Flame-resistant shape-easily-adjustable hot-continuous-rolled high-strength open flat plate, and production method therefor and use thereof

Abstract

Disclosed in the present invention are a flame-resistant shape-easily-adjustable hot-continuous-rolled high-strength open flat plate, and a production method therefor and the use thereof. The open flat plate comprises the following chemical components in percentages by weight: C: 0.10-0.18%, Si≤0.095%, Mn: 0.8-1.50%, P≤0.020%, S≤0.010%, Ti: 0.010-0.025%, Nb: 0.005-0.025%, Al: 0.015-0.060%, Mg: 0.0002-0.0022%, and the balance of Fe and inevitable impurities. The preparation steps comprise smelting, plate blank heating, hot continuous rolling, laminar cooling, coiling and straightening transverse cutting. The open flat plate of the present invention has high strength and high toughness, and a low yield ratio, and is beneficial for flame correction after deformation; and the local plate shape is easy to adjust after welding. The open flat plate serving as steel for a ship hull structure improves the high-temperature flame-resistance and the client-side shape-adjustable performance of a ship plate.

Description

Fire-resistant easy-shaping hot continuous rolling high-strength flat plate and production method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the field of micro-alloyed steel manufacturing, and particularly relates to a fire-resistant easy-shaping hot continuous rolling high-strength flat plate and a production method and application thereof. BACKGROUND

[0002] In the shipbuilding process, a large amount of micro-alloyed steel plates are used, and the plates are involved in shaping, welding and fire treatment during the manufacture of the ship body. The post-welding fire strength of ordinary micro-alloyed steel plates is prone to decrease. Some steel plates are shaped by fire, but the shaping process is difficult. In the process of splicing the thin-gauge ship plates, the welding workload of the spliced plates is large, and the welding deformation problem is prominent. After deformation, the fire shaping task is heavy, and there are problems such as difficult shaping in the conventional high-strength plate shaping process. The yield ratio represents the ability of uniform deformation of the material, the deformation capacity from plastic deformation to final fracture, and is also a kind of ability to resist from yield to plastic deformation. A lower yield ratio has good plastic deformation capacity, is beneficial to post-deformation fire correction, has large correction operability, is not easy to deform out of control, and has a good guarantee effect on the stability of the ship body structure.

[0003] Moreover, at present, the single-rolled plates produced by the medium plate production line are generally used for ship body manufacturing, but the medium plate production line produces thin plates below 10 mm, and the production efficiency is low and the plate shape precision is poor.

[0004] Under the above background, the inventors propose that the high-strength flat plate steel produced by the hot continuous rolling production line is used as structural steel instead of the medium plate production line, and therefore the present application provides a fire-resistant, easy-to-shape, low-yield-ratio, high-strength plate especially suitable for ship body structure, i.e., the fire-resistant easy-shaping hot continuous rolling high-strength flat plate, to solve the problems of the micro-alloyed steel for ship body structure in fire and shaping in the prior art. SUMMARY

[0005] In view of the above-mentioned deficiencies in the prior art, the present application provides a fire-resistant easy-shaping hot continuous rolling high-strength flat plate and a production method thereof. The obtained flat plate has high strength and high toughness, and a low yield ratio, which is beneficial to post-deformation fire correction, and the post-welding local plate shape is good and easy to shape, thereby improving the high-temperature fire resistance and customer-shapeability of the plate.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] The application discloses a kind of anti-firework easily adjustable shape hot continuous rolling high-strength flat plate, and chemical components are as follows according to percentage by weight: C 0.10%~0.18%, Si≤0.095%, Mn 0.8%~1.50%, P≤0.020%, S≤0.010%, Ti 0.010%~0.025%, Nb 0.005%~0.025%, Al 0.015~0.060%, Mg 0.0002%~0.0022%, the balance is Fe and inevitable impurities.

[0008] According to the above scheme, the yield strength R eH Or R p0.2 ≥390MPa, tensile strength Rm 510~630MPa, yield ratio≤0.79, elongation≥21%, impact energy≥34J. Preferably, the impact is low temperature impact, i.e. impact energy≥34J at different temperatures of 0℃, -20℃, -40℃, -60℃.

