LU103043B1

LU103043B1 - Heavy Rail Steel and Preparation Method thereof

Info

Publication number: LU103043B1
Application number: LU103043A
Authority: LU
Inventors: Yanping Bao; Zhongliang Wang; Chao Gu
Original assignee: Univ Beijing Science & Technology
Priority date: 2022-07-01
Filing date: 2022-11-29
Publication date: 2023-06-01
Also published as: CN114807779A; CN114807779B

Abstract

Provided is a preparation method for heavy rail steel. The preparation method includes the following Steps: Sl, adopting "high carbon pulling and low final temperature" Operation mode in BOF process; adding pre-melting refming slag after the BOF process, and controlling the total amount of FeO and MnO in the refming slag to be below l wt%; S2, when LF arrives at the Station, immediately sending electricity to raise the temperature, adding lime to complete the slagging, and controlling the alkalinity of the refming slag; S3, performing carburization or decarburization in RH-OB process according to the difference between the steel composition and temperature and the target composition and temperature requirements; and S4, performing protective casting in the whole process of continuous casting process (CC process).

Description

188P3LU 25.11.2022

Heavy Rail Steel and Preparation Method thereof LU103043

Technical Field

The present invention relates to the technical field of ferrous metallurgy, specifically to a heavy rail steel and its preparation process.

Background

The railway is a main artery and a great civil engineering of national economy and plays a vital role in social development. With the increasing of the comprehensive national force of

China, the transportation mode of high-speed passenger transportation and heavy-load freight transportation becomes the main development direction of railway transportation. The constantly increased train speed and axle load can lead to the condition of being in active service more abominable of heavy rail, and then make the heavy rail receive bigger damage. which also puts forward higher requirement to the quality of heavy rail steel. Therefore, in the production of heavy rail steel, raw material conditions need to be optimized. the technological process needs to be strictly controlled, a detection evaluation system is perfected, the number of non-metallic inclusions causing discontinuity of a steel matrix is reduced. or the inclusions are denatured by utilizing various regulation and control means. The process commonly adopted for producing the heavy rail steel at home and abroad is BOF/EAF — LF — RH/VD — CC. Silicomanganese, silicon-calcium-barium alloy and the like are used for deoxidation during tapping and LF refining, high alkalinity, high fluidity, and low oxidizability white slag are produced to reduce the content of oxygen, sulfur and inclusions in the molten steel, to ensure that the final steel composition to meet the standard requirements. The production process is mature, but the following problems which cannot be avoided by existing technologies: (1) Cleanliness of molten steel: Because the alloy of silicon-manganese. silicon-calcium-barium, etc. is used for deoxidation in the whole process, the C-type inclusion which is uniformly dispersed in the molten steel is directly formed. Meanwhile, the heavy gauge steel smelting process added a large number of Si, Mn, Ca, etc. on the traditional refining slag Al2O3 has a reducing effect, making Al into the steel combined with O. the formation of B inclusions. Although there are control means such as inclusion modification. ladle soft blowing, tundish and crystallizer metallurgy in the later process, the inclusions 1

I88P3LU 25.11.2022 cannot be removed from the root, and further improvement of the cleanliness of the heavy rail U103043 steel is hindered. (2) Controlling alloy consumption: The silicon element and the manganese element play a role in deoxidation and alloying in the heavy rail steel. The end point temperature, the oxygen content and the alloy components of each steel converter are different, so the alloy yield fluctuation is large. The alloy consumption is unstable when 0.1% of alloy elements are added in the steel, and a field operator adopts middle limit or upper limit operation to ensure the components to be qualified, so that a large amount of ferroalloy waste is caused. And most ferroalloy enterprises only provide main element components for quality protection, the control means of impurity elements and inclusions is deficient, so the use of large amounts of ferroalloy will even cause secondary pollution of the steel. (3) Production rhythm: In the traditional process, in order to make the end point phosphorus. carbon and temperature reach the standard, the process of ‘peroxidation’ is carried out, namely oxygen far exceeding the requirement in steel is blown in. These excess oxygen in the molten steel combined with alloying elements is present as oxides and requires a sufficiently long residence time in the soft blow and tundish to allow it to float sufficiently.

The reciprocating process requirement prolongs the smelting period of each furnace steel, and increases the energy dissipation of the whole process, and forms huge energy consumption and greenhouse gas emission.

Summary of the Invention

Aiming at the problems of precipitation deoxidation by adopting silicomanganese and silicon-calcium-barium alloys in the traditional heavy rail steel smelting process. the invention provides a pollution-free steel-making process which does not need a deoxidized ferroalloy, which can obviously improve the cleanliness of molten steel, stably control the alloy yield, and shorten the production period and the heavy rail steel prepared by the process.

The process mainly adopts a combined deoxidation mode based on slag surface diffusion deoxidation and vacuum carbon deoxidation to replace ferroalloy precipitation deoxidation. disassembles a smelting task and reasonably distributes the smelting task to each reactor to achieve coordinated control of temperature, oxygen content and alloy composition in heavy gauge steel. 2

188P3LU 25.11.2022

To solve the above technical problem, according to an aspect of the present invention. J103043 the present invention provides the following technical solutions:

A heavy rail steel with C 0.73-0.80, Si 0.55-0.75, Mn 0.75-1.00, Cr 0.33-0.48. V 0.06-0.12, and the balance of Fe and unavoidable impurities in weight percentages. The above heavy rail steel was prepared by a pollution-free deoxidation process.

As a preferred scheme of the heavy rail steel of the present invention, wherein: in the heavy rail steel, the weight percentage of Al: is less than or equal to 0.0015 percent, the weight percentage of O is less than or equal to 0.0015 percent, the weight percentage of N is less than or equal to 0.0040 percent and the weight percentage of S is less than or equal to 0.0080 percent.

The pollution-free deoxidation process is characterized in that no alloy deoxidizer is added in the preparation process of the heavy rail steel. The process combined deoxidation mode based on slag surface diffusion deoxidation and vacuum carbon deoxidation to replace ferroalloy precipitation deoxidation. Disassembles a smelting task and reasonably distributes the smelting task to each reactor to achieve coordinated control of temperature, oxygen content and alloy composition in heavy gauge steel.

In order to solve the above technical problem, according to another aspect of the present invention, the present invention provides the following technical solutions:

A process for preparing heavy rail steel features that no alloy deoxidizer is added during its preparing process.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: BOF — LF — RH-OB — CC.

As a preferred scheme of the preparation process of the heavy rail steel. the preparation process comprises the following steps:

S1. BOF process adopts "high carbon pulling and low final temperature" operation mode; add pre-melting refining slag after BOF, and control the total amount of FeO and MnO in the refining slag to be below 1 wt%.

