A hot-dip galvanized steel and a method for manufacturing the same

Abstract

The application relates to the technical field of hot-dip galvanizing and automobile plate manufacturing, in particular to a hot-dip galvanized steel and a preparation method thereof. The method comprises the following steps: annealing a strip steel with a set chemical composition, controlling the running speed of the strip steel, then carrying out hot-dip galvanizing to obtain a first hot-dip galvanized steel; wherein the annealing comprises the following steps: homogenizing the strip steel, controlling the temperature of the homogenizing, then cooling, inductively heating the cooled strip steel, and controlling the temperature of the inductive heating according to seasons; carrying out stage cooling on the first hot-dip galvanized steel, controlling the process parameters of the stage cooling according to seasons, and obtaining a target hot-dip galvanized steel. The application solves the technical problem that the horizontal and vertical strength difference of the existing hot-dip galvanized steel is large, and the horizontal and vertical strength difference is reduced to within 40 MPa, and the uniformity of the plating layer and the uniformity of the steel matrix are good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot-dip galvanizing and automobile plate manufacturing, and particularly relates to a hot-dip galvanized steel and a preparation method thereof. BACKGROUND

[0002] At present, in order to ensure formability, the Si element added in the ultra-high strength steel is generally high, which leads to poor uniformity of the surface zinc layer when galvanizing, so that the transverse and longitudinal strength difference of the steel plate becomes large. During the cooling process after galvanizing, the different zinc layer hardnesses at different positions of the strip steel caused by the inappropriate cooling speed, the uneven thickness of the zinc layer in the subsequent leveling process are more obvious, and the thickness difference is large in different seasons. The selective oxidation of the Mn element on the surface of the strip steel is intensified, which also causes poor wettability at local positions, serious thickness of the zinc layer, and large transverse and longitudinal strength difference of the steel plate.

[0003] Therefore, it is urgent to prepare an ultra-high strength steel with small transverse and longitudinal strength difference. SUMMARY

[0004] The present application provides a hot-dip galvanized steel and a preparation method thereof, to solve the technical problem of large transverse and longitudinal strength difference of the existing hot-dip galvanized steel.

[0005] In a first aspect, the present application provides a preparation method of a hot-dip galvanized steel, the method comprising:

[0006] annealing a strip steel with a set chemical composition, and controlling the running speed of the strip steel, and then performing hot-dip galvanizing to obtain a first hot-dip galvanized steel; wherein the annealing comprises:

[0007] homogenizing the strip steel, and controlling the temperature of the homogenizing, and then cooling,

[0008] induction heating the strip steel after cooling, and controlling the temperature of the induction heating according to the season;

[0009] stage cooling the first hot-dip galvanized steel, and controlling the process parameters of the stage cooling according to the season to obtain a target hot-dip galvanized steel.

[0010] Optionally, the running speed of the strip steel is 60-80 m / min.

[0011] Optionally, the temperature of the homogenizing is 860-880℃.

[0012] Optionally, the end point temperature of the cooling is 200-300℃.

[0013] Optionally, the temperature of the induction heating is controlled according to the season, including:

[0014] If the season is the first season or the fourth season, the temperature of the induction heating is 360-380℃.

[0015] Optionally, the temperature of the induction heating is controlled according to the season, including:

[0016] If the season is the second season or the third season, the temperature of the induction heating is 320-350℃.

[0017] Optionally, the first hot-dip galvanized steel is cooled in stages, and process parameters of the stage cooling are controlled according to the season to obtain a target hot-dip galvanized steel, including:

[0018] If the season is the first season or the fourth season, the first hot-dip galvanized steel is cooled in the first cooling stage and then in the second cooling stage; wherein,

[0019] The speed of the first cooling stage is 20-25℃ / s, and the speed of the second cooling stage is 10-15℃ / s,

[0020] The end temperature of the first cooling stage is 350-400℃, and the end temperature of the second cooling stage is 160-200℃.

[0021] Optionally, the first hot-dip galvanized steel is cooled in stages, and process parameters of the stage cooling are controlled according to the season to obtain a target hot-dip galvanized steel, including:

[0022] If the season is the second season or the third season, the first hot-dip galvanized steel is cooled in the third cooling stage and then in the fourth cooling stage; wherein,

[0023] The speed of the third cooling stage is 15-20℃ / s, and the speed of the fourth cooling stage is 10-15℃ / s,

[0024] The end temperature of the third cooling stage is 320-360℃, and the end temperature of the fourth cooling stage is 180-220℃.

