Super duplex stainless steel spectrum standard sample and development method thereof

Abstract

The invention belongs to the technical field of chemical analysis of metallurgical standard samples, and discloses a super duplex stainless steel spectrum standard sample with high quality, high uniformity, high stability and accurate fixed value and a development method thereof. The method comprises the following steps: component design and raw material proportioning, smelting and casting, forging and homogenization treatment, primary inspection of uniformity and sample processing, uniformity inspection, constant value analysis and mathematical statistics, determination of characteristic values of standard samples, stability analysis of the standard samples after long-term storage, and traceability guarantee measures. The super duplex stainless steel spectrum standard sample comprises the following components in percentage by mass: 25%-26% of Cr, 6.50%-7.50% of Ni, 3.50%-4.50% of Mo, 0.23%-0.27% of N, 0.5%-1.0% of Cu, 0.5%-1.0% of W, and the balance of iron and inevitable impurities, and the content of trace elements including sulfur, aluminum and boron is controlled in a specific ppm level range.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis of metallurgical reference samples, and particularly relates to a spectral reference sample for super duplex stainless steel and a method for developing the same. Background Art

[0002] Due to the excellent properties of duplex stainless steel, which combines the advantages of austenite and ferrite (such as high strength, corrosion resistance and good weldability), it has been widely used in high-end fields such as ocean engineering, chemical equipment, and energy transmission. Among them, high-nitrogen and high-molybdenum super duplex stainless steel further improves the resistance to pitting and crevice corrosion by adding nitrogen and molybdenum elements, and has become a key material in harsh environments. However, its complex composition (such as high nitrogen content) and two-phase microstructure pose higher requirements for the accuracy of chemical composition analysis.

[0003] Spectral analysis is the core method for detecting the composition of materials, and its accuracy highly depends on the quality of reference samples. Currently, there is a lack of dedicated spectral reference samples for high-nitrogen and high-molybdenum super duplex stainless steel in the market, resulting in difficulties in ensuring the accuracy and reliability of measurement results during spectral analysis. The precise control and uniform distribution of high nitrogen content have always been difficult problems in the production of such stainless steel. At the same time, due to the special microstructure of high-nitrogen and high-molybdenum super duplex stainless steel, conventional methods for preparing reference samples are difficult to ensure the high uniformity of its internal composition. This leads to the inability to provide an accurate and reliable calibration basis for the composition detection of high-nitrogen and high-molybdenum super duplex stainless steel when using existing reference samples, thus affecting the accuracy of product quality control and performance evaluation.

[0004] Therefore, it is of great practical significance to develop a reference sample suitable for spectral analysis of high-nitrogen and high-molybdenum super duplex stainless steel and a reliable preparation method. Summary of the Invention

[0005] The purpose of the present invention is to provide a spectral reference sample for super duplex stainless steel with high quality, high uniformity and stability and accurate certification value, as well as a method for developing the same, so as to solve the problems existing in existing reference samples and ensure the accuracy and reliability of measurement results during spectral analysis.

[0006] The preparation method of the super duplex stainless steel spectrum standard sample according to the present invention comprises at least the following steps: Step 1: Composition design and raw material ratio: design the chemical composition according to mass percentage, wherein Cr: 25%-26%, Ni: 6.50-7.50%, Mo: 3.50-4.50%, N: 0.23%-0.27%, Cu: 0.5%-1.0%, W: 0.5%-1.0%, and at least the content of trace elements sulfur, aluminum, and boron is controlled within a specific ppm level range, and the remainder is iron and impurities; Step 2: Smelting and casting: smelt the raw materials obtained in step 1 at 1600±50°C for ≥60 minutes, and then continuously heat the melt at 900-950°C. The continuous casting billet is cast, and the continuous casting billet is sampled and at least segregation test and macroscopic structure test are performed to obtain a defect-free continuous casting billet; Step 3: Forging and homogenization treatment: The defect-free continuous casting billet is cut into small ingots for forging, and the small ingots are homogenized and annealed at 1150-1250°C for 12-18 hours under the protection of inert gas, and then forged at 950-1050°C to form steel bars with a forging ratio of 6-8; Step 4: Preliminary uniformity inspection and sample processing: The steel bars obtained in step 3 are subjected to physical macroscopic structure inspection and spectral uniformity preliminary inspection, and after passing the inspection, they are processed into standard samples of specified sizes and marked; Step 5: Uniformity inspection: Randomly select multiple standard samples for variance inspection to ensure that the F value is less than F α Critical value; Step 6: Fixed value analysis and mathematical statistics: entrust multiple domestic and foreign laboratories to conduct fixed value analysis, and conduct multiple tests on the data through mathematical statistics to determine whether the element statistics are qualified; Step 7: Determine the characteristic value of the standard sample, and measure and analyze the standard sample after long-term storage to determine the stable validity period of the component; Step 8: Traceability assurance measures: Use multiple laboratories to collaborate in fixed value determination to ensure the traceability of the fixed value.

