Method for eliminating twinning grain boundaries of TP316H austenitic stainless steel

Abstract

The invention relates to a method for eliminating twin grain boundaries of TP316H austenitic stainless steel. The method comprises the following steps: grinding and polishing a TP316H austenitic stainless steel sample to be detected; a nitric acid aqueous solution with the volume fraction larger than 60% is used as an electrolytic agent to be poured into an electrolytic bath, after electrolytic corrosion is conducted, the corrosion face of the TP316H austenitic stainless steel sample is placed under a microscope to be observed, the non-twinning grain boundary of the TP316H austenitic stainless steel sample is completely visible, and the twinning grain boundary of the TP316H austenitic stainless steel sample is invisible. According to the method, the twinning grain boundaries of the grains of the TP316H austenitic stainless steel in the forging state or the forging solid solution state can be effectively eliminated, only non-twinning grain boundaries are reserved, interference of the twinning grain boundaries of the TP316H austenitic stainless steel on grain size evaluation and measurement is eliminated, and the purpose of accurate evaluation and measurement is achieved. According to the method, generation of twinning grain boundaries of the TP316H austenitic stainless steel can be inhibited in the ionization process of high-concentration NO3 <-> ions in the nitric acid solution, and only the non-twinning grain boundaries of the TP316H austenitic stainless steel are displayed.

Description

Technical Field

[0001] The invention belongs to the technical field of physical detection of metal materials, and in particular relates to a method for eliminating twin grain boundaries of TP316H austenitic stainless steel. Background Art

[0002] Grain size is an important microscopic technical parameter of steel materials, which can directly reflect its intrinsic properties, especially hot processing properties, such as grain size control in high temperature treatment, mixed crystal inhomogeneity caused by thermal deformation, and the relationship between deformed grains and recrystallization. Therefore, the accuracy of grain size assessment is crucial. Grain size assessment first requires appropriate corrosion methods to display grain boundaries, and the rating is completed by microscopic observation and comparison with standard maps. TP316H austenitic stainless steel, as a special steel, generally displays grain boundaries through electrolysis or electrochemical solution corrosion. In this process, twin grain boundaries are prone to appear, which interferes with grain size assessment. Summary of the invention

[0003] The invention provides a method for eliminating twin grain boundaries of TP316H austenitic stainless steel, and the technical problem to be solved is: to make TP316H austenitic stainless steel only display actual grain boundaries but not twin grain boundaries.

[0004] In order to solve the above technical problems, the present invention provides a method for eliminating twin grain boundaries of TP316H austenitic stainless steel, characterized in that the steps are as follows:

[0005] Step 1: Grind and polish the TP316H austenitic stainless steel sample to be tested;

[0006] Step 2: Use a nitric acid aqueous solution with a volume fraction greater than 60% as an electrolytic agent and pour it into the electrolytic cell;

[0007] Step 3: Place the lead plate bent into an "L" shape as the cathode and connect the cathode fixture to the electrolytic cell. The electrolytic cell is powered on with a working current of 1.5A to 2.0A. After the anode fixture is clamped on the TP316H austenitic stainless steel sample, the test surface is immersed in the electrolytic agent for 40 to 60 seconds of corrosion.

[0008] Step 4: After the electrolytic corrosion step, take out the TP316H austenitic stainless steel sample, rinse it under clean water, spray it with anhydrous ethanol, and blow it dry.

[0009] Beneficial effects: The present invention utilizes the fact that during the electrolysis test, corrosion preferentially reacts between the high-energy area of ​​the grain boundary with a higher potential difference and the low-energy area inside the grain. The large amount of NO3- in the high-concentration nitric acid solution inhibits the electrolysis reaction between the twin grain boundaries with a lower potential difference and the interior of the grain. The purpose of eliminating the twin boundaries is achieved by controlling factors that affect the corrosion effect, such as current density, electrolytic corrosion time, and cathode plate material selection.

[0010] The present invention can effectively eliminate the twin grain boundaries of TP316H austenitic stainless steel in a forged state or a forged solid solution state, retain only non-twin grain boundaries, eliminate the interference of the twin grain boundaries of TP316H austenitic stainless steel on the evaluation and measurement of grain size, and achieve the purpose of accurate evaluation and measurement.

[0011] The invention can make the high-concentration NO3- ions in the nitric acid solution inhibit the generation of twin grain boundaries of TP316H austenitic stainless steel during the ionization process, and only display the non-twin grain boundaries of TP316H austenitic stainless steel.

