CN113866055A - Method for detecting grain size of quenched and tempered steel - Google Patents
Method for detecting grain size of quenched and tempered steel Download PDFInfo
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- 238000001514 detection method Methods 0.000 claims abstract description 69
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- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
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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
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Abstract
The invention provides a method for detecting grain size of quenched and tempered steel, and relates to the technical field of steel material detection. The method for detecting the grain size of the quenched and tempered steel comprises the following steps: decarbonization: heating the sample to be tested to be lower than the critical point A of the steel gradeC1Keeping the temperature at 20-40 ℃ below the temperature until the carbide of the tempered sorbite on the surface of the sample to be tested is oxidized and diffused; polishing: cooling after decarburization treatment, grinding to remove an oxide layer, and polishing to expose a decarburized layer; and (3) corrosion: corroding the decarburized layer by using a corrosive agent to obtain a sorbite interface; measurement: and measuring the grain size of the surface of the corroded sample to be measured to obtain the grain size of the quenched and tempered steel. The detection method has the advantages of good safety, high accuracy and real and reliable detection result.
Description
Technical Field
The invention relates to the technical field of steel material detection, in particular to a method for detecting grain size of quenched and tempered steel.
Background
The quenched and tempered steel is quenched and tempered carbon steel and alloy steel subjected to high-temperature tempering, the metallographic microstructure of the quenched and tempered carbon steel and alloy steel is generally a tempered sorbite, and the quenched and tempered carbon steel and alloy steel have excellent comprehensive mechanical properties, namely high strength, good plasticity and toughness, and can be widely applied to manufacturing parts with complex requirements on load and stress under different working conditions in industries such as automobiles, machine tools, aerospace and nuclear power.
In general, a metal material used at normal temperature has better plasticity and toughness as the crystal grains become finer and the strength and hardness become higher, but in a high-temperature environment, the strength of the metal material is rather lowered by refining the crystal grains. Meanwhile, the technical specifications of many products have clear regulations on the grain size level index, and it is clear that the crystal grains of the steel are necessary to be displayed. However, in the case of quenched and tempered steel, since the interfacial energy of the prior austenite grain boundaries is generally lower than that of the in-grain tempered precipitate phase, the microstructure, and the like, corrosion is performed using a general etchant (e.g., 4% nital solution), and instead, the inside of the grains is corroded, showing its microstructure (see fig. 1). How to show the actual grain size of the quenched and tempered state of steel without distortion is a constant difficulty faced in the art.
Bechet and Beaujard in 1955 created a method for developing alloy steel grains using a saturated aqueous picric acid solution and wetting agent reagent that inhibited some steel matrix formations from developing, i.e. having some selective corrosion, preferentially corroding grain boundaries, while the matrix formation corroded less, although this method has been used to date. However, the picric acid has strong explosiveness, corrosive liquid needs to be added and heated to slight boiling in the using process, toxic gas is generated, great potential safety hazard exists, the picric acid is listed as an explosive dangerous medicine, and the production and marketing are strictly controlled; moreover, the aqueous picric acid solution has a long erosion time and low efficiency, is only suitable for certain specific steels, and has certain limitations (see fig. 2). In the prior art, a sulfosalicylic acid method is adopted to replace a saturated picric acid water solution method, but the problems of poor universality and poor repeatability exist. At present, the detection and evaluation of the grain size in the industry depend on the experience of inspectors, the subjectivity is strong, the detection results of different inspectors are different, the detection reliability is low, and hidden dangers are brought to the subsequent manufacturing and safe use of parts.
Therefore, it is necessary to develop a method for detecting the grain size of a quenched and tempered steel with high safety and accuracy.
Disclosure of Invention
Therefore, it is necessary to provide a method for detecting the grain size of quenched and tempered steel, which has the advantages of good safety, high accuracy and real and reliable detection result.
A method for detecting the grain size of quenched and tempered steel comprises the following steps:
decarbonization: heating the sample to be tested to be lower than the critical point A of the steel gradeC1At a temperature of 20 to 40 ℃ below AC1Keeping the temperature at the critical temperature of the tissue transformation in the steel heating process until the carbide of the tempered sorbite on the surface of the sample to be detected is oxidized and diffused;
polishing: cooling after decarburization treatment, grinding to remove an oxide layer until the surface is bright, and polishing to expose a decarburized layer;
and (3) corrosion: corroding the decarburized layer by using a corrosive agent to obtain a sorbite interface;
measurement: and measuring the grain size of the surface of the corroded sample to be measured to obtain the grain size of the quenched and tempered steel.
