CN118726838A

CN118726838A - High-surface-quality aluminum-clad plate strip suitable for nitriding and production method thereof

Info

Publication number: CN118726838A
Application number: CN202310334059.3A
Authority: CN
Inventors: 宋凤明; 庞厚君; 温东辉; 王巍
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2023-03-30
Filing date: 2023-03-30
Publication date: 2024-10-01

Abstract

A high surface quality aluminum-clad strip suitable for nitriding and a production method thereof are provided, wherein the steel strip and the aluminum strip are clad, the weight percentage of the chemical components of the steel strip is ：C 0.01～0.07％,0＜Si≤0.005％,Mn 0.40～1.20％,P 0.008～0.020％,S≤0.008％,0＜Al≤0.005％,Cr0.03～0.60％,N 0.011～0.03％,0＜O≤0.01％,Cu 0.01～0.15％,Ca0.001～0.004％,, one or more of 0.01 to 0.06 percent of Ti, 0.01 to 0.03 percent of Nb and 0.01 to 0.03 percent of V are added, and the balance comprises Fe and unavoidable impurities; and needs to satisfy simultaneously: 0.5C+3.83N+O+0.05Cu+0.047Cr-0.89Al-1.15Si is more than or equal to 0.085;150 (C-0.01) +60P+300N+5Mn+3Cr is not less than 12.0. The aluminum-clad plate strip has good steel-aluminum combination property, stamping and deep drawing property and surface quality, can adapt to high-temperature nitriding or other high-temperature treatment, and simultaneously keeps good steel-aluminum combination property and cold bending property.

Description

High-surface-quality aluminum-clad plate strip suitable for nitriding and production method thereof

Technical Field

The invention belongs to the field of low alloy steel manufacturing, and particularly relates to a high-surface-quality aluminum-clad plate strip suitable for nitriding and a production method thereof.

Background

The aluminum-clad plate strip is a composite strip formed by rolling an aluminum layer on the surface of strip steel at room temperature, and structurally has a steel-aluminum structure as well as a steel-aluminum-steel or aluminum-steel-aluminum structure. The aluminum-clad plate has the strength of the existing steel, has the characteristics of good heat radiation, corrosion resistance, light weight, attractive appearance and the like of aluminum, and greatly reduces the cost compared with pure aluminum materials, so the aluminum-clad plate has been widely applied to the fields of radiator fins, corrosion-resistant pipelines, household appliance panels and the like, and gradually expands to the fields of automobile engine shields, new energy automobile parts, atmospheric corrosion resistance, cookers, buildings and the like.

The aluminum-clad plate strip is required to have good steel-aluminum bonding performance and also has the requirements of high surface and high strength. In the kitchen ware field, the novel frying pan adopting the steel-aluminum-steel structure has the strength of steel, and has the characteristic of good Al heat dissipation, so that the defects of uneven heat dissipation and easy burning of an iron frying pan are avoided, and the frying pan is lighter. In addition, when using aluminum-clad sheet strips for producing products such as woks, nitriding the surface of the aluminum-clad sheet strips is required to obtain high surface hardness. After the conventional aluminum-clad plate is subjected to high-temperature nitriding treatment, on one hand, the problem of strength reduction occurs, and on the other hand, high temperature provides power for the formation of brittle phases at a steel-aluminum interface, so that the steel-aluminum bonding performance is reduced and even layered.

Chinese patent CN101660087 discloses an aluminium-steel-aluminium composite material and its preparation method, which is to cold-roll aluminium and steel after surface treatment into high-precision aluminium strip and steel strip respectively, then cold-roll again into high-precision aluminium-steel-aluminium composite strip, and anneal at 650-850 ℃ for 1-4 hours. Since the melting point of aluminum is about 640 c, annealing at such a high temperature seriously deteriorates the interfacial bonding strength of steel aluminum. The performance and surface quality requirements of the current application field of the aluminum-clad plate strip cannot be met.

Chinese patent CN102019727 discloses "aluminum coated steel strip for cooler, method for preparing same and steel strip and aluminum alloy strip used thereby", which mainly relates to aluminum coated steel strip for heat dissipation and substrate used thereby, single pass press down rate 58-62%. The structure is steel-aluminum, the thickness is about 1.5mm, and the thickness of the aluminum film is 50-80 mu m. The patent does not relate to the properties of the aluminum coated strip after high temperature nitriding treatment.

An aluminum-coated plate strip with excellent heat dissipation effect and a production method thereof are disclosed in Chinese patent CN107881410A, and an aluminum-coated plate strip with high surface quality and easy punching processing and a production method thereof are disclosed in Chinese patent CN108796384A, wherein the aluminum-coated plate is mainly used for producing radiator fins, household appliance panels and the like, and nitriding treatment is not involved in the production process. The strength of the conventional aluminum-clad plate strip is obviously reduced after nitriding treatment, and the cookware is easy to deform in the flanging process of the production cookware. These two patents are significantly different from the present invention in terms of function and application.

