Optimization method for hot continuous rolling ultra-low carbon IF steel ultimate thin gauge plate type quality

Abstract

The invention relates to the technical field of plate shape control, in particular to a hot continuous rolling ultra-low carbon IF steel ultimate thin specification plate shape quality optimization method which at least comprises at least one of the following means: (1) rough rolling adopts a negative convexity roller shape; (2) the roll shape of the finish rolling working roll is optimized, the roll shape formula after optimization is R (x) = R0 + 1.250883 * 10 <-3 > * x <-1.258488 * 10 <-6 > * x < 2 > + 3.621548 * 10 <-10 > * x < 3 >, R (x) represents the radius of any point x on the working roll, and R0 is the reference radius of the roll; (3) increasing the thickness of an intermediate billet, wherein the finish rolling outlet temperature is not lower than 880 DEG C; and (4) the heating temperature is controlled to be not lower than 1260 DEG C, and all the cold-rolled materials are put into edge heating. After optimization of the measure, the IF steel ultimate thin specification convexity profile is smooth, the hit rate (+ / -20 [mu] m) reaches 99.5%, and the height of a cat ear with the thickness smaller than or equal to 2.5 mm is smaller than 10 [mu] m.

Description

Technical Field

[0001] The invention relates to the technical field of plate shape control, and in particular to a method for optimizing the quality of extremely thin plate shape of hot-rolled ultra-low carbon IF steel. Background Art

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

[0003] Ultra-low carbon IF steel has excellent deep drawing performance. Its elongation and r value can reach 50% and above 2.0, so it has a small load during hot rolling and is also called "soft steel". Due to the high rolling temperature and small load, the plate shape control of ultra-low carbon IF steel during hot rolling becomes a major problem. Especially for ultra-low carbon IF steel with a thickness of less than 2.5 mm, the plate shape after hot rolling is irregular, with convexity fluctuations, "cat ears" and "flat top" problems. Summary of the invention

[0004] Aiming at the problem of plate shape control of ultra-low carbon IF steel with a thickness of ≤2.5 mm during hot rolling, the present invention provides a method for optimizing the plate shape quality of ultra-low carbon IF steel with an ultra-thin specification during hot rolling.

[0005] The technical solution of the present invention is as follows: A method for optimizing the quality of ultra-low carbon IF steel plate with extremely thin specifications after hot rolling, comprising at least one of the following means: ① The rough rolling adopts negative crown roller type; ② Optimize the roller shape of the finishing work roll. The roller shape formula after optimization is: R(x)=R0+1.250883×10 -3 ×x-1.258488×10 -6 × 2 +3.621548×10 -10 × 3 , Where R(x) represents the radius at any point x on the working roll, and R0 is the base radius of the roll; ③ Increase the thickness of the intermediate billet, and the finishing rolling outlet temperature should not be lower than 880℃; ④ The heating temperature is controlled not lower than 1260°C, and all cold rolled materials are heated at the edge. Further, the rough rolling using negative crown roll type described in ① specifically means that the rough rolling R2 working roll uses a negative crown of -150μm.

[0006] Furthermore, the optimization of the work roll shape of the finishing rolling described in ② is specifically the optimization of the work roll shape of the finishing rolling F5, F6, and F7 work rolls. The minimum value of the equivalent convexity after optimization is -0.5mm and the maximum value is 0.4mm.

[0007] Furthermore, the increasing the thickness of the intermediate billet in ③ specifically refers to increasing the thickness of the intermediate billet to 40 mm.

[0008] Furthermore, in ④, the heating temperature of the edge heater is increased to 80°C during rolling.

[0009] Furthermore, ④ also includes controlling the temperature deviation of each heating furnace after it comes out of the furnace to not exceed 25°C.

[0010] Furthermore, the ultra-low carbon IF steel is selected from DC05-DC07 and other similar varieties and specifications, and can be promoted and applied in similar varieties of extreme thin specifications steel.

