Manufacturing method for improving anti-delayed cracking performance of heavy rail steel

Abstract

The present invention discloses a manufacturing method for improving the anti-delayed cracking performance of heavy rail steel. The technical solution is as follows: The steel composition by weight percentage includes C: 0.68% - 0.78%, Si: 0.43% - 0.63%, Mn: 1.2% - 2.2%, P ≤ 0.010%, S ≤ 0.004%, (Nb + V + Ti): 0.020 - 0.050%, Als ≤ 0.003%, Cr: 2.2% - 3.2%, Re: 0.0010 - 0.0020%, H ≤ 0.00005%, and the rest are Fe and impurity elements. It is completed through deep desulfurization of molten iron, LF refining, continuous casting of molten steel, and rolling. The process of the present invention is simple, easy to control, has low production cost, and excellent performance, and can effectively improve the anti-delayed cracking performance of heavy rail steel.

Description

Technical Field

[0001] The present invention belongs to the field of high-strength steel production in the metallurgical industry, and specifically relates to a manufacturing method for improving the anti-delayed cracking performance of heavy rail steel. Background Art

[0002] With the development of high-speed railways and heavy-haul railways in China, more and more high-strength heavy rails are applied to infrastructure construction. The service life and safety of the rails are directly related to the maintenance cost and the safety of people's lives and property. The current tensile strength of the rails is 1000 MPa, and there is a risk of hydrogen-induced delayed cracking under this strength condition. A large number of studies have confirmed that the delayed cracking of steel is caused by hydrogen in the material and the service environment of the material, which is unpredictable and sudden, and often leads to relatively serious safety problems. Therefore, delayed cracking has always been a problem that heavy rail products must face.

[0003] The main reason for the hydrogen-induced delayed cracking of the rails is the hydrogen content in the steel. The hydrogen in the steel mainly comes from two processes. One is that the water in the ore and raw materials decomposes to produce hydrogen during the smelting process, and the other is that the rails absorb hydrogen from the environment during long-term service. How to control the hydrogen content during production and how to prevent hydrogen absorption and reduce the impact of hydrogen on material properties during the long-term service of the rails are very crucial.

[0004] The current main factors affecting the delayed cracking of heavy rail steel are the MnS inclusions generated during the smelting process and the control of the hydrogen content in the steel. A large amount of hydrogen accumulates in the MnS inclusions, which will lead to the delayed cracking of the steel. Therefore, it will become the crack source of the delayed cracking, and the cracking sensitivity of the steel is very high.

[0005] CN 109082500 A, a method for controlling the hydrogen content of rails, provides a method for controlling the hydrogen content of rails, including: selecting hot metal with low sulfur and low phosphorus and scrap steel after baking and drying for converter smelting; after the molten steel enters the LF refining, heating and temperature rising, slag making, and component fine-tuning are carried out; after the molten steel leaves the LF refining, it enters the secondary refining VD vacuum degassing; before the molten steel is cast, the refractory material of the tundish is fully baked, and during the casting process, the large-package nozzle is sealed and protected with argon; after casting is completed, the billet enters the slow-cooling pit for stacking and slow cooling; the temperature when entering the pit is 600-700 °C, and the slow-cooling time is 5 days; the billet enters the heating furnace for heating, secondary blooming, and slow cooling with a heat preservation cover for 5 days; secondary heating, through rough rolling and finish rolling, and finally enters the warehouse for slow cooling. Through the technical solution of the present invention, the hydrogen content in the rails is effectively controlled, the toughness of the high-strength rails is significantly improved, especially the stability and reliability of the rail performance, and the risk of high-strength rails during railway service is reduced.

[0006] CN 110923405 A Process control method for reducing hydrogen hazards in steel rails This invention relates to a process control method for reducing hydrogen hazards in steel rails, including hot metal pretreatment, converter smelting, LF refining, RH refining and bloom continuous casting processes; in the hot metal pretreatment process, after the hot metal desulfurization pretreatment is completed, the sulfur content in the hot metal is controlled between 0.010 - 0.015 wt%; in the converter process, during the alloying addition after smelting is completed, a synthetic slag with main components of CaO and SiO2 is added, and the argon blowing time is maintained for more than 3 minutes. While quickly forming slag after the converter taps the steel, it ensures that inclusions fully float up. By controlling the contents of MnS and inclusions in the molten steel during the smelting process, this invention achieves the purpose of adding "hydrogen traps" without exceeding the inclusion content standard, thus minimizing the hydrogen hazards in the steel rails.

