The 1.550 MPa-level low-alloy high-strength cold-rolled steel plate is characterized in that: the steel plate comprises the following chemical components in percentage by mass: 0.050% -0.090% of C, 0.010% -0.20% of Si, 1.00% -1.30% of Mn, less than or equal to 0.020% of P, less than or equal to 0.012% of S, 0.03-0.08% of Nb, 0.02-0.05% of Ti, 0.020% -0.070% of Als, and the balance of Fe and inevitable impurities.

2. The method for producing the 550MPa grade low alloy high strength cold rolled steel plate as claimed in claim 1, wherein: the method comprises the following steps: smelting to obtain molten steel with the chemical components, continuously casting the molten steel into a steel billet, and heating, roughly rolling, finely rolling, pickling, cooling, coiling, cold rolling and continuously annealing the steel billet to obtain the steel plate.

3. The production method according to claim 2, characterized in that: the heating temperature is 1220-1250 ℃, and the heating time is 200-260 min.

4. The production method according to claim 2, characterized in that: the rough rolling adopts 5 passes of rolling; further, the first pass reduction rate of rough rolling is 13-18%, and the second pass reduction rate of rough rolling is 18-20%.

5. The production method according to claim 2, characterized in that: the start rolling temperature of the finish rolling is 1150-1190 ℃, and the finish rolling temperature is 850-900 ℃.

6. The production method according to claim 2, characterized in that: the coiling temperature is 550-600 ℃.

7. The production method according to claim 2, characterized in that: the cold rolling reduction rate is 50-65%.

8. The production method according to claim 2, characterized in that: the running speed of the strip steel during continuous annealing is 80-200 m/min, the annealing soaking temperature is 800-840 ℃, the slow cooling end point temperature is 650-680 ℃, the overaging temperature is 400-430 ℃, and the finishing elongation is 1.3-1.5%.

Background

With the development of the automobile industry, the automobile holding capacity is increased, and three problems of energy consumption, environmental emission and safety are caused while convenience is brought to people for going out. A large number of experiments show that the light weight of the automobile is an important means for energy conservation and emission reduction of the automobile, and the weight of the passenger car is reduced by 10 percent, the oil can be saved by 6 to 8 percent, and the emission is reduced by 4 percent. The weight reduction of automobiles requires lightweight materials on the one hand and high-strength materials on the other hand.

The production process of the cold-rolled high-strength steel mainly comprises the following steps: the method has the advantages that firstly, the low-carbon low-alloy composition design is adopted, the process of incomplete annealing is carried out after cold rolling strengthening, the cold rolling work hardening is fully utilized, the method is suitable for products with low requirements on material plasticity, the process is simple, and the production cost is low; secondly, through C, Mn solid solution strengthening, the material strength is obviously reduced during annealing under the composition, and the method is suitable for product design with relatively low strength; thirdly, microalloy strengthening is performed, two-phase particles are formed to obtain stable refined original grains, and then a certain cold rolling annealing process is combined, the design is most common at present, but microalloy such as Nb, Ti, Cr and the like has high price and insufficient economy.

Disclosure of Invention

The invention aims to provide a 550 MPa-level low-alloy high-strength cold-rolled steel plate and a production method thereof.

The invention firstly provides a 550 MPa-level low-alloy high-strength cold-rolled steel plate, which comprises the following chemical components in percentage by mass: 0.050% -0.090% of C, 0.010% -0.20% of Si, 1.00% -1.30% of Mn, less than or equal to 0.020% of P, less than or equal to 0.012% of S, 0.03-0.08% of Nb, 0.02-0.05% of Ti, 0.020% -0.070% of Als, and the balance of Fe and inevitable impurities.

The invention also provides a production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, which comprises the following steps: smelting to obtain molten steel with the chemical components, continuously casting the molten steel into a billet, and heating, roughly rolling, finely rolling, pickling, cooling, coiling, cold rolling and continuously annealing the billet to obtain the steel plate.

In the production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, the heating temperature is 1220-1250 ℃. The heating time is 200-260 min.

In the production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, the rough rolling adopts 5-pass rolling.

Further, in the production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, the reduction rate of the first pass of rough rolling is 13-18%, and the reduction rate of the 2 nd to 5 th passes of rough rolling is 18-20%.

In the production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, the rolling temperature of finish rolling is 1150-1190 ℃, and the finishing temperature is 850-900 ℃.

In the production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, the coiling temperature is 550-600 ℃.

In the production method of the 550 MPa-grade low-alloy high-strength cold-rolled steel plate, the cold rolling reduction rate is 50-65%.

In the production method of the 550 MPa-grade low-alloy high-strength cold-rolled steel plate, the running speed of the strip steel during continuous annealing is 80-200 m/min, the annealing soaking temperature is 800-840 ℃, the slow cooling end point temperature is 650-680 ℃, the overaging temperature is 400-430 ℃, and the finishing elongation is 1.3-1.5%.

Compared with the prior art, the invention has the beneficial effects that:

the alloy components are combined with the process, and the mechanical property of the prepared finished product meets the requirements of yield strength of 550-650MPa, tensile strength of 610-750MPa and elongation of more than or equal to 16.0 percent.

Detailed Description

The invention provides a 550 MPa-level low-alloy high-strength cold-rolled steel plate which comprises the following chemical components in percentage by mass: 0.050% -0.090% of C, 0.010% -0.20% of Si, 1.00% -1.30% of Mn, less than or equal to 0.020% of P, less than or equal to 0.012% of S, 0.03-0.08% of Nb, 0.02-0.05% of Ti, 0.020% -0.070% of Als, and the balance of Fe and inevitable impurities.

