Method for preparing acid leaching test blocks

Abstract

This invention discloses a method for manufacturing an acid etching test block, aiming to provide a versatile and reliable acid etching test block. The invention is achieved through the following technical solution: Based on the acid etching test standards for steel parts, at least 8mm thick high-carbon steel is used for acid etching to prepare a standard test block for steel tempering and acid etching inspection. Samples are then taken and observed under a metallographic microscope, and compared with the actual acid etching test results. Based on the materials, various types of test blocks conforming to the standards are selected: tempered burn test blocks are designated as Type A, over-tempered burn test blocks as Type B, unburned test blocks as Type C, and quenched burn test blocks as Type D. Acid etching is performed based on the test results of the high-carbon steel acid etching test blocks. The color difference displayed on the surface of the obtained test blocks is then measured using a photographic block or other effective replica. For the first batch of standard test pieces that pass inspection, the metallographic test sample corresponds to the acid etching sample, and the metallographic sample should be located on the burn spots.

Description

Technical Field

[0001] This invention relates to a general testing method for preparing acid immersion test blocks, particularly for the preparation and application of acid immersion test blocks for acid immersion testing of high carbon steel workpieces after grinding. Background Technology

[0002] Acid leaching is a common method used to inspect internal structural defects in steel ingots, continuously cast billets, or steel products, and to assess their quality. It is one of the most frequently used methods in macroscopic inspection. Acid leaching is a test method that reveals the low-magnification structure of steel materials. Acid leaching detection is a type of special inspection, belonging to the category of methods. It is a method of judging the degree of grinding burn by observing the color change of the ground surface of carbon steel after being corroded by a weak acid, and judging the degree of grinding burn based on the difference in color between this change and the normal surface color. Acid leaching is a process of chemically etching the surface of high-strength steel under strict control of personnel, machinery, materials, methods, environment, and testing. It's a method of comparing the appearance quality of parts to determine their qualification. Key and challenging aspects of this process include: ① Determining the material, shape, heat treatment method, welding, and temperature selection parameters for acid leaching test blocks; ② Establishing criteria for judging overheating and burning using acid leaching and metallographic microscopy observation, employing different test block processing methods, and comparing the appearance quality of the grain structure on the part surface using acid leaching; ③ Determining the testing process parameters, and preparing samples and test blocks. Grinding burns are essentially an irreversible change in the microstructure of the workpiece material surface under high temperature in the grinding zone, making it a highly complex phenomenon. Its manifestations are diverse, including changes in metallographic structure, surface color and morphology, residual stress, and microhardness. However, currently, acid leaching and metallographic testing are the most effective methods for inspecting grinding burns. Defects in steel, such as inclusions, segregation, porosity, and pinholes, are difficult to identify with the naked eye due to their small size or the fact that they are connected to the steel matrix by plastic deformation. However, by selecting an appropriate corrosive agent, selective etching can be applied to these defects and the steel matrix. Acid etching is a commonly used method in low-magnification inspection of steel, primarily because the equipment is simple, the operation is convenient, and it can clearly reveal various defect structures in steel materials, such as cracks, inclusions, porosity, segregation, and gas pores, especially in forgings. In steel quality inspection, acid etching is listed as the first inspection item in sequence. It is essential for detecting and determining the quality and scrap of parts. Acid etching tests can be divided into three types: hot acid etching, cold acid etching, and electrolytic etching. Acid etching methods are further divided into hot acid etching, cold acid etching, and electrolytic etching, etc. During production inspection, one of the three etching methods can be selected, with hot acid etching being the most widely used. The hot acid leaching test is an inspection method that uses hot acid to corrode low-magnification samples of steel products to reveal the macrostructure and defects of the steel. The cold acid leaching test uses a specific acid solution at room temperature to corrode low-magnification samples or forgings to reveal the macrostructure and defects of the steel. It is suitable for forgings where low-magnification samples are difficult to obtain, certain corrosion-resistant high-alloy steels, and stainless steels. To effectively utilize the acid leaching test to evaluate the quality of steel, representative samples should be selected.Samples must be taken from the most defect-prone areas to avoid missing any. For newly designed ingot molds, using new casting methods, and smelting new steel grades, it is best to dissect the ingot for acid etching tests to examine the distribution of various defects before determining the sampling location. For ingots that are wider at the top and narrower at the bottom, improper application of the mold coating or excessive coating thickness can sometimes lead to carburization on the outer surface, resulting in black spots after acid etching. These areas also tend to have more bubbles and silicate inclusions, so bottom samples should also be taken for inspection. When sampling ingots that are wider at the top and narrower at the bottom to inspect for white spots, or to study the sensitivity of steel to white spots, sampling for surface defects such as quenching cracks, grinding cracks, and quenching soft spots should be performed on the outer surface of the steel or part for acid etching tests. In square billets rolled from ingots that are wider at the bottom than the top, defects are most severe at the smaller end, followed by the middle, with the larger end being the least affected. At the bottom of the larger-at-the-top ingot, there are also more bubbles and silicate inclusions. When casting several ingot trays from a single batch of molten sodium, more macroscopic defects are found in the first and last trays. In steel ingot sampling and metal material testing, defects are generally more severe at the smaller end of the square billet rolled from ingots that are wider at the top than the bottom, followed by the middle, with the larger end being the least affected. Therefore, the national standard (GB226-91) for hot corrosion testing of steel stipulates that sampling should be taken near the ingot cap. In general inspections, it is better to sample from the billet rather than the steel itself, as defects are more easily detected after acid etching on the billet. If no serious defects are found on the billet, this test is unnecessary for the steel. The sampling direction should be determined according to the inspection items. For general inspections, transverse samples are often taken to observe the quality of the entire cross-section; if checking for flow lines, banding, etc., longitudinal samples can be taken. If a batch of steel shows unacceptable or excessive defects during acid etching inspection, other inspections are unnecessary. During application, the concentration of the solution changes dynamically due to bath loss or natural evaporation, causing fluctuations in process parameters. This can lead to misjudgments during tempering and acid etching inspection, thus affecting product quality.

