Rare earth microalloyed steel bar performance evaluation method

Abstract

The invention provides a rare earth microalloyed steel bar performance evaluation method, and relates to the technical field of metal material performance evaluation.The method includes the steps that a steel bar longitudinal section metallographic specimen is prepared, inclusion macroscopic rating is conducted under a microscope, an inclusion automatic analysis system is adopted for microanalysis, and the rare earth adding amount range is controlled to be 0.015-0.030 wt%; according to collaborative evaluation on the low-temperature impact toughness of the rare earth reinforcing steel bar, the impact energy is required to be greater than or equal to 200J under the condition of-20 DEG C, meanwhile, the rare earth reinforcing steel bar structure is evaluated, the ferrite volume fraction is required to be greater than or equal to 60%, and a high-toughness rare earth reinforcing steel bar product needs to meet the requirements of inclusion rating, impact energy and ferrite content; harmful inclusions are converted into spherical rare earth compounds through rare earth modification, the low-temperature toughness is remarkably improved, the comprehensive performance is superior to the national standard by 30% or above, standardized production and wide application of high-toughness rare earth steel bar products are promoted, and safety and reliability of constructional engineering are improved.

Description

Technical Field

[0001] This invention relates to the field of performance evaluation technology for metallic materials, specifically to a method for controlling inclusions in rare earth microalloyed steel bars, a method for synergistic evaluation of low-temperature impact toughness, and high-toughness steel bar products. Background Technology

[0002] As a commonly used building material, the performance of steel reinforcement has a crucial impact on the quality of construction projects. However, in actual production and application, ordinary steel reinforcement still has certain limitations in terms of inclusion control and low-temperature impact toughness, making it difficult to meet the requirements of some special engineering structures for high toughness and good comprehensive performance. Rare earth elements have unique physicochemical properties, and their use in microalloying treatment holds promise for improving the performance of steel reinforcement. However, there is currently a lack of an accurate and effective evaluation method specifically for rare earth microalloyed steel reinforcement, as well as clear specifications for high-toughness rare earth steel reinforcement products. Summary of the Invention

[0003] Evaluation method for rare earth microalloyed steel bars

[0004] Metallographic specimens of the longitudinal section of the reinforcing steel were prepared, and the inclusions were macroscopically rated under a 100x microscope. The following special rating requirements were specified for rare earth-modified HRB400E reinforcing steel:

[0005] For Class A (sulfide type), the requirement is ≤2.0 grade, while for ordinary steel bars, the requirement is ≥3.0 grade. This improvement is achieved by replacing long strips of MnS with spherical rare earth oxysulfides (RE2O2S) and sulfides (RE2S3).

[0006] For Class B (alumina) steel bars ≤ 1.0 grade and ordinary steel bars ≥ 1.5 grade, spherical rare earth oxides (RE2O3) are used to replace chain-like Al2O3.

[0007] For Class C (silicates) ≤ Grade 1.0 and ordinary steel bars ≥ Grade 1.5, spherical rare earth oxides (RE202S) and oxides (RE2O3) are used to replace chain silicates.

[0008] For Class D (spherical oxide type) ≥ Grade 2.0 and ordinary steel bars ≤ Grade 1.5, RE-O-Si-Ca-Al composite spheres shall be used to replace O-Si-Ca-Al composite spheres.

[0009] For DS type (single-particle spherical type) ≥ grade 1.0 and ordinary steel bars ≤ grade 0.5, the O-Si-Ca-Al composite spheres are replaced by RE-O-Si-Ca-Al composite spheres.

[0010] For inclusion analysis, an automated inclusion analysis system was used, with the detection conditions set as follows: accelerating voltage 20kV, amplification 1000X, and analysis area ≥30mm². 2Furthermore, the smallest size of the detected inclusions is 1 μm, and the standard for judging rare earth inclusions is the presence of CeLα (5.26 keV) or LaLα (5.04 keV) characteristic peaks.

[0011] For the chemical composition of steel reinforcement, the rare earth content should be controlled within the range of 0.015-0.030 wt%, where [RE] represents the total mass fraction of rare earth.

[0012] Synergistic Evaluation Method for Low-Temperature Impact Toughness of Rare Earth Steel Bars

[0013] The impact energy of the V-notch was tested at -20℃, and the impact energy was specified to be ≥200J.

[0014] Evaluation method of rare earth steel reinforcement structure

[0015] Rare earth steel bars are required to have a ferrite volume fraction ≥ 60%.

