Method for controlling low titanium content of railway wheel steel

Abstract

The invention relates to a method for controlling the low titanium content of high-grade railway wheel steel, which comprises the following steps of: adopting carbon scrap steel and molten iron as raw materials, controlling the molten iron ratio and the molten iron temperature, forbidding Ti-containing scrap steel and adopting a low-titanium refractory material. The TiO2 content of the high-grade wheel steel is reduced by selecting low-titanium raw and auxiliary materials and adjusting a slag system through analysis and calculation, so that low-Ti content control of the high-grade wheel steel is realized, the concentration product of N and Ti in the smelting process is reduced from the source, the purity of a high-grade wheel is improved, and the running safety performance of the high-grade wheel is finally met.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for controlling low titanium content in railway wheel steel. Background Art

[0002] Ti is an easily oxidizable element, and it is difficult to control the Ti element during the smelting process of railway wheel steel. If the Ti content is high (Ti>0.005%) during the smelting process of railway wheel steel, large-sized titanium nitride inclusions are extremely easy to be generated. Large-sized titanium nitride inclusions are hard and brittle inclusions that can significantly reduce the performance and fatigue life of steel. TiN inclusions do not deform, and their harm can only be reduced by reducing their size. One of the effective ways to reduce the size of TiN is to reduce the concentration product of Ti and N in molten steel. With the increasing requirements of railway wheel steel for metal material cleanliness and organizational uniformity, it is urgent to develop a smelting method for low-Ti wheel steel.

[0003] The object of the present invention is to achieve low titanium content control in the smelting of high-grade wheel steel, thereby reducing the N and Ti concentration product in the smelting process at the source, improving the purity of high-grade wheels, and thus meeting the running safety performance of high-grade wheels. In addition, the purpose of the present invention is to provide steel that solves the above-mentioned problems, and a steel product composed of the steel. Summary of the invention

[0004] The purpose of the present invention is to provide a method for controlling the low titanium content of railway wheel steel in view of the above problems.

[0005] The object of the present invention is achieved as follows: A method for controlling low titanium content in railway wheel steel comprises the following steps: Step 1: charging an electric furnace with molten iron, the molten iron accounts for 80%-100%, the rest is carbon scrap steel, the molten iron temperature is 1320-1500°C, Ti-containing scrap steel is prohibited, 2-3t of lime is added, and the C content of the molten steel is controlled to 0.95%-1.15%; Step 2: reducing the molten iron adding speed to 3-5 t / min, and controlling the C content of the molten steel to 0.2%-0.5%, oxidizing Ti into slag, and removing Ti through a large amount of slag removal; Step 3: increasing the molten iron adding speed to 6-8 t / min, adding 0.3-1.2 t of lime in 1-3 batches according to the fluidity of the slag t, keep the slag boiling; Step 4: control the C content to the range of 0.2-0.5%, end the blowing, and tap the electric furnace; Step 5: keep the steel and slag, and it is strictly forbidden to discharge slag from the electric furnace; Step 6: analyze the Ti or TiO2 content of all raw and auxiliary materials related to steel, calculate the theoretical Ti increase under ideal conditions for each raw and auxiliary material, and replace the raw and auxiliary materials with higher Ti increase with the raw and auxiliary materials with lower theoretical Ti increase to achieve low Ti content control of wheel steel; the Ti content of the raw and auxiliary materials is A, the amount of the raw and auxiliary materials added during the smelting process is B kg, and the total amount of molten steel is Ct, then the theoretical Ti increase Y of the raw and auxiliary materials under ideal conditions is: Y=AB / 1000C, if the raw and auxiliary materials are mainly TiO2, and their TiO2 content is D, then the Ti content of the raw and auxiliary materials is A=47.867D / 79.865; Step 7: Compare the use of low-Ti raw and auxiliary materials to replace high-Ti raw and auxiliary materials, and adjust the slag system to reduce its TiO2 content.