S2. When LF arrives at the station, immediately send electricity to raise the temperature. while adding lime to complete the slagging and control the alkalinity of the refining slag.

S3. RH-OB process to increase or decarbonize the operation according to the difference 3

188P3LU 25.11.2022 between the steel composition and temperature and the target composition and temperatur& U103043 requirements. The end point of RH-OB requires the C and O content to reach the standard. the steel temperature is 10-20 °C higher than that required by the conventional deoxidation process, and the pre-molten liquid alloy is added to the ladle according to the smelting steel composition requirements.

S4. The whole process of continuous casting is carried out protective casting.

As a preferred scheme of the preparation process of the heavy rail steel, wherein: in the step S1, the converter oxygen lance is operated by a sectional pressure-variable lance.

As a preferred scheme of the preparation process of the heavy rail steel, wherein: in the step SI. the charging scrap ratio, the slag basicity, and the FeO content of the slag are controlled.

As a preferred scheme of the preparation process of the heavy rail steel, wherein: in the step S3. the RH-OB step performs vacuum step control.

As a preferred scheme of the preparation process of the heavy rail steel, wherein: the preparation process comprises the following steps: in the step S3, the liquid alloy is added to the ladle using the refractory tube.

To solve the above technical problem, according to another aspect of the present invention, the present invention further provides the following technical solutions:

A heavy rail steel, prepared by the above-mentioned heavy rail steel preparation process.

The invention has the following beneficial effects:

The invention provides a heavy rail steel and a preparation process. aiming at the problems of the traditional heavy rail steel smelting process that silicon-manganese and silicon-calcium-barium alloys are adopted for precipitation deoxidation, no deoxidated ferroalloy is added in the preparation process of the heavy rail steel. The process combined deoxidation mode based on slag surface diffusion deoxidation and vacuum carbon deoxidation to replace ferroalloy precipitation deoxidation. Disassembles a smelting task and reasonably distributes the smelting task to each reactor to achieve coordinated control of temperature, oxygen content and alloy composition in heavy gauge steel. The process can significantly improve the cleanliness of the steel, steadily control the alloy yield, shorten the production cycle, and is suitable for the preparation of all types of heavy rail steels. 4

BB 25.11.2022

Brief Description of the Drawings LU103043

To clarify the embodiments or technical solutions of the present invention. the drawings used in the embodiments or technical solutions of the prior art will be briefly described below.

It is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

Figure 1 is a graph showing the number distribution of each type of inclusions in embodiment 1 of the present invention.

Figure 2 is a graph showing the number distribution of each type of inclusions in embodiment 2 of the present invention.

Figure 3 is a graph showing the number distribution of each type of inclusions in embodiment 3 of the present invention.

Figure 4 is a graph showing the number distribution of each type of inclusions in comparative embodiment 1.

Figure 5 is a graph showing the number distribution of each type of inclusions in comparative embodiment 2.

Figure 6 is a graph showing the number distribution of each type of inclusions in comparative embodiment 3.

Figure 7 is a graph showing the number distribution of each type of inclusions in comparative embodiment 4.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description of the Invention

The following will clearly and completely describe the technical solutions in the embodiments, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments. which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

____188P3LU 25.11.2022

The invention provides heavy rail steel and a preparation process, wherein no alloy] 103043 deoxidizer is added in the preparation process of the heavy rail steel, so that pollution-free deoxidation can be realized. (1) Improving the cleanliness of molten steel

The invention mainly adopts vacuum carbon deoxidation to realize low oxygen control. does not use any deoxidized ferroalloy. and deoxidized products are CO or CO». The gas products directly escape from the molten steel, so that any adverse effect on the quality of steel is avoided, and the generation of B-type inclusions which have the greatest harm on the service performance of the heavy rail is fundamentally prevented. After deep deoxidation in alloying process, the deoxidation limit of the alloy elements is approached, and the added Si cannot be combined with oxygen in molten steel to generate C-type inclusions in a large amount. (2) Stable alloy yield

In the traditional heavy rail steel production, silicomanganese, silico-calcium-barium and the like are added for alloying in the converter tapping process or the early stage of LF smelting, the alloying is carried out simultaneously along with deoxidation, and multiple factors can influence the alloy yield. The method directly adds the pre-melted liquid alloy near the tail end of the whole process, prevents secondary oxidation caused by exposure of the steel liquid surface in the process, stably improves the alloy yield, and ensures low impurity content through quality inspection of the pre-melted alloy. (3) Quickening the production rhythm

The converter has high carbon drawing and low temperature at the end point, and the total blowing time can be shortened by about 1 min. The LF process only plays a role in heating molten steel and making white slag, extra heat is not needed to be provided for alloy melting, and the time can be shortened by about 10 min. The RH-OB procedure reaches the ultimate vacuum degree in three steps, the pre-vacuum pumping can achieve good carbon-oxygen reaction control effect, and the vacuum treatment time is reduced by about 2 min. The soft blowing of the steel ladle only needs to uniformly mix the pre-molten liquid alloy with the molten steel, docs not need to prolong the time for the inclusion to float 6

I88P3LU 25.11.2022 upwards. and can save the time by about 5 min. By combining the above, the method can, y103043 accelerate the production rhythm and meet the requirement of high-efficiency production.

According to one aspect of the invention, the invention provides the following technical scheme:

The preparation process of the heavy rail steel comprises the following steps of (by weight percentage), 0.73-0.80% of C, 0.55-0.75% of Si, 0.75-1.00% of Mn, 0.33-0.48% of Cr. 0.06-0.12% of V, and the balance of iron and inevitable impurities;

The preparation process comprises the following steps: BOF — LF — RH-OB — CC, and no deoxidation ferroalloy is added in the preparation process of the heavy rail steel.

The preparation process specifically comprises the following steps:

S1. BOF process adopts "high carbon pulling and low final temperature” operation mode. and controlling the end point w[P] to be less than or equal to 0.013 percent, the w[C] to be 0.4-0.85 percent, the w[O] to be 40-75 ppm and the end point temperature 1505-1545 °C. The converter end point control can be adjusted according to the actual smelting seed requirement;

After converter tapping, adding pre-melted refining slag according to 2.2-3.0 kg/t, and other slag regulating agents are added according to the components of the refining slag. CaO in refining slag is controlled at 38-42 wt%, SiOz is controlled at 40-45 wt%, and controlling the total amount of FeO and MnO in the refining slag to be below 1 wt%.

