A quenched and tempered high-strength steel Q1500 and its production method

Abstract

This invention discloses a quenched and tempered high-strength steel Q1500 and its production method, belonging to the field of steel rolling technology. The quenched and tempered high-strength steel Q1500, by weight percentage, comprises the following chemical composition: C: 0.27%, Si: 0.31%, Mn: 0.99%, Alt: 0.043%, Cr: 0.45%, Nb: 0.026%, V: 0.045%, Ti: 0.015%, Mo: 0.48%, Ni: 1.02%, with the balance being Fe and unavoidable impurities, Ceq = 0.7%. The finished high-strength steel Q1500, produced through smelting, continuous casting, heating, rolling, and quenching and tempering heat treatment, has a yield strength ≥1500 MPa, tensile strength ≥1550 MPa, elongation ≥8%, and a thickness of 10-25 mm. The quenching and tempering heat treatment process is less complex and simplifies the process steps, effectively improving production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling production technology, specifically relating to a quenched and tempered high-strength steel Q1500 and its production method. Background Technology

[0002] Using high-strength, easily weldable structural steel to manufacture components for mobile equipment such as beams of engineering machinery, crane booms, and dump truck bodies reduces equipment weight, fuel consumption, and improves work efficiency. With increasing international competition, the use of high-strength, easily weldable structural steel in the manufacture of components for mobile equipment such as port machinery, mining machinery, excavators, loaders, crane booms, and dump truck bodies has become a trend. Due to the development requirements of high performance, large size, and lightweight engineering machinery, the strength level of steel used in engineering machinery is constantly increasing, rapidly rising from 500-600 MPa to 700 MPa, 800 Pa, and even above 1000 MPa. Ultra-high-strength steel for engineering machinery, due to its harsh operating environment and stress conditions, has strict requirements for steel quality, including strength performance, impact performance, bending performance, weldability, and plate shape. Among the many ultra-high strength steels used in engineering machinery, Q1500 high-strength steel stands out due to its excellent strength characteristics, good corrosion resistance and weldability. It can withstand greater pressure and load during application and has a certain degree of operability in the welding process. In addition, although Q1500 has high strength, it has a relatively low density and is therefore relatively light, which makes Q1500 advantageous in applications where structural weight reduction is required.

[0003] However, there are currently few domestic enterprises producing high-strength steel plates with a yield strength of 1500MPa, and the production process is difficult. Furthermore, the chemical composition and process conditions for producing steel with a yield strength of 1500MPa and a grade of Q1500 are more demanding, requiring strict control of the chemical element composition and production process of Q1500 to produce qualified Q1500 products. Summary of the Invention

[0004] The purpose of this invention is to provide a quenched and tempered high-strength steel Q1500 and its production method, so as to solve the problem in the prior art that it is difficult to produce high-strength steel with a yield strength greater than 1500MPa.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A quenched and tempered high-strength steel Q1500 has the following chemical composition by weight percentage: C: 0.27%, Si: 0.31%, Mn: 0.99%, Alt: 0.043%, Cr: 0.45%, Nb: 0.026%, V: 0.045%, Ti: 0.015%, Mo: 0.48%, Ni: 1.02%, with the balance being Fe and unavoidable impurities, and a carbon equivalent Ceq = 0.7%.

[0007] The quenched and tempered high-strength steel Q1500 has a yield strength ≥1500MPa, tensile strength ≥1550MPa, and elongation ≥8%.

[0008] A method for producing quenched and tempered high-strength steel Q1500 includes the following steps:

[0009] 1) Smelting: Smelting according to the weight percentage of the above chemical components;

[0010] 2) Continuous casting: Protective casting is used to form a 350mm thick billet; during the casting process, the liquid level fluctuation in the crystallizer is controlled within ±5mm, the crystallizer vibration frequency is 200-250 times / min, and the casting speed is 0.65m / min; the billet is rolled to 150mm, the slab is air-cooled to ≥80℃, and then subjected to heated cutting.

[0011] 3) Heating: A hot-feeding and hot-charging walking beam furnace is adopted. The slab needs to be preheated to ≥200℃ before entering the furnace. The furnace pressure is controlled at 5-20Pa. The slab stays in the furnace for 180-480 minutes. The slab exit temperature is 1200-1225℃. The maximum furnace temperature is ≤1280℃.

