CN115181891A

CN115181891A - 980 MPa-level low-carbon low-alloy hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method

Info

Publication number: CN115181891A
Application number: CN202110360519.0A
Authority: CN
Inventors: 王健; 李俊; 张理扬; 刘华飞
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
Anticipated expiration: 2041-04-02
Also published as: CN115181891B

Abstract

The 980 MPa-level low-carbon low-alloy hot-dip galvanized dual-phase steel and the rapid heat treatment hot-dip galvanizing manufacturing method comprise the following components in percentage by mass: 0.05 to 0.12 percent of C, 0.1 to 0.5 percent of Si, 1.4 to 2.2 percent of Mn, 0.02 to 0.04 percent of Nb, 0.03 to 0.05 percent of Ti, 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 and V, wherein the sum of 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 galvanizing step comprises: quick heating, short-time heat preservation, quick cooling, hot galvanizing and quick cooling (hot galvanizing of a pure zinc GI product); rapid heating, short-time heat preservation, rapid cooling, hot galvanizing, reheating, alloying treatment and rapid cooling (alloying hot galvanizing GA product). The invention changes the recovery of the deformed structure, the ferrite recrystallization and the austenite phase transformation process in the annealing process by rapid heat treatment, increases the recrystallization and austenite core points, shortens the grain growth time, finally obtains the dual-phase steel with the metallographic structure of uniformly distributed ferrite and martensite dual-phase structures, and improves the strength of the material.

Description

980 MPa-level low-carbon low-alloy hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method

Technical Field

The invention belongs to the technical field of rapid heat treatment of materials, and particularly relates to 980 MPa-grade low-carbon low-alloy hot-dip galvanized dual-phase steel (comprising hot-dip pure zinc GI products and alloyed hot-dip galvanized GA products) and a rapid heat treatment hot-dip galvanized 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 materials, and the automobile industry adopts hot-dip galvanized high-strength steel plates to reduce the thickness of the steel plates, and simultaneously can improve the corrosion resistance, dent resistance, durability strength, large deformation impact strength, safety and the like of automobiles, so the automobile steel plates are bound to develop towards the directions of high strength, high toughness, corrosion resistance and easy forming and processing.

The hot-dip galvanized dual-phase steel has the most extensive application and the best application prospect in hot-dip galvanized high-strength steel for automobiles. The low-carbon low-alloy hot-dip galvanized dual-phase steel has the characteristics of low yield ratio, high initial work hardening rate, good strength and plasticity matching property and the like, and becomes the steel which is widely used at present and has high strength and good formability and is used for stamping automobile structures.

The hot galvanized dual-phase steel is obtained by annealing low-carbon steel or low-alloy high-strength steel in a critical area or hot rolling, rolling and cooling, and the microstructure of the hot galvanized dual-phase steel mainly comprises ferrite and martensite. The principle of 'composite material' is utilized by the hot dip galvanized dual phase steel, so that the advantages of each phase (ferrite and martensite) in the steel are utilized as much as possible, and simultaneously, the disadvantage or disadvantage of one phase is reduced or eliminated due to the existence of other phases.

The mechanical properties of the hot galvanizing dual-phase steel are mainly determined by the following three aspects:

1. the grain size and the distribution of alloy elements of the matrix phase;

2. the size, shape, distribution and volume fraction of the second phase;

3. the combination of the matrix and the second phase.

Therefore, how to obtain a hot-dip galvanized dual-phase steel product with low cost, high performance and good strong plasticity matching becomes a target pursued by various large steel enterprises, and is widely concerned by the majority of steel enterprises and automobile users.

The hot-dip galvanized dual-phase steel is obtained by carrying out hot-dip galvanizing process after soaking, heat preservation and rapid cooling treatment in a critical zone, and the process comprises the following steps: heating the strip steel to the temperature of a two-phase critical zone, preserving heat, then cooling the sample to a certain temperature at a cooling speed higher than that required by martensite phase transformation, preserving heat for a period of time, reheating to the temperature of 450-460 ℃ for hot galvanizing treatment, and cooling after hot galvanizing to obtain a certain amount of martensite and ferrite dual-phase structures.

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

Chinese patent CN105950998B discloses a production method of 1000MPa hot-dip galvanized dual-phase steel, and the chemical components of the high-strength dual-phase steel are as follows by weight percent: c:0.05 to 0.10%, si:0.2 to 0.6%, mn:1.4 to 1.9Percent, cr:0.20 to 0.7%, mo:0.2 to 0.5%, al:0.02 to 0.06%, B: 0.001-0.003%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, N is less than or equal to 0.006%, ti:0.02 to 0.05%, nb:0.01 to 0.04 percent, and the balance of Fe and other inevitable impurities. The steel is subjected to initial rolling at 1050-1070 ℃, final rolling at 850-950 ℃, coiling at 600-700 ℃, cold rolling reduction of 51-53%, annealing at 830-840 ℃, fast cooling at 35-45 ℃/s to the temperature of a zinc pool of 440-460 ℃ for hot galvanizing treatment, and then cooling to room temperature at the cooling speed of 6-8 ℃/s after galvanizing. The mechanical properties of the dual-phase steel are as follows: yield strength Rp _0.2 = 630-700 MPa, tensile strength R _m And the elongation is 11 to 14 percent at most, wherein the elongation is 1010 to 1050 MPa. The method adopts the traditional slow heating annealing hot galvanizing process, so more alloy elements such as Cr, mo, ti, nb, B and the like, particularly more noble metal elements such as Mo, nb, ti and the like are added to obtain high strength and good platability, thereby not only increasing the cost, but also bringing difficulty to each manufacturing procedure.

Chinese patent CN104561812B discloses a preparation process and a method of 1000MPa grade high-aluminum hot-dip galvanized dual-phase steel, and the chemical components of the high-strength dual-phase steel are as follows by weight percent: c: 0.14-0.16%, si is less than or equal to 0.05%, mn:1.7 to 1.9%, cr:0.40 to 0.6%, mo:0.2 to 0.3%, al:0.7 to 0.9 percent of the total weight of the alloy, less than or equal to 0.009 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.005 percent of N, and the balance of Fe and other inevitable impurities. The hot galvanizing treatment is carried out by the processes of initial rolling at a temperature of more than 1150 ℃, final rolling at 800-850 ℃, coiling at 600-700 ℃, cold rolling reduction of 60-70%, annealing at 760-840 ℃, annealing for 60-120s, fast cooling at 15-22 ℃/s to the temperature of a zinc pool of 450-470 ℃, and cold cooling to room temperature at a cooling speed of 10-20 ℃/s after galvanizing. The yield strength is 459-510 MPa, the tensile strength is about 1020-1082 MPa, and the elongation is about 12-13%. The method mainly uses aluminum to replace silicon, and avoids the defects of plating leakage and the like caused by enrichment and oxidation of Si element on the surface of a steel plate. Meanwhile, the strength and the toughness of the steel are improved by adding Mn, cr, mo and other elements. Although the hot-dip galvanized dual-phase steel with excellent comprehensive mechanical properties and surface quality is obtained by optimizing chemical components and a preparation method, the C, mn element content is high, the welding property of the material is remarkably reduced, and the alloy cost is improved by adding high-content noble metal elements such as Cr, mo and the like; meanwhile, the high aluminum content is adopted, so that the production difficulty is obviously increased, and the problems of high aluminum steel water plugging and the like in the casting process are easily caused.

