Corrosive agent and method for detecting grain size of GCr15 steel after hot rolling and spheroidizing annealing

Abstract

The invention discloses an etchant for detecting the grain size of GCr15 steel by hot rolling spheroidizing annealing and a detection method. The etchant composition and content are: 5-10 ml of nitric acid, 2-4 g of sodium dodecylbenzene sulfonate and 100 ml of distilled water. The etchant for detecting the grain size of GCr15 steel by hot rolling spheroidizing annealing replaces picric acid as a corrosive solution for detecting the grain size of GCr15 steel by hot rolling spheroidizing annealing. The etchant has common and easily available raw material components, a simple preparation process, is not an explosive product, and has a low detection safety risk. Therefore, the etchant can effectively solve the problem that the grain size of the spheroidized structure of GCr15 steel needs to be detected by picric acid at present, and the picric acid is an explosive product and is not easy to obtain, so that the detection of the grain size of the spheroidized structure of GCr15 steel is very limited. The invention provides a new technical means for detecting the grain size of the spheroidized structure of GCr15 steel.

Description

Technical Field

[0001] The present invention relates to the field of steel material detection, and in particular to an etchant and a detection method for detecting the grain size of GCr15 steel subjected to hot rolling and spheroidizing annealing. Background Art

[0002] GCr15 steel is a widely used bearing steel with a low alloy content and high hardenability. After quenching and tempering, it has high and uniform hardness, good wear resistance, and high contact fatigue performance. Therefore, it is widely used in the production of various bearing rings and rolling elements or molds, measuring tools and other items.

[0003] In applications, GCr15 steel often requires spheroidization. Its original hot-rolled microstructure consists of pearlite and a network of carbides. During sample processing, its cutting performance is poor, and to improve this, the material needs to be spheroidized. The typical spheroidization method involves spheroidizing the pearlite during the steel mill production process by slowly cooling it after hot rolling to obtain a spheroidized pearlite structure to improve cutting performance. The spheroidized pearlite structure obtained by slow cooling after rolling is a spheroidal carbide structure dispersed in a ferrite matrix. In this microstructure, the ferrite grain boundaries are unrecognizable, making it impossible to measure the grain size using this process.

[0004] The performance of the material is closely related to the size of the grains. On the one hand, the grain size distribution directly reflects the degree of grain growth during the heating process of the material and reflects the influence of the process system on the organization. On the other hand, the grain size also has a great influence on the mechanical properties of the material. Therefore, the detection of the grain size of the spheroidized organization is of great significance for process reference and performance research.

[0005] At present, for the measurement of the grain size of GCr15 steel after spheroidizing annealing after rolling, there are some papers such as: Grain size display method of GCr15 steel under different heat treatment states, Yu Yajie and Shi Jingsong, Physical and Chemical Testing (Physical Section), 2019, 55(08); this method needs to display austenite grain boundaries, and uses picric acid reagent as a grain boundary display agent. Publication No. CN103344532A discloses a method for rapid metallographic determination of the grain size of GCr15 steel bearing components, and Publication No. CN101187606A discloses a metallographic corrosion method for displaying the original austenite grain boundaries of GCr15. These two patented methods use picric acid as the main corrosion agent regardless of the form of grain boundaries displayed.

[0006] Typically, the inspection method involves corroding the sample in a heated, supersaturated aqueous solution of picric acid and Seagull shampoo. However, picric acid is an explosive material, presenting risks during use and subject to regulatory controls, making its procurement difficult. In the absence of picric acid, coupled with the difficulty in visualizing grain boundaries in the spheroidized annealed structure of GCr15 steel, grain size inspection of the spheroidized structure of GCr15 steel becomes challenging. Summary of the Invention

[0007] In view of this, the present disclosure provides a corrosive agent and a detection method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing, which solves the problem that the grain size of the spheroidized structure of GCr15 steel currently needs to be detected using picric acid. Since picric acid is an explosive substance and is difficult to obtain, the detection of the grain size of the spheroidized structure of GCr15 steel is very limited.

[0008] 2. To achieve the above-mentioned object of the invention, in the first aspect, the etchant for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing comprises:

[0009] Nitric acid, sodium dodecylbenzenesulfonate and water;

[0010] Based on 100 ml of water, the amount of nitric acid is 5-10 ml, and the amount of sodium dodecylbenzenesulfonate is 2-4 g.

[0011] In a second aspect, a method for preparing a corrosive agent for detecting the grain size of GCr15 steel subjected to hot rolling and spheroidizing annealing according to the first aspect comprises:

[0012] After dissolving nitric acid in distilled water, sodium dodecylbenzenesulfonate is dissolved in the mixture of the nitric acid and the distilled water, and the mixture is shaken evenly using an ultrasonic device to obtain the etchant for detecting the grain size of GCr15 steel hot-rolled spheroidizing annealing.

[0013] In a third aspect, the method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing comprises:

[0014] Sample preparation, sample corrosion and grain size measurement;

[0015] The sample is corroded using the corrosive agent for detecting the grain size of the GCr15 steel hot-rolled spheroidizing annealing described in the first aspect.

[0016] In the present disclosure and possible embodiments, the sample corrosion time is 5 to 10 minutes.

[0017] In the present disclosure and possible embodiments, the sample corrosion method includes:

[0018] The test surface of the sample is immersed in the corrosive agent. After the corrosion time is over, the corrosion products on the surface of the test surface are removed by light polishing and washing with running water, and then the test surface is dried.

[0019] In the present disclosure and possible embodiments, the method for measuring the grain size is to place the dried test surface under a microscope, observe and capture the grain morphology of the spheroidized pearlite at a magnification of 500X, and complete the grain size measurement of the sample.

[0020] In the present disclosure and possible embodiments, the sample preparation method includes:

[0021] The quenched specimen is cut into samples, and the detection surface of the sample is inlaid, ground and polished until the detection surface reaches a mirror state.

[0022] In the present disclosure and possible embodiments, a method for grinding and polishing a detection surface of a sample includes:

[0023] After grinding the samples in sequence from coarse to fine with sandpaper, the samples are polished in sequence from large to small particle sizes with diamond polishing liquid until the sample surface reaches a mirror effect.

[0024] The present invention has the following beneficial effects:

[0025] The etchant for detecting the grain size of GCr15 steel subjected to hot rolling and spheroidizing annealing of the present invention replaces picric acid as a etchant solution for detecting the grain size of GCr15 steel subjected to hot rolling and spheroidizing annealing. The etchant is common and readily available in its raw material components, has a simple preparation process, is non-explosive, and has a low safety risk in detection. Therefore, the etchant can effectively solve the problem that the grain size of the spheroidized structure of GCr15 steel currently needs to be detected using picric acid, which is an explosive and difficult to obtain substance, resulting in a very limited detection of the grain size of the spheroidized structure of GCr15 steel. The etchant provides a new technical means for detecting the grain size of the spheroidized structure of GCr15 steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The microstructure of GCr15 steel was etched with 4% nitric acid alcohol solution.

[0027] Figure 2 This is the grain boundary morphology of GCr15 steel when corroded by the corrosive agent of Example 1. DETAILED DESCRIPTION

[0028] The present disclosure is described below based on examples, but it is worth noting that the present disclosure is not limited to these examples. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure. At the same time, unless the context clearly requires otherwise, the words "including", "comprising" and similar words throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, as "including but not limited to".

[0029] The method for detecting the grain size of GCr15 steel after hot rolling and spheroidization treatment in the embodiment of the present disclosure comprises the following steps:

[0030] 1. Preparation of corrosive agent:

[0031] The composition and content of the corrosive agent are: 5-10 ml of nitric acid; 2-4 g of sodium dodecylbenzenesulfonate; and 100 ml of distilled water.

[0032] Preparation method: Take 100 ml of distilled water and add it to a beaker, then put nitric acid into the beaker and stir until it is completely dissolved, then put sodium dodecylbenzenesulfonate and stir until it is completely dissolved, and stir evenly to obtain the chemical reagent.

[0033] 2. Sample preparation:

[0034] The quenched sample is prepared according to the metallographic microstructure inspection method of GB / T13298. The sample surface is prepared according to the process flow. After mounting, grinding and polishing, the inspection surface of the sample reaches a mirror state.

[0035] 3. Sample corrosion:

[0036] Immerse the test surface of the sample in the above-prepared corrosive agent for about 5 to 10 minutes. As the corrosion time increases, the test surface changes from a mirror surface to gray. After light polishing to remove surface corrosion products, rinse the sample under running water. After drying the test surface of the sample, it can be observed under a microscope.

[0037] 4. Sample testing:

[0038] For the test surface after corrosion treatment, the grain morphology of spheroidized pearlite can be observed more clearly under a microscope at a magnification of 500X.

[0039] 5. Grain size measurement:

[0040] After image acquisition, the grain size of the sample is measured according to the displayed grain morphology according to the GB6394 standard method.

