420MPa-grade high-performance super-thick steel plate for building and manufacturing method thereof

Abstract

The invention relates to a 420MPa-grade high-performance super-thick steel plate for a building and a manufacturing method of the 420MPa-grade high-performance super-thick steel plate. The steel plate comprises the following chemical components in percentage by mass: 0.07-0.1% of C and 0.10-0.35% of Si; mn: 1.40 to 1.55%; cr: 0 to 0.25%; 0.025% to 0.040% of Nb; 0.008-0.020% of Ti, and the balance Fe and other inevitable elements. The steel plate is produced by adopting a continuous casting billet and an on-line controlled rolling and controlled cooling process, the maximum thickness of the steel plate is 150mm, the impact energy at-40 DEG C is not lower than 100J, the yield strength is 400-480MPa, the tensile strength is 510-630MPa, the ductility is greater than 20%, and the yield ratio is not greater than 0.83.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and specifically relates to a 420MPa-grade high-performance extra-thick steel plate for construction and a manufacturing method thereof. Background Art

[0002] With the development of high-rise buildings, super high-rise buildings and large-span buildings, the demand for thick steel plates for construction is becoming more and more urgent, especially for box columns in super high-rise buildings.

[0003] Traditional high-strength and extra-thick steel plates are mainly produced by die casting-rolling-quenching and tempering (quenching + high-temperature tempering) process. However, the low efficiency and low yield of die casting limit its wide application, and the quenching and tempering process consumes a lot of energy, has high alloy cost and long production cycle.

[0004] Chinese patent CN 104018071 A discloses a "production method for low-carbon equivalent high-toughness Q420E steel plate". This method uses the traditional TMCP process to produce Q420E steel plates, which cannot get rid of the limitation of compression ratio and is only suitable for the production of steel plates below 30 mm, but not for the production of extra-thick steel plates.

[0005] Chinese patent CN 102776443 A discloses "a 420MPa grade low alloy high strength extra thick steel plate and its manufacturing method", which is smelted by electroslag remelting method and then subjected to normalizing heat treatment process after rolling to produce Q420D grade extra thick steel plate. The production process is complex, the production cycle is long, the alloy cost is high, and the carbon equivalent Ceq is also high.

[0006] Chinese patent CN 103540848 A discloses "a 420MPa grade normalized extra-thick structural steel plate and its manufacturing method". The invention content is to produce extra-thick Q420E steel plate by normalizing + rapid cooling process. The production process is complicated, the alloy cost is high, and the Ceq is high. At the same time, this method cannot get rid of the limitation of compression ratio. Using 400mm thick continuous casting billets, only products with a maximum thickness of 120mm can be produced.

[0007] To solve the above problems of high alloy cost and complicated production process, TMCP technology is the most effective. By adopting TMCP, the amount of alloy elements added in steel can be reduced, Ceq can be reduced, and the steel plate can have good welding performance. In addition, the TMCP process has simple production procedures, short production cycle, and no subsequent heat treatment, which can greatly reduce energy consumption and belongs to green manufacturing. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a 420MPa grade high performance extra thick steel plate for construction with a maximum thickness of 150mm, which is produced by online controlled rolling and controlled cooling process using continuous casting billets as raw materials.

[0009] The technical solution adopted by the present invention to solve the above problems is: a 420MPa grade high-performance extra-thick steel plate for construction, whose chemical composition mass percentage is C: 0.07-0.1%, Si: 0.10-0.35%; Mn: 1.40-1.55%; Cr: 0-0.25%; Nb: 0.030-0.050%; Ti: 0.008-0.020%, and Fe and other inevitable elements. This extra-thick steel plate is produced by continuous casting billet through online controlled rolling and controlled cooling process, and the yield strength of the steel plate is 400-480MPa, the tensile strength is 510-630MPa, the yield strength ratio is not more than 0.83, the elongation is greater than 20%, and the -40℃ Charpy impact energy is not less than 100J.

[0010] To achieve the above purpose, the reasons for limiting the chemical elements in the embodiments of the present invention are as follows:

[0011] C: 0.07~0.1%

[0012] The carbon element is the cheapest and most effective strengthening element in steel, so the lower limit of carbon is 0.07%. Too high a carbon content leads to poor welding performance and deteriorates impact resistance, so the upper limit of carbon is 0.1%. When the carbon content is ≥0.09%, peritectic reaction is likely to occur during the solidification of molten steel, causing longitudinal cracks in the ingot, which affects the surface quality of the steel plate. Preferably, the range of C is 0.07~0.09%.

[0013] Si: 0.1% to 0.35%

[0014] Si is a common deoxidizing element and can improve the strength of ferrite through solid solution strengthening. Therefore, the lower limit of silicon is 0.1%. Too much silicon will promote the formation of Mahō Island structure in the heat affected zone of welding, which is not conducive to the decomposition of Mahō Island structure and deteriorates welding performance. Therefore, the upper limit of silicon is 0.35%.

[0015] Mn: 1.40~1.55%

[0016] Mn is a common solid solution strengthening element, which can effectively improve the strength at both room temperature and high temperature, and is beneficial to improving the hardenability of steel. Therefore, the lower limit of manganese is 1.40%. Too much manganese can easily cause segregation and deteriorate impact toughness. Therefore, the upper limit of manganese is 1.55%.

[0017] Cr: 0~0.25%;

[0018] The Cr element can improve strength and hardenability. Too much Cr will affect impact toughness and deteriorate welding performance. Therefore, the upper limit of Cr is 0.25%.

[0019] Nb: 0.030~0.050%;

[0020] Nb is a very effective grain-refining strengthening element, which can effectively control the size of the original austenite and refine the bainite grains. The carbides formed by Nb have high thermal stability, which can improve the room temperature and high temperature properties of steel at the same time. The limit range of Nb is 0.030%~0.05%.

[0021] Ti: 0.008% to 0.02%

[0022] Ti is a strong nitrogen-fixing element. Titanium nitride can prevent the growth of grains during heating, rolling and welding of the ingot, and improve the toughness of the base material and the heat-affected zone of welding. Excessive Ti will cause the coarsening of titanium nitride and affect the low-temperature toughness of the steel plate. Therefore, the limit range of Ti is 0.008%~0.02%.

[0023] To obtain the above steel plate, preferably, the microstructure of the steel plate is polygonal ferrite+bainite and a small amount of pearlite.

[0024] Preferably, the manufacturing of the steel plate mainly includes smelting, continuous casting, heating, and online controlled rolling and controlled cooling, which specifically includes the following steps:

[0025] (1) Smelting: The smelting raw materials are sequentially subjected to KR hot metal pretreatment, converter smelting, LF smelting, RH vacuum smelting and continuous casting to produce continuous casting billets that meet the composition requirements and have a thickness of ≥300 mm. The center segregation of the continuous casting billet is C-class ≤0.5 level, and the center porosity is ≤0.5 level;

[0026] (2) Heating: The heating temperature of the continuous casting billet is 1160~1250℃, and the holding time is 2~6 hours;

[0027] (3) Online controlled rolling and controlled cooling: Double-stand rolling is adopted, and the steel plate is obtained after rough rolling, finish rolling and post-rolling cooling. The present invention uses the characteristics of slow temperature drop of extra-thick plates through reasonable setting of composition and controlled rolling and controlled cooling process to obtain a structure dominated by polygonal ferrite and bainite during the post-rolling cooling process.

[0028] Preferably, the rough rolling temperature range is 1150-1000°C, the single-pass reduction rate is not less than 15%, the cumulative reduction rate is not less than 50%, and an intermediate billet is obtained, the intermediate billet thickness is not less than 1.4h, and h is the finished product thickness.

[0029] Preferably, the finishing rolling temperature ranges from 770 to 820° C., and the pass reduction rate is 15 to 20%.

[0030] Preferably, the post-rolling cooling process includes: controlling the speed after the finishing mill to match the appropriate start cooling temperature of 760~860℃, and accurately controlling the final cooling and red-returning temperatures by adjusting the water group, water volume and roller speed, so that the final cooling temperature is lower than the bainite transformation end temperature, the red-returning temperature of the steel plate is 350~500℃, and the average cooling rate is 1~5℃ / s.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] The present invention uses continuous casting billets as raw materials and adopts an online controlled rolling and controlled cooling process to produce 80~150mm thick high-strength 420MPa grade steel plates, replacing the offline or NAC normalizing process. The production process is short, the process is simple, energy saving, consumption reduction and emission reduction are achieved, and production efficiency is significantly improved, which is conducive to shortening delivery time. The steel plates produced using this composition and process have the characteristics of low yield strength ratio, narrow yield strength fluctuation range (≤80MPa), small thickness effect and high toughness, and are very suitable for steel structures with seismic design requirements, including but not limited to the construction field. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a typical microstructure of 1 / 4 thickness of the 150 mm thick 420 MPa grade extra thick plate of the present invention.

[0034] Figure 2 It is a typical microstructure of 1 / 2 thickness of the 150 mm thick 420 MPa grade extra thick plate of the present invention. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0036] A 80-150mm thick 420MPa grade high performance extra thick steel plate for construction, the chemical composition mass percentage of which is C: 0.07-0.1%, Si: 0.10-0.35%; Mn: 1.40-1.55%; Cr: 0-0.25%; Nb: 0.030-0.050%; Ti: 0.008-0.020%, as well as Fe and other inevitable elements. This extra thick steel plate is produced by continuous casting billet through online controlled rolling and controlled cooling process, the yield strength of the steel plate is 400-480MPa, the tensile strength is 510-630MPa, the yield strength ratio is not more than 0.83, the elongation is greater than 20%, and the Charpy impact energy at -40℃ is not less than 100J.

[0037] The core purpose of the present invention is to produce a 80-150mm thick 420MPa grade high-performance special thick steel plate for construction by matching the composition and the controlled rolling and controlled cooling process using continuous casting billets. The yield strength of the steel plate is 400-480MPa, the tensile strength is 510-630MPa, the yield strength ratio is not greater than 0.83, the elongation is greater than 20%, and the Charpy impact energy at -40°C is not less than 100J. The microstructure of the steel plate is bainite + polygonal ferrite.

[0038] The following describes embodiments of the present invention to make the features and advantages of the above-mentioned high-performance extra-thick steel plate for construction more obvious and easy to understand.

[0039] After the continuous casting slab with the composition determined in Table 1 is kept at 1200℃ for 5 hours, it is descaled under high pressure and then rough rolled at 1150~1100℃ to obtain intermediate slabs of different thicknesses, and then hot rolled plates are obtained after controlled rolling and controlled cooling. The process is shown in Table 2. The mechanical properties of the extra-thick steel plate provided in the embodiment are tested, and the test results are shown in Table 3, where the tensile properties are for transverse specimens and the Charpy impact is for longitudinal specimens. The room temperature tensile properties and impact properties tests are carried out in accordance with the standards "GB / T228.1 Metal Material Tensile Test Part 1: Room Temperature Test Method" and "GB / T229 Metal Material Charpy Pendulum Impact Test Method".

[0040] Table 1 shows the main chemical compositions of the steel plates of various embodiments and comparative examples of the present invention.

[0041] Table 2 shows the main process parameters of various embodiments and comparative examples of the present invention.

[0042] Table 3 shows the conventional mechanical properties of various embodiments and comparative examples of the present invention.

[0043] Table 1

[0044] C Si Mn P S Cr Nb Ti other Ceq Example 1 0.076 0.25 1.42 0.012 0.001 0.06 0.032 0.015 0.03V 0.33 Example 2 0.087 0.32 1.52 0.008 0.001 0.20 0.043 0.018 — 0.37 Comparative Example 1 0.060 0.22 1.56 0.010 0.002 0.16 0.024 0.018 0.23Ni0.15Cu 0.38

[0045] Note: - means no addition; Ceq = [C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15]

[0046] The C content of each embodiment of the present invention and the comparative example is selected to be 0.06%~0.09%, because C is the cheapest strengthening element and can significantly improve the strength of low alloy steel. However, the present invention aims to develop a high-toughness steel plate with a quality grade of E grade (-40°C), and too high C will deteriorate the toughness of the steel plate. In addition, the building structure steel plate needs to be welded during subsequent use. Studies have shown that in the weld of low alloy steel, if the C content is higher than 0.09%, the toughness of the weld metal will be significantly reduced. Therefore, the C content of the parent material should be controlled below 0.12%, so the C content is limited to below 0.10% this time.

[0047] After Nb is added to alloy steel, the effect is remarkable: niobium can perform fine grain strengthening and precipitation strengthening, etc., and in combination with the TMCP process, it can not only improve the strength of the material but also improve the plasticity and toughness of the material. However, Nb can have a harmful effect on the toughness of the low-alloy high-strength steel weld metal, causing the toughness of the Mn-Si series weld metal to decrease. Generally, Nb is not added to the welding materials of low-alloy high-strength steel. The Nb content in the weld is mainly transitioned from the base material. If the Nb content in the weld metal is not more than 0.045%, the weld will not become too brittle. Therefore, the Nb content is controlled below 0.045% this time.

[0048] Table 2 shows the slab heating and rolling processes of various embodiments and comparative examples of the present invention.

[0049] Billet specifications / mm Thickness at temperature / mm Finish rolling temperature / ℃ Water inlet temperature / ℃ Red return temperature / ℃ Average cooling rate℃ / s Microstructure type Example 1 360 160 770 762 475 3.6 Polygonal ferrite + bainite Example 2 450 210 780 775 395 2.3 Polygonal ferrite + bainite Comparative Example 1 / / 735 435 368 5.2 Proeutectoid ferrite + bainite

[0050] Table 3 shows the tissue types and conventional mechanical properties of various embodiments and comparative examples of the present invention

[0051]

[0052] From the mechanical property data in Table 3, it can be seen that the steel plate having the composition of the present invention and obtained by the manufacturing process of the present invention has the advantages of low alloy composition, high strength and easy production compared with the comparative example. Specifically, it is not necessary to use the production method of relaxation rolling that affects the production rhythm. Only by the TMCP process, under the conditions of achieving a yield strength greater than 400MPa, a tensile strength greater than 510MPa, a yield strength ratio less than 0.83, and an elongation greater than 20%, a -40°C Charpy impact value (single value) greater than 100J can be achieved. The comprehensive technical indicators far exceed the existing technology.

[0053] Analysis of the microstructure of the steel of the present invention shows that the microstructure of the steel of the present invention includes a composite structure of bainitic ferrite and a small amount of polygonal ferrite.

[0054] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A 420MPa high-performance extra-thick steel plate for construction, characterized in that: The chemical composition weight percentage of the steel plate is C: 0.07-0.1%, Si: 0.10-0.35%; Mn: 1.40-1.55%; Cr: 0-0.25%; Nb: 0.030-0.050%; Ti: 0.008~0.020%, as well as Fe and other inevitable elements.

2. The 420MPa high-performance extra-thick steel plate for construction according to claim 1, characterized in that: The maximum thickness of the steel plate is 150 mm, the yield strength of the steel plate is 400-480 MPa, the tensile strength is 510-630 MPa, the yield strength ratio is not greater than 0.83, the elongation is greater than 20%, and the Charpy impact energy at -40°C is not less than 100 J.

3. The 420MPa high-performance extra-thick steel plate for construction according to claim 1, characterized in that: The microstructure of the steel plate is polygonal ferrite+bainite and a small amount of pearlite.

4. A method for manufacturing a 420MPa high-performance extra-thick steel plate for construction as claimed in claim 1, characterized in that: The method comprises the following steps: (1) Smelting: The smelting raw materials are sequentially subjected to KR hot metal pretreatment, converter smelting, LF smelting, RH vacuum smelting and continuous casting to produce continuous casting billets that meet the composition requirements and have a thickness of ≥300 mm. The center segregation of the continuous casting billet is C-class ≤0.5 level, and the center porosity is ≤0.5 level; (2) Heating: The heating temperature of the continuous casting billet is 1160~1250℃, and the holding time is 2~6 hours; (3) Online controlled rolling and controlled cooling: Double-stand rolling is adopted to obtain steel plates after rough rolling, finish rolling and post-rolling cooling.

5. The method for manufacturing a 420MPa high-performance extra-thick steel plate for construction according to claim 4, characterized in that: Step 3) The medium rough rolling temperature range is 1150~1000℃, the single pass reduction rate is not less than 15%, the cumulative reduction rate is not less than 50%, and the intermediate billet is obtained. The thickness of the intermediate billet is not less than 1.4h, where h is the thickness of the finished product.

6. The method for manufacturing a 420MPa high-performance extra-thick steel plate for construction according to claim 4, characterized in that: In step 3), the finishing rolling temperature ranges from 770 to 820°C, and the pass reduction rate is 15 to 20%.

7. The method for manufacturing a 420MPa high-performance extra-thick steel plate for construction according to claim 4, characterized in that: In step 3), the speed after the finishing mill is controlled to match the appropriate start cooling temperature of 760~860℃. The final cooling and red-returning temperatures are accurately controlled by adjusting the water group, water volume and roller speed, so that the final cooling temperature is lower than the end temperature of bainite transformation. The red-returning temperature of the steel plate is 350~500℃, and the average cooling rate is 1~5℃ / s.

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