CN112501516A

CN112501516A - Production method of 1080 MPa-grade high-strength high-plasticity hot rolled steel

Info

Publication number: CN112501516A
Application number: CN202011370638.6A
Authority: CN
Inventors: 陈宇; 王中辉; 赵景全; 王大伟; 李晓冬
Original assignee: Rizhao Steel Holding Group Co Ltd
Current assignee: Rizhao Steel Holding Group Co Ltd
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2021-03-16

Abstract

The invention discloses 1080 MPa-grade high-strength high-plasticity hot rolled steel and a production method thereof, belonging to the field of hot rolled high-strength steel, wherein the chemical components in percentage by weight are as follows: 0.13 to 0.23%, Si: 1.2-2.0%, Mn: 1.2-2.0%, Al: 1.2-1.7%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Re: 0.002-0.006%, Nb: 0.02 to 0.07%, Ti: 0.02-0.07%, Cr: 0.2-0.6%, and the balance of Fe and inevitable impurities. Compared with the prior art, the invention has the characteristics of high strength and high plasticity, and is beneficial to high-strength thinning and plastic forming of parts.

Description

Production method of 1080 MPa-grade high-strength high-plasticity hot rolled steel

Technical Field

The invention relates to the field of hot-rolled high-strength steel, in particular to a high-strength high-plasticity hot-rolled steel plate with high tensile strength of 1080MPa and a production method of a steel strip.

Background

In recent years, higher requirements are put forward for the comprehensive properties of the hot rolled steel plate, such as strength, plasticity, surface quality and the like, in the industries of vehicles, machinery, buildings, electric power, highways and the like, so that the aims of high strength and thinning, energy conservation and emission reduction and cost reduction are fulfilled.

Generally, hot-rolled high-strength steel with tensile strength of more than 1000MPa has obviously reduced plasticity with increasing strength, and cannot meet the requirements of high-strength thinning and plastic processing.

Disclosure of Invention

The invention aims at overcoming the defects of the prior art and provides a production method of high-strength high-plasticity hot rolled steel with a tensile strength of 1080MPa level, which is used for promoting light weight, high strength and thinning of parts in the fields of vehicles, machinery, buildings, electric power, roads and the like.

The technical scheme for solving the technical problem is as follows: a1080 MPa level high strength high plasticity hot rolled steel which characterized in that: the chemical components by weight percentage are as follows: 0.13 to 0.23%, Si: 1.2-2.0%, Mn: 1.2-2.0%, Al: 1.2-1.7%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Re: 0.002-0.006%, Nb: 0.02 to 0.07%, Ti: 0.02-0.07%, Cr: 0.2-0.6%, and the balance of Fe and inevitable impurities.

The Nb + Ti is less than or equal to 0.12 percent.

The Al/Re ratio is 280-550, and the P/Re ratio is 2-4.5.

Compared with the prior art, the invention starts from the principle of structure phase transformation strengthening design, adopts ultrahigh-strength chemical component design, and obtains ferrite, bainite, retained austenite and fine-grain strengthening structures which are beneficial to strength increase and plasticity improvement through an ultrafast cooling and lubrication rolling process. The retained austenite in the steel is transformed into martensite under the action of external force, so that the strength can be obviously improved; the residual austenite absorbs external stress, so that crack initiation in steel can be relieved, and good plasticity is obtained; the lubricating rolling process can effectively reduce rolling load and is beneficial to thin rolling and plate shape control. Meanwhile, the ultra-fast cold fine grain strengthening is adopted, so that the cost can be reduced, the strength can be improved, and the plasticity can be improved. The product has the tensile strength of more than 1080MPa and the elongation of more than 15 percent, has the characteristics of high strength and high plasticity, is beneficial to high-strength thinning and plastic forming of parts, and has wide application range and large market potential.

Detailed Description

The present invention will be further described with reference to the following embodiments.

The invention is used for producing a high-strength high-plasticity hot-rolled strip steel with a tensile strength of 1080MPa grade, and the strip steel comprises the following chemical components in percentage by weight: 0.13 to 0.23%, Si: 1.2-2.0%, Mn: 1.2-2.0%, Al: 1.2-1.7%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Re: 0.002-0.006%, Nb: 0.02 to 0.07%, Ti: 0.02-0.07%, Cr: 0.2-0.6%, and the balance of Fe and inevitable impurities.

The principle of the elements and the content is as follows:

c: the strength can be obviously improved, and the gap solid solution strengthening effect is achieved; the stability of austenite can be increased to obtain retained austenite. However, the C content should not be too high to ensure formability and weldability. The C content of the invention is not more than 0.23%.

Si: the strength can be improved through solid solution strengthening, the segregation of manganese and phosphorus can be inhibited, the carbon content in austenite can be increased, the residual austenite is favorably obtained, but the plasticity of the steel is influenced by too high Si content. However, in the present invention, the silicon content is 1.2 to 2.0%.

Mn: strength can be improved by solid solution strengthening; the phase transformation temperature of the steel can be reduced, and the crystal grains can be refined; and the stability of austenite can be increased, which is beneficial to obtaining residual austenite. However, too high Mn content increases the cost and also increases the band structure in the steel. The Mn content of the invention is 1.2-2.0%.

P: segregation is easily formed in steel, high-temperature cracks are easily generated, low-temperature crack sensitivity is easily increased, and plasticity of the material is reduced. The P content of the invention is below 0.015 percent.

S: sulfide inclusions are generated in the steel, and the mechanical properties of the steel are seriously influenced. The present invention requires that the S content is 0.005% or less.

Re: in steel, compounds with a high melting point are formed with low-melting harmful impurity elements such as phosphorus, and segregation of these impurities in grain boundaries can be suppressed, thereby improving the plasticity of the material. The Re content of the invention is 0.002-0.006%.

Al: the aluminum alloy is combined with N atoms in steel to form AlN, so that the aluminum alloy has a fine grain strengthening effect; meanwhile, retained austenite can be formed, so that the alloy has a phase transformation strengthening effect and improves plasticity. In the prior art, the Al content is generally controlled within 1 percent, because the graphitization of the steel is promoted when the adding amount of the aluminum in the low-carbon steel is too much, the carbon dissolution concentration in an alloy phase is reduced, and the strength is influenced. And coarsening the crystal grains of the steel, deteriorating the mechanical properties of the steel, and the cleavage of the crystal is very weak, affecting the hot workability, weldability, and machinability of the steel. Re is added into the austenite grain boundary alloy, so that a compound with a melting point of about 1800 ℃ can be formed with aluminum, the compound is mainly positioned in austenite grains, the number of aluminum-phosphorus eutectic crystals on the austenite grain boundary can be reduced, the harmful effect of Al can be reduced, and the mechanical property of steel can be improved. Therefore, the Al content of the invention can be increased to 1.1-1.8%. The Al/Re ratio is ensured to be 280-550, the P/Re ratio is ensured to be 2-4.5, and the negative effect cannot be inhibited by antagonism when the P/Re ratio is beyond the range.

Nb, Ti: the microalloying elements have obvious precipitation strengthening effect. The Nb + Ti content is less than or equal to 0.12 percent.

Cr: the strengthening element has obvious solid solution strengthening effect, and the Cr content of the invention is 0.2-0.6%.

The production method of the high-strength high-plasticity hot rolled strip steel with the tensile strength of 1080MPa level comprises the following steps: the method comprises the following steps of converter smelting, LF refining, slab continuous casting, slab heating, high-pressure water descaling, lubrication rolling, controlled cooling and low-temperature coiling, and comprises the following specific process steps:

(1) smelting:

molten iron → converter smelting → LF refining → continuous casting → plate blank;

(2) a heating process:

and (3) charging the plate blank into a furnace by adopting a cold blank, wherein the heating temperature is 1130-1290 ℃, and the heating time is 170-220 min. The cold blank charging can increase the amount of retained austenite, and the retained austenite can be transformed into martensite under the subsequent action of compressive stress and tensile stress.

In the optimization scheme, a three-section heating and one-section soaking mode is adopted, wherein the three-section heating temperatures are respectively as follows: 830 ℃ 1060 ℃, 1110 ℃ 1250 ℃, 1220 ℃ 1290 ℃ and soaking temperature 1130-1290 ℃.

(3) The rolling process comprises the following steps:

the rough rolling is 5-pass reversible rolling, and the thickness of the intermediate blank is 32-40 mm; and (3) descaling with high-pressure water before rough rolling, wherein the pressure is 30 Pa.

The finish rolling is 7-pass continuous rolling, the finish rolling temperature is 800-840 ℃, and lubrication rolling is adopted between frames of an F2-F7 finish rolling machine: in order to avoid the difficulty of natural biting during the rolling of the strip steel caused by the lubricating liquid, in 7 frame rolling mills, for high-strength steel with the grade of 1080MPa, the flow of the lubricating liquid fed into the first frame is 10 percent of the maximum flow, and the flow of the lubricating liquid fed into other frames is 70 to 80 percent. The saponification value of the rolling oil can be 45 (mgKOH. g)^-1)。

(4) And (3) a cooling process:

adopting full-section ultra-fast cooling, wherein the cooling rate is more than or equal to 53 ℃/s;

(5) and (3) a coiling process:

and (3) adopting low-temperature coiling, wherein the coiling temperature is 350-430 ℃.

To better compare the formulations of the present application with the prior art, comparative tests were performed.

The chemical composition (wt%) of the steels in the specific examples and comparative examples is shown in the following table:

grouping	C	Si	Mn	P	S	Al	Re	Nb	Ti	Cr
											Example 1	0.210	1.700	1.500	0.009	0.003	1.100	0.002	0.022	0.043	0.280
Example 2	0.230	1.200	1.700	0.013	0.005	1.210	0.004	0.045	0.070	0.400
											Example 3	0.160	2.000	2.000	0.012	0.004	1.690	0.006	0.055	0.020	0.520
Example 4	0.130	1.400	1.200	0.011	0.003	1.800	0.005	0.070	0.050	0.600
											Comparative example 1	0.210	1.500	1.700	0.014	0.004	1.800	0.002	0.058	0.053	0.049
Comparative example 2	0.170	1.700	1.800	0.012	0.005	1.200	-	0.049	0.052	0.037

The manufacturing process parameters of the steels in the various examples and comparative examples of the invention are shown in the following table:

the tensile properties of the steels in the examples and comparative examples of the present invention are shown in the following table (the product performance is tested by the national standard of "Metal Material tensile test method at Room temperature GB/T228"):

as can be seen from the above table, the low-carbon hot-rolled sheet strips produced by the components and the process in the examples 1 to 4 have excellent mechanical properties and surface quality (yield strength Rel: 915-930 MPa, tensile strength Rm: 1095-1110 MPa, and elongation after fracture A16-16.5%). The production process is less, the common cold rolling and annealing process is saved, and the energy consumption and the cost are low.

While the component of comparative example 1 has no control of Al/Re ratio despite the addition of Re, and the component of comparative example 2 has no addition of Re, although the two groups have the same controlled rolling and cooling at the later stage, the corresponding negative effects caused by high Al cannot be inhibited in an antagonistic manner, the crystal grains of the steel are coarsened, the mechanical properties are deteriorated, the elongation after fracture is lower than that of each example group, and the wear resistance is poor.

It should be noted that while the invention has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various obvious changes can be made therein without departing from the spirit and scope of the invention.

Claims

1. A1080 MPa level high strength high plasticity hot rolled steel which characterized in that: the chemical components by weight percentage are as follows: 0.13 to 0.23%, Si: 1.2-2.0%, Mn: 1.2-2.0%, Al: 1.2-1.7%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Re: 0.002-0.006%, Nb: 0.02 to 0.07%, Ti: 0.02-0.07%, Cr: 0.2-0.6%, and the balance of Fe and inevitable impurities.

2. The hot-rolled steel with high strength and high plasticity of a level of 1080MPa according to claim 1, characterized in that: the Nb + Ti content is less than or equal to 0.12 percent.

3. The hot-rolled steel with high strength and high plasticity of a level of 1080MPa according to claim 1, characterized in that: the ratio of Al to Re is 280-550, and the ratio of P to Re is 2-4.5.