Chinese patent CN101348885B discloses '1000 MPa grade cold-rolled hot-galvanized dual-phase steel and a manufacturing method thereof', and the chemical components of the high-strength dual-phase steel are as follows by weight percent: c: 0.06-0.18%, si is less than or equal to 0.1%, mn:1.2 to 2.5%, cr:0.05 to 0.6%, mo:0.05 to 0.5%, al:0.005 to 0.05%, ti:0.01 to 0.05%, nb:0.01 to 0.06 percent, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, less than or equal to 0.005 percent of N, and the balance of Fe and other inevitable impurities. Finish rolling at 800-900 ℃, coiling at 600-700 ℃, cold rolling at 60-75% of rolling reduction, annealing at 780-840 ℃, soaking for 40-100 s, cooling to 450-470 ℃ at a cooling speed of 10-20 ℃/s for hot galvanizing treatment, and cooling to room temperature at a cooling speed of 8-20 ℃/s after galvanizing. The yield strength is 598-688 MPa, the tensile strength is 1022-1156 MPa, and the elongation is 9.5-12.2%. The method mainly adopts Cr and Mo to replace Si elements so as to enlarge two-phase regions of austenite and ferrite and improve the hardenability of the dual-phase steel. Meanwhile, nb and Ti are added to refine grains so as to improve the strength and toughness of the steel, so that the steel has good weldability and usability. Although the hot-dip galvanized dual-phase steel with excellent comprehensive mechanical properties and surface quality is obtained by optimizing chemical components and a preparation method, the C, mn has high element content, the welding property of the material is obviously reduced, the requirement of an automobile factory on carbon equivalent (generally, the carbon equivalent is required to be less than or equal to 0.24) cannot be met, and meanwhile, more noble metal elements such as Cr, mo, nb, ti and the like are added, so that the alloy cost is increased, and the manufacturing difficulty of the working procedure before heat treatment is increased.

Chinese patent CN108441763A discloses a cold-rolled hot-galvanized dual-phase steel with tensile strength of 1000MPa and a preparation method thereof. The high-strength dual-phase steel comprises the following chemical components in percentage by weight: c:0.06 to 0.11%, si:0.3 to 0.5%, mn:1.0 to 3.0%, cr:0.2 to 0.5%, mo:0.1 to 0.3%, als: 0.03-0.06%, P is less than or equal to 0.015%, S is less than or equal to 0.004%, N is less than or equal to 0.005%, and the alloy contains at least one of (a) Nb + Ti + V is less than or equal to 0.18%, and (B) B is less than or equal to 0.005%, and the balance of Fe and other unavoidable impurities. The hot rolled coil is subjected to the processes of rolling at the temperature of 1000-1150 ℃, final rolling at the temperature of 860-920 ℃, coiling at the temperature of 450-600 ℃, hood-type annealing at the temperature of 600-800 ℃ for 24-72h, cold rolling reduction at the temperature of 45-60%, annealing at the temperature of 760-830 ℃ by heating at the traditional heating rate, soaking in the annealing for 60-120 s, hot galvanizing treatment by cooling to the temperature of 470-500 ℃ at the cooling rate of 12-28 ℃/s, and cooling to the room temperature at the cooling rate of more than 5 ℃/s after galvanizing. The yield strength 563-647 MPa, the tensile strength 989-1034 MPa and the elongation rate 14.4-16.2% are about. The invention mainly adopts Cr and Mo to reduce the content of Si element and improve the hardenability and the welding performance of steel, but the content of Si in the invention still ranges from 0.3 to 0.5 percent, and the hot rolled coil of the invention also needs to be subjected to cover annealing for 24 to 72 hours. Although the hot-dip galvanized dual-phase steel with comprehensive mechanical properties and good surface quality is obtained by optimizing chemical components and a preparation method, the content of C, si and Mn elements is high, the welding property of the material is reduced, more noble metal elements such as Cr, mo, nb, ti, V or B are added, the alloy cost is increased, and meanwhile, after hot rolling and coiling, before cold rolling, cover annealing is added to improve the structure and the cold rolling processing property, obviously, the working procedure and the manufacturing cost are increased.

Chinese patent CN106471147B discloses 'a high-strength multi-phase steel, a production method and application', and the chemical components of the high-strength multi-phase steel are as follows by weight percent: c:0.05 to 0.15%, mn: 2.0-3.0%, al is less than or equal to 0.1%, si:0.3 to 1.5%, nb:0.01 to 0.05 percent, less than or equal to 0.02 percent of N, cr + Mo:0.1 to 1.0%, B: 0.0001-0.0025%, less than or equal to 0.5% of Ti, less than or equal to 0.01% of V, less than or equal to 0.01% of S, less than or equal to 0.05% of P, and the balance of Fe and other unavoidable impurities. The method comprises the steps of rolling at a temperature higher than 1180 ℃, finishing at a temperature higher than 800 ℃, coiling at 500-800 ℃, reducing at 40-60% of cold rolling, heating to 500-750 ℃ at a conventional heating rate, oxidizing strip steel by 0.2-0.4% of oxygen in a certain oxidizing atmosphere, annealing at 750-950 ℃, reducing the surface of the steel plate, annealing for 30-300 seconds, cooling to 440-470 ℃ at a cooling rate of 12-28 ℃/s, aging for 30-180 seconds, hot galvanizing in a zinc bath, galvanizing at a cooling rate of more than 1 ℃/sCooling to room temperature. Its yield strength Rp _0.2 596 to 833MPa, the tensile strength is about 1066 to 1294MPa, and the elongation is about 8.3 to 13.8 percent. The invention contains higher C, mn and Si elements which influence the welding performance, and noble metal elements such as Cr, mo, nb, ti, V and the like are added, so that the alloy cost is improved, and the aging treatment is required before hot galvanizing, so that the cost and the difficulty of continuous annealing production are obviously increased.

Chinese patent 201711385129.9 discloses 780 MPa-grade low-carbon low-alloy hot-galvanized TRIP steel and a rapid heat treatment method thereof, which comprises the following chemical components in percentage by mass: c:0.16-0.22%, si:1.2-1.6%, mn:1.6-2.2%, the balance being Fe and other unavoidable impurity elements, obtained by a rapid thermal processing process comprising: rapidly heating the strip steel from room temperature to a two-phase region of austenite and ferrite at the temperature of 790-830 ℃, wherein the heating rate is 40-300 ℃/s; heating the target temperature in the two-phase region for 60-100s; rapidly cooling the strip steel from the temperature of the two-phase region to 410-430 ℃, wherein the cooling speed is 40-100 ℃/s, and the strip steel stays in the temperature region for 200-300s; the strip steel is heated to 460-470 ℃ from 410-430 ℃ and then is immersed in a zinc pot for heat preservation. After the strip steel is galvanized, rapidly cooling the strip steel from 460 to 470 ℃ (the cooling rate is 50 to 150 ℃/s) to room temperature to obtain a hot-dip pure zinc (GI) product; after hot galvanizing of the strip steel, the strip steel can also be heated (the heating rate is 10-300 ℃/s) to 480-550 ℃ for alloying treatment for 5-20 seconds, and the alloyed hot Galvanized (GA) product is obtained after the alloying treatment and rapid cooling (the cooling rate is 10-250 ℃/s) to room temperature. The method is characterized in that: the TRIP steel metallographic structure is a bainite, ferrite and austenite three-phase structure; the TRIP steel has obviously refined average grain size, tensile strength of 950-1050 MPa, elongation of 21-24% and strength-elongation product of 24GPa%.

The defects of the patent mainly comprise the following aspects:

firstly, the patent discloses a 780 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel product and a process technology thereof, but the tensile strength of the TRIP steel product is 950-1050 MPa, the tensile strength of the TRIP steel product is too high as that of the 780 MPa-grade product, the use effect of a user is not good, and the tensile strength of the TRIP steel product is too low as that of the 980 MPa-grade product, so that the strength requirement of the user can not be well met;

secondly, the patent adopts one-stage rapid heating, the same rapid heating rate is adopted in the whole heating temperature interval, the materials are not processed differently according to the change of the organizational structures of the materials in different temperature sections, and the materials are all rapidly heated at the speed of 40-300 ℃/s, so that the production cost of the rapid heating process is inevitably increased;

thirdly, the soaking time of the patent is set to be 60-100s, which is similar to that of the traditional continuous annealing, and the increase of the soaking time inevitably partially weakens the grain refining effect generated by rapid heating, thus being very unfavorable for improving the strength and the toughness of the material;

fourth, the patent must perform a bainite isothermal treatment time of 200-300s, which is actually too long for rapid heat treatment of the product to function as intended and is not necessary. And the increase of soaking time and isothermal treatment time is not favorable for saving energy, reducing the investment of unit equipment and the occupied area of the unit, and is also not favorable for the high-speed stable operation of strip steel in the furnace.

Chinese patent CN105543674B discloses a method for manufacturing cold-rolled ultrahigh-strength dual-phase steel with high local forming performance, and the chemical components of the high-strength dual-phase steel comprise the following components in percentage by weight: c:0.08 to 0.12%, si:0.1 to 0.5%, mn:1.5 to 2.5%, al:0.015 to 0.05 percent, and the balance of Fe and other inevitable impurities. Selecting and matching raw materials of the chemical components, and smelting the raw materials into a casting blank; heating the casting blank at 1150-1250 ℃ for 1.5-2 hours, and then carrying out hot rolling, wherein the initial rolling temperature of the hot rolling is 1080-1150 ℃, and the final rolling temperature is 880-930 ℃; cooling to 450-620 ℃ at a cooling speed of 50-200 ℃/s after rolling, and coiling to obtain a hot rolled steel plate with bainite as a main structure type; and (2) cold rolling the hot rolled steel plate, heating to 740-820 ℃ at the speed of 50-300 ℃/s, annealing, keeping the temperature for 30s-3min, cooling to 620-680 ℃ at the cooling speed of 2-6 ℃/s, and then cooling to 250-350 ℃ at the cooling speed of 30-100 ℃/s, and carrying out overaging treatment for 3-5min to obtain the ferrite and martensite dual-phase structure ultrahigh-strength dual-phase steel. The yield strength of the ultrahigh-strength dual-phase steel is 650-680MPa, the tensile strength is 1023-1100MPa, the elongation is 12.3-13%, and the ultrahigh-strength dual-phase steel is not cracked after being bent for 180 degrees along the rolling direction.

The method is mainly characterized in that the control of cooling conditions after hot rolling is combined with the rapid heating in the continuous annealing process, namely, the cooling process after hot rolling is controlled to eliminate banded structures and realize the homogenization of the structures; and rapid heating is adopted in the subsequent continuous annealing process, so that the tissue thinning is realized on the basis of ensuring the tissue uniformity. Therefore, the patent technology adopts rapid heating annealing, and the premise is that the hot rolling raw material with bainite as a main structure is obtained after hot rolling, and the purpose is mainly to ensure the uniformity of the structure and avoid the defect of local deformation caused by the occurrence of banded structures.

The defects of the patent mainly lie in that:

firstly, the hot rolling raw material with a bainite structure is obtained, and has high strength and large deformation resistance, thereby bringing great difficulty to subsequent pickling and cold rolling production;

secondly, the understanding of the rapid heating is limited to shortening the heating time and refining the layer of crystal grains, the heating rate is not divided according to the change of the material structure of different temperature sections, and the material is heated at the speed of 50-300 ℃/s, so that the production cost of the rapid heating is increased;

thirdly, the soaking time is 30s-3min, and the increase of the soaking time inevitably partially weakens the grain refining effect generated by rapid heating and is not beneficial to improving the strength and the toughness of the material;

fourth, the patent must be overaged for 3-5 minutes, which is actually too long for rapid heat treating DP steels and is not necessary. And the increase of soaking time and overaging time is not beneficial to saving energy, reducing the investment of unit equipment and the occupied area of the unit, and is also not beneficial to the high-speed stable operation of the strip steel in the furnace, obviously, the rapid heat treatment process is not strictly defined.

Chinese patent CN108774681A discloses a method for rapid heat treatment of high-strength steel, which adopts a ceramic wafer electric heating device, can obtain a heating rate of which the maximum value reaches 400 ℃/s, and is cooled to room temperature at a cooling speed of about 3000 ℃/s after being heated to 1000-1200 ℃. The steel of the invention contains 0.16-0.55% of carbon, and simultaneously contains: alloying elements such as Si, mn, cr, mo and the like; the method is mainly suitable for steel wires, wire rods or steel belts with the thickness less than 5 mm. The patent describes a rapid heat treatment method by ceramic plate electric heating, and the invention mainly aims to solve the problems of low heat treatment efficiency, energy waste and environmental pollution of products such as high-strength steel wires, wire rods and the like; the influence and effect of rapid heating on the material structure properties are not mentioned; the invention does not combine the grade components and the structure characteristics of the steel grade, adopts a fan blowing cooling mode, the fastest cooling speed is close to 3000 ℃/s, which means the instantaneous cooling speed of a high-temperature section, and the average cooling speed is less than 3000 ℃/s; meanwhile, the high-temperature section adopts an overhigh cooling speed to produce the wide thin strip steel, which can cause the problems of overlarge internal stress, poor steel plate profile and the like, and is not suitable for large-scale industrial continuous heat treatment production of the wide thin strip steel.

Chinese patent CN107794357B and US2019/0153558A1 disclose 'a method for producing a super-strength martensite cold-rolled steel plate by a super-rapid heating process', and the chemical components of the high-strength dual-phase steel are as follows by weight percent: c:0.10 to 0.30%, mn:0.5 to 2.5%, si:0.05 to 0.3%, mo:0.05 to 0.3%, ti:0.01 to 0.04%, cr:0.10 to 0.3%, B:0.001 to 0.004 percent, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of Fe and other inevitable impurities. The mechanical properties of the dual-phase steel are as follows: yield strength Rp _0.2 Greater than 1100MPa, tensile strength R _m The elongation is maximally 12.3 percent and the uniform elongation is 5.5 to 6 percent, wherein the elongation is 1800 to 2300 MPa. The invention provides a super-fast heating production process of an ultrahigh strength martensite cold-rolled steel plate, which is characterized in that the cold-rolled steel plate is heated to 300-500 ℃ at the speed of 1-10 ℃/s, and then is heated to a single-phase austenite region 850-950 ℃ at the heating speed of 100-500 ℃/s; and then, immediately cooling the steel plate to room temperature after keeping the temperature for not more than 5 seconds to obtain the ultrahigh-strength cold-rolled steel plate.

The disadvantages of the process described in this patent include:

firstly, the steel contains more alloy elements, which brings certain difficulty to the manufacturing of the previous process and the use of the subsequent users;

secondly, the ultra-fast heating annealing method adopts the heat preservation time not more than 5s, which can cause the uneven distribution of alloy elements in the final product and the low plasticity of the product;

thirdly, the final quick cooling adopts water quenching to cool to room temperature without necessary tempering treatment, so that the final product structure property and the distribution condition of alloy elements in the final structure can not enable the product to obtain the optimal obdurability, the final product has excessive strength, and the plasticity and the toughness are insufficient;

fourthly, the method of the invention causes the problems of poor plate shape, surface oxidation and the like of the steel plate due to overhigh water quenching speed, so the patented technology has no great practical application value or low practical application value.

At present, limited by the capacity of the traditional continuous annealing furnace production line equipment, cold-rolled dual-phase steel products and related researches of annealing processes are based on the heating rate (5-20 ℃/s) of the existing industrial equipment to slowly heat strip steel so that the strip steel is sequentially subjected to recovery, recrystallization and austenitizing phase change, so that the heating time is long, the soaking time of the traditional continuous hot galvanizing production line is generally required to be 1-3 min, the soaking time of the strip steel in a high-temperature furnace section is long, and the number of rollers in the high-temperature section is large (the number of rollers in the high-temperature furnace section of the traditional production line with the unit speed of 180 m/min is different from 20-40). This is disadvantageous to the investment, energy consumption and production cost of the unit equipment.

Disclosure of Invention

The invention aims to provide 980 MPa-grade low-carbon low-alloy hot-dip galvanized dual-phase steel and a rapid heat treatment hot-dip galvanized manufacturing method, wherein the recovery, recrystallization and austenite phase transformation processes of a deformed structure are changed through rapid heat treatment, the nucleation rate (including the recrystallization nucleation rate and the austenite phase transformation rate) is increased, the grain growth time is shortened, grains are refined, the yield strength of the obtained dual-phase steel is 543-709 MPa, the tensile strength is 989-1108 MPa, the elongation is 11.9-15.2%, and the product of strength and elongation is 12.2-15.2 GPa%; the strength of the material is improved, and meanwhile, good plasticity and toughness are obtained; the rapid heat treatment process is adopted, so that the production efficiency is improved, the production cost and the energy consumption are reduced, the number of furnace rollers is obviously reduced, and the surface quality of the steel plate is improved.

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

the 980 MPa-level low-carbon low-alloy hot-dip galvanized dual-phase steel comprises the following chemical components in percentage by mass: c:0.05 to 0.12%, si:0.1 to 0.5%, mn:1.4 to 2.2%, nb:0.02 to 0.04%, ti: 0.03-0.05%, 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 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%;

4) Rapid heat treatment hot galvanizing

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; 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 soaking, slowly cooling to 670-770 ℃ at a cooling rate of 5-15 ℃/s, then rapidly cooling to 460-470 ℃ at a cooling rate of 50-150 ℃/s, and immersing in a zinc pot for hot galvanizing;

after hot galvanizing, rapidly cooling to room temperature at a cooling rate of 30-150 ℃/s to obtain a hot-dip pure zinc GI product; alternatively, the first and second liquid crystal display panels may be,

after hot galvanizing, heating to 480-550 ℃ at the heating rate of 30-200 ℃/s for alloying treatment, wherein the alloying treatment time is 10-20 s; after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-250 ℃/s to obtain an alloying hot galvanizing GA product.

Preferably, the content of C is 0.05 to 0.10%.

Preferably, the Si content is 0.15 to 0.45%.

Preferably, the Mn content is 1.6 to 2.0%.

Preferably, the time for the whole rapid thermal processing galvanizing process is 30 to 142 seconds.

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 a heating rate of 30-300 ℃/s, and the second section is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 80-300 ℃/s.

The metallographic structure of the hot galvanizing dual-phase steel is a ferrite and martensite dual-phase structure which is uniformly distributed, and the average grain size is 1-3 mu m.

The hot-dip galvanized dual-phase steel has yield strength of 543-709 MPa, tensile strength of 989-1108 MPa, elongation of 11.9-15.2% and product of strength and elongation of 12.2-15.2 GPa%.

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 amount 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 deteriorated, and 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 pearlite is indirectly enhanced. Manganese can also strongly enhance the hardenability of steel, further improving the strength thereof.

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 less than that of the manganese element in ferrite, the austenite grains controlled by the manganese diffusion have longer time to grow, and the manganese element can be distributed in the austenite for a longer time. When heating is carried out in the critical zone, if the holding time is shorter, the manganese element is inThe austenite is not uniformly distributed, 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 temperature, and therefore the manganese containing steel, will yield 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 cooling is not proper after the smelting pouring and the hot forging rolling, white spots are easily generated in the carbon steel. In consideration of the above factors, the manganese content is designed to be within the range of 1.4-2.2%.

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 the 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%.

Nb: nb element is a carbide and nitride forming element and can satisfy such a requirement at a relatively low concentration. At normal temperature, most of the steel exists in the form of carbide, nitride, or carbonitride, and a small amount thereof is dissolved in the ferrite. The addition of Nb can prevent austenite grains from growing and improve the coarsening temperature of steel grains. Nb element and carbon form stable NbC, and the addition of trace amount of Nb element in steel can raise the strength of matrix by means of its precipitation strengthening effect. The Nb element has obvious inhibition effect on the growth of ferrite recrystallization and the growth of austenite grains, can refine the grains and improve the strength and toughness of the steel; the Nb element may affect the mobility of grain boundaries, and also the phase transformation behavior and the formation of carbides. Nb can increase the content of carbon in the residual austenite, hinder the formation of bainite, promote martensite nucleation, obtain a dispersed martensite structure, improve the stability of the residual austenite, improve the strength of the dual-phase steel by adding Nb element, obtain the dual-phase steel with certain strength under the conditions of low content of martensite and low content of C, and improve the obdurability of the dual-phase steel; an additional benefit of adding Nb simultaneously is that the strength of the steel can be increased over a wider annealing temperature range. In the invention, the Nb element is a necessary addition element, and the addition amount is not suitable to be excessive in consideration of factors such as cost increase and the like.

Ti: ti is a microalloy element, belongs to a ferrite forming element of a closed gamma region, can improve the critical point of steel, and can form stable TiC with Ti and C in the steel, and the TiC is extremely difficult to dissolve in the austenitizing temperature range of general heat treatment. Since TiC particles refine austenite grains, the chances of new phase nucleation increase during austenite decomposition transformation, which accelerates austenite transformation. Ti forms TiC and TiN precipitates with C and N, and is more stable than carbonitride of Nb and V, and significantly reduces the diffusion rate of C in austenite to significantly reduce the austenite formation rate, and the formed carbonitride precipitates in the matrix and pins at the austenite grain boundary to inhibit the austenite grain growth. In the cooling process, the precipitated TiC has the precipitation strengthening effect; in the tempering process, ti slows down the diffusion of C in an alpha phase, slows down the precipitation and growth of carbides such as Fe, mn and the like, increases the tempering stability, and can play a role in secondary hardening through TiC precipitation. The high temperature strength of the steel can be improved by microalloying of Ti.

A trace amount of Ti is added into the steel, so that the strength and the welding performance of the steel can be improved while the carbon equivalent content is reduced; secondly, fixing impurities such as oxygen, nitrogen, sulfur, etc., thereby improving weldability of steel; thirdly, 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. In the invention, ti is an essential additive element, and the addition amount is not too large in consideration of factors such as cost increase and the like.

Cr: the main function of chromium in steel is to improve hardenability, so that the steel has better comprehensive mechanical properties after quenching and tempering. Chromium forms a continuous solid solution with iron, narrowing the austenite phase region, forms multiple carbides with carbon, and has a greater affinity for carbon than 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 has more obvious effect when being used with other alloy elements. Since Cr increases the quenching ability of steel during air cooling, it adversely affects the weldability of 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., coexistent 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 inhibits the transformation of pearlite region and accelerates the transformation in the intermediate temperature region, so that Mo-containing steel can form a certain amount of bainite under the condition of higher cooling speed, and the formation of ferrite and pearlite is eliminated, which is one of the reasons why Mo has favorable influence on 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.

V: v is a ferrite stabilizing element and a strong carbide forming element, has strong grain refining effect and can make the steel structure compact. The addition of V to the steel results in the simultaneous improvement of the strength, plasticity and toughness of the steel. Vanadium also improves the high temperature strength of structural steels. Vanadium does not improve hardenability. The addition of trace microalloy element V in the steel can ensure that the steel has good weldability and other service performances by the dispersion precipitation of carbon and nitride particles (the size is less than 5 nm) and the solid solution of V to refine grains under the condition of low carbon equivalent.

A trace amount of V is added into the steel, so that the strength and the welding performance of the steel can be improved while the carbon equivalent content is reduced; secondly, fixing impurities such as oxygen, nitrogen, sulfur, etc., thereby improving weldability of steel; thirdly, due to the effect of microscopic particles such as the insolubility of V (CN) at high temperature, coarsening of grains in the heat-affected zone is prevented, and the toughness of the heat-affected zone is improved, thereby improving the weldability of the steel. 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; recrystallization and grain growth of different phase structures mainly occur in the high-temperature section, and relatively high heating rate and short soaking time are adopted to shorten the retention time of the material in the high-temperature section so as to ensure that the grain growth is small or 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. By short-time heat preservation and quick cooling, the time for grain growth 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 hot galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot galvanizing 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 and 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 and ferrite two-phase region at the temperature of 750-845 ℃; 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;

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 and hot galvanizing

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 460-470 ℃ at the cooling rate of 50-150 ℃/s, and immersing the strip steel or the steel plate into a zinc pot for hot galvanizing;

d) After hot galvanizing strip steel or steel plate, rapidly cooling to room temperature at a cooling rate of 50-150 ℃/s to obtain a hot-dip pure zinc GI product; alternatively, the first and second electrodes may be,

after hot galvanizing strip steel or steel plate, heating to 480-550 ℃ at the heating rate of 30-200 ℃/s for alloying treatment, wherein the alloying treatment time is 10-20 s; after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-250 ℃/s to obtain an alloying hot galvanizing GA product.

Preferably, the time for the whole process of the rapid thermal treatment and the hot galvanizing is 30 to 142 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 step 4), the final temperature of rapid heating is 790 to 845 ℃.

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 40 seconds.

Preferably, in the step 4), the strip steel or the steel plate is subjected to alloying treatment and then is rapidly cooled to room temperature at a cooling rate of 30-200 ℃/s, so as to obtain an alloying hot dip galvanizing GA product.

In the rapid heat treatment hot galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot galvanizing dual-phase steel, which is disclosed by the invention, the following steps are carried out:

1. heating rate control

The recrystallization kinetics of the continuous heating process is quantitatively described by the relationship influenced by the heating rate, and the volume fraction of ferrite recrystallized in the continuous heating process is a function of the temperature T as follows:

wherein X (t) is ferrite recrystallization volume fraction; n is an Avrami index, is related to a phase transition mechanism and depends on the decay period of the recrystallization nucleation rateThe period is generally 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 sequentially subjected to reversion, recrystallization and grain growth, then the phase transformation from ferrite to austenite is generated, the phase transformation nucleation points are mainly concentrated at the grown ferrite grain boundary, the nucleation rate is lower, and the finally obtained grain structure is thicker.

Under the rapid heating condition, the phase transformation from ferrite to austenite begins to occur before the deformation matrix is recovered, or the recrystallization is just completed, the austenite phase transformation occurs before the crystal grains grow up, and because the crystal grains are fine and the grain boundary area 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. Finally, the final product structure with refined grains, reasonable elements and various phase distributions can be obtained. 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 sets the heating rate to be 50-500 ℃/s when one-stage rapid heating is adopted and 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 selection of the soaking temperature needs to be combined with the control of the material structure evolution process in each temperature stage of the heating process, and meanwhile, the evolution and the control of the structure in the subsequent rapid cooling process need to be considered, so that the optimal structure and distribution can be finally obtained.

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 870 ℃. 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 soaking zone temperature is obliquely increased and the soaking zone temperature is obliquely decreased, 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.

The dual-phase steel after cold rolling has a large amount of undissolved fine evenly 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 the abnormal growth of austenite grains can be prevented, the content of each alloy element in a 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 to 50 ℃. For ultra-high strength steel, carbide forming elements exist to inhibit the transformation of the affected compounds, so the soaking temperature can be properly increasedHigh. By combining the factors, the invention selects 750-845 ℃ as soaking temperature to obtain more ideal and reasonable final tissue.

3. Soaking time control

The influence factor of the soaking time also depends on the contents of carbon and alloy elements in the steel, when the contents of the carbon and the alloy elements in the steel 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 invention adopts rapid heating, the material contains a large amount of dislocation in the 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 the austenite can be formed very rapidly; the shorter the soaking and heat preservation time is, the shorter the diffusion distance of carbon atoms is, the larger the concentration gradient of carbon in austenite is, and the more the content of residual austenite carbon is finally reserved; however, if the heat preservation 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 soaking time is also related to the content of carbon and alloy elements in the steel, when the content of the carbon and the alloy elements in the steel is increased, the thermal conductivity of the steel is reduced, and the alloy elements obviously delay the structural transformation of the steel because the diffusion speed of the alloy elements is slower than that of the carbon elements, and the soaking time is prolonged appropriately. In conclusion, the soaking and heat preservation time is set to be 10-60 s.

4. Fast cooling rate control

In order to obtain a martensite strengthening phase, the cooling speed of the material during rapid cooling must be greater than the critical cooling speed to obtain a martensite structure, the critical cooling speed mainly depends on the material components, the content of Si in the invention is 0.1-0.5%, the content of Mn is 1.4-2.2%, and the content is relatively high, so that the hardenability of the dual-phase steel is greatly enhanced by Si and Mn, and the critical cooling speed is reduced.

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 phase structure distribution and alloy element distribution. The cooling rate is too low to obtain a martensite structure, so that the strength is reduced, and the mechanical property cannot meet the requirement; too large cooling rate can generate larger quenching stress (namely, structural stress and thermal stress) to cause serious defect of the plate shape, and the defect of the plate shape is particularly serious when the cooling is not uniform, and even the sample is easy to be seriously deformed and cracked. Therefore, the rapid cooling speed is set to be 50-150 ℃/s.

5. Hot dip galvanizing and alloying control

The invention realizes the rapid heat treatment hot galvanizing process by modifying the rapid heating and rapid cooling process of the traditional continuous annealing hot galvanizing unit, can greatly shorten the length of the heating and soaking sections of the annealing furnace (at least one third shorter than the traditional continuous annealing furnace), improves the production efficiency of the traditional continuous annealing hot galvanizing unit, reduces the production cost and energy consumption, obviously reduces the number of furnace rollers of the continuous annealing hot galvanizing furnace, particularly the number of furnace rollers of the high-temperature furnace section, thereby improving the surface quality control capability of strip steel and obtaining the strip steel product with high surface quality.

For high-strength hot-dip galvanized products, the rapid heat treatment process reduces the retention time of 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 platability of the high-strength hot-dip galvanized products is improved, the surface plating leakage defect is reduced, the corrosion resistance is improved, and the yield can be improved.

Meanwhile, by establishing a novel continuous annealing hot galvanizing unit of a rapid heat treatment hot galvanizing process technology, the purposes of short and simple unit, flexible material transition, strong regulation and control capability and the like can be realized; for the product material, the crystal grains 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 procedures before heat treatment and hot galvanizing are reduced, and the use performances of the material, such as forming, welding and the like, of users are improved.

Compared with the traditional heat treatment technology, the invention has the advantages that:

(1) The invention inhibits the recovery of a deformed structure and a ferrite recrystallization process in the heat treatment process by rapid heat treatment, overlaps the recrystallization process with an austenite phase transformation process, increases the nucleation points of recrystallized grains and austenite grains, shortens the grain growth time, and obtains a dual-phase steel with a uniformly distributed ferrite and martensite dual-phase structure, the average grain size is 1-3 mu m, the ferrite and martensite structures are mainly blocky and are more uniformly distributed, thereby obtaining a good strong plasticity matching of a hot galvanizing dual-phase steel product.

(2) Compared with the hot-galvanized dual-phase steel obtained by the traditional continuous annealing hot-galvanized mode, on the premise that the manufacturing conditions of the previous process are not changed, the average grain size of the dual-phase steel obtained by the rapid heat treatment method is 1-3 mu m, the grain size is reduced by 10-30%, and a good fine grain strengthening effect can be obtained. The yield strength is 543-709 MPa, the tensile strength is 989-1108 MPa, the elongation is 11.9-15.2%, and the product of strength and elongation is 12.2-15.2 GPa%.

