated by utilizing metallographic analysis software or other image processing software to obtain the martensite content of the dual-phase steel. The Lepera reagent corrosion method belongs to the category of color metallographic phase, each phase is displayed by forming a layer of coloring film on the surface of a sample, the method has a good coloring corrosion effect on a large-size martensite island in low-strength dual-phase steel, but the method has high requirements on the quality of a polished surface of the sample, has a strict requirement on corrosion conditions, and has influence on operation due to weather temperature, so that only a person with skilled operation experience can well control the coloring degree, otherwise, the method is easy to fail and is not easy to standardize; meanwhile, picric acid has toxicity and explosiveness, belongs to a control chemical reagent, and is relatively inconvenient for some colleges and universities or enterprises to obtain the picric acid reagent, and the waste picric acid needs a strict treatment mode or pollutes the environment.
Patent application No. CN201310674981.3 discloses a quantitative determination method for massive martensite in low carbon steel, which comprises the following steps performed in sequence: A. cutting low-carbon steel containing massive martensite structures into samples to be tested; B. placing the sample to be tested in a heat treatment furnace, heating to 200-650 ℃, preserving heat for more than 30 minutes, and cooling the sample to be tested in the furnace or in the air to room temperature; C. grinding and polishing the heat-treated sample to be measured to prepare a metallographic sample, corroding the surface to be measured of the metallographic sample by adopting a nitric acid-alcohol solution with the mass concentration of 1-4%, cleaning and drying the metallographic sample; D. and acquiring a surface image of the to-be-measured surface of the metallographic sample through image acquisition equipment, analyzing the surface image by adopting metallographic image analysis software, and calculating to obtain the content of the massive martensite in the to-be-measured sample. The method of the invention can be used for uniformly, conveniently, efficiently and accurately measuring the content of the massive martensite and ensuring the reliability of measured data. The method has the same good effect on the dual-phase steel with lower strength level, at the moment, the size of the martensite island is larger, the influence of the grain boundary is relatively small, but the complete structure form is corroded by the later stage, partial grain boundary is introduced more or less in the image processing process, and the error of the analysis result is caused; and the martensite is decomposed by heat treatment, the state of the original structure cannot be reproduced, the original state cannot be analyzed and further analysis cannot be carried out, and certain limitations are also provided.
The patent with the application number of CN200910053846.0 discloses a method for distinguishing martensite in as-cast ferritic stainless steel and calculating the proportion of two phases of the as-cast ferritic stainless steel, which can accurately and quickly quantitatively calculate the martensite content in the annealed ferritic stainless steel by the steps of cutting a sample, grinding, electropolishing, cleaning and drying, EBSD analysis, selecting crystal grains, adopting an image quality diagram by analysis software, adding grid lines by a metallographic microscope, repeatedly selecting areas to calculate the martensite content and obtaining an average value. The invention solves the technical problems of difficult resolution of ferrite and martensite in the annealed ferrite stainless steel and difficult quantitative calculation. Meanwhile, the technology can be widely applied to quantitative calculation of two-phase proportion with similar crystal structure and different internal stress. The EBSD uses an electron back scattering diffraction method to determine the lattice structure of a sample so as to obtain different phase contents, but the diffraction method is not very ideal for distinguishing martensite from ferrite, because the martensite and the ferrite both belong to alpha-Fe structures and have the same lattice structure, the martensite content is obtained only by a later software correction method, the analysis resolution and the accuracy are limited, and the EBSD equipment belongs to large-scale analysis equipment, is expensive, is not owned by all college enterprises, and is not easy to popularize.
Therefore, an analysis device capable of rapidly and accurately quantitatively determining the martensite island content in the high-strength grade dual-phase steel is needed.
Disclosure of Invention
In order to solve the technical problems, the invention discloses a method for detecting the martensite content in high-strength dual-phase steel, which can quickly and effectively detect the martensite content in high-strength dual-phase steel under the condition of not changing the martensite structure and provides an important standard for judging the performance of the dual-phase steel.
In order to achieve the aim, the invention discloses a method for detecting the martensite content in high-strength dual-phase steel, which comprises the following steps:
1) taking a sample to be analyzed and carrying out low-temperature tempering heat treatment;
2) preparing a metallographic sample: preparing a metallographic sample from the sample prepared in the step 1) according to a corresponding standard, and then grinding, thinning and polishing until a polished surface has no stress;
3) erosion of the sample: placing the sample prepared in the step 2) into an etchant for processing until the martensite island structure boundary and the ferrite grain boundary in the sample are displayed; the aggressive agent mainly comprises a mixture consisting of nitric acid, ferric chloride, ethanol and hexamethylenetetramine;
4) image acquisition and processing: acquiring different view field pictures of the sample prepared in the step 3) by adopting a metallographic microscope, further carrying out binary segmentation processing and analysis on the pictures to obtain a martensite content value in the sample, and analyzing the martensite island element distribution by using an electronic probe to obtain martensite island size, high-power morphology and element distribution conditions.
