CN115181840A

CN115181840A - 780MPa grade high-forming hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel and rapid heat treatment manufacturing method

Info

Publication number: CN115181840A
Application number: CN202110360129.3A
Authority: CN
Inventors: 王健; 李俊; 张理扬; 杜小峰; 丁志龙; 刘华飞; 任玉苓; 杜瑶
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2021-04-02
Filing date: 2021-04-02
Publication date: 2022-10-14

Abstract

780 MPa-grade high-formability hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel and a rapid heat treatment manufacturing method, wherein the steel comprises the following components in percentage by mass: 0.05 to 0.12 percent of C, 0.01 to 0.5 percent of Si, 1.2 to 2.0 percent of MnP, less than or equal to 0.015 percent of P, less than or equal to 0.003 percent of S, 0.02 to 0.055 percent of Al, and also can contain one or two of Cr, mo, ti, nb and V, wherein Cr + Mo + Ti + Nb + V is less than or equal to 0.5 percent, and the balance of Fe and other inevitable impurities. The hot dipping step comprises: rapid heating, short-time heat preservation, rapid cooling, hot-dip aluminum-zinc coating, rapid cooling (hot-dip aluminum-zinc coating AZ products); rapid heating, short-time heat preservation, rapid cooling, hot galvanizing aluminum magnesium and rapid cooling (hot galvanizing aluminum magnesium AM product). The invention changes the recovery of the deformed structure, the ferrite recrystallization and the austenite phase transformation process in the annealing process through rapid heat treatment, increases the crystal nucleation point, shortens the grain growth time, and finally obtains fine and uniformly distributed ferrite and martensite dual-phase structures; improves the strength and the forming performance (n) of the material while improving the heat treatment efficiency ₉₀ Value), extending the range of material properties.

Description

780MPa grade high-forming hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel and rapid heat treatment manufacturing method

Technical Field

The invention belongs to the technical field of rapid heat treatment of materials, and particularly relates to 780 MPa-grade high-formability hot-dip aluminum zinc or hot-dip zinc aluminum magnesium dual-phase steel (comprising hot-dip aluminum zinc AZ products and hot-dip zinc aluminum magnesium AM products) and a rapid heat treatment manufacturing method.

Background

With the gradual improvement of people's awareness of energy conservation and material service safety, many automobile manufacturers select high-strength steel as automobile material, wherein the exhaust system of automobiles requires the material to have high strength, high toughness and high corrosion resistance, and also needs certain heat resistance; meanwhile, household electrical appliances and building materials need to be high in strength and thin, and the coating layer is required to have good corrosion resistance, so that the requirements on corrosion resistance, dent resistance, durability strength, large-deformation impact strength and safety of the coating products in the fields of automobiles, household electrical appliances, buildings and the like are higher and higher.

However, with the increasing demand for corrosion resistance of steel products, hot-dip pure zinc has gradually failed to meet the demand, and the development of new high corrosion-resistant coating varieties is urgently needed. Therefore, hot-dip aluminum-zinc and hot-dip zinc aluminum-magnesium coatings with better corrosion resistance are increasingly researched. Correspondingly, hot-dip aluminum-zinc and hot-dip zinc aluminum-magnesium high-strength steel products are produced.

At present, the main means for developing hot-dip aluminum-zinc and zinc-aluminum-magnesium plating dual-phase steel is to change the structure property of the hot-dip dual-phase steel by adding alloy elements and adjusting the soaking temperature, time and cooling speed in a critical annealing process.

Chinese patent CN201710994660.X discloses a 550 MPa-level structural hot-dip aluminum-zinc plated steel plate and a preparation method thereof, wherein the chemical components are as follows: 0.02-0.07%, si is less than or equal to 0.03%, mn:0.15-0.30%, P is less than or equal to 0.020%, si is less than or equal to 0.020%, nb:0.015 to 0.030%, als:0.020-0.070%, and is cold-rolled by adopting a low cold rolling reduction rate of 55-60%, the yield strength is more than 550MPa, the tensile strength is 560MPa, and the elongation is about 10%.

Chinese patent CN102363857B discloses a production method of a color-coated plate with a yield strength of 550MPa, wherein Ti and Nb are respectively 0.05 percent and 0.045 percent at most, and the yield strength Rp of Ti and Nb is _0.2 Reaching 550-600MPa; tensile strength R _m 560-610MPa, elongation after break A ₈₀ mm is more than or equal to 6 percent, and the strengthening mode mainly keeps most of non-recrystallized banded structures through low-temperature annealing, improves the strength, but has poor plasticity and also has influence on the forming.

Chinese patent CN100529141C discloses a 'full-hard aluminum-zinc-plated steel plate and a production method thereof', the yield strength of the steel plate prepared by the method reaches more than 600MPa, the fracture elongation is less than or equal to 7%, the total content of Ti and Nb is 0.15-0.100%, the annealing temperature is controlled at 630-710 ℃, the full-hard steel plate is obtained by a low-temperature recovery annealing mode, the elongation of the steel plate product obtained by the method is too low, and the requirement of the current processing on the forming performance cannot be met.

Chinese patent CN201911161556.8 discloses a hot-dip galvanized aluminum-magnesium high-strength steel, a preparation method and application, the hot-dip galvanized aluminum-magnesium high-strength steel comprises a base material and a zinc-aluminum-magnesium alloy coating on the surface of the base material, and a production process is controlled on the basis of component design to form a CSP sheet billet continuous casting and rolling production line and a common hot galvanizing production line as core processes, namely a process production scheme and a core production technology of smelting, hot rolling, cold rolling and annealing. The yield strength of the hot-dip galvanized aluminum-magnesium high-strength steel is more than 550MPa, and the elongation is more than 17%. The forming property is poor, so that the method is only suitable for industries such as photovoltaic supports, highway guardrails and the like which require high corrosion resistance but have low forming property requirements.

Chinese patent CN106811686a discloses "high strength zinc aluminum magnesium plated steel sheet with good surface quality and manufacturing method thereof", the chemical composition of the steel sheet comprises C:0.09-0.18%, si:0.40-1.60%, mn:0.80-2.10%, S:0.001-0.008% and optionally Cr:0.01-0.60%, and/or Mo:0.01 to 0.30 percent. The chemical composition of the plating layer is Al:1-14%, mg:1.0-5.0%, and the balance of zinc and unavoidable impurities. Although the patent provides a method for producing a high-strength zinc-aluminum-magnesium coated steel plate, the cost is high, the problem of surface quality is easily caused due to the overhigh Si content, the yield strength is overhigh, the elongation is lower, and the subsequent processing and forming are influenced.

