A method for optimizing the quality of an ultra-low-carbon IF steel in a hot continuous rolling ultra-thin gauge plate shape

Abstract

The present application relates to plate type control technical field, specifically to a kind of optimization method of limit thin gauge plate type quality of hot continuous rolling ultra-low carbon IF steel, at least including at least one of the following means: ① rough rolling adopts negative crown roll shape;② optimize finishing work roll shape, the formula of optimized roll shape is R (x)=R0+1.250883×10 ‑3 ×x‑1.258488×10 ‑6 ×x 2 +3.621548×10 ‑10 ×x 3 , wherein R (x) indicates the radius of any point x at work roll, R0 is the reference radius of roll;③ increase intermediate blank thickness, finishing exit temperature is not less than 880 DEG C;④ control heating temperature is not less than 1260 DEG C, and all cold rolling materials are used side heating.By the optimization of the present application, the crown profile of IF steel limit thin gauge is smooth, the hit rate (±20 μm) reaches 99.5%, and the cat ear height of ≤2.5mm thickness is less than 10 μm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of plate shape control technology, and particularly relates to a method for optimizing the plate shape quality of hot continuous rolling ultra-low carbon IF steel. BACKGROUND

[0002] IF steel, i.e. interstitial-free steel, has been widely used in the automobile industry. Since the C and N contents in the IF steel are low, by adding a certain amount of titanium, niobium and other strong carbonitride forming elements, the carbon and nitrogen interstitial atoms can be completely fixed as carbonitride, so as to obtain a clean ferrite steel without interstitial atoms, i.e. ultra-low carbon IF steel.

[0003] The ultra-low carbon IF steel has excellent deep drawing performance, and the elongation and r value can reach 50% and 2.0 or more, so the load is small during hot rolling, and it is also called "soft steel". Since the rolling temperature is high and the load is small, the plate shape control of the ultra-low carbon IF steel during hot continuous rolling becomes a big problem. Especially for the limit thin gauge ultra-low carbon IF steel with a thickness of less than 2.5 mm, the plate shape profile after hot continuous rolling is irregular, and the crown fluctuation, "cat ear" and "flat top" problems are prominent. SUMMARY

[0004] In view of the plate shape control problem of the limit thin gauge ultra-low carbon IF steel with a thickness of less than 2.5 mm during hot continuous rolling, the present application provides a method for optimizing the plate shape quality of hot continuous rolling ultra-low carbon IF steel.

[0005] The technical scheme of the present application is as follows:

[0006] The method for optimizing the plate shape quality of hot continuous rolling ultra-low carbon IF steel at least includes one of the following means:

[0007] ① The rough rolling adopts a negative crown roll shape;

[0008] ② The work roll shape of the finishing rolling is optimized, and the formula of the optimized roll shape is:

[0009] R(x)=R0+1.250883×10 -3 ×x-1.258488×10 -6 ×x 2 +3.621548×10 -10 ×x 3 ,

[0010] wherein R(x) represents the radius of any point x on the work roll, and R0 is the reference radius of the roll;

[0011] ③ The intermediate blank thickness is increased, and the finishing rolling outlet temperature is not less than 880℃;

[0012] (4) control the heating temperature to be not less than 1260 DEG C, and the edge of the cold rolling material is heated by the edge heater; further, the negative crown roll type is used in the rough rolling in (1), and the R2 work roll is used with a negative crown of -150 mu.

[0013] Further, the work roll profile of the optimized finishing rolling in (2) is the work roll profile of F5, F6 and F7, and the minimum value of the equivalent crown after optimization is -0.5 mm and the maximum value is 0.4 mm.

[0014] Further, the thickness of the intermediate slab is increased to 40 mm in (3).

[0015] Further, the temperature of the edge heater is increased to 80 DEG C in (4).

[0016] Further, the temperature deviation of each heating furnace after the furnace is controlled to be not more than 25 DEG C.

[0017] Further, the ultra-low carbon IF steel is selected from DC05-DC07 and other similar specifications, and can be applied to the limit thin specification steel of similar varieties.

