CN108796173A - Improve the smelting process of heavy rail steel cleanness - Google Patents

Abstract

The invention discloses a smelting method for improving the cleanliness of heavy rail steel, belonging to the technical field of iron and steel metallurgy. The technical problem solved by the invention is that the cleanliness of existing domestic heavy rail steels is difficult to meet the requirements of high-speed railways. The method includes molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting. In the process of converter smelting, the molten iron is blown by double slag method, and the amount of active lime used for the first slagging material is 5-20kg/t Molten iron; the dosage of quartz sand is 5-10kg/t molten iron; the dosage of high-magnesia lime is 5-10kg/t molten iron; the dosage of active lime for the second slagging material is 5-10kg/t molten iron; t molten iron; the dosage of high magnesium lime is 5-10kg/t molten iron. The method of the invention can control P+S+O+N+H≤160ppm, and various ratings of inclusions≤1.0, which significantly improves the cleanliness of heavy rail steel and has certain social benefits.

Description

The Smelting Method of Improving the Cleanliness of Heavy Rail Steel

technical field

The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a smelting method for improving the cleanliness of heavy rail steel.

Background technique

Heavy rail steel is the main component of railway tracks. During railway transportation, steel rails provide effective support and guidance for locomotives and must bear huge vertical pressure from wheels. Based on the development needs of my country's infrastructure construction, railway transportation is developing at a rapid speed, and it is becoming more and more high-speed and heavy-duty. This undoubtedly puts forward stricter requirements on the quality of the rails.

When the rail is in contact with the wheel, it bears the reciprocating and variable load of the locomotive. Its cleanliness has an important impact on the life of the rail. The inclusions in the steel are the main reasons for the internal damage and fatigue damage of the heavy rail. The impediment effect of inclusions in the steel on the continuity of the matrix structure of the steel makes the steel separate from the inclusions during rolling, heat treatment and use, resulting in gaps, which have a negative impact on the mechanical properties, corrosion resistance and other indicators of the steel. For the production of rails, a series of influencing factors such as deformation rolling, complex heat treatment process, special stress conditions and climate environment are unfavorable to the rating of rail inclusions.

With the rapid development of my country's high-speed rail and the speed-up of heavy-rail railways, the demand for high-speed steel rails is increasing. High-speed railways have very high requirements on fatigue performance, and the cleanliness of heavy rail steel can greatly affect its fatigue performance. In order to improve fatigue performance, it is necessary to control the cleanliness of heavy rail steel. Generally speaking, cleanliness includes P+S+O+N+H and inclusions. Before the development of this technology, the cleanliness of domestic heavy rail steel was P+S+O+N+H≤200ppm, and the ratings of various inclusions were ≤1.5. In order to meet the requirements of high-speed railways and further improve the cleanliness of molten steel, it is necessary to develop high-speed rail production technology with P+S+O+N+H≤160ppm and various ratings of inclusions≤1.0.

Patent CN104975130A discloses a method for controlling the cleanliness of heavy rail steel. The method includes converter smelting, LF refining, RH vacuum treatment and continuous casting. In the LF refining process, active lime, silicon carbide and quartz sand are used for slag refining. Controlling the sulfur content of the prepared heavy rail steel continuous casting slab to ≤0.006%, the inclusions in the steel A are 1.5-2.0, and B, C, and D are 0.5, which is difficult to meet the requirements of high-speed railways.

Contents of the invention

The technical problem to be solved by the present invention is that the cleanliness of the existing domestic heavy rail steel is difficult to meet the requirements of high-speed railways P+S+O+N+H≤160ppm, and various ratings of inclusions≤1.0.

The technical scheme that the present invention adopts for solving its technical problem is to provide a kind of smelting method that improves the cleanliness of heavy rail steel, and this method comprises the following steps:

a. Hot metal pretreatment: use active lime and passivated magnesium powder as desulfurizers to desulfurize the hot metal to obtain desulfurized hot metal with an S content of ≤0.003% and a P content of 0.080% to 0.120%;

b. Converter smelting: add molten iron after desulfurization in step a into the converter, use active lime, quartz sand and high-magnesium lime as slagging materials for double slag dephosphorization, the amount of active lime for the first slagging material is 5 ~ 20kg/ t molten iron; the dosage of quartz sand is 5-10kg/t molten iron; the dosage of high magnesium lime is 5-10kg/t molten iron; the dosage of active lime for the second slagging material is 5-10kg/t molten iron; the dosage of quartz sand 5-10kg/t molten iron; the amount of high-magnesium lime is 5-10kg/t molten iron, and oxygen lance is used for blowing at the same time. After blowing, molten steel with P content ≤ 0.003% can be obtained. During tapping of molten steel, add Low nitrogen alloy;