[0007] Furthermore, in step one, the weight percentage of each element is: Cr: 24.80-25.50%; Ni: 6.50-7.50%; Mo: 3.50-4.50%; N: 0.240-0.250%; Cu: 0.50-0.80%; W: 0.50-0.80%; S: 0.0001-0.0015%; Al: 0.005-0.010%; B: 0.0005-0.0050%.

[0008] Furthermore, in step one, the chemical composition, by mass percentage, also includes: C: 0.005-0.025%; Si: 0.20-0.80%; Mn: 0.60-1.00%; P: 0.010-0.030%.

[0009] Furthermore, in step 1, metal raw materials and intermediate alloys with a purity of ≥99.9% are selected as raw materials.

[0010] Further, in Step 1, the raw materials are subjected to conventional X-ray fluorescence spectrometry analysis, chemical wet analysis detection, and the purity of the raw materials is deeply detected using a high-resolution mass spectrometer. If the purity or composition deviation of the raw materials exceeds the allowable range, the raw materials are selected again.

[0011] Further, in Step 2, the method for intercepting and sampling the continuous casting billet includes: avoiding the head and tail of the continuous casting billet, and taking the continuous casting billet at the central part of the continuous casting billet; before performing segregation inspection and macrostructure inspection on the defect-free continuous casting billet after intercepting and sampling, X-ray diffraction and ultrasonic flaw detection are performed.

[0012] Further, it also includes Step 9: nitrogen and oxygen element analysis: accurately determining the nitrogen and oxygen element contents of the standard sample.

[0013] Further, Step 5 also includes performing uniformity statistics after uniformity inspection: statistically obtaining the non-uniform variance S of each assigned component of the standard sample bb 2 and the variance statistic F.

[0014] Further, in Step 6, the statistical test strategies adopted in mathematical statistics include: method precision test, normality test, outlier test, and equal-precision test.

[0015] According to the super duplex stainless steel spectral standard sample of the present invention, the above-mentioned method for developing the super duplex stainless steel spectral standard sample is adopted during the preparation process.

[0016] Compared with the prior art, the super duplex stainless steel spectral standard sample and its development method of the present invention have the following beneficial effects:

[0017] 1) Component accuracy and coverage: The chemical composition of the standard sample of the present invention is reasonably designed, accurately covering the common content ranges of the main elements in the high-nitrogen and high-molybdenum super duplex stainless steel. In particular, the content control of key elements such as molybdenum, nitrogen, and oxygen is precise, and it can meet the spectral analysis requirements of high-nitrogen and high-molybdenum super duplex stainless steel products. Through the optimized combination of the contents of each element, a reliable reference standard is provided for accurately detecting the chemical composition of high-nitrogen and high-molybdenum super duplex stainless steel.

[0018] 2) High uniformity: The unique preparation method, including process steps such as electric furnace smelting, continuous casting, multi-pass forging, and high-temperature homogenization treatment, ensures a high degree of uniformity of the internal components of the standard sample. After detection, the element content deviation of different parts of the standard sample is extremely small, effectively avoiding spectral analysis errors caused by non-uniform composition. This high degree of uniformity greatly improves the accuracy and repeatability of spectral analysis results, enabling a stable and reliable benchmark to be provided for the component detection of high-nitrogen and high-molybdenum super duplex stainless steel when using this standard sample for calibration.

[0019] 3) Good traceability: During the raw material preparation stage, strict quality inspections and precise chemical composition determinations were carried out on key raw materials. This gives the standard sample good traceability, providing a strong guarantee for its wide application in the field of chemical composition detection of high-nitrogen and high-molybdenum super duplex stainless steel.

[0020] 4) Improve production efficiency and product quality: Using the standard sample of the present invention for spectral analysis can quickly and accurately detect the chemical composition of high-nitrogen and high-molybdenum super duplex stainless steel, helping production enterprises to adjust the production process in a timely manner to ensure that the product quality meets the standard requirements. This not only improves production efficiency, reduces production delays and waste rates caused by inaccurate composition detection, but also enhances the quality stability and market competitiveness of the products, which is of great significance for promoting the healthy development of the high-nitrogen and high-molybdenum super duplex stainless steel industry. Description of the Drawings

[0021] Figure 1 It is a schematic flow chart of the method for developing a spectral standard sample of super duplex stainless steel according to an embodiment of the present invention. Detailed Embodiments

[0022] In order to better understand the purpose, structure and function of the present invention, the present invention will be further described in detail below with reference to the drawings.

[0023] Figure 1 It shows the flow of the method for developing a spectral standard sample of super duplex stainless steel according to an embodiment of the present invention. As Figure 1 shown, the method for developing the spectral standard sample of super duplex stainless steel may include the following steps: Step 1 S1: Composition design and raw material ratio: Design the chemical composition by mass percentage, where Cr: 25%-26%, Ni: 6.50-7.50%, Mo: 3.50-4.50%, N: 0.23%-0.27%, Cu: 0.5%-1.0%, W: 0.5%-1.0%, and the balance is iron and impurities. At the same time, control the content of at least trace elements sulfur, aluminum, and boron within a specific ppm range to ensure that the standard sample covers the typical composition range of super duplex stainless steel and provides a comprehensive calibration benchmark for spectral analysis.