The high-strength aluminum-clad plate strip and the manufacturing method thereof disclosed in Chinese patent CN107781426A ensure the aluminum bonding property of the aluminum-clad plate strip by N, O and controlling Si and Al, and have the yield strength of 280-400MPa, but the tensile property after annealing at a lower temperature is also not related to high-temperature nitriding treatment, and the property of the aluminum-clad plate strip after high temperature is not known. The aluminum-coated material is mainly used for producing radiator fins, household appliance panels and the like, and cannot meet the application of the high-temperature heat treatment process.

The Chinese patent CN114250411A discloses an aluminum-clad plate strip for kitchen ware and a production method thereof, wherein the aluminum-clad plate strip is used for manufacturing a frying pan, nitriding treatment is also involved in the processing process, and the strength requirement after nitriding is provided. But the aluminum-clad plate strip only requires that the tensile strength is more than or equal to 320MPa, and meanwhile, the yield and the tensile strength of the used base plate are respectively less than or equal to 280MPa and 380MPa, which are obviously lower than the invention. In addition, the steel strip related to this patent requires control of the carbon content to be below 0.005% in composition and limits P, S content to not more than 0.012% and 0.006% respectively, which increases the difficulty of steel making and the production cost. In the application field, the application is limited to processing of aluminum coated materials for frying pans, and the thickness of the aluminum layer accounts for about 40-60% of the total thickness; and cannot be used for other aluminum coating materials with high strength requirements.

From the comparison result, the existing steel-aluminum covered belt material is poor in steel-aluminum combination performance or does not meet nitriding treatment and high-strength requirements, wherein the thickness of an aluminum layer is more than 100 mu m, and the steel-aluminum covered belt material is mainly used in the fields of radiator fins, household appliance panels, food trays and the like and mainly utilizes the characteristic of high heat dissipation coefficient of aluminum.

Disclosure of Invention

The invention aims to provide a high-surface-quality aluminum-clad plate strip suitable for nitriding and a production method thereof, wherein the aluminum-clad plate strip has good steel-aluminum combination property, stamping drawing property and surface quality, the yield strength is more than or equal to 300MPa, the tensile strength is more than or equal to 360MPa, the elongation A50 is more than or equal to 25%, the aluminum-clad plate strip still has high strength after high-temperature nitriding or other high-temperature treatment, meanwhile, the aluminum-steel combination property and the cold bending property are kept, the D=1a and 180 DEG cold bending requirements are met, and the aluminum-clad plate strip is suitable for production and processing of a frying pan or other products with high-strength requirements, and has the characteristics of portability, good heat dissipation performance and easiness in cold forming and processing.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

A high surface quality aluminum-clad plate strip suitable for nitriding is formed by cladding a steel strip and an aluminum strip, wherein the weight percentage of chemical components of the steel strip is ：C：0.01～0.07％,0＜Si≤0.005％,Mn：0.40～1.20％,P：0.008～0.020％,S≤0.008％,0＜Al≤0.005％,Cr：0.03～0.60％,N：0.011～0.03％,0＜O≤0.01％,Cu：0.01～0.15％,Ca：0.001～0.004％,, and Ti is selectively added: 0.01 to 0.06 percent, nb:0.01 to 0.03 percent, V:0.01 to 0.03%, the balance comprising Fe and other unavoidable impurities; and needs to satisfy simultaneously:

0.5C+3.83N+O+0.05Cu+0.047Cr-0.89Al-1.15Si≥0.085；

150(C-0.01)+60P+300N+5Mn+3Cr≥12.0。

further, the balance being Fe and other unavoidable impurities.

The yield strength of the steel belt is more than or equal to 280MPa, the tensile strength is more than or equal to 340MPa, and the elongation is more than or equal to 30%.

The yield strength of the aluminum-clad plate strip is more than or equal to 300MPa, the tensile strength is more than or equal to 360MPa, and the elongation A50 is more than or equal to 25%.

The aluminum clad plate strip is in a steel-aluminum, aluminum-steel-aluminum or steel-aluminum-steel structure.

In the design of the chemical composition of the steel belt of the aluminum-clad plate with excellent nitriding performance, the invention comprises the following steps:

C improves yield strength through solid solution strengthening and phase change strengthening, inhibits Al from diffusing in steel and forming iron-aluminum compounds, and the excessively high C content is unfavorable for the subsequent stamping, drawing and other processing performances of the material; however, higher C tends to be biased in defective positions such as dislocation, and the surface quality is not good. According to the actual steelmaking process, the content of C is controlled to be 0.01-0.07%.

Si is a deoxidizing element and also a solid solution strengthening element, so that the yield strength is increased, the elongation is reduced, and a proper amount of Si is favorable for improving the bonding performance of a steel-aluminum interface, but simultaneously, the inhibition effect of O (oxygen) on the formation of a brittle compound layer of the steel-aluminum interface is weakened. Therefore, the invention controls Si content to be more than 0 and less than or equal to 0.005 percent.

Mn is also a common strengthening element in steel, and improves yield strength through solid solution strengthening, so that elongation is reduced; the proper amount of Mn can be combined with S in steel to generate MnS, so that the hot brittleness of the steel is reduced, but too high Mn solid solution prevents the recovery of a structure and inhibits the growth of recrystallized grains, reduces the strength of gamma texture (ND <111 >), is unfavorable for the stamping forming of the steel plate, and increases the cost, so the content of Mn is controlled to be 0.40-1.20%.

