CN115948701A - A kind of 1470MPa grade galvanized high-strength steel and its preparation method - Google Patents

Abstract

The invention belongs to the technical field of high-strength cold-rolled steel, and in particular relates to a 1470MPa grade galvanized high-strength steel and a preparation method thereof. : 1.8%～2.5%, Cr: 0.3%～0.8%, Mo: 0.15%～0.3%, Ti: 0.015%～0.03%, P≤0.01%, S≤0.01%, N≤0.004%, the balance is Fe and trace elements, the metallographic structure of the steel is: hard bainitic ferrite and retained austenite. In the preparation method of the present invention, 90 Hard bainitic ferrite phase matrix of more than 5% and hard interphase film-like retained austenite of more than 5%, the fine and uniform hard phase matrix in the structure provides strength, and the film-like retained austenite enriched in high carbon provides The ductility of steel is improved, and the uniform structure provides high yield strength, making it ultra-high-strength steel with high yield strength and high elongation.

Description

A kind of 1470MPa grade galvanized high-strength steel and its preparation method

technical field

The invention belongs to the technical field of high-strength cold-rolled steel, and in particular relates to a 1470MPa grade galvanized high-strength steel and a preparation method thereof.

Background technique

With the development of automobiles in the direction of energy saving, environmental protection, safety and comfort, while the body is developing in the direction of lightweight, the requirements for corrosion resistance and impact resistance are also getting higher and higher. Coupled with the competitive pressure from materials such as aluminum, magnesium, and plastics, steel sheets for automobiles are forced to develop in the direction of high-strength coatings. With the continuous expansion of the use of galvanized ultra-high-strength steel, the performance requirements are getting higher and higher, not only high strength, but also good formability, such as high elongation, high yield, bendability, and hole expansion etc.

In high-strength steel, the TRIP structure contains highly plastic ferrite, and local strain concentration occurs in the nearby soft phase, so it has a low yield strength. By adopting flat pre-yielding or introducing precipitates, although the hardness difference between the hard phase and the soft phase can be reduced, the yield strength can be increased to a certain extent, and the local formability of the steel can be improved, but its essential structure has not changed, and it cannot completely solve the phase change induced The local formability of plastic steel, but also a certain loss of elongation. Therefore, how to produce ultra-high-strength steel with high yield strength without loss of elongation is a big problem.

Contents of the invention

In view of the above-mentioned problems, the present invention is proposed in order to provide a kind of 1470MPa grade galvanized high-strength steel and its preparation method that overcomes the above-mentioned problems or at least partially solves the above-mentioned problems, so as to solve the problem that ultra-high-strength steels in the prior art cannot have high yield strength at the same time and high elongation issues.

In the first aspect, the embodiment of the present invention provides a 1470MPa grade galvanized high-strength steel, the chemical composition of the steel is as follows in mass fraction:

C: 0.19%～0.22%, Si: 1.0%～1.5%, Mn: 1.8%～2.5%, Cr: 0.3%～0.8%, Mo: 0.15%～0.3%, Ti: 0.015%～0.03%, P≤ 0.01%, S≤0.01%, N≤0.004%, the balance is Fe and trace elements. The metallographic structure of the steel is: hard bainitic ferrite and retained austenite.

Optionally, in terms of volume fraction, the content of the hard bainitic ferrite is 90%-95%, and the content of the retained austenite is 5%-10%.

Optionally, the grain size of the hard bainitic ferrite is 0.8 μm˜1.5 μm, and the grain size of the retained austenite is 0.1 μm˜0.3 μm.

In a second aspect, the present invention provides a method for preparing a 1470MPa grade galvanized high-strength steel, which is used to prepare a 1470MPa grade galvanized high-strength steel described in any one of the first aspect, the method comprising:

obtaining chilled rolls containing said chemical composition;

Carry out heating treatment to described chill coil, when heating up to the first preset temperature, stop heating up;

Under the conditions of the first set temperature and the first set time length, heat-insulate the chilled coil after the heating treatment;

Under the condition of the set cooling rate, the cooling process is performed on the chilled coil after heat preservation, and when the temperature is lowered to the second set temperature, the cooling is stopped;

Under the conditions of the second set temperature and the second set time length, the chilled coils after the cooling treatment are kept warm.

