Production method of heat-treated Q690MPa-grade longitudinal variable-thickness steel plate

Abstract

The invention relates to a production method of a heat-treated Q690MPa-grade longitudinal variable-thickness steel plate, and belongs to the technical field of steel production. The method comprises the following steps: obtaining a steel billet with set chemical components; the steel billet is heated and then rolled, and a semi-finished longitudinal variable-thickness steel plate is obtained; carrying out quenching treatment on the semi-finished longitudinal variable-thickness steel plate; and the quenched semi-finished longitudinal variable-thickness steel plate is subjected to tempering treatment, and the finished longitudinal variable-thickness steel plate is obtained. The components of the Q690MPa-grade longitudinal variable-thickness steel plate are reasonably designed, a proper amount of Cr, Mn and B are added to improve the hardenability, a small amount of Nb and Ti are added to achieve microalloy strengthening, the plate shape control of the variable-thickness steel plate is achieved through rolling speed control and the like, and the performance control of the variable-thickness steel plate is achieved through a quenching process, a tempering process and the like. And a whole set of production method for heat treatment of the Q690MPa-grade longitudinal variable-thickness steel plate is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of steel production, and particularly relates to a production method of a heat-treated Q690MPa longitudinal variable-thickness steel plate. BACKGROUND

[0002] At present, the medium plate is generally of ordinary physical properties, i.e. the thickness of the plate is uniform. With the upgrading of the use requirements of engineering machinery, bridges, ships and the like, the ordinary physical property medium plate gradually cannot meet the use requirements, and the longitudinal variable-thickness steel plate is proposed. The steel plate significantly reduces the structure weight and the welding seam in the use process, improves the safety of the steel structure, and has a broad engineering application prospect.

[0003] The current domestic and foreign research focuses on the variable-thickness steel plate produced by the controlled rolling method of Q355MPa, Q420MPa and the like, but the strength requirements of the steel plate of the user are from the initial Q355MPa level to Q690MPa or even higher strength level. The single controlled rolling cannot meet the strength use requirements, and it is urgent to develop the production method of the heat-treated Q690MPa longitudinal variable-thickness steel plate to meet the use requirements of the downstream user. SUMMARY

[0004] The present application provides a production method of a heat-treated Q690MPa longitudinal variable-thickness steel plate to solve the following technical problem: how to improve the yield strength of the heat-treated longitudinal variable-thickness steel plate.

[0005] In a first aspect, the present application provides a production method of a heat-treated Q690MPa longitudinal variable-thickness steel plate, and the method comprises the following steps.

[0006] obtaining a billet with a set chemical composition;

[0007] heating the billet, and then rolling to obtain a semi-finished longitudinal variable-thickness steel plate;

[0008] quenching the semi-finished longitudinal variable-thickness steel plate;

[0009] tempering the semi-finished longitudinal variable-thickness steel plate after the quenching to obtain a finished longitudinal variable-thickness steel plate; the set chemical composition of the billet comprises, in terms of mass fraction, C: 0.12% to 0.16%, Si: 0.2% to 0.3%, Mn: 1.1% to 1.5%, Cr: 0.2% to 0.4%, Nb: 0.01% to 0.04%, Ti: 0.01% to 0.03%, and B: 0.001% to 0.003%.

[0010] Optionally, the heating temperature is 1150°C to 1170°C, the heating time T 加热 =A*H钢 ;

[0011] Wherein, A is heating time thickness coefficient, A=0.9-1.1 is taken;

[0012] H 钢 is the thickness of the steel billet;

[0013] If H 钢 is in mm, then T 加热 is in min.

[0014] Optionally, the final rolling temperature of the rolling is 900-950 DEG C, the speed of the rolling is 1-3 m / s, and the upper limit of the HGC setting speed of the rolling is 10-20 mm / s.

[0015] Optionally, the heating time T 淬火 of the quenching treatment is B*H 厚 +20;

[0016] Wherein, B is quenching heating time thickness coefficient, B=1.6-1.8 is taken;

[0017] H 厚 is the maximum thickness of the semi-finished product longitudinal variable-thickness steel plate;

[0018] If H 厚 is in mm, then T 淬火 is in min.

[0019] Optionally, during the quenching treatment, the roll gap width of the quenching machine of the quenching treatment is 0.5-1.5 mm larger than the maximum thickness H 厚 of the semi-finished product longitudinal variable-thickness steel plate.

[0020] Optionally, the heating time T 回火 of the tempering treatment is C*H 厚 +20;

[0021] Wherein, C is tempering heating time thickness coefficient, C=3.3-3.5 is taken;

[0022] H 厚 is the thickness of the thickest part of the steel plate, in mm;

[0023] If H 厚 is in mm, then T 回火 is in min.

[0024] Optionally, the thickness of the finished product longitudinal variable-thickness steel plate is 10-100 mm.

[0025] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0026] The application provides a production method of a heat-treated Q690MPa longitudinal variable thickness steel plate, and the method comprises the following steps: obtaining a billet with a set chemical composition; heating the billet, and then rolling to obtain a semi-finished longitudinal variable thickness steel plate; performing quenching treatment on the semi-finished longitudinal variable thickness steel plate; performing tempering treatment on the semi-finished longitudinal variable thickness steel plate after the quenching treatment to obtain a finished longitudinal variable thickness steel plate; the set chemical composition of the billet comprises the following components in mass fraction: C: 0.12% to 0.16%, Si: 0.2% to 0.3%, Mn: 1.1% to 1.5%, Cr: 0.2% to 0.4%, Nb: 0.01% to 0.04%, Ti: 0.01% to 0.03%, and B: 0.001% to 0.003%. By reasonably designing the composition of the longitudinal variable thickness steel plate, adding appropriate Cr, Mn and B to improve the hardenability, and adding a small amount of Nb and Ti to realize micro-alloy strengthening, the shape control of the variable thickness steel plate is realized through the rolling speed control, the performance control of the variable thickness steel plate is realized through the quenching process control and tempering process control, and the yield strength of the heat-treated longitudinal variable thickness steel plate is improved to reach the 690MPa level. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without creative labor.

[0029] Figure 1 A flowchart of a production method of a heat-treated Q690MPa longitudinal variable thickness steel plate provided by the embodiments of the present application is shown.

[0030] Figure 2 A side view of a finished longitudinal variable thickness steel plate provided by the embodiments of the present application is shown.

[0031] Figure 3 A metallographic structure diagram of a finished longitudinal variable thickness steel plate provided by the embodiments of the present application is shown. DETAILED DESCRIPTION

[0032] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0033] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values in the range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers in the range, such as 1, 2, 3, 4, 5 and 6, which applies to any range; in addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0034] In this document, the term includes "includes" and the like means "including but not limited to". The relationship terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. "And / or", which describes the relationship between the associated objects, means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone; wherein A and B can be singular or plural. "At least one" means one or more, and "multiple" means two or more; "at least one", "at least one of the following" or the like means any combination of the items, including single item or any combination of multiple items; for example, "at least one of a, b or c", or "at least one of a, b and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, c can be single or multiple. Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0035] Figure 1 A flowchart of a production method of a heat-treated Q690MPa grade longitudinal variable thickness steel plate according to an embodiment of the present application;

[0036] As Figure 1As shown, the embodiments of the present application provide a production method of heat-treated Q690MPa grade longitudinal variable thickness steel plate, which comprises:

[0037] S1, obtaining a billet with a set chemical composition;

[0038] In some embodiments, the set chemical composition of the billet includes, in mass fraction: C: 0.12%~0.16%, Si: 0.2%~0.3%, Mn: 1.1%~1.5%, Cr: 0.2%~0.4%, Nb: 0.01%~0.04%, Ti: 0.01%~0.03%, B: 0.001%~0.003%.

[0039] According to the composition designed for the thickest part of the variable thickness steel plate, the final performance of the variable thickness steel plate can be fully guaranteed.

[0040] The positive effect of limiting the content of C to 0.12%~0.16%: C is an important strengthening element in steel, and a C content of 0.12%~0.16% can improve the hardness and strength of the steel. In Q690MPa grade steel, this C content range can ensure that the steel plate reaches the required strength level, while not excessively sacrificing its toughness. In addition, this C content range can guarantee the hardenability of the steel grade, while having good welding performance. For example, the content of C can be 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, etc.

[0041] The positive effect of limiting the content of Si to 0.2%~0.3%: Si can be dissolved in ferrite and austenite in steel to form solid solution strengthening, thereby improving the strength and hardness of the steel. For example, the content of Si can be 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, etc.

[0042] The positive effect of limiting the content of Mn to 1.1%~1.5%: Mn can expand the stability region of austenite, making it easier for the steel to obtain uniform and fine martensite structure during quenching. This is of great significance to improving the comprehensive mechanical properties of the steel plate and reducing heat treatment distortion. In the production of Q690MPa grade steel plate, good hardenability can ensure that the steel plate obtains uniform performance in the thickness direction, meeting the use requirements under complex working conditions. In addition, Mn forms MnS with a higher melting point than FeS, which can prevent the hot brittleness phenomenon caused by FeS. For example, the content of Mn can be 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0043] The positive effect of limiting the content of Cr to 0.2% to 0.4% is that Cr can expand the stability region of austenite, making it easier for the steel to obtain a uniform and fine structure during quenching. For Q690MPa grade steel plates, this means that the martensitic transformation can be more fully realized during quenching, thereby obtaining better mechanical properties and dimensional stability. In addition, during the tempering process, Cr helps to promote the precipitation and dispersion of carbides. This not only improves the tempering stability of the steel plate, preventing excessive tempering softening, but also improves the toughness and fatigue resistance of the steel plate to some extent. For example, the content of Cr can be 0.2%, 0.24%, 0.28%, 0.32%, 0.36%, 0.4%, etc.

[0044] The positive effect of limiting the content of Nb to 0.01% to 0.04% is that Nb is a strong carbide-forming element in steel, which helps to improve the strength and toughness of the steel by refining the grain size and increasing the recrystallization temperature of the steel. In Q690MPa grade steel plates, a Nb content of 0.01% to 0.04% can significantly enhance the comprehensive mechanical properties of the steel plate, enabling it to have good toughness while ensuring high strength, to meet the requirements of complex working conditions. For example, the content of Nb can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, etc.

[0045] The positive effect of limiting the content of Ti to 0.01% to 0.03% is that Ti is a strong carbide and nitride-forming element in steel. Adding 0.01% to 0.03% Ti to the steel can form fine TiC or TiN particles. These particles act as pinning points for grain boundaries, effectively preventing grain growth at high temperatures, thereby refining the grain structure of the steel. Refining the grain can significantly improve the strength and toughness of the steel. For example, the content of Ti can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, etc.

[0046] The positive effect of limiting the content of B to 0.001%-0.003%: B is one of the trace elements in steel and has a significant impact on the hardenability of steel. During quenching, B can expand the stability region of austenite and reduce the critical cooling rate of steel, so that the steel can obtain a martensite structure within a wider range of cooling speeds. This is particularly important for the production of longitudinal variable thickness steel plates with uneven thickness, as there may be differences in cooling speed at different thickness locations. By adding an appropriate amount of B, it can be ensured that the entire steel plate obtains uniform and fine martensite structure after quenching, thereby improving the overall strength and toughness of the steel plate. B can also refine the grains of steel to some extent. During heating and rolling, B helps to promote grain boundary migration and recrystallization, thereby forming a more fine-grained structure. The refined grains can significantly improve the strength and toughness of the steel, while also improving the processing performance and fatigue resistance of the steel. For example, the content of B can be 0.001%, 0.0015%, 0.002%, 0.0025%, 0.003%, etc.

[0047] S2, heating and then rolling the billet to obtain a semi-finished longitudinal variable thickness steel plate;

[0048] In some embodiments, the heating temperature is 1150°C-1170°C.

[0049] The positive effect of limiting the heating temperature to 1150°C-1170°C: heating within the temperature range of 1150°C-1170°C can ensure that the structure of the billet is fully austenitized, and the austenite grains are not too coarse. Austenite is the precursor of martensite formed during quenching, and its uniformity and fineness directly affect the mechanical properties of the steel plate after quenching. Therefore, the selection of this temperature range helps to obtain uniform and fine austenite structure, laying a good foundation for subsequent quenching. Heating temperature higher than 1170°C can cause decarburization and severe oxidation on the surface of the billet, and even cause overheating and burning defects, while temperature lower than 1150°C can cause incomplete austenitization, affecting the quenching effect. Controlling the heating temperature between 1150°C and 1170°C and adjusting the heating time according to the thickness of the billet can effectively avoid these heating defects and ensure the heating quality of the billet. For example, the heating temperature can be 1150°C, 1155°C, 1160°C, 1165°C, 1170°C, etc.

[0050] In some embodiments, the heating time T 加热 =A*H 钢 ;

[0051] wherein A is the heating time thickness coefficient, and A=0.9-1.1;

[0052] H 钢 is the thickness of the billet;

[0053] If H 钢 The unit of T 加热 The unit of T is min.

[0054] The calculation of heating time is based on the thickness of the billet, making the heating process more scientific and reasonable. For billets of different thicknesses, adjusting the heating time can ensure that they all achieve the desired heating effect, without causing energy waste or production delays due to excessive or insufficient heating time. This heating strategy helps improve production efficiency and reduce production costs. For example, the value of the heating time thickness coefficient A can be 0.9, 0.95, 1.0, 1.5, 1.1, etc.

[0055] The steel plate rolling process follows a one-stage rolling process, which ensures the accuracy of the steel plate's external dimensions. The high deformation temperature of the billet can significantly reduce the deformation resistance of the steel plate and reduce the dynamic rolling load of the rolling mill.

[0056] In some embodiments, the final rolling temperature of the rolling process is 900℃-950℃, the rolling speed is 1m / s-3m / s, and the upper limit of the HGC (Hydraulic Gap Control) set speed is 10mm / s-20mm / s.

[0057] The positive effect of limiting the final rolling temperature of the rolling process to 900℃-950℃: This temperature range helps the billet maintain good plasticity and toughness during the rolling process, reducing the occurrence of rolling cracks. For example, the final rolling temperature can be 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, etc.

[0058] The positive effect of limiting the rolling speed to 1m / s-3m / s: A rolling speed of 1m / s-3m / s is moderate, ensuring rolling efficiency while avoiding the internal organizational inhomogeneity and stress concentration caused by a rolling speed greater than 3m / s. For example, the rolling speed can be 1m / s, 1.4m / s, 1.8m / s, 2.2m / s, 2.6m / s, 3m / s, etc.

[0059] The HGC (Hydraulic Gap Control) system precisely adjusts the roll gap during the rolling process, with a set upper speed limit of 10mm / s-20mm / s, ensuring that the thickness variation of the steel plate in the longitudinal direction meets the design requirements, improving the dimensional accuracy and consistency of the product, and reducing the difficulty and cost of subsequent processing. For example, the upper limit of the HGC set speed can be 10mm / s, 12mm / s, 14mm / s, 16mm / s, 18mm / s, 20mm / s, etc.

[0060] S3, quenching the semi-finished product longitudinal variable thickness steel plate;

[0061] Quenching is to rapidly cool the steel plate to produce a high hardness of martensite structure, thereby significantly improving the strength and hardness of the steel plate. The steel plate is quenched by non-rolling method, and the quenching medium is water.

[0062] In some embodiments, the semi-finished longitudinal variable thickness steel plate has a thickest portion and a thinnest portion, the thickest portion being the head of the steel plate, and the thinnest portion being the tail of the steel plate.

[0063] During quenching, the steel plate will deform due to the sharp change of temperature. By setting the thickest portion at the head, it can be ensured that during quenching, the thicker portion first contacts the cooling medium, thereby effectively reducing the deformation difference caused by the different thicknesses of each portion. If the thicker portion is located at the tail of the steel plate, it may be pierced into the quenching machine roll gap due to deformation during quenching, resulting in production interruption or damage to the steel plate. By placing it at the head, this problem can be avoided, ensuring the continuity and safety of production. In addition, since the thickest portion first contacts the cooling medium, it can ensure that the cooling rate of the entire steel plate during quenching is relatively uniform. This helps to form a more consistent microstructure, improving the overall performance of the steel plate.

[0064] In some embodiments, the heating temperature of the quenching treatment is 880-920°C.

[0065] The positive effect of limiting the heating temperature of the quenching treatment to 880-920°C is that the austenitization of the steel plate is more sufficient, while avoiding excessive grain growth affecting the strength and toughness of the final steel plate. For example, the heating temperature of the quenching treatment can be 880°C, 890°C, 900°C, 910°C, 920°C, etc.

[0066] In some embodiments, the heating time T 淬火 of the quenching treatment is B*H 厚 +20;

[0067] wherein B is the quenching heating time thickness coefficient, and B=1.6-1.8;

[0068] H 厚 is the maximum thickness of the semi-finished longitudinal variable thickness steel plate;

[0069] If the unit of H 厚 is mm, then the unit of T 淬火 is min.

[0070] The accurate quenching heating time helps to ensure that the steel plate can fully and uniformly complete the transformation from austenite to martensite during quenching, so as to obtain an ideal microstructure and performance. Through the preset quenching heating time formula, the quenching heating time of steel plates of different thicknesses can be quickly calculated, thereby ensuring the consistency of the temperature in the thickness direction of the steel plate. For example, the thickness coefficient B of the quenching heating time can be 1.6, 1.65, 1.7, 1.75, 1.8, etc.

[0071] In some embodiments, the quenching machine roll gap width of the quenching treatment is slightly wider than the maximum thickness H of the semi-finished longitudinally variable-thickness steel plate 厚 0.5mm to 1.5mm.

[0072] By setting the quenching machine roll gap width to be slightly wider than the thickest part of the steel plate (0.5mm to 1.5mm), it can be ensured that the cooling medium can uniformly and fully contact the surface of the steel plate during quenching, thereby reducing the difference in cooling speed caused by the change in thickness of the steel plate. This helps to achieve uniform quenching of the steel plate and avoid problems such as local hardness unevenness or internal stress concentration caused by uneven cooling. In addition, due to the longitudinally variable-thickness characteristic of the steel plate, thermal stress and microstructure stress may be caused by the difference in cooling speed during quenching, leading to deformation or cracking of the steel plate. By adjusting the quenching machine roll gap width, the cooling speed can be balanced to some extent, thereby reducing the risk of deformation and cracking caused by stress concentration and improving the yield and quality stability of the product. For example, the quenching machine roll gap can be 0.5mm, 0.7mm, 0.9mm, 1.1mm, 1.3mm, 1.5mm, etc. wider than the thickest part of the steel plate.

[0073] S4, performing a tempering treatment on the semi-finished longitudinally variable-thickness steel plate after the quenching treatment to obtain a finished longitudinally variable-thickness steel plate.

[0074] In some embodiments, the heating temperature of the tempering treatment is 560°C to 600°C.

[0075] The main purpose of the tempering treatment is to eliminate residual stress and brittle phase generated during quenching, and to adjust the hardness and toughness of the steel plate to achieve the best performance balance. By setting the heating temperature in the range of 560°C to 600°C, the steel plate can obtain good toughness while maintaining a high strength level, thereby meeting the performance requirements of Q690MPa grade steel plates. For example, the heating temperature of the tempering treatment can be 560°C, 570°C, 580°C, 590°C, 600°C, etc.

[0076] In some embodiments, the heating time T of the tempering treatment is 回火 =C*H 厚 +20;

[0077] Wherein, C is the tempering heating time thickness coefficient, C = 3.3-3.5;

[0078] H 厚 is the thickness of the thickest part of the steel plate, unit mm;

[0079] If H 厚 is in mm, then T 回火 is in min.

[0080] The heating time is accurately calculated according to the thickness of the thickest part of the steel plate. This setting can achieve consistent temperature in the thickness direction of the steel plate, ensuring that the steel plate in different thickness areas can achieve ideal tempering effect, avoiding the problems of over-tempering or insufficient tempering. The steel plate after high-temperature tempering has a main organization of tempered sorbite, which has good strength and toughness. For example, the tempering heating time thickness coefficient C can be 3.3, 3.35, 3.4, 3.45, 3.5, etc.

[0081] In some embodiments, the finished longitudinal variable-thickness steel plate has a thickness of 10-100 mm.

[0082] This method can prepare finished steel plates with a thickness range of 10-100 mm, meeting the diversified needs of different industries and fields for steel plate thickness. For example, the finished longitudinal variable-thickness steel plate can have a thickness of 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc.

[0083] The present application will be further described below in conjunction with specific examples. The experimental methods in the following examples are generally determined according to industry standards unless otherwise specified; if there is no corresponding industry standard, the general international standard, conventional conditions, or the conditions recommended by the manufacturer are used.

[0084] The side view of the finished longitudinal variable-thickness steel plate is shown in Figure 2 .

[0085] Example 1

[0086] The billet size is thick*wide*long = 200mm*2195*2600mm. After rolling, the billet size H1 = 14mm, H2 = 18mm, L1 = 2000mm, L2 = 5000mm, L3 = 10000mm, the width is 2960mm, and the L2 part is a single slope transition area.

[0087] The chemical composition of the billet is shown in the table below.

[0088]

[0089] The billet heating temperature is 1150°C, and the heating time is 200 minutes. The finish rolling temperature is 940°C, the rolling speed is 2 m / s, and the HGC setting speed upper limit is 15 mm / s. The quenching heating temperature is 900°C, the quenching heating time is 51 minutes, and the quenching machine roll gap value is 18.5 mm. The tempering heating temperature is 580°C, and the tempering heating time is 81 minutes. The yield strength of the finished product longitudinal variable thickness steel plate at the 18 mm thickness position is 801 MPa, the tensile strength is 845 MPa, the elongation is 19%, and the -40°C impact energy is 262 J.

[0090] Example 2

[0091] The billet size is thick*wide*long=250 mm*2400*2600 mm. After rolling, the billet size H1=30 mm, H2=50 mm, L1=3000 mm, L2=5000 mm, L3=7200 mm, the width is 2400 mm, and the L2 part is a single slope transition area.

[0092] The chemical composition of the billet is shown in the following table.

[0093]

[0094] The billet heating temperature is 1150°C, and the heating time is 250 minutes. The finish rolling temperature is 960°C, the rolling speed is 3 m / s, and the HGC setting speed upper limit is 15 mm / s. The quenching heating temperature is 900°C, the quenching heating time is 105 minutes, and the quenching machine roll gap value is 51 mm. The tempering heating temperature is 580°C, and the tempering heating time is 190 minutes. The yield strength of the finished product longitudinal variable thickness steel plate at the 50 mm thickness position is 715 MPa, the tensile strength is 767 MPa, the elongation is 15.5%, and the -40°C impact energy is 208 J.

[0095] Example 3

[0096] The billet size is thick*wide*long=300 mm*2400*3000 mm. After rolling, the billet size H1=100 mm, H2=80 mm, L1=3000 mm, L2=5000 mm, L3=2100 mm, the width is 2400 mm, and the L2 part is a single slope transition area.

[0097] The chemical composition of the billet is shown in the following table.

[0098]

[0099] The billet heating temperature is 1170℃, the heating time is 300 minutes, the finish rolling temperature is 980℃, the rolling speed is 1m / s, the HGC setting speed upper limit is 15mm / s, the quenching heating temperature is 900℃, the quenching heating time is 190 minutes, the quenching machine roll gap value is 101.5mm, the tempering heating temperature is 580℃, and the tempering heating time is 360 minutes. The yield strength of the finished product longitudinal variable thickness steel plate at the 100mm thickness position is 675MPa, the tensile strength is 727MPa, the elongation is 16%, and the -40℃ impact energy is 198J.

[0100] From the embodiments 1-3, it can be seen that the chemical composition and production process of the embodiments are located in the required range of the application, and the yield strength of the finished product longitudinal variable thickness steel plate reaches the 690MPa level.

[0101] The detailed description of the application is as follows: Figure 3

[0102] The detailed description of the application is as follows: Figure 3 The metallographic structure diagram of the finished product longitudinal variable thickness steel plate provided by the embodiments of the application is shown in FIG. 1, and the metallographic structure of the finished product longitudinal variable thickness steel plate mainly includes tempered sorbite. The finished product longitudinal variable thickness steel plate has a refined and uniform structure. Figure 3

[0103] The one or more technical solutions in the embodiments of the application have at least the following technical effects or advantages:

[0104] The production method of the heat-treated Q690MPa grade longitudinal variable thickness steel plate not only improves the mechanical properties and structural requirements of the steel plate, but also meets the special requirements of the steel plate thickness variation in specific engineering fields, has significant technical effects and wide application prospects.

[0105] The above is only the specific embodiments of the application, so that those skilled in the art can understand or implement the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined in the application can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to these embodiments shown in the application, but will conform to the widest scope consistent with the principles and novel features of the application claimed.​​

Claims

1. A method for producing a heat treated Q690 MPa grade longitudinal variable thickness steel plate, characterized in that, The method comprises: obtaining a billet with a set chemical composition; heating the billet, post-rolling to obtain a semi-finished longitudinal variable thickness steel plate; quenching the semi-finished longitudinal variable thickness steel plate; tempering the semi-finished longitudinal variable thickness steel plate after quenching to obtain a finished longitudinal variable thickness steel plate; the set chemical composition of the billet comprises, in mass fraction, C: 0.12% to 0.16%, Si: 0.2% to 0.3%, Mn: 1.1% to 1.5%, Cr: 0.2% to 0.4%, Nb: 0.01% to 0.04%, Ti: 0.01% to 0.03%, and B: 0.001% to 0.003%.

2. The method of claim 1, wherein, The temperature of the heating is 1150°C to 1170°C, the time T of the heating 加热 = A*H 钢 ; wherein A is a heating time thickness coefficient, and A = 0.9 to 1.1; H 钢 for the thickness of the billet; If H 钢 is in mm, then T 加热 is in min.

3. The method of claim 1, wherein, the final rolling temperature of the rolling is 900°C to 950°C, the speed of the rolling is 1 m / s to 3 m / s, and the upper limit of the HGC setting speed of the rolling is 10 mm / s to 20 mm / s.

4. The method of claim 1, wherein, the heating temperature of the quenching is 880°C to 920°C.

5. The method according to claim 1 or 4, characterized in that, the heating time T of the quenching treatment 淬 fire = B * Hthick + 20; wherein B is a quenching heating time thickness coefficient, and B = 1.6 to 1.8; H 厚 H is the maximum thickness of the semi-finished longitudinal variable-gauge steel sheet; If H 厚 is in mm, then T 淬火 is in min.

6. The method of claim 1, wherein, The quenching machine roll gap width of the quenching treatment is less than the maximum thickness H of the semi-finished product longitudinal variable thickness steel plate 厚 0.5 mm to 1.5 mm.

7. The method of claim 1, wherein, the heating temperature of the tempering is 560°C to 600°C.

8. The method according to claim 1 or 7, characterized in that, The heating time T of the tempering treatment 回 fire = C * Hthick + 20; wherein C is a tempering heating time thickness coefficient, and C = 3.3 to 3.5; H 厚 thickness of the thickest portion of the steel sheet, unit: mm If H 厚 is in mm, then T 回火 is in min.

9. The method of claim 1, wherein, the thickness of the finished longitudinal variable thickness steel plate is 10 mm to 100 mm.

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