[0018] Further, the chemical composition and mass percentage of the ultra-low carbon IF steel are as follows: C 0.04%-0.06%, Si 0.20%-0.30%, Mn 1.45%-1.55%, P ≤0.015%, S ≤0.002%, Nb 0.02%-0.03%, B ≤0.0005%, Cr 0.24%-0.35%, Ti 0.01%-0.02%, Al 0.02%-0.05%, and the balance is Fe and inevitable impurities, the ultra-low carbon design is adopted, and the deformation resistance is small in the rolling process.

[0019] The beneficial effects of the present application are as follows:

[0020] The method for optimizing the quality of the limit thin specification plate of the hot continuous rolling ultra-low carbon IF steel provided by the present application is analyzed from the component design and process requirements of the steel grade, is targeted, comprehensively analyzes the causes of the plate shape profile irregularity, crown fluctuation, cat ear and flat top and the corresponding measures, and makes the plate shape profile of the ultra-low carbon IF steel smooth and the production control of the high crown hit rate in the production process, and creates good product quality and thin specification for the cold rolling process. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to make the technical solutions in the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0022] Figure 1 is the roll shape comparison curve before and after adjustment of example 1.

[0023] Figure 2 is the roll shift position comparison chart before and after adjustment of the roll shape of example 1.

[0024] Figure 3 is the full-length crown chart of the steel plate with roll number H11249128178 in example 2.

[0025] Figure 4 is the full-length crown chart of the steel plate with roll number H23249128099 in example 2.

[0026] Figure 5 is the shape profile chart of the steel plate with “cat ear” and “flat top” problems in example 3.

[0027] Figure 6 is the shape profile chart of the steel plate after process optimization in example 3. DETAILED DESCRIPTION

[0028] In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings 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. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort should belong to the protection scope of the present application.

[0029] Example 1

[0030] In view of the problems that the roll shift often reaches the limit position and the actual target crown is small in the hot rolling production site, the limit thin gauge plate shape quality of the hot continuous rolling ultra-low carbon IF steel is optimized, specifically, the R2 work roll is changed to-150 μm negative crown, and the roll shape of the F5, F6 and F7 work rolls in the finishing rolling process is adjusted.

[0031] After the R2 work roll is changed to-150 μm negative crown, the plate shape is observed continuously for two weeks, the plate shape control remains good, and the roll shift position of F1 is improved and no longer stays at the limit position.

[0032] The roll shape formula of the F5, F6 and F7 work rolls in the finishing rolling process before adjustment is as follows:

[0033] R(x) = R0 + 1.378542 x 10 -3 -6 2 + 3.621548 x 10 -10 3

[0034] The adjusted roll shape formula is:

[0035] R(x) = R0 + 1.250883 x 10 -3 -6 2 + 3.621548 x 10 -10 3

[0036] wherein R(x) represents the radius of any point x on the working roll, and R0 is the reference radius of the roll.

[0037] The comparison curves of roll shapes before and after adjustment are shown in Figure 1 , wherein CVC-old represents the roll shape before adjustment, and CVC-new represents the roll shape after adjustment. After installing the new roll shape, the strip shape is continuously tracked, and it is found that the overall strip shape is good, and the roll shifting position is obviously improved (as shown in Figure 2 ). Before improvement (the part of the horizontal coordinate before 60 in Figure 2 ), the roll shifting basically fluctuates at +150 mm, and after improvement (the part between the horizontal coordinates 60-180 in Figure 2 ), it periodically shifts around 0 mm.

[0038] Example 2

[0039] Taking DC05 steel as an example, in view of the convexity fluctuation problem of the limit thin gauge steel plate of hot continuous rolling ultra-low carbon IF steel, the strip shape quality is optimized, specifically, the intermediate billet thickness is increased to 40 mm, and the finish rolling exit temperature is not less than 880℃. The relationship among the rough rolling exit temperature RDT, the finish rolling entry temperature FET and the finish rolling exit temperature FDT of four different intermediate billet thicknesses is shown in Table 1; Figure 3 Figure 4 ​​​​​​​​​The full length convexity of the steel plate with roll number H11249128178 and the steel plate with roll number H23249128099 in Table 1, respectively. It can be seen that the full length average convexity of the steel plate with roll number H11249128178 is 38.53 μm, the average value of the convexity is small, and the fluctuation range is 20-50 μm, the fluctuation is large; the full length average convexity of the steel plate with roll number H23249128099 is 57.90 μm, the average value of the convexity is large, and the fluctuation range is 40-60 μm, the fluctuation is small. It is shown that increasing the intermediate blank thickness and controlling the finishing rolling exit temperature not less than 880 °C is helpful to increase the full length average convexity and reduce the fluctuation range.