Optionally, the value of the first set temperature is 850°C to 950°C; and/or

The value of the set cooling rate is 30°C/s-50°C/s; and/or

The value of the second set temperature is 250°C to 350°C, and the value of the second set duration is 60s to 120s; and/or

The value of the first set duration is 60s˜150s.

Optionally, said obtaining chilled rolls containing said chemical composition includes:

Under the condition of setting the cold rolling reduction rate, the hot-rolled coil is cold-rolled to obtain a chilled coil containing the chemical composition;

Wherein, the cold rolling reduction parameter is set to a value of 50% to 60%.

Optionally, under the conditions of the first set temperature and the first set time length, the heat preservation of the chilled coil after the heating treatment includes:

Under the conditions of the first set temperature, the first set duration and the set atmosphere, heat-insulate the chilled coil after the heating treatment;

Wherein, the parameters for setting the atmosphere include: [O ₂ ]<0.1% and/or [H ₂ O]≧1%, [O ₂ ] represents the volume concentration of oxygen, and [H ₂ O] represents the volume concentration of water .

Optionally, the chilled coil is subjected to heating treatment, and when the temperature reaches the first set temperature, the heating is stopped, including:

Under the condition of the first heating rate, the temperature of the chilled coil is raised to a third set temperature;

Under the condition of the second heating rate, heating the chilled coil with the third set temperature to the fourth set temperature;

Under the third heating rate condition, when the temperature of the chilled coil with the fourth set temperature is raised to the first set temperature, the temperature increase is stopped.

Optionally, the value of the first heating rate is 8°C/s-12°C/s, and the value of the third set temperature is 200°C-240°C; and/or

The value of the second heating rate is 3°C/s-8°C/s, and the value of the fourth set temperature is 640°C-660°C; and/or

The value of the third heating rate is 1° C./s˜3° C./s.

Optionally, under the condition of the second heating rate, heating the chilled coil with the third set temperature to the fourth set temperature includes:

Under the second heating rate and set atmospheric conditions, heating the chilled coil with the third set temperature to a fourth set temperature;

Wherein, the parameters for setting the atmosphere include: [O ₂ ]≧0.1% and/or [H ₂ O]≧1%, [O ₂ ] represents the volume concentration of oxygen, and [H ₂ O] represents the volume concentration of water .

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

A 1470MPa grade galvanized high-strength steel provided by the embodiment of the present invention has the following chemical composition in terms of mass fraction: C: 0.19%-0.22%, Si: 1%-1.5%, Mn: 1.8%-2.5%, Cr: 0.3%～0.8%, Mo: 0.15%～0.3%, Ti: 0.015%～0.03%, P≤0.01%, S≤0.01%, N≤0.004%, the balance is Fe and trace elements, by using pre-oxidation- High temperature heating-low temperature aging heating treatment process mode, obtain more than 90% hard bainitic ferrite phase matrix and more than 5% hard interphase film-like retained austenite, the fine and uniform hard phase matrix in this structure provides strength , High carbon-enriched membranous retained austenite provides the ductility of steel, while the uniform structure provides high yield strength, making it ultra-high-strength steel with high yield strength and high elongation.

The above description is only an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable , the specific embodiments of the present invention are enumerated below.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings that need to be used in the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Figure 1 is a photo of the microstructure of the 1470MPa grade galvanized high-strength steel provided by the embodiment of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be presented more clearly. Those skilled in the art should understand that these specific implementations and examples are used to illustrate the present invention, not to limit the present invention.

Throughout the specification, unless otherwise specified, terms used herein should be understood as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, this specification shall take precedence.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

The technical solution of the embodiment of the present application is to solve the above-mentioned technical problems, and the general idea is as follows:

According to a typical embodiment of the present invention, a 1470MPa grade galvanized high-strength steel is provided. The chemical composition of the steel is: C: 0.19%-0.22%, Si: 1.0%-1.5%, Mn: 1.8%～2.5%, Cr: 0.3%～0.8%, Mo: 0.15%～0.3%, Ti: 0.015%～0.03%, P≤0.01%, S≤0.01%, N≤0.004%, the balance is Fe and trace elements. The metallographic structure of the steel is: hard bainitic ferrite and retained austenite.