[0025] Optionally, the chemical composition includes:

[0026] C, Mn, Si, Cr and Al; wherein, in terms of mass fraction,

[0027] The content of C is 0.20-0.25%, the content of Mn is 1.9-2.3%, the content of Si is 0.3-0.5%, the content of Cr is ≤0.3%, and the content of Al is 0.6-0.8%.

[0028] In a second aspect, the present application provides a hot-dip galvanized steel prepared by the method of any one of claims 1-9.

[0029] Compared with the prior art, the above technical solution provided by the embodiments of the present application has the following advantages:

[0030] The preparation method of the hot-dip galvanized steel provided by the embodiments of the present application does not substantially increase the base alloy, and by controlling the annealing and post-plating cooling process according to the characteristics of different quarters, the uniformity of the coating structure and the uniformity of the steel matrix structure of the 980MPa or higher grade hot-dip galvanized high-strength steel are improved, so that the transverse and longitudinal strength difference of the micro-alloyed steel strip is reduced to within 40MPa. The method does not increase the cost of alloy and equipment, only adjusts the process and equipment parameters, is simple, has strong applicability, and has remarkable effect. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0033] Figure 1 A flowchart of a preparation method of a hot-dip galvanized steel provided by the embodiments of the present application;

[0034] Figure 2 A microstructure effect diagram of a hot-dip galvanized steel provided by Embodiment 1 of the present application; wherein (a) is a transverse microstructure and (b) is a longitudinal microstructure;

[0035] Figure 3 A microstructure effect diagram of a hot-dip galvanized steel provided by Comparative Example 1 of the present application; wherein (a) is a transverse microstructure and (b) is a longitudinal microstructure;

[0036] Figure 4 A microstructure effect diagram of a hot-dip galvanized steel provided by Comparative Example 2 of the present application; wherein (a) is a transverse microstructure and (b) is a longitudinal microstructure. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0038] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description 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 in the range, such as 1, 2, 3, 4, 5 and 6, which applies to any range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0039] In the present application, the orientation words such as "upper" and "lower" are specific to the orientation of the drawing surface in the accompanying drawings. In addition, in the description of the specification, the terms "include", "contain" and the like mean "include but not limited to". In this document, the relationship terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In this document, "and / or" describes the relationship between the associated objects, which means that there can be three relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Where A and B can be singular or plural. In this document, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0040] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0041] In a first aspect, the present application provides a method for preparing a hot-dip galvanized steel, which comprises Figure 1 , and the method comprises:

[0042] S1, annealing a strip steel with a set chemical composition, controlling a running speed of the strip steel, and then hot-dip galvanizing to obtain a first hot-dip galvanized steel; wherein the annealing comprises:

[0043] homogenizing the strip steel, controlling a temperature of the homogenizing, and then cooling,

[0044] induction heating the cooled strip steel, and controlling a temperature of the induction heating according to a quarter;

[0045] In some embodiments, the set chemical composition comprises:

[0046] C, Mn, Si, Cr and Al; wherein, in terms of mass fraction,

[0047] the content of C is 0.20-0.25%, the content of Mn is 1.9-2.3%, the content of Si is 0.3-0.5%, the content of Cr is ≤0.3%, and the content of Al is 0.6-0.8%.

[0048] In the embodiments of the present application, the positive effect of controlling the content of C to be 0.20-0.25% is that C element forms martensite to provide strength elements. However, C element is prone to segregation, and the content of C element in steel should not be too high. When the content of C element in steel is too high, center segregation is prone to gather to form banded structure, increase the in-plane anisotropy of the strip steel, and the difference between transverse and longitudinal strength is large, which is also not conducive to the plasticity and weldability of the strip steel. Specifically, the content of C can be 0.20%, 0.23%, 0.25%, etc.

[0049] The positive effect of controlling the content of Mn to be 1.9-2.3% is that Mn element can improve the overall strength of the material, can expand the austenite phase region, and can ensure the strength of the material under the condition of reducing alloying elements, but Mn element is prone to segregation, and the content of Mn element in steel should not be too high. Specifically, the content of Mn can be 1.9%, 2.1%, 2.3%, etc.

