CN115181896B

CN115181896B - 980 MPa-grade low-carbon low-alloy hot dip galvanized TRIP steel and rapid heat treatment hot dip galvanizing manufacturing method

Info

Publication number: CN115181896B
Application number: CN202110360529.4A
Authority: CN
Inventors: 李俊; 孟庆格; 王健; 张利祥; 马新建; 陈云鹏
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: 2023-09-12
Anticipated expiration: 2041-04-02
Also published as: CN115181896A

Abstract

980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel and a rapid heat treatment hot dip galvanizing manufacturing method, wherein the steel comprises the following components in percentage by mass: 0.17 to 0.23 percent of C, 1.1 to 1.7 percent of Si, 1.6 to 2.2 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 0.02 to 0.05 percent of Al, and the alloy also can contain one or two of Cr, mo, ti, nb, V, less than or equal to 0.5 percent of Cr+Mo+Ti+Nb+V, and the balance of Fe and other unavoidable impurities. The rapid hot galvanizing step comprises the following steps: quick heating, short-time heat preservation, quick cooling, bainite isothermal treatment, reheating, hot galvanizing and quick cooling (hot galvanizing pure zinc GI product); or reheating, alloying and rapid cooling (alloying hot dip galvanizing GA products) after hot dip galvanizing; the heating rates are different in different temperature intervals during the rapid heating process. By controlling the recrystallization and phase change process in the heating process and the phase change process in the cooling process, the strength of the material is obviously improved, and meanwhile, good plasticity and toughness are obtained; meanwhile, the rapid heat treatment improves the mechanical property of the material and expands the range of the material property interval while improving the heat treatment efficiency.

Description

980 MPa-grade low-carbon low-alloy hot dip galvanized TRIP 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-level low-carbon low-alloy hot dip galvanized TRIP steel (comprising a hot dip galvanizing GI product and a hot dip galvanizing GA product) and a rapid heat treatment hot dip galvanizing manufacturing method.

Background

With the gradual increase of people's awareness of energy saving and material safety service, the use of high-strength steel, especially advanced high-strength steel, is increasing, so that iron and steel enterprises and scientific research institutions pay attention to the development of advanced high-strength steel.

In order to further increase the strength-plastic product, particularly the elongation thereof, development of advanced high-strength steels typified by TRIP (transformation induced plasticity) steels is increasingly gaining attention. The cold-rolled transformation induced plasticity TRIP steel structure is composed of ferrite matrix containing bainite and retained austenite, and during plastic deformation, metastable retained austenite is transformed into martensite, so that the cold-rolled transformation induced plasticity TRIP steel structure has excellent elongation and formability during high-strength processing. The forming property of the steel is improved by the deformation induced transformation effect of metastable residual austenite in a large strain range, the total elongation of the steel can reach 20-40%, and the tensile strength of the steel is generally not more than 980MPa due to the existence of softer polygonal ferrite structure. The mechanical properties of TRIP steel are determined by the volume fraction, strength and morphology and distribution of each phase of ferrite, bainite and austenite, and particularly the stability of retained austenite in inhibiting strain-induced martensitic transformation. The heat treatment process of TRIP steel mainly comprises two main stages of austenitizing annealing process and bainite isothermal treatment process.

1. Heating and austenitizing process

In the continuous heating annealing process, the deformed matrix structure is first restored and recrystallized, and cementite in the matrix begins to dissolve in ferrite in the temperature range. When the heating temperature exceeds A _C1 Thereafter, if the temperature is high and the time is abundant, cementite may be completely dissolved in austenite, completing the austenitizing process. Carbon enrichment in the Austenitic phase to A by critical annealing _c3 Line, thereafter, if the proeutectoid cementite is suppressed by the alloying elements Si, al, etc., the carbon concentration reaches T during austempering ₀ Or T' ₀ 。

2. Rapid cooling and bainite isothermal process

After austenitizing, the material is rapidly cooled, heat preservation (isothermal) treatment is carried out when the material is cooled to the bainite transformation temperature, the bainite transformation starts to occur at the supercooled austenite grain boundary, the carbon content in the bainite is lower than the carbon content in the austenite, after the austenite grain boundary forms the bainite, the residual carbon diffuses into the austenite which does not undergo the transformation reaction to form carbon-rich austenite, when the carbon content in the carbon-rich austenite reaches a certain critical value, the phase transformation of the carbon-rich austenite is stopped in the cooling process, and the residual austenite is formed after the cooling to the room temperature.

At present, aiming at the development of a hot dip galvanized TRIP process, the structural performance of hot dip galvanized TRIP steel is changed mainly by adding alloy elements and adjusting the temperature and time of quenching and distribution processes in the hot dip galvanized TRIP process.

Chinese patent CN104451400a discloses a TRIP high strength steel for hot dip galvanization and a production method thereof, which comprises the following chemical components in percentage by mass: c:0.16 to 0.20 percent, als:1.1 to 1.2 percent, mn:0.6 to 0.8 percent, P:0.06-0.08%, si:0.03 to 0.05 percent, nb:0.05 to 0.07 percent, mo:0.19-0.21%, cr:0.19 to 0.21 percent, and the balance of Fe and other unavoidable impurities. After hot rolling, the processes of ultra-fast cooling, heat treatment after cold rolling, high-temperature short-time heat preservation, slow cooling of a bainite region, continuous annealing and galvanization and the like are adopted, so that the production time can be effectively shortened, and the efficiency is improved. The strength is improved by reducing the addition amount of Si and Mn and adding P, nb, mo, cr and other alloys, the selective oxidation in the continuous annealing galvanization process is greatly reduced, the platability is improved, the strong plastic product is ensured to be more than 20GPa percent, but the requirement on hot rolling and cold rolling equipment is obviously improved by adopting an ultra-fast cooling technology after hot rolling, the energy consumption in the cold rolling process is increased, and the addition of Mo, nb, cr and other expensive metal elements also brings about the cost improvement.

Japanese patent JP2010-053020 discloses "a high-strength hot-dip galvanized steel sheet excellent in workability and a method for producing the same", which comprises the following components in mass percent: c:0.04 to 0.15 percent, mn:0.8 to 2.2 percent, si:0.7 to 2.3 percent, P is less than or equal to 0.1 percent, S is less than or equal to 0.01 percent, al is less than or equal to 0.1 percent, N is less than or equal to 0.008 percent, and the balance is Fe and other unavoidable impurity elements. The structure is composed of more than 70% ferrite phase, 2-10% bainite phase, 0-12% pearlite phase and 1-8% residual austenite phase. The average grain size of ferrite is 18 μm or less, and the average grain size of retained austenite is 2 μm or less. The steel of the invention has tensile strength of more than 590MPa and excellent processing performance (ductility and hole expansibility). The invention is a common high-strength steel with tensile strength of 600-700MPa, and the strength requirement of the ultrahigh-strength steel cannot be met.

Chinese patent CN105274301B discloses a "method for producing iron-zinc alloy coated steel sheet with yield strength not less than 220 MPa", which comprises desulfurizing molten iron, smelting in a converter, and continuously casting into billets; hot rolling: rough rolling temperature is 1045 ℃, and finish rolling temperature is 880 ℃; coiling temperature is 675 ℃; cold rolling to a required thickness; continuously hot galvanizing, wherein the unit speed is 100-130m/min, and the temperature of zinc liquid is 460 ℃; rapidly cooling at a cooling speed of 43 ℃/s; and cooling by adopting aerosol after zinc-iron alloying, wherein the cooling speed is 38 ℃/s. The invention can ensure that the yield strength is 220-260MPa, the tensile strength is 300-380MPa, the grain size on the surface of the zinc-iron alloy coating is tiny, the size distribution is even, the occupied area ratio of the cavity on the surface of the coating is less than or equal to 5%, the surface is free from microcracks, and the coating is not easy to be chalked and fall off during stamping forming, namely, the 90 DEG V bending test rating reaches level 2.

The invention is mainly characterized in that the zinc-iron alloy coating is rapidly cooled under the premise of ensuring the mechanical property, so as to obtain the coating performance of small surface grains, uniform size distribution, few surface hollows of the coating, no microcrack and difficult pulverization and falling-off of the coating during stamping forming. The method is just to obtain better zinc-iron alloy plating performance through rapid cooling after plating or alloying; the structure and performance of the substrate cannot be adjusted through the process adjustment of the whole heat treatment and hot plating process, so that the strength of the obtained substrate is not high.