[0006] In step seven, the slag system is adjusted to reduce its TiO2 content as follows: low-aluminum ferrosilicon is replaced by low-carbon ferrosilicon, high-carbon ferromanganese is replaced by high-carbon manganese balls, primary lime is replaced by secondary lime, low-carbon ferrochrome is replaced by high-carbon ferrochrome, and the use of synthetic slag is replaced by increasing the amount of lime by 200-500kg and the amount of fluorite by 40-100kg, thereby finally achieving control of low Ti content in wheel steel.

[0007] The beneficial effects of the present invention are as follows: the present invention removes Ti through oxidation in an electric furnace and avoids slagging, calculates the theoretical Ti increase of steel-related raw and auxiliary materials under ideal conditions during the smelting process, and replaces raw and auxiliary materials with lower Ti increase with raw and auxiliary materials with higher Ti increase. Ultimately, the smelting of wheel steel with low Ti content is achieved. According to the test results, the present invention ultimately achieves a wheel steel Ti content of 9ppm, which better achieves the control of low Ti content in wheel steel. The present invention reduces the N and Ti concentration product in the smelting process from the source, improves the purity of high-grade wheels, and ultimately meets the operating safety performance of high-grade wheels. DETAILED DESCRIPTION

[0008] The object of the present invention is to control the titanium content to ≤ 0.0015% in the production practice of wheel steel, thereby further improving the fracture toughness of the finished wheel and meeting various performance requirements of railway heavy-duty wheels.

[0009] The process route of the wheel steel in the present invention is: electric furnace smelting→LF refining→VD deep vacuum treatment→continuous casting→slow cooling (or annealing)→finishing→determination and delivery to the warehouse.

[0010] To achieve the above object, the technical concept adopted by the present invention is: by comparing the oxidation free energy of the main alloying elements in steelmaking, it is found that their reducing abilities are: Al>Ti>Si>Mn. Under standard conditions, Al combines with O preferentially over Ti, and Ti combines with O preferentially over Si and Mn. As long as Si and Mn in molten iron are oxidized in large quantities, Ti can be oxidatively removed.

[0011] Ti in the molten steel is oxidized and then enters the slag, and then the Ti is automatically discharged by slag discharge, so that Ti can be reliably removed from the molten steel, and finally the molten steel composition is adjusted before steel is tapped.

[0012] The method for controlling the low titanium content of high-grade railway wheel steel of the present invention comprises the following steps: 1. The present invention adopts carbon scrap steel and molten iron as raw materials, the molten iron ratio is ≥80%, the molten iron temperature is ≥1320°C, Ti-containing scrap steel is prohibited and low-titanium refractory materials are adopted, and steel-related raw and auxiliary materials adopt low-titanium raw and auxiliary materials.

[0013] 2. Add about 2.5t of lime to the molten iron in the electric furnace charge. Control the oxygen blowing intensity, molten iron adding speed and the uniform decarburization and boiling of the molten pool of the electric furnace and automatic slag discharge.

[0014] 3. Reduce the speed of adding molten iron and control the C content of molten steel according to the type of steel being smelted, improve the oxidizability of the slag, oxidize Ti into the slag, and remove Ti through a large amount of slag discharge.

[0015] 4. Increase the speed of adding molten iron, add 300 kg of lime in batches, control the oxygen supply intensity and the amount and speed of lime addition, and keep the slag boiling.

[0016] 5. Control the C content to 0.20-0.40% and end blowing. Determine the composition and temperature according to the specific steel type before tapping.

[0017] 6. Keep steel and slag, and it is strictly forbidden to slag in the electric furnace.

[0018] 7. Analyze the Ti or TiO2 content of all raw materials and auxiliary materials involved in steel, calculate the theoretical Ti increase under ideal conditions for each raw material and auxiliary material, and replace the raw materials with higher Ti increase with raw materials with lower theoretical Ti increase to achieve low Ti content control in wheel steel. The Ti content of the raw materials is A, the amount of raw materials added during smelting is B kg, and the total amount of molten steel is C t. The theoretical Ti increase Y of the raw materials under ideal conditions is: Y=AB / 1000C. If the raw materials are mainly TiO2 and their TiO2 content is D, then the Ti content of the raw materials is A=47.867D / 79.865.

