A v-b-ti microalloyed 690mpa grade engineering machinery steel

Abstract

The application discloses a V-B-Ti microalloyed 690MPa grade engineering machinery steel and belongs to the field of metal processing. The chemical composition of the steel comprises the following components in percentage by weight: C 0.13-0.17%, Si 0.15-0.25%, Mn 1.55-1.7%, P≤0.02%, S≤0.015%, Ti 0.017-0.0250%, Cr 0.1-0.2%, Als 0.015-0.045%, V 0.05-0.08%, B 0.0015-0.0020%, N 0.005-0.0095%, Ti / N=3.4-3.8, and the balance of Fe and inevitable impurities, wherein the total amount of other impurity elements is less than 0.05%, so that the problems of low toughness and unevenness of the steel plate are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal processing, and particularly relates to a V-B-Ti micro-alloyed 690MPa grade engineering machinery steel with a thickness specification of 10-50mm. BACKGROUND

[0002] In recent years, with the continuous progress of steel materials, welding material manufacturing and welding process technology, the strength grade of structural steel is continuously improved. The 690MPa grade high-strength steel is more used in the fields of offshore cranes, marine liquid tanks, self-elevating offshore platform legs, coal mine hydraulic supports, etc. Especially for the field of engineering machinery steel, the 690MPa grade high-strength steel has become an important steel grade. This kind of steel is mainly based on carbon manganese steel, and micro-alloying elements such as Nb, V, Cr, Mo and Ni are added to the steel to form carbonitride or strong quenching elements, so as to improve the strength and toughness of the steel plate through solid solution strengthening, precipitation strengthening and fine grain strengthening. According to statistics, the yield of medium plate of this strength grade accounts for 5-10% of the annual output. Therefore, it is of great significance to develop the manufacturing technology of such low-cost steel plates. At present, the research on online quenching process of high-strength steel plates with a thickness of 50mm and below is gradually increasing. The online thermal mechanical control (TMCP) process is a kind of short process, reduced production of quenched and tempered steel green process, which can not only save energy but also shorten the delivery cycle of finished steel plates. With the continuous progress of post-rolling water cooling equipment and shape control ability, such as super-fast cooling, pre-straightening machine, warm straightening machine and other equipment, the hardware support for process popularization is provided. Relying on new equipment, various medium plate plants have carried out research and application of process, and solved the problems such as performance consistency. However, the impact toughness and shape requirements of the product are obviously lower than those of the offline quenching production process, which is one of the common problems faced by the industry. Many steel plants use the method of increasing tempering temperature to improve the toughness of the product and offline straightening to ensure the shape, but the effect is not obvious and also increases the production cost. Therefore, in view of the above problems existing in the conventional 690MPa high-strength steel plate, it is urgent to develop a low-cost, high-strength and tough 690MPa grade steel plate with low requirements for production equipment, so as to meet the urgent needs of the rapidly developing manufacturing industry for high-strength steel with excellent performance and low cost.

[0003] TMCP process is considered as a process of saving alloy and energy and being beneficial to environmental protection because it produces high strength and high toughness steel without adding too much alloy element and without complicated subsequent heat treatment, and has become an indispensable technology for producing low alloy steel plate. With the increasing requirements of the market for TMCP steel, the TMCP process itself is also continuously developing in application. From the research work in recent years, the focus is on controlled cooling, especially accelerated cooling. By accelerating the cooling speed after rolling, not only the grain growth can be inhibited, but also the ultra-fine ferrite structure or bainite structure required for high strength and high toughness can be obtained, and even martensite structure can be obtained. However, with the optimization of alloy cost and steelmaking process of 690MPa grade steel plate, the steel plate after alloy and process reduction needs to be produced by TMCP process. With the decrease of alloy content, the rolling and controlled cooling process window is becoming narrower. At present, the austenite uncrystallization zone direct cooling process is generally used. The steel plate produced by this process has high strength and low impact toughness. The reason is that the austenite grains of the steel plate after rolling mainly present a flat shape. This morphology of austenite is easy to form martensite lath penetrating the original austenite grain during subsequent direct cooling, and the orientation is relatively uniform, which is not conducive to preventing crack propagation, so the toughness is low, which does not reach the level of offline quenching, and the internal stress of the steel plate is large, and the plate shape cannot be guaranteed, which limits the high-efficiency and low-cost production of 690MPa grade engineering machinery steel with thickness of 10-50mm.

[0004] Compared with the prior art:

[0005] So far, there is little research on the high-efficiency and low-cost production method of 690MPa grade engineering structure steel with thickness of 10-50mm. Before the present application, the journal paper "Effect of tempering temperature on microstructure and properties of Q690D high-strength structural steel" (Hot Working Technology, 2014.8) mainly enhances the toughness of the steel plate by using offline tempering heat treatment, but due to the use of offline tempering heat treatment, the production cycle and cost are greatly increased.

[0006] The effect of tempering temperature on the microstructure and properties of Q690D high-strength structural steel disclosed in the above document can solve the problem of toughness of the steel plate, but it is not suitable for controlling and solving the high-efficiency and low-cost production method of economic, yield strength 690MPa grade steel plate with thickness of 10-50mm produced by TMCP instead of offline heat treatment process. The technical scheme provided by the present application can effectively overcome the above-mentioned defects and solve the problems of low toughness and uneven plate shape of 690MPa grade hot-rolled steel plate with thickness of 10-50mm produced by using 250mm and below thickness continuous casting billet online cooling process. SUMMARY

[0007] The purpose of the present application is to overcome the above-mentioned technical problems and deficiencies, provide a V-B-Ti micro-alloyed 690MPa grade engineering machinery steel plate, which has the characteristics of high efficiency and low cost, and finally solves the problems of low toughness and unevenness of the plate shape of the 690MPa grade hot-rolled steel plate with a thickness of 10-50mm produced by the on-line cooling process.

[0008] To achieve the above-mentioned purpose, the technical scheme of the present application is:

[0009] A V-B-Ti micro-alloyed 690MPa grade engineering machinery steel plate, the chemical composition of which comprises, by weight percentage: C 0.13%-0.17%, Si 0.15%-0.25%, Mn 1.55%-1.7%, P≤0.02%, S≤0.015%, Ti 0.017%-0.0250%, Cr 0.1%-0.2%, Als 0.015%-0.045%, V 0.05%-0.08%, B 0.0015%-0.0020%, N 0.005%-0.0095%, Ti / N=3.4-3.8, and the balance being Fe and unavoidable impurities, and the total amount of other impurity elements being less than 0.05%.

[0010] The effects of each main element in the chemical composition of the steel of the present application are as follows:

[0011] C: the most economical and basic strengthening element in steel, which has a significant effect on improving the strength of the steel through solid solution strengthening and precipitation strengthening, but increasing the C content has a negative impact on the plasticity, toughness and weldability of the steel. Therefore, the C content range is set to 0.13%-0.17% in the present application.

[0012] Mn: improves the strength of the steel through solid solution strengthening, and compensates for the loss of plate strength caused by the reduction of C content. In addition, it can also reduce the gamma-alpha phase transition temperature, thereby refining the ferrite grains, which helps to obtain fine low-temperature phase transformation products and improve their toughness. However, increasing the Mn content will exacerbate the center segregation of the continuous casting billet, which is not conducive to the improvement of the low-temperature toughness of the steel plate, and also cannot guarantee the uniformity of the cross-section structure of the steel plate. Therefore, the Mn content range is designed to be 1.55%-1.70% in the present application.

[0013] Si: has the effects of steelmaking deoxidization and improving the strength of the matrix, increasing the Si content can purify the ferrite and reduce the content of pearlite, which is beneficial to reducing the Bauschinger effect of the matrix material. However, excessive Si will reduce the toughness of the base material in the welding heat affected zone. Therefore, the Si content is set to 0.15%-0.25% in the present application.

[0014] Ti, N: In addition to forming fine TiN particles to refine austenite grains, N in steel is easy to form BN with B, which affects the yield of free B and reduces the hardenability of the steel plate, so the TiN binding capacity is combined with BN, and therefore the N content range selected by the present application is 0.005% to 0.0095%, which ensures that Ti / N is controlled at 3.4 to 3.8, and the remaining Ti is combined with C to form TiC, which plays a dispersion strengthening role.

[0015] V: is a strong solid N element, which exists in the form of VN in continuous casting billets. Fine VN particles can effectively inhibit the growth of austenite grains during reheating of the continuous casting billets, and help to improve the solid solubility of Nb in austenite, and improve the impact toughness of the welding heat affected zone. When the V addition exceeds a certain value, the VC particles will be coarsened, and the stress concentration level of the particle interface and the matrix will be improved. Therefore, the V content range selected by the present application is 0.05% to 0.08%.

[0016] Al: is usually used as a deoxidizer in steel, and has a refining effect when AlN is formed. When the content of Al exceeds 0.045%, excessive alumina inclusions will reduce the cleanliness of the steel. If the content of Al is too low, the deoxidation will be insufficient, and Ti and other easily oxidized elements will form oxides, so the lower limit of the content of Al is set to 0.015%.

[0017] Cr: can effectively improve the hardenability, inhibit the formation of ferrite, and promote the formation of bainite, which is a main element for controlling phase change structure, promoting the formation of a large number of polygonal ferrite, pearlite and acicular ferrite with a large number of dislocations distributed in the intracrystalline at medium and low temperature zones, and improving the strength, plasticity and toughness of the steel plate. The content range of Cr selected by the present application is 0.1% to 0.2%.

[0018] B: significantly improves the hardenability of the steel, and is an effective element, which is easily segregated at the grain boundary and prevents the precipitation of carbon. A small amount of boron can have a significant effect. However, if the content of boron is too high, boron carbonitride is easy to form, which reduces the toughness and causes thermal embrittlement. The reasonable range of the content of boron is controlled at 0.0015% to 0.0020%.

[0019] P, S: are impurity elements in steel, which should be as low as possible. However, due to the consideration of smelting cost and process, it cannot be too low. Therefore, the upper limits of the contents of P and S are set to 0.020% and 0.015% respectively.

[0020] The V-B-Ti micro-alloyed 690MPa grade engineering machinery steel of the present application is a hot-rolled steel plate, the thickness target is 10-50mm, and the continuous casting billets with a thickness of 250mm or less are used to produce the steel plate on a medium plate reciprocating mill, and the cooling medium is water.

[0021] The purpose of the present application is achieved by the following technical scheme:

[0022] The application provides a preparation method of a V-B-Ti micro-alloyed 690MPa grade engineering machinery steel, which has the characteristics of high efficiency and low cost, and comprises the following steps of molten steel smelting, LF refining+RH vacuum degassing, B alloying, continuous casting, casting blank heating, controlled rolling and cooling and hot straightening.

[0023] 1) molten steel smelting to continuous casting: smelting according to the following components, the chemical components include C 0.13% to 0.17%, Si 0.15% to 0.25%, Mn 1.55% to 1.7%, P≤0.02%, S≤0.015%, Ti 0.017% to 0.0250%, Cr 0.1% to 0.2%, Als 0.015% to 0.045%, V 0.05% to 0.08%, B 0.0015% to 0.0020%, N 0.005% to 0.0095%, Ti / N=3.4 to 3.8, and the balance of Fe and inevitable impurities, and the total amount of other impurity elements is less than 0.05%; the molten iron is subjected to pretreatment, converter smelting, LF refining, RH vacuum degassing and continuous casting; after the RH vacuum degassing treatment is completed, Al is added according to the requirement of Als; then, Ti-Fe alloy is added for micro-titanium treatment, and then B-Fe alloy is added for B alloying; the addition is ensured in the molten steel to avoid floating on the slag layer; then slab continuous casting is performed, the overheat degree of continuous casting is 15 to 20 ℃, and the casting blank speed is 0.9 to 1.2 m / min (the control of the pouring overheat degree and the continuous casting blank speed can effectively reduce the quality defects of the casting blank core and corner); the electromagnetic stirring current intensity of the secondary cooling zone in the continuous casting stage is controlled to be 200 to 250 A, and the secondary cooling water quantity is 1.8 L / kg to 2.5 L / kg (the carbon segregation index is reduced, the segregation is inhibited, the secondary cooling intensity is limited, and the trend of the deterioration of the center crack of the casting blank is inhibited).

[0024] 2) casting blank heating: the casting blank is sent into a walking beam furnace for heating, wherein the temperature range of the preheating section is 900 to 1050 ℃ (the carbonide or nitride of Ti and V is quickly and fully solid-solved in the matrix, and is fully diffused), the temperature of the soaking section and the heating section is 1220 to 1245 ℃, the total time of the soaking section and the heating section is 3 to 3.5 hours, and the total in-furnace time of the preheating section, the soaking section and the heating section is 4 to 5.5 hours (high heating temperature is adopted, and the in-furnace time of the soaking section and the heating section is ensured, and the total in-furnace time is ensured to effectively promote the full diffusion of C, Mn, H, B and other elements, and ensure the uniformity of the as-rolled steel plate organization);

[0025] 3) Controlling rolling, cooling and straightening: the slab is rolled in two stages, the first stage is recrystallization rolling (rough rolling), the rough rolling starting temperature is equal to or greater than 1100°C, the rough rolling finishing temperature is in the range of 970-1020°C, the rough rolling stage is less than four passes (using high temperature deformation induction effect, promoting VC phase to precipitate in austenite crystal, providing nucleation sites for acicular ferrite, achieving the purpose of promoting intracrystalline acicular ferrite formation, improving strength and toughness; at the same time, TiN is induced to precipitate, and BN is inhibited from precipitating), the intermediate blank thickness is 2-4 times the thickness of the finished product; during the intermediate blank waiting process, 2 passes of descaling water are sprayed, the descaling time is 0.5-1.5 min, and the descaling machine pressure is 15-20 MPa (inhibiting the growth of austenite grains, at the same time, a temperature gradient is generated on the inner and outer surfaces of the billet, promoting the penetration of rolling deformation to the center of the thickness, refining the grains at the thickness of 1 / 2, which is beneficial to improve the core organization of thick gauge steel plate and reduce the generation of organizational stress caused by uneven organization, at the same time, the intermediate blank temperature is reduced, and the waiting time is reduced); the second stage is recrystallization rolling (finish rolling), the finish rolling starting temperature is in the range of 850-910°C, the finish rolling finishing temperature is in the range of 750-780°C, and the finish rolling is less than seven passes (by controlling the rough rolling finishing temperature, ensuring that the intermediate blank is in the austenite recrystallization temperature range during the waiting and finish rolling processes, ensuring the uniformity of the organization, at the same time, the descaling water is sprayed during the intermediate blank waiting process, ensuring the core penetration of the finish rolling stage, increasing the dislocation density, vacancies and deformation band number in the austenite, promoting VC precipitation, providing more nucleation sites, promoting ferrite phase transition, refining ferrite organization, and ensuring the strength and toughness of the steel plate). Subsequently, laminar cooling is used for online temperature control quenching, the cooling starting temperature is in the range of 680-710°C, the cooling finishing temperature is in the range of 500-530°C, and the cooling speed is 10-15°C / s (through calculation, the VC precipitation fastest temperature range is 690-720°C, the cooling starting temperature is controlled to ensure the VC precipitation density, which can significantly improve the mechanical properties of the steel through precipitation strengthening, in addition, B and Cr addition can improve the hardenability of the steel, increase the austenite stability, improve the phase transition driving force, promote the bainite transformation, based on this, high finishing temperature and slow cooling speed are adopted to ensure the shape of the steel plate after cooling); then hot straightening is performed, the straightening temperature is below 400°C, and then air cooling to room temperature.

[0026] Further, in step 1), the raw material is subjected to KR molten iron pretreatment, the content of S is controlled to be less than 0.015%, and after slagging, it enters the converter; during the converter smelting, the content of P is controlled to be less than or equal to 0.02%, the content of C at the end of the converter smelting is controlled to be in the range of 0.13-0.17%, and argon gas is blown for 20-30 min during tapping (the argon blowing and settling before continuous casting can promote the removal of inclusions in the molten steel, and improve the composition uniformity of the molten steel); then LF refining and RH vacuum degassing are performed; at the same time, the RH vacuum is maintained for more than 20 min.

[0027] Further, in the converter smelting process, double slag method is adopted to remove P.

[0028] Further, in step 2), the coal gas heat value is controlled to be 2000-2500 J / kg.

[0029] Further, in step 2), the temperature difference between the upper and lower surfaces of the cast blank is ensured to be within 15 DEG C.

[0030] Further, in step 3), the cooling medium of the laminar flow cooling is water.

[0031] Further, in step 3), the straightening force of the hot straightening is between 2800 KN and 3600 KN, the leading-in roller position is -0.8 mm to -1.5 mm, and the leading-out roller position is -2.1 mm to -2.6 mm (the straightening process is optimized to promote the further full release of internal stress).

[0032] The above-mentioned component and process scheme are adopted to obtain a high-efficiency and low-cost production method of a 690MPa-grade V-B-Ti micro-alloyed steel plate with a thickness specification of 10-50 mm.

[0033] The beneficial effects of the present application are as follows:

[0034] 1. By adopting argon blowing, the inclusions in the molten steel can be removed before continuous casting, and the composition uniformity of the molten steel is improved; the overheat degree of continuous casting and the strand pulling rate can effectively reduce the quality defects of the center and corner of the cast blank, the current intensity of the electromagnetic stirring in the second cooling zone and the secondary cooling water quantity can reduce the average index of carbon segregation, inhibit segregation, and the secondary cooling intensity is limited to inhibit the trend of deterioration of the center crack of the cast blank; the input light pressing down can help to reduce the segregation of the steel blank, refine the austenite grains, and reduce the internal structure defects.

[0035] 2. By limiting the preheating section temperature, the heating section and soaking section temperature and the total in-furnace time of the high-temperature section, the carbides and nitrides of Ti, V and B are ensured to be rapidly and fully solid-solved in the matrix, and are fully diffused, the coal gas heat value and the total in-furnace time are ensured, the diffusion of alloy elements Mn, B, V, N and other elements is further promoted, the influence of composition segregation on the structure and performance is reduced, and the austenite grains are also prevented from being coarsened due to the long in-furnace time, and the toughness of the steel plate is reduced.

[0036] 3、The designed component is reasonable, and the alloy addition amount is low, through the V-B-Ti composite design, the alloy cost and the high temperature deformation resistance in the rough rolling and finish rolling stage are greatly reduced, which is beneficial to improve the pass reduction, and is beneficial to ensure the comprehensive performance of the ultra-steel plate. The influence of B on the stability of austenite is related to the solid solution amount of B in the steel, in order to increase the solid solution B content in the boron-containing steel, Ti should be added which has stronger combination force than B and N; the V content in the steel almost does not affect the solid solution B content, through calculation, when the Ti content is 3.4-3.8 times of the N content in the steel, B can exist in the form of free.

[0037] 4、Adopting two-stage controlled rolling process, through controlling the finish rolling temperature in the rough rolling stage, it is ensured that the intermediate blank is in the austenite recrystallization temperature interval during the waiting temperature process, the uniformity of the structure is ensured, at the same time, the rolling reduction in the two-stage rolling, the thickness of the intermediate blank is limited, the high temperature deformation induced effect is utilized, the VC phase is promoted to precipitate in the austenite grains, the nucleation sites are provided for the acicular ferrite, the purpose of promoting the formation of intracrystalline acicular ferrite is achieved, the strength and toughness are improved; at the same time, TiN is induced to precipitate, BN is inhibited from precipitating; the spray scale water is used, the austenite grain growth is inhibited, at the same time, the temperature gradient is generated on the inner and outer surfaces of the steel blank, the penetration of rolling deformation to the center of the thickness is promoted, the grains at the 1 / 2 of the thickness are refined, which is beneficial to improve the core structure of the thick steel plate and reduce the generation of structure stress caused by the uneven structure; through calculation, the VC precipitation fastest temperature interval is 690-720℃, the open cooling temperature is controlled, the VC precipitation density is ensured, the VC precipitation can obviously improve the mechanical properties of the steel through precipitation strengthening, in addition, the addition of B and Cr can improve the hardenability of the steel, increase the austenite stability, improve the phase transformation driving force, promote the bainite transformation, based on this, the high red temperature and slow cooling speed are adopted, the plate shape after the cooling of the steel plate is ensured, at the same time, the straightening process is optimized, the internal stress is fully released.

[0038] 5、Adopting the above-mentioned component and process scheme, a high-efficiency and low-cost production method of a V-B-Ti micro-alloyed hot-rolled steel plate of 690MPa level and thickness specification 10-50mm is obtained, through optimizing the component design, steelmaking, heating, rolling, cooling and straightening process, the toughness and flatness problems of the 690MPa level hot-rolled steel plate of thickness 10-50mm produced by the on-line cooling process are finally solved. The specific performance is that: the yield strength performance of the 10-50mm thick 690MPa steel plate in the transverse direction is between 700-770MPa, the tensile strength is between 890-905MPa, the elongation is ≥17%, the transverse Charpy impact energy at-40℃ is ≥100J, and the flatness is below 5mm / 2m. DETAILED DESCRIPTION

[0039] The following examples are used to specifically illustrate the content of the present application, which are only general description of the content of the present application, and do not limit the content of the present application.

[0040] A V-B-Ti micro-alloyed 690 MPa grade engineering machinery steel, the chemical composition of which includes, in percentage by weight: C 0.13%-0.17%, Si 0.15%-0.25%, Mn 1.55%-1.7%, P≤0.02%, S≤0.015%, Ti 0.017%-0.0250%, Cr 0.1%-0.2%, Als 0.015%-0.045%, V 0.05%-0.08%, B 0.0015%-0.0020%, N 0.005%-0.0095%, Ti / N=3.4-3.8, the balance being Fe and unavoidable impurities, and the total amount of other impurities being less than 0.05%. The thickness of the steel plate is 10-50 mm, and the steel plate is produced on a medium plate reciprocating mill using a continuous casting billet with a thickness of less than 250 mm, and the cooling medium is water.

[0041] A preparation method of the above-mentioned V-B-Ti micro-alloyed 690 MPa grade engineering machinery steel, comprising the following steps: molten steel smelting→ LF refining+RH vacuum degassing→ B alloying→ continuous casting→ reheating of the billet→ controlled rolling and cooling→ hot straightening.

[0042] 1) Molten steel smelting to continuous casting: smelting according to the above-mentioned composition. The raw materials are subjected to KR hot metal pretreatment, the content of S is controlled to be lower than 0.015%, and the molten steel is then introduced into a converter after slagging; a double-slag method is used to remove P in the converter smelting, the content of P is controlled to be ≤0.02%, the content of C is controlled to be 0.13-0.17% at the end of the converter smelting, and argon is blown for 20-30 min when the molten steel is tapped; then, LF refining and RH vacuum degassing are performed; the RH vacuum is maintained for more than 20 min; after the degassing treatment, Al is added according to the requirement of Als; then, Ti-Fe alloy is added for micro-titanium treatment, and B-Fe alloy is added for B alloying; the addition is ensured to be in the molten steel to avoid floating on the slag layer; then, slab continuous casting is performed, the overheat degree is 15-20℃, and the continuous casting withdrawal rate is 0.9-1.2 m / min; the current intensity of electromagnetic stirring in the secondary cooling zone in the continuous casting stage is controlled to be 200-250 A, the secondary cooling water quantity is 1.8 L / kg-2.5 L / kg, the light press-down is introduced at the horizontal fan-shaped section, i.e. the solidification end, and the press-down amount of the continuous casting billet is 10-15 mm.

[0043] 2) Reheating of the billet: the billet (with a thickness of less than 250 mm) is sent into a walking beam furnace for reheating, and the billet is sequentially discharged after passing through a preheating section, a heating section and a soaking section; the temperature range of the preheating section is 900-1050℃, the temperature of the heating section and the soaking section is 1220-1245℃, the total time of the soaking section and the heating section is 3-3.5 hours, and the total time of the preheating section, the soaking section and the heating section in the furnace is 4-5.5 hours; the calorific value of the coal gas is controlled to be 2000-2500 J / kg.

[0044] 3) Controlling rolling, cooling and straightening: the cast blank is rolled in two stages, the first stage is recrystallization rolling (rough rolling), the rough rolling starting temperature is ≥1100℃, the rough rolling finishing temperature is in the range of 970-1020℃, the rough rolling stage has no less than 30% reduction per pass, the pass locking function is used, the rough rolling stage has less than four passes, the intermediate blank thickness is 2-4 times of the finished product thickness; during the intermediate blank waiting process, 2 passes of descaling water are sprayed, the descaling time is 0.5-1.5 min, the descaling machine pressure is 15-20 MPa; the second stage is recrystallization rolling (finish rolling), the finish rolling starting temperature is in the range of 850-910℃, the finish rolling finishing temperature is in the range of 750-780℃, the finish rolling has no more than seven passes. Subsequently, laminar cooling is used for online temperature control quenching, the cooling starting temperature is in the range of 680-710℃, the cooling finishing temperature is in the range of 500-530℃, the cooling speed is 10-15℃ / s; then hot straightening is performed, the straightening temperature is below 400℃, the straightening force is between 2800 KN and 3600 KN, the entry roller position is -0.8mm~ -1.5mm, the exit roller position is -2.1mm~ -2.6mm, and then air cooling is performed to room temperature.

[0045] Examples 1-6

[0046] Table 1 is the chemical composition of the example steel, Table 2 is the smelting to continuous casting process schedule of the example steel, Table 3 is the heating schedule of the cast blank of the example steel, Table 4 is the rolling parameter of the example steel, Table 5 is the cooling and straightening main process parameter of the example steel, and Table 6 is the performance and quality index of the example steel plate.

[0047] Table 1 Chemical composition of the example steel (wt, %)

[0048]

[0049] Note: the impurity elements in the steel are P≤0.02%, S≤0.015%, and the total amount of other impurity elements is less than 0.05%.

[0050] Table 2 Smelting to continuous casting process schedule of the example steel

[0051]

[0052] Table 3 Heating schedule of the cast blank of the example steel

[0053]

[0054] Table 4 Rolling parameter of the example steel

[0055]

[0056] Table 5 Cooling and straightening main process parameters of example steel

[0057]

[0058] Table 6 Performance and quality indexes of example steel plate

[0059]

[0060] It can be seen that, compared with the prior art, the purpose of the present application is to overcome the above-mentioned problems and deficiencies of the prior art, and to provide a high-efficiency and low-cost production method of a V-B-Ti micro-alloyed hot-rolled steel plate of 690MPa level and thickness specification 10-50mm. Through optimization of component design, steelmaking, heating, rolling, cooling and straightening process, the problem of low toughness and unevenness of plate shape of the 690MPa level hot-rolled steel plate with a thickness of 10-50mm produced by the online cooling process is finally solved.

[0061] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A V-B-Ti microalloyed 690 MPa grade engineering machinery steel, characterized in that, The chemical composition includes, by weight percentage: C 0.13%-0.17%, Si 0.15%-0.25%, Mn 1.55%-1.7%, P≤0.02%, S≤0.015%, Ti 0.017%-0.0250%, Cr 0.1%-0.2%, Als 0.015%-0.045%, V 0.05%-0.08%, B 0.0015%-0.0020%, N 0.005%-0.0095%, Ti / N=3.4-3.8, the balance being Fe and unavoidable impurities, and the total amount of other impurities being less than 0.05%; The preparation method of the V-B-Ti micro-alloyed 690MPa grade engineering machinery steel comprises the following steps: 1) molten steel smelting to continuous casting: the molten steel is pretreated, smelted in a converter, refined in a LF, degassed in a RH, and then continuously cast; after the RH vacuum degassing treatment is completed, Al is added according to the Al requirement, then Ti-Fe is added for micro-titanium treatment, and then B-Fe alloy is added for B alloying; then slab continuous casting is carried out, the continuous casting superheat is 15-20 ℃, and the continuous casting withdrawal rate is 0.9-1.2 m / min; the electromagnetic stirring current intensity of the secondary cooling zone in the continuous casting stage is controlled to be 200-250 A, the secondary cooling water quantity is 1.8 L / kg-2.5 L / kg, light pressing is carried out at the horizontal fan-shaped section, i.e. the solidification end, and the continuous casting billet pressing amount is 10-15 mm; 2) casting billet heating: the casting billet is sent into a walking beam heating furnace for heating, and the casting billet is sequentially discharged after passing through a preheating section, a heating section and a soaking section; the preheating section temperature is 900-1050 ℃, the soaking section and the heating section temperature is 1220-1245 ℃, the total time of the soaking section and the heating section is 3-3.5 hours, and the total time of the preheating section, the soaking section and the heating section in the furnace is 4-5.5 hours; 3) controlled rolling, cooling and straightening: the casting billet is rolled in two stages, the first stage is rough rolling, the rough rolling starting temperature is greater than or equal to 1100 ℃, the rough rolling final rolling temperature is 970-1020 ℃, the rough rolling stage has a two-pass rolling rate of not less than 30% per pass, the rough rolling stage has less than four rolling passes, and the intermediate billet thickness is 2-4 times the finished product thickness; during the intermediate billet waiting process, 2-pass descaling water is sprayed, the descaling time is 0.5-1.5 min, and the descaling machine pressure is 15-20 MPa; the second stage is finish rolling, the finish rolling starting temperature is 850-910 ℃, the finish rolling final rolling temperature is 750-780 ℃, and the finish rolling has not more than seven passes; then online temperature-controlled quenching is carried out by adopting laminar cooling, the cooling starting temperature is 680-710 ℃, the cooling final temperature is 500-530 ℃, and the cooling speed is 10-15 ℃ / s; then hot straightening is carried out, the hot straightening straightening temperature is below 400 ℃, and then air cooling is carried out to room temperature; In step 1), the raw material is pretreated by KR hot metal, the content of S is controlled to be less than 0.015%, and then the raw material enters the converter after slagging; in the converter smelting, the content of P is controlled to be less than or equal to 0.02%, the content of C is controlled to be 0.13-0.17% at the end of the converter smelting, and argon is blown for 20-30 min when tapping; then, LF refining and RH vacuum degassing are carried out; at the same time, the RH vacuum is kept for more than 20 min; In step 3), the cooling medium of the laminar flow cooling is water; the straightening force of the hot straightening is between 2800 KN and 3600 KN, the leading-in roller position is -0.8 mm to -1.5 mm, and the leading-out roller position is -2.1 mm to -2.6 mm; The yield strength of the steel in the transverse tension is 700-770 MPa, the tensile strength is 890-905 MPa, the elongation is greater than or equal to 17%, the transverse Charpy impact energy at -40 ℃ is greater than or equal to 100 J, and the flatness is less than 5 mm / 2 m.

2. The V-B-Ti microalloyed 690 MPa grade engineering machinery steel according to claim 1, characterized in that, The thickness of the steel is 10-50 mm.

3. The V-B-Ti microalloyed 690 MPa grade engineering machinery steel according to claim 1, characterized in that, In the converter smelting process, a double-slag method is used to remove P.

4. The V-B-Ti microalloyed 690 MPa grade engineering machinery steel according to claim 1, characterized in that, The thickness of the casting blank is less than or equal to 250 mm; the steel is a hot-rolled steel plate, and the casting blank is rolled on a medium plate reciprocating mill.

5. The V-B-Ti microalloyed 690 MPa grade engineering machinery steel according to claim 1, characterized in that, In step 2), the calorific value of the coal gas is controlled to be 2000-2500 J / kg.

6. The V-B-Ti microalloyed 690 MPa grade engineering machinery steel according to claim 1 characterized in that, In step 2), the temperature difference between the upper and lower surfaces of the casting blank is ensured to be within 15 ℃.

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