Chinese patent 201711385129.9 discloses 780 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel and a rapid heat treatment method thereof, wherein the steel 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 treatment process comprising: the strip steel is rapidly heated to an austenite and ferrite two-phase region at the temperature of 790-830 ℃ from room temperature, and the heating rate is 40-300 ℃/s; heating the target temperature interval in the two-phase region for 60-100s; the strip steel is rapidly cooled to 410-430 ℃ from the temperature of the two-phase region, the cooling speed is 40-100 ℃/s, and the strip steel stays for 200-300s in the temperature region; the strip steel is reheated from 410 to 430 ℃ to 460 to 470 ℃ and immersed into a zinc pot for heat preservation. After the strip steel is galvanized, rapidly cooling the strip steel from 460-470 ℃ to room temperature (the cooling rate is 50-150 ℃/s) to obtain a hot-dip pure zinc (GI) product; after hot galvanizing, the strip steel can be reheated (the reheating rate is 10-300 ℃/s) to 480-550 ℃ for 5-20 seconds for alloying treatment, and the strip steel is rapidly cooled (the cooling rate is 10-250 ℃/s) to room temperature after the alloying treatment to obtain an alloyed hot Galvanizing (GA) product. The method is characterized in that: the TRIP steel metallographic structure is a bainitic, ferritic and austenitic three-phase structure; the average grain size of the TRIP steel is obviously refined; tensile strength is 950-1050 MPa; the elongation rate is 21-24%; the maximum product of strong plastic can reach 24GPa percent.

The deficiencies of this patent are mainly the following:

firstly, the patent discloses a 780 MPa-level 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 780 MPa-level, the use effect of a user cannot be good, the tensile strength of the TRIP steel product is 980 MPa-level, and the strength requirement of the user cannot be well met;

secondly, the patent adopts one-section rapid heating, the same rapid heating rate is adopted in the whole heating temperature interval, and the rapid heating is carried out at a speed of 40-300 ℃/s without distinguishing treatment according to the material tissue structure change of different temperature sections, so that the production cost of the rapid heating process is necessarily 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 necessarily partially weakens the grain refining effect generated by rapid heating, which is very unfavorable for improving the strength and toughness of the material;

fourth, the patent must be subjected to a bainite isothermal treatment time of 200-300 seconds, which is in fact too long for a rapid thermal treatment product, with limited effectiveness, and is not necessary. And the increase of soaking time and isothermal treatment time is unfavorable for saving energy, reducing the investment of unit equipment and the occupied area of the unit, and is unfavorable for the high-speed stable operation of the strip steel in the furnace.

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

The main characteristics of the patent are: the control of cooling conditions after hot rolling is combined with the rapid heating in the continuous annealing process, namely, the strip-shaped structure is eliminated by controlling the cooling process after hot rolling, so that the homogenization of the structure is realized; and rapid heating is adopted in the subsequent continuous annealing process, so that the tissue refinement is realized on the basis of ensuring the tissue uniformity. The patent technology can be seen to adopt rapid heating annealing, and the premise is that hot rolling is carried out to obtain a hot rolling raw material taking bainite as a main structure, so that the aim is to ensure the uniformity of the structure and avoid the defect of local deformation caused by the occurrence of a strip structure.

The disadvantages of this patent are mainly:

firstly, to obtain a hot rolled raw material with a bainite structure, the hot rolled raw material has high strength and high deformation resistance in subsequent cold rolling, and great difficulty is brought to subsequent pickling and cold rolling production;

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

thirdly, the soaking time is 30s-3min, and the increase of the soaking time necessarily partially weakens the grain refining effect generated by rapid heating, which is unfavorable for improving the strength and toughness of the material;

Fourth, the patent must be over-aged for 3-5 minutes, which is in fact too long for rapid heat treatment of DP steel, and is not necessary. 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 not beneficial to the high-speed stable operation of strip steel in a furnace, and obviously, the method is not a rapid heat treatment process in a strict sense.

Chinese patent CN108774681a discloses a "rapid heat treatment method for high strength steel", which uses a ceramic plate electric heating device, and can obtain a heating rate of 400 ℃/s at maximum, and after heating to 1000-1200 ℃, rapidly cool to room temperature at a cooling rate of approximately 3000 ℃/s. The carbon content of the high-strength steel which generates beneficial effects is 0.16-0.55%, and the high-strength steel contains: si, mn, cr, mo and other alloying elements; the method disclosed by the method is mainly suitable for steel wires, wire rods or steel belts with the diameter of less than 5 mm. The patent describes a rapid thermal treatment method by electric heating of ceramic sheets, which must be in surface contact with the product to obtain a high heating rate, which may lead to problems such as the surface quality of the product being unable to be ensured; the invention mainly aims to solve the problems of low heat treatment efficiency, energy waste and environmental pollution of high-strength steel; the effect and effect of rapid heating on the material tissue properties are not mentioned; the invention does not combine the components and the tissue characteristics of steel types, and the excessively high cooling speed can cause poor plate shape and is not suitable for the industrialized continuous heat treatment production of wide thin steel plates.

Chinese patent CN103805840B discloses "a high formability hot dip galvanized ultra-high strength steel sheet and method for manufacturing the same", the steel comprises the following chemical components in weight percentage: c:0.15 to 0.25 percent of Mn:1.5 to 3.0 percent of Si:1.0 to 2.0 percent, N is less than or equal to 0.008 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.012 percent, and the balance is Fe and other unavoidable impurities. The room temperature structure of the steel is ferrite 10-30% + martensite 60-80% + residual austenite 5-15%; the yield strength is 600-900MPa, the tensile strength is 980-1200MPa, and the elongation is 15-20%. The steel is mainly characterized in that through proper component design adjustment and adopting the traditional continuous annealing production process, the Si and Mn content is improved, and the annealing and furnace atmosphere control process is combined, so that the material has high strength and better plasticity. The method of the invention has high continuous annealing temperature and rapid cooling initial temperature, which puts higher demands on production organization and plate type control, the invention adopts high Si and high Mn content to improve strength, which is easy to increase difficulty for each production and manufacturing process, and simultaneously, the high Si and high Mn alloy content brings corresponding difficulty for downstream users, the platability of the hot plating process is also very difficult, and the surface quality and corrosion resistance of the product are also affected.

Chinese patent CN107794357B and US patent US2019/0153558A1 disclose "a method for producing an ultra-high strength martensitic cold-rolled steel sheet by an ultra-rapid heating process", wherein the high strength dual-phase steel composition comprises, in weight percent: c:0.10 to 0.30 percent of Mn:0.5 to 2.5 percent of Si:0.05 to 0.3 percent of Mo:0.05 to 0.3 percent of Ti:0.01 to 0.04 percent of Cr:0.10 to 0.3 percent, B: 0.001-0.004%, P is less than or equal to 0.02%, S is less than or equal to 0.02%, and the balance is Fe and other unavoidable impurities. Mechanical properties of the dual-phase steel: yield strength Rp _0.2 More than 1100MPa, tensile strength R _m =1800-2300 MPa, elongation is maximum 12.3%, uniform elongation is 5.5-6%. The invention provides an ultra-fast heating production process of an ultra-high strength martensitic cold-rolled steel plate, which is characterized in that firstly, the cold-rolled steel plate is heated to 300-500 ℃ at a speed of 1-10 ℃/s, and then is reheated to a single-phase austenite region of 850-950 ℃ at a heating speed of 100-500 ℃/s; and then, immediately cooling the steel plate to room temperature after heat preservation is not more than 5 seconds, and obtaining the ultra-high strength cold-rolled steel plate.

The disadvantages of the process described in this patent include:

firstly, the steel contains more alloy elements (such as Mo, ti, cr, B and the like), and the yield strength and the tensile strength of the material are both more than 1000MPa, so that great difficulty is brought to the heat treatment process, the manufacturing of the working procedure before the heat treatment and the subsequent use of users;

Secondly, the ultra-rapid heating and annealing method of the invention adopts a heat preservation time of not more than 5s, which can lead to uneven distribution of alloy elements in the final product and uneven and unstable structure performance of the product;

thirdly, the final quick cooling adopts water quenching to cool to room temperature, and necessary tempering treatment is not carried out, so that the obtained final product has uneven structure property and alloy element distribution in a final structure, poor toughness matching, excessive strength of the final product and insufficient plasticity and toughness;

fourth, the method of the invention causes problems of poor plate shape and surface oxidation of the steel plate due to the excessively high water quenching speed, so the technology of the patent has no great practical application value or little practical application value, and particularly, the patent only relates to cold-rolled products and does not relate to hot-dip galvanized products.