[0024] Preferably, in Step 1, metal raw materials and master alloys with a purity of ≥99.9% can be selected as raw materials. According to the target chemical composition of super duplex stainless steel, the precise addition amount of each raw material is determined through a calculation model. By selecting high-purity elemental metals such as iron, chromium, nickel, molybdenum, copper, tungsten, etc., as well as high-purity nitrogen, silicon, and specific master alloys as raw materials, ensuring that the purity of the metal raw materials is not less than 99.9%, it can effectively reduce the influence of impurity elements on the performance and composition uniformity of the standard sample at the source, reduce the subsequent detection and correction costs, provide a basic guarantee for the preparation of high-quality super duplex stainless steel spectral standard samples, help improve the purity and performance stability of the standard sample, and further enhance its accuracy and reliability in spectral analysis, ensuring the authenticity and credibility of the detection results.

[0025] Also preferably, in Step 1, the raw materials can be subjected to conventional X-ray fluorescence spectroscopy analysis, chemical wet analysis detection, and in-depth detection of the purity of the raw materials using a high-resolution mass spectrometer. If the purity or composition deviation of the raw materials exceeds the allowable range, the raw materials are selected again. Through the combination of X-ray fluorescence spectroscopy, chemical wet analysis, and high-resolution mass spectrometer, the composition of the raw materials can be comprehensively screened, and out-of-tolerance raw materials can be removed in real time, improving the process fault tolerance rate, shortening the R & D cycle, and avoiding unqualified finished products caused by raw material deviations.

[0026] Step 2 S2: Smelting and casting: The raw materials obtained by proportioning in Step 1 S1 are melted at 1600 ± 50 °C for ≥60 minutes to ensure that the raw materials are completely melted and uniformly mixed. At the same time, the composition of the melt in the furnace is monitored using a process sample analysis system to ensure its uniformity and accuracy. Then, the melt is continuously cast at 900 - 950 °C to obtain a continuous casting billet. The continuous casting billet is intercepted and sampled, and at least segregation inspection and macrostructure inspection are carried out to obtain a defect-free continuous casting billet. Segregation inspection is used for multi-site sampling spectral analysis to determine whether segregation exists, and macrostructure inspection is used to determine whether the internal organizational structure is good. This step can significantly improve the uniformity of the internal composition of the sample and avoid segregation defects.

[0027] Preferably, in Step 2, the method of intercepting and sampling the continuous casting billet can include: avoiding the head and tail of the continuous casting billet, taking the continuous casting billet at the central part of the continuous casting billet to ensure the composition uniformity of the sampling area, ensuring that the dimensions are maintained in the height and width directions, sampling parallel along the length direction, and performing X-ray diffraction and ultrasonic flaw detection on the defect-free continuous casting billet after intercepting and sampling before segregation inspection and macrostructure inspection. Through X-ray diffraction and ultrasonic flaw detection, internal cracks, pores, and segregation defects in the continuous casting billet can be effectively identified, reducing the scrap rate.

[0028] Step Three S3: Forging and homogenization treatment: Cut the defect-free continuous casting billet into small ingots and perform forging. Anneal the small ingots at 1150 - 1250 °C for 12 - 18 hours under the protection of inert gas. This process can adopt an intelligent temperature control system to ensure that the temperature fluctuation is within ±5 °C. During the annealing process, the inert gas circulation system can ensure uniform and stable furnace atmosphere, preventing oxidation of the ingot surface. Then, perform forging processing at 950 - 1050 °C to form steel bars. During the forging process, advanced small-tonnage numerical control forging equipment can be used to precisely program and control the forging force, forging speed, and forging stroke. And the temperature distribution of the forging is monitored in real time through an infrared thermal imager to ensure uniform forging process. The forging ratio can be 6 - 8, and the forging method can adopt multi-pass forging.

[0029] In a preferred embodiment, to ensure forging quality, the forging dies can be regularly inspected and maintained with high precision. If the die wear or deformation exceeds the allowable range, repair or replacement should be carried out in a timely manner.

[0030] Step Four S4: Preliminary inspection of uniformity and sample processing: Conduct physical macrostructure inspection and preliminary spectral uniformity inspection on the steel bars obtained in Step Three. After passing the inspection, process them into standard samples of specified dimensions and mark them. In this step, a sample piece about 20 mm thick can be randomly cut from one end of the above steel bar for physical macrostructure inspection. After passing the physical macrostructure inspection, the cut ends of the steel bar are excited on an ARL4460 direct-reading spectrometer, and the main elements and easily segregated elements are selected for preliminary uniformity inspection. After passing the physical macrostructure inspection and preliminary spectral uniformity inspection, the steel bar can be turned into a spectral block sample of specified dimensions and processed into a block standard sample using high-precision numerical control cutting equipment and grinding and polishing equipment, and then marked.

