High-titanium S700MC high-strength steel plate and preparation method thereof

Abstract

The invention discloses a high-titanium S700MC high-strength steel plate, which relates to the technical field of steel production and comprises the following chemical components in percentage by mass: 0.050 to 0.080 percent of C, 0.10 to 0.30 percent of Si, 1.70 to 2.00 percent of Mn, not more than 0.018 percent of P, not more than 0.003 percent of S, 0.070 to 0.090 percent of Nb, 0.010 to 0.04 percent of V, 0.09 to 0.15 percent of Ti, not more than 0.020 percent of Ni, not more than 0.30 percent of Cr, 0.10 to 0.20 percent of Mo, not more than 0.30 percent of Cu, 0.030 to 0.070 percent of Al, 0.0008 to 0.0030 percent of Ca, not more than 0.0008 percent of B, not more than 0.0040 percent of N and the balance of Fe and inevitable impurities. The mechanical properties of the prepared steel plate meet the conditions that the longitudinal tensile yield strength is larger than or equal to 700 MPa, the tensile strength ranges from 750 MPa to 950 MPa, the ductility is larger than or equal to 15%, and the longitudinal impact energy at the temperature of minus 40 DEG C is larger than or equal to 40 J.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a high-titanium S700MC high-strength steel plate and a preparation method thereof. Background Art

[0002] High-strength steel for engineering machinery is developing in the direction of reducing weight and improving strength. 700MPa high-strength steel plates are widely used in hydraulic supports, port machinery, excavators and other engineering machinery equipment. Ordinary 700MPa high-strength steel is mainly improved by tempering treatment to produce bainite tempering structure, but due to the poor toughness and plasticity of bainite, it cannot meet the high bending requirements of some parts with bending diameter d=2a (a is the thickness of the steel plate) and bending 90°. Therefore, it is urgent to develop a 700MPa high-strength steel that can meet the high bending requirements. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the disadvantages of the prior art and provide a high-titanium S700MC high-strength steel plate and a preparation method thereof.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows: A high-titanium S700MC high-strength steel plate, whose chemical composition and mass percentage are: C: 0.050%-0.080%, Si: 0.10%-0.30%, Mn: 1.70%-2.00%, P≤0.018%, S≤0.003%, Nb: 0.070%-0.090%, V: 0.010%-0.04%, Ti: 0.09-0.15%, Ni≤0.020%, Cr: ≤0.30%, Mo: 0.10%-0.20%, Cu≤0.30%, Al: 0.030%-0.070%, Ca: 0.0008%-0.0030%, B≤0.0008%, N≤0.0040%, and the balance is Fe and unavoidable impurities.

[0005] As a preferred embodiment of the high-titanium S700MC high-strength steel plate described in the present invention, its chemical composition and mass percentage are: C: 0.050%-0.070%, Si: 0.10%-0.20%, Mn: 1.80%-1.90%, P≤0.018%, S≤0.003%, Nb: 0.075%-0.085%, V: 0.015%-0.025%, Ti: 0.10-0.13%, Ni≤0.020%, Cr: ≤0.30%, Mo: 0.10%-0.20%, Cu≤0.30%, Al: 0.030%-0.060%, Ca: 0.0008%-0.0030%, B≤0.0008%, N≤0.0040%, and the balance is Fe and unavoidable impurities.

[0006] The present invention also provides a method for preparing a high-titanium S700MC high-strength steel plate, which comprises the following steps in sequence: smelting, continuous casting, rolling, slow cooling, and flattening; Wherein, the smelting process includes: The steel is smelted in a top-bottom combined-blowing converter, and deoxidation and alloying treatment is performed during the steel-making process, and the oxygen content of the steel is controlled to be ≤500ppm; The molten steel is sent to LF for refining, deoxidation, slag making and alloy proportioning; Adopt RH vacuum treatment, control vacuum degree ≤3.0mbar, high vacuum holding time ≥20min, carry out calcium treatment after vacuum ends, and stir statically for 15-20min after calcium treatment.

[0007] As a preferred solution of the preparation method of the high-titanium S700MC high-strength steel plate described in the present invention, the continuous casting process includes: sending the refined molten steel to a continuous casting machine for casting, controlling the superheat of the molten steel in the tundish to 5-30°C, using special protective slag for high-Ti steel, and using a dynamic light reduction process, and stacking and inspecting the ingot after cutting.