[0011] Furthermore, the chemical composition and mass percentage of the ultra-low carbon IF steel are: 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%, Cr0.24%-0.35%, Ti 0.01%-0.02%, Al 0.02%-0.05%, the balance is Fe and unavoidable impurities. It adopts an ultra-low carbon design and has low deformation resistance during rolling.

[0012] The beneficial effects of the present invention are: The present invention provides a method for optimizing the quality of ultra-thin plate shape of hot-rolled ultra-low carbon IF steel. The method analyzes the composition design and process requirements of the steel type itself, is highly targeted, and comprehensively analyzes the causes and targeted measures of irregular plate shape profile, convexity fluctuation, "cat ears" and "flat top" problems, so that the ultra-low carbon IF steel has a smooth plate shape profile and a high convexity hit rate during production, and creates good product quality and thin specifications for the cold rolling process. The method of the present invention can guide the hot rolling process production of ultra-low carbon IF steel, improve the hot rolling yield rate, and reduce the product defect rate and production process cost of the downstream process, and has good economic benefits and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 It is the roller shape comparison curve before and after adjustment of Example 1.

[0015] Figure 2 This is a comparison diagram of the roller position before and after adjusting the roller shape in Example 1.

[0016] Figure 3 This is the full-length convexity diagram of the steel plate with roll number H11249128178 in Example 2.

[0017] Figure 4 This is the full-length convexity diagram of the steel plate with roll number H23249128099 in Example 2.

[0018] Figure 5 This is a plate profile diagram of the steel plate having the "cat ears" and "flat top" problems in Example 3.

[0019] Figure 6 This is the plate profile diagram of the steel plate after process optimization in Example 3. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] Example 1 In view of the problems that the roll shifting in the hot rolling production site often reaches the limit position and the actual target convexity is smaller than the actual target convexity, the quality of the ultra-low carbon IF steel ultra-thin plate shape of hot rolling is optimized. Specifically, the R2 working roll is changed to -150μm negative convexity, and the roll shape of the F5, F6, and F7 working rolls in the finishing rolling process is adjusted.

[0022] After changing the R2 working roll to -150μm negative convexity, the plate shape was observed for two consecutive weeks. The plate shape control remained good, and the F1 roll shifting position was improved and no longer stayed at the extreme position.

[0023] The roll shape formula of F5, F6 and F7 working rolls before adjustment in the finishing rolling process is: R(x)=R0+1.378542×10 -3 ×x-1.312811×10 -6 × 2 +3.621548×10 -10 × 3 , The adjusted roll shape formula is: R(x)=R0+1.250883×10 -3 ×x-1.258488×10 -6 × 2 +3.621548×10 -10 × 3 , Among them, R(x) represents the radius at any point x on the working roll, and R0 is the reference radius of the roll.

[0024] The roller shape comparison curve before and after adjustment is as follows: Figure 1 As shown in the figure, CVC-old indicates the roll shape before adjustment, and CVC-new indicates the roll shape after adjustment. After installing the new roll shape, the strip shape was continuously tracked and it was found that the overall shape was good and the roll shifting position was significantly improved (such as Figure 2 Before improvement ( Figure 2 The roller shifting basically fluctuates at +150mm in the first 60mm of the horizontal coordinate. After improvement ( Figure 2 The part between the horizontal coordinate 60-180) moves periodically around 0mm.

