CN117551938A - A high-strength IF steel hot-dip galvanized steel plate and its preparation method - Google Patents

Abstract

The invention discloses a high-strength IF steel hot-dip galvanized steel plate and a preparation method thereof, and belongs to the technical field of steel manufacturing. The steel plate comprises the following components in percentage by mass: c:0.003% -0.012%; mn:0.3 to 1.0 percent; si: less than or equal to 0.05 percent; p: less than or equal to 0.03 percent; s: less than or equal to 0.005%; als:0.02% -0.07%; n: less than or equal to 0.003%; b:0.0003 to 0.0008 percent; ti:0.02% -0.09%; wherein [ Ti ] -4 [ C ] -3.43 [ N ] is more than or equal to 0.01%, and [ P ]/[ B ] is less than or equal to 90, and the balance is Fe. The invention also discloses a production method of the hot dip galvanized steel sheet, which comprises the steps of controlling hot rolling, cold rolling and continuous hot dip galvanizing annealing processes, and adding Ti and C microalloy elements to form TiC, so that fine grain strengthening and precipitation strengthening achieve the mechanical properties of high-strength IF steel; the content of P, si is reduced, the P/B ratio is reasonably proportioned, the secondary processing embrittlement performance is improved, meanwhile, mn element is changed from external oxidation to internal oxidation through dew point control, the surface quality of a coating is improved, and the high-strength IF steel hot dip galvanized steel sheet has excellent mechanical properties, secondary processing brittleness and surface quality.

Description

A high-strength IF steel hot-dip galvanized steel plate and its preparation method

Technical field

The invention relates to the technical field of steel manufacturing, and in particular to a high-strength IF steel hot-dip galvanized steel plate and a preparation method thereof.

Background technique

IF (Interstitial-Free) steel is an interstitial-free steel. It uses vacuum degassing technology to control the C and N solid solution elements in the steel to extremely low contents, and adds a certain amount of Ti or Nb and other alloying elements to remove the remaining elements in the steel. The solid solution atoms are fixed. IF steel has good formability and is produced by continuous annealing or continuous hot-dip galvanizing. It is mostly used for complex formed parts of automobiles and home appliances.

Although IF steel has excellent formability, it has low strength, poor dent resistance and weak deformation resistance. In order to solve this problem, Si, Mn, P and other strengthening elements are added to IF steel to improve the strength to obtain high-strength IF steel, which has been widely used.

The increase of Si, Mn and P elements not only improves the strength of IF steel, but also brings adverse effects. On the one hand, Si, Mn, and P are all easily oxidized elements, and oxidation reactions easily occur during hot rolling and annealing. The accumulation of oxides on the surface of the steel plate affects the continuity and uniformity of the coating; on the other hand, IF steel is pure and crystalline. The bonding force of the boundary is low, and the steel plate is prone to grain boundary fracture when it is deformed at low temperature and high speed. This characteristic is called secondary processing brittleness, and the segregation of phosphorus at the grain boundary aggravates the occurrence of this phenomenon. This kind of steel plate is very prone to brittle fracture when used in cold areas, and is prone to safety hazards when used in winter in northern China and North America. Secondary processing brittleness is mainly measured by the secondary processing embrittlement temperature. The lower the embrittlement temperature, the better the ability to resist low-temperature brittleness.

Contents of the invention

The invention proposes a high-strength IF steel hot-dip galvanized steel plate and a preparation method thereof. By controlling the hot-rolling process, cold-rolling process, hot-dip galvanizing, and surface finishing processes, a high-strength IF steel sheet is obtained that is beneficial to improving strength, secondary processing brittleness, and surface quality. IF steel hot-dip galvanized steel plate preparation method, the invented galvanized steel plate has a yield strength greater than 230MPa, a secondary processing embrittlement temperature ≤ -60°C, and good surface quality, which solves or partially solves the problems of high-strength IF steel in the existing technology. Technical issues such as surface quality issues and poor secondary processing brittleness.

