Economical niobium-free 690 pa-grade tempered high-strength steel plate and manufacturing method

Abstract

Disclosed in the present invention are an economical niobium-free 690 Pa-grade tempered high-strength steel plate and a manufacturing method. The present invention belongs to the technical field of steel production. The steel plate comprises the following chemical components: C, Si, Mn, P, S, Ti, V, Cr, Mo, Alt, B and the balance of Fe and impurities. The method comprises the following steps: a smelting process, a continuous casting process, a heating process, a rolling and tempering process, etc. The present invention provides an economical 690 MPa high-strength steel plate having good comprehensive performance and a production method therefor. Lath bainite and granular bainite are obtained, and the structure is uniform and fine; and the structure of the lath bainite and the granular bainite is beneficial for maintaining strength and good plasticity and toughness.

Description

An economical niobium-free 690Pa grade quenched and tempered high-strength steel plate and its manufacturing method Technical Field

[0001] The present invention relates to the technical field of steel production, and relates to an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate and a manufacturing method thereof. Background Art

[0002] In the existing technology, 690Pa grade quenched and tempered high-strength steel plate is a high-strength weldable steel plate that has been quenched and tempered according to American standards. Its main use is in places requiring high tensile strength and high yield strength, such as engineering machinery booms and engineering car lifting gears. The overall development trend of high-strength steel is: high strength and toughness, lightweight, and easy to weld.

[0003] The application of 690Pa grade quenched and tempered high-strength steel plates has many advantages. The application of high-strength steel can not only reduce material costs, transportation costs, and production costs; it can also save welding material consumption, reduce post-weld stress during welding, reduce welding preheating temperature, and reduce post-weld heat treatment requirements.

[0004] With continuous advancements in steel materials, welding material manufacturing, and welding process technology, the strength levels of structural steel continue to rise, with grades exceeding 1000 MPa becoming commonplace. The overall demand for high-strength steel continues to increase annually. Q690 high-strength steel is widely used in offshore cranes, marine tanks, jack-up platform legs, and coal mine hydraulic supports. Ultra-high-strength steels such as Q800, Q890, and Q960, as well as even higher-strength grades such as Q1100, Q1300, and Q1600, are used in automobiles, containers, construction machinery pump trucks, and cranes. Within the high-strength steel sector, 690 MPa-grade high-strength steel has become the most widely used grade. While other high-strength steels such as Q800 and Q960 have also been explored, successful applications of these higher-strength steels remain limited due to limitations in material welding.

[0005] Therefore, it is necessary to develop an economical niobium-free 690Pa grade tempered high-strength steel plate, forming a complete set of steelmaking, rolling cooling and tempering processes to reduce production costs, make the process easy to operate, and stabilize product performance.

[0006] Summary of the Invention

[0007] Purpose of the invention: The purpose of the present invention is to provide an economical 690MPa high-strength steel plate with excellent comprehensive performance and a production method thereof; the present invention obtains lath bainite plus granular bainite, and the structure is uniform and fine; in addition, the structure of lath bainite plus granular bainite is conducive to maintaining strength and excellent plasticity and toughness.

[0008] Technical solution: The economical niobium-free 690Pa-grade quenched and tempered high-strength steel plate described in the present invention has the following chemical composition and mass percentages: C: 0.15-0.18%, Si: 0.20-0.35%, Mn: 0.7-1.00%, P: ≤0.013%, S: ≤0.003%, Ti: 0.010-0.020%, V: 0.030-0.050%, Cr: 0.45-0.55%, Mo: 0.15-0.25%, Alt: 0.020-0.040%, B: 0.0005-0.005%, and the balance is Fe and impurities.

