Phase-change-free low-temperature tempering oxidation method grain size display method

Abstract

The invention relates to the technical field of physical and chemical detection, in particular to a grain size display method based on a phase-change-free low-temperature tempering oxidation method. The phase-change-free low-temperature tempering oxidation method grain size display method comprises the following steps: providing a to-be-detected sample, and polishing the to-be-detected sample to obtain a pretreated sample; the pretreated sample is heated for tempering oxidation, and a tempered oxidation sample is obtained; the tempering oxidation temperature is calculated according to the formula T oxygen = T return + / -(30-100 DEG C); and polishing and corroding the tempered and oxidized sample, and then detecting the grain size. According to the method, oxidation heat treatment of reaustenitizing does not need to be carried out on the sample, the grain size of the sample is not influenced, decarburization influence is avoided, picric acid does not need to be used, the grain size can be truly displayed, and operation is easy and convenient.

Description

Technical Field

[0001] The invention relates to the technical field of physical and chemical detection, and in particular to a method for displaying grain size using a phase-change-free low-temperature tempering oxidation method. Background Art

[0002] Grain size is a measure of the size of the grains, which has a great influence on the mechanical properties and processing properties of the metal.

[0003] At present, the display of grain size requires special heat treatment methods, such as simulated carburizing, carburizing and oxidation. However, these methods all require heat treatment above the austenitizing temperature. However, in actual production, due to the inconsistency between the austenitizing temperature of these methods and the heat treatment temperature of the product, repeated heat treatment, surface decarburization and other reasons, the displayed grain size is inconsistent with the actual grain, and is often not accepted by users; in addition, in order to reduce the use of corrosive agents in the process of grain size display, picric acid is often added to the current corrosive agent, but picric acid is a controlled reagent and is difficult to purchase.

[0004] In the prior art, Chinese patent CN103454187A discloses a method for displaying the original austenite grain boundary of tempered bainite structure at room temperature, and specifically discloses that the method includes the following steps: a. Sample preparation: Use a CNC lathe to process a φ15mm*20mm sample, which is a sample size recommended in reference to the metallographic standard GB / T13298, and subject the sample to coarse grinding, fine grinding, and polishing, so that the sample observation surface reaches a mirror effect, and the surface is free of scratches, water marks, dirt, etc. when observed under a microscope; b. Prepare a corrosive solution; c. Corrosion: Immerse the polished sample into the prepared corrosive solution, take it out after 2 minutes, rinse it with water, then rinse it with alcohol, and then blow it dry with hot air, and observe the grain boundary under a microscope; d. Grain size determination: According to the actual grain size display photo, evaluate it according to the GB / T6394-2002 metal average grain size determination method. The raw materials of the etching solution are 30ml of supersaturated picric acid and 5-15ml of sodium dodecylbenzene sulfonate solution with a concentration of 8-15%. The preparation method of the etching solution is as follows: a. Add picric acid to 100ml of distilled water and stir continuously until the picric acid no longer dissolves, filter out the undissolved picric acid through a filter, and then measure 30ml of supersaturated picric acid; b. Weigh 8-12g of the sodium dodecylbenzene sulfonate, then add water to 100ml, and stir continuously to dissolve it fully and evenly, and measure 5-15ml of sodium dodecylbenzene sulfonate solution; c. Add the above 5-15ml sodium dodecylbenzene sulfonate solution with a concentration of 8-15% to 30ml of supersaturated picric acid, stir continuously to mix the solution evenly, and the etching solution is ready. The method does not go through high temperature, heating and other processes, has no effect on the austenite grains of the sample, and the observed grain boundaries belong to the original austenite grain boundaries. However, this method is still not applicable to other materials that are difficult to show grain boundaries, and it also uses picric acid to prepare the etching agent.

[0005] In view of this, it is of great significance to provide a method for displaying grain size by low-temperature tempering oxidation without phase change. Summary of the invention

[0006] The present invention provides a method for displaying grain size by a phase-change-free low-temperature tempering oxidation method. The method does not require re-austenitizing oxidation heat treatment of the sample, does not affect the grain size of the sample, has no decarburization effect, does not require the use of picric acid, can display the grain size more realistically, and is simple and convenient to operate.

