A method for preparing a rare earth steel standard sample

Abstract

The application discloses a preparation method of rare earth steel spectrum standard sample blank, which adopts an industrial production rare earth steel continuous casting slab, detects the rare earth content in the thickness direction of the slab by a chemical method, detects the rest except the rare earth in the steel by a spectrum direct-reading method, and saws and processes the slab with close component content into 10-30mm thick plates. Then, the plates are connected together by adopting an explosive welding mode, the final thickness reaches more than 70mm, and the blank with good component uniformity is formed. By adopting the method, the component segregation formed in the solidification process of the molten steel and the non-uniformity of the blank caused by the problems such as the 1 / 4 inner arc and center segregation of the inclusions in the continuous casting process can be completely avoided. By adopting the method, the high homogenization standard sample can be directly forged and prepared from the blank, and the cost of the heat treatment process is reduced.

Description

Technical Field

[0001] This invention relates to the field of metallurgical analysis and testing, and in particular to a method for preparing rare earth steel standards. Background Technology

[0002] Rare earth content in steel is generally detected using chemical methods, which cannot provide reliable data for timely adjustment and control of rare earth content during production. In actual production, only the amount of rare earth added can be controlled, resulting in significant fluctuations in the actual rare earth content range, which is detrimental to the stable control of rare earth steel product performance. Currently, the compositional homogeneity of rare earth steel spectral standard samples being developed is insufficient to meet the accuracy requirements for online detection of rare earth content, and the preparation cost is also high. Therefore, improving the accuracy of spectral detection by preparing highly homogenized rare earth steel spectral standard sample billets is a key issue for the widespread adoption of rare earth steel.

[0003] The literature "Measures to Improve the Uniformity of Alloy Steel Spectral Standard Samples" (Metal Casting, Forging and Welding Technology, May 2009) introduces the preparation process of alloy steel spectral standard samples and elaborates on methods to improve the uniformity of spectral standard samples from aspects such as the preparation process, the method of adding each element, and process inspection, ensuring that the prepared standard samples have uniform chemical composition and can meet the requirements of spectral analysis. However, it cannot fundamentally avoid the non-uniformity of composition distribution on the cross-section of the ingot caused by metal solidification segregation.

[0004] Patent CN 111487097A discloses a method for preparing standard samples of low-carbon aluminum-silicon steel. Specifically, it involves sampling from continuously cast billets, avoiding sampling locations at 1 / 4 and 1 / 2 of the billet's cross-section where inclusions and impurity elements accumulate. A 50mm section is removed from the edge to avoid the influence of protective slag on the billet, ensuring the uniformity of elemental composition in the sample. However, this method has certain requirements regarding billet thickness; otherwise, the sample size will be too small, making it difficult to forge and roll into 40mm diameter round bars for preparing standard samples.

[0005] Patent CN 113814360A discloses a rare earth steel spectral standard and its preparation method. The method involves melting rare earth steel in a magnesium crucible, casting it into ingots, and then forging, slow cooling, and homogenizing annealing to prepare the standard. By designing the magnesium crucible composition and coordinating it with the process design during preparation, the resulting rare earth steel sample exhibits good chemical composition uniformity and a high rare earth content hit rate, meeting the requirements for a rare earth steel spectral standard. However, this invention cannot avoid the influence of component segregation during the ingot casting process, affecting the standard sample qualification rate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing rare earth steel standard samples, wherein the billet is made by cutting portions of similar composition from industrially produced continuous casting slabs and connecting them together by welding.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for preparing rare earth steel standards, comprising the following steps:

[0009] 1) Rare earth steel smelting

[0010] Rare earth steel smelting process: desulfurization pretreatment—converter smelting—LF refining, controlling the oxygen content in the steel to be no more than 15ppm and the sulfur content to be no more than 15ppm, and adding rare earth La, or rare earth Ce or rare earth Y at the end of refining.

[0011] 2) Rare earth steel continuous casting

[0012] The entire casting process is carried out without oxidation protection, and the nitrogen increase during continuous casting is controlled to be no more than 3 ppm; an alkaline tundish covering agent and a high magnesium oxide tundish lining are used, and the silica content is no more than 5%;

[0013] 3) Sampling of rare earth steel continuous casting slab billets

[0014] Spectroscopic samples were prepared along the thickness direction at the middle and 1 / 4 and 3 / 4 of the width of the continuously cast slab. Starting from the center of the sample, one component detection point was set every 1 cm on both sides. The content of all components except rare earth elements was detected by direct spectral reading, and the content of rare earth elements was detected by chemical method. Based on the component detection results, the part with a standard deviation of no more than 3% was selected, and the continuously cast slab was sawn to take samples with a thickness of 10-30 mm and a length and width of no less than 500 mm.

[0015] 4) Sample preparation for connecting rare earth steel continuous casting slab billets

[0016] The above-mentioned slab blanks are joined together using an explosive welding process, resulting in a final thickness of over 60mm. After the explosively welded blanks are straightened, they are cut into forging blanks with a length and width of 150-300mm.

[0017] 5) Composition analysis of rare earth steel standard billet

[0018] Samples were taken from the weld for composition analysis and compared with the composition of samples taken from the rare earth steel continuous casting slab. Samples with a standard deviation of no more than 3% were used as standard samples for direct reading of rare earth steel spectrometers in the forging process.

[0019] Furthermore, highly homogeneous standard samples can be prepared by direct forging of billets without the need for diffusion annealing.

[0020] Furthermore, an explosive welding process is used to join the above-mentioned slab blanks together, resulting in a final thickness of over 70mm.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0022] By using the process method of the present invention to prepare spectral direct-reading standard billets, the non-uniformity of the billets caused by compositional segregation during the solidification process of molten steel and the aggregation of inclusions in the inner arc 1 / 4 and center of the billet during continuous casting can be completely avoided.

[0023] This method allows for the direct forging of billets to prepare highly homogeneous standard samples, reducing the cost of heat treatment processes. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] Figure 1 This is a direct-reading spectral dot distribution diagram of the billet along the thickness direction.

[0026] Figure 2 This is a diagram showing the distribution of rare earth element La content in the thickness direction of the cast billet.

[0027] Figure 3 This is a distribution diagram of the segregation ratio of each component in the thickness direction of the Q355B cast billet sample. Detailed Implementation

[0028] A method for preparing rare earth steel spectral standard billets, the main steps and process parameters are as follows:

[0029] 1. Rare earth steel smelting

[0030] Rare earth steel smelting process: desulfurization pretreatment—converter smelting—LF refining, controlling the oxygen content in the steel to be no more than 15ppm and the sulfur content to be no more than 15ppm, and adding rare earth La, or rare earth Ce or rare earth Y at the end of refining.

[0031] 2. Rare earth steel continuous casting

[0032] The entire casting process is carried out under oxidation-free protection, with nitrogen increase controlled to no more than 3 ppm during continuous casting. An alkaline tundish covering agent and a high-magnesium oxide tundish lining are used, with silica content not exceeding 5%.

[0033] 3. Sampling of rare earth steel continuous casting slab billets

[0034] Spectroscopically direct-reading samples were prepared along the thickness direction at the middle and 1 / 4 and 3 / 4 of the width of the continuously cast slab. Starting from the center of the sample, one component detection point was set every 1 cm on both sides. The content of all components except rare earth elements was determined using direct-reading spectroscopy, and the rare earth element content was determined using chemical methods. Based on the component detection results, samples with a standard deviation of no more than 3% were selected. The continuously cast slab was then sawn to obtain samples with a thickness of 10–30 mm and a length and width of no less than 500 mm.

[0035] 4. Sample preparation for connecting rare earth steel continuous casting slab billets

[0036] The above-mentioned slab blanks are joined together using an explosive welding process, with a thickness of not less than 70 mm. After the explosively welded blanks are straightened, they are cut into forging blanks with a length and width of 150-300 mm.

[0037] 5. Composition analysis of rare earth steel standard billet

[0038] Samples were taken from the weld for composition analysis and compared with the composition of samples taken from the rare earth steel continuous casting slab. Samples with a standard deviation of no more than 3% were used as standard samples for direct reading of rare earth steel spectrometers in the forging process.

[0039] Taking Q355B as an example, the segregation ratio distribution of each component in its cast billet sample along the thickness direction is as follows: Figure 3 As shown.

[0040] This invention utilizes industrially produced rare-earth steel continuously cast slabs. The rare-earth content in the thickness direction of the slab is detected using chemical methods, and the content of other components besides rare-earth is detected using direct-reading spectral methods. Slabs with similar component contents are sawn into plates 10–30 mm thick. These plates are then joined together using explosive welding, resulting in a final thickness of over 70 mm, forming a slab with excellent compositional homogeneity. This method completely avoids component segregation during steel solidification and the non-uniformity of the slab caused by inclusions clustering in the inner quarter and center of the slab during continuous casting. Furthermore, this method allows for direct forging of the slab to prepare highly homogeneous standard samples, reducing the cost of heat treatment processes.

[0041] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing rare earth steel standard samples, characterized in that, The steps include the following: 1) Rare earth steel smelting Rare earth steel smelting process: desulfurization pretreatment—converter smelting—LF refining, controlling the oxygen content in the steel to be no more than 15ppm and the sulfur content to be no more than 15ppm, and adding rare earth La, or rare earth Ce or rare earth Y at the end of refining. 2) Rare earth steel continuous casting The entire casting process is carried out without oxidation protection, and the nitrogen increase during continuous casting is controlled to be no more than 3 ppm; an alkaline tundish covering agent and a high magnesium oxide tundish lining are used, and the silica content is no more than 5%; 3) Sampling of rare earth steel continuous casting slab billets Spectroscopic samples were prepared along the thickness direction at the middle and 1 / 4 and 3 / 4 of the width of the continuously cast slab. Starting from the center of the sample, one component detection point was set every 1 cm on both sides. The content of all components except rare earth elements was detected by direct spectral reading, and the content of rare earth elements was detected by chemical method. Based on the component detection results, the part with a standard deviation of no more than 3% was selected, and the continuously cast slab was sawn to take samples with a thickness of 10-30 mm and a length and width of no less than 500 mm. 4) Sample preparation for connecting rare earth steel continuous casting slab billets The above-mentioned slab blanks are joined together using an explosive welding process, resulting in a final thickness of over 60mm. After the explosively welded blanks are straightened, they are cut into forging blanks with a length and width of 150-300mm. 5) Composition analysis of rare earth steel standard billet Samples were taken from the weld for composition analysis and compared with the composition of samples taken from the rare earth steel continuous casting slab. Samples with a standard deviation of no more than 3% were used as standard samples for direct reading of rare earth steel spectrometers in the forging process.

2. The method for preparing rare earth steel standards according to claim 1, characterized in that, Highly homogeneous standard samples can be prepared by direct forging of billets without the need for diffusion annealing.

3. The method for preparing rare earth steel standard samples according to claim 1, characterized in that, The above-mentioned slab blanks are joined together using an explosive welding process, resulting in a final thickness of over 70mm.

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