[0031] Step Five S5: Uniformity inspection: Multiple standard samples can be randomly selected for variance test to ensure that the F value < F α Critical value. In this step, multiple samples can be randomly selected. Under the same instrument analysis conditions and measurement environment, three independent data are measured for each bottle of all elements, and the variance test method is used for uniformity inspection. The F value of the variance statistic of each element is less than F α Critical value, proving that the uniformity of the standard sample meets the requirements.

[0032] Furthermore, Step Five can also include uniformity statistics after uniformity inspection: Statistically calculate the non-uniform variance S bb 2 And the variance statistic F of each fixed value component of the standard sample. By statistically calculating the non-uniform variance S bb 2Together with the variance statistic F, it can more comprehensively and deeply evaluate the homogeneity of the reference sample, providing a more accurate and objective quantitative basis for judging whether it meets the relevant standards and usage requirements, further ensuring the homogeneity quality of the reference sample, enhancing its representativeness and reliability in practical applications, and helping to improve the accuracy and repeatability of spectral analysis results.

[0033] Step Six S6: Certified value analysis and mathematical statistics: It is possible to entrust multiple domestic and foreign laboratories to conduct certified value analysis to ensure that the reference sample can be traced back to SI units and international and national standards; through mathematical statistics, various tests are carried out on the data to determine whether the element statistics are qualified.

[0034] Specifically, during the certified value analysis, after the sample homogeneity test is qualified, several steel bars can be randomly selected and turned into smaller-sized steel bars, and the chip-shaped samples are collected. After mixing and bottling, they are entrusted to the collaborative certified value unit for certified value analysis. To ensure the accuracy and reliability of the certified value of the reference sample, the certified value work can invite units with rich experience in the certified value analysis of reference samples for many years to conduct collaborative certified value. At least 6 - 8 domestic and foreign laboratories participate in the certified value. During the certified value analysis, the reference analysis method (such as gravimetric analysis and titrimetric analysis) or the collaboration of two methods with different principles (using two or more accurate and reliable analysis methods with different principles) can be adopted to ensure that this reference sample can be traced back to SI units and international and national standards. The analysis methods adopted by each laboratory need to be accurate and reliable and meet the requirements for the development of metallurgical reference samples.

[0035] During mathematical statistics, the following statistical test strategies can be adopted: method precision test, normality test, outlier test, and equal precision test. Through statistical tests, it is determined whether the elements of each item are statistically qualified. Those that are statistically qualified are retained, and for those that are statistically unqualified, it is determined whether to retain them, analyze the reasons, or eliminate them. This test strategy can strictly review and control the certified value analysis data from different angles, effectively identify and eliminate abnormal data, ensure that the finally determined element statistical results are true, reliable, and accurate, provide a solid data support and quality guarantee for the certified value of the reference sample, and improve the credibility and authority of the reference sample.

[0036] Specifically, its statistical methods and statistical principles can be the following four aspects:

[0037] 1) Method precision test: Use 1.3 times the in-house precision (r) of this method or the allowable difference to review and judge whether there are outliers for the four analysis data of each collaborative unit. After there are no outliers, calculate the average value of each group.

[0038] 2) Normality test: Use the Shapiro-Wilk method to test the normality of all data of all elements and the unit average data. When the statistic W > W0.05, the data conforms to the normal distribution; when W0.01 < W < W0.05, the data is ɑ normally distributed or approximately normally distributed at the significance level of

[0039] α = 0.01 and is retained; when W < W0.01, the data is not normally distributed and is generally excluded. ɑ 3) Outlier test: Use the Grubbs method to test the outliers of the unit average values of all elements. When the statistics Gmin, Gmax < G0.05, there are no outliers; when G0.01 > Gmin, Gmax > G0.05, the data

[0040] has no outliers at the significance level of ɑ α = 0.01 and no outlier treatment is performed; when Gmin, Gmax > G0.01, there are highly significant outliers and are generally excluded.

[0041] Step S7: Determine the characteristic values (i.e., the standard value and the expanded uncertainty) of the reference material, and conduct measurement and analysis on the reference material after long-term storage to determine the stable validity period of the composition. Through the verification of composition stability, ensure that there are no significant changes in the composition of the sample during long-term use, and reduce the calibration frequency and cost.

[0042] In this step, the characteristic values of the reference material can be obtained in the following ways:

[0043] 1) Determination of the standard value

[0044] Take the mean of the means of the certified values of each element in each laboratory as the standard value of this element.

[0045] 2) Determination of the standard deviation

[0046] Take the standard deviation of the means of the certified values of each element in each laboratory as the standard deviation of this element.

[0047] 3) Determination of the standard uncertainty

[0048] The standard uncertainty of the characteristic value is calculated according to the following formula.