In a first aspect, the invention provides a high-strength IF steel hot-dip galvanized steel sheet. The mass percentage of each chemical component of the high-strength IF steel hot-dip galvanized steel sheet is: C: 0.003% to 0.012%; Mn: 0.3% to 0.3%. 1.0%; Si: ≤0.05%; P: ≤0.03%; S: ≤0.005%; Als: 0.02%～0.07%; N: ≤0.003%; B: 0.0003%～0.0008%; Ti: 0.02%～0.09% ;

Among them, [Ti]-4*[C]-3.43*[N]≥0.01%, [P]/[B]≤90, and the balance is Fe;

[Ti] represents the mass fraction of Ti, [C] represents the mass fraction of C, [N] represents the mass fraction of N, [P] represents the mass fraction of P, and [B] represents the mass fraction of B.

Further, the average diameter of TiC particles in the high-strength IF steel hot-dip galvanized steel sheet is 4 nm to 10 nm, and the average grain size of the obtained steel is 6 μm to 10 μm.

In a second aspect, the present invention also provides a method for preparing high-strength IF steel hot-dip galvanized steel sheets, which is characterized in that it includes the following steps:

Prepare a cast slab, the weight percentage of the chemical composition of the cast slab is: C: 0.003% ~ 0.012%; Mn: 0.3% ~ 1.0%; Si: ≤ 0.05%; P: ≤ 0.03%; S: ≤ 0.005%; Als :0.02%～0.07%; N: ≤0.003%; B: 0.0003%～0.0008%; Ti: 0.02%～0.09%;

The cast slab is sequentially subjected to hot rolling, coiling, pickling, cold rolling, annealing, continuous hot-dip galvanizing and skin finishing processes to obtain a high-strength IF steel hot-dip galvanized steel plate.

Further, during the hot continuous rolling process, the heating temperature is 1200°C to 1300°C.

Further, the opening rolling temperature is 1050°C to 1150°C, and the final rolling temperature is 880°C to 950°C.

Further, the coiling temperature is 400°C to 650°C.

Further, during the cold continuous rolling process, the total reduction rate is 60% to 85%.

Further, the heating section temperature of the continuous hot-dip galvanizing is 720°C to 800°C, the soaking section temperature is 720°C to 800°C, the slow cooling section outlet temperature is 600°C to 680°C, and the rapid cooling section outlet temperature is 460°C. ±10℃, the temperature of the zinc pot is 460±5℃.

Furthermore, the dew point of the atmosphere in the furnace is controlled between -40°C and -10°C.

Furthermore, during the finishing process, a constant elongation control mode is adopted.

Furthermore, the elongation is controlled at 0.3% to 2.0%.

Compared with the prior art, the present invention has the following advantages:

The invention provides a high-strength IF steel hot-dip galvanized steel plate and its preparation method. By adding Ti and C micro-alloying elements to form TiC, fine grain strengthening and precipitation strengthening achieve the mechanical properties of high-strength IF steel; reducing P, The Si content and reasonable ratio of P/B improve the embrittlement performance of secondary processing. At the same time, the Mn element is changed from external oxidation to internal oxidation through dew point control, which improves the surface quality of the coating and makes high-strength IF steel hot-dip galvanized steel sheets. It has excellent mechanical properties, secondary processing brittleness and surface quality.

Description of the 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 explain the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to describe the embodiments or the prior art. Obviously, for those of ordinary skill in the art, It is said that other drawings can be obtained based on these drawings without exerting creative labor.

Figure 1 is a scanning electron microscope microstructure photo of a high-strength IF steel hot-dip galvanized steel sheet provided by an embodiment of the present invention.

Figure 2 is a photo of TiC precipitated particles of the high-strength IF steel hot-dip galvanized steel sheet provided by the embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments These are part of the embodiments of this application, but not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

Various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and simplicity and should not be understood as a hard limit to the scope of the present application; therefore, the described scope should be considered The description has specifically disclosed all possible subranges as well as the single numerical values within that range. For example, a description of a range from 1 to 6 should be considered to have specifically disclosed subranges, 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., and A single number within the stated range, such as 1, 2, 3, 4, 5, and 6, applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it is intended to include any cited number (fractional or whole) within the indicated range.