[0009] Furthermore, the present invention ensures the alloy composition and impurity element content through smelting, and combines the smelting process with calcium treatment, and combines the casting process with dynamic soft reduction and electromagnetic stirring to improve the internal quality of the ingot; and adopts the process of precise rolling and precise controlled cooling in the controlled rolling and controlled cooling stage;

[0010] Firstly, the smelting process ensures the alloy composition and impurity element content, and the calcium treatment smelting process ensures the control of inclusions in the steel plate;

[0011] Secondly, the casting process of dynamic soft reduction and electromagnetic stirring is adopted to improve the internal quality of the ingot, effectively reducing the level of macro and micro segregation in the center of the ingot;

[0012] Precise controlled rolling and quenching and tempering processes use weak cooling to control the cooling rate to a lower level during the controlled cooling stage, resulting in a more ductile structure. The toughness of the steel plate is improved through inclusion control and structure control.

[0013] Finally, quenching and subsequent high-temperature tempering, also known as quenching and tempering, are used. This quenched and tempered steel exhibits excellent combined mechanical properties of strength, ductility, and toughness, making it widely used in various important structural components made from medium-carbon structural steel, such as engine crankshafts, connecting rods, machine tool spindles, and gears.

[0014] Furthermore, a method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate is provided, wherein the specific preparation steps are as follows:

[0015] Step (1), smelting process;

[0016] Step (2), continuous casting process;

[0017] Step (3), heating process;

[0018] Step (4), rolling process;

[0019] Step (5), tempering process.

[0020] Furthermore, in step (1), the smelting process is specifically: pre-desulfurization through molten iron pretreatment, converter blowing, and then LF refining to adjust the alloy composition, RH vacuum treatment is used to improve the purity of the molten steel, and a calcium treatment smelting process is implemented after the soft stirring is completed to ensure that the molten steel with high purity and qualified composition is obtained.

[0021] Furthermore, in step (2), the continuous casting process specifically comprises: adopting dynamic soft reduction and electromagnetic stirring technology to achieve excellent internal quality of the cast billet.

[0022] Furthermore, in step (3), the heating process is specifically as follows: the 260mm thick ingot billet enters the heating furnace, the heating temperature of the ingot billet is 1160-1200℃, the time in the furnace is 230-350min, and the temperature out of the furnace is 1160-1200℃.

[0023] Furthermore, in step (4), the rolling process is specifically as follows: a two-stage rolling process is performed, with a rough rolling temperature of 950-1150°C, a finishing rolling start temperature of 850-900°C, and a finishing rolling temperature of 800-850°C; followed by laminar cooling with a return temperature of 640-700°C. The cooling rate is 1-20°C / s. The finished steel plate has a thickness of 6-50 mm.

[0024] Furthermore, in step (5), the tempering process is a tempering heat treatment, specifically: the quenching temperature is 900-950°C, the time is 15-100 minutes; the tempering temperature is 500-650°C, and the tempering time is 20-200 minutes.

[0025] The present invention develops an economical niobium-free 690Pa grade tempered high-strength steel plate, forming a complete set of steelmaking, rolling cooling and tempering processes, thereby reducing production costs, facilitating process operation and ensuring stable product performance.

[0026] Beneficial effects: Compared with the prior art, the present invention is characterized by: 1. A smelting process that ensures the alloy composition and impurity element content while simultaneously performing calcium treatment is adopted, combined with a casting process of dynamic soft reduction and electromagnetic stirring to improve the internal quality of the ingot and ensure the plasticity and toughness of the steel plate; 2. The manufacturing method of the present invention is simple in process and low in cost. It uses a 260mm thick ingot and produces an economical, niobium-free, high-strength, and easily weldable 690Pa-grade tempered high-strength steel plate through a controlled rolling and controlled cold tempering process; 3. The manufacturing method of the present invention has stable performance: the yield strength is between 700 and 800MPa, the elongation A50 is ≥17%, and the impact energy at -20°C is ≥120J. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a typical microstructure of a 20 mm thick weather-resistant bridge steel plate obtained after quenching and tempering treatment in Example 1 of the present invention under a metallographic microscope;

[0028] FIG2 is a typical microstructure image of a 50 mm thick weather-resistant bridge steel plate obtained after quenching and tempering treatment in Example 2 of the present invention under a metallographic microscope. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the embodiments.