The reasons for the selection of chemical compositions and ranges thereof in the present invention are as follows: the selection of the carbon content range mainly considers the matching of strength, formability and welding performance, if the carbon content is lower than 0.05 percent, the strength of the steel plate is low, more other strengthening alloy elements are required to be added to meet the requirement of high strength, and the design of low cost is not met; above 0.090%, the formability and weldability of the steel sheet are reduced, and the performance control at low strength level is not facilitated. The addition of small amounts of silicon and phosphorus provides a solid solution strengthening effect, and more importantly, purifies recrystallized ferrite, promotes pearlite transformation, and improves the anti-aging properties of the test steel. Mn is mainly in a solid solution strengthening mode to improve the strength and is combined with sulfur to form MnS, thereby preventing hot cracking caused by FeS, and the welding performance of steel is influenced due to the excessively high Mn content. S exists as a residual element and is controlled to be less than or equal to 0.012 percent. Aluminum is mainly added as a deoxidizing element, the content of the aluminum is required to be more than 0.010 percent to realize complete deoxidation, but the excessive aluminum influences the welding performance of steel and the control of casting blank inclusions, so the content of the aluminum is preferably selected to be 0.020 to 0.070 percent. The microalloy Ti is added to effectively fine grains and is combined with C, N elements to form a Ti (C, N) reinforced ferrite matrix so as to achieve the aim of high strength, and the microalloy Ti is designed to be 0.020-0.050% according to the requirement of the strength grade. The microalloy Nb is added to effectively fine grains by increasing the austenite recrystallization temperature, and is combined with C, N elements to form a Nb (C, N) reinforced ferrite matrix so as to achieve the aim of high strength, and the Nb is designed to be 0.030-0.080% according to the strength grade requirement.

The invention also provides a production method of the 550 MPa-level low-alloy high-strength cold-rolled steel plate, which comprises the following steps: smelting to obtain molten steel containing the chemical components, and continuously casting the molten steel into a continuous casting billet with the thickness of 220 +/-10 mm; heating the continuous casting slab to 1220-1250 ℃, wherein the in-furnace time is 200-260 min; carrying out rough rolling, wherein the rough rolling adopts 5-pass rolling, the first-pass reduction rate of the rough rolling is 13-18%, the 2 nd-5 th-pass reduction rate of the rough rolling is 18-20%, the total phosphorus removal is carried out, a heat preservation cover is used in the rolling process, and the thickness of a hot-rolled intermediate plate blank is 39-43 mm; the start rolling temperature of finish rolling is 1150-1190 ℃, and the finish rolling temperature range is 850-900 ℃; and after finish rolling, cooling the front section to 550-600 ℃ in a cooling mode, coiling, wherein the thickness of the hot rolled plate is 2.5-5.0 mm, after the hot rolled plate is cleaned by alkali washing, the cold rolling reduction rate is determined to be 50-65% by combining the capacity of a cold rolling mill, the running speed of the continuous annealing strip steel is controlled to be 80-200 m/min, the annealing soaking temperature is controlled to be 800-840 ℃, the slow cooling end point temperature is controlled to be 650-680 ℃, the overaging temperature is controlled to be 400-430 ℃, and the finishing elongation rate is controlled to be 1.3-1.5%.

The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.

Examples

According to the conventional molten iron desulfurization, converter smelting and LF furnace treatment, the components of molten steel are controlled as shown in the following table 1, the molten steel is continuously cast into a continuous casting slab with the thickness of 230mm, the continuous casting slab is roughly rolled to obtain an intermediate slab with the thickness of 41mm, and a hot rolled plate with the thickness of 3.25mm is obtained through finish rolling, and the hot rolled plate is obtained through acid washing, cooling, coiling, cold rolling and continuous annealing.

TABLE 1 molten steel composition

Numbering	C	Si	Mn	P	S	Nb	Ti	Als
									Example 1	0.070	0.11	1.25	0.010	0.002	0.037	0.035	0.030
Example 2	0.060	0.10	1.30	0.012	0.009	0.040	0.029	0.038
									Comparative example 1	0.06	0.07	0.66	0.014	0.007	0.016	0.028	0.035
Comparative example 2	0.05	0.07	0.62	0.012	0.006	0.014	0.025	0.032

(1) The hot rolling process parameters are shown in table 2 below:

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	1230	1160	868	580
Example 2	1226	1152	871	579
					Comparative example 1	1233	1135	935	755
Comparative example 2	1238	1136	935	746

(2) And pickling the hot rolled coil, and cold rolling the hot rolled coil into thin strip steel, wherein the cold rolling reduction rate is 53.8 percent respectively.

(3) The continuous annealing process parameters are shown in table 3:

TABLE 3 continuous annealing Main Process parameters

Numbering	Annealing temperature/. degree.C	Slow cooling end point temperature/. degree.C	Overaging temperature/. degree C	Percent of the finished elongation
					Example 1	823	680	428	1.43
Example 2	821	675	423	1.50
					Comparative example 1	828	636	400	1.40
Comparative example 2	830	638	400	1.35

(4) The mechanical properties of the steel sheets prepared by the above process are shown in table 4 below.

TABLE 4 mechanical Properties of Cold-rolled Steel sheets

Numbering	Thickness/mm	Rp0.2/MPa	Rm/MPa	Elongation A80/％
					Example 1	1.5	578	629	18.0
Example 2	1.5	583	631	17.5
					Comparative example 1	1.5	470	598	16.0
Comparative example 2	1.5	4675	596	15.0