[0050] The positive effect of controlling the content of Si to be 0.3-0.5%: Si can purify ferrite, so that the ferrite in the steel is more pure, and the pure ferrite can provide better plasticity of the steel, in addition, Si and C have mutual inhibition, the presence of Si makes C more enter into the martensite, so as to ensure that the steel obtains higher strength, therefore, adding appropriate amount of Si element in the steel can not only play a certain strengthening effect, but also can improve the plasticity of the steel, too much Si is not conducive to the surface, which leads to poor uniformity of the surface zinc layer and large difference between transverse and longitudinal strength during galvanizing. Specifically, the content of Si can be 0.3%, 0.4%, 0.5%, etc.

[0051] The positive effect of controlling the content of Cr to be ≤0.3%: Cr can improve the hardenability of the material and improve the strength of the material, but too high Cr element is easy to lead to poor surface after galvanizing. Specifically, the content of Cr can be 0.30%, 0.28%, 0.25%, etc.

[0052] The positive effect of controlling the content of Al to be 0.6-0.8%: Al element can further improve the plasticity of the steel, Al element enters ferrite, so that the ferrite polygon is more sufficient during annealing, so that the microstructure of the steel is uniform, the in-plane anisotropy of the steel is improved, and the mechanical properties of the steel in transverse and longitudinal directions are reduced. Specifically, the content of Al can be 0.6%, 0.7%, 0.8%, etc.

[0053] In some embodiments, the running speed of the strip steel is 60-80 m / min.

[0054] In some embodiments, the temperature of the soaking is 860-880°C.

[0055] The positive effect of controlling the running speed of the strip steel to be 60-80 m / min to ensure appropriate annealing time, and controlling the temperature of the soaking to be 860-880°C: the soaking temperature and the annealing time have the most significant effect on the mechanical properties, too high soaking temperature or too long annealing time both lead to insufficient strength of the strip steel, on the contrary, it may lead to insufficient decomposition of iron carbide or pearlite in the strip steel and insufficient recrystallization of ferrite organization, the grains are fibrous, which is not conducive to reducing anisotropy, and the difference between transverse and longitudinal strength is large. Specifically, the running speed of the strip steel can be 60 m / min, 70 m / min, 80 m / min, etc., and the temperature of the soaking can be 860°C, 870°C, 880°C, etc.

[0056] In some embodiments, the end point temperature of the cooling is 200-300°C.

[0057] The cooling includes slow cooling and high hydrogen fast cooling, and the positive effect of controlling the end point temperature of the cooling to be 200-300℃ is: controlling the effect of martensite phase change, and at the same time, at a lower temperature and a faster cooling speed, a more refined grain structure can be obtained. Specifically, the end point temperature of the cooling can be 200℃, 250℃, 300℃, etc.

[0058] In some embodiments, the temperature of the induction heating is controlled according to the season, including:

[0059] If the season is the first season or the fourth season, the temperature of the induction heating is 360-380℃.

[0060] In some embodiments, the temperature of the induction heating is controlled according to the season, including:

[0061] If the season is the second season or the third season, the temperature of the induction heating is 320-350℃.

[0062] The selection of the induction heating temperature determines the morphology and size of the martensite in the steel to a great extent, and the influence of different seasons is also very significant, because the microstructure inherited from the hot-rolled raw material to the initial cold-rolled annealing is affected by the season, thereby affecting the difference between the transverse and longitudinal strengths; when the ambient temperature is low, i.e. the first season or the fourth season, the induction heating temperature is slightly higher; when the ambient temperature is high, i.e. the second season or the third season, the induction heating temperature is slightly lower. Specifically, if the season is the first season or the fourth season, the temperature of the induction heating can be 360℃, 370℃, 380℃, etc., and if the season is the second season or the third season, the temperature of the induction heating can be 320℃, 330℃, 340℃, 350℃, etc.

[0063] S2, the first hot-dip galvanized steel is subjected to staged cooling, and process parameters of the staged cooling are controlled according to the season to obtain a target hot-dip galvanized steel.

