CN108677089A - The preparation method of ultra low carbon steel slab - Google Patents

Abstract

The invention discloses a method for preparing an ultra-low carbon steel plate, belonging to the technical field of iron and steel product production. In order to solve the technical problem of performance classification control of different brands of ultra-low carbon steel plates and poor performance consistency of products of the same brand and different specifications in the prior art, the present invention provides a preparation method of ultra-low carbon steel plates, which adopts steelmaking→hot rolling →cooling→coiling→acid rolling→continuous annealing→leveling process, through the graded control of DC03 and DC04 ultra-low carbon steel plate annealing process and leveling process, and the annealing temperature and leveling elongation gradient design according to the thickness specification, so that the product performance can be graded It is more obvious that the performance consistency of products of the same brand is better, and it can better meet the requirements of automatic high-speed stamping in the manufacture of auto parts, and has a good prospect for promotion and use.

Description

Preparation method of ultra-low carbon steel plate

technical field

The invention belongs to the technical field of steel product production, and in particular relates to a method for preparing an ultra-low carbon steel plate.

Background technique

With the rapid development of my country's automobile industry, its body-in-white parts manufacturing is basically fully automated. Especially in stamping and forming parts, many of them are formed by fully automatic high-speed stamping in China. In the high-speed stamping forming process, higher requirements are put forward for the performance of materials, which are specifically manifested in: first, users put forward higher requirements for precise control of material performance; Require.

For ultra-low carbon steel sheets, it is difficult to achieve graded control of interstitial atoms such as C and N (usually requiring C≤50ppm, N≤35ppm) in its composition, and the process has a greater impact on the performance of the finished product. Therefore, the precise control of ultra-low carbon steel plate performance (graded control) and the performance consistency of different specifications of products of the same brand are poor. As shown in the performance standards of DC03 and DC04 in Table 1, the performance of the two has obvious crossover, and the performance range of the same brand is very wide. This has brought many difficulties to the reasonable selection of materials by users, and at the same time increased the quality objections raised by enterprises due to improper selection of materials by users.

Table 1 Mechanical properties

For the above-mentioned technical problems, there are no relevant solutions in the current domestic and foreign literature and patents. It is more about the composition design and process selection of ultra-low carbon steel plates of a certain strength level, and the optimal choice of annealing process.

Contents of the invention

The first technical problem to be solved by the present invention is to provide a method for preparing ultra-low carbon steel plates with more obvious performance classification.

The technical method adopted by the present invention to solve the above-mentioned technical problems is to provide a preparation method of ultra-low carbon steel plate, which adopts steelmaking → hot rolling → cooling → coiling → acid rolling → continuous annealing → smoothing process, the ultra-low carbon The chemical composition of the steel plate is calculated by weight percentage: C: ≤0.0035%, Si: 0～0.02%, Mn: 0.11～0.15%, Ti: 0.050～0.070%, N: ≤0.0035%, P≤0.010%, S≤ 0.012%, Als: 0.020-0.050%, and the rest is Fe.

Wherein, in the above-mentioned preparation method of the ultra-low carbon steel plate, the grades of the ultra-low carbon steel plate are DC03 and DC04.

Wherein, in the above-mentioned method for preparing ultra-low carbon steel sheets, when preparing DC03 and DC04 ultra-low carbon steel sheets, the finishing temperature and coiling temperature in the hot continuous rolling process are controlled to be 910-950°C and 720-760°C, respectively.

Wherein, in the preparation method of the above-mentioned ultra-low carbon steel plate, when preparing DC03 and DC04 ultra-low carbon steel plates, the cold rolling reduction rate in the acid rolling process is controlled to 60%-85%.

Wherein, in the above-mentioned method for preparing ultra-low carbon steel plates, when preparing DC03 and DC04 ultra-low carbon steel plates, the strip speed in the continuous annealing process section of cold-rolled steel plates is 80-240 m/min.

Wherein, in the preparation method of the above-mentioned ultra-low carbon steel plate, when preparing the DC03 ultra-low carbon steel plate, the temperature of the continuous annealing soaking section of the cold-rolled steel plate is 780-820°C; when preparing the DC04 ultra-low-carbon steel plate, the continuous The temperature of the annealing soaking section is 810-850°C.

