CN111172465A - Low-carbon equivalent large-thickness Q390GJ steel plate for building structure and manufacturing method thereof - Google Patents

Abstract

The invention relates to a steel plate for a low-carbon equivalent large-thickness Q390GJ building structure and a manufacturing method thereof, wherein the steel plate comprises the following chemical components in percentage by weight: 0.10% -0.139%, Si: 0.20-0.39%, Mn: 1.30-1.44%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Nb: 0.020-0.039%, Ti: 0.006-0.016%, Al 0.01-0.04%, Ceq: 0.32 to 0.38, and the balance of iron and inevitable impurities; the microstructure of the steel plate mainly comprises fine polygonal ferrite and pearlite, wherein the volume percentage of the polygonal ferrite is 25-40%, the maximum thickness of the steel plate is 120mm, the yield strength is more than or equal to 390MPa, the tensile strength is 550MPa, the elongation after fracture is more than or equal to 28%, the yield ratio is less than or equal to 0.77, the Z-direction performance in the thickness direction is more than or equal to 60%, and the impact energy at minus 40 ℃ is more than or equal to 200J. The steel plate product produced according to the chemical components and the production process requirements of the invention has the advantages of large thickness, high strength and toughness, high plasticity, low yield ratio, excellent welding performance and lamellar tearing resistance.

Description

Low-carbon equivalent large-thickness Q390GJ steel plate for building structure and manufacturing method thereof

Technical Field

The invention relates to the technical field of metal materials, in particular to a low-carbon equivalent large-thickness steel plate for a Q390GJ building structure and a manufacturing method thereof.

Background

Along with the continuous development of building engineering equipment manufacturing technology, the demand of green building steel structures is increasing day by day, and super high-rise and large-span building structures are more and more constructed, and in order to guarantee the overall safety of high-rise buildings, the demand of the steel plate for the building, which has high strength, high and low temperature toughness, good welding performance and large thickness size, is vigorous. The high strength and toughness and large thickness steel plate manufactured according to the conventional production method inevitably needs a slab with a large thickness section as a rolling condition, the carbon equivalent is high, and in addition, the rolled steel plate also needs to be subjected to heat treatment such as normalizing, tempering and the like, which inevitably increases the production cost and reduces the production efficiency.

At present, some researches on steel plates for construction have been made at home and abroad:

the Chinese patent application with the publication number of CN101987330A discloses a method for manufacturing an ultra-thick lamellar tearing-resistant steel plate, which comprises the steps of smelting, ingot casting, forging, rolling and heat treatment, and is used for producing the lamellar tearing-resistant steel plate with the thickness of 130-400 mm. A forging process is arranged between the ingot casting processes, and the steel ingot is forged into a steel plate blank and subjected to post-forging heat treatment. The initial forging temperature of the forging process is 1225-1250 ℃, the final forging temperature is 850-900 ℃, and the compression ratio is not less than 3. The defects are that: the casting adopts die casting and forging, and compared with the current mature slab continuous casting mode, the cost is high and the efficiency is low.

Chinese patent with publication number CN102876970B discloses a steel with yield strength more than or equal to 390MPa for high-rise buildings and a production method thereof, the steel comprises the following components by mass percent: 0.14-0.18% of C, 0.3-0.5% of Si, 0.6% of Mn, 1.45-1.6% of Mn, 0.035-0.050% of Nb, 0.045-0.065% of V, 0.007-0.017% of Ti, 0.015-0.050% of Al, 0.001-0.005% of Ca0.005% of P, less than 0.025% of S, and the balance of Fe and inevitable impurities. The method comprises the steps of molten iron pretreatment, converter smelting, LF refining, RH treatment, continuous casting, heating, rolling, laminar cooling, normalizing and small-amount water spray cooling, and the thick steel plate for the building, which has the yield strength of 370-490MPa, the tensile strength of more than or equal to 490MPa, the yield ratio of less than or equal to 0.77, the low-temperature impact energy of more than or equal to 100J at minus 20 ℃ and the reduction of area of more than or equal to 35%, is produced. The disadvantages are that: the steel plate has higher content of design components, and the carbon equivalent exceeds the upper limit of TMCP delivery state products specified in the national standard GB/T19879-2015, thus not meeting the requirements of new national standards.