The adding amount of the pre-melted refining slag can be adjusted according to the requirement of actual smelting steel seeds. For the heavy rail steel components, the adding amount of the pre-melted refining slag is, for example, but not limited to. any one of 2.2 kg/t, 2.3 kg/t, 2.4 kg/t, 2.5 kg/t, 2.6 kg/t, 2.7 kg/t, 2.8 kg/t, 2.9 kg/t, and 3.0 kg/t or the range between any two. The composition control of the refining slag can also be adjusted according to the requirements of the actual smelting steel type. For the heavy rail steel components, the content of CaO in the refining slag can be, for example, but not limited to, any one of 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt% or a range between any two. The content of SiO2 in the refining slag can be, for example, but not limited to, any one of 40 wt%, 41 wt%, 42 wt%. 43 wt%, 44 wt%, 45 wt%, or a range between any two.

S2. After the LF arrives at the station, immediately transmitting electricity to heat up to 1590-1630 °C, simultaneously adding lime according to 0.8-1.5 kg/t to complete slagging. 7

ES 25112022

The LF refining time is required to be less than or equal to 35min, the alkalinity of tha u103043 refining slag is required to be 1.50-1.70. The LF end point requires w[C] is 0.4-0.9%. w[O] is less than or equal to 80ppm, and w[S] is less than or equal to 0.007%.

The LF end point control can be adjusted according to the actual smelting steel seed requirement. The temperature at which the heavy rail steel component is immediately heated by power transmission is, for example, but not limited to, one of 1590 °C, 1600 °C, 1610 °C, 1620 °C and 1630 °C, or a range between any two of them. The lime addition amount is, for example. but not limited to, any one of 0.8 kg/t, 0.9 kg/t, 1.0 kg/t, 1.1 kg/t, 1.2 kg/t, 1.3 kg/t, 1.4 kg/t, 1.5 kg/t or a range between any two. Refining slag basicity is, for example, but not limited to. any one of 1.50, 1.55, 1.60, 1.65, 1.70 or a range between any two.

S3. Performing vacuum step control in RH-OB, keeping high vacuum below 67 Pa for 5-6 min. Performing carbon adding for re-carburizing operation or performing decarburization operation by using an RH-OB oxygen lance according to the difference value between the current molten steel component and temperature and the target requirement. The RH-OB end point requires that the C, O content reaches the standard. the temperature is 10-20 °C higher than the conventional deoxidation process requirement of smelting steel types, and pre-melted low-oxygen low-nitrogen low-hydrogen liquid alloy is added into a ladle according to the component requirement of the smelting steel types.

S4. Carrying out protective casting in the whole continuous casting process.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: the step S1 is preceded by a step SO. wherein the step

SO is KR pretreatment, and w{S] is less than or equal to 50 ppm when KR pretreatment is outbound.

As a preferred scheme of the preparation process of the heavy rail steel. the preparation process comprises the following steps: in the step SO, after the KR pretreatment of the molten iron, the molten iron charging operation of the converter is completed within 10 min.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: in the step S1, in order to prevent the converter from splashing and rapidly slag and melt iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.50-1.75 m, the oxygen pressure is 0.95-1.00 8

188P3LU 25.11.2022

MPa, and the oxygen supply intensity is 4.4-4.8 m°/(min-t) within 2.5 min after blowing. The| (J103043 lance position is 1.35-1.55 m, the oxygen pressure is 0.92-0.96 MPa, and the oxygen supply intensity is 4.2-4.5 m°/(min:t) when blowing for 2.5-12 min. The lance position is 1.45-1.60 m, the oxygen pressure is 0.88-0.94 MPa, and the oxygen supply intensity is 3.6-4.0 m°/(min-t) after blowing for 12 min.

The operation of the converter oxygen lance sectional variable pressure lance can be adjusted according to the actual smelting steel seed requirements. Aiming at the heavy rail steel components, the lance position is, for example but not limited to, one of 1.50 m, 1.55 m, 1.60 m, 1.65 m, 1.70, and 1.75 m, or a range between any two of them within 2.5min after the starting the blowing. The oxygen pressure is, for example but not limited to, one of 0.95 MPa, 0.96 MPa, 0.97 MPa, 0.98 MPa, 0.99 MPa, and 1.00 MPa, or a range between any two of them within 2.5 min after the starting the blowing. The oxygen supply strength is, for example but not limited to, one of 4.4 m°/(min-t), 4.5 m°/(min-t). 4.6 m°/(min-t), 4.7 m*/(min-t), and 4.8 m°/(min-t), or a range between any two of them within 2.5min after the starting the blowing. When blowing for 2.5-12 min, wherein the gun position is in the range of any one or any two of 1.35 m, 1.40 m, 1.45 m 1.50 m, and 1.55 m, the oxygen pressure is in the range of any one or any two of 0.92 MPa, 0.93 MPa, 0.94 MPa, 0.95 MPa, 0.96 MPa, and the oxygen supply intensity is in the range of any one or any two of 4.2 m°/(min-t), 4.3 m°/(min-t), 4.4 m*/(min-t), 4.5 m°/(min-t). After blowing for 12min, the lance position is, for example but not limited to, any one of 1.45 m, 1.50 m, 1.55 m and 1.60 m or a range between any two. The oxygen pressure is, for example but not limited to, any one of 0.88 MPa, 0.89 MPa, 0.90 MPa, 0.91 MPa, 0.92 MPa, 0.93 MPa, and 0.94 MPa or a range between any two. The oxygen supply intensity is, for example but not limited to, 3.6 m°/(min-t), 3.7 m*/(min-t), 3.8 m*/(min-t), 3.9 m*/(min-t), 4.0 m°/(min-t), or a range between any two.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: in the step S1, in order to ensure the dephosphorization effect, the ratio of the fed scrap steel is less than 8.5%, the alkalinity of the slag is controlled to be 2.4-3.0 in the blowing process, and the FeO content is 16.5-20 wt%.

The scrap charging ratio is, for example, but not limited to, any one of 8.5%, 8%, 7.5%, 7%, 6%, 5%, or a range between any two of the above heavy rail steel components. The 9 blowing process controls the slag basicity to be, for example, but not limited to. any one Of U103043 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 or a range between any two. The FeO content is, for example. but not limited to, any one of 16.5 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%. or a range between any two.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: in the step S1, the converter slag is added in multiple batches, the lime with the total amount of 1/2 and the dolomite with the total amount of 1/3 are added within ! min after the start of blowing. The balance is added for 3-5 times according to the slagging condition, and the charging is completed within 12 min after the start of blowing. The tapping process adopts pneumatic slag stopping, and the tapping time is less than or equal to 3.5 min.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: in the step S2, 1.1-1.3kg/t of silicon carbide is added into the slag surface, and diffusion deoxidation is carried out to reduce the oxygen content of the molten steel.

