CN112662941B - Q420GJ medium steel plate for low-yield-ratio, low-cost and high-performance building structure - Google Patents
Q420GJ medium steel plate for low-yield-ratio, low-cost and high-performance building structure Download PDFInfo
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Abstract
The invention provides a Q420GJ medium-thickness steel plate for a low-yield-ratio, low-cost and high-performance building structure, which comprises the following chemical components in percentage by weight: 0.14 Wt% -0.17 Wt%, Si: 0.20 Wt% -0.40 Wt%, Mn: 1.4 Wt% -1.6 Wt%, P: less than or equal to 0.020Wt%, S: less than or equal to 0.01 Wt%, Alt: 0.020-0.050 Wt%, Nb: 0.040 Wt% -0.055 Wt%, V: 0.025 Wt% -0.040 Wt%, Ti: 0.015 Wt% -0.030 Wt%, CEV: less than or equal to 0.44 Wt%, and the balance of Fe and inevitable trace elements; the yield ratio is 0.72-0.78. The invention can obtain qualified high-performance Q420GJ for building structures with low yield ratio and low cost.
Description
Technical Field
The invention relates to the field of metallurgy, in particular to a Q420GJ medium plate for a low-yield-ratio low-cost high-performance building structure, which belongs to the field of steel production and manufacturing.
Background
The earthquake resistance of steel structure buildings is a core concern, and the earthquake resistance is closely related to the yield ratio of steel. The yield ratio refers to the ratio of the yield strength to the tensile strength of the steel, and the index is an important coefficient for measuring the strength reserve of the steel. When the yield ratio of the steel material is higher, the material has stronger deformation resistance and is not easy to generate plastic deformation under the action of external force, but the material has poorer external force impact resistance, higher risk of brittle failure and lower reliability. Therefore, the low yield ratio of the steel for the building structure is a key index of the seismic performance and the safety and reliability of the material. In order to ensure the earthquake-resistant performance of high-rise buildings and avoid the inclination or collapse of the high-rise buildings, the yield ratio of the steel for the high-performance building structure is required to be below 0.83 by the nation.
Although high-rise building steels with low yield ratios have an attractive shock resistance, there are many technical and cost problems associated with the practical production of such steels, especially as strength increases, and yield ratios are difficult to maintain at low levels.
In summary, the following problems exist in the prior art: q420GJ medium steel plate, the yield ratio is higher.
Disclosure of Invention
The invention provides a Q420GJ medium plate steel for a low-yield-ratio low-cost high-performance building structure, which aims to solve the problem that the Q420GJ medium plate steel has a high yield ratio.
Therefore, the invention provides a Q420GJ medium-thickness steel plate for a low-yield-ratio low-cost high-performance building structure, which comprises the following chemical components in percentage by weight: 0.14 Wt% -0.17 Wt%, Si: 0.20 Wt% -0.40 Wt%, Mn: 1.4 Wt% -1.6 Wt%, P: less than or equal to 0.020Wt%, S: less than or equal to 0.01 Wt%, Alt: 0.020-0.050 Wt%, Nb: 0.040 Wt% -0.055 Wt%, V: 0.025 Wt% -0.040 Wt%, Ti: 0.015 Wt% -0.030 Wt%, CEV: less than or equal to 0.44 Wt%, and the balance of Fe and inevitable trace elements; the yield ratio is 0.72-0.78.
Further, the Q420GJ medium steel plate for the building structure with low yield ratio, low cost and high performance comprises the following chemical components in percentage by weight: 0.15 Wt%, Si: 0.37 Wt%, Mn: 1.52 Wt%, P: 0.013 Wt%, S: 0.002 Wt%, Alt: 0.035 Wt%, Nb: 0.047 Wt%, V: 0.029 Wt%, Ti: 0.026 Wt%, CEV: 0.42 Wt%.
Further, the Q420GJ medium steel plate for the building structure with low yield ratio, low cost and high performance comprises the following chemical components in percentage by weight: 0.14 Wt%, Si: 0.34 Wt%, Mn: 1.49 Wt%, P: 0.015 Wt%, S: 0.001 Wt%, Alt: 0.040 Wt%, Nb: 0.046 Wt%, V: 0.028 Wt%, Ti: 0.027 Wt%, CEV: 0.40 Wt%.