[0049]

[0050] Wherein:

[0051] 4) Determination of expanded standard uncertainty

[0052] The formula for calculating the expanded uncertainty of the characteristic value is: U = ku CRM

[0053] Wherein, the uncertainty component u bb 2 is S in the uniformity statistical table bb 2 Since the stability of the metallurgical reference sample is very good, u lts (long-term stability uncertainty) and u sts (short-term stability uncertainty) can be neglected. S is the single measurement standard deviation of fixed-value statistics, n is the number of data groups, u char is the standard uncertainty caused by the determination, k is the coverage factor. When calculated according to the 95% confidence interval, k = 2 is taken.

[0054] Based on this, the standard value, standard deviation and expanded uncertainty can be determined.

[0055] The measurement and analysis of the reference sample after long-term storage can be carried out in the following ways: 1) The reference sample is stored for 1 to 3 years, and measurement and analysis are carried out at the beginning, middle and end, and it is compared that there is no significant change in the chemical composition before and after. 2) The stability of this type of sample is tracked and the stability of similar reference samples is investigated to determine the stable validity period of its components.

[0056] Step Eight S8: Traceability guarantee measures: Multiple laboratories can be used to collaborate on value determination to ensure the traceability of value determination. Specifically, the following measures can be adopted to ensure the traceability of its quantity value: 1) At least 8 laboratories are used to collaborate on value determination; all these collaborating units are accredited by national laboratories or ISO9000 certified; their value determination capabilities ensure the traceability of the samples. 2) For the determination of each element, reference methods or other two accurate and reliable analytical methods are used. For example, nickel is determined by dimethylglyoxime gravimetric method, silicon is determined by perchloric acid dehydration gravimetric method, chromium is determined by visual titration method, and N is determined by neutralization titration method. 3) The instruments of each testing laboratory have passed metrological verification or calibration to ensure the accuracy and traceability of value determination. 4) During the testing process, certified reference materials (CRM) are used for quality control of the measurement process.

[0057] Step Nine S9: Nitrogen and Oxygen Element Analysis: Accurately determine the nitrogen and oxygen element content in the sample. Specifically, finished spectral samples can be selected, sliced into sample pieces with a high-precision cutting machine in two cuts, bean-shaped samples obtained using a punching machine, and a nitrogen and oxygen analyzer used to accurately determine the nitrogen and oxygen element content. Nitrogen and oxygen element analysis is of great significance for the performance and quality control of super duplex stainless steel. The nitrogen element has a significant impact on its properties such as corrosion resistance and strength, while the oxygen element content also affects the processing performance and tissue stability of the material, etc. By accurately measuring the nitrogen and oxygen element content, the composition determination of the standard sample can be further improved, its accuracy and applicability in spectral analysis can be enhanced, and a more comprehensive and reliable basis can be provided for the quality control and product R & D of related industries.

[0058] According to the present invention, in a preferred embodiment, in Step One, the weight percentages of each element are as follows: Cr: 24.80 - 25.50%; Ni: 6.50 - 7.50%; Mo: 3.50 - 4.50%; N: 0.240 - 0.250%; Cu: 0.50 - 0.80%; W: 0.50 - 0.80%; S: 0.0001 - 0.0015%; Al: 0.005 - 0.010%; B: 0.0005 - 0.0050%. This embodiment further precisely defines the weight percentage ranges of each main element, making the chemical composition design more reasonable and precise, being able to better meet the performance requirements of super duplex stainless steel in different application scenarios, and also helping to improve the representativeness and applicability of the standard sample, providing a clearer composition control target for the subsequent smelting and processing processes, and ensuring that the final product has more stable and consistent performance.

[0059] Furthermore, in Step One, by mass percentage, the chemical composition also includes: C: 0.005 - 0.025%; Si: 0.20 - 0.80%; Mn: 0.60 - 1.00%; P: 0.010 - 0.030%. By controlling the contents of C, Si, Mn, and P, the strength and toughness of the material are balanced, component fluctuations caused by carbide precipitation are avoided, and the reasonable ratio of Si and Mn can improve the fluidity during continuous casting and forging processes, reduce the risk of hot cracks, and increase the finished product rate.

[0060] The present invention also provides a spectral standard sample of super duplex stainless steel, and the above method for developing the spectral standard sample of super duplex stainless steel is adopted during the preparation process. In a preferred embodiment, the chemical composition of the spectral standard sample of super duplex stainless steel is as follows by mass percentage: Cr: 24.80 - 25.50%; Ni: 6.50 - 7.50%; Mo: 3.50 - 4.50%; N: 0.240 - 0.250%; C: 0.005 - 0.025%; Si: 0.20 - 0.80%; Mn: 0.60 - 1.00%; P: 0.010 - 0.030%; S: 0.0001 - 0.0015%; Cu: 0.50 - 0.80%; W: 0.50 - 0.80%; Al: 0.005 - 0.010%; B: 0.0005 - 0.0050%, and the balance is iron and unavoidable impurities. The spectral standard sample of super duplex stainless steel has accurate composition, high uniformity and low expanded uncertainty of assigned value, and can be directly used to calibrate the direct-reading spectrometer, improving the detection efficiency and qualification rate of high-nitrogen and high-molybdenum super duplex stainless steel products (such as steel for offshore platforms).