c. LF refining: Send the molten steel obtained in step b to the LF ladle furnace, add calcium carbide and high-alkalinity refining slag and heat it. After refining for 20-30 minutes, add quartz sand to the molten steel. After refining for 5-10 minutes, the molten steel is treated with calcium , the molten steel exits the station after argon blowing;

d. RH refining: After LF refining is completed, the molten steel is transferred to the RH ladle furnace for vacuum treatment, and low-nitrogen alloy is added. After the vacuum treatment is completed, the molten steel is treated with calcium, and the molten steel leaves the station after argon blowing treatment;

e. Continuous casting: performing continuous casting on the molten steel obtained in step d.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, the first slagging material is added for blowing for 8 to 10 minutes to pour slag, and then the second slagging material is added to continue blowing for 5 to 8 minutes, and the slag is poured out of steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step a, the dosage of the active lime is 4-6 kg/t molten iron; the dosage of passivating magnesium powder is 1-3 kg/t molten iron.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in steps a and b, the active lime contains more than 90% of CaO, and the remainder is impurities; the quartz sand contains more than 95% of SiO ₂ , and the remainder is impurities; High magnesium lime contains 30% to 40% of MgO, 50% to 60% of CaO, and the rest are impurities.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, during the tapping process of the molten steel, a low-nitrogen alloy is added when the tapping amount is more than 1/2.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, during the blowing process, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, during the blowing process, the temperature is controlled at 1640-1670°C.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, the dosage of the calcium carbide is 0.2-0.8kg/t molten steel; the dosage of the high-alkalinity refining slag is 1-5kg/t molten steel; The dosage of the quartz sand is 0.2-0.8kg/t molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in steps c and d, the flow rate of the LF and RH refining argon blowing treatment is 50-80 NL/min, and the duration is 5-10 min.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the calcium carbide in step c contains more than 95% of CaC ₂ , and the rest is impurities; the high-basicity refining slag contains 60%-70% _of CaO, Al ₂ O ～10%, SiO ₂ 20%～30%, and the rest are impurities.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, the LF refining temperature is 1580-1595°C.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, the calcium treatment in the LF refining process is to add 1 to 3 m/t of iron-calcium line to the molten steel; in step d, the calcium treatment in the RH refining process is to add Add 3~5m/t iron-calcium wire to molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the composition of the iron-calcium wire includes 68% Fe and 30% Ca by mass percentage, and the rest are impurities; the specification of the iron-calcium wire is 200g/ m; the diameter of the iron-calcium wire is 10 mm.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, the RH refining temperature is 1535-1550°C.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, the RH refining controls the vacuum degree ≤ 100 Pa, and the vacuum treatment is 15-20 minutes.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in steps b and d, the nitrogen content of the low-nitrogen alloy added in the converter smelting and RH refining is ≤0.01%.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the low-nitrogen alloy includes ferrosilicon with a nitrogen content of 0.005%, silicon-manganese with a nitrogen content of 0.003%, ferrosilicon with a nitrogen content of 0.002%, Ferromanganese with a nitrogen content of 0.001%.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the composition of the ferrosilicon alloy with a nitrogen content of 0.005% is 75% Si, 24% Fe, and 0.005% N by mass percentage, and the remainder is impurities; The composition of the silicon-manganese alloy with a nitrogen content of 0.003% is 28% Si, 70% Mn, 0.003% N by mass percentage, and the remainder is impurities; the composition of the silicon-iron alloy with a nitrogen content of 0.002% is by mass percentage It is 75% Si, 24% Fe, 0.002% N, and the rest are impurities; the composition of the ferromanganese alloy with a nitrogen content of 0.001% is 75% Mn, 24% Fe, 0.001% N, and the rest are impurities .

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the amount of ferrosilicon alloy with nitrogen content of 0.005% added in the smelting process is 10-15kg/t molten steel, and the amount of silicon-manganese alloy with nitrogen content of 0.003% is added The amount is 15-20kg/t molten steel; the amount of ferrosilicon alloy with nitrogen content of 0.002% added in the RH refining process is 1-3kg/t molten steel, and the amount of ferromanganese alloy with nitrogen content of 0.001% is 1-3kg /t molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step e, the continuous casting process adopts bloom continuous casting to produce a generous continuous casting billet product with a cross section of more than 250mm×250mm.

The beneficial effects of the present invention are:

The method of the invention improves the cleanliness of the heavy rail steel, controls the P+S+O+N+H in the rail to ≤160ppm, and the various ratings of the inclusions≤1.0, which meets the current requirements for high-speed rails and directly improves the quality of the rails. Fatigue performance and mechanical properties provide strong technical support for the production of next-generation rails and have significant social benefits. The method of the invention can control P ≤ 0.0060%, S ≤ 0.0030%, O ≤ 0.0010%, N ≤ 0.0050% and H ≤ 0.00015% in heavy rail steel, and is suitable for P, S, O, N and H with control requirements steel type. The method of the invention adopts a double slag method in converter smelting, adding slagging materials active lime, quartz sand and high magnesium lime into the converter twice to blow molten iron, and controlling the P content at the end point of the converter within 0.003%. When the steel is tapped after the smelting process of the method of the present invention is completed, when the tapped amount is more than 1/2, a low-nitrogen alloy is added for deoxidation, so as to inhibit nitrogen from entering molten steel and effectively control the nitrogen content in molten steel.

Detailed ways

Based on the cleanliness of the existing domestic heavy rail steel P+S+O+N+H≤200ppm, and the various ratings of inclusions≤1.5, it is difficult to meet the requirements of high-speed railways. In order to find a way to improve the cleanliness of heavy rail steel, the invention Through a lot of research, people have provided a method to improve the cleanliness of heavy rail steel, which can make the cleanliness P+S+O+N+H≤160ppm, and the ratings of various inclusions≤1.0.

The invention provides a method for improving the cleanliness of heavy rail steel, the method comprising the steps of:

a. Hot metal pretreatment: use active lime and passivated magnesium powder as desulfurizers to desulfurize the hot metal to obtain desulfurized hot metal with an S content of ≤0.003% and a P content of 0.080% to 0.120%;

b. Converter smelting: add molten iron after desulfurization in step a into the converter, use active lime, quartz sand and high-magnesium lime as slagging materials for double slag dephosphorization, the amount of active lime for the first slagging material is 5 ~ 20kg/ t molten iron; the dosage of quartz sand is 5-10kg/t molten iron; the dosage of high magnesium lime is 5-10kg/t molten iron; the dosage of active lime for the second slagging material is 5-10kg/t molten iron; the dosage of quartz sand 5-10kg/t molten iron; the amount of high-magnesium lime is 5-10kg/t molten iron, and oxygen lance is used for blowing at the same time. After blowing, molten steel with P content ≤ 0.003% can be obtained. During tapping of molten steel, add Low nitrogen alloy;

c. LF refining: Send the molten steel obtained in step b to the LF ladle furnace, add calcium carbide and high-alkalinity refining slag and heat it. After refining for 20-30 minutes, add quartz sand to the molten steel. After refining for 5-10 minutes, the molten steel is treated with calcium , the molten steel exits the station after argon blowing;

d. RH refining: After LF refining is completed, the molten steel is transferred to the RH ladle furnace for vacuum treatment, and low-nitrogen alloy is added. After the vacuum treatment is completed, the molten steel is treated with calcium, and the molten steel leaves the station after argon blowing treatment;

