Method for modifying inclusions in heavy rail steel by tellurium or calcium telluride complex treatment

Abstract

This invention belongs to the field of iron and steel metallurgical refining technology, specifically relating to a method for treating inclusions in heavy rail steel using tellurium or calcium tellurium composite treatment. To reduce the Class A inclusion rating of heavy rail steel, this invention provides a method for treating inclusions in heavy rail steel using tellurium or calcium tellurium composite treatment. This method involves performing tellurium or calcium tellurium composite treatment during RH refining to improve the morphology of sulfides in the heavy rail steel. The tellurium or calcium tellurium composite treatment process employs inert gas soft blowing to enhance the circulation of molten steel in the ladle, thereby improving the effect of the tellurium or calcium tellurium composite treatment, reducing the Class A inclusion rating, and improving the machinability of the steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgical refining technology, specifically relating to a method for treating inclusions in modified heavy rail steel using tellurium or calcium tellurium composite treatment. Background Technology

[0002] Heavy rail steel is a high-carbon, high-strength, fine-pearlitic steel. The presence of MnS inclusions in heavy rail steel can reduce the harmful effects of hydrogen, but excessively long MnS inclusions can cause inclusion ratings to exceed limits or even fail ultrasonic testing. MnS inclusions have good deformability, but they negatively impact the hot working of the steel, significantly reducing the material's transverse properties. Therefore, measures must be taken to promote the miniaturization of MnS inclusions, precipitating them as early as possible in the form of high-melting-point, low-plasticity single-phase or multi-phase substances in spherical or spindle shapes, thereby avoiding the formation of large-sized pure MnS.

[0003] Currently, heavy rail production often uses calcium treatment of molten steel to modify sulfide inclusions and improve steel quality. Calcium treatment of molten steel has significant effects on deoxidation, desulfurization, changing the morphology of inclusions, improving the casting performance of molten steel, ensuring smooth casting, and improving steel quality. However, calcium treatment still has certain drawbacks, such as excessively violent reactions in the steel.

[0004] Researchers have used tellurium to treat inclusions in other steels, such as bearing steel, rail steel, or wheel steel. For example, patent CN113913704A discloses a tellurium-sulfur synergistic-treated aluminum deoxidized steel, its preparation method, and its application. The tellurium-sulfur synergistic-treated aluminum deoxidized steel has the following composition: C 0.06%–0.09%, Al 0.01%–0.02%, Si 0.01%–0.03%, Mn 1.0%–1.5%, S 0.08%–0.1%, P 0.045%–0.055%, and Te 0.04%–0.15%. The preparation method includes: smelting molten iron in a converter, deoxidizing and alloying during tapping; performing LF refining, adding ferrosulfide alloy and tellurium wire, and then continuous casting to obtain the tellurium-sulfur synergistic-treated aluminum deoxidized steel. However, the aluminum deoxidized steel with tellurium-sulfur synergistic treatment provided by this patent aims to limit the aggregation and growth of alumina, increase cutting lubricity, and avoid the problem of nozzle nodule formation, without involving the modification of sulfides.

[0005] For example, patent CN114250417A discloses a tellurium-containing medium-carbon high-sulfur free-cutting steel, wire rod, and a method for producing wire rod. The tellurium-containing medium-carbon high-sulfur free-cutting steel has the following chemical composition by mass percentage: C: 0.40-0.50%, Si: 0.10-0.4%, Mn: 1.3-1.7%, P: 0-0.025%, S: 0.24-0.33%, Al: 0.001-0.008%, Pb: 0.001-0.005%, Te: 0.005-0.03%, Ca: 0.0001-0.0005%, with the remainder being Fe and unavoidable impurities; wherein the mass percentages of Mn, S, and Te satisfy the following relationship: Mn / Te: 43-300, Te / S: 0.015-0.125. The preparation method of this free-cutting steel includes the tellurium modification treatment. After RH treatment, 1.45–8 m / t of tellurium-containing cored wire is fed into the molten steel at a feeding speed of 166–189 m / min and a feeding angle of 75°–105°. The uniformly dispersed inclusions in this free-cutting steel are mainly type I MnS, type I MnTe, and composite inclusions of the two. The material plasticity is improved, mitigating cracking problems that are prone to occur during continuous casting, hot rolling, and subsequent drawing, hot forging, and cutting processes. It also improves elongation after fracture, reduction of area, and machinability. However, this patent modifies the sulfide inclusions in free-cutting steel through tellurium modification treatment, mainly to improve the machinability of the steel. It is applicable to medium-carbon, high-sulfur free-cutting steel and does not involve heavy rail steel.

[0006] CN115161562A discloses a tellurium-treated deoxidized aluminum steel and its preparation method. The tellurium-treated deoxidized aluminum steel provides a composite inclusion of manganese telluride encapsulating alumina, avoiding the problems of nozzle nodule formation caused by high-melting-point inclusions such as alumina and stress concentration caused by alumina inclusions, which lead to reduced service life. However, this patent mainly targets aluminum deoxidized steel with high aluminum content, forming a composite inclusion of manganese telluride encapsulating alumina. The primary purpose is to improve nozzle nodule formation; therefore, controlling the amount of tellurium added is crucial, and controlling the resulting product is relatively difficult.

[0007] CN116200663A discloses an easy-to-machine non-quenched and tempered crankshaft steel and its preparation method. The easy-to-machine non-quenched and tempered crankshaft steel provided by this patent has good machinability, easy processing performance, and good quality, improving its pass rate. However, this patent feeds tellurium wire after RH refining without using soft blowing, resulting in poor tellurium treatment effect. Summary of the Invention

[0008] To reduce the Class A inclusion rating of heavy rail steel, this invention provides a method for modifying inclusions in heavy rail steel using tellurium or calcium tellurium composite treatment. During RH refining, tellurium or calcium tellurium composite treatment is performed to improve the morphology of sulfides in the heavy rail steel. The tellurium or calcium tellurium composite treatment process employs bottom blowing argon into the ladle to enhance the circulation of molten steel in the ladle, thereby improving the effect of the tellurium or calcium tellurium composite treatment, reducing the Class A inclusion rating, and improving the machinability of the steel.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for treating inclusions in modified heavy rail steel using tellurium or calcium tellurium composite treatment includes the following steps:

[0011] After the molten steel is smelted in a converter and refined in the LF furnace, when it reaches the RH refinement stage, the composition of the molten steel is analyzed to ensure that the S content is <0.08wt%. Then, the RH refinement is carried out. 3-4 minutes before the end of the RH refinement, tellurium or calcium tellurium composite treatment is carried out, and inert gas soft blowing is performed. After the RH refinement is completed, heavy rail steel is prepared by conventional continuous casting and subsequent processes.

[0012] The chemical composition of the heavy rail steel, by mass percentage, includes: C: 0.60%–0.82%, Si: 0.15%–0.35%, Mn: 0.70%–1.00%, P: 0–0.035%, S: 0–0.045%, Te: 0.003–0.01%, with the balance being Fe and unavoidable impurities.

[0013] The tellurium or calcium tellurium composite is added by feeding tellurium or calcium tellurium cored wire into molten steel using a wire feeder.

[0014] The amount of tellurium or calcium tellurium complex added is based on the S content, and the Te / S ratio is controlled to be 0.01 to 0.1.

[0015] Preferably, the calcium tellurium complex comprises: Ca ≥ 50 wt%, Te ≥ 15 wt%, and Fe < 35 wt%.

[0016] Among them, the tellurium or calcium tellurium composite treatment process requires bottom blowing argon operation in a steel ladle.

[0017] The bottom blowing argon in the ladle adopts a dual-hole bottom blowing argon method, and the bottom blowing argon flow rate is controlled at 80-100 NL / min.

[0018] During the smelting process, the thickness of the ladle slag is controlled at 200-300 mm to ensure that the bottom-blown argon agitates the molten steel and that the surface of the molten steel is not exposed.

[0019] The present invention also provides heavy rail steel prepared by the above-described processing method.

[0020] Beneficial effects: In the production process of heavy rail steel, this invention employs tellurium or calcium tellurium composite treatment during RH refining to improve the morphology of sulfides in the heavy rail steel, spheroidize MnS inclusions, reduce the harm of MnS inclusions, and improve steel quality. The tellurium or calcium tellurium composite treatment process uses bottom blowing argon in the ladle to enhance the circulation of molten steel in the ladle, improve the effect of tellurium or calcium tellurium composite treatment, reduce the Class A inclusion rating, and improve the machinability of the steel. Moreover, since the reaction of simple calcium treatment is relatively violent, the use of calcium tellurium composite treatment is more cost-effective, and by strengthening stirring, the tellurium yield can also be improved. Detailed Implementation

[0021] To reduce the Class A inclusion rating of heavy rail steel, this invention provides a method for treating inclusions in modified heavy rail steel using tellurium or calcium tellurium composite treatment, specifically including the following steps:

[0022] After smelting in a converter and refining in the LF furnace, the molten steel reaches the RH refining stage. The composition of the molten steel is analyzed to ensure that the sulfur content is <0.08wt%. Then, RH refining is carried out. 3-4 minutes before the end of RH refining, tellurium or calcium tellurium cored wire is fed into the molten steel using a wire feeder. The Te / S ratio is controlled at 0.01-0.1. Double-hole bottom blowing argon is performed, with the bottom blowing argon flow rate controlled at 80-100NL / min. The slag thickness in the ladle is controlled at 200-300mm during the smelting process to ensure that the bottom blowing argon agitates the molten steel and that the molten steel surface is not exposed. After the RH refining is completed, heavy rail steel is prepared by conventional continuous casting and subsequent processes.