P is generally controlled as an impurity element in steel, and the addition of P is only allowed in a few special purpose steels. For example, P is added to sulfur-containing free-cutting steel in an amount of not more than 0.15% to make it solid-soluble in ferrite, thereby causing strengthening and embrittlement to improve cutting properties. In addition, P is a main corrosion resistant element in the traditional atmospheric corrosion resistant steel, and P in the steel can accelerate the uniform dissolution of the steel and the oxidation rate of Fe ²⁺, thereby being beneficial to forming a uniform FeOOH rust layer on the surface of the steel, promoting the generation of an amorphous iron oxyhydroxide FeO _x(OH)_3-2x compact protective film and effectively improving the atmospheric corrosion resistant performance of the steel. Since the corrosion resistance is generally optimal when the P content is 0.08 to 0.15%, P is added as a corrosion resistant element to the early part of the atmospheric corrosion resistant steel. However, too much P causes "cold embrittlement" of the steel, deteriorates plasticity and impact toughness, and deteriorates weldability and cold bending property of the steel, so that the addition amount of the steel grade having a high requirement for low-temperature impact toughness or forming property is definitely defined. In recent years, some atmospheric corrosion resistant steels also have reduced P content, and other substitute corrosion resistant elements are selected to ensure corrosion resistance, even if the corrosion resistant steels are controlled as impurity elements, the required content is less than or equal to 0.015%, but controlling the P content at such a low level increases the difficulty of steelmaking and increases the manufacturing cost. The invention improves the strength of the steel belt and the strength after nitriding by means of solid solution strengthening, phase change strengthening and the like, and simultaneously improves the steel-aluminum bonding performance by utilizing the steel belt strength after nitriding. Therefore, 0.008 to 0.020% of P is added in the present invention.

S is unfavorable for the performance of steel, is easy to cause the hot brittleness of the steel, reduces the low-temperature toughness of the steel, and simultaneously worsens the aluminum interface bonding performance of the steel. Mn can be added to form MnS with S, so that the Mn/S ratio can be improved, the hot ductility can be improved, the content of the Mn/S ratio is required to be controlled to be as low as possible, and the steel-making difficulty and the production cost are increased in consideration of the excessively low control content, so that the S content is controlled to be less than 0.008%.

Al is an important deoxidizing element in steel, but higher Al is easy to diffuse to the steel-aluminum bonding interface, and the interface bonding strength is deteriorated. Therefore, the content of the aluminum alloy must be controlled within a certain range, and the aluminum alloy is controlled as an impurity element in the invention, wherein the content of the aluminum alloy is controlled to be more than 0 and less than or equal to 0.005 percent.

Cr forms a continuous solid solution with Fe in steel, has a solid solution strengthening effect, and forms various types of carbides such as M ₃C、M₇C₃ and M ₂₃C₆ with C, etc., resulting in a secondary strengthening effect. Meanwhile, the addition of Cr is beneficial to inhibiting the diffusion of Al and improving the bonding performance of steel and aluminum. In addition, cr is also an effective nitriding element, and can simultaneously improve the surface hardness and the nitriding layer depth. Conventional nitrided grades typically incorporate up to 3% Cr, which adds significant cost; meanwhile, higher Cr is unfavorable for toughness, the welding difficulty is increased, and Cr is a noble alloy element, so the content of the Cr is controlled to be 0.03-0.6%.

Cu has the functions of solid solution and precipitation strengthening, and tempering has the secondary hardening effect at proper temperature when the content is higher, so that the strength is improved, and the strength is kept during nitriding high-temperature treatment. Meanwhile, the addition of Cu is also beneficial to improving the steel-aluminum bonding performance. Too high Cu causes cracks to occur in the billet during heating and hot rolling, deteriorating the surface properties, so the content of the Cu is controlled to be 0.01-0.15%.

N can form AlN particles with Al in the steel, so that the effect of binding the Al is achieved, and the diffusion of the Al in the steel is limited; meanwhile, N is similar to C, and is easy to form a Korotkoff gas mass by offset polymerization at a dislocation, so that strain concentration is caused, the phenomenon of uneven strain is generated in the processing process of the aluminum-clad material, the surface quality is affected, and the impact toughness is also deteriorated by excessively high N, so that the content of the aluminum-clad material is controlled to be 0.011-0.030%.

The oxygen (O) element can suppress the adverse effect of Al element on the aluminum-coating property in steel, so that it is required to appropriately add a certain O element. However, too high oxygen can generate defects such as subcutaneous bubbles, looseness and the like, and aggravate the thermal embrittlement effect of sulfur, so that the defects such as skin tilting, slag inclusion and the like are easy to occur on the surface of the steel strip, and the defects can influence the subsequent steel-aluminum combination and the surface quality. During solidification of the steel, oxygen will precipitate in large amounts in the form of oxides, reducing the plasticity, impact toughness, etc. of the steel. Therefore, the invention controls the O content to be more than 0 and less than or equal to 0.01 percent.