e. Continuous casting: performing continuous casting on the molten steel obtained in step d.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, the first slagging material is added for blowing for 8 to 10 minutes to pour slag, and then the second slagging material is added to continue blowing for 5 to 8 minutes, and the slag is poured out of steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step a, the dosage of the active lime is 4-6 kg/t molten iron; the dosage of passivating magnesium powder is 1-3 kg/t molten iron. Hot metal pretreatment uses inert gas to mix active lime powder and passivated magnesium powder, and uses a rotary desulfurization spray gun to spray into molten iron for 15 to 30 minutes. After the injection is completed, desulfurized molten iron is obtained, wherein the S content is ≤0.003%. The P content is 0.080% to 0.120%. In the present invention, the molten iron before desulfurization is the common molten iron for steelmaking. The S content range of the molten iron can be 0.060% to 0.120%, and it can also be implemented if it is greater than 0.012%, but it will prolong the desulfurization time and affect the production progress.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in steps a and b, the active lime contains more than 90% of CaO, and the remainder is impurities; the quartz sand contains more than 95% of SiO ₂ , and the remainder is impurities; High magnesium lime contains 30% to 40% of MgO, 50% to 60% of CaO, and the rest are impurities. In the present invention, active lime, quartz sand, and high-magnesia lime are added in batches. First, active lime, quartz sand, and high-magnesia lime are added respectively. After the slag is melted, active lime, quartz sand, and high-magnesia lime are added respectively. Join once to join all. The chemical composition of the slagging material composed of active lime, quartz sand and high-magnesium lime is uniform and stable, which can reduce the slag in advance, shorten the smelting time and effectively dephosphorize.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, during the blowing process, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, during the blowing process, the temperature is controlled at 1640-1670°C. The temperature should not exceed 1670°C. If the temperature is too high, it is not conducive to the dephosphorization reaction.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step b, in order to ensure a lower nitrogen content in molten steel, during the tapping process of molten steel, when the tapping amount is more than 1/2, a low-nitrogen alloy is added for diffusion Deoxidation and alloying of molten steel ensure that the oxygen activity of molten steel is high in the early stage of tapping, thereby inhibiting nitrogen from entering molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, the dosage of the calcium carbide is 0.2-0.8kg/t molten steel; the dosage of the high-alkalinity refining slag is 1-5kg/t molten steel; The dosage of the quartz sand is 0.2-0.8kg/t molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, the calcium carbide contains more than 95% of CaC ₂ , and the rest is impurities; the high-alkalinity refining slag contains 60% to 70% of CaO, Al ₂ O ₃ 0-10%, SiO ₂ 20%-30%, and the rest are impurities. The purpose of adding calcium carbide and high alkalinity refining slag can evenly reduce the oxidation of steel slag in LF furnace, lower its melting point, facilitate the adsorption of inclusions in molten steel, carry out diffusion deoxidation, and control the oxygen activity in molten steel ≤0.0015%. On the one hand, it is to control inclusions and prevent the oxidation of Al, Si and other elements in molten steel during continuous casting; on the other hand, it is to increase the yield of Ca and reduce the oxidation of iron-calcium wire to CaO by O in molten steel after it is added to molten steel.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, in the LF refining process, in order to oxidize the small amount of metal aluminum brought into the alloy, the brittle Al ₂ O ₃ inclusions with large particles and high melting point produced Calcium-aluminate inclusions with low melting point can effectively promote the floating of inclusions and improve the cleanliness of molten steel. Add 1-3m/t iron-calcium wire of molten steel to the ladle for calcium treatment.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, during the LF refining process, in order to promote the chemical reaction between steel slags, accelerate the material transfer between steel slags, and facilitate the deoxidation and desulfurization of molten steel, calcium After the treatment, blow argon into the LF furnace at 50-80 NL/min for 5-10 minutes.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step c, the LF refining temperature is 1580-1595°C. LF refining can deeply deoxidize, desulfurize, reduce molten steel inclusions, and improve the cleanliness of molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, the RH refining controls the vacuum degree ≤ 100 Pa, and the vacuum treatment is 15-20 minutes.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, the RH refining temperature is 1535-1550°C.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, in order to alloy the molten steel and ensure that the composition of the molten steel meets the target requirements, the molten steel enters the RH ladle furnace for vacuum treatment for 8 minutes and then starts to add low-nitrogen alloys to control the nitrogen in the molten steel. The content is ≤0.0050%, and the oxygen activity in molten steel is controlled to be ≤0.0010%.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, in order to ensure that the residual S and Ca in the molten steel can be effectively combined, it is necessary to have a certain calcium content in the molten steel, so as to avoid the formation of a large number of large MnS inclusions, and to Add iron-calcium wire of 3-5m/t molten steel into the ladle for calcium treatment.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step d, blowing argon with an argon flow rate of 50-80 NL/min for 5-10 minutes in order to ensure that calcium can be evenly distributed in the molten steel.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the composition of the iron-calcium wire includes 68% Fe and 30% Ca by mass percentage, and the rest are impurities; the specification of the iron-calcium wire is 200g/ m; the diameter of the iron-calcium wire is 10 mm.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the nitrogen content of the low-nitrogen alloy added in the converter smelting and RH refining is ≤0.01%.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the low-nitrogen alloy includes ferrosilicon with a nitrogen content of 0.005%, silicon-manganese with a nitrogen content of 0.003%, ferrosilicon with a nitrogen content of 0.002%, Ferromanganese with a nitrogen content of 0.001%.