Chinese patent CN104419867A discloses 'a 1250MPa grade ultrahigh strength zinc-aluminum-magnesium coating steel plate and a production method thereof', the steel plate comprises the following chemical components in percentage by weight: c:0.15 to 0.35%, si:0.50 to 1.80%, mn:2.0 to 5.0 percent, mn/Si is not less than 2, and the balance is iron and inevitable impurities; the coating comprises the following chemical components in percentage by weight: al:1 to 15%, mg: 1-5%, al/Mg is more than or equal to 1, and the balance is Zn and inevitable impurities. The production method comprises smelting-continuous casting-hot continuous rolling-cold continuous rolling-continuous hot dipping process, the high-corrosion-resistance and ultrahigh-strength zinc-aluminum-magnesium plated steel plate manufactured according to the invention has the strength of 1250-1500 MPa, the elongation after fracture of 12-18 percent, the corrosion resistance of more than 4 times of that of a common galvanized plate, and the plating layer has no crack and no stripping when bent at 180-degree 5a, thereby meeting the requirement of high corrosion resistance and high strength reduction. Although the patent provides a production method of a high-strength zinc-aluminum-magnesium coated steel plate, the problem of surface quality is easy to occur due to the overhigh content of Si, and the subsequent processing and forming are influenced due to the overhigh content of C and poor weldability.

Chinese patents CN 108823507A, CN 107829038B, CN 105543674B and CN107794357B disclose that continuous annealing or hot-dip plating pure zinc dual-phase steel with 780MPa grade or above is produced by utilizing the traditional cold rolling process, and the production cost is higher.

In summary, the current hot-dip aluminum-zinc and hot-dip zinc-aluminum-magnesium products have the problems of high cost, poor surface quality and poor matching of strength or elongation, which leads to subsequent processing and forming. Meanwhile, limited by the production facilities of enterprises in the past, most of the related researches are based on the heating rate (5-20 ℃/s) of the existing heating equipment to heat the strip steel to complete recrystallization and austenitization (Chinese patent CN 104988391A). In recent years, the development of rapid heating technologies such as transverse magnetic induction heating and novel direct-fired heating has led to the industrial application of rapid thermal treatment processes. The cold-rolled strip steel can possibly complete the austenitizing process within tens of seconds or even seconds from room temperature, thereby greatly shortening the length of the heating section of the furnace and improving the speed and the production efficiency of the unit. Meanwhile, the recrystallization and austenitization processes completed in a very short time also provide a more flexible and flexible structure design, and further improve the material performance on the premise of not changing the alloy components and the rolling process.

The high-corrosion-resistant advanced high-strength steel represented by the dual-phase steel has wide application prospect, the rapid heat treatment technology has great development value, and the combination of the two technologies can provide a larger space for the development of the dual-phase steel.

Disclosure of Invention

The invention aims to provide 780 MPa-grade high-formability hot-dip aluminized zinc or hot-dip galvanized aluminum-magnesium biphaseSteel (including hot-dip aluminium-zinc AZ and hot-dip zinc aluminium-magnesium AM products) and its quick heat treatment production method, and utilizes quick heating to control the processes of recovery of deformed base body, ferrite recrystallization, austenite transformation and grain growth in the annealing process, and after the heat treatment is finally completed, the fine ferrite structure and polymorphic reinforced phase structure can be obtained, and the toughness also can be improved, and the yield strength of the obtained two-phase steel is 476-556 MPa, tensile strength is 786-852 MPa, elongation is 20.1-24.8%, product of strength and elongation is 16.7-20.2 GPa%, strain hardening index n is strain hardening index n, and its product is 16.7-20.2 GPa% ₉₀ The value is greater than 0.20.

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

780 MPa-grade high-formability hot-dip aluminum-zinc and hot-dip zinc-aluminum-magnesium dual-phase steel comprises the following chemical components in percentage by mass: c:0.05 to 0.12%, si:0.01 to 0.5%, mn: 1.2-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.003%, al: 0.02-0.055%, one or two of Cr, mo, ti, nb and V, wherein Cr + Mo + Ti + Nb + V is less than or equal to 0.5%, and the balance of Fe and other inevitable impurities, and is obtained by the following process:

1) Smelting and casting

Smelting according to the chemical components and casting into a plate blank;

2) Hot rolling and coiling

The coiling temperature is 550-680 ℃;

3) Cold rolling of steel

The cold rolling reduction rate is 40-85%;

4) Rapid heat treatment hot-dip aluminum zinc or hot-dip zinc aluminum magnesium

Rapidly heating the cold-rolled steel plate to 750-845 ℃, wherein the rapid heating adopts a one-stage type or two-stage type;

when one-stage rapid heating is adopted, the heating rate is 50-500 ℃/s;

when two-section type rapid heating is adopted, the first section is heated from room temperature to 550-650 ℃ at the heating rate of 15-500 ℃/s, and the second section is heated from 550-650 ℃ to 750-845 ℃ at the heating rate of 50-500 ℃/s;

then, soaking is carried out, and the soaking temperature: 750-845 ℃, soaking time: 10-60 s;

after the heat equalizing is finished, slowly cooling to 670-770 ℃ at a cooling rate of 5-15 ℃/s, then rapidly cooling to 580-600 ℃ at a cooling rate of 50-150 ℃/s, and immersing in a zinc pot for hot-dip aluminum-zinc plating or hot-dip zinc-aluminum-magnesium plating;

after hot-dip aluminum and zinc plating, rapidly cooling to room temperature at a cooling rate of 30-150 ℃/s to obtain a hot-dip aluminum and zinc AZ product; alternatively, the first and second electrodes may be,

and after hot-dip galvanizing aluminum magnesium, rapidly cooling to room temperature at the cooling rate of 10-300 ℃/s to obtain a hot-dip galvanized aluminum magnesium AM product.

Preferably, the content of C is 0.07 to 0.10%.

Preferably, the Si content is 0.1 to 0.4%.

Preferably, the Mn content is 1.5 to 1.8%.

Preferably, the dual-phase steel can contain one or two of Cr, mo, ti, nb and V, and Cr + Mo + Ti + Nb + V is less than or equal to 0.4 percent.

Preferably, the whole process of the rapid heat treatment hot-dip aluminum zinc plating or hot-dip zinc aluminum magnesium plating uses 29 to 159s.

Preferably, in the step 2), the hot rolling temperature is more than or equal to A _r3 。

Preferably, in the step 2), the coiling temperature is 580 to 650 ℃.

Preferably, in the step 3), the cold rolling reduction is 60 to 80%.

Preferably, in the step 4), the rapid heating is performed in a one-stage heating mode, and the heating rate is 50-300 ℃/s.

Preferably, in the step 4), the rapid heating adopts two-stage heating: the first section is heated from room temperature to 550-650 ℃ at the heating rate of 15-300 ℃/s, and the second section is heated from 550-650 ℃ to 750-845 ℃ at the heating rate of 50-300 ℃/s.

Preferably, in the step 4), the rapid heating adopts two-stage heating: the first section is heated from room temperature to 550-650 ℃ at the heating rate of 30-300 ℃/s, and the second section is heated from 550-650 ℃ to 750-845 ℃ at the heating rate of 80-300 ℃/s.

Preferably, in the step 4), after hot-dip galvanizing aluminum magnesium, the hot-dip galvanized aluminum magnesium is rapidly cooled to room temperature at a cooling rate of 30-250 ℃/s, so as to obtain a hot-dip galvanized aluminum magnesium AM product.

The metallographic structure of the dual-phase steel is a ferrite and martensite dual-phase structure which is uniformly distributed, and the average grain size is 1-5 mu m.

The yield strength of the dual-phase steel is 476-556 MPa, the tensile strength is 786-852 MPa, the elongation is 20.1-24.8%, the product of strength and elongation is 16.7-20.2 GPa%, and the strain hardening index n ₉₀ The value is greater than 0.20.

In the composition and process design of the steel of the invention:

c: carbon is the most common strengthening element in steel, and increases the strength and reduces the plasticity of steel, but for forming steel, low yield strength, high uniform elongation and total elongation are required, so the carbon content is not too high. The carbon content has great influence on the mechanical property of the steel, the pearlite quantity can be increased along with the increase of the carbon content, the strength and the hardness of the steel can be greatly improved, but the plasticity and the toughness of the steel can be obviously reduced, if the carbon content is too high, obvious net-shaped carbide can appear in the steel, the strength, the plasticity and the toughness of the steel can be obviously reduced due to the existence of the net-shaped carbide, the strengthening effect generated by the increase of the carbon content in the steel can be obviously weakened, the technological property of the steel is poor, and therefore the carbon content is reduced as much as possible on the premise of ensuring the strength.

For dual phase steels, the carbon element mainly affects the volume fraction of austenite formed during annealing, during which the diffusion process of the carbon element in austenite or ferrite actually acts as a process of controlling the growth of austenite grains. The volume fraction of austenite is increased along with the increase of the carbon content or the increase of the heating temperature of a critical area, so that the structure of a martensite phase formed after cooling is increased, the strength of the material is increased, and the strength of the material in the processes of obdurability matching and rapid annealing are comprehensively considered. The invention limits the carbon content to 0.05-0.12%.

Mn: manganese can form a solid solution with iron, so that the strength and hardness of ferrite and austenite in the carbon steel are improved, fine pearlite with high strength is obtained in the cooling process of the steel after hot rolling, and the content of the pearlite is increased along with the increase of the content of Mn. Manganese is a forming element of carbide at the same time, and the carbide of manganese can be dissolved into a cementite, so that the strength of the pearlite is indirectly enhanced. Manganese also strongly enhances the hardenability of the steel, further improving its strength.

In the case of dual phase steel, manganese is one of the elements that significantly affects the austenite formation kinetics during intercritical annealing, and manganese mainly affects the transformation and growth process of austenite to ferrite after austenite formation and the final equilibrium process of austenite and ferrite. Because the diffusion speed of the manganese element in austenite is far lower than that of the manganese element in ferrite, the austenite grains controlled by manganese diffusion have longer time, and the manganese element can be distributed in the austenite for a longer time. When heating is carried out in the critical region, if the holding time is short, the manganese element cannot be uniformly distributed in the austenite, and then the cooling rate is insufficient, so that a uniform martensite island structure cannot be obtained. In the dual-phase steel produced by adopting the rapid heat treatment process (such as a water quenching continuous annealing production line), the manganese content is generally higher, so that the austenite has higher manganese content after being generated, the hardenability of an austenite island is ensured, and uniform martensite island structure and more uniform performance are obtained after cooling. In addition, manganese expands the gamma phase region and reduces A _c1 And A _c3 The manganese containing steel will therefore get a higher martensite volume fraction than the low carbon steel under the same heat treatment conditions. However, when the manganese content is higher, the grains in the steel tend to be coarsened, and the overheating sensitivity of the steel is increased; when the cooling is not proper after the smelting casting and the hot forging rolling, white spots are easily generated in the carbon steel. Considering the above factors comprehensively, the manganese content is designed to be within the range of 1.2-2.0%.

Si: silicon forms a solid solution in ferrite or austenite, thereby enhancing the yield strength and tensile strength of steel, and silicon increases the cold working deformation hardening rate of steel, and is a beneficial element in alloy steel. In addition, silicon has an obvious enrichment phenomenon on the surface of a fracture along the grain boundary of the silicon-manganese steel, and the segregation of silicon at the position of the grain boundary can slow down the distribution of carbon and phosphorus along the grain boundary, so that the embrittlement state of the grain boundary is improved. Silicon can improve the strength, hardness and wear resistance of the steel without causing the plasticity of the steel to be obviously reduced. Silicon has strong deoxidizing capacity, is a common deoxidizing agent in steel making, and can increase the fluidity of molten steel, so that the general steel contains silicon, but when the content of the silicon in the steel is too high, the plasticity and the toughness of the steel are obviously reduced.

For dual phase steels, the main effect of silicon is to reduce the austenite volume fraction at final equilibrium for a given annealing time. Silicon has no obvious influence on the growth rate of austenite, but has obvious influence on the formation form and distribution of the austenite. Therefore, the present invention determines the silicon content to be in the range of 0.1 to 0.5%.

Cr: the main role of chromium in steel is to increase hardenability. The steel has better comprehensive mechanical properties after quenching and tempering. Chromium forms a continuous solid solution with iron, narrowing the austenite phase region. Chromium forms many carbides with carbon and has a greater affinity for carbon than the elements iron and manganese. Chromium and iron may form an intermetallic sigma phase (FeCr), chromium reducing the concentration of carbon in pearlite and the limiting solubility of carbon in austenite; chromium slows down the decomposition speed of austenite and obviously improves the hardenability of steel. But also increases the temper brittleness tendency of the steel. The chromium element can improve the strength and the hardness of the steel, and other alloy elements are added, so that the effect is obvious. Since Cr increases the quenching ability of the steel during air cooling, it adversely affects the weldability of the steel. However, when the chromium content is less than 0.3%, the adverse effect on weldability is negligible; when the content is more than this, defects such as cracks and slag inclusion are likely to occur during welding. When Cr is present with other alloying elements (e.g., with V), the adverse effect of Cr on weldability is greatly reduced. If Cr, mo, V, etc. are present in the steel at the same time, the weld properties of the steel are not significantly adversely affected even if the Cr content reaches 1.7%. The chromium element is a beneficial and unnecessary addition element, and the addition amount is not suitable to be too much in consideration of factors such as cost increase and the like.

Mo: molybdenum can inhibit the self-diffusion of iron and the diffusion speed of other elements. The atomic radius of Mo is larger than that of alpha-Fe atoms, so that when Mo is dissolved in the alpha solid solution, the solid solution generates strong lattice distortion, and meanwhile, the crystal lattice atomic bond attraction can be increased by Mo, and the recrystallization temperature of alpha ferrite is increased. The strengthening effect of Mo in pearlite type, ferrite type and martensite type steel is also obvious even in high-alloy austenitic steel. The good effect of Mo in steel also depends on the interaction with other alloying elements in the steel. When strong carbide forming elements V, nb and Ti are added into steel, the solid solution strengthening effect of Mo is more obvious. This is because, when a strong carbide-forming element is combined with C into a stable carbide, mo can be promoted to be more efficiently dissolved into solid solution, thereby contributing more to the improvement of the heat strength of the steel. Addition of Mo can also increase the hardenability of the steel, but the effect is less pronounced than C and Cr. Mo suppresses the transformation of pearlite region and accelerates the transformation in the intermediate temperature region, so that Mo-containing steel can form bainite in a certain amount even at a high cooling rate and eliminate the formation of ferrite, which is one of the reasons why Mo favorably affects the heat strength of low-alloy heat-resistant steel. Mo also significantly reduces the hot embrittlement tendency of the steel and reduces the pearlite nodularisation rate. When the Mo content is 0.15% or less, the weldability of the steel is not adversely affected. The molybdenum element is a beneficial and unnecessary addition element, and the addition amount is not too large in consideration of factors such as cost increase and the like.

Microalloying elements Ti, nb, V: the addition of trace microalloy elements Nb, V and Ti in the steel can ensure that the steel has good weldability and usability by the dispersion precipitation of carbon and nitride particles (the size is less than 5 nm) and the solid solution of Nb, V and Ti to refine grains under the condition of low carbon equivalent. Nb, V and Ti are carbide-forming elements and nitride-forming elements which satisfy such a requirement at a relatively low concentration, and most of Nb, V and Ti are present as carbides, nitrides and carbonitrides in the steel at normal temperature, and a small part of Nb, V and Ti is dissolved in ferrite. The addition of Nb, V and Ti can prevent austenite grains from growing and improve the coarsening temperature of the steel. The reason is that the dispersed small particles of the carbon and the nitride can fix the austenite grain boundary, hinder the migration of the austenite grain boundary, improve the recrystallization temperature of the austenite, enlarge the unrecrystallized area, namely prevent the austenite grain from growing. On one hand, the steel can improve the strength while reducing the carbon equivalent content by adding a small amount of Nb, V and Ti, thereby improving the welding performance of the steel; on the other hand, impurities such as oxygen, nitrogen, sulfur, etc. are fixed, thereby improving weldability of steel; secondly, due to the effect of microscopic particles, such as insolubility of TiN at high temperature, coarsening of grains in the heat affected zone is prevented, toughness of the heat affected zone is improved, and thus weldability of steel is improved. The microalloy elements are beneficial and unnecessary addition elements, and the addition amount is not excessive in consideration of factors such as cost increase and the like.

The invention controls the processes of recovery, recrystallization, austenite transformation, grain growth and the like of a deformation structure in the continuous heat treatment process through the rapid heat treatment process of rapid heating, short-time heat preservation and rapid cooling, not only forms a ferrite matrix phase in the cooling process, but also generates various strengthening phases and component gradient distribution in the phases, and finally obtains a fine ferrite structure and a polymorphic strengthening phase structure, so that the material obtains better obdurability matching, the alloy cost and the manufacturing difficulty of each process are reduced, and the welding performance and other service performances of the steel grades with the same strength are improved.

The specific principle is as follows: different heating rates are adopted in different temperature stages of the heating process, the low-temperature stage mainly recovers deformed tissues, and a relatively low heating rate can be adopted to reduce energy consumption; in the high temperature zone, recrystallization and grain growth of different phase structures mainly occur, and a relatively high heating rate is needed to shorten the retention time of the structures in the high temperature zone so as to ensure that the grains cannot grow. The recovery of a deformed structure and a ferrite recrystallization process in the heating process are inhibited by controlling the heating rate in the heating process, so that the recrystallization process is overlapped with the austenite phase transformation process, the nucleation points of recrystallized grains and austenite grains are increased, and the grains are refined finally. Through short-time heat preservation and quick cooling, the grain growth time in the soaking process is shortened, and the fine and uniform distribution of grain structures is ensured.

The invention relates to a rapid heat treatment manufacturing method of 780MPa grade high-formability hot-dip aluminum zinc and hot-dip zinc aluminum magnesium dual-phase steel, which comprises the following steps:

1) Smelting and casting

Smelting according to the chemical components and casting into a plate blank;

2) Hot rolling and coiling

The coiling temperature is 550-680 ℃;

3) Cold rolling

The cold rolling reduction rate is 40-85%, and the rolling hard strip steel or steel plate is obtained after cold rolling;

4) Rapid heat treatment hot galvanizing

a) Rapid heating

Rapidly heating the cold-rolled strip steel or the steel plate from room temperature to a target temperature of an austenite-ferrite two-phase region at the temperature of 750-845 ℃, wherein the rapid heating adopts a one-stage type or two-stage type;

when one-stage rapid heating is adopted, the heating rate is 50-500 ℃/s;

b) Soaking heat

Soaking at 750-845 ℃ in an austenite and ferrite two-phase region, wherein the soaking time is 10-60 s;

c) Cooling down

Slowly cooling the band steel or the steel plate to 670-770 ℃ at a cooling rate of 5-15 ℃/s after the heat equalization; then rapidly cooling to 580-600 ℃ at a cooling rate of 50-150 ℃/s;

d) Hot-dip aluminium-zinc or hot-dip zinc-aluminium-magnesium alloy

Rapidly cooling the strip steel or the steel plate to 580-600 ℃, and immersing the strip steel or the steel plate into a zinc pot for hot-dip aluminum-zinc plating or hot-dip zinc-aluminum-magnesium plating;

e) After hot-dip coating aluminum and zinc, rapidly cooling to room temperature at a cooling rate of 30-150 ℃/s to obtain a hot-dip coating aluminum and zinc AZ product; alternatively, the first and second electrodes may be,

Preferably, the whole process of the rapid heat treatment hot-dip aluminum zinc plating or hot-dip zinc aluminum magnesium plating is 29 to 159 seconds.

Preferably, in the step 2), the coiling temperature is 580 to 650 ℃.

Preferably, in the step 3), the cold rolling reduction is 60 to 80%.

Preferably, in the step 4), the rapid heating is performed in two stages, wherein the first stage is heated from room temperature to 550-650 ℃ at a heating rate of 15-300 ℃/s, and the second stage is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 50-300 ℃/s.

Preferably, in the step 4), the rapid heating is performed in two stages, wherein the first stage is heated from room temperature to 550-650 ℃ at a heating rate of 30-300 ℃/s, and the second stage is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 80-300 ℃/s.

Preferably, in the step 4), the final temperature of the rapid heating is 770 to 830 ℃.

Preferably, in the soaking process in the step 4), after the strip steel or the steel plate is heated to the target temperature of the two-phase region of austenite and ferrite, soaking is carried out while keeping the temperature unchanged.

Preferably, in the soaking process in the step 4), the temperature of the strip steel or the steel plate is raised or lowered within a small range within the soaking time period, the temperature after the temperature rise is not more than 845 ℃, and the temperature after the temperature reduction is not less than 750 ℃.

Preferably, the soaking time is 10 to 40s

The invention relates to a rapid heat treatment manufacturing method of 780 MPa-grade high-formability hot-dip aluminum zinc and hot-dip zinc aluminum magnesium dual-phase steel, which comprises the following steps:

1. heating rate control

The recrystallization kinetics of the continuous heating process can be quantitatively described by the relationship affected by the heating rate, the volume fraction of ferrite recrystallized during continuous heating as a function of temperature T:

wherein X (t) is the ferrite recrystallization volume fraction; n is an Avrami index, is related to a phase change mechanism, depends on the decay period of the recrystallization nucleation rate, and generally takes a value within the range of 1-4; t is the heat treatment temperature; t is _star Is the recrystallization onset temperature; β is the heating rate; b (T) is obtained by the following formula:

b＝b ₀ exp(-Q/RT)

it can be derived from the above formula and the related experimental data that the recrystallization onset temperature (T) increases with the rate of heating _star ) And end temperature (T) _fin ) All rise; when the heating rate is above 50 ℃/s, the austenite transformation and recrystallization processes are overlapped, the recrystallization temperature is raised to the temperature of the two-phase region, and the faster the heating rate, the higher the ferrite recrystallization temperature.

The traditional heat treatment process adopts slow heating, under the condition, the deformation matrix is subjected to reversion, recrystallization and grain growth in sequence, then phase transformation from ferrite to austenite is carried out, phase-change nucleation points are mainly concentrated at the grown ferrite grain boundary, the nucleation rate is low, and the finally obtained grain structure is relatively thick.

Under the rapid heating condition, the phase transformation from ferrite to austenite begins to occur before the deformation matrix completes the recovery, or the recrystallization is just completed, the austenite phase transformation occurs before the crystal grains grow up, because the crystal grains are fine and the area of the crystal boundary is large when the recrystallization is just completed, the nucleation rate is obviously improved, and the austenite crystal grains are obviously refined. Particularly, after the ferrite recrystallization and the austenite phase transformation process are overlapped, a large number of crystal defects such as dislocation and the like are reserved in the ferrite crystal, so that a large number of nucleation points are provided for austenite, the austenite presents explosive nucleation, and austenite grains are further refined. Meanwhile, the reserved high-density dislocation line defects also become channels for high-speed diffusion of carbon atoms, so that each austenite grain can be quickly generated and grown, and the volume fraction of austenite is increased.

The structural evolution and the distribution of alloy elements and phase components are finely controlled in the rapid heating process, and a good foundation is laid for the growth of an austenite structure in the subsequent soaking process, the distribution of the alloy components and the transformation from austenite to martensite in the rapid cooling process. The final product structure with refined grains, reasonable elements and phase distribution can be obtained finally. The invention comprehensively considers the factors of the effect of rapidly heating and thinning crystal grains, the manufacturing cost, the manufacturability and the like, and the heating rate is set to be 50-500 ℃/s when one-stage rapid heating is adopted, and the heating rate is set to be 15-500 ℃/s when two-stage rapid heating is adopted.

In different temperature interval ranges, rapid heating has different influences on the structure evolution processes of recovery, recrystallization, grain growth and the like of the material, and in order to obtain optimal structure control, the optimal heating rates of different heating temperature intervals are different: the heating rate has the greatest influence on the recovery process from 20 ℃ to 550-650 ℃, and is controlled to be 15-300 ℃/s, and more preferably 30-300 ℃/s; the heating temperature is from 550-650 ℃ to the austenitizing temperature of 750-845 ℃, the influence of the heating rate on the growth process of crystal grains is the largest, and the heating rate is controlled to be 50-300 ℃/s; more preferably 80 to 300 ℃/s.

2. Soaking temperature control

The soaking temperature generally depends on the C content, the C content in the dual-phase steel of the invention is 0.05-0.12%, and the A content in the steel of the invention _C1 And A _C3 Respectively at about 730 ℃ and 867 ℃. In the rapid heat treatment process of the invention, the strip steel is heated to A _C1 To A _C3 The rapid heat treatment method can obtain more and finer austenite structures compared with the traditional continuous annealing process.

The invention firstly proposes the soaking temperature to be increased and decreased within a certain range for the control of the soaking temperature: namely, the temperature of the soaking zone is increased obliquely and the temperature is decreased obliquely, but the soaking temperature must be kept within a certain range. The benefits of this are: in the process of rapidly increasing and decreasing the temperature within the temperature range of the two-phase region, the superheat degree and the supercooling degree are actually further increased, the rapid phase transformation process is facilitated, when the temperature increasing and decreasing amplitude is large enough, and the temperature increasing and decreasing speed is also large enough, grains can be further refined through repeated transformation from ferrite to austenite and transformation from austenite to ferrite, and meanwhile, certain influence is exerted on carbide formation and uniform distribution of alloy elements, and finally, finer structures and alloy elements with uniform distribution are formed.

After cold rolling, the dual-phase steel has a large amount of undissolved fine and uniformly distributed carbides, and in the heating process, the dual-phase steel can play a role in mechanical obstruction to the growth of austenite grains, thereby being beneficial to refining the grain size of high-strength steel. However, if the soaking temperature is too high, the number of undissolved carbides is greatly reduced, which impairs the effect of this inhibition, increases the tendency of grains to grow, and further lowers the strength of the steel. When the amount of undissolved carbides is too large, aggregation may occur, resulting in uneven distribution of local chemical components, and when the carbon content in the aggregated portion is too high, local overheating may also occur. Ideally, a small amount of fine granular undissolved carbides should be uniformly distributed in the steel, so that not only can the abnormal growth of austenite grains be prevented, but also the content of each alloy element in the matrix can be correspondingly increased, and the aim of improving the mechanical properties of the alloy steel, such as strength, toughness and the like, is fulfilled.

The soaking temperature is also selected to obtain fine and uniform austenite grains, so that the coarse austenite grains are avoided, and the purpose of obtaining a fine martensite structure after cooling is achieved. The austenite grains are coarse due to the overhigh soaking temperature, and the martensite structure obtained after quick cooling is also coarse, so that the mechanical property of the steel is poor; but also increases the amount of retained austenite, reduces the amount of martensite, and reduces the hardness and wear resistance of the steel. Too low soaking temperature can lead the carbon and alloy elements dissolved in the austenite to be insufficient, lead the concentration distribution of the alloy elements in the austenite to be uneven, greatly reduce the hardenability of the steel and cause adverse effect on the mechanical property of the steel. The soaking temperature of the hypoeutectoid steel should be Ac ₃ + 30-50 ℃. For ultra-high strength steels, carbide forming elements are present,the transformation of carbide is inhibited, so that the soaking temperature can be appropriately increased. By combining the factors, the invention selects 750-845 ℃ as soaking temperature so as to obtain more ideal and more reasonable final tissue.