[0007] The method for displaying grain size by low-temperature tempering oxidation method without phase change comprises the following steps:

[0008] 1) Sample preparation: providing a sample to be tested, and polishing the sample to be tested to obtain a pretreated sample;

[0009] 2) Tempering oxidation: heating the pretreated sample prepared in step 1) for tempering oxidation to obtain a tempered oxidation sample;

[0010] The tempering oxidation temperature is calculated by the following formula (1):

[0011] T 氧 =T 回 -(30~100℃) (1);

[0012] Among them, T 氧 Expressed as the tempering oxidation temperature;

[0013] T 回 It is expressed as the tempering temperature of the sample to be tested in the final heat treatment;

[0014] 3) Inspection: After lightly polishing the tempered oxidized sample obtained in step 2), the sample is etched with an etchant, and finally the grain size is inspected.

[0015] In a specific embodiment of the present invention, the steel material is carbon steel or alloy steel.

[0016] In a specific embodiment of the present invention, the tempering temperature is a minimum tempering temperature.

[0017] In a specific embodiment of the present invention, step 2) tempering oxidation, the tempering oxidation time is 5 to 10 hours.

[0018] In a specific embodiment of the present invention, based on 100 mL, the nitric acid in the nitric acid ethanol solution is 5 to 10 mL.

[0019] In a specific embodiment of the present invention, the concentration of the nitric acid is 65-68 wt %.

[0020] In a specific embodiment of the present invention, in step 3), the time of etching with the etching agent is 10 to 180 seconds.

[0021] In a specific embodiment of the present invention, in step 3) detection, the polishing surface is slightly tilted relative to the polishing disk during the light polishing.

[0022] In a specific embodiment of the present invention, in step 3) detection, the light polishing is performed using a polishing machine, and the rotation speed of the polishing machine is less than 800 rpm.

[0023] In a specific embodiment of the present invention, in step 3), the grain size is detected using a metallographic microscope.

[0024] The beneficial effects of the present invention are as follows: the tempering oxidation temperature of the present invention is determined according to the tempering temperature of the steel in the final heat treatment, thereby avoiding the influence of the oxidation heat treatment of re-austenitizing the sample to be tested and the influence of the temperature higher than the maximum tempering temperature on the grain size, without the influence of decarburization, and being able to truly feedback the grain size of the steel; the present invention only uses the etchant of nitric acid-ethanol to corrode the sample to be tested, without the need to use picric acid, and the sample preparation and corrosion operations are simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A local microstructure morphology image of the detection surface of the USS122G sample provided in Example 1 of the present invention;

[0026] Figure 2 Another local microstructure morphology image of the USS122G sample detection surface provided in Example 1 of the present invention;

[0027] Figure 3 A local microstructure morphology image of the detection surface of the 18MND5 sample provided in Example 2 of the present invention;

[0028] Figure 4 Another local microstructure morphology image of the 18MND5 sample detection surface provided in Example 3 of the present invention;

[0029] Figure 5 This is a local microstructure morphology diagram of the USS122G sample test surface provided in Comparative Example 1 of the present invention;

[0030] Figure 6 This is a local microstructure morphology diagram on the test surface of the 18MND5 sample provided in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0032] The method for displaying grain size by low-temperature tempering oxidation method without phase change comprises the following steps:

[0033] 1) Sample preparation: providing a sample to be tested, and polishing the sample to be tested to obtain a pretreated sample;

[0034] 2) Tempering oxidation: heating the pretreated sample prepared in step 1) for tempering oxidation to obtain a tempered oxidation sample;

[0035] The tempering oxidation temperature is calculated by the following formula (1):

[0036] T 氧 =T 回 -(30~100)℃ Formula (1);

[0037] Among them, T 氧 Expressed as the tempering oxidation temperature;

[0038] T 回 It is expressed as the tempering temperature of the sample to be tested in the final heat treatment;

[0039] 3) Inspection: After lightly polishing the tempered oxidized sample obtained in step 2), the sample is etched with an etchant, and finally the grain size is inspected.

[0040] In some examples, in step 1) sample preparation, the steel material is carbon steel or alloy steel.

[0041] In some examples, step 2) is tempering oxidation, and the tempering temperature is the lowest tempering temperature.

[0042] In some examples, in step 2), the tempering and oxidation are performed for 5 to 10 hours.

[0043] In some examples, based on 100 mL of the nitric acid ethanol solution, the amount of nitric acid is 5 to 10 mL.

[0044] In some examples, the concentration of the nitric acid is 65-68 wt %.

[0045] In some examples, in step 3), the time of etching with the etchant is 10 to 180 seconds.

[0046] In some examples, in step 3), the polishing surface is slightly tilted relative to the polishing plate during the light polishing.

[0047] In some examples, in step 3), the light polishing is performed using a polishing machine, and the rotation speed of the polishing machine is less than 800 rpm.

[0048] In some examples, in step 3), the polishing machine is used at a rotation speed of less than 800 rpm during polishing.

[0049] In some examples, in step 3), the grain size is detected using a metallographic microscope.

[0050] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0051] Example 1

[0052] This embodiment provides a method for displaying grain size by low-temperature tempering oxidation without phase change, and the steps are as follows:

[0053] 1. Take a sample from USS122G (10Cr13Co13Mo5N i 3W1VE), polish the surface of the sample, and take it out after tempering and oxidation at 520℃ for 6h;

[0054] 2. Lightly polish the tempered and oxidized sample, and corrode the sample with a nitric acid-ethanol solution for 60 seconds; wherein the volume concentration of nitric acid in the nitric acid-ethanol solution is 5 vol%; and detect the grain size with a metallographic microscope.

[0055] The effect of different local grain sizes can be found in the attached Figure 1 and attached Figure 2 .

[0056] Example 2

[0057] This embodiment provides a method for displaying grain size by low-temperature tempering oxidation without phase change, and the steps are as follows:

[0058] 1. Take a sample from 18MND5, polish the surface of the sample, and take it out after tempering and oxidation at 550℃ for 6h;

[0059] 2. Lightly polish the tempered and oxidized sample, and corrode the sample with a nitric acid-ethanol solution for 20 seconds; wherein the volume concentration of nitric acid in the nitric acid-ethanol solution is 5 vol%; and detect the grain size with a metallographic microscope.

[0060] The effect of different local grain sizes can be found in the attached Figure 3 and attached Figure 4 .

[0061] Comparative Example 1

[0062] This comparative example provides a method for displaying grain size, and the steps are as follows:

[0063] 1. Take samples from USS122G (10Cr13Co13Mo5N i 3W1VE) and polish the surface of the samples.

[0064] 2. Instead of using the tempering oxidation method, directly corrode the sample with a mixed solution of 5 g FeCl3, 50 mL HCl and 100 mL H2O for 60 seconds and then detect the grain size with a metallographic microscope.

[0065] The local grain size effect is shown in the attached Figure 5 .

[0066] Comparative Example 2

[0067] This comparative example provides a method for displaying grain size, and the steps are as follows:

[0068] 1. Take a sample from 18MND5 and polish the surface of the sample.

[0069] 2. Instead of using the tempering oxidation method, directly corrode the sample with 5 to 10 mL of nitric acid-ethanol solution for 20 seconds and then use a metallographic microscope to detect the grain size.

[0070] The local grain size effect is shown in the attached Figure 6 .

Claims

1. A method for displaying grain size by low-temperature tempering oxidation without phase change, characterized in that: The following steps are involved: 1) Sample preparation: providing a sample to be tested, and polishing the sample to be tested to obtain a pretreated sample; 2) Tempering oxidation: heating the pretreated sample prepared in step 1) for tempering oxidation to obtain a tempered oxidation sample; The tempering oxidation temperature is calculated by the following formula (1): T 氧 =T 回 -(30~100℃) (1); Among them, T 氧 Expressed as the tempering oxidation temperature; T 回 It is expressed as the tempering temperature of the sample to be tested in the final heat treatment; 3) Inspection: After lightly polishing the tempered oxidized sample obtained in step 2), the sample is etched with an etchant, and finally the grain size is inspected.

2. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Step 1) sample preparation, the sample to be tested is carbon steel or alloy steel.

3. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Step 2) tempering oxidation, wherein the tempering temperature is the lowest tempering temperature.

4. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Step 2) tempering, wherein the tempering oxidation time is 5 to 10 hours.

5. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Based on 100 mL, the nitric acid in the nitric acid ethanol solution is 5 to 10 mL.

6. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 5, characterized in that: The concentration of the nitric acid is 65-68 wt %.

7. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 3, characterized in that: Step 3) detection, the etching time with the etchant is 10 to 180 seconds.

8. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Step 3) detection: during the light polishing, the polishing surface is slightly tilted relative to the polishing disk.

9. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Step 3) detection, the light polishing adopts a polishing machine, and the rotation speed of the polishing machine is less than 800rpm.

10. The method for displaying grain size by low temperature tempering oxidation without phase change according to claim 1, characterized in that: Step 3) Detection: The grain size is detected using a metallographic microscope.

Images