[0061] The following are specific examples of the spectral standard sample of super duplex stainless steel and its development method according to the present invention:

[0062] (1) Chemical composition design

[0063] With reference to the composition range in the technical standard "Technical Conditions for Duplex Stainless Steel", this chemical composition was designed, as shown in Table 1.

[0064] Table 1 Composition design table of standard sample (%)

[0065]

[0066] (2) The weight percentages of the main elements are as follows: Cr: 24.80 - 25.50%; Ni: 6.80 - 7.20%; Mo: 3.70 - 4.20%; N: 0.240 - 0.250%.

[0067] The weight percentages of other elements are as follows: C: 0.010 - 0.025%; Si: 0.30 - 0.70%; Mn: 0.70 - 0.95%; P: 0.010 - 0.025%; S: 0.0001 - 0.0015%; Cu: 0.50 - 0.80%; W: 0.50 - 0.80%; Al: 0.005 - 0.015%; B: 0.0010 - 0.0040%; and the balance is iron and other unavoidable impurities.

[0068] (3) Raw material selection and precise proportioning

[0069] Select high-purity elemental metals such as iron, chromium, nickel, molybdenum, copper, tungsten, etc., as well as high-purity nitrogen, silicon, and specific intermediate alloys as raw materials to ensure that the purity of the metal raw materials is not less than 99.9%.

[0070] According to the target chemical composition of the super duplex stainless steel, use a high-precision calculation model to determine the precise addition amount of each raw material, and strictly control the content range of the main elements. For example, the chromium content is 25%-26%, the nickel content is 6.5%-7.5%, the molybdenum content is 3.5%-4.5%, the nitrogen content is 0.24%-0.26%, the copper content is 0.5%-1.0%, the tungsten content is 0.5%-1.0%, etc. At the same time, accurately control the content of trace elements within a specific ppm-level range to ensure that the standard sample covers the typical composition range of the super duplex stainless steel.

[0071] In the raw material selection process, in addition to conducting routine X-ray fluorescence spectrometry analysis and chemical wet analysis testing on each batch of raw materials, a high-resolution mass spectrometer is also used to deeply detect the purity of the raw materials. If the purity or composition deviation of the raw materials exceeds the allowable range, the raw materials are selected again.

[0072] (4) Standard sample smelting

[0073] Mix the above raw materials in proportion and smelt them in an electric furnace. Control the melting temperature at 1600±50°C and the melting time to be greater than 60 minutes to ensure that the raw materials are completely melted and evenly mixed. At the same time, use a process sample analysis system to monitor the composition of the melt in the furnace to ensure its uniformity and accuracy.

[0074] (5) Standard sample sampling and segregation inspection

[0075] After that, continuously cast the melt at 900-950°C. Take continuous casting billets from the central part of the continuous casting billet, avoiding the head and tail of the continuous casting. The weight of the continuous casting billet is between 400-600 kg, and the dimensions are guaranteed to be maintained in the height and width directions, and samples are taken parallel along the length direction.

[0076] After sampling, conduct segregation inspection and macrostructure inspection.

[0077] Use X-ray diffraction and ultrasonic flaw detection for inspection. If defects such as cracks, pores, or composition segregation are found inside, the ingot is discarded.

[0078] Segregation inspection: Take samples from multiple parts for spectral analysis to determine whether segregation exists.

[0079] Macrostructure inspection: Conduct macro inspection to determine whether the internal organizational structure is good.

[0080] (6) Standard sample cutting and forging

[0081] After the segregation inspection and macrostructure inspection are qualified, cut into pieces, each piece weighing about 15 - 20 kg, and forge using small ingots. Anneal the small ingots at 1150 - 1250 °C for 12 - 18 hours using an intelligent temperature control system to ensure the temperature fluctuation is within ±5 °C. During the annealing process, use an inert gas circulation system to ensure the uniformity and stability of the furnace atmosphere and prevent the surface oxidation of the ingots. After homogenization treatment, forge at 950 - 1050 °C, control the forging ratio at 6 - 8. During the forging process, use advanced small-tonnage numerical control forging equipment to precisely program and control the forging force, forging speed, and forging stroke, and use an infrared thermal imager to monitor the temperature distribution of the forgings in real time to ensure the forging process is uniform and consistent.

[0082] Forged into Ф50mm steel bars, each bar is 950mm - 1250mm long. To ensure the forging quality, regularly conduct high-precision inspection and maintenance on the forging dies. If the die wear or deformation exceeds the allowable range, repair or replace them in a timely manner.

[0083] (7) Macro inspection and initial uniformity inspection

[0084] For the above-mentioned Ф50mm steel bars, randomly cut a Ф50mm steel bar and take a sample piece about 20mm thick from the head for physical macrostructure inspection. The macro inspection report shows that the sample has no porosity, bubbles, ingot type segregation, and dot segregation, and fully meets the requirements of the standard sample for spectral analysis. The inspection results are shown in Table 2.

