A method for controlling the composition of 400Mpa hot-rolled threaded steel

Abstract

The present invention belongs to the field of iron and steel metallurgy technology and relates to a composition control method for 400 MPa grade hot-rolled threaded steel. The method comprises the following steps: 1) establishing a carbon blending method for hot-rolled threaded steel, for blending carbon to a target carbon content through molten iron; 2) after carbon blending is completed, detecting the content of each element in the molten steel, and using a pre-established hot-rolled threaded steel strength performance prediction model to calculate the average yield strength σ of the hot-rolled threaded steel corresponding to the molten steel composition. 屈服 ;3) Using the unit price of the alloy, calculate the increase in the yield strength of the steel, and under the same unit price, the alloy type with the largest increase in the yield strength of the steel is recorded as the alloy type with the best cost performance; 4) Through the target yield strength value σ 目标 and the average yield strength σ 屈服 The yield strength difference between the two groups is calculated, and the weight of the most cost-effective alloy to be added to the molten steel is calculated to compensate for the strength difference. This method can reduce alloy costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and in particular, relates to a composition control method for 400 MPa grade hot-rolled threaded steel. Background Art

[0002] 400Mpa grade hot-rolled rebar is currently the most widely used construction steel, with an annual usage of approximately 200 million tons. The output is huge, and proper composition control and process optimization can generate huge economic benefits.

[0003] The primary construction process for rebar involves bending it to a certain angle, then connecting it by welding or bundling, and finally pouring it into cement concrete. Compared to other steel types, rebar experiences less deformation during use and places lower demands on its plasticity and toughness. By limiting the content of elements harmful to toughness and plasticity, such as C, S, and P, to no more than the upper limits specified in GB / T 1499.2, "Steel for reinforced concrete - Part 2: Hot-rolled ribbed bars," the toughness and plasticity requirements of 400 MPa-grade rebar can be met.

[0004] As the main load-bearing material of construction, rebar has high requirements for its strength performance. Strength is the most important property of rebar, and the composition of steel is the key to determining its strength performance. When controlling the composition of rebar, steel mills control C, Si, Mn, P, and V within a fixed range. To improve the performance qualification rate, theoretically, the rebar's yield strength requirement of greater than 400 MPa should be achieved even if the components of C, Si, Mn, P, and V are all controlled at the lower limit of the range. However, the actual components of C, Si, Mn, P, and V fluctuate within the range. Steelmaking operators cannot accurately control the components of Si, Mn, and V at the lower limit of the range. Si, Mn, and V may all be controlled at the upper limit of the range, or two of Si, Mn, and V may be controlled at the upper limit of the range. This results in the waste of certain alloys and creates redundant strength performance.

[0005] When controlling the composition of rebar, steel mills control C, Si, Mn, P, and V within a fixed range. They do not dynamically optimize and adjust the composition of molten steel according to the market price of the alloy, nor do they dynamically increase the "addition amount of alloys with falling prices" or reduce the "addition amount of alloys with rising prices." However, the market price of alloys fluctuates, and this method of molten steel composition control is insufficient to adapt to the drastic fluctuations in alloy prices, resulting in an increase in the cost of molten steel alloys.

[0006] Carbon in steel is an inexpensive element with a good strengthening effect, but steel mills lack the ability to accurately control the carbon content in rebar. Most steel mills increase the carbon content in molten steel by adding carbon powder to the molten steel. However, the density of carbon powder is lower than that of molten steel. After being added to the molten steel, some carbon powder floats on the surface of the molten steel, causing fluctuations in the carbon powder recovery rate. Some steel mills also increase carbon by adding molten iron to the molten steel, but they all choose to add some molten iron to the ladle before tapping the converter. Since the carbon content in the molten steel cannot be accurately detected at this time, the amount of molten iron added is not accurate enough, and it is impossible to accurately adjust the carbon content in the molten steel to the upper limit. Summary of the Invention

[0007] In view of the shortcomings of the above technologies, the present invention provides a method for controlling the composition of 400Mpa grade hot-rolled threaded steel, which can reduce the alloy cost.

[0008] The present invention provides a method for controlling the composition of 400 MPa grade hot-rolled threaded steel, comprising the following steps:

[0009] 1) Establishing a carbon blending method for hot-rolled rebar to blend the molten iron to a target carbon content;

[0010] 2) After carbon blending is completed, the content of each element in the molten steel is detected, and the pre-established hot-rolled rebar strength performance prediction model is used to calculate the average yield strength σ of the hot-rolled rebar corresponding to the molten steel composition. 屈服 ;

[0011] 3) Using the unit price of the alloy, calculate the increase in yield strength of the steel. Under the same unit price, the alloy type with the greatest increase in yield strength of the steel is recorded as the alloy type with the best cost performance.