[0007] CN 112280939 A discloses a low-hydrogen hypereutectoid steel rail and its preparation method. The method includes converter smelting or electric furnace smelting, LF refining, RH vacuum treatment, protected casting, cooling, heating furnace heating, rolling, heat treatment and post-treatment; during the RH vacuum treatment process, fluorite and CaO are sprayed into the molten steel, and the mass ratio of fluorite to CaO is 1:14; the depth of the vacuum pump inserted into the molten steel is 450 - 700 mm; the argon flow rate is 1200 - 1400 NL / min; the vacuum treatment time is ≥15 min, and the treatment time with a vacuum degree ≤3 mbar is ≥12 min. The method of this invention can significantly improve the comprehensive performance of the steel rail while reducing the hydrogen content in the high-strength hypereutectoid steel rail, meeting the requirements of steel rails for heavy-haul railways. The hydrogen content in the steel rail steel prepared by it is ≤1.2 ppm, the tensile strength is ≥1400 MPa, and the elongation is ≥10%.

[0008] CN 112301200 A discloses a rail with anti-delayed fracture performance and a preparation method thereof. The method includes smelting furnace charge into molten steel by converter smelting or electric furnace smelting, non-aluminum deoxidation, LF refining, RH vacuum treatment or VD vacuum treatment, continuous casting of molten steel into steel billets, continuous cooling of steel billets, heating of steel billets in a heating furnace, online rolling of steel billets into rails, online heat treatment and post-treatment; the online heat treatment includes using the waste heat of finish rolling to cool the rail head and web with compressed air, and the cooling rate is controlled at 2.6 - 4.2 °C / s; the initial cooling temperature of the rail head is controlled at 830 - 880 °C, and when the cooling temperature of the rail head is lower than 500 °C, the rail is air-cooled to room temperature. For the rail prepared by this method, the average pearlite lamellar spacing of the rail head is significantly reduced, the hydrogen content of the rail is reduced to a certain extent, the crack propagation rate and the impact toughness of the rail head are optimized, and the anti-delayed fracture performance of the rail is significantly improved. CN 115161435 A, during the molten steel refining process, removes sulfur and sulfide powder by blowing from the bottom of the ladle. During the reaction of the powder at the bottom of the ladle, countless fine and viscous molten slag particles are formed. During the upward floating process of the molten slag particles in the ladle, the purpose of desulfurization and surface adhesion to remove sulfide inclusions is achieved, and even other inclusions can adhere to the surface of the molten slag particles. The advantages are: it is applicable to the production of high-speed heavy rail steel with very high requirements for type A inclusions, can not only achieve deep removal of sulfur in steel, but also achieve removal of sulfides in steel, and even can achieve the purpose of adhesion and removal of other inclusions.

[0009] Research shows that anti-delayed cracking cannot be solved by a single step or parameter. The above methods cannot comprehensively propose a solution for anti-delayed cracking from the entire process of rail manufacturing and service. Summary of the Invention

[0010] The purpose of the present invention is to solve the above technical problems and provide a manufacturing method for improving the anti-delayed cracking performance of heavy rail steel with simple process, easy control, low production cost and excellent performance.

[0011] The method of the present invention is as follows: The steel composition by weight percentage includes C: 0.68% - 0.78%, Si: 0.43% - 0.63%, Mn: 1.2% - 2.2%, P ≤ 0.010%, S ≤ 0.004%, (Nb + V + Ti): 0.020 - 0.050%, Als ≤ 0.003%, Cr: 2.2% - 3.2%, Re: 0.0010 - 0.0020%, H ≤ 0.00005%, and the rest are Fe and impurity elements. After deep desulfurization of hot metal, LF refining, continuous casting of molten steel, and rolling are completed,

[0012] Among them, in the LF refining step: first, soft blowing is carried out for 3 - 8 minutes, controlling T[O] ≤ 0.0020 wt%, and at the same time, aluminum pellets or aluminum wire, lime, and calcium carbide are added to the molten steel to form slag and carry out desulfurization operation, controlling the composition of the slag by mass percentage W(CaO) / W(Al2O3) to be 2.0 - 2.5; then calcium treatment is carried out. The specific treatment process is to feed pure calcium wire into the molten steel. After calcium treatment, the molten steel is subjected to soft blowing with argon for 5 - 10 minutes, and finally RH vacuum treatment is carried out.