Further, in the step 1), the sample to be analyzed is placed in a heat treatment furnace, the heat treatment temperature is controlled to be 150-300 ℃, and after treatment for 10-30 min, the sample is taken out for water quenching and cooling.
Further, in the step 1), the heat treatment is carried out in a manner of entering a furnace at a warm temperature, and the protective atmosphere is N2Or H2。
Further, the preparation process of the etchant in the step 3) is as follows:
slowly adding nitric acid into an ethanol solution, uniformly mixing to obtain a mixed solution, adding ferric chloride and a corrosion inhibitor, wherein the volume ratio of the nitric acid to the ethanol solution is (0.5-2) to (99.5-98), the adding amount of the ferric chloride is 0.1-0.3 g per 100mL of the mixed solution, and the adding amount of the corrosion inhibitor accounts for 3-6% of the volume percentage of the mixed solution.
Further, in the step 3), the sample prepared in the step 2) is placed in an etchant for processing for 5-20 s.
Further, after the erosion is finished, cleaning and blow-drying by using alcohol.
Further, in the step 2), the polishing comprises multi-pass polishing by using a diamond suspension and a silica suspension, or multi-pass polishing by using a diamond suspension and etching by using a nitric alcohol solution.
Further, when the diamond suspension and/or the silicon dioxide suspension are used for polishing, polishing treatment is carried out from the suspension with large particle size to the suspension with small particle size from front to back.
Furthermore, the grinding force of a single sample is controlled to be 5-15N during polishing treatment, and the time is controlled to be 60-150 s.
Further, in the step 2), the grinding and thinning are performed manually or automatically, grinding discs with the mesh number from small to large are used for processing in sequence, the grinding force of a single sample is controlled to be 10-25N, and the grinding time is controlled to be 60-90 s.
Has the advantages that:
the detection method designed by the invention overcomes the defects of the conventional quantitative analysis method for martensite, prepares and analyzes the quantitative analysis sample for the martensite in the high-strength-level dual-phase steel under the condition of not using a Lepera reagent for coloring and corroding, retains the information of the body characteristics of the martensite in the sample, and effectively solves the difficulty in preparing the quantitative analysis sample for the martensite. Meanwhile, martensite is analyzed by combining with related image analysis software and an electronic probe, and a new analysis method and thought are provided for researching the content, distribution, size and element composition of martensite in the high-strength-level dual-phase steel by combining with related production processes.
Drawings
FIG. 1 is a field of view image of a sample taken using a metallographic microscope;
FIG. 2 is a diagram illustrating the acquisition of a binary segmentation image with a martensite network and matrix segmentation of the sample of FIG. 1 using image analysis software;
FIG. 3 is a test chart of the martensite content in FIG. 1;
FIG. 4 is a secondary electron phase morphology of the sample of FIG. 1;
FIG. 5 is a plot of elemental silicon in a steel substrate;
FIG. 6 is a distribution pattern of elemental molybdenum in a steel substrate;
FIG. 7 is a plot of elemental manganese in a steel substrate;
fig. 8 is a plot of elemental chromium in a steel substrate.
Detailed Description
The invention provides a method for detecting the content of martensite in high-strength dual-phase steel, aiming at solving the technical problem that the existing detection and analysis means for the content of martensite islands in high-strength dual-phase steel has relevant defects.
The detection method adopts the following instruments and types:
box muffle furnace: ZDF-2.5-10;
grinding a sample machine: struers LaboSystem;
an optical microscope: OLMPUS GX 71;
image processing software: sisc IAS v 8;
electron probe island jin: EMPA 1720.
It comprises the following steps:
1) taking a sample to be analyzed, and carrying out low-temperature tempering heat treatment: specifically, a sample to be analyzed is cut into block samples with required sizes, such as length multiplied by width multiplied by (100-200 mm), and then the block samples are put into a heat treatment furnace for low-temperature heat treatment2Or H2And the temperature is controlled to be 150-300 ℃, and the heating time is 10-up toAnd (3) after heating is finished, putting the sample into water, quenching with water, cooling, and drying for later use. The invention adopts a low-temperature tempering mode to separate out the carbon element part in the martensite in the dual-phase steel in the form of particle-shaped carbide, and because the treatment temperature is lower and the heat treatment time is shorter, the martensite can not be decomposed into pearlite or other structures, the shape of the martensite can not be changed, and the ferrite crystal grains can not grow up at low temperature.