[0009] According to the above scheme, the flat plate has a levelness of ≤3mm / m.

[0010] The mechanism of action of each alloying element in the steel is as follows:

[0011] The carbon (C) content of the application is 0.10%~0.18%. Carbon is one of the indispensable elements for increasing the strength of steel, and is the main alloying element for forming pearlite in steel. It can also form micro-alloy carbides with Ti, Nb, etc. in steel to play a precipitation strengthening role. Since the steel of the application contains a certain amount of Nb and Ti, a certain amount of carbon is needed to form NbC and TiC. Therefore, the carbon content is limited to 0.08~0.18%, which can not only increase the strength of the steel, but also stabilize the amount and volume fraction of pearlite at high temperature, ensuring the mechanical strength at high temperature, especially for reducing the influence of high-temperature firework on performance.

[0012] The manganese (Mn) content of the application is 0.8%~1.50%, which can reduce the phase transition temperature of austenite to ferrite, expand the hot working temperature range, and is beneficial to the control of plate shape and the refinement of ferrite grain size, thereby improving the yield strength and tensile strength of the steel.

[0013] The phosphorus (P) content of the application is ≤0.020%, and the sulfur (S) content is ≤0.010%. Phosphorus has adverse effects in steel, such as causing segregation and reducing impact performance. Sulfur easily combines with manganese to form MnS inclusions, affecting the impact performance and plasticity of the steel. Therefore, the application should minimize the adverse effects of phosphorus and sulfur on the performance of the steel, control the content of phosphorus and sulfur by deep desulfurization pretreatment of molten iron, and thereby reduce the adverse effects.

[0014] The silicon (Si) content of the present application is ≤0.095%. Si is dissolved in the steel, and moderate Si has a solid solution strengthening effect, and when the silicon content is too high, it will cause the material surface to be gray, and therefore, in order to ensure the smooth surface of the steel plate, the Si content in the steel is controlled to be ≤0.095%.

[0015] The titanium (Ti) content of the present application is selected to be 0.010% to 0.025%. Titanium is a strong carbide and nitride forming element, which prevents the growth of austenite grains during reheating and high-temperature austenite zone rough rolling, and the fine and dispersed TiC precipitated during rolling and cooling of the steel plate can have a significant precipitation strengthening effect. Therefore, the present application steel adopts a certain Ti content, thereby effectively improving the strength of the steel plate, and in addition, a certain Ti content has a grain coarsening inhibition effect during the welding process of the steel plate.

[0016] The magnesium (Mg) content of the present application is selected to be 0.0002% to 0.0022%. Mg is a micro-alloying and modification element participating in inclusion treatment, and a large amount of hard Al2O3 inclusions is generated during the steelmaking process, which is easy to gather and grow into clusters, and is distributed in the rolling direction after rolling, which seriously endangers the mechanical, corrosion, and fatigue properties of the steel. The present application uses the combined effect of Mg and Ti, Mn, S, and other elements to modify the micro-alloying of Al2O3 inclusions, reduce the size and type of large-size Al2O3 inclusions. During the steelmaking process, small, hard, and spinel-type hard oxides are formed, and during the solidification process of the molten steel, the soft sulfide wraps the hard oxide, and this kind of small-size hard-core soft-interface inclusion distributed in dispersion greatly improves the mechanical, corrosion, and fatigue properties of the steel, and also reduces the yield strength ratio to a certain extent. In the welding or pyrotechnic process, it is also beneficial to inhibit the growth of the structure and improve the strength and toughness.

[0017] The niobium (Nb) content of the present application is 0.005% to 0.035%. A small amount of niobium can significantly refine the grain size and improve the tensile strength of the present application steel. During controlled rolling, niobium can increase the recrystallization temperature of the steel, reduce the rolling load, and be beneficial to the control of the plate shape. At the same time, by inhibiting recrystallization and preventing grain growth, the austenite grain size can be refined. During the cooling process after rolling, NbC and NbN microparticles are precipitated, which can have a precipitation strengthening effect.

[0018] The aluminum (Al) content of the present application is 0.015 to 0.060%, which mainly functions to remove oxygen (O) from the molten steel and prevent titanium from being oxidized and losing effectiveness; a small amount of Al also has a certain effect of refining the grain size.

[0019] The performance design of the present application steel is yield strength R eH / R p0.2≥390MPa, tensile Rm 510~630MPa, yield ratio ≤0.79, elongation ≥21, (0℃, -20℃, -40℃, -60℃) different temperature impact energy ≥34J, can meet the demand of 355MPa, 395MPa grade AH, DH, EH, FH and other multiple brand high-strength high-toughness ship plate.

[0020] The application also provides a production method of the above fire-resistant easy-to-shape hot continuous rolling high-strength flat-rolled plate, which comprises the steps of smelting, slab heating, hot continuous rolling, laminar flow cooling, coiling and straightening and cross cutting.

[0021] According to the above scheme, in the slab heating step, the slab heating temperature is set to 1150~1250℃, and the temperature is kept for 1~3 hours, so that the alloy elements are fully solid-solved through high-temperature heating, the strength of the steel plate is effectively improved, and the slab temperature is uniform.

[0022] According to the above scheme, in the hot continuous rolling step, the rough rolling end temperature is 950~1050℃, and the reduction is 70%~90%, so that the original austenite grains are fully recrystallized through high-temperature large deformation, the grains are uniform and small, and the organizational stress caused by uneven organization is reduced; and the finish rolling final rolling temperature is 810~900℃.

[0023] According to the above scheme, in the laminar flow cooling step, the steel plate is cooled by cold laminar flow after rolling, so as to ensure the mechanical properties through controlling the organization transformation, and ensure the mechanical uniformity and plate shape quality of the whole coil through uniform cooling.

[0024] According to the above scheme, in the coiling step, the coiling temperature is 550~700℃.

[0025] According to the above scheme, in the straightening and cross cutting step, the steel coil is straightened and cut into plates, and the unevenness of the treated steel plate reaches ≤3mm / m.

[0026] The above fire-resistant easy-to-shape hot continuous rolling high-strength flat-rolled plate provided by the application can be used as a ship plate in the ship structure, and is especially used as a ship plate of an ocean-going ship.

[0027] The beneficial effects of the application are as follows:

[0028] 1. The application provides a fire-resistant easy-to-shape hot continuous rolling high-strength flat-rolled plate, which adopts a medium-high carbon low-silicon micro-niobium magnesium alloy system, has the characteristics of high strength and high toughness and low yield ratio, and can meet the demand of 355MPa, 395MPa grade AH, DH, EH, FH and other multiple brand high-strength high-toughness ship plates.

[0029] 2. This invention provides a method for producing hot-rolled high-strength slab plates that are resistant to pyrotechnics and easily reshapeable. Through a C-Si-Mn-Nb-Mg-Ti alloy composition design, the core-shell morphology of inclusions in the finished steel product is guaranteed, thereby improving the crack-arresting and toughening properties of the steel plate. Simultaneously, by combining the process steps of "slab heating, hot rolling, straightening, and cross-cutting," a high-slab plate with high surface finish, unevenness ≤3mm, and low yield strength ratio is produced, exhibiting high strength and high toughness, and possessing pyrotechnic resistance. The low yield strength ratio of the slab plate described in this invention facilitates pyrotechnic reshaping after localized deformation occurs during narrow splicing. Furthermore, the pyrotechnic mechanical properties of the slab plate ensure that it does not undergo significant changes during localized or even high-temperature pyrotechnic processes. This enables the application of hot-rolled high-strength slab plates for ocean-going vessels, solving the problems of significant welding deformation during the splicing of thin-gauge hull plates, and the heavy and difficult pyrotechnic reshaping task after deformation. Attached Figure Description

[0030] Figure 1 shows the microstructure of the upper, middle and lower surfaces (corresponding to left, middle and right) of the steel plate obtained in Example 1.

[0031] Figure 2 shows the morphology of inclusions in the finished flat plate produced in Example 2.

[0032] Figure 3 is a schematic diagram of the crack arrest and toughening of inclusions in the finished open plate produced by the present invention under stress field.

[0033] Figure 4 shows the surface of the steel plate obtained in Example 3.

[0034] Figure 5 shows the surface of the steel plate obtained in Comparative Example 1.

[0035] Figure 6 shows the surface of the steel plate obtained in Example 3 after it has been used to form the hull steel plate.

[0036] Figure 7 shows the surface of the steel plate obtained in Comparative Example 1 after it has been used to form the hull steel plate. Detailed Implementation

[0037] To better explain the present invention, the present invention will be further described in detail below with reference to specific embodiments, but the content of the present invention is not limited to the following embodiments.

[0038] For the present application, the provided anti-fire easy-to-adjust hot continuous rolling high-strength sheet, the chemical composition in terms of percentage by weight is: C 0.10%~0.18%, Si≤0.095%, Mn 0.8%~1.50%, P≤0.020%, S≤0.010%, Ti 0.010%~0.025%, Nb 0.005%~0.025%, Al 0.015~0.060%, Mg 0.0002%~0.0022%, the balance being Fe and unavoidable impurities, the key steps of the production method and its characteristic process parameters include:

[0039] In the slab heating step, the slab heating temperature is set to 1150~1250℃, and the holding time is 1~3 hours;

[0040] In the hot continuous rolling step, the rough rolling end temperature is 950~1050℃, and the reduction is 70%~90%; the finish rolling final rolling temperature is 810~900℃;

[0041] In the coiling step, the coiling temperature is 550~700℃;

[0042] In the straightening and cross-cutting step, the steel coil is straightened and cut into sheets, and the treated steel plate reaches a levelness of≤3mm / m.

[0043] In the following examples, the production method of the anti-fire easy-to-adjust hot continuous rolling high-strength sheet, the specific steps are as follows:

[0044] (1) Smelting: using blast furnace molten iron or electric furnace scrap steel as raw material, decarburizing and dephosphorizing treatment in converter or electric furnace, then LF deep deoxidizing and desulfurizing treatment of molten steel in ladle furnace, followed by alloying and alloy fine adjustment, after alloy addition and composition adjustment, Mg alloy modification treatment is carried out on the molten steel to reach the target composition (i.e. to reach the chemical composition of sheet, for each example, it is to reach the target composition of Table 1, which can be achieved by conventional smelting operation to reach the target composition), then low superheat (10~40℃) protective atmosphere continuous casting is carried out to obtain slab (the slab center segregation is required to be≤0.5 level).

[0045] (2) Slab heating: after the above continuous casting production, the slab is directly loaded into the heating furnace for soaking after cutting, the heating temperature is set to 1150~1250℃, and the holding time is 1~3 hours, the heating furnace time is not less than 120 minutes (the time in the heating furnace includes the time from the loading temperature to the set heating temperature, and the holding time, here it means that the total time in the furnace from loading to the end of holding is not less than 120 minutes; and if the loading temperature is lower than 600℃, the holding time is at least 2 hours).

[0046] (3) Hot continuous rolling: the heated slab is subjected to hot continuous rolling, and is subjected to 5-7 passes of large deformation rough rolling (7 passes of rough rolling are specifically adopted in each example and the comparative example), the reduction per pass is between 10-15%, the total reduction is 70%-90%, the rough rolling end temperature is 950-1050℃, and the thickness of the intermediate slab after rough rolling is 30-60mm (the thickness of the intermediate slab in each example and the comparative example is specifically 40mm); then the intermediate slab is subjected to 5-7 passes of finish rolling (7 passes of finish rolling are specifically adopted in each example and the comparative example), the reduction per pass is greater than 10-12%, and the finish rolling temperature is 810-900℃.

[0047] (4) Laminar cooling: after finish rolling, laminar cooling is adopted to obtain uniform pearlite + ferrite structure, prevent the proportion of large-size ferrite in the structure from increasing greatly, the cooling rate is 8-12℃ / s, and the final cooling temperature is the coiling temperature 550-700℃.

[0048] (5) Coiling: after laminar cooling, the steel coil is rapidly coiled by a coiler, the coiling temperature is 550-700℃, and then the steel coil is transferred to a heat preservation room for slow cooling.

[0049] (6) Straightening and cross cutting: after the steel coil is slowly cooled to 100℃, the steel coil is opened and cross cut, and the opening is used as the criterion; in the straightening process, the opened steel coil is reversely bent, and the upward bending of the short part of the steel plate is greater than or equal to 100mm; then multi-roll fine straightening is performed to control the levelness of the steel plate to be less than or equal to 3mm / m; finally, the steel plate is cut to a fixed size by a cutting mechanism.

[0050] The production method of each example and the comparative example is carried out according to the above steps, and the characteristic process parameters of the key steps are shown in Table 2. Examples 1-6

[0051] The chemical composition and mass percentage of the fire-resistant easy-to-shape hot continuous rolling high-strength open flat plate in the examples 1-6 of the present application are shown in Table 1, and the balance is Fe and unavoidable impurities.

[0052] The production process of the hot-rolled ship plate includes smelting, slab heating, hot continuous rolling, laminar cooling, coiling and straightening and cross cutting, wherein: in the slab heating step, the slab heating temperature is set to 1150-1250℃, and the temperature is maintained for 1-3 hours, the alloy elements are fully solid-solved through high-temperature heating, the strength of the steel plate is effectively improved, and the slab temperature is uniform.

[0053] In the hot continuous rolling step, the rough rolling end temperature is 950-1050℃, and the reduction is 70%-90%, the original austenite grains are fully recrystallized through large deformation at high temperature, the grains are uniform and small, and the stress caused by uneven structure is reduced; the finish rolling temperature is 810-900℃;

[0054] In the laminar cooling step, the steel plate is cooled by laminar cooling after rolling, and the mechanical properties are ensured by controlling the microstructure transformation, and the mechanical uniformity and shape quality of the whole coil are ensured by uniform cooling.

[0055] In the coiling step, the coiling temperature is 550-700℃.

[0056] Once straightening and sizing cutting: the steel coil is straightened and cut, and the unevenness of the treated steel plate can reach ≤3mm / m.

[0057] Finally, the package is delivered.

[0058] The process parameters of the production method of the embodiments 1-6 of the present application and the properties of the obtained Q235B steel plates are shown in Table 2, and the product thickness of the final Q235B steel plate is 6mm. Comparative examples 1-2

[0059] The chemical composition and mass percentage of the Q235B steel plate in the comparative examples 1-2 are shown in Table 1 (the balance is Fe and unavoidable impurities), and the production method is the same as the embodiments, and the process parameters of the production method and the properties of the obtained Q235B steel plate are shown in Table 2.

[0060] Table 1. Chemical composition of the steel in the embodiments 1-6 and the comparative examples 1-2 (wt%)

[0061]

[0062] Table 2. Process parameters in the embodiments 1-6 and the comparative examples 1-2

[0063]

[0064] Table 3. Performance test results in the embodiments 1-6 and the comparative examples 1-2

[0065]

[0066] Note: In Table 3, the yield strength, tensile strength, elongation, shape unevenness and-60℃ impact energy are measured according to the “Material and Welding Specification 2023” of China Classification Society; in addition, the yield strength and tensile strength ratio is the ratio of the yield strength and the tensile strength, Rm 火工 refers to the tensile strength after 700℃ fire, Rm-Rm 火工 refers to the difference between the tensile strength before and after 700℃ fire.

[0067] As can be seen from Table 3, the anti-fire easy-shaping hot continuous rolling high-strength Q235B steel plate of the present application has a yield strength R eH or R p0.2 The yield strength is greater than 390 MPa, the tensile strength Rm is 540-584 MPa, the yield strength ratio is less than or equal to 0.79, the elongation is greater than or equal to 23.9%, the impact energy at different temperatures (0 DEG C, -20 DEG C, -40 DEG C, -60 DEG C) is greater than or equal to 110 J, and the plate flatness is less than or equal to 3 mm / m, which can meet the requirements of multiple grades of ship plates such as 355 MPa, 395 MPa grade AH, DH, EH and FH. Among them, taking AH40 as an example, the mechanical property requirements are yield strength greater than or equal to 390 MPa, tensile strength 510-660 MPa, and 0 DEG C impact energy greater than or equal to 41 J; and the physical properties of the application are better, which can meet the requirements of multiple grades such as AH36-FH40.

[0068] Comparative examples 1 and 2 use a low-carbon high-Si high-Nb composition system, and the basic process route is the same, but the coiling temperature after rolling is lower, and the bainite type of microstructure appears in the microstructure transformation process after rolling, which causes the yield strength and yield strength ratio of the physical properties to be much higher than those of the examples. The low yield strength ratio of the application is beneficial to the splicing and forming of the local deformation of the narrow part, and it is convenient to adjust the shape by using a fire.

[0069] From the comparison of the physical steel plates of the examples and the comparative examples (see Figures 4-7), the steel plate of example 3 in the open flat state is shown in Figure 4, and the surface of the ship body steel plate after forming is shown in Figure 6; the steel plate of comparative example 1 in the open flat state is shown in Figure 5, and the surface of the ship body steel plate after forming is shown in Figure 7. Compared with each other, there is a big difference in surface state and forming application performance, and the surface of the comparative example is relatively serious. The surface of the steel plate after forming is relatively poor.

[0070] Moreover, from the comparison of the fire test data at 700 DEG C, after the fire test, the tensile strength of the example decreases by 10-15 MPa; and the tensile strength of the comparative example decreases by 30-31 MPa. The example has obvious fire resistance mechanical guarantee capability, which ensures the ability of the open flat plate not to change significantly under local fire or high temperature fire.

[0071] It should be understood that those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the application.

Claims

1. A fire resistant, exothermic, high strength, open sheet, which is tailor rolled, characterized in that, The chemical composition of the open flat plate is as follows in terms of percentage by weight: C 0.10%-0.18%, Si≤0.095%, Mn 0.8%-1.50%, P≤0.020%, S≤0.010%, Ti 0.010%-0.025%, Nb 0.005%-0.025%, Al 0.015-0.060%, Mg 0.0002%-0.0022%, and the balance of Fe and inevitable impurities.

2. The fire resistant exothermic shape high strength high flat plate of claim 1, wherein, The yield strength of the open flat plate is ≥390 MPa, the tensile strength is 510-630 MPa, the elongation is ≥21%, and the impact energy is ≥34 J.

3. The fire resistant, exothermic, shapeable, high strength, rolled sheet of claim 1, wherein, The yield strength of the open flat plate is ≥390 MPa, the tensile strength is 510-630 MPa, the elongation is ≥21%, and the impact energy is ≥34 J.

4. The fire resistant, exothermic, shapeable, hot rolled high strength sheet of claim 1, wherein, The levelness of the open flat plate is ≤3 mm / m.

5. A method of producing the fire resistant, exothermic, shapeable, high strength, high ductility, and flat-rolled sheet of claim 1, wherein, The steps include smelting, slab heating, hot continuous rolling, laminar cooling, coiling and straightening cross-cutting.

6. The production method according to claim 5, characterized by, In the slab heating step, the slab heating temperature is set to 1150-1250℃, and the holding time is 1-3 hours.

7. The production method according to claim 5, characterized by, In the hot continuous rolling step, the rough rolling end temperature is 950-1050℃, and the reduction is 70%-90%; the finish rolling final rolling temperature is 810-900℃.

8. The production method according to claim 5, characterized by, In the coiling step, the coiling temperature is 550-700℃.

9. The production method according to claim 5, characterized by, In the straightening cross-cutting step, the steel coil is straightened and cut into plates, and the treated steel plate has a levelness of ≤3 mm / m.

10. Application of the fire-resistant workable hot continuous rolling high-strength open flat plate of claim 1 as a ship plate in a ship body structure.

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