Chinese patent No. CN101676427B discloses "a high-strength low-yield-ratio steel sheet", which comprises the following chemical components: 0.15-0.20% of C, 1.0-2.0% of Si, 1.8-2.0% of Mn1.0%, less than or equal to 0.036% of Al, 0.05-0.1% of V, less than or equal to 0.01% of P, less than or equal to 0.005% of S, 0.8-1.0% of Cr0.8, and the balance of Fe and other inevitable impurities. The hot rolled steel plate with high strength and low yield ratio is obtained through a traditional TMCP rolling process, the strength reaches 1200-1500 MPa, and meanwhile, the hot rolled steel plate has good low-temperature impact toughness. The disadvantages are that: the steel plate has high design component content, and the carbon equivalent reaches over 0.65, which has adverse effect on the welding performance of the steel plate.

Chinese patent with publication number CN101613828B discloses a super-thick steel plate for construction with yield strength of 460MPa grade and low yield ratio and a manufacturing method thereof, the steel plate comprises the following components by weight percent: 0.14-0.18% of C, 0.35-0.45% of Si, 1.40-1.50% of Mn, 0.025-0.035% of Nb0.040-0.050% of V, 0.010-0.020% of Tis, less than 0.020% of P, less than 0.008% of S and the balance of Fe; the rolling process comprises the following steps: the heating temperature is 1220-1250 ℃, and two stages of austenite recrystallization region and austenite non-recrystallization region are adopted to control rolling. The heat treatment process comprises the following steps: heating the steel plate to a two-phase region of 800-850 ℃, keeping the temperature for 10-20 ℃, and then quenching by water cooling, wherein the final cooling temperature is controlled to be less than or equal to 100 ℃; and tempering the quenched steel plate at 450-600 ℃ to finally obtain the low-yield-ratio high-strength steel plate for the building. The disadvantages are that: the heat treatment of the steel plate adopts quenching and tempering, the process is more complex, and the production period is longer.

According to the document 'development of 120mm large-thickness Q390GJC-Z35 steel for high-rise buildings' (rolled steel, No. 5 of No. 28 of 10 month in 2011, published by Zhu Shu), aiming at the problems of large production difficulty, low yield and the like of the large-thickness steel for the high-rise buildings, the 120mm large-thickness Q390GJC-Z35 steel plate for the high-rise buildings is trial-produced by optimizing components, rolling and heat treatment processes; the chemical components of the steel plate are C: 0.15 to 0.18%, Si: 0.3-0.45%, Mn: 1.45-1.55%, P is less than or equal to 0.015%, S is less than or equal to 0.003%, Nb + V + Ti is less than or equal to 0.22%, Als: 0.03 to 0.05 percent, and the balance of Fe and inevitable impurities. The Q390GJC thick steel plate for buildings is produced by adopting molten iron pretreatment, converter smelting, LF refining, VD treatment, die casting, heating, rolling control cooling control, normalizing and water spraying cooling methods. The steel plate production process related to the document is die casting, normalizing treatment is needed after rolling, and the carbon equivalent is high.

In conclusion, the existing industry has insufficient research on 390MPa grade low-carbon equivalent large-thickness steel for building structures.

Disclosure of Invention

The invention provides a low-carbon equivalent large-thickness Q390GJ steel plate for a building structure and a manufacturing method thereof, and the steel plate product produced according to the chemical components and the production process requirements of the invention has large thickness (the maximum thickness can reach 120mm), high strength and toughness, high plasticity, low yield ratio, excellent welding performance and lamellar tearing resistance.