[0025] Example 2 Taking DC05 steel as an example, the convexity fluctuation problem of ultra-low carbon IF steel ultra-thin gauge steel plates in hot continuous rolling is optimized by increasing the intermediate billet thickness to 40 mm and the finishing outlet temperature to no less than 880 ° C. Table 1 shows the relationship between the rough rolling outlet temperature RDT, the finishing steel feed temperature FET and the finishing outlet temperature FDT for four different intermediate billet thicknesses; Figure 3 , Figure 4 They are the full-length convexity of the steel plate with coil number H11249128178 and the steel plate with coil number H23249128099 in Table 1. It can be seen that the full-length average convexity of the steel plate with coil number H11249128178 is 38.53μm, the average convexity is small, the fluctuation range is 20-50μm, and the fluctuation is large; the full-length average convexity of the steel plate with coil number H23249128099 is 57.90μm, the average convexity is large, the fluctuation range is 40-60μm, and the fluctuation is small. It shows that increasing the thickness of the intermediate billet and controlling the finishing outlet temperature to not less than 880℃ are conducive to increasing the full-length average convexity and reducing the fluctuation range.

[0026] Table 1 Relationship between different intermediate billet thickness, temperature and average convexity

[0027] Example 3 For the "cat ears" and "flat top" phenomena of ultra-low carbon IF steel ultra-thin gauge steel plates (such as Figure 5As shown), the optimization method for its plate quality is to stabilize the steel burning quality of the heating furnace, ensure that the temperature deviation of each heating furnace after leaving the furnace is no more than 25°C, and increase the heating temperature to control the heating temperature to no less than 1260°C. It is required that all edge heating be used during the production of ultra-low carbon IF steel, and the set temperature of the edge heater be increased to 80°C. Table 2 shows the specific process parameters for improving the "cat ears" and "flat top" problems of DC06 steel (2.5mm*1268mm) using the above technical means. Through process optimization, the temperature trend of the cross section of the strip is improved, the temperature difference in the middle of the strip is reduced, and the fluidity of the edge metal along the longitudinal direction is enhanced, thereby making the cat ears smooth and lower (such as Figure 6 as shown).

[0028] Table 2 Specific process parameters of the solution to improve the “cat ears” and “flat top” phenomena

[0029] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for optimizing the quality of ultra-low carbon IF steel plate with extremely thin specifications after hot rolling, characterized in that: At least one of the following means: ① The rough rolling adopts negative crown roller type; ② Optimize the roller shape of the finishing rolling work roll. The roller shape formula after optimization is: R(x)=R0+1.250883×10 -3 ×x-1.258488×10 -6 ×x 2 +3.621548×10 -10 ×x 3 , Where R(x) represents the radius at any point x on the working roll, and R0 is the base radius of the roll; ③ Increase the thickness of the intermediate billet, and the finishing rolling outlet temperature should not be lower than 880℃; ④Control the heating temperature not lower than 1260℃, and all cold-rolled materials shall be heated at the edges.

2. The optimization method according to claim 1, characterized in that: The rough rolling described in ① adopts a negative crown roll type, specifically the rough rolling R2 working roll adopts a negative crown of -150μm.

3. The optimization method according to claim 1, characterized in that: The optimization of the work roll shape of the finishing rolling described in ② specifically optimizes the work roll shape of the finishing rolling F5, F6, and F7 work rolls. The minimum value of the equivalent convexity after optimization is -0.5mm and the maximum value is 0.4mm.

4. The optimization method according to claim 1, characterized in that: Increasing the thickness of the intermediate billet as described in ③ specifically refers to increasing the thickness of the intermediate billet to 40 mm.

5. The optimization method according to claim 1, characterized in that: ④ During rolling, the edge heater temperature is increased to 80°C.

6. The optimization method according to claim 1, characterized in that: ④ It also includes controlling the temperature deviation of each heating furnace after it comes out of the furnace to not exceed 25℃.

7. The optimization method according to claim 1, characterized in that: The ultra-low carbon IF steel is selected from the DC05-DC07 series.

8. The optimization method according to claim 1, characterized in that: The chemical composition and mass percentage of ultra-low carbon IF steel are: C 0.04%-0.06%, Si 0.20%-0.30%, Mn 1.45%-1.55%, P ≤0.015%, S ≤0.002%, Nb0.02%-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 unavoidable impurities.

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