Wherein, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the composition of the ferrosilicon alloy with a nitrogen content of 0.005% is 75% Si, 24% Fe, and 0.005% N by mass percentage, and the remainder is impurities; The composition of the silicon-manganese alloy with a nitrogen content of 0.003% is 28% Si, 70% Mn, 0.003% N by mass percentage, and the remainder is impurities; the composition of the silicon-iron alloy with a nitrogen content of 0.002% is by mass percentage It is 75% Si, 24% Fe, 0.002% N, and the rest are impurities; the composition of the ferromanganese alloy with a nitrogen content of 0.001% is 75% Mn, 24% Fe, 0.001% N, and the rest are impurities .

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, the amount of ferrosilicon alloy with nitrogen content of 0.005% added in the smelting process is 10-15kg/t molten steel, and the amount of silicon-manganese alloy with nitrogen content of 0.003% is added The amount is 15-20kg/t molten steel; the amount of ferrosilicon alloy with nitrogen content of 0.002% added in the RH refining process is 1-3kg/t molten steel, and the amount of ferromanganese alloy with nitrogen content of 0.001% is 1-3kg /t molten steel.

Among them, in the above-mentioned smelting method for improving the cleanliness of heavy rail steel, in step e, in the continuous casting process, the tundish is blown with argon for 5 minutes to 10 minutes before pouring; the long nozzle is sealed with a sealing gasket; Large square continuous casting slab products over 250mm.

The present invention will be described in detail below through specific examples.

Example 1

Molten iron pretreatment: use molten iron as raw material, use carrier gas to mix 4kg/t molten iron active lime and 1kg/t molten iron passivated magnesium powder, use rotary desulfurization spray gun to spray into molten iron, the injection time is 15min, after desulfurization Obtain low sulfur molten iron, S content: 0.001%, P content: 0.082%.

Converter smelting: Add molten iron after desulfurization into the converter, add active lime of 7kg/t molten iron, quartz sand of 8kg/t molten iron and high-magnesium lime of 10kg/t molten iron as the first slagging materials, and supply oxygen with oxygen lance at the same time For blowing, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m, the temperature of the blowing process is 1655°C, and the second slagging material 10kg/t molten iron active lime, 10kg/t Quartz sand of molten iron and high-magnesia lime of 10kg/t molten iron, after continuous blowing for 5 minutes, slag is dumped and then steel is tapped, the P content is 0.0024%. After the converter smelting is completed, the steel is tapped. When the tapping amount is more than 1/2, 10kg/t of ferrosilicon with a nitrogen content of 0.005% in molten steel is added, and 15kg/t of silicon manganese with a nitrogen content of 0.003% in molten steel is added.

LF refining: Send molten steel obtained from converter smelting to LF furnace ladle for refining. Before heating in LF furnace, add 0.2kg/t molten steel calcium carbide and 1kg/t molten steel high alkalinity refining slag into the ladle, and heat to 1580 ℃, after refining for 20 minutes, add 0.2kg/t molten steel quartz sand into the ladle, continue refining for 5 minutes, add 1m/t molten steel iron-calcium wire to the ladle for calcium treatment, after the calcium treatment, pour 50NL of molten steel into the LF furnace Argon is blown at a flow rate of /min for 5 minutes, and the molten steel leaves the station.

RH refining: After finishing refining in LF furnace, transfer molten steel to RH furnace ladle for vacuum treatment, control the vacuum degree to 70Pa, refining temperature at 1535°C, and start adding 2.5kg/t molten steel containing nitrogen after entering RH ladle furnace for vacuum treatment for 8 minutes 0.002% ferrosilicon, and 2.5kg/t molten steel with 0.001% nitrogen ferromanganese was added. After vacuum treatment for 18 minutes, add iron-calcium wire of 3m/t molten steel to the ladle for calcium treatment. After calcium treatment, blow argon gas at a flow rate of 50NL/min for 5 minutes, and the molten steel leaves the station.

Continuous casting: The molten steel is sent to the continuous casting process, and the tundish is blown with argon for 5 minutes before pouring; the long nozzle is sealed with a sealing gasket, and a large continuous casting billet product with a cross section of 280mm×380mm is produced.

The obtained continuous casting slab is rolled into 60kg steel rail, the produced steel rail P+S+O+N+H=0.0144%, wherein, P0.0060%, S 0.0030%, O 0.0010%, N 0.0043%, H 0.0001 %. Various ratings of inclusions: Class A is 1.0, Class B, Class C, and Class D are all grade 0.