[0019] Taking the Taigang Steelmaking Plant No. 1 of China Baowu Shanxi Taigang Stainless Steel Co., Ltd. as an example, after calculation, the Ti / TiO2 content of various raw and auxiliary materials used and the theoretical Ti increase under ideal conditions are shown in the following table.

[0020]

[0021] 8. Compare and replace high-Ti raw and auxiliary materials with low-Ti raw and auxiliary materials, and adjust the slag system to reduce its TiO2 content. For example, low-aluminum ferrosilicon (special grade I) can be used to replace low-aluminum ferrosilicon, high-carbon ferromanganese can be used to replace high-carbon manganese balls, first-grade lime can be used to replace second-grade lime, and low-carbon ferrochrome can be used to replace high-carbon ferrochrome. In addition, the use of synthetic slag can be replaced by increasing the amount of lime (increase by about 200kg) and fluorite (increase by about 50kg), and finally the low Ti content of wheel steel can be controlled to less than or equal to 20ppm.

[0022] The present invention is further described below in conjunction with specific implementation modes, but is not intended to limit the protection scope thereof.

[0023] To avoid repetition, the process routes, production lines and materials involved in the specific implementation methods are described as follows and will not be repeated in the embodiments: the trial production process route of the wheel steel is: electric furnace smelting → LF refining → VD deep vacuum treatment → continuous casting → slow cooling (or annealing) → finishing → rolling into wheels.

[0024] The production line is the carbon steel continuous casting production line of the No. 1 Steelmaking Plant of China Baowu Shanxi Taigang Stainless Steel Co., Ltd. Example 1

[0025] A method for controlling the low titanium content of high-grade railway wheel steel. The steps of the control method described in this embodiment are: Steel type: ER8 high-speed railway wheel steel. Steel output 80t, smelting composition requirements [C] = 0.52% ~ 0.55%, [Si] = 0.28% ~ 0.38%, [Mn] = 0.68% ~ 0.78%, [P] ≤ 0.015%, [S] = 0.004 ~ 0.013%, [V] = 0.02 ~ 0.05%, [Cr] = 0.15 ~ 0.20%, Ti ≤ 0.002% The specific steps are as follows: Electric furnace smelting conditions: the proportion of molten iron in the furnace = 86%.

[0026] Electric furnace endpoint control: endpoint [C]=0.275%, P=0.006%, S=0.021%, Cr=0.079; steel tapping temperature T=1649℃.

[0027] (3) Steelmaking in an electric furnace: Avoid overoxidation of molten steel, retain steel and slag, and strictly prohibit slag discharge.

[0028] (4) Adding carbon powder to the electric furnace: Add a first-class coke powder recarburizer with a carbon content of ≥92% into the ladle during steelmaking.

[0029] (5) Molten steel stirring during steel tapping: The steel tapping time is 5 minutes. Ar stirring is performed at the bottom of the steel tapping process. The bottom blowing argon flow rate is controlled at 500Nl / min. After leaving the station, it enters the ladle furnace. The amount of first-grade lime used for smelting is 3391kg, the amount of fluorite used is 227kg, and the addition of synthetic slag is cancelled. 523kg of high-carbon ferromanganese and 49kg of aluminum shots are added with the steel flow.