Further, the Q420GJ medium steel plate for the building structure with low yield ratio, low cost and high performance comprises the following chemical components in percentage by weight: 0.15 Wt%, Si: 0.36 Wt%, Mn: 1.50 Wt%, P: 0.014 Wt%, S: 0.002 Wt%, Alt: 0.038 Wt%, Nb: 0.047 Wt%, V: 0.030 Wt%, Ti: 0.023 Wt%, CEV: 0.40 Wt%.
Further, the Q420GJ medium steel plate for the building structure with low yield ratio, low cost and high performance comprises the following chemical components in percentage by weight: 0.15 Wt%, Si: 0.36 Wt%, Mn: 1.54 Wt%, P: 0.014 Wt%, S: 0.001 Wt%, Alt: 0.036 Wt%, Nb: 0.051 Wt%, V: 0.032 Wt%, Ti: 0.026 Wt%, CEV: 0.40 Wt%.
Further, the thickness of the finished product is 20mm, and the yield ratio is 0.74.
Furthermore, the thickness of the finished product is 30mm, and the yield ratio is 0.75.
Furthermore, the thickness of the finished product is 40mm, and the yield ratio is 0.75.
Further, the thickness of the finished product is 60mm, and the yield ratio is 0.73.
According to the invention, through component design and process control, on the basis of adding a small amount of Nb, V, Ti and other alloy elements, the qualified high-performance Q420GJ for the building structure with low yield ratio and low cost can be obtained without RH vacuum smelting of a converter and subsequent heat treatment of a medium plate. In addition, by combining proper rolling process control, the same composition can meet the requirements of Q420GJC, Q420GJD and all products with the thickness specification of less than 80mm, including Z15/Z25/Z35, thereby achieving the purposes of simplifying production organization and further reducing production cost. Finally, a process production scheme and a production technology of smelting, continuous casting and rolling are formed by taking a medium plate production line as a core process.
Drawings
Fig. 1 is a photograph (200 times magnified) of the metallographic structure of an example of the invention.
Detailed Description
The present invention will now be described in order to more clearly understand the technical features, objects, and effects of the present invention.
The technical scheme adopted by the invention is as follows: the steel grade of the Q420GJ medium steel plate for the low yield ratio and high performance building structure comprises the following chemical components in percentage by weight: 0.14 Wt% -0.17 Wt%, Si: 0.20 Wt% -0.40 Wt%, Mn: 1.4 Wt% -1.6 Wt%, P: less than or equal to 0.020Wt%, S: less than or equal to 0.01 Wt%, Alt: 0.020-0.050 Wt%, Nb: 0.040 Wt% -0.055 Wt%, V: 0.025 Wt% -0.040 Wt%, Ti: 0.015 Wt% to 0.030 Wt%, CEV (carbon equivalent): less than or equal to 0.44 Wt%, and the balance of Fe and inevitable trace elements.
Carbon is the cheapest reinforcing element in steel, C can promote the formation of cementite and pearlite and the precipitation of other carbides, the strength of the steel is improved through solid solution strengthening, structure strengthening and precipitation strengthening, particularly, the tensile strength can be obviously improved, so that the yield ratio of the steel is reduced, but the plasticity of the steel is reduced, and the welding performance and the low-temperature impact toughness are not good. Therefore, the content of C needs to be controlled in a proper interval, the addition of other precious alloy elements is reduced on the premise of ensuring the product performance, and the production cost is reduced, wherein the content of C: 0.14 Wt% -0.17 Wt%.
Si can improve the strength of the steel plate and is a good deoxidizer in the smelting process, but Si seriously damages the low-temperature toughness and weldability of the steel plate, especially the low-temperature toughness and fatigue resistance of a welding heat affected zone during high-heat input welding. Therefore, the Si content is not suitable to be controlled too high, the economy and operability of the steelmaking process are integrated, and the Si content is controlled to be 0.20 Wt% -0.40 Wt%.
Mn as an alloy element in the steel plate can improve the strength and the toughness, expand an austenite phase region and reduce Ac1、Ac3、Ar1、Ar3Temperature, refinement of ferrite grainsAnd (4) granulating. However, too high Mn content causes center segregation of the product, and reduces the uniformity of the mechanical properties and the low-temperature toughness of the steel plate, and in addition, too high Mn content causes higher production cost. By combining the above factors, Mn is controlled to be 1.4 Wt% -1.6 Wt%.
The P content mainly affects the plasticity of the steel, and has great damage to the low-temperature impact toughness and weldability of the steel plate. S is taken as a harmful inclusion of steel grade and mainly influences the impact toughness and the ductile-brittle transition temperature of steel, and sulfide inclusions in the steel influence the anisotropy of the steel. P, S, the lower the content, the better, but considering the steel-making condition and cost, the P: less than or equal to 0.020Wt%, S: less than or equal to 0.01 Wt%:
al in the steel can fix free [ N ] in the steel, reduce the free [ N ] in a welding heat affected zone and promote ferrite to be precipitated in a welding cooling cycle, so that the low-temperature impact toughness of the welding heat affected zone is improved. However, excessive Al forms a large amount of dispersed needle-like Al2O3 inclusions in the steel, and deteriorates the low-temperature impact toughness and weldability of the steel sheet. According to the analysis of the steel plate composition system, the Alt: 0.020-0.050 Wt%.
The Nb, V and Ti composite micro-alloying is adopted, and the Nb: 0.040 Wt% -0.055 Wt%, V: 0.025 Wt% -0.040 Wt%, Ti: 0.015 Wt% -0.030 Wt%.
Nb can increase TNRTemperature, delayed deformation austenite recrystallization, refined ferrite grains and improved toughness of the steel plate. If the Nb content is too low, the rolling control function in the non-recrystallization region and the two-phase region cannot be effectively exerted, the strengthening ability is insufficient, and if too high, the production cost is increased, and the weldability is affected.
V can be precipitated in ferrite/bainite by V (C, N) to improve the strength of the steel sheet, and the upper limit of the V content can be appropriately set as the thickness of the steel sheet increases. When the content of V is too low, too little V (C, N) is precipitated, the strengthening ability is insufficient, and when it is too high, the production cost increases, and the low-temperature toughness, elongation, and weldability of the steel sheet are impaired.
Because Ti and N have strong affinity, TiN particles are formed and begin to form at a temperature above 1150 ℃, therefore, in a series of processes of continuous casting billet heating, steel plate rolling and the like, the TiN particles can prevent the generation of deformed austenite dynamic recrystallization and the growth of austenite recrystallization grains, refine the grains, play a role in fine grain strengthening, reduce inclusions and improve the elongation of steel. However, when Ti is added in a large amount, TiN particles are coarsened, and the low-temperature toughness of the steel sheet is lowered.
The invention relates to a manufacturing method of a medium steel plate, which comprises the following process routes: blast furnace molten iron smelting → molten iron desulphurization pretreatment → converter molten steel smelting → LF molten steel refining treatment → slab continuous casting → medium plate rolling → warehousing.
Molten iron desulphurization pretreatment: KR is adopted for desulfurization, and S is controlled to be less than or equal to 0.0050 Wt% in molten iron fed into the furnace
Smelting molten steel in a converter: the binary basicity R (CaO/Al2O3) of the slag is controlled to be 3-4, argon is blown from the bottom in the whole smelting process, the end point C of the converter is 0.06-0.1 Wt%, and P is less than or equal to 0.020 Wt%.
LF molten steel refining treatment: performing deoxidation and alloying processes of Al, Mn, Nb, V, Ti and the like, refining the top slag with binary basicity R (CaO/Al)2O3) Controlling the molten steel to be 8-12, and carrying out Ca treatment on the molten steel according to the formula of [ Ca]/[Als]Controlling the temperature to be 0.10-0.14, carrying out soft argon blowing on the ladle for 8-10 min after Ca treatment is finished, and controlling the ladle molten steel calming time to be more than or equal to 18min between the end of the soft argon blowing and the start of continuous casting ladle pouring.
Slab continuous casting: the automatic slag discharging detection control of the ladle is required, the superheat degree of pouring of the tundish is 10-25 ℃, the tundish uses an alkaline covering agent, the slab low alloy steel is used for protection, the casting blank pulling speed is 1.0-1.15 m/min, the liquid level fluctuation of the crystallizer is automatically controlled, and the fluctuation range is controlled to be +/-3 mm. The continuous casting uses dynamic soft reduction, the reduction interval (solid phase ratio during casting blank solidification) is 0.5-0.8, the reduction is 5.0mm, and electromagnetic stirring is carried out at 430A and 6.0 Hz. The thickness of the continuous casting slab is 220 mm.
Rolling a medium plate:
the heating and soaking temperature of the casting blank is controlled to be 1220-1250 ℃, so that the steel blank is fully austenitized, most alloying elements are fully dissolved, and preparation is made for obtaining uniformly refined structures and second-phase particles;
in the rough rolling stage, rolling is carried out in an austenite recrystallization region, a longitudinal-transverse-longitudinal rolling mode is adopted, the initial rolling temperature is 1110-1170 ℃, and the rough rolling finishing temperature is more than or equal to 1000 ℃. Increasing the single-pass reduction rate, wherein the reduction rate of each pass after broadening is more than 15%, the reduction rate of the last 2-3 passes is more than 20%, and the total reduction rate is more than 60%;
in the finish rolling stage, rolling is mainly carried out in an austenite non-recrystallization region, rolling in a partial recrystallization region or a two-phase region is avoided, and the purpose is mainly to control the grain structure of the steel plate and avoid the phenomena of coarse grains and mixed crystals, which cause the surface quality problem or the performance incompatibility of the steel plate. Meanwhile, in order to improve the low-temperature impact toughness of the steel plate, enough pass reduction rate should be ensured. The rolling temperature of the finish rolling is 900-940 ℃, the temperature of the finish rolling is 800-850 ℃, the single-pass reduction rate (except the plate shape control pass) is increased, the pass reduction rate is more than 10%, the total reduction rate is more than 60%, and the rolling temperature is properly reduced for thick specifications.
And in the cooling stage after rolling, the steel plate with the thickness less than or equal to 40mm is air-cooled to room temperature, the steel plate with the thickness more than 40mm is rapidly cooled by ACC, the control range of the final cooling temperature is 640-680 ℃, and the steel plates of all specifications do not need to be subjected to subsequent heat treatment.
Effect
The yield strength ReL of the Q420GJ medium-thickness steel plate for the building structure with low yield ratio, low cost and high performance, obtained by the invention, is 440-490 MPa, the tensile strength Rm is 580-630 MPa, the yield ratio is 0.72-0.76, the elongation A is 22-28%, and the impact energy A at 0-20 DEG CKVThe average value is 160 and 220J, and the cold bending is qualified.
According to the Q420GJ medium plate for the building structure with low yield ratio, low cost and high performance and the manufacturing method thereof, the qualified Q420GJ for the building structure with low yield ratio and low cost can be obtained without RH vacuum smelting of a converter and subsequent heat treatment of a medium plate on the basis of adding a small amount of Nb, V, Ti and other alloy elements through component design and process control. In addition, by combining with proper rolling process control, the same composition can meet the requirements of Q420GJC and Q420GJD products with thickness of below 80mm, including Z15/Z25/Z35, so that the aims of simplifying production organization and further reducing production cost are fulfilled. Finally, a process production scheme and a production technology of smelting, continuous casting and rolling are formed by taking a medium plate production line as a core process.
The Q420GJ medium plate for the building structure with low yield ratio, low cost and high performance and the manufacturing method thereof adopt the following component proportions and specific processes. Wherein, Table 1 shows the compositions (in weight%) of the steels of the respective examples. Table 2 shows the process parameters corresponding to the example steels described in table 1. Table 3 shows the properties of the steel compositions according to the examples of Table 1.
TABLE 1 product chemistry (Wt%)
TABLE 2 specific Process parameters for the examples
TABLE 3 comprehensive Properties of the steel sheets obtained in the examples
Where "/" in addition to a ratio of two parameters, also means a unit,
ReL is yield strength, Rm is tensile strength, A is elongation, Re/Rm is yield ratio, Z is reduction of area representing Z-direction, and KV2 is impact energy.
Examples 1-1 and 1-2 all used the chemical composition of example 1, examples 1-1 and 1-2 are different routes of example 1;
examples 2-1 and 2-2 all used the chemical composition of example 2, examples 2-1 and 2-2 are different routes of example 2;
examples 3-1 and 3-2 all used the chemical composition of example 3, examples 3-1 and 3-2 are different routes of example 1;
examples 4-1 and 4-2 all used the chemical composition of example 4, and examples 4-1 and 4-2 are different routes of example 4;
examples 5-1 and 5-2 all used the chemical composition of example 5, and examples 5-1 and 5-2 are each different routes to example 5;
the typical metallographic structure of the steel for high-performance building structures Q420GJ of the above example was as follows: the structure is ferrite + pearlite and the grain size is grade 8, wherein the metallographic structure of example 2-1 is shown in FIG. 1.
The above description is only an exemplary embodiment of the present invention, and is not intended to limit the scope of the present invention. In order that the components of the present invention may be combined without conflict, it is intended that all equivalent changes and modifications made by those skilled in the art without departing from the spirit and principles of the present invention shall fall within the protection scope of the present invention.
Claims (2)
1. The Q420GJ medium plate for the low-yield-ratio low-cost high-performance building structure is characterized in that the Q420GJ medium plate for the low-yield-ratio low-cost high-performance building structure comprises the following chemical components in percentage by weight: 0.14w t% -0.17 w t%, Si: 0.20w t% -0.40 w t%, Mn: 1.4w t% -1.6 w t%, P: less than or equal to 0.020w t%, S: less than or equal to 0.01w t percent, Alt: 0.020% -0.050 w t%, Nb: 0.0459-0.055 w t%, V: 0.025w t-0.0296 w t%, Ti: 0.0232w t% -0.030 w t%, CEV: less than or equal to 0.44w t percent, and the balance of Fe and inevitable trace elements; the yield ratio is 0.72-0.78;
the thickness of the Q420GJ medium steel plate for the building structure with low yield ratio, low cost and high performance is less than or equal to 40 mm;
the manufacturing method of the Q420GJ medium plate for the building structure with low yield ratio, low cost and high performance comprises the following process routes: smelting blast furnace molten iron, desulfurizing and pretreating the molten iron, smelting converter molten steel, refining LF molten steel, continuously casting plate blanks and rolling medium plates;
wherein, smelting molten steel in a converter: controlling the binary basicity R of the slag to be 3-4, adopting bottom blowing argon in the whole smelting process, wherein the end point C of the converter is 0.06-0.1 Wt%, and P is less than or equal to 0.020 Wt%;
LF molten steel refining treatment: performing deoxidation and alloying processes of Al, Mn, Nb, V, Ti and the like, refining the top slag with binary basicity R (CaO/Al)2O3) Controlling the molten steel to be 8-12, and carrying out Ca treatment on the molten steel according to the formula of [ Ca]/[Als]Controlling the temperature to be 0.10-0.14, carrying out soft argon blowing on the ladle for 8-10 min after Ca treatment is finished, and controlling the molten steel calming time of the ladle between the end of the soft argon blowing and the start of continuous casting steel ladle casting to be more than or equal to 18 min;
soaking temperature: 1220 and 1250 ℃;
the rough rolling stage is to roll in an austenite recrystallization region, and adopts a longitudinal-transverse-longitudinal rolling mode, wherein the initial rolling temperature is 1110-1170 ℃, the rough rolling final rolling temperature is more than or equal to 1000 ℃, the reduction rate of each pass is more than 15% after widening, the reduction rate of the last 2-3 passes is more than 20%, and the total reduction rate is more than 60%;
the start rolling temperature of finish rolling is 900-940 ℃, the finish rolling temperature of finish rolling is 800-850 ℃, the pass reduction rate is more than 10%, and the total reduction rate is more than 60%; in the cooling stage after rolling, the steel plate with the thickness less than or equal to 40mm is air-cooled to room temperature;
0 ℃ impact energy AKVThe average value was 181-219J.
2. The low yield ratio, low cost and high performance Q420GJ medium gauge steel plate for building structures of claim 1, wherein the finished product thickness is 30mm and the yield ratio is 0.76.
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