2) Preparing a metallographic sample: preparing a metallographic sample from the sample prepared in the step 1) according to a corresponding standard, and then grinding, thinning and polishing until a polished surface has no stress;
specifically, the invention selects the standard inspection method according to GB/T13298-2015 to carry out sampling cutting, inlaying and the like on the sample prepared in the step 1). The grinding thinning comprises automatic sample grinding equipment or manual sample grinding, the automatic sample grinding equipment is preferably adopted, grinding discs with the mesh numbers from small to large are sequentially used for processing, the grinding force of a single sample is controlled to be 10-25N, and the grinding time is 60-90 s. For example, 200-mesh, 500-mesh and 1000-mesh diamond grinding discs are sequentially used for grinding, and the rotating speed of the diamond grinding discs is controlled to be 100-200 r/min, or 280-mesh, 400-mesh, 800-mesh and 1200-mesh sand paper is sequentially used for grinding by using a manual grinding and polishing mode.
And then carrying out multi-pass polishing by using the diamond suspension and the silicon dioxide suspension, or carrying out multi-pass polishing by using the diamond suspension and the etching by using the nitric alcohol solution. When the diamond suspension and/or the silicon dioxide suspension are used for polishing, polishing treatment is carried out from the suspension with large particle size to the suspension with small particle size from front to back. And the grinding force of a single sample is controlled to be 5-15N during polishing treatment, and the time is controlled to be 60-150 s. For example, the sample was polished with a diamond suspension of 9 μm, 3 μm and 1 μm and a silica suspension in this order. Or polishing with 2.5 μm diamond suspension for 60-90 s, and eroding with 3% nitric acid alcohol to show internal two-phase structure. And polishing at least 2 times until internal stress caused by sample preparation is effectively removed, so that the internal structure of the sample can better present the body characteristics.
3) Erosion of the sample: placing the sample prepared in the step 2) into an etchant for processing until the martensite island structure boundary and the ferrite grain boundary in the sample are displayed; the aggressive agent mainly comprises a mixture consisting of nitric acid, ferric chloride, ethanol and hexamethylene tetramine;
the preparation process of the destructive agent is as follows:
slowly adding nitric acid into an ethanol solution, uniformly mixing to obtain a mixed solution, adding ferric chloride and a corrosion inhibitor, wherein the volume ratio of the nitric acid to the ethanol solution is (0.5-2) to (99.5-98), the adding amount of the ferric chloride is 0.1-0.3 g per 100mL of the mixed solution, and the adding amount of the corrosion inhibitor accounts for 3-6% of the volume percentage of the mixed solution. The amount added here is preferably volume.
The nitric acid adopted is a commercially available analytical reagent;
the ethanol solution used was also a commercially available analytical reagent.
And (3) generally, treating the sample prepared in the step 2) in an etchant for 5-20 s, after the etching is finished, cleaning and drying the sample by using alcohol, and observing and judging the etching degree by using a metallographic microscope, wherein the judgment standard is that the martensite island structure boundary in the dual-phase steel is shown and the ferrite grain boundary is not shown. According to the invention, the ferric nitrate chloride alcoholic solution with low concentration matched with the corrosion inhibitor is selected, so that the corrosion of ferrite in steel is slowed down, the corrosion rate of martensite is accelerated due to carbide precipitation during heat treatment, the ferrite is preferentially corroded before appearing, therefore, the corroded tissue only comprises the contour boundary of martensite, the contour of the ferrite boundary is not appeared, and the accuracy of subsequent analysis is favorably improved.
4) Image acquisition and processing: acquiring different view field pictures of the sample prepared in the step 3) by adopting a metallographic microscope, further carrying out binary segmentation processing and analysis on the pictures to obtain a martensite content value in the sample, and analyzing the martensite island element distribution by using an electronic probe to obtain martensite island size, high-power morphology and element distribution conditions.
The high-strength dual-phase steel selected by the invention comprises dual-phase steel with the grade above 780MPa and 780MPa, and as the size of the martensite with the high-strength grade is correspondingly reduced along with the increase of the strength, a high-power optical microscope is required to obtain an image, but the area is smaller along with the increase of the magnification, the content measurement error is increased, so that the acquisition requirement of the area is more when the magnification is higher, and the error is reduced, therefore, the invention selects 500-time or 1000-time optical lenses of the metallographic microscope to acquire the image, can adopt a yellow optical filter, selects a manual exposure mode, sets ISO as 50-100, acquires 3-5 pictures at different parts of a sample at 500 times, and acquires 6-10 pictures at 1000 times; a typical site of uniform internal tissue sampling of the specimen is usually selected. If imaging is influenced by excessive light in a field of view due to the fact that the martensite island is fine and the magnification factor is too high, 3-5 pictures can be shot in the same field of view for stacking processing, the pictures shot in the same field of view are led in by using image processing software for stacking processing, and a microscopic image with enhanced imaging quality can be obtained. Wherein 3-5 areas are sampled at 500 times, and 6-8 areas are sampled at 1000 times; when the multiple is higher, the obtained image is darker, the imaging quality is reduced, the resolution of post-image processing is reduced, and the error is increased, so that a plurality of high-power pictures are processed in an image stacking mode to obtain an image with higher resolution.
The martensite content in a sample is measured by obtaining the martensite content value of each field and averaging. And further obtaining the size, the high power morphology and the element distribution of the martensite island, further adopting an electronic probe to analyze the element distribution of the martensite island, carrying out quantitative analysis according to GB/T19500-containing 2004 general rules of quantitative analysis methods of electronic probes and GB/T15616-containing 2008-containing quantitative analysis methods of electronic probes of metals and alloys, further adopting the electronic probe to scan and analyze the wave normal surface of the elements in the martensite, obtaining the element distribution condition in the martensite, obtaining semi-quantitative element distribution and visually showing the element state in the martensite. Through the analysis, the content, distribution and size of martensite in the high-strength-level dual-phase steel can be effectively analyzed, the martensite element in the high-strength-level dual-phase steel is quantitatively analyzed, and accurate determination and accurate component analysis of the martensite content are realized.
For a better explanation of the invention, the following detailed description is given with reference to specific examples:
the embodiment discloses a method for determining and analyzing the content of martensite in 780 MPa-grade high-strength dual-phase steel, which comprises the following steps:
1. cutting a cold-rolled sheet sample into 200mm × 200mm × 2mm block-shaped samples, placing the samples in a muffle furnace for heat treatment at 270 ℃, heating the samples in the furnace for 20min until the temperature reaches the temperature, and keeping the temperature in the furnace under the protection atmosphere of N2And after heating, cooling by using water quenching, cleaning and blow-drying.
2. Cutting the sample subjected to heat treatment into a plurality of small blocks by using a metallographic cutting machine for embedding; grinding and thinning by using 200-mesh, 500-mesh and 1000-mesh diamond grinding disks in sequence, wherein the rotating speed of a sample grinding machine is 200r/min, the grinding force is single sample 20N, and the grinding time of each pass is 120 s; and then polishing the sample by using diamond suspension liquid and silicon dioxide suspension liquid with the granularity of 9 mu m, 3 mu m and 1 mu m in sequence, wherein the rotating speed is 150r/min, the grinding force is 15N for a single sample, and the grinding time is 120s per pass.
3. Taking one 500mL beaker, measuring 297mL of ethanol by using a measuring cylinder, pouring 3mL of nitric acid into the beaker, and adding 0.6g of FeCl3Stirring uniformly by using a glass rod; 15mL of hexamethylenetetramine are then metered in and added using a pipette and stirred homogeneously. The prepared solution is put into a glass bottle to be sealed and kept stand for 1h to avoid volatilization.
4. And (3) placing the prepared sample in the prepared solution for erosion for 10s, and cleaning and drying the sample by using alcohol for later use.
5. The shot picture is observed by using a metallographic microscope, the magnification is 500 times, the manual exposure mode is adopted, the ISO is set to be 50, the exposure time is 1/2s, three different fields are obtained, and fig. 1 is an image of one field, so that only martensite islands are shown, and no ferrite grain boundary is shown. Using image analysis software to perform binary segmentation to obtain a binary segmentation image with a martensite network and a matrix segmentation, as shown in fig. 2, further performing image analysis to obtain the martensite percentage of 37.3% in fig. 1, and performing binary segmentation and image analysis to the other two field images to obtain the martensite percentages of 36.45% and 38.52%, and taking the average of the martensite percentages of the two fields to obtain the martensite content of 37.4% in the steel, as shown in the test report shown in fig. 3.