The amount of silicon carbide added to the heavy rail steel composition is, for example. but not limited to, any one of 1.1 kg/t, 1.2 kg/t, 1.3 kg/t, or a range between any two of them.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: in step S3, the vacuum step control specifically includes: the pressure of the vacuum chamber is kept for 3-5 min at 40-50 kPa, the pressure of the vacuum chamber is kept for 7-10 min at 5-10 kPa, the pressure of the vacuum chamber is kept for 8-10 min at the pressure of less than or equal to 67 Pa. The carbon-oxygen reaction can be gradual, and the phenomenon that the violent reaction causes the large jet of the molten steel is avoided. The pressure ranges and the holding time of all levels of vacuum step control can be adjusted according to the actual smelting steel variety requirements.

As a preferred scheme of the preparation process of the heavy rail steel, the preparation process comprises the following steps: in the step S3, the liquid alloy is added into the ladle through the refractory material tube, and the ladle is soft-blown for 4-6 min to mix uniformly.

For example, a zirconium refractory material tube can be used.

U 25112022

As a preferred scheme of the preparation process of the heavy rail steel, the preparation | 103043 process comprises the following steps: in step S4, the continuous casting process requires less than 2 ppm of increased oxygen and less than 5 ppm of increased nitrogen.

The heavy rail steel is prepared by adopting the preparation process of the heavy rail steel.

Embodiment 1

The process for preparing the heavy rail steel by adopting the process of the invention comprises the following steps: 1) The molten iron was pre-desulfurized by KR, and the S content is 34 ppm at the time of leaving the station, and finishing the molten iron charging operation of the converter 8 min after the desulfurization is finished. 2) The converter process adopts a high carbon-drawing and low final temperature operation mode. In order to prevent the converter from large spray, and to achieve rapid slagging and iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.65 m, the oxygen pressure is 0.97 Mpa and the oxygen supply intensity is 4.55 m*/(min-t) within 2.5 min after blowing. When blowing is started for 2.5-12min, the lance position is 1.45 m, the oxygen pressure is 0.94 Mpa and the oxygen supply intensity is 4.35 m°/(min-t). After blowing for 12 min, with the lance position at 1.55 m. oxygen pressure at 0.90 Mpa, and oxygen supply intensity at 3.85 m*/(min-t). In order to ensure the dephosphorization effect, the ratio of the steel scrap entering the furnace is 8.2 percent, the slag alkalinity in the blowing process is 2.5 to 2.9, and the FeO content is 16.6 to 19 weight percent. Adding the converter slag-making materials in multiple batches. adding the total amount of 1/2 lime and 1/3 dolomite within 1 min after blowing, adding the balance of 4 times according to the slag melting condition, and finishing feeding 10 min after blowing.

And pneumatic slag blocking is adopted in the tapping process, and the tapping time is 3.2 min. The temperature of the converter end point is 1541 °C, and the sampling analysis result is as follows: w[P] = 0.0062%, w[C] = 0.65%, w[O] = 51 ppm. 3) After tapping for 100s after the furnace, pre-melted refining slag is added according to 2.5 kg/t, and other slag regulating agents are added according to the requirements. Adding silicon carbide on the slag surface according to the proportion of 1.15 kg/t, and performing 11

_Is3LU 00000000 nina diffusion deoxidation to reduce the oxygen content of the molten steel. The refined slag Was 1103043 sampled and analyzed, and contained 39.37 wt% of CaO and 42.21 wt% of SiO>. the total amount of FeO and MnO was 0.93 wt%. 4) And immediately transmitting electricity to raise the temperature to 1623 °C after LF arrives at the station, and simultaneously adding refined lime according to 1.4 kg/t to complete slagging. LF refining time is 29min. LF end point sampling analysis results: the basicity of refining slag is 1.68, W[C] of molten steel is 0.73%, W[O] is 39 ppm, and W[S] is 0.0037%. 5) And performing vacuum step control in RH-OB, keeping the pressure of the vacuum chamber at 45 KPa for 4.6 min, keeping the pressure of the vacuum chamber at 9 KPa for 8.8 min, keeping the pressure of the vacuum chamber at 67 Pa or less for 8.3 min. so that the carbon-oxygen reaction is gradual, and the violent reaction is avoided to cause large molten steel spraying. After keeping the high vacuum below 67 Pa for 5 min, carbon powder is added into the molten steel according to the proportion of 0.3 kg/t. 6) RH-OB endpoint sampling results: w[C] is 0.75%, w[O] is 10.3ppm, temperature is 1581 °C. Then, a zirconium refractory material tube is used for adding low-oxygen low-nitrogen low-hydrogen liquid alloy which is pre-melted according to the component requirement into a steel ladle, and the steel ladle is soft-blown for 5.2 min and mixed evenly. 7) The whole continuous casting process is used for protecting casting and preventing secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.75% of C, 0.69% of Si, 0.91% of Mn, 0.35% of Cr, 0.08% of V, 10.5 ppm of residual elements O, 20 ppm of N, 64 ppm of P and 41 ppm of S. The alloy yields were calculated, with the Si yield being 92.7%, the Mn yield being 97.2%, the Cr yield being 98.9%, and the V yield being 95.4%. The number of each type of inclusion in the casting blank is counted by using a ZEISS-EVOI18 type full-automatic inclusion analysis system, and the result is shown in Figure 1.

Embodiment 2

The process for preparing the heavy rail steel by adopting the process of the invention comprises the following steps: 12

I88P3LU 25.11.2022 1) The molten iron was pre-desulfurized by KR, and the S content is 39 ppm at the timq (J103043 of leaving the station, and finishing the molten iron charging operation of the converter 9 min after the desulfurization is finished. 2) The converter process adopts a high carbon-drawing and low final temperature operation mode. In order to prevent the converter from large spray, and to achieve rapid slagging and iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.70 m, the oxygen pressure is 0.95 Mpa and the oxygen supply intensity is 4.60 m”/(mint) within 2.5 min after blowing. When blowing is started for 2.5-12min, the lance position is 1.49 m, the oxygen pressure is 0.93 Mpa and the oxygen supply intensity is 4.27 m°/(min-t). After blowing for 12 min, with the lance position at 1.53 m. oxygen pressure at 0.89 Mpa, and oxygen supply intensity at 3.75 m*/(min-t). In order to ensure the dephosphorization effect, the ratio of the steel scrap entering the furnace is 7.9 percent, the slag alkalinity in the blowing process is 2.4 to 2.8, and the FeO content is 17.2 to 19.4 weight percent. Adding the converter slag-making materials in multiple batches, adding the total amount of 1/2 lime and 1/3 dolomite within 1 min after blowing, adding the balance of 4 times according to the slag melting condition, and finishing feeding 11 min after blowing.