[0003] Many factors influence the results of acid etching tests, among which the activity of the acid solution is crucial. To verify the acid solution's quality, a standard test block with overheating defects must be used. International acid etching standards stipulate that the solution must pass the test using a 300M steel standard block with overheating defects before acid etching can proceed. Domestic standards, such as the "300M Steel Parts Tempering Acid Etching Inspection Process Instruction Manual," also specify that a standard block made of 300M steel with overheating defects should be used to verify the acid solution's quality during acid etching. In actual parts, due to varying processing conditions, overheated surfaces can take many forms. However, they can be broadly categorized into three zones: the untempered zone (re-quenched zone), the over-tempered zone, and the normal zone. This is primarily determined by the heat density and heat dissipation during processing. Generally, the temperature is highest in a certain area, gradually decreasing around this area. Due to the difference in the degree of corrosion between the defect and the substrate, the color intensity of the defect on the sample or photographic paper differs from that of the substrate, and can be distinguished by the naked eye or a magnifying glass of about 10x. The overheated surface of an actual part may exhibit the following two forms: (1) The heat generated in a certain area causes the temperature of the metal to exceed the austenite phase transformation point. After cooling, a re-quenched martensite structure is formed. Around this area, as the temperature gradually decreases, high-temperature, medium-temperature and low-temperature tempering zones are formed in sequence. After acid etching, the re-quenched martensite is bright white (or grayish-white). Around this bright white zone, the colors are black, dark gray and normal light gray in sequence.

[0004] (2) Overheating occurs in a certain area, but the temperature does not exceed the austenite phase transformation point, forming a dark gray or black area.