Wherein, in the preparation method of the above-mentioned ultra-low carbon steel plate, when preparing the DC03 ultra-low carbon steel plate, the flat elongation is controlled at 0.5% to 1.0%; when the DC04 ultra-low carbon steel plate is prepared, the flat elongation is controlled at 0.3% to 1.0%. 0.7%.

The second technical problem to be solved by the present invention is to provide a preparation method in which the fluctuation of the yield strength of the above-mentioned ultra-low carbon steel plate is within 20 MPa, which is realized by controlling the soaking temperature in the annealing section and the gradient of the flat elongation for different thickness specifications of the same brand .

Wherein, in the preparation method of the above-mentioned ultra-low carbon steel plate, when preparing DC03 and DC04 ultra-low carbon steel plates, the temperature gradient control of the annealing process is performed according to the following table for different thickness specifications of the strip steel after acid rolling:

Wherein, in the above-mentioned method for preparing the ultra-low carbon steel plate, the slow cooling cooling rate is 0.6-4° C./s.

Wherein, in the above-mentioned method for preparing the ultra-low carbon steel plate, the cooling rate of the rapid cooling is 30-100° C./s.

Wherein, in the preparation method of the above-mentioned ultra-low carbon steel plate, when preparing DC03 and DC04 ultra-low carbon steel plates, the different thickness specifications of the strip steel after acid rolling are controlled according to the following table:

The beneficial effects of the present invention are:

1. The method of the present invention realizes DC03 and DC04 performance classification by controlling DC03 and DC04 ultra-low carbon steel plate annealing process and leveling process classification. DC03 average yield strength, tensile strength, A80 elongation after fracture, r90 and n90 are respectively 140～160MPa, 295～305MPa, 41～43%, 2.2～2.4, 0.23～0.24, DC04 average yield strength, tensile strength, A80 elongation after fracture, r90 and n90 are 120～140MPa, 285～295MPa, 44 ~46%, 2.6~2.9, 0.25~0.26;

2. The method of the present invention realizes stable performance control of products of the same brand as DC03 and DC04 by performing annealing temperature and flat elongation gradient design on DC03 and DC04 ultra-low carbon steel plates according to thickness specifications, and the yield strength, tensile strength, and A80 after fracture of DC03 are controlled. The elongation, r90 and n90 fluctuations are 20MPa, 10MPa, 2%, 0.2, 0.01 respectively, and the yield strength, tensile strength, A80 elongation after breaking of DC04, r90 and n90 fluctuations are 20MPa, 10MPa, 2%, 0.3 respectively , 0.01;

3. The performance classification of products prepared by the method of the present invention is more obvious, the performance consistency of products of the same brand is better, and it can better meet the requirements of automatic high-speed stamping in the manufacture of auto parts, and has a good prospect for popularization and use.

Detailed ways

The technical method adopted by the present invention to solve the above-mentioned technical problems is to provide a preparation method of ultra-low carbon steel plate, which adopts steelmaking → hot rolling → cooling → coiling → acid rolling → continuous annealing → smoothing process, the ultra-low carbon The chemical composition of the steel plate is calculated by weight percentage: C: ≤0.0035%, Si: 0～0.02%, Mn: 0.11～0.15%, Ti: 0.050～0.070%, N: ≤0.0035%, P≤0.010%, S≤ 0.012%, Als: 0.020-0.050%, and the rest is Fe.

The method of the invention is particularly suitable for preparing ultra-low carbon steel plates with grades DC03 and DC04. When preparing DC03 and DC04 ultra-low carbon steel plates, the cold-rolled steel plate hot rolling process of the two brand ultra-low carbon steel plates (hot rolling process includes hot rolling → cooling → coiling) is the same, and the final rolling temperature and coiling temperature 910-950°C and 720-760°C respectively; the cold-rolling process in the pickling process of cold-rolled steel plate (pickling includes pickling and cold rolling) is consistent, and the cold-rolling reduction rate in the pickling process is controlled to 60%-85% .

When the DC03 and DC04 ultra-low carbon steel plates are prepared by the method of the present invention, the speed of the strip steel in the continuous annealing process section of the cold-rolled steel plate is 80-240 m/min.