C is the most effective solid solution strengthening element and the most important element to ensure the hard phase content of the steel. Therefore, the weight percentage of C needs to be controlled within 0.19% to 0.22%. If it is too small, the hard phase content cannot be guaranteed. It is difficult to achieve the required strength, and if it is too large, the weldability will be deteriorated.

Si is an important element to inhibit the precipitation of cementite, so the weight percentage of Si needs to be controlled at 1 to 1.5%. If it is too small, it is difficult to inhibit the precipitation of cementite, resulting in a small amount of retained austenite, which affects the ductility of steel , Excessive assembly deteriorates flanging.

Mn is a solid solution strengthening element and an important element for stabilizing austenite. Therefore, the present invention controls the weight percentage of Mn at 1.8% to 2.5%. If it is too small, it is difficult to ensure the hard phase of the steel, and it is difficult to achieve high strength. Great deterioration of workability and weldability.

Cr is a solid solution strengthening element, which improves the hardenability and the strength of the steel plate. In the present invention, the weight percentage of Cr is controlled at 0.3%-0.8%. If it is too small, it is difficult to ensure the hard phase of the steel, and it is difficult to achieve high strength, and if it is too large, it will deteriorate the workability.

Mo is a solid solution strengthening element, which improves hardenability and steel plate strength, and also promotes bainite transformation. In the present invention, the mass fraction of Mo is 0.15% to 0.3%. If it is too small, it is difficult to ensure the hard phase of the steel, and it is difficult to achieve high strength, and if it is too large, it will deteriorate the workability.

Ti can effectively refine grains and improve the uniformity of steel structure. The present invention controls the mass fraction of Ti to be 0.015%-0.03%. If it is too small, the effect of grain refinement cannot be achieved, and if it is too large, titanium oxide inclusions will be formed and the ductility will be deteriorated.

P is easy to significantly reduce the plasticity and toughness of steel, so the content is required to be as low as possible, and the weight percentage of P needs to be controlled below 0.01%.

S is a harmful impurity element in steel, which causes hot brittleness of steel, reduces the ductility and toughness of steel, and causes cracks during forging and rolling. Therefore, the weight percentage of S is controlled at 0.01% or less.

Like C, N is also a solid solution element. With the increase of N content in steel, it will lead to the deterioration of its stamping performance. At the same time, solid solution N is the main reason for the aging of galvanized sheet products, especially for the strain aging effect after flattening. The influence of nitrogen is particularly large. Therefore, N is required to be as low as possible. For the present invention, the N content in the steel should be controlled at 0.004% or below.

As an optional implementation manner, in terms of volume fraction, the content of the hard bainitic ferrite is 90%-95%, and the content of the retained austenite is 5%-10%.

In this embodiment, 90% to 95% of the volume fraction of bainitic ferrite provides strength. If the hard bainitic martensite phase matrix is less than 90%, the strength is insufficient, and if it is greater than 95%, the residual austenitic Insufficient tenite and ferrite may lead to poor ductility of steel; 5% to 10% residual austenite provides ductility, if the residual austenite is less than 5%, the ductility is insufficient, if it is greater than 10%, making Insufficient bainitic ferrite phase may result in low strength of the steel.

As an optional implementation manner, the grain size of the hard bainitic ferrite is 0.8 μm to 1.5 μm, and the grain size of the retained austenite is 0.1 μm to 0.3 μm.

According to another typical embodiment of the present invention, a method for preparing 1470MPa grade galvanized high-strength steel is provided, which is used to prepare a 1470MPa grade galvanized high-strength steel described in any one of the first aspect, the method comprising:

obtaining chilled rolls containing said chemical composition;

Carry out heating treatment to described chill coil, when heating up to the first preset temperature, stop heating up;

Under the conditions of the first set temperature and the first set time length, heat-insulate the chilled coil after the heating treatment;

Under the condition of the set cooling rate, the cooling process is performed on the chilled coil after heat preservation, and when the temperature is lowered to the second set temperature, the cooling is stopped;

Under the conditions of the second set temperature and the second set time length, the chilled coils after the cooling treatment are kept warm.

