A production process for high-strength-yield ratio series earthquake-resistant steel

Abstract

The present invention relates to the field of metallurgical technology, and proposes a high-strength yield ratio series earthquake-resistant steel and its production process. The high-strength yield ratio series earthquake-resistant steel includes the following components in mass percentage: C: 0.16-0.20%, Si: 0.25-0.40%, Mn: 1.25-1.40%, P: ≤0.035%, S: ≤0.035%, V: 0.02-0.03%, Tb: 0.0015-0.0020%, Pr: 0.0035-0.0045%, and the balance is Fe; the production process of the high-strength yield ratio series earthquake-resistant steel includes: converter smelting → LF refining → continuous casting → heating → rolling. Through the above technical scheme, the problems of low strength and strength-yield ratio of steel in the prior art, and thus poor earthquake resistance and shockproof performance and low flaw detection pass rate are solved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a production process of high-strength yield ratio series earthquake-resistant steel. Background Art

[0002] Buildings in various countries around the world have developed in the direction of large-scale, long life, energy conservation and environmental protection, high safety and reliability. At present, the domestic structural steel for construction is mainly Q355B ordinary steel, and the use of Q345KZ steel is also increasing significantly, and it is widely used in large-scale building facilities. From the foreign construction industry, 355MPa and above steel with high toughness, easy welding and seismic performance has been widely used. In recent years, the application of steel structures in modern buildings has become more and more common, especially high-rise buildings, which are almost inseparable from steel structures. my country is a country prone to earthquakes, and the research on steel structures combined with seismic resistance has also received more and more attention. Since the Wenchuan earthquake in 2008, the issue of improving the seismic performance of buildings has attracted great attention from the government and enterprises, and seismic steel has also received increasing attention. As a building structure, steel is the most important material to ensure the safety of buildings. In order to meet the demand for building steel and meet the safety of buildings, the country has also put forward some requirements for the seismic resistance of buildings, and has issued a series of standards. The product standard of seismic steel in my country, GB / T 28414-2012, formally stipulates the requirements for the seismic performance of steel. To this end, combined with Xinghua's production equipment and process conditions, the research and development of Q345KZ steel was proposed. Many research results have been included in the design specifications for seismic steel. A large number of experiments and studies have put forward five indicators, namely high-stress bending low-cycle fatigue performance, strain aging sensitivity, ductile-brittle transition temperature, weldability and strength-plasticity coordination. These indicators are relatively scientific and comprehensive as seismic performance indicators of steel, and are also the controlling direction for the development, supply and production of steel used in seismic-resistant steel structures.

[0003] The seismic performance of a building requires that during its use, the building should have different resistance to earthquakes of different frequencies and intensities, and achieve "no damage in a small earthquake, repairable in a medium earthquake, and no collapse in a large earthquake" in accordance with the overall requirements of domestic and foreign seismic fortification targets. Therefore, to achieve this requirement, it is crucial that the system and overall structure of the building are seismic resistant. In other words, as the skeleton of the building, the status of steel in seismic design is self-evident.

[0004] Based on the characterization of the seismic-resistant performance of major domestic and foreign steel sections, they all have strict requirements on strength, plasticity, strength-to-yield ratio and weldability. The most obvious difference compared with general-purpose steel sections is the requirements for strength fluctuation and uniform ductility, which is the key to meeting seismic fortification requirements.

[0005] In addition to the strength and toughness requirements, seismic steel also has strict technical requirements for seismic resistance, especially in converters and small production lines with limited control methods. There are mainly the following key technologies and difficulties:

[0006] (1) Suitable for composition design with high strength, high plasticity and high strength-to-yield ratio;

[0007] (2) Performance stability and strength-to-yield ratio control technology for small-size products;

[0008] (3) Control technology for cold bending and reverse bending performance of large-size and high-strength products.

[0009] Steel requires high toughness, and the toughness of steel is related to the metal lattice type, organization type, grain size, solid solution alloy type, etc. The toughness level can be improved by adjusting the inclusion content, refining the grains, and even adding high-toughness alloys; however, it is difficult to control the strength-to-yield ratio. All strengthening factors have an impact on the strength-to-yield ratio. The control of the strength-to-yield ratio should actually be reflected in how to control the grain size in the microstructure and the ratio of soft and hard phases.

[0010] In addition, the current flaw detection generally has the problem of low pass rate, and the pass rate of steel flaw detection is only 80-85%. The main reason for the failure of steel plate flaw detection is the occurrence of delamination defects or point density defects in the steel plate.

[0011] Therefore, in order to improve the seismic resistance and shockproof performance and pass rate of steel sections, technical personnel in this field are committed to studying how to improve the strength-to-yield ratio performance and pass rate by regulating the composition design and organizational factors, so as to achieve steel sections with both good seismic resistance and shockproof performance and high flaw detection pass rate. Summary of the invention

[0012] The present invention provides a production process for a high strength-to-yield ratio series earthquake-resistant steel sections, which solves the problems in the related art of low strength and strength-to-yield ratio of the steel sections, and thus poor earthquake resistance and shockproof performance and low flaw detection pass rate.

[0013] The technical solution of the present invention is as follows:

[0014] A high-strength yield ratio series earthquake-resistant steel comprises the following components in percentage by mass: C: 0.16-0.20%, Si: 0.25-0.40%, Mn: 1.25-1.40%, P: ≤0.035%, S: ≤0.035%, V: 0.02-0.03%, Tb: 0.0015-0.0020%, Pr: 0.0035-0.0045%, and the balance is Fe.

[0015] As a further technical solution, the mass ratio of Pr to Tb is ≤2:1.

[0016] The invention also proposes a production process of a high-strength yield ratio series earthquake-resistant steel, comprising: converter smelting→LF refining→continuous casting→heating→rolling.

[0017] As a further technical solution, the converter smelting end point C≥0.08%; the steel tapping time during the converter smelting process is ≥2min.

[0018] As a further technical solution, during the converter smelting process, a deoxidizer is added after the alloy accounts for 1 / 3 of the total mass of the alloy, with the added amount being 1.5 to 2.0 kg / t steel.

[0019] As a further technical solution, during the converter smelting process, a deoxidizer is added after the alloy is added, with the added amount being 1.5 to 2.0 kg / t steel.

[0020] As a further technical solution, during the LF refining process, soft blowing is performed after wire feeding, and the soft blowing time is ≥8 minutes.

[0021] As a further technical solution, during the continuous casting process, the superheat of the molten steel is 10-25° C., and the pulling speed fluctuation is ≤0.2 m / s.

[0022] As a further technical solution, during the heating, the absorptive temperature is 1120-1180° C. and the heating time is 60-120 min.

[0023] Ensure that the billet temperature is uniform and burned through, but avoid overburning.

[0024] As a further technical solution, the starting rolling temperature is 1090-1150°C, and the final rolling temperature is 1110-1130°C; and the rolling process also includes cooling on a cooling bed, and the cooling temperature of the cooling bed is 200-300°C.

[0025] The working principle and beneficial effects of the present invention are:

[0026] 1. The present invention provides a high-strength-yield ratio series earthquake-resistant steel. By regulating the heavy rare earth element Tb and the light rare earth element Pr in the components, the ingot has good structure, uniform composition, stable process parameters, and reasonable and feasible chemical composition design. The final carbon content of the steelmaking process is strictly controlled to ensure the alloy yield and the stability and uniformity of the steel billet composition. The out-of-furnace treatment adopts "soft blowing" after wire feeding, and the continuous casting adopts protective pouring, which ensures that the steel is clean, the structure is uniform, and the segregation is low, thereby ensuring that the requirements of rolling for raw materials are met. The heating temperature is strictly controlled to ensure that the obtained steel has high strength and strength-yield ratio, has good earthquake resistance and shockproof performance, and the flaw detection pass rate reaches more than 98.2%.

[0027] 2. The development and promotion of earthquake-resistant steel can effectively improve the earthquake resistance of buildings, which is an effective guarantee for the safety of human life and property, accelerates the upgrading of construction steel, and has good social benefits. At the same time, according to the principle of high quality and high price, the development and promotion of earthquake-resistant steel can also bring good economic benefits to production enterprises.

[0028] (1) Production practice shows that the chemical composition of the 345MPa hot-rolled earthquake-resistant steel formulated by the present invention reaches the predetermined target and meets the specification requirements.

[0029] (2) The present invention produces a seismic-resistant steel by rationally designing the composition, strictly narrowing the composition smelting, stabilizing the continuous casting process parameters, and reducing the fluctuation of the heating temperature.

[0030] (3) After using the 345MPa hot-rolled earthquake-resistant steel provided by the present invention, users can save steel usage, reduce project costs, and improve the earthquake resistance and safety of buildings, which has won unanimous praise from users. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] Figure 1 a and b are low-magnification photos of the ingots in furnaces 10370 and 10378 of Example 1 of the present invention, respectively;

[0033] Figure 2 a and b are respectively a two-dimensional contour map and a three-dimensional distribution map of the C element distribution in the ingot of Example 1 of the present invention;

[0034] Figure 3 a and b are respectively a two-dimensional contour map and a three-dimensional distribution map of Si element distribution in the ingot of Example 1 of the present invention;

[0035] Figure 4 a and b are respectively a two-dimensional contour map and a three-dimensional distribution map of the Mn element distribution in the ingot of Example 1 of the present invention;

[0036] Figure 5 a and b are respectively a two-dimensional contour map and a three-dimensional distribution map of P element distribution in the ingot of Example 1 of the present invention;

[0037] Figure 6 a and b are respectively a two-dimensional contour map and a three-dimensional distribution map of the S element distribution in the ingot of Example 1 of the present invention;

[0038] Figure 7 In the figure a and b are respectively the two-dimensional contour map and the three-dimensional distribution map of the V element distribution in the ingot of Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The process of the present invention is as follows:

[0041] S1. Converter smelting:

[0042] During the blowing process, the slag is kept well and the molten steel is strictly prohibited from being overoxidized; the converter smelting end point C ≥ 0.08%;

[0043] Slag should be well blocked in the early and late stages of steel tapping. No molten steel flow or slag rolling is allowed at the tapping port, and the tapping time should be ≥2 minutes;

[0044] Deoxidation alloying: silicon manganese is used for deoxidation alloying. The timing of adding the deoxidizer is: when the alloy is added to 1 / 3 of the total mass of the alloy or after the alloy is added, the deoxidizer is added in an amount of 1.5 to 2.0 kg / t steel.

[0045] S2, LF refining:

[0046] Raw material requirements: Slag-making materials (lime, fluorite) must be confirmed to be dry before use;

[0047] Before entering the station for heating, argon blowing and stirring should be carried out to melt the slag to ensure that the added slag-making material is well-melted and there is no large agglomeration; after the slag is well-melted, heating is carried out for 20 to 30 minutes at a temperature of 1500°C to 1600°C; white slag should be made during the refining process to promote the adsorption of inclusions in the steel; wire feeding is carried out before leaving the station, with a feeding amount of 1.5 to 2.0 m / t steel, and soft blowing is carried out after wire feeding, with a soft blowing time of ≥8 minutes. After LF refining, the oxygen content in the molten steel is ≤15ppm.

[0048] S3, continuous casting: superheat is controlled at 10 ~ 25 ℃; during the casting process, the pulling speed is controlled and kept stable, and the pulling speed fluctuation is ≤ 0.2m / s.

[0049] S4. Heating: The uniform heating temperature is 1120-1180℃, and the heating time is 60-120min. This ensures that the billet temperature is uniform and burned through, but overburning is prohibited.

[0050] S5. Rolling: starting rolling temperature 1090~1150℃, final rolling temperature 1110~1130℃.

[0051] S6. Cooling on cooling bed: Control the cooling temperature of the steel cooling bed to 200-300℃.

[0052] The mass percentage of the high-strength yield ratio series earthquake-resistant steel prepared by the above process is as follows: C: 0.16-0.20%, Si: 0.25-0.40%, Mn: 1.25-1.40%, P: ≤0.035%, S: ≤0.035%, V: 0.02-0.03%, Tb: 0.0015-0.0020%, Pr: 0.0035-0.0045%, and the balance is Fe.

[0053] C: 0.16~0.20%

[0054] C content is the most important element that determines the strength and toughness of steel. Every 0.01% increase in C content can increase the tensile strength of steel by an average of 7 to 10 MPa and the yield strength by 4 to 5 MPa. As the C content increases, although the strength of the steel increases, the plasticity and toughness decrease, and the weldability also deteriorates significantly. When the C content exceeds 0.20%, the risk of brittle fracture of the steel increases. Because when the C content is high, the cementite (Fe3C) content in the pearlite structure of the steel increases accordingly. The characteristics of Fe3C are hard and brittle, which reduces the weldability of the steel and increases the fracture sensitivity. For this reason, under the premise of ensuring the strength of the steel, the C content needs to be controlled at 0.16 to 0.20%.

[0055] Si: 0.25-0.40%

[0056] The effect of Si on σb and σs is similar to that of C, but the effect of C is more obvious in degree. Si is a strengthening element of steel. It can significantly increase the tensile strength of steel and slightly increase the yield strength of steel, while the plasticity, toughness and strength-yield ratio (σb / σs) decrease. However, when the Si content exceeds 0.40%, the cold brittleness of steel will increase, so the Si content is controlled at 0.25-0.40%.

[0057] Mn: 1.25~1.40%

[0058] Mn can form carbides and sulfides in steel, but most of them enter ferrite, strengthening ferrite, thereby increasing the yield strength and tensile strength of steel. Increasing the Mn content can increase the strength of steel, but Mn is an element with strong hardenability and has a strong effect of delaying phase transformation. Compared with the CCT curve with low Mn content, the CCT curve with high Mn content has a longer incubation period, a rightward shift of the CCT curve, and a decrease in the critical transformation temperature of steel. When the Mn content exceeds 1.40%, the increase in the incubation period causes the cooling curve to easily pass through the bainite transformation zone, thereby forming bainite; at the same cooling rate, when the Mn content is lower than 1.25%, due to the short incubation period, the cooling curve will not pass through the bainite phase transformation zone. At the same time, when the Mn content exceeds 1.40%, the plasticity and toughness will decrease, and the weldability will deteriorate. In order to ensure the stable performance of the steel, the Mn content should be controlled between 1.25 and 1.40%.

[0059] P: ≤0.035%, S: ≤0.035%

[0060] S and P are both harmful elements in steel. S causes a significant decrease in the ductility and toughness of the steel, while P easily causes low-temperature brittle fracture of the steel.

[0061] V: 0.02~0.03%

[0062] V has a strong affinity for C and N and can form carbonitrides. CN compounds will precipitate during the cooling process, producing precipitation strengthening and increasing the strength of the steel. At the same time, CN compounds precipitate at the austenite / ferrite interface, effectively preventing the growth of ferrite grains and refining the grains. In addition, the solid solution strengthening effect of these elements can significantly improve the strength of the steel.

[0063] V element precipitation strengthening and grain refinement are strong, and the V recovery rate is high and stable, and there are no special requirements for continuous casting and steel rolling processes. Adding a trace amount of V to steel can ensure that the steel has a low C equivalent, through the dispersion precipitation of its carbon and nitride material points (size less than 5nm) and the solid solution of V, the grains are refined, greatly improving the strength and toughness of the steel, especially the low-temperature toughness, so that the steel has good weldability and usability.

[0064] Example 1

[0065] A high-strength yield ratio series earthquake-resistant steel comprises the following components in percentage by mass: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.03%, S: 0.025%, V: 0.02%, Tb: 0.0020%, Pr: 0.0035%, and the balance is Fe.

[0066] The production process is as follows:

[0067] S1, converter smelting: converter smelting end point C is 0.08%; steel tapping time is 3min;

[0068] Deoxidation alloying: Silicon manganese is used for deoxidation alloying. The timing of adding the deoxidizer is: when the alloy is added to 1 / 3 of the total mass of the alloy, the deoxidizer is added in an amount of 1.5kg / t steel.

[0069] S2. LF refining: Before entering the station for heating, argon blowing and stirring are carried out to melt the slag; after slagging, heating is carried out for 25 minutes at a temperature of 1550°C; white slag must be produced during the refining process; wire feeding is carried out before leaving the station, with a feeding amount of 1.5m / t steel, and soft blowing is carried out after wire feeding for 10 minutes. After LF refining, the oxygen content in the molten steel is 10ppm.

[0070] S3, continuous casting: superheat is controlled at 20℃; during the casting process, the pulling speed is controlled and kept stable, and the pulling speed fluctuation is 0.1m / s.

[0071] S4. Heating: soaking temperature 1150°C, heating time 100 min.

[0072] S5. Rolling: starting rolling temperature 1100°C, final rolling temperature 1120°C.

[0073] S6. Cooling on cooling bed: Control the cooling temperature of the steel cooling bed to 250℃.

[0074] Example 2

[0075] A high-strength yield ratio series earthquake-resistant steel comprises the following components in percentage by mass: C: 0.16%, Si: 0.25%, Mn: 1.32%, P: 0.035%, S: 0.035%, V: 0.026%, Tb: 0.0020%, Pr: 0.0040%, and the balance is Fe.

[0076] The production process is as follows:

[0077] S1, converter smelting: converter smelting end point C is 0.11%; steel tapping time is 2min;

[0078] Deoxidation alloying: silicon manganese is used for deoxidation alloying. The timing of adding the deoxidizer is: adding the deoxidizer after adding the alloy, and the addition amount is 1.8kg / t steel.

[0079] S2. LF refining: Before entering the station for heating, argon blowing and stirring are carried out to melt the slag; after slagging, heating is carried out for 20 minutes at a temperature of 1600°C; white slag must be produced during the refining process; wire feeding is carried out before leaving the station, with a feeding amount of 1.8m / t steel, and soft blowing is carried out after wire feeding for 8 minutes. After LF refining, the oxygen content in the molten steel is 15ppm.

[0080] S3, continuous casting: superheat is controlled at 10℃; during the casting process, the pulling speed is controlled and kept stable, and the pulling speed fluctuation is 0.1m / s.

[0081] S4. Heating: the soaking temperature is 1180°C and the heating time is 60 min.

[0082] S5. Rolling: starting rolling temperature 1090°C, final rolling temperature 1110°C.

[0083] S6. Cooling on cooling bed: Control the cooling temperature of the steel cooling bed to 200℃.

[0084] Example 3

[0085] A high-strength yield ratio series earthquake-resistant steel comprises the following components in percentage by mass: C: 0.20%, Si: 0.40%, Mn: 1.40%, P: 0.025%, S: 0.030%, V: 0.03%, Tb: 0.0018%, Pr: 0.0035%, and the balance is Fe.

[0086] The production process is as follows:

[0087] S1, converter smelting: converter smelting end point C is 0.12%; steel tapping time is 4min;

[0088] Deoxidation alloying: Silicon manganese is used for deoxidation alloying. The timing of adding the deoxidizer is: when the alloy is added to 1 / 3 of the total mass of the alloy, the deoxidizer is added in an amount of 2.0kg / t steel.

[0089] S2. LF refining: Before entering the station for heating, argon blowing and stirring are carried out to melt the slag; after slagging, heating is carried out, the heating time is 30 minutes, and the heating temperature is 1500℃; white slag must be produced during the refining process; wire feeding is carried out before leaving the station, and the feeding amount is 2.0m / t steel. After wire feeding, soft blowing is carried out, and the soft blowing time is 12 minutes. After LF refining, the oxygen content in the molten steel is 8ppm.

[0090] S3, continuous casting: superheat is controlled at 25℃; during the casting process, the pulling speed is controlled and kept stable, and the pulling speed fluctuation is 0.2m / s.

[0091] S4. Heating: soaking temperature 1120°C, heating time 120 min.

[0092] S5. Rolling: starting rolling temperature 1150°C, final rolling temperature 1130°C.

[0093] S6. Cooling on cooling bed: Control the cooling temperature of the steel cooling bed to 300℃.

[0094] Example 4

[0095] A high-strength yield ratio series earthquake-resistant steel comprises the following components in percentage by mass: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.03%, S: 0.025%, V: 0.02%, Tb: 0.0020%, Pr: 0.0045%, and the balance is Fe.

[0096] The production process is as follows:

[0097] S1, converter smelting: converter smelting end point C is 0.08%; steel tapping time is 3min;

[0098] Deoxidation alloying: Silicon manganese is used for deoxidation alloying. The timing of adding the deoxidizer is: when the alloy is added to 1 / 3 of the total mass of the alloy, the deoxidizer is added in an amount of 1.5kg / t steel.

[0099] S2. LF refining: Before entering the station for heating, argon blowing and stirring are carried out to melt the slag; after slagging, heating is carried out for 25 minutes at a temperature of 1550°C; white slag must be produced during the refining process; wire feeding is carried out before leaving the station, with a feeding amount of 1.5m / t steel, and soft blowing is carried out after wire feeding for 10 minutes. After LF refining, the oxygen content in the molten steel is 10ppm.

[0100] S3, continuous casting: superheat is controlled at 20℃; during the casting process, the pulling speed is controlled and kept stable, and the pulling speed fluctuation is 0.1m / s.

[0101] S4. Heating: soaking temperature 1150°C, heating time 100 min.

[0102] S5. Rolling: starting rolling temperature 1100°C, final rolling temperature 1120°C.

[0103] S6. Cooling on cooling bed: Control the cooling temperature of the steel cooling bed to 250℃.

[0104] Example 5

[0105] A high-strength yield ratio series earthquake-resistant steel comprises the following components in percentage by mass: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.03%, S: 0.025%, V: 0.02%, Tb: 0.0015%, Pr: 0.0035%, and the balance is Fe.

[0106] The production process is as follows:

[0107] S1, converter smelting: converter smelting end point C is 0.08%; steel tapping time is 3min;

[0108] Deoxidation alloying: Silicon manganese is used for deoxidation alloying. The timing of adding the deoxidizer is: when the alloy is added to 1 / 3 of the total mass of the alloy, the deoxidizer is added in an amount of 1.5kg / t steel.

[0109] S2. LF refining: Before entering the station for heating, argon blowing and stirring are carried out to melt the slag; after slagging, heating is carried out for 25 minutes at a temperature of 1550°C; white slag must be produced during the refining process; wire feeding is carried out before leaving the station, with a feeding amount of 1.5m / t steel, and soft blowing is carried out after wire feeding for 10 minutes. After LF refining, the oxygen content in the molten steel is 10ppm.

[0110] S3, continuous casting: superheat is controlled at 20℃; during the casting process, the pulling speed is controlled and kept stable, and the pulling speed fluctuation is 0.1m / s.

[0111] S4. Heating: soaking temperature 1150°C, heating time 100 min.

[0112] S5. Rolling: starting rolling temperature 1100°C, final rolling temperature 1120°C.

[0113] S6. Cooling on cooling bed: Control the cooling temperature of the steel cooling bed to 250℃.

[0114] Comparative Example 1

[0115] The only difference from Example 1 is the steel section, which includes the following components in mass percentage: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.03%, S: 0.025%, V: 0.02%, Pr: 0.0035%, and the balance is Fe.

[0116] Comparative Example 2

[0117] The only difference from Example 1 is the steel section, which includes the following components in mass percentage: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.03%, S: 0.025%, V: 0.02%, Tb: 0.0020%, and the balance is Fe.

[0118] Comparative Example 3

[0119] The only difference from Example 1 is the steel section, which includes the following components in mass percentage: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.03%, S: 0.025%, V: 0.02%, and the balance is Fe.

[0120] The steel sections with a specification of 200×200 obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were tested for yield strength and tensile strength with reference to GB / T 28414-2012, and for flaw detection pass rate with reference to NB / T 47013.3-2015. The test results are recorded in Table 1.

[0121] Table 1 Mechanical properties and flaw detection pass rates of steels in Examples 1 to 5 and Comparative Examples 1 to 3

[0122]

[0123] It can be seen from Table 1 that the steel sections provided by Examples 1 to 5 of the present invention have a yield strength of more than 384 MPa, a tensile strength of more than 541 MPa, a strength-to-yield ratio of more than 1.41, a flaw detection grade of all being Grade I, and a flaw detection pass rate of more than 98.2%. The difference between Comparative Example 1 and Example 1 is only that Tb is not added to the steel section composition; the difference between Comparative Example 2 and Example 1 is only that Pr is not added to the steel section composition; the difference between Comparative Example 3 and Example 1 is only that Tb and Pr are not added to the steel section composition; the mechanical properties and flaw detection pass rates of the steel sections provided by Comparative Examples 1 to 3 are not as good as those of Example 1, mainly because the present invention adds rare earth elements Tb and Pr to the steel section components, and at the same time adjusts the mass ratio of the elements Tb and Pr to make the structure of each element in the ingot good and the composition distribution uniform, thereby improving the strength, strength-to-yield ratio and flaw detection pass rate of the steel section, and having good anti-seismic and anti-vibration properties.

[0124] Example 1 The low magnification photo of the ingot is as follows Figure 1 The analysis of the low-power mass of the ingot is shown in Table 2.

[0125] Table 2Q345KZ steel billet low power mass

[0126]

[0127] from Figure 1 As can be seen from Table 2, the cracks of the ingot provided in Example 1 of the present invention are controlled below level 1.0, the central porosity is controlled below level 1.5, there are no obvious shrinkage cavities, and the low-multiple quality is good, which provides guarantee conditions for stable finished product performance.

[0128] Composition segregation of ingot: Figures 2 to 7 This is a two-dimensional contour map of the element distribution of the ingot in Example 1 of the present invention and its three-dimensional distribution map, wherein the colored surface in the map represents the content of alloy elements, and the alloy content decreases in the order of red, orange, yellow, green, cyan, blue, and purple; the coordinate of the Z axis in the three-dimensional distribution map represents the level of alloy element content at a certain point, and the larger the Z axis coordinate value, the higher the alloy content; the two-dimensional contour map represents the content by color.

[0129] from Figure 2 It can be seen that the maximum segregation degree of C element is 1.372[59.6,52]; Figure 3 It can be seen that the maximum segregation degree of Si element is 1.273[29.4, 59.8]; Figure 4 It can be seen that the maximum segregation degree of Mn element is 1.117[40,38.2]; Figure 5 It can be seen that the maximum segregation of P element is 1.284[40.4,54.2]; Figure 6 It can be seen that the maximum segregation degree of S element is 1.387[38.6,0]; Figure 7It can be seen that the maximum segregation degree of V element is 1.044[4.00,36.00].

[0130] from Figures 2 to 7 It can be seen that the segregation degree of most of the component elements in the ingot in Example 1 of the present invention is about 1.3, which proves that the present invention makes the distribution of each element in the ingot more uniform by regulating the heavy rare earth element Tb and the light rare earth element Pr in the alloy components without obvious segregation phenomenon.

[0131] The following are the various properties of a large batch of Q345KZ earthquake-resistant steel produced according to the high-strength yield ratio series earthquake-resistant steel production process provided by the present invention.

[0132] 1. Melting composition:

[0133] Since the development of Q345KZ earthquake-resistant steel, a total of 16,300 tons of various specifications have been produced and sold. The statistical values ​​of the composition of mass production are shown in Table 3.

[0134] Table 3 Statistical values ​​of smelting components

[0135]

[0136] From the test and analysis results in Table 3, C = 0.16 ~ 0.19%, an average of 0.17%; Si = 0.28 ~ 0.37%, an average of 0.31%; Mn = 1.25 ~ 1.37%, an average of 1.33%; V = 0.021 ~ 0.028%, an average of 0.024%; P, S ≤ 0.032%; Tb = 0.0018 ~ 0.0020%, an average of 0.0019%; Pr = 0.0035 ~ 0.0040%, an average of 0.00375%. From the chemical composition results, the chemical composition of the billet all meets the national standard requirements, the composition qualification rate is 100%, and it meets the control standard requirements.

[0137] 2. Casting quality:

[0138] Oxygen and nitrogen samples of the ingots from some smelting furnaces of the present invention were randomly selected for gas content analysis. The gas content in some Q345KZ smelting ingots is shown in Table 4.

[0139] Table 4 Gas content in Q345KZ steel

[0140] Serial number Brand Furnace No. N / ppm O / ppm 1 Q345KZ 10361 0.0083 0.0034 2 Q346KZ 10365 0.0069 0.0055 3 Q347KZ 10368 0.0063 0.0034 4 Q348KZ 10369 0.0065 0.0049 5 Q349KZ 10370 0.0076 0.0035 6 Q350KZ 10371 0.0094 0.0059 7 Q351KZ 10372 0.0076 0.0039 8 Q352KZ 10376 0.0095 0.0043 9 Q353KZ 10377 0.0086 0.003 10 Q354KZ 10378 0.0094 0.0046 11 Q354KZ 10379 0.0075 0.005 12 Q354KZ 10380 0.0085 0.0029

[0141] It can be seen from Table 4 that the N content is controlled and stabilized in the range of 60 to 100 ppm, the recovery rate is high and stable, which promotes and stabilizes the precipitation strengthening effect of V; the O content is below 55 ppm, the cleanliness of the molten steel is high, which is conducive to the product having good cold bending, reverse bending and ductility.

[0142] 3. Different batches of Q345KZ steel were obtained according to the production process of Examples 1 to 5 of the present invention. Some Q345KZ steel were randomly selected to test the yield strength, tensile strength and elongation after fracture with reference to GB / T 28414-2012. The test results are shown in Table 5.

[0143] Table 5 Statistics of mechanical properties of Q345KZ steel

[0144]

[0145]

[0146] It can be seen from Table 5 that the mechanical properties of the test steels of various specifications provided by the present invention basically meet the test design objectives and meet the requirements of the latest version of the national standard for seismic structural steel GB / T 28414-2012 promulgated in 2012 (yield strength R eL : 345~450MPa, tensile strength R m : 490~610MPa, elongation after fracture A: 20%), the main characteristics of each specification are: stable product performance and ideal strength margin.

[0147] V. Timeliness Analysis

[0148] In order to test the aging performance of steel, three sets of aging samples were taken from the same steel of each batch of 300×150 steel according to the test batch number, and 3-day and 15-day aging performance tests were carried out respectively. The aging results are shown in Table 6.

[0149] Table 6 Comparison results of aging performance

[0150]

[0151] It can be seen from Table 6 that through comparative analysis of mechanical properties after aging, it is found that after 3 days (72 hours) of aging, the yield strength decreases by an average of 13.5MPa, the tensile strength increases by 1.5MPa, and the strength-yield ratio, elongation and elongation under maximum tension increase; after 15 days (360 hours) of aging, the yield strength decreases by 16.25MPa, the tensile strength increases by 2MPa, and the elongation increases slightly. It can be seen that the performance of the steel is basically stable after 3 days of aging.

[0152] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-strength yield ratio series earthquake-resistant steel, characterized in that: The invention relates to a composite material having the following components in mass percentage: C: 0.16-0.20%, Si: 0.25-0.40%, Mn: 1.25-1.40%, P: ≤0.035%, S: ≤0.035%, V: 0.02-0.03%, Tb: 0.0015-0.0020%, Pr: 0.0035-0.0045%, and the balance is Fe; the mass ratio of Pr to Tb is ≤2:

1.

2. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 1, characterized in that: include: Converter smelting → LF refining → continuous casting → heating → rolling.

3. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: The converter smelting endpoint C is ≥ 0.08%; the steel tapping time during the converter smelting process is ≥ 2 min.

4. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: During the converter smelting process, the deoxidizer is added after the alloy accounts for 1 / 3 of the total mass of the alloy, and the added amount is 1.5-2.0 kg / t steel.

5. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: During the converter smelting process, a deoxidizer is added after the alloy is added, with the added amount being 1.5-2.0 kg / t steel.

6. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: During the LF refining process, soft blowing is performed after wire feeding, and the soft blowing time is ≥8 minutes.

7. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: During the continuous casting process, the superheat of the molten steel is 10-25° C., and the casting speed fluctuation is ≤0.2 m / s.

8. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: During the heating, the soaking temperature is 1120-1180° C. and the heating time is 60-120 min.

9. The production process of a high-strength yield ratio series earthquake-resistant steel according to claim 2, characterized in that: The starting rolling temperature of the rolling is 1090-1150°C, and the final rolling temperature is 1110-1130°C; the rolling process also includes cooling on a cooling bed, and the cooling temperature of the cooling bed is 200-300°C.

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