Production method of high-strength non-tuned online quenched steel

Abstract

The invention discloses a production method of high-strength non-tuned online quenched steel. The high-strength non-tuned online quenched steel is prepared from the following components in percentage by weight: 0.42 to 0.44 percent of carbon (C), 0.43 to 0.48 percent of silicon (Si), 1.38 to 1.44 percent of manganese (Mn), 0.16 to 0.19 percent of chromium (Cr), 0.008 to 0.028 percent of niobium (Nb), 0.005 to 0.085 percent of vanadium (V), 0.012 to 0.022 percent of aluminum (A1), less than or equal to 0.01 percent of titanium (Ti), less than or equal to 0.01 percent of nitrogen (N), less than or equal to 0.010 percent of phosphorus (P), less than or equal to 0.008 percent of sulfur (S) and the balance of Fe and inevitable impurities. According to the mechanical properties of the steel, the impact is 38-42 J, the yield strength is 600-757 MPa, the tensile strength is 860-1022 MPa, the ductility is 15-16.5%, the percentage reduction of area is 35%-37.5%, and the hardness is 260-300 HBW; and the depth of the through quenching layer is 5-10 mm. The matrix structure of the steel through-quenching layer is 85%-95% of tempered troostite, and the rest structure is ferrite and carbide. The production method mainly comprises the following steps of converter treatment, LF furnace treatment, RH furnace treatment, continuous casting, casting blank heating, rolling, online quenching and slow cooling. And the produced steel has the advantages of short production period, low energy consumption, cost saving and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling and relates to a production method of high-strength non-adjustable online quenching steel. Background Art

[0002] Non-quenched and tempered steel is a medium carbon manganese steel with microalloying elements such as vanadium, titanium and niobium added to it, which are dissolved in austenite during heating, because the solid solubility of vanadium, titanium and niobium in austenite decreases with cooling. Microalloying elements such as vanadium, titanium and niobium will precipitate in the first precipitated ferrite and pearlite in the form of fine carbides and nitrides. These precipitates maintain a coherent relationship with the parent phase, strengthening the steel. The mechanical properties of this type of steel in the hot-rolled, forged or normalized state reach or approach those of tempered steel, which not only shortens the production cycle but also saves energy.

[0003] The online quenching process refers to the direct quenching of steel during hot rolling or hot processing to obtain the desired structure and performance. This process eliminates the heating, insulation, quenching and other steps required for offline quenching, thereby simplifying the production process and improving production efficiency. At the same time, due to the high temperature of the steel during the online quenching process, the structure after quenching is more uniform and the performance is more stable. By combining the production process of non-adjustable steel and the online quenching process, a high-strength non-adjustable online quenching steel production method is obtained.

[0004] Chinese invention patent CN117646144A discloses a method for preparing Mn-B non-tempered steel. Through the control of steel-out conditions, wire feeding process after vacuum treatment, and end-point composition, the cleanliness and material properties of Mn-B non-tempered steel are improved, and the material performance requirements for quenched and tempered steel are met. This invention only achieves the purpose of the invention through strict control of the composition and optimization of the feeding sequence during the smelting process, and has a narrow scope of application. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to control the product composition, billet heating temperature, quenching process, slow cooling process, etc. to ensure the uniformity of the steel structure so as to obtain high-strength non-adjustable online quenching steel with qualified mechanical properties.

[0006] In order to solve the above technical problems, the present invention provides a production method of high-strength non-adjustable online quenching steel, the core of which is to directly heat treat the non-adjustable steel through an online quenching process to obtain high-strength and excellent performance non-adjustable steel.

[0007] The technical solution of the present invention is as follows:

[0008] A production method of high-strength non-adjustable online quenching steel, characterized in that the steel is composed of the following components in weight percentage: carbon (C): 0.42% to 0.44%, silicon (Si): 0.43% to 0.48%, manganese (Mn): 1.38% to 1.44%, chromium (Cr): 0.16% to 0.19%, niobium (Nb): 0.008% to 0.028%, vanadium (V): 0.005% to 0.085%, aluminum (A1): 0.012% to 0.022%, titanium (Ti) ≤0.01, nitrogen (N) ≤0.01%, phosphorus (P) ≤0.010%, sulfur (S) ≤0.008%, and the rest are Fe and unavoidable impurities.

[0009] Furthermore, the mechanical properties of the high-strength non-adjustable online quenching steel are impact 38-42J, yield strength 600-757MPa, tensile strength 860-1022MPa, elongation 15-16.5%, cross-sectional shrinkage 35%-37.5%, hardness 260-300HBW; the depth of the hardened layer is 5-10mm.