[0008] As a preferred embodiment of the method for preparing the high-titanium S700MC high-strength steel plate of the present invention, the rolling process comprises: Send the blanks after surface inspection to the heating furnace for heating at a temperature of 1250±20℃; Controlled rolling is adopted, and the final rolling temperature is 820-860℃; Ultra-fast cooling is used for cooling, and the red-return temperature is 550-600℃.

[0009] As a preferred solution of the method for preparing the high-titanium S700MC high-strength steel plate of the present invention, the slow cooling time of the slow cooling process is greater than 72 hours.

[0010] As a preferred solution of the method for preparing the high-titanium S700MC high-strength steel plate of the present invention, the thickness of the prepared steel plate is 6-10 mm, and the unevenness of the steel plate satisfies 3 mm / m and 6 mm / 2m.

[0011] As a preferred solution of the method for preparing the high-titanium S700MC high-strength steel plate of the present invention, the microstructure of the prepared steel plate is bainite + ferrite structure, and the grain size is ≥12 grades.

[0012] As a preferred scheme of the preparation method of the high-titanium S700MC high-strength steel plate described in the present invention, the mechanical properties of the prepared steel plate meet the following requirements: longitudinal tensile yield strength ≥700MPa, tensile strength of 750~950MPa, elongation ≥15%, -40℃ longitudinal impact energy ≥40J, and the bending diameter of the cut parts d=2a, a is the thickness of the steel plate, and it is intact when bent at 90°.

[0013] The beneficial effects of the present invention are: (1) The present invention does not adopt offline heat treatment. By means of grain refinement during rolling and precipitation strengthening of fine TiC particles during curling and stack cooling, a 700MPa grade high-strength steel plate with good strength and toughness matching is produced. Its mechanical properties meet the following requirements: longitudinal tensile yield strength ≥700MPa, tensile strength 750-950MPa, elongation ≥15%, and longitudinal impact energy ≥40J at -40°C.

[0014] (2) The steel plate produced by the present invention can meet the high bending requirements of large parts with a bending diameter of d=2a (d is the bending diameter and a is the thickness of the steel plate) and a 90° bend intact.

[0015] (3) The steel plate produced by the present invention has high flatness and small processing deformation, thus eliminating the need for a leveling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0017] Figure 1 This is a schematic structural diagram of a high-titanium S700MC high-strength steel plate prepared in Example 2; Figure 2 This is an electron probe scanning image of TiC particles in the high-titanium S700MC high-strength steel plate prepared in Example 2. DETAILED DESCRIPTION

[0018] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation modes and in combination with the accompanying drawings.

[0019] Example 1: This embodiment provides a high-titanium S700MC high-strength steel plate and a production method thereof. The steel plate has a thickness of 6 mm, and its chemical composition and mass percentage are as follows: C: 0.050%, Si: 0.15%, Mn: 1.90%, P: 0.015%, S: 0.002%, Nb: 0.075%, V: 0.025%, Ti: 0.11%, Ni: 0.01%, Cr: 0.02%, Mo: 0.15%, Cu: 0.03%, Al: 0.035%, Ca: 0.0015%, B: 0.0004%, N: 0.0035%, and the remainder is Fe and unavoidable impurities.

[0020] This embodiment also provides a method for preparing a high-titanium S700MC high-strength steel plate, comprising the following steps: S1. Smelting: top and bottom combined blowing converter is used for smelting, deoxidation and alloying treatment is carried out during the steel-making process, and the oxygen content of the steel-making is 500ppm; the molten steel is sent to LF for refining, deoxidation, slag making and alloy proportioning are carried out, 880kg of ferrotitanium is added at one time in the late stage of LF, RH vacuum treatment is adopted, the vacuum degree is 1.67mbar, and the high vacuum holding time is 22min. After the vacuum is over, calcium treatment is carried out, and static stirring is carried out for 18min; S2. Continuous casting: The molten steel after refining is sent to the continuous casting machine for casting. The superheat of the molten steel in the middle package is 30℃. Special protective slag for high-Ti steel is used. Electromagnetic stirring is not used. Dynamic light pressure is used. After the ingot is cut, it is pile-cooled and inspected. S3, rolling: the billet after surface inspection and acceptance is sent to the heating furnace for heating, the heating temperature is 1260℃, controlled rolling is adopted, the final rolling temperature is 820-850℃, ultra-fast cooling is adopted for cooling, and the red-returning temperature is 580~600℃; S4, slow cooling: After rolling, the steel coil is coiled using a down coiler, and the steel coil is surrounded by hot coils and slowly cooled for 72 hours.

[0021] S5, leveling: After slow cooling, leveling and cutting sampling are carried out. The steel plate needs to be straightened three times by a strong cold straightening machine.