[0085] Table 2 Physical macro inspection results

[0086]

[0087] After the physical macro inspection is qualified, cut the two ends of the Ф50±2mm steel bar for excitation on an ARL4460 direct-reading spectrometer, and conduct initial uniformity inspection and statistics on the main elements and easily segregated elements. Compare the range with the precision of the analysis method. If the range Δ between all data of each element is < 2r, it is judged that the initial inspection is qualified. The initial inspection results are shown in Table 3. The data shows that there is no obvious difference in the content of each element, which meets the requirements for the development of the standard sample, and the initial uniformity inspection is qualified.

[0088] Table 3 Initial uniformity inspection results

[0089]

[0090]

[0091] (8) Sample preparation and identification

[0092] After the physical macro inspection and initial uniformity inspection are qualified, turn the Ф50mm steel bar into a Ф40mm steel bar and prepare and process it into a Ф40mm×40mm spectral bulk sample.

[0093] Process into Ф40mm×40mm bulk samples using high-precision numerical control cutting equipment and grinding and polishing equipment, and carry out numbering and marking.

[0094] (9) Homogeneity test

[0095] Randomly select 20 samples, use direct-reading spectroscopy analysis, and under the same instrument analysis conditions and measurement environment, measure three independent data for each bottle of all elements, and conduct a homogeneity test using the variance test method.

[0096] The F value of the variance statistic of each element is less than F α0.05 critical value, proving that the homogeneity of this reference material meets the requirements.

[0097] And according to the relevant formula, calculate the between-bottle inhomogeneity variance S of the samples bb 2 , and provide the determined homogeneity test data, statistic F, and inhomogeneity variance S bb 2 . The results of the homogeneity test are shown in Table 4.

[0098] Table 4 Results of the homogeneity test

[0099]

[0100]

[0101] According to the analysis of variance method, conduct homogeneity statistics, and count the inhomogeneity variance S of each certified component of the reference material bb 2 and statistic F. Calculate the between-bottle inhomogeneity variance S of the samples according to the "Guide for the Work of Reference Materials" in the GB / T 15000 series bb 2 .

[0102] When the statistic F < F α , there is no significant difference between the within-group and between-group data, and the homogeneity test is qualified.

[0103] When the statistic F > F α , there is a significant difference between the within-group and between-group data, and the homogeneity test is unqualified.

[0104] Conclusion: The F values of the statistics of each element obtained by the variance method are all less than F 0.05 (1.85), indicating that the homogeneity of each element of this reference material for spectroscopic analysis is good and meets the requirements of the reference material for homogeneity.

[0105] (10) Certification analysis

[0106] Randomly select three Ф40mm steel bars and turn them into Ф20mm steel bars, collect the chip-like samples, mix them evenly, put them into bottles, and entrust the collaborative value-assignment unit to conduct value-assignment analysis. According to the requirements of the guidelines and implementation guides, in order to ensure the accuracy and reliability of the value assignment of the reference sample, the value assignment work for the development of this reference sample invited units with rich experience in the value assignment analysis of reference samples to conduct collaborative value assignment throughout the year. A total of 8 domestic laboratories participated in the value assignment.

[0107] For the value assignment analysis method, it is required to select the reference analysis method, such as gravimetric analysis and titrimetric analysis; if a non-reference analysis method is selected, then two or more accurate and reliable analysis methods with different principles are required.

[0108] Ensure that this reference sample can be traced back to SI units and international and national standards. The analysis methods adopted by each laboratory are accurate and reliable, meeting the requirements for the development of metallurgical reference samples.

[0109] (11) Mathematical statistics

[0110] This invention patent is carried out according to the following statistical test strategies, adopting method precision test, normality test, outlier test and equal-precision test.

[0111] After statistical testing, determine whether each project element is statistically qualified. Those that are statistically qualified are retained, and for those that are statistically unqualified, determine whether to retain them, analyze the reasons, or reject them.

[0112] (12) Determine the standard value and uncertainty

[0113] The standard value, standard deviation and expanded uncertainty are shown in Table 5.

[0114] Table 5 Summary Table of Standard Value, Standard Deviation and Uncertainty

[0115]

[0116] (13) Stability determination and investigation

[0117] 1) After the reference sample is stored for 1 to 3 years, measurements and analyses are carried out at the beginning, middle and end, and it is found that there are no significant changes in the chemical composition before and after.

[0118] 2) Track the stability of this type of sample and investigate the stability of similar reference samples to determine the stable validity period of their components.

[0119] (14) Traceability guarantee measures

[0120] Adopt the foregoing measures to ensure the traceability of its quantity value.

