A production method of Q460GJ thick steel plate

Abstract

A method for producing a Q460GJ thick steel plate. The steel plate has a thickness of 80-150 mm, and the chemical composition of the steel is as follows by weight: C=0.18%-0.20%, Si≤0.10%, Mn=1.20%-1.50%, P≤0.008%, S≤0.005%, Al=0.008%-0.015%, Cu=0.30%-0.50%, Ni=0.30%-0.50%, Mo=0.08%-0.10%, Ti=0.015%-0.020%, V=0.04%-0.08%, Mg=0.0010%-0.0025%, B=0.0012%-0.0025%, N≤0.0040%, the balance being Fe and unavoidable impurity elements, and the carbon equivalent (CEV) is ≤0.54%. The process includes smelting, refining, continuous casting, controlled rolling and cooling, normalizing, and tempering. The steel plate produced using this method exhibits high strength and toughness, a low yield ratio, and excellent weldability: yield strength ≥460 MPa, tensile strength ≥570 MPa, elongation ≥18%, yield ratio ≤0.83, and impact energy absorption at 0°C ≥47 J. Furthermore, the steel plate exhibits high uniformity of microstructure and properties throughout its thickness.

Description

Technical Field

[0001] The invention belongs to the technical field of low-alloy high-strength steel production, and relates to a production method of Q460GJ thick steel plate. Background Art

[0002] Structural steel is widely used in the construction industry due to its advantages such as high strength, good toughness, short construction period, and environmental friendliness. However, with the further expansion of the use of structural steel, changes in the operating environment, and more stringent safety and service requirements, higher requirements have been placed on the performance of structural steel. High strength is the development direction of structural steel and an important guarantee for its safety performance. To mitigate the damage caused by earthquakes, it is necessary not only to ensure the high strength and high toughness of structural steel, but also to improve the seismic performance of structural steel. The seismic performance of steel refers to the ability of steel to absorb high plastic energy. For structural steel plates, the yield strength ratio can effectively reflect the seismic performance of the steel plate.

[0003] Because structural steel requires extensive welding during construction, high requirements are placed on its weldability. Controlling steel's weldability is primarily achieved by manipulating its chemical composition to control its carbon equivalent (CEV) and weld crack sensitivity coefficient (Pcm). It's generally accepted that steel with a CEV less than 0.4% exhibits excellent weldability, while a CEV greater than 0.6% exhibits poor weldability. Furthermore, with the trend toward taller and larger buildings, the thickness requirements for structural steel plates are constantly increasing. The 2015 edition of the Chinese national standard "Steel for Building Structures" increased the maximum thickness of Q460GJ from 100mm to 150mm. However, for high-strength Q460GJ thick steel plates, in order to obtain lower carbon equivalent and welding crack sensitivity coefficient, the added carbon content and alloying elements must be limited. In order to ensure the high strength of thick steel plates, tempering process is usually required. However, tempered steel often has a higher yield ratio. It can be seen that there is a contradiction between high strength, low yield ratio and weldability. Summary of the Invention

[0004] In response to the above-mentioned problems in the existing technology, the present invention aims to propose a method for producing Q460GJ thick steel plates with high strength, low yield ratio and good weldability. The produced steel plates have a yield strength of ≥460MPa, a tensile strength of ≥570MPa, an elongation after fracture of ≥18%, a yield ratio of ≤0.83, and an impact energy absorption of ≥47J at 0°C.

[0005] The technical solution of the present invention:

[0006] A method for producing a Q460GJ thick steel plate, wherein the thickness of the steel plate is 80-150 mm, and the weight percentage of the steel is C=0.18%-0.20%, Si≤0.10%, Mn=1.20%-1.50%, P≤0.008%, S≤0.005%, Al=0.008%-0.015%, Cu=0.30%-0.50%, Ni=0.30%-0.50%, Mo=0.08%-0.10%, Ti=0.015%-0.020%, V=0.04 %~0.08%, Mg=0.0010%~0.0025%, B=0.0012%~0.0025%, N≤0.0040%, the balance being Fe and unavoidable impurity elements, where carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.54%; steel plate yield strength ≥460MPa, tensile strength ≥570MPa, elongation after fracture ≥18%, yield strength ratio ≤0.83, 0℃ impact absorption energy ≥47J; key process steps include:

[0007] 1) Smelting: After pretreatment to remove sulfur from the molten iron, it is smelted in a converter. During the tapping process, aluminum iron, metallic manganese, nickel plate, copper plate, and ferromolybdenum are added for deoxidation and alloying. After tapping, the oxygen content in the molten steel is controlled to O=50~100ppm. Then, argon is blown from the bottom of the ladle and stirred for more than 5 minutes before refining.

[0008] 2) Refining: After the LF makes alkaline slag to remove sulfur, aluminum particles are added for diffusion deoxidation to control the oxygen content in the molten steel between O=30~50ppm. At this time, Mg alloy cored wire is fed, and then it is allowed to stand for 3 minutes before feeding Al wire to adjust the composition, and then Ca treatment is carried out. B iron is added before the LF leaves the station. After LF refining, RH vacuum treatment is used.

[0009] 3) Continuous casting: Use full-process protective pouring, control the superheat at 12-18°C, use soft reduction in the secondary cooling zone but do not use electromagnetic stirring; take the cross section of the continuous casting billet for macroscopic evaluation, and the requirements are that the central segregation is ≤ Class C 1.5, the central porosity is ≤ Class C 1.0, and there are no shrinkage cavities or internal cracks;

[0010] 4) Controlled rolling and cooling: Control the heating temperature to 1220-1250°C; Set the reduction ratio to ≥3.0; When the rolling temperature is above 1050°C, at least one pass reduction ratio must be ≥20%, and when the rolling temperature is below 820°C, the cumulative rolling reduction ratio must be ≥50%; After rolling, water cool to 720-680°C at a cooling rate of 1-3°C / s, and then air cool to room temperature;

[0011] 5) Normalizing: Normalizing temperature is 880±10℃, holding time is (0.4~0.5)min / mm× t ,in t is the thickness of the steel plate;

[0012] 6) Tempering: Control the tempering temperature to 600~650℃ and the holding time to (0.8~1.0)min / mm× t .

[0013] In the composition design of the present invention, C and Mn are used to improve the matrix strength, Mo, V and Cu are added to disperse and precipitate to play a precipitation strengthening role; low P and low Si are used to improve toughness, and Ni is added to toughen the α -Fe matrix, B is added at the same time and Ti is added to solid N to make B solid solution and segregate to the grain boundaries, which can inhibit the formation of grain boundary ferrite, thereby preventing the appearance of upper bainite and widmanstattenite which are extremely detrimental to toughness; Mg is added and the Al content is controlled to form fine MgO. MgO particles can promote the formation of acicular ferrite in the crystal and refine the grains, thereby improving the strength and toughness of the steel. In process design, the oxidizability of molten steel is controlled when Mg is added to generate a sufficient amount of fine MgO; at the same time, the timing of adding Al, Mg, Ca, B, etc. is controlled to control the shape and size of oxides and nitrides; moderate superheat is used in continuous casting, if the superheat is too high, central segregation and central porosity will be serious, if the superheat is too low, dendritic segregation and banded structure will be serious; the degree of reduction in the controlled rolling and controlled cooling process is adjusted, on the one hand, the core of the steel plate can be deformed to a certain extent and pressed loose, and on the other hand, fine structure can be obtained before the steel plate is heat treated; the present invention adopts normalizing + tempering heat treatment, which makes the matrix structure fine and uniform while reducing the banded structure, and makes the precipitates dispersed and finely distributed, thereby obtaining good comprehensive mechanical properties.

[0014] The beneficial effects of the present invention are as follows: (1) The present invention controls the carbon equivalent CEV≤0.54%, and adopts low P, low Si, and adds alloys such as high Ni and Cu, so that the steel plate has good weldability and weldability. At the same time, the steel plate is added with trace alloys such as B, V, and Mg, so that it has high strength and toughness and low yield strength ratio: yield strength ≥460MPa, tensile strength ≥570MPa, elongation after fracture ≥18%, yield strength ratio ≤0.83, and impact absorption energy at 0℃ ≥47J; (2) The present invention adopts normalizing + tempering for delivery, and the uniformity of the steel plate structure and performance is high. Even for a 150mm thick steel plate, the strength differences at the surface, 1 / 4 thickness, and 1 / 2 thickness are all within 30MPa; (3) The steel plate of the present invention can achieve a high heat input of 30~50kJ / cm for welding, has good welding performance, and significantly improves welding efficiency; (4) The production method adopted by the present invention is easy to implement under existing equipment conditions and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 、 Figure 2 、 Figure 3 These are the metallographic structures of the steel plate surface, 1 / 4 thickness and 1 / 2 thickness of Example 1. DETAILED DESCRIPTION Example 1

[0016] A method for producing a Q460GJ thick steel plate, wherein the steel plate has a thickness of 150 mm and a weight percentage composition of the steel: C=0.20%, Si=0.07%, Mn=1.45%, P=0.007%, S=0.003%, Al=0.012%, Cu=0.44%, Ni=0.42%, Mo=0.09%, Ti=0.018%, V=0.065%, Mg=0.0020%, B=0.0018%, N=0.0036%, and the remainder is Fe and unavoidable impurity elements. The carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15=0.54%. The key process steps include:

[0017] 1) Smelting: After pretreatment to remove sulfur from the molten iron, it is smelted in a converter. When about 1 / 3 of the steel is tapped, aluminum iron, metallic manganese, nickel plate, copper plate, ferromolybdenum, etc. are added for deoxidation and alloying. After tapping, the oxygen content in the molten steel is 80ppm. Then, argon is blown from the bottom of the ladle and stirred for 6 minutes before being transported to the LF station for refining;

[0018] 2) Refining: After the LF makes alkaline slag to remove sulfur, aluminum particles are added for diffusion deoxidation to make the oxygen content in the molten steel 42ppm. At this time, special alloy cored wire containing elements such as Mg is fed. After standing for 3 minutes, Al wire is fed to control the composition and Ca treatment is performed. Finally, B iron is added before the LF leaves the station. After LF refining, RH vacuum treatment is used.

[0019] 3) Continuous casting: Fully protected pouring was used, with superheat controlled at 15-16°C. Soft reduction was used in the secondary cooling zone, but electromagnetic stirring was not used. Macroscopic evaluation of the cross-section of the continuously cast slab revealed a central segregation of Class C 1.0, a central porosity of Class C 1.0, and no shrinkage cavities or internal cracks.

[0020] 4) Controlled rolling and controlled cooling: The heating temperature is controlled at 1235°C; the reduction ratio is 3.0; the maximum pass reduction is 21.2% when the rolling temperature is above 1050°C; there are 6 rolling passes with a rolling temperature below 820°C, with a cumulative reduction of 52.4%; after rolling, the steel is water-cooled to 720-680°C at a cooling rate of about 1.2°C / s, and then air-cooled to room temperature;

[0021] 5) Normalizing: Normalizing temperature is 880±10℃, holding time is 70min;

[0022] 6) Tempering: Control the tempering temperature to 640±10℃ and the holding time to 140min. Example 2

[0023] A method for producing a Q460GJ thick steel plate, wherein the steel plate has a thickness of 120 mm and a weight percentage composition of the steel: C=0.19%, Si=0.08%, Mn=1.42%, P=0.007%, S=0.004%, Al=0.011%, Cu=0.45%, Ni=0.35%, Mo=0.10%, Ti=0.017%, V=0.055%, Mg=0.0018%, B=0.0021%, N=0.0032%, with the remainder being Fe and unavoidable impurity elements, wherein the carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15=0.52%. The key process steps include:

[0024] 1) Smelting: After pretreatment to remove sulfur from the molten iron, it is smelted in a converter. When about 1 / 3 of the steel is tapped, aluminum iron, metallic manganese, nickel plate, copper plate, ferromolybdenum, etc. are added for deoxidation and alloying. After tapping, the oxygen content in the molten steel is 75ppm. Then, argon is blown from the bottom of the ladle and stirred for 7 minutes before refining begins at the LF station.

[0025] 2) Refining: After the LF makes alkaline slag to remove sulfur, aluminum particles are added for diffusion deoxidation to make the oxygen content in the molten steel 45ppm. At this time, special alloy cored wire containing elements such as Mg is fed. After standing for 3 minutes, Al wire is fed to control the composition and Ca treatment is performed. Finally, B iron is added before the LF leaves the station. After LF refining, RH vacuum treatment is used.

[0026] 3) Continuous casting: Fully protected pouring was used, with superheat controlled at 16°C. Soft reduction was used in the secondary cooling zone, but electromagnetic stirring was not used. Macroscopic evaluation of the cross-section of the continuously cast slab revealed a central segregation of Class C 1.5, a central porosity of Class C 1.0, and no shrinkage cavities or internal cracks.

[0027] 4) Controlled rolling and controlled cooling: The heating temperature is controlled at 1230°C; the reduction ratio is 3.75; the maximum pass reduction is 23.2% when the rolling temperature is above 1050°C; there are 7 rolling passes with a rolling temperature below 820°C, and the cumulative reduction is 63.8%; after rolling, the steel is water-cooled to 720-680°C at a cooling rate of about 1.6°C / s, and then air-cooled to room temperature;

[0028] 5) Normalizing: Normalizing temperature is 880±10℃, holding time is 50min;

[0029] 6) Tempering: Control the tempering temperature to 630±10℃ and the holding time to 100min. Example 3

[0030] A method for producing a Q460GJ thick steel plate, wherein the steel plate has a thickness of 80 mm and a weight percentage composition of the steel: C=0.18%, Si=0.09%, Mn=1.28%, P=0.006%, S=0.003%, Al=0.014%, Cu=0.40%, Ni=0.31%, Mo=0.08%, Ti=0.017%, V=0.045%, Mg=0.0022%, B=0.0017%, N=0.0035%, with the remainder being Fe and unavoidable impurity elements, wherein the carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15=0.48%. Key process steps include:

[0031] 1) Smelting: After pretreatment to remove sulfur from the molten iron, it is smelted in a converter. When about 1 / 3 of the steel is tapped, aluminum iron, metallic manganese, nickel plate, copper plate, ferromolybdenum, etc. are added for deoxidation and alloying. After tapping, the oxygen content in the molten steel is 92ppm. Then, argon is blown from the bottom of the ladle and stirred for 5 minutes before refining begins at the LF station.

[0032] 2) Refining: After the LF makes alkaline slag to remove sulfur, aluminum particles are added for diffusion deoxidation to reduce the oxygen content in the molten steel to 36ppm. At this time, special alloy cored wire containing elements such as Mg is fed, and then it is allowed to stand for 3 minutes before feeding Al wire to control the composition and Ca treatment. Finally, B iron is added before the LF leaves the station. After LF refining, RH vacuum treatment is used.

[0033] 3) Continuous casting: Fully protected pouring was used, with superheat controlled at 15°C. Soft reduction was used in the secondary cooling zone, but electromagnetic stirring was not used. A cross-section of the continuously cast slab was taken for macroscopic evaluation, and the central segregation was Class C 0.5, the central porosity was Class C 0.5, and there were no shrinkage cavities or internal cracks.

[0034] 4) Controlled rolling and controlled cooling: The heating temperature is controlled at 1232°C; the compression ratio is 4.375; the maximum pass reduction is 24.5% when the rolling temperature is above 1050°C; there are 5 rolling passes with a rolling temperature below 820°C, with a cumulative reduction of 55.5%; after rolling, the steel is water-cooled to 720-680°C at a cooling rate of about 2.3°C / s, and then air-cooled to room temperature;

[0035] 5) Normalizing: Normalizing temperature is 880±10℃, holding time is 35min;

[0036] 6) Tempering: Control the tempering temperature to 615±10℃ and the holding time to 80min.

[0037] Mechanical property testing was performed on the surface, 1 / 4 thickness, and 1 / 2 thickness of the example steel plate. The results are shown in Table 1. It can be seen that the example steel plate has good strength and toughness and a low yield strength ratio. The performance difference along the thickness of the steel plate is small, and the yield strength and tensile strength fluctuations are all within 30 MPa. Figure 1 、 Figure 2 and Figure 3 The metallographic structures of the surface, 1 / 4 thickness and 1 / 2 thickness of the steel plate of Example 1 are shown respectively. It can be seen that the microstructure of the steel plate of Example 1 is uniform throughout the thickness direction, mainly composed of fine ferrite and pearlite, with a grain size of 9-10.

[0038] Welding procedure qualification tests were conducted on the steel plates of Example 1. Solid-wire gas shielded arc welding (GMAW) was used for butt welding, with a single V-groove and a heat input of 30 to 50 kJ / cm. Tensile and impact tests were also conducted, and the results are shown in Table 2.

[0039] Table 1 Mechanical properties test results of steel produced in Example

[0040] .

[0041] Table 2 Tensile and impact test results of steel produced in Example

[0042] .

[0043] Table 2 It can be seen that the Q460GJ thick steel plate developed by the present invention has good welding performance, the impact toughness of the coarse-grained zone in the heat-affected zone and the strength of the fine-grained zone in the heat-affected zone have not been significantly deteriorated, and high heat input welding can be achieved.

Claims

1. A method for producing Q460GJ thick steel plate with a thickness of 80-150 mm, characterized by: The weight percentage of steel is C=0.18%~0.20%, Si≤0.10%, Mn=1.20%~1.50%, P≤0.008%, S≤0.005%, Al=0.008%~0.015%, Cu=0.30%~0.50%, Ni=0.30%~0.50%, Mo=0.08%~0.10%, Ti=0.015%~0.020%, V=0.04%~0.08%, Mg =0.0010%~0.0025%, B=0.0012%~0.0025%, N≤0.0040%, the balance being Fe and unavoidable impurity elements, carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.54%; the steel's yield strength ≥460MPa, tensile strength ≥570MPa, elongation after fracture ≥18%, yield strength ratio ≤0.83, and impact energy absorbed at 0℃ ≥47J; The key process steps include: 1) Smelting: After pretreatment to remove sulfur from the molten iron, it is smelted in a converter. During the tapping process, aluminum iron, metallic manganese, nickel plate, copper plate, and ferromolybdenum are added for deoxidation and alloying. After tapping, the oxygen content in the molten steel is controlled to O=50~100ppm. Then, argon is blown from the bottom of the ladle and stirred for more than 5 minutes before refining. 2) Refining: After the LF makes alkaline slag and removes sulfur, aluminum particles are added for diffusion deoxidation to control the oxygen content in the molten steel between O=30~50ppm. At this time, Mg alloy cored wire is fed, and after standing for 3 minutes, Al wire is fed to adjust the composition, and then Ca treatment is performed. B iron is added before the LF leaves the station. After LF refining, RH vacuum treatment is used. 3) Continuous casting: Use full-process protective pouring, control the superheat at 12-18°C, use soft reduction in the secondary cooling zone but do not use electromagnetic stirring; take the cross section of the continuous casting billet for macroscopic evaluation, and the requirements are that the central segregation is ≤ Class C 1.5, the central porosity is ≤ Class C 1.0, and there are no shrinkage cavities or internal cracks; 4) Controlled rolling and cooling: Control the heating temperature to 1220-1250°C; Set the reduction ratio to ≥3.0; When the rolling temperature is controlled to be above 1050°C, at least one pass reduction ratio must be ≥20%, and when the rolling temperature is controlled to be below 820°C, the cumulative rolling reduction ratio must be ≥50%; After rolling, water cool to 720-680°C at a cooling rate of 1-3°C / s, and then air cool to room temperature; 5) Normalizing: Normalizing temperature is 880±10℃, holding time is (0.4~0.5)min / mm× t ,in t is the thickness of the steel plate; 6) Tempering: Control the tempering temperature to 600~650℃ and the holding time to (0.8~1.0)min / mm× t .

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