[0010] Furthermore, the matrix structure of the hardened layer of the high-strength non-tuning online quenching steel is 85% to 95% tempered troostite, and the remaining structure is ferrite and carbide.

[0011] Furthermore, the remaining structures are ferrite 70% to 75% + bainite 15% to 20% + martensite 5% to 15%.

[0012] Further, a production method of high-strength non-adjustable online quenching steel is characterized in that it mainly comprises the following steps: converter, LF furnace, RH furnace, continuous casting, billet heating, rolling, online quenching, and slow cooling;

[0013] Converter: treatment time 28-32min, control the C content at the end point, and the temperature reaches 1620±30℃ for steel tapping;

[0014] LF furnace: turn on the bottom blowing of argon, heat the graphite electrode with electricity, adjust the slag and further deoxidize it. After 22 to 27 minutes of treatment, adjust the temperature of the molten steel to 1590±10℃;

[0015] RH furnace: When the temperature of molten steel reaches 1550±10℃, vacuum degassing treatment is carried out for no less than 10 minutes in a vacuum environment of no more than 0.5tor;

[0016] Continuous casting: The temperature of the molten steel in the middle package is controlled at 1525-1540℃, and the whole process is cast in argon closed atmosphere. The casting superheat is controlled at 15-25℃, and the steel enters the clamping roller table in the full roller area, the roller table in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller, and the continuous casting billet of 280mm*280mm*6000mm is obtained by flame cutting;

[0017] Ingot heating: The continuous casting ingot is sent to the walking beam furnace and heated to 1160-1200℃ step by step, and kept warm in the soaking section for 1-2 hours. The total heating time is controlled within 5-7 hours.

[0018] Rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the two-roller reversible unit for rolling. The rolling temperature is 1080-1120℃, and it enters the continuous rolling unit for rolling and forming at 930-950℃.

[0019] Online quenching: water inlet temperature 750-850℃, quenching time 30-60s, water outlet temperature 100-240℃;

[0020] Slow cooling: Slow cooling is carried out on the cooling bed. After returning to red, the entry temperature is 550-650℃, and the exit temperature is 300-350℃.

[0021] Furthermore, the converter end point C is controlled at 0.09% to 0.15%.

[0022] The working mechanism of the production method of high-strength non-adjustable online quenching steel of the present invention is as follows:

[0023] 1. The V content of the present invention is in the range of 0.005% to 0.085%, preferably in the range of 0.075% to 0.085%. The V element has the effects of precipitation strengthening, grain refinement and improving resistance to HIC and sulfide stress cracking. It forms nano-sized VC and V (C, N) particles with C and N in steel to improve strength and hinder the phase transformation of austenite to ferrite, achieving the effects of grain refinement and toughening. At the same time, it acts as a hydrogen trap to improve the resistance to hydrogen-induced cracking and sulfide stress cracking in an acid environment.

[0024] 2. The Nb content of the present invention is in the range of 0.008% to 0.028%, preferably in the range of 0.018% to 0.028%. The Nb element is a strong carbide-forming microalloying element, and nano-scale NbC is precipitated during the tempering process, providing effective precipitation strengthening contribution.

[0025] Beneficial effects of the present invention:

[0026] 1. The online quenching process plus the control of V / Nb composition can obtain non-adjustable online quenching steel with excellent mechanical properties and good processing performance without the need for additional heating equipment and heat treatment equipment; at the same time, due to the simplification of the production process, the production cost is also reduced; compared with the traditional offline quenching process, this method has the advantages of short production cycle, low energy consumption and cost saving.

[0027] 2. During the online quenching process, the temperature of the steel is high and the quenching speed is fast, which is conducive to obtaining a uniform and fine structure. This structure not only improves the strength of the steel, but also improves its toughness and fatigue resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 is the microstructure diagram of the core of Example 1;

[0030] Figure 2 This is the microstructure diagram of the core of Example 2;

[0031] Figure 3 is the hardened layer depth of Example 3;

[0032] Figure 4 This is the microstructure diagram of the hardened layer of Example 3. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Table 1, Table 2 and Table 3 respectively list the chemical composition, production process and mechanical properties of the embodiments of the present invention and the comparative examples.

[0035] Comparative Example:

[0036] The chemical composition, by weight percentage, includes the following components: C: 0.42%, Si: 0.43%, Mn: 1.40%, Cr: 0.16%, Nb: 0.025%, V: 0.075%, A1: 0.012%, Ti: 0.0075%, N: 0.0026%, P: 0.009%, S: 0.005%, and the rest is Fe and unavoidable impurities.

[0037] The specific production method steps are as follows:

[0038] Converter: treatment time 28-32min, end point C controlled at 0.09%-0.15%, temperature reaches 1620±30℃ for steel tapping;

[0039] LF furnace: turn on the bottom blowing of argon, energize and heat the graphite electrode, adjust the slag and further deoxidize it. After 25 minutes of treatment, adjust the temperature of the molten steel to 1590±10℃;

[0040] RH furnace: When the temperature of molten steel reaches 1550±10℃, vacuum degassing treatment is carried out for 12 minutes in a vacuum environment of no more than 0.5tor;

[0041] Continuous casting: The temperature of the molten steel in the middle package is controlled at 1525-1540℃, and the whole process is cast in argon closed atmosphere. The casting superheat is controlled at 15-25℃, and the steel enters the clamping roller table in the full roller area, the roller table in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller, and the continuous casting billet of 280mm*280mm*6000mm is obtained by flame cutting;

[0042] Heating of slab: The continuous casting slab is sent to the walking beam furnace and heated to 1200℃ step by step, and kept in the soaking section for 2 hours;

[0043] Rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the two-roller reversible unit for rolling. The starting rolling temperature is 1100℃. After 11 passes of rolling by the two-roller reversible unit, it is rolled into a semi-finished product with a cross-section of 190*210mm, and then enters the continuous rolling unit at 950℃ to be rolled into a round steel with a diameter of 120mm;

[0044] Slow cooling: Slow cooling is carried out in a 880℃ heat preservation hood, and the temperature out of the hood is 480℃.

[0045] Embodiment 1:

[0046] The chemical composition, by weight percentage, includes the following components: C: 0.42%, Si: 0.43%, Mn: 1.40%, Cr: 0.16%, Nb: 0.025%, V: 0.075%, A1: 0.012%, Ti: 0.0075%, N: 0.0026%, P: 0.009%, S: 0.005%, and the rest is Fe and unavoidable impurities.

[0047] The specific production method steps are as follows:

[0048] Converter: treatment time 30min, end point C controlled at 0.09%~0.15%, temperature reaches 1620±30℃ for steel tapping;

[0049] LF furnace: turn on the bottom blowing of argon, energize and heat the graphite electrode, adjust the slag and further deoxidize it. After 25 minutes of treatment, adjust the temperature of the molten steel to 1590±10℃;

[0050] RH furnace: When the temperature of molten steel reaches 1550±10℃, vacuum degassing treatment is carried out for 12 minutes in a vacuum environment of no more than 0.5tor;

[0051] Continuous casting: The temperature of the molten steel in the tundish is controlled at 1525-1540℃, and the whole process is cast in argon closed atmosphere. The casting superheat is controlled at 23℃, and the steel enters the clamping roller table in the full roller area, the roller table in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller, and the continuous casting billet of 280mm*280mm*6000mm is obtained by flame cutting;

[0052] Ingot heating: The continuous casting ingot is sent to the walking beam furnace and heated to 1200℃ in sections, and kept in the soaking section for 2 hours;

[0053] Rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the two-roller reversible unit for rolling. The starting rolling temperature is 1100℃. After 11 passes of rolling by the two-roller reversible unit, it is rolled into a semi-finished product with a cross-section of 190*210mm, and then enters the continuous rolling unit at 950℃ to be rolled into a round steel with a diameter of 120mm;

[0054] Online quenching: The round steel after final rolling is conveyed to sawing through rollers, with water inlet temperature of 759°C, quenching time of 41s, and water outlet temperature of 164°C;

[0055] Slow cooling: The round steel after online quenching is sent to the cooling bed for slow cooling. After returning to red, the temperature entering the hood is 628℃ and the temperature out of the hood is 321℃.

[0056] Figure 1 The core microstructure of Example 1 is shown.

[0057] Embodiment 2:

[0058] The chemical composition, by weight percentage, includes the following components: C: 0.42%, Si: 0.43%, Mn: 1.40%, Cr: 0.16%, Nb: 0.025%, V: 0.075%, A1: 0.012%, Ti: 0.0075%, N: 0.0026%, P: 0.009%, S: 0.005%, and the rest is Fe and unavoidable impurities.

[0059] The specific production method steps are as follows:

[0060] Converter: treatment time 30min, end point C controlled at 0.09%~0.15%, temperature reaches 1620±30℃ for steel tapping;

[0061] LF furnace: turn on the bottom blowing of argon, energize and heat the graphite electrode, adjust the slag and further deoxidize it. After 25 minutes of treatment, adjust the temperature of the molten steel to 1590±10℃;

[0062] RH furnace: When the temperature of molten steel reaches 1550±10℃, vacuum degassing treatment is carried out for 12 minutes in a vacuum environment of no more than 0.5tor;

[0063] Continuous casting: The temperature of the molten steel in the tundish is controlled at 1525-1540℃, and the whole process is cast in argon closed atmosphere. The casting superheat is controlled at 23℃, and the steel enters the clamping roller table in the full roller area, the roller table in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller, and the continuous casting billet of 280mm*280mm*6000mm is obtained by flame cutting;

[0064] Ingot heating: The continuous casting ingot is sent to the walking beam furnace and heated to 1200℃ in sections, and kept in the soaking section for 2 hours;

[0065] Rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the two-roller reversible unit for rolling. The starting rolling temperature is 1100℃. After 11 passes of rolling by the two-roller reversible unit, it is rolled into a semi-finished product with a cross-section of 190*210mm, and then enters the continuous rolling unit at 950℃ to be rolled into a round steel with a diameter of 120mm;

[0066] Online quenching: The round steel after final rolling is conveyed to sawing through rollers, with water inlet temperature of 823°C, quenching time of 59s, and water outlet temperature of 134°C;

[0067] Slow cooling: The round steel after online quenching is sent to the cooling bed for slow cooling. After returning to red, the temperature entering the hood is 598℃ and the temperature out of the hood is 313℃.

[0068] Figure 2 The core microstructure of Example 2 is shown.

[0069] Embodiment 3:

[0070] The chemical composition, by weight percentage, includes the following components: C: 0.42%, Si: 0.43%, Mn: 1.40%, Cr: 0.16%, Nb: 0.013%, V: 0.052%, A1: 0.012%, Ti: 0.0075%, N: 0.0026%, P: 0.009%, S: 0.005%, and the rest is Fe and unavoidable impurities.

[0071] The specific production method steps are as follows:

[0072] Converter: treatment time 30min, end point C controlled at 0.09%~0.15%, temperature reaches 1620±30℃ for steel tapping;

[0073] LF furnace: turn on the bottom blowing of argon, energize and heat the graphite electrode, adjust the slag and further deoxidize it. After 25 minutes of treatment, adjust the temperature of the molten steel to 1590±10℃;

[0074] RH furnace: When the temperature of molten steel reaches 1550±10℃, vacuum degassing treatment is carried out for 12 minutes in a vacuum environment of no more than 0.5tor;

[0075] Continuous casting: The temperature of the molten steel in the tundish is controlled at 1525-1540℃, and the whole process is cast in argon closed atmosphere. The casting superheat is controlled at 23℃, and the steel enters the clamping roller table in the full roller area, the roller table in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller, and the continuous casting billet of 280mm*280mm*6000mm is obtained by flame cutting;

[0076] Ingot heating: The continuous casting ingot is sent to the walking beam furnace and heated to 1200℃ in sections, and kept in the soaking section for 2 hours;

[0077] Rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the two-roller reversible unit for rolling. The starting rolling temperature is 1100℃. After 11 passes of rolling by the two-roller reversible unit, it is rolled into a semi-finished product with a cross-section of 190*210mm, and then enters the continuous rolling unit at 950℃ to be rolled into a round steel with a diameter of 120mm;

[0078] Online quenching: The round steel after final rolling is conveyed to sawing through rollers, the water inlet temperature is 811℃, the quenching time is 57s, and the water outlet temperature is 138℃;

[0079] Slow cooling: The round steel after online quenching is sent to the cooling bed for slow cooling. After returning to red, the temperature entering the hood is 603℃ and the temperature out of the hood is 317℃.

[0080] Figure 3 The depth of the hardened layer of Example 3 is shown, and the depth is 5 mm;

[0081] Figure 4 The microstructure of the hardened layer of Example 3 is shown, in which tempered troostite accounts for 88% and the rest is ferrite and carbide.

[0082] Table 1 Chemical composition of the embodiments of the present invention and the comparative examples (mass percentage)

[0083] chemical composition Contrast steel Example 1 Example 2 Example 3 C 0.42 0.42 0.42 0.42 Si 0.43 0.43 0.43 0.43 Mn 1.40 1.40 1.40 1.40 Cr 0.16 0.16 0.16 0.16 Nb 0.025 0.025 0.025 0.018 V 0.075 0.075 0.075 0.052 A1 0.012 0.012 0.012 0.012 Ti 0.0075 0.0075 0.0075 0.0075 N 0.0026 0.0026 0.0026 0.0026 P 0.009 0.009 0.009 0.009 S 0.005 0.005 0.005 0.005

[0084] Table 2 Production process parameters of the embodiments of the present invention and the comparative examples

[0085]

[0086]

[0087] Table 3 Mechanical properties data of the embodiments of the present invention

[0088]

[0089] From the above data, it can be seen that the method according to the embodiment of the present invention can produce high-strength non-adjustable online quenching steel with an impact of 38-42J, a yield strength of 600-757MPa, a tensile strength of 860-1022MPa, an elongation of 15-16.5%, a cross-sectional shrinkage of 35%-37.5%, a hardness of 260-300HBW, and a hardened layer depth of 5-10mm. The mechanical properties of the steel after online quenching are significantly better than those of the steel without online quenching.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for producing high-strength non-adjustable online quenching steel, characterized in that: It is composed of the following components in weight percentage: carbon (C): 0.42% to 0.44%, silicon (Si): 0.43% to 0.48, manganese (Mn): 1.38% to 1.44%, chromium (Cr): 0.16% to 0.19%, niobium (Nb): 0.008% to 0.028%, vanadium (V): 0.005% to 0.085%, aluminum (A1): 0.012% to 0.022%, titanium (Ti) ≤0.01, nitrogen (N) ≤0.01%, phosphorus (P) ≤0.010%, sulfur (S) ≤0.008%, and the rest are Fe and unavoidable impurities.

2. The method for producing high-strength non-adjustable online quenching steel according to claim 1, characterized in that: The mechanical properties of the high-strength non-adjustable online quenching steel are 38-42J impact, 600-757MPa yield strength, 860-1022MPa tensile strength, 15-16.5% elongation, 35%-37.5% cross-sectional shrinkage, 260-300HBW hardness; the depth of the hardened layer is 5-10mm.

3. The method for producing high-strength non-adjustable online quenching steel according to claim 2, characterized in that: The matrix structure of the hardened layer of the high-strength non-adjustable online quenching steel is 85% to 95% tempered troostite, and the remaining structure is ferrite and carbide.

4. The method for producing high-strength non-adjustable online quenching steel according to claim 3, characterized in that: The remaining structures are ferrite 70% to 75% + bainite 15% to 20% + martensite 5% to 15%.

5. A method for producing high-strength non-adjustable online quenching steel according to any one of claims 1 to 4, characterized in that: The main steps include: Converter, LF furnace, RH furnace, continuous casting, billet heating, rolling, online quenching, slow cooling; Converter: treatment time 28-32min, control the end point C content, and tap steel at 1620±30℃; LF furnace: start bottom blowing argon, energize and heat the graphite electrode, adjust the slag and further deoxidize, after 22-27 minutes of treatment, adjust the molten steel temperature to 1590±10℃; RH furnace: When the temperature of molten steel reaches 1550±10℃, vacuum degassing treatment is carried out for no less than 10 minutes in a vacuum environment of no more than 0.5tor; Continuous casting: The temperature of the molten steel in the middle package is controlled at 1525-1540℃, and the whole process is cast in argon closed atmosphere. The casting superheat is controlled at 15-25℃, and the steel enters the clamping roller table in the full roller area, the roller table in the secondary cooling area, the fan-shaped segment bending roller and the straightening roller, and the continuous casting billet of 280mm*280mm*6000mm is obtained by flame cutting; Ingot heating: The continuous casting ingot is sent to the walking beam furnace and heated to 1160-1200℃ in sections, and kept warm in the soaking section for 1-2 hours. The total heating time is controlled within 5-7 hours. Rolling: The continuous casting slab is pushed out of the heating furnace and sent to the descaling machine through the conveyor roller. The surface oxide scale is removed by high-pressure water, and then sent to the two-roller reversible unit for rolling. The rolling temperature is 1080-1120℃, and it enters the continuous rolling unit for rolling and forming at 930-950℃. Online quenching: water inlet temperature 750-850℃, quenching time 30-60s, water outlet temperature 100-240℃; Slow cooling: Slow cooling is carried out on the cooling bed. After returning to red, the entry temperature is 550-650℃, and the exit temperature is 300-350℃.

6. The method for producing high-strength non-adjustable online quenching steel according to claim 5, characterized in that: The converter end point C is controlled at 0.09% to 0.15%.

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