Ca can change the shape of sulfide when being added into steel, inhibit the hot shortness of S and improve the toughness. And titanium sulfide or titanium carbosulfide may be formed with sulfide when excess Ti is present in the steel. The effect is not obvious when the Ca content is too low, the size of Ca (O, S) formed by the Ca content exceeding 0.005% is too large, the brittleness is increased, the Ca can become a crack starting point, the purity of the steel is reduced, and the toughness of a welding heat affected zone is deteriorated. Therefore, the content of the invention is controlled to be 0.001-0.004%.

In addition to the above elements, the present invention requires the optional addition of Ti:0.01 to 0.06 percent, nb:0.01 to 0.03 percent, V:0.01 to 0.03% by weight of a metal alloy, thereby further improving room temperature strength and strength after nitriding. Wherein:

Ti has high chemical activity, is easy to form a compound with C, N, O, S and the like, and is separated out in the rolling and cooling processes, fine precipitates can be nailed to roll grain boundaries to refine austenite grains, and meanwhile, the growth of grains in a welding heat affected zone is prevented, so that the welding performance of steel is improved. In addition, ti has strong affinity with N, can increase the surface hardness and the depth of a permeation layer, improves the nitriding temperature, has great effect on shortening the nitriding time, and is an important added element of the rapid nitriding steel. When the Ti content is too high, titanium nitride particles are easy to grow up and agglomerate at high temperature, and the plasticity and toughness of the steel are damaged. Therefore, the Ti content is controlled to be 0.01-0.06% in the invention.

Nb is a strong nitrogen carbide forming element, and can combine with carbon and nitrogen in steel to form intermediate phases such as NbC, nb (CN), nbN and the like in the cooling process after rolling, and the formed fine carbide particles can refine the structure, generate fine crystal strengthening and precipitation strengthening effects, and remarkably improve the strength of the steel. When the Nb content is high, coarse carbonitride particles are formed at grain boundaries, and impact toughness is deteriorated. Therefore, the Nb content is controlled to be 0.01 to 0.03% in the present invention.

V is a strong carbon-nitrogen compound forming element and can be separated out in the phase change process. The carbonitride V ₄C₃ formed by V has a lower precipitation temperature than that of Ti carbonitride, and has the functions of preventing dislocation movement, inhibiting grain boundary movement and grain growth. V and C, N and other microalloy elements in the steel are combined to have good precipitation strengthening effect in low-temperature medium-temperature heat treatment. Particularly, the precipitation temperature of V (C, N) is generally not higher than 700 ℃, the lower the temperature is, the finer the precipitation is, the better the strengthening effect is, the nitriding treatment temperature is generally 550-580 ℃, and the carbon nitrogen compounds of V are precipitated in a large quantity at the temperature, so that the aluminum-clad plate strip still has good strength after nitriding treatment. N forms BN and AlN with B, al in the steel preferentially, V is added to form VN with the rest N in the steel, and C, N compound of V is used for precipitation strengthening, so that high strength is ensured during nitriding treatment. Meanwhile, the addition of V can obviously improve the hardness of the nitriding layer, deepen the depth of the nitriding layer, and has good toughness and good impact resistance. When the V content is high, coarse carbonitride particles are formed, and the impact toughness of the weld heat affected zone is significantly deteriorated. Therefore, the content of the invention is controlled to be 0.01-0.03%.

The steel belt used for the aluminum-clad plate belt has high strength, is suitable for nitriding and has good steel-aluminum combination property, so as to meet the use requirement of maintaining high-strength products after nitriding or other high-temperature treatment, and the yield strength of the steel belt is controlled to be more than or equal to 280MPa and the tensile strength of the steel belt is controlled to be more than or equal to 340MPa. In order to meet the performance requirements, the invention strictly designs components according to the influence of different alloy elements on the performance, and realizes the performance requirements through the comprehensive action of multiple elements. Wherein, the addition of C has the functions of solid solution strengthening and phase change strengthening, and the existing aluminum-coated steel patent (such as China patent CN 114250411A) is to ensure that the plasticity is generally controlled to be less than or equal to 0.005 percent, thus greatly increasing the steelmaking difficulty. The invention adopts 0.01 to 0.07 percent of C in order to ensure high strength after nitriding treatment and simultaneously requires the yield strength of the steel belt to be more than 280 MPa. On one hand, the steel strip has the function of solid solution strengthening, and on the other hand, the strength is improved by controlling rolling and cooling after rolling to form a ferrite and a small amount of bainite structure in the steel in the production process of the steel strip.

Because the steel strip is subjected to annealing heat treatment and subsequent nitriding heat treatment in the production process, the conventional fine grain strengthening means has no obvious effect after heat treatment, and the solid solution strengthening is not limited by the heat treatment. The higher the steel strip strength, the higher the strength of the finished aluminum clad material. For this reason, 0.4 to 1.2% of Mn is added in the present invention, the strength of the substrate is ensured by solid solution strengthening of Mn, and such strengthening effect is present even if subjected to heat treatment.