[0012] The present invention has the following characteristics:

[0013] 1. Strong pertinence, suitable for TP316H austenitic stainless steel;

[0014] 2. The electrolytic corrosion method is simple and easy to operate;

[0015] 3. The matrix is ​​bright white, the non-twinned grain boundaries are clearly displayed, and the formation of twinned grain boundaries is inhibited;

[0016] 4. The non-twinned grain boundaries of the grains are displayed completely without twin interference, which improves the accuracy of grain size measurement and evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an existing technology, a picture showing the effect of electrolytic corrosion of a TP316H austenitic stainless steel sample by 10% oxalic acid aqueous solution and observation under a microscope at 100 times magnification;

[0018] Figure 2 This is a grain corrosion effect diagram of the TP316H austenitic stainless steel sample of Example 1 of the present invention in the experimental example;

[0019] Figure 3 This is a grain corrosion effect diagram of the TP316H austenitic stainless steel sample of Example 2 of the present invention in the experimental example;

[0020] Figure 4 This is a grain corrosion effect diagram of the TP316H austenitic stainless steel sample of Example 3 of the present invention in the experimental example. DETAILED DESCRIPTION

[0021] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0022] The present invention provides a method for eliminating twin grain boundaries of TP316H austenitic stainless steel, comprising the following steps:

[0023] Step 1: Prepare TP316H austenitic stainless steel sample and make polished sample according to the metallographic sample preparation procedure;

[0024] Step 2: Prepare the electrolytic cell equipment and configure the voltage limiting function. The maximum output voltage does not exceed 15V. The electrolytic cell is equipped with two external holes or wires connected to the sample metal fixture as cathode and anode respectively;

[0025] Step 3: Prepare a lead plate as the cathode plate, with a size of 100mm to 120mm in width and 2mm to 3mm in thickness, which can provide a reliable reaction current. An inert material with excellent conductive properties is preferred, which does not chemically react with concentrated nitric acid in a static state, and has good component uniformity, ensuring uniform electrolysis output current. The present invention selects a lead plate as the cathode plate.

[0026] Step 4: Pour a nitric acid aqueous solution with a volume ratio greater than 60% into the electrolytic cell as an electrolytic agent. The solute nitric acid is analytical grade and the water can be industrial water. The minimum liquid level is 20mm;

[0027] Step 5: Bend the lead plate in an "L" shape along the length direction of the lead plate and place it in the electrolyte in the electrolytic cell, and place it in full contact with the bottom of the electrolytic cell and place it steadily. Use the cathode clamp to clamp the lead plate, and the lowest clamping position is more than 10mm above the surface of the electrolytic agent. Power on the electrolytic cell with a working current of 1.5A to 2.0A. Use the anode clamp to clamp the TP316H austenitic stainless steel sample and immerse the test surface in the electrolytic agent. During the corrosion process, hold the sample steadily and keep a horizontal distance of more than 10mm from the cathode lead plate. The corrosion time is 40 seconds to 60 seconds.

[0028] In this preferred embodiment, the volume concentration of the nitric acid aqueous solution is 80%, the working current is 1.5A, the sample corrosion time is 50 seconds, and the distance from the cathode lead plate is maintained at 20mm. The corrosion process is best carried out in a ventilated kitchen, and a small amount of nitric acid solution will evaporate during the electrolysis process.

[0029] Step 6: After the electrolytic corrosion step is completed, take out the TP316H austenitic stainless steel sample, rinse it with clean water for 5 to 10 seconds, and blow it dry; in this preferred embodiment, rinse it with clean water for 6 seconds and blow it with a hair dryer at medium speed; spray anhydrous ethanol on the inspection surface and blow it dry;

[0030] Step 7: The corroded surface of the TP316H austenitic stainless steel sample was placed under a microscope to observe the grain morphology at 100 times, 200 times or 400 times. It was found that the twin grain boundary of the TP316H austenitic stainless steel sample was eliminated.

[0031] By adopting the above electrolysis conditions, the grain boundaries of the TP316H austenitic stainless steel sample can be displayed completely and clearly, and the twin boundaries are not displayed.

[0032] Further: the working current is 2.0A, the volume ratio concentration of the nitric acid aqueous solution is 90%, the horizontal distance between the cathode lead plate and the anode sample is 20mm, the sample is immersed for 45 seconds, and rinsed with clean water for 6 seconds.

[0033] The electrolysis process should be carried out in a ventilated environment, and the test personnel should wear masks and plastic gloves while working.

