High-strength steel with obvious yield point and low yield ratio and manufacturing method of high-strength steel

Abstract

The invention discloses high-strength steel with an obvious yield platform and a low yield ratio and a manufacturing method thereof. The high-strength steel comprises the following chemical components in percentage by weight: 0.14-0.20% of C, 0.45-1.20% of Si, 0.6-1.6% of Mn, less than or equal to 0.015% of P, less than or equal to 0.0050% of S, 0.05-1.20% of Cr, less than or equal to 0.20% of Ni, less than or equal to 0.10% of Mo, less than or equal to 0.20% of Cu, less than or equal to 0.30% of W, 0.01-0.06% of Al, less than or equal to 0.02% of Nb, less than or equal to 0.1% of V, 0.006-0.015% of Ti, 0.0005-0.0030% of Mg and the balance of Fe and other inevitable impurities. 0.5 < = alpha < = 0.8 and 780 < = beta < = 800 are simultaneously satisfied. The high-strength steel has high strength and also has an obvious yield platform and low-yield-ratio tensile property, the yield strength of the high-strength steel is larger than or equal to 460 MPa, the tensile strength is 570-720 MPa, the ductility is larger than or equal to 18%, the impact energy at the temperature of-20 DEG C is larger than or equal to 200 J, the yield ratio is smaller than or equal to 0.83, and the high-strength steel can be used for construction of high-rise and large-span building steel structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-alloy high-strength steel, and particularly relates to a high-strength steel with an obvious yield plateau and a low yield ratio and a manufacturing method thereof. Background Art

[0002] With the rapid development of urbanization, urban buildings and infrastructure are developing towards high-rise and large-span directions. Due to the advantages of high space utilization rate, large span, and fast construction, steel structures are increasingly becoming the mainstream form of large buildings in cities. At present, with the large-scale application of steel structure buildings and the in-depth concept of low-carbon and green, high-strength steel is increasingly used in buildings, and the proportion of the output value of steel structures in the total output value of the construction industry generally shows an upward trend.

[0003] As a special steel plate for steel structure construction, high-strength steel must adapt to the complex stress conditions of high-rise building structures and resist earthquake damage. The lower the yield ratio, the higher the uniform elongation rate of the steel, that is, the ability of the steel to produce stable plastic deformation before fracture, and the more evenly the steel can distribute the plastic deformation over a wider range. Therefore, the lower the yield ratio of the steel, the better the seismic performance of the steel. Generally, it is required that the yield ratio of high-rise building steel for earthquake resistance is less than 0.83. An obvious yield plateau enables the steel to have a high plastic strain energy under the yield condition and reduces the damage caused by earthquakes.

[0004] Chinese Patent CN101613828A discloses "a super-thick building steel plate with a yield strength of 460 MPa and a low yield ratio and a manufacturing method thereof". The chemical composition of the patented steel plate in weight percentage is: C 0.14-0.18%, Si 0.35-0.45%, Mn 1.40-1.50%, Nb 0.025-0.035, V 0.040-0.050, Ti 0.010-0.020, P < 0.020%, S < 0.008%, and the rest is iron Fe. It adopts a composition design of high-carbon niobium and vanadium microalloying and is combined with a two-stage rolling and two-phase zone quenching and tempering process. The yield ratio of the produced steel plate is less than 0.72 and the performance is good. However, the quenching and tempering process has a high cost and increases the construction cost.

[0005] Chinese Patent CN104846277A discloses "A building steel with a yield strength ≥ 460 MPa and excellent resistance to lamellar tearing and its manufacturing method". The chemical composition of the building steel described in this patent is by weight percentage: C: 0.150 - 0.180%, Si: 0.25 - 0.45%, Mn: 1.45 - 1.65%, Nb: 0.035 - 0.055%, V: 0.04 - 0.06%, Ti: 0.007 - 0.015%, Ni: 0.08 - 0.15%, P ≤ 0.015%, S ≤ 0.005%, and the rest is iron and inevitable impurities, and Ti + Nb + V ≤ 0.22% is satisfied. It also adopts a high-carbon and high-niobium microalloying composition system and uses a normalizing process to produce 460 MPa grade building steel with thick specifications. However, the steel type in this patent does not have an obvious yield plateau and cannot meet the requirements of earthquake resistance.