The P content is controlled to be 0.008-0.020% in the invention. On one hand, the solid solution strengthening effect of P is achieved, and on the other hand, the influence of P on the steel-aluminum combination property and the production cost is considered. P is usually controlled as an impurity element in steel, so that it is desired that the lower the content is, the better the content is, and it is generally required to be controlled to 0.015% or less or even lower, but the lower the content is, the higher the steelmaking cost is, and the greater the difficulty is. Since P is an element of the same family as N, proper P is advantageous for steel-aluminum bonding properties, but the study of the present invention found that the effect of improving steel-aluminum bonding properties is not linear, and that the deterioration of steel-aluminum bonding properties starts when the P content exceeds 0.020%. Therefore, the steel-making difficulty, the steel-making cost and the performance requirements of the invention are comprehensively considered, the upper control limit of P is widened to 0.020%, the steel-aluminum combination performance is ensured, the strength is improved, and the steel-making cost is reduced.

The steel of the present invention is required to have nitriding characteristics, and it is desirable that the steel is liable to form a nitrided layer during nitriding. Cr has a secondary strengthening effect in addition to solid solution strengthening in steel. However, the nitriding performance of the steel can be improved by adding 0.03-0.6% of Cr in the invention besides improving the strength. However, the current nitriding steels such as 35MoCrAl and 42CrMo generally have Cr content of more than 3 percent, cr is a noble alloy element, and the high content obviously increases the cost. The research of the invention shows that Cr can promote the diffusion of N in the steel strip and form a nitriding layer rapidly, so that the steel strip has good nitriding characteristics. The steel strip covered with the aluminum plate strip is added with a proper amount of N at the same time so as to improve the combination property of steel and aluminum, and the N in the steel is matched with Cr, so that the formation of a nitriding layer is further promoted, a matrix is reinforced, and the strength of the steel strip is improved. The steel belt used for the aluminum-clad plate belt only needs to have the nitriding layer hardness of about 500Hv, and the thickness of the nitriding layer is not more than 100 mu m, so that the required thickness and hardness of the nitriding layer can be obtained by adding 0.03-0.6% of Cr into the steel belt. Higher Cr plays a rich role and increases costs.

Cu also has a solid solution strengthening effect in steel, and can enhance strength by precipitation strengthening during heat treatment. However, the invention mainly utilizes the addition of Cu to further improve the steel-aluminum bonding performance, because the steel is subjected to annealing heat treatment and nitriding treatment in the production and use processes, and the brittle iron-aluminum compound is easily promoted to form at high temperature in the heat treatment process, so that the steel-aluminum bonding performance is deteriorated. Therefore, the steel belt has higher requirements on the steel-aluminum combination property than the existing steel for the aluminum-clad plate belt, and the addition of a proper amount of Cu is beneficial to improving the steel-aluminum combination property and improving the strength after nitriding treatment.

According to the strengthening effect of the elements on the steel strip, the contents of C, P, N and Mn and Cr in the steel are required to be controlled to satisfy the relation 1:150 (C-0.01) +60P+300N+5Mn+3Cr.gtoreq.12.0, and if the value of the relational expression is lower than 12.0, the problem of lower strength is liable to occur.

The formation of the iron-aluminum compound is very sensitive to temperature, and the high temperature during nitriding provides power for the formation of the iron-aluminum compound, so that the formation of the iron-aluminum compound is easier to induce, and the iron-aluminum delamination is caused. Therefore, the steel has higher requirements on the steel-aluminum bonding performance than the existing steel for the aluminum-clad plate strip, and the key of the steel-aluminum bonding performance is to control the formation of brittle iron-aluminum compounds at the steel-aluminum interface in the aluminum-clad plate. The research of the invention shows that the formation of the iron-aluminum compound is closely related to the diffusion of Al in steel, and the formation of the iron-aluminum compound can be inhibited within a certain temperature range by controlling the diffusion of Al. Therefore, the invention further improves the steel-aluminum bonding performance through the synergistic effect of a plurality of elements such as C, cr, cu, O, N and the like, and O (oxygen) and N can inhibit the diffusion of Al and reduce the formation of brittle iron-aluminum compounds, thereby improving the steel-aluminum bonding performance. However, too high O can cause defects of submerged bubbles, looseness and the like of a casting blank, and aggravate the hot embrittlement effect of sulfur, so that the defects of skin tilting, slag inclusion and the like are easy to occur on the surface of the steel strip, the O content is limited to be less than or equal to 0.01%, and the bonding performance of steel and aluminum is ensured by using 0.011-0.03% of N. Si and Al as deoxidizing elements hinder the improvement of the aluminum bonding properties of steel by O, so the content thereof should be limited.

According to the invention, through the synergistic effect of multiple elements such as C, cr, cu, O, N and the like, good steel-aluminum bonding performance is obtained. According to C, N, O, cu, cr and the strength of the action of Al and Si on the steel-aluminum bonding performance, the content of the aluminum alloy is required to satisfy the relation 2:0.5C+3.83N+O+0.05Cu+0.047Cr-0.89Al-1.15Si is more than or equal to 0.085, thereby ensuring that the steel has excellent steel-aluminum bonding performance, and if the relational value is lower than 0.085, the aluminum-clad plate strip prepared from the steel is easy to be layered in the subsequent nitriding treatment.

In general, the invention adopts the component system required by the above, comprehensively considers the combination property, strength and nitriding property of steel and aluminum, and can obtain the steel for the aluminum-clad plate strip meeting the requirements through the combined action of all elements.

