A method for distinguishing the origin and proportion of DS inclusions in steel

Abstract

The present invention relates to the technical field of steelmaking, and in particular to a method for distinguishing the source and proportion of DS inclusions in steel, comprising the following steps: (1) Test 1: a converter adopts a blowing method to decarburize, dephosphorize and ensure that the tapping temperature is ≥1580°C; Test 2: a converter adopts a blowing method to decarburize, dephosphorize and ensure that the tapping temperature is ≥1580°C; (2) Test 1: after LF arrives at the station, smelting is carried out according to the smelting method, and ferrosilicon alloy is added; Test 2: 200kgBaCO3 is added after LF arrives at the station, and silicon carbide or aluminum particles are added during the LF process; (3) Test 1: RH vacuum; Test 2: RH vacuum; (4) Test 1 and Test 2: a continuous casting process adopts full-process protective casting, combined with a method of combining endogenous inclusion type control and BaCO3 tracer tracing, the source of DS inclusions in steel can be distinguished, and the corresponding DS inclusion quantity and proportion can be judged at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a method for distinguishing the sources and proportions of DS inclusions in steel. Background Art

[0002] High purity has a great influence on the fatigue life of gear and bearing steels, among which the control of DS inclusions is particularly important. The fewer DS inclusions in the steel, the easier it is to obtain bearing steel and gear steel with a long life. Therefore, how to achieve smelting with very few DS inclusions has become a key issue in the high purity steel smelting industry. For the control research of DS inclusions, it is usually necessary to distinguish the source of DS inclusions in order to study the corresponding control measures.

[0003] After searching, many people at home and abroad have conducted many studies on the source and proportion of DS inclusions, but there are many differences with this patent. The document "Application of slag tracers to investigate source of non-metallic inclusions" points out that by adding BaCO3 to the refined slag to trace whether the final inclusions contain BaO to confirm the source of the inclusions, the author finally believes that 30% of the inclusions contain BaO; but in the scheme studied by the author, the endogenous inclusions in the molten steel are also DS-type low-melting-point inclusions, and the number and proportion of DS inclusions other than the endogenous inclusions and non-refined slag inclusions cannot be distinguished. Secondly, since the SEM-EDS energy spectrum analysis cannot completely distinguish whether the inclusions must be BaO inclusions, the distinction between endogenous inclusions and inclusions involved in refined slag is relatively vague. The document "Tracing study on the source of large-particle inclusions in 20CrMo steel" points out that the BaCO3 tracer method is used to calibrate the source of large-particle inclusions in 20CrMo steel. The tracer calibration method includes (1) adding tracers at the beginning of LF furnace refining and (2) adding tracers at the end of VD. The results of SEM analysis show that: the tracer calibration method (1) Ba-containing inclusions gradually transfer into the steel during LF furnace refining, and all inclusions after VD and in the bar contain Ba elements; the tracer calibration method (2) did not find Ba-containing inclusions in the inspection at the end of soft blowing and in the bar. The above shows that the source of inclusions in 20Cr Mo steel is the fine slag droplets involved in the molten steel from the top slag of the LF refining and VD treatment ladle, which then reacts chemically with the molten steel and is not floated up and removed in time, forming the final large particle inclusion form. Similarly, the author can only trace the possibility that the DS inclusions in the steel contain the involvement of refined slag, and cannot give the number and proportion of endogenous DS inclusions; the number and proportion of DS inclusions involved in refined slag. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in order to overcome the problem of how to distinguish the sources of DS inclusions in the prior art, a method for distinguishing the sources and proportions of DS inclusions in steel is provided.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for distinguishing the source and proportion of DS inclusions in steel, using a "BOF-LF-(RH)-CC" process route, comprising the following steps:

[0006] (1) Test 1: The converter adopts the blowing method to decarbonize, dephosphorize and ensure that the tapping temperature is ≥1580°C; the final temperature of the converter is controlled at 1610-1670°C, and the final carbon is ≥0.05%; aluminum is first added to the converter for deoxidation, and then a small amount of ferrosilicon is added to partially alloy Si. After the alloy is added, lime and refined slag are added for slagging;

[0007] Test 2: The converter adopts the blowing method, which is responsible for decarburization, dephosphorization and ensuring that the tapping temperature is ≥1580℃; the final temperature of the converter is controlled at 1610~1670℃, and the final carbon is ≥0.05%; aluminum is first added to the converter for deoxidation, and then ferrosilicon is added for Si alloying, and the Si element content is controlled to be the standard lower limit minus 0.07%. The standard here mainly refers to steel containing Si. For example, for steel with 0.25% Si content, Si alloy is added according to the standard of 0.18% when tapping, and lime and refined slag are added after the alloy is added for slagging;

[0008] (2) Test 1: After LF arrived at the station, it was smelted according to the smelting method, ferrosilicon alloy was added, calcium carbide was used for deoxidation, the content of (TFe+MnO+Cr2O3) in the slag was controlled below 1.50%, and the basicity of the refined slag was controlled at 3.0-7.0;

[0009] Test 2: 200kgBaCO3 was added as a tracer after LF arrived at the station. Silicon carbide or aluminum particles were added during the LF process to deoxidize the slag surface and adjust the Si content. The (TFe+MnO+Cr2O3) content in the slag was controlled below 1.50%, and the basicity of the refined slag was controlled at 3.0-7.0. Ferrosilicon and calcium carbide were prohibited during the refining process.