[0041] Example 1

[0042] Taking GCr15SiMn produced by Benxi Iron and Steel as an example, the spheroidizing annealing grain size is tested according to the method of the present invention, and the steps are as follows:

[0043] 1. Sample preparation:

[0044] The samples were prepared according to the metallographic microstructure examination method of GB / T13298.

[0045] (1) The hot-rolled and spheroidized annealed specimens were cut to obtain samples, and the samples were inlaid.

[0046] (2) Sample grinding:

[0047] The mounted samples were first ground with sandpaper, using 320#, 600#, and 800# sandpaper in order from coarse to fine to complete the grinding work.

[0048] Diamond polishing liquid with particle sizes of 3 μm, 1 μm, and 0.05 μm was used in sequence for polishing until the sample surface reached a mirror effect.

[0049] 2. Corrosion samples:

[0050] The etchant was prepared by 5 ml of nitric acid, 2 g of sodium dodecylbenzenesulfonate, and 100 ml of distilled water.

[0051] Preparation method: Take 100 ml of distilled water and add it to a beaker, then put nitric acid into the beaker and stir until it is completely dissolved, then put sodium dodecylbenzenesulfonate and stir until it is completely dissolved. After stirring evenly, the corrosive agent is obtained.

[0052] In addition, 4% nitric acid alcohol solution was selected as the etching agent for comparison with the etching agent in Example 1.

[0053] Take out 20 ml of the corrosive agent and put it into the culture dish. Gently place the sample into the culture dish. Under the premise that the test surface is guaranteed to be in contact with the corrosive agent, the total corrosion time is 5 minutes.

[0054] 3. Grain size measurement:

[0055] After the sample was corroded with 4% nitric acid alcohol solution, it was observed under a microscope at 500X magnification. The results are as follows: Figure 1 As shown, the ferrite grain boundaries are not clearly distinguishable;

[0056] After the sample was corroded by the corrosive agent prepared in Example 1, it was observed under a microscope at a magnification of 500X. Figure 2 As shown, the grain boundaries can be shown more clearly. Using the grain boundary morphology, the grain size of the sample is measured according to the GB6394 standard method. In this example, the spheroidizing annealing grain size of the GCr15SiMn steel is measured to be level 10.

[0057] The above-described embodiments are merely examples of implementation methods of the present disclosure, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications, equivalent substitutions, and improvements without departing from the scope of the present disclosure, and these modifications are all within the scope of protection of the present disclosure. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A corrosive agent for detecting the grain size of GCr15 steel hot-rolled spheroidizing annealing, characterized in that: Its composition includes: Nitric acid, sodium dodecylbenzene sulfonate and water; Based on 100 ml of water, the nitric acid is 5-10 ml, and the sodium dodecylbenzene sulfonate is 2-4 g.

2. A method for preparing the etchant according to claim 1, characterized in that: include: After dissolving nitric acid in distilled water, sodium dodecylbenzene sulfonate is dissolved in the mixture of the nitric acid and the distilled water, and the mixture is shaken evenly with an ultrasonic device to obtain the corrosive agent for detecting the grain size of the GCr15 steel hot-rolled spheroidizing annealing.

3. A method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing, characterized in that: include: Sample preparation, sample corrosion and grain size measurement; The sample is corroded using the corrosive agent for detecting the grain size of GCr15 steel hot-rolled spheroidizing annealing as claimed in claim 1.

4. The method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing according to claim 3, characterized in that: The corrosion time of the sample corrosion is 5 to 10 minutes.

5. The method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing according to claim 4, characterized in that: The sample corrosion method comprises: The detection surface of the sample is immersed in the corrosive agent. After the corrosion time is over, the corrosion products on the surface of the detection surface are removed by light polishing and washing with running water, and then the detection surface is dried.

6. The method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing according to claim 5, characterized in that: The method for measuring the grain size is to place the dried test surface under a microscope, observe and collect the grain morphology of spheroidized pearlite at a magnification of 500X, and complete the grain size measurement of the sample.

7. The method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing according to claim 5, characterized in that: The sample preparation method comprises: The quenched specimen is cut into samples, and the detection surface of the sample is inlaid, ground and polished until the detection surface reaches a mirror surface state.

8. The method for detecting the grain size of GCr15 steel after hot rolling and spheroidizing annealing according to claim 7, characterized in that: The method for grinding and polishing the detection surface of the sample comprises: After grinding the samples in sequence from coarse to fine with sandpaper, the samples are polished in sequence from large to small particle sizes with diamond polishing liquid until the sample surface reaches a mirror effect.

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