Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a preparation method of a low delta r value micro-carbon steel cold-rolled steel plate, which comprises the following steps:
(1) smelting: smelting the micro-carbon steel into a casting blank according to chemical components of the micro-carbon steel; the chemical components of the micro-carbon steel comprise the following components in percentage by weight: c: less than or equal to 0.03%, Si: less than or equal to 0.02 percent, Mn: 0.10-0.30%, P: 0.005-0.015%, S: 0.005-0.015%, Als: 0.020-0.070%, and the balance of Fe and inevitable impurities;
(2) a hot rolling procedure: heating a casting blank, removing phosphorus, roughly rolling, finely rolling, cooling and coiling to obtain a hot-rolled coil; wherein the start rolling temperature of finish rolling is 900-930 ℃, the finish rolling temperature is 740-760 ℃, and the coiling temperature is 560-600 ℃;
(3) acid rolling process: pickling the hot rolled coil and then cold rolling the pickled hot rolled coil into thin strip steel;
(4) and (3) annealing: continuously annealing the thin strip steel to obtain a micro-carbon steel cold-rolled steel plate; wherein the temperatures of the strip steel at the slow cooling end point, the fast cooling end point and the overaging end point of the continuous annealing furnace are respectively controlled at 670-700 ℃, 410-430 ℃ and 380-410 ℃.
Wherein, in the hot rolling procedure in the step (2), the steel is heated to 1110-1150 ℃, the furnace time is 200-260 min, and then 5-pass rough rolling is adopted.
Wherein, in the acid rolling procedure in the step (3), the cold rolling reduction is 75-85%.
Wherein in the annealing procedure in the step (4), the speed of the unit is 220-320 m/min, the temperature of the heating section is 670-730 ℃, and the temperature of the soaking section is 770-800 ℃.
Wherein, in the annealing procedure in the step (4), the finishing elongation is controlled to be 0.7-1.0%.
Has the advantages that: the invention aims at the micro-carbon steel cold-rolled steel plate, strictly controls the technological parameters of hot rolling, cold rolling and annealing, and prepares the micro-carbon steel cold-rolled steel plate with good stamping forming performance, wherein the delta r of the micro-carbon steel cold-rolled steel plate is lower than 0.10, and Rp0.2150-180 MPa, tensile strength 280-350 MPa, elongation rate not less than 42.0%, r90 not less than 2.0, n90 not less than 0.21 and r not less than 1.6.
Detailed Description
The invention provides a preparation method of a low delta r value micro-carbon steel cold-rolled steel plate, which comprises the following steps:
(1) smelting: smelting the micro-carbon steel into a casting blank according to chemical components of the micro-carbon steel; the thickness of the casting blank is 200 mm;
(2) a hot rolling procedure: heating the casting blank to 1110-1150 ℃, keeping the temperature in the furnace for 200-260 min, then carrying out rough rolling, wherein the rough rolling adopts 5-pass rolling, the total phosphorus removal of the whole length is realized, a heat preservation cover is used in the rolling process, and the thickness of the intermediate plate blank after the rough rolling is 39-43 mm; carrying out finish rolling after rough rolling, wherein the start rolling temperature of the finish rolling is 900-930 ℃, and the finish rolling temperature is 740-760 ℃; after finish rolling, naturally cooling to 560-600 ℃ for coiling to obtain a steel plate with the thickness of 3.5 mm;
(3) acid rolling process: pickling the hot rolled coil, and then cold rolling the pickled hot rolled coil into thin strip steel, wherein the cold rolling reduction rate is 75-85%;
(4) and (3) annealing: annealing the cold-rolled coil in a continuous annealing furnace, wherein the speed of a unit is 220-320 m/min, the temperature of a heating section is 670-730 ℃, and the temperature of a soaking section is 770-800 ℃; the temperatures of the strip steel at the slow cooling end point, the fast cooling end point and the overaging end point of the continuous annealing furnace are respectively controlled at 670-700 ℃, 410-430 ℃ and 380-410 ℃; and finally, cooling the strip steel to room temperature through a liquid tank, and performing finishing, wherein the elongation is controlled to be 0.7-1.0%.