Example 2

Molten iron pretreatment: use molten iron as raw material, use carrier gas to mix 6kg/t molten iron active lime and 3kg/t molten iron passivated magnesium powder, use rotary desulfurization spray gun to spray into molten iron, the injection time is 30min, after desulfurization Obtain low sulfur molten iron, S content: 0.001%, P content: 0.120%.

Converter smelting: Add molten iron after desulfurization into the converter, add active lime of 10kg/t molten iron, quartz sand of 7kg/t molten iron and high-magnesium lime of 9kg/t molten iron as the first slagging materials, and supply oxygen with oxygen lance at the same time For blowing, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m, the temperature of the blowing process is 1658°C, and the second slagging material 10kg/t molten iron active lime, 10kg/t Quartz sand of molten iron and high-magnesia lime of 10kg/t molten iron, after continuous blowing for 8 minutes, slag is dumped and then steel is tapped, the P content is 0.0022%. After the converter smelting is completed, the steel is tapped. When the tapping amount is more than 1/2, 15kg/t of ferrosilicon with a nitrogen content of 0.005% is added, and 20kg/t of silicomanganese with a nitrogen content of 0.003% is added.

LF refining: Send the molten steel obtained from converter smelting to the ladle of LF furnace for refining. Before heating in LF furnace, add calcium carbide of 0.8kg/t molten steel and high alkalinity refining slag of 5kg/t molten steel into the ladle, and heat to 1595 ℃, after refining for 30 minutes, add 0.8kg/t molten steel quartz sand into the ladle, continue refining for 10 minutes, add 3m/t molten steel iron-calcium wire into the ladle for calcium treatment, after the calcium treatment, pour 60NL of molten steel into the LF furnace Argon is blown for 10 minutes at a flow rate of /min, and the molten steel leaves the station.

RH refining: After the LF furnace refining is completed, the molten steel is transferred to the RH furnace ladle for vacuum treatment. The vacuum degree is controlled at 60Pa, and the refining temperature is 1550°C. For 0.002% ferrosilicon, add 1kg/t molten steel with 0.001% nitrogen ferromanganese. After vacuum treatment for 19 minutes, add iron-calcium wire of 5m/t molten steel to the ladle for calcium treatment. After calcium treatment, blow argon gas at a flow rate of 60NL/min for 10 minutes, and the molten steel leaves the station.

Continuous casting: The molten steel is sent to the continuous casting process, and the tundish is blown with argon for 10 minutes before pouring; the long nozzle is sealed with a sealing gasket, and a large continuous casting slab product with a cross section of 280mm×380mm is produced.

The obtained continuous casting slab is rolled into 60kg steel rail, and the produced steel rail P+S+O+N+H=0.0127%, wherein, P0.0050%, S 0.0030%, O 0.0006%, N 0.0040%, H 0.0001 %. Various ratings of inclusions: Class A 0.5, Class B, Class C, and Class D are all 0.

Example 3

Molten iron pretreatment: use molten iron as raw material, use carrier gas to mix 5kg/t molten iron active lime and 2kg/t molten iron passivated magnesium powder, use rotary desulfurization spray gun to spray into molten iron, the injection time is 20min, after desulfurization Obtain low sulfur molten iron, S content: 0.0006%, P content: 0.105%.

Converter smelting: add molten iron after desulfurization into the converter, add active lime of 8kg/t molten iron, quartz sand of 8kg/t molten iron and high-magnesium lime of 8kg/t molten iron as the first slagging materials, and supply oxygen with oxygen lance at the same time For blowing, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m, the temperature of the blowing process is 1653°C, and the slag is poured after 9 minutes of blowing, and then the second slagging material 8kg/t of active lime of molten iron, 8kg/t of molten iron are added Quartz sand of molten iron and high-magnesia lime of 8kg/t molten iron continue blowing for 7 minutes, and the slag is poured before tapping. The P content is 0.0021%. After the converter smelting is completed, the steel is tapped. When the tapping amount is more than 1/2, 12kg/t of ferrosilicon with a nitrogen content of 0.005% is added, and 18kg/t of silicon manganese with a nitrogen content of 0.003% is added.

