A production method of low-cost HRB400E third-grade screw steel

Abstract

The application discloses a production method of low-cost HRB400E tertiary screw steel, and belongs to the technical field of micro-alloy steel production. After the steel tapping, deoxidation and alloying, a kind of alloy core wire made of TiN, MnSiN+Cr and other alloy ultrafine powder is fed into a post-furnace refining argon blowing station or an LF ladle furnace, through the control of end-point carbon, tapping temperature, deoxidation process and suitable argon blowing intensity, the nitride alloy of Ti in the core wire forms stable C compound with C in the steel, and through controlled cooling in the casting and rolling process, the TiN(C) compound in the steel is in solid high-temperature ceramic ultrafine nanophase and is precipitated at the grain boundary of the steel to play a pinning effect; Cr, as a strong quenching metal strengthening element, can significantly improve the mechanical property indexes of the steel, such as yield, tensile strength and elongation, by more than 25%, can realize the reduction or complete replacement of Nb and V alloy elements in the steel, reduces the production cost of the HRB400E tertiary screw steel, and has remarkable economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of microalloyed steel production technology, specifically, it relates to a low-cost method for producing HRB400E grade III rebar. Background Technology

[0002] In the production of microalloyed steel, trace elements such as V, Nb, Al, and Ti, which have strong effects on refining grains and promoting precipitation, are typically added to give the steel high strength, high weldability, and good formability after hot rolling. However, the drawbacks are that the trace elements V, Nb, Al, and Ti added to the steel are expensive, keeping production costs high. Furthermore, Al and Ti are reactive elements that readily react with oxygen in the steel to form high-melting-point oxide inclusions, which are difficult to remove, contaminating the molten steel and affecting normal continuous casting production.

[0003] 1. In the early 20th century, foreign countries began to study the alloying effect of non-metallic nitrogen (N) in steel, focusing on the strengthening mechanism of nitrides and carbonitrides in steel. Research results showed that N, with trace amounts of V, Nb, Al, Ti, and C in steel, can form high-melting-point, high-strength carbides, nitrides, and carbonitrides. During secondary heating and cooling, these compounds can disperse and precipitate on the grain boundary surface and anchor between grain boundaries, effectively inhibiting grain growth. Therefore, N's effect on grain refinement and precipitation is more significant than that of trace elements such as V, Nb, Al, and Ti, effectively reducing the amount of trace elements V, Nb, Al, and Ti required and lowering the production cost of microalloyed steel. In the mid-to-late 20th century, my country introduced this technology, using non-metallic nitrogen alloying with V, Nb, Al, Ti, and C as the most economical and effective additive for high-strength low-alloy steel, and it is widely used in the production of high-strength hot-rolled ribbed steel bars with a strength of HRB400 and above.

[0004] 2. Nitride cermets possess excellent oxidation resistance, thermochemical stability, superior corrosion resistance, ultra-high temperature resistance, ultra-high strength, and ultra-high hardness, giving them broad application prospects.

[0005] ① Ultra-high temperature metal ceramic matrix. Due to their high price (300,000-2,000,000 RMB / ton), ultra-high purity, nano-scale nitride metal ceramics are mostly used as additives in ultra-high temperature ceramics based on metal ceramics in aerospace and powder metallurgy. For example, adding TiN at a ratio of 5-10% to ceramics can significantly improve the strength, toughness, and hardness of the matrix.

[0006] ② High-strength cermet steel. Research by Mitsubishi Corporation of Japan on the dispersion of TiN powder into high-speed steel shows that the addition of TiN cermet components improves the steel's wear resistance and toughness, achieving a hardness of HRC67 and a flexural strength of 3.5*10. 7 Pa, tensile strength 2.1*0 7Pa, with a strength reaching HRC65 even at a high temperature of 600℃.

[0007] In the production of rebar, domestic companies such as Jiuquan Iron & Steel and Hebei Xuanhua Iron & Steel use titanium alloys, combined with the optimization of microalloying and deoxidation processes, and the optimization of rolling processes. They have basically achieved the production of HRB400E grade steel bars without niobium and vanadium, which has greatly reduced the production cost of rebar.

[0008] 3. Strengthening mechanism of metal nitride alloys

[0009] ① Mechanism and function of grain refinement. George and Irani of the Institution of Steel Research in the UK pointed out that when the temperature reaches about 1200℃, fine and dispersed nitride cermet particles have an influence on the control of austenite grain size.

[0010] Stvatcor discussed the mechanism of grain boundary pinning in nitride-ceramic particles. Zener proposed the following relationship between particle radius, particle volume percentage, and austenite grain radius:

[0011] R = 3 / 4 * r / f

[0012] R—Austenite grain radius

[0013] r—particle radius

[0014] f—Volume percentage of the nailed particles

[0015] Therefore, to obtain fine austenite grain size, it is necessary to make the particles fine or increase the volume percentage of nitride cermet particles in the steel.

[0016] When fine second-phase particles (nitride cermet particles) are introduced into the austenite matrix of steel, the particles interact with the grain boundaries. These second-phase particles typically reside on the grain boundaries, and some grain boundaries are replaced by these particles. Furthermore, surface energy ensures the stability of the relative positions of the grain boundaries. Therefore, grain boundary migration (grain growth) is hindered by these particles, which in turn refine the austenite grains.

[0017] The presence of second-phase particles (such as nitride cermet particles) in the steel matrix plays a crucial role in the mechanical and physicochemical properties of steel due to variations in their type, content, size, morphology, and distribution. Studies have found that the precipitation of fine-sized nanoscale nitride cermet particles in steel exhibits excellent strengthening effects. Therefore, obtaining fine-sized second-phase particles in steel is one of the most valuable research areas for future advancements in strengthening the mechanical properties of steel materials.

[0018] There are generally two methods for introducing second-phase particles into steel for strengthening: endogenous and exogenous. Endogenous strengthening refers to the precipitation of dispersed, fine intermetallic compounds, inclusions, and carbide particles by controlling metallurgical and solidification process parameters; exogenous strengthening involves adding fine nitride cermet particles into the steel through external factors. Endogenous strengthening is suitable for continuous casting processes with high steel purity and rapid cooling rates. Exogenous strengthening, on the other hand, has lower requirements for steel purity, is simpler to control, and can overcome the uncertainty and uncontrollability of the number of endogenous particles in the endogenous strengthening process.

[0019] ② Dispersion strengthening effect. The strengthening effect of dispersed two-phase particles in steel is very similar to that of V nitrides in microalloyed steel, high-strength low-alloy steel, and non-quenched and tempered steel. Alloying elements such as V, Ti, and Al in steel have a strong affinity for N, and the resulting TiN, AlN, and VN have very high solubility at high temperatures. During low-temperature solidification, they can precipitate very fine second-phase particles that disperse and anchor at the austenite grain boundaries. In addition to refining the austenite grains, the dispersed distribution of these particles at the grain boundaries can play a precipitation strengthening role, and can also inhibit creep deformation of steel at high temperatures, improving creep strength and endurance strength. Summary of the Invention

[0020] The purpose of this invention is to provide a low-cost method for producing HRB400E grade III rebar, in order to solve the technical problem mentioned in the background art that "the trace elements V, Nb, Al and Ti added to the steel are expensive, which keeps the production cost high. At the same time, Al and Ti are active elements that easily react with oxygen in the steel to form high-melting-point oxide inclusions that are difficult to remove."

[0021] The objective of this invention can be achieved through the following technical solutions:

[0022] A low-cost method for producing HRB400E grade III rebar includes the following steps:

[0023] a. Mix two or more ultrafine alloy powders of Ti, Mn and Si with a particle size of 700-1000 mesh, with Ti accounting for 30-60% by weight, Mn accounting for 20-35% by weight and Si accounting for 15-35% by weight, and set aside for later use.

[0024] b. After uniformly mixing ultrafine alloy powder, water-soluble binder, and catalyst, the mixture is moistened, shaped into spheres or blocks, dried, and then placed in a high-temperature vacuum nitriding furnace. The temperature is controlled at 1000-1350℃, the nitrogen pressure at 0.03-0.05MPa, and nitriding is carried out for 24-36 hours to produce nitride alloys such as Ti, Mn, and Si. The water-soluble binder is 200-400 mesh, easily soluble in water, and does not chemically react with the alloy powder. After high-temperature nitriding, the main products are low-residue industrial starch and lignocellulose, with water and carbon dioxide, added at a ratio of 0-4%. The catalyst is ultrafine reduced iron powder (600 mesh or finer), silicon nitride powder, and ammonium salt, which can catalyze and accelerate the nitriding of metal alloy powder. The weight ratio of the three is (5-10):(10-15):(5-8), and the catalyst addition ratio is 5-15%.

[0025] c. Nitride alloys such as Ti, Mn, and Si are processed into 0-3mm thick wires and mixed with 150-200 mesh Cr fine powder in a ratio of (6-8):(2-4). The mixture is then tightly wrapped with a low-carbon steel strip with a thickness of 0.34-0.45mm to form an alloy cored wire with a diameter of Ф9-13mm.

[0026] d. The final tapping concentration C is ≥0.08% and the final tapping temperature is ≥1650℃.

[0027] e. For converters with a capacity of ≥100 tons, deoxidation and alloying are performed when 1 / 3 of the steel is tapped: For HRB400E rebar with a diameter of φ20 or less, MnSi alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, and Si 0.28-0.33%, without adding V or Nb alloying; For HRB400E rebar with a diameter of φ20 or more, MnSi alloying is used, with appropriate amounts of V or Nb alloying, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, Si 0.28-0.33%, and V 0.018-0.022% or Nb 0.018-0.022% (V or Nb addition reduced by 25-30%).

[0028] A composite deoxidation method using 0.5-1.0 kg / t metallic Al and 1.0 kg / t BaCaSi is employed to reduce the oxygen content in the molten steel to below 30 ppm. 1-2 kg / t of active lime is added to create a high-basicity slag (basicity 2.5-3.5). After high-intensity argon blowing and stirring at the refining argon blowing station for 5-8 minutes, 2.5-3.5 m / t of alloy cored wire is fed in at a speed controlled at 3-4 m / s. Strong argon blowing and stirring are used during the wire feeding process. After feeding, the molten steel is allowed to stand and then gently stirred with argon for 5-8 minutes. The target concentrations of [N] in the molten steel are controlled at 95-100 ppm, Ti at 0.08-0.015%, and Cr at 0.015-0.025%. Temperature measurement and sampling are performed before casting.

[0029] f. For steel tapped from a converter with a capacity of ≤100 tons, deoxidation and alloying are carried out according to step e. After controlling the smelting composition and producing high-basicity slag according to different specifications of rebar, the molten steel enters the LF ladle furnace for refining. During refining, 0.5-1 kg / t of pre-melted refining slag, 0.5 kg / t of silicon carbide, and 0.5 kg / t of aluminum powder are added to further modify and deoxidize the ladle top slag. After controlling FeO+MnO≦1% in the ladle top slag, 2.5-3.0 m / t of alloy cored wire is fed in at a feeding speed of 3-4 m / s. Strong argon blowing and stirring are used during the feeding process. After feeding, the molten steel is allowed to stand and weakly stirred with argon blowing for 5-8 minutes. The target control for [N] in the molten steel is 95-100 ppm, the target control for Ti is 0.08-0.015%, and the target control for Cr is 0.015-0.025%. Temperature measurement and sampling are performed before casting.

[0030] g. During casting, the tundish temperature is controlled at 1535-1545℃, the casting speed is 2.4-2.65m / min, the water content is 0.5-0.8L / kg, and the surface temperature of the billet before straightening is 900-950℃, so as to facilitate the rapid cooling and precipitation of TiN(C).

[0031] h. The billet is heated in the heating furnace at a temperature of 1200-1250℃, the initial rolling temperature is controlled at 1030-1080℃, and the finishing rolling temperature is controlled at 840-870℃. In the second stage of finishing rolling, 30%-40% of atomized water is used for controlled cooling to ensure the secondary precipitation of TiN(C) nanophase, so as to enhance the microstructure and properties.

[0032] The beneficial effects of this invention are:

[0033] This invention addresses the high cost and production burden of precious alloying elements such as Nb and V in microalloyed steel. It introduces alloying elements with relatively lower prices than Nb and V, such as Ti, Mn, Si, and Cr, which react with N at high temperatures to form nitride alloys of Ti, Mn, and Si. These alloys are then mixed with metallic Cr in a specific ratio to form cored wire. This cored wire is added to molten steel via wire feeding during the refining argon blowing station or LF refining process. By controlling the final tapping temperature, wire feeding amount, feeding speed, argon blowing operation, N content in the steel, and controlled cooling rolling process, the production of microalloyed steel can be fully optimized. By utilizing the high-melting-point, high-strength carbides, nitrides, and carbonitrides that Ti, N, Cr, and C can form, rapid cooling during the primary casting and secondary heating rolling process allows them to disperse and precipitate on the grain boundary surface and anchor between grain boundaries. This effectively inhibits grain growth. The high-melting-point, high-strength carbides, nitrides, and carbonitrides formed by Ti, N, Cr, and C can achieve a grain refinement and precipitation effect comparable to that of trace elements such as V and Nb. This can effectively reduce the amount of trace elements V and Nb added, thereby lowering the production cost of microalloyed steel.

[0034] Furthermore, by adding the cored wire to molten steel, the nitrogen-titanium alloy wire can be fed deep into the molten steel, reducing burn-off or oxidation losses. This avoids the problem of nitrogen-containing materials being easily oxidized by oxygen in the molten steel when added in bulk alloy form, resulting in poor nitrogen fixation and unstable nitrogen recovery.

[0035] This invention involves the deoxidation and alloying of HRB400E grade III rebar after smelting. Then, at the furnace refining argon blowing station or LF ladle furnace, an alloy cored wire with a diameter of Ф9-13mm, made of ultrafine alloy powders such as TiN, MnSiN+Cr, etc., is fed. Through precise control of the final carbon content, tapping temperature, deoxidation process, and appropriate argon blowing intensity, under the strong stirring action of bottom-blown argon gas in the ladle, the Ti and other nitride alloys in the cored wire form stable C compounds with the C in the steel. During casting and rolling, controlled cooling is employed, causing the TiN(C) compounds in the steel to precipitate as solid-state high-temperature ceramic ultrafine nanophases at the grain boundaries of the steel. It acts as a pinning agent, which can hinder cell growth, refine grains, and significantly enhance dispersion strengthening. As a metal strengthening element with strong hardenability, Cr plays a role in solid solution strengthening in steel, while the Cr(C) generated can lower the phase transformation temperature and promote the early precipitation of TiN(C) compounds, thereby effectively improving the performance of steel. It can significantly improve and increase the mechanical properties of steel such as yield, tensile strength, and elongation by more than 25%. It can reduce or completely replace Nb and V alloying elements in steel, reduce the production cost of HRB400E grade III rebar by 25-50 yuan / t, and has significant economic benefits. Detailed Implementation

[0036] 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.

[0037] Example 1

[0038] A low-cost method for producing HRB400E grade III rebar includes the following steps:

[0039] a. Mix Ti, Mn, and Si ultrafine alloy powders with a particle size of 700-1000 mesh in a weight percentage of 30% Ti, 35% Mn, and 35% Si for later use.

[0040] b. After uniformly mixing ultrafine alloy powder, water-soluble binder (200-400 mesh industrial starch, 1% added), and catalyst (a mixture of ultrafine reduced iron powder of 600 mesh or above, silicon nitride powder and ammonium salt, with a weight ratio of 5:10:5, 5% added), the mixture is moistened, shaped into spheres or blocks, dried, and then sent to a high-temperature vacuum nitriding furnace. The temperature is controlled at 1000℃, the nitrogen pressure is 0.03MPa, and nitriding is carried out for 24 hours to produce nitride alloys such as Ti, Mn, and Si.

[0041] c. Nitride alloys such as Ti, Mn, and Si are processed into 0-3mm thick wires and mixed with 150-200 mesh Cr fine powder in a 6:4 ratio. Then, they are tightly wrapped with a 0.34mm thick low-carbon steel strip to form an alloy cored wire with a diameter of Ф9-13mm.