[0012] 4) Through the target yield strength value σ 目标 and the average yield strength σ 屈服 The yield strength difference is calculated, and the weight of the most cost-effective alloy that needs to be added to the molten steel to make up for the strength difference is calculated.

[0013] Preferably, in step 1), the amount of molten iron required to achieve the target carbon content is calculated by detecting the carbon content in the molten iron:

[0014] W 铁水 =[W 钢包钢水 ×(N-ω 钢包钢水-c )] / (ω 铁水-c )

[0015] Among them, W 铁水 The amount of molten iron required to adjust the carbon content in molten steel to the target carbon content, t; W 钢包钢水 is the weight of molten steel in the ladle, t; N is the target C content, %; ω 钢包钢水-cis the mass percentage of C element in molten steel in the ladle, %; ω 铁水-c is the mass percentage of C element in molten iron, %.

[0016] Preferably, a device for supporting a container containing molten iron is provided directly above the waiting station of the LF refining furnace. The device for supporting the molten iron container is equipped with a weighing system for displaying the weight of the molten iron container and determining the amount of molten iron added based on the weight change of the molten iron container.

[0017] Preferably, in step 1), the target carbon content is 0.24%.

[0018] Preferably, in step 2), the strength performance prediction model of the hot-rolled threaded steel is:

[0019] σ 屈服 =186+280(ω C )+52(ω Si )+84(ω Mn )+350(ω P -0.015)+2600(ω V )+68(ω Cr );

[0020] Among them, ω C 、ω Si 、ω Mn 、ω P 、ω V 、ω Cr Corresponding to the mass percentage of C, Si, Mn, P, V, and Cr elements in the rolled material, %; σ 屈服 is the average yield strength of hot-rolled rebar, MPa.

[0021] Preferably, in step 2), after the ladle enters the LF refining furnace, the molten steel is refined in the LF refining furnace for 5-10 minutes, and then samples are taken to detect the composition of the molten steel.

[0022] Preferably, in step 2), the contents of Si, Mn and V elements in the rebar molten steel are detected. If the lower limits of the Si, Mn and V elements are lower than 0.15%, 1.0% and 0.028% respectively, alloys are added to adjust the contents of Si, Mn and V elements to above the lower limits.

[0023] Preferably, in step 3), the alloy is one or more of silicon-manganese alloy, high-carbon ferromanganese alloy and vanadium-nitrogen alloy, wherein the carbon content of the high-carbon ferromanganese alloy is about 6-7%.

[0024] Preferably, in step 3), the increase in yield strength of the steel material caused by adding different types of alloys with the same unit price is calculated, and the alloys with the highest cost performance are prioritized, which are:

[0025] (1) The increase in yield strength of steel by adding silicon-manganese alloy with a unit price of M yuan / ton of steel is:

[0026]

[0027] (2) The increase in yield strength of steel by adding high carbon ferromanganese alloy with a unit price of M yuan / ton of steel is:

[0028]

[0029] (3) The increase in yield strength of steel by adding vanadium-nitrogen alloy with a unit price of M yuan / ton of steel is:

[0030]

[0031] Among them, P 硅锰 、P 废钢 、P 高锰 、P 钒氮 The prices of silicon manganese alloy, scrap steel, high carbon ferromanganese alloy and vanadium nitrogen alloy are RMB / kg respectively; ω 硅锰-Mn is the mass percentage of manganese element in silicon-manganese alloy, %; ω 硅锰-Si is the mass percentage of silicon in silicon-manganese alloy, %; ω 高锰-Mn is the mass percentage of manganese in high carbon ferromanganese alloy, %; ω 钒氮-V is the mass percentage of vanadium in vanadium-nitrogen alloy, %; q Mn ,q Si ,q V are the recovery rates of manganese, silicon and vanadium added to molten steel (%); K 硅锰 , K 高锰 , K 钒氮 The values ​​of increase in yield strength of steel by adding silicon-manganese alloy with a unit price of M yuan / ton of steel, high-carbon manganese-iron alloy with a unit price of M yuan / ton of steel, and vanadium-nitrogen alloy with a unit price of M yuan / ton of steel, respectively, in MPa;

[0032] By comparing K 硅锰 , K 高锰 , K 钒氮 Value, select the maximum value and record it as K 性价比—高 , and the corresponding alloy is the most cost-effective alloy.