6. The distribution of martensite elements in the dual-phase steel is subjected to element bopp analysis by using an electronic probe, wherein fig. 4 shows the secondary electron phase morphology of an analysis area selected when the electronic probe is used for analysis in the embodiment of the present invention, which has a corresponding relationship with fig. 5 to 8, and is shown in fig. 5, 6, 7 and 8, which shows that only Mn element in a martensite island is segregated, and other elements, such as Cr, Mo, Si, and the like, are uniformly distributed in a steel matrix without obvious segregation phenomenon.
Based on the quantitative analysis of martensite in 780MPa grade high-strength dual-phase steel, the martensite is subjected to low-temperature short-time heat treatment, mechanical grinding and polishing, and is corroded by matching with a new corrosion solution, martensite island boundaries are shown on the premise that ferrite grain boundaries are not shown, so that the martensite floats on the surface of a prepared sample, the martensite content is analyzed and determined by adopting an optical microscope and image processing software, the martensite form and the component distribution thereof are obtained, the tissue content is obtained, and a new research idea is provided for researching the strengthening mechanism, the strength and plasticity matching relationship of the high-strength grade dual-phase steel.
The above examples are merely preferred examples and are not intended to limit the embodiments of the present invention. In addition to the above embodiments, the present invention has other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (9)
1. A method for detecting the martensite content in high-strength dual-phase steel is characterized by comprising the following steps:
1) taking a sample to be analyzed and carrying out low-temperature tempering heat treatment;
2) preparing a metallographic sample: preparing a metallographic sample from the sample prepared in the step 1) according to a corresponding standard, and then grinding, thinning and polishing until a polished surface has no stress;
3) erosion of the sample: placing the sample prepared in the step 2) into an etchant for processing until the martensite island structure boundary and the ferrite grain boundary in the sample are displayed; the aggressive agent mainly comprises a mixture consisting of nitric acid, ferric chloride, ethanol and hexamethylenetetramine; and the preparation process of the etching agent is as follows:
slowly adding nitric acid into an ethanol solution, uniformly mixing to obtain a mixed solution, and adding ferric chloride and hexamethylenetetramine, wherein the volume ratio of the nitric acid to the ethanol solution is (0.5-2) to (99.5-98), the adding amount of the ferric chloride is 0.1-0.3 g per 100mL of the mixed solution, and the adding amount of the hexamethylenetetramine accounts for 3-6% of the volume percentage of the mixed solution;
4) image acquisition and processing: acquiring different view field pictures of the sample prepared in the step 3) by adopting a metallographic microscope, further carrying out binary segmentation processing and analysis on the pictures to obtain a martensite content value in the sample, and analyzing the martensite island element distribution by using an electronic probe to obtain martensite island size, high-power morphology and element distribution conditions.
2. The method for detecting the martensite content in the high-strength dual-phase steel according to claim 1, wherein in the step 1), the sample to be analyzed is placed in a heat treatment furnace, the heat treatment temperature is controlled to be 150-300 ℃, and after treatment for 10-30 min, the sample is taken out for water quenching and cooling.
3. The method according to claim 2, wherein in step 1), the heat treatment is performed in a warm-in-furnace manner under a protective atmosphere of N2Or H2。
4. The method for detecting the martensite content in the high-strength dual-phase steel according to claim 1, wherein in the step 3), the sample obtained in the step 2) is taken and placed in an etchant for treatment for 5-20 s.
5. The method for detecting the martensite content in the high-strength dual-phase steel according to any one of claims 1 to 4, wherein after the completion of the erosion, the steel is cleaned and blown dry by using alcohol.
6. The method for detecting the martensite content in the high-strength dual-phase steel according to claim 5, wherein in the step 2), the polishing comprises multi-pass polishing by using a diamond suspension and a silica suspension, or multi-pass polishing by using a diamond suspension and etching by using a nitric alcohol solution.
7. The method as claimed in claim 6, wherein the polishing is performed sequentially from a suspension having a large particle size to a suspension having a small particle size from the front to the rear when the diamond suspension and/or the silica suspension is used for polishing.
8. The method for detecting the martensite content in the high-strength dual-phase steel according to claim 7, wherein the grinding force of a single sample is controlled to be 5-15N during polishing treatment, and the time is controlled to be 60-150 s.
9. The method for detecting the martensite content in the high-strength dual-phase steel according to claim 1, 2, 3, 4, 6, 7 or 8, wherein in the step 2), the grinding and thinning are performed manually or automatically, grinding discs with the meshes from small to large are used for processing in sequence, the grinding force of a single sample is controlled to be 10-25N, and the grinding time is controlled to be 60-90 s.
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