The value Δ r represents the change in the anisotropy coefficient r with direction in the sheet surface, which results in a difference in sidewall height (called a ledge) when the cylindrical cup is press formed. The magnitude of the value Δ r determines the extent of formation of the upper lug of the cup-shaped drawing part.
The Δ r value is defined as: Δ r ═ r0-2r45+r90) 2; in the formula, subscripts 0, 45, and 90 indicate angles between the orientations of the uniaxial tensile specimens and the sheet rolling direction.
The larger the Δ r value, the more severe the anisotropy in the sheet surface, which is manifested by the uneven edges of the drawn piece forming lugs and the uneven wall thickness aggravating the quality of the formed piece. Δ r > 0, the draw piece lugs are in the 0 ° and 90 ° directions; Δ r < 0, and the drawing piece lug is in the 45 ° direction.
The plate material has an important effect on the rectangular drawing piece relative to the direction of anisotropy, and the direction with a large r value is preferably pointed to the four corners of the rectangle, and the four corners are formed by requiring the real drawing performance with the large r value. The maximum r value of most low-carbon aluminum killed steel cold-rolled steel sheets is perpendicular to the rolling direction, so that a large amount of waste materials can be caused when the rectangular drawing part blank is placed in the four-angle mode in the rolling direction. The micro-carbon steel has the characteristics of low strength and high elongation, and the material flow in all directions is uniform and the anisotropy is good during stamping. Therefore, the invention selects the micro-carbon steel for smelting, and the chemical components of the micro-carbon steel comprise the following components in percentage by weight: c: less than or equal to 0.03%, Si: less than or equal to 0.02 percent, Mn: 0.10-0.30%, P: 0.005-0.015%, S: 0.005-0.015%, Als: 0.020-0.070%, and the balance of Fe and inevitable impurities.
In the hot rolling procedure, the rough rolling aims at carrying out austenite deformation at low temperature, so that a casting blank is heated to 1110-1150 ℃ for 200-260 min in a furnace, then rough rolling is carried out, 5-pass rolling is adopted in the rough rolling, phosphorus is removed in the whole length, and a heat preservation cover is used in the rolling process.
Since the micro carbon steel has a different austenite recrystallization temperature and a different transformation temperature from other steels, such as IF steel, the hot rolling process is different for the purpose of rolling in the austenite region.
Because the influence of hot rolling on the texture is obvious, and more {111} textures are generated, which is beneficial to reducing the delta r value, the invention controls the initial rolling temperature of finish rolling to be 900-930 ℃, the finishing rolling temperature to be 740-760 ℃ and the coiling temperature to be 560-600 ℃ in order to obtain the micro-carbon steel cold-rolled steel plate with a low delta r value.
The speed of the unit in the annealing procedure is set according to the equipment capability of the unit and the complete recrystallization condition of the strip steel, the speed of the unit is low, and crystal grains are easy to grow excessively; the speed of the unit is high, and incomplete recrystallization is easy to occur, so that the speed of the unit is controlled to be 220-320 m/min.
The heating temperature in the annealing procedure is set according to the soaking temperature and the self temperature in the furnace, if the temperature is too low, the temperature in the furnace is reduced, and the realization is difficult; the temperature is too high, which directly influences the requirement of the subsequent soaking temperature, so the temperature of the heating section is 670-730 ℃.
The soaking temperature in the annealing procedure is determined according to the recrystallization temperature range of the strip steel, the temperature is too low, the tissue of the strip steel is not recrystallized, and the crack is easy to occur in the stamping process; the temperature is too high, the grains continue to grow excessively after recrystallization is finished, and orange peel cracks can appear in the stamping process, so that the temperature of the soaking section is controlled to be 770-800 ℃.