[0033] Preferably, in step 4), the amount of alloy added is:

[0034] σ 屈服-差值 =σ 目标 -σ 屈服

[0035]

[0036] Among them, σ 屈服 is the yield strength value of hot-rolled rebar corresponding to the existing molten steel composition, MPa; σ 目标 is the expected yield strength of hot-rolled rebar, MPa; σ 屈服-差值 is σ 屈服 Value and σ 目标 The difference between the two, MPa; P 性价比—高 The price of the most cost-effective alloy is RMB / kg; P 废钢 is the price of scrap steel, RMB / kg; M is the unit price of the most cost-effective alloy, RMB / ton steel; K 性价比—高 The increase in yield strength of hot-rolled rebar by adding the most cost-effective alloy per unit price, m 性价比—高 The weight of the most cost-effective alloy to be added, kg / ton of steel

[0037] Specifically, the present invention provides a method for controlling the composition of 400Mpa grade hot-rolled threaded steel, the specific measures of which are:

[0038] 1. Establish a strength performance prediction model for 400Mpa grade hot-rolled rebar

[0039] σ 屈服 =186+280(ω C )+52(ω Si )+84(ω Mn )+350(ω P -0.015)+2600(ω V )+68(ω Cr )①;

[0040] In the above formula ①, ω C 、ω si 、ω Mn 、ω P 、ω V 、ω Cr Corresponding to the mass percentage of C, Si, Mn, P, V, and Cr elements in the rolled material, %; σ 屈服 is the yield strength of hot-rolled rebar, MPa;

[0041] When formulating the control range requirements for the molten steel composition of 400Mpa grade hot-rolled rebar, steel mills no longer use the control of a certain element within a small range as the control requirement for the composition. Instead, they use formula ① to calculate the strength of hot-rolled rebar and use the yield strength in formula ① to meet the target of being greater than or equal to 450Mpa as the control requirement for the six elements of C, Si, Mn, V, Cr, and P. The σ after these six elements are substituted into formula ① is 屈服 The value must be greater than or equal to 450Mpa.

[0042] The yield strength calculated by formula ① is the average value of the yield strength, while the actual value of the yield strength is discretely distributed, and the actual value varies. Therefore, in order to ensure that the lowest value of the actual yield strength can still meet the standard requirement of greater than 400Mpa, the yield strength requirement set in formula ① should be greater than the standard value or the user's required value. Through statistics of actual production test data, it is found that if the average yield strength is set to greater than or equal to 450Mpa, the standard requirement that the lowest yield strength is also greater than 400Mpa can be met.

[0043] 2. Calculate the yield strength increase of steel strengthened with silicon-manganese alloy, high carbon ferromanganese alloy, and vanadium-nitrogen alloy per unit price.

[0044] Specifically: calculate the increase in the yield strength of steel by adding silicon-manganese alloy, high-carbon manganese-iron alloy and vanadium-nitrogen alloy at a price of 10 yuan / ton of steel respectively.

[0045] (1) Adding silicon-manganese alloy with a price of 10 yuan / ton of steel increases the yield strength of steel by:

[0046]

[0047] (2) Adding high carbon ferromanganese alloy with a price of RMB 10 / ton of steel will increase the yield strength of steel by:

[0048]

[0049] (3) The increase in yield strength of steel by adding vanadium-nitrogen alloy with a price of 10 yuan / ton of steel is:

[0050]

[0051] In formula ②③④, P 硅锰 、P 废钢 、P 高锰 、P 钒氮 are the prices of silicon manganese alloy, scrap steel, high carbon ferromanganese alloy, and vanadium nitrogen alloy, respectively (yuan / kg); ω 硅锰-Mn is the mass percentage of manganese in silicon-manganese alloy, (%); ω 硅锰-Si is the mass percentage of silicon in silicon-manganese alloy, (%); ω 高锰-Mn is the mass percentage of manganese in high carbon ferromanganese alloy, (%); ω 钒氮-V is the mass percentage of vanadium in vanadium-nitrogen alloy (%); q Mn ,q Si ,q V are the recovery rates of manganese, silicon and vanadium added to molten steel (%); K 硅锰 , K 高锰 , K 钒氮The increase in yield strength of steel caused by adding silicon-manganese alloy, high carbon manganese-ferroalloy and vanadium-nitrogen alloy at a price of 10 yuan / ton of steel respectively (Mpa).

[0052] Select K 硅锰 , K 高锰 , K 钒氮 The largest value among them is recorded as K 性价比—高 , which means: the increase in yield strength of steel by adding the most cost-effective alloy with a price of 10 yuan / ton of steel, and the corresponding alloy is the alloy with the highest cost-effectiveness.