[0022] Example 2: This embodiment provides a high-titanium S700MC high-strength steel plate and a production method thereof. The steel plate is 8 mm thick, and its chemical composition and mass percentage are as follows: C: 0.060%, Si: 0.13%, Mn: 1.80%, P: 0.015%, S: 0.002%, Nb: 0.080%, V: 0.020%, Ti: 0.12%, Ni: 0.02%, Cr: 0.02%, Mo: 0.18%, Cu: 0.03%, Al: 0.045%, Ca: 0.0020%, B: 0.0004%, N: 0.0032%, and the remainder is Fe and unavoidable impurities.

[0023] This embodiment also provides a method for preparing a high-titanium S700MC high-strength steel plate, comprising the following steps: S1. Smelting: top and bottom combined blowing converter is used for smelting, deoxidation and alloying treatment is carried out during the steel-making process, and the oxygen content of the steel-making is 490ppm; the molten steel is sent to LF for refining, deoxidation, slag making and alloy proportioning are carried out, 900kg of ferrotitanium is added at one time in the late stage of LF, RH vacuum treatment is adopted, the vacuum degree is 1.65mbar, and the high vacuum holding time is 25min. After the vacuum is over, calcium treatment is carried out, and static stirring is carried out for 16min; S2. Continuous casting: The molten steel after refining is sent to the continuous casting machine for casting. The superheat of the molten steel in the middle package is 25℃. Special protective slag for high-Ti steel is used. Electromagnetic stirring is not used. Dynamic light pressure is used. After the ingot is cut, it is pile-cooled and inspected. S3, rolling: the billet after surface inspection and acceptance is sent to the heating furnace for heating, the heating temperature is 1255℃, controlled rolling is adopted, the final rolling temperature is 830-860℃, ultra-fast cooling is adopted for cooling, and the red-returning temperature is 580~600℃; S4, slow cooling: After rolling, the steel coil is coiled using a down coiler, and the steel coil is surrounded by hot coils and slowly cooled for 72 hours.

[0024] S5, leveling: After slow cooling, leveling and cutting sampling are carried out. The steel plate needs to be straightened three times by a strong cold straightening machine.

[0025] Example 3: This embodiment provides a high-titanium S700MC high-strength steel plate and a production method thereof. The steel plate has a thickness of 10 mm, and its chemical composition and mass percentage are as follows: C: 0.070%, Si: 0.16%, Mn: 1.70%, P: 0.015%, S: 0.002%, Nb: 0.085%, V: 0.015%, Ti: 0.12%, Ni: 0.01%, Cr: 0.02%, Mo: 0.20%, Cu: 0.03%, Al: 0.050%, Ca: 0.0020%, B: 0.0004%, N: 0.0037%, and the remainder is Fe and unavoidable impurities.

[0026] This embodiment also provides a method for preparing a high-titanium S700MC high-strength steel plate, comprising the following steps: S1. Smelting: top and bottom combined blowing converter is used for smelting, deoxidation and alloying treatment is carried out during the steel tapping process, and the oxygen content of the steel tapping is 500ppm; the molten steel is sent to LF for refining, deoxidation, slag making and alloy proportioning are carried out, 880kg of ferrotitanium is added at one time in the late stage of LF, RH vacuum treatment is adopted, the vacuum degree is 1.68mbar, and the high vacuum holding time is 24min. After the vacuum is over, calcium treatment is carried out, and static stirring is carried out for 20min; S2. Continuous casting: The molten steel after refining is sent to the continuous casting machine for casting. The superheat of the molten steel in the middle package is 20℃. Special protective slag for high-Ti steel is used. Electromagnetic stirring is not used. Dynamic light pressure is used. After the ingot is cut, it is pile-cooled and inspected. S3, rolling: the billet after surface inspection and acceptance is sent to the heating furnace for heating, the heating temperature is 1260℃, controlled rolling is adopted, the final rolling temperature is 840-860℃, ultra-fast cooling is adopted for cooling, and the red-returning temperature is 580~600℃; S4, slow cooling: After rolling, the steel coil is coiled using a down coiler, and the steel coil is surrounded by hot coils and slowly cooled for 72 hours.

[0027] S5, leveling: After slow cooling, leveling and cutting sampling are carried out. The steel plate needs to be straightened three times by a strong cold straightening machine.

[0028] The steel plates in the examples were sampled for mechanical properties testing, wherein the longitudinal tensile properties were tested according to the room temperature tensile test method for metal materials in GB / T228-2002, and the longitudinal low temperature impact energy was tested according to the metal Charpy V-notch impact test method in GB / T 229-2007. The performance test results are shown in Table 1: The unevenness of the steel plate in the example was measured using 1m and 2m levels, and the results are also shown in Table 1.

[0029]

[0030] Table 1 It can be seen from Table 1 that the mechanical properties of the steel plate obtained in this embodiment meet the following requirements: longitudinal tensile yield strength ≥ 700 MPa, tensile strength 750-950 MPa, elongation ≥ 15%, -40°C longitudinal impact energy ≥ 40 J, and flatness 3 mm / m and 6 mm / 2 m.

[0031] The steel plate in the embodiment was sampled and corroded with 4% nitric acid alcohol solution. The microstructure was observed under a metallographic microscope. The microstructure of the steel plate was bainite + ferrite structure, and the grain size reached level 12.

[0032] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A high-titanium S700MC high-strength steel plate, characterized in that: Its chemical composition and mass percentage are: C: 0.050%~0.080%, Si: 0.10%~0.30%, Mn: 1.70%~2.00%, P≤0.018%, S≤0.003%, Nb: 0.070%~0.090%, V: 0.010%~0.04%, Ti: 0.09~0.15%, Ni≤0.020%, Cr: ≤0.30%, Mo: 0.10%~0.20%, Cu≤0.30%, Al: 0.030%~0.070%, Ca: 0.0008%~0.0030%, B≤0.0008%, N≤0.0040%, and the balance is Fe and unavoidable impurities.

2. The high-titanium S700MC high-strength steel plate according to claim 1, characterized in that: Its chemical composition and mass percentage are: C: 0.050%~0.070%, Si: 0.10%~0.20%, Mn: 1.80%~1.90%, P≤0.018%, S≤0.003%, Nb: 0.075%~0.085%, V: 0.015%~0.025%, Ti: 0.10~0.13%, Ni≤0.020%, Cr: ≤0.30%, Mo: 0.10%~0.20%, Cu≤0.30%, Al: 0.030%~0.060%, Ca: 0.0008%~0.0030%, B≤0.0008%, N≤0.0040%, and the balance is Fe and unavoidable impurities.

3. A method for preparing the high-titanium S700MC high-strength steel plate according to claim 1 or 2, characterized in that: It includes the following processes in sequence: smelting, continuous casting, rolling, slow cooling, and leveling; Wherein, the smelting process includes: The steel is smelted in a top-bottom combined-blowing converter, and deoxidation and alloying treatment is performed during the steel-making process, and the oxygen content of the steel is controlled to be ≤500ppm; The molten steel is sent to LF for refining, deoxidation, slag making and alloy proportioning; Adopt RH vacuum treatment, control vacuum degree ≤3.0mbar, high vacuum holding time ≥20min, carry out calcium treatment after vacuum ends, and stir statically for 15-20min after calcium treatment.

4. The method for preparing the high-titanium S700MC high-strength steel plate according to claim 3, characterized in that: The continuous casting process includes: sending the refined molten steel to a continuous casting machine for casting, controlling the superheat of the molten steel in the tundish to 5-30° C., using special protective slag for high-Ti steel, and using a dynamic light reduction process, and stacking and cooling the ingot after cutting and surface inspection.

5. The method for preparing the high-titanium S700MC high-strength steel plate according to claim 3, characterized in that: The rolling process comprises: Send the blanks after surface inspection to the heating furnace for heating at a temperature of 1250±20℃; Controlled rolling is adopted, and the final rolling temperature is 820-860℃; Ultra-fast cooling is used for cooling, and the red-return temperature is 550-600℃.

6. The method for preparing the high-titanium S700MC high-strength steel plate according to claim 3, characterized in that: The slow cooling time of the slow cooling step is greater than 72 hours.

7. The method for preparing the high-titanium S700MC high-strength steel plate according to claim 3, characterized in that: The thickness of the prepared steel plate is 6-10 mm, and the unevenness of the steel plate meets 3 mm / m and 6 mm / 2m.

8. The method for preparing the high-titanium S700MC high-strength steel plate according to claim 3, characterized in that: The microstructure of the steel plate is bainite + ferrite, and the grain size is ≥12 levels.

9. The method for preparing the high-titanium S700MC high-strength steel plate according to claim 3, characterized in that: The mechanical properties of the steel plate obtained meet the following requirements: longitudinal tensile yield strength ≥700MPa, tensile strength 750~950MPa, elongation ≥15%, -40℃ longitudinal impact energy ≥40J, and the bending diameter of the cut parts d=2a, a is the thickness of the steel plate, and the parts are intact when bent 90°.

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