More specifically, the hot rolling process: the tapping temperature of the slab is 1220-1240°C, and the heating time, soaking time, and total time in the furnace are 100-150 min, 50-80 min, and 150-230 min, respectively. After 5 passes of rough rolling, it is rolled into a 38-42mm intermediate billet. The intermediate billet is continuously rolled into 3.25-6.0mm by 7 stands, and the final rolling temperature is 910-950°C, and it is cooled to 720-760°C by laminar flow before forming into a coil.

Acid rolling process: the hot-rolled thin steel strip is welded at the head of the acid rolling unit to form a continuous steel strip, which is continuously rolled after straightening, pickling, alkali washing, drying, and edge trimming. Various conventional cold tandem rolling units can be used, such as 4-5 stand cold tandem rolling units, the thickness of the steel plate is reduced to the raw material thickness of the annealing unit after acid rolling, and the cold rolling reduction rate is controlled at 60% to 85%. The acid rolling step can adopt methods and techniques known to those skilled in the art.

Continuous annealing and smoothing process: the thin steel strip after acid rolling is welded at the entrance of the continuous annealing unit to form a continuous steel strip, and the continuous annealing is performed after the surface is continuously cleaned and dried. The cleaning process is a method well known to those skilled in the art. The annealing process is a continuous annealing method. The steel strip is preheated by the annealing unit, recrystallized annealed and soaked, once cooled, rapidly cooled, over-aged, and finally cooled for flattening and coiling. Key annealing process and leveling process parameters in the continuous annealing and leveling process are controlled according to the parameter requirements provided by the method of the present invention; the time for controlling the soaking stage is 55～165s, the thinner the strip steel, the faster the running speed, and the shorter the time used, The cooling rate of slow cooling is 0.6-4°C/s, the cooling rate of fast cooling is 30-100°C/s, and the time of over-aging stage is 240-720s.

In order to achieve more obvious performance classification of DC03 and DC04, when preparing DC03 ultra-low carbon steel plates, the temperature of the continuous annealing soaking section of cold-rolled steel plates is 780-820 ° C, and the flat elongation is controlled at 0.5% to 1.0%; to prepare DC04 ultra-low carbon steel plates , the temperature in the soaking section of the continuous annealing of the cold-rolled steel plate is 810-850°C, and the flat elongation is controlled to be 0.3%-0.7%.

In addition to realizing the performance classification between DC03 and DC04, it is also necessary to achieve the performance consistency of products of the same brand. Therefore, the present invention also controls the soaking temperature of the annealing section and the gradient of flattening elongation for different thickness specifications of the same brand, so that the ultra-low carbon steel plate The preparation method whose yield strength fluctuation is within 20MPa.

On the basis of the preparation method of the ultra-low carbon steel plate described above, when preparing DC03 and DC04 ultra-low carbon steel plates, further control is carried out on the same brand and different thickness specifications.

Among them, the temperature gradient control of the annealing process is carried out according to Table 2 for different thickness specifications of the strip steel after acid rolling:

Table 2 Annealing process temperature gradient

Gradient control of flat elongation for different thickness specifications of strip steel after pickling according to Table 3:

Table 3 Flat elongation gradient

The method of the present invention realizes DC03 and DC04 performance classification by controlling DC03 and DC04 ultra-low carbon steel plate annealing process and leveling process classification, DC03 average yield strength, tensile strength, elongation after A80 breaking, r90 and n90 are respectively 140～ 160MPa, 295～305MPa, 41～43%, 2.2～2.4, 0.23～0.24, DC04 average yield strength, tensile strength, A80 elongation after fracture, r90 and n90 are 120～140MPa, 285～295MPa, 44～46 respectively %, 2.6～2.9, 0.25～0.26; further, DC03 and DC04 ultra-low carbon steel plates were designed according to the thickness specification of the annealing soaking temperature and flat elongation gradient, and realized the stable control of the performance of DC03 and DC04 products of the same grade, and the yield strength of DC03 , tensile strength, A80 elongation after fracture, r90 and n90 fluctuations are 20MPa, 10MPa, 2%, 0.2, 0.01, DC03 yield strength, tensile strength, A80 elongation after fracture, r90 and n90 fluctuations are 20MPa , 10MPa, 2%, 0.3, 0.01; compared with the same level of cold-rolled ultra-low carbon steel plate produced by the conventional continuous annealing process, the product performance classification of this technology is more obvious, the performance consistency of the same brand product is better, and it is more suitable for auto parts Manufacture of full-automatic high-speed stamping requires good prospects for popularization and use.