Currently limited by the equipment capacity of the traditional continuous hot galvanizing production line, the related researches of hot galvanizing TRIP steel products and annealing technology are based on the heating rate (5-20 ℃/s) of the existing industrial equipment to slowly heat the strip steel, so that the strip steel is subjected to recrystallization and austenitizing phase transformation in sequence, and the heating time is longer; meanwhile, the common soaking time of the traditional continuous hot galvanizing production line is required to be 1-3min, the soaking time of the existing strip steel in the high-temperature furnace section is long, and the number of rollers in the high-temperature furnace section is more (the number of rollers in the high-temperature furnace section is 20-40 for the traditional production line with the unit speed of about 180 meters/min). This is disadvantageous in terms of energy consumption and correspondingly increases in terms of equipment requirements, which necessarily increases in terms of equipment investment. The difficulty in controlling the surface quality of the strip steel is increased.

In recent years, development of rapid heating technologies such as transverse magnetic induction heating and novel direct fire heating has led to industrial application of rapid heat treatment processes. The cold-rolled strip steel finishes the austenitizing process within tens of seconds or even a few seconds from room temperature, greatly shortens the length of a heating section, and is convenient for improving the unit speed and the production efficiency. Meanwhile, the austenitizing process completed in a very short time also provides a more flexible and flexible tissue design and production line design method, so that the performance of the TRIP steel material is improved on the premise of not changing alloy components and rolling technology.

The advanced high-strength steel represented by the transformation induced plasticity TRIP steel has wide application prospect, and the rapid heat treatment technology has great development value, and the combination of the two can provide a larger space for the development and production of the TRIP steel.

Disclosure of Invention

The invention aims to provide 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel and a rapid heat treatment hot dip galvanizing manufacturing method, wherein the recovery, recrystallization and phase change processes of a deformed structure are changed through rapid heat treatment, the grain growth time is shortened, grains are refined, and bainite in a metallographic structure of the TRIP steel is submicron-level granular; austenite is equiaxed grains distributed in an island shape; the bainite and the austenite are uniformly distributed on the ferrite matrix, the yield strength is 549-620 MPa, and the tensile strength is improved to 1030-1164 MPa; the elongation is 20.1 to 24.4 percent; the product of strong plastic is 20.7-25.8 GPa; the strength of the material is obviously improved, and meanwhile, good plasticity and toughness are obtained; the rapid heat treatment process improves the production efficiency, reduces the production cost and the energy consumption, obviously reduces the number of furnace rollers and improves the surface quality of the steel strip.

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

980 MPa-grade low-carbon low-alloy hot dip galvanized TRIP steel comprises the following chemical components in percentage by mass: c:0.17 to 0.23 percent, si:1.1 to 1.7 percent, mn:1.6 to 2.2 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.002 percent, al: 0.02-0.05%, and may further contain one or two of Cr, mo, ti, nb, V, wherein Cr+Mo+Ti+Nb+V is less than or equal to 0.5%, and the balance is Fe and other unavoidable impurities, and is obtained by the following process:

1) Smelting and casting

Smelting and casting the steel into a slab according to the chemical components;

2) Hot rolling and coiling

The final rolling temperature of hot rolling is more than or equal to A _r3 The coiling temperature is 550-680 ℃;

3) Cold rolling

The cold rolling reduction rate is 40-80%;

4) Quick heat treatment and hot galvanizing

The cold rolled steel plate is quickly heated to 770-860 ℃, and the quick heating is one-section or two-section;

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

when two-section rapid heating is adopted, the first section is heated to 550-625 ℃ from room temperature at a heating rate of 15-500 ℃/s, and the second section is heated to 770-860 ℃ from 550-625 ℃ at a heating rate of 50-500 ℃/s; soaking, soaking temperature: 770-860 ℃ and soaking time: 30-120 s;

Slowly cooling to 670-770 ℃ at a cooling rate of 5-15 ℃/s after soaking, and then rapidly cooling to 410-430 ℃ at a cooling rate of 40-100 ℃/s; isothermal treatment is carried out in the temperature range, and the isothermal treatment time is 60-150 s; heating to 460-470 ℃ at a heating rate of 10-30 ℃/s after the isothermal treatment is finished, and then immersing into 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; or alternatively, the process may be performed,

after hot galvanizing, heating to 480-550 ℃ at a heating rate of 30-300 ℃/s for alloying treatment, wherein the alloying treatment time is 5-20 s; and after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-250 ℃/s to obtain an alloyed hot dip galvanizing GA product.

Preferably, the C content is 0.19 to 0.21%.

Preferably, the Si content is 1.3 to 1.5%.

Preferably, the Mn content is 1.8 to 2.0%.

Preferably, the whole process of rapid heat treatment and hot galvanizing is 118-328 s.

Preferably, in step 2), the hot rolling temperature is not less than A _r3 。

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

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

Preferably, in the step 4), the heating rate is 50-300 ℃/s when the rapid heating is performed by adopting one-stage heating.

Preferably, in step 4), the rapid heating is performed by two-stage heating, wherein the first stage is heated from room temperature to 550 to 625 ℃ at a heating rate of 15 to 300 ℃/s and the second stage is heated from 550 to 625 ℃ to 770 to 860 ℃ at a heating rate of 50 to 300 ℃/s.

Preferably, in step 4), the rapid heating is performed by two-stage heating: the first section is heated from room temperature to 550-625 ℃ at a heating rate of 30-300 ℃/s, and the second section is heated from 550-625 ℃ to 770-860 ℃ at a heating rate of 80-300 ℃/s.

The metallographic structure of the hot dip galvanized TRIP steel is a three-phase structure of 35-75% of bainite, 10-60% of ferrite and 5-15% of austenite, and the average grain size is 1-3 mu m; bainite is in submicron-level particles; austenite is equiaxed grains distributed in an island shape; the bainite and austenite are uniformly distributed on the ferrite matrix.

The yield strength of the hot dip galvanized TRIP steel is 549-620 MPa, and the tensile strength is improved to 1030-1164 MPa; the elongation is 20.1 to 24.4 percent; the product of strong plastic is 20.7-25.8 GPa percent.

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

C: carbon is the most common strengthening element in steel, and carbon increases the strength and decreases the plasticity of steel, but for steel for forming, low yield strength, high uniform elongation and total elongation are required, so that the carbon content is not excessively high. There are generally two ways in which carbon phases in steel exist: the ferrite and cementite have great influence on the mechanical properties of the steel, and as the carbon content increases, the number of strengthening phases such as bainite, pearlite and martensite increases, so that the strength and hardness of the steel are greatly improved, but the plasticity and toughness of the steel are obviously reduced, if the carbon content is too high, obvious netlike carbide appears in the steel, the strength, plasticity and toughness of the steel are obviously reduced due to the existence of the netlike carbide, and the strengthening effect generated by the increase of the carbon content in the steel is also obviously weakened, so that the technological properties of the steel are deteriorated, and the carbon content is reduced as much as possible on the premise of ensuring the strength.

For transformation-induced plasticity TRIP steel, carbon element is dissolved in austenite in a solid solution manner, so that an austenite phase region can be enlarged, the quantity of residual austenite is increased, the stability of the retained austenite is improved, a C curve of pearlite and bainite transformation is shifted to the right, the transformation of pearlite and bainite is delayed, and the Ms point temperature is reduced. The carbon content in the austenite determines the amount and stability of the retained austenite, and the higher the carbon content of the retained austenite, the better the stability of the retained austenite, and the content of the retained austenite increases as the carbon content increases. However, too high carbon content reduces the formability and weldability of the steel; too low a carbon content results in a considerable reduction in the stability of the retained austenite, even without the TRIP effect occurring. Therefore, the present invention limits the carbon content to a range of 0.17 to 0.23%.

Mn: manganese can form solid solution with iron, so that the strength and hardness of ferrite and austenite in carbon steel are improved, finer pearlite with higher strength is obtained in the cooling process of steel after hot rolling, and the content of pearlite is increased along with the increase of the content of Mn. Manganese is also a carbide forming element, and the carbide of manganese can be dissolved into the cementite, thereby indirectly enhancing the strength of pearlite. Manganese can also strongly enhance the hardenability of the steel, further increasing its strength.