As an optional implementation manner, the value of the first set temperature is 850°C to 950°C; and/or

The value of the set cooling rate is 30°C/s-50°C/s; and/or

The value of the second set temperature is 250°C to 350°C, and the value of the second set duration is 60s to 120s; and/or

The value of the first set duration is 60s˜150s.

In this embodiment, if the heating temperature of the first set temperature is less than 850°C, the austenite content cannot be guaranteed, resulting in the inability to obtain the required hard phase in the subsequent phase transformation process. If it is greater than 950°C, full austenite will be obtained. body, resulting in the acquisition of the full hard phase in the subsequent phase transformation process, and the soft phase ferrite that cannot be obtained affects the elongation. Set the cooling rate to 30°C/s-50°C/s. When the cooling rate is less than 30°C/s, a large amount of ferrite transformation occurs, it is difficult to ensure the hard phase of the steel, and it is difficult to achieve high strength. °C/s results in all hard phases, making it difficult to ensure the desired elongation. The value of the second set temperature is 250°C to 350°C, and the value of the second set time is 60s to 120s; and/or if the aging temperature is lower than 250°C, there is no aging effect, which will affect the local formability of the steel , if the aging temperature is higher than 350 ° C, it will affect the formation of hard phase or cause the precipitation of cementite, which will affect the strength. If the aging time is less than 60s, the aging effect cannot be guaranteed, which will affect the local formability. If it is longer than 120s, cementite will be precipitated. The value of the first set duration is 60s˜150s. If the heating time is less than 60s, the original austenite structure cannot be homogenized, and if the heating time is longer than 120s, the original austenite grains will be coarsened, which will affect the performance of the steel.

As an optional implementation, the obtaining of chilled rolls containing the chemical composition includes:

Under the condition of setting the cold rolling reduction rate, the hot-rolled coil is cold-rolled to obtain a chilled coil containing the chemical composition;

Wherein, the cold rolling reduction parameter is set to a value of 50% to 60%.

In this embodiment, if the cold rolling reduction is less than 50%, it will affect the recrystallization and phase transformation of the subsequent annealed sheet, and if it is greater than 60%, it will cause rolling difficulties.

As an optional implementation manner, under the conditions of the first set temperature and the first set duration, the heat preservation of the chilled coil after the temperature rise treatment includes:

Under the conditions of the first set temperature, the first set duration and the set atmosphere, heat-insulate the chilled coil after the heating treatment;

Wherein, the parameters for setting the atmosphere include: [O ₂ ]<0.1% and/or [H ₂ O]≧1%, [O ₂ ] represents the volume concentration of oxygen, and [H ₂ O] represents the volume concentration of water , the role is to regulate a reasonable oxidation atmosphere to fully oxidize the chilled coil and improve the surface quality.

In this embodiment, the effect of [O ₂ ]<0.1% and/or [H ₂ O]≧1% is to regulate a reasonable oxidation atmosphere to fully oxidize the chilled coil and improve the surface quality.

As an optional implementation, the chilled coil is subjected to a temperature rise treatment, and when the temperature reaches the first set temperature, the temperature rise is stopped, including:

Under the condition of the first heating rate, the temperature of the chilled coil is raised to a third set temperature;

Under the condition of the second heating rate, heating the chilled coil with the third set temperature to the fourth set temperature;

Under the third heating rate condition, when the temperature of the chilled coil with the fourth set temperature is raised to the first set temperature, the temperature increase is stopped.

As an optional implementation, the value of the first heating rate is 8°C/s-12°C/s, and the value of the third set temperature is 200°C-240°C; and/or

The value of the second heating rate is 3°C/s-8°C/s, and the value of the fourth set temperature is 640°C-660°C; and/or

The value of the third heating rate is 1° C./s˜3° C./s.

As an optional implementation manner, the heating of the chilled coil with the third set temperature to the fourth set temperature under the second temperature increase rate condition includes:

Under the second heating rate and set atmospheric conditions, heating the chilled coil with the third set temperature to a fourth set temperature;

Wherein, the parameters for setting the atmosphere include: [O ₂ ]≧0.1% and/or [H ₂ O]≧1%, [O ₂ ] represents the volume concentration of oxygen, and [H ₂ O] represents the volume concentration of water .

