CN116815051B

CN116815051B - Hot-rolled pickled plate and preparation method thereof

Info

Publication number: CN116815051B
Application number: CN202310764204.1A
Authority: CN
Inventors: 王畅; 张衍; 于洋; 王林; 郭子峰; 张亮亮; 高小丽; 谢春乾; 潘丽梅
Original assignee: Shougang Group Co Ltd
Current assignee: Shougang Group Co Ltd
Priority date: 2023-06-27
Filing date: 2023-06-27
Publication date: 2025-08-12
Anticipated expiration: 2043-06-27
Also published as: CN116815051A

Abstract

This application relates to the technical field of steel production, and more particularly to a hot-rolled pickled steel plate and its preparation method. The chemical composition of the hot-rolled pickled steel plate includes C, Si, Mn, Cr, Ti, Nb, B, Cu, and N; the Nb content is 0.02-0.05% by weight, and the Cu content is 0.02-0.05% by weight. This application addresses the technical problem of poor hydrogen embrittlement resistance of existing hot-rolled pickled steel plates.

Description

Hot-rolled pickled plate and preparation method thereof

Technical Field

The application relates to the technical field of steel preparation, in particular to a hot-rolled pickled plate and a preparation method thereof.

Background

The automobile parts produced by the hot stamping technology have higher strength, so that the thickness of the automobile parts is thinned on the premise that the product meets the performance requirement, and finally the aim of reducing the weight of the automobile is fulfilled. The application of high-strength steel is one of the main solutions for promoting the weight reduction of automobiles, and is therefore highly valued by the manufacturing industry, especially the automobile industry, in recent years. The 22MnB5 hot-rolled pickled plate is subjected to heat treatment to form martensite for the car door anti-collision rod, and the steel is required to have certain rigidity when being impacted by side, can absorb impact energy of collision, and can prevent personal injury caused by reduction of crashworthiness due to breakage of the anti-collision rod and sharp angles generated after breakage.

At present, various components using ultra-high strength steel pipes are also immersed in steel due to hydrogen generated by corrosion reaction in the atmospheric environment, and there is a possibility that the components may be damaged by sudden delay during use. The different strength metals respond to the hydrogen embrittlement phenomenon to a different extent, which is less pronounced in medium and low strength ferritic steels, but is quite severe in high strength martensitic steels, especially high strength hot formed steels, which shows a very large correlation of hydrogen embrittlement with the strength and microstructure of the metal.

Disclosure of Invention

The application provides a hot-rolled pickled plate and a preparation method thereof, which are used for solving the technical problem that the existing hot-rolled pickled plate is poor in hydrogen embrittlement resistance.

In a first aspect, the present application provides a hot rolled pickled sheet comprising the chemical components of:

C. si, mn, cr, ti, nb, B, cu and N, wherein,

The Nb content is 0.02-0.05 wt%, and the Cu content is 0.02-0.05 wt%.

Optionally, the hot-rolled pickled plate comprises 0.22-0.25 wt% of C, 0.25-0.3 wt% of Si, 1.25-1.35 wt% of Mn, 0.2-0.25 wt% of Cr, 0.02-0.04 wt% of Ti, 0.002-0.003 wt% of B and less than or equal to 50ppm of N.

In a second aspect, the present application provides a method for preparing a hot-rolled pickled sheet according to any one of the embodiments of the first aspect, the method comprising:

continuously casting the molten steel, and controlling the technological parameters of continuous casting to obtain a casting blank;

Heating the casting blank to enable the heated casting blank to have target temperature and the chemical components of the surface iron oxide scale of the casting blank to have target FeO content, wherein the heating comprises the steps of controlling the heating rate in stages and controlling the heat preservation time of a heat homogenizing section;

carrying out staged rolling on the heated casting blank to obtain a hot rolled plate;

Under the condition of setting cooling rate, carrying out laminar cooling on the hot rolled plate, coiling, and controlling the coiling temperature to obtain a hot rolled coil;

and (3) carrying out water-cooling soaking on the hot rolled coil, and then carrying out pickling to obtain a hot-rolled pickled plate.

Optionally, the technological parameters of continuous casting comprise that the withdrawal speed is 1.5-1.7m/min, and the straightening temperature of a withdrawal and straightening machine is

The temperature is more than or equal to 950 ℃, and the electromagnetic stirring current is 120-160A.