For transformation induced plasticity TRIP steel, manganese element plays roles of solid solution strengthening and Ms point reduction in the steel, so that the stability of residual austenite is improved, and research has also been conducted on the premise that when two elements of Si and Mn exist in the steel at the same time, the existence of Si element can increase the segregation degree of Mn element, strengthen the dragging action of Mn on C atoms and delay the formation of bainite. However, when the manganese content is high, on one hand, the structure is in a banded shape, on the other hand, the residual austenite is excessively stable, which is unfavorable for the occurrence of phase transformation, and meanwhile, the coarsening of crystal grains in the steel is also caused, the overheat sensitivity of the steel is increased, and when the steel is cooled improperly after smelting, casting and forging, white spots are easily generated in the carbon steel. In addition, increasing the Mn content increases alloy cost, increases pre-heat treatment process production cost, and increases production difficulty. In consideration of the above factors, the manganese content is designed to be within the range of 1.6-2.2%.

Si: silicon forms a solid solution in ferrite or austenite, thereby enhancing the yield strength and tensile strength of the steel, and silicon can increase the cold working deformation hardening rate of the steel, and is a beneficial element in alloy steel. In addition, silicon has obvious enrichment phenomenon on the surface of the crystal boundary of the silicon-manganese steel, and the segregation of silicon at the crystal boundary position can slow down the distribution of carbon and phosphorus along the crystal boundary, thereby improving the embrittlement state of the crystal boundary. Silicon can improve the strength, hardness and wear resistance of steel, and the plasticity of steel can not be obviously reduced in a certain range. The silicon deoxidizer has strong capability, is a deoxidizer commonly used in steelmaking, and can increase the fluidity of molten steel, so that the common steel contains silicon, but when the silicon content in the steel is too high, the plasticity and toughness of the steel can be obviously reduced.

For transformation induced plasticity TRIP steel, si element is ferrite forming element, so that the stability of residual austenite can be improved, and the solid solution strengthening effect is also realized, thereby improving the strength of the TRIP steel. Meanwhile, the silicon element has the effects of reducing the austenite phase region and improving the activity of the C element in ferrite. Higher silicon content is advantageous for obtaining more retained austenite, but excessively high silicon content causes the steel to generate such as hard oxide layer, poor surface properties, reduced wettability of the hot rolled steel sheet, surface quality problems, and the like. Too low a content of silicon element does not bring about a stable and satisfactory TRIP effect, so that the silicon content must be controlled within a certain range. The main effect of silicon is to reduce the austenite volume fraction at the final equilibrium for a given annealing temperature time. Silicon has no significant effect on the rate of austenite growth, but has significant effect on the morphology and distribution of austenite formation. By combining the factors, the invention determines the silicon content to be in the range of 1.1-1.7 percent.

Cr: chromium has the main function of improving hardenability in steel, so that the steel has better comprehensive mechanical property after quenching and tempering. Chromium forms a continuous solid solution with iron, shrinking the austenite phase region, and chromium forms various carbides with carbon, with greater affinity than iron and manganese elements. Chromium and iron can form intermetallic compound sigma phase (FeCr), chromium reduces 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 embrittlement tendency of the steel. The chromium element can improve the strength and hardness of the steel, and can be used together with other alloy elements, so that the effect is obvious. Cr improves the quenching ability of steel in air cooling, and thus has an adverse effect on the welding performance of steel. However, at a chromium content of 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., coexisting with V), the adverse effect of Cr on weldability is greatly reduced. If elements such as Cr, mo, V and the like are simultaneously present in the steel, even if the Cr content reaches 1.7%, the welding performance of the steel is not significantly adversely affected. The chromium element is beneficial and unnecessary, and the addition amount is not excessive in consideration of factors such as cost increase and the like.

Mo: the molybdenum element can inhibit self-diffusion of iron and diffusion rate of other elements. Mo atoms have larger radius than alpha-Fe atoms, so that when Mo is dissolved in alpha solid solution, the solid solution is subjected to strong lattice distortion, and meanwhile, mo can increase the bond attraction of lattice atoms and improve the recrystallization temperature of alpha ferrite. Mo has remarkable strengthening effect in pearlite, ferrite and martensite steels, and even in high alloy austenitic steels. The good effect of Mo in steel is also dependent on the interactions with other alloying elements in the steel. When the strong carbide forming elements V, nb and Ti are added into the steel, the solid solution strengthening effect of Mo is more remarkable. This is because when a strong carbide-forming element is combined with C to form a stable carbide, mo is promoted to be more effectively dissolved into solid solution, thereby more contributing to the improvement of the heat resistance of steel. The addition of Mo also increases the hardenability of the steel, but the effect is less pronounced than C and Cr. Mo suppresses transformation in the pearlite area and accelerates transformation in the medium temperature area, so that Mo-containing steel forms a certain amount of bainite strengthening phases and eliminates ferrite formation even at a high cooling rate, which is one of the reasons why Mo has a favorable effect on the heat resistance of low alloy heat resistant steel. Mo also significantly reduces the hot embrittlement tendency of the steel and reduces the pearlite spheroidization speed. When the Mo content is 0.15% or less, there is no adverse effect on the weldability of the steel. The molybdenum element is beneficial and unnecessary, and the addition amount is not excessive in consideration of factors such as cost increase and the like.

Microalloying elements Ti, nb, V: the addition of trace amounts of microalloy elements Nb, V and Ti in the steel can ensure that the steel has good weldability and usability by the dispersion precipitation of carbon and nitride particles (the size is smaller than 5 nm) and solid solution of Nb, V and Ti under the condition of low carbon equivalent, thereby refining grains, greatly improving the strength and toughness of the steel, particularly the low-temperature toughness. Nb, V, ti are carbide-and nitride-forming elements that meet this requirement at relatively low concentrations, nb, V, ti being strong carbide-forming elements, and at ordinary temperatures, most of them exist in the form of carbides, nitrides, carbonitrides in steel, and a small portion thereof is solid-dissolved in ferrite.

In the case of TRIP steel, addition of microalloying elements can strengthen the ferrite matrix by grain refinement and precipitation, and can also delay bainite formation. The reason why the bainite formation is delayed is to strengthen the ferrite formation upon cooling, which is a result of the fine microstructure grains. The formation of ferrite results in carbon enrichment of the retained austenite, delaying the transformation of austenite to bainite, while the fine dispersed carbonitrides suppress bainite nucleation and thus also delay bainite formation. The addition of Nb, V and Ti can prevent austenite grains from growing and increase the coarsening temperature of steel, because small particles dispersed by carbon and nitride can fix the austenite grain boundaries, prevent the migration of the austenite grain boundaries, increase the recrystallization temperature of austenite, and enlarge the non-recrystallized region, namely prevent the austenite grains from growing.

The efficacy of adding trace amounts of Nb, V and Ti into steel is as follows:

first, the strength can be improved while the carbon equivalent content is reduced, and the welding performance of the steel is improved;

second, impurities such as oxygen, nitrogen, sulfur, etc. are fixed, thereby improving weldability of the steel;

third, due to the effect of microscopic particles, such as the undissolved property of TiN at high temperature, coarsening of grains in the heat affected zone can be prevented, and the toughness of the material in the heat affected zone can be improved, thereby improving the welding performance of the steel. The microalloy elements are beneficial and unnecessary, and the addition amount is not excessive in consideration of factors such as cost increase and the like.

The recovery, recrystallization and phase change processes of the deformed structure of the hard rolled strip steel in the heat treatment process are finely controlled by a rapid heat treatment hot galvanizing method (comprising rapid heating, short-time temperature and rapid cooling processes), and finally, all the tissue structures with fine, uniform and dispersed distribution and good strong plastic matching are obtained.

The concrete principle is as follows: different heating rates are adopted at different temperature stages in the heating process, recovery of deformed tissues mainly occurs at a low-temperature stage, and relatively low heating rate can be adopted to reduce energy consumption; the high temperature section mainly generates recrystallization and grain growth of different phase structures, and the residence time of the structures in the high temperature section must be shortened by adopting a relatively high heating rate to ensure that the grains cannot grow or grow inconspicuously. The recovery of the deformed structure and the ferrite recrystallization process in the heating process are restrained by controlling the heating rate in the heating process, so that the recrystallization process is overlapped with the austenite transformation process, nucleation points of recrystallized grains and austenite grains are increased, the grains are refined finally, the time of grain growth in the soaking process is shortened by short-time heat preservation and rapid cooling, and the fine and uniform distribution of the grain structure is ensured.

