CN113740131B - Grain boundary display method of bainitic steel - Google Patents
Grain boundary display method of bainitic steel Download PDFInfo
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- CN113740131B CN113740131B CN202111042026.9A CN202111042026A CN113740131B CN 113740131 B CN113740131 B CN 113740131B CN 202111042026 A CN202111042026 A CN 202111042026A CN 113740131 B CN113740131 B CN 113740131B
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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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F1/00—Etching metallic material by chemical means
- C23F1/10—Etching compositions
- C23F1/14—Aqueous compositions
- C23F1/16—Acidic compositions
- C23F1/28—Acidic compositions for etching iron group metals
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention provides a grain boundary display method of bainitic steel, which comprises the following steps: a) Heat treatment is carried out on the bainitic steel sample, the temperature of the heat treatment is 350-400 ℃, the heat preservation time is 0.5-1.5 h, and then cooling is carried out; b) Grinding and polishing the sample obtained in the step A) to obtain a metallographic sample, and corroding the metallographic sample by adopting a saturated picric acid aqueous solution; c) And acquiring grain boundary information of the corroded metallographic specimen through image acquisition software. The method and the device corrode the bainitic steel tempered at medium temperature through the saturated aqueous solution of picric acid, so that actual crystal grains and crystal boundaries of the sample can be clearly displayed.
Description
Technical Field
The invention relates to the technical field of physical inspection of metal materials, in particular to a grain boundary display method of a bainite steel rail.
Background
With the development of railways to high speed and heavy load, higher requirements are put on the performance of steel rails, and under the existing technical conditions, the strength and the wear resistance of the pearlitic steel rails are difficult to further improve. The bainite steel rail has the characteristics of good toughness, high fatigue strength, good wear resistance and the like, and gradually becomes the research focus of research institutions and steel rail production enterprises.
The bainitic steel rail is mainly bainitic/martensitic complex phase steel, carbide-free bainitic steel and the like, cementite in a bainitic structure is likely to become a crack initiation source, precipitation of carbide is required to be inhibited through alloy element Si, and the cementite is replaced by carbon-rich residual austenite in the structure transformation process to form a special bainitic steel rail structure. JinJiyongetalshowthattemperingat350℃leadsthemicrostructuretomainlycompriseM-Aislands,lathbainiticferrite,residualausteniteandaverysmallamountofferritewithdifferentdimensions,whilebainiteinthemicrostructureisobviouslyprecipitatedwithcarbideat450℃,andtheresidualausteniteisdecomposedwiththeriseoftemperingtemperaturetohaveadverseeffectsonthemechanicalpropertiesofmaterials,sothatthestabilityofthestructureandthepropertiesisensuredbylow-temperaturetemperingatpresentinindustry,butcarbidecanbeprecipitatedonaustenitegrainboundariesbyreasonablyadoptingintermediate-temperaturetempering,andthebainitegrainboundariescanbeclearlydisplayedbyadoptingaspecificcorrosionmethod.
The display of austenite grain boundaries at present includes a carburization method, a simulated carburization method, a ferrite network method, an oxidation method, a direct hardening method, a cementite network method, and a fine pearlite network method, wherein the carbide is formed to display grain boundaries and the mainly cementite network method without adding an atmosphere is adopted, but the method is to heat a sample to about 820 ℃ of austenitizing temperature, keep the temperature for 30min, cool to below a lower critical temperature at a sufficiently slow cooling rate, and precipitate the carbide from the austenite grain boundaries, and the method is required to determine the critical temperature of steel grade. The austenite grain size of the pearlite steel rail is usually prepared by adopting a fine pearlite net method and a direct hardening method, wherein the fine pearlite net method is mainly aimed at eutectoid steel, a sample is incompletely hardened or a gradient hardening method is adopted, so that austenite grains are surrounded by fine pearlite; the direct hardening method needs to heat the sample to the complete austenitizing temperature, preserve heat for 1h, quench with a larger cooling speed to obtain a martensitic structure, tempering for 15min at about 230 ℃ before corrosion to improve contrast, finally preparing the sample obtained by heat treatment into a metallographic sample, adopting picric acid aqueous solution, detergent and other active agents to corrode at a certain temperature to display grain boundaries according to a certain concentration ratio.
Disclosure of Invention
The technical problem solved by the invention is to provide a method for displaying the grain boundary of bainite steel, which can clearly display the bainite grain boundary.
In view of this, the present application provides a grain boundary display method of bainitic steel, comprising the steps of:
a) Heat treatment is carried out on the bainitic steel sample, the temperature of the heat treatment is 350-400 ℃, the heat preservation time is 0.5-1.5 h, and then cooling is carried out;
b) Grinding and polishing the sample obtained in the step A) to obtain a metallographic sample, and corroding the metallographic sample by adopting a saturated picric acid aqueous solution;
c) And acquiring grain boundary information of the corroded metallographic specimen through image acquisition software.
Preferably, the temperature of the heat treatment is 360-390 ℃, and the heat preservation time is 0.8-1.2 h.
Preferably, the temperature of the saturated aqueous picric acid solution is 30-70 ℃.
Preferably, the etching time is 5 to 20 seconds.
Preferably, the corrosion process is specifically as follows:
wiping the metallographic sample with absorbent cotton until the surface is light gray, then wiping with soapy water, and finally washing with running water and drying.
Preferably, the histogram mode of the image acquisition software is a Spline mode or Best Fit.
The application provides a method for displaying grain boundaries of bainitic steel, which adopts medium-temperature tempering at 350-400 ℃ to enable decomposition of residual austenite to form along-crystal cementite, wherein the formed cementite net is actual grains of the bainitic steel, and the medium-temperature tempered bainitic steel is corroded through a saturated aqueous solution of picric acid, so that actual grains and grain boundaries of a sample can be clearly displayed.
Drawings
FIG. 1 is a metallographic photograph of a bainitic steel rail sample prepared in example 1 of the present invention;
fig. 2 is a metallographic photograph of a bainitic steel rail sample prepared in example 2 of the present invention.
Detailed Description
For a further understanding of the present invention, preferred embodiments of the invention are described below in conjunction with the examples, but it should be understood that these descriptions are merely intended to illustrate further features and advantages of the invention, and are not limiting of the claims of the invention.
The climbing steel has the function of strongly preventing carbide precipitation by utilizing silicon, and the part where carbide is precipitated in the bainite steel first exists in the form of residual austenite, so that series of quasi-bainite steels are successfully developed. The bainitic steel is typically composed of bainitic ferrite and residual austenite, and the residual austenite is distributed among bainitic ferrite laths and grain boundaries in a discontinuous film shape; however, it is difficult to show grain boundaries of carbide bainite and bainite steel bainite by conventional corrosion methods. Therefore, the application provides a method for displaying the grain boundary of the bainitic steel, in particular to a method for displaying the grain boundary of a bainitic steel rail, wherein the difficulty in displaying the grain boundary of the bainitic steel rail is that the actual grain boundary of the bainitic steel does not move; and after the conventional bainite steel rail is heated to austenitizing and rapidly cooled to form martensite, conventional metallographic grinding, polishing and corrosion methods are adopted, and the test structure is the intrinsic grain size of the bainite steel rail, but not the actual grain size. Specifically, the embodiment of the invention discloses a method for displaying grain boundaries of bainitic steel, which comprises the following steps:
a) Heat treatment is carried out on the bainitic steel sample, the temperature of the heat treatment is 350-400 ℃, the heat preservation time is 0.5-1.5 h, and then cooling is carried out;
b) Grinding and polishing the sample obtained in the step A) to obtain a metallographic sample, and corroding the metallographic sample by adopting a saturated picric acid aqueous solution;
c) And acquiring grain boundary information of the corroded metallographic specimen through image acquisition software.
In the present application, a bainitic steel sample is heated to 350-400 ℃ for medium temperature tempering, unstable residual austenite on grain boundaries in a structure begins to decompose into carbide, and a cementite network formed is an actual grain of a bainitic steel rail. In the process, the heat preservation time is 0.5-1.5 h, and then the cooling is furnace cooling and is cooled to room temperature.
According to the conventional mode in the art, grinding and polishing the cooled sample in sequence to obtain a metallographic sample, and corroding the metallographic sample by adopting a saturated picric acid aqueous solution, wherein the saturated picric acid aqueous solution has the effect of preferentially corroding cementite grain boundaries, and the corrosion temperature is controlled to be 30-70 ℃ for 5-20 seconds, so that the tissue contrast ratio of the grain boundaries to a matrix is better increased, and the grain boundaries are displayed more clearly. The specific corrosion process is as follows: wiping the metallographic sample with absorbent cotton until the surface is light gray, then wiping with soapy water, and finally washing with running water and drying.
According to the method, the grain boundary information of the corroded metallographic specimen is finally obtained through image acquisition software, and in the process, a Spline mode and a Best Fit are selected in a histogram mode, so that the image quality reaches the optimal state.
In order to further understand the present invention, the method for displaying grain boundaries of bainitic steel according to the present invention will be described in detail with reference to examples, and the scope of the present invention is not limited by the following examples.
The composition of the PB2 bainite rail in the following examples is shown in table 1;
TABLE 1 bainitic rail composition data sheet
| Name of the name | C | Si | Mn | P | S | Cr | Mo |
| PB2 | 0.23 | 1.58 | 1.97 | 0.010 | 0.006 | 0.80 | 0.30 |
Example 1
Cutting a 10mm sample to be tested on a PB2 bainitic steel rail produced by climbing steel, placing the sample in a heat treatment furnace, heating to 400 ℃ and preserving heat for 1h, cooling to room temperature, grinding and polishing the heat treated sample to prepare a metallographic sample, wiping the sample with absorbent cotton in a 50 ℃ saturated picric acid aqueous solution until the surface is light gray, scrubbing with a soapy aqueous solution, and finally washing with running water and blow-drying; grain boundary information is obtained by image acquisition software, as shown in fig. 1.
Example 2
Cutting a 10mm sample to be tested on a PB2 bainitic steel rail produced by climbing steel, placing the sample in a heat treatment furnace, heating to 380 ℃ and preserving heat for 1h, cooling to room temperature, grinding and polishing the heat treated sample to prepare a metallographic sample, wiping the sample with absorbent cotton in a saturated picric acid solution at 40 ℃ until the surface is light gray, scrubbing with a soapy aqueous solution, and finally washing with running water and blow-drying; grain boundary information is obtained by image acquisition software, as shown in fig. 2.
After the method is used in fig. 1 and fig. 2, the matrix is light brown, the grain boundary is black, if the matrix and the grain boundary are both black by using the nitric acid alcohol solution, the contrast ratio is not obvious enough, if the method of adding the picric acid and the corrosion inhibitor is used, the black grain boundary can be realized, the matrix is not corroded, the contrast ratio is obvious, but the method has more complicated control on the dosage of the corrosion inhibitor and the corrosion temperature, and the method achieves relatively better corrosion effect by using the simplest corrosion method.
The above description of the embodiments is only for aiding in the understanding of the method of the present invention and its core ideas. It should be noted that it will be apparent to those skilled in the art that various modifications and adaptations of the invention can be made without departing from the principles of the invention and these modifications and adaptations are intended to be within the scope of the invention as defined in the following claims.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (4)
1. A method for displaying grain boundaries of bainitic steel, comprising the steps of:
a) Performing heat treatment on the bainite steel sample to decompose residual austenite to form along-grain cementite and form a cementite network; the temperature of the heat treatment is 380-400 ℃, the heat preservation time is 1h, and then the heat treatment is carried out;
b) Grinding and polishing the sample obtained in the step A) to obtain a metallographic sample, and corroding the metallographic sample by adopting a saturated picric acid aqueous solution; the temperature of the saturated picric acid aqueous solution is 40-50 ℃;
c) And acquiring the grain boundary information of the corroded metallographic specimen through image acquisition software, wherein the grain boundary is black, and the matrix is not corroded.
2. The grain boundary display method according to claim 1, wherein the etching time is 5 to 20 seconds.
3. The grain boundary display method according to claim 1, wherein the etching process is specifically:
wiping the metallographic sample with absorbent cotton until the surface is light gray, then wiping with soapy water, and finally washing with running water and drying.
4. The grain boundary display method according to claim 3, wherein the histogram mode of the image acquisition software is a Spline mode or Best Fit.
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| CN104458511A (en) * | 2014-12-01 | 2015-03-25 | 上海交通大学 | Method for testing autstenitic grain size of steel bainite structure for nuclear pressure vessel |
| CN105628480A (en) * | 2015-12-21 | 2016-06-01 | 中车戚墅堰机车车辆工艺研究所有限公司 | Corrosive for displaying grain boundary of original austenite of tempered martensite and corroding method |
| CN110468416A (en) * | 2019-08-08 | 2019-11-19 | 重庆科技学院 | Show the corrosive liquid and preparation method and application of super-high strength steel austenite grain boundary and transgranular bainite and martensite |
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