Preparation method of small Charpy V-shaped notch standard impact specimen

Abstract

The invention discloses a preparation method of a small Charpy V-shaped notch standard impact specimen, which comprises the following steps: selecting high-purity metal as a raw material, carrying out batch smelting by adopting a vacuum furnace and electroslag remelting smelting process to obtain a blank material, and rolling the blank material into a plate; a sample blank with a uniform internal organization structure is obtained by performing various heat treatments on a finished blank; and performing specific sampling and machining on the sample blank to prepare the small Charpy V-shaped notch standard impact sample. According to the prepared small Charpy V-shaped notch standard impact sample, the geometric dimension processing quality is superior to the requirements of domestic and foreign standards, and the metering indexes of the small Charpy V-shaped notch standard impact sample have good consistency and stability.

Description

Technical Field

[0001] The present invention relates to the field of preparation of standard materials, and specifically to a method for preparing a small Charpy V-notch standard impact specimen. As an important component of the impact energy value transmission system, the standard impact specimen realizes the traceability of impact energy in material testing, better meets the traceability needs of high-precision fields such as new material manufacturing and high-end equipment manufacturing in my country, and mainly serves my country's aerospace, high-speed railway, steel manufacturing, special equipment and other industries. Background Art

[0002] Charpy V-notch standard impact specimens are an important part of the national impact energy transmission system and an important means of transferring the standard value of impact energy. They are used in the verification, calibration, various comparison tests, and period verification of pendulum impact testing machines, and are one of the important quality control methods of laboratories. With the development of additive manufacturing, nuclear industry, large-scale special equipment and other fields in my country, micro-damage detection technology has begun to be used in large quantities, and the application demand for small Charpy impact tests has become increasingly prominent. Therefore, there is an urgent need to accurately measure small Charpy impact testing machines. At present, this small Charpy V-notch standard impact specimen has been mentioned in the international standard ISO 14556 and the national standard GB / T19748-2019, but whether in specimen development or value transfer, the research on this type of impact specimen in China is almost blank.

[0003] The existing technology has the following disadvantages in practical application: 1. The appearance of the Charpy V-notch standard impact specimen currently used in China is processed in accordance with the provisions of GB / T 18658. Since the specimen size is 55mm long, 10mm wide and 10mm high, it can only be used for the calibration of metal pendulum impact testing machines with anvil span of 40mm. Due to the limitations of the specimen length, width and height, the Charpy V-notch standard impact specimen is not suitable for placement on the support surface of a low-energy pendulum impact testing machine with anvil span of 22mm, resulting in the inability to effectively measure and trace the energy value indicators of the impact testing machine.

[0004] 2. In addition, the existing Charpy V-notch standard impact specimens do not cover all energy levels. At present, the minimum energy level of relevant domestic standard impact specimens is about 15J, and there is no official report on standard impact specimens below 15J. With the large-scale application of low-energy pendulum impact testers (maximum impact energy not exceeding 15J) at home and abroad, the energy value of the existing Charpy V-notch standard impact specimens exceeds the maximum impact energy of the impact tester, and can no longer meet the energy indication and measurement needs of such testers.

[0005] 3. There are many factors that affect the impact energy of the small Charpy V-notch standard specimen. Since the bottom radius of the V-notch is only 0.1mm, its sensitivity to material defects and dimensional deviations is further enhanced. For example, inclusions in the material itself, defects generated during heat treatment, specimen processing and preparation process, and specimen geometric dimensional deviations will all lead to a large standard deviation in the impact energy value of the standard impact specimen, making it difficult to meet the standard requirements.

[0006] In summary, the existing Charpy V-notch standard impact specimens can no longer meet the metrological needs of energy value verification and calibration of low-energy pendulum impact testing machines in my country. Therefore, my country urgently needs to develop small Charpy V-notch standard impact specimens below 15J and study their preparation methods to fill the gaps in related technical fields. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing a small Charpy V-notch standard impact specimen, which selects a modulated alloy steel as the raw material, adopts a vacuum furnace and an electroslag remelting smelting process to perform batch smelting to obtain a blank and roll it into a plate; by performing a variety of heat treatments on the blank, a finished blank with different impact properties is obtained; and the finished blank is mechanically processed to prepare a small Charpy V-notch standard impact specimen. Thus, the material defects of the small Charpy V-notch standard specimen are reduced, the machining accuracy of the specimen geometric dimensions is improved, and the standard deviation of the impact energy value of the standard specimen is further reduced, and a small-sized Charpy V-notch standard impact specimen below 15J is prepared.

[0008] In order to achieve the above object, the present invention proposes a method for preparing a small Charpy V-notch standard impact specimen, comprising: High-purity metals are selected as raw materials, and the vacuum furnace plus electroslag remelting smelting process is adopted for smelting to obtain blanks with uniform metallographic structure and chemical composition, few non-metallic inclusions and no harmful phase precipitation; The blank is forged into a flat slab and then hot-rolled to refine its grains and eliminate microstructural defects to obtain a rolled plate; Normalizing the rolled plate at a temperature of 850° C. to 1000° C., keeping the temperature for 1 h to 2 h to reduce residual stress and further refine grains to eliminate structural defects, thereby obtaining a finished billet; The finished blank is heat treated at 850°C to 1000°C for 0.5h to 1h, quenched and cooled to room temperature, kept at 200°C to 650°C for 1h to 2h, and air-cooled to room temperature. The finished blank is cryogenically treated at -70°C for 3h, then reduced to -120°C for 8h, and returned to room temperature with the furnace to obtain an impact test blank; The impact test specimen blank is machined, and a blank sample is obtained by wire cutting on the sample blank. It is first processed into a blank sample with a length of 55 mm, a width of 10 mm, and a height of 10 mm. The blank sample is cut in the length, width, and thickness directions in sequence by wire cutting to obtain a small blank sample. When sampling, ensure that the final notch direction of all samples is consistent with the angle between the rolling direction of the plate. The six planes of the small blank sample are processed by a grinder to make the surface roughness Ra≤2.0μm. The notch processing method is to first use wire cutting to roughly process the V shape, and then use an optical projection curve grinder to finely grind the notch bottom radius and the notch side to make the notch surface roughness Ra≤1.6μm, and finally processed into a small Charpy V-notch standard impact specimen.

[0009] The blank obtained by smelting contains carbon, silicon, manganese, sulfur, phosphorus, copper, chromium, molybdenum, nickel, vanadium, niobium, titanium and iron. The composition of the blank is designed as (wt%): carbon C: 0.36~0.43, silicon Si: 0.15~0.35, manganese Mn: 0.60~0.90, sulfur S: ≤0.025, phosphorus P: ≤0.025, copper Cu: ≤0.35, chromium Cr: 0.60~1.00, molybdenum Mo: 0.15~0.30, nickel Ni: 1.60~2.00, vanadium V: ≤0.025, niobium Nb: ≤0.025, titanium Ti: ≤0.025, and the balance is Fe and unavoidable inclusions.

[0010] The beneficial effects of the present invention are: 1. The vacuum furnace plus electroslag remelting smelting process is used for batch smelting to ensure the uniformity of the material composition during the smelting process, reduce the impurity content and improve the purity of the alloy.

[0011] 2. Through different heat treatment processes for the blanks, strictly controlling the temperature, time and other influencing factors during the heat treatment process, the heat treatment performance of each batch of materials is guaranteed to be as consistent as possible, thereby ensuring the consistency of the organizational structure of the standard impact test specimen blanks.

[0012] 3. Obtain small blank samples from the blank sample at the specified position by wire cutting sampling, and use optical projection curve grinder to finely grind the V-notch, so as to visually observe the notch fine grinding process and ensure the accuracy of the notch arc size and the consistency of impact performance.

[0013] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of the present invention in conjunction with the accompanying drawings.

[0015] Figure 1 A schematic diagram of heat treatment of a method for preparing a small Charpy V-notch standard impact specimen according to an embodiment of the present invention is shown.

[0016] Figure 2 A schematic diagram of a deep cold tempering heat treatment process of a method for preparing a small Charpy V-notch standard impact specimen according to an embodiment of the present invention is shown.

[0017] Figure 3 The sampling position of the method for preparing a small Charpy V-notch standard impact specimen according to one embodiment of the present invention is shown, and the small blank sample is obtained from the blank sample by wire cutting.

[0018] Figure 4 A schematic diagram comparing a small Charpy V-notch standard impact specimen prepared by a method for preparing a small Charpy V-notch standard impact specimen according to an embodiment of the present invention and a large-size Charpy V-notch standard impact specimen is shown. DETAILED DESCRIPTION

[0019] The present invention will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0020] The method for preparing a small Charpy V-notch standard impact specimen according to the present invention comprises: High-purity metals are selected as raw materials for smelting to obtain blanks with stable structure.

[0021] Rolling the blank to obtain a rolled plate; Normalizing the rolled plate to obtain a finished billet with stable structure; Performing heat treatment on the finished blank to obtain an impact test specimen blank; The impact specimen blank is machined to obtain a small Charpy V-notch standard impact specimen.

[0022] The blank obtained by smelting contains carbon, silicon, manganese, sulfur, phosphorus, copper, chromium, molybdenum, nickel, vanadium, niobium, titanium and iron. The composition of the blank is designed as (wt%): carbon C: 0.36~0.43, silicon Si: 0.15~0.35, manganese Mn: 0.60~0.90, sulfur S: ≤0.025, phosphorus P: ≤0.025, copper Cu: ≤0.35, chromium Cr: 0.60~1.00, molybdenum Mo: 0.15~0.30, nickel Ni: 1.60~2.00, vanadium V: ≤0.025, niobium Nb: ≤0.025, titanium Ti: ≤0.025, and the balance is Fe and unavoidable inclusions.

[0023] Specifically, the alloy is smelted in a certain proportion to ensure the purity of the blank, and the blank is obtained by batch smelting using a vacuum furnace plus electroslag remelting smelting process and rolled into a plate; the blank is subjected to a variety of heat treatments to obtain finished blanks with different impact properties; the finished blank is subjected to specific mechanical processing to produce a small Charpy V-notch standard impact specimen.

[0024] In one example, the modulated alloy steel is batch smelted using a vacuum furnace smelting and vacuum consumable furnace remelting process to ensure the uniformity of the material composition during the smelting process and then rolled into a plate shape.

[0025] In one example, the heat treatment of the rolled plate includes: normalizing at a temperature of 850°C to 1000°C, keeping at that temperature for 1h-2h, air cooling to room temperature, referring to Figure 1 .

[0026] In one example, heat treatment of the finished blank further includes: keeping at 800°C-950°C for 0.5h-1h, quenching and cooling to room temperature, keeping at 200°C-650°C for 1h-2h, air cooling to room temperature, referring to Figure 1 .

[0027] Specifically, the small Charpy V-notch standard impact specimen has high requirements on the microstructure of the specimen blank, and the consistency of the microstructure needs to be strictly controlled. Therefore, the small Charpy V-notch standard impact specimen has relatively high requirements on the uniformity and stability of the temperature field. Therefore, during heat treatment, the temperature uniformity of each point in the temperature field of the heat treatment furnace is strictly controlled not to exceed ±10°C and the temperature fluctuation does not exceed ±5°C to ensure that the heat treatment performance of each batch of materials is as consistent as possible, thereby controlling the consistency of the microstructure of the small Charpy V-notch standard impact specimen. Through heat treatment, the performance of the small Charpy V-notch standard impact specimen meets the requirements of consistency of impact performance at different energy levels.

[0028] In one example, the finished blank was cryogenically treated at -70°C for 3 hours, then lowered to -120°C for 8 hours, and returned to room temperature with the furnace to obtain a sample blank with uniform internal microstructure. Figure 2 .

[0029] In one example, the sample blank is processed by wire cutting to obtain a blank sample, which is first processed into a blank sample with a length of 55 mm, a width of 10 mm, and a height of 10 mm. When sampling, ensure that the final notch direction of all samples is consistent with the angle of the plate rolling direction. Figure 3 The wire cutting method is used to cut the length, width and thickness of the blank sample in turn to obtain a small blank sample. When sampling, ensure that the angle between the final notch direction of all samples and the rolling direction of the plate should be consistent. The six planes of the small blank sample are processed by a grinder to make the surface roughness Ra≤2.0μm. The notch processing method of the sample is to first use wire cutting to roughly process the V shape, and then use an optical projection curve grinder to finely grind the notch bottom radius and the notch side to make the notch surface roughness Ra≤1.6μm, and finally process it into a small Charpy V-notch standard impact specimen.

[0030] Specifically, experiments have shown that in the Charpy impact test, the measurement results of the impact energy are related to the sampling direction of the specimen. To ensure the consistency of the specimen impact results, the angle between the notch direction of all specimens and the rolling direction of the plate should be consistent. In addition, because the arc at the bottom of the V-notch of the specimen will produce tip stress concentration during the impact process, the smaller the radius, the more obvious the stress concentration, and the impact cracks are generated in the stress concentration area. To ensure the consistency of the metrological performance of the impact specimen, first of all, it is necessary to strictly control the V-notch angle, the arc radius at the bottom, and the notch roughness of the small Charpy V-notch standard impact specimen. Secondly, stress concentration should be avoided during the mechanical processing of the V-notch of the specimen. The V-notch is processed and formed using an optical projection curve grinder, which can directly observe the dimensional changes during the fine grinding process and reduce stress concentration. The above measures can ensure the dimensional consistency and impact performance consistency of the V-notch of the small Charpy V-notch standard impact specimen.

[0031] The present invention is described in more detail by the following examples. The size and shape of the small Charpy V-notch standard impact specimen prepared in each example are better than those specified in GB / T19748-2019. Example

[0032] The alloy is smelted by electroslag remelting in a vacuum furnace, and the modulated alloy steel contains: carbon, silicon, manganese, sulfur, phosphorus, copper, chromium, molybdenum, nickel, and iron. The components of the modulated alloy steel are designed to be (wt%): carbon C: 0.41, silicon Si: 0.35, manganese Mn: 0.85, sulfur S: 0.002, phosphorus P: 0.002, copper Cu: 0.21, chromium Cr: 0.83, molybdenum Mo: 0.28, nickel Ni: 1.88, and the balance is Fe and inevitable inclusions.

[0033] The smelted alloy raw material is rolled into a plate, and the rolled plate is normalized, wherein the normalizing temperature is 1000°C to obtain a finished billet; the finished billet is heat treated, kept at 910°C for 30 minutes, quenched and cooled to room temperature, kept at 200°C for 90 minutes, and air-cooled to room temperature. The finished billet is cryogenically treated, kept at -70°C for 3 hours, then reduced to -120°C for 8 hours, and returned to room temperature with the furnace.

[0034] The finished blank after heat treatment is machined, and samples are taken from the finished blank in sequence by wire cutting. The notch direction of the sample is consistent with the angle of the plate rolling direction. The six faces of the sample are machined by a grinder, and the V-notch of the sample is machined by an optical projection curve grinder to obtain a small Charpy V-notch standard impact specimen. The impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 1, and the geometric dimension detection data are shown in Table 2. Example

[0035] A small Charpy V-notch standard impact specimen was prepared according to the method of Example 1, except that the heat treatment temperature was kept at 250° C. for 90 minutes. The impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 1. Example

[0036] A small Charpy V-notch standard impact specimen was prepared according to the method of Example 1, except that the heat treatment process was different, and the finished blank was not subjected to deep cold treatment, that is, it was not kept at -70°C for 3 hours, then cooled to -120°C for 8 hours, and then returned to room temperature with the furnace. The impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 1.

[0037] Comparative Example 1: A small Charpy V-notch standard impact specimen was prepared according to the method of Example 1, except that the sulfur and phosphorus contents in the alloy composition were too high, that is, the sulfur content was 0.04% and the phosphorus content was 0.035%. The impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 1.

[0038] Comparative Example 2: A small Charpy V-notch standard impact specimen was prepared according to the method of Example 1, except that the heat treatment temperature field was not uniform and stable enough, the temperature uniformity of each point in the temperature field was ±15°C to ±20°C, and the temperature fluctuation range was ±9°C. The impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 1.

[0039] Comparative Example 3: Small Charpy V-notch standard impact specimens were prepared according to the method of Example 1, except that there were various angles between the V-notch groove direction of the specimen and the rolling direction of the plate during machining, and the V-notch groove direction of different specimens and the rolling direction of the plate had an angle between 0 degrees and 90 degrees. The impact performance data of the prepared small Charpy V-notch standard impact specimens are shown in Table 1.

[0040] Comparative Example 4: A small Charpy V-notch standard impact specimen was prepared according to the method of Example 1. The V-notch of the specimen was not processed by fine grinding with an optical projection curve grinder, but by a vertical broaching machine. The notch size and impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 1.

[0041] The performance of small Charpy V-notch standard impact test specimens of each embodiment and comparative example was tested, and the results are shown in Table 1 below. The performance and geometric dimension test data of the small Charpy V-notch standard impact specimen of Example 1 are taken, and the results are shown in Table 2 below. Embodiment 4: The alloy is smelted by electroslag remelting in a vacuum furnace, and the modulated alloy steel contains: carbon, silicon, manganese, sulfur, phosphorus, copper, chromium, molybdenum, nickel, and iron. The components of the modulated alloy steel are designed to be (wt%): carbon C: 0.41, silicon Si: 0.35, manganese Mn: 0.85, sulfur S: 0.002, phosphorus P: 0.002, copper Cu: 0.21, chromium Cr: 0.93, molybdenum Mo: 0.28, nickel Ni: 1.88, and the balance is Fe and inevitable inclusions.