(3) According to the low-carbon low-alloy high-formability 980 MPa-level 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 30-142 s, 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 and time of the heating section and the soaking section of the continuous hot galvanizing annealing furnace (the length of the heating section and the soaking section can be shortened by 60-80 percent compared with the traditional continuous hot galvanizing annealing furnace) and the time of the whole heat treatment process, can save energy, reduce emission and consumption, remarkably reduce one-time investment of furnace equipment, and remarkably reduce the production running cost and the equipment maintenance cost; the alloy content of the product produced by the process is lower, the production cost of the heat treatment and the previous working procedure can be reduced, and the manufacturing difficulty of each working procedure before the heat treatment can be 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 is adopted, the heating process and soaking process time can be reduced, the length of the furnace is shortened, the number of furnace rollers is obviously reduced, the probability of surface defects of the strip steel in the furnace is reduced, and the product surface quality is obviously improved. In addition, due to the refinement of product grains and the reduction of material alloy content, 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 low-carbon low-alloy 980 MPa-grade hot-dip galvanized dual-phase steel obtained by the invention has important values for the development of new-generation light-weight transportation tools such as automobiles, trains, ships, airplanes and the like and corresponding industries and the healthy development of advanced manufacturing industry.

Drawings

FIG. 1 is a photograph of the microstructure of a hot-dip galvanized dual-phase steel (GI) produced in example 1, which is test steel A of the present invention.

FIG. 2 is a photograph of the microstructure of hot-dip galvanized dual-phase steel (GI) produced by conventional process 1, which is test steel A of the present invention.

FIG. 3 is a photograph showing the microstructure of a galvannealed dual phase steel (GA) produced in example 17, which is test steel I of the present invention.

FIG. 4 is a photograph of the microstructure of hot-dip galvanized dual-phase steel (GI) produced in example 22, which is test steel D of the present invention.

FIG. 5 is a photograph showing the microstructure of a galvannealed dual phase steel (GA) produced in example 34 of test steel I of the present invention.

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 components of the test steel of the invention are shown in table 1, and the specific parameters of the embodiment of the invention and the traditional process are shown in table 2 (one-stage heating) and table 3 (two-stage heating); tables 4 and 5 show the main properties of GI and GA hot dip galvanized dual phase steels prepared according to the examples in tables 2 and 3 and the conventional process, which are the compositions of the test steels of the present invention.

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 yield strength of the dual-phase steel obtained by the method is 543-709 MPa, the tensile strength is 989-1108 MPa, the elongation is 11.9-15.2%, and the product of strength and elongation is 12.2-15.2 GPa%.

FIGS. 1 and 2 are structural diagrams of a typical composition A steel passing through example 1 and comparative conventional process example 1. The structures after hot dip galvanizing are very different from each other in the two figures. The structure (figure 1) of the A steel after the rapid heat treatment of the invention is a fine and uniform martensite structure and carbide composition which are dispersed and distributed on a fine ferrite matrix, and the ferrite, the martensite grain structure and the carbide are very fine and uniformly dispersed and distributed, which is very beneficial to improving the strength and the plasticity of the material. The A steel structure (figure 2) treated by the traditional process is a typical dual-phase steel structure diagram, namely a small amount of black martensite structures exist on the boundaries of a large white ferrite structure. Due to element segregation and other reasons, the material structure treated by the traditional process presents certain directionality, and the ferrite structure of the material presents long-strip distribution along the rolling direction. The tissue characteristics of the traditional heat treatment 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.

FIG. 3 is a structural diagram of a typical composition I steel obtained in example 17 (GA), and FIG. 4 is a structural diagram of a typical composition D steel obtained in example 22 (GI). FIG. 5 is a structural diagram obtained by subjecting a typical composition I steel to example 34 (GA). Examples 17, 22 and 34 are all processes with a short overall heat treatment period. As can be seen from the figure, by adopting the rapid heat treatment hot galvanizing method, the alloying treatment can also obtain very uniform, fine and dispersedly distributed phase structures (figures 3 and 5). The preparation method of the hot galvanizing dual-phase steel can refine crystal grains, so that each phase structure of the material is uniformly distributed in a matrix, the material structure is further improved, and the material performance is improved.

The invention carries out process transformation on the traditional continuous annealing hot-dip galvanizing unit by adopting the rapid heating and rapid cooling processes, realizes the rapid heat treatment hot-dip galvanizing process, can greatly shorten the lengths of the heating section and the soaking section of the traditional continuous annealing hot-dip galvanizing furnace, improves the production efficiency of the traditional continuous annealing hot-dip galvanizing unit, reduces the production cost and the energy consumption, reduces the number of furnace rollers of the continuous annealing hot-dip galvanizing furnace, can improve the surface quality control capability of strip steel, and obtains a strip steel product with high surface quality; meanwhile, by establishing a novel continuous annealing hot galvanizing unit adopting a rapid heat treatment hot galvanizing process technology, the purposes of short and simple unit, flexible transition of product specification and variety, 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 performances of the material for users such as forming, welding and the like are improved.

In conclusion, the invention adopts the rapid heat treatment hot galvanizing process to greatly promote the technical progress of the continuous annealing hot galvanizing process of the cold-rolled strip steel, the austenitizing process of the cold-rolled strip steel from room temperature to the last can be finished within ten seconds or even several seconds, the heating section length of a continuous annealing hot galvanizing furnace is greatly shortened, the speed and the production efficiency of a continuous annealing hot galvanizing unit are conveniently improved, the number of rollers in the furnace of the continuous annealing hot galvanizing unit is obviously reduced, the number of rollers in the high-temperature furnace section of a rapid heat treatment hot galvanizing production line with the unit speed of about 180 m/min is not more than 10, and the surface quality of the strip steel can be obviously improved. Meanwhile, the rapid heat treatment hot galvanizing process method for 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 alloy components, rolling process and other previous process conditions.

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

Claims

1.980 MPa-level low-carbon low-alloy hot-dip galvanized dual-phase steel comprises the following chemical components in percentage by mass: c:0.05 to 0.12%, si:0.1 to 0.5%, mn:1.4 to 2.2%, nb:0.02 to 0.04%, ti: 0.03-0.05%, 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 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 and hot galvanizing

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;

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

2. The 980MPa grade low-carbon low-alloy hot-dip galvanized dual-phase steel according to claim 1, characterized in that the C content is 0.05-0.10%.

3. The 980MPa grade low carbon low alloy hot dip galvanized dual phase steel according to claim 1, wherein the Si content is 0.15-0.45%.

4. The 980MPa grade low carbon low alloy hot dip galvanized dual phase steel according to claim 1, wherein the Mn content is 1.6-2.0%.

5. The 980MPa grade low-carbon low-alloy hot-dip galvanized dual-phase steel according to claim 1, wherein the time of the whole process of the rapid heat treatment hot-dip galvanizing is 30-142 s.

6. The 980MPa grade low-carbon low-alloy hot-dip galvanized dual-phase steel according to claim 1, wherein the hot rolling temperature is not less than A in the step 2) _r3 。

7. The 980MPa grade low carbon low alloy hot dip galvanized dual phase steel according to claim 1 or 6, wherein the coiling temperature in step 2) is 580-650 ℃.

8. The 980MPa grade low carbon low alloy hot dip galvanized dual phase steel according to claim 1, wherein in step 3), the cold rolling reduction is 60 to 80%.

9. The 980MPa grade low-carbon low-alloy hot-dip galvanized dual-phase steel as claimed in claim 1, wherein in the step 4), the rapid heating adopts one-stage heating, and the heating rate is 50-300 ℃/s.

10. The 980MPa grade low-carbon low-alloy hot-dip galvanized 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 15-300 ℃/s; the second section is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 50-300 ℃/s.

11. The 980MPa grade low-carbon low-alloy hot-dip galvanized 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; the second section is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 80-300 ℃/s.

12. The 980MPa grade low carbon low alloy hot dip galvanized dual phase steel according to any of the claims 1 to 11, characterized in that the metallographic structure of the hot dip galvanized dual phase steel is a uniformly distributed ferrite and martensite dual phase structure with an average grain size of 1 to 3 μm.

13. The 980 MPa-grade, low-carbon, low-alloy, hot-dip galvanized dual-phase steel according to any one of claims 1 to 12, wherein the yield strength of the hot-dip galvanized dual-phase steel is 543 to 709MPa, the tensile strength is 989 to 1108MPa, the elongation is 11.9 to 15.2%, and the product of strength and elongation is 12.2 to 15.2 GPa.

14. The rapid heat treatment hot dip galvanizing manufacturing method of 980MPa grade low carbon low alloy hot dip galvanizing dual phase steel according to any one of claims 1 to 13, characterized by comprising 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

4) Rapid heat treatment and 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 and ferrite two-phase region at 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

c) Cooling and hot galvanizing

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 460-470 ℃ at the cooling rate of 50-150 ℃/s, and immersing the strip steel or the steel plate into a zinc pot for hot galvanizing;

d) After hot galvanizing of strip steel or steel plate, cooling to room temperature at a cooling rate of 50-150 ℃/s to obtain a hot-dip pure zinc GI product; alternatively, the first and second electrodes may be,

after hot galvanizing of strip steel or steel plate, heating to 480-550 ℃ at the heating rate of 30-200 ℃/s for alloying treatment, wherein the alloying treatment time is 10-20 s; after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-250 ℃/s to obtain an alloying hot galvanizing GA product.

15. The method for rapidly heat-treating hot-dip galvanized steel sheet according to claim 14, wherein the time required for the entire processes of rapid heat treatment and hot-dip galvanizing is 30-142 s.

16. The method for rapid thermal processing hot dip galvanizing manufacturing of 980MPa grade low-carbon low-alloy hot dip galvanizing dual-phase steel according to claim 14, wherein the hot rolling temperature is not less than A in the step 2) _r3 。

17. The method for manufacturing the duplex steel for rapid heat treatment hot dipping zinc of 980MPa grade low carbon low alloy hot dipping zinc according to claim 14 or 16, wherein the coiling temperature in the step 2) is 580-650 ℃.

18. The method for rapid thermal processing hot dip galvanizing manufacturing of 980MPa grade low-carbon low-alloy hot dip galvanized dual phase steel according to claim 14, wherein the cold rolling reduction in step 3) is 60 to 80%.

19. The method for rapid thermal processing hot dip galvanizing manufacturing of 980MPa grade low-carbon low-alloy hot dip galvanizing dual-phase steel according to claim 14, wherein in the step 4), the rapid heating adopts one-stage heating with a heating rate of 50-300 ℃/s.

20. The method for rapid thermal processing hot dip galvanizing manufacturing of 980MPa grade low-carbon low-alloy hot dip galvanized dual-phase steel according to claim 14, characterized in that in the step 4), the rapid heating adopts two-stage heating, the first stage is heated from room temperature to 550-650 ℃ at a heating rate of 15-300 ℃/s; the second section is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 50-300 ℃/s.

21. The method for rapid thermal processing hot dip galvanizing manufacturing of 980MPa grade low-carbon low-alloy hot dip galvanized dual-phase steel according to claim 14, characterized in that in the step 4), the rapid heating adopts two-stage heating, the first stage is heated from room temperature to 550-650 ℃ at a heating rate of 30-300 ℃/s; the second section is heated from 550-650 ℃ to 750-845 ℃ at a heating rate of 80-300 ℃/s.

22. The method for rapid heat treatment hot dip galvanizing manufacturing of 980MPa grade low carbon low alloy hot dip galvanized dual phase steel according to claim 14, 20 or 21, wherein in the step 4), the rapid heating final temperature is 790 to 845 ℃.

23. The method for rapid heat treatment of dual-phase 980MPa grade low-carbon and low-alloy hot-dip galvanized steel according to claim 14, wherein the strip or steel sheet is heated to the target temperature of the two-phase austenite and ferrite region during the soaking step of step 4), and then soaked while maintaining the temperature.

24. The rapid heat treatment galvanizing manufacturing method of 980MPa grade low-carbon low-alloy hot-dip galvanized dual-phase steel according to claim 14, characterized in that in the soaking process of step 4), the strip steel or the steel plate is heated or cooled with small amplitude within the soaking time period, the temperature after heating does not exceed 845 ℃, and the temperature after cooling does not fall below 750 ℃.

25. The method for manufacturing duplex steel for rapid heat treatment hot dipping zinc of 980MPa class low carbon low alloy hot dipping zinc according to claim 14, 23 or 24, wherein the soaking time is 10-40 s.

26. The method for rapidly heat-treating hot-dip galvanized steel sheet of 980MPa grade low-carbon low-alloy hot-dip galvanized dual-phase steel according to claim 14, wherein in step 4), the strip steel or steel sheet is rapidly cooled to room temperature at a cooling rate of 30-200 ℃/s after alloying treatment to obtain the GA product of alloying hot-dip galvanized steel.