[0064] In some embodiments, the first hot-dip galvanized steel is subjected to staged cooling, and process parameters of the staged cooling are controlled according to the season to obtain a target hot-dip galvanized steel, including:

[0065] If the season is the first season or the fourth season, the first hot-dip galvanized steel is subjected to first cooling and then subjected to second cooling; wherein,

[0066] The speed of the first cooling is 20-25℃ / s, and the speed of the second cooling is 10-15℃ / s,

[0067] The end point temperature of the first cooling is 350-400℃, and the end point temperature of the second cooling is 160-200℃.

[0068] In some embodiments, the first hot-dip galvanized steel is subjected to a staged cooling, and process parameters of the staged cooling are controlled according to seasons to obtain a target hot-dip galvanized steel, comprising:

[0069] If the season is the second season or the third season, the first hot-dip galvanized steel is subjected to a third cooling and then subjected to a fourth cooling; wherein,

[0070] The third cooling has a speed of 15-20℃ / s, and the fourth cooling has a speed of 10-15℃ / s,

[0071] The third cooling has an end temperature of 320-360℃, and the fourth cooling has an end temperature of 180-220℃.

[0072] The positive effect of the staged cooling after plating: the material strength can be accurately controlled, and the matrix phase change process is controlled. The post-plating cooling determines the strength of the steel matrix, and also determines the grain size of the plating layer and the surface hardness of the plating layer. In order to control the strength fluctuation of the steel in different seasons at a low level, i.e., to control the transverse and longitudinal strength difference, different cooling speeds and cooling temperatures are set according to the high and low of the ambient temperature. Specifically, for the first cooling, the cooling speed can be 20℃ / s, 23℃ / s, 25℃ / s, etc., and the final cooling temperature can be 350, 370, 400, etc.

[0073] For the second cooling, the cooling speed can be 10℃ / s, 13℃ / s, 15℃ / s, etc., and the final cooling temperature can be 160℃, 180℃, 200℃, etc.

[0074] For the third cooling, the cooling speed can be 17℃ / s, 20℃ / s, 15℃ / s, etc., and the final cooling temperature can be 360℃, 320℃, 340℃, etc.

[0075] For the fourth cooling, the cooling speed can be 10℃ / s, 13℃ / s, 15℃ / s, etc., and the final cooling temperature can be 220℃, 180℃, 200℃, etc.

[0076] In a second aspect, the present application provides a hot-dip galvanized steel prepared by the method of any one of claims 1-9. The hot-dip galvanized steel is a 980MPa or higher grade hot-dip galvanized high-strength steel.

[0077] The hot-dip galvanized steel is realized based on the above-mentioned hot-dip galvanized steel preparation method. The specific steps of the hot-dip galvanized steel preparation method can be referred to the above-mentioned embodiments. Since the hot-dip galvanized steel adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here.

[0078] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. The experimental methods in the following examples, if no specific conditions are noted, are generally determined according to national standards. If there is no corresponding national standard, the general international standards, conventional conditions, or the conditions suggested by the manufacturer are used.

[0079] The application provides a preparation method of hot-dip galvanized steel, which comprises the following steps:

[0080] S1, annealing a strip steel with a set chemical composition, controlling the running speed of the strip steel, and then performing hot-dip galvanizing to obtain a first hot-dip galvanized steel; wherein the annealing comprises:

[0081] S2, performing stage cooling on the first hot-dip galvanized steel, and controlling the process parameters of the stage cooling according to the quarter to obtain a target hot-dip galvanized steel. The specific process parameters are shown in Tables 1-2.

[0082] S2, performing stage cooling on the first hot-dip galvanized steel, and controlling the process parameters of the stage cooling according to the quarter to obtain a target hot-dip galvanized steel. The specific process parameters are shown in Tables 1-2.

[0083] S2, performing stage cooling on the first hot-dip galvanized steel, and controlling the process parameters of the stage cooling according to the quarter to obtain a target hot-dip galvanized steel. The specific process parameters are shown in Tables 1-2.

[0084] Table 1 Chemical composition of the steel matrix of the hot-dip galvanized steel (wt%)

[0085] Serial number C Si Mn Cr Al Example 1 0.24 0.38 2.3 0.29 0.6 Example 2 0.25 0.5 2.0 0.3 0.8 Example 3 0.20 0.3 1.9 0.28 0.7 Comparative Example 1 0.17 0.50 2.1 0.21 0.6 Comparative Example 2 0.27 0.42 2.0 0.28 0.7

[0086] Table 2 Preparation process parameters of the hot-dip galvanized steel

[0087]

[0088]

[0089]

[0090] The hot-dip galvanized steels in the above examples and comparative examples are subjected to mechanical property tests, and the results are shown in Table 3.