[0010] (3) Test 1: No alloy or slag was added during the RH vacuum process, and calcium treatment was performed after the soft blowing was completed;

[0011] Test 2: No alloy or slag is added during the RH vacuum process, and calcium treatment is prohibited after the soft blowing is completed;

[0012] (4) Test 1 and Test 2: The continuous casting process adopts full protection casting;

[0013] (5) Test 1: After steelmaking is completed, rolling production is carried out. After rolling is completed, samples are taken for analysis. The number of samples taken from each heat of steel is required to be ≥ 20. After each sample is polished, DS inclusions are detected using an optical microscope and the number is recorded;

[0014] Test 2: After steelmaking, rolling production is carried out. After rolling, samples are taken for analysis. The number of samples taken from each heat of steel is required to be ≥ 20. After each sample is ground and polished, DS inclusions are detected using an optical microscope and circled;

[0015] (6) Test 2: Use a scanning electron microscope to detect the composition of the circled inclusions to determine whether they contain BaO. It is required that a clear BaO precipitation band pattern must appear in the inclusion photo taken, and the EDS analysis of the BaO precipitation band position must show that the Ba atomic mass fraction is ≥7%.

[0016] It further includes that the steel type is aluminum deoxidized steel, the Al content is usually required to be ≥0.01%, and there is no obvious requirement for the Si content. If the Si content is low, ferrosilicon may not be added during the steelmaking process. The Si content standard is too low, which means that this steel does not need to be silicon alloyed, and no Si alloy needs to be added. Aluminum particles are used for deoxidation during the smelting process.

[0017] It further includes determining in Test 2 whether the DS inclusion is a BaO-containing inclusion, based on whether it contains an obvious high-BaO precipitation band morphology, and the Ba mass fraction of the precipitation band in SEM-EDS energy spectrum analysis is ≥7%.

[0018] Further comprising the total amount of barium carbonate added in the refining in Test 2, accounting for ≥10% of the total amount of all slag materials.

[0019] The beneficial effect of the present invention is that the method provided by the present invention for distinguishing the sources and proportions of DS inclusions in steel, combined with the method of combining endogenous inclusion type control and BaCO3 tracer tracing, can distinguish the sources of DS inclusions in steel (endogenous DS inclusions, DS inclusions involved in refining and other DS inclusions), and at the same time determine the corresponding number and proportion of DS inclusions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0021] Figure 1 This is the inclusion distribution diagram in the steel at the end of LF for test 1;

[0022] Figure 2 This is the distribution diagram of inclusions in the continuous casting steel slab for experiment 1;

[0023] Figure 3 This is the inclusion distribution diagram in the steel at the end of LF for test 2;

[0024] Figure 4 This is the enlarged distribution diagram of inclusions in steel at the end of LF in Experiment 2;

[0025] Figure 5 This is the inclusion analysis diagram of the continuous casting steel in Experiment 2;

[0026] Figure 6 This is test 2, corresponding to the typical morphology of DS inclusions containing BaO in the rolled material. DETAILED DESCRIPTION

[0027] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0028] like Figure 1 Schematic diagram of the structure of the present invention, a method for distinguishing the source and proportion of DS inclusions in steel, using the "BOF-LF-(RH)-CC" process route, including the following steps:

[0029] (1) Test 1: The converter adopts the blowing method to decarbonize, dephosphorize and ensure that the tapping temperature is ≥1580°C; the final temperature of the converter is controlled at 1610-1670°C, and the final carbon is ≥0.05%; aluminum is first added to the converter for deoxidation, and then a small amount of ferrosilicon is added to partially alloy Si. After the alloy is added, lime and refined slag are added for slagging;

[0030] Test 2: The converter adopts the blowing method to decarbonize, dephosphorize and ensure that the tapping temperature is ≥1580℃; the final temperature of the converter is controlled at 1610~1670℃, and the final carbon is ≥0.05%; aluminum is first added to the converter for deoxidation, and then ferrosilicon is added for Si alloying, and the Si element content is controlled to be the standard lower limit minus 0.07%. After the alloy is added, lime and refined slag are added for slagging;

[0031] (2) Test 1: After LF arrived at the station, it was smelted according to the smelting method, ferrosilicon alloy was added, calcium carbide was used for deoxidation, the content of (TFe+MnO+Cr2O3) in the slag was controlled below 1.50%, and the basicity of the refined slag was controlled at 3.0-7.0;

[0032] Test 2: 200kgBaCO3 was added as a tracer after LF arrived at the station. Silicon carbide or aluminum particles were added during the LF process to deoxidize the slag surface and adjust the Si content. The (TFe+MnO+Cr2O3) content in the slag was controlled below 1.50%, and the basicity of the refined slag was controlled at 3.0-7.0. Ferrosilicon and calcium carbide were prohibited during the refining process.

[0033] (3) Test 1: No alloy or slag was added during the RH vacuum process, and calcium treatment was performed after the soft blowing was completed;

[0034] Test 2: No alloy or slag is added during the RH vacuum process, and calcium treatment is prohibited after the soft blowing is completed;

[0035] (4) Test 1 and Test 2: The continuous casting process adopts full protection casting;

[0036] (5) Test 1: After steelmaking is completed, rolling production is carried out. After rolling is completed, samples are taken for analysis. The number of samples taken from each heat of steel is required to be ≥ 20. After each sample is polished, DS inclusions are detected using an optical microscope and the number is recorded;

[0037] Test 2: After steelmaking, rolling production is carried out. After rolling, samples are taken for analysis. The number of samples taken from each heat of steel is required to be ≥ 20. After each sample is ground and polished, DS inclusions are detected using an optical microscope and circled;

[0038] (6) Test 2: Use a scanning electron microscope to detect the composition of the circled inclusions to determine whether they contain BaO. It is required that a clear BaO precipitation band pattern must appear in the inclusion photo taken, and the EDS analysis of the BaO precipitation band position must show that the Ba atomic mass fraction is ≥7%.

[0039] The steel type is aluminum-deoxidized steel, and the Al content is usually required to be ≥0.01%. There is no obvious requirement for the Si content. If the Si content is low, ferrosilicon may not be added during the steel-making process, and aluminum particles may be used for deoxidation during the smelting process. Ferrosilicon may not be added during the steel-making process, and silicon carbide may not be used for deoxidation during the smelting process, but aluminum particles may be used for deoxidation instead.

[0040] The purpose of controlling ferrosilicon and eliminating calcium treatment in Experiment 2 is to control the endogenous inclusions in the entire smelting process to be non-DS type low-melting point inclusions.

[0041] In Test 2, whether the DS inclusion is a BaO-containing inclusion is determined based on whether it contains an obvious high-BaO precipitation band morphology and the Ba mass fraction of the precipitation band is ≥7% according to the SEM-EDS energy spectrum analysis.

[0042] In Experiment 2, the total amount of barium carbonate added during refining accounts for ≥10% of the total amount of all slag materials.

[0043] 20 steel is produced using a 130-ton converter, a 130-ton refining furnace and a continuous casting machine.

[0044] Embodiment 1:

[0045] Test 1:

[0046] The composition of the finished steel is C: 0.199%, Si: 0.211%, Mn: 0.381%, S: 0.007%, Cr: 0.053%, Al: 0.0149%.

[0047] 50kg ferrosilicon is added during BOF steelmaking.

[0048] 260kg ferrosilicon is used at the LF station, and 360kg silicon carbide is used for deoxidation. After LF is finished, 120m calcium wire is fed, and soft blowing is performed for 21 minutes after calcium treatment, and the ladle is hoisted to CCM for continuous casting.

[0049] The inclusions in LF finished steel are mainly low melting point calcium aluminate and magnesium aluminate spinel, such as Figure 1 (Scanning area 60mm 2 , scanning inclusion size ≥ 1μm).

[0050] The continuous casting adopts full protection casting. Low-magnification samples are taken from the continuous casting billet for inclusion analysis, such as Figure 2 As shown, it is mainly low melting point calcium aluminate and magnesium aluminum spinel (scanning area 60mm 2 , scanning inclusion size ≥ 1μm).

[0051] The corresponding furnace ingots are rolled into φ50mm specification rolled products, and sampling is carried out according to the inclusion detection requirements. The number of samples taken is 24, and each DS inclusion is tested and the number is recorded.

[0052] Test 2:

[0053] The composition of the finished steel is C: 0.196%, Si: 0.209%, Mn: 0.436%, S: 0.006%, Cr: 0.043%, Al: 0.0165%.

[0054] 146kg ferrosilicon is added during BOF steelmaking.

[0055] 200kg barium carbonate is added when LF arrives at the station. Ferrosilicon and calcium carbide are prohibited. 220kg silicon carbide is used for deoxidation. LF is finished, no calcium treatment is performed, soft blowing is performed for 20 minutes, and the ladle is hoisted to CCM continuous casting.