[0023] In the above methods, the tellurium or calcium tellurium composite treatment process uses inert gas soft blowing, preferably bottom blowing argon into the ladle, which can enhance the circulation of molten steel in the ladle, improve the tellurium or calcium tellurium composite treatment effect, reduce the Class A inclusion rating, and improve the machinability of the steel.

[0024] In the above method, by introducing tellurium or calcium tellurium composites, the MnS inclusions in the steel are modified to form Mn-Te-S or Mn-Ca-Te-S composite inclusions. The morphology of sulfides in heavy rail steel is improved, the Class A inclusion rating is reduced, and the machinability of the steel is improved.

[0025] In the above method, the S content is ensured to be <0.08wt%, and then RH refining is carried out. The purpose is to control MnS inclusions in heavy rail steel. Excessive S content will lead to the failure of Class A inclusion rating.

[0026] In the above method, the advantage of performing tellurium or calcium tellurium composite treatment 3-4 minutes before the end of RH refining is that it ensures that tellurium or calcium tellurium has a certain reaction time.

[0027] Among the methods described above, the reaction is more gradual compared to simple calcium treatment. The use of calcium-tellurium composite treatment can reduce the impact of calcium sulfide inclusions on the castability of molten steel.

[0028] In the above method, the chemical composition of the prepared heavy rail steel by mass percentage includes: C: 0.60% to 0.82%, Si: 0.15% to 0.35%, Mn: 0.70% to 1.00%, P: 0 to 0.035%, S: 0 to 0.045%, Te: 0.003 to 0.01%, with the balance being Fe and unavoidable impurities.

[0029] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0030] Example 1: Method for treating inclusions in modified heavy rail steel using tellurium.

[0031] For a 120t ladle, heavy rail steel is produced, and the steel composition by mass percentage includes: C: 0.72%, Si: 0.22%, Mn: 0.76%, P: 0.014%, S: 0.035%, Te: 0.006%, with the balance being Fe and unavoidable impurities.

[0032] (1) After the molten steel is smelted in a converter and refined in the LF, it reaches the RH refining process. Temperature is measured and samples are taken to analyze the composition of the molten steel and ensure that the sulfur mass percentage is below 0.08%.

[0033] (2) After the insertion tube enters the molten steel, RH begins normal processing operation;

[0034] (3) Alloying is carried out according to the composition of the molten steel entering the station;

[0035] (4) After RH vacuum treatment for 14 min, the vacuum treatment is ended;

[0036] (5) Feed the tellurium wire according to the S content at the station for tellurium treatment. The Te / S ratio should be controlled at 0.08. At the same time, open the double-hole bottom blowing argon for soft blowing. The bottom blowing argon flow rate should be 80NL / min.

[0037] (6) After 3 minutes of soft blowing, the RH treatment is completed.

[0038] Using this method, MnS inclusions are modified to form Mn-Te-S composite inclusions, which improves the morphology of sulfides in heavy rail steel, reduces the Class A inclusion rating, and improves the machinability of the steel.

[0039] Example 2: Method for treating inclusions in modified heavy rail steel using tellurium

[0040] For a 150t ladle, the production of heavy rail steel includes, by mass percentage: C: 0.72%, Si: 0.22%, Mn: 0.76%, P: 0.014%, S: 0.035%, Te: 0.006%, with the balance being Fe and unavoidable impurities.

[0041] (1) After the molten steel is smelted in a converter and refined in the LF, it reaches the RH refining process. Temperature is measured and samples are taken to analyze the composition of the molten steel and ensure that the sulfur mass percentage is below 0.08%.

[0042] (2) After the insertion tube enters the molten steel, RH begins normal processing operation;

[0043] (3) Alloying is carried out according to the composition of the molten steel entering the station;

[0044] (4) After RH vacuum treatment for 14 min, the vacuum treatment is ended;

[0045] (5) Feed the tellurium wire into the station according to the S content for tellurium treatment. The Te / S ratio should be controlled at 0.08. At the same time, open the double-hole bottom blowing argon for soft blowing. The bottom blowing argon flow rate should be 100 NL / min.

[0046] (6) After 4 minutes of soft blowing, the RH treatment is completed.

[0047] Using this method, MnS inclusions are modified to form Mn-Te-S composite inclusions, which improves the morphology of sulfides in heavy rail steel, reduces the Class A inclusion rating, and improves the machinability of the steel.

[0048] Example 3: Method for treating inclusions in modified heavy rail steel using calcium-tellurium composite treatment

[0049] For a 120t ladle, the production of heavy rail steel includes, by mass percentage: C: 0.72%, Si: 0.22%, Mn: 0.76%, P: 0.014%, S: 0.035%, Te: 0.006%, with the balance being Fe and unavoidable impurities.

[0050] (1) After the molten steel is smelted in a converter and refined in the LF, it reaches the RH refining process. Temperature is measured and samples are taken to analyze the composition of the molten steel and ensure that the sulfur mass percentage is below 0.08%.

[0051] (2) After the insertion tube enters the molten steel, RH begins normal processing operation;

[0052] (3) Alloying is carried out according to the composition of the molten steel entering the station;

[0053] (4) After RH vacuum treatment for 14 min, the vacuum treatment is ended;

[0054] (5) Feed calcium tellurium wire (Ca≥50wt%, Te≥15wt%, Fe<35wt%) according to the S content at the station for calcium tellurium treatment. The Te / S ratio should be controlled at 0.08. At the same time, open the double-hole bottom blowing argon for soft blowing. The bottom blowing argon flow rate should be selected as 80NL / min.

[0055] (6) After 3 minutes of soft blowing, the RH treatment is completed.

[0056] Using this method, MnS inclusions are modified to form Mn-Ca-Te-S composite inclusions, which improves the morphology of sulfides in heavy rail steel, reduces the Class A inclusion rating, and improves the machinability of the steel.

[0057] Example 4: Method for treating inclusions in modified heavy rail steel using calcium-tellurium composite treatment

[0058] For a 150t ladle, the production of heavy rail steel includes, by mass percentage: C: 0.72%, Si: 0.22%, Mn: 0.76%, P: 0.014%, S: 0.035%, Te: 0.006%, with the balance being Fe and unavoidable impurities.

[0059] (1) After the molten steel is smelted in a converter and refined in the LF, it reaches the RH refining process. Temperature is measured and samples are taken to analyze the composition of the molten steel and ensure that the sulfur mass percentage is below 0.08%.

[0060] (2) After the insertion tube enters the molten steel, RH begins normal processing operation;

[0061] (3) Alloying is carried out according to the composition of the molten steel entering the station;

[0062] (4) After RH vacuum treatment for 14 min, the vacuum treatment is ended;

[0063] (5) Feed calcium tellurium wire (Ca≥50wt%, Te≥15wt%, Fe<35wt%) according to the S content at the station for calcium tellurium treatment. The Te / S ratio should be controlled at 0.08. At the same time, open the double-hole bottom blowing argon for soft blowing. The bottom blowing argon flow rate should be 100NL / min.

[0064] (6) After 4 minutes of soft blowing, the RH treatment is completed.

[0065] Using this method, MnS inclusions are modified to form Mn-Ca-Te-S composite inclusions, which improves the morphology of sulfides in heavy rail steel, reduces the Class A inclusion rating, and improves the machinability of the steel.

Claims

1. A method for treating inclusions in modified heavy rail steel using tellurium or calcium tellurium composite treatment, characterized in that: Includes the following steps: After being smelted in a converter and refined in LF, the molten steel reaches the RH refining stage. The steel composition is analyzed to ensure that the S content is <0.08wt%. Then, RH refining is carried out. 3-4 minutes before the end of RH refining, tellurium or calcium tellurium composite treatment is performed, followed by inert gas soft blowing. After RH refining, conventional continuous casting and subsequent processes are used to prepare heavy rail steel. The chemical composition of the heavy rail steel, by mass percentage, includes: C: 0.60%-0.82%, Si: 0.15%-0.35%, Mn: 0.70%-1.00%, P: 0-0.035%, S: 0-0.045%, Te: 0.003-0.01%, with the balance being Fe and unavoidable impurities. During the smelting process, the thickness of the ladle slag is controlled at 200-300 mm to ensure that the bottom-blown argon agitates the molten steel and that the surface of the molten steel is not exposed. The amount of tellurium or calcium tellurium complex added is based on the S content, and the Te / S ratio is controlled to be 0.01 to 0.

1. The calcium-tellurium complex comprises: Ca ≥ 50 wt%, Te ≥ 15 wt%, Fe < 35 wt%; The tellurium or calcium tellurium composite treatment process requires bottom blowing argon in a ladle; the bottom blowing argon in the ladle adopts a dual-hole bottom blowing argon, and the bottom blowing argon flow rate is controlled at 80-100 NL / min.

2. The method for treating inclusions in modified heavy rail steel using tellurium or calcium tellurium composite treatment according to claim 1, characterized in that: The tellurium or calcium tellurium composite is added by feeding tellurium or calcium tellurium cored wire into the molten steel using a wire feeder.

3. Heavy rail steel prepared by the method of claim 1 or 2.