[0091] Table 3 Test results of the mechanical properties of the hot-dip galvanized steel

[0092]

[0093] By using the method of the application, the coating uniformity of the hot-dip galvanized high-strength steel prepared in Examples 1-3 is good, and the difference between the transverse and longitudinal strengths is reduced to less than 40 MPa. The microstructure of the steel of Example 1 is shown in FIG. 1, wherein (a) and (b) represent the microstructures in the transverse and longitudinal directions, and the uniformity of the microstructures in the transverse and longitudinal directions is good. Figure 2 The microstructure of the steel of Example 1 is shown in FIG. 1, wherein (a) and (b) represent the microstructures in the transverse and longitudinal directions, and the uniformity of the microstructures in the transverse and longitudinal directions is good.

[0094] In Comparative Example 1, the microstructure of the hot-dip galvanized steel is shown below. Figure 3 As shown, the uniformity of the microstructure is poor in both the transverse and longitudinal directions. Compared to this embodiment, the C element content is slightly lower, and the induction heating temperature and post-plating cooling process parameters in the preparation process have been changed, resulting in... Figure 3 Performance a is below the lower limit, with a large difference between the transverse and longitudinal tensile strengths.

[0095] In Comparative Example 2, the microstructure of the hot-dip galvanized steel is shown below. Figure 4 As shown, the uniformity of the microstructure in both the transverse and longitudinal directions is poor. Compared to this embodiment, the C element content is slightly higher, and the induction heating temperature and post-plating cooling process parameters are changed, resulting in a larger difference in tensile strength between the transverse and longitudinal directions.

[0096] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for producing hot-dip galvanized steel, characterized by, The method comprises: annealing a strip steel with a set chemical composition, controlling a running speed of the strip steel, and then hot-dip galvanizing to obtain a first hot-dip galvanized steel; wherein the annealing comprises: soaking the strip steel and controlling a temperature of the soaking, and then cooling, induction heating the cooled strip steel and controlling a temperature of the induction heating according to a quarter; staging cooling the first hot-dip galvanized steel and controlling process parameters of the staging cooling according to the quarter to obtain a target hot-dip galvanized steel. The running speed of the strip steel is 60-80 m / min. The temperature of the soaking is 860-880 ℃. The end temperature of the cooling is 200-300 ℃. The controlling of the temperature of the induction heating according to the quarter comprises: if the quarter is the first quarter or the fourth quarter, the temperature of the induction heating is 360-380 ℃. The controlling of the temperature of the induction heating according to the quarter comprises: if the quarter is the second quarter or the third quarter, the temperature of the induction heating is 320-350 ℃. The staging cooling the first hot-dip galvanized steel and controlling process parameters of the staging cooling according to the quarter to obtain a target hot-dip galvanized steel comprises: if the quarter is the first quarter or the fourth quarter, first cooling the first hot-dip galvanized steel and then second cooling; wherein, the speed of the first cooling is 20-25 ℃ / s, and the speed of the second cooling is 10-15 ℃ / s, the end temperature of the first cooling is 350-400 ℃, and the end temperature of the second cooling is 160-200 ℃. The staging cooling the first hot-dip galvanized steel and controlling process parameters of the staging cooling according to the quarter to obtain a target hot-dip galvanized steel comprises: if the quarter is the second quarter or the third quarter, third cooling the first hot-dip galvanized steel and then fourth cooling; wherein, the speed of the third cooling is 15-20 ℃ / s, and the speed of the fourth cooling is 10-15 ℃ / s, the end temperature of the third cooling is 320-360 ℃, and the end temperature of the fourth cooling is 180-220 ℃.

2. The method of claim 1, wherein, The set chemical composition comprises: C, Mn, Si, Cr, and Al; wherein, in terms of mass fraction, the content of C is 0.20-0.25%, the content of Mn is 1.9-2.3%, the content of Si is 0.3-0.5%, the content of Cr is ≤0.3%, and the content of Al is 0.6-0.8%.

3. A hot-dip galvanized steel characterized by, The hot-dip galvanized steel is prepared by the method of claim 1 or 2.

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