1. A60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate is characterized by comprising the following chemical components in percentage by mass: 0.06-0.10% of C, less than or equal to 0.10% of Si, 1.40-1.70% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, less than or equal to 0.004% of N, 0.03-0.04% of Nb, less than or equal to 0.03% of Ti, 0.025-0.045% of Als, and the balance of Fe and inevitable impurities.

2. The method for producing the 60 kilogram grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate as claimed in claim 1, wherein the method comprises the working procedures of smelting, continuous casting, hot rolling, acid continuous rolling, continuous annealing and flattening.

3. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate as claimed in claim 2, wherein the continuous casting process parameters are as follows: the pulling speed is controlled to be 1.2-1.7 m/min.

4. The production method of the 60 kilogram grade low silicon easy-welding cold-rolled low alloy high strength steel plate as claimed in claim 2, characterized in that the technological parameters in the hot rolling process are as follows: the heating temperature is controlled to be 1210-1260 ℃, the final rolling temperature is controlled to be 860-890 ℃, and the steel is rapidly cooled after rolling, wherein the coiling temperature is 490-575 ℃.

5. The production method of the 60 kilogram grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate as claimed in claim 2, wherein the technological parameters of the acid continuous rolling process are as follows: and controlling the rolling reduction rate to be 55-75%.

6. The production method of the 60 kilogram grade low silicon easy-welding cold-rolled low alloy high strength steel plate as claimed in claim 2, wherein the continuous annealing process is as follows:

1) the temperature is reduced to 750 ℃ and 820 ℃, and the annealing time is 125-260 s;

2) cooling to 645-660 ℃ at a cooling speed of 1.3-3.6 ℃/s;

3) cooling to 410-425 ℃ at a cooling rate of 10-18 ℃/s;

4) the temperature is reduced to 285-300 ℃, and the annealing time is 470-950 s.

7. The production method of the 60 kilogram-level low-silicon easy-welding cold-rolled low-alloy high-strength steel plate as claimed in claim 2, wherein the technological parameters in the leveling procedure are as follows: the elongation is controlled to be 1.0-1.4%.

Background

The current automobile industry shows the trend of environmental protection and reduction, and more high-strength steel plates are required to be used due to the requirement of weight reduction. The steel plate with the tensile strength of 60 kilograms is increasingly used on automobile parts, and the steel with the strength level can effectively reduce the weight of an automobile body, improve the safety and reduce the oil consumption, and has the advantage of lower manufacturing cost compared with ultrahigh-strength steel.

The traditional low-alloy high-strength steel has higher strength because of containing higher elements such as C, Si, Mn and the like, but has poor welding defect easily when being used for welding parts with higher welding requirements because of higher carbon equivalent. CN106636937A discloses 'tensile strength 600MPa grade easy welding structural steel and a production method thereof', which comprises 0.05-0.09% of C, 0.30-0.40% of Si, 1.40-1.55% of Mn, 0.02-0.03% of Nb, 0.010-0.025% of Ti, 0.015-0.045% of Als, 0.010-0.0018% of B, and the balance of Fe and inevitable impurities, wherein the content of impurity elements is controlled to be less than or equal to 0.015%, the content of S is less than or equal to 0.007%, [ N ] is less than or equal to 0.0030%, and [ O ] is less than or equal to 0.0020%. The steel plate is added with Si (0.30-0.40%), the low-temperature toughness and the weldability of the steel plate are seriously damaged while the strength of the steel plate is improved, and particularly under the condition of large-linear-quantity welding, Si promotes the formation of M-A islands with large sizes and uneven distribution, and the toughness of a welding Heat Affected Zone (HAZ) is seriously damaged. Further, the patent only studies hot rolled steel sheets, and does not mention how to improve the weldability of cold rolled annealed steel sheets. The microstructure of the obtained hot rolled coil is a mixed structure of ferrite, pearlite and bainite. CN105200329A discloses a tensile strength 700MPa grade easy-welding low internal stress structural steel plate and a manufacturing method thereof, wherein the chemical components of the steel plate comprise 0.04-0.09% of C, 0.20-0.48% of Si, 1.40-1.70% of Mn, less than or equal to 0.30% of Cr, 0.020-0.045% of Nb, 0.012-0.020% of Ti, 0.005-0.030% of V, 0.020-0.038% of Als, 0.0012-0.0028% of B, less than 0.015% of P, less than 0.006% of S, less than or equal to 0.0060% of N, and the balance of Fe and inevitable impurities. This steel sheet is not advantageous for two points in the above patent CN106636937A, and V is an element which forms strong carbonitrides, and forms carbonitrides to prevent austenite grains from growing large and refine grains, thereby improving the strength of the steel sheet, and when it is present together with Cr, complicated carbonitrides are formed to lower the ductility and toughness of the welded joint. CN 107012392A discloses a 600MPa grade high-strength low-alloy cold-rolled strip steel and a production method thereof, wherein the chemical components of the strip steel are 0.08-0.11% of C, 0.4-0.5% of Si, 1.65-1.75% of Mn, less than or equal to 0.015% of P, less than or equal to 0.012% of S, 0.02-0.045% of Als, less than or equal to 0.005% of N, 0.02-0.03% of Ti, 0.03-0.04% of Nb and the balance of Fe. The components are wide, the stable production is not facilitated, the content of Ti and Nb noble metal alloy is high, and the production cost of the steel plate is high.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the low-silicon easy-welding cold-rolled low-alloy high-strength steel plate with the tensile strength of 60 kilograms and the production method thereof, and the obtained cold-rolled low-alloy high-strength steel plate with the tensile strength of 60 kilograms has the characteristics of simple components, high strength and excellent welding performance. Meanwhile, excessive alloy elements such as Nb and Ti are not added into the steel, so that the cost is relatively low.

In order to achieve the above object, a first technical solution proposed by the present invention is as follows:

a60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate comprises the following chemical components in percentage by mass: 0.06-0.10% of C, less than or equal to 0.10% of Si, 1.40-1.70% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, less than or equal to 0.004% of N, 0.03-0.04% of Nb, less than or equal to 0.03% of Ti, 0.025-0.045% of Als, and the balance of Fe and inevitable impurities.

The second technical scheme provided by the invention is as follows:

the production method of the low-alloy and high-strength steel plate which is easy to weld and is low in silicon and 60 kilograms comprises the working procedures of smelting, continuous casting, hot rolling, acid continuous rolling, continuous annealing and leveling.

Preferably, the continuous casting process parameters are as follows: the pulling speed is controlled to be 1.2-1.7 m/min.

Preferably, the technological parameters in the hot rolling process are as follows: the heating temperature is controlled to be 1210-1260 ℃, the final rolling temperature is controlled to be 860-890 ℃, and the steel is rapidly cooled after rolling, wherein the coiling temperature is 490-575 ℃.

Preferably, the technological parameters of the acid continuous rolling procedure are as follows: and controlling the rolling reduction rate to be 55-75%.

Preferably, the continuous annealing process is as follows:

1) the temperature is reduced to 750 ℃ and 820 ℃, and the annealing time is 125-260 s;

2) cooling to 645-660 ℃ at a cooling speed of 1.3-3.6 ℃/s;

3) cooling to 410-425 ℃ at a cooling rate of 10-18 ℃/s;

4) the temperature is reduced to 285-300 ℃, and the annealing time is 470-950 s.

Preferably, the technological parameters in the flattening process are as follows: the elongation is controlled to be 1.0-1.4%.

Aiming at the problem of high welding performance requirement of the 60 kg-grade cold-rolled low-alloy high-strength steel plate, the invention can obtain better welding performance and excellent comprehensive mechanical property under the normal working procedure condition through proper component design and process design. The ideal low-carbon equivalent component is obtained through reasonable design of carbon, silicon, manganese, phosphorus, sulfur, niobium and titanium, and the welding is easy to carry out. A lower carbon content range is selected, so that the enrichment degree of C in steel is reduced, and the tendency of banded structures is reduced; the lower Si content is selected, so that the toughness of a welding heat affected zone is improved, certain manganese and a small amount of niobium are adopted to ensure hardenability and strength, and a small amount of titanium is added to further improve the weldability. And through low-temperature coiling and low-temperature annealing, the mechanical property is ensured, the energy consumption is reduced, and finally a mixed structure of ferrite and bainite is formed.

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

in the structure of the steel plate, ferrite is uniformly distributed, a banded structure is slight, and the steel plate has small quantity of inclusions and is uniformly distributed; according to the invention, the cold-rolled low-alloy high-strength steel plate with the strength of 60 kg can be produced, and has higher strength and good uniformity of mechanical properties; meanwhile, the carbon equivalent is low, which is beneficial to welding and has good surface quality. The low-alloy high-strength steel disclosed by the invention has excellent welding performance under high strength and can be well adapted to the production requirement of automobile parts with higher spot welding requirements.

Drawings

FIG. 1 is a typical metallographic structure diagram of example 6 of the present invention.

Detailed Description

The embodiments of the present invention are further described, and these examples are for describing the technical solutions in detail, but not for limiting the technical solutions. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Examples 1 to 9

The components of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate provided by the embodiments 1 to 5 are shown in table 1:

TABLE 1 compositions of steel sheets of examples 1-9

The production method of the 60 kilogram-level low-silicon easy-welding cold-rolled low-alloy high-strength steel plate provided by the embodiments 1 to 9 of the invention comprises the following steps:

1. the production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 1 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled at 1230 ℃, the finishing temperature is controlled at 875 ℃, and the rolled steel is rapidly cooled, wherein the coiling temperature is 510 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 750 ℃, and the annealing time is 160 s; b) cooling to 650 ℃ at a cooling rate of 2.1 ℃/s; c) then cooling to 425 ℃ at a cooling speed of 14.6 ℃/s; d) then aging at 295 deg.C for 587 s.

6) Leveling: the flat elongation was 1.3%.

2. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 2 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled at 1210 ℃, the finish rolling temperature is controlled at 870 ℃, and the rolled steel is rapidly cooled, wherein the coiling temperature is 500 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 820 ℃, and the annealing time is 185 s; b) cooling to 660 ℃ at a cooling rate of 2.9 ℃/s; c) then cooling to 410 ℃ at the cooling speed of 13.9 ℃/s; d) then ageing treatment is carried out at 295 ℃ for 685 s.

6) Leveling: the flat elongation was 1.3%.

3. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 3 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled at 1220 ℃, the finishing temperature is controlled at 860 ℃, and the rolled steel is rapidly cooled, wherein the coiling temperature is 520 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 805 ℃, and the annealing time is 185 s; b) cooling to 660 ℃ at a cooling rate of 2.7 ℃/s; c) then cooling to 410 ℃ at the cooling speed of 13.9 ℃/s; d) and aging at 290 deg.C for 685 s.

6) Leveling: the flat elongation was 1.3%.

4. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 4 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled at 1230 ℃, the finishing temperature is controlled at 880 ℃, and the rolled steel is rapidly cooled, wherein the coiling temperature is 495 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 760 ℃, and the annealing time is 210 s; b) cooling to 660 ℃ at a cooling rate of 1.6 ℃/s; c) then cooling to 415 ℃ at a cooling speed of 12.1 ℃/s; d) then treated with aging treatment at 285 ℃ for 771 s.

6) Leveling: the flat elongation was 1.1%.

5. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 5 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled to be 1220 ℃, the finishing temperature is controlled to be 880 ℃, the rolled steel is rapidly cooled, and the coiling temperature is 505 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 760 ℃, and the annealing time is 260 s; b) cooling to 660 ℃ at a cooling rate of 1.3 ℃/s; c) then cooling to 415 ℃ at a cooling speed of 10 ℃/s; d) then carrying out aging treatment at 285 ℃ for 949 s.

6) Leveling: the flat elongation was 1.3%.

6. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 6 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled to be 1235 ℃, the finishing temperature is controlled to be 885 ℃, the rolled steel is rapidly cooled, and the coiling temperature is 575 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 785 ℃, and the annealing time is 140 s; b) cooling to 660 ℃ at a cooling rate of 3.0 ℃/s; c) then cooling to 420 ℃ at the cooling speed of 17.8 ℃/s; d) then aging at 300 deg.C for 514 s.

6) Leveling: the flat elongation was 1.3%.

7. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 7 comprises the following production steps and process parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled to be 1260 ℃, the finishing temperature is controlled to be 885 ℃, the rolled steel is rapidly cooled, and the coiling temperature is 550 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 820 ℃, and the annealing time is 150 s; b) cooling to 660 ℃ at a cooling rate of 3.6 ℃/s; c) then cooling to 415 ℃ at a cooling speed of 16.6 ℃/s; d) then aging at 290 ℃ for 561 s.

6) Leveling: the flat elongation was 1.1%.

8. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 8 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled to be 1235 ℃, the finishing temperature is controlled to be 885 ℃, and the rolled steel is rapidly cooled, wherein the coiling temperature is 570 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 750 ℃, and the annealing time is 130 s; b) cooling to 645 ℃ at a cooling rate of 2.8 ℃/s; c) then cooling to 420 ℃ at a cooling speed of 18 ℃/s; d) then treated with aging treatment at 290 ℃ for 474 s.

6) Leveling: the flat elongation was 1.1%.

9. The production method of the 60 kilogram-grade low-silicon easy-welding cold-rolled low-alloy high-strength steel plate in the embodiment 9 comprises the following production steps and technological parameters:

1) smelting: adding and refining in a converter, deeply removing S, controlling the S to be below 0.004 percent, and reducing MnS inclusions.

2) Continuous casting: the continuous casting speed is 1.5 m/min, which is beneficial to floating of inclusions and reduction of segregation.

3) Hot rolling: the heating temperature is controlled to 1215 ℃, the finishing temperature is controlled to 890 ℃, and the rolled steel is rapidly cooled, wherein the coiling temperature is 525 ℃.

4) Acid continuous rolling: the reduction rate was 56%.

5) Annealing: a) the annealing temperature is 750 ℃, and the annealing time is 165 s; b) cooling to 660 ℃ at a cooling rate of 1.8 ℃/s; c) then cooling to 420 ℃ at a cooling speed of 14.8 ℃/s; d) then the mixture is subjected to ageing treatment at 295 ℃ for 617 s.

6) Leveling: the flat elongation was 1.3%.

The mechanical properties of the 60 kilogram-level low-silicon easy-welding cold-rolled low-alloy high-strength steel plates prepared by the method of the invention and used in the examples 1-9 are tested, and the test results are shown in the following table 2:

TABLE 2 mechanical Properties of the Steel sheets

As can be seen from tables 1 and 2, the easy-welding cold-rolled low-alloy high-strength steel plate with the tensile strength of more than 60 kilograms can be produced by adopting the technical scheme of the invention, and the mechanical property is good; meanwhile, the invention adopts a low-carbon equivalent design and has good welding performance.

FIG. 1 shows a typical microstructure of example 6. As can be seen from the figure, the steel produced by the invention has the thickness of about 2.0mm, is ferrite + bainite, has uniform ferrite distribution, slight banded structure, small quantity of inclusions, uniform distribution and good surface quality.

According to the invention, through reasonable matching of alloy element components, the low-silicon easy-to-weld cold-rolled low-alloy high-strength steel plate with the tensile strength of 60 kilograms can be prepared, the production of high-strength vehicle body parts with certain welding performance requirements can be well met, the balance performance of excellent welding performance and high-strength steel mechanical performance is obtained, and the problem of poor welding performance of the cold-rolled low-alloy high-strength steel plate with the tensile strength of 60 kilograms is solved. Compared with the design with high Si content, the method can avoid the inclusion caused by Si and the problems of poor low-temperature toughness and weldability. The steel of the present invention is different from and superior to the prior art in various aspects such as composition design and final obtained results.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.