And pneumatic slag blocking is adopted in the tapping process, and the tapping time is 3.4 min. The temperature of the converter end point is 1534 °C, and the sampling analysis result is as follows: w[P] = 0.0053%, w[C] = 0.54%, w[O] = 62 ppm. 3) After tapping for 100s after the furnace, pre-melted refining slag is added according to 2.3 kg/t, and other slag regulating agents are added according to the requirements. Adding silicon carbide on the slag surface according to the proportion of 1.2 kg/t, and performing diffusion deoxidation to reduce the oxygen content of the molten steel. The refined slag was sampled and analyzed, and contained 38.77 wt% of CaO and 43.13 wt% of SiO». the total amount of FeO and MnO was 0.97 wt%. 4) And immediately transmitting electricity to raise the temperature to 1626 °C after LF arrives at the station, and simultaneously adding refined lime according to 1.5 kg/t to complete slagging. LF refining time is 31min. LF end point sampling analysis results: the basicity of refining slag is 1.64, W[C] of molten steel is 0.66%, W[O] is 44 ppm, and W[S] is 0.0044%. 13

I88P3LU 25.11.2022 5) And performing vacuum step control in RH-OB, keeping the pressure of the vacuum; y103043 chamber at 48 KPa for 4.5 min, keeping the pressure of the vacuum chamber at 8.5 KPa for 9.1 min. keeping the pressure of the vacuum chamber at 67 Pa or less for 8.7 min, so that the carbon-oxygen reaction is gradual, and the violent reaction is avoided to cause large molten steel spraying. After keeping the high vacuum below 67 Pa for 5.5 min, carbon powder is added into the molten steel according to the proportion of 1.0 kg/t. 6) RH-OB endpoint sampling results: w[C] is 0.76%, w[O] is 11.7ppm, temperature is 1575 °C. Then, a zirconium refractory material tube is used for adding low-oxygen low-nitrogen low-hydrogen liquid alloy which is pre-melted according to the component requirement into a steel ladle, and the steel ladle is soft-blown for 4.4 min and mixed evenly. 7) The whole continuous casting process is used for protecting casting and preventing secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.76% of C, 0.63% of Si, 0.82% of Mn, 0.41% of Cr, 0.08% of V, 11.8 ppm of residual elements O, 22 ppm of N, 55 ppm of P and 47 ppm of S. The alloy yields were calculated, with the Si yield being 92.4%, the Mn yield being 96.8%, the Cr yield being 98.5%, and the V yield being 95.9%. The number of each type of inclusion in the casting blank is counted by using a ZEISS-EVOI18 type full-automatic inclusion analysis system, and the result is shown in Figure 2.

Embodiment 3

The process for preparing the heavy rail steel by adopting the process of the invention comprises the following steps: 1) The molten iron was pre-desulfurized by KR, and the S content is 35 ppm at the time of leaving the station, and finishing the molten iron charging operation of the converter 9.3 min after the desulfurization is finished. 2) The converter process adopts a high carbon-drawing and low final temperature operation mode. In order to prevent the converter from large spray, and to achieve rapid slagging and iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.54 m, the oxygen pressure is 0.96 Mpa and the oxygen supply intensity is 4.42 m°/(min-t) within 2.5 min after blowing. When blowing is started for 14

___I88P3LU 0000000000000 25112022 2.5-12min. the lance position is 1.40 m, the oxygen pressure is 0.92 Mpa and the Oxygen 103043 supply intensity is 4.21 m°/(min-t). After blowing for 12 min, with the lance position at 1.60 m. oxygen pressure at 0.91 Mpa, and oxygen supply intensity at 3.85 m°*/(min-t). In order to ensure the dephosphorization effect, the ratio of the steel scrap entering the furnace is 8.3 percent. the slag alkalinity in the blowing process is 2.6 to 3.0, and the FeO content is 17.5 to 19.8 weight percent.

Adding the converter slag-making materials in multiple batches. adding the total amount of 1/2 lime and 1/3 dolomite within 1 min after blowing, adding the balance of 5 times according to the slag melting condition, and finishing feeding 9.5 min after blowing.

And pneumatic slag blocking is adopted in the tapping process, and the tapping time is 2.9 min.

The temperature of the converter end point is 1514 °C, and the sampling analysis result is as follows: w[P] = 0.0053%, w[C] = 0.73%, w[O] = 45 ppm.

3) After tapping for 100s after the furnace, pre-melted refining slag is added according to 2.7 kg/t, and other slag regulating agents are added according to the requirements.

Adding silicon carbide on the slag surface according to the proportion of 1.1 kg/t, and performing diffusion deoxidation to reduce the oxygen content of the molten steel.

The refined slag was sampled and analyzed, and contained 41.73 wt% of CaO and 42.55 wt% of SiO», the total amount of FeO and MnO was 0.89 wt%.

4) And immediately transmitting electricity to raise the temperature to 1608 °C after LF arrives at the station, and simultaneously adding refined lime according to 0.9 kg/t to complete slagging.

LF refining time is 32min.

LF end point sampling analysis results: the basicity of refining slag is 1.55, W[C] of molten steel is 0.79%, W[O] is 31 ppm, and W[S] is 0.0039%.

5) And performing vacuum step control in RH-OB, keeping the pressure of the vacuum chamber at 42 KPa for 3.8 min, keeping the pressure of the vacuum chamber at 10 KPa for 8 min, keeping the pressure of the vacuum chamber at 67 Pa or less for 9.1 min.

This operation allows the carbon and oxygen reaction to progress gradually, avoiding a violent reaction triggering a large spray of steel.

Since the carbon content is within the steel grade requirements, there is no need for carbon powder addition or oxygen blowing operation.

6) RH-OB endpoint sampling results: w[C] is 0.77%, w[O] is 10.7 ppm, temperature is 1590 °C.