[0034] Embodiment 1:

[0035] The method for eliminating twin grain boundaries of TP316H austenitic stainless steel comprises the following steps:

[0036] Step 1: Prepare TP316H austenitic stainless steel sample and make polished sample according to the metallographic sample preparation procedure;

[0037] Step 2: Prepare the electrolytic cell equipment and configure the voltage limiting function. The maximum output voltage does not exceed 15V. The electrolytic cell is equipped with two external holes or wires connected to the sample metal fixture as cathode and anode respectively;

[0038] Step 3: Prepare lead plate as cathode plate, with size specification of 100mm width and 3mm thickness, which can provide reliable reaction current;

[0039] Step 4: Pour 80% nitric acid aqueous solution as electrolyte into the electrolytic cell, with the liquid level at 25 mm. Bend the lead plate in an "L" shape along the length of the lead plate and place it in the electrolyte in the electrolytic cell, and place it in full contact with the bottom of the electrolytic cell and place it stably. Clamp the lead plate with a cathode clamp, with the lowest clamping position 20 mm away from the surface of the electrolyte.

[0040] Step 5: Power on the electrolytic cell with a working current of 1.5A. Use the cathode clamp to clamp the lead plate and place it in the electrolytic agent in the electrolytic cell. Use the anode clamp to clamp the TP316H austenitic stainless steel sample and immerse the test surface in the electrolytic agent. During the corrosion process, hold the sample steadily and keep a horizontal distance of 15mm from the cathode lead plate. The corrosion time is 50 seconds.

[0041] Step 6: Take out the TP316H austenitic stainless steel sample, rinse it with clean water for 6 seconds, and blow dry it with a hair dryer at medium speed;

[0042] Step 7: Place the corroded surface of the TP316H austenitic stainless steel sample under a microscope at 100 times magnification to observe the grain morphology, and it is found that the twin grain boundaries of the TP316H austenitic stainless steel sample are eliminated. Figure 2 As shown, it is the grain corrosion effect of the TP316H austenitic stainless steel sample in the present invention, showing only the non-twinned grain boundaries.

[0043] Embodiment 2:

[0044] The method for eliminating twin grain boundaries of TP316H austenitic stainless steel comprises the following steps:

[0045] Step 1: Prepare TP316H austenitic stainless steel sample and make polished sample according to the metallographic sample preparation procedure;

[0046] Step 2: Prepare the electrolytic cell equipment and configure the voltage limiting function. The maximum output voltage does not exceed 15V. The electrolytic cell is equipped with two external holes or wires connected to the sample metal fixture as cathode and anode respectively;

[0047] Step 3: Prepare lead plate as cathode plate, with size specification of 110mm width and 2mm thickness, which can provide reliable reaction current;

[0048] Step 4: Pour a 90% nitric acid aqueous solution as an electrolyte into the electrolytic cell, with a liquid level of 30 mm. Bend the lead plate in an "L" shape along the length of the lead plate and place it in the electrolyte in the electrolytic cell, and place it in full contact with the bottom of the electrolytic cell and place it stably. Clamp the lead plate with a cathode clamp, with the lowest clamping position 20 mm away from the surface of the electrolyte.

[0049] Step 5: Power on the electrolytic cell with a working current of 1.8A. Use the cathode clamp to clamp the lead plate and place it in the electrolytic agent in the electrolytic cell. Use the anode clamp to clamp the TP316H austenitic stainless steel sample and immerse the test surface in the electrolytic agent. During the corrosion process, hold the sample steadily and keep a horizontal distance of 20mm from the cathode lead plate. The corrosion time is 45 seconds.

[0050] Step 6: Take out the TP316H austenitic stainless steel sample, rinse it with clean water for 8 seconds, and blow dry it with a hair dryer at medium speed;

[0051] Step 7: Place the corroded surface of the TP316H austenitic stainless steel sample under a microscope at 100 times magnification to observe the grain morphology, and it is found that the twin grain boundaries of the TP316H austenitic stainless steel sample are eliminated. Figure 3 As shown, it is the grain corrosion effect of the TP316H austenitic stainless steel sample in the present invention, showing only the non-twinned grain boundaries.

[0052] Embodiment 3:

[0053] The method for eliminating twin grain boundaries of TP316H austenitic stainless steel comprises the following steps:

[0054] Step 1: Prepare TP316H austenitic stainless steel sample and make polished sample according to the metallographic sample preparation procedure;

[0055] Step 2: Prepare the electrolytic cell equipment and configure the voltage limiting function. The maximum output voltage does not exceed 15V. The electrolytic cell is equipped with two external holes or wires connected to the sample metal fixture as cathode and anode respectively;

[0056] Step 3: Prepare lead plate as cathode plate, with size specification of 120mm width and 3mm thickness, which can provide reliable reaction current;

[0057] Step 4: Pour 100% nitric acid pure solution as electrolyte into the electrolytic cell, with the liquid level at 20mm. Bend the lead plate in an "L" shape along the length of the lead plate and place it in the electrolyte in the electrolytic cell, and place it in full contact with the bottom of the electrolytic cell and place it stably. Clamp the lead plate with a cathode clamp, with the lowest clamping position 20mm away from the surface of the electrolyte.