By comprehensively controlling the whole heat treatment process: the method comprises the steps of rapid heating (heating speed is controlled by sections), short-time soaking and rapid cooling, so that the optimal grain size, the uniform distribution of alloy elements and phase structures can be obtained through fine control, and finally the optimal obdurability matching product is obtained.

The average grain size of the ferrite, austenite and bainite multiphase structure obtained by the rapid heat treatment method is 1-3 mu m, the strength of the material can be improved by grain refinement, good plasticity and toughness are obtained, and the service performance of the material is improved; the ferrite, bainite and residual austenite obtained by the method mainly have various forms such as blocks, grains and the like, and are more uniformly distributed, so that better strong plasticity can be obtained in the deformation stage.

The invention relates to a rapid heat treatment hot galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot galvanizing TRIP steel, which comprises the following steps:

1) Smelting and casting

2) Hot rolling and coiling

The final rolling temperature of hot rolling is more than or equal to A _r3 Then cooling to 550-680 ℃ for coiling;

3) Cold rolling

The cold rolling reduction rate is 40-80%, and the rolled hard strip steel or steel plate is obtained;

4) Quick heat treatment and hot galvanizing

a) Rapid heating

Rapidly heating the cold-rolled strip steel or steel plate from room temperature to 770-860 ℃ austenite and ferrite two-phase region target temperature, wherein the rapid heating adopts one-section or two-section;

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

when two-section rapid heating is adopted, the first section is heated to 550-625 ℃ from room temperature at a heating rate of 15-500 ℃/s, and the second section is heated to 770-860 ℃ from 550-625 ℃ at a heating rate of 50-500 ℃/s;

b) Soaking heat

Soaking at 770-860 ℃ in the austenite and ferrite two-phase region target temperature for 30-120 s;

c) Cooling

Slowly cooling the steel strip or the steel plate to 670-770 ℃ at a cooling rate of 5-15 ℃/s after soaking; then rapidly cooling to 410-430 ℃ at a cooling rate of 40-100 ℃/s;

d) Bainite isothermal treatment

The strip steel or the steel plate is subjected to bainite isothermal treatment at the temperature of 410-430 ℃ for 60-150 s;

e) Reheat of

Heating to 460-470 ℃ at a heating rate of 10-30 ℃/s after the isothermal treatment is finished;

f) Hot galvanizing

Then immersing the strip steel or the steel plate into a zinc pot for hot galvanizing;

g) After hot galvanizing the strip steel or the steel plate, rapidly cooling to room temperature at a cooling rate of 30-150 ℃/s to obtain a hot-dip pure zinc GI product; or alternatively, the process may be performed,

After hot galvanizing the strip steel or the steel plate, heating to 480-550 ℃ at a heating rate of 30-300 ℃/s for alloying treatment, wherein the alloying treatment time is 5-20 s; and after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-250 ℃/s to obtain an alloyed hot dip galvanizing GA product.

Preferably, in step 2), the hot rolling temperature is not less than A _r3 。

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

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

Preferably, in the step 4), the rapid heating adopts two-stage heating, wherein the first stage is heated from room temperature to 550-625 ℃ at a heating rate of 30-300 ℃/s, and the second stage is heated from 550-625 ℃ to 770-860 ℃ at a heating rate of 80-300 ℃/s.

Preferably, in step 4), the rapid heating final temperature is 790 to 860 ℃.

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

Preferably, in the soaking process of the step 4), the strip steel or the steel plate is heated or cooled in a small extent in the soaking time period, the temperature after heating is not more than 860 ℃, and the temperature after cooling is not less than 770 ℃.

Preferably, in the step 4), after the hot galvanizing of the strip steel or the steel plate, heating to 480-550 ℃ at a heating rate of 30-200 ℃/s for alloying treatment, wherein the alloying treatment time is 5-20 s; and after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-200 ℃/s to obtain an alloyed hot dip galvanizing GA product.

The rapid heat treatment hot dip galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel comprises the following steps:

1. heating rate control

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

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

b＝b ₀ exp(-Q/RT)

from the above formula and the related experimental data, it can be seen that the recrystallization onset temperature (T _star ) End temperature (T) _fin ) Are all raised; when the heating rate is above 50 ℃/s, the austenite transformation and recrystallization processes are overlapped, the recrystallization temperature is increased to the temperature of the two-phase region, and the faster the heating rate is, the higher the ferrite recrystallization temperature is.

Under the traditional slow heating condition, the deformed matrix is recovered, recrystallized and the grains grow up, then ferrite phase transformation to austenite occurs, the phase transformation nucleation points are mainly concentrated at ferrite grain boundaries where the grains grow up, the nucleation rate is lower, and finally the obtained grain structure is coarser.

Under the condition of rapid heating, the deformed matrix starts to recrystallize without fully recovering, and the recrystallization is not completed or the grain growth is not started, so that the phase transformation from ferrite to austenite starts to occur. Particularly, after ferrite recrystallization and austenite transformation process are overlapped, a large number of crystal defects such as dislocation and the like are reserved in ferrite crystals, a large number of nucleation points are provided for austenite, so that the austenite presents explosive nucleation, and austenite grains are further refined. The retained high-density dislocation line defects also become channels for the high-speed diffusion of carbon atoms, so that each austenite grain can be rapidly generated, and the volume fraction of austenite increases.

By finely controlling the tissue evolution and the alloy element and each phase component distribution in the rapid heating process, a good foundation is laid for the austenite tissue growth in the subsequent soaking process, the distribution of each alloy component and the transformation from austenite to martensite phase in the rapid cooling process. The final product structure with refined grains, reasonable elements and distribution of each phase can be finally obtained. The invention sets the heating rate of one-section type rapid heating to 50-500 ℃/s and adopts two-section type rapid heating to 15-500 ℃/s by comprehensively considering the effects of rapid heating and refining crystal grains, manufacturing cost, manufacturability and other factors.

Because the influence of rapid heating on the material recovery, recrystallization, grain growth and other tissue evolution processes is different in different temperature ranges, the optimal tissue control is obtained, so that the optimal heating rate is also different in different heating temperature ranges: the heating rate has the greatest influence on the recovery process from 20 ℃ to 550-625 ℃, and is controlled to be preferably 15-300 ℃/s, more preferably 30-300 ℃/s; the heating temperature is from 550 to 625 ℃ to 770 to 860 ℃ of austenitizing temperature, the heating rate has the greatest influence on the growth process of the crystal grains, and the heating rate is controlled to be preferably 50 to 300 ℃/s; further preferably 80 to 300 ℃/s.

2. Soaking temperature control

The soaking temperature is selected by combining the material tissue evolution process control of each temperature stage in the heating process, and simultaneously considering the tissue evolution and control of the subsequent rapid cooling process, so that the optimal tissue structure and distribution can be finally obtained.

Soaking temperature is generally dependent on C content in steel, conventional heatThe soaking temperature is generally set at A in the treatment process _C1 To A _C3 Between, or A _C3 The temperature is 30-50 ℃. The invention uses the rapid heating technology to retain a large amount of dislocation in the ferrite which is not fully recrystallized, and provides nucleation work for austenite transformation, so that the soaking temperature is only required to be heated to A _C1 To A _C3 More austenite can be obtained, and the content of C of the TRIP steel is as follows: 0.17-0.23%, A _C1 And A _C3 At about 730 ℃ and 870 ℃, respectively.

The TRIP steel has a large amount of undissolved tiny evenly distributed carbide, can play a role in mechanically obstructing the growth of austenite grains in the heating process, is beneficial to refining the grain size of the alloy steel, but if the heating temperature is too high, the number of undissolved carbide is greatly reduced, the obstructing effect is weakened, the growth tendency of the grains is enhanced, and the strength of the steel is further reduced. When the amount of undissolved carbide is too large, aggregation may be caused, resulting in uneven distribution of local chemical components, and when the carbon content at the aggregation site is too high, local overheating may be caused. Therefore, in ideal conditions, a small amount of fine granular undissolved carbide should be uniformly distributed in the alloy steel, so that not only can the abnormal growth of austenite grains be prevented, but also the content of each alloy element in the matrix can be correspondingly increased, and the aim of improving the mechanical properties such as strength, toughness and the like of the alloy steel is achieved.

The soaking temperature should also be selected to obtain fine and uniform austenite grains in order to obtain fine and uniform ferrite, bainite and retained austenite after cooling. The austenite grains are coarse due to the excessive soaking temperature, the workpiece is easy to crack in the quenching process, and the structure obtained after quenching is coarse, so that the mechanical property of the steel is poor; too low soaking temperature can lead to insufficient content of carbon and alloy elements dissolved in austenite, uneven concentration distribution of austenite carbon, greatly reduced hardenability of steel and adverse effect on mechanical properties of alloy steel. Soaking temperature of hypoeutectoid steel should be Ac ₃ +30 to 50 ℃. For ultra-high strength steels, the presence of carbide forming elements can impede carbideThe soaking temperature can be appropriately increased by the transition. By combining the factors, 770-860 ℃ is selected as soaking temperature, so as to obtain reasonable quenching process and ideal organization performance.

3. Soaking time control

Because the invention adopts rapid heating, the material in the two-phase region contains a large number of dislocation, provides a large number of nucleation sites for austenite formation, and provides a rapid diffusion channel for carbon atoms, so that the austenite can be formed extremely rapidly; the shorter the soaking and heat preserving time is, the shorter the diffusion distance of carbon atoms is, the larger the carbon concentration gradient in the austenite is, and finally, the more the carbon content of the retained austenite is; however, if the heat preservation time is too short, the alloy elements in the steel are unevenly distributed, so that austenitization is insufficient; the austenite grains are easily coarse due to the long heat preservation time.

The soaking time is also related to the content of carbon and alloy elements in the steel, when the content of carbon and alloy elements in the steel is increased, not only the thermal conductivity of the steel is reduced, but also 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, so that the heat preservation time is properly prolonged. Therefore, the soaking time is controlled by strictly combining soaking temperature, rapid cooling and rapid heating process to be comprehensively considered and formulated, so that ideal organization and element distribution can be finally obtained. In conclusion, the soaking and heat preserving time is set to be 30-120 s.

4. Fast cooling rate control

In order to obtain bainite, the cooling rate of a sample during rapid cooling is required to be larger than the critical cooling rate to obtain the bainite structure, the critical cooling rate mainly depends on the material composition, the content of Si in the TRIP steel is 1.1-1.7%, the content of Mn in the TRIP steel is 1.6-2.2%, and the content of Mn is relatively high, so that the hardenability of the TRIP steel is greatly enhanced by Si and Mn, and the critical cooling rate is reduced.

The cooling rate also needs to comprehensively consider the structure evolution and alloy diffusion distribution results of the early heating process and the soaking process so as to finally obtain reasonable structure distribution of each phase and alloy element distribution. Too low a cooling rate to obtain a bainitic structure can lead to unsatisfactory mechanical properties; and too large cooling rate can generate larger quenching stress (namely tissue stress and thermal stress) to cause serious bad plate shape, and even serious deformation and cracking of the sample are easy to cause. The present invention sets the rapid cooling rate to 40-100 deg.c/s.

5. Isothermal treatment temperature of bainite

The bainite isothermal temperature of TRIP steel is generally selected to be at a temperature at which the free energy of bainite, ferrite and austenite are equal (T ₀ ) In the following, the free energy of bainite is smaller than the free energy of austenite at this time, and the decrease of the free energy provides a phase transformation driving force for the transformation of bainite. The chemical components of the steel materials are different, the isothermal treatment temperature of the bainite is also different, the isothermal treatment temperature of the bainite is generally selected to be between 350 and 550 ℃, when the isothermal treatment temperature is higher, the atomic diffusion capability is strong, the austenite part is transformed into granular bainite, carbide is separated out, the stability of supercooled austenite is reduced, and the volume fraction of residual austenite is lower. In isothermal treatment at lower temperature, the bainite transformation requiring atom diffusion is difficult to carry out, martensite transformation without atom diffusion possibly occurs, martensite is a supersaturated structure of C, in isothermal process, the C diffusion is too slow, enrichment in supercooled austenite is difficult, and the volume fraction of residual austenite is also reduced, so the isothermal temperature of bainite is selected in a temperature range of 410-430 ℃.

6. Isothermal treatment time of bainite

If the bainite isothermal time is short, the bainite transformation is not sufficiently performed, the enrichment degree of the C element into austenite is low, the content of austenite C is low, the stability of the austenite C is poor, and supercooled austenite is transformed into a large amount of martensite in the subsequent cooling process. The martensitic structure has the characteristics of high strength and low elongation, and is therefore disadvantageous in improving the strength and plasticity. As the isothermal time is prolonged, the bainite is fully transformed, and the volume fraction of bainite in the TRIP steel of the present invention is increased. The isothermal time is prolonged, the SEM microstructure is not obviously changed, the volume fraction and morphology of bainite are not greatly changed, at the moment, the process of enriching C element into residual austenite is mainly carried out, the residual austenite content and the carbon content thereof are increased along with the prolonged heat preservation time, the stability is increased, the residual austenite can continuously generate martensitic transformation along with the occurrence of strain in the use process of the TRIP steel material, the material strength of the transformation area is enhanced, so that the strain can be transferred to other areas of the material, and the material elongation can be obviously improved. Therefore, the bainite isothermal time is set to 60-150 s.

7. Hot galvanizing and alloying treatment control

For high-strength hot dip galvanized products, the rapid heat treatment process reduces the residence time of the strip steel in a high-temperature furnace, so that the enrichment 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 omission defect is reduced, the corrosion resistance is improved, and the yield is improved.

By the method, the alloy content in the same grade steel can be reduced, grains are refined, and good matching of soft and hard phase structure constitution, strength and toughness is obtained; meanwhile, the rapid heating and rapid cooling process is improved for the traditional continuous hot galvanizing unit, so that the rapid heat treatment process is realized, the heating and heat equalizing section length of the annealing furnace can be greatly shortened (at least one third shorter than that of the traditional continuous annealing furnace), the production efficiency of the traditional continuous hot galvanizing unit is improved, the production cost and the energy consumption are reduced, the number of furnace rollers of the continuous annealing furnace, particularly the number of furnace rollers of a high-temperature furnace section, is obviously reduced, and the energy consumption and the investment to equipment can be reduced.

The novel continuous hot galvanizing unit adopting the rapid heat treatment process technology can realize the purposes of short and small unit, flexible material transition, strong regulation and control capability and the like; the material can refine the grain of the strip steel, further improve the strength of the material, reduce the alloy cost and the manufacturing difficulty of the working procedure before heat treatment, and improve the use performance of users such as forming, welding and the like of the material.

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

(1) The invention suppresses the recovery of deformed structure and ferrite recrystallization process in the heat treatment process through rapid heat treatment, so that the recrystallization process is overlapped with the austenite transformation process, the nucleation points of recrystallized grains and austenite grains are increased, and the grain growth time is shortened. Compared with the phase transformation induced plasticity TRIP steel of the same grade obtained by the traditional heat treatment mode, the phase transformation induced plasticity TRIP steel alloy composition obtained by the invention can be greatly reduced, and the average grain size is reduced by 30-50%; the metallographic structure of the steel after the rapid heat treatment is a three-phase structure of bainite (35-75%), ferrite (10-60%) and austenite (5-15%), and the average grain size is 1-3 mu m; bainite is in submicron-level particles; austenite is equiaxed grains distributed in an island shape; the bainite and the austenite are uniformly distributed on the ferrite matrix; and austenite with different orientations and different forms can continuously generate TRIP effect under different strain conditions, so that the plasticity is obviously improved, and the strength of the material can be improved through grain refinement, so that good strong plasticity and toughness can be obtained at the same time, and the service performance of the material is improved.

(2) Compared with the phase transition induced plasticity TRIP steel obtained by the traditional heat treatment mode, the TRIP steel obtained by the invention has a multiphase structure with fine grains, the average grain size is 1-3 mu m, the toughness of the material can be obviously improved, the yield strength can reach 549-620 MPa, and the tensile strength can be improved to 1030-1164 MPa; the elongation is 20.1 to 24.4 percent; the product of strong plastic is 20.7-25.8 GPa percent.

(3) According to the hot dip galvanized TRIP steel heat treatment process, the shortest heat treatment time can be shortened to 118s, the time of the whole rapid heat treatment process (the conventional continuous annealing process TRIP heat treatment hot dip time is usually 9-11 min), and particularly the residence time at high temperature (600 ℃) is shortened, so that the production efficiency is improved, the energy consumption is reduced, and the production cost is reduced.

