CN111979470A

CN111979470A - Production method of ultrahigh-strength cold-rolled martensite steel plate with good bending property

Info

Publication number: CN111979470A
Application number: CN202010777271.3A
Authority: CN
Inventors: 孙荣生; 刘仁东; 王植; 王静; 刘军友; 蔡顺达; 金晓龙; 李岩; 刘英明; 解志彪; 阮国庆
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2020-08-05
Filing date: 2020-08-05
Publication date: 2020-11-24

Abstract

The invention relates to a production method of an ultrahigh-strength cold-rolled martensite steel plate with good bending property, which comprises the following chemical components in percentage by mass: 0.21 to 0.22 percent of C, 0.3 to 0.4 percent of Si, 1.6 to 1.7 percent of Mn, 0.02 to 0.07 percent of Al, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities; the tensile strength of the steel plate is greater than 1600MPa, and the elongation is greater than 6%; the metallographic structure is a 100% tempered martensite structure. On the basis of reducing addition of basic elements such as C, Si, Mn and the like and no addition of other rare alloy elements, the invention fully utilizes the equipment capability of the existing high-strength continuous annealing unit to develop the cold-rolled martensite steel plate with more than 1600MPa grade and good bending property, and besides the strength of the cold-rolled martensite steel plate reaches the national standard requirement, the elongation of the cold-rolled martensite steel plate is higher than the national standard requirement.

Description

Production method of ultrahigh-strength cold-rolled martensite steel plate with good bending property

Technical Field

The invention relates to the technical field of cold-rolled steel sheet production, in particular to a production method of an ultrahigh-strength cold-rolled martensite steel sheet with good bending property.

Background

In recent years, driven by the demand for weight reduction of automobile bodies, the high reinforcement of automobile body structural members is more and more rapid. The cold-rolled martensite steel plate has the characteristic of high strength and limited plasticity, but is increasingly applied to the manufacturing of automobile structural parts, and mainly used for manufacturing automobile body structural parts such as bumpers, threshold reinforcements and the like in a rolling processing mode.

The market has a common characteristic for the requirements of the steel plates for the automobiles, namely, the lowest cost is pursued on the premise that the performance meets the requirements. At present, few steel enterprises can produce martensitic steel products with strength of more than 1600MPa internationally, and the mainstream technology of the martensitic steel at present is to add certain strengthening rare alloy or a large amount of alloy elements, so that the production cost is high.

Chinese invention patent with patent publication No. CN108018484B discloses 'a cold-rolled high-strength steel with tensile strength above 1500MPa and excellent formability', which comprises the following chemical elements in percentage by mass: 0.25 to 0.40 percent of C, 1.50 to 2.50 percent of Si, 2.0 to 3.0 percent of Mn, 0.03 to 0.06 percent of Al, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, less than or equal to 0.01 percent of N, 0.1 to 1.0 percent of at least one of Cr and 0.1 to 0.5 percent of Mo, and the balance of Fe and other inevitable impurities; the microstructure of the cold-rolled high-strength steel has 5 to 20% of retained austenite and 70 to 90% of martensite. Correspondingly, the invention also discloses a manufacturing method of the cold-rolled high-strength steel, which has high strength and excellent formability through reasonable component design and microstructure control.

Chinese patent application with patent publication No. CN 109321828A discloses 'a 1600 MPa-grade cold-rolled martensite steel and a production method thereof', and the steel plate comprises the following components in percentage by weight: c: 0.23% -0.28%, Si: 0.5% -1.0%, Mn: 1.8% -2.3%, Al: 0.02% -0.07%, P: less than or equal to 0.02 percent, S: less than or equal to 0.005 percent, N: less than or equal to 0.005 percent, and the balance of Fe and inevitable impurities. The production method of the steel plate comprises smelting → continuous casting → hot rolling → acid cleaning → cold rolling → continuous annealing; the steel plate has simple chemical components, does not add any rare or noble metal elements except C, Si and Mn, belongs to a low-cost economic product, can manufacture an ultrahigh-strength cold-rolled steel plate with the tensile strength of more than 1600MPa and the elongation of more than 5 percent by adopting the component design and the production method provided by the steel plate, and can be used for rolling and processing high-strength automobile body parts required by the automobile industry.