A 1470MPa grade galvanized high-strength steel of the present application and its preparation method will be described in detail below in combination with examples, comparative examples and experimental data.

A kind of production method of 1470MPa grade galvanized high-strength steel provided by the embodiment of the present invention comprises the following steps:

The chemical composition is calculated by mass fraction: C: 0.19%~0.22%, Si: 1~1.5%, Mn: 1.8%~2.5%, Cr: 0.3%~0.8%, Mo: 0.15%~0.3%, Ti: 0.015 %～0.03%, P≤0.01%, S≤0.01%, N≤0.004%, and the balance is Fe and trace elements.

Step S1: Continuous casting of molten steel containing the above chemical components to obtain a slab; during the smelting process, the target temperature at the end point of the converter is 1650-1670°C. During the tapping process, slag is added, specifically adding 200-800kg of slag lime, 0-1000kg of pre-melted slag, and 0-400kg of fluorite. In the early stage of tapping, slag is added along with the steel flow, and the tapping amount reaches 1 Add all slag materials before /5, the amount of slag under tapping is ≤80mm, and the tapping time is ≥4 minutes.

Step S2: heating the slab, and then rough rolling and finishing rolling to obtain a hot-rolled sheet, then laminar cooling the hot-rolled sheet, and coiling it into a hot-rolled coil after cooling; the heating of the slab The temperature is 1220-1280°C; the finish rolling temperature is 870-920°C; the coiling temperature of the hot-rolled plate is 550-620°C. Among them, low-temperature coiling is adopted, so that the head and tail of the hot-rolled plate and the width direction edge have uniform structure properties, and avoid subsequent performance fluctuations of the subsequent chilled hard plate. In addition, low-temperature coiling is adopted to avoid grain boundary oxidation so that hot-rolled raw materials with good surfaces can be obtained.

Step S3: cold-rolling the hot-rolled coil to obtain a chilled coil; when the hot-rolled coil is cold-rolled, the cold-rolling reduction is 50%-60%, so as to facilitate the cold-rolling process.

Step S4: subjecting the chilled coil to continuous annealing treatment to obtain steel strip.

Step S5: Coiling the steel strip into a finished product after being flattened.

Wherein, in step S4, obtaining the steel strip through the continuous annealing treatment of the chilled coil includes:

Step S41: Preheating the chilled coil to 220°C to obtain strip steel at a heating rate of 8°C/s-12°C/s; during this process, the cold deformed ferrite recovers.

Step S42: Heating the preheated steel strip to 640°C-660°C to oxidize to obtain steel strip, the heating rate is 3°C/s-8°C/s; pre-oxidation is realized during this process, wherein O ₂ ≧0.1%, H ₂ O≧1% atmosphere;

Step S43: further heating the preheated steel strip to 850°C-950°C at a heating rate of 1°C/s-3°C/s; this process realizes the recrystallization of the cold-rolled ferrite structure, and the pearlescent The body first transforms into austenite and grows towards ferrite.

Step S44: keeping the further heated steel strip at a temperature range of 850° C. to 950° C. for 60 s to 150 s. This process realizes full or partial austenitization and obtains more austenite. At the same time, the reduction is carried out in an atmosphere of O ₂ <0.1%, H ₂ O≧1%;

Step S45: Quickly cool to an aging temperature of 250°C to 350°C by blowing air, and keep warm within the temperature range for 60s to 120s to obtain annealed steel strip; in this process, a certain proportion of bainite martensite and untransformed austenite is obtained , C, Mn and other elements are further aggregated into the austenite through heat preservation;

Step S45: Heating the annealed steel strip to a galvanizing temperature of 450°C-460°C by induction heating, and cooling to 420°C-430°C by air knife blowing and scraping after galvanizing; The residence time of the strip in the equalization section, furnace nose and zinc pot to avoid partial austenite decomposition at high temperature.

Step S46: After the front-end air cooling between the air knife and the top roller and the rear-end air cooling, finally cool to 250°C-300°C at a cooling rate of 6°C/s-9°C/s; during this process, a small amount of austenite phase transformed into martensitic phase.