3. Soaking time control

The soaking time is also influenced by the contents of carbon and alloy elements in the steel, and when the contents are increased, the thermal conductivity of the steel is reduced, and because the diffusion speed of the alloy elements is slower than that of the carbon elements, the alloy elements obviously delay the structure transformation of the steel, and the soaking time is properly prolonged. Because the process adopts rapid heating, and the material contains a large amount of residual dislocation in a two-phase region, a large amount of nucleation points are provided for the formation of austenite and a rapid diffusion channel is provided for carbon atoms, so that the austenite can be formed very rapidly, and the shorter the soaking and heat-preserving time is, the shorter the diffusion distance of the carbon atoms is, the larger the carbon concentration gradient in the austenite is, and the more the carbon content of the residual austenite is finally reserved; however, if the soaking and heat-preserving time is too short, the distribution of alloy elements in the steel is uneven and the austenitizing is insufficient; too long heat preservation time easily causes coarse austenite grains. The influence factor of the soaking and heat-preserving time also depends on the contents of carbon and alloy elements in the steel, when the contents are increased, the thermal conductivity of the steel is reduced, and because the diffusion speed of the alloy elements is slower than that of the carbon elements, the alloy elements obviously delay the structure transformation of the steel, and the heat-preserving time is properly prolonged. Therefore, the soaking time needs to be controlled by strictly combining the soaking temperature, the rapid cooling and the rapid heating process, and the ideal tissue and element distribution can be finally obtained. In conclusion, the invention sets the heat preservation time to be 10-60 s.

4. Rapid cooling rate control

The control of the rapid cooling process needs to be combined with comprehensive factors such as the evolution result of each structure and the diffusion distribution result of alloy elements in the early heating and soaking processes, and the like, so that the ideal material structure with each phase structure and reasonably distributed elements is finally obtained.

In order to obtain enough martensite strengthening phase, the cooling speed of the sample during quenching must be larger than the critical cooling speed to obtain the martensite structure, the critical cooling speed mainly depends on the material composition, and the Si content in the invention is as follows: 0.1-0.4%, mn content of 1.2-2.0%, relatively high content, so that the hardenability of the dual-phase steel is greatly enhanced by Si and Mn, thereby reducing the critical cooling speed. Meanwhile, the cooling rate also needs to comprehensively consider the structure evolution and alloy diffusion distribution results of the heating process and the soaking process so as to finally obtain reasonable structure distribution and alloy element distribution of each phase. The cooling rate is too low to obtain martensite structure, so that the strength is reduced, and the mechanical property cannot meet the requirement; however, too much cooling rate will generate large quenching stress (i.e. structural stress and thermal stress), which is liable to cause deformation or even cracking of the sample. The present invention sets the cooling rate to 50-150 c/s.

For high-strength hot-dip aluminum zinc and hot-dip zinc aluminum magnesium products, the rapid heat treatment process reduces the retention time of the strip steel in a high-temperature furnace, so that the enrichment amount of alloy elements on the surface of the high-strength strip steel in the heat treatment process is obviously reduced, the improvement of the platability of the high-strength hot-dip zinc product is facilitated, the reduction of the plating leakage defects on the surface of the high-strength hot-dip zinc product and the improvement of the corrosion resistance are facilitated, and the yield can be improved; in addition, due to the refinement of product grains and the reduction of the alloy content of the material, the processing and forming performances such as hole expansion performance, bending performance and the like and the user service performances such as welding performance and the like of the dual-phase steel product obtained by adopting the technology are also improved.

The rapid heat treatment process technology reduces the time of the heating process and the soaking process, shortens the furnace length (at least one third of the furnace length compared with the traditional continuous annealing furnace), obviously reduces the number of furnace rollers, reduces the probability of generating surface defects in the furnace, and obviously improves the surface quality of products.

Compared with the prior art, the invention has the advantages that:

(1) The invention inhibits the recovery of a deformed structure and a ferrite recrystallization process in a heat treatment process by rapid heat treatment, so that the recrystallization process is overlapped with an austenite phase transformation process, the nucleation points of recrystallized grains and austenite grains are increased, the grain growth time is shortened, the metallographic structure of the obtained dual-phase steel is a ferrite and martensite dual-phase structure which is uniformly distributed, and fine martensite in the structure after rapid heat treatment is characterized by having various shapes such as blocks, strips, granules and the like, and the distribution is more uniform, so that the dual-phase steel product can obtain good strong plasticity matching.

(2) Compared with the hot-galvanized dual-phase steel obtained by the traditional continuous annealing hot-galvanized mode, the average grain size of the dual-phase steel obtained by the rapid heat treatment of the invention is 1-5 mu m under the premise of unchanged manufacturing conditions of the previous process, and the good fine grain strengthening effect can be obtained. The yield strength is 476-556 MPa, the tensile strength is 786-852 MPa, the elongation is 20.1-24.8%, the product of strength and elongation is 16.7-20.2 GPa%, and the strain hardening index n ₉₀ The value is greater than 0.20.

(3) According to the low-carbon low-alloy high-formability 780 MPa-grade low-carbon low-alloy hot-dip galvanized dual-phase steel rapid heat treatment process, the time of the whole heat treatment process can be shortened to 29-159s, the time of the whole heat treatment process is greatly reduced (the time of a traditional continuous annealing process is usually 5-8 min), the production efficiency is remarkably improved, the energy consumption is reduced, and the production cost is reduced.

(4) Compared with the traditional dual-phase steel and the heat treatment process thereof, the rapid heat treatment method shortens the length (at least one third, the time and the whole heat treatment process time) of the heating section and the soaking section of the continuous hot galvanizing annealing furnace, can save energy, reduce emission and consumption, obviously reduces one-time investment of furnace equipment, and obviously reduces the production running cost and the equipment maintenance cost; in addition, the alloy content can be reduced by producing products with the same strength grade through rapid heat treatment, the production cost of the heat treatment and the previous working procedures is reduced, and the manufacturing difficulty of each working procedure before the heat treatment is reduced.

(5) In the aspect of product quality, compared with the dual-phase steel obtained by the traditional continuous annealing treatment, the rapid heat treatment process technology reduces the time of the heating process and the soaking process, shortens the length of the furnace, obviously reduces the number of furnace rollers, reduces the probability of generating surface defects in the furnace, and obviously improves the surface quality of the product; for high-strength hot-dip aluminum zinc and hot-dip zinc aluminum magnesium products, the rapid heat treatment process reduces the retention time of the strip steel in a high-temperature furnace, so that the enrichment amount of alloy elements on the surface of the high-strength strip steel in the heat treatment process is obviously reduced, and the improvement of the platability of the products is facilitated, so that the reduction of the plating leakage defects and the improvement of the corrosion resistance of the surfaces of the high-strength hot-dip aluminum zinc and hot-dip zinc aluminum magnesium products are facilitated, and the yield can be improved; in addition, due to the refinement of product grains and the reduction of the alloy content of the material, the processing and forming performances such as hole expansion performance, bending performance and the like and the user service performances such as welding performance and the like of the dual-phase steel product obtained by adopting the technology are also improved.

