960MPa-grade non-quenched and tempered easy-to-weld high-strength medium-thickness plate and manufacturing method thereof

Abstract

The 960MPa-grade non-quenched and tempered easy-to-weld high-strength medium-thickness plate comprises the following components in percentage by weight: 0.05 to 0.20 percent of C, 0.15 to 0.95 percent of Si, 0.80 to 1.80 percent of Mn, less than or equal to 0.20 percent of Al, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, 0.01 to 0.05 percent of Ti, 0.02 to 0.08 percent of Nb, 0.02 to 0.10 percent of V, 0.05 to 0.15 percent of Mo, 0.001 to 0.002 percent of B, and the balance of Fe and inevitable impurities, wherein 840C, 140Mn, 21Si, 210Mo and 60V are less than or equal to 465. The manufacturing method comprises the steps of smelting, casting, slab heating, controlled rolling, controlled cooling, stacking and slow cooling to the room temperature. According to the 960MPa-grade non-quenched and tempered easy-to-weld high-strength medium-thickness plate, the manufacturing thickness ranges from 12 mm to 60 mm, the yield strength of the 960MPa-grade non-quenched and tempered easy-to-weld high-strength medium-thickness plate is larger than or equal to 960MPa, the tensile strength of the 960MPa-grade non-quenched and tempered easy-to-weld high-strength medium-thickness plate is larger than or equal to 1000 MPa, the percentage elongation after fracture

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-strength medium plate, and particularly relates to a 960MPa grade non-quenched and tempered type easy-to-weld high-strength medium plate and a manufacturing method thereof. BACKGROUND

[0002] High-strength medium plates for engineering machinery and mechanical structures have very strict requirements on welding performance. In recent years, with the development of various engineering constructions towards large-scale, the requirement for structure weight reduction is increasingly urgent, and the strength grade of steel materials is gradually increased from the traditional 235MPa and 345MPa grade to 690MPa, 890MPa, 960MPa and 1100MPa, and is still increasing. However, as the increase of the strength grade of steel plates, the content of strengthening alloy elements in the steel plates is also increasing, and the carbon equivalent of the steel plates is increased, which reduces the welding performance of the steel plates and increases the welding cracking tendency of the steel plates. For high-strength steel plates with a strength grade of 600MPa or above, in order to ensure the stability of the welded structure, the steel plates need to be preheated before welding. For the welding of large-scale structural parts, the preheating before welding will seriously affect the processing and manufacturing efficiency of the structural parts.

[0003] At present, the production of high-strength medium plates is divided into two types of quenched and tempered and non-quenched and tempered in process. The quenched and tempered process is a traditional method for producing high-strength steel plates, which is to heat the steel plate after rolling to quench and high-temperature tempering to make the steel plate reach the required mechanical properties. The quenched and tempered process has the characteristics of good process stability and is suitable for steel plates of various thicknesses. However, the quenched and tempered process has the problems of relatively complex process, long production cycle and high cost of steel plates due to the need for two heat treatments. In addition, the steel plates produced by the quenched and tempered process have high carbon equivalent due to high content of alloy elements and carbon in the composition, which increases the subsequent welding crack tendency and causes the problem of complex process in the processing process.

[0004] The non-quenched and tempered process is based on hot mechanical rolling and comprehensively utilizes various strengthening methods. The steel plate does not need to be heat treated after rolling, which can significantly shorten the production cycle of the steel plate, improve the production efficiency and reduce the production cost. However, due to the limitations of the slab thickness, rolling capacity of the rolling mill and cooling equipment, the non-quenched and tempered process is difficult to adapt to some relatively backward rolling mills. At the same time, the non-quenched and tempered process also has limitations in the thickness specifications and strength of the steel plates that can be produced compared with the traditional quenched and tempered process. It is difficult to produce steel plates with a thickness greater than 40mm and a strength higher than 800MPa by using the non-quenched and tempered process, and there are certain problems in the control of plate shape and residual stress.

[0005] At present, due to the fact that domestic steel plants still use quenching and tempering process when producing 960MPa grade steel plate, the alloying elements thereof are mainly C, Mn, Cr, Ni, Mo system, and a small amount of micro-alloying elements are added as auxiliary strengthening means. The production process of such steel plate generally includes smelting, rolling, quenching and high temperature tempering treatment, and the yield strength of the steel plate reaches 960MPa or above. Due to the use of quenching and high temperature tempering treatment, the content of noble metal elements such as Cr, Ni and Mo in the steel is high, otherwise the strength of the steel plate after tempering cannot meet the requirements, but the high content of alloying elements will increase the carbon equivalent of the steel plate, increasing the welding cracking tendency of the steel plate. In addition, with the large fluctuation of the prices of metal elements such as Mn, Ni and Mo in recent years, the production cost of the steel plate often fluctuates greatly in the actual production process, which cannot adapt to the current market environment; at the same time, the additional quenching and high temperature tempering treatment will also increase the production cost of the steel plate, and will also increase the energy consumption per ton of steel and the carbon dioxide emission, which does not meet the development goal of reducing carbon and waste of the country.

[0006] Chinese patent CN102134680A discloses "a yield strength of 960MPa grade ultra-high strength steel and its production method", the chemical composition thereof is as follows in terms of weight percentage: C: 0.07-0.09%; Si: 0.15-0.25%; Mn: 1.00-1.20%; Cr: 1.05-1.15%; Mo: 0.15-0.20%; Al: 0.01-0.06%; P≤0.02%; S≤0.01%; N≤0.008%; the balance is Fe and inevitable impurities; the production method is as follows: smelting and casting into billet; heating to 1150-1250℃; final rolling temperature is 840-900℃; final cooling temperature is 640-700℃; quenching and tempering treatment is carried out, quenching heating temperature is 880-920℃, holding time is 20-60min, tempering heating temperature is 150-450℃, holding time is 90-180min. The material meets the performance requirements of 960MPa ultra-high strength steel, and has good elongation and impact toughness.

[0007] Chinese patent CN101451221A discloses "high-strength steel plate and its preparation method", the chemical composition of the steel plate is as follows in weight percentage: C 0.14-0.18%, Si 0.20-0.50%, Mn 0.90-1.30%, P≤0.020%, S≤0.010%, Ni 0.70-0.10%, V 0.04-0.08%, Nb 0.020-0.060%, Al 0.020-0.060%, Cr 0.30-0.80%, Mo 0.30-0.60%, Ti 0.010-0.030%, B 0.0010-0.0030%, the balance being Fe and inevitable impurities. The invention is prepared by reasonable design of alloy composition, mainly quenching and tempering process control, the thickness of the steel plate can reach 80mm, the yield strength is high, the welding performance, cold bending performance, low temperature toughness is good, the steel plate shape is good, and the steel plate has excellent comprehensive performance.

[0008] Chinese patent CN101397640A discloses "yield strength 960MPa grade welding structural steel", the components and weight percentage are as follows: C: 0.14-0.19, Si: 0.15-0.40, Mn: 1.40-<1.7, Mo: 0.41-0.60, B: 0.0005-0.002, Cr: 0-0.50, Ni: 0-0.40, Nb: 0-0.03, Ti: 0.010-0.050, Als: 0.01-0.06, P: ≤0.020, S: ≤0.010, the balance being Fe and inevitable impurities; meanwhile, it satisfies: carbon equivalent CEV(%) <0.65 or Pcm(%) <0.35. The invention has simple rolling and heat treatment process, and the rolling process does not need controlled cooling, and the controllable range of the heat treatment process is wide.

[0009] Chinese patent CN104328350A discloses "a yield strength of 960 MPa grade quenched and tempered steel and its manufacturing method", control the mass percentage content of carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum, niobium, vanadium, titanium, aluminum and boron and carbon equivalent of the quenched and tempered steel. The pretreated blast furnace desulfurization molten iron is fed into a converter for smelting, the smelted qualified molten steel is continuously cast into a billet after LF+HR+calcium treatment, the billet is heated to 1100-1250℃ in a furnace / heating furnace and then rolled into a steel plate, the final rolling temperature is 820-880℃, after the final rolling, 50-100℃ / S ultrafast cooling and 10-25℃ / S laminar cooling are used, the coiling temperature is controlled at 500-700℃ to coil the steel plate, the steel plate with a temperature lower than 80℃ is transversely cut and straightened into a steel plate, the straightened steel plate is quenched at 850-880℃ / 20-60min and tempered at 500-700℃ / 90-180min. The steel plate obtained by the above manufacturing method has a tensile strength (Rel) ≥980Mpa and a Charpy impact energy AKv(-40℃) ≥47J, and its practical and popularization value is obvious.

[0010] From the current disclosed 960 MPa grade medium plate high strength steel, the traditional quenching and tempering process is still used for production, the carbon equivalent of the steel plate is at a high level, and in the actual welding process, a high temperature preheating before welding is necessary, which reduces the production efficiency of the structure and equipment. If a 960 MPa grade medium plate high strength steel product of non-quenching and tempering process can be developed, not only the traditional quenching and tempering treatment can be avoided, the amount of noble metal elements can be reduced, the production cost of the steel plate can be reduced, the manufacturing efficiency of the steel plate can be improved, but also the carbon equivalent of the steel plate itself can be reduced, the welding cracking tendency of the steel plate can be reduced, the preheating temperature before welding of the steel plate can be reduced, and the efficiency of downstream steel structure processing can be improved. SUMMARY

[0011] The purpose of the present application is to provide a 960 MPa grade non-quenched and tempered type easy-to-weld high strength medium plate and its manufacturing method, the obtained non-quenched and tempered type medium plate high strength steel has a yield strength ≥960 MPa, a tensile strength ≥1000 MPa, a post-break elongation more than 10%, a Charpy impact energy at-40℃ ≥34J, and a thickness of 12-60mm; compared with the existing same grade quenched and tempered steel, the amount of noble metal elements such as Cr, Ni and Mo is reduced, the welding performance of the steel plate is improved, the preheating temperature before welding of the steel plate is reduced, and the efficiency of downstream steel structure processing is improved; the non-quenching and tempering process is used for production, compared with the traditional quenching and tempering process, the production cycle of the steel plate can be significantly shortened, the production efficiency can be improved, and the production cost can be reduced.

[0012] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0013] The 960MPa grade non-quenched and tempered type easy-to-weld high-strength medium plate has the following component weight percentages: C: 0.05-0.20%, Si: 0.15-0.95%, Mn: 0.80-1.80%, Al<=0.20%, P<=0.02%, S<=0.02%, Ti: 0.01-0.05%, Nb: 0.02-0.08%, V: 0.02-0.10%, Mo: 0.05-0.15%, B: 0.001-0.002%, the rest including Fe and inevitable impurities, and the above components should also satisfy: 840C+140Mn+21Si+210Mo+60V<=465.

[0014] Further, the rest is Fe and inevitable impurities.

[0015] The medium plate has a microstructure including 85-95% lath martensite and 5-15% residual austenite by volume fraction.

[0016] The medium plate has a yield strength >=960MPa, a tensile strength >=1000MPa, an elongation after break >=10%, and a Charpy impact energy at -40 DEG C >=34J.

[0017] The medium plate has a thickness of 12-60mm.

[0018] In the component design of the 960MPa grade non-quenched and tempered type easy-to-weld high-strength medium plate:

[0019] Carbon C: can ensure the strength of the material and also precipitate fine dispersed carbides with Nb, V and Ti micro-alloy elements. Low carbon content in the steel will lead to low carbon content in the martensite in the steel plate, small volume fraction of precipitated carbides, and no effective strengthening effect; but when the carbon content in the steel is too high, the carbon equivalent of the steel plate is increased and the cracking tendency in the welding process is increased. Therefore, the carbon content in the present application is controlled to be 0.05-0.20%.

[0020] Silicon Si: silicon has a solid solution strengthening effect, can improve the corrosion resistance and high temperature oxidation resistance of the steel, and the addition of Si can effectively improve the elastic modulus of the steel plate; but too high content will lead to serious decarburization on the surface of the steel and reduce the welding performance. At the final cooling temperature, the supersaturated carbon atoms in the martensite will precipitate in the form of cementite, which will strengthen the steel plate. The addition of Si element can effectively inhibit the precipitation of cementite, so that more carbon atoms are enriched from the supersaturated martensite to the untransformed residual austenite under the diffusion effect, the carbon enrichment stability of the austenite is improved, and the content of the residual austenite in the steel at room temperature is further improved. Therefore, the silicon content in the present application is controlled to be 0.15-0.95%.

[0021] Manganese Mn: Manganese is the main element of stabilizing austenite in steel, higher manganese content can ensure the material matrix structure is stable austenite structure, every 1% of manganese can reduce the steel martensite transformation temperature about 35~50℃. A small amount of manganese element is conducive to the increase of austenite stability in steel plate, delay the temperature of austenite to pearlite ferrite transformation in steel, expand the process window of steel plate hot mechanical rolling; But too high manganese content can significantly reduce the martensite transformation temperature of the steel plate, at the same time, the heart of the steel plate is easy to produce segregation, increase the carbon equivalent, reduce the welding performance of the steel plate. Therefore, the manganese content of the application is controlled at 0.80~1.80%.

[0022] Aluminum Al: Aluminum can effectively refine the grain, and has great benefit to improve the toughness of the steel plate. However, if the aluminum content in the steel is too high, it will increase the difficulty of smelting and pouring, and increase the manufacturing cost, and form excessive oxides to deteriorate the quality of the steel plate. Therefore, the aluminum content is controlled to be ≤0.20% in the application.

[0023] Titanium Ti: Titanium is a strong carbide forming element, which can form TiN in steel, as the nucleation point of austenite, and play a role in refining austenite grains. In the application, a small amount of Ti is added to mainly play a role in refining austenite grains. If the Ti content is too high, it will lead to the precipitation of TiC, consume C in the steel, reduce the solid solubility of C in austenite, and cause the decrease of austenite stability. Therefore, the Ti content is controlled to be 0.01~0.05% in the application.

[0024] Niobium Nb: Niobium is the most effective grain refining micro-alloying element. In the process of rolling, the niobium element in solid solution is easy to segregate on the dislocation line, which strongly inhibits the climbing of dislocation, delays the recrystallization of austenite and greatly strengthens the effect of grain refinement. When the niobium content is low, with the increase of niobium content, the strength of the steel increases rapidly. With the increase of niobium content, the strengthening effect of the steel plate appears a peak value, and after adding more niobium, the strengthening effect is not significant. Therefore, the niobium content is controlled to be 0.02~0.08% in the application.

[0025] Vanadium V: Vanadium is a strong carbide forming element, which has the effects of precipitation strengthening and fine grain strengthening in the material. Because the Mn content in the steel is too high, it is easy to cause grain coarsening, and a small amount of vanadium element is added to refine the structure and improve the strength of the alloy. At the same time, the precipitation of V carbide has the effect of dispersion strengthening, which can further improve the strength of the steel. Therefore, the vanadium content is controlled to be 0.02~0.10% in the application.

[0026] Molybdenum Mo: Molybdenum can improve the hardenability and thermal strength of the steel plate in the steel, so that the thick steel plate of large section is quenched and hardened. In high carbon steel, molybdenum can reduce the tendency of continuous network formation of carbide on the grain boundary, reduce the residual austenite in the steel, and relatively increase the hardness and wear resistance of the steel plate matrix. Similarly, molybdenum is also a noble metal, and the cost is high, therefore, the content of molybdenum in the application is controlled at 0.05-0.15%.

[0027] Boron B: The most significant role of boron in steel is to improve the hardenability of the steel plate and the maximum producible thickness specification of the steel plate, and a small amount of boron can improve the hardenability of the steel plate; at the same time, boron in steel can also reduce the chemical inhomogeneity of continuous casting billet, refine the columnar crystal, and finally form a good continuous casting structure. Therefore, the content of boron in the application is controlled at 0.001-0.002%.

[0028] P, S: are inevitable harmful elements in steel, and the lower the better, therefore, the application controls P≤0.02%, S≤0.02%.

[0029] The application improves the strength of the steel plate by adding C element, combined with the addition of a small amount of Nb, V, Ti micro-alloying elements, at the same time, combined with the addition of Mo, B, the hardenability of the steel plate is improved, and in the case of thick steel plate, higher strength can also be obtained. The above elements should also satisfy 840C+140Mn+21Si+210Mo+60V≤465 (when calculating, only the value before the corresponding element percentage sign is substituted, for example, the content of C is 0.05%, only 0.05 is substituted when calculating), the formula is a variant formula of the carbon equivalent calculation formula, the traditional carbon equivalent formula involves fractions and decimals, and there is a situation that the calculation cannot be rounded, and the application is deformed, the composition percentage can be directly brought into the calculation, the calculation result is more accurate, and the requirement of satisfying the above formula is equivalent to the carbon equivalent calculation being less than a certain range value, so that the steel plate can satisfy the design requirement of the martensite starting temperature while having good welding performance, and then the required proportion of lath martensite and residual austenite volume fraction in the steel can be generated at the final cooling temperature, so that the steel plate has good welding performance while the yield strength is≥960MPa.

[0030] The manufacturing method of the 960MPa grade non-quenched and tempered type easy-to-weld high-strength medium plate, comprising the following steps:

[0031] 1) Smelting and casting

[0032] Smelting and casting into ingots or billets according to the above composition;

[0033] 2) Slab heating

[0034] The obtained steel ingot is formed into a slab after being broken down, and the slab or the cast blank is heated at a heating temperature of 1150-1250℃ and a heating time t=1-2H, wherein t is in min and H is the thickness of the slab or the cast blank in mm;

[0035] 3) controlling rolling

[0036] The rolling is divided into two stages, and the first stage is rolled at a temperature of 1050-1150℃ to a thickness of 3-4 times the thickness of the finished steel plate;

[0037] The second stage is rolled at a temperature of 880-920℃ to a thickness of 12-60 mm.

[0038] 4) on-line water cooling

[0039] The steel plate is cooled at a cooling temperature of 840-860℃ and a final cooling temperature of 250-350℃, and then is stacked and slowly cooled to room temperature.

[0040] Preferably, in step 3), the steel plate is naturally cooled or water cooled to the second stage rolling temperature after the first stage rolling is completed.

[0041] Preferably, in step 4), the cooling rate is 5-15℃ / s.

[0042] The rolling of the present application adopts two-stage rolling, and the first stage is rolled at a temperature of 1050-1150℃, which is above the recrystallization temperature of the material. The material is deformed sufficiently at this temperature range, which is beneficial to the recrystallization of the steel plate during the rolling deformation and between passes.

[0043] Meanwhile, the rolling deformation is beneficial to the precipitation of the carbonitride of the micro-alloying elements such as Nb added in the steel, and the micro-alloying carbonitride precipitated at the austenite grain boundary can pin the austenite grain boundary and prevent the austenite grain from growing and coarsening, thereby refining the austenite grain size.

[0044] The first stage is rolled at a temperature of 1050-1150℃, and the deformation and recrystallization are alternately performed through the high-temperature stage rolling, thereby refining the high-temperature stage rolling structure. During the high-temperature rolling, the slab is cooled naturally and is heated by the deformation, so that the temperature of the steel plate does not decrease too much after each pass. When the steel plate is rolled to a thickness of 3-4 times the thickness of the finished steel plate, the temperature of the steel plate is still above the recrystallization temperature. At this time, the first stage rolling deformation is completed, and the original structure is significantly refined through the deformation and recrystallization of multiple passes, thereby providing a guarantee for the subsequent deformation.

[0045] The steel plate completed the first stage rolling is kept on the roller way, and a small amount of spray cooling water can be used to increase the cooling rate of the whole steel plate, thereby reducing the rolling process time of the steel plate and improving the production efficiency.

[0046] When the temperature of the steel plate is reduced to 880-920℃, the second stage rolling is started. The purpose of the second stage rolling is to elongate the fully recrystallized austenite grains by deformation and generate a large number of deformation bands in the grains, which is beneficial to provide more nucleation sites for the bainite and martensite phase transformation in the subsequent cooling process, thereby refining the martensite size and improving the toughness of the steel plate. Meanwhile, the niobium and other micro-alloying elements in the steel are more likely to precipitate carbonitride in the low-temperature deformation stage, which increases the recrystallization temperature of the steel plate to some extent, so that the second stage rolling can be carried out at a higher temperature, thereby reducing the deformation resistance in the rolling process. The above-mentioned carbonitride precipitation points can provide more nucleation sites for the phase transformation of martensite in the subsequent cooling process, thereby refining the martensite laths, and finally improving the strength and toughness of the steel plate.

[0047] After the two-stage rolling of the steel plate, the steel plate is directly cooled online at a high speed, the cooling starting temperature is 840-860℃, and the final cooling temperature is 250-350℃. Since the A3 temperature of the steel plate according to the composition range is 839-858℃, the starting temperature of the cooling process cannot be lower than the A3 temperature to ensure that proeutectoid ferrite is not generated in the steel. However, the formation temperature of the proeutectoid ferrite should be lower than the A3 temperature in the actual cooling process, so the cooling starting temperature of the steel plate should be 840-860℃ in the actual cooling process.

[0048] The carbon, manganese and molybdenum added in the steel have the effect of delaying the pearlite transformation, moving the "C" curve to the right, and significantly reducing the critical cooling rate. Therefore, the cooling rate used in the cooling process of the present application is 5-15℃ / s, and under this cooling rate, the steel will not generate pearlite and bainite and other structures.

[0049] The final cooling temperature of the steel plate is 250-350℃, and the martensite transformation temperature of the steel plate is 390-440℃ according to the actual composition. Cooling the steel plate from above A3 temperature to below the martensite transformation temperature can make the matrix structure of the steel plate be martensite + untransformed austenite.

[0050] In the subsequent stack cooling process, the untransformed austenite in the steel plays a role in carbon enrichment and stability through short-range diffusion of carbon atoms. The carbon atoms in the steel will diffuse from the supersaturated martensite formed in the quenching process to the untransformed austenite, thereby increasing the carbon content of the austenite and improving the chemical stability of the untransformed austenite, which can be retained to room temperature. The matrix structure of the steel plate contains a part of residual austenite after cooling to room temperature, thereby improving the plasticity and toughness of the steel plate during deformation. Meanwhile, the carbonitride of niobium and other micro-alloying elements in the steel can be dispersed and precipitated during the low-temperature slow cooling process, thereby playing a role in precipitation strengthening and further improving the strength of the steel plate.

[0051] Compared with the prior art, the present application has the beneficial effects of:

[0052] In the component design of the present application, higher C and Si elements, and the addition of Nb, V and Ti micro-alloy elements are used to improve the strength of the steel plate, and at the same time, a small amount of Mo and B is added to improve the hardenability of the steel plate, so that a higher strength can be obtained even in the case of a thicker steel plate. The above elements should also satisfy 840C+140Mn+21Si+210Mo+60V≤465, so that the steel plate has a higher strength and good welding performance. Compared with the existing quenched and tempered steel with a strength level of 980MPa, the content of noble metal elements such as Cr, Ni and Mo in the composition is relatively high. Higher alloy element content leads to an increase in the carbon equivalent of the steel plate, increasing the tendency of the steel plate to crack during welding. The steel plate often needs high-temperature preheating before welding, which seriously affects the processing and manufacturing efficiency of the structural member. However, the existing non-quenched and tempered steel composition is difficult to produce a steel plate with a thickness of more than 40mm and a strength of more than 800MPa.

[0053] Based on the component design, the present application uses a non-quenched and tempered process to produce the steel plate by means of two-stage controlled rolling and controlled cooling, fully utilizes the advantages of the controlled rolling and controlled cooling process in the production process of the steel plate, uses two-stage controlled rolling to control the precipitation of Nb, V and Ti carbonitride, and significantly refines the microstructure of the steel plate, thereby improving the strength and plasticity and toughness of the steel plate. The subsequent controlled cooling stage controls the cooling temperature and cooling rate to prevent the formation of pro-eutectoid ferrite, and finally forms a lath martensite + residual austenite structure, so that the steel plate obtained by the non-quenched and tempered process has a yield strength of ≥960MPa. The performance of the traditional quenched and tempered steel is obtained by subsequent quenching and high-temperature tempering. During the tempering process, the internal dislocations of the quenched martensite in the steel are effectively recovered, the strength of the steel plate is reduced, the toughness is improved, and the precipitation of alloy carbides such as Cr and Ni plays a certain precipitation strengthening role, thereby enabling the steel plate to maintain a high yield strength.

[0054] The present application uses a non-quenched and tempered process to obtain a steel plate with a thickness of 12-60mm, a yield strength of ≥960MPa, a tensile strength of ≥1000MPa, an elongation of ≥10%, and a Charpy impact energy of ≥34J at -40℃. The use of noble metal elements such as Cr, Ni and Mo is reduced, the welding performance of the steel plate is improved, the preheating temperature before welding is reduced, and the efficiency of downstream steel structure processing is improved. The use of the non-quenched and tempered process for production avoids the quenching + tempering process in the traditional quenched and tempered production process, reduces the energy consumption in the production process of the steel plate, shortens the production process of the steel plate, and improves the production efficiency of the steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 The present application is a microstructure photograph of the steel plate. DETAILED DESCRIPTION

[0056] The application will be further described in connection with the embodiments and the accompanying drawings.

[0057] The 960MPa grade non-quenched and tempered type easy-to-weld high strength medium plate and the manufacturing method thereof described in the application will be further described according to specific embodiments. However, the application is not limited to the following embodiments, and various technical solutions derived from the changes shall belong to the protection scope of the application.

[0058] The components of the embodiments of the application are shown in Table 1, and Table 2 shows the performance parameters of the steel embodiments of the application.

[0059] Figure 1 The microstructure photograph of the steel plate obtained in the embodiment 1 of the application is shown in the picture, and it can be seen from the picture that the microstructure of the steel plate of the application is a typical lath martensite + residual austenite structure.

[0060] The steel plate manufactured by using the components and the process of the application has a thickness of 12-60mm, a yield strength of ≥960MPa, a tensile strength of ≥1000MPa, an elongation after fracture of ≥10%, and a Charpy impact energy at -40℃ of ≥34J.

[0061] Compared with the steel plate produced by using the off-line quenching + tempering heat treatment method in the prior art production technology, the production rhythm is greatly improved, and the industrialized production efficiency of the steel plate is improved. At the same time, the energy consumption of the steel plate production process is significantly reduced, the addition of alloy elements in the steel is reduced, the actual production cost of the steel plate is also significantly reduced, and the steel plate is suitable for batch production in the medium plate factory.

[0062]

[0063]

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Claims

1. A 960 MPa grade high strength medium plate of non-quenched and tempered type and easy to weld, having the following composition in weight percent: C: 0.05-0.20%, Si: 0.15-0.95%, Mn: 0.80-1.80%, Al ≤ 0.20%, P ≤ 0.02%, S ≤ 0.02%, Ti: 0.01-0.05%, Nb: 0.02-0.08%, V: 0.02-0.10%, Mo: 0.05-0.15%, B: 0.001-0.002%, the balance comprising Fe and unavoidable impurities, and the above composition further satisfies: 840C + 140Mn + 21Si + 210Mo + 60V ≤ 465. The balance is Fe and unavoidable impurities.

2. The 960 MPa grade high strength heavy gauge sheet that is non-quenched and tempered and is easy to weld according to claim 1, characterized by, The microstructure of the medium plate comprises 85-95% lath martensite and 5-15% residual austenite by volume fraction.

3. The 960 MPa grade high-strength heavy gauge sheet that is non-quenched and tempered and easily weldable according to claim 1 or 2, characterized by, The medium plate has a yield strength ≥ 960 MPa, a tensile strength ≥ 1000 MPa, an elongation after fracture ≥ 10%, and a Charpy impact energy at -40°C ≥ 34 J.

4. The 960 MPa grade high strength heavy gauge sheet as claimed in claim 1 or 2 or 3, wherein, The thickness of the medium plate is 12-60 mm.

5. The 960 MPa grade high strength medium thick plate of non-quenched and tempered type which is easy to weld according to claim 1 or 2 or 3 or 4, characterized in that, The method comprises the following steps:

6. The method of producing a 960 MPa grade high-strength medium-thick plate of the un- quenched and tempered type which is easy to weld according to any one of claims 1 to 5, characterized by, 1) Smelting and casting Smelting and casting a steel ingot or a casting blank according to the composition of claim 1 or 2; 2) Slab heating The obtained steel ingot is formed into a slab after cogging, and the slab or casting blank is heated at a temperature of 1150-1250°C for a time t = 1-2H, where t is the heating time in minutes and H is the thickness of the slab or casting blank in mm; 3) Controlled rolling Two-stage rolling, the first stage being at a rolling temperature of 1050-1150°C and rolled to 3-4 times the thickness of the finished steel plate; The second stage being at a rolling temperature of 880-920°C and rolled to a steel plate of 12-60 mm thick; 4) Cooling The steel plate is cooled at a temperature of 840-860°C and a final cooling temperature of 250-350°C, and then stacked and slowly cooled to room temperature. In step 3), the steel plate is naturally cooled or water cooled to the second stage rolling temperature after the first stage rolling is completed.

7. The production method according to claim 6, wherein In step 4), the cooling rate is 5-15°C / s.

8. The production method according to claim 6, wherein ​

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