[0005] It should be noted that the overheated surface of actual parts, due to uneven temperature distribution, exhibits uneven color and hardness of its overheated structure. The grinding overheated surface characteristics commonly found in ground parts are comparable to the hardness and color exhibited when heated to 500-600℃. Standard blocks can display overheated structures, thus they possess high sensitivity. When using standard blocks to test acid leaching solutions, if the display of overheated structures is unsatisfactory, the etching time should be adjusted appropriately until an ideal overheated surface is displayed. If the standard block fails to display defects within the standard-specified time, it indicates that the solution has failed and should be reprepared. For failure analysis, in addition to selecting samples from the failed areas, samples should also be selected from unfailed areas for comparison. For example, for bearing steel, carburizing steel, high-strength steel, and ultra-high-strength steel, improper machining can cause overheating, resulting in over-tempering and re-quenching. To prevent overheating, cutting parameters must be strictly controlled during the machining of steel parts. In acid solutions, the color reflected by the martensitic structure after tempering and before tempering determines whether a part is acceptable or unacceptable. Many factors influence the results of acid etching inspections, among which the activity of the acid is a crucial one. To verify the acid's quality, a standard test block with overheating defects must be used to test the solution, following international acid etching inspection standards.

[0006] Currently, there are no corresponding standards, either domestically or internationally, for the preparation of acid-etching test blocks for high-carbon steel workpieces after grinding, resulting in a lack of criteria for judging grinding burns caused by high-speed turning and grinding. In practical work, there are differences in detection methods and difficulties in establishing judgment criteria. Compared with general steel, high-carbon steel workpieces experience higher grinding forces, temperatures, and energies during grinding. Due to the low thermal conductivity of this material, grinding burns are highly likely to occur. After grinding burns, the surface of the part softens, severely affecting the wear resistance and service life of the workpiece. The essence of grinding burns is an irreversible change in the microstructure of the workpiece material surface under the high temperature of the grinding zone. Therefore, it is a rather complex phenomenon. Its manifestations are diverse, including changes in metallographic structure, surface color and morphology, residual stress, and microhardness. However, acid-etching and metallographic testing are not yet effective means of inspecting grinding burns. Therefore, acid-etching testing should be performed on all high-carbon steel workpieces after grinding. Acid leaching testing is a type of special inspection, belonging to the category of methods. It involves observing the color change of a ground carbon steel surface after weak acid corrosion, and judging the degree of grinding burn based on the difference in color between this change and the normal surface. The acid leaching process involves chemically etching the surface of high-strength steel under strict control of personnel, machinery, materials, methods, environment, and testing. The appearance quality of the part is compared to determine its qualification. However, current acid leaching testing techniques require manual intervention or rely on worker experience, lacking professional verification results for comparison. Controlling the solution concentration and preparing test blocks are key and challenging aspects of this inspection method. Acid leaching testing involves observing the color change of a ground structural steel surface after weak acid corrosion. Key points of acid leaching testing include: solution concentration, immersion time, solution temperature, and subsequent dehydrogenation treatment. It is a crucial step in identifying whether a part is burned, judging the degree of grinding burn based on the difference in color between the new and normal surface. The main technical challenge in preparing test blocks is the formation of an oxide film on the workpiece surface after grinding and subsequent reheating. Currently, the most common industrial processing methods for achieving oxide film formation on workpieces or test blocks include grinding, heat treatment, and welding. Therefore, developing acid-etching test blocks for acid etching testing is of paramount importance. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing acid immersion test blocks that is simple in principle, easy to use, highly versatile, and can be used for acid immersion testing and verification of parts. This method is mainly used for acid immersion testing of high-carbon steel workpieces after grinding, thus solving the problem that acid immersion testing requires manual intervention or determination based on worker experience, without the need for professional verification results for comparison.