Example 1

The chemical composition meets: C: 0.19%~0.22%, Si: 1~1.5%, Mn: 1.8%~2.5%, Cr: 0.3%~0.8%, Mo: 0.15%~0.3%, Ti: 0.015%~0.03% , P≤0.01%, S≤0.01%, N≤0.004%, and the balance is Fe and trace elements. Heating the slab that satisfies the above composition, then rough rolling and finish rolling to obtain a hot-rolled sheet, then laminar cooling the hot-rolled sheet, and coiling it into a hot-rolled coil after cooling, wherein the heating temperature of the slab is It is 1220°C, the final rolling temperature of finish rolling is 870°C, and the coiling temperature of hot-rolled plate is 550°C. The hot-rolled coil is cold-rolled to obtain a chilled coil, and the reduction rate of the cold rolling is 50%. The chilled coil is subjected to continuous annealing treatment to obtain a strip steel. During the annealing treatment, the strip steel is further heated to 850°C after preheating, and the The heating rate is 1.5°C/s. The heated strip is kept at a temperature range of 850°C for 120s, cooled rapidly by air blowing to an aging temperature of 250°C, and kept at this temperature range for 120s to obtain annealed steel strip.

Example 2

The chemical composition meets: C: 0.19%~0.22%, Si: 1~1.5%, Mn: 1.8%~2.5%, Cr: 0.3%~0.8%, Mo: 0.15%~0.3%, Ti: 0.015%~0.03% , P≤0.01%, S≤0.01%, N≤0.004%, and the balance is Fe and trace elements. Heating the slab that satisfies the above composition, then rough rolling and finish rolling to obtain a hot-rolled sheet, then laminar cooling the hot-rolled sheet, and coiling it into a hot-rolled coil after cooling, wherein the heating temperature of the slab is It is 1220°C, the final rolling temperature of finish rolling is 870°C, and the coiling temperature of hot-rolled plate is 550°C. The hot-rolled coils are cold-rolled to obtain chilled coils, and the cold rolling reduction rate is 50%. The chilled coils are subjected to continuous annealing treatment to obtain strip steel. During the annealing treatment, the strip steel is further heated to 880°C after preheating, and the The heating rate is 4°C/s, and the heated strip is kept at a temperature range of 880°C for 120s, then rapidly cooled to an aging temperature of 280°C by blowing air, and kept at this temperature range for 100s to obtain annealed steel strip.

Example 3

The chemical composition meets: C: 0.19%~0.22%, Si: 1~1.5%, Mn: 1.8%~2.5%, Cr: 0.3%~0.8%, Mo: 0.15%~0.3%, Ti: 0.015%~0.03% , P≤0.01%, S≤0.01%, N≤0.004%, and the balance is Fe and trace elements. Heating the slab that satisfies the above composition, then rough rolling and finish rolling to obtain a hot-rolled sheet, then laminar cooling the hot-rolled sheet, and coiling it into a hot-rolled coil after cooling, wherein the heating temperature of the slab is It is 1280°C, the finishing temperature of finish rolling is 920°C, and the coiling temperature of hot-rolled plate is 620°C. The hot-rolled coil is cold-rolled to obtain a chilled coil, and the reduction rate of the cold rolling is 60%. The chilled coil is subjected to continuous annealing treatment to obtain a strip steel. During the annealing treatment, the strip steel is further heated to 910°C after preheating, and The heating rate is 3°C/s, and the heated strip is kept at a temperature range of 910°C for 100s, then rapidly cooled to an aging temperature of 320°C by air blowing, and kept at this temperature range for 80s to obtain annealed steel strip.

Example 4

The chemical composition meets: C: 0.19%~0.22%, Si: 1~1.5%, Mn: 1.8%~2.5%, Cr: 0.3%~0.8%, Mo: 0.15%~0.3%, Ti: 0.015%~0.03% , P≤0.01%, S≤0.01%, N≤0.004%, and the balance is Fe and trace elements. Heating the slab that satisfies the above composition, then rough rolling and finish rolling to obtain a hot-rolled sheet, then laminar cooling the hot-rolled sheet, and coiling it into a hot-rolled coil after cooling, wherein the heating temperature of the slab is It is 1280°C, the finishing temperature of finish rolling is 920°C, and the coiling temperature of hot-rolled plate is 620°C. The hot-rolled coil is cold-rolled to obtain a chilled coil, and the reduction rate of the cold rolling is 60%. The chilled coil is subjected to continuous annealing treatment to obtain a strip steel. During the annealing treatment, the strip steel is further heated to 950°C after preheating, and The heating rate is 2°C/s, and the heated strip is kept in the temperature range of 950°C for 80s, quickly cooled to the aging temperature of 350°C by blowing air, and kept in this temperature range for 60s to obtain annealed steel strip.