[0006] Chinese Patent CN102400053A discloses "A steel plate for building structures with a yield strength of 460 MPa grade and its manufacturing method". The weight percentage of the chemical composition of the steel plate is: C 0.05 - 0.10%, Si 0.2 - 0.3%, Mn 1.40 - 1.60%, Nb 0.025 - 0.060%, Ti 0.015 - 0.030%, Als 0.015 - 0.045%, and it also contains one of Cr 0.2 - 0.4%, Mo 0.10 - 0.30%, B 0.0010 - 0.0020%, and the balance is Fe and inevitable impurities. This patent adopts a low-carbon, high-manganese and high-niobium composition design and uses a two-stage TMCP process for production, and the yield ratio is less than 0.80. However, the steel type in this patent does not have an obvious yield plateau and cannot meet the requirements of earthquake resistance. Summary of the Invention

[0007] The purpose of the present invention is to provide a high-strength steel with an obvious yield plateau and a low yield ratio and its manufacturing method. The steel type has an obvious yield plateau and a tensile property of low yield ratio while having high strength. Its yield strength ≥ 460 MPa, tensile strength is 570 - 720 MPa, elongation ≥ 18%, impact energy at -20 °C ≥ 200 J, and yield ratio ≤ 0.83, and it can be used for the construction of high-rise and long-span building steel structures.

[0008] To achieve the above purpose, the technical solution of the present invention is:

[0009] A high-strength steel with an obvious yield plateau and a low yield ratio, the chemical composition of which is in weight percentage: C: 0.14 - 0.20%, Si: 0.45 - 1.20%, Mn: 0.6 - 1.6%, P ≤ 0.015%, S ≤ 0.0050%, Cr: 0.05 - 1.20%, Ni ≤ 0.20%, Mo ≤ 0.10%, Cu ≤ 0.20%, W ≤ 0.30%, Al: 0.01 - 0.06%, Nb ≤ 0.02%, V ≤ 0.1%, Ti: 0.006 - 0.015%, Mg: 0.0005 - 0.0030%, and the balance includes Fe and other inevitable impurities; and it needs to satisfy simultaneously:

[0010] 0.5 ≤ α ≤ 0.8, α = C + (Mn + Si) / 6 + (Cr + Ni + Cu + Mo) / 10 + 2Nb + V;

[0011] 780 ≤ β ≤ 800, β = 810 - 230C - 21Mn - 15Ni + 32Mo + 60Si + 13W + 104V + 275P + 1522S - 20Cr - 20Cu - 1532Nb + 40Al.

[0012] Furthermore, the balance is Fe and other inevitable impurities.

[0013] The microstructure of the high-strength steel of the present invention is ferrite + pearlite, wherein the volume fraction of ferrite is 40 - 60%, the volume fraction of pearlite is 40 - 60%, the ferrite grain size is 5 - 15 microns, and the dislocation density in ferrite is 10 8 ~10 10 / cm 2 , the pearlite colony size is 10 - 20 microns, and the pearlite interlamellar spacing is 30 - 60 nm.

[0014] The yield strength of the high-strength steel of the present invention is ≥460 MPa, the tensile strength is 570 - 720 MPa, the elongation is ≥18%, the impact energy at -20 °C is ≥200 J, the yield ratio is ≤0.83, and it has an obvious yield plateau.

[0015] In the chemical composition design of the high-strength steel of the present invention:

[0016] C: The present invention adopts a high-carbon design. On the one hand, by using the interstitial strengthening and precipitation strengthening effects of carbon, it ensures that the steel plate of the invention has high strength; on the other hand, it prevents the cold and hot working properties and welding properties of the steel plate from being reduced due to excessive carbon content. Therefore, the C content in the present invention is controlled at 0.14 - 0.20%.

[0017] Si: The solid solution strengthening effect of Si is utilized to enhance the strength of the steel plate. Meanwhile, the effect of Si promoting ferrite phase transformation is used to reduce the yield ratio of high-strength steel plates. However, excessive silicon exacerbates decarburization on the steel plate surface and reduces the toughness of the steel. Therefore, in this invention, the Si content is controlled within 0.45 - 1.20%.

[0018] Mn: It is the most basic alloying element in low-alloy high-strength steel grades, and it improves the strength of the steel through solid solution strengthening. However, too high Mn content is prone to cause segregation at the center position of the steel plate and reduce the low-temperature toughness. Therefore, in this invention, the Mn content is within 0.6 - 1.6%.

[0019] P: It is an inevitable harmful impurity element in steel. Phosphorus is unevenly distributed in the steel and concentrated at grain boundaries, affecting the grain boundary structure and being prone to cold brittleness at low temperatures. Therefore, in this invention, P ≤ 0.015% is controlled.

[0020] S: It is an inevitable harmful impurity element in steel, which is prone to form defects such as segregation and inclusions, deteriorating the welding performance, impact toughness, and fatigue performance of the steel plate. Therefore, in this invention, S ≤ 0.0050% is controlled, and through inclusion modification technology, the inclusion morphology should be spheroidized, the size should be refined, and the distribution should be uniform to reduce its influence on toughness and corrosion resistance.

[0021] Cr: It can improve the strength and corrosion resistance of the steel. However, Cr is a precious metal element. Considering the cost, in this invention, the Cr content is controlled within 0.05 - 1.20%.

[0022] Ni: It can improve the strength, low-temperature toughness, and corrosion resistance of the steel plate, but the cost of adding Ni is relatively high. Therefore, in this invention, the Ni content is controlled ≤ 0.20%.

[0023] Mo: It can improve the hardenability of the steel and enhance the uniformity of properties in the thickness direction. However, too much Mo will increase the cold cracking tendency of the steel plate and also increase the cost. Therefore, in this invention, the Mo content is controlled ≤ 0.10%.

[0024] Copper Cu: Appropriately increasing the hardenability of the steel can improve the atmospheric corrosion resistance of the steel. However, too high Cu will deteriorate the welding performance of the steel. Therefore, in this invention, the Cu content is controlled ≤ 0.20%.

[0025] W: It can appropriately improve the hardenability of the steel, enhance the strength of the steel plate, and promote ferrite phase transformation. However, too high W deteriorates the processing performance and welding performance of the steel plate. Therefore, in this invention, the W content is controlled ≤ 0.30%.

[0026] Al: An element added to the steel for deoxidation. After complete deoxidation, it reduces the oxygen content in the material and improves the aging performance. In addition, an appropriate amount of Al is beneficial to refining the grains and improving the strength and toughness of the steel. Therefore, in the present invention, the Al content is controlled within 0.01 - 0.06% to meet the deoxidation requirements.

[0027] Nb: Nb is a strong carbide and nitride forming element, which enhances the strength and toughness of the steel plate through precipitation strengthening. However, excessive Nb inhibits the ferrite and pearlite phase transformations, affecting the yield ratio and yield plateau of the steel plate. Therefore, in the present invention, the Nb content is controlled ≤ 0.02%.

[0028] V: It is a strong carbide and nitride forming element, which enhances the strength and toughness of the steel plate through precipitation strengthening. However, excessive V affects the yield ratio and yield plateau of the steel plate. Therefore, in the present invention, the V content is controlled ≤ 0.1%.

[0029] Ti: It is a strong nitrogen-fixing element, which inhibits the adverse effects of excessive N content on the steel performance. At the same time, the formation of TiN precipitation phase can inhibit the excessive growth of grains during the heating process of the slab and steel plate. Therefore, in the present invention, the Ti content is controlled within 0.006 - 0.015%.

[0030] Magnesium Mg: It can improve the sulfide morphology, refine the inclusions, and enhance the corrosion resistance of the steel plate. If the Mg content is too low, it cannot play the role of inclusion modification, and if it is too high, it is easy to form excessive MgO and MgS, blocking the nozzle. Therefore, in the present invention, the Mg content is controlled within 0.0005 - 0.0030%.

[0031] Furthermore, in the high-strength steel described in the present invention, the mass percentage contents of each chemical element also meet the following requirements: 0.5 ≤ α ≤ 0.8, 780 ≤ β ≤ 800, where:

[0032] α = C + (Mn + Si) / 6 + (Cr + Ni + Cu + Mo) / 10 + 2Nb + V;

[0033] β = 810 - 230C - 21Mn - 15Ni + 32Mo + 60Si + 13W + 104V + 275P + 1522S - 20Cr - 20Cu - 1532Nb + 40Al.

[0034] For each chemical element in the formula, the value before the percentage sign of the mass percentage content of this chemical element is substituted.

[0035] The setting of the α value enables the steel to obtain a good strength and toughness match. An excessively low α value reduces the strength of the steel plate and does not meet the requirement that the yield strength is greater than 460 MPa; an excessively high α value results in high hardenability of the steel plate and reduces the toughness of the steel plate.

[0036] The setting of the β value makes the steel plate prone to ferrite phase transformation, promotes the formation of soft-phase ferrite tissue, reduces the yield ratio, and obtains an obvious tensile yield plateau.

[0037] The present invention also provides a manufacturing method of the high-strength steel with an obvious yield plateau and a low yield ratio, including the following steps:

[0038] 1) Smelting and continuous casting

[0039] Smelt according to the above composition and cast into slabs;

[0040] 2) Reheating

[0041] Slab heating temperature Unit: °C;

[0042] 3) Controlled rolling

[0043] Adopt two-stage controlled rolling. The starting rolling temperature T sr1 = 0.95T h ±15°C; the finishing rolling temperature

[0044] The starting rolling temperature T of the second stage sr2 = β - 10°C; the finishing rolling temperature T fr2 = β - 30°C, β = 810 - 230C - 21Mn - 15Ni + 32Mo + 60Si + 13W + 104V + 275P + 1522S - 20Cr - 20Cu - 1532Nb + 40Al, unit: °C;

[0045] 4) Controlled cooling

[0046] The starting cooling temperature is β - 50°C, the finishing cooling temperature = (-3.33t + 700) ± 20°C, the cooling rate = (-0.11t + 17.2) ± 2°C / s, where t is the thickness of the steel plate, and the unit is mm;

[0047] After cooling, when the temperature of the steel plate is above 300°C, it needs to be stacked and cooled in a heat preservation pit.

[0048] Furthermore, in step 1), hot metal pretreatment, oxygen blowing smelting, RH refining, inclusion beneficial treatment, and continuous casting are carried out in sequence. Among them, in the inclusion beneficial treatment stage, a composite inclusion with MgO + Al 2 O 3 as the core and coated with (Ca, Mn)S is formed. The size of the composite inclusion is 0.5 - 3.0 μm, and the number of the composite inclusions in this size range accounts for more than 80% of the total number of inclusions.

[0049] Furthermore, in step 1), during the hot metal pretreatment desulfurization stage, ensure that the sulfur content in the hot metal is ≤ 0.005%; during the RH refining stage, perform vacuum treatment with a vacuum treatment time of ≥ 22 min; during the inclusion beneficial treatment stage, add Mg wire in the form of cored wire with a wire feeding speed of 200 - 300 m / min.

[0050] Preferably, in step 3), in the first stage, the reduction per single pass of rolling is 7 - 13%, and the cumulative reduction is ≥ 33%.

[0051] Preferably, in step 3), in the second stage, the reduction per single pass of rolling is 10 - 12%, and the cumulative reduction is ≥ 50%.

[0052] In the manufacturing method described in the present invention:

[0053] First, perform pre - desulfurization on the incoming hot metal to ensure that the sulfur content in the hot metal is ≤ 0.0050%; then perform oxygen blowing smelting, carry out alloying of Cr, Ni, Cu, and Mo, and slag - stopping tapping. Then perform RH vacuum treatment with a vacuum treatment time of ≥ 22 min. After breaking the vacuum, perform inclusion beneficial treatment, add Mg wire in the form of cored wire with a wire feeding speed of 200 - 300 m / min.

[0054] During the inclusion beneficial treatment stage, modify the core Al 2 O 3 inclusions to form a composite inclusion with MgO + Al 2 O 3 as the core and coated with (Ca, Mn)S, and the proportion of the composite inclusion in the total oxide inclusions is greater than 80%. The size of the MgO + Al 2 O 3 core composite inclusion is mainly between 0.5 - 3 μm.

[0055] Control the slab heating temperature In units of °C, set the above - mentioned slab reheating temperature to ensure the full solution of Nb, V, Ti micro - alloyed carbonitrides and promote the homogenization of alloying elements, and reduce the macro and micro segregation in the steel.

[0056] During the rolling process, in the first - stage rolling, control the starting rolling temperature T sr1 = 0.95T h ± 15 °C; mainly to ensure that the steel plate is rolled at a relatively high temperature in the recrystallization zone to fully recrystallize and form uniform equiaxed austenite grains.

[0057] Final rolling temperature Unit: °C. For each chemical element in the above formula, substitute the value before the percentage sign of the mass percentage content of that chemical element. This can ensure that the steel plate is rolled above the non-static recrystallization temperature, preventing mixed crystals and uneven grain sizes; secondly, it ensures that there is sufficient temperature drop space during the rolling process.

[0058] Furthermore, the reduction per pass in the first-stage controlled rolling is 7 - 13%, and the cumulative reduction ≥ 33%. This is mainly to ensure that the steel plate has sufficient recrystallization driving force in each pass, while having enough rolling passes to homogenize the grain size of the steel plate, so as to meet the requirement that the original austenite grain size after rolling remains between 20 - 25 μm.

[0059] In the second-stage rolling, the starting rolling temperature T sr2 = β - 10 °C; both the starting rolling temperature and the finishing rolling temperature are the surface temperatures of the steel plate, and the unit parameter is °C. Ensure that the steel plate is rolled in the ferrite transformation zone to accumulate deformation energy and promote ferrite transformation. Control the finishing rolling temperature T fr2 = β - 30 °C, in order to ensure that ferrite transformation only occurs within a thickness of 10 mm under the surface.

[0060] Furthermore, the reduction per pass in the second-stage rolling is 10 - 12%, and the cumulative reduction ≥ 50%. In order to enable the steel plate to have sufficient deformation energy to promote the subsequent formation of ferrite, so as to reduce the yield ratio and promote the formation of an obvious yield plateau.

[0061] During the controlled cooling process, the starting cooling temperature is β - 50 °C, in order to enable the alloy within a thickness of 10 - 15 mm under the surface of the steel plate to fully undergo ferrite and pearlite phase transformations, and not to undergo martensite phase transformation under the rapid cooling of cooling water. The finishing cooling temperature = (-3.33t + 700) ± 20 °C, in order to enable the metal at the core of the steel plate to form ferrite and pearlite tissues at an appropriately high temperature. The cooling rate = (-0.11t + 17.2) ± 2 °C / s. The setting of the cooling rate is based on considering the heat transfer in the thickness direction of the steel plate, so that the steel plate has an appropriate cooling rate, and ferrite and pearlite tissues are formed throughout the full thickness cross-section of the steel plate.

[0062] After cooling, when the temperature of the steel plate is above 300 °C, it needs to be stacked and cooled in a heat preservation pit to promote hydrogen diffusion and eliminate tissue stress.

[0063] Compared with the prior art, the present invention has the following advantages:

[0064] Existing high-strength structural steels adopt low-carbon, high-manganese and high-niobium composition designs or high-carbon niobium-vanadium microalloying composition designs. Although the strength and yield ratio can meet the requirements, there is no obvious yield plateau, and the cost is relatively high.

[0065] In the composition design of the present invention, a special composition design of high carbon, high silicon, medium manganese, high chromium, and low micro-alloying elements is adopted, and the mass percentage contents of each chemical element are controlled to also meet the following requirements: 0.5 ≤ α ≤ 0.8, 780 ≤ β ≤ 800, so that the steel plate has high strength performance, good impact toughness, low yield ratio, and obvious tensile yield plateau at the same time. The obvious yield plateau enables the steel to have high plastic strain energy under yield conditions, adapts to the complex stress conditions of high-rise building structures, and reduces the damage caused by earthquakes.

[0066] Based on the composition design, the present invention adopts a special smelting and rolling cooling manufacturing process design. Through beneficial treatment of inclusions, large reduction rolling, and microstructural control cooling technology for the steel plate thickness section, a high-strength ferrite + pearlite microstructure with reasonable matching of soft and hard phases is obtained, where the volume fraction of ferrite is 40 - 60%, the volume fraction of pearlite is 40 - 60%, the ferrite grain size is 5 - 15 microns, the dislocation density in ferrite is 10 8 ~10 10 / cm 2 , the pearlite colony size is 10 - 20 microns, and the pearlite lamellar spacing is 30 - 60 nm. Designing from aspects such as composition design, microstructure control, and production process, steel plates with a strength requirement of 460 MPa grade, good impact toughness, low yield ratio, and obvious yield plateau can be produced.

[0067] The yield strength of the high-strength steel of the present invention is ≥460 MPa, the tensile strength is 570 - 720 MPa, the elongation is ≥18%, the impact energy at -20 °C is ≥200 J, the yield ratio is ≤0.83, and it has an obvious yield plateau, and can be used for the construction of high-rise and long-span building steel structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is the tensile stress-strain curve of the steel plate in Example 1 of the present invention.

[0069] Figure 2 is the tensile stress-strain curve of the steel plate in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0070] The present invention will be further described below in conjunction with examples and drawings.

[0071] The chemical composition of the steel in the examples of the present invention is shown in Table 1, and the balance includes Fe and inevitable impurities; the specific manufacturing process parameters are shown in Table 2.

[0072] The finished steel plates obtained in the present invention are subjected to tensile and Charpy V-notch impact tests. The performance results of the steel plates in the examples and comparative examples of the present invention are shown in Table 3.

[0073] The present invention adopts unique chemical compositions and process designs to manufacture steel plates with excellent strength and toughness properties, a low yield ratio, and an obvious yield plateau, and can produce steel plates for building structures with a thickness specification of ≤120 mm. The thick steel plates produced by the present invention can be used in the construction of steel structures with earthquake resistance requirements and have broad application prospects.

[0074] Comparative example 1 uses the common compositions and processes of current construction steel.

[0075] Figure 1 It is the tensile stress-strain curve graph of the steel plate of Example 1 of the present invention. It can be seen from the picture that there is an obvious section where the stress does not change with the strain, indicating that the steel of the present invention has an obvious yield plateau.

[0076] Figure 2 It is the tensile stress-strain curve graph of the steel plate of Comparative Example 1. It can be seen from the picture that the steel in Comparative Example 1 does not have an obvious yield plateau.

[0077]

[0078]

[0079]

Claims

1. A high-strength steel with an obvious yield plateau and a low yield ratio, the chemical composition of which is in weight percentage: C: 0.14 - 0.20%, Si: 0.45 - 1.20%, Mn: 0.6 - 1.6%, P ≤ 0.015%, S ≤ 0.0050%, Cr: 0.05 - 1.20%, Ni ≤ 0.20%, Mo ≤ 0.10%, Cu ≤ 0.20%, W ≤ 0.30%, Al: 0.01 - 0.06%, Nb ≤ 0.02%, V ≤ 0.1%, Ti: 0.006 - 0.015%, Mg: 0.0005 - 0.0030%, and the balance includes Fe and other inevitable impurities; and it needs to satisfy simultaneously 0.5 ≤ α ≤ 0.8, where α = C + (Mn + Si) / 6 + (Cr + Ni + Cu + Mo) / 10 + 2Nb + V; 780 ≤ β ≤ 800, where β = 810 - 230C - 21Mn - 15Ni + 32Mo + 60Si + 13W + 104V + 275P + 1522S - 20Cr - 20Cu - 1532Nb + 40Al.

2. The high-strength steel with an obvious yield plateau and a low yield ratio as described in claim 1, characterized in that the balance is Fe and other inevitable impurities.

3. The high-strength steel with an obvious yield plateau and a low yield ratio as described in claim 1 or 2, characterized in that The microstructure of the high-strength steel is ferrite + pearlite, where the volume fraction of ferrite is 40 - 60%, the volume fraction of pearlite is 40 - 60%, the ferrite grain size is 5 - 15 microns, and the dislocation density in ferrite is 10 8 ~10 10 / cm 2 , the pearlite colony size is 10 - 20 microns, and the pearlite interlamellar spacing is 30 - 60 nm.

4. The high-strength steel with an obvious yield plateau and a low yield ratio as described in claim 1 or 2 or 3, characterized in that the yield strength of the high-strength steel is ≥ 460 MPa, the tensile strength is 570 - 720 MPa, the elongation is ≥ 18%, the impact energy at -20 °C is ≥ 200 J, the yield ratio is ≤ 0.83, and the room-temperature tensile curve has an obvious yield plateau.

5. The manufacturing method of the high-strength steel with an obvious yield plateau and a low yield ratio as described in any one of claims 1 - 4, characterized in that it includes the following steps: 1) Smelting and continuous casting Smelt according to the composition described in claim 1 or 2, and cast into slabs; 2) Reheating Slab heating temperature Unit: °C; 3) Controlled rolling Two-stage controlled rolling is adopted. The starting rolling temperature T sr = 0.95T h ±15 °C; the finishing rolling temperature Unit: °C The starting rolling temperature T in the second stage sr2 = β - 10°C; the finishing rolling temperature T fr2 = β - 30°C, where β = 810 - 230C - 21Mn - 15Ni + 32Mo + 60Si + 13W + 104V + 275P + 1522S - 20Cr - 20Cu - 1532Nb + 40Al, with the unit of °C; 4) Controlled cooling The starting cooling temperature is β - 50 °C, the final cooling temperature = (-3.33t + 700) ± 20 °C, and the cooling rate = (-0.11t + 17.2) ± 2 °C / s, where t is the thickness of the steel plate in mm; When the temperature of the steel plate after cooling is above 300 °C, it needs to be stacked and cooled in a heat preservation pit.

6. The manufacturing method as described in claim 5, characterized in that In step 1), hot metal pretreatment, oxygen blowing smelting, RH refining, inclusion beneficial treatment and continuous casting are carried out in sequence. In the inclusion beneficial treatment stage, a composite inclusion with MgO + Al 2 O 3 as the core and coated with (Ca, Mn)S is formed. The size of the composite inclusion is 0.5 - 3.0 μm, and the number of the composite inclusions in this size range accounts for more than 80% of the total number of inclusions.

7. The manufacturing method as described in claim 6, characterized in that In step 1), during the hot metal pretreatment desulfurization stage, ensure that the sulfur in the hot metal is ≤ 0.0050%; carry out vacuum treatment during the RH refining stage, and the vacuum treatment time is ≥ 22 min; during the inclusion beneficial treatment stage, add Mg wire in the form of cored wire, and the wire feeding speed is 200 - 300 m / min.

8. The manufacturing method as described in claim 5, characterized in that in step 3), in the first stage, the reduction per single rolling pass is 7 - 13%, and the cumulative reduction is ≥ 33%.

9. The manufacturing method as described in claim 5 or 8, characterized in that In step 3), in the second stage, the reduction per pass of rolling is 10-12%, and the cumulative reduction ≥ 50%.

Images