LF refining: Send molten steel obtained from converter smelting to LF furnace ladle for refining. Before heating in LF furnace, add calcium carbide of 0.6kg/t molten steel and high alkalinity refining slag of 3kg/t molten steel to the ladle, and heat to 1595 ℃, after refining for 25 minutes, add 0.6kg/t molten steel quartz sand into the ladle, continue refining for 8 minutes, add 2m/t molten steel iron-calcium wire into the ladle for calcium treatment, after the calcium treatment, pour 80NL of molten steel into the LF furnace Argon is blown for 8 minutes at a flow rate of /min, and the molten steel leaves the station.

RH refining: After the LF furnace refining is completed, the molten steel is transferred to the RH furnace ladle for vacuum treatment. The vacuum degree is controlled at 70Pa, and the refining temperature is 1545°C. For 0.002% ferrosilicon, add 2kg/t molten steel with 0.001% nitrogen ferromanganese. After vacuum treatment for 18 minutes, add iron-calcium wire of 4m/t molten steel to the ladle for calcium treatment. After calcium treatment, blow argon gas at a flow rate of 50NL/min for 8 minutes, and the molten steel leaves the station.

Continuous casting: The molten steel is sent to the continuous casting process, and the tundish is blown with argon for 8 minutes before pouring; the long nozzle is sealed with a sealing gasket, and a large continuous casting billet product with a cross section of 280mm×380mm is produced.

The obtained continuous casting slab is rolled into 60kg steel rail, the produced steel rail P+S+O+N+H=0.0112%, wherein, P0.0050%, S 0.0010%, O 0.0008%, N 0.0043%, H 0.0001 %. Various ratings of inclusions: Class A 0.5, Class B, Class C, and Class D are all 0.

Comparative example 1

Molten iron pretreatment: use molten iron as raw material, use carrier gas to mix 5kg/t molten iron active lime and 2kg/t molten iron passivated magnesium powder, use rotary desulfurization spray gun to spray into molten iron, the injection time is 20min, after desulfurization Obtain low sulfur molten iron, S content: 0.0006%, P content: 0.099%.

Converter smelting: Add molten iron after desulfurization into the converter, add active lime of 3kg/t molten iron, quartz sand of 4kg/t molten iron and high magnesium lime of 6kg/t molten iron as the first slagging materials, and supply oxygen with oxygen lance at the same time For blowing, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m, the temperature of the blowing process is 1653°C, and the second slagging material 4kg/t molten iron active lime, 4kg/t Quartz sand of molten iron and high-magnesia lime of 4kg/t molten iron continue blowing for 7 minutes, and the slag is poured before tapping. The P content is 0.0071%. After the converter smelting is completed, the steel is tapped. When the tapping amount is more than 1/2, 12kg/t of ferrosilicon with a nitrogen content of 0.005% in molten steel is added, and 12kg/t of molten steel with a nitrogen content of 0.003% of silicon manganese is added.

LF refining: Send molten steel obtained from converter smelting to LF furnace ladle for refining. Before heating in LF furnace, add 0.6kg/t molten steel calcium carbide and 3kg/t molten steel high alkalinity refining slag into the ladle, and heat to 1590 ℃, after refining for 25 minutes, add 0.6kg/t molten steel quartz sand into the ladle, continue refining for 8 minutes, add 2m/t molten steel iron-calcium wire to the ladle for calcium treatment, after the calcium treatment, pour 60NL of molten steel into the LF furnace Argon is blown for 8 minutes at a flow rate of /min, and the molten steel leaves the station.

RH refining: After the LF furnace refining is completed, the molten steel is transferred to the RH furnace ladle for vacuum treatment. The vacuum degree is controlled at 70Pa, and the refining temperature is 1545°C. For 0.002% ferrosilicon, add 2kg/t molten steel with 0.001% nitrogen ferromanganese. After vacuum treatment for 18 minutes, add iron-calcium wire of 4m/t molten steel to the ladle for calcium treatment. After calcium treatment, blow argon gas at a flow rate of 70NL/min for 8 minutes, and the molten steel leaves the station.

Continuous casting: The molten steel is sent to the continuous casting process, and the tundish is blown with argon for 8 minutes before pouring; the long nozzle is sealed with a sealing gasket, and a large continuous casting billet product with a cross section of 280mm×380mm is produced.

The obtained continuous casting slab is rolled into 60kg steel rail, the produced steel rail P+S+O+N+H=0.0166%, wherein, P0.0080%, S 0.0030%, O 0.0010%, N 0.0045%, H 0.0001 %. Various ratings of inclusions: Class A 0.5, Class B, Class C, and Class D are all 0.