[0030] (6) LF refining: After the ladle enters the LF station, the temperature is measured and the power is supplied to increase the temperature. The temperature is measured at 1500℃, 150 kg of calcium carbide is added per furnace, and the mixture is stirred for 5 to 8 minutes at an argon flow rate of 250 to 300 Nl / min. After that, samples are taken and alloys are added according to the C and Si contents according to the target of the finished product. 160 kg of micro-carbon ferrosilicon (super-quality grade I), 271 kg of high-carbon ferromanganese, 163 kg of micro-carbon ferrochrome, 12 kg of ferromolybdenum, 43 kg of ferrovanadium, and 150 m of aluminum wire are added. After the C, Si, Mn and other components of the LF ladle furnace are fine-tuned, pure power is supplied for 10 minutes, and the mixture is stirred for 5 to 8 minutes at an argon flow rate of 250 to 300 Nl / min; the white slag is kept for 42 minutes. During refining, lime is added at a rate of ≤50 kg / batch to maintain the viscosity of lime-saturated refined slag. Finally, 411 kg of first-grade lime and 44 kg of fluorite are added. It is forbidden to add other alloys in the middle and late stages of LF. The final LF outbound composition is shown in Table 1.

[0031] (7) VD vacuum furnace treatment: maintain high vacuum degree ≤67Pa for 15min, and after vacuum treatment, the composition and temperature of molten steel meet the requirements (except for S element), and then carry out wire feeding operation. Wire feeding operation: first feed CaSi wire (wire diameter Φ13mm, Ca content about 30%, added amount 1.1m / t steel) into the molten steel in the ladle, then, after blowing argon and stirring for ≥2 minutes, feed sulfur cored wire; ③ again, blow argon and stir for ≥15 minutes, and the stirring intensity should be such that the slag surface of the ladle just starts to creep and does not break the slag surface.

[0032] The outbound components of VD are shown in Table 1 .

[0033]

[0034] (8) The finished product smelting composition is shown in Table 1 after sampling from the tundish. The Ti content of the finished ingot is 9 ppm, which achieves low Ti content control in wheel steel.

[0035] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for controlling low titanium content in railway wheel steel, characterized in that: The following steps are involved: Step 1: Charge the electric furnace with molten iron, which accounts for 80%-100% and the rest is carbon scrap steel. The temperature of the molten iron is 1320-1500℃. Ti-containing scrap steel is prohibited. 2-3t of lime is added to control the C content of the molten steel to 0.95%-1.15%; Step 2: Reduce the molten iron addition rate to 3-5 t / min, and control the C content of molten steel to 0.2%-0.5%, oxidize Ti into slag, and remove Ti through large amounts of slag removal; Step 3: Increase the molten iron addition rate to 6-8 t / min, add 0.3-1.2 t of lime in 1-3 batches according to the slag fluidity, and keep the slag boiling; Step 4: Control the C content to the range of 0.2-0.5%, end blowing, and tap the steel from the electric furnace; Step 5: Keep the steel and slag, and do not slag in the electric furnace; Step 6: Analyze the Ti or TiO2 content of all raw and auxiliary materials related to steel, calculate the theoretical Ti increase of each raw and auxiliary material under ideal conditions, and replace the raw and auxiliary materials with higher Ti increase with the raw and auxiliary materials with lower theoretical Ti increase to achieve low Ti content control of wheel steel; The Ti content of the raw and auxiliary materials is A, the amount of the raw and auxiliary materials added during the smelting process is B kg, and the total amount of molten steel is Ct. The theoretical Ti increase Y of the raw and auxiliary materials under ideal conditions is: Y=AB / 1000C. If the raw and auxiliary materials are mainly TiO2, and their TiO2 content is D, then the Ti content of the raw and auxiliary materials is A=47.867D / 79.865; Step 7: Use low-Ti raw and auxiliary materials to replace high-Ti raw and auxiliary materials, and adjust the slag system to reduce its TiO2 content.

2. The method for controlling low titanium content in railway wheel steel according to claim 1, characterized in that: In step seven, the slag system is adjusted to reduce its TiO2 content as follows: low-aluminum ferrosilicon is replaced by low-carbon ferrosilicon, high-carbon ferromanganese is replaced by high-carbon manganese balls, primary lime is replaced by secondary lime, low-carbon ferrochrome is replaced by high-carbon ferrochrome, and the use of synthetic slag is replaced by increasing the amount of lime by 200-500kg and the amount of fluorite by 40-100kg, thereby finally achieving control of low Ti content in wheel steel.

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