[0053] The calculation ideas in formulas ②③④ are: first calculate the increase in the concentration of alloying elements in the molten steel composition caused by the addition of an alloy priced at 10 yuan / ton of steel, and then use the method in formula ① to calculate the contribution of this part of the alloying element concentration to the yield strength of the rebar; it should be noted that since the addition of alloys to molten steel can increase the weight of the molten steel and correspondingly reduce the consumption of scrap steel, the actual price of the alloy in steelmaking production is "the unit price of the alloy minus the unit price of the scrap steel".

[0054] 3. Determine the amount of alloy to be added based on the component content in the molten steel after carbon addition.

[0055] Since Si, Mn and V elements not only have the function of improving the strength of steel, but also have the functions of deoxidation, sulfur fixation and nitrogen fixation, the content of Si, Mn and V elements in molten steel cannot be too low. Therefore, the content of Si, Mn and V elements still needs to set a lower limit. After comprehensive consideration, the lower limits of Si, Mn and V elements in 400Mpa grade hot-rolled rebar molten steel are 0.15%, 1.0% and 0.028% respectively, and the control range is required to be relaxed to 2 to 3 times the original range.

[0056] During the steelmaking process in the converter, silicon-manganese alloy, high-carbon ferromanganese alloy and vanadium-nitrogen alloy are used to adjust the Mn, Si and V content in the molten steel to above the lower limit of the range.

[0057] At the waiting station of the LF refining furnace, the carbon content in the molten steel is first adjusted to 0.24% by using the "carbon adjustment to target carbon content by molten iron" technology described in the present invention. Specifically:

[0058] After the steel is tapped and the ladle enters the argon station, samples are taken to detect the carbon content in the molten steel using spectroscopy. Based on the carbon content detected in the molten steel, the carbon content is adjusted to 0.24% using molten iron.

[0059] The molten iron carbon addition process is as follows:

[0060] The ladle is transported to the waiting station of the LF refining furnace. A device that can support a "container containing molten iron" is set directly above the waiting station of the LF refining furnace. The bottom of the container containing molten iron is equipped with a water inlet, which can be closed and opened by a slide. The molten iron is put into the ladle directly under the turntable through the water inlet. After the carbon addition is completed, the water inlet is closed.

[0061] The device supporting the "molten iron container" is equipped with a weighing system that can display the weight of the molten iron container in real time. Steelmaking operators can determine the amount of molten iron to be added based on the weight change of the molten iron container.

[0062] First, detect the carbon content in the molten iron and use the following formula to calculate the amount of molten iron to be added

[0063] W 铁水 =[W 钢包钢水 ×(0.24-ω 钢包钢水 )] / (ω 铁水 )⑤

[0064] In the above formula ⑤, W 铁水 The amount of molten iron required to adjust the carbon content in molten steel to 0.24%, t; W 钢包钢水 is the weight of molten steel in the ladle, t; ω 钢包钢水-c is the mass percentage of C element in molten steel in the ladle, %; ω 铁水-c is the mass percentage of C element in molten iron, %;

[0065] After the ladle enters the LF refining furnace, the molten steel is refined in the LF refining furnace for 5-10 minutes, and then samples are taken to test the composition of the molten steel.

[0066] Since Cr and P elements are not added intentionally in 400Mpa grade hot-rolled rebar, the Cr and P in the steel exist in the form of residual elements. The residual Cr and P content of different heats fluctuates, so the contribution of residual Cr and P to the strength in different heats also fluctuates. Based on the C, Cr, P, Si, Mn and V contents of the molten steel detected by sampling, the yield strength value σ under the sampled molten steel composition is calculated by substituting them into formula ①. 屈服 , and σ 屈服 The difference between the value and 450Mpa σ 屈服-差值 And add the most cost-effective alloy to the molten steel to make up for the strength difference of this part. The amount of this alloy added is:

[0067] σ 屈服-差值 =450-σ 屈服 ⑥

[0068]

[0069] In formula ⑦, P 性价比—高is the price of the most cost-effective alloy (yuan / kg); P 废钢 is the price of scrap steel, (yuan / kg);

[0070] K 性价比—高 The increase in yield strength of steel by adding the most cost-effective alloy with a price of RMB 10 per ton of steel (Mpa); m 性价比—高 The amount of the most cost-effective alloy to be added, kg / ton of steel.

[0071] Compared with the prior art, the advantages of the present invention are:

[0072] (1) C, Cr, and P are all cheap or residual elements, which basically do not increase the cost of threaded steel alloy. By using the technology described in the present invention, the C element is first adjusted to the highest value, and the content of C, Si, Mn, V, Cr, and P elements in the molten steel is detected, and then the content is brought into the threaded steel strength prediction model to determine the amount of more expensive alloy elements to be added. This can maximize the contribution of the cheap C, Cr, and P elements in the steel to the yield strength of the steel, improve the accuracy of the alloy addition amount, reduce the occurrence of excessive addition of Si, Mn, and V alloys, reduce strength redundancy, and reduce alloy cost.

[0073] (2) The present invention provides a calculation method for the most cost-effective alloy type, which can flexibly adjust the control requirements of Si, Mn, and V components in molten steel according to the alloy price, thereby reducing the alloy cost.

[0074] (3) The present invention does not stick to fixing the composition of a certain element within a certain smaller range, but controls the sum of the comprehensive yield strength contributions of these elements to meet the standard control requirements. This method takes into account the influence of the inevitable fluctuation of the composition range on the strength and can reduce the alloy waste caused by the difference in the composition control level of the steelmaking operators. DETAILED DESCRIPTION

[0075] The present invention will be further described below with reference to specific embodiments.

[0076] Example 1

[0077] A steel plant used the method of the present invention to control the composition of 400 MPa grade hot-rolled rebar, and carried out 5 heats of production:

[0078] (1) The lower limits of Si, Mn and V in the composition of 400 MPa grade hot-rolled rebar are set to 0.15%, 1.0% and 0.028% respectively, and the composition control range is required to be relaxed to more than twice the original range, as shown in Table 1 below:

[0079] Table 1. Composition control requirements for 400Mpa grade hot-rolled rebar

[0080]

[0081]

[0082] (2) The carbon content of the converter smelting endpoint is controlled at C≥0.08%. Nitrogen is blown from the bottom of the ladle during the converter discharge process. No recarburizer is added during the converter tapping process. Silicon-manganese alloy, high-carbon manganese-iron alloy, and vanadium-nitrogen alloy are used to adjust the Mn, Si, and V elements in the molten steel to above the lower limit. The weight of the molten steel in the ladle is weighed using the weighing system on the ladle car.

[0083] After the steel is tapped and the ladle enters the argon station, samples are taken to detect the carbon content in the molten steel using spectroscopy. Based on the carbon content detected in the molten steel, the carbon content is adjusted to 0.24% using molten iron.

[0084] The molten iron carbon addition process is as follows:

[0085] The ladle is transported to the waiting station of the LF refining furnace. A device that can support a "container containing molten iron" is set directly above the waiting station of the LF refining furnace. The bottom of the container containing molten iron is equipped with a water inlet, which can be closed and opened by a slide. The molten iron is put into the ladle directly under the turntable through the water inlet. After the carbon addition is completed, the water inlet is closed.

[0086] The device supporting the "molten iron container" is equipped with a weighing system that can display the weight of the molten iron container in real time. Steelmaking operators can determine the amount of molten iron to be added based on the weight change of the molten iron container.

[0087] First, detect the carbon content in the molten iron and use the following formula to calculate the amount of molten iron to be added

[0088] W 铁水 =[W 钢包钢水 ×(0.24-ω 钢包钢水 )] / (ω 铁水 )①

[0089] In the above formula ①, W 铁水 The amount of molten iron required to adjust the carbon content in molten steel to 0.24%, t; W 钢包钢水 is the weight of molten steel in the ladle, t; ω 钢包钢水-c is the mass percentage of C element in molten steel in the ladle, %; ω 铁水-c is the mass percentage of C element in molten iron, %;

[0090] (3) Establish a strength performance prediction model for 400Mpa grade hot-rolled threaded steel.

[0091] A statistical regression analysis was conducted on the production data of the steel plant in the past 3 to 5 years to establish the corresponding relationship equation between the average composition of steel grades and the average yield strength, as shown in Equation ② below.

[0092] σ屈服 =186+280(ω C )+52(ω Si )+84(ω Mn )+350(ω P -0.015)+2600(ω V )+68(ω Cr )②;

[0093] In the above formula ②, ω C 、ω Si 、ω Mn 、ω P 、ω V 、ω Cr Corresponding to the mass percentage of C, Si, Mn, P, V, and Cr elements in the rolled material, %; σ 屈服 is the yield strength of hot-rolled rebar, MPa;

[0094] (4) Calculate the yield strength increase of steel strengthened with silicon-manganese alloy, high carbon ferromanganese alloy and vanadium-nitrogen alloy per unit price.

[0095] Specifically: calculate the increase in the yield strength of steel by adding silicon-manganese alloy, high-carbon manganese-iron alloy and vanadium-nitrogen alloy at a price of 10 yuan / ton of steel respectively.

[0096] The increase in yield strength of steel by adding silicon-manganese alloy with a price of 10 yuan / ton of steel is:

[0097]

[0098] The increase in yield strength of steel by adding high carbon ferromanganese alloy with a price of RMB 10 / ton is:

[0099]

[0100] The increase in yield strength of steel by adding vanadium-nitrogen alloy with a price of 10 yuan / ton of steel is:

[0101]

[0102] In formula ③④⑤, P 硅锰 、P 废钢 、P 高锰 、P 钒氮 are the prices of silicon manganese alloy, scrap steel, high carbon ferromanganese alloy, and vanadium nitrogen alloy, respectively (yuan / kg); ω 硅锰-Mn is the mass percentage of manganese in silicon-manganese alloy, (%); ω 硅锰-si is the mass percentage of silicon in silicon-manganese alloy, (%); ω 高锰-Mn is the mass percentage of manganese in high carbon ferromanganese alloy, (%); ω 钒氮-Vis the mass percentage of vanadium in vanadium-nitrogen alloy (%); q Mn ,q Si ,q V are the recovery rates of manganese, silicon and vanadium added to molten steel (%); K 硅锰 , K 高锰 , K 钒氮 The increase in yield strength of steel caused by adding silicon-manganese alloy, high carbon manganese-ferroalloy and vanadium-nitrogen alloy at a price of 10 yuan / ton of steel respectively (Mpa).

[0103] The specific values ​​of the parameters in formulas ③④⑤ in this embodiment are shown in Table 2 below:

[0104] Table 2. Specific values ​​of the parameters in formulas ③, ④, and ⑤ in this embodiment

[0105]

[0106]

[0107] Substituting the specific values ​​of the parameters in Table 2 into equations ③④⑤, we can obtain:

[0108]

[0109]

[0110]

[0111] Select K 硅锰 , K 高锰 , K 钒氮 The largest value among them is recorded as K 性价比—高 , which means: the increase in yield strength of steel by adding the most cost-effective alloy with a price of 10 yuan / ton of steel, and the corresponding alloy is the alloy with the highest cost-effectiveness.

[0112] Through the above comparison, it is found that high carbon manganese iron alloy is the most cost-effective alloy. 性价比—高 The value is 14.47Mpa.

[0113] (5) Use the most cost-effective alloy to increase the yield strength of steel to the target value.

[0114] Five heats of molten steel were produced using the above method. After each heat of molten steel was fed into the LF refining furnace, nitrogen was blown from the bottom of the ladle throughout the LF refining process. After refining the molten steel in the LF refining furnace for 5-10 minutes, samples were taken to test the composition of the molten steel. The results of the molten steel composition test are shown in Table 3 below. Substituting the molten steel composition into Equation 2, the yield strength value σ for the sampled molten steel composition was calculated. 屈服 , and σ屈服 The difference between the value and 450Mpa σ 屈服-差值 And add the most cost-effective alloy to the molten steel to make up for the strength difference of this part. The calculation method of adding the amount of this type of alloy is as follows: ⑥⑦, σ 屈服 , σ 屈服-差值 、m 性价比—高 The calculation results are shown in Table 4 below.

[0115] σ 屈服-差值 =450-σ 屈服 ⑥

[0116]

[0117] In formula ⑦, P 性价比—高 is the price of the most cost-effective alloy (yuan / kg); P 废钢 is the price of scrap steel, (yuan / kg);

[0118] K 性价比—高 The increase in yield strength of steel by adding the most cost-effective alloy with a price of RMB 10 per ton of steel, (Mpa), m 性价比—高 The mass of the most cost-effective alloy to be added is kg / ton of steel.

[0119] After the molten steel is refined, it is continuously cast into ingots. The total amount of alloy added to the molten steel and the total alloy cost of this heat are calculated, as shown in Table 5 below. The ingots are rolled into HRB400E rebar with a specification of Φ18. The composition and mechanical properties of the rolled products are tested. The composition of the rolled products is shown in Table 6, and the test results of the mechanical properties of the rolled products are shown in Table 7 below.

[0120] Table 3. Composition of molten steel before refining and alloy addition (%)

[0121] Furnace number C Si Mn P S V Cr 2-1895 0.24 0.14 1.07 0.025 0.021 0.029 0.045 2-1896 0.24 0.15 1.06 0.028 0.025 0.032 0.052 2-1897 0.24 0.13 1.12 0.026 0.023 0.030 0.041 2-1898 0.24 0.14 1.03 0.035 0.026 0.035 0.027 2-1899 0.24 0.13 1.05 0.029 0.028 0.031 0.062

[0122] Table 4. Calculated amount of the most cost-effective alloy to be added

[0123] Furnace number <![CDATA[σ 屈服 (Mpa)]]> <![CDATA[σ 屈服-差值 (Mpa)]]> <![CDATA[m 性价比—高 (kg / ton steel)]]> 2-1895 423.57 26.43 5.09 2-1896 431.526 18.474 3.56 2-1897 429.578 20.422 3.93 2-1898 434.586 15.414 2.97 2-1899 427.726 22.274 4.29

[0124] Table 5. Total amount of alloy added to molten steel and total alloy cost

[0125]

[0126] Table 6. Composition of rolled materials (%)

[0127]

[0128]

[0129] Table 7 Mechanical properties of rolled materials

[0130]

[0131] As can be seen from Table 3, before refining and adding alloys, the composition of Si, Mn, and V in the molten steel fluctuates. The fluctuation range of Si is 0.13-0.15%, the fluctuation range of Mn is 1.03-1.12%, and the fluctuation range of V is 0.029-0.035%. As described in the background technology of the present invention: Steelmaking operators cannot accurately control the lower limit of the range of the composition of Si, Mn, and V. It is possible that Si, Mn, and V are all controlled at the upper limit of the range, or it is possible that two elements among Si, Mn, and V are controlled at the upper limit of the range. This results in the waste of certain alloys and creates redundant strength properties. To solve this problem, the technology provided by the present invention is not limited to fixing the composition of a certain element within a certain small range, but controls the sum of the comprehensive yield strength contributions of these elements to meet the standard control requirements. This method takes into account the impact of the inevitable fluctuation of the composition range on strength and can reduce the alloy waste caused by the difference in the composition control level of steelmaking operators. As shown in Table 4, in the technology described in the present invention, the yield strength value σ corresponding to the composition of the molten steel before adding alloys is first calculated 屈服 , and σ 屈服 The difference between the value and 450Mpa σ 屈服-差值 , and then calculate the amount of alloy that needs to be added to the molten steel to make up for the strength difference of this part. This method can adapt to the differences in the operator's control of the molten steel composition level to the greatest extent. The final total alloy cost of the furnace is shown in Table 5. The total alloy cost of different furnaces is not much different. The occurrence rate of two or three of the Si, Mn, and V elements being controlled at the upper limit of the center range is reduced, which can reduce the amount of more expensive alloy added and reduce the alloy cost.

[0132] It can be seen from Tables 3 and 6 that after adopting the molten iron carbon dosing process, the carbon content in the molten steel is very stable, and the molten iron can be used to very stably dosing the carbon content in the molten steel to 0.24%. The reason is as described in the present invention: before adding the molten iron into the ladle, the carbon content in the molten steel and the carbon content in the molten iron have been sampled and tested, so the amount of molten iron required to dosing to the target carbon content can be accurately calculated, and the carbon atoms and iron atoms in the molten iron are in a mutually soluble state, and the carbon atoms in the molten iron can be quickly diffused into the molten steel, thereby improving the carbon element recovery rate and the carbon dosing accuracy.

[0133] It can be seen from Tables 3 and 6 that Cr and P in steel exist in the form of residual elements. The residual Cr and P content in different heats fluctuates, so the contribution of residual Cr and P to strength in different heats also fluctuates. Based on the C, Cr, P, Si, Mn, and V contents of the molten steel detected by sampling, and bringing them into the rebar strength prediction model to determine the addition amount of more expensive alloying elements, the contribution of the cheap C, Cr, and P elements in steel to the yield strength of the steel can be maximized, and the accuracy of the alloy addition amount can be improved, the occurrence of excessive addition of Si, Mn, and V alloys can be reduced, strength redundancy can be reduced, and alloy costs can be reduced.

[0134] As shown in Table 7, the yield strength of the mechanical properties of rolled products with different compositions and different heats is close to the same, and the fluctuation range of the mechanical properties of the rolled products is small. The reason is that the "amount of alloy added in the later stage of refining" is calculated through the rebar strength prediction model. The expected "yield strength after alloy addition" for different heats is 450 MPa, which reduces the influence of composition on the mechanical properties of the rolled products. The fluctuation range of the mechanical properties of the rolled products will naturally decrease, which can reduce the number of heats with high performance and reduce the alloy cost.

[0135] Formulas ③④⑤ of the embodiment also provide a method for calculating the most cost-effective alloy type, which can flexibly adjust the control requirements of Si, Mn, and V components in molten steel according to the alloy price, and select the most cost-effective alloy to improve steel strength and reduce alloy costs.

[0136] Any content not described in detail in the present invention can be based on conventional technical knowledge in the art.

[0137] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for controlling the composition of 400 MPa grade hot-rolled threaded steel, comprising the following steps: 1) Establish a carbon blending method for hot-rolled rebar to blend the molten iron to the target carbon content; 2) After carbon blending is completed, the content of each element in the molten steel is detected, and the pre-established hot-rolled rebar strength performance prediction model is used to calculate the average yield strength of the hot-rolled rebar corresponding to the molten steel composition. ; 3) Using the unit price of the alloy, calculate the increase in yield strength of the steel. Under the same unit price, the alloy type with the greatest increase in yield strength of the steel is recorded as the alloy type with the best cost performance. 4) Pass the target yield strength value Average yield strength The difference in yield strength is used to calculate the weight of the most cost-effective alloy that needs to be added to the molten steel to make up for the strength difference. In step 1), the carbon content in the molten iron is detected and the amount of molten iron required to achieve the target carbon content is calculated: W 铁水 =[W 钢包钢水 ×(N-ω) 钢包钢水-c )] / (ω 铁水-c ); Among them, W 铁水 The amount of molten iron required to adjust the carbon content in molten steel to the target carbon content, t; W 钢包钢水 is the weight of molten steel in the ladle, t; N is the target C content, %; ω 钢包钢水-c is the mass percentage of C element in the molten steel in the ladle, %;ω 铁水-c is the mass percentage of C element in molten iron, %; In step 3), the increase in yield strength of steel by adding different types of alloys with the same unit price is calculated, and the alloys with the best cost-effectiveness are prioritized, which are: (1) Add unit price as The increase in yield strength of steel by silicon-manganese alloy at the price of RMB / ton of steel is: ； (2) Add unit price The increase in yield strength of steel by high carbon ferromanganese alloy with a price of RMB / ton of steel is: ； (3) Add unit price The increase in yield strength of steel due to vanadium-nitrogen alloy at the price of RMB / ton of steel is: ； in, 、 、 、 The prices of silicon manganese alloy, scrap steel, high carbon ferromanganese alloy and vanadium nitrogen alloy are RMB / kg respectively; is the mass percentage of manganese element in silicon-manganese alloy, %; is the mass percentage of silicon in silicon-manganese alloy, %; is the mass percentage of manganese element in high carbon ferromanganese alloy, %; is the mass percentage of vanadium element in vanadium nitrogen alloy, %; 、 、 are the recovery rates of manganese, silicon and vanadium added to molten steel, respectively (%); 、 、 Add unit price Yuan / ton steel price of silicon manganese alloy, adding unit price is Yuan / ton steel high carbon manganese ferroalloy, unit price is The added value of vanadium-nitrogen alloy on the yield strength of steel at the price of RMB / ton steel, MPa; By comparison 、 、 Value, select the maximum value and record it as , the corresponding alloy is the most cost-effective alloy; In step 4), the amount of alloy added is: ； ； in, The yield strength value of hot-rolled rebar corresponding to the existing molten steel composition, MPa; is the expected yield strength of hot-rolled rebar, MPa; for Value and The difference between them, MPa; The price of the most cost-effective alloy, RMB / kg; is the price of scrap steel, RMB / kg; M is the unit price of the most cost-effective alloy, RMB / ton of steel; To add the most cost-effective alloy per unit price to the yield strength of hot-rolled rebar, The weight of the most cost-effective alloy to be added, kg / ton of steel.

2. The composition control method of 400Mpa grade hot-rolled threaded steel according to claim 1, characterized in that: A device for supporting a container containing molten iron is set directly above the waiting station of the LF refining furnace. The device for supporting the molten iron container is equipped with a weighing system for displaying the weight of the molten iron container and determining the amount of molten iron added based on the weight change of the molten iron container.

3. The composition control method of 400Mpa grade hot-rolled threaded steel according to claim 1, characterized in that: In step 1), the target carbon content is 0.24%.

4. The composition control method of 400 MPa grade hot-rolled threaded steel according to claim 1, characterized in that: In step 2), the strength performance prediction model of the hot-rolled threaded steel is: in, 、 、 、 、 、 They correspond to the mass percentage of C, Si, Mn, P, V and Cr elements in the rolled material composition, %; is the average yield strength of hot-rolled rebar, MPa.

5. The composition control method of 400 MPa grade hot-rolled threaded steel according to claim 1, characterized in that: In step 2), after the ladle enters the LF refining furnace, the molten steel is refined in the LF refining furnace for 5-10 minutes, and then samples are taken to detect the composition of the molten steel.

6. The composition control method of 400 MPa grade hot-rolled threaded steel according to claim 5, characterized in that: In step 2), the contents of Si, Mn, and V in the rebar molten steel are detected. If the lower limits of Si, Mn, and V are lower than 0.15%, 1.0%, and 0.028%, respectively, alloys are added to adjust the contents of Si, Mn, and V to above the lower limits.

7. The composition control method of 400 MPa grade hot-rolled threaded steel according to claim 1, characterized in that: In step 3), the alloy is one or more of silicon-manganese alloy, high-carbon manganese-iron alloy and vanadium-nitrogen alloy.

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