Comparative example 1

The chemical composition meets: C: 0.19%~0.22%, Si: 1~1.5%, Mn: 1.8%~2.5%, Cr: 0.3%~0.8%, Mo: 0.15%~0.3%, Ti: 0.015%~0.03% , P≤0.01%, S≤0.01%, N≤0.004%, and the balance is Fe and trace elements. Heating the slab that satisfies the above composition, then rough rolling and finish rolling to obtain a hot-rolled sheet, then laminar cooling the hot-rolled sheet, and coiling it into a hot-rolled coil after cooling, wherein the heating temperature of the slab is It is 1220°C, the final rolling temperature of finish rolling is 870°C, and the coiling temperature of hot-rolled plate is 550°C. The hot-rolled coil is cold-rolled to obtain a chilled coil, and the reduction rate of the cold rolling is 50%. The chilled coil is subjected to continuous annealing treatment to obtain a strip steel. During the annealing treatment, the strip steel is further heated to 800°C after preheating, and The heating rate is 3°C/s, and the heated strip is kept at a temperature range of 800°C for 100s, then quickly cooled to an aging temperature of 350°C by blowing air, and kept at this temperature range for 150s to obtain annealed steel strip.

The key process parameters in the annealing treatment of each embodiment of the present invention are specifically shown in Table 1.

Table 1

Example 1 2 3 4 comparative example Heating rate ℃/s 1.5 4 3 2 3 Heating temperature °C 850 880 910 950 800 Holding time s 120 120 100 80 100 Aging temperature ℃ 250 280 320 350 350 Aging time s 120 100 80 60 150

Related experiments:

The properties of the steels prepared in Examples 1-4 and Comparative Example 1 were tested, and the test results are shown in Table 2.

Related test methods:

The metallographic structure type and its content are tested by EBSD analysis.

The test method of metallographic structure particle size is GB6394-86 metallographic method.

The test method of mechanical properties is GB/T228-2002 "Metallic Materials Tensile Test Method at Room Temperature".

The structure of the 1470MPa grade galvanized high-strength steel obtained in the embodiment of the present invention is a mixed structure of fine lath bainitic ferrite hard matrix, film-like residual austenite, and tempered martensite. The mechanical properties of the continuously annealed high-strength steel obtained in the present invention are shown in Table 2.

Table 2

R_p0.2, N/mm² R_m, N/mm² A₅₀,% comparative example 780 1310 13 Example 1 1080 1485 12 Example 2 1112 1503 11.5 Example 3 1195 1519 12.5 Example 4 1143 1497 12

As can be seen from Table 2, a kind of production method of 1470MPa grade galvanized high-strength steel provided by the embodiment of the present invention, the obtained 1470MPa grade galvanized bainite matrix transformation-induced plasticity steel is compared with the conventional transformation-induced plasticity of the comparative example. Steel has high yield strength and elongation. The tensile strength is greater than 1470MPa, the yield strength is greater than 1000MPa, and the A50 elongation is greater than 10%.

The production method of a 1470MPa grade galvanized high-strength steel provided by the present invention adopts the pre-oxidation-high temperature heating-low temperature aging process mode to obtain a lath bainitic ferrite hard matrix and a mixture of thin film residual austenite Organization of high-strength steel. This type of structure is different from the ferrite soft phase as the matrix. It is mainly lath or membranous fine structure, with few massive structures. The overall structure is relatively uniform and refined, and will not cause local strain concentration. The hard phase matrix in the structure provides strength, the TRIP effect of retained austenite provides the ductility of the steel, and the fine and uniform structure provides matching high yield strength and elongation. According to the present invention, 1470MPa-grade galvanized high-strength steel can be obtained, so that the special requirements for processing performance of auto parts can be met.