The slow cooling temperature in the annealing procedure of the invention is made according to the gamma/alpha phase transformation, the {111} texture is developed, the content of the solid solution carbon is increased, if the temperature is too high, the development is not complete, and if the temperature is too low, the quick cooling temperature is influenced. The fast cooling end point temperature is determined by considering the overfull of the solid solution carbon, if the temperature is too high, the slow cooling influence is insufficient, and if the temperature is too low, the subsequent overaging temperature is influenced. The overaging temperature is determined by the precipitation effect of solid solution carbon, the temperature is too high, the solid solution carbon cannot be fully precipitated, the temperature is too low, and the product quality and the production rhythm are affected, so that the temperatures of the slow cooling end point, the fast cooling end point and the overaging finished strip steel of the continuous annealing furnace are controlled to be 670-700 ℃, 410-430 ℃ and 380-410 ℃ respectively in comprehensive consideration.
The finishing elongation is set according to the elimination of a yield platform and the surface quality, the finishing elongation is too low, the elimination of the yield platform is incomplete, and yield transverse striations can occur when a user uses the finishing elongation; the finishing elongation is too high, the yield strength is improved, and the use performance of users is influenced. Therefore, the elongation at the finish is controlled to be 0.7 to 1.0%.
Examples
The following examples and comparative examples were all smelted into casting blanks according to the chemical compositions in table 1; the thickness of the casting blank is 200 mm;
heating and rough rolling the casting blank, wherein the furnace time is 240min, 5-pass rolling is adopted for rough rolling, phosphorus is removed from the whole length, a heat preservation cover is used in the rolling process, and the thickness of the intermediate plate blank after rough rolling is 42.0 mm; then obtaining a hot rolled coil after finish rolling, cooling and coiling;
pickling the hot rolled coil, and cold rolling the hot rolled coil into thin strip steel, wherein the cold rolling reduction rates are respectively 80.0 percent;
and finally, obtaining the micro-carbon steel cold-rolled steel plate through an annealing process. Wherein the speed of the unit is 243m/min, the temperature of the heating section is 728 ℃, and the temperature of the over-aged strip steel is 400 ℃; the annealing temperature refers to the soaking section temperature.
Specific process parameters of the hot rolling and annealing processes are shown in tables 2 and 3, and the mechanical properties of the obtained cold-rolled steel sheet are shown in table 4.
TABLE 1 chemical composition of micro-carbon steel cold-rolled steel sheet
Numbering
|
C
|
Si
|
Mn
|
P
|
S
|
Als
|
Example 1
|
0.025
|
0.005
|
0.19
|
0.009
|
0.010
|
0.036
|
Example 2
|
0.027
|
0.006
|
0.21
|
0.010
|
0.009
|
0.037
|
Comparative example 1
|
0.045
|
0.01
|
0.23
|
0.013
|
0.011
|
0.043
|
Comparative example 2
|
0.039
|
0.01
|
0.22
|
0.014
|
0.012
|
0.042 |
TABLE 2 Hot Rolling Main Process parameters
Numbering
|
Heating temperature/. degree.C
|
Finish rolling temperature/. degree.C
|
Final Rolling temperature/. degree.C
|
Coiling temperature/. degree.C
|
Example 1
|
1130
|
916
|
743
|
577
|
Example 2
|
1125
|
918
|
750
|
583
|
Comparative example 1
|
1230
|
1031
|
930
|
746
|
Comparative example 2
|
1235
|
1030
|
931
|
740 |
TABLE 3 continuous annealing Main Process parameters
Numbering
|
Annealing temperature/. degree.C
|
Slow cooling end point/. degree.C
|
Fast Cooling end Point/. deg.C
|
Percent of the finished elongation
|
Example 1
|
800
|
678
|
421
|
0.79
|
Example 2
|
798
|
679
|
423
|
0.78
|
Comparative example 1
|
820
|
675
|
436
|
0.88
|
Comparative example 2
|
821
|
675
|
435
|
0.89 |
TABLE 4 mechanical Properties of Cold-rolled Steel sheets