(4) Compared with the traditional transformation induced plasticity TRIP steel and the heat treatment process thereof, the rapid heat treatment method of the TRIP steel shortens the length and time of the heating section and the soaking section of the continuous hot galvanizing annealing furnace (compared with the traditional continuous hot galvanizing annealing furnace, the length of the heating section and the soaking section can be shortened by 60-80 percent) and the whole heat treatment process time, can save energy, reduce emission and consumption, obviously reduce the one-time investment of furnace equipment and obviously reduce the production operation cost and the equipment maintenance cost; the product with the same strength grade is produced, the alloy content in the product produced by the process is lower, the production cost of heat treatment and previous working procedures can be reduced, and the manufacturing difficulty of each working procedure before heat treatment is reduced.

(5) Compared with the traditional transformation induced plasticity TRIP steel and the heat treatment process thereof, the rapid heat treatment process technology is adopted, so that the heating process and soaking process time can be reduced, the furnace length is shortened, the number of furnace rollers is obviously reduced, the probability of generating surface defects in the furnace is reduced, and the surface quality of the product is obviously improved.

In addition, due to the refinement of product grains and the reduction of the alloy content of the material, the reaming performance, bending performance and other processing forming performance, welding performance and other user using performance of the TRIP steel product obtained by adopting the technology are also improved.

The 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel obtained by the invention has important value for the development of new-generation light-weight vehicles such as automobiles, trains, ships, airplanes and the like, the corresponding industry and the healthy development of advanced manufacturing industry.

Drawings

FIG. 1 is a photograph of the microstructure of hot-dip galvanized TRIP steel (GI) produced as in example 1 for test steel A according to the invention.

FIG. 2 is a photograph of the microstructure of hot-dip galvanized pure TRIP steel (GI) produced under conventional process 1 for test steel A according to the present invention.

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

FIG. 4 is a photograph of the microstructure of hot-dip galvanized dual phase steel (GI) as produced in example 22 for test steel D according to the invention.

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

Detailed Description

The present invention is further described below with reference to examples and drawings, and the examples are provided on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of protection of the present invention is not limited to the examples described below.

The composition of the test steel according to the invention is shown in Table 1, the specific parameters of the examples according to the invention and of the conventional process are shown in Table 2 (one-stage heating) and Table 3 (two-stage heating); tables 4 and 5 show the main properties of the GI and GA hot dip galvanized TRIP steels of the invention, which were prepared according to the examples and conventional processes in tables 2 and 3.

As can be seen from tables 1 to 5, by the method of the present invention, the alloy content in the same grade steel can be reduced, the grains can be refined, and the matching of the material structure and the strength and toughness can be obtained. The TRIP steel obtained by the method can reach 549-620 MPa in yield strength, and the tensile strength is improved to 1030-1164 MPa; the elongation is 20.1 to 24.4 percent; the product of strong plastic is 20.7-25.8 GPa percent.

Fig. 1 and 2 are structural diagrams of typical composition a steel through example 1 and comparative conventional process example 1. From the two figures, there is a great difference in the structure after hot dip galvanization of the two processes. The structure (figure 1) of the A steel subjected to the rapid heat treatment is mainly composed of fine and uniform martensitic structure and carbide which are dispersed and distributed on a fine ferrite matrix, and ferrite, martensitic grain structure and carbide are very fine and uniformly dispersed and distributed, so that the A steel is very beneficial to improving the strength and plasticity of the material. Whereas the a steel structure (fig. 2) treated by the conventional process is a typical TRIP steel structure diagram. I.e. a small amount of bainite and retained austenite structure is present at the grain boundaries of the white ferrite structure. Due to element segregation and other reasons, the material structure treated by the traditional process shows a certain directionality, and the structure is distributed in a strip shape along the rolling direction. The tissue treated by the traditional process is characterized in that: the grains are large, a certain banded structure exists, bainite and residual austenite are distributed in a net shape along the grain boundary of ferrite, the ferrite grains are relatively coarse, and the ferrite and bainite two-phase structure is unevenly distributed.

Fig. 3 is a structure diagram of a typical composition I steel obtained through example 17 (GA), and fig. 4 is a structure diagram of a typical composition D steel obtained through example 22 (GI). FIG. 5 is a structure chart obtained by passing a typical composition I steel through example 34 (GA). Examples 17, 22, 34 are all short-term processes for the entire heat treatment cycle. As can be seen from the figure, the rapid heat treatment hot galvanizing method of the invention is adopted to obtain very uniform, fine and dispersed phase structures after alloying treatment, and in the metallographic structure of the steel strip prepared by the traditional process, the ferrite structure is coarse, and the bainite and residual austenite structures are distributed on ferrite grain boundaries, thus being typical hot galvanized TRIP steel structures. Therefore, the preparation method of hot dip galvanized TRIP steel can refine grains, so that each phase structure of the material is uniformly distributed in the matrix, thereby improving the material structure and the material performance.

According to the invention, the traditional continuous annealing hot dip galvanizing unit is subjected to process transformation by adopting a rapid heating and rapid cooling process, so that the rapid heat treatment hot dip galvanizing process is realized, the lengths of a heating section and a soaking section of the traditional continuous annealing hot dip galvanizing furnace can be greatly shortened, the production efficiency of the traditional continuous annealing hot dip galvanizing unit is improved, the production cost and the energy consumption are reduced, the number of furnace rollers of the continuous annealing hot dip galvanizing furnace is reduced, the surface defects such as roll marks, pits, scratch and the like are obviously reduced, the control capability of the surface quality of strip steel is improved, and the strip steel product with high surface quality is easy to obtain; meanwhile, by establishing a novel continuous annealing unit adopting a rapid heat treatment hot galvanizing process technology, the advantages of short and precise hot galvanizing unit, flexible material transition, strong regulation and control capability and the like can be realized; the zinc-plated substrate material can refine grains, further improve the material strength, reduce the alloy cost and the manufacturing difficulty of the working procedure before heat treatment, and improve the use performance of users such as forming, welding and the like of the material.

In summary, the rapid heat treatment hot galvanizing process is adopted to greatly promote the technical progress of the continuous annealing hot galvanizing process of the cold-rolled strip steel, the cold-rolled strip steel is expected to finish the austenitizing process from room temperature to finish in tens of seconds or even a few seconds, the length of a heating section 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 a high-temperature furnace section of the rapid heat treatment hot galvanizing production line with the unit speed of about 180 meters/minute 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 of the recrystallization and austenitizing process completed in a very short time also provides a more flexible and flexible high-strength steel structure design method, so that the material structure is improved and the material performance is improved on the premise of not changing the alloy components, the rolling process and other pre-process conditions.

The hot dip galvanized advanced high-strength steel represented by the transformation induced plasticity TRIP steel has wide application prospect, and the rapid heat treatment technology has huge development and application values, and the combination of the rapid heat treatment technology and the hot dip galvanized TRIP steel can provide a larger space for development and production of the hot dip galvanized TRIP steel.

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Claims

1.980MPa low-carbon low-alloy hot dip galvanized TRIP steel comprises the following chemical components in percentage by mass: c: 0.17-0.23%, si:1.1 to 1.7%, mn: 1.6-2.2%, P is less than or equal to 0.015%, S is less than or equal to 0.002%, al: 0.02-0.05%, one or two of Cr, mo, ti, nb, V, cr+Mo+Ti+Nb+V less than or equal to 0.5%, and the balance Fe and other unavoidable impurities, and is obtained by the following process:

1) Smelting and casting

2) Hot rolling and coiling

3) Cold rolling

The cold rolling reduction rate is 40-80%;

4) Quick heat treatment and hot galvanizing

The cold rolled steel plate is rapidly heated to 770-860 ℃, and the rapid heating is one-section or two-section;

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

slowly cooling to 670-770 ℃ at a cooling rate of 5-15 ℃/s after soaking, and then rapidly cooling to 410-430 ℃ at a cooling rate of 40-100 ℃/s; and bainite isothermal treatment is carried out in the temperature range, and the isothermal treatment time is 60-150 s; heating to 460-470 ℃ at a heating rate of 10-30 ℃/s after the isothermal treatment is finished, and then immersing into a zinc pot for hot galvanizing;

2. The 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel of claim 1, wherein the C content is 0.19-0.21%.

3. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to claim 1, characterized in that the Si content is 1.3-1.5%.

4. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to claim 1, characterized in that the Mn content is 1.8-2.0%.

5. The 980 MPa-grade low-carbon low-alloy hot dip galvanized TRIP steel of claim 1, wherein the rapid heat treatment and hot dip galvanizing total process use time is 118-328 s.

6. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to claim 1, wherein in step 2), the hot rolling temperature is equal to or higher than A _r3 。

7. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to claim 1, characterized in that in step 2), the coiling temperature is 580-650 ℃.

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

9. The 980 MPa-level low-carbon low-alloy hot-dip galvanized TRIP steel of claim 1, wherein in step 4), the rapid heating adopts a one-stage heating at a heating rate of 50-300 ℃/s.

10. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to claim 1, characterized in that in step 4) the rapid heating uses two-stage heating: the first stage is heated from room temperature to 550-625 ℃ at a heating rate of 15-300 ℃/s, and the second stage is heated from 550-625 ℃ to 770-860 ℃ at a heating rate of 50-300 ℃/s.

11. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to claim 1, characterized in that in step 4) the rapid heating uses two-stage heating: the first stage is heated from room temperature to 550-625 ℃ at a heating rate of 30-300 ℃/s, and the second stage is heated from 550-625 ℃ to 770-860 ℃ at a heating rate of 80-300 ℃/s.

12. 980 MPa-grade low-carbon low-alloy hot-dip galvanized TRIP steel according to any one of claims 1 to 11, characterized in that the hot-dip galvanized TRIP steel has a metallographic structure of 35 to 75% of bainite, 10 to 60% of ferrite and 5 to 15% of austenite, and has an average grain size of 1 to 3 μm; bainite is in submicron-level particles; austenite is equiaxed grains distributed in an island shape; the bainite and austenite are uniformly distributed on the ferrite matrix.

13. 980 MPa-grade low-carbon low-alloy hot dip galvanized TRIP steel according to any one of claims 1 to 11, characterized in that the yield strength of the hot dip galvanized TRIP steel is 549 to 620MPa, the tensile strength is improved to 1030 to 1164MPa, the elongation is 20.1 to 24.4%, and the plastic product is 20.7 to 25.8gpa%.

14. The 980 MPa-level low-carbon low-alloy hot-dip galvanized TRIP steel of claim 12, wherein the hot-dip galvanized TRIP steel has a yield strength of 549-620 MPa, a tensile strength increased to 1030-1164 MPa, an elongation of 20.1-24.4%, and a yield strength of 20.7-25.8 gpa%.

15. The rapid heat treatment hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to any one of claims 1 to 11, characterized by comprising the steps of:

1) Smelting and casting

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

2) Hot rolling and coiling

3) Cold rolling

The cold rolling reduction rate is 40-80%, and the rolled hard strip steel or steel plate is obtained after cold rolling;

4) Quick heat treatment and hot galvanizing

a) Rapid heating

Rapidly heating cold-rolled strip steel or a steel plate from room temperature to 770-860 ℃ austenite and ferrite two-phase region target temperature, wherein the rapid heating adopts one-section or two-section;

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

b) Soaking heat

Soaking at 770-860 ℃ in the target temperature of the austenite and ferrite two-phase region for 30-120 s;

c) Cooling

d) Bainite isothermal treatment

e) Reheat of

f) Hot galvanizing

g) 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; or alternatively, the process may be performed,

16. The method for manufacturing 980 MPa-grade low-carbon low-alloy hot dip galvanized TRIP steel by rapid heat treatment and hot dip galvanizing of claim 15, wherein the total time for the rapid heat treatment and hot dip galvanizing is 118-328 s.

17. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in step 2), the hot rolling temperature is equal to or higher than a _r3 。

18. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15 or 17, wherein in step 2), the coiling temperature is 580-650 ℃.

19. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in the step 3), the cold rolling reduction is 60 to 80%.

20. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in the step 4), the rapid heating adopts a heating rate of 50-300 ℃/s in one-stage heating.

21. The method for rapid thermal processing hot dip galvanizing manufacturing of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, characterized in that in step 4), the rapid heating adopts two-stage heating, the first stage heating from room temperature to 550 to 625 ℃ at a heating rate of 15 to 300 ℃/s, and the second stage heating from 550 to 625 ℃ to 770 to 860 ℃ at a heating rate of 50 to 300 ℃/s.

22. The method for rapid thermal processing hot dip galvanizing manufacturing of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, characterized in that in step 4), the rapid heating adopts two-stage heating, the first stage heating from room temperature to 550 to 625 ℃ at a heating rate of 30 to 300 ℃/s, and the second stage heating from 550 to 625 ℃ to 770 to 860 ℃ at a heating rate of 80 to 300 ℃/s.

23. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in step 4), the rapid heating final temperature is 790-860 ℃.

24. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 20, wherein in step 4), the rapid heating final temperature is 790-860 ℃.

25. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 21, wherein in step 4), the rapid heating final temperature is 790-860 ℃.

26. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in the soaking process of step 4), the steel strip or the steel plate is heated to the target temperature of the austenite and ferrite two-phase region, and then the soaking is performed while keeping the temperature unchanged.

27. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in the soaking process of step 4), the temperature of the strip steel or the steel plate is raised or lowered by a small extent in the soaking time period, the temperature after the temperature is raised is not more than 860 ℃, and the temperature after the temperature is lowered is not less than 770 ℃.

28. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, wherein in the step 4), after the hot dip galvanizing of the steel strip or the steel plate, the steel strip or the steel plate is heated to 480-550 ℃ at a heating rate of 30-200 ℃/s for alloying treatment, and the alloying treatment time is 5-20 s; and after alloying treatment, rapidly cooling to room temperature at a cooling rate of 30-200 ℃/s to obtain an alloyed hot dip galvanizing GA product.

29. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, 16 or 17, wherein the metallographic structure of the hot dip galvanized TRIP steel is a three-phase structure of 35-75% of bainite, 10-60% of ferrite and 5-15% of austenite, and the average grain size is 1-3 μm; bainite is in submicron-level particles; austenite is equiaxed grains distributed in an island shape; the bainite and austenite are uniformly distributed on the ferrite matrix.

30. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 18, wherein the hot dip galvanized TRIP steel has a metallographic structure of 35-75% of bainite, 10-60% of ferrite and 5-15% of austenite, and has an average grain size of 1-3 μm; bainite is in submicron-level particles; austenite is equiaxed grains distributed in an island shape; the bainite and austenite are uniformly distributed on the ferrite matrix.

31. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to any one of claims 19 to 28, wherein the metallographic structure of the hot dip galvanized TRIP steel is a three-phase structure of 35 to 75% of bainite, 10 to 60% of ferrite and 5 to 15% of austenite, and the average grain size is 1 to 3 μm; bainite is in submicron-level particles; austenite is equiaxed grains distributed in an island shape; the bainite and austenite are uniformly distributed on the ferrite matrix.

32. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 15, 16 or 17, wherein the yield strength of the hot dip galvanized TRIP steel is 549-620 MPa, the tensile strength is improved to 1030-1164 MPa, the elongation is 20.1-24.4%, and the plastic product is 20.7-25.8 gpa%.

33. The rapid thermal processing hot dip galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 18, wherein the yield strength of the hot dip galvanized TRIP steel is 549-620 MPa, the tensile strength is improved to 1030-1164 MPa, the elongation is 20.1-24.4%, and the plastic product is 20.7-25.8 gpa%.

34. The rapid thermal processing hot dip galvanizing manufacturing method for 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to any one of claims 19 to 28, wherein the yield strength of the hot dip galvanized TRIP steel is 549 to 620MPa, the tensile strength is improved to 1030 to 1164MPa, the elongation is 20.1 to 24.4%, and the plastic product is 20.7 to 25.8gpa%.

35. The rapid thermal processing hot dip galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 27, wherein the yield strength of the hot dip galvanized TRIP steel is 549-620 MPa, the tensile strength is improved to 1030-1164 MPa, the elongation is 20.1-24.4%, and the plastic product is 20.7-25.8 gpa%.

36. The rapid thermal processing hot dip galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 28, wherein the yield strength of the hot dip galvanized TRIP steel is 549-620 MPa, the tensile strength is improved to 1030-1164 MPa, the elongation is 20.1-24.4%, and the plastic product is 20.7-25.8 gpa%.

37. The rapid thermal processing hot dip galvanizing manufacturing method of 980 MPa-level low-carbon low-alloy hot dip galvanized TRIP steel according to claim 29, wherein the yield strength of the hot dip galvanized TRIP steel is 549-620 MPa, the tensile strength is improved to 1030-1164 MPa, the elongation is 20.1-24.4%, and the plastic product is 20.7-25.8 gpa%.