The present invention will be further described in detail through the examples below, but the protection scope of the present invention is not limited to the scope of the examples.

Example 1

a. Steelmaking composition (mass percentage, %): C: 0.0020, Si: 0.01, Mn: 0.13, Ti: 0.062, N: 0.0018, P: 0.008, S: 0.005, Als: 0.032, and the rest is Fe.

b. Hot rolling: the slab heating time, soaking time, and total time in the furnace are 120min, 60min, and 180min respectively, and the tapping temperature is 1227°C; after 5 passes of rough rolling, it is rolled into a 39mm intermediate billet. The intermediate billet is rolled into 3.75mm by 7-stand hot continuous rolling, the final rolling temperature is 932°C, it is cooled to 745°C by laminar flow, and then coiled.

c. Pickling rolling: pickling according to the conventional process, adopting 5-stand cold continuous rolling, the cold rolling reduction rate is 81.3%, and the thickness after rolling is 0.7mm.

d. Continuous annealing: After the strip steel is subjected to conventional alkali cleaning, scrubbing, electrolytic cleaning, rinsing, and squeezed dry, it enters the continuous annealing furnace. The strip steel running speed in the furnace is 200m/min. After cooling to 668°C (slow cooling end point temperature) at ℃/s, rapidly cool to 434 (fast cooling end point temperature) at 80°C/s, then overaging at 411°C for 244s, then water quench to room temperature. After being squeezed, it enters the tempering machine. The elongation rate control mode is adopted for leveling, and the average leveling elongation rate is controlled at 0.55%. Finally, it is rolled and packed into storage.

The mechanical properties of the obtained DC03 finished products are shown in Table 4.

Example 2

The preparation method is the same as in Example 1, except that the components of molten steel obtained by converter smelting are C: 0.0032, Si: 0.01, Mn: 0.11, Ti: 0.068, N: 0.0022, P: 0.010, S: 0.006, Als: 0.035, The rest is Fe, (Wt,%). For the hot-rolled steel plate produced with the aforementioned molten steel, the slab exit temperature is 1220°C, the final rolling temperature is 927°C, the coiling temperature is 725°C, the hot-rolled thickness is 4.50mm, and the acid-rolled thickness is 1.0mm; the running speed in the strip steel furnace is 180m /min, the annealing soaking temperature is 792°C, the soaking time is 73s, the slow cooling end point is 674°C, the overaging temperature is 408°C, and the flat elongation is 0.78%.

The mechanical properties of the obtained DC03 finished products are shown in Table 4.

Example 3

The preparation method is the same as in Example 1, except that the components of molten steel obtained by converter smelting are C: 0.0017, Si: 0.02, Mn: 0.14, Ti: 0.062, N: 0.0025, P: 0.007, S: 0.004, Als: 0.041, The rest is Fe, (Wt,%). The hot-rolled steel plate produced with the aforementioned molten steel has a slab exit temperature of 1231°C, a finish rolling temperature of 936°C, a coiling temperature of 746°C, a hot-rolled thickness of 5.50mm, and an acid-rolled thickness of 1.5mm; the operating speed of the strip furnace is 120m /min, the annealing soaking temperature is 805°C, the soaking time is 110s, the end point of slow cooling is 678°C, the overaging temperature is 416°C, and the flat elongation is 0.84%.

The mechanical properties of the obtained DC03 finished products are shown in Table 4.

Example 4

The preparation method is the same as in Example 1, except that the components of molten steel obtained by converter smelting are C: 0.0032, Si: 0.01, Mn: 0.11, Ti: 0.067, N: 0.0016, P: 0.007, S: 0.004, Als: 0.043, The rest is Fe, (Wt,%). For the hot-rolled steel plate produced by using the aforementioned molten steel, the slab exit temperature is 1237°C, the final rolling temperature is 941°C, the coiling temperature is 752°C, the hot-rolled thickness is 6.0mm, and the acid-rolled thickness is 2.0mm; the operating speed in the strip steel furnace is 90m /min, the annealing soaking temperature is 814°C, the soaking time is 147s, the slow cooling end point is 680°C, the overaging temperature is 409°C, and the smooth elongation is 0.92%.