From Examples 1 to 3 and Comparative Example 1, it can be seen that the method of the present invention controls P, S, O, N and H in molten steel so that P+S+O+N+H≤160ppm, and the various ratings of inclusions≤ 1.0 level, which significantly improves the cleanliness of heavy rail steel, has significant social benefits, and is worthy of popularization and application.

Claims (10)

1. The smelting method for improving the cleanliness of heavy rail steel is characterized in that it comprises the following steps: a. Hot metal pretreatment: use active lime and passivated magnesium powder as desulfurizers to desulfurize the hot metal to obtain desulfurized hot metal with an S content of ≤0.003% and a P content of 0.080% to 0.120%; b. Converter smelting: Add molten iron after desulfurization in step a into the converter, use active lime, quartz sand and high-magnesium lime as slagging materials for double slag dephosphorization, and the amount of active lime for the first slagging material is 5-20kg/ t molten iron; the dosage of quartz sand is 5-10kg/t molten iron; the dosage of high magnesium lime is 5-10kg/t molten iron; the dosage of active lime for the second slagging material is 5-10kg/t molten iron; the dosage of quartz sand 5-10kg/t molten iron; the amount of high-magnesium lime is 5-10kg/t molten iron, and at the same time blowing with oxygen lance supply oxygen, after the blowing is completed, the molten steel with P content ≤ 0.003% is obtained, and the molten steel is added during the tapping process Low nitrogen alloy; c. LF refining: Send the molten steel obtained in step b to the LF ladle furnace, add calcium carbide and high-alkalinity refining slag and heat it. After refining for 20-30 minutes, add quartz sand to the molten steel. After refining for 5-10 minutes, the molten steel is treated with calcium , the molten steel leaves the station after argon blowing; d. RH refining: After LF refining is completed, the molten steel is transferred to the RH ladle furnace for vacuum treatment, and low-nitrogen alloy is added. After the vacuum treatment is completed, the molten steel is treated with calcium, and the molten steel leaves the station after argon blowing treatment; e. Continuous casting: performing continuous casting on the molten steel obtained in step d. 2. The smelting method for improving the cleanliness of heavy rail steel according to claim 1, characterized in that: in step b, the first slagging material is added for blowing for 8-10 minutes and then the second slagging material is added Continue blowing for 5 to 8 minutes, pour out the slag and tap out the steel. 3. The smelting method for improving the cleanliness of heavy rail steel according to claim 1 or 2, characterized in that: in step a, the consumption of the active lime is 4 to 6kg/t molten iron; the consumption of passivated magnesium powder is 1~3kg/t molten iron. 4. The smelting method for improving the cleanliness of heavy rail steel according to any one of claims 1 to 3, characterized in that: during the tapping process of the molten steel described in step b, when the tapping amount is more than 1/2, low-nitrogen is added alloy. 5. The smelting method for improving the cleanliness of heavy rail steel according to any one of claims 1-4, characterized in that: during the blowing process described in step b, the blowing lance position of the oxygen lance is controlled at 1.5-2.5m . 6. The smelting method for improving the cleanliness of heavy rail steel according to any one of claims 1 to 5, characterized in that: in step c, the dosage of the calcium carbide is 0.2 to 0.8 kg/t molten steel; the high The dosage of the alkalinity refining slag is 1-5kg/t molten steel; the dosage of the quartz sand is 0.2-0.8kg/t molten steel. 7. The smelting method for improving the cleanliness of heavy rail steel according to any one of claims 1-6, characterized in that: in steps c and d, the flow rate of the LF and RH refining argon blowing treatment is 50-80NL/ min, and the duration is 5-10 min. 8. The smelting method for improving the cleanliness of heavy rail steel according to any one of claims 1-7, characterized in that in step d, the RH refining controls the vacuum degree to be ≤ 100 Pa, and the vacuum treatment lasts for 15-20 minutes. 9. The method for improving the cleanliness of heavy rail steel according to any one of claims 1 to 8, characterized in that in steps b and d, the nitrogen content of the low-nitrogen alloy added in the converter smelting and RH refining is ≤ 0.01%. 10. The method for improving the cleanliness of heavy rail steel according to any one of claims 1 to 9, characterized in that: in step e, the continuous casting process adopts bloom continuous casting to produce a cross section of 250mm×250mm The above generous continuous casting billet products.