The invention relates to a production method of an aluminum-clad plate strip with excellent nitriding performance, which comprises the following steps:

1) Cleaning and polishing the covering surfaces of the aluminum belts and the steel belts;

2) Rolling

The aluminum strip and the steel strip are clad-rolled at room temperature to form a clad aluminum strip, and the single-pass rolling deformation is 50-85%;

3) Annealing

Coiling and annealing in a bell-type furnace; wherein the annealing temperature is 480-530 ℃, the annealing heat preservation time t=120+3H, t units of min, H is the thickness of the aluminum-coated steel coil, and the unit cm, after the annealing is finished, the steel coil is cooled to below 200 ℃, and finally cooled to below 80 ℃ along with the furnace and discharged;

Or alternatively, the first and second heat exchangers may be,

Continuous annealing and coiling; wherein the annealing temperature is 480-530 ℃, the continuous annealing time t0= (h+1) ×1.5+ -1 min, h is the thickness of the aluminum-clad plate strip, the unit mm, and h is more than or equal to 1mm; h is less than 1mm, and the annealing time is more than or equal to 2min;

4) And (5) finishing.

Preferably, in step 1), the surface cleaning includes pickling, degreasing and drying.

Preferably, in step 1), the surface cleaning comprises sandblasting or shot blasting.

Preferably, in step 1), the polishing uses an abrasive belt or a grinding wheel, and the polishing direction is parallel to the rolling direction.

Preferably, in step 2), the rolling is 1-pass rolling or 2-pass rolling.

In the production process of the aluminum-clad plate strip, the following steps are adopted:

the surface cleaning of the aluminum belt and the steel belt comprises necessary acid washing, degreasing and drying, or direct sand blasting and shot blasting treatment to remove greasy dirt, rust, oxide skin and the like on the covered surfaces of the aluminum belt and the steel belt.

The polishing is to improve the roughness of the surface to be covered and expose fresh base metal to improve the mechanical bonding strength of steel and aluminum in the aluminum-covered rolling process. The polishing is preferably carried out by adopting an abrasive belt or an abrasive wheel, so that a rough surface can be obtained, the mechanical occlusion of aluminum and steel in the aluminum cladding rolling process is improved, and better steel-aluminum bonding strength is obtained; and the surface to be covered is polished to form a microscopic work hardening layer, the hardening layer is rolled in the aluminum covering rolling process to expose a fresh metal matrix, so that the point contact combination of steel and aluminum is realized, and the steel and aluminum combination strength is improved.

When the steel aluminum is rolled at room temperature, single-pass rolling deformation is controlled to be within the range of 50-85%. And rolling the steel belts and the aluminum belts with different specifications into the aluminum-clad belt with the required thickness and structure through 1-2 times according to the requirements. When the deformation is low, the rolling pass is increased, repeated feeding and threading are needed, the production time is prolonged, the production efficiency is low, and the cost is high; and when the deformation amount is too low, the interface bonding strength is insufficient, so that steel and aluminum are directly layered. The single-pass deformation is overlarge, the rolling efficiency is high, but the rolling load is large, and the requirement on equipment is high; the specific choice of 1 pass or 2 passes to finish rolling can be determined according to equipment capacity and finished product specifications.

The strip needs to be annealed after aluminum-clad rolling. On the one hand, the annealing aims at eliminating work hardening generated in the room temperature rolling process, recovering the plasticity of the coated aluminum material and facilitating the forming processing of subsequent products; on the other hand, the steel-aluminum interface atoms are mutually diffused in the annealing process, and the mechanical bonding during rolling is transited to metallurgical bonding, so that the interface bonding strength is further improved.

Because the melting point of aluminum is about 640 ℃ (the content of other alloys in aluminum fluctuates according to the difference), the corresponding recrystallization temperature is about 250 ℃, and the minimum annealing temperature is controlled to be 100-200 ℃ above the recrystallization temperature. The lower annealing temperature greatly increases the annealing time, reduces the production efficiency and increases the production cost; the annealing temperature is too high, so that the energy consumption is increased, the production cost is increased, meanwhile, the higher temperature provides power for the formation of brittle phases of the steel-aluminum interface, and the bonding strength of the steel-aluminum interface is reduced, therefore, the annealing temperature is controlled to be 480-530 ℃, and the annealing temperature is determined according to the dimension specification and the finished product performance of the aluminum-clad plate strip.

There are generally two annealing modes, including conventional bell furnace annealing and continuous annealing. The annealing heat preservation time T of the aluminum-clad plate strip is comprehensively determined according to the thickness h (mm) of the aluminum-clad plate strip and the annealing furnace temperature T (DEG C) and the annealing mode.

When continuous annealing is adopted, the annealing time t ₀ = (h+1) multiplied by 1.5+/-1 min, wherein h is more than or equal to 1mm. h is less than 1mm, and the annealing time is not less than 2min.