In conclusion, the 780MPa grade high-forming hot-dip aluminum zinc and hot-dip zinc aluminum magnesium dual-phase steel obtained by the method has important values on the development of new-generation light-weight transportation tools such as automobiles, trains, ships, airplanes and the like, the healthy development of corresponding industries and the healthy development of advanced manufacturing industries.

Drawings

FIG. 1 is a photograph of the microstructure of a hot-dip aluminum-zinc dual-phase steel (AZ) produced according to example 4 (single-stage heating) of the present invention as test steel D.

FIG. 2 is a photograph of the microstructure of hot-dip aluminum-zinc dual phase steel (AZ) produced by conventional process 4 (one-stage heating) of test steel D of the present invention.

FIG. 3 is a photograph of the microstructure of a hot dip aluminum zinc dual phase steel (AZ) produced in accordance with example 15 (two-stage heating) of the present invention as test steel N.

FIG. 4 is a photograph showing the microstructure of a hot dip galvanized aluminum magnesium dual phase steel (AM) produced according to example 17 (two-stage heating) of the present invention in test steel E.

Detailed Description

The present invention is further illustrated by the following examples and the accompanying drawings, wherein the examples are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are provided, but the scope of the present invention is not limited to the following examples.

The composition of the test steel of the present invention is shown in table 1, the specific parameters of the one-stage rapid heat treatment of the present invention and the conventional process are shown in table 2, the specific parameters of the two-stage rapid heat treatment of the present invention and the conventional process are shown in table 3, table 4 shows the main properties of the two-phase steel obtained by the one-stage heating of the composition of the test steel of the present invention and the conventional process, and table 5 shows the main properties of the two-phase steel obtained by the two-stage heating of the composition of the test steel of the present invention and the conventional process.

As can be seen from tables 1 to 5, by the method of the present invention, the alloy content in the steel of the same grade can be reduced, the crystal grains are refined, and the material structure composition and the matching of the strength and the toughness are obtained. The dual-phase steel obtained by the method has the yield strength of 476-556 MPa, the tensile strength of 786-852 MPa, the elongation of 20.1-24.8 percent, the product of strength and elongation of 16.7-20.2 GPa percent, and the strain hardening index n ₉₀ The value is greater than 0.20.

Fig. 1 and 2 are structural diagrams of experimental steel D of the present invention after example 4 of the present invention and comparative conventional process example 4 (one-stage heating), fig. 3 is a microstructure picture of hot-dip aluminum-zinc dual-phase steel (AZ) produced by experimental steel N of the present invention through example 15 of the present invention (two-stage heating), and fig. 4 is a microstructure picture of hot-dip zinc-aluminum-magnesium dual-phase steel (AM) produced by experimental steel E of the present invention through conventional heating rate in example 17 of the present invention (two-stage heating).

As seen from the figure, all the material structures consist of ferrite, martensite and a small amount of carbide. The tissue characteristics treated by the traditional process are as follows: the grains are coarse and have a certain banded structure, martensite and carbide are in a net distribution along ferrite grain boundaries, ferrite grains are relatively coarse, and the two-phase structure of ferrite and martensite is not uniformly distributed. The tissue treated by the process of the invention is as follows: ferrite, martensite grain structure and carbide are all very fine and uniformly distributed in the matrix, which is very beneficial to improving the strength and the plasticity of the material. Therefore, by adopting the method, each phase structure which is very uniform, fine and dispersedly distributed can be obtained by removing the aging treatment section. Therefore, the preparation method of the dual-phase steel can refine the crystal grains, and make each phase structure of the material uniformly distributed in the matrix, thereby improving the material structure and the material performance.

The invention carries out process transformation on the traditional continuous annealing unit by adopting the rapid heating and rapid cooling processes, so that the rapid heat treatment process is realized, the lengths of the heating section and the soaking section of the traditional continuous annealing furnace can be greatly shortened, the production efficiency of the traditional continuous annealing unit is improved, the production cost and the energy consumption are reduced, the number of furnace rollers of the continuous annealing furnace is reduced, the surface quality control capability of strip steel can be improved, and the strip steel product with high surface quality is obtained; meanwhile, by establishing a novel continuous annealing unit adopting a rapid heat treatment process technology, the advantages of short and bold unit, flexible product specification and variety transition, strong regulation and control capability and the like can be realized; for the material, the grain of the strip steel can be refined, the strength of the material is further improved, the alloy cost and the manufacturing difficulty of the working procedure before heat treatment are reduced, and the use performance of the material for users such as forming, welding and the like is improved.

In conclusion, the invention adopts the rapid heat treatment process, so that the technological progress of the continuous annealing process of the cold-rolled strip steel is greatly promoted, the austenitizing process of the cold-rolled strip steel from room temperature to the last completion can be completed within tens of seconds or even seconds, the heating section length of the continuous annealing furnace is greatly shortened, the speed and the production efficiency of a continuous annealing unit are conveniently improved, the number of rollers in the furnace of the continuous annealing unit is obviously reduced, the number of rollers in the high-temperature furnace section of a rapid heat treatment production line with the unit speed of about 180 meters per minute is not more than 10, and the surface quality of the strip steel can be obviously improved. Meanwhile, the rapid heat treatment process method of the recrystallization and austenitization process completed in a very short time also provides a more flexible and flexible high-strength steel structure design method, so that the material structure is improved and the material performance is improved on the premise of not changing the alloy components, the rolling process and other previous process conditions.

The high corrosion resistance coating advanced high-strength steel represented by the dual-phase steel has wide application prospect, the rapid heat treatment technology has great development value, and the combination of the two has great space for the development and production of the dual-phase steel.

Claims

1.780 MPa-grade high-formability hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel comprises the following chemical components in percentage by mass: c:0.05 to 0.12%, si:0.01 to 0.5%, mn: 1.2-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.003%, al: 0.02-0.055%, one or two of Cr, mo, ti, nb and V, wherein Cr + Mo + Ti + Nb + V is less than or equal to 0.5%, and the balance of Fe and other inevitable impurities, and is obtained by the following process:

1) Smelting and casting

Smelting according to the chemical components and casting into a plate blank;

2) Hot rolling and coiling

The coiling temperature is 550-680 ℃;

3) Cold rolling

The cold rolling reduction rate is 40-85%;

Rapidly heating the cold-rolled steel plate to 750-845 ℃, wherein the rapid heating adopts a one-section type or two-section type;

when one-stage rapid heating is adopted, the heating rate is 50-500 ℃/s;

then, soaking, wherein the soaking temperature is as follows: 750-845 ℃, soaking time: 10-60 s;

after hot-dip aluminum and zinc plating, cooling to room temperature at a cooling rate of 30-150 ℃/s to obtain a hot-dip aluminum and zinc AZ product; alternatively, the first and second electrodes may be,

and after hot-dip galvanizing aluminum magnesium, cooling to room temperature at a cooling rate of 10-300 ℃/s to obtain a hot-dip galvanizing aluminum magnesium AM product.

2. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein the C content is 0.07-0.10%.

3. The 780MPa grade high formability hot-dip aluminized zinc or hot-dip galvanized aluminum-magnesium dual-phase steel according to claim 1, wherein the Si content is 0.1 to 0.4%.

4. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein the Mn content is 1.5 to 1.8%.

5. The 780MPa grade high formability hot dip aluminized zinc or hot dip galvanized aluminum magnesium dual-phase steel according to claim 1, wherein the dual-phase steel may contain one or two of Cr, mo, ti, nb and V, and Cr + Mo + Ti + Nb + V is less than or equal to 0.4%.

6. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein the rapid heat treatment hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel is used for 29-159s.

7. The 780MPa grade high-formability hot-dip aluminized zinc or hot-dip galvanized aluminum-magnesium dual-phase steel according to claim 1, wherein the hot rolling temperature in the step 2) is not less than A _r3 。

8. The 780 MPa-grade high-formability hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel according to claim 1 or 7, wherein the coiling temperature in step 2) is 580 to 650 ℃.

9. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein in step 3), the cold rolling reduction is 60 to 80%.

10. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein in the step 4), the rapid heating is performed in a one-stage heating mode, and the heating rate is 50-300 ℃/s.

11. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein in step 4), the rapid heating is performed in two stages: the first section is heated from room temperature to 550-650 ℃ at a heating rate of 15-300 ℃/s, and the second section is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 50-300 ℃/s.

12. The 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 1, wherein in step 4), the rapid heating is performed in two stages: the first section is heated from room temperature to 550-650 ℃ at the heating rate of 30-300 ℃/s, and the second section is heated from 550-650 ℃ to 750-845 ℃ at the heating rate of 80-300 ℃/s.

13. The 780MPa grade high-formability hot-dip aluminized zinc or hot-dip galvanized aluminum-magnesium dual-phase steel according to claim 1, wherein in the step 4), after hot-dip galvanizing aluminum-magnesium, the steel plate is rapidly cooled to room temperature at a cooling rate of 30-250 ℃/s, and a hot-dip galvanized aluminum-magnesium AM product is obtained.

14. The 780MPa grade high formability hot dip aluminized zinc or hot dip galvanized aluminum magnesium dual phase steel according to any of claims 1 to 13, wherein the dual phase steel has a homogeneous distribution of ferrite and martensite dual phase structure and an average grain size of 1 to 5 μm.

15. The 780MPa grade high formability hot dip aluminized zinc or hot dip galvanized aluminum magnesium dual phase steel according to any one of claims 1 to 14, wherein the dual phase steel has a yield strength of 476 to 556MPa, a tensile strength of 786 to 852MPa, an elongation of 20.1 to 24.8%, a product of strength and elongation of 16.7 to 20.2GPa%, and a strain hardening index n ₉₀ The value is greater than 0.20.

16. The method for producing 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to any of claims 1 to 15, comprising the steps of:

1) Smelting and casting

Smelting according to the chemical components and casting into a plate blank;

2) Hot rolling and coiling

The coiling temperature is 550-680 ℃;

3) Cold rolling

a) Rapid heating

when one-stage rapid heating is adopted, the heating rate is 50-500 ℃/s;

b) Soaking heat

c) Cooling down

d) Hot-dip aluminium-zinc or hot-dip zinc-aluminium-magnesium alloy

e) After hot-dip aluminum and zinc plating, rapidly cooling to room temperature at a cooling rate of 30-150 ℃/s to obtain a hot-dip aluminum and zinc AZ product; alternatively, the first and second electrodes may be,

after hot-dip galvanizing aluminum magnesium, rapidly cooling to room temperature at a cooling rate of 10-300 ℃/s,

obtaining the hot galvanizing aluminum magnesium AM product.

17. The method for producing 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 16, wherein the time for the whole process of the hot dip aluminum zinc or hot dip zinc aluminum magnesium is 29 to 159s.

18. The 780MPa grade high formability fast hot dip aluminized zinc or hot dip galvanized aluminum magnesium dual phase steel of claim 16The heat treatment manufacturing method is characterized in that in the step 2), the hot rolling temperature is more than or equal to A _r3 。

19. The rapid heat treatment manufacturing method of 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 16 or 18, characterized in that in step 2), the coiling temperature is 580 to 650 ℃.

20. The method for producing 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel by rapid heat treatment according to claim 16, wherein the cold rolling reduction in step 3) is 60 to 80%.

21. The method for producing 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel by rapid heat treatment according to claim 16, wherein in the step 4), the rapid heating is performed in a single stage at a heating rate of 50 to 300 ℃/s.

22. The method for rapidly heat-treating 780MPa grade high-formability hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel according to claim 16, wherein in the step 4), the rapid heating is performed in two stages, the first stage is heated from room temperature to 550-650 ℃ at a heating rate of 15-300 ℃/s, and the second stage is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 50-300 ℃/s.

23. The method for rapidly heat-treating 780MPa grade high-formability hot-dip aluminum-zinc or hot-dip zinc-aluminum-magnesium dual-phase steel according to claim 16, wherein in the step 4), the rapid heating is performed in two stages, the first stage is heated from room temperature to 550-650 ℃ at a heating rate of 30-300 ℃/s, and the second stage is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 80-300 ℃/s.

24. The method for producing 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 16, 22 or 23, wherein the rapid heating final temperature in step 4) is 770 to 830 ℃.

25. The method for manufacturing 780MPa grade high formability hot dip aluminum zinc or hot dip zinc aluminum magnesium dual phase steel according to claim 16, wherein in the soaking step of step 4), the strip steel or the steel plate is heated to the target temperature of the two phase region of austenite and ferrite, and then soaked while keeping the temperature constant.

26. The rapid thermal processing manufacturing method of 780MPa grade high formability hot-dip aluminum zinc or hot-dip zinc aluminum magnesium dual-phase steel according to claim 16, characterized in that in the soaking process of step 4), the strip steel or the steel plate is heated up or cooled down in a small amplitude within the soaking time period, the temperature after heating up is not more than 845 ℃, and the temperature after cooling down is not less than 750 ℃.

27. The method for producing 780MPa grade high formability hot dip aluminized zinc or hot dip galvanized aluminum magnesium dual phase steel according to claim 16, 25 or 26, wherein the soaking time is 10 to 40 seconds.