Then. a zirconium refractory material tube is used for adding low-oxygen

I88P3LU 25.11.2022 low-nitrogen low-hydrogen liquid alloy which is pre-melted according to the component) y103043 requirement into a steel ladle, and the steel ladle is soft-blown for 5.2 min and mixed evenly. 7) The whole continuous casting process is used for protecting casting and preventing secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.77% of C, 0.72% of Si, 0.77% of Mn, 0.36% of Cr, 0.09% of V, 11.4 ppm of residual elements O, 25 ppm of N, 51 ppm of P and 42 ppm of S. The alloy yields were calculated, with the Si yield being 91.9%, the Mn yield being 97.3%, the Cr yield being 98.2%, and the V yield being 96.3%. The number of each type of inclusion in the casting blank is counted by using a ZEISS-EVOI18 type full-automatic inclusion analysis system, and the result is shown in Figure 3.

Comparative Embodiment 1

The heavy rail steel is prepared by adopting the existing deoxidation process as follows: 1) The molten iron was pre-desulfurized by KR, and the S content is 40 ppm at the time of leaving the station, and finishing the molten iron charging operation of the converter 10 min after the desulfurization is finished. 2) The converter process adopts a 'one-blow-to-bottom' operation mode. The oxygen lance is controlled by constant lance and variable pressure, and the gun position is stabilized at 1.55m. The oxygen pressure is 0.98 Mpa and the oxygen supply intensity is 4.80 m°/(min-t) within 5 min after blowing. When blowing is started for 5-10 min, the oxygen pressure is 0.94

Mpa and the oxygen supply intensity is 4.60 m°/(min-t). After blowing for 10 min, oxygen pressure at 0.88 Mpa, and oxygen supply intensity at 4.30 m°/(min-t). The ratio of the steel scrap entering the furnace is 14.2 percent, the slag alkalinity in the blowing process is 2.2 to 2.5, and the FeO content is 21 to 25 weight percent. Adding the converter slag-making materials in multiple batches, adding the total amount of 2/3 lime and 1/2 dolomite after starting the blowing process, adding the balance of 2 times according to the slag melting condition, and finishing feeding 15 min after blowing. The slag ball is used to block the slag during the steel discharge process, and the tapping time is 3.7 min. The temperature of the converter end point is 1614 °C, and the sampling analysis result is as follows: w[P] = 0.0034%, w[C] = 0.10%, w[O] = 259 ppm. 16

188P3LU 25.11.2022 3) After tapping for 120s after the furnace, pre-melted refining slag is added according tO U103043 1.8 kg/t, refining lime according to 1.1 kg/t, and other slag regulating agents are added according to the requirements. After the steel is discharged, a silica-calcium-barium alloy containing 55 wt% Si, 23 wt% Ca, 17 wt% Ba, and 0.4 wt% Al is added for deoxidation according to 0.6 kg/t. The refined slag was sampled and analyzed, and contained 51.18 wt% of CaO and 24.49 wt% of SiO», the total amount of FeO and MnO was 0.98 wt%. 4) And in the LF process, mainly performing white slag making and component fine adjustment. Adding refined lime according to 0.35 kg/t after power is supplied, and adding ferroalloy according to the component requirement of heavy rail steel. LF refining time is 46 min. LF end point sampling analysis results: the basicity of refining slag is 2.96. W[C] of molten steel is 0.83%, W[O] is 22 ppm, and W[S] is 0.0017%. 5) Further degassing in the RH refining process, exhausting for 14 min to make the pressure in the vacuum chamber less than or equal to 67 Pa, and maintaining high vacuum for 19 min. RH endpoint sampling results: w[C] is 0.81%, w[O] is 9.7 ppm, temperature is 1566 °C. Adding carbonized rice hulls to the surface of the molten steel after the molten steel is taken out of the station, and carrying out soft blowing for 28 min to enable inclusions to fully float upwards. 6) The whole continuous casting process is used for protecting casting and preventing secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.80% of C, 0.70% of Si, 0.86% of Mn, 0.41% of Cr, 0.11% of V. 9.9 ppm of residual elements O, 37 ppm of N, 37 ppm of P and 22 ppm of S. The alloy yields were calculated, with the Si yield being 87.5%, the Mn yield being 90.4%, the Cr yield being 93.2%. and the V yield being 94.8%. The number of each type of inclusion in the casting blank is counted by using a ZEISS-EVOIS type full-automatic inclusion analysis system. and the result is shown in Figure 4.

Comparative Embodiment 2

The process for preparing the heavy rail steel without adopting the operation mode of high carbon-drawing and low final temperature comprises the following steps: 17

EP 95.11.2022 1) The molten iron was pre-desulfurized by KR, and the S content is 37 ppm at the timq y103043 of leaving the station, and finishing the molten iron charging operation of the converter 8.5 min after the desulfurization is finished. 2) In order to prevent the converter from large spray, and to achieve rapid slagging and iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.62 m, the oxygen pressure is 0.96 Mpa and the oxygen supply intensity is 4.50 m°/(min-t) within 2.5 min after blowing. When blowing is started for 2.5-12min. the lance position is 1.43 m, the oxygen pressure is 0.95 Mpa and the oxygen supply intensity is 4.40 m°/(min-t). After blowing for 12 min, with the lance position at 1.50 m, oxygen pressure at 0.93 Mpa, and oxygen supply intensity at 3.93 m’/(min-t). In order to ensure the dephosphorization effect, the ratio of the steel scrap entering the furnace is 8.4 percent, the slag alkalinity in the blowing process is 2.6 to 2.9, and the FeO content is 17 to 19.2 weight percent. Adding the converter slag-making materials in multiple batches, adding the total amount of 1/2 lime and 1/3 dolomite within 1 min after blowing, adding the balance of 4 times according to the slag melting condition, and finishing feeding 11.3 min after blowing.