In order to achieve the purpose, the invention adopts the following technical scheme:

a steel plate for a low-carbon equivalent large-thickness Q390GJ building structure comprises the following chemical components in percentage by weight: 0.10% -0.139%, Si: 0.20-0.39%, Mn: 1.30-1.44%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Nb: 0.020-0.039%, Ti: 0.006-0.016%, Al 0.01-0.04%, Ceq: 0.32 to 0.38, and the balance of iron and inevitable impurities;

the microstructure of the steel plate mainly comprises fine polygonal ferrite and pearlite structures, wherein the volume percentage of the polygonal ferrite is 25-40%, the grain size is more than 9 grades, and the average grain size of the polygonal ferrite is less than 20 microns;

the maximum thickness of the steel plate is 120mm, the yield strength is more than or equal to 390MPa, the tensile strength is 550MPa, the elongation after fracture is more than or equal to 28%, the yield ratio is less than or equal to 0.77, the Z-direction performance in the thickness direction is more than or equal to 60%, and the impact energy at minus 40 ℃ is more than or equal to 200J.

A manufacturing method of a steel plate with low carbon equivalent and large thickness Q390GJ for a building structure comprises the processes of molten iron pretreatment, converter smelting, external refining, continuous casting, rolling, cooling and straightening;

1) in the continuous casting process, the casting superheat degree of a continuous casting blank is 10-25 ℃, and the ratio of the thickness of the continuous casting blank to the thickness of a finished steel plate is 2.5-5; the temperature of a heating section of the continuous casting billet is 1201-1249 ℃, the temperature of a soaking section is 1195-1220 ℃, and the heating time of the soaking section is not less than 65 min;

2) in the rolling process, the initial rolling temperature of rough rolling is 1070-1095 ℃, the final rolling temperature of rough rolling is 1010-1045 ℃, the deformation rate of each pass of at least the last 2 passes in the rough rolling stage is more than 15%, the pass interval is not more than 15s, and the accumulated reduction rate is more than or equal to 50%; the thickness of the intermediate temperature-waiting blank is 1.25 t-2.5 t, and t is the thickness of a finished steel plate; the start rolling temperature of finish rolling is 820-849 ℃, the finish rolling temperature is 750-779 ℃, and the single-pass deformation rate in the finish rolling stage is not lower than 10%;

3) in the cooling process, after rolling, the temperature of the steel plate is kept, the water cooling temperature is 690-720 ℃, the temperature of red returning is 450-570 ℃, and the cooling speed is 12-20 ℃/s; subsequently, hot straightening and air cooling are performed.

Compared with the prior art, the invention has the beneficial effects that:

1) in the chemical composition design of the steel plate, the toughness of the material is improved through low-C and low-Mn design, the Nb and Ti elements are utilized to inhibit the growth of austenite grains, and the nucleation promoting effect in the austenite transformation process is utilized to refine the grains, control the thickness core structure of the steel plate and improve the uniformity of the structure; by matching with a corresponding production process, the problem of matching technical indexes such as high strength, low yield ratio, low temperature toughness and the like of the building steel is solved;

2) the Ceq in the steel plate is only 0.32-0.38, the welding performance of the steel plate is excellent, and the processing efficiency of a component can be improved;

3) the steel plate disclosed by the invention does not contain precious alloy elements, so that the alloy cost is reduced, and the plasticity and toughness of the steel plate are further improved;

4) the invention realizes low-phosphorus and low-carbon control through smelting and continuous casting processes, improves the quality of casting blanks and further improves the performance of final products;

5) the invention adopts TMCP technology to obtain stable complex phase structure composed of ferrite and pearlite with proper proportion; the strength and the ductility and the toughness of the steel plate can be optimally matched by properly controlling the content ratio of the steel plate and the plastic plate, so that the aims of improving the strength and reducing the yield ratio are fulfilled, and good anti-seismic performance is obtained;

6) the steel plate is manufactured by adopting a TMCP (thermal mechanical control processing) process, does not need subsequent heat treatment, has simple working procedures, and can further improve the production efficiency;

7) the low-carbon equivalent large-thickness Q390GJ steel plate for the building structure has the maximum thickness of 120mm, the yield strength of more than or equal to 390MPa, the tensile strength of 550MPa, the elongation after fracture of more than or equal to 28 percent, the yield ratio of less than or equal to 0.77, the Z-direction performance in the thickness direction of more than or equal to 60 percent, and the impact energy at minus 40 ℃ of more than or equal to 200J, and meets the requirements of steel for ultra-high-rise and large-thickness building structures under the low-temperature condition.

Drawings

FIG. 1 is a photograph of the metallographic structure of a steel plate for building structures according to the invention, which has a low carbon equivalent and a large thickness of Q390 GJ.

Detailed Description

The invention relates to a low-carbon equivalent large-thickness Q390GJ steel plate for a building structure, which comprises the following chemical components in percentage by weight: 0.10% -0.139%, Si: 0.20-0.39%, Mn: 1.30-1.44%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Nb: 0.020-0.039%, Ti: 0.006-0.016%, Al 0.01-0.04%, Ceq: 0.32 to 0.38, and the balance of iron and inevitable impurities;

the microstructure of the steel plate mainly comprises fine polygonal ferrite and pearlite structures, wherein the volume percentage of the polygonal ferrite is 25-40%, the grain size is more than 9 grades, and the average grain size of the polygonal ferrite is less than 20 microns;

the maximum thickness of the steel plate is 120mm, the yield strength is more than or equal to 390MPa, the tensile strength is 550MPa, the elongation after fracture is more than or equal to 28%, the yield ratio is less than or equal to 0.77, the Z-direction performance in the thickness direction is more than or equal to 60%, and the impact energy at minus 40 ℃ is more than or equal to 200J.

A manufacturing method of a steel plate with low carbon equivalent and large thickness Q390GJ for a building structure comprises the processes of molten iron pretreatment, converter smelting, external refining, continuous casting, rolling, cooling and straightening;

1) in the continuous casting process, the casting superheat degree of a continuous casting blank is 10-25 ℃, and the ratio of the thickness of the continuous casting blank to the thickness of a finished steel plate is 2.5-5; the temperature of a heating section of the continuous casting billet is 1201-1249 ℃, the temperature of a soaking section is 1195-1220 ℃, and the heating time of the soaking section is not less than 65 min;

2) in the rolling process, the initial rolling temperature of rough rolling is 1070-1095 ℃, the final rolling temperature of rough rolling is 1010-1045 ℃, the deformation rate of each pass of at least the last 2 passes in the rough rolling stage is more than 15%, the pass interval is not more than 15s, and the accumulated reduction rate is more than or equal to 50%; the thickness of the intermediate temperature-waiting blank is 1.25 t-2.5 t, and t is the thickness of a finished steel plate; the start rolling temperature of finish rolling is 820-849 ℃, the finish rolling temperature is 750-779 ℃, and the single-pass deformation rate in the finish rolling stage is not lower than 10%;

3) in the cooling process, after rolling, the temperature of the steel plate is kept, the water cooling temperature is 690-720 ℃, the temperature of red returning is 450-570 ℃, and the cooling speed is 12-20 ℃/s; subsequently, hot straightening and air cooling are performed.

The design principle of the chemical components of the steel plate for the low-carbon equivalent large-thickness Q390GJ building structure is as follows:

c can play a strengthening role through interstitial solid solution, can also form fine carbide precipitation with alloy elements such as Nb and the like, and is precipitated before rolling deformation or austenite transformation, so that the effects of inhibiting grain growth, improving nucleation rate and refining tissues are achieved; meanwhile, the C can also block dislocation movement, effectively improve tensile strength and reduce yield ratio. Therefore, the content of C in the steel plate is not suitable to be too low; however, an increase in C has an adverse effect on toughness, particularly on low-temperature toughness; further, an increase in C increases the carbon equivalent of the steel, deteriorating the weldability of the steel sheet. Therefore, the C content cannot be too high; therefore, the content of C is controlled to be 0.10-0.139 percent.

Si is one of deoxidizing elements in steel, has strong solid solution strengthening effect, can purify ferrite, reduces the content of pearlite, is favorable for reducing the Bauschinger effect of a base material, and reduces the yield ratio of the steel plate. However, excessive Si lowers the toughness of the weld heat affected zone of the base metal, and deteriorates the toughness and weldability of the steel. Therefore, the Si content is controlled to be 0.20-0.39 percent in the invention.

Mn improves the strength of steel through solid solution strengthening, reduces austenite phase transition temperature, and inhibits phase transition crystal grains of the steel plate from growing before accelerated cooling, thereby playing a role of refining the crystal grains and improving the strength of the steel plate; however, too high Mn content may inhibit ferrite transformation, affect the yield strength of the steel, and be detrimental to the reduction of yield ratio; in addition, excessive Mn content can induce segregation, deteriorate the structural uniformity and the lamellar tearing performance of the steel plate and is not beneficial to welding, so that the Mn content is controlled to be 1.30-1.44 percent.

P, S is harmful impurity element, the lower the content is, the better; wherein, too high P can cause tissue segregation and has obvious adverse effect on low-temperature toughness, and P is controlled to be less than or equal to 0.010 percent; the increase of S content can promote the generation and growth of inclusions and deteriorate the low-temperature performance and the performance in the thickness direction, so that the S content is controlled to be less than or equal to 0.003 percent.

The beneficial effects of Nb in the present invention include (1) solid solution strengthening; (2) the steel is precipitated in the rolling process and before accelerated cooling, the grain boundary is pinned, nucleation is promoted, and crystal grains are effectively refined, so that the strength is improved, and the toughness is improved; (3) the austenite phase transition temperature is reduced, and the grains can be refined. However, too high an amount of Nb deteriorates the toughness of the weld and the heat-affected zone, and also increases the cost; therefore, the content of Nb is controlled to be 0.02-0.039 percent.

Ti can exert nitrogen fixation effect, form a precipitation phase mainly comprising TiN, inhibit the growth of austenite grains under high temperature condition and improve the toughness of a heat affected zone after welding; in the welding process, the TiN particles can prevent heat from influencing the grain growth of the coarse crystal area, and the low-temperature toughness of the welding joint is improved. In addition, Ti is easy to appear in a form of interphase precipitation in the transformation process from austenite to ferrite due to low solid solubility, and is favorable for improving the strength. However, too much Ti reduces the toughness of the steel; therefore, the Ti content is controlled to be 0.006-0.016 percent.

Al is a strong deoxidizing element and can be combined with N to form AlN, so that the effect of refining grains can be achieved, the low-temperature impact toughness is improved, and the brittle transition temperature of steel is reduced. AlN also has the effect of refining the structure. However, when the content of Al exceeds 0.040%, excessive alumina inclusions lower the cleanliness of the steel. If the Al content is too low, the deoxidation is insufficient, and easily-oxidized elements such as Ti and the like can form oxides; therefore, the invention controls the Al content to be 0.01-0.04%.

The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation processes are given, but the scope of the invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[ examples ] A method for producing a compound

In the present example, the chemical compositions of a steel plate for a low carbon equivalent large thickness Q390GJ building structure are shown in table 1; the corresponding smelting continuous casting and slab heating process parameters are shown in table 2; the corresponding rough rolling process parameters are shown in table 3; the corresponding finish rolling process parameters are shown in table 4; the corresponding cooling process parameters are shown in table 5; the properties and microstructure proportions of the final steel sheet are shown in Table 6.

TABLE 1 chemical composition in wt% of steel sheet

Examples	C	Si	Mn	P	S	Nb	Ti	Al	Ceq
										1	0.101	0.20	1.30	0.010	0.003	0.021	0.006	0.015	0.32
2	0.114	0.22	1.33	0.009	0.002	0.023	0.008	0.023	0.34
										3	0.135	0.36	1.44	0.008	0.003	0.036	0.015	0.033	0.38
4	0.125	0.30	1.41	0.010	0.001	0.039	0.013	0.037	0.36
										5	0.128	0.38	1.38	0.009	0.002	0.029	0.010	0.019	0.36
6	0.134	0.24	1.40	0.008	0.003	0.030	0.014	0.028	0.37
										7	0.138	0.32	1.43	0.010	0.002	0.034	0.015	0.034	0.38
8	0.116	0.25	1.32	0.008	0.003	0.025	0.011	0.025	0.34

TABLE 2 continuous casting and billet heating Process parameters

TABLE 3 roughing Process parameters

TABLE 4 Fine Rolling Process parameters

TABLE 5 Cooling Process parameters

TABLE 6 Final Steel plate Properties and microstructure proportions

In table 6, Rel represents yield strength; rm represents tensile strength; a represents elongation after fracture; zz represents the thickness direction Z-direction performance; the-40 ℃ KV2/J represents the-40 ℃ impact energy.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (2)

1. The steel plate for the building structure is characterized by comprising the following chemical components in percentage by weight: 0.10% -0.139%, Si: 0.20-0.39%, Mn: 1.30-1.44%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, Nb: 0.020-0.039%, Ti: 0.006-0.016%, Al 0.01-0.04%, Ceq: 0.32 to 0.38, and the balance of iron and inevitable impurities;

the microstructure of the steel plate mainly comprises fine polygonal ferrite and pearlite structures, wherein the volume percentage of the polygonal ferrite is 25-40%, the grain size is more than 9 grades, and the average grain size of the polygonal ferrite is less than 20 microns;

the maximum thickness of the steel plate is 120mm, the yield strength is more than or equal to 390MPa, the tensile strength is 550MPa, the elongation after fracture is more than or equal to 28%, the yield ratio is less than or equal to 0.77, the Z-direction performance in the thickness direction is more than or equal to 60%, and the impact energy at minus 40 ℃ is more than or equal to 200J.

2. A method for manufacturing a steel plate for building structures of low carbon equivalent large thickness Q390GJ according to claim 1, comprising the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, rolling, cooling and straightening; the method is characterized in that:

1) in the continuous casting process, the casting superheat degree of a continuous casting blank is 10-25 ℃, and the ratio of the thickness of the continuous casting blank to the thickness of a finished steel plate is 2.5-5; the temperature of a heating section of the continuous casting billet is 1201-1249 ℃, the temperature of a soaking section is 1195-1220 ℃, and the heating time of the soaking section is not less than 65 min;

2) in the rolling process, the initial rolling temperature of rough rolling is 1070-1095 ℃, the final rolling temperature of rough rolling is 1010-1045 ℃, the deformation rate of each pass of at least the last 2 passes in the rough rolling stage is more than 15%, the pass interval is not more than 15s, and the accumulated reduction rate is more than or equal to 50%; the thickness of the intermediate temperature-waiting blank is 1.25 t-2.5 t, and t is the thickness of a finished steel plate; the start rolling temperature of finish rolling is 820-849 ℃, the finish rolling temperature is 750-779 ℃, and the single-pass deformation rate in the finish rolling stage is not lower than 10%;

3) in the cooling process, after rolling, the temperature of the steel plate is kept, the water cooling temperature is 690-720 ℃, the temperature of red returning is 450-570 ℃, and the cooling speed is 12-20 ℃/s; subsequently, hot straightening and air cooling are performed.

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