[0042] The smelted alloy raw material is rolled into a plate, and the rolled plate is normalized, wherein the normalizing temperature is 1000°C to obtain a finished billet; the finished billet is heat treated, kept at 910°C for 30 minutes, quenched and cooled to room temperature, kept at 600°C for 90 minutes, and air-cooled to room temperature. The finished billet is cryogenically treated, kept at -70°C for 3 hours, then reduced to -120°C for 8 hours, and returned to room temperature with the furnace.

[0043] The finished blank after heat treatment is machined, and samples are sequentially taken from the finished blank by wire cutting, and the six surfaces of the sample are machined by a grinder, and the V-notch of the sample is machined by fine grinding with an optical projection curve grinder to obtain a small Charpy V-notch standard impact specimen. The notch size and impact performance data of the obtained small Charpy V-notch standard impact specimen are shown in Table 3. Example

[0044] A small Charpy V-notch standard impact specimen was prepared according to the method of Example 1, except that the heat treatment temperature was kept at 650° C. for 90 minutes. The impact performance data of the prepared small Charpy V-notch standard impact specimen are shown in Table 3.

[0045] The performance geometric dimension test data of the small Charpy V-notch standard impact specimens of Example 4 and Example 5 are taken, and the results are shown in Table 3 below. Those skilled in the art should understand that the purpose of the above description of the embodiments of the present invention is only to exemplarily illustrate the beneficial effects of the embodiments of the present invention, and is not intended to limit the embodiments of the present invention to any given examples.

[0046] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a small Charpy V-notch standard impact specimen, comprising: The high-purity metal raw materials are smelted twice to obtain a blank with uniform and stable structure; Rolling the blank to obtain a rolled plate; Normalizing the rolled plate to obtain a finished billet with stable structure; Performing heat treatment on the finished blank to obtain an impact test specimen blank; Mechanically processing the impact specimen blank to obtain a small Charpy V-notch standard impact specimen; The blank obtained by smelting contains carbon, silicon, manganese, sulfur, phosphorus, copper, chromium, molybdenum, nickel, vanadium, niobium, titanium and iron. The composition of the blank is designed as (wt%): carbon C: 0.36~0.43, silicon Si: 0.15~0.35, manganese Mn: 0.60~0.90, sulfur S: ≤0.025, phosphorus P: ≤0.025, copper Cu: ≤0.35, chromium Cr: 0.60~1.00, molybdenum Mo: 0.15~0.30, nickel Ni: 1.60~2.00, vanadium V: ≤0.025, niobium Nb: ≤0.025, titanium Ti: ≤0.025, and the balance is Fe and unavoidable inclusions.

2. The method for preparing a small Charpy V-notch standard impact specimen according to claim 1, wherein: The two smelting processes are vacuum furnace smelting and vacuum consumable furnace remelting to carry out batch smelting.

3. The method for preparing a small Charpy V-notch standard impact specimen according to claim 1, wherein: The rolled plate is normalized; specifically: the normalizing temperature is 850° C. to 1000° C., kept warm for 1 h to 2 h, and air-cooled to room temperature.

4. The method for preparing a small Charpy V-notch standard impact specimen according to claim 1, wherein the finished blank is heat treated; characterized in that: Follow the steps below: Step 1: keep the finished blank at 800°C-950°C for 0.5h-1h, quench and cool to room temperature, keep it at 200°C-650°C for 1.5h-4h, and air cool to room temperature; Step 2: After rough processing, the finished blank is subjected to deep cold treatment, kept at -70°C for 3 hours, then lowered to -120°C for 8 hours, and returned to room temperature with the furnace.

5. The method for preparing a small Charpy V-notch standard impact specimen according to claim 1, characterized in that: Follow the steps below to process: Step 1: A sample is obtained by wire cutting on the sample blank. The sample is first processed into a sample with a length of 55 mm, a width of 10 mm, and a height of 10 mm. When sampling, ensure that the final notch direction of all samples is consistent with the angle of the plate rolling direction; Step 2: Use wire cutting to cut the blank sample in the length, width and thickness directions in sequence to obtain a small blank sample. When sampling, ensure that the final notch direction of all samples is consistent with the angle of the plate rolling direction; Step 3, using a grinder to process six planes of the small blank sample to make the surface roughness Ra ≤ 2.0 μm; Step 4: The notch processing method is to first use wire cutting to roughly process the V shape, and then use an optical projection curve grinder to fine-grind the notch bottom radius and notch side, and finally process it into a small Charpy V-notch standard impact specimen.

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