The inventor finds that the detection method in the prior art mainly focuses on the detailed display of tempered sorbite structure of quenched and tempered steel, namely, the distribution of fine carbides on a ferrite matrix is observed under a microscope, so that although the detailed structure is highlighted, the display of grain boundaries is weakened, and the dense distribution of carbides confuses the grain boundaries, so that the grain size cannot be effectively and correctly evaluated under the prior art.
Based on the above findings, the inventors have found that the metal material is made to be lower than A according to the principle of metallographyC1The critical point temperature is heated, namely the steel is not austenitized, and is subjected to heat preservation and oxidation for a period of time, so that the size of sorbite grains is not changed in the process, and the phenomenon of decarburization and oxidation only occurs on the surface. The tempered sorbite is basically characterized in that: fine granular carbides are distributed on a ferrite matrix, the ferrite serves as a matrix of tempered sorbite, and the grain boundary of the ferrite is the grain boundary of the sorbite. According to the principle, the invention adopts the surface decarburization principle, so that carbon elements on the surface of the sample react with oxygen to generate carbon oxides or gas, the carbon oxides or the gas are diffused, the ferrite matrix is kept unchanged, and the sorbite grain size can be obtained by measuring the ferrite grain size.
The detection method can clearly and completely display the grain boundaries and the grain sizes of the tempered sorbite, and has the advantages of real and effective grain size evaluation result, high accuracy, simple detection process, less material consumption and high safety.
In one embodiment, in the decarbonization step, the sample to be tested is carbon steel, and the heat preservation time is 50-70 min.
In one embodiment, in the decarbonization step, the sample to be tested is alloy steel, and the heat preservation time is 60-80 min.
In one embodiment, in the etching step, the cooling is air cooling to 15-30 ℃.
In one embodiment, in the polishing step, the force application direction and the surface of the sample to be measured are inclined by an included angle of 10-20 degrees during polishing.
In one embodiment, in the etching step, the etchant is a nitric acid alcohol solution with the volume concentration of 2-5%, and the sample to be tested is cleaned and dried after etching.
In one embodiment, in the measuring step, the grain size is measured by observation or photographing under a metallographic microscope.
In one embodiment, in the measuring step, the method for measuring the grain size adopts a comparison method, an intercept method or an area method of GB/T6394-.
In one embodiment, the steel grade of the test specimen to be tested is selected from: 20Cr1Mo1VTiB, 12Cr1MoV, 40CrNiMo, SA-387M Gr.22CL1.1, 12Cr2.25Mo1, 16MND5, 18MND5, SA-508Gr3.Cl2, SA-336MGr.F22CL1.1, SA-540MGr.B24CL.3, SA-193MGr.7B, 42CrMo, SA-213M T22, 18MnNiMo, 16 MnNiMo.
Compared with the prior art, the invention has the following beneficial effects:
the detection method can clearly and completely display the grain boundary and the grain size of the tempered sorbite, is real and effective in the grain size detection result of the tempered steel, and has the advantages of high accuracy, simple detection process, less material consumption and high safety.
Drawings
FIG. 1 is a microstructure (100X) of a quenched and tempered 20Cr1Mo1VTiB etched with a nital solution.
FIG. 2 is a microstructure (100X) of a quenched and tempered 20Cr1Mo1VTiB corroded by saturated picric acid solution.
FIG. 3 is a grain size morphology (100X) of a decarburized 20Cr1Mo1VTiB quenched and tempered steel sample in example.
FIG. 4 is a graph (100X) showing the morphology of the 20Cr1Mo1VTiB of the comparative example after heat treatment at 740 ℃.
Detailed Description
To facilitate an understanding of the invention, a more complete description of the invention will be given below in terms of preferred embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Example 1
The method for detecting the grain size of the 20Cr1Mo1VTiB quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the steel grade in the mechanical and electrical engineering metal material handbookC1，AC1Setting the heat treatment temperature to be 780 ℃ at 800-810 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: air cooling to room temperature, with metallographic abrasive paper to treat the test piece and polish in advance, force application direction and the inclination of the sample surface of awaiting measuring are about 10 contained angles during polishing, reuse metallographic abrasive paper from thick to thin polishes the oxide layer to just show metallic luster, adopts long term polishing to carry out polishing treatment to the surface, and to expose decarburized layer (being the test bed), the decarburized layer thickness is about 1 mm.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary (ferrite matrix) can be clearly and completely observed, a grain size morphology graph is shown in figure 2, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 metal average grain size determination method.