Finally, it should also be noted that the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, but also Other elements not expressly listed, or inherent to the process, method, article, or apparatus are also included.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (10)

1. The 1470 MPa-grade galvanized high-strength steel is characterized by comprising the following chemical components in percentage by mass:

c:0.19 to 0.22 percent, si:1.0% -1.5%, mn: 1.8-2.5%, cr:0.3% -0.8%, mo:0.15% -0.3%, ti: 0.015-0.03%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, N is less than or equal to 0.004%, and the balance is Fe and trace elements; the metallographic structure of the steel is as follows: hard bainitic ferrite and residual austenite.

2. The 1470MPa grade galvanized high-strength steel according to claim 1, characterized in that the content of hard bainitic ferrite is 90-95% and the residual austenite is 5-10% by volume fraction.

3. The 1470 MPa-grade galvanized high-strength steel according to claim 1, wherein the grain size of the hard bainitic ferrite is 0.8 to 1.5 μm, and the grain size of the retained austenite is 0.1 to 0.3 μm.

4. A method for preparing 1470MPa grade galvanized high-strength steel, characterized in that the method is used for preparing 1470MPa grade galvanized high-strength steel according to any one of claims 1 to 3, and the method comprises the following steps:

obtaining a chilled coil containing the chemical composition;

heating the cold hard coil, and stopping heating when the temperature is raised to a first set temperature;

preserving the heat of the cold hard coil subjected to the temperature rise treatment under the conditions of the first set temperature and the first set time length;

under the condition of a set cooling rate, cooling the cold hard coil after heat preservation, and stopping cooling when the temperature is reduced to a second set temperature;

and preserving the heat of the cooled hard coil under the conditions of the second set temperature and the second set time length.

5. The preparation method according to claim 4, wherein the first set temperature is 850 ℃ to 950 ℃; and/or

The value of the set cooling rate is 30-50 ℃/s; and/or

The value of the second set temperature is 250-350 ℃, and the value of the second set time is 60-120 s; and/or

The value of the first set time length is 60 s-150 s.

6. The method of manufacturing according to claim 4 or 5, wherein the obtaining of the chilled coil containing the chemical component includes:

under the condition of setting the cold rolling reduction rate, cold rolling the hot-rolled coil to obtain a cold-hard coil containing the chemical components;

wherein the value of the cold rolling reduction rate parameter is set to be 50-60%.

7. The method for preparing according to claim 4 or 5, wherein the maintaining the chilled coil after the temperature raising treatment under the first set temperature and the first set time comprises:

preserving the heat of the cold hard coil subjected to the temperature rise treatment under the conditions of the first set temperature, the first set time and the set atmosphere;

wherein the parameters for setting the atmosphere comprise: [ O ] ₂ ]<0.1% and/or [ H% ₂ O]≧1％，[O ₂ ]Represents the volume concentration of oxygen, [ H ] ₂ O]Indicating the volumetric concentration of water.

8. The method according to claim 4 or 5, wherein the step of heating the chilled coil to a first set temperature and stopping the heating includes:

under the condition of a first temperature rise rate, raising the temperature of the chilled coil to a third set temperature;

under the condition of a second temperature rise rate, raising the temperature of the cold hard roll with a third set temperature to a fourth set temperature;

and under the condition of a third temperature rise rate, stopping temperature rise when the cold hard coil with a fourth set temperature is heated to the first set temperature.

9. The preparation method according to claim 8, wherein the first temperature rise rate takes a value of 8 ℃/s to 12 ℃/s, and the third set temperature takes a value of 200 ℃ to 240 ℃; and/or

The second heating rate is 3 ℃/s-8 ℃/s, and the fourth set temperature is 640-660 ℃; and/or

The value of the third heating rate is 1-3 ℃/s.

10. The method according to claim 8 or 9, wherein the warming up the chilled coil having the third set temperature to a fourth set temperature under the second temperature rise rate condition includes:

under the conditions of the second temperature rise rate and set atmosphere, raising the temperature of the cold hard coil with the third set temperature to a fourth set temperature;

wherein the parameters for setting the atmosphere comprise: [ O ] ₂ ]≧ 0.1% and/or [ H ] ₂ O]≧1％，[O ₂ ]Represents the volume concentration of oxygen, [ H ] ₂ O]Indicating the volume concentration of water.

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