[0030] As shown in the figure, the present invention uses a smelting process to ensure the alloy composition and impurity element content while also performing calcium treatment, combined with a casting process of dynamic soft reduction and electromagnetic stirring to improve the internal quality of the ingot; in the controlled rolling and controlled cooling stage, precise rolling and precise controlled cooling processes are used;

[0031] Firstly, the smelting process ensures the alloy composition and impurity element content, and the calcium treatment smelting process ensures the control of inclusions in the steel plate;

[0032] Secondly, the casting process of dynamic soft reduction and electromagnetic stirring is adopted to improve the internal quality of the ingot, effectively reducing the level of macro and micro segregation in the center of the ingot;

[0033] Precise controlled rolling and quenching and tempering processes use weak cooling to control the cooling rate to a lower level during the controlled cooling stage to obtain more tough structure; the toughness of the steel plate is improved through inclusion control and structure control.

[0034] Finally, quenching and subsequent high-temperature tempering, i.e., quenching and tempering treatment, are used; the steel plate after quenching and tempering treatment has good comprehensive mechanical properties of strength, plasticity and toughness, and is widely used in various important structural parts made of medium-carbon structural steel, such as engine crankshafts, connecting rods, machine tool spindles and gears.

[0035] Specifically, the present invention includes smelting process, continuous casting process, heating process, rolling and tempering process, etc.

[0036] The specific parameters controlled in the process are as follows:

[0037] (1) Smelting: Pre-desulfurization of molten iron, converter blowing, LF refining to adjust alloy composition, RH vacuum treatment to improve molten steel purity, and calcium treatment after soft stirring to ensure high purity and qualified molten steel;

[0038] (2) Continuous casting: Dynamic soft reduction and electromagnetic stirring technology are used to achieve excellent internal quality of the cast billet;

[0039] (3) Heating: 260mm thick billet enters the heating furnace, the billet is heated to 1160-1200℃, the time in the furnace is 230-350min, and the temperature out of the furnace is 1160-1200℃;

[0040] (4) Rolling: Two-stage rolling is adopted, with the rough rolling temperature at 950-1150℃, the finishing rolling starting temperature at 850-900℃, and the finishing rolling temperature at 800-850℃; followed by laminar cooling, with the red-return temperature at 640-700℃. The cooling rate is 1-20℃ / s. The finished steel plate thickness is 6-50mm;

[0041] (5) Heat treatment: Quenching temperature is 900-950℃, time is 15-100min; tempering temperature is 500-650℃, tempering time is 20-200min.

[0042] The steel of the present invention comprises the following components by weight: C: 0.15-0.18%, Si: 0.20-0.35%, Mn: 0.7-1.00%, P: ≤0.013%, S: ≤0.003%, Ti: 0.010-0.020%, V: 0.030-0.050%, Cr: 0.45-0.55%, Mo: 0.15-0.25%, Alt: 0.020-0.040%, B: 0.0005-0.005%, and the balance is Fe and impurities.

[0043] Example 1

[0044] An economical niobium-free 690Pa grade quenched and tempered high-strength steel plate and a production method thereof, the composition of which is shown in Table 1 by weight percentage.

[0045] The specific requirements for the production method of the above-mentioned economical niobium-free 690Pa grade quenched and tempered high-strength steel plate and production method are as follows:

[0046] Controlled Rolling and Controlled Cooling (TMCP) is a two-stage rolling process. 260mm thick ingots are heated to 1160-1200°C for 230-350 minutes in the heating furnace, and discharged from the furnace at 1160-1200°C. Rough rolling is performed at 950-1150°C, finishing at 850-900°C, and finishing at 800-850°C. Laminar cooling is then applied, with a return to red temperature of 640-700°C. The cooling rate is 1-20°C / s. The finished plate thickness ranges from 6-50mm.

[0047] Quenching and tempering process: quenching temperature is 900-950℃, time is 15-100min; tempering temperature is 500-650℃, tempering time is 20-200min.

[0048] Figures 1 and 2 show typical microstructures of the 690Pa-grade quenched and tempered high-strength steel plate obtained after quenching and tempering in the example, as viewed under a metallographic microscope. The structure is uniform and fine. A close examination of Figures 1 and 2 reveals a combination of lath bainite and granular bainite, resulting in a uniform and fine structure. This combination of lath bainite and granular bainite contributes to maintaining both strength and excellent ductility and toughness.

[0049] The properties of the finished steel plates are shown in Table 2-3.

[0050] Table 1 Chemical composition of the examples of the present invention (wt%)

[0051] Table 2 Tensile properties

[0052] Table 3 Series temperature shock performance

[0053] It can be seen that the mechanical properties of Examples 1 and 2 both meet the requirements of 690 MPa grade quenched and tempered high-strength steel plates; specifically, the properties of the steel plates reach the following levels: yield strength between 700 and 800 MPa, elongation A50 ≥ 17%, and impact energy at -20°C ≥ 120 J.

[0054] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. An economical niobium-free 690Pa grade quenched and tempered high-strength steel plate, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.15-0.18%, Si: 0.20-0.35%, Mn: 0.7-1.00%, P: ≤0.013%, S: ≤0.003%, Ti: 0.010-0.020%, V: 0.030-0.050%, Cr: 0.45-0.55%, Mo: 0.15-0.25%, Alt: 0.020-0.040%, B: 0.0005-0.005%, and the balance is Fe and impurities.

2. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 1, characterized in that: The smelting process ensures the alloy composition and impurity element content while using calcium treatment, combined with the casting process of dynamic soft pressure and electromagnetic stirring to improve the internal quality of the ingot; the process of precise rolling and precise controlled cooling is adopted in the controlled rolling and controlled cooling stage; Firstly, the smelting process ensures the alloy composition and impurity element content, and the calcium treatment smelting process ensures the control of inclusions in the steel plate; Secondly, the casting process of dynamic soft pressure and electromagnetic stirring is adopted to improve the internal quality of the ingot and reduce the level of macro and micro segregation in the center of the ingot; Precise controlled rolling process and quenching and tempering process, using weak cooling to control the cooling rate to a lower level in the controlled cooling stage to obtain tough structure; improving the toughness of the steel plate through inclusion control and structure control; Finally, quenching and subsequent high temperature tempering, i.e., quenching and tempering treatment, is used in various important structural parts made of medium carbon structural steel.

3. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 2, characterized in that: The specific preparation steps are as follows: Step (1), smelting process; Step (2), continuous casting process; Step (3), heating process; Step (4), rolling process; Step (5), tempering process.

4. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 3, characterized in that: In step (1), the smelting process is specifically: pre-desulfurization through molten iron pretreatment, converter blowing, and then LF refining to adjust the alloy composition, RH vacuum treatment is used to improve the purity of the molten steel, and after soft stirring, a calcium treatment smelting process is implemented to obtain a high-purity molten steel with qualified composition.

5. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 3, characterized in that: In step (2), the continuous casting process specifically includes: using dynamic soft reduction and electromagnetic stirring technology to achieve the internal quality of the ingot.

6. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 3, characterized in that: In step (3), the heating process is as follows: the 260 mm thick ingot is placed into a heating furnace, the heating temperature of the ingot is 1160-1200°C, the time in the furnace is 230-350 minutes, and the temperature out of the furnace is 1160-1200°C.

7. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 3, characterized in that: In step (4), the rolling process is specifically: adopting two-stage rolling, and the two-stage rolling includes rough rolling and finish rolling.

8. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 7, characterized in that: The rough rolling temperature is 950-1150°C; The starting temperature of the finishing rolling is 850-900°C, and the final rolling temperature of the finishing rolling is 800-850°C; followed by laminar cooling, the red-returning temperature is 640-700°C; the cooling rate is 1-20°C / s.

9. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 8, characterized in that: The finished steel plate has a thickness of 6-50 mm.

10. The method for manufacturing an economical niobium-free 690Pa grade quenched and tempered high-strength steel plate according to claim 3, characterized in that: In step (5), the tempering process is heat treatment, specifically: the quenching temperature is 900-950°C, the time is 15-100 minutes; the tempering temperature is 500-650°C, and the tempering time is 20-200 minutes.

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