Q1100MPa-grade ultrahigh-strength steel and preparation method thereof

Abstract

The invention discloses Q1100MPa-grade ultrahigh strength steel, which relates to the technical field of steel production and comprises the following chemical components in percentage by mass: 0.15 to 0.18 percent of C, 0.10 to 0.30 percent of Si, 0.80 to 1.10 percent of Mn, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, 0.020 to 0.040 percent of Nb, 0.030 to 0.060 percent of V, 0.008 to 0.020 percent of Ti, 0.20 to 0.50 percent of Ni, 0.30 to 0.60 percent of Cr, 0.30 to 0.60 percent of Mo, less than or equal to 0.30 percent of Cu, 0.030 to 0.070 percent of Al, 0.0008 to 0.0040 percent of Ca, 0.0008 to 0.0020 percent of B, less than or equal to 0.0040 percent of N and the balance of Fe and inevitable impurities.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel production, in particular to a Q1100MPa grade ultra-high strength steel and a preparation method thereof. BACKGROUND

[0002] The Q1100MPa grade ultra-high strength steel is mainly applied to manufacture a boom of a large-tonnage truck crane, a drag plate of a crawler crane and a telescopic arm of a truck crane, and high requirements are put forward for the strength and toughness matching, bending performance, welding performance and residual stress of the steel plate, especially the bending process of the arm cylinder of the telescopic arm of the truck crane, the bending radius and bending angle of which are more severe than those of the boom of the truck crane, and therefore higher requirements are put forward for the bending performance of the steel plate.

[0003] The ultra-high strength steel plate produced by hot continuous rolling has good grain refinement effect due to the cumulative reduction in the finishing rolling stage, and therefore the strength and toughness of the steel plate are good, and the bending requirements of the arm cylinder of the telescopic arm of the truck crane can be basically met. However, due to the limitation of the width of the hot continuous rolling steel plate, the steel plate with a thickness of ≥12mm and a width of ≥2200mm can only be produced by a plate mill, and the existing patents have less research on the bending performance of the ultra-high strength steel, and therefore a method for improving the bending performance of the Q1100MPa grade ultra-high strength steel needs to be developed to meet the demand of the truck crane for the Q1100MPa grade ultra-high strength steel plate. SUMMARY

[0004] The present application solves the technical problems of overcoming the defects of the prior art and providing a Q1100MPa grade ultra-high strength steel and a preparation method thereof.

[0005] In order to solve the above technical problems, the technical scheme of the present application is as follows: A Q1100MPa grade ultra-high strength steel, the chemical components and mass percentages of which are as follows: C: 0.15%-0.18%, Si: 0.10%-0.30%, Mn: 0.80%-1.10%, P≤0.010%, S≤0.003%, Nb: 0.020%-0.040%, V: 0.030%-0.060%, Ti: 0.008-0.020%, Ni: 0.20-0.50%, Cr: 0.30-0.60%, Mo: 0.30%-0.60%, Cu≤0.30%, Al: 0.030%-0.070%, Ca: 0.0008%-0.0040%, B: 0.0008-0.0020%, N≤0.0040%, and the balance is Fe and inevitable impurities.

[0006] The present application also provides a preparation method of the Q1100MPa grade ultra-high strength steel, which comprises the following steps in sequence: smelting, continuous casting, rolling, heat treatment and straightening. The smelting process comprises: using top and bottom combined blowing converter smelting, and carrying out deoxidization and alloying treatment during tapping, then conveying the molten steel to the LF refining furnace to carry out deoxidization, slagging and alloying, then carrying out RH vacuum treatment, and carrying out calcium treatment after the vacuum treatment is completed; The continuous casting process comprises: conveying the treated molten steel to the continuous casting machine for casting, and using electromagnetic stirring process in the continuous casting secondary cooling zone, and using dynamic soft reduction process at the end of the continuous casting, and carrying out heat preservation cover stack cooling after the billet is cut; The rolling process comprises: conveying the billet to the heating furnace for heating, and using controlled rolling after heating, and carrying out air cooling after rolling; The heat treatment process comprises: quenching + tempering heat treatment on the rolled steel plate; The straightening process comprises: at least 3 times of strong cold straightening on the heat treated steel plate.

[0007] As a preferred scheme of the preparation method of the Q1100MPa grade ultra-high strength steel, in the smelting process, the oxygen content of the tapping is controlled to be less than or equal to 500ppm, the vacuum degree of the RH vacuum treatment is controlled to be less than or equal to 3.0mbar, the vacuum holding time is greater than or equal to 25min, and the static stirring time after calcium treatment is greater than or equal to 20min.

[0008] As a preferred scheme of the preparation method of the Q1100MPa grade ultra-high strength steel, in the continuous casting process, the superheat degree of the tundish molten steel is controlled to be 5-25℃, the heat preservation cover stack cooling time is controlled to be greater than or equal to 48h, and the low-magnification center segregation of the billet is controlled to be C1.0 or less.

[0009] As a preferred scheme of the preparation method of the Q1100MPa grade ultra-high strength steel, in the rolling process, the heating temperature of the heating furnace is controlled to be 1200±20℃, and the finish rolling temperature is controlled to be 830±20℃.

[0010] As a preferred scheme of the preparation method of the Q1100MPa grade ultra-high strength steel, in the heat treatment process, the quenching temperature is controlled to be 890±10℃, the heating rate is 1.5min / mm, and the holding time is 5-15min; the tempering temperature is controlled to be 170±10℃, the heating rate is 3.8min / mm, and the holding time is 40-60min.

[0011] As a preferred scheme of the preparation method of the Q1100MPa grade ultra-high strength steel, the prepared steel plate has a thickness of less than or equal to 15mm, a width of 3000-3200mm, a yield strength of greater than or equal to 1100MPa, a tensile strength of greater than or equal to 1200MPa, an elongation of greater than or equal to 10%, and an impact value at-40℃ of greater than or equal to 50J.

[0012] As a preferred scheme of the preparation method of the Q1100MPa-grade ultra-high-strength steel, the unevenness of the prepared steel plate satisfies 3mm / m and 5mm / 2m, and satisfies a bending radius r≥3.3a, a being the thickness of the steel plate.

[0013] The beneficial effects of the present application are: The component proportion and preparation method of the Q1100MPa-grade ultra-high-strength steel can effectively improve the bending performance of the Q1100MPa-grade ultra-high-strength steel, so that the prepared Q1100MPa-grade ultra-high-strength steel satisfies the strict bending requirements of the telescopic arm cylinder of the truck-mounted crane. DETAILED DESCRIPTION

[0014] In order to make the content of the present application more easily and clearly understood, the present application will be further described in detail according to the specific embodiments.

[0015] Embodiment 1: The present embodiment provides a Q1100MPa-grade ultra-high-strength steel, and the chemical components and mass percentages are as follows: C: 0.16%, Si: 0.25%, Mn: 1.00%, P: 0.0008%, S: 0.002%, Nb: 0.020%, V: 0.045%, Ti: 0.015%, Ni: 0.40%, Cr: 0.40%, Mo: 0.50%, Cu≤0.30%, Al: 0.045%, Ca: 0.0020%, B: 0.0015%, N: 0.0040%, and the balance being Fe and inevitable impurities.

[0016] The present embodiment also provides a preparation method of the Q1100MPa-grade ultra-high-strength steel, which sequentially comprises the following processes: smelting, continuous casting, rolling, heat treatment, and straightening. Specifically, the preparation method comprises the following steps: (1) Smelting: top and bottom combined blowing converter smelting is adopted, and deoxidation and alloying treatment is performed during tapping, and the oxygen content during tapping is 500ppm; the molten steel is sent to LF for refining, and deoxidation, slagging, and alloy proportioning are performed, and RH vacuum treatment is adopted, the vacuum degree is 1.67mbar, the high vacuum holding time is 26min, calcium treatment is performed after the vacuum ends, and the static stirring time after calcium treatment is 25min; (2) Continuous casting: the molten steel after refining treatment is sent to a continuous casting machine for casting, the superheat degree of the molten steel in the tundish is 25℃, electromagnetic stirring process is used in the secondary cooling zone of the continuous casting, dynamic soft reduction is used at the end of the continuous casting, the casting blank is subjected to heat preservation cover stack cooling for 48 hours after being cut, and the C1.0 of the center segregation of the casting blank is 1.0; (3) Rolling: the blank after acceptance is sent to a heating furnace for heating, the heating temperature is 1210℃, controlled rolling is adopted, the intermediate blank thickness is 3.0h, the final rolling temperature is 835℃, and air cooling is adopted after rolling; (4) Heat treatment: The rolled steel plate is subjected to quenching and tempering heat treatment. The quenching temperature is 890℃, the heating rate is 1.5min / mm, and the holding time is 10min; the tempering temperature is 170℃, the heating rate is 3.8min / mm, and the holding time is 40min.

[0017] (5) Straightening: The heat-treated steel plate is subjected to strong cold straightening three times.

[0018] Example 2: This example provides a Q1100MPa grade ultra-high strength steel with the following chemical composition and mass percentage: C: 0.17%, Si: 0.20%, Mn: 0.80%, P: 0.0008%, S: 0.02%, Nb: 0.025%, V: 0.040%, Ti: 0.012%, Ni: 0.50%, Cr: 0.50%, Mo: 0.50%, Cu≤0.30%, Al: 0.050%, Ca: 0.0025%, B: 0.0014%, N: 0.0035%, with the balance being Fe and unavoidable impurities.

[0019] This embodiment also provides a method for preparing Q1100MPa grade ultra-high strength steel, which includes the following steps in sequence: smelting, continuous casting, rolling, heat treatment, and straightening. Specifically: (1) Smelting: Top and bottom blowing converter is used for smelting. Deoxidation and alloying treatment is carried out during the tapping process. The oxygen content of the tapped steel is 470ppm. The molten steel is sent to LF for refining, deoxidation, slag making and alloying. RH vacuum treatment is used with a vacuum degree of 1.65mbar and a high vacuum holding time of 25min. After the vacuum is completed, calcium treatment is carried out. The static stirring time after calcium treatment is 28min. (2) Continuous casting: The refined molten steel is sent to the continuous casting machine for casting. The molten steel in the tundish is superheated by 20°C. The electromagnetic stirring process is used in the second cooling zone of the continuous casting. Dynamic light pressure is used at the end of the continuous casting. After the billet is cut, it is stacked under the heat preservation cover for 48 hours. The billet has low magnification center segregation C1.0. (3) Rolling: The qualified billet is sent to the heating furnace for heating at a temperature of 1200℃. Controlled rolling is adopted, with an intermediate billet thickness of 3.0h and a final rolling temperature of 840℃. After rolling, air cooling is adopted. (4) Heat treatment: The rolled steel plate is subjected to quenching and tempering heat treatment. The quenching temperature is 900℃, the heating rate is 1.5min / mm, and the holding time is 10min; the tempering temperature is 180℃, the heating rate is 3.8min / mm, and the holding time is 40min.

[0020] (5) Straightening: The heat-treated steel plate is subjected to strong cold straightening three times.

[0021] The mechanical properties and 1m and 2m unevenness measurements of the steel plate obtained in this embodiment are shown in the table below.

[0022] Table 1. Mechanical properties and unevenness measurement data of the steel plates obtained in Examples 1 and 2.

[0023] As can be seen from Table 1, the mechanical properties of the steel plate obtained in this embodiment meet the standard requirements: yield strength ≥1100MPa, tensile strength ≥1200MPa, elongation ≥10%, and impact value at -40℃ ≥50J.

[0024] An industrial bending test was conducted on a 2000 (rolling direction) * 400mm sample of the steel plate obtained in this embodiment. The bending radius used was 50mm and the bending angle was 127.5°. No cracks appeared on the outer surface after bending.

[0025] Therefore, the component ratio and preparation method of Q1100MPa grade ultra-high strength steel provided by the technical solution of this application can effectively improve the bending performance of Q1100MPa grade ultra-high strength steel, so that the Q1100MPa grade ultra-high strength steel obtained can meet the stringent bending requirements of the boom of truck crane telescopic boom.

[0026] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A Q1100MPa grade ultra-high strength steel, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.15%~0.18%, Si: 0.10%~0.30%, Mn: 0.80%~1.10%, P≤0.010%, S≤0.003%, Nb: 0.020%~0.040%, V: 0.030%~0.060%, Ti: 0.008~0.020%, Ni: 0.20~0.50%, Cr: 0.30-0.60%, Mo: 0.30%~0.60%, Cu≤0.30%, Al: 0.030%~0.070%, Ca: 0.0008%~0.0040%, B: 0.0008-0.0020%, N≤0.0040%, with the balance being Fe and unavoidable impurities.

2. A method for preparing Q1100MPa grade ultra-high strength steel according to claim 1, characterized in that: The processes include, in sequence: smelting, continuous casting, rolling, heat treatment, and straightening; The smelting process includes: smelting in a top-and-bottom blown converter, and deoxidation and alloying treatment during the tapping process. Then, the molten steel is transported to an LF refining furnace for deoxidation, slag formation and alloy proportioning. After that, RH vacuum treatment is performed, and calcium treatment is performed after the vacuum treatment is completed. The continuous casting process includes: conveying the treated molten steel to the continuous casting machine for casting, and using electromagnetic stirring technology in the second cooling zone of continuous casting, using dynamic light reduction technology at the end of continuous casting, and stacking the billet under a heat insulation cover after it is cut. The rolling process includes: conveying the billet into a heating furnace for heating, then controlling the rolling process after heating, and finally air cooling after rolling; The heat treatment process includes: quenching and tempering heat treatment of the rolled steel plate; The straightening process includes: performing at least three high-intensity cold straightening operations on the heat-treated steel plate.

3. The method for preparing Q1100MPa grade ultra-high strength steel according to claim 2, characterized in that: In the smelting process, the oxygen content of the steel is controlled to be less than or equal to 500 ppm, the vacuum degree of the RH vacuum treatment is controlled to be less than or equal to 3.0 mbar, the vacuum holding time is greater than or equal to 25 min, and the static stirring time after calcium treatment is greater than or equal to 20 min.

4. The method for preparing Q1100MPa grade ultra-high strength steel according to claim 2, characterized in that: In the continuous casting process, the superheat of the molten steel in the tundish is controlled to be 5-25°C, the cooling time of the insulation hood is controlled to be greater than or equal to 48 hours, and the low-magnification center segregation of the billet is controlled to be C1.0 or below.

5. The method for preparing Q1100MPa grade ultra-high strength steel according to claim 2, characterized in that: In the rolling process, the heating temperature of the heating furnace is controlled at 1200±20℃, and the final rolling temperature is controlled at 830±20℃.

6. The method for preparing Q1100MPa grade ultra-high strength steel according to claim 2, characterized in that: In the heat treatment process, the quenching temperature is controlled at 890±10℃, the heating rate is 1.5min / mm, and the holding time is 5-15min; the tempering temperature is controlled at 170±10℃, the heating rate is 3.8min / mm, and the holding time is 40-60min.

7. The method for preparing Q1100MPa grade ultra-high strength steel according to claim 2, characterized in that: The resulting steel plate has a thickness of less than or equal to 15 mm, a width of 3000-3200 mm, a yield strength of greater than or equal to 1100 MPa, a tensile strength of greater than or equal to 1200 MPa, an elongation of greater than or equal to 10%, and an impact value of greater than or equal to 50 J at -40℃.

8. The method for preparing Q1100MPa grade ultra-high strength steel according to claim 2, characterized in that: The resulting steel plate has a flatness of 3mm / m and 5mm / 2m, and a bending radius r ≥ 3.3a, where a is the thickness of the steel plate.

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