[0013] Preferably, the Re is 0.0013 - 0.0018% (0.0010 - 0.0020%), and the Cr is 2.5 - 3.0%.

[0014] Preferably, during the calcium treatment in the LF refining step, the addition amount of pure calcium wire is 0.15 - 0.40 kg per ton of molten steel.

[0015] Preferably, the RH vacuum treatment time in the LF refining step is 30 - 50 minutes, the vacuum degree ≤ 50 Pa. During RH vacuum treatment, Re wire is fed into the molten steel, and after the RH vacuum treatment, soft blowing is carried out for 5 - 10 minutes.

[0016] Preferably, during the RH vacuum treatment in the LF refining step, the addition amount of Re wire is 0.1 - 0.25 Kg / ton of molten steel.

[0017] Preferably, in the continuous casting step of molten steel: control the slow cooling time of the cast slab after pouring to be 36 - 72 hours.

[0018] Preferably, in the rolling step, the steel billet is heated, rough rolled, and finished rolled into a rail, and then slowly cooled to room temperature, with a slow cooling rate of 0.2℃ / s - 0.5℃ / s.

[0019] Preferably, the heating temperature of the steel billet is 1230 - 1260℃.

[0020] The inventors have found through multiple studies that the main factors currently affecting the delayed cracking of heavy rail steel are the MnS inclusions generated during the smelting process and the control of the hydrogen content in the steel. A large amount of hydrogen accumulation in MnS inclusions will lead to the delayed cracking of the steel, so it will become the crack source of delayed cracking, and the cracking sensitivity of the steel is very high. To solve the above problems, improvements need to be made from multiple aspects:

[0021] 1) Adding Cr element: It is generally believed that chromium can improve hardenability, enabling the steel to have good comprehensive mechanical properties after quenching and tempering. However, the inventor further studied and found that Cr also has excellent hydrogen-repelling ability, can block hydrogen absorption, and inhibit hydrogen diffusion. Therefore, the content of Cr was increased and controlled in the range of 2.20 - 3.2%, more preferably 2.5 - 3.0%. The content of Cr within these ranges can effectively form a continuous oxide layer to block the penetration of hydrogen atoms from the surface into the steel. Excessive content will affect the strength and surface quality of the steel, while too low content will affect the continuity of the surface oxide layer and reduce the hydrogen-blocking effect.

[0022] 2) Using Re compounded with (Nb + V + Ti): Rare earth treatment can further modify and refine inclusions, improving the cleanliness of the steel. At the same time, Re is an excellent hydrogen trap that can pin hydrogen atoms, thus greatly reducing the sensitivity to delayed cracking; the precipitation phases of (Nb + V + Ti) are good hydrogen traps and can play a role in pinning hydrogen. When the two are compounded, it can enhance the hydrogen adsorption effect, promote the formation of finer and more dispersed hydrogen traps, and thus produce excellent anti-hydrogen effects. Considering the compounding situation here, the content of Re is limited to 0.0010 - 0.0020%, more preferably 0.0013 - 0.0018%. Excessive content will result in an unclear synergistic effect, while too little content will not be able to capture hydrogen. The content of (Nb + V + Ti) is preferably within the range of 0.020 - 0.050%.

[0023] 3) In the LF refining step, the calcium treatment was improved. Specifically, soft blowing was first carried out for 3 - 5 minutes, controlling T[O] ≤ 0.0020 wt%; aluminum pellets or aluminum wire, lime, and calcium carbide were added to the molten steel to form slag and carry out desulfurization operations, controlling the composition of the obtained slag to have a mass percentage of W(CaO) / W(Al2O3) of 2.0 - 2.5; calcium treatment was carried out on the molten steel, and pure calcium wire was fed into the molten steel. The addition amount of pure calcium wire was 0.15 - 0.40 kg per ton of molten steel.

[0024] 4) Regarding the control of other elements, P: Phosphorus is a harmful element in steel, which is likely to cause center segregation of the continuous casting billet and significantly increase the brittleness of the steel. Its content is controlled below 0.008%; S: Sulfur is a very harmful element. Sulfur in steel often exists in the form of manganese sulfide inclusions, and these sulfide inclusions will deteriorate the toughness of the steel. It is necessary to control the sulfur content in the steel as low as possible. Considering the manufacturing cost, the sulfur content in the steel is controlled below 0.003%.

[0025] In summary, in view of the problems that there are a large number of MnS inclusions in the existing heavy rail steel, these inclusions are large in size, have strong ductility, become film-like strips during rolling, are prone to adsorb hydrogen, resulting in a relatively high sensitivity to hydrogen-induced delayed cracking, and there is a risk of cracking during use. The present invention modifies the inclusions in the steel through calcium treatment, converts the MnS inclusions into calcium sulfide and calcium aluminate inclusions, reduces the influence of inclusions on delayed cracking; reduces the size and quantity of the remaining inclusions in the steel through RH treatment, improves the cleanliness of the molten steel, and controls the hydrogen content during the smelting process; adds a small amount of Re to continue to modify the inclusions, improves the cleanliness of the molten steel, and at the same time, as a hydrogen trap, Re can preferably adsorb and pin hydrogen, reducing the diffusion rate of hydrogen in the steel; adds Cr to enhance the ability of the steel to block hydrogen penetration, improves the ability of the rail to reduce the penetration of hydrogen in the environment. Through multiple means, the heavy rail steel has a relatively high tensile strength, excellent anti-delayed cracking performance, and excellent application prospects and economic benefits. Specific Embodiments

[0026] Example 1

[0027] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.68%, Si: 0.43%, Mn: 1.4%, P: 0.008, S: 0.004%, (Nb + V + Ti): 0.043%, Als: 0.003%, Cr: 2.2%, Re: 0.0010, H: 0.00005%, and the rest are Fe and impurity elements

[0028] 1) Deep desulfurization of the molten iron is carried out. Converter smelting is adopted, scrap steel is added for smelting, and the tapping temperature is controlled at 1651 °C;

[0029] 2) Soft blowing is carried out during the LF refining process. The soft blowing time is 5 min, and T[O] ≤ 0.0020% is controlled; Aluminum pellets or aluminum wire, lime, and calcium carbide are added to the molten steel to make slag and carry out desulfurization operations. The composition of the obtained slag is W(CaO) / W(Al2O3) = 2.1 in terms of mass percentage; Calcium treatment is carried out on the molten steel. The addition amount of pure calcium wire is 0.25 Kg per ton of molten steel. After calcium treatment, soft blowing of argon is carried out on the molten steel, and the soft blowing time is 6 min; RH vacuum treatment is carried out for 35 min, and the vacuum degree is 45 Pa. During the RH vacuum treatment, Re wire is fed into the molten steel. After the RH vacuum treatment is completed, soft blowing is carried out for 5 - 10 min.

[0030] 3) Continuous casting of the molten steel is carried out. Protective casting is carried out using a large ladle long nozzle and a mold submerged nozzle. A heat preservation cover is covered on the casting blank for slow cooling to promote the escape of hydrogen in the steel blank and reduce the hydrogen content in the steel blank. The slow cooling time is 38 hours;

[0031] 4) Heat the steel billet to 1223 °C, carry out rough rolling, and after finish rolling, form rails, then slowly cool to room temperature, with a slow cooling rate of 0.32 °C / s.

[0032] Example 2

[0033] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.69%, Si: 0.45%, Mn: 1.5%, P: 0.007, S: 0.003%, (Nb + V + Ti): 0.043%, Als: 0.003%, Cr: 2.5%, Re: 0.0012, H: 0.00005%, and the rest are Fe and impurity elements

[0034] 1) Conduct deep desulfurization of hot metal, use converter smelting, add scrap steel for smelting, and control the tapping temperature at 1653 °C;

[0035] 2) Carry out soft blowing during LF refining, with a soft blowing time of 4 min, and control T[O] ≤ 0.0019%; add aluminum pellets or aluminum wire, lime, and calcium carbide to the molten steel to make slag and carry out desulfurization operations, and the composition of the obtained slag is W(CaO) / W(Al2O3) = 2.2 in terms of mass percentage; conduct calcium treatment on the molten steel, with the addition amount of pure calcium wire being 0.26 Kg per ton of molten steel, and after calcium treatment, carry out soft blowing of argon on the molten steel, with a soft blowing time of 7 min; conduct RH vacuum treatment, with a time of 45 min and a vacuum degree of 42 Pa, feed Re wire into the molten steel during RH vacuum treatment, and carry out soft blowing for 5 - 10 min after the end of RH vacuum treatment.

[0036] 3) Continuously cast the molten steel, use a large ladle long nozzle and a submerged nozzle in the mold for protected casting, cover the cast billet with a heat preservation cover for slow cooling to promote the escape of hydrogen in the steel billet and reduce the hydrogen content in the steel billet, with a slow cooling time of 48 hours;

[0037] 4) Heat the steel billet to 1265 °C, carry out rough rolling, and after finish rolling, form rails, then slowly cool to room temperature, with a slow cooling rate of 0.31 °C / s.

[0038] Example 3

[0039] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.71%, Si: 0.48%, Mn: 1.5%, P: 0.008, S: 0.004%, (Nb + V + Ti): 0.033%, Als: 0.003%, Cr: 2.7%, Re: 0.0013, H: 0.00004%, and the rest are Fe and impurity elements

[0040] 1) Conduct deep desulfurization of hot metal, use converter smelting, add scrap steel for smelting, and control the tapping temperature at 1654 °C;

[0041] 2) Soft blowing is carried out during LF refining, with a soft blowing time of 7 min, and T[O] is controlled to be ≤0.0019%; aluminum pellets or wires, lime, and calcium carbide are added to the molten steel to form slag and carry out desulfurization operation. The composition of the obtained slag is W(CaO) / W(Al2O3) = 2.2 by mass percentage; calcium treatment is carried out on the molten steel, the addition amount of pure calcium wire is 0.27 Kg per ton of molten steel, and after calcium treatment, soft blowing of argon is carried out on the molten steel with a soft blowing time of 8 min; RH vacuum treatment is carried out for 50 min with a vacuum degree of 40 Pa. During RH vacuum treatment, Re wire is fed into the molten steel, and soft blowing for 8 min is carried out after the end of RH vacuum treatment.

[0042] 3) Continuous casting of molten steel is carried out, using a large ladle long nozzle and a submerged entry nozzle in the mold for protected casting. A heat preservation cover is covered on the cast billet for slow cooling to promote the escape of hydrogen in the steel billet and reduce the hydrogen content in the steel billet. The slow cooling time is 68 hours;

[0043] 4) The steel billet is heated to 1230 °C, rough rolling is carried out, and after finish rolling, it becomes a rail, and it is slowly cooled to room temperature with a slow cooling rate of 0.28 °C / s.

[0044] Example 4

[0045] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.72%, Si: 0.49%, Mn: 1.6%, P: 0.007, S: 0.004%, (Nb + V + Ti): 0.038%, Als: 0.003%, Cr: 2.8%, Re: 0.0014, H: 0.00004%, and the rest are Fe and impurity elements

[0046] 1) Deep desulfurization of hot metal is carried out, using a converter for smelting, adding scrap steel for smelting, and controlling the tapping temperature at 1644 °C;

[0047] 2) Soft blowing is carried out during LF refining, with a soft blowing time of 5 min, and T[O] is controlled to be ≤0.0018%; aluminum pellets or wires, lime, and calcium carbide are added to the molten steel to form slag and carry out desulfurization operation. The composition of the obtained slag is W(CaO) / W(Al2O3) = 2.3 by mass percentage; calcium treatment is carried out on the molten steel, the addition amount of pure calcium wire is 0.25 Kg per ton of molten steel, and after calcium treatment, soft blowing of argon is carried out on the molten steel with a soft blowing time of 7 min; RH vacuum treatment is carried out for 43 min with a vacuum degree of 42 Pa. During RH vacuum treatment, Re wire is fed into the molten steel, and soft blowing for 7 min is carried out after the end of RH vacuum treatment.

[0048] 3) Continuous casting of molten steel is carried out, using a large ladle long nozzle and a submerged entry nozzle in the mold for protected casting. A heat preservation cover is covered on the cast billet for slow cooling to promote the escape of hydrogen in the steel billet and reduce the hydrogen content in the steel billet. The slow cooling time is 64 hours;

[0049] 4) Heat the steel billet to 1238 °C, carry out rough rolling, and after finish rolling, form a rail, then slowly cool it to room temperature with a slow cooling rate of 0.29 °C / s.

[0050] Example 5

[0051] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.73%, Si: 0.51%, Mn: 1.7%, P: 0.006, S: 0.003%, (Nb + V + Ti): 0.035%, Als: 0.002%, Cr: 2.7%, Re: 0.0015, H: 0.00004%, and the rest are Fe and impurity elements

[0052] 1) Conduct deep desulfurization of molten iron, use converter smelting, add scrap steel for smelting, and control the tapping temperature at 1644 °C;

[0053] 2) During the LF refining process, carry out soft blowing for 5 minutes, and control T[O] ≤ 0.0018%; add aluminum pellets or aluminum wire, lime, and calcium carbide to the molten steel to make slag and carry out desulfurization operations. The composition of the slag is W(CaO) / W(Al2O3) = 2.2 by mass percentage; carry out calcium treatment on the molten steel, the addition amount of pure calcium wire is 0.28 Kg per ton of molten steel, and after calcium treatment, carry out soft blowing of argon for 8 minutes; carry out RH vacuum treatment for 45 minutes with a vacuum degree of 42 Pa. During the RH vacuum treatment, feed Re wire into the molten steel, and carry out soft blowing for 8 minutes after the RH vacuum treatment ends.

[0054] 3) Continuously cast the molten steel, use a large ladle long nozzle and a submerged entry nozzle in the mold for protected casting, cover the cast billet with a heat preservation cover for slow cooling to promote the escape of hydrogen in the steel billet and reduce the hydrogen content in the steel billet. The slow cooling time is 54 hours;

[0055] 4) Heat the steel billet to 1248 °C, carry out rough rolling, and after finish rolling, form a rail, then slowly cool it to room temperature with a slow cooling rate of 0.31 °C / s.

[0056] Example 6

[0057] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.75%, Si: 0.52%, Mn: 1.8%, P: 0.006, S: 0.003%, (Nb + V + Ti): 0.025%, Als: 0.002%, Cr: 2.8%, Re: 0.0017, H: 0.00004%, and the rest are Fe and impurity elements

[0058] 1) Conduct deep desulfurization of molten iron, use converter smelting, add scrap steel for smelting, and control the tapping temperature at 1642 °C;

[0059] 2) Soft blowing is carried out during the LF refining process. The soft blowing time is 4 min, and T[O] is controlled to be ≤0.0019%. Aluminum pellets or wires, lime, and calcium carbide are added to the molten steel to form slag and carry out desulfurization operations. The composition of the slag is W(CaO) / W(Al2O3) = 2.3 by mass percentage. Calcium treatment is carried out on the molten steel. The addition amount of pure calcium wire is 0.24 Kg per ton of molten steel. After calcium treatment, soft blowing of argon is carried out on the molten steel, and the soft blowing time is 8 min. RH vacuum treatment is carried out for 45 min with a vacuum degree of 42 Pa. During the RH vacuum treatment, Re wire is fed into the molten steel. After the RH vacuum treatment is completed, soft blowing for 8 min is carried out.

[0060] 3) Continuous casting of molten steel is carried out. Protective casting is carried out using a large ladle long nozzle and a mold immersion nozzle. A heat preservation cover is covered on the casting blank for slow cooling to promote the escape of hydrogen in the steel blank and reduce the hydrogen content in the steel blank. The slow cooling time is 54 hours.

[0061] 4) The steel blank is heated to 1255 °C, rough rolling is carried out, and after finishing rolling, it becomes a rail, and then it is slowly cooled to room temperature with a slow cooling rate of 0.26 °C / s.

[0062] Example 7

[0063] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.77%, Si: 0.55%, Mn: 1.9%, P: 0.006, S: 0.003%, (Nb + V + Ti): 0.035%, Als: 0.002%, Cr: 3.1%, Re: 0.0019, H: 0.00004%, and the rest are Fe and impurity elements.

[0064] 1) Deep desulfurization of hot metal is carried out. Converter smelting is used, and scrap steel is added for smelting. The tapping temperature is controlled at 1641 °C.

[0065] 2) Soft blowing is carried out during the LF refining process. The soft blowing time is 8 min, and T[O] is controlled to be ≤0.0018%. Aluminum pellets or wires, lime, and calcium carbide are added to the molten steel to form slag and carry out desulfurization operations. The composition of the slag is W(CaO) / W(Al2O3) = 2.5 by mass percentage. Calcium treatment is carried out on the molten steel. The addition amount of pure calcium wire is 0.34 Kg per ton of molten steel. After calcium treatment, soft blowing of argon is carried out on the molten steel, and the soft blowing time is 8 min. RH vacuum treatment is carried out for 45 min with a vacuum degree of 41 Pa. During the RH vacuum treatment, Re wire is fed into the molten steel. After the RH vacuum treatment is completed, soft blowing for 8 min is carried out.

[0066] 3) Continuous casting of molten steel is carried out. Protective casting is carried out using a large ladle long nozzle and a mold immersion nozzle. A heat preservation cover is covered on the casting blank for slow cooling to promote the escape of hydrogen in the steel blank and reduce the hydrogen content in the steel blank. The slow cooling time is 66 hours.

[0067] 4) Heat the steel billet to 1268 °C, carry out rough rolling, and after finish rolling, form rails, and slowly cool to room temperature, with a slow cooling rate of 0.27 °C / s.

[0068] Example 8

[0069] A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, the components and their weight percentages include C: 0.73%, Si: 0.51%, Mn: 2.1%, P: 0.006, S: 0.003%, (Nb + V + Ti): 0.042%, Als: 0.002%, Cr: 2.9%, Re: 0.0020, H: 0.00004%, and the rest are Fe and impurity elements

[0070] 1) Carry out deep desulfurization of molten iron, use a converter for smelting, add scrap steel for smelting, and control the tapping temperature at 1643 °C;

[0071] 2) Carry out soft blowing during LF refining, with a soft blowing time of 5 min, and control T[O] ≤ 0.0019%; add aluminum pellets or aluminum wire, lime, and calcium carbide to the molten steel to make slag and carry out desulfurization operations, and the composition of the obtained slag is W(CaO) / W(Al2O3) = 2.4 in terms of mass percentage; carry out calcium treatment on the molten steel, with the addition amount of pure calcium wire being 0.33 Kg per ton of molten steel, and carry out soft blowing of argon on the molten steel after calcium treatment, with a soft blowing time of 8 min; carry out RH vacuum treatment, with a time of 46 min and a vacuum degree of 40 Pa, feed Re wire into the molten steel during RH vacuum treatment, and carry out soft blowing for 9 min after the end of RH vacuum treatment.

[0072] 3) Continuously cast the molten steel, use a large ladle long nozzle and a submerged entry nozzle in the mold for protected casting, cover the cast billet with a heat preservation cover for slow cooling to promote the escape of hydrogen in the steel billet and reduce the hydrogen content in the steel billet, with a slow cooling time of 70 hours;

[0073] 4) Heat the steel billet, carry out rough rolling, and after finish rolling, form rails, and slowly cool to room temperature, with a slow cooling rate of 0.24 °C / s.

[0074] Comparative Example 1

[0075] Except that the addition amount of Cr is changed to 1.8%, the rest is the same as in Example 4.

[0076] Comparative Example 2

[0077] Except for not adding Re, the rest is the same as in Example 4.

[0078] Comparative Example 3

[0079] Except for not adding (Nb + V + Ti), the rest is the same as in Example 4.

[0080] Comparative Example 4

[0081] C: 0.72%, Si: 0.49%, Mn: 1.6%, P: 0.007, S: 0.004%, (Nb + V + Ti): 0.038%, Als: 0.003%, Cr: 2.8%, Re: 0.0014, H: 0.00004%, the balance being Fe and impurity elements

[0082] 1) Deep desulfurization of molten iron is carried out. Converter smelting is adopted, scrap steel is added for smelting, and the tapping temperature is controlled at 1644 °C;

[0083] 2) Soft blowing is carried out during LF refining. The soft blowing time is 5 min, and T[O] is controlled ≤ 0.0020%; Lime and calcium carbide are added to the molten steel to make slag and carry out desulfurization operation. The composition of the obtained slag is W(CaO) / W(Al2O3) = 1.5 by mass percentage. Composition fine-tuning and alