High-strength coated plate strip easy to form and production method

Abstract

The invention discloses an easy-to-form high-strength clad plate strip and a production method, the easy-to-form high-strength clad plate strip comprises a steel substrate and a low-alloy steel layer on at least one surface of the steel substrate, and a transition layer is formed on a contact interface of the steel substrate and the low-alloy steel layer; the tensile strength of the steel base plate is larger than or equal to 1300 MPa, and the hardness of the steel base plate is larger than or equal to 420 HBW. The low alloy steel comprises the following chemical components in percentage by weight: 0.001-0.04% of C, less than or equal to 0.1% of Si, 0.05-0.20% of Mn, less than or equal to 0.015% of P, less than or equal to 0.006% of S, 0.01-0.04% of Al, 0.01-0.04% of Ti, less than or equal to 0.005% of N and the balance of Fe. And the balance of Fe and inevitable impurity elements. The tensile strength of the low alloy steel is smaller than or equal to 350 MPa, the hardness is smaller than or equal to 120 Hv, and the ductility is larger than or equal to 30%. The produced clad plate strip has good interface bonding performance, cold bending processing performance and surface quality, the yield strength of the clad plate strip is larger than or equal to 1100 MPa, the tensile strength of the clad plate strip is larger than or equal to 1250 MPa, the ductility of the clad plate strip is larger than or equal to 10%, the machining requirements for 90-degree bending of D = 3a are met, and the clad plate strip is suitable for producing and machining structural parts in the field of engineering machinery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of low-alloy cladding material manufacturing, and particularly relates to an easy-to-form high-strength cladding plate strip and a production method. BACKGROUND

[0002] In the field of engineering machinery, with the increasing requirements for the functions of equipment, especially the load, lightweight, and forming processing, the requirements for steel grades are also increasingly high. The strength gradually transitions from the initial plain carbon steel to 500-600 MPa and 960 MPa, and the highest strength grade of high-strength steel used in crane booms has reached 1100 MPa or even 1300 MPa. With the increase in the strength grade, the forming processing problem of high-strength steel is becoming increasingly prominent. Currently, the 960 MPa grade high-strength steel can only meet the requirements of D = 5a-6a and 90° bending, and the steel plate of a higher strength grade can only meet the cold bending requirements of D = 7a and 8a, which obviously increases the processing difficulty of users. Therefore, there is an urgent need for easy-to-form high-strength steel plates in the field of engineering machinery.

[0003] Chinese patent CN102747303A discloses "a high-strength steel plate with a yield strength of 1100 MPa and a manufacturing method thereof", which needs to add 0.2-0.7% Mo, 0.6-2.0% Ni, and 0-0.07% Nb, V, etc. on the composition of the steel plate. Although high strength is achieved, the forming processing performance is not improved, and the cost is high.

[0004] With the increasing use requirements, a single material is difficult to meet the performance requirements in multiple aspects. A composite plate prepared by selecting multiple metal materials through various processes combines the advantages of multiple metals, thereby meeting the needs of engineering applications. Currently, common composite plates include copper-clad, aluminum-clad, or titanium-steel, stainless steel-steel composite materials.

[0005] Chinese patents CN201645923U and CN201721090U disclose "a copper-clad steel strip" and "a copper-plain carbon steel composite plate", which are a steel-steel combined strip and plate, respectively. The former does not involve a specific method, and only stipulates that the Cu content in the copper-clad strip is 5-20%; the latter is obtained by stacking the copper plate and the steel plate after cleaning the surfaces, and then rolling after heating, which is low in efficiency.

[0006] Chinese patent CN113106327B discloses "a high-corrosion-resistant steel strip and a manufacturing method thereof", which obtains a stainless steel-steel cladding material by cladding a stainless steel on the surface of a carbon steel, thereby obtaining the corrosion resistance of stainless steel while significantly reducing the cost. However, the patent involves complex grouping technology, including surface pickling, polishing treatment, welding, vacuum extraction, etc., and then uses a conventional hot continuous rolling process to complete the production of the steel strip, which is complex in the preparation process of the composite blank and high in production cost.

[0007] Chinese patent CN106310218B discloses "a composite bulletproof steel plate and its production method", which adopts low-strength soft steel and high-strength steel with 600HBW hardness level to form a multi-layer soft and hard combined clad material through interactive cladding, realizing better bulletproof performance. The cladding technology involved in the patent needs complex assembly and vacuum welding, and the process is complex and the cost is high, which is unbearable for the current mechanical engineering field.

[0008] From the prior art, the high-strength steel grade for engineering machinery needs to add more Cr, Ni, Mo, Nb, V and other elements, which is high in cost and difficult to meet the forming performance requirements. Limited cladding plate strips and preparation technologies, the materials involved are low in strength and not suitable for engineering machinery field, or the cladding process is complex and the cost is high. SUMMARY

[0009] The purpose of the present application is to provide an easy-to-form high-strength cladding plate strip and a production method. The produced cladding plate strip has good interface bonding performance, cold bending processing performance and surface quality, the yield strength is ≥1100MPa, the tensile strength is ≥1250MPa, the elongation is ≥10%, and it meets the requirements of D=3a, 90° bending processing, and is suitable for the production and processing of structural parts in engineering machinery field. Moreover, the present application realizes the cladding of steel and steel in the conventional hot continuous rolling production process, omits the complex assembly and welding process in the existing cladding production process, has higher production efficiency and lower cost.

[0010] To achieve the above purpose, the technical scheme of the present application is as follows:

[0011] An easy-to-form high-strength cladding plate strip, comprising a steel base plate and at least one low-alloy steel layer on the surface of the steel base plate, and a transition layer formed at the contact interface between the steel base plate and the low-alloy steel layer.

[0012] The tensile strength of the steel base plate is ≥1300MPa, and the hardness is ≥420HBW.

[0013] The chemical composition of the low-alloy steel is as follows: C: 0.001-0.04%, Si≤0.1%, Mn: 0.05-0.20%, P≤0.015%, S≤0.006%, Al: 0.01-0.04%, Ti: 0.01-0.04%, N≤0.005%; the rest includes Fe and inevitable impurity elements.

[0014] The tensile strength of the low-alloy steel is ≤350MPa, the hardness is ≤120Hv, and the elongation is ≥30%.

[0015] Preferably, the steel substrate has the following chemical composition by weight: C: 0.18-0.24%, Si: 0.1-0.3%, Mn: 0.6-0.9%, P≤0.015%, S≤0.006%, Al: 0.01-0.04%, Cr: 0.1-0.3%, N≤0.005%, Ti: 0.01-0.03%, B: 0.001-0.003%, and the rest including Fe and inevitable impurities.

[0016] Further, the low-alloy steel has the following chemical composition: the rest including Fe and inevitable impurities, and the steel substrate has the following chemical composition: the rest including Fe and inevitable impurities.

[0017] The low-alloy steel has an equiaxed ferrite microstructure with a grain size of ≥10 μm.

[0018] The clad plate strip has a thickness of 1.5-8.0 mm, and the low-alloy steel layer has a thickness of 1.5-12% of the total thickness of the clad plate strip.

[0019] The clad plate strip has a yield strength of ≥1100 MPa, a tensile strength of ≥1250 MPa, and an elongation of ≥10%, and meets the D=3a, 90° bending requirement.

[0020] The steel plate generally improves the strength through solid solution strengthening, precipitation strengthening, dislocation strengthening and grain boundary strengthening. The low-alloy steel used in the present application requires excellent plasticity, i.e. maintains an equiaxed ferrite microstructure even under quenching and cooling conditions, so as to control the tensile strength to ≤350 MPa. In order to effectively reduce the yield strength and improve the elongation, the addition amount of alloying elements must be reduced as much as possible, and the strengthening factors must be reduced, and the reasons for limiting the specific chemical composition are as follows:

[0021] C: has solid solution strengthening, which increases the yield strength and reduces the elongation. The content should be reduced as much as possible. When the carbon content is >0.04%, pearlite structure is easily formed in the steel, and even martensite structure is formed during cooling, which is not conducive to plasticity and cold bending performance. Therefore, the C content is controlled to be 0.001-0.04% in the present application.

[0022] Si: is a deoxidizing element and a solid solution strengthening element, which increases the yield strength and reduces the elongation, so the addition amount of Si should be reduced as much as possible; however, too low Si content increases the difficulty of steelmaking and production cost. Therefore, the Si content is controlled to be ≤0.1% in the present application.

[0023] Mn: is a common strengthening element in steel, which increases the yield strength through solid solution strengthening and reduces the elongation. Therefore, the Mn content is controlled to be 0.05-0.20% in the present application.

[0024] P: can also improve the strength, and make the steel plate brittle, affect the toughness, so should try to reduce the content of P in steel. Therefore, the present application controls P≤0.015%.

[0025] S: can improve the yield strength of steel, and make the steel plate brittle, reduce the low temperature toughness of steel, therefore, the present application controls S≤0.006%.

[0026] Al: is a ferrite forming element, usually added in steel as a deoxidizer in the steelmaking process, trace amounts of Al form fine AlN precipitates during steelmaking, which has the effect of refining austenite grains during subsequent cooling, improving the strength and toughness of steel. Al is also used as a N fixing agent in steel, AlN exists independently as a non-metallic inclusion in steel, which destroys the continuity of the steel substrate, especially when the Al content is high, the amount of AIN formed is more, and the harm is more serious, and at the same time, the plasticity of the oxide is poor. Therefore, the present application controls the content of Al in 0.01-0.04%.

[0027] N: solid solution can significantly improve the strength of steel, N in steel can form compounds with Al and Ti, and fine precipitates have the effect of pinning grain boundaries to refine austenite grains. N forms AlN particles with Al in steel, which plays a role in binding Al and limits the diffusion of Al in steel. Higher N in steel combines with Al to form AlN, thereby significantly increasing the amount of nitride in steel. AlN exists independently as a non-metallic inclusion in steel, which destroys the continuity of the steel matrix, especially when the Al content is high, the amount of AIN formed is more, and the harm is more serious, and at the same time, the plasticity of the oxide is poor; and higher N is easy to enrich at defects, which worsens the low temperature impact toughness. Therefore, the present application controls N≤0.005%.

[0028] Ti: used to fix C, N atoms to reduce their hindering effect on dislocation movement. Ti in steel can form TiN→Ti4C2S2→TiS and TiC in turn, eliminating free C, N atoms in steel, thereby reducing the yield strength. At the same time, the coarsening of TiC, TiN particles makes them lose the effect of grain boundary pinning, increases the grain size, and reduces the grain boundary strengthening effect. However, too much Ti will reduce the elongation of the steel plate. Therefore, the present application controls the content of Ti in 0.01-0.04%.

[0029] The low alloy steel used in the present application adopts very low C-Si-Mn composition design and fixes C, N interstitial atoms by Ti, eliminating the solid solution strengthening effect of C, N atoms, and using coarse TiN, TiC particles to obtain larger grain size, so that the surface layer of low alloy steel layer can still obtain equiaxed ferrite substrate structure even in quenched state, and the hardness value is≤120Hv.

[0030] The steel substrate used in the present application requires high strength to meet the requirements of high-strength weight reduction. The substrate mainly obtains high strength through phase transformation strengthening of C, and further improves the strength and toughness through Cr, Ti, B, etc. Therefore, the present application recommends the following steel substrate composition design (wt%): C: 0.18-0.24%, Si: 0.1-0.3%, Mn: 0.6-0.9%, P≤0.015%, S≤0.006%, Al: 0.01-0.04%, Cr: 0.1-0.3%, N≤0.005%, Ti: 0.01-0.03%, B: 0.001-0.003%, and the rest including Fe and unavoidable impurity elements. Among them:

[0031] C is the most economical strengthening element in steel, but too high C makes the high-temperature steel billet prone to cracking during cooling, which is not conducive to the preservation of the steel billet and increases the production difficulty. Therefore, the C content in the steel substrate of the present application is controlled at 0.18-0.24%.

[0032] Si is a deoxidizing element and also a solid solution strengthening element. Si replaces Fe atoms in the steel in a substitutional manner, hindering dislocation movement and thus achieving solid solution strengthening. In addition, the effect of Si on increasing strength is less than that of C, and it increases the work hardening rate during cold working, which to some extent reduces the toughness and plasticity of the steel. And too high Si promotes graphitization of C, which is not conducive to toughness; at the same time, it is not conducive to surface quality and welding performance. Therefore, the Si content in the steel substrate of the present application is controlled at 0.1-0.3%.

[0033] Mn is also a common strengthening element in steel, which promotes the formation of austenite. Mn increases the yield strength through solid solution strengthening, which reduces the elongation; appropriate amount of Mn can combine with S in the steel to form MnS, reducing the hot brittleness of the steel. At the same time, Mn can expand the austenite region, reduce the transformation temperature of undercooled austenite, promote the microstructure transformation at medium and low temperature, and refine the microstructure of the steel, which is an important strengthening and toughening element. However, too much Mn will lead to segregation, deteriorate the substrate structure and form large MnS inclusions, thereby deteriorating the weldability of the steel plate and the toughness of the heat-affected zone. Moreover, high Mn reduces the M s point, leading to an increase in residual austenite, reducing the yield ratio of the steel plate, and increasing the temper brittleness of the steel plate. Therefore, the Mn content in the steel substrate of the present application is controlled at 0.6-0.9%.

[0034] P and S make the steel plate brittle and affect the toughness, especially P is prone to induce segregation, so they are controlled as impurity elements in the present application. Therefore, the P content in the steel substrate of the present application is controlled at ≤0.015%, and the S content is controlled at ≤0.006%.

[0035] Ti is a strong ferrite forming element and carbonitride forming element, which reduces the austenite zone. Ti is easy to form compounds with C, N and other elements, and the melting point of Ti compound is high, which hinders the growth of austenite at heating. Ti reduces the temper brittleness of steel at 250-400℃, and the addition of B can significantly reduce the temper brittleness. The precipitation strengthening effect of titanium in proeutectoid ferrite increases the yield strength. When the content of Ti is too high, the titanium nitride particles are easy to grow and agglomerate at high temperature, which damages the plasticity and toughness of the steel. Therefore, the content of Ti in the steel substrate of the application is controlled at 0.01-0.03%.

[0036] B has good hardenability, thereby improving the hardness of the steel plate, but too high B content is not conducive to welding, therefore, the content of B in the steel substrate of the application is controlled at 0.001-0.003%;

[0037] Cr has a solid solution strengthening effect, but Cr is a valuable alloying element, therefore, the content of Cr in the steel substrate of the application is controlled at 0.1-0.3%.

[0038] The steel substrate uses a higher C content and adds B element to improve the hardenability, and Mn in the substrate has a solid solution strengthening effect, especially under the strong phase transition strengthening effect of C, a high-strength martensite structure is obtained after heat treatment, realizing high strength, the tensile strength is ≥1300MPa, and the hardness value is ≥420HBW.

[0039] The application realizes high strength and improves the cold forming performance of the clad plate strip by the composition design of low alloy steel strip and the cladding of high-strength steel substrate. Even if the yield strength is ≥1100MPa, it can still meet the 3a, 90° cold bending requirement. Finally, a clad plate strip with yield strength ≥1100MPa, tensile strength ≥1250MPa, elongation ≥10% and meeting the D=3a, 90° bending requirement is obtained.

[0040] The production method of the easy-to-form high-strength clad plate strip comprises the following steps:

[0041] 1) smelting and casting

[0042] According to the composition of the above steel substrate, smelting, refining and casting into a billet are carried out;

[0043] 2) heating

[0044] The heating temperature is 1100-1200℃, and the heating time is ≥2h;

[0045] 3) rough rolling

[0046] The rough rolling obtains an intermediate billet, and the cumulative deformation of the rough rolling stage is ≥80%;

[0047] 4) surface treatment

[0048] The intermediate blank is surface polished, and the low-alloy steel strip surface is treated to remove surface stains;

[0049] 5) finish rolling

[0050] The low-alloy steel strip is attached to the intermediate blank, and the low-alloy steel strip head is welded to the intermediate blank, and then finish rolling is performed to obtain a clad strip; the finish rolling starting temperature is ≥ 950℃, the finish rolling final rolling temperature is 870-910℃, and the deformation amount in the finish rolling stage is ≥ 80%;

[0051] 6) cooling and coiling

[0052] After rolling, water cooling or air cooling is performed to 650-750℃ for coiling;

[0053] 7) heat treatment

[0054] Then quenching treatment and tempering treatment are performed;

[0055] Quenching, quenching temperature ≥ (steel base plate A c3 + 5-30℃), quenching holding time ≥ 2.5×clad plate strip thickness, the clad plate strip thickness is in mm, the quenching holding time is in min, after the quenching holding time ends, cooling to room temperature at a speed of ≥ 50℃ / s,

[0056] Tempering, tempering temperature is 200-260℃, and tempering holding time is 15-60 min.

[0057] Preferably, in step 5), the welding method of welding the low-alloy steel strip to the intermediate blank is laser welding or resistance welding.

[0058] Preferably, in step 7), before quenching heat treatment, uncoiling, straightening and cutting are sequentially performed.

[0059] Preferably, the intermediate blank surface polishing, the attachment process of the low-alloy steel strip to the intermediate blank and welding are all performed under protection of a protective atmosphere, and the protective atmosphere is one or both of N2 and CO2.

[0060] The present application realizes the production of steel-steel clad plate strip by adopting an online hot continuous rolling process, and uses the high-temperature intermediate blank in the hot continuous rolling process to cover the low-alloy steel strip to be covered, thereby saving the complex assembly process. The key process is to obtain a clad blank between rough rolling and finish rolling.

[0061] The heating temperature of the casting blank is 1100-1200 DEG C, and the heating time is greater than or equal to 2 hours. If the heating temperature is too high, austenite grains are coarsened, and the surface is seriously oxidized, which increases the loss; and if the heating temperature is too low, the rolling load is increased, and the rolling equipment is damaged. Similarly, if the holding time is too short, the inside of the casting blank cannot be heated sufficiently, which results in abnormal structure and temperature in the core and the surface layer, and the deformation of the surface layer and the core is inconsistent in the rolling process, and the plate shape is poor; and if the holding time is too long, the structure of the casting blank is coarse, and even the casting blank is overburned, which results in cracking of the casting blank in the rolling process. The heating temperature of 1100-1200 DEG C and the heating time greater than or equal to 2 hours are selected by comprehensive consideration.

[0062] In order to ensure the recrystallization and refine the grains to improve the strength and toughness, the cumulative deformation in the rough rolling stage is required to be greater than or equal to 80%.

[0063] The purpose of the surface polishing of the intermediate blank is to remove the surface oxide layer, and to increase the roughness, which is beneficial to improve the copper-steel bonding strength in the clad rolling process.

[0064] The surface of the low-alloy steel strip also needs to be pre-treated (such as pickling or degreasing cleaning), and the main purpose is to remove the oxide scale and various surface stains, especially no oil stains. If the surface of the copper strip is polished in advance, the copper-steel bonding strength can be further improved.

[0065] The surface polishing of the intermediate blank, the pasting process of the copper strip and the intermediate blank, and the welding are all carried out under the protection of a protective atmosphere, so as to reduce the oxidation of the intermediate blank at high temperature, and improve the copper-steel bonding strength, and the protective atmosphere is one or both of N2 and CO2.

[0066] The low-alloy steel strip is pasted to the intermediate blank, and the low-alloy steel strip and the intermediate blank are welded, and then the clad strip is obtained by finish rolling, and the finish rolling start temperature is greater than or equal to 950 DEG C, and the finish rolling finish temperature is 870-910 DEG C. By using high finish rolling temperature, the rolling load can be effectively reduced, the energy consumption can be reduced, and the cost can be reduced; but the higher finish rolling temperature requires higher casting blank heating temperature, which increases the heating cost. The finish rolling start temperature is limited to be higher than 950 DEG C by comprehensive consideration. The A c3 temperature is 860-870 DEG C, and the finish rolling finish temperature is limited to be higher than 870 DEG C, so that the complete austenite zone rolling can be realized, the mixed grains in the base plate structure are avoided, and the rolling mill load is stable in the rolling process. If the finish rolling finish temperature is too high, the higher finish rolling start temperature is required, and the energy consumption and the cost are also increased. Therefore, the finish rolling finish temperature is limited to be 870-910 DEG C. In order to ensure the interface bonding strength of the low-alloy steel layer and the steel base plate, the deformation in the finish rolling stage is required to be greater than or equal to 80%.

[0067] After rolling, the water cooling or air cooling is carried out to 650-750 DEG C, and the obtained clad plate strip is thin, and the air cooling can be carried out for the clad plate strip with a thickness less than or equal to 2.0 mm.

[0068] The steel-steel clad plate after coiling is uncoiled and straightened, then cut into sheets, and then quenched and tempered, the quenching temperature is A c3 at least 5-30 DEG C higher than the temperature, the quenching holding time is determined according to the thickness of the clad plate strip, and the quenching holding time is usually 2.5 times or more of the thickness of the clad plate strip, and after the quenching holding is finished, the quenching is directly water-quenched to room temperature, and the cooling speed is required to be greater than or equal to 50 DEG C / s.

[0069] Then, tempering is performed at a temperature range of 200-260 DEG C, the tempering holding time is 15-60 min, so as to slow down and eliminate quenching stress and improve toughness.

[0070] The quenched and tempered clad plate strip is subjected to finishing treatment (straightening and edge cutting), and is delivered after the performance is qualified.

[0071] Compared with the prior art, the present application has the following beneficial effects:

[0072] The steel substrate used in the present application has a tensile strength greater than or equal to 1300 MPa and a hardness greater than or equal to 420 HBW, and the low-alloy steel layer of the surface layer is designed with low carbon and low alloy without adding any reinforcing alloy element, so that the substrate has equiaxed ferrite structure with a grain size greater than or equal to 10 mu m, and even in the quenched state, it still has a ferrite soft phase structure with a tensile strength less than or equal to 350 MPa and an elongation greater than or equal to 30%, and has good plasticity. The clad plate strip produced has good interface bonding performance, cold bending processing performance and surface quality, and has high strength and excellent forming performance, with a yield strength greater than or equal to 1100 MPa, a tensile strength greater than or equal to 1250 MPa and an elongation greater than or equal to 10%, and meets the 3a, 90 DEG cold bending requirement. The forming performance of the existing high-strength steel with a strength greater than 960 MPa can only meet the D=7a-8a, 90 DEG cold bending requirement.

[0073] The clad steel plate is metallurgically bonded in a hot-rolled state, and since the steel substrate and the clad layer are both low-alloy steel, there is no diffusion resistance problem between different metals at the interface, so the interlayer bonding is good, and no obvious delamination can be seen on the macroscopic cross section. Compared with the floatation material obtained by cladding ordinary steel substrates and different metals, such as steel-aluminum, copper-aluminum or copper-steel, the clad layer and the substrate are different metals, and due to the difference in material, there is a clear interface between the clad layer and the substrate, and the atoms of the clad layer and the substrate have diffusion resistance between different materials at the interface, the bonding is mainly physical bonding (mechanical interlocking) + local metallurgical bonding, the bonding strength is limited, and there is an obvious transition layer on the cross section, and the clad layer and the substrate are obviously layered.

[0074] The present application realizes the lamination of the steel base plate and the low alloy steel strip in the finishing stage in the hot continuous rolling production process of the steel plate, realizes the online rolling of the steel base plate and the low alloy steel strip, the interlayer metal realizes metallurgical bonding under high temperature rolling, the bonding strength is high, and the interlayer metal is not easy to separate; and the complex grouping, welding process in the existing cladding production process is omitted, which is not only high in efficiency, but also low in cost. The processes for preparing the cladding plate strip involved in Chinese patents CN113106327B and CN106310218B have complex grouping and vacuum welding processes, high cost and low production efficiency; and the grouping process has high requirements on the size precision of the bonding surface, and the processing difficulty is greater. BRIEF DESCRIPTION OF DRAWINGS

[0075] Figure 1 The structure diagram of the cladding plate strip of the present application is shown.

[0076] Figure 2 The microstructure photo of the steel base plate of the cladding plate strip of the present application is shown.

[0077] Figure 3 The microstructure photo of the surface low alloy steel layer of the cladding plate strip of the present application is shown. DETAILED DESCRIPTION

[0078] The present application will be further described below in combination with the embodiments and the drawings.

[0079] The process flow for preparing the cladding plate of the present application is: intermediate plate blank heating → rough rolling → surface grinding → cladding rolling → controlled cooling → coiling → uncoiling → straightening → plate cutting → heat treatment → finishing → delivery.

[0080] The chemical composition of the steel base plate used in the cladding plate strip of the present application is shown in Table 1, and the rest includes Fe and inevitable impurity elements.

[0081] The chemical composition of the surface low alloy steel layer of the cladding plate strip of the present application is shown in Table 2, and the rest includes Fe and inevitable impurity elements.

[0082] The production process parameters of the cladding plate strip of the present application are shown in Tables 3 and 4.

[0083] The performance of the cladding plate strip obtained in the present application is shown in Table 5.

[0084] Figure 1 The structure diagram of the cladding plate strip obtained in the present application is shown, wherein 1 is a low alloy steel layer, and 2 is a steel base plate.

[0085] Figure 2 The microstructure photo of the steel base plate of the cladding plate strip of the present application is shown, and it can be seen from the picture that the steel base plate forms high-strength martensite structure after heat treatment, the tensile strength is ≥1300MPa, and the hardness is ≥420HBW.

[0086] Figure 3 The microstructure of the low alloy steel layer of the coated plate strip of embodiment 1 is shown in the figure, and the microstructure of the low alloy steel layer after quenching heat treatment is still equiaxed ferrite, maintaining low strength and high plasticity.

[0087] Currently, there is no unified and standard detection method for the interface bonding strength of metals. In NBT47002-4-2009, Explosion Welding Composite Plate for Pressure Vessels Part 4-Copper Steel Composite Plate, the quality requirement for interface bonding is that the area of the interface that is not compounded should not exceed 5%, and D=4a, 180° bending should not delaminate; in the standard YS-T 1045-2015 Decorative Copper Steel Composite Sheet and Strip, when evaluating the quality of copper steel composite, D=3-4a, 180° repeated cold bending until fracture without delamination is required. In order to test the interface bonding performance of the copper clad plate, the coated plate is repeatedly bent at D=3a, 90° until cracking, and whether the interface is well bonded is determined according to whether there is delamination at the cracking position.

[0088] The coated steel plate strip obtained according to the steel composition design range and rolling process of the present application has a yield strength of ≥1100MPa, a tensile strength of ≥1250MPa, and an elongation of ≥10%, and excellent cold bending performance, which can meet the 3a, 90° cold bending requirement. The plasticity is much better than that of the existing 1100MPa strength level high-strength steel, and the copper-steel interface bonding performance is excellent, and there is no delamination at the fracture after repeated bending until fracture, which meets the complex processing requirements of high-strength structural parts in the mechanical engineering industry.

[0089] The above specifications, coating types, base plate thicknesses and low alloy steel layer thicknesses are only for implementation examples, and the upper and lower low alloy steel layers in the embodiments are of equal thickness. In actual applications, appropriate production processes can be used to combine low alloy steel layers and base plates of different thicknesses to prepare more coated plate strips that meet the needs.

[0090]

[0091]

[0092]

[0093]

[0094]

Claims

1. A type of easily formable high-strength clad sheet strip, characterized in that, It includes a steel substrate and a low-alloy steel layer on at least one of its surfaces, and a transition layer formed at the contact interface between the steel substrate and the low-alloy steel layer. The steel substrate has a tensile strength ≥1300MPa and a hardness ≥420HBW; The chemical composition of the low alloy steel by weight percentage is as follows: C: 0.001–0.04%, Si ≤ 0.1%, Mn: 0.05–0.20%, P ≤ 0.015%, S ≤ 0.006%, Al: 0.01–0.04%, Ti: 0.01–0.04%, N ≤ 0.005%; the remainder includes Fe and unavoidable impurity elements. The low alloy steel has a tensile strength ≤350MPa, a hardness ≤120Hv, and an elongation ≥30%.

2. The easily formable high-strength coated sheet and strip as described in claim 1, characterized in that, The chemical composition of the steel substrate by weight percentage is as follows: C: 0.18-0.24%, Si: 0.1-0.3%, Mn: 0.6-0.9%, P≤0.015%, S≤0.006%, Al: 0.01-0.04%, Cr: 0.1-0.3%, N≤0.005%, Ti: 0.01-0.03%, B: 0.001-0.003%, with the remainder including Fe and unavoidable impurity elements.

3. The easily formable high-strength coated sheet and strip as described in claim 1 or 2, characterized in that, The remaining chemical composition of the low alloy steel is Fe and unavoidable impurity elements, and the remaining chemical composition of the steel substrate is Fe and unavoidable impurity elements.

4. The easily formable high-strength coated sheet and strip as described in claim 1, 2, or 3, characterized in that, The microstructure of the low alloy steel is equiaxed ferrite with a grain size ≥10μm.

5. The easily formable high-strength coated sheet and strip as described in claim 1, 2, 3, or 4, characterized in that, The thickness of the cladding strip is 1.5 to 8.0 mm, and the thickness of the low alloy steel layer is 1.5 to 12% of the total thickness of the cladding strip.

6. The easily formable high-strength coated sheet and strip as described in claim 1, 2, 3, 4, or 5, characterized in that, The cladding strip has a yield strength ≥1100MPa, a tensile strength ≥1250MPa, and an elongation ≥10%, meeting the requirements of D=3a and 90° bending.

7. The method for producing easily formable high-strength clad strips as described in any one of claims 1 to 6, characterized in that, Includes the following steps: 1) Smelting and casting The steel substrate is smelted and refined according to the composition of claim 2, and then cast into a billet. 2) Heating The heating temperature is between 1100 and 1200℃, and the heating time is ≥2 hours. 3) Rough rolling The intermediate billet is obtained by rough rolling, and the cumulative deformation during the rough rolling stage is ≥80%. 4) Surface treatment The intermediate billet is surface-polished, and the low-alloy steel strip is surface-treated to remove surface stains. 5) Finish rolling Low-alloy steel strip is applied to the intermediate billet, and the head of the low-alloy steel strip is welded to the intermediate billet. Then, it is finished rolled to obtain the cladding strip. The finishing rolling start temperature is ≥950℃, the finishing rolling end temperature is 870~910℃, and the deformation in the finishing rolling stage is ≥80%. 6) Cooling and winding After rolling, the coil is water-cooled or air-cooled to 650–750°C and then wound. 7) Heat treatment Then, quenching and tempering are performed; Quenching, quenching temperature ≥ (steel substrate A) c3 +5~30℃), quenching and holding time ≥2.5×coating strip thickness, where the coating strip thickness is in mm and the quenching and holding time is in min. After quenching and holding, cool to room temperature at a rate of ≥50℃ / s. Tempering, tempering temperature is 200-260℃, tempering holding time is 15-60min.

8. The production method as described in claim 7, characterized in that, In step 5), the welding method for welding the low alloy steel strip to the intermediate billet is laser welding or resistance welding.

9. The production method as described in claim 7, characterized in that, In step 7), before the quenching heat treatment, the coil is uncoiled, straightened and cut in sequence.

10. The production method as described in claim 7, characterized in that, The grinding of the intermediate billet surface, the application of the low alloy steel strip to the intermediate billet, and the welding are all carried out under a protective atmosphere, which is one or both of N2 and CO2.

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