[0056] The inclusions in the LF finished steel are mainly magnesia-alumina spinel (scanning area 60mm 2 , scanning inclusion size ≥ 1μm), such as Figure 3 .

[0057] The continuous casting adopts full protection casting. Low-magnification samples are taken from the continuous casting billet for inclusion analysis, such as Figure 4 As shown, it is mainly magnesium aluminum spinel with a small amount of high melting point calcium aluminate (scanning area 60mm 2 , scanning inclusion size ≥ 1μm).

[0058] The corresponding furnace casting slab is rolled into φ50mm specification rolled material, and sampling is carried out according to the inclusion detection requirements. The number of samples taken is 24, and each test is ≥13μm spherical or nearly spherical DS inclusions. After marking, the composition analysis is carried out using SEM-EDS. The inclusions with BaO content ≥7% and the presence of obvious high BaO precipitation bands are used as the basis for determining whether they are BaO-type inclusions. The typical morphology of BaO inclusions is shown in Figure 5 (Light grey stripes high BaO precipitation bands).

[0059] A comparative analysis was conducted on all DS inclusions detected in Test 1 and Test 2. In Test 1, a total of 89 DS inclusions were found, and in Test 2, a total of 51 DS inclusions were found, of which 40 inclusions had a BaO content ≥ 7% and had obvious high BaO precipitation bands, and 11 other DS inclusions.

[0060] According to this method, the process conditions are determined for production: 38 endogenous DS inclusions, accounting for 42.7%; 40 DS inclusions involved in refined slag, accounting for 44.9%; and 11 other types of DS inclusions, accounting for 12.3%.

[0061] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for distinguishing the source and proportion of DS inclusions in steel, characterized in that: The "BOF-LF-(RH)-CC" process route is adopted, including the following steps: (1) Test 1: The converter adopts the blowing method to decarbonize, dephosphorize and ensure that the tapping temperature is ≥1580℃; the final temperature of the converter is controlled at 1610~1670℃, and the final carbon is ≥0.05%; aluminum is first added to the converter for deoxidation, and then a small amount of ferrosilicon is added to partially alloy Si. After the alloy is added, lime and refined slag are added for slagging; Test 2: The converter adopts the blowing method to decarbonize, dephosphorize and ensure that the tapping temperature is ≥1580℃; the final temperature of the converter is controlled at 1610~1670℃, and the final carbon is ≥0.05%; aluminum is first added to the converter for deoxidation, and then ferrosilicon is added for Si alloying. The Si element content is controlled to be the standard lower limit minus 0.07%. After the alloy is added, lime and refined slag are added for slagging; (2) Test 1: After LF arrived at the station, it was smelted according to the smelting method, ferrosilicon alloy was added, calcium carbide was used for deoxidation, the content of (TFe+MnO+Cr2O3) in the slag was controlled below 1.50%, and the basicity of the refined slag was controlled between 3.0 and 7.0; Test 2: 200kgBaCO3 was added as a tracer after LF arrived at the station. Silicon carbide or aluminum particles were added during the LF process to deoxidize the slag surface and adjust the Si content. The (TFe+MnO+ Cr2O3) content in the slag was controlled below 1.50%, and the basicity of the refined slag was controlled at 3.0~7.

0. In Test 2, the total amount of barium carbonate added to the refining was ≥10% of the total amount of all slag materials. (3) Test 1: No alloy or slag was added during the RH vacuum process, and calcium treatment was performed after the soft blowing was completed; Test 2: No alloy or slag was added during the RH vacuum process, and calcium treatment was prohibited after the soft blowing. (4) Test 1 and Test 2: The continuous casting process adopts full protection casting; (5) Test 1: After steelmaking, rolling production is carried out. After rolling, samples are taken for analysis. The number of samples taken from each heat of steel is required to be ≥ 20. After each sample is polished, DS inclusions are detected using an optical microscope and the number is recorded; Test 2: After steelmaking, rolling production is carried out. After rolling, samples are taken for analysis. The number of samples taken from each heat of steel is required to be ≥ 20. After each sample is ground and polished, DS inclusions are detected using an optical microscope and circled; (6) Test 2: Use a scanning electron microscope to detect the composition of the circled inclusions to determine whether they contain BaO. It is required that a clear BaO precipitation band pattern must appear in the photograph of the inclusions, and the EDS analysis of the BaO precipitation band position must show that the Ba atomic mass fraction is ≥7%.

2. A method for distinguishing the sources and proportions of DS inclusions in steel according to claim 1, characterized in that: The steel is aluminum deoxidized steel, and the Al content is usually required to be ≥0.01%. If the Si content is low, ferrosilicon may not be added during the steelmaking process, and aluminum particles are used for deoxidation during the smelting process.

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