And pneumatic slag blocking is adopted in the tapping process, and the tapping time is 2.8 min. The temperature of the converter end point is 1607 °C, and the sampling analysis result is as follows: w[P] = 0.0032%, w[C] = 0.09%, w[O] = 275 ppm. 3) After tapping for 100s after the furnace, pre-melted refining slag is added according to 2.3 kg/t, and other slag regulating agents are added according to the requirements. Adding silicon carbide on the slag surface according to the proportion of 1.5 kg/t, and performing diffusion deoxidation to reduce the oxygen content of the molten steel. The refined slag was sampled and analyzed, and contained 40.28 wt% of CaO and 42.91 wt% of SiOx. the total amount of FeO and MnO was 1.77 wt%. 4) And after LF arrives at the station, adding refined lime according to the proportion of 1.2kg/t to complete slagging. LF refining time is 32min. LF end point sampling analysis results: the basicity of refining slag is 1.59, W[C] of molten steel is 0.17%, W[O] is 114 ppm. and W[S] is 0.0032%. 5) And performing vacuum step control in RH-OB, keeping the pressure of the vacuum chamber at 50 KPa for 5 min, keeping the pressure of the vacuum chamber at 10 KPa for 10 18 min, keeping the pressure of the vacuum chamber at 67 Pa or less for 10 min. After the high U103043 vacuum is kept below 67 Pa for 6 min, carbon powder is added into the molten steel according to the proportion of 3 kg/t. Carbon and oxygen react violently after the carbon powder is added into the molten steel due to the high oxygen content of the molten steel. so that splashing is generated in a vacuum chamber. 6) RH-OB endpoint sampling results: w[C] is 0.39%, w[O] is 41 ppm, temperature is 1573 °C. Then, a zirconium refractory material tube is used for adding low-oxygen low-nitrogen low-hydrogen liquid alloy which is pre-melted according to the component requirement into a steel ladle, and the steel ladle is soft-blown for 4 min and mixed evenly. 7) The whole continuous casting process is used for protecting casting and preventing secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.39% of C, 0.60% of Si, 0.84% of Mn, 0.37% of Cr, 0.06% of V, 19 ppm of residual elements O, 28 ppm of N, 34 ppm of P and 35 ppm of S. The alloy yields were calculated, with the Si yield being 81.2%, the Mn yield being 88.7%, the Cr yield being 03.9%. and the V yield being 93.1%. The number of each type of inclusion in the casting blank is counted by using a ZEISS-EVO18 type full-automatic inclusion analysis system, and the result is shown in Figure 5.

Comparative Embodiment 3

The heavy rail steel is prepared without LF refining as follows: 1) The molten iron was pre-desulfurized by KR, and the S content is 35 ppm at the time of leaving the station, and finishing the molten iron charging operation of the converter 8.5 min after the desulfurization is finished. 2) The converter process adopts a high carbon-drawing and low final temperature operation mode. In order to prevent the converter from large spray, and to achieve rapid slagging and iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.65 m, the oxygen pressure is 0.96 Mpa and the oxygen supply intensity is 4.60 m’/(min‘t) within 2.5 min after blowing. When blowing is started for 2.5-12min, the lance position is 1.40 m, the oxygen pressure is 0.92 Mpa and the oxygen supply intensity is 4.35m*/(min-t). After blowing for 12 min, with the lance position at 1.50 m, 19

188P3LU 25.11.2022 oxygen pressure at 0.88 Mpa, and oxygen supply intensity at 3.70 m*/(min-t). In order toLU103043 ensure the dephosphorization effect, the ratio of the steel scrap entering the furnace is 7.8 percent. the slag alkalinity in the blowing process is 2.4 to 2.9, and the FeO content is 17.6 to 19.5 weight percent.

Adding the converter slag-making materials in multiple batches, adding the total amount of 1/2 lime and 1/3 dolomite within 1 min after blowing, adding the balance of 4 times according to the slag melting condition, and finishing feeding 10.9 min after blowing.

And pneumatic slag blocking is adopted in the tapping process, and the tapping time is 3.1 min.

The temperature of the converter end point is 1533 °C, and the sampling analysis result is as follows: w[P] = 0.0057%, w[C] = 0.81%, w[O] = 39 ppm.

3) After tapping for 100s after the furnace, pre-melted refining slag is added according to 2.6 kg/t. and other slag regulating agents are added according to the requirements.

Adding silicon carbide on the slag surface according to the proportion of 1.2 kg/t, and performing diffusion deoxidation to reduce the oxygen content of the molten steel.

The refined slag was sampled and analyzed, and contained 39.86 wt% of CaO and 41.11 wt% of SiO», the total amount of FeO and MnO was 0.95 wt%.

4) Because the process does not have an LF refining procedure, oxygen blowing and temperature rising are needed in an RH-OB procedure.

The vacuum chamber pressure was maintained at 50 KPa for 4.8 min and 9.5 KPa for 9 min.

Then blowing oxygen to the molten steel surface through an oxygen lance, wherein the oxygen pressure is 0.45 Mpa, and the oxygen supply intensity is 2.14 m*/(min-t). When the temperature rose to 1577 °C, the oxygen supply was stopped.

Due to the requirement of heavy rail steel for w[C]=0.73-0.80%., the superheat temperature of casting is required to be 20 °C, and at the moment, the molten steel is sampled by w[C]=0.37%, carbon powder is needed to be added into the molten steel.

The vacuum chamber is kept at a pressure of less than or equal to 67 Pa for 8.5 min by continuing pumping, the carbon-oxygen reaction is always in a controllable range, and a large splashing phenomenon does not occur.

5) RH-OB endpoint sampling results: w[C] is 0.74%, w[O} is 15.1 ppm, temperature is 1569 °C.

Then, a zirconium refractory material tube is used for adding low-oxygen low-nitrogen low-hydrogen liquid alloy which is pre-melted according to the component requirement into a steel ladle, and the steel ladle is soft-blown for 4.8 min and mixed evenly.

I88P3LU 25.11.2022 6) The whole continuous casting process is used for protecting casting and preventing 5103043 secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.74% of C, 0.61% of Si, 0.82% of Mn, 0.43% of Cr. 0.07% of V. 15.5 ppm of residual elements O, 26 ppm of N, 60 ppm of P and 42 ppm of S. The alloy vields were calculated. with the Si yield being 91.5%, the Mn yield being 94.7%, the Cr yield being 96.9%, and the V yield being 95.3%. The number of each type of inclusion in the casting blank is counted by using a ZEISS-EVOI8 type full-automatic inclusion analysis system. and the result is shown in Figure 6.

Comparative Embodiment 4

The heavy rail steel is prepared by replacing RH-OB with VD as follows: 1) The molten iron was pre-desulfurized by KR, and the S content is 44 ppm at the time of leaving the station, and finishing the molten iron charging operation of the converter 9.5 min after the desulfurization is finished. 2) In order to prevent the converter from large spray, and to achieve rapid slagging and iron, the converter oxygen lance is operated by a sectional variable pressure lance. The lance position is 1.58 m, the oxygen pressure is 0.99 Mpa and the oxygen supply intensity is 4.70 m*/(min-t) within 2.5 min after blowing. When blowing is started for 2.5-12min, the lance position is 1.49 m. the oxygen pressure is 0.95 Mpa and the oxygen supply intensity is 4.40 m°/(min-t). After blowing for 12 min, with the lance position at 1.54 m, oxygen pressure at 0.93 Mpa, and oxygen supply intensity at 3.65 m°/(min-t). In order to ensure the dephosphorization effect, the ratio of the steel scrap entering the furnace is 8.0 percent, the slag alkalinity in the blowing process is 2.4 to 2.9, and the FeO content is 16.5 to 18.8 weight percent. Adding the converter slag-making materials in multiple batches. adding the total amount of 1/2 lime and 1/3 dolomite within 1 min after blowing, adding the balance of 4 times according to the slag melting condition, and finishing feeding 11.1 min after blowing.

And pneumatic slag blocking is adopted in the tapping process, and the tapping time is 3.5 min. The temperature of the converter end point is 1545 °C, and the sampling analysis result is as follows: w[P] = 0.0055%, w[C] = 0.55%, w[O] = 57 ppm. 21

3) After tapping for 100s after the furnace, pre-melted refining slag is added according 10 103043 2.5 kg/t, and other slag regulating agents are added according to the requirements. Adding silicon carbide on the slag surface according to the proportion of 1.2 kg/t. and performing diffusion deoxidation to reduce the oxygen content of the molten steel. The refined slag was sampled and analyzed, and contained 39.89 wt% of CaO and 44.24 wt% of SiO:. the total amount of FeO and MnO was 0.96 wt%. 4) And immediately transmitting electricity to raise the temperature to 1627 °C after LF arrives at the station, and simultaneously adding refined lime according to the proportion of 1.16 kg/t to complete slagging. LF refining time is 32 min. LF end point sampling analysis results: the basicity of refining slag is 1.63, W[C] of molten steel is 0.63%, W[O] is 38 ppm, and W[S] is 0.0041%. 5) And step control is carried out in the VD refining process, the pressure of the vacuum chamber is kept for 6 min at 45 KPa, the pressure of the vacuum chamber is kept for 8 min at 9.5 KPa, the pressure of the vacuum chamber is kept for 18 min at the pressure of 67 Pa or less. The carbon-oxygen reaction is always in a controllable range, and a large splashing phenomenon does not occur. 6) VD endpoint sampling results: w[C] is 0.61%, w[O] is 17.9 ppm, temperature is 1577 °C. As heavy rail steel requires w[C] to be 0.73-0.80%. and VD vacuum process cannot feed. carbon powder needs to be added into molten steel after breaking the air. But the carbon powder is not completely melted after being added, and part of the carbon powder floats on the molten steel surface in a solid state. Then using zirconium refractory material tube to add low-oxygen low-nitrogen low-hydrogen liquid alloy which is pre-melted according to the requirements of components into steel ladle, soft-blowing steel ladle for 5.2min and uniformly mixing, and the w[O] of molten steel is 13.6 ppm. 7) The whole continuous casting process is used for protecting casting and preventing secondary oxidation caused by air suction.

Sampling and detecting the casting slab, and determining the components of the steel sample (in mass percent): 0.69% of C, 0.70% of Si, 0.92% of Mn, 0.38% of Cr. 0.09% of V. 14.3 ppm of residual elements O, 25 ppm of N, 61 ppm of P and 42 ppm of S. The alloy yields were calculated, with the Si yield being 91.3%, the Mn yield being 96.6%, the Cr yield 22

I88P3LU 25.11.2022 being 98.2%. and the V yield being 95.7%. The number of each type of inclusion in the 103043 casting blank is counted by using a ZEISS-EVOIS type full-automatic inclusion analysis system, and the result is shown in Figure 7.

It can be seen that the oxygen content, alloy yield, and inclusion level of the heavy rail steel casting slab prepared in embodiments 1-3 of the present invention were comparable.

Through comparison of embodiment 1 and comparative embodiment 1. the oxygen content and the sulfur content of the heavy rail steel casting slab smelted by the prior art are lowe.

However, the whole-process smelting time is prolonged, the alloy yield is reduced, and the number of B-type, C-type and D-type inclusions is obviously increased. By comparative embodiment 1 with comparative embodiment 2, it is found that if the operation mode of high-pulling carbon and low-final temperature is not adopted, the oxygen content at the end point of the converter is high, the diffusion deoxidation cannot achieve the expected effect.

And the oxygen content and the carbon content in the final casting slab are unqualified due to the splash generated in the RH process caused by the violent carbon-oxygen reaction. the alloy yield is low, and the inclusions of C-type and D-type are increased. By comparative embodiment 1 with comparative embodiment 3, it is found that if LF in the process is climinated. the temperature raising function is transferred to the RH-OB process, excessive oxygen blowing causes unqualified oxygen content in the casting slab, the alloy yield is reduced. and the number of the C-type and D-type inclusions is obviously increased. By comparative embodiment 1 with the comparative embodiment 4, it is found that if RH-OB is replaced by VD, the carbon-oxygen reaction kinetic condition is poor, deep deoxidation cannot be completed in VD, the effect of adding carbon powder after the blank is broken is not good, the carbon powder cannot completely enter molten steel, the carbon content in the casting blank is unqualified, part of alloy is used for deoxidation, the yield is reduced. and the number of C-type inclusions is slightly increased.

The above description is only a preferred embodiment of the present invention. and not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the present specification and directly/indirectly applied to other related technical fields within the spirit of the present invention are included in the scope of the present invention. 23

Claims

188P3LU 25.11.2022 WHAT IS CLAIMED IS: LU103043

1. A preparation method for heavy rail steel, characterized in that no alloy deoxidizer is added during its preparing process; the preparation method comprises the following steps:

S1. adopting "high carbon pulling and low final temperature” operation mode in BOF process; adding pre-melting refining slag after the BOF process, and controlling the total amount of FeO and MnO in the refining slag to be below 1 wt%;

S2. when LF arrives at the station, immediately sending electricity to raise the temperature. adding lime to complete the slagging, and controlling the alkalinity of the refining slag: S3, performing carburization or decarburization in RH-OB process according to the difference between the steel composition and temperature and the target composition and temperature requirements; the end point of the RH-OB process requires the C and O content to reach the standard, the steel temperature is 10-20 °C higher than that required by the conventional deoxidation process, and the pre-molten liquid alloy is added to the ladle according to the smelting steel composition requirements; and S4, performing protective casting in the whole process of continuous casting process, CC process.

2. The preparation method according to claim 1. characterized in that in the step SI, the converter oxygen lance is operated by a sectional pressure-variable lance.

3. The preparation method according to claim 1, characterized in that in the step SI. the charging scrap ratio, the slag basicity, and the FeO content of the slag are controlled.

4. The preparation method according to claim 1, characterized in that in the step S3, the RH-OB process performs vacuum step control.

5. The preparation method according to claim 1, characterized in that in the step S3, the liquid alloy is added to the ladle using the refractory tube.

6. A heavy rail steel, prepared by the preparation method of any one of claims 1-5. 1