Compared with the technical scheme disclosed above, the invention relies on the extremely strong cooling capacity (on-line quenching capacity) and tempering function of the existing continuous annealing production equipment, does not add any rare or noble metal elements except C, Si and Mn, simultaneously reduces the components of C, Si and Mn, has simple chemical components, low smelting cost and simple and convenient process control, and belongs to a low-cost economic product. The produced steel plate has high strength, certain forming performance and excellent bending performance, and may be used in rolling and machining high strength automobile parts.

Disclosure of Invention

The invention provides a production method of a cold-rolled martensite steel plate with good bending property and ultrahigh strength, which develops the cold-rolled martensite steel plate with more than 1600MPa grade and good bending property by fully utilizing the equipment capability of the existing high-strength continuous annealing unit on the basis of reducing and adding basic elements such as C, Si, Mn and the like and not adding other rare alloy elements, and has the elongation higher than the national standard requirement except that the strength meets the national standard requirement.

In order to achieve the purpose, the invention adopts the following technical scheme:

the production method of the ultrahigh-strength cold-rolled martensite steel plate with good bending property comprises the following chemical components in percentage by mass: 0.21 to 0.22 percent of C, 0.3 to 0.4 percent of Si, 1.6 to 1.7 percent of Mn, 0.02 to 0.07 percent of Al, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities;

the production process of the cold-rolled martensite steel plate with high bending property and ultrahigh strength comprises the following steps: smelting, continuous casting, hot rolling, acid washing, cold rolling and continuous annealing; the method comprises the following specific steps:

(1) smelting and continuous casting: smelting molten steel according to the design components, and then continuously casting the molten steel into a plate blank;

(2) hot rolling: the heating temperature of the plate blank is 1200-1220 ℃, the heat preservation is carried out for more than 200min, the initial rolling temperature of hot rolling is 1030-1080 ℃, the final rolling temperature is 870-890 ℃, and the coiling temperature is 570-590 ℃;

(3) acid pickling and cold rolling: the hot rolled plate is acid-washed and then cold-rolled, and the cold rolling reduction rate is controlled to be between 40 and 50 percent;

(4) and (3) continuous annealing: heating at 880-890 ℃, and keeping the temperature for 100-120 s; the water quenching water temperature is 740-760 ℃; the tempering temperature is 220-260 ℃, and the tempering time is 380-400 s.

The tensile strength of the steel plate is greater than 1600MPa, and the elongation is greater than 6%; the metallographic structure is a 100% tempered martensite structure.

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

1) by adopting the component design and the production method provided by the invention, the martensite ultrahigh-strength cold-rolled steel plate with the tensile strength of more than 1600MPa, the elongation of more than 6 percent and good bending property can be produced, and the strength and plasticity standards of the martensite ultrahigh-strength cold-rolled steel plate exceed the requirements of the current national standard;

2) the steel plate has simple chemical components, does not add any rare or noble metal elements except C, Si and Mn, has low smelting cost and simple and convenient process control, and belongs to a low-cost economic product;

3) the produced steel plate not only has high strength, but also has certain forming performance and good bending performance, and can be applied to rolling and processing high-strength automobile body parts required by the automobile industry.

Drawings

FIG. 1 is a metallographic structure photograph of an ultra-high strength cold-rolled martensitic steel sheet having good bending properties according to the present invention.

Detailed Description

The invention relates to a production method of an ultrahigh-strength cold-rolled martensite steel plate with good bending property, which comprises the following chemical components in percentage by mass: 0.21 to 0.22 percent of C, 0.3 to 0.4 percent of Si, 1.6 to 1.7 percent of Mn, 0.02 to 0.07 percent of Al, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities;

The design principle of the chemical components of the ultrahigh-strength cold-rolled martensite steel plate with good bending property is as follows:

c: c is one of the most effective strengthening elements in steel, plays a role in improving the hardness of martensite in the invention, has obvious influence on the strength of the steel plate, and the strength of the steel plate is obviously improved along with the improvement of the content of C. The carbon content is too low, the hardness of the martensite is reduced, and the strength cannot meet the requirement. If the carbon content is too high, the plasticity of the steel sheet is reduced, and the formability and weldability are lowered. Therefore, the invention requires that the content of C is between 0.21 and 0.22 percent.

Si: si is a non-carbide forming element, has the functions of inhibiting carbide precipitation, delaying the transformation of carbide to cementite and preventing carbide from coarsening, and is favorable for keeping the hardness of martensite in the tempering process. Si is easy to enrich and form an oxide film on the surface of the steel plate, and the surface quality is reduced due to the excessively high content of Si, and meanwhile, the plasticity and the welding performance are influenced. Therefore, the Si content in the invention is between 0.3% and 0.4%.

Mn: is one of effective solid solution strengthening elements, can effectively improve the hardenability of products and can promote the formation of martensite; the Mn content in the steel is too low, the martensite formation is insufficient, and the strength is reduced; if the Mn content is too high, serious component segregation occurs to form a band-shaped structure, which is disadvantageous in uniformity of the structure. Therefore, the Mn content is controlled to be between 1.6 and 1.7 percent in the invention.

Al: al plays a role in deoxidizing and refining grains in steel, and the content of Al is too high to be beneficial to continuous casting, so the Al content is required to be between 0.02 and 0.07 percent.

P, S, N: p, S is a residual element, P is easy to cause steel plate center segregation, seriously damages the impact toughness of steel, has secondary processing brittleness and is not beneficial to the hot processing and weldability of the steel plate; s is easy to form non-metallic inclusions with Mn, so that the cold bending and hole expansion performance of the steel plate are reduced, and the cold bending and hole expansion performance and the hole expansion performance of the steel plate are controlled to be lower as much as possible; n is interstitial atom, so that a yield platform is easy to appear in the stretching process, and the forming performance is influenced. Therefore, the invention controls P to be less than or equal to 0.02 percent, S to be less than or equal to 0.005 percent and N to be less than or equal to 0.005 percent.

Fig. 1 is a photograph of a metallographic structure of the ultra-high strength cold-rolled martensitic steel sheet having good bending properties according to the present invention, and it can be seen from fig. 1 that the metallographic structure thereof is a typical martensitic structure and the martensitic structure content in the steel is 100%.

The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation processes are given, but the scope of the invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[ examples ] A method for producing a compound

In the embodiment, the chemical components of the ultrahigh strength cold-rolled martensitic steel sheet with good bending property are shown in table 1:

TABLE 1 chemical composition (wt%)

Examples	C	Si	Mn	P	S	Al	N	Fe
									1	0.215	0.35	1.63	0.013	0.0026	0.04	0.0036	Balance of
2	0.216	0.35	1.64	0.018	0.0028	0.05	0.0035	Balance of
									3	0.218	0.36	1.66	0.016	0.0026	0.04	0.0042	Balance of
4	0.217	0.34	1.66	0.016	0.0020	0.03	0.0026	Balance of
									5	0.216	0.38	1.67	0.019	0.0028	0.05	0.0032	Balance of
6	0.216	0.37	1.68	0.011	0.0024	0.04	0.0036	Balance of

In this example, the rolling process parameters are shown in table 2:

TABLE 2 Rolling Process parameters

In this embodiment, the continuous annealing process parameters are shown in table 3:

TABLE 3 continuous annealing Process parameters

In this example, the mechanical properties of the product steel sheet are shown in table 4:

TABLE 4 mechanical Properties of the Steel sheets

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. The production method of the ultrahigh-strength cold-rolled martensite steel plate with good bending property is characterized in that the steel plate comprises the following chemical components in percentage by mass: 0.21 to 0.22 percent of C, 0.3 to 0.4 percent of Si, 1.6 to 1.7 percent of Mn, 0.02 to 0.07 percent of Al, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable impurities;

2. The method for producing the ultra-high strength cold-rolled martensitic steel sheet with good bending properties as claimed in claim 1, wherein the steel sheet has a tensile strength of more than 1600MPa and an elongation of more than 6%; the metallographic structure is a 100% tempered martensite structure.