In this application, unless otherwise specified, the directional words used such as "upper" and "lower" specifically refer to the direction of the drawing in the drawings. In addition, in the description of this application, the terms "including", "including" and the like mean "including but not limited to". In this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation and do not necessarily require or imply that there is a relationship between these entities or operations. There is no such actual relationship or sequence. In this article, "and/or" describes the association of associated objects, indicating that there can be three relationships. For example, A and/or B can mean: A alone exists, A and B exist simultaneously, and B exists alone. . Where A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "at least one of the following" or similar expressions thereof refers to any combination of these items, including any combination of a single item (items) or a plurality of items (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 ( That is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple respectively.

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

In the first aspect, the invention provides a high-strength IF steel hot-dip galvanized steel sheet. The mass percentage of each component includes: C: 0.003~0.012%, Mn: 0.3%~1.0%, Si: ≤0.05%, P: ≤0.03%, S: ≤0.005%, Als: 0.02%～0.07%, N: ≤0.003%, B: 0.0003%～0.0008%, Ti: 0.02%～0.09%, among which [Ti]-4*[C] -3.43*[N]≥0.01%, [P]/[B]≤90, the balance is Fe; where [Ti] represents the mass fraction of Ti, [C] represents the mass fraction of C, [N] represents N The mass fraction of , [P] represents the mass fraction of P, [B] represents the mass fraction of B.

In some embodiments, the average diameter of TiC particles in the high-strength IF steel hot-dip galvanized steel sheet is 4 nm to 10 nm, and the average grain size of the obtained steel is 6 μm to 10 μm.

The following explains the design principle of the ratio of each chemical element in this technical solution:

Carbon (C) element is the basis for improving the strength of steel. It can directly strengthen the matrix through solid solution strengthening, and can also form precipitated particles with micro-alloying elements in the steel to improve the strength. However, as the carbon content increases, the r value decreases and the forming Performance is affected. In the present invention, the C content is selected to be C: 0.003% to 0.012%, which is higher than conventional IF steel and can form fine TiC particles with the Ti element in the steel, thereby improving the precipitation strengthening effect and reaching the strength level of high-strength IF steel.

Manganese (Mn) element not only reacts with S to form manganese sulfide, eliminating the brittleness of S; the addition of Mn element can refine the grains and improve the strength and toughness of steel. In addition, Mn is an easily oxidized element and affects the surface quality of the coating. Therefore, the manganese (Mn) in the present invention is selected from Mn: 0.3% to 1.0%, which does not affect the surface quality of the coating without eliminating the brittleness of S and improving the strength and toughness of steel. .

Silicon (Si) element is one of the conventional steel strengthening factors. Appropriate Si content can improve the strength of steel, but Si element easily forms oxides on the surface of the steel plate, thereby affecting the surface quality of the coating. Therefore, the present invention uses the Si element The content is limited to an extremely low range Si: ≤0.05%.

For traditional high-strength IF steel, P is an important solid solution strengthening element, which is generally controlled above 0.03%. However, since P element is prone to oxidation, it affects the plateability of the steel plate. In addition, P is also an important element that aggravates the deterioration of secondary processing brittleness and needs to be strictly controlled. The present invention controls the P content within 0.03% by combining with other elements.

Generally speaking, sulfur (S) is an impurity element in steel and affects the plasticity of steel. Moreover, the S element will also react with Ti and C to form TiS or Ti ₄ S ₄ C ₂ , which reduces the total amount of TiC precipitation and thus affects the strength of the steel. Therefore, the present invention strictly controls the content of the S element: S ≤ 0.005%.

Aluminum is a strong deoxidizer and can inhibit the formation of other oxides. The aluminum (Als) in the present invention is selected from Als: 0.02% to 0.07%.

Nitrogen (N) exists as a residual element in steel, which will affect the plasticity of the steel. The lower the content, the better. Moreover, N will consume the Ti content, thereby reducing the Ti content combined with C, reducing the formation of TiC, thus affecting the strength. The nitrogen (N) in the present invention is selected to be N: ≤0.003%.

Boron (B) element competes with P element to precipitate at the grain boundary, which can reduce the brittleness of finished steel. Too little addition of B element will not have the effect of reducing the embrittlement temperature, but excessive addition of B element will also damage the formability of the steel. , the boron (B) of the present invention is selected when B: 0.0003% to 0.0008%, and [P]/[B]≤90 is limited, where [P] represents the mass fraction of P, and [B] represents the mass fraction of B , at this time, the comprehensive properties of the prepared steel are the best.

Titanium (Ti) can combine with C in steel to form TiC precipitated particles with a size within 10nm, which has a significant precipitation strengthening effect, thus improving the strength of steel. In addition, C and N interstitial atoms have a great influence on the formability and will significantly reduce the r value of the material. There must be enough Ti element to fully ensure the formability of the steel and improve the strength. The titanium (Ti) content of the present invention is selected between Ti : 0.02% ~ 0.09%, the effective Ti* content must satisfy the following relationship: [Ti]-4*[C]-3.43*[N]≥0.01%, [Ti] represents the mass fraction of Ti, [C] represents C The mass fraction of N, [N] represents the mass fraction of N.

In a second aspect, the present invention also provides a manufacturing method of the automobile steel, the steps of which are:

Prepare a cast slab, the weight percentage of the chemical composition of the cast slab is: C: 0.003% ~ 0.012%; Mn: 0.3% ~ 1.0%; Si: ≤ 0.05%; P: ≤ 0.03%; S: ≤ 0.005%; Als :0.02%～0.07%; N: ≤0.003%; B: 0.0003～0.0008%; Ti: 0.02%～0.09%;

The cast slab is sequentially subjected to heating, hot rolling, coiling, pickling, cold rolling, annealing, continuous hot-dip galvanizing and skin finishing processes to obtain a high-strength IF steel hot-dip galvanized steel plate.

In some embodiments, the heating temperature of the steel billet is controlled at 1200°C to 1300°C to ensure that the steel billet is fully austenitized and the coarse precipitates in the cast billet are fully dissolved so that they can be re-precipitated during the subsequent rolling and cooling processes. Improve the strength of steel. At the same time, using this heating temperature also prevents the steel billet from overburning and overheating, and suppresses excessive grain growth.

In some embodiments, during the hot continuous rolling process, the opening rolling temperature is 1050°C ~ 1150°C, the final rolling temperature is 880°C ~ 950°C, and the coiling temperature is controlled at 400°C ~ 650°C. These three key temperatures The parameters are mainly to ensure stable rolling and grain refinement, among which the coiling temperature is also used to control the size of TiC precipitated particles. The higher the coiling temperature, the coarser the size of TiC particles, which reduces the precipitation strengthening effect and is not conducive to the improvement of strength. , although the precipitation of TiC will be inhibited during low-temperature coiling, it can precipitate during the subsequent annealing process.

In some embodiments, during the cold rolling process, the total reduction rate is 60% to 85%. Sufficient distortion energy is generated in the cold-rolled steel to produce work hardening, which provides driving energy for subsequent continuous annealing and recrystallization. At the same time, within this range of cold rolling reduction rate, the steel plate has the highest r value and the best performance.

In some embodiments, the heating section temperature of the annealing and continuous hot-dip galvanizing is 720°C to 800°C, the soaking section temperature is 720°C to 800°C, the slow cooling section outlet temperature is 600°C to 680°C, and the rapid cooling section temperature is 720°C to 800°C. The outlet temperature of the section is 460±10℃, and the temperature entering the zinc pot is 460±5℃. The entire annealing and continuous hot-dip galvanizing process ensures complete recrystallization and texture development, thereby achieving a fine and uniform equiaxed grain structure and good formability, while maintaining a large number of finely dispersed second phase particles or achieving higher strength. , the average diameter of TiC particles obtained in the final IF steel is between 4nm and 10nm, and the average grain size of the obtained steel is 6μm and 10μm.

In some embodiments, in order to improve the easy oxidation characteristics of Si, Mn, and P elements, the water vapor content in the hot-dip galvanizing furnace is increased to change the external oxidation of oxides accumulated on the surface of the steel plate into internal oxidation, thereby improving the coating properties. Surface quality, i.e. dew point control. However, generally in traditional high-strength IF steel, due to the different dew point temperatures at which the internal oxidation reactions of the three elements Si, Mn, and P occur, internal oxidation reactions cannot be formed simply through dew point control. The present invention only retains a certain amount of Mn element, so the surface quality is improved by controlling the dew point of the atmosphere in the furnace to -40°C to -10°C.

In some embodiments, during the finishing process, a constant elongation control mode is adopted, and the elongation is controlled at 0.3% to 2.0%.

The present application will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. Experimental methods without specifying specific conditions in the following examples are usually measured in accordance with national standards. If there is no corresponding national standard, general international standards, conventional conditions, or conditions recommended by the manufacturer shall be followed.

Table 1 is the chemical composition of Examples 1 to 4 and Comparative Examples 1 to 3. Table 2 is their corresponding production method parameters. Table 3 is the corresponding mechanical properties and secondary processing embrittlement temperature. Among them, in Example 1 The scanning electron microscope photo of the metallographic structure of the provided high-strength IF steel hot-dip galvanized steel plate is shown in Figure 1, and the photo of TiC precipitated particles in the steel plate is shown in Figure 2.

Table 1 Chemical composition of examples and comparative examples (mass fraction, %)

C Si Mn P S Als N B Ti [P]/[B] [Ti]-4*[C]-3.43*[N] Example 1 0.003 0.005 0.42 0.015 0.002 0.035 0.002 0.0005 0.03 30 0.011 Example 2 0.006 0.01 0.36 0.024 0.005 0.025 0.002 0.0004 0.05 60 0.019 Example 3 0.008 0.006 0.53 0.014 0.004 0.045 0.003 0.0006 0.07 twenty three 0.028 Example 4 0.01 0.008 0.63 0.014 0.003 0.05 0.0025 0.0008 0.07 17.5 0.021 Comparative example 1 0.005 0.01 0.15 0.050 0.012 0.025 0.005 0.0004 0.06 125 0.023 Comparative example 2 0.003 0.04 0.18 0.072 0.012 0.035 0.006 0.0007 0.07 102.8 0.037 Comparative example 3 0.003 0.004 0.18 0.012 0.012 0.035 0.006 0 0.02 - -0.013

Table 2 Main parameters of the examples and comparative examples

Table 3 Examples and Comparative Examples Mechanical properties, secondary processing brittle transition temperature, coating quality

serial number Yield strength/MPa Tensile strength/MPa Elongation/% r value Secondary processing embrittlement temperature/℃ Surface Quality Example 1 246 379 37.0 1.85 -60 good Example 2 248 388 37.5 2.02 -60 good Example 3 235 386 38.5 1.93 -60 good Example 4 256 398 35.0 1.87 -60 good Comparative example 1 242 388 37 1.83 -20 The zinc layer has undulations Comparative example 2 246 393 34.5 1.78 -25 The zinc layer has undulations Comparative example 3 145 305 45 2.65 -20 good

In summary, it can be concluded that the high-strength IF steel hot-dip galvanized steel sheet provided by the embodiment of the present invention strictly controls the chemical elements in the steel and maintains a certain C content. This trace amount of C can combine with the Ti element to form fine precipitates. The second phase particles improve the strength and can also nail the grain boundaries to increase the bonding force between the grain boundaries, which is beneficial to improving the secondary processing brittleness of the steel. In addition, the embodiment strictly controls the content of P and S brittle elements, and introduces B elements to react with the brittle elements to offset the effects of harmful elements, thereby improving the secondary processing brittleness. In addition, only a small amount of Mn element is retained, making it possible to solve surface problems by improving the dew point in the furnace area to achieve internal oxidation.

The production method of high-strength IF steel hot-dip galvanized steel sheet provided by the invention balances the temperatures of each stage of hot rolling and the temperature of each section of annealing. The hot rolling process of this method moderately reduces the coiling temperature, which can avoid excessively coarse grains and refine the grains, which will form fine TiC precipitated particles. In this method, maintaining appropriate soaking temperature during the annealing process can achieve coordinated control of formability and strength. In addition, through the dew point control in the furnace area, the Mn element is internally oxidized to improve the surface quality.

The high-strength IF steel hot-dip galvanized steel plate and its production method provided by the embodiment of the present invention are optimized by controlling the chemical composition, hot rolling, cold rolling and continuous hot-dip galvanizing process. The produced steel plate has high formability and high resistance to secondary processing. The brittleness characteristics improve the surface quality of the product and can bring considerable economic benefits.

Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those of ordinary skill in the art will understand that the technical solutions of the present invention can be carried out. Modifications or equivalent substitutions without departing from the spirit and scope of the technical solution of the present invention shall be included in the scope of the claims of the present invention.

Claims (10)

1. A high-strength IF steel hot-dip galvanized steel sheet, characterized in that the mass percentage of each chemical component of the steel sheet is: C: 0.003% ~ 0.012%; Mn: 0.3% ~ 1.0%; Si: ≤ 0.05% ;P: ≤0.03%; S: ≤0.005%; Als: 0.02%～0.07%; N: ≤0.003%; B: 0.0003%～0.0008%; Ti: 0.02%～0.09%; Among them, [Ti]-4*[C]-3.43*[N]≥0.01%, [P]/[B]≤90, and the balance is Fe. 2. The high-strength IF steel hot-dip galvanized steel sheet according to claim 1, characterized in that the average diameter of TiC particles in the high-strength IF steel hot-dip galvanized steel sheet is 4nm-10nm, and the average grain size of the obtained steel type It is 6μm~10μm. 3. A method for preparing high-strength IF steel hot-dip galvanized steel sheets, which is characterized by including the following steps: Prepare a cast slab, the weight percentage of the chemical composition of the cast slab is: C: 0.003% ~ 0.012%; Mn: 0.3% ~ 1.0%; Si: ≤ 0.05%; P: ≤ 0.03%; S: ≤ 0.005%; Als :0.02%～0.07%; N: ≤0.003%; B: 0.0003%～0.0008%; Ti: 0.02%～0.09%; The cast slab is sequentially subjected to hot rolling, coiling, pickling, cold rolling, annealing, continuous hot-dip galvanizing and skin finishing processes to obtain a high-strength IF steel hot-dip galvanized steel plate. 4. The preparation method according to claim 2, characterized in that, during the hot continuous rolling process, the heating temperature is 1200°C to 1300°C. 5. The preparation method according to claim 2, characterized in that, during the hot continuous rolling process, the opening rolling temperature is 1050-1150°C, and the final rolling temperature is 880°C-950°C. 6. The preparation method according to claim 2, characterized in that the coiling temperature is 400°C to 650°C. 7. The preparation method according to claim 2, characterized in that, during the cold continuous rolling process, the total reduction rate is 60% to 85%. 8. The preparation method according to claim 2, characterized in that the heating section temperature of the continuous hot-dip galvanizing is 720°C to 800°C, the soaking section temperature is 720°C to 800°C, and the slow cooling section outlet temperature is 600℃～680℃, the outlet temperature of the quick cooling section is 450℃～470℃, and the temperature entering the zinc pot is 455℃～465℃. 9. The preparation method according to claim 2, during the continuous hot-dip galvanizing process, the dew point of the atmosphere in the furnace is controlled between -40°C and -10°C. 10. The preparation method according to claim 2, characterized in that, during the finishing process, a constant elongation control mode is adopted, and the elongation is controlled at 0.3% to 2.0%.