[0042] d. The final tapping concentration C is ≥0.08% and the final tapping temperature is ≥1650℃.

[0043] e. For converters with a capacity of ≥100 tons, deoxidation and alloying are performed when 1 / 3 of the steel is tapped: For HRB400E rebar with a diameter of φ20 or less, MnSi alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, and Si 0.28-0.33%, without adding V or Nb alloying; For HRB400E rebar with a diameter of φ20 or more, MnSi alloying with an appropriate amount of V alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, Si 0.28-0.33%, and V 0.018-0.022%.

[0044] A composite deoxidation method using 0.5 kg / t metallic Al and 1.0 kg / t BaCaSi was employed to reduce the oxygen content in the molten steel to below 30 ppm. 1 kg / t of active lime was added to create a high-basicity slag (basicity 2.5). After 5 minutes of high-intensity argon blowing and stirring at the refining argon blowing station, 2.5 m / t alloy cored wire was fed in at a speed controlled at 3 m / s. Strong argon blowing and stirring were used during the feeding process. After feeding, the molten steel was allowed to stand and then gently stirred with argon blowing for 5-8 minutes. The target concentrations of [N] in the molten steel were controlled at 95-100 ppm, Ti at 0.08-0.015%, and Cr at 0.015-0.025%. After temperature measurement and sampling, the steel was cast on the platform.

[0045] f. For steel tapped from the 100-ton converter using step e, deoxidation and alloying are performed. After controlling the smelting composition and producing high-basicity slag according to different specifications of rebar, the molten steel enters the LF ladle furnace for refining. During refining, 0.5 kg / t pre-melted refining slag, 0.5 kg / t silicon carbide, and 0.5 kg / t aluminum powder are added to further modify and deoxidize the ladle top slag. After controlling FeO+MnO≦1% in the ladle top slag, 2.5 m / t alloy cored wire is fed in at a feeding speed of 3 m / s. Strong argon blowing and stirring are used during the feeding process. After feeding, the molten steel is allowed to stand and weakly stirred with argon blowing for 5 minutes. The target control for [N] in the molten steel is 95-100 ppm, the target control for Ti is 0.08-0.015%, and the target control for Cr is 0.015-0.025%. Temperature measurement and sampling are performed before casting.

[0046] g. During casting, the tundish temperature is controlled at 1535℃, the casting speed is 2.4m / min, the water content is 0.5L / kg, and the surface temperature of the billet before straightening is 900℃, so as to facilitate the rapid cooling and precipitation of TiN(C).

[0047] h. The billet is heated to 1200℃ in the heating furnace, the initial rolling temperature is controlled at 1030℃, and the final rolling temperature is controlled at 840℃. The second stage of finishing rolling uses 30% atomized water for cooling to ensure the secondary precipitation of TiN(C) nanophase, thereby enhancing the microstructure and properties.

[0048] Example 2

[0049] A low-cost method for producing HRB400E grade III rebar includes the following steps:

[0050] a. Mix Ti, Mn, and Si ultrafine alloy powders with a particle size of 700-1000 mesh according to the following weight percentages: Ti 45%, Mn 28%, and Si 27%.

[0051] b. After uniformly mixing ultrafine alloy powder, water-soluble binder (200-400 mesh lignocellulose, added at a ratio of 2.5%), and catalyst (a mixture of ultrafine reduced iron powder of 600 mesh or higher, silicon nitride powder, and ammonium salt, with a weight ratio of 8:12:7, added at a ratio of 10%), the mixture is moistened, shaped into spheres or blocks, dried, and then sent into a high-temperature vacuum nitriding furnace. The temperature is controlled at 1280℃, the nitrogen pressure is 0.04MPa, and nitriding is carried out for 30 hours to produce nitride alloys such as Ti, Mn, and Si.

[0052] c. Nitride alloys such as Ti, Mn, and Si are processed into 0-3mm thick wires and mixed with 150-200 mesh Cr fine powder in a 7:3 ratio. Then, they are tightly wrapped with a 0.39mm thick low-carbon steel strip to form an alloy cored wire with a diameter of Ф9-13mm.

[0053] d. The final tapping concentration C is ≥0.08% and the final tapping temperature is ≥1650℃.

[0054] e. For converters with a capacity of ≥100 tons, deoxidation and alloying are performed when 1 / 3 of the steel is tapped: For HRB400E rebar with a diameter of φ20 or less, MnSi alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, and Si 0.28-0.33%, without adding V or Nb alloying; For HRB400E rebar with a diameter of φ20 or more, MnSi alloying with an appropriate amount of Nb alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, Si 0.28-0.33%, and Nb 0.018-0.022%.

[0055] A composite deoxidation method using 0.8 kg / t metallic Al and 1.0 kg / t BaCaSi was employed to reduce the oxygen content in the molten steel to below 30 ppm. 1.5 kg / t of active lime was added to create a high-basicity slag (basicity 3). After 7 minutes of high-intensity argon blowing and stirring at the refining argon blowing station, 3 m / t alloy cored wire was fed in at a speed controlled at 3-4 m / s. Strong argon blowing and stirring were used during the feeding process. After feeding, the molten steel was allowed to stand and then gently stirred with argon for 7 minutes. The target concentrations of [N] in the molten steel were controlled at 95-100 ppm, Ti at 0.08-0.015%, and Cr at 0.015-0.025%. After temperature measurement and sampling, the steel was cast on the platform.

[0056] f. For steel tapped from a converter with a capacity of ≤100 tons, deoxidation and alloying are carried out according to step e. After controlling the smelting composition and producing high-basicity slag according to different specifications of rebar, the molten steel enters the LF ladle furnace for refining. During refining, 0.8 kg / t pre-melted refining slag, 0.5 kg / t silicon carbide, and 0.5 kg / t aluminum powder are added to further modify and deoxidize the ladle top slag. After controlling FeO+MnO≦1% in the ladle top slag, 2.8 m / t alloy cored wire is fed in at a feeding speed of 3.5 m / s. Strong argon blowing and stirring are used during the feeding process. After feeding, the molten steel is allowed to stand and weakly stirred with argon blowing for 7 minutes. The target control for [N] in the molten steel is 95-100 ppm, the target control for Ti is 0.08-0.015%, and the target control for Cr is 0.015-0.025%. Temperature measurement and sampling are performed before casting.

[0057] g. During casting, the tundish temperature is controlled at 1540℃, the casting speed is 2.55m / min, the water content is 0.65L / kg, and the surface temperature of the billet before straightening is 925℃, so as to facilitate the rapid cooling and precipitation of TiN(C).

[0058] h. The billet is heated to 1225℃ in the heating furnace, the initial rolling temperature is controlled at 1055℃, and the finishing rolling temperature is controlled at 855℃. The second stage of finishing rolling uses 35% atomized water for cooling to ensure the secondary precipitation of TiN(C) nanophase, so as to enhance the microstructure and properties.

[0059] Example 3

[0060] A low-cost method for producing HRB400E grade III rebar includes the following steps:

[0061] a. Mix Ti, Mn, and Si ultrafine alloy powders with a particle size of 700-1000 mesh according to the following weight percentages: Ti 60%, Mn 20%, and Si 20%.

[0062] b. After uniformly mixing ultrafine alloy powder, water-soluble binder (200-400 mesh industrial starch, 4% added), and catalyst (a mixture of ultrafine reduced iron powder of 600 mesh or above, silicon nitride powder and ammonium salt, with a weight ratio of 10:15:8, 15% added), the mixture is moistened, shaped into spheres or blocks, dried, and then sent to a high-temperature vacuum nitriding furnace. The temperature is controlled at 1350℃, the nitrogen pressure is 0.05MPa, and nitriding is carried out for 36 hours to produce nitride alloys such as Ti, Mn, and Si.

[0063] c. Nitride alloys such as Ti, Mn, and Si are processed into 0-3mm thick wires and mixed with 150-200 mesh Cr fine powder in an 8:2 ratio. The mixture is then tightly wrapped with a 0.45mm thick low-carbon steel strip to form an alloy cored wire with a diameter of Ф9-13mm.

[0064] d. The final tapping concentration C is ≥0.08% and the final tapping temperature is ≥1650℃.

[0065] e. For converters with a capacity of ≥100 tons, deoxidation and alloying are performed when 1 / 3 of the steel is tapped: For HRB400E rebar with a diameter of φ20 or less, MnSi alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, and Si 0.28-0.33%, without adding V or Nb alloying; For HRB400E rebar with a diameter of φ20 or more, MnSi alloying with an appropriate amount of V alloying is used, with the smelting composition controlled at C 0.23-0.25%, Mn 1.25-1.30%, Si 0.28-0.33%, and V 0.018-0.022%.

[0066] A composite deoxidation method using 1.0 kg / t metallic Al and 1.0 kg / t BaCaSi was employed to reduce the oxygen content in the molten steel to below 30 ppm. 2 kg / t of active lime was added to create a high-basicity slag (basicity 3.5). After 8 minutes of high-intensity argon blowing and stirring at the refining argon blowing station, 3.5 m / t alloy cored wire was fed in at a speed controlled at 4 m / s. Strong argon blowing and stirring were used during the feeding process. After feeding, the molten steel was allowed to stand and then gently stirred with argon blowing for 8 minutes. The target concentrations of [N] in the molten steel were controlled at 95-100 ppm, Ti at 0.08-0.015%, and Cr at 0.015-0.025%. After temperature measurement and sampling, the steel was cast on the platform.

[0067] f. For steel tapped from the 100-ton converter using step e, deoxidation and alloying are performed. After controlling the smelting composition and producing high-basicity slag according to different specifications of rebar, the molten steel enters the LF ladle furnace for refining. During refining, 1 kg / t of pre-melted refining slag, 0.5 kg / t of silicon carbide, and 0.5 kg / t of aluminum powder are added to further modify and deoxidize the ladle top slag. After controlling FeO+MnO≦1% in the ladle top slag, 3.0 m / t of alloy cored wire is fed in at a feeding speed of 4 m / s. Strong argon blowing and stirring are used during the feeding process. After feeding, the molten steel is allowed to stand and weakly stirred with argon blowing for 8 minutes. The target control for [N] in the molten steel is 95-100 ppm, the target control for Ti is 0.08-0.015%, and the target control for Cr is 0.015-0.025%. Temperature measurement and sampling are performed before casting.

[0068] g. During casting, the tundish temperature is controlled at 1545℃, the casting speed is 2.65m / min, the water content is 0.8L / kg, and the surface temperature of the billet before straightening is 950℃, so as to facilitate the rapid cooling and precipitation of TiN(C).

[0069] h. The billet is heated to 1250℃ in the heating furnace, the initial rolling temperature is controlled at 1080℃, and the final rolling temperature is controlled at 870℃. The second stage of finishing rolling uses 40% atomized water for cooling to ensure the secondary precipitation of TiN(C) nanophase, so as to enhance the microstructure and properties.

[0070] As can be seen from the products of Examples 1-3, reducing the amount of V or Nb added during the implementation process by 25-30% can reduce the production cost of HRB400E grade III rebar by 25-50 yuan / t.

[0071] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A low-cost method for producing HRB400E grade III rebar, characterized in that, Includes the following steps: a. Mix two or more ultrafine alloy powders of Ti, Mn, and Si with a particle size of 700-1000 mesh for later use; b. After uniformly mixing ultrafine alloy powder, water-soluble binder and catalyst, the mixture is moistened, shaped into spheres or blocks, dried and then sent into a high-temperature vacuum nitriding furnace to produce Ti, Mn and Si nitride alloys. c. Ti, Mn, Si nitride alloys are processed into 0-3mm diameter wires and mixed with fine Cr powder in a certain proportion. Then, they are tightly wrapped with low-carbon steel strips to form alloy cored wires. d. The final tapping concentration C ≥ 0.08% and the final tapping temperature ≥ 1650℃; e. For converters with a capacity of more than 100 tons, deoxidation and alloying are carried out when 1 / 3 of the steel is tapped: For HRB400E rebar with a diameter of less than φ20, MnSi alloy is used for alloying; for HRB400E rebar with a diameter of more than φ20, MnSi, a suitable amount of V or Nb alloy is used for alloying. A composite deoxidation method using 0.5-1.0 kg / t metallic Al and 1.0 kg / t BaCaSi is employed to reduce the oxygen content in the molten steel to below 30 ppm. 1-2 kg / t of active lime is added to create a high-basicity slag. After high-intensity argon blowing and stirring at the refining argon blowing station for 5-8 minutes, 2.5-3.5 m / t of alloy cored wire is fed in at a speed controlled at 3-4 m / s. Strong argon blowing and stirring are used during the feeding process. After feeding, the molten steel is allowed to stand and then gently blown with argon for 5-8 minutes. The target concentrations of [N] in the molten steel are controlled at 95-100 ppm, Ti at 0.015-0.08%, and Cr at 0.015-0.025%. Temperature measurement and sampling are performed before casting. f. For steel tapped from a converter with a capacity of ≤100 tons, deoxidation and alloying are carried out according to step e. After controlling the smelting composition and producing high-basicity slag according to different specifications of rebar, the molten steel enters the LF ladle furnace for steel refining. During refining, 0.5-1 kg / t of pre-melted refining slag, 0.5 kg / t of silicon carbide, and 0.5 kg / t of aluminum powder are added to further modify and deoxidize the ladle top slag. After controlling FeO+MnO≦1% in the ladle top slag, 2.5-3.0 m / t of alloy cored wire is fed in, with the feeding speed controlled at 3-4 m / s. Strong argon blowing and stirring are used during the wire feeding process. After the wire is fed, the molten steel is allowed to stand and weakly stirred with argon blowing for 5-8 minutes. The target control for [N] in the molten steel is 95-100 ppm, the target control for Ti is 0.015-0.08%, and the target control for Cr is 0.015-0.025%. Temperature measurement and sampling are performed before casting on the platform. g. During casting, the tundish temperature is controlled at 1535-1545℃, the casting speed is 2.4-2.65m / min, the water content is 0.5-0.8L / kg, and the surface temperature of the billet before straightening is 900-950℃; h. The billet is heated in the heating furnace at a temperature of 1200-1250℃, the initial rolling temperature is controlled at 1030-1080℃, the finishing rolling temperature is controlled at 840-870℃, and the second stage of finishing rolling uses 30%-40% atomized water for controlled cooling.

2. The method for producing HRB400E grade III rebar at low cost according to claim 1, characterized in that, In step a, the ultrafine alloy powder contains 30-60% Ti, 20-35% Mn, and 15-35% Si by weight percentage.

3. The method for producing HRB400E grade III rebar at low cost according to claim 1, characterized in that, The nitriding parameters in step b are as follows: temperature controlled at 1000-1350℃, nitrogen pressure at 0.03-0.05MPa, and nitriding time at 24-36 hours.

4. The method for producing HRB400E grade III rebar at low cost according to claim 1, characterized in that, In step c, the ratio of Ti, Mn, Si nitride alloy to Cr fine powder is (6-8):(2-4); the particle size of the metallic Cr fine powder is 150-200 mesh; the thickness of the low carbon steel strip is 0.34-0.45 mm; and the diameter of the alloy cored wire is Ф9-13 mm.

5. The method for producing HRB400E grade III rebar at low cost according to claim 1, characterized in that, In step e, the alkalinity of the high-alkalinity slag produced by the active lime is 2.5-3.

5.

6. The method for producing HRB400E grade III rebar at low cost according to claim 1, characterized in that, In step e, for HRB400E rebar with a diameter < φ20, the smelting composition is controlled at C 0.23-0.25%, Mn 1.25-1.30%, and Si 0.28-0.33%, without adding V or Nb alloying; for HRB400E rebar with a diameter greater than φ20, the smelting composition is controlled at C 0.23-0.25%, Mn 1.25-1.30%, Si 0.28-0.33%, and V 0.018-0.022% or Nb 0.018-0.022%.