[0008] The above-mentioned objective of this invention can be achieved by the following measures: a method for manufacturing an acid etching test block, characterized in that: according to the acid etching test standard for steel parts, at least 8mm thick high-carbon steel acid-etched material is taken to manufacture a standard test block, i.e., a standard block, for steel tempering acid etching inspection, using the following three methods: (1) Based on the material properties of each standard block, two methods were adopted: heat treatment quenching and quenching plus tempering. For both methods, a test block was set with a variation of at least 50℃. (2) Select welding parameters of 150A, 60V and 120A, 60V for single-sided welding and double-sided forming to make corresponding test blocks and observe the changes in the microstructure of the test blocks in the heat-affected zone. (3) Select the machining grinding parameters with and without coolant as the variable amount, so that an oxide film is formed on the surface of the workpiece or test block. Then, use acid immersion to observe the oxide film formed on the grinding surface of carbon steel after weak acid corrosion. Observe the color change of the oxide film and judge the degree of grinding burn of the test block made by grinding parameters based on the difference between the oxide film and the normal body color. Then, samples were taken and observed under a metallographic microscope and compared with the actual acid leaching test results. Based on their respective materials, various test blocks that meet the standards were selected: tempered burn test blocks were designated as type A test blocks, over-tempered burn test blocks were designated as type B test blocks, unburned test blocks were designated as type C test blocks, and quenched burn test blocks were designated as type D test blocks. Test blocks were prepared and numbered using the three methods described above. Samples were taken and observed under a metallographic microscope, and the results were compared and analyzed with the actual acid leaching test results. Based on the materials, A-type, B-type, C-type, and D-type test blocks that met the standards were selected. Each type of test block was numbered and a report was issued. Based on the test results of the high-carbon steel acid leaching test blocks, acid leaching was performed. The color difference displayed on the surface of the obtained test blocks was measured using photographic blocks or other effective replicas. For standard test pieces that passed the initial inspection, a 1:1 scale photograph of the base test piece was retained. Select manual arc welding with single-sided welding and double-sided forming to make corresponding test blocks, and observe the changes in the heat-affected zone of the test blocks made with welding parameters; perform acid immersion testing and metallographic testing on the above test pieces, with the metallographic test sample corresponding to the acid immersion sample, and the metallographic sample should be on the burn spot. The microstructure of the test block made by the heat treatment parameters after normal quenching and tempering of steel is tempered martensite. After pickling, it is gray or shows no obvious change. After acid etching in the low-temperature fire zone, the re-quenched martensite is bright white or grayish-white. The area around this bright white zone is still black, dark gray and normal.

[0009] Compared with existing technologies, this invention has the following advantages: simple principle, convenient use, strong versatility, and can be used for joint acid etching testing and verification of parts. The acid etching process involves chemically eroding the surface of steel metal under strict control of six aspects: personnel, machinery, materials, methods, environment, and measurement. It compares the appearance quality of the grain structure on the surface of the parts to determine whether the parts are qualified. In this process, the control of solution concentration and the comparative inspection between the test piece and the part are particularly crucial. After the standard acid etching test piece has been tested and verified in the early stages, its application in subsequent acid etching tests improves the accuracy and sensitivity of the test, increasing the testing efficiency by 20%.

[0010] The test is accurate and reliable, with a simple principle, and is suitable for preparing acid-etching test pieces for various steel materials after grinding and burning. It can optimize the acid-etching testing process and curing time, and verify and calibrate the process. The application of the test pieces reduces the labor intensity and lowers the skill requirements for workers, solving the problem of needing manual intervention or relying on worker experience for acid-etching testing without professional verification results for comparison, which has a crucial impact on product quality assurance. Implementation

[0011] According to the present invention, firstly, based on the acid etching test standard for steel parts, a high-carbon steel material with a thickness of at least 8 mm is used to prepare a standard test block, i.e., a standard block, for steel tempering acid etching inspection. The following three methods are employed: (1) Based on the material properties of each standard block, two methods were adopted: heat treatment quenching and quenching plus tempering. For both methods, a test block was set with a variation of at least 50℃. (2) Select welding parameters of 150A, 60V; 120A, 60V for single-sided welding and double-sided forming to make corresponding test blocks and observe the changes in the microstructure of the heat-affected zone of the test blocks; (3) Select the machining grinding parameters with and without coolant as the variable amount, so that an oxide film is formed on the surface of the workpiece or test block. Then, use acid immersion to observe the oxide film formed on the grinding surface of carbon steel after weak acid corrosion. Observe the color change of the oxide film and judge the degree of grinding burn of the test block made by grinding parameters based on the difference between the oxide film and the normal body color. Then, samples were taken and observed under a metallographic microscope and compared with the actual acid leaching test results. Based on their respective materials, various test blocks that meet the standards were selected: tempered burn test blocks were designated as type A test blocks, over-tempered burn test blocks were designated as type B test blocks, unburned test blocks were designated as type C test blocks, and quenched burn test blocks were designated as type D test blocks. Secondly, test blocks were prepared and numbered using the three methods described above. Samples were taken and observed under a metallographic microscope, and the results were compared and analyzed with the actual acid leaching test results. Based on the materials, A-type, B-type, C-type, and D-type test blocks that met the standards were selected. The test blocks were numbered and reports were issued. Based on the test results of the high-carbon steel acid leaching test blocks, acid leaching was performed. The color difference displayed on the surface of the obtained test blocks was measured using photographic blocks or other effective replicas. For the standard test pieces that passed the initial inspection, a 1:1 scale photograph of the base test piece was retained. Select manual arc welding with single-sided welding and double-sided forming to make corresponding test blocks, and observe the changes in the heat-affected zone of the test blocks made with welding parameters; perform acid immersion testing and metallographic testing on the above test pieces, with the metallographic test sample corresponding to the acid immersion sample, and the metallographic sample should be on the burn spot. The microstructure of the test block made by the heat treatment parameters after normal quenching and tempering of steel is tempered martensite. After pickling, it is gray or shows no obvious change. After acid etching in the low-temperature fire zone, the re-quenched martensite is bright white or grayish-white. The area around this bright white zone is still black, dark gray and normal.

[0012] In optional embodiments, the welding parameters are at least 150A and 60V; 120A and 60V single-sided welding double-sided forming is used to prepare corresponding test blocks. The main observation is on the changes in the microstructure of the test block in the heat-affected zone. After the burn tissue on the grinding surface is corroded by acid, the color will change. The degree of grinding burn can be judged based on the difference between its color and that of the normal substrate.

[0013] The grinding wheel material selected is white fused alumina WA60K, and the grinding wheel material is single-crystal fused alumina SA46K. The machining grinding parameters are: grinding wheel linear speed va 9 m / s-131 m / s, grinding wheel depth of cut ap = 0.02 mm-0.035 mm; grinding speed va = 19 m / s. (va represents grinding wheel linear speed, ap represents grinding wheel depth of cut, WA represents white fused alumina alumina, and SA represents single-crystal fused alumina alumina.)

[0014] The grinding process mainly involves varying the grinding speed (10 m / s), depth of cut (0.01 mm), WA and SA, and the presence or absence of coolant. Test blocks with different variations are prepared to observe the changes in the microstructure of the heat-affected zone. After the burned microstructure on the grinding surface is corroded with mild acid, the degree of grinding burn can be judged by the color change of the burned microstructure compared to the normal matrix.