[0040] Table 1 Relationship between different intermediate blank thickness and temperature and average convexity

[0041]

[0042] Example 3

[0043] In view of the "cat ear" and "flat top" phenomenon (as shown in Figure 5 ) of the limit thin gauge steel plate of the hot continuous rolling ultra-low carbon IF steel, the optimization method for the shape quality of the plate is specifically to stabilize the burning quality of the heating furnace, to ensure that the temperature deviation after the discharge of each heating furnace is not more than 25 °C, to increase the heating temperature, to control the heating temperature not less than 1260 °C, to require that the edge heating is used during the production of the ultra-low carbon IF steel, and to increase the setting temperature of the edge heater to 80 °C. Table 2 is the specific process parameters for improving the "cat ear" and "flat top" problem of the DC06 steel (2.5 mm*1268 mm) by using the above technical means. Through the process optimization, the temperature trend of the cross section of the strip steel is improved, the intermediate temperature difference of the strip steel is reduced, and the edge metal flowability along the longitudinal direction is enhanced, so that the cat ear is smoothly reduced (as shown in Figure 6 ).

[0044] Table 2 Specific process parameters of the "cat ear" and "flat top" improvement scheme

[0045]

[0046] Although the present application has been described in detail by referring to the preferred embodiments thereof, it is to be understood that the present application is not limited to them. It is to be appreciated that those skilled in the art, upon attaining an understanding of the essential characteristics of the present application, can freely utilize words in the specification and / or claims to formulate other embodiments of the present application without departing from the spirit and scope thereof. Any modification and / or replacement within the technical scope of the present application disclosed herein should be covered by the scope of the present application.

Claims

1. A method for optimizing the quality of an ultra-low-carbon IF steel hot-rolled ultra-thin gauge sheet product, characterized in that, At least one of the following means is included: ① a negative convexity roll shape is used in rough rolling; ② a work roll shape of finish rolling is optimized, and the optimized roll shape formula is: R(x) = R0+ 1.250883 x 10 -3 -1.258488 x 10 -6 -1.258488 x 10 2 -1.258488 x 10 -10 -1.258488 x 10 3 , wherein R(x) represents a radius of an arbitrary point x on the work roll, and R0 is a reference radius of the roll; ③ an intermediate blank thickness is increased, and a finish rolling exit temperature is not lower than 880 DEG C; ④ a heating temperature is controlled to be not lower than 1260 DEG C, and all of the cold rolling materials are heated by edge heaters.

2. The optimization method of claim 1, wherein, The rough rolling using the negative convexity roll shape in ① is specifically that a rough rolling R2 work roll uses a negative convexity of -150 μm.

3. The optimization method of claim 1, wherein, The work roll shape of the finish rolling optimized in ② is specifically that work roll shapes of finish rolling F5, F6 and F7 are optimized, and minimum and maximum values of the equivalent convexity after optimization are -0.5 mm and 0.4 mm respectively.

4. The optimization method of claim 1, wherein, The intermediate blank thickness increased in ③ is specifically increased to 40 mm.

5. The optimization method of claim 1, wherein, The edge heater heating temperature increased in ④ is increased to 80 DEG C during rolling.

6. The optimization method of claim 1, wherein, ④ also includes that a temperature deviation after each heating furnace is discharged is controlled to be not more than 25 DEG C.

7. The optimization method of claim 1, wherein, The ultra-low carbon IF steel is selected from a DC05-DC07 series.

8. The optimization method of claim 1, wherein, The chemical composition of the ultra-low carbon IF steel and the mass percentage are as follows: C 0.04%-0.06%, Si 0.20%-0.30%, Mn 1.45%-1.55%, P ≤0.015%, S ≤0.002%, Nb 0.02%-0.03%, B ≤0.0005%, Cr 0.24%-0.35%, Ti 0.01%-0.02%, Al 0.02%-0.05%, and the balance is Fe and inevitable impurities.

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