[0016] High-toughness rare earth steel reinforcement products

[0017] The product must simultaneously meet the above-mentioned inclusion rating requirements for rare earth microalloyed steel bars, impact energy at -20℃ ≥200J, and ferrite volume fraction ≥60%.

[0018] Beneficial effects of this invention:

[0019] By modifying rare earth elements, harmful inclusions are transformed into spherical rare earth compounds, which significantly improves low-temperature toughness.

[0020] The morphology of inclusions, impact toughness and ferrite content were evaluated in a coordinated manner, and the overall performance was more than 30% better than the national standard.

[0021] A systematic evaluation method specifically for rare earth microalloyed steel bars is provided, which comprehensively and accurately evaluates the performance of rare earth modified steel bars from multiple dimensions, including macroscopic rating of inclusions, microscopic analysis, chemical composition control, low-temperature impact toughness and microstructure evaluation, filling the gap in existing standards in this field.

[0022] By clarifying the requirements for the type, morphology, and content of rare earth inclusions, we can effectively guide the rational application of rare earths in steel bar production, give full play to the advantages of rare earth elements in improving inclusion characteristics and enhancing steel toughness, thereby improving the overall performance and quality of HRB400E steel bars and making them more suitable for building projects and special engineering structures with high toughness requirements.

[0023] The document clearly defines the comprehensive performance indicators that high-toughness rare earth steel bars must meet, providing manufacturers with clear product quality control targets and offering effective judgment criteria for market applications and quality supervision departments. This will help promote the standardized production and widespread application of high-toughness rare earth steel bars, and improve the safety and reliability of construction projects. Attached Figure Description

[0024] Figure 1 Spherical rare earth composite inclusions in rare earth modified steel bars;

[0025] Figure 2 Comparison of chain-like MnS inclusions in ordinary steel bars and rare earth steel bars;

[0026] Figure 3 Schematic diagram of the impact specimen. Detailed Implementation

[0027] This invention provides a method for evaluating the performance of rare earth steel bars, comprising the following steps:

[0028] Using steel without rare earth components as a control steel, macroscopic rating of inclusions, automatic analysis of inclusions, microstructure detection, and impact performance evaluation were performed on the control steel and rare earth steel respectively.

[0029] In this invention, the rare earth rebar grades include one or more of HRB400, HRB400E, and HRB500E. In this invention, the rare earth elements in the rare earth steel are preferably one or more of La, Ce, and Y.

[0030] In this invention, the control steel does not contain any rare earth elements compared to rare earth steel.

[0031] In this invention, inclusion evaluation is performed according to the "GB / T 10561-2023 Standard Rating Chart Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel" to conduct macroscopic evaluation of inclusions. A polishing area of ​​200 mm is preferred. 2 The inspection adopts Method A, which means that for each type of inclusion, the level of the standard picture that matches the worst field of view on the inspected surface is recorded according to the fine and coarse systems.

[0032] In this invention, the microstructure is analyzed according to GB / T13298-2015, "Methods for Testing the Microstructure of Metals." Preferably, samples are taken from the cross-section of the rebar, mechanically ground and polished, and then etched with a 4% nitric acid-alcohol solution. The microstructure of the rebar is observed using a Leica metallographic microscope. Twenty images are taken for each metallographic sample, and the ferrite grain size and ferrite volume fraction are calculated using Image Pro Plus 6.0 software.

[0033] In this invention, the inclusion analysis system employs the Euroton OTS one-button inclusion analysis system, with an accelerating voltage of 20kV, a magnification of 1000X, and an analysis area ≥30mm². 2 Furthermore, the smallest size of the detected inclusions is 1 μm.

[0034] In this invention, the impact energy of rare earth steel bars was tested using a "direct measurement method." The sample had a nominal diameter of 14 mm and dimensions as shown in the figure. Figure 1 As shown, the sample is 55mm long. A notch with a depth of 2mm is machined in the middle of the two transverse ribs of the sample. The bottom angle of the notch is 45°. The process is carried out at -20℃.

[0035] The following detailed description of the method for evaluating the performance of rare earth steel bars provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] Rare earth steel HRB400RE was used as the test material, and HRB400 was used as the control steel. The specific chemical composition (wt.%) is shown in Table 1:

[0038] Table 1 Chemical composition of rare earth steel and reference steel

[0039] element C Si Mn P S 0 RE(La+Ce) Fe HRB400 0.22 0.50 1.25 0.030 0.025 0.008 - margin HRB400RE 0.023 0.50 1.30 0.027 0.024 0.006 0.0186 margin

[0040] Macroscopic inclusion rating, automatic inclusion analysis, microstructure detection, and impact test were performed on the control steel and rare earth steel. The results are shown in Table 2.