[0121] (15) Analysis of nitrogen and oxygen elements

[0122] Determine the value of the oxygen and nitrogen element contents. Select finished spectral samples Using a high-precision cutting machine, slice the sample into two cuts to obtain a sample piece with a thickness of 2-3 mm. Use a punching machine to punch bean-shaped samples to obtain about bean-shaped samples. Use a nitrogen-oxygen analyzer to accurately determine the contents of nitrogen and oxygen elements. The determined value of oxygen element is 0.0037%, and the determined value of nitrogen element is 0.24%.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for developing a spectral standard sample of super duplex stainless steel, characterized in that, At least the following steps are included: Step 1: Composition design and raw material ratio: design the chemical composition by mass percentage, including Cr: 25%-26%, Ni: 6.50-7.50%, Mo: 3.50-4.50%, N: 0.23%-0.27%, Cu: 0.5%-1.0%, W: 0.5%-1.0%, and at least control the content of trace elements sulfur, aluminum, and boron within a specific ppm level range, and the balance is iron and unavoidable impurities; Step 2: smelting and casting: smelting the raw materials obtained in the step 1 at 1600±50°C for ≥60 minutes, then continuously casting the melt at 900-950°C to obtain a continuous casting billet, cutting and sampling the continuous casting billet and performing at least segregation inspection and macrostructure inspection to obtain a defect-free continuous casting billet; Step 3: Forging and homogenization treatment: the defect-free continuous casting billet is cut into small ingots forging, the small ingots are homogenized and annealed at 1150-1250° C. for 12-18 hours under inert gas protection, and then forged at 950-1050° C. to form steel bars with a forging ratio of 6-8; Step 4: Preliminary inspection of uniformity and sample processing: Physical macroscopic inspection and preliminary inspection of spectral uniformity are performed on the steel bars obtained in step 3. After passing the inspection, the steel bars are processed into standard samples of specified sizes and marked; Step 5: Uniformity test: Randomly select multiple of the said standard samples for variance test to ensure that the F value < F α critical value; Step 6: Fixed value analysis and mathematical statistics: entrust several domestic and foreign laboratories to conduct fixed value analysis, and conduct various tests on the data through mathematical statistics to determine whether the element statistics are qualified; Step 7: Determine the characteristic values of the standard samples, and measure and analyze the standard samples after long-term storage to determine the stable validity period of the components; Step 8: Traceability assurance measures: Use collaborative valuation by multiple laboratories to ensure the traceability of the valuation.

2. The method for developing a spectral standard sample of super duplex stainless steel according to claim 1, characterized in that, In the step 1, the weight percentage of each element is: Cr: 24.80-25.50%; Ni: 6.50-7.50%; Mo: 3.50-4.50%; N: 0.240-0.250%; Cu: 0.50-0.80%; W: 0.50-0.80%; S: 0.0001-0.0015%; Al: 0.005-0.010%; B：0.0005-0.0050％。 3. The method for developing a spectral standard sample of super duplex stainless steel according to claim 2, characterized in that, In the step 1, the chemical composition further includes, by mass percentage: C: 0.005-0.025%; Si: 0.20-0.80%; Mn: 0.60-1.00%; P: 0.010-0.030%.

4. The method for developing a spectral standard sample of super duplex stainless steel according to any one of claims 1 to 3, characterized in that, In the step 1, metal raw materials and intermediate alloys with a purity of ≥99.9% are selected as raw materials.

5. The method for developing a spectral standard sample of super duplex stainless steel according to claim 4, characterized in that, In the step 1, the raw materials are subjected to conventional X-ray fluorescence spectroscopy analysis, chemical wet analysis detection, and in-depth detection of the purity of the raw materials using a high-resolution mass spectrometer. If the purity or composition deviation of the raw materials exceeds the allowable range, the raw materials are reselected.

6. The method for developing a spectral standard sample of super duplex stainless steel according to any one of claims 1 to 3, characterized in that, In the second step, the method for intercepting and sampling the continuous casting billet includes: avoiding the head and tail of the continuous casting billet, taking the continuous casting billet at the central part of the continuous casting billet; before performing segregation inspection and macrostructure inspection on the defect-free continuous casting billet after intercepting and sampling, performing X-ray diffraction and ultrasonic flaw detection.

7. The method for developing a spectral standard sample of super duplex stainless steel according to any one of claims 1 to 3, characterized in that, It further includes step nine: nitrogen and oxygen element analysis: accurately determining the content of nitrogen and oxygen elements in the standard sample.

8. The method for developing a spectral standard sample of super duplex stainless steel according to any one of claims 1 to 3, characterized in that, Step 5 further includes performing uniformity statistics after the uniformity test: calculating the non-uniform variance S of each certified component of the standard sample bb 2 and the variance statistic F.

9. The method for developing a spectral standard sample of super duplex stainless steel according to any one of claims 1 to 3, characterized in that, In the sixth step, the statistical test strategies adopted in mathematical statistics include: method precision test, normality test, outlier test, and equal precision test.

10. A spectral standard sample of super duplex stainless steel, characterized in that, During the preparation process, the development method of the spectral standard sample of super duplex stainless steel according to any one of claims 1-9 is adopted.

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