[0058] Step 5: Power on the electrolytic cell with a working current of 2.0A. Use the cathode clamp to clamp the lead plate and place it in the electrolytic agent in the electrolytic cell. Use the anode clamp to clamp the TP316H austenitic stainless steel sample and immerse the test surface in the electrolytic agent. During the corrosion process, hold the sample steadily and keep a horizontal distance of 30mm from the cathode lead plate. The corrosion time is 40 seconds.

[0059] Step 6: Take out the TP316H austenitic stainless steel sample, rinse it with clean water for 10 seconds, and blow dry it with a hair dryer;

[0060] Step 7: Place the corroded surface of the TP316H austenitic stainless steel sample under a microscope at 100 times magnification to observe the grain morphology, and it is found that the twin grain boundaries of the TP316H austenitic stainless steel sample are eliminated. Figure 4 As shown, it is the grain corrosion effect of the TP316H austenitic stainless steel sample in the present invention, showing only the non-twinned grain boundaries.

[0061] The present invention selects a suitable solution and a suitable cathode plate, and controls the working current, corrosion time, solution properties and concentration. The elimination method comprises the following steps: grinding and polishing a TP316H austenitic stainless steel sample to be tested; using a nitric acid aqueous solution with a volume fraction greater than 60% as an electrolytic agent and pouring it into an electrolytic cell; placing a lead plate bent into an "L" shape as a cathode connecting metal clamp in the electrolytic cell, and electrifying the electrolytic cell with a working current of 1.5A to 2.0A; clamping the TP316H austenitic stainless steel sample with an anode clamp and immersing the inspection surface in the electrolytic agent for a corrosion time of 40 seconds to 60 seconds, holding the sample stably during the corrosion process and maintaining a horizontal distance of more than 10 mm from the cathode lead plate; after the electrolytic corrosion step is completed, taking out the TP316H austenitic stainless steel sample, rinsing it with clean water, spraying it with anhydrous ethanol, and blowing it dry; placing the corrosion surface of the TP316H austenitic stainless steel sample under a microscope for observation, the non-twinned grain boundary of the TP316H austenitic stainless steel sample is completely visible, and the twinned grain boundary of the TP316H austenitic stainless steel sample is invisible.

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for eliminating twin grain boundaries in TP316H austenitic stainless steel. It is characterized in that Here are the steps: Step 1: Grind and polish the TP316H austenitic stainless steel sample to be tested; Step 2: Use a nitric acid aqueous solution with a volume fraction greater than 60% as an electrolytic agent and pour it into the electrolytic cell; Step 3: Place the lead plate bent into an "L" shape as the cathode and connect the cathode fixture to the electrolytic cell. The electrolytic cell is powered on with a working current of 1.5A to 2.0A. After the anode fixture is clamped on the TP316H austenitic stainless steel sample, the test surface is immersed in the electrolytic agent for 40 seconds to 60 seconds of corrosion. Step 4: After the electrolytic corrosion step, take out the TP316H austenitic stainless steel sample, rinse it under clean water, spray it with anhydrous ethanol, and blow it dry.

2. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: During the corrosion process, the sample should be clamped steadily and maintained at a horizontal distance of more than 10 mm from the cathode lead plate.

3. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: The electrolytic cell is equipped with a voltage limiting function, and the maximum output voltage does not exceed 15V. The electrolytic cell is provided with two external holes or wires for connecting with the metal fixture of the sample as cathode and anode respectively.

4. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: The lead plate dimensions are 100mm to 120mm in width and 2mm to 3mm in thickness.

5. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: The solute nitric acid is analytical grade and industrial water can be used.

6. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: The minimum liquid level of the electrolyte poured into the electrolytic cell is 20mm.

7. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: After the electrolytic corrosion step is completed, the TP316H austenitic stainless steel sample is taken out, rinsed with clean water for 5 to 10 seconds, and blown dry.

8. A method for eliminating twin grain boundaries of TP316H austenitic stainless steel according to claim 1, Features: The corroded surface of the corroded TP316H austenitic stainless steel sample was placed under a microscope to observe the grain morphology at 100 times, 200 times or 400 times, and it was found that the twin grain boundary of the TP316H austenitic stainless steel sample was eliminated.

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