[0041] Table 2. Inclusion rating, automatic inclusion analysis, microstructure detection, and impact test results for rare earth steel and control steel.

[0042]

[0043]

[0044] Example 2

[0045] Rare earth steel HRB400ERE was used as the test material, and HRB400E was used as the control steel. The specific chemical composition (wt.%) is shown in Table 3:

[0046] Table 3 Chemical composition of rare earth steel and reference steel

[0047] element C Si Mn P S O RE(La+Ce) Fe HRB400E 0.23 0.46 1.42 0.044 0.021 0.007 - margin HRB400ERE 0.23 0.44 1.37 0.039 0.020 0.007 0.0206 margin

[0048] Macroscopic inclusion rating, automatic inclusion analysis, microstructure detection, and impact test were performed on the control steel and rare earth steel. The results are shown in Table 4.

[0049] Table 4. Inclusion rating, automatic inclusion analysis, microstructure detection, and impact test results for rare earth steel and control steel.

[0050]

[0051]

[0052] Example 3

[0053] Rare earth steel HRB500ERE was used as the test material, and HRB500E was used as the control steel. The specific chemical composition (wt.%) is shown in Table 5:

[0054] Table 5 Chemical composition of rare earth steel and reference steel

[0055] element C Si Mn P S O RE(La+Ce) Fe HRB500E 0.23 0.44 1.37 0.039 0.006 0.005 - margin HRB500ERE 0.24 0.51 1.35 0.035 0.005 0.004 0.0130 margin

[0056] Macroscopic inclusion rating, automatic inclusion analysis, microstructure detection, and impact test were performed on the control steel and rare earth steel. The results are shown in Table 6.

[0057] Table 6. Inclusion rating, automatic inclusion analysis, microstructure detection, and impact test results for rare earth steel and reference steel.

[0058]

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the performance of rare earth microalloyed steel bars, characterized in that: Includes the following steps: Rare earth modified steel bars must meet the following special rating requirements: Class A (sulfide-based) steel bars ≤ Grade 2.0, ordinary steel bars ≥ Grade 3.0 Spherical rare earth oxides (RE2O2S) and sulfides (RE2S3) replace long strips of MnS Class B (alumina type) ≤ Grade 1.0, ordinary steel bars ≥ Grade 1.5 Spherical rare earth oxides (RE2O3) replace chain-like Al2O3 Class C (silicate) steel bars ≤ Grade 1.0, ordinary steel bars ≥ Grade 1.5 Spherical rare earth oxides (RE2O2S) and oxides (RE2O3) replace chain silicates Category D (spherical oxide type) ≥ Grade 2.0, ordinary steel bars ≤ Grade 1.5 RE-O-Si-Ca-Al composite spheres replace O-Si-Ca-Al composite spheres DS type (single-particle spherical type) ≥ Grade 1.0, ordinary steel bars ≤ Grade 0.5 RE-O-Si-Ca-Al composite spheres replace O-Si-Ca-Al composite spheres.

2. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 1, characterized in that: Inclusion Analysis System: An automatic inclusion analysis system with the following detection conditions: accelerating voltage 20kV, magnification 1000X, and analysis area ≥30mm². 2 The smallest size of the inclusions detected was 1 μm; The criteria for identifying rare earth inclusions are the presence of characteristic peaks of Ce Lα (5.26 keV) or La Lα (5.04 keV).

3. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 1, characterized in that: The chemical composition of the steel reinforcement must meet the rare earth addition range of 0.015-0.030 wt%, where [RE] is the total mass fraction of rare earth.

4. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 1, characterized in that: Test the impact energy of the V-notch at -20℃, and the impact energy is required to be ≥200J.

5. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 4, characterized in that: The sample has a nominal diameter of 14 mm and a length of 55 mm. A notch with a depth of 2 mm is machined in the middle of the two transverse ribs of the sample, and the bottom angle of the notch is 45°.

6. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 2, characterized in that: The proportion of rare earth inclusions to the total number of inclusions is ≥30%, and the spheroidization rate of rare earth inclusions is ≥90%.

7. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 6, characterized in that: The proportion of rare earth inclusions with an axis ratio ≤ 1.

5.

8. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 1, characterized in that: Rare earth steel bars have a ferrite volume fraction ≥60%.

9. The method for evaluating the performance of rare earth microalloyed steel bars as described in claim 1, characterized in that: Simultaneously satisfy: The inclusion rating requirements as described in claim 1; The impact energy at -20℃ as described in claim 4 is ≥200J; The ferrite volume fraction of claim 8 is ≥60%.

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