[0015] In optional embodiments, for both heat treatment methods such as quenching and quenching followed by tempering, a test block is set up with a temperature variation of 50°C intervals. For example, for 300 steel, the upper temperature limit is 1100°C and the lower temperature limit is 600°C. For welding processing test blocks, since the welding temperature can reach 1500°C, manual arc welding is selected to produce corresponding test blocks with single-sided welding and double-sided forming. The thickness of the test block is not less than 8mm, mainly to observe the changes in the heat-affected zone. The above test pieces are subjected to acid leaching and metallographic testing. It should be noted that the metallographic test sample should correspond to the acid leaching sample, and the metallographic sample should be on the burn spot. The microstructure of steel after normal quenching and tempering heat treatment is tempered martensite, which is gray or shows no obvious change after pickling. After grinding burns, over-tempered martensite or untempered martensite appears on the surface. Over-tempered martensite has weak corrosion resistance and is black after pickling, while untempered martensite is more corrosion resistant and is white after pickling. The following are the most obvious microstructures of the test blocks after welding and heat treatment: Each batch of material consists of parts and test blocks from the same heat number and heat treatment process. Each acid-etched test block should be engraved with a permanent standardized item mark, preferably on the back of the observation surface. The permanent mark on the test block should not affect its performance. Each batch of material consists of materials and quantities from the same heat number and heat treatment process. Each batch of test blocks consists of two acid-etched test blocks individually. Formal inspection is recommended in the following situations: Based on HB7717-2002 "Inspection of Acid Etching and Burning of Aerospace Steel Parts" and the US Department of Defense standard MIL-STD-867, the instruction manual specifies the following qualitative requirements for the materials and solution concentration used in the test: The relative molecular weights of hydrochloric acid (HCl) and nitric acid (HNO3) were determined to be 36.46, 63.01, and 39.9971, respectively, according to GB / T622-2006 standard. The relative molecular weights of ethanol (C2HO) were determined to be 46.07, and the relative molecular weights of chloroform and diethyl ether were determined to be 39.9971, respectively, according to GB / T678-2002 standard.

[0016] Preparation of acid leaching solutions: 5% hydrochloric acid / ethanol solution (volume ratio: 5%), c = 1000 * 5% / 36.5 = 1.37 mol / L, pH = -log(1.37) = 0.137; 4% nitric acid / ethanol solution (volume ratio: ethanol / nitric acid solution: 4%), c = 1000 * 4% / 63 = 0.635 mol / L, pH = -log(0.365) = 0.438; Sodium hydroxide solution > 0.1 mol / L, i.e., 4g sodium hydroxide : 1 liter of water > pH = 13; When the pH value of the hydrochloric acid / nitric acid solution exceeds the above requirements by ±20%, or the pH value of the sodium hydroxide solution is ≦ 13, it should be discontinued. The newly prepared solution can only be used after passing the test. The procurement of the above items should comply with the relevant requirements in Q / 16DL07.07.05 "Procurement Control Procedure".

[0017] The prepared sample was etched with acid to reveal its macrostructure and defects.

[0018] By utilizing the varying degrees of acid etching on different parts of steel material specimens, the macroscopic structure and defects of the steel can be revealed. Based on the distribution of the low-magnification structure and the presence of defects, hot acid etching tests are conducted on low-magnification steel products to reveal the macroscopic structure and defects. Evaluation is then carried out according to the relevant technical standards and rating criteria, specifically GB / T 226-1991 Acid Etching Test Method for Low-Magnification Structure and Defects of Steel and GB / T1979-2001 Rating Chart for Low-Magnification Structure Defects of Structural Steel. Furthermore, by inferring the causes of defects, feasible process improvements are implemented to enhance product quality.

[0019] The surface finish of the acid-etched sample inspection surface should be determined according to the inspection purpose, technical requirements, and the etching agent used. The following points can be used as a reference: (1) Sawing surfaces can be used to inspect defects such as large pores, severe internal cracks and looseness, shrinkage cavities, and large foreign non-metallic inclusions; (2) Rough turning and fine turning surfaces can be used to inspect pores, looseness, inclusions, dendritic structures, segregation, and flow lines; (3) Finely machined turning, milling, planing, grinding, and polishing surfaces are generally used to inspect the decarburization depth, banded structure, phosphorus segregation, and strain lines of steel, and other macroscopic structural details. Generally, a weaker etching agent is used for etching in a cold state. The cold acid leaching test method uses a proportioned acid solution to etch low-magnification samples or forgings at room temperature. The cold acid leaching test method is used to display the macroscopic structure and defects of steel. In order to effectively use the acid leaching test to evaluate the quality of steel, representative samples should be selected. The samples must be taken from the parts most prone to defects so as not to miss any.

[0020] Equipment and materials: There should be containers that do not react with acid or alkali solutions, preferably made of polyethylene or ethylene polymer materials.

[0021] An alarm clock or timer should be provided. Precision pH test strips, with accuracy grades of 0.1 and 0.01; grade 0.1 tests within the range of 13-14; grade 0.01 tests within the range of 0.1-0.5. A water pressure gauge should be installed on the water pipe of the washing tank, and the water pressure gauge should be inspected annually according to metrological verification standards. The water pressure must not be lower than 0.3 MPa when cleaning parts, and the discharged water should be connected to the company's wastewater treatment system. The white light illuminance measurement range should generally not be lower than 10000 LX. LED low-temperature white light lamps: white light illuminance at 100mm should not be lower than 2500 LX.

[0022] Requirements for submitted parts: Submitted parts must pass surface quality inspection before acid immersion testing. To ensure sufficient testing requirements are met, submitted parts should be free of metal shavings, oil, abrasives, and other impurities. Parts that have undergone aging treatment should have their surfaces polished before inspection.

[0023] Type testing of test blocks shall be conducted by a laboratory that has obtained GB / T15481 accreditation and has type testing services for acid leaching test blocks; each acid leaching test block product shall be engraved with a permanent standardized item mark, preferably on the back of the observation surface, and the permanent mark on the test block shall not affect the performance of the test block.

[0024] Under the same test conditions, the test blocks prepared above will be subjected to acid leaching and metallographic tests respectively, and observed under a low magnification microscope as a basis for comparison. Each acid leaching test block should be engraved with a permanent standardized item mark, which should preferably be engraved on the back of the observation surface. After each use, it should be stored in oil to prevent corrosion. If the corrosion is not clear during use, it can be sandblasted. The number of sandblasting treatments should not exceed 3. For the first inspection of the qualified standard test piece, a 1:1 scale photograph of the test piece should be retained.

[0025] Without any creative effort, other technical solutions can be obtained from the above embodiments, and equivalent changes made within the scope of protection of this invention should also fall within the scope of protection of this invention.

Claims

1. A method for manufacturing an acid leaching test block, characterized in that: According to the acid etching test standard for steel parts, take at least 8mm thick high-carbon steel acid-etched material and prepare a standard test block, i.e., a standard block, for steel tempering acid etching inspection. This includes the following three methods: (1) Based on the material properties of each standard block, two methods were adopted: heat treatment quenching and quenching followed by tempering. For both methods, a test block was set up with a variation of at least 50°C. (2) Select welding parameters of 150A, 60V; 120A, 60V for single-sided welding and double-sided forming to prepare corresponding test blocks, and observe the changes in the microstructure of the heat-affected zone of the test blocks. We selected manual arc welding to fabricate test blocks with single-sided welding and double-sided forming, and observed the changes in the heat-affected zone of the test blocks fabricated using welding parameters. (3) Select the machining grinding parameters and use the application of coolant and the absence of coolant as the variable amount to form an oxide film on the surface of the test block. Then use acid immersion to observe the oxide film formed on the grinding surface of carbon steel after weak acid corrosion. Observe the color change of the oxide film and judge the degree of grinding burn of the test block made by grinding parameters based on the difference between the oxide film and the normal body color. Test blocks were prepared and numbered using the three methods described above. Samples were then observed under a metallographic microscope, and the results were compared with those from actual acid leaching tests. Based on the materials used, tempered burn test blocks meeting the standards were selected as Type A blocks, tempered burn test blocks as Type B blocks, unburned test blocks as Type C blocks, and quenched burn test blocks as Type D blocks. Each type of test block was numbered and a report was issued. Based on the test results of the high-carbon steel acid leaching test blocks, acid leaching was performed. The color difference observed on the surface of the obtained test blocks was applied to photographic blocks or other valid replicas. For standard test pieces that passed the initial inspection, a 1:1 scale photograph of the original test piece was retained. The above standard test pieces are tested according to acid leaching and metallographic methods. The metallographic test sample corresponds to the acid leaching sample, and the metallographic sample should be on the burn spot. The microstructure of the test block made by the heat treatment parameters after normal quenching and tempering of steel is tempered martensite. After pickling, it is gray or shows no obvious change. After acid etching in the low-temperature fire zone, the re-quenched martensite is bright white or grayish-white. The area around this bright white zone is still black, dark gray and normal.

2. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: For machining and grinding, the following parameters are selected: grinding wheel linear speed va 9m / s-131m / s, grinding wheel depth of cut ap=0.02mm-0.035mm; grinding speed va=19m / s; grinding wheel material selection: white corundum abrasive WA60K, or single crystal corundum abrasive SA46K.

3. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: Using the following variables as variations: increasing the grinding linear speed by 10 m / s, the depth of cut by 0.01 mm, WA and SA, and applying or not applying coolant, test blocks with different variations were prepared to observe the changes in the microstructure of the heat-affected zone. After the burned microstructure on the grinding surface was corroded by weak acid, the degree of grinding burn was judged based on the color change of the burned microstructure compared with the normal matrix.

4. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: For heat treatment processing, both quenching and quenching plus tempering methods are used, with a test block set at 50℃ intervals as the temperature variation. For 300 steel, the upper temperature limit is 1100℃ and the lower temperature limit is 600℃. For welding processing, the welding temperature of the test block reaches 1500℃. Manual electric arc welding is used to make the corresponding test block with single-sided welding and double-sided forming. The thickness of the test block is not less than 8mm, and the changes in the heat-affected zone are observed.

5. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: The microstructure of steel after normal quenching and tempering heat treatment is tempered martensite, which appears gray or shows no obvious change after pickling; after grinding burns, tempered martensite or untempered martensite appears on the surface, which appears black after pickling, while untempered martensite appears white after pickling.

6. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: The materials and quantities of parts and test blocks of the same furnace number and the same heat treatment process are consistent, and each batch of test blocks consists of two acid-etched test blocks.

7. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: According to GB / T622-2006 standard, the relative molecular weight of hydrochloric acid (HCl) is 36.46, the relative molecular weight of nitric acid (HNO3) is 63.01, and the relative molecular weight of sodium hydroxide (NaOH) is 39.9971; according to GB / T678-2002 standard, the relative molecular weight of ethanol (C2H6O) is 46.07, and ethanol is miscible with chloroform and diethyl ether.

8. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: Preparation of acid leaching solution: A hydrochloric acid-ethanol solution, wherein the volume ratio of hydrochloric acid is 5%, c = 1000 × 5% / 36.5 = 1.37 mol / L, and the pH of the hydrochloric acid-ethanol solution is -log(1.37) = 0.137; A nitric acid-ethanol solution, wherein the volume ratio of nitric acid is 4%, c = 1000 × 4% / 63 = 0.635 mol / L, and the pH of the nitric acid-ethanol solution is -log(0.365) = 0.438; The pH of a solution prepared by mixing 4g of sodium hydroxide with 1 liter of water is 13. When the pH value of hydrochloric acid-ethanol solution or nitric acid-ethanol solution exceeds the above-mentioned requirements by ±20%, or when the pH value of sodium hydroxide solution is <13, discontinue use. The newly prepared solution can be reused after passing the test.

9. The method for manufacturing the acid leaching test block as described in claim 1, characterized in that: By utilizing the different degrees of etching of various parts of steel material test blocks with acid leaching solution, the macroscopic structure and defects of steel can be revealed. Based on the distribution of low-magnification structure and the presence of defects in steel materials, hot acid is used to corrode low-magnification samples of steel products using hot acid leaching test method to reveal the macroscopic structure and defects of steel. Evaluation is carried out according to its corresponding technical standards and rating standards. The evaluation is carried out according to GB / T226-1991 Low-magnification structure and defect acid etching test method of steel and GB / T1979-2001 Low-magnification structure defect rating chart of structural steel.