CN-122016443-A - Corrosion method of austenitic grains of composite board stainless steel

Abstract

The invention discloses a corrosion method of austenitic grains of stainless steel of a composite plate, which comprises the following steps of step 1, preheating a sample, namely soaking and preheating a metallographic sample in hot water to obtain a preheated sample, step 2, corroding and cleaning the sample in a hot water bath, namely corroding the preheated sample in step 1 by adopting corrosive liquid, cleaning and heating the sample in the hot water after the reaction rate is reduced, removing a surface passivation layer, repeating the operation until the surface of the sample is gray, no reflection exists, and drying to obtain the corroded sample. The corrosion method can effectively improve the austenitic grain corrosion effect, quicken the corrosion speed and solve the problem that the austenitic grain boundary of the composite board stainless steel shows unclear.

Inventors

• YANG JING
• WANG XIAOFENG
• HUANG LEI
• XU RONGJIE

Assignees

• 鞍钢股份有限公司

Dates

Publication Date

20260512

Application Date

20260209

Claims (6)

1. 1. The corrosion method of the austenitic grains of the stainless steel of the composite plate is characterized by comprising the following steps: step 1, preheating a sample, namely soaking and preheating a metallographic sample in hot water to obtain a preheated sample; And 2, corroding and cleaning the sample in a hot water bath, namely corroding the preheated sample in the step 1 by adopting a corrosive liquid, placing the sample in the hot water for cleaning and heating after the reaction rate is reduced, removing a surface passivation layer, repeating the operation until the surface of the sample is gray, has no reflection, and drying to obtain the sample after corrosion treatment.
2. 2. The etching method according to claim 1, wherein the preheating conditions in step 1 are as follows: The preheating temperature is 60-100 ℃; the preheating time is 1-2 min.
3. 3. The corrosion method according to claim 1, wherein the corrosion liquid in the step 2 is a mixed liquid of concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1:3-5, wherein the concentration of the concentrated nitric acid is 14-16 mol/L, and the concentration of the concentrated hydrochloric acid is 11.6-12.4 mol/L.
4. 4. The corrosion method according to claim 1, wherein the corrosion treatment in the step 2 is specifically carried out by immersing the preheated sample in a corrosion solution for 30-60 s to carry out corrosion reaction, and adjusting the volume ratio of hydrochloric acid in the corrosion solution according to the intensity of corrosion, so that no bubbles appear on the corrosion surface and the reaction rate is high.
5. 5. The etching method according to claim 1, wherein the temperature of the hot water in the step 2 is 60 to 100 ℃, the heating time is 30 to 60 seconds, and the steps are repeated 1 to 3 times.
6. 6. The method of etching according to claim 1, wherein the sample after the etching treatment obtained in step 2 has austenite grain boundaries with sharp grain boundaries.

Description

Corrosion method of austenitic grains of composite board stainless steel Technical Field The invention belongs to the technical field of microstructure analysis quantitative characterization detection, and particularly relates to a corrosion method for austenitic grains of stainless steel of a composite plate. Background Composite boards, generally referred to as plates that achieve a strong metallurgical bond of two or more metals of different materials by rolling, explosion or bead welding processes. Composite panels of common steels (e.g., carbon steel such as Q235B, Q345R or low alloy steel) and stainless steels (e.g., 304, 316L, etc.) are one of the most widely used types. The core design concept is complementary advantages, namely the strength, rigidity and low cost of common steel materials are used as a base material (base layer), and the excellent corrosion resistance of stainless steel is used as a covering material (multi-layer). On the premise of ensuring the corrosion resistance of the contact corrosion medium surface, the manufacturing cost of the equipment is greatly reduced. Stainless steel generally only accounts for 10% -20% of the whole thickness (the thickness of a common cladding is 1.5-3 mm), but 100% of corrosion resistance is provided, and a large amount of noble metal is saved. Grain size is an index for measuring the size of the internal grains of a metal, and has a decisive influence on the performance of the metal material. For austenitic stainless steel cladding, its grain size is a key metallographic index for assessing its quality and performance. The fine-grained composite layer has higher strength, and is less prone to cracking or generating defects when being deformed in cooperation with the base layer (such as equipment bearing or rolling). Under the low-temperature environment, the fine grains can prevent crack growth, and the low-temperature impact toughness of the material is remarkably improved. Coarse grains can embrittle the material. For composite board equipment (such as liquefied natural gas storage tanks) used in low temperature environments, fine grains of the clad stainless steel are critical to ensure the safety of the overall structure. Grain boundaries are regions of high energy in the material, typically where corrosion (especially intergranular corrosion) is likely to begin. The grains are coarse and the number of grain boundaries per unit area is reduced, but the segregation of impurities (such as carbides) at each grain boundary may be more serious, forming a continuous corrosion channel, and significantly reducing the intergranular corrosion resistance. The crystal grains are fine, the total number of crystal boundaries is increased, the corrosion path becomes tortuous, the impurity concentration on the unit crystal boundary is relatively low, the formation of continuous corrosion channels is destroyed, and the inter-crystal corrosion resistance is improved. The fine grain structure generally means a more uniform microstructure, can reduce the initiation point of pitting corrosion, and has a positive effect on pitting corrosion resistance. Corrosion resistance is the core mission of the cladding. The control of the composite layer to be a fine grain structure is a key for ensuring that the composite board does not have corrosion failure in the design life. Therefore, the requirement of evaluating whether the composite board has austenite grain size or not is an important index for evaluating whether the composite board is qualified or not. Conventional corrosion cannot uniformly and clearly corrode crystal grains on one side of the austenitic steel of the composite plate, and the assessment of the austenitic grain size can be influenced. Therefore, aiming at the problem that the grain boundary of the austenite crystal grain of the composite board is difficult to display, a novel method for corroding the austenite microstructure of the composite board is innovatively formed from a corrosive agent, a corrosion method and a preparation method. Disclosure of Invention The invention aims to provide a metallographic specimen preparation technology for corroding austenitic grains of composite board stainless steel, which adopts a special method for treating corrosive liquid to corrode the specimen, and the specimen preparation method is repeated for a plurality of times to remove a surface passivation film and accelerate the corrosion speed, so that the austenitic grain corrosion effect can be effectively improved, the corrosion speed is accelerated, and the problem that the austenitic grain boundaries of the composite board stainless steel are not clearly displayed is solved. According to an aspect of the present invention, there is provided a method of etching austenite grains of a composite plate stainless steel, comprising the steps of: step 1, preheating a sample, namely soaking and preheating a metallographic sample in hot water to obtain a preheated sam