When the bell-type furnace annealing is adopted, the annealing time comprises three stages of a heating stage, a heat preservation stage and a cooling stage. The length of the annealing time is closely related to the thickness of the aluminum-clad plate strip, and the difference between the inner radius and the outer radius of the aluminum-clad steel coil corresponds to the aluminum-clad steel coil. Generally in a linear relationship, the specific proportions being offset from the actual ones. According to the thickness H (difference between inner and outer radiuses of the aluminum-coated steel coil) of the aluminum-coated steel coil, the annealing time t (min) of the heat preservation section is controlled, and the requirements are met: t=120+3h, wherein H is in cm. According to the inner diameter of the bell-type furnace, the outer diameter of the aluminum-coated coil is generally below 1800mm, the inner diameter is about 560mm, and the heat preservation time of the aluminum-coated steel coil in the bell-type furnace is not more than 306min and is about 5h. When the aluminum-coated coil is annealed by adopting a bell-type furnace in the prior art, the heat preservation time is set according to the experience of operators, the heat preservation time is more than 15-18 hours, in addition, the temperature is increased by 6-8 hours, and the temperature is reduced by about 6 hours.

The invention has the advantages of clear linear relation between the annealing heat preservation time and the steel coil specification, and stronger operability. Compared with the prior art, the annealing process greatly shortens the heat treatment time, reduces the energy consumption, improves the production efficiency and reduces the production cost.

The annealed aluminum-clad coil needs to be finished, on one hand, the shape of the coil is improved, and meanwhile, the edge is cut, and on the other hand, the surface quality is further improved through micro-pressing.

The invention has the following advantages:

1. According to the characteristic that the solid solution strengthening and phase change strengthening effects are not affected by subsequent annealing and nitriding heat treatment, the simple C-Mn design is adopted in the aspect of component design, and C, P, N and Mn and Cr contents are controlled to meet the relational expression: 150 (C-0.01) +60P+300N+5Mn+3Cr is more than or equal to 12.0, and higher strength is obtained. The yield strength of the steel belt is more than or equal to 280MPa the tensile strength is more than or equal to 340MPa, so that the yield strength of the obtained aluminum-clad plate strip is more than or equal to 300MPa, and the tensile strength is more than or equal to 360MPa. Meanwhile, the selective addition of Cu, nb, V and Ti ensures the high strength after heat treatment so as to meet the use requirements of more application fields.

The steel provided by the invention is required to meet the requirement of subsequent nitriding treatment, so that the steel-aluminum bonding performance of the steel is higher, and the content of the steel is required to meet the relation expression according to C, N, O, cu, cr and the action of Al and Si on the steel-aluminum bonding performance in the component design: 0.5C+3.83N+O+0.05Cu+0.047Cr-0.89Al-1.15Si is more than or equal to 0.085, thereby ensuring that the steel has excellent steel-aluminum bonding performance. The obtained aluminum-clad plate strip can adapt to the later high-temperature nitriding treatment process, does not form iron-aluminum compounds, and does not have the phenomena of steel-aluminum layering and strength reduction. The steel has high strength after nitriding heat treatment and simultaneously maintains good steel-aluminum bonding performance.

The invention adopts the low-oxygen high-nitrogen component design, limits the O content to be less than 0 and less than or equal to 0.01 percent, and compensates the steel aluminum bonding performance by using 0.011 to 0.03 percent of N. Therefore, the defects of submerged bubbles, looseness and the like of a high-oxygen component casting blank are overcome, the defects of skin tilting, slag inclusion and the like on the surface of the steel belt are reduced, and the steel-aluminum combination property and the surface quality of the aluminum-clad plate belt are further improved.

According to the influence of Cr on nitriding and the nitriding layer requirement of the steel belt, a small amount of Cr is added: 0.03-0.6%, promoting the diffusion of N in the steel strip, and forming a nitriding layer rapidly, so that the steel strip has good nitriding characteristics, the obtained aluminum-clad strip still maintains high strength after nitriding treatment, and the performance meets the subsequent processing and use requirements. Compared with the existing nitriding steel, the method saves noble alloy elements, reduces cost and obtains good nitriding characteristics.

The invention further improves the steel-aluminum binding property of steel by controlling the P content to be 0.008-0.020 percent and utilizing the solid solution strengthening effect of P and the influence effect on the steel-aluminum binding property, and the aluminum-clad plate strip still has higher steel-aluminum binding property after high-temperature nitriding treatment, and simultaneously reduces the steelmaking difficulty and steelmaking cost and has higher production efficiency.

The invention can adopt cover annealing or continuous annealing in the annealing stage, establishes the linear relation between the annealing heat preservation time and the steel coil specification, obviously shortens the annealing time compared with the traditional cover annealing process, reduces the energy consumption, improves the production efficiency, reduces the production cost and has stronger operability.

Drawings

FIG. 1 is a schematic structural view of a composite aluminum sheet strip of the present invention.

FIG. 2 is a schematic structural view of the composite aluminum sheet strip of the present invention.

FIG. 3 is a schematic structural view of the composite aluminum sheet strip of the present invention.

Detailed Description

The invention is further described below with reference to examples and figures.

Referring to fig. 1, 2 and 3, there are structural schematic diagrams of an embodiment of the aluminum-clad plate strip according to the present invention, wherein 1 is a steel strip and 2 is an aluminum strip.

According to the chemical composition requirements of steel belts of the aluminum-clad plate and strip, the aluminum-clad plate and strip is obtained by selecting steel belts 1 and 2 with different specifications, cleaning the surfaces, polishing, performing aluminum-clad rolling and annealing. The thickness of the finished product of the aluminum-clad plate strip is 0.5-2.0 mm.