Optionally, the target temperature is 1200-1230 ℃, and the target FeO content is more than or equal to 90 wt%.

Optionally, the controlling the temperature rising rate and controlling the heat preservation time of the soaking section in stages includes:

If the heating temperature is less than 1050 ℃, the heating rate is 5-10 ℃ per minute;

If the heating temperature is equal to or higher than 1050 ℃, the heating rate is 8-12 ℃ per minute;

the heat preservation time of the soaking section is less than or equal to 30min.

Optionally, the step of rolling the heated casting blank in stages to obtain a hot rolled plate includes:

Rough rolling is carried out on the heated casting blank, wherein the R2 rough rolling mill adopts 1, 3, 4 and 5 times of descaling;

and (3) performing finish rolling on the casting blank after rough rolling to obtain a hot rolled plate, wherein the outlet temperature of the finish rolling is 1030-1050 ℃, and double-pass descaling is started.

Optionally, the set cooling rate is 70-100 ℃ per second, and the coiling temperature is 550-600 ℃.

Optionally, the water-cooling soaking is performed on the hot rolled coil, and then the hot rolled coil is pickled to obtain a hot-rolled pickled plate, which comprises the following steps:

Carrying out water cooling soaking on the hot rolled coil under the condition of set time, wherein the initial soaking temperature of the outer ring of the hot rolled coil is controlled;

And (3) pickling the soaked hot rolled coil, and controlling the pickling speed to obtain a hot-rolled pickled plate.

Optionally, the set time is 200-300min, the initial soaking temperature of the outer ring of the hot rolled coil is 350-400 ℃, and the pickling speed is 100-120m/min.

Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:

according to the hot-rolled pickled plate provided by the embodiment of the application, cu is added, the hydrogen overvoltage is increased, the cathode reaction is inhibited, the intrusion of hydrogen is reduced, the delayed damage characteristic is improved, and the addition of Nb forms highly dispersed nano NbC particles serving as effective hydrogen traps and plays a decisive role in hydrogen embrittlement resistance. Meanwhile, the Nb alloying technology can obviously reduce the grain size of the prior austenite, further obviously increase the number of the grain boundaries of the prior austenite, and reduce the hydrogen concentration on the unit grain boundaries, thereby reducing the possibility of enriching hydrogen atoms to critical fracture concentration. NbC as a Kelvin gas mass can improve the slip activation energy, inhibit dislocation slip and only further reduce the occurrence of hydrogen embrittlement.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.

In order to more clearly illustrate the embodiments of the application or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.

FIG. 1 is a schematic flow chart of a method for producing a hot-rolled pickled plate according to an embodiment of the present application;

FIG. 2 is a microscopic image of nano precipitates formed after hot stamping after adding Nb elements provided by an embodiment of the present application;

FIG. 3 is an image of the center segregation of C-Mn element in the steel grade provided by the embodiment of the application;

FIG. 4 is a microscopic image of the diffusion of Cu in the primary iron sheet provided by the embodiment of the application;

fig. 5 is a microscopic image of the Cu element distributed in the iron scale (white spot) according to the embodiment of the present application;

FIG. 6 is a microscopic image of the high temperature coiling resulting in intergranular oxidation provided by an embodiment of the present application;

fig. 7 is a graph of hydrogen embrittlement evaluation by the bending method provided in the example of the present application.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

Various embodiments of the application may exist in a range format, it being understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the application, as the range format described above specifically disclosing all possible sub-ranges and individual values within the range. For example, it should be considered that a description of a range from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1,2, 3, 4, 5, and 6, wherever applicable. In addition, whenever a numerical range is referred to herein, it is meant to include any reference number (fractional or integer) within the indicated range.

In the present application, unless otherwise specified, terms such as "upper" and "lower" are used specifically to refer to the orientation of the drawing in the figures. In addition, in the description of the present specification, the terms "include", "comprising" and the like mean "including but not limited to". Relational terms such as "first" and "second", and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Herein, "and/or" describes an association relationship of an association object, which means that there may be three relationships, for example, A and/or B, and may mean that A exists alone, while A and B exist together, and B exists alone. Wherein A, B may be singular or plural. Herein, "at least one" means one or more, and "a plurality" means two or more. "at least one", "at least one" or the like refer to any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (a), b, or c)", or "at least one (a, b, and c)", may each represent a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present application are commercially available or may be prepared by existing methods.

C. si, mn, cr, ti, nb, B, cu and N, wherein,

The Nb content is 0.02-0.05 wt%, and the Cu content is 0.02-0.05 wt%.

In the embodiment of the application, the positive effect of controlling the Nb content to be 0.02-0.05 wt% is that highly dispersed nano NbC particles are formed to serve as effective hydrogen traps and play a decisive role in hydrogen embrittlement resistance. And NbC > TiC > VC in the hydrogen capturing capacity. Meanwhile, the Nb alloying technology can obviously reduce the grain size of the prior austenite, further obviously increase the number of the grain boundaries of the prior austenite, and reduce the hydrogen concentration on the unit grain boundaries, thereby reducing the possibility of enriching hydrogen atoms to critical fracture concentration. NbC as a Kelvin gas mass can increase the slip activation energy, inhibit dislocation slip, and can only further reduce hydrogen embrittlement, as shown in FIG. 2. If the Nb content is too high, the production cost of the product can be improved to a certain extent, on the other hand, if the Nb content is too low, the precipitation of massive Nb is easy to cause, the hydrogen trapping capacity is reduced, and if the Nb content is too low, the fine grain strengthening and precipitation strengthening effects can not be effectively realized to a certain extent. Specifically, the Nb content may be 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, or the like.

The positive effect of controlling Cu content to 0.02-0.05 wt% is that by adding Cu, hydrogen overvoltage is increased, cathode reaction is suppressed, intrusion of hydrogen is reduced, and delayed fracture characteristics are improved. If the Cu content is too high, the hot-rolled sheet surface may be thermally brittle due to massive liquefaction and precipitation of Cu element to some extent, and if the Cu content is too low, the hydrogen atom penetration inhibition ability may not be effectively achieved to some extent. Specifically, the Cu content may be 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, or the like.

In some embodiments, the hot-rolled pickled plate has a chemical composition of 0.22 to 0.25 wt% of C, 0.25 to 0.3 wt% of Si, 1.25 to 1.35 wt% of Mn, 0.2 to 0.25 wt% of Cr, 0.02 to 0.04 wt% of Ti, 0.002 to 0.003 wt% of B, and less than or equal to 50ppm of N.

The positive effect of controlling the content of C to be 0.22-0.25 wt% is that the mechanical property of the product is ensured and the strength grade of the product is ensured. Specifically, the content of C may be 0.22 wt%, 0.23 wt%, 0.24 wt%, 0.25 wt%, or the like.

The positive effect of controlling the Si content to be 0.25-0.3 wt% is that the addition of Si reduces the quantity of Cu-rich phases at the steel/iron sheet interface, which helps to reduce the surface hot embrittlement sensitivity, and meanwhile, the internal oxidation of Si helps to reduce the penetration of the Cu-rich phases. Specifically, the Si content may be 0.25 wt%, 0.26 wt%, 0.27 wt%, 0.28 wt%, 0.29 wt%, 0.3 wt%, or the like.

The positive effect of controlling the Mn content to be 1.25-1.35 wt% is that the mechanical property of the product is ensured and the strength grade of the product is ensured. Specifically, the Mn content may be 1.25 wt%, 1.30 wt%, 1.35 wt%, or the like.

The positive effect of controlling the Cr content to be 0.2-0.25 wt% is that the element for improving the hardenability of the steel grade promotes the martensitic transformation in the heat treatment process and ensures the product strength of the steel grade. Specifically, the content of Cr may be 0.wt%, 0.021 wt%, 0.22 wt%, 0.23 wt%, 0.24 wt%, 0.25 wt%, and the like.

The positive effects of controlling the Ti content to be 0.02-0.04 wt% and the N content to be less than or equal to 50ppm are that the binding force of titanium and nitrogen is stronger than that of boron, and free nitrogen is mostly fixed by titanium, so that fine titanium nitride (with a nano-scale size) is preferentially formed, coarse boron nitride (with a micro-scale size) is reduced to be separated out along a grain boundary, the effect of weakening the grain boundary by the boron nitride is weakened, the high-temperature plasticity of a continuous casting blank is further improved, and a straightening section of the casting blank is not easy to crack in casting. Specifically, the Ti content may be 0.02 wt%, 0.03 wt%, 0.04 wt%, etc., and the N content may be 50ppm, 49ppm, 48ppm, 47ppm, etc.

The positive effect of controlling the content of B to be 0.002-0.003 wt% is that the element for improving the hardenability of the steel grade promotes the martensitic transformation in the heat treatment process and ensures the product strength of the steel grade. Specifically, the content of B may be 0.002 wt%, 0.0025 wt%, 0.003 wt%, or the like.

In a second aspect, the present application provides a method for preparing a hot-rolled pickled plate, referring to fig. 1, for preparing a hot-rolled pickled plate according to any one of the embodiments of the first aspect, the method comprising:

s1, continuously casting molten steel, and controlling technological parameters of continuous casting to obtain a casting blank;

S2, heating the casting blank to enable the heated casting blank to have target temperature and the chemical components of the surface oxide scale of the casting blank to have target FeO content, wherein the heating comprises the steps of controlling the heating rate in stages and controlling the heat preservation time of a heat equalizing section;

S3, carrying out staged rolling on the heated casting blank to obtain a hot rolled plate;

S4, carrying out laminar cooling on the hot rolled plate under the condition of setting cooling rate, coiling, and controlling the coiling temperature to obtain a hot rolled coil;

S5, carrying out water cooling soaking on the hot rolled coil, and then carrying out pickling to obtain a hot rolled pickled plate.

In the embodiment of the application, the Nb-Cu composite addition is added in the alloy design to improve the hydrogen embrittlement sensitivity, and meanwhile, a continuous casting-hot rolling-pickling optimization process route is designed based on the characteristic of alloy element addition to improve the product yield.

In some embodiments, the technological parameters of continuous casting comprise a withdrawal speed of 1.5-1.7m/min, a straightening temperature of a withdrawal and straightening machine of not less than 950 ℃ and an electromagnetic stirring current of 120-160A.

And B, adding a fixed N element through the influence of the addition of the Ti element on the transverse crack of the slab angle, and analyzing the plastic change of the steel grade by utilizing a high-temperature thermoplastic experiment to find that the plastic still has a reducing trend within the range of 750-850 ℃, wherein the plastic is reduced to below 70%, and the straightening section in the continuous casting process is prevented from falling into the temperature range. The occurrence of embrittled grain boundaries is prevented from being greatly caused by the precipitation, and a weak cooling mode is adopted in the continuous casting process.

The positive effect of controlling the withdrawal speed to be 1.5-1.7m/min and the straightening temperature of the withdrawal and straightening machine to be more than or equal to 950 ℃ is that the occurrence of a large amount of precipitates as embrittled grain boundaries is prevented. Specifically, the draw rate may be 1.5m/min, 1.6m/min, 1.7m/min, etc., and the straightening temperature may be 952 ℃, 954 ℃, 956 ℃, etc.

The positive effect of controlling the electromagnetic stirring current to be 120-160A is to inhibit center segregation in the continuous casting process of the C/Mn element, as shown in figure 3. Specifically, the electromagnetic stirring current may be 120A, 130A, 140A, 150A, 160A, or the like.

In some embodiments, the target temperature is 1200-1230 ℃, and the target FeO content is greater than or equal to 90 wt%.

The design of inhibiting hydrogen embrittlement sensitivity by adding Cu element can cause thermal embrittlement when Cu element is contained in Cu steel, so that small tilted skins are dispersed on the surface of the hot rolled strip steel. Cu has a low solubility in the FeO phase and a melting point of 1083 ℃ for metallic Cu, so that liquid Cu easily migrates through FeO grain boundaries and matrix grain boundaries. As shown in fig. 4, it was found through research that liquid Cu can migrate through FeO grain boundaries under heating and then dissolve in Fe ₃O₄, and increasing FeO in the as-grown iron sheet is beneficial to reducing the interfacial Cu element enrichment. The hot rolling heating process is controlled by adopting weak reducing atmosphere, the lambda value is controlled to be 0.8-1.0, and lambda is the air excess coefficient.

The target temperature represents the tapping temperature, the target FeO content represents the FeO content in the chemical components of the surface iron scale of the cast blank, and the tapping temperature is controlled to be 1200-1230 ℃ and has the positive effect of ensuring that Nb-Ti precipitates separated out in the continuous casting process are dissolved back. Specifically, the tapping temperature may be 1200 ℃, 1210 ℃, 1220 ℃, 1230 ℃, etc., and the heating time is 160-200min.

The method has the advantages that the FeO content in the chemical components of the iron scale on the surface of the cast blank is controlled to be more than or equal to 90 weight percent, on one hand, feO occupies a higher iron scale structure, the scale is easy to remove, the defect of iron scale pressing in the hot rolling process can be greatly avoided, and on the other hand, the solubility of Cu in the FeO phase is very low. The melting point of metallic Cu is 1083 ℃, so liquid Cu easily migrates through FeO grain boundaries and matrix grain boundaries. Cu diffuses to the surface of the iron sheet along FeO crystal boundary under the high temperature condition and evaporates in the form of Cu gas, so that the enrichment of Cu at the iron sheet/steel interface can be reduced, and the occurrence of Cu brittle defects is avoided. Referring to fig. 5, cu diffusion in the iron sheet is ensured, and interfacial Cu element enrichment is reduced. Specifically, the FeO content may be 90 wt%, 91 wt%, 92 wt%, 93 wt%, or the like.

In some embodiments, the controlling the rate of temperature rise in stages and controlling the soak time of the soaking section comprises:

When the heating temperature is controlled to be less than 1050 ℃, the heating rate is controlled to be 5-10 ℃ per minute, and the positive effects of ensuring that the slab is burnt through and the internal and external temperatures are uniform in the low-temperature heating process, simultaneously, the temperature is lower than the Cu liquefying temperature, and the heating rate can be slower, so that Cu liquefying precipitation in the oxidation process is avoided. Specifically, when the heating temperature is <1050 ℃, the temperature rise rate may be 5 ℃,6 ℃,7 ℃,8 ℃, 9 ℃,10 ℃, or the like.

When the heating temperature is controlled to be equal to or higher than 1050 ℃, the heating rate is controlled to be 8-12 ℃ per min, and the heating speed is improved after the melting point range of Cu element is reached, so that the enrichment content and concentration of the Cu surface layer are reduced. Specifically, when the heating temperature is equal to or higher than 1050 ℃, the temperature rising rate may be 8 ℃, 9 ℃,10 ℃, 11 ℃, 12 ℃ or the like.

The heat preservation time of the soaking section is controlled to be less than or equal to 30 minutes, so that the enrichment content and concentration of the Cu surface layer are reduced on the premise of ensuring that the slab is burnt out, and the occurrence of Cu brittle defects is avoided. The incubation time may be 30min, 28min, 26min, 24min, etc.

In some embodiments, the step of rolling the heated cast slab in stages to obtain a hot rolled plate includes:

In rough rolling, the R2 roughing mill adopts 1, 3, 4 and 5 times of descaling, and has the positive effects that the iron scale stickiness caused by the formation of fayalite phase is reduced due to the fact that higher Cu/Si element is added in the steel. After the slab is discharged from the furnace, the primary descaling is utilized to remove iron sheets, the descaling pressure is ensured to be higher than 25Mpa, a 1+5 rolling mode is adopted, the iron sheets are easy to be sticky due to the fact that the higher Cu/Si element is added in the steel, R1 adopts 1-pass descaling, the temperature in the rough rolling process is reduced to 150-170 ℃, a plate coil box is utilized after rough rolling, the descaling effect is increased, and the thickness of an intermediate billet is controlled to be 35-38mm.

Controlling the outlet temperature of the finish rolling to 1030-1050 ℃ and starting the positive effect of double-pass descaling, namely ensuring the surface quality of the hot coil. And (3) starting scale removal water between the F1 and F2 frames in the finish rolling process, controlling the scale removal water pressure to be 10-15Mpa, controlling the rolling speed in the finish rolling process to be 10-15m/s, and controlling the thickness of a finished product to be 1.8-2.5mm after finish rolling. The outlet temperature of the finish rolling may be 1030 ℃, 1040 ℃, 1050 ℃ or the like.

In some embodiments, the set cooling rate is 70-100 ℃ per second and the temperature of the winding is 550-600 ℃.

As shown in FIG. 6, since the steel grade contains higher Mn-Si element, the inter-crystal oxidation easily occurs in the coiling process, in the embodiment of the application, the laminar cooling adopts an ultra-fast low-pressure mode, the 'set cooling rate' represents the ultra-fast cooling speed, and the positive effect of controlling the cooling speed to be 70-100 ℃ per second is that the residence time of the strip steel in a two-phase area is shortened, and the formation of the inter-crystal oxidation is avoided. The cooling rate can be 70 ℃, 80 ℃, 90 ℃, 100 ℃ and the like, wherein the water pressure is 0.35MPa, the water flow is 100m ³/h, and the water flow is 80m ³/h.

The positive effect of controlling coiling temperature to 550-600 ℃ is that the coiling temperature of the strip steel is reduced, and the formation of inter-crystal oxidation in the coiling process is avoided. Specifically, the coiling temperature can be 550 ℃, 560 ℃, 570 ℃, 580 ℃, 590 ℃, 600 ℃ and the like, and meanwhile, in order to ensure the uniformity of head-tail performance, a head-tail U-shaped coiling process is adopted, the coiling temperature is increased by 30-40 ℃ by 50m, the precipitation uniformity of Nb element is ensured, and the coiling temperature is increased by 30-50 ℃ by 150m at the tail.

In some embodiments, the water-cooling soaking the hot rolled coil, and then pickling to obtain a hot-rolled pickled plate, comprising:

In some embodiments, the set time is 200-300min, the initial soaking temperature of the outer ring of the hot rolled coil is 350-400 ℃, and the pickling speed is 100-120m/min.

The set time represents the soaking time, and the soaking time is controlled to be 200-300min, so that after the phase change of the strip steel is completed in the coiling process, the retention time of the middle part of the strip steel in the high-temperature section can be shortened in the soaking water, and the formation of inter-crystal oxidation is avoided. Specifically, the soaking time may be 200min, 250min, 300min, etc.

The method has the beneficial effects that the soaking initial temperature of the outer ring of the hot rolled coil is controlled to be 350-400 ℃, so that after the strip steel seeds finish phase transition, the stay time of the middle part of the strip steel in a high-temperature section is shortened, and the formation of inter-crystal oxidation is avoided. In particular, the temperature may be 350 ℃, 360 ℃, 370 ℃, 380 ℃, 390 ℃, 400 ℃, etc.

The positive effect of controlling the pickling speed to be 100-120m/min is that the pickling speed is slower to ensure that the surface layer sporadic inter-crystal oxide layer is removed by pickling. In particular, the rate of the pickling may be 100m/min, 110m/min, 120m/min, etc. The acid washing process also comprises a withdrawal and straightening process, wherein the withdrawal and straightening process adopts a two-bending one-straightening process, the insertion amount of a bending section is controlled to be 25-30mm, the straightening section is controlled to be 10-15mm, and the extensibility is set to be 3-5%.

The preparation method of the hot-rolled pickled plate is realized based on the hot-rolled pickled plate, and the chemical dust component of the hot-rolled pickled plate can be specifically referred to the above embodiment.

The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. The experimental procedures, which are not specified in the following examples, are generally determined according to national standards. If the corresponding national standard does not exist, the method is carried out according to the general international standard, the conventional condition or the condition recommended by the manufacturer.

TABLE 1 chemical composition (wt.%) of hot rolled pickled plate

Sequence number	C	Si	Mn	Cr	Nb	Cu	Ti	N(ppm)
									Example 1	0.22	0.25	1.25	0.2	0.02	0.02	0.02	50
Example 2	0.25	0.3	1.35	0.25	0.05	0.05	0.04	48
									Example 3	0.24	0.27	1.30	0.23	0.03	0.03	0.03	47
Comparative example 1	0.23	0.15	1.5	0.15	0	0	0.04	45

Table 2 preparation process parameters of hot rolled pickled plate

Table 3 hydrogen embrittlement evaluation results of hot-rolled pickled plate

Sequence number	Bending angle	Hydrogen induced delayed cracking time
			Example 1	80°	500H without cracking
Example 2	75°	500H without cracking
			Example 3	70°	Cracking for 1000 hours
Comparative example 1	50°	210H of cracking

When the high-end turning rabbet is used for purchasing and authenticating the hot forming steel, the bending angle of the hot forming steel in a quenching state is required to exceed 60 degrees and 65 degrees so as to be purchased and used, and meanwhile, the hot forming steel three-point bending experiment is carried out in a designated solution so as to meet the condition that no hydrogen embrittlement fracture occurs in a certain time (generally 300 h). In the embodiment of the application, the bending angle of the steel grade is improved by solving the problems of center segregation, inter-crystal oxidation, surface cracking and the like, the bending at more than 65 degrees is ensured not to crack, and meanwhile, the characteristic of adding alloy elements into the steel grade is adopted for hydrogen embrittlement evaluation by adopting a four-point bending method as shown in fig. 7, the hydrogen embrittlement delay cracking time is obviously improved, and the surface hydrogen embrittlement resistance is better. In contrast, the comparative examples, which do not employ the embodiments of the present application, result in a steel sheet having a lower bending angle, a shorter hydrogen induced delayed cracking time, and a lower hydrogen embrittlement fracture resistance.

The foregoing is only a specific embodiment of the application to enable those skilled in the art to understand or practice the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hot-rolled pickled plate, characterized in that the chemical composition of the hot-rolled pickled plate consists of the following: C content of 0.22-0.25% by weight, Si content of 0.25-0.3% by weight, Mn content of 1.25-1.35% by weight, Cr content of 0.2-0.25% by weight, Ti content of 0.02-0.04% by weight, B content of 0.002-0.003% by weight, Nb content of 0.02-0.05% by weight, Cu content of 0.02-0.05% by weight, N content of ≤50ppm; the remainder is Fe.

2. A method for preparing a hot-rolled pickled plate, characterized in that it is used to prepare the hot-rolled pickled plate according to claim 1, the method comprising:

Continuously casting the molten steel and controlling the process parameters of the continuous casting to obtain a cast billet;

The ingot is heated so that the heated ingot has a target temperature and the chemical composition of the surface iron oxide scale of the ingot has a target FeO content; wherein the heating includes: controlling the heating rate in stages and controlling the holding time of the soaking section;

The heated ingot is rolled in stages to obtain a hot-rolled plate;

Under a set cooling rate condition, laminar cooling is performed on the hot-rolled plate, and then coiling is performed while controlling the coiling temperature to obtain a hot-rolled coil;

The hot-rolled coil is immersed in water for cooling and then pickled to obtain a hot-rolled pickled plate.

3. The method according to claim 2, characterized in that the process parameters of the continuous casting include: a billet drawing rate of 1.5-1.7 m/min, a straightening temperature of a straightening machine of ≥950°C, and an electromagnetic stirring current of 120-160A.

4. The method according to claim 2, wherein the target temperature is 1200-1230°C, and the target FeO content is ≥90 wt%.

5. The method according to claim 2, wherein the step of controlling the heating rate and the holding time of the soaking section in stages comprises:

If the heating temperature is <1050°C, the heating rate is 5-10°C/min;

If the heating temperature is ≥1050°C, the heating rate is 8-12°C/min;

The holding time of the soaking section is ≤30 min.

6. The method according to claim 2, wherein the step of rolling the heated ingot in stages to obtain a hot-rolled plate comprises:

The heated ingot is subjected to rough rolling; wherein the R2 rough rolling mill adopts 1, 3, 4, and 5 passes for descaling;

The rough-rolled ingot is subjected to finish rolling to obtain a hot-rolled plate; wherein the outlet temperature of the finish rolling is 1030-1050° C., and double-pass descaling is started.

7. The method according to claim 2, characterized in that the set cooling rate is 70-100°C/s and the coiling temperature is 550-600°C.

8. The method according to claim 2, wherein the step of water-immersing the hot-rolled coil and then pickling the hot-rolled pickled plate comprises:

Under the condition of a set time, the hot-rolled coil is immersed in water for cooling; wherein the initial immersion temperature of the outer ring of the hot-rolled coil is controlled;

The hot-rolled coil after soaking is pickled, and the pickling rate is controlled to obtain a hot-rolled pickled plate.

9. The method according to claim 8, characterized in that the setting time is 200-300 minutes, the initial immersion temperature of the outer ring of the hot-rolled coil is 350-400°C, and the pickling rate is 100-120 m/min.