[0012] 4) Rolling: High-chromium iron rolls are used, and the rolling process is carried out in roughing and finishing stages; the roughing rolling start temperature is ≥1030℃, the roughing rolling reduction rate is ≥16%, the finishing rolling finish temperature is ≥800℃, the cumulative reduction rate of finishing rolling is ≥60%, the bending roll force in the finishing stage is 1500KN, and the surface temperature of the slab in the last two passes of roughing and the first three passes of finishing is between 900-1050℃, to obtain steel plates with a thickness of 10-25mm, and the surface is shot blasted.

[0013] 5) Quenching and tempering heat treatment: Quenching temperature is 900-920℃, heating rate is 2.3-3min / mm, holding time is 15-20min, after taking it out of the furnace, water quench to room temperature (25-30℃); Tempering temperature is 190-210℃, heating rate is 2.5-3.5min / mm, holding time is 15-32min, after taking it out of the furnace, air cool to obtain finished steel.

[0014] Furthermore, the crystallizer vibrates at a frequency of 250 times per minute.

[0015] Furthermore, the fuel used in the heating furnace is converter gas and coke oven gas, with a converter-to-coke ratio of 1:1.

[0016] Furthermore, the furnace pressure is ±11 Pa.

[0017] Furthermore, before the first pass of roughing and finishing rolling, high-pressure water descaling is required, with a descaling water pressure ≥16MPa and a descaling speed ≤1.0m / s. Other rolling passes are descaled normally according to the rolling conditions (temperature, surface oxidation, etc.).

[0018] Furthermore, the descaling tank has a descaling water pressure of 17 MPa and a descaling speed of 0.5 m / s.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention provides a high-strength steel of grade Q1500, with a yield strength ≥1500MPa, tensile strength ≥1550MPa, elongation ≥8%, and thickness of 10-25mm; it adopts a quenching and tempering heat treatment process, which is less difficult and simplifies the process steps, effectively improving production efficiency.

[0021] 2. This invention adopts a C-Mn composition system, strictly limiting its composition to 0.27% and 0.99% respectively, and achieves martensitic phase transformation strengthening and microstructure strengthening at a low Mn content through quenching and tempering heat treatment. The composition and weight percentage of the remaining chemical elements of the steel are also clearly defined. The presence of complex carbide-forming elements such as Nb, V, Ti, and Mo reduces Ms, resulting in precipitation hardening and refining austenite grains. The addition of Ti improves the weldability of the ultra-high strength steel plate. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] A method for producing quenched and tempered high-strength steel Q1500 includes the following steps:

[0025] 1) Smelting: By weight percentage, the chemical composition of the smelting is C: 0.27%, Si: 0.31%, Mn: 0.99%, Alt: 0.043%, Cr: 0.45%, Nb: 0.026%, V: 0.045%, Ti: 0.015%, Mo: 0.48%, Ni: 1.02%, with the balance being Fe and unavoidable impurities, Ceq = 0.7%;

[0026] 2) Continuous casting: Protective casting is used to form a 350mm thick billet; during the casting process, the liquid level fluctuation in the crystallizer is controlled within ±5mm, the crystallizer vibration frequency is 250 times / min, and the casting speed is 0.65m / min; the billet is rolled to 150mm, the slab is air-cooled to 87℃, and then subjected to heated cutting.

[0027] 3) Heating: A hot-charged walking beam furnace is used. The slab needs to be preheated to 210°C before entering the furnace. The fuel used in the furnace is converter gas and coke oven gas, with a converter-coke ratio of 1:1. The furnace pressure is controlled at ±11Pa. The billet stays in the furnace for 180 minutes, the billet exit temperature is 1205°C, and the maximum furnace temperature is 1276°C.

[0028] 4) Rolling: High-chromium iron rolls are used. The descaling water pressure in the descaling box is 17MPa, and the descaling speed is 0.5m / s. The rolling process is carried out in roughing and finishing stages. The roughing rolling start temperature is ≥1030℃, the roughing rolling reduction rate is ≥16%, the finishing rolling finish temperature is ≥800℃, the cumulative reduction rate of finishing rolling is ≥60%, the bending roll force in the finishing stage is 1500KN, and the slab surface temperature in the last two passes of roughing and the first three passes of finishing rolling is between 900-1050℃ to obtain a steel plate with a thickness of 10mm. The surface of the plate is then shot blasted.

[0029] 5) Quenching and tempering heat treatment: Quenching temperature is 900℃, heating rate is 3min / mm, holding time is 15min, and after taking it out of the furnace, it is water quenched to room temperature; Tempering temperature is 200℃, heating rate is 2.5min / mm, holding time is 15min, and after taking it out of the furnace, it is air cooled to obtain the finished steel.