The mechanical properties of the obtained DC03 finished products are shown in Table 4.

Example 5

The preparation method is basically the same as that of Example 1, except that the acid rolling thickness is 0.7mm, the annealing soaking temperature is 823°C, and the flattening elongation is 0.38%. The mechanical properties of the obtained DC04 finished products are shown in Table 4.

Example 6

The preparation method is basically the same as that of Example 2, except that the acid rolling thickness is 1.0 mm, the annealing soaking temperature is 820° C., and the flattening elongation is 0.53%. The mechanical properties of the obtained DC04 finished products are shown in Table 4.

Example 7

The preparation method is basically the same as that of Example 3, except that the acid rolling thickness is 1.5 mm, the annealing soaking temperature is 837° C., and the flattening elongation is 0.55%. The mechanical properties of the obtained DC04 finished products are shown in Table 4.

Example 8

The preparation method is the same as that of Example 4, except that the acid rolling thickness is 2.0 mm, the annealing soaking temperature is 844° C., and the flat elongation is 0.63%. The mechanical properties of the obtained DC04 finished products are shown in Table 4.

Table 4 Embodiment 1～8 finished product performance

From Examples 1 to 8, it can be seen that the DC03 and DC04 ultra-low carbon steel products prepared by the method of the present invention have more obvious performance classification, and the performance consistency of products of the same brand is better, and can better adapt to the requirements of full-automatic high-speed stamping in the manufacture of auto parts. The outlook is good.

Claims (10)

1. The preparation method of the ultra-low carbon steel plate adopts steelmaking→hot rolling→cooling→coiling→acid rolling→continuous annealing→levelling process, characterized in that: the chemical composition of the ultra-low carbon steel plate is calculated by weight percentage: C: ≤0.0035%, Si: 0～0.02%, Mn: 0.11～0.15%, Ti: 0.050～0.070%, N: ≤0.0035%, P≤0.010%, S≤0.012%, Als: 0.020～0.050%, The rest is Fe. 2. The preparation method of the ultra-low carbon steel plate according to claim 1, characterized in that: the grades of the ultra-low carbon steel plate are DC03 and DC04. 3. The preparation method of ultra-low carbon steel plate according to claim 2, characterized in that: when preparing DC03 and DC04 ultra-low carbon steel plates, the final rolling temperature and coiling temperature in the hot continuous rolling process are controlled to be 910-950°C respectively and 720~760°C. 4. The preparation method of the ultra-low carbon steel plate according to claim 2, characterized in that: when preparing DC03 and DC04 ultra-low carbon steel plates, the cold rolling reduction in the acid rolling process is controlled to 60%-85%. 5. The method for preparing ultra-low carbon steel plates according to claim 2, characterized in that: when preparing DC03 and DC04 ultra-low carbon steel plates, the strip speed in the continuous annealing process section of cold-rolled steel plates is 80-240 m/min. 6. The preparation method of ultra-low carbon steel plate according to claim 2, characterized in that: when preparing DC03 ultra-low carbon steel plate, the temperature in the soaking section of continuous annealing of cold-rolled steel plate is 780-820°C; for preparing DC04 ultra-low carbon steel plate , the temperature in the soaking section of the continuous annealing of the cold-rolled steel plate is 810-850°C. 7. The preparation method of ultra-low carbon steel plate according to claim 2, characterized in that: when preparing DC03 ultra-low carbon steel plate, the flat elongation rate is controlled to be 0.5% to 1.0%; when preparing DC04 ultra-low carbon steel plate, the flattening rate is controlled The elongation rate is 0.3% to 0.7%. 8. The preparation method of the ultra-low carbon steel plate according to claim 6, characterized in that: when preparing DC03 and DC04 ultra-low carbon steel plates, the temperature gradient control of the annealing process is carried out according to the following table for different thickness specifications of the strip steel after acid rolling: 9. The method for preparing ultra-low carbon steel plate according to claim 8, characterized in that: the cooling rate of slow cooling is 0.6-4°C/s; the cooling rate of rapid cooling is 30-100°C/s. 10. The preparation method of the ultra-low carbon steel plate according to claim 7, characterized in that: when preparing DC03 and DC04 ultra-low carbon steel plates, the flat elongation gradient control is carried out according to the table below for different thickness specifications of the strip steel after acid rolling: