A low-cost method for producing HRB500E hot-rolled ribbed steel bars

Abstract

The present invention discloses a low-cost method for producing HRB500E hot-rolled ribbed steel bars. The chemical composition by mass percentage is as follows: C: 0.19-0.25%, Si: 0.40-0.60%, Mn: 1.40-1.55%, S: ≤0.04%, P: ≤0.04%, N: 0.015-0.025%, Ti: 0.01-0.02%, V: 0.07-0.1%, and a V / N ratio ≥3.5. Nitrogen is added by adjusting the ionized nitrogen in the LF furnace gear, and further nitrogen is fixed by using a low-cost VFe alloy microalloying smelting process and process steps, followed by soft blowing and then feeding a TiFe wire. High nitrogen is controlled to 0.015-0.025%, and the V / N ratio is ≥3.5, achieving Ti and V composite microalloying to produce hot-rolled ribbed steel bars. This method can effectively reduce production costs and improve market competitiveness.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a method for producing HRB500E hot-rolled ribbed steel bars at low cost. Background Art

[0002] HRB500E is a high-strength steel bar, an upgraded version of hot-rolled concrete rebar. Microalloying has become a dominant concept in the design of ribbed seismic rebar. The use of V has become the primary microalloying element in ribbed seismic rebar. The optimal combination of V and N, in particular, significantly improves the strength of ribbed seismic rebar and reduces alloy costs, opening up a new path for cost savings amidst the current sluggish steel market. Nitrogen, when combined with microalloying elements such as Ti, Nb, and V in steel, has the effects of precipitation strengthening and grain refinement. Extensive research has demonstrated that nitrogen is a highly effective alloying element for enhancing strength in hot-rolled ribbed rebar. Nitrogen can be fully utilized, combined with microalloying elements such as Ti, Nb, and V, to reduce alloy content and lower costs.

[0003] For example, in their paper "Research and Development of Low-Cost HRB500E Earthquake-Resistant Steel Bars," published in Shanxi Metallurgy, Issue 3, 2016, An Yong and Zhi Xubo argue that increasing the nitrogen content in vanadium steel, due to the strong affinity between nitrogen and vanadium, promotes the precipitation of vanadium-carbon and vanadium-nitrogen, converting more vanadium in solution into precipitation, thus enhancing precipitation strengthening. Furthermore, the increased nitrogen content effectively inhibits ferrite grain growth, refining the ferrite grains. The optimal grain refinement effect is achieved when the m(V):m(N) ratio in the steel reaches 4:1. Although the paper specifies an optimal m(V):m(N) ratio of 4:1, the composition design in the paper only contains 0.06-0.07% v, and the nitrogen content is not specified (equivalent to an m(N) content of only 0.015-0.0175%). The control of nitrogen content, as reflected in the paper, is conventionally achieved through vanadium-nitrogen alloying. Lower nitrogen contents are detrimental to nitrogen strengthening. Nitrogen can also cause aging in hot-rolled ribbed steel bars. Therefore, microalloying elements are needed to fix nitrogen and inhibit aging. Publicly available information typically only specifies nitrogen ranges and V, Ti, and Nb content ranges, without specifying the specific microalloying elements used for strengthening and nitrogen fixation. GB / T1499.2-2018 specifies upper limits for C, Si, Mn, P, and S, as well as an upper limit for Ceq (carbon equivalent). Elements such as V, Nb, and Ti may be added as needed. It also stipulates that the nitrogen content in steel should not exceed 0.012%. If the steel contains a sufficient amount of nitrogen-binding elements, the nitrogen content may be relaxed appropriately, but no upper limit for the relaxation of the nitrogen content is specified. The structural requirements for the steel are primarily ferrite plus pearlite, with no tempered martensite on the base circle. Hot-rolled ribbed steel bars are products with production licenses. The "Implementation Rules for Production Licenses for Construction Steel Bar Products" stipulate that a refining furnace must be used to produce steel billets for 500-grade earthquake-resistant hot-rolled ribbed steel bars and corrosion-resistant steel bars, 600-grade hot-rolled ribbed steel bars, and various grades of stainless steel bars.

[0004] HRB500E is typically manufactured by adding strengthening elements to HRB400E, achieving the desired mechanical properties through conventional hot rolling or post-rolling controlled cooling. Domestically, HRB500E is primarily produced using VN microalloying technology, typically increasing the V content to around 0.09%, essentially double that of HRB400E. This places high costs on the production side. Vanadium-nitrogen alloys are relatively expensive and have fluctuated significantly in recent years. In 2018, prices continued to rise, from 200,000 yuan / ton at the beginning of the year to 800,000 yuan / ton in November. Even in 2021, prices remained around 150,000 yuan / ton, significantly increasing the cost of HRB500E compared to HRB400E. Ferrotitanium alloys have a lower price, remaining stable at around 10,000 yuan / ton for many years. However, reports on the use of titanium alloys to strengthen HRB400E are rare, and even fewer on the use of titanium alloys to strengthen HRB500E. This is primarily due to the highly reactive chemical properties of the titanium element, which readily reacts with oxygen in slag and steel during the smelting and alloying process. This results in low and unstable Ti yields during the smelting process, making production difficult to control. Refining helps increase Ti yield, refines grains in the steel, and strengthens the steel. HRB500E production requires refining equipment, which facilitates the use of Ti microalloying to produce HRB500E. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-cost method for producing HRB500E hot-rolled ribbed steel bars. The method is to strengthen the hot-rolled ribbed steel bars with nitrogen and use low-cost VFe\TiFe composite microalloys to strengthen the bars, which can effectively reduce the production costs of enterprises and improve market competitiveness.

[0006] The technical solution adopted by the present invention is a method for producing HRB500E hot-rolled ribbed steel bars at low cost, wherein the chemical composition mass percentage is as follows: C: 0.19-0.25%, Si: 0.40-0.60%, Mn: 1.40-1.55%, S: ≤0.04%, P: ≤0.04%, N: 0.015-0.025%, Ti: 0.01-0.02%, V: 0.07-0.1%, V / N ratio ≥3.5; by adjusting the LF furnace gear The whole ionized nitrogen is used to increase nitrogen, and the low-cost VFe alloy microalloying smelting process technology and process steps are used as well as the TiFe wire is fed after soft blowing to further fix nitrogen, and the high nitrogen is controlled to be 0.015~0.025%, and the V / N ratio is ≥3.5, so as to realize the Ti, V composite microalloying production of hot-rolled ribbed steel bars. The specific implementation steps are as follows: 1. After the converter taps the steel and sees the molten steel in the ladle, a pre-deoxidized composite slag detergent is added, and its mass percentage composition is: fluorite 5-10%, calcium carbide 65-75%, limestone 15-2 5%; the amount of slag wash added is: when the carbon content of the converter end point is ≤0.06%, the amount of pre-deoxidation composite slag wash added is 2.0kg / t; when the carbon content of the converter end point is [0.07%, 0.08%], the amount of pre-deoxidation composite slag wash added is 1.5kg / t; when the carbon content of the converter end point is (0.08%, 0.12%], the amount of pre-deoxidation composite slag wash added is 1.2kg / t; when the carbon content of the converter end point is (0.12%, 0.14%], the amount of pre-deoxidation composite slag wash added is 1.0kg / t; if the converter end point carbon content is between 0.14% and 0.16%, the pre-deoxidation composite slag wash addition amount is 0.8kg / t; if the converter end point carbon content is between 0.16% and 0.20%, the pre-deoxidation composite slag wash addition amount is 0.6kg / t; 2. After adding the pre-deoxidation composite slag wash after converter tapping, silicon-manganese alloy and ferrosilicon are added in order, with the addition amount set according to the composition requirements. All alloys must be added starting when 1 / 3 of the steel is tapped and completed by 3 / 4 of the steel is tapped; 3. During and after tapping, nitrogen stirring must be performed for at least 4 minutes; 4. Nitrogen control parameters for the LF refining process are: waiting process control flow rate 5Nm 3 / h, Actual blown diameter: The liquid surface moves slightly, and the molten steel is not exposed; the flow rate during power transmission is controlled at 8-15 Nm 3 / h, the actual blown diameter is 200mm; the control flow rates of alloying / carburizing process and desulfurization process are 20-30 Nm 3 / h, the actual blown diameter is 400mm; the control flow rate of the soft blowing process is 3-5 Nm 3 / h, the actual blown diameter is 200-300mm; 5. LF refining process power supply and refining time control, after the molten steel enters the station, the power is supplied at gear 1, and after the power supply time is ≥5min, the composition is adjusted to the design requirement range and VFe is added, and then the gear is lowered to ensure that the refining and smelting time is ≥20min, and the process starts - the ladle is hoisted away; the soft blowing time is ≥5min; vanadium iron is added in the LF refining furnace; soft blowing is carried out after the vanadium iron alloy is added, and the soft blowing time is 5-7min. After rapid analysis of the sample, the titanium iron wire is fed. The soft blowing effect is based on the exposed diameter of the broken slag molten steel being 100-200mm.

[0007] According to the requirements of the present invention, φ12mm-φ25mm HRB500E was produced. The sampling test data are shown in the following table:

[0008] ;

[0009] ;

[0010] Invention ideas: 1. Control the nitrogen content in the ingredients (150~250)×10 -6 1. The V / N ratio is controlled above 3.5 to give full play to the strengthening effect of nitrogen. In order to control costs, a trace amount of Ti is added to fix nitrogen together with V to inhibit the adverse effects of nitrogen on aging; other elements C, Si, Mn, P, S and Ceq comply with the requirements of GB / T1499.2-2018 "Rebar for reinforced concrete Part 2: Hot-rolled ribbed bars"; 2. The nitrogen increase method is nitrogen blowing in the LF furnace, and low-cost VFe and TiFe are used to replace high-cost VN alloys to achieve micro-alloy strengthening and nitrogen fixation effects; 3. According to the LF station entry temperature and molten steel composition, high-level nitrogen blowing is first used after entering the station to achieve temperature increase and ionized nitrogen, promote nitrogen increase in the molten steel and ensure nitrogen content. The present invention's method replaces VN microalloying with low-cost VFe microalloying to produce hot-rolled ribbed steel bars, bypassing the expensive VN alloy. Nitrogen blowing is used to increase nitrogen content and control nitrogen concentration, as well as nitrogen fixation by V and Ti. Based on the LF furnace's inlet temperature and composition, power is initially supplied at a high setting to ionize nitrogen for rapid nitrogen addition. The setting is then lowered and maintained for a specified period. VFe alloy is then added, controlling the V / N ratio to above 3.5 to promote the combination of V and nitrogen to form V(CN). A TiFe wire is then fed before tapping for further nitrogen fixation, suppressing the adverse effects of nitrogen on aging. This method enables low-cost production of HRB500E hot-rolled ribbed steel bars. Implementation Method

[0011] A method for producing HRB500E hot-rolled ribbed steel bars at low cost, wherein the chemical composition by mass percentage is as follows: C: 0.19-0.25%, Si: 0.40-0.60%, Mn: 1.40-1.55%, S: ≤0.04%, P: ≤0.04%, N: 0.015-0.025%, Ti: 0.01-0.02%, V: 0.07-0.1%, the balance being iron and unavoidable impurities, with a V / N ratio ≥3.5; and the steel bars are heated to a temperature of 1000°C in a 1000°C furnace. Adjust the nitrogen addition of ionized nitrogen, use the low-cost VFe alloy microalloying smelting technology and process steps and soft blowing followed by feeding TiFe wire to further fix nitrogen, control the high nitrogen to 0.015~0.025%, V / N ratio ≥3.5, and realize Ti, V composite microalloying to produce hot-rolled ribbed steel bars. The specific implementation steps are as follows: 1. After the converter taps the steel and sees the molten steel in the ladle, add a pre-deoxidized composite slag washer, whose mass percentage composition is: fluorite 5-10%, calcium carbide 65-75%, limestone 15- 25%; the amount of slag wash added is: if the carbon content at the converter end is ≤0.06%, the amount of pre-deoxidation composite slag wash added is 2.0kg / t; if the carbon content at the converter end is [0.07%, 0.08%], the amount of pre-deoxidation composite slag wash added is 1.5kg / t; if the carbon content at the converter end is (0.08%, 0.12%], the amount of pre-deoxidation composite slag wash added is 1.2kg / t; if the carbon content at the converter end is (0.12%, 0.14%], the amount of pre-deoxidation composite slag wash added is The pre-deoxidation composite slag detergent is 1.0 kg / t; if the converter end point carbon content is between 0.14% and 0.16%, the pre-deoxidation composite slag detergent addition amount is 0.8 kg / t; if the converter end point carbon content is between 0.16% and 0.20%, the pre-deoxidation composite slag detergent addition amount is 0.6 kg / t. 2. After adding the pre-deoxidation composite slag detergent after converter tapping, silicon-manganese alloy and ferrosilicon are added in order, with the addition amount set according to the composition requirements. All alloys must be added starting when 1 / 3 of the steel is tapped and completed when 3 / 4 of the steel is tapped. 3. During and after tapping, nitrogen stirring must be performed for at least 4 minutes. 4. The nitrogen control parameters for the LF refining process are: waiting process control flow rate is 5 Nm 3 / h, Actual blown diameter: The liquid surface moves slightly, and the molten steel is not exposed; the flow rate during power transmission is controlled at 8-15 Nm 3 / h, the actual blown diameter is 200mm; the control flow rates of alloying / carburizing process and desulfurization process are 20-30 Nm 3 / h, the actual blown diameter is 400mm; the control flow rate of the soft blowing process is 3-5 Nm 3 / h, the actual blown diameter is 200-300mm; 5. LF refining process power supply and refining time control, after the molten steel enters the station, the power is supplied at gear 1, and after the power supply time is ≥5min, the composition is adjusted to the design requirement range and VFe is added, and then the gear is lowered to ensure that the refining and smelting time is ≥20min, and the process starts - the ladle is hoisted away; the soft blowing time is ≥5min; vanadium iron is added in the LF refining furnace; soft blowing is carried out after the vanadium iron alloy is added, and the soft blowing time is 5-7min. After rapid analysis of the sample, the titanium iron wire is fed. The soft blowing effect is based on the exposed diameter of the broken slag molten steel being 100-200mm.

Claims

1. A method for producing HRB500E hot-rolled ribbed steel bars at low cost, characterized by: The mass percentage of the chemical composition is: C: 0.19-0.25%, Si: 0.40-0.60%, Mn: 1.40-1.55%, S: ≤0.04%, P: ≤0.04%, N: 0.015-0.025%, Ti: 0.01-0.02%, V: 0.07-0.1%, and V / N ratio ≥3.5; by adjusting the LF furnace gear to increase nitrogen by ionized nitrogen, using low-cost VFe alloy microalloying smelting technology and process steps and soft blowing followed by feeding TiFe wire for further nitrogen fixation, high nitrogen is controlled to 0.015-0.025%, and V / N ratio ≥3.5, to achieve Ti, V composite microalloying and production of hot-rolled ribbed steel bars, and the specific implementation steps are as follows: 1). After the converter is tapped and the molten steel is seen in the ladle, a pre-deoxidation composite slag wash is added. The weight percentage of the components is: fluorite 5-10%, calcium carbide 65-75%, and limestone 15-25%. The amount of the slag wash added is: if the converter end carbon content is ≤0.06%, the amount of the pre-deoxidation composite slag wash added is 2.0 kg / t; if the converter end carbon content is between [0.07%, 0.08%], the amount of the pre-deoxidation composite slag wash added is 1.5 kg / t; if the converter end carbon content is between (0 0.08%, 0.12%], the amount of pre-deoxidation composite slag wash agent added is 1.2kg / t; the carbon content at the converter end is (0.12%, 0.14%], the amount of pre-deoxidation composite slag wash agent added is 1.0kg / t; the carbon content at the converter end is (0.14%, 0.16%], the amount of pre-deoxidation composite slag wash agent added is 0.8kg / t; the carbon content at the converter end is (0.16%, 0.20%], the amount of pre-deoxidation composite slag wash agent added is 0.6kg / t; 2) After adding the pre-deoxidized composite slag detergent during the converter tapping, add silicon-manganese alloy and ferrosilicon in sequence. The amount added is set according to the composition requirements. All alloys must be added when 1 / 3 of the steel is tapped and all alloys must be added when 3 / 4 of the steel is tapped. 3) During and after tapping, nitrogen stirring must be performed for more than 4 minutes; 4). The nitrogen control parameters of the LF refining process are: waiting process control flow rate is 5Nm 3 / h, Actual blown diameter: The liquid surface moves slightly, and the molten steel is not exposed; the flow rate during power transmission is controlled at 8-15 Nm 3 / h, the actual blown diameter is 200mm; the control flow rates of alloying / carburizing process and desulfurization process are 20-30 Nm 3 / h, the actual blown diameter is 400mm; the control flow rate of the soft blowing process is 3-5 Nm 3 / h, the actual blown diameter is 200-300mm; 5). Control of power supply and refining time during LF refining process: after molten steel enters the station, power supply is applied at gear 1. After power supply time ≥5min, adjust the composition to the design requirement range and add VFe. Then adjust the gear to a lower level to ensure refining and smelting time ≥20min. Processing starts - ladle is hoisted away; soft blowing time ≥5min; ferrovanadium is added in LF refining furnace; soft blowing is carried out after vanadium-iron alloy is added. The soft blowing time is 5-7min. Samples are taken for rapid analysis and then fed to titanium-iron wire. The soft blowing effect is measured by the exposed diameter of molten steel of broken slag of 100-200mm.