And (3) measuring results: the detection result of the contrast method is 7.5 grade, the detection result of the intercept method is 7.5 grade, and the detection result of the area method is 7.5 grade. The results of the detection methods specified by the three standards are highly consistent, and the results of the grain size detection of the quenched and tempered steel by adopting the method are real and reliable, and the method has high accuracy, good stability and reproducibility.
Example 2
The method for detecting the grain size of 12Cr1MoV quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the steel grade in the mechanical and electrical engineering metal material handbookC1，AC1Setting the temperature of heat treatment to be 774-783 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: air cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, inclining the force application direction to the surface of the to-be-tested sample by about 10 degrees of included angle during polishing, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
Example 3
The method for detecting the grain size of the 40CrNiMo quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the steel grade in the mechanical and electrical engineering metal material handbookC1，AC1Setting the heat treatment temperature to 710 ℃ at 732 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: air cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, inclining the force application direction to the surface of the to-be-tested sample by about 10 degrees of included angle during polishing, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 7 grades, the detection result of the intercept method is 7 grades, and the detection result of the area method is 7 grades.
Example 4
The method for detecting the grain size of the SA-387M Gr.22CL1.1 quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the same kind of steel in the handbook of electromechanical engineering metal materialsC1，AC1Setting the heat treatment temperature to be 750 ℃ at 770-800 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: air cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, inclining the force application direction to the surface of the to-be-tested sample by about 10 degrees of included angle during polishing, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394-.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
Example 5
The method for detecting the grain size of the 12Cr2.25Mo1 quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the steel grade in the mechanical and electrical engineering metal material handbookC1，AC1Setting the heat treatment temperature to be 750 ℃ at 770-800 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: air cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, inclining the force application direction to the surface of the to-be-tested sample by about 10 degrees of included angle during polishing, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6.5 grade, the detection result of the intercept method is 6.5 grade, and the detection result of the area method is 6.5 grade.
Example 6
The method for detecting the grain size of 16MND5 quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to 680 ℃ at about 700 ℃, heating the sample to be tested to the heat treatment temperature, and preserving the heat for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
Example 7
The method for detecting the grain size of 18MND5 quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to be 690 ℃ at about 710 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
Example 8
The method for detecting the grain size of SA-508Gr3.Cl2 quenched and tempered steel comprises the following steps:
(1) decarbonization: : the critical point A of the steel grade is found in' nuclear power large-scale forging SA508 Gr3 steel metallographyC1Setting the heat treatment temperature at 735 ℃ and 700 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 7 grades, the detection result of the intercept method is 7 grades, and the detection result of the area method is 7 grades.
Example 9
The method for detecting the grain size of the SA-336MGr.F22CL1.1 quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to 750 ℃ at about 770-800 ℃, heating the sample to be tested to the heat treatment temperature, and preserving heat for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
Example 10
The detection method of the grain size of the SA-540MGr.B24CL.3 quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the temperature of the heat treatment to be about 732 ℃ and 710 ℃, heating the sample to be tested to the heat treatment temperature, and preserving the heat for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 9 grades, the detection result of the intercept method is 9 grades, and the detection result of the area method is 9 grades.
Example 11
The method for detecting the grain size of SA-193MGr.7B quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to 680 ℃ at about 700 ℃, heating the sample to be tested to the heat treatment temperature, and preserving the heat for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 7 grades, the detection result of the intercept method is 7 grades, and the detection result of the area method is 7 grades.
Example 12
The method for detecting the grain size of 42CrMo quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to be 710 ℃ at about 730 ℃, heating the sample to be tested to the heat treatment temperature, and preserving the heat for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 7 grades, the detection result of the intercept method is 7 grades, and the detection result of the area method is 7 grades.
Example 13
The method for detecting the grain size of the SA-213M T22 quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the steel grade in the mechanical and electrical engineering metal material handbookC1Setting the heat treatment temperature to be 750 ℃ at 770-800 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using nitric acid alcohol with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6.5 grade, the detection result of the intercept method is 6.5 grade, and the detection result of the area method is 6.5 grade.
Example 14
The method for detecting the grain size of 18MnNiMo quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to be 690 ℃ at about 710 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
Example 15
The method for detecting the grain size of the 16MnNiMo quenched and tempered steel comprises the following steps:
(1) decarbonization: after calculating the carbon equivalent according to the actual chemical composition, the critical point A of the steel grade is found on an iron-carbon equilibrium diagramC1Setting the heat treatment temperature to 680 ℃ at about 700 ℃, heating the sample to be tested to the heat treatment temperature, and preserving the heat for 1 h.
(2) Polishing: and air-cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metal luster, and polishing the surface by using long-time polishing until the decarburized layer is exposed.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the sorbite crystal boundary can be clearly and completely observed, and the grain size is measured by respectively adopting a contrast method, an intercept point method and an area method of GB/T6394 plus 2017 'Metal average grain size determination method'.
And (3) measuring results: the detection result of the contrast method is 6 grades, the detection result of the intercept method is 6 grades, and the detection result of the area method is 6 grades.
The important parameters and the results of the method for detecting the grain size of the quenched and tempered steel in the above examples are summarized in table 1.
TABLE 1 example grain size detection parameters and results of quenched and tempered steels
Comparative example 1
The method for detecting the grain size of the 20Cr1Mo1VTiB quenched and tempered steel comprises the following steps:
(1) decarbonization: inquiring the critical point A of the steel grade in the mechanical and electrical engineering metal material handbookC1Setting the temperature of the heat treatment to be 740 ℃ at 800-810 ℃, heating the sample to be tested to the heat treatment temperature, and keeping the temperature for 1 h.
(2) Polishing: and air cooling to room temperature, pre-polishing the to-be-tested piece by using metallographic abrasive paper, polishing the oxide layer by using the metallographic abrasive paper from coarse to fine until the oxide layer just shows metallic luster, and polishing the surface by using long-term polishing.
(3) And (3) corrosion: and corroding the surface of the sample by using a nitric acid alcohol solution with the volume concentration of 4%, and cleaning and blow-drying.
(4) Measurement: the corrosion surface is observed under a metallographic microscope, the decarburization phenomenon does not occur, the grain boundary does not appear, the structure is sorbite and bainite, and the grain size measurement cannot be carried out, which is shown in figure 4.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (9)
1. The method for detecting the grain size of quenched and tempered steel is characterized by comprising the following steps of:
decarbonization: heating the sample to be tested to be lower than the critical point A of the steel gradeC1At a temperature of 20 to 40 ℃ below AC1Keeping the temperature at the critical temperature of the tissue transformation in the steel heating process until the carbide of the tempered sorbite on the surface of the sample to be detected is oxidized and diffused;
polishing: cooling after decarburization treatment, grinding to remove an oxide layer until the surface is bright, and polishing to expose a decarburized layer;
and (3) corrosion: corroding the decarburized layer by using a corrosive agent to obtain a sorbite interface;
measurement: and measuring the grain size of the surface of the corroded sample to be measured to obtain the grain size of the quenched and tempered steel.
2. The detection method according to claim 1, wherein in the decarburization step, the sample to be measured is carbon steel, and the holding time is 50 to 70 min.
3. The detection method according to claim 1, wherein in the decarburization step, the sample to be measured is alloy steel, and the holding time is 60-80 min.
4. The detection method according to claim 1, wherein in the polishing step, the cooling mode is air cooling, and the cooling is carried out to 15-30 ℃.
5. The detection method according to claim 1, wherein in the polishing step, the force application direction is inclined at an angle of 10-20 degrees with respect to the surface of the sample to be detected during polishing.
6. The detection method according to claim 1, wherein in the etching step, the etchant is a nital solution with a volume concentration of 2-5, and the sample to be detected is cleaned and dried after etching.
7. The inspection method according to claim 1, wherein in the measuring step, the grain size is measured by observation under a metallographic microscope or by photographing.
8. The detecting method according to claim 1, wherein in the measuring step, the contrast method, the intercept method or the area method of GB/T6394-.
9. The detection method according to any one of claims 1 and 3 to 8, wherein the sample steel type to be detected is selected from the group consisting of: 20Cr1Mo1VTiB, 12Cr1MoV, 40CrNiMo, SA-387M Gr.22CL1.1, 12Cr2.25Mo1, 16MND5, 18MND5, SA-508Gr3.Cl2, SA-336MGr.F22CL1.1, SA-540MGr.B24CL.3, SA-193MGr.7B, 42CrMo, SA-213M T22, 18MnNiMo, 16 MnNiMo.
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