304 austenitic stainless steel grain size by etching

Abstract

The application discloses a corrosion method for grain size of 304 austenitic stainless steel, and comprises the following steps: (1) mixing sulfuric acid aqueous solution and potassium permanganate to obtain a corrosion agent; (2) placing a 304 austenitic stainless steel sample with a detection surface upward in the corrosion agent, and taking out after heating; (3) wiping the detection surface of the sample with an oxalic acid aqueous solution, washing, drying, and observing under a metallographic microscope. The corrosion reagent raw materials, i.e. potassium permanganate, concentrated sulfuric acid, water and oxalic acid, are easy to obtain; the corrosion agent is heated to small bubbles, the temperature is low, there is no spatter, and the safety is high; the corrosion time can be adjusted according to the corrosion condition, the operation is simple, the austenitic grain boundary can be uniformly and clearly displayed, and the success rate of the grain size corrosion is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel corrosion, in particular to a corrosion method for 304 austenitic stainless steel grain size. BACKGROUND

[0002] Stainless steel has high corrosion resistance, so the corrosion reagent for showing its microstructure must have strong corrosion, so as to clearly show the structure. The corrosion of stainless steel is usually selected according to the composition and heat treatment state of the steel. At present, the picric acid hydrochloric acid alcohol solution corrosion method is commonly used as a kind of detection method for stainless steel corrosion, and is widely used for detecting the grain size of stainless steel. The disadvantages are: (1) picric acid (trinitrophenol) is toxic, which can easily cause skin yellowing, and is a material for making explosives, which is difficult to buy; (2) the method for showing grain size is not easy to master for inexperienced operators, and often fails, resulting in incomplete corrosion of grain boundary, and the result of judging the grain size of austenitic steel cannot be determined.

[0003] Therefore, there is an urgent need for a stainless steel corrosion method which is easy to operate, safe and environmentally friendly. SUMMARY

[0004] The purpose of the present application is to provide a corrosion method for 304 austenitic stainless steel grain size, which has the advantages of easy-to-obtain reagent, low cost, easy operation, safety, environmental protection, high success rate, etc., can ensure clear and complete corrosion of grain boundary, avoid twin crystal, and clearly observe the grain boundary of the corrosion sample under the optical microscope, which is beneficial to the grain size rating, and has high popularization and application value in the industry.

[0005] In order to achieve the above purpose, the present application provides a corrosion method for 304 austenitic stainless steel grain size, which comprises:

[0006] (1) mixing sulfuric acid aqueous solution and potassium permanganate to obtain a corrosion agent;

[0007] (2) placing the 304 austenitic stainless steel sample detection surface upward in the corrosion agent, and taking it out after heating;

[0008] (3) wiping the sample detection surface with oxalic acid aqueous solution, washing, drying, and observing under a metallographic microscope.

[0009] Through the above technical solution, the present application selects potassium permanganate, concentrated sulfuric acid, water and oxalic acid as the raw materials of the corrosion reagent, which is easy to obtain; the corrosion agent is heated to small bubbles, the temperature is low, there is no spatter, and the safety is high; the corrosion time can be adjusted according to the corrosion condition, the operation is simple, the austenitic grain boundary can be clearly and uniformly displayed, and the success rate of grain size corrosion is greatly improved.

[0010] Other features and advantages of the present application will be described in detail in the following specific embodiments. Attached Figure Description

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0012] Figure 1 This is a grain size diagram of potassium permanganate-sulfuric acid aqueous solution corrosion in Example 1;

[0013] Figure 2 This is a grain size diagram of potassium permanganate-sulfuric acid aqueous solution corrosion in Example 2;

[0014] Figure 3 Comparative Example 1: Grain size diagram of picrate acid-alcohol solution corrosion.

[0015] Figure 4 This is a grain size diagram of potassium permanganate-sulfuric acid aqueous solution corrosion under short-term conditions, as shown in Comparative Example 2.

[0016] Figure 5 This is a grain size diagram of potassium permanganate-sulfuric acid aqueous solution used for long-term corrosion in Comparative Example 3. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0018] This invention provides a method for etching 304 austenitic stainless steel according to grain size, the method comprising:

[0019] (1) A corrosive agent is obtained by mixing an aqueous solution of sulfuric acid with potassium permanganate;

[0020] (2) Place the 304 austenitic stainless steel sample with the test surface facing up in the corrosive agent, heat it and then take it out;

[0021] (3) Wipe the test surface of the sample with oxalic acid aqueous solution, wash, dry, and observe under a metallographic microscope.

[0022] The corrosion method of the present invention uses readily available corrosive materials, is safe and convenient to operate, and has a high success rate.

[0023] According to a preferred embodiment of the present invention, the ratio of sulfuric acid aqueous solution can be selected within a wide range. However, in order to improve the corrosive effect of the corrosive agent, in step (1), the volume ratio of concentrated sulfuric acid to water in the sulfuric acid aqueous solution is 1:8-9.

[0024] According to a preferred embodiment of the present application, the mass ratio of potassium permanganate to aqueous sulfuric acid solution can be selected in a wide range, but in order to improve the corrosion effect of the corrosion agent, in step (1), the mass ratio of potassium permanganate to aqueous sulfuric acid solution is 1:45-50.

[0025] According to a preferred embodiment of the present application, the state of the 304 austenitic stainless steel sample can be selected in a wide range, but in order to obtain better corrosion effect, in step 2), the 304 austenitic stainless steel sample is a well-polished 304 stainless steel sample.

[0026] According to a preferred embodiment of the present application, the amount of corrosion agent can be selected in a wide range, but in order to make the grain boundary corrosion of the obtained sample clear and complete, in step (2), the amount of corrosion agent is 2-3 times the height of the sample.

[0027] According to a preferred embodiment of the present application, the heating condition can be selected in a wide range, but in order to make the grain boundary corrosion of the obtained sample clear and complete, in step (2), the heating condition is to place the solution on a hot plate with a heat insulation pad for heating, and when continuous bubbles appear in the solution, continue heating and take out the sample after timing for 20-25 min.

[0028] According to a preferred embodiment of the present application, the mass fraction of oxalic acid in the aqueous oxalic acid solution is selected in a wide range, but in order to make the corrosion effect better, in step (3), the mass fraction of oxalic acid in the aqueous oxalic acid solution is 1%-5%.

[0029] According to a preferred embodiment of the present application, the wiping condition can be selected in a wide range, but in order to make the corrosion effect better, in step (3), the wiping condition is to stop wiping when the detection surface of the sample is uniformly light gray.

[0030] According to a preferred embodiment of the present application, the washing condition can be selected in a wide range, but in order to make the observation effect better, in step (3), the washing condition is to rinse the entire sample with flowing clean water.

[0031] According to a preferred embodiment of the present application, the drying condition can be selected in a wide range, but in order to make the observation effect better, in step (3), the drying condition is to dry the surface of the sample with a hair dryer.

[0032] The present application will be described in detail below through examples. In the following examples, the drugs and reagents are all conventional commercially available products.

[0033] Example 1

[0034] (1) 10 mL of concentrated sulfuric acid was added into a beaker containing 90 mL of deionized water, and 2 g of potassium permanganate reagent was added, and stirred with a glass rod to dissolve completely for use;

[0035] (2) The polished 304 stainless steel sample test surface was placed in an empty beaker with the test surface facing up, then the prepared etchant of step (1) was added, the height of the etchant was 2 times the height of the sample, then it was placed on the electric heating plate with heat insulation pad for heating, when continuous bubbles appeared in the solution, the timing started, after heating for 20 min, the sample was taken out, then the sample test surface was wiped with 1% oxalic acid aqueous solution, when the test surface was uniform light gray, the whole sample was rinsed with flowing water, then the sample was blown dry immediately;

[0036] (3) The dried sample was placed under a metallographic microscope for observation.

[0037] As shown in Figure 1 , it can be seen that the sample grain boundary is clear and no mixed crystal appears.

[0038] Example 2

[0039] (1) 10 mL of concentrated sulfuric acid was added into a beaker containing 90 mL of deionized water, and 2 g of potassium permanganate reagent was added, and stirred with a glass rod to dissolve completely for use;

[0040] (2) The polished 304 stainless steel sample test surface was placed in an empty beaker with the test surface facing up, then the prepared etchant of step (1) was added, the height of the etchant was 2 times the height of the sample, then it was placed on the electric heating plate with heat insulation pad for heating, when continuous bubbles appeared in the solution, the timing started, after heating for 20 min, the sample was taken out, then the sample test surface was wiped with 1% oxalic acid aqueous solution, when the test surface was uniform light gray, the whole sample was rinsed with flowing water, then the sample was blown dry immediately;

[0041] (3) The dried sample was placed under a metallographic microscope for observation.

[0042] As shown in Figure 2 , it can be seen that the sample grain boundary is clear and no mixed crystal appears.

[0043] Example 3

[0044] (1) 10 mL of concentrated sulfuric acid was added into a beaker containing 90 mL of deionized water, and 2 g of potassium permanganate reagent was added, and stirred with a glass rod to dissolve completely for use;

[0045] (2) Put the polished 304 stainless steel sample with the test surface facing up in an empty beaker, then add the prepared etchant of step (1), the height of the etchant is 3 times the height of the sample, then place it on the electric heating plate with a heat insulation pad for heating, start timing when there are continuous bubbles in the solution, take out the sample after heating for 20 min, then wipe the test surface of the sample with 5% oxalic acid aqueous solution, when the test surface is uniformly light gray, then rinse the entire sample with flowing clean water, and then immediately dry the sample;

[0046] (3) Place the dried sample under a metallographic microscope for observation.

[0047] The etching result of the sample is the same as that of Example 1, and the grain boundaries of the sample are clearly visible, and no mixed crystals appear.

[0048] Comparative Example 1

[0049] (1) Weigh 4g of picric acid, and measure 5mL of hydrochloric acid and 100mL of alcohol into a clean 150mL beaker, and stir with a glass rod to dissolve completely for later use;

[0050] (2) Place the polished 304 stainless steel sample with the test surface facing up in an empty beaker, then pour the prepared picric acid etchant into the beaker containing the sample until the etchant completely covers the height of the sample, then constantly shake the sample beaker and start timing, take out the sample after 10 min, then clean the test surface of the sample with alcohol solution, and then immediately dry the sample;

[0051] (3) Finally, place the sample under a metallographic microscope to observe the grain size and grain boundary corrosion.

[0052] As shown in Figure 3 , it can be seen that the sample has no clear etched grain boundaries.

[0053] Comparative Example 2

[0054] According to the method of Comparative Example 1, except that the etching time is extended to 20 min.

[0055] The etching result of the sample is the same as that of Comparative Example 1, and the sample has no clear etched grain boundaries.

[0056] Comparative Example 3

[0057] The operation is the same as that of Comparative Example 1, except that the etching time is extended to 30 min.

[0058] The etching result of the sample is the same as that of Comparative Example 1, and the sample has no clear etched grain boundaries.

[0059] Comparative Example 4

[0060] (1) 10mL of concentrated sulfuric acid is added into a beaker containing 100mL of deionized water, and then 5g of potassium permanganate reagent is added, which is fully dissolved by stirring with a glass rod for standby;

[0061] (2) The polished 304 stainless steel sample test surface is placed in an empty beaker with the test surface facing up, and then the prepared etchant of step (1) is added, the height of the etchant is 2 times the height of the sample, and then it is placed on the electric heating plate with a heat insulation pad for heating, when continuous bubbles appear in the solution, timing starts, after heating for 10min, the sample is taken out, and then the test surface of the sample is wiped with 1% oxalic acid aqueous solution, when the test surface is uniformly light gray, the whole sample is washed with flowing clean water, and then the sample is blown dry immediately;

[0062] (3) The dried sample is placed under a metallographic microscope for observation.

[0063] As shown in Figure 4 , it can be seen that the grain boundary of the sample is unevenly displayed, and there is a mixed crystal phenomenon.

[0064] Comparative Example 5

[0065] (1) 10mL of concentrated sulfuric acid is added into a beaker containing 100mL of deionized water, and then 5g of potassium permanganate reagent is added, which is fully dissolved by stirring with a glass rod for standby;

[0066] (2) The polished 304 stainless steel sample test surface is placed in an empty beaker with the test surface facing up, and then the prepared etchant of step (1) is added, the height of the etchant is 2 times the height of the sample, and then it is placed on the electric heating plate with a heat insulation pad for heating, when continuous bubbles appear in the solution, timing starts, after heating for 30min, the sample is taken out, and then the test surface of the sample is wiped with 1% oxalic acid aqueous solution, when the test surface is uniformly light gray, the whole sample is washed with flowing clean water, and then the sample is blown dry immediately;

[0067] (3) The dried sample is placed under a metallographic microscope for observation.

[0068] As shown in Figure 5 , it can be seen that the grain boundary of the sample is unevenly displayed, and there is a mixed crystal phenomenon.

[0069] From the above examples, it can be seen that in the present application, in order to ensure that the sample has clear grain boundaries and no mixed crystal phenomenon, the optimal proportion of the etchant is 10mL of concentrated sulfuric acid, 90mL of deionized water and 2g of potassium permanganate, and the optimal etching time is 20min.

[0070] The above describes the preferred embodiments of the present application, but the present application is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0071] It should be further noted that any technically feasible combination of the various technical features described in the above embodiments is possible, provided that there is no contradiction, and the disclosure of the present application should be deemed to include all such technically feasible combinations.

[0072] Furthermore, any combination of the various embodiments of the present application is possible, provided that there is no contradiction, and the disclosure of the present application should be deemed to include all such technically feasible combinations.

Claims

1. A method of etching the grain size of 304 austenitic stainless steel, characterized by, The method comprises: 1) mixing sulfuric acid aqueous solution and potassium permanganate to obtain a corrosive agent; 2) placing a 304 austenitic stainless steel sample with the detection surface facing upward in the corrosive agent, and taking out after heating; 3) wiping the detection surface of the sample with oxalic acid aqueous solution, washing, drying, and observing under a metallographic microscope; In step 1), the volume ratio of concentrated sulfuric acid to water in the sulfuric acid aqueous solution is 1:8-9; In step 1), the mass ratio of potassium permanganate to sulfuric acid aqueous solution is 1:45-50; In step 2), the 304 austenitic stainless steel sample is a well-polished 304 stainless steel sample; In step 2), the amount of the corrosive agent is 2-3 times the height of the sample; In step 2), the heating condition is that the solution is placed on an electric heating plate with a heat insulation pad for heating, and the sample is taken out after 20-25 min of continuous bubble appearance in the solution; In step 3), the mass fraction of oxalic acid in the oxalic acid aqueous solution is 1%-5%; In step 3), the wiping condition is that when the detection surface of the sample is uniformly light gray, the wiping is stopped; In step 3), the washing condition is that the whole sample is rinsed with flowing clean water; In step 3), the drying condition is that the surface of the sample is blown dry with a hair dryer.

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