[0030] The finished steel with a thickness of 10mm was subjected to performance tests, and the tensile strength test results are shown in Table 1:

[0031] Table 1

[0032] Grade (steel grade) thickness Yield strength tensile strength elongation standard —— —— ≥1500MPa 1550-1900MPa ≥7％ head Q1500 10 1530 1612 9 tail Q1500 10 1538 1623 8

[0033] Example 2

[0034] A method for producing quenched and tempered high-strength steel Q1500 includes the following steps:

[0035] 1) Smelting: By weight percentage, the chemical composition of the smelting is C: 0.27%, Si: 0.31%, Mn: 0.99%, Alt: 0.043%, Cr: 0.45%, Nb: 0.026%, V: 0.045%, Ti: 0.015%, Mo: 0.48%, Ni: 1.02%, with the balance being Fe and unavoidable impurities, Ceq = 0.7%;

[0036] 2) Continuous casting: Protective casting is used to form a 350mm thick slab; during the casting process, the liquid level fluctuation in the crystallizer is controlled within ±5mm, the crystallizer vibration frequency is 250 times / min, and the casting speed is 0.65m / min; the slab is rolled to 150mm, air-cooled to 85℃, and then hot-cut.

[0037] 3) Heating: A hot-charged walking beam furnace is used. The slab needs to be preheated to 200°C before entering the furnace. The fuel used in the furnace is converter gas and coke oven gas, with a converter-coke ratio of 1:1. The furnace pressure is controlled at ±11Pa. The slab stays in the furnace for 451 minutes, the slab exit temperature is 1223°C, and the highest furnace temperature is 1276°C.

[0038] 4) Rolling: High-chromium iron rolls are used. The descaling water pressure in the descaling box is 17MPa, and the descaling speed is 0.5m / s. The rolling process is carried out in roughing and finishing stages. The roughing rolling start temperature is ≥1030℃, the roughing rolling reduction rate is ≥16%, the finishing rolling finish temperature is ≥800℃, the cumulative reduction rate of finishing rolling is ≥60%, the bending roll force in the finishing stage is 1500KN, and the slab surface temperature in the last two passes of roughing and the first three passes of finishing is between 900-1050℃ to obtain a steel plate with a thickness of 24mm. The surface of the plate is then shot blasted.

[0039] 5) Quenching and tempering heat treatment: Quenching temperature is 910℃, heating rate is 2.3min / mm, holding time is 20min, and after taking it out of the furnace, it is water quenched to room temperature; Tempering temperature is 190℃, heating rate is 3.5min / mm, holding time is 32min, and after taking it out of the furnace, it is air cooled to obtain the finished steel.

[0040] The finished steel with a thickness of 24mm was subjected to performance tests, and the tensile strength test results are shown in Table 2:

[0041] Table 2

[0042] Grade (steel grade) thickness Yield strength tensile strength elongation standard —— —— ≥1500MPa 1550-1900MPa ≥7％ head Q1500 24 1542 1592 8 tail Q1500 24 1538 1603 10

[0043] Example 3

[0044] A method for producing quenched and tempered high-strength steel Q1500 includes the following steps:

[0045] 1) Smelting: By weight percentage, the chemical composition of the smelting is C: 0.27%, Si: 0.31%, Mn: 0.99%, Alt: 0.043%, Cr: 0.45%, Nb: 0.026%, V: 0.045%, Ti: 0.015%, Mo: 0.48%, Ni: 1.02%, with the balance being Fe and unavoidable impurities, Ceq = 0.7%;

[0046] 2) Continuous casting: Protective casting is used to form a 350mm thick slab; during the casting process, the liquid level fluctuation in the crystallizer is controlled within ±5mm, the crystallizer vibration frequency is 250 times / min, and the casting speed is 0.65m / min; the slab is rolled to 150mm, air-cooled to 82℃, and then hot-cut.

[0047] 3) Heating: A hot-charged walking beam furnace is used. The slab needs to be preheated to 210°C before entering the furnace. The fuel used in the furnace is converter gas and coke oven gas, with a converter-coke ratio of 1:1. The furnace pressure is controlled at ±11Pa. The billet stays in the furnace for 324 minutes, the billet exit temperature is 1216°C, and the highest furnace temperature is 1276°C.

[0048] 4) Rolling: High-chromium iron rolls are used. The descaling water pressure in the descaling box is 17MPa, and the descaling speed is 0.5m / s. The rolling process is carried out in roughing and finishing stages. The roughing rolling start temperature is ≥1030℃, the roughing rolling reduction rate is ≥16%, the finishing rolling finish temperature is ≥800℃, the cumulative reduction rate of finishing rolling is ≥60%, the bending roll force in the finishing stage is 1500KN, and the slab surface temperature in the last two passes of roughing and the first three passes of finishing rolling is between 900-1050℃ to obtain a steel plate with a thickness of 18mm. The surface of the plate is then shot blasted.

[0049] 5) Quenching and tempering heat treatment: Quenching temperature is 920℃, heating rate is 2.7min / mm, holding time is 18min, and after taking it out of the furnace, it is water quenched to room temperature; Tempering temperature is 210℃, heating rate is 3min / mm, holding time is 24min, and after taking it out of the furnace, it is air cooled to obtain finished steel.

[0050] The finished steel with a thickness of 18mm was subjected to performance tests, and the tensile strength test results are shown in Table 3.

[0051] Table 3

[0052] Grade (steel grade) thickness Yield strength tensile strength elongation standard —— —— ≥1500MPa 1550-1900MPa ≥7％ head Q1500 18 1537 1601 9 tail Q1500 18 1539 1609 10

[0053] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing quenched and tempered high-strength steel Q1500, characterized in that, The quenched and tempered high-strength steel Q1500, by weight percentage, comprises the following chemical composition: C: 0.27%, Si: 0.31%, Mn: 0.99%, Alt: 0.043%, Cr: 0.45%, Nb: 0.026%, V: 0.045%, Ti: 0.015%, Mo: 0.48%, Ni: 1.02%, with the balance being Fe and unavoidable impurities, Ceq=0.7%. The quenched and tempered high-strength steel Q1500 has a yield strength ≥1500 MPa, tensile strength ≥1550 MPa, elongation ≥8%, and a thickness of 10-25 mm. The production method includes the following steps: 1) Smelting: Smelting according to the weight percentage of the above chemical components; 2) Continuous casting: Protective casting is used to form a 350mm thick billet; during the casting process, the liquid level fluctuation in the crystallizer is controlled within ±5mm, the crystallizer vibration frequency is 200-250 times / min, and the casting speed is 0.65m / min; the billet is rolled to 150mm, the slab is air-cooled to ≥80℃, and then subjected to heated cutting. 3) Heating: A walking beam furnace is used. The slab needs to be preheated to ≥200℃ before entering the furnace. The furnace pressure is controlled at 5-20Pa. The slab stays in the furnace for 180-480 minutes. The slab exit temperature is 1200-1225℃. The maximum furnace temperature is ≤1280℃. 4) Rolling: High-chromium iron rolls are used, and the rolling process is carried out in roughing and finishing stages; the roughing rolling start temperature is ≥1030℃, the roughing rolling reduction rate is ≥16%, the finishing rolling finish temperature is ≥800℃, the cumulative reduction rate of finishing rolling is ≥60%, the bending roll force in the finishing stage is 1500KN, and the surface temperature of the slab in the last two passes of roughing and the first three passes of finishing is between 900-1050℃, to obtain steel plates with a thickness of 10-25mm, and the surface is shot blasted. 5) Quenching and tempering heat treatment: Quenching heating temperature is 900-920℃, heating rate is 2.3-3min / mm, holding time is 15-20min, and after taking it out of the furnace, it is water quenched to room temperature; Tempering heating temperature is 190-210℃, heating rate is 2.5-3.5min / mm, holding time is 15-32min, and after taking it out of the furnace, it is air cooled to obtain the finished steel.

2. The method for producing quenched and tempered high-strength steel Q1500 according to claim 1, characterized in that, The crystallizer vibrates at a frequency of 250 times per minute.

3. The method for producing quenched and tempered high-strength steel Q1500 according to claim 1, characterized in that, The heating furnace uses converter gas and coke oven gas as fuel, with a converter-to-coke ratio of 1:

1.

4. The method for producing quenched and tempered high-strength steel Q1500 according to claim 1, characterized in that, The pressure inside the furnace is ±11 Pa.

5. The method for producing quenched and tempered high-strength steel Q1500 according to claim 1, characterized in that, Before the first pass of roughing and finishing rolling, high-pressure water descaling is required, with a descaling water pressure ≥16MPa and a descaling speed ≤1.0m / s.

6. The method for producing quenched and tempered high-strength steel Q1500 according to claim 5, characterized in that, The descaling tank has a descaling water pressure of 17MPa and a descaling speed of 0.5m / s.