The chemical components of the steel strip of the embodiment of the invention are shown in table 1, the specific production process parameters are shown in table 2, and the finished product performance is shown in table 3.

The chemical composition of the steel strip used in the aluminum clad strips of comparative examples 1-4 was also low in si—al design and added with a certain amount O, N, but the composition was generally different from the present application. The properties obtained finally also differ greatly from the application, see in particular Table 3.

The values of formula 1 and formula 2 of comparative examples 1 and 2 are lower than those of the examples of the present invention; comparative example 3 although the value of formula 1 satisfies the requirements of the present invention, the value of formula 2 is lower than the examples of the present invention; comparative example 4 formula 1 has a lower value.

As can be seen from the results of Table 3, the strength of comparative examples 1 and 2 is significantly lower than that of the examples of the present invention, and the aluminum-coating property after the simulated nitriding high-temperature heat treatment is poor.

Comparative example 3 although the strength was high, iron-aluminum compound was present at the steel-aluminum interface after the high temperature heat treatment by simulated nitriding.

Comparative example 4 satisfies the requirements of the final steel-aluminum bonding properties, but has a lower strength and does not satisfy the requirements of the present invention.

The aluminum-clad plate strip prepared by the components and the process has the yield strength of more than or equal to 300MPa, the tensile strength of more than or equal to 360MPa and the elongation A50 of more than or equal to 25 percent; the steel-aluminum interface bonding performance is excellent (no iron-aluminum compound is formed). To verify the strength and aluminum coating performance of the aluminum coated plate strip after high temperature nitriding, the aluminum coated plate strip was subjected to a heat treatment at 550 ℃ for 4 hours in a simulated nitriding process, and the tensile properties were tested, and the results are shown in table 3, wherein the strength of the sample plate after heat treatment was limited, no delamination occurred, and no iron-aluminum compound was produced, indicating that the finished aluminum coated plate product still had high strength after high temperature heat treatment in the subsequent processing process.

Claims

1. A high surface quality aluminum-clad plate strip suitable for nitriding is formed by cladding a steel strip and an aluminum strip, wherein the weight percentage of chemical components of the steel strip is ：C：0.01～0.07％,0＜Si≤0.005％,Mn：0.40～1.20％,P：0.008～0.020％,S≤0.008％,0＜Al≤0.005％,Cr：0.03～0.60％,N：0.011～0.03％,0＜O≤0.01％,Cu：0.01～0.15％,Ca：0.001～0.004％,, and Ti is selectively added: 0.01 to 0.06 percent, nb:0.01 to 0.03 percent, V:0.01 to 0.03%, the balance comprising Fe and other unavoidable impurities; and needs to satisfy simultaneously:

0.5C+3.83N+O+0.05Cu+0.047Cr-0.89Al-1.15Si≥0.085；

150(C-0.01)+60P+300N+5Mn+3Cr≥12.0。

2. a high surface quality aluminum coated strip suitable for nitriding of claim 1, wherein the balance is Fe and other unavoidable impurities.

3. The high surface quality aluminum coated strip suitable for nitriding of claim 1 or 2, wherein said strip has a yield strength of greater than or equal to 280MPa, a tensile strength of greater than or equal to 340MPa, and an elongation of greater than or equal to 30%.

4. A high surface quality aluminum coated strip suitable for nitriding of claim 1, 2 or 3, wherein said aluminum coated strip has a yield strength of greater than or equal to 300MPa, a tensile strength of greater than or equal to 360MPa, and an elongation a50 of greater than or equal to 25%.

5. A high surface quality aluminum coated strip suitable for nitriding of any one of claims 1 to 4, wherein said aluminum coated strip is a steel-aluminum, aluminum-steel-aluminum or steel-aluminum-steel structure.

6.A method for producing a high surface quality aluminum coated strip suitable for nitriding of any one of claims 1 to 5, comprising the steps of:

2) Rolling

3) Annealing

Coiling and annealing in a bell-type furnace; wherein the annealing temperature is 480-530 ℃, the annealing heat preservation time t=120+3H, t units of min, H is the thickness of the aluminum-coated steel coil, and the unit is cm; after annealing, water cooling to below 200 ℃, and finally cooling to below 80 ℃ along with the furnace and discharging;

Or alternatively, the first and second heat exchangers may be,

Continuous annealing and coiling; wherein the annealing temperature is 480-530 ℃, the continuous annealing time t ₀ = (h+1) multiplied by 1.5+/-1 min, h is the thickness of the aluminum-clad plate strip, the unit mm is that h is more than or equal to 1mm;

h is less than 1mm, and the annealing time is more than or equal to 2min;

4) And (5) finishing.

7. The method of claim 6, wherein in step 1), the surface cleaning comprises pickling, degreasing, and drying.

8. The method of claim 6, wherein in step 1), the surface cleaning comprises blasting and shot blasting.

9. The method according to claim 6, wherein in step 1), the polishing is performed using an abrasive belt or a grinding wheel, and the polishing direction is parallel to the rolling direction.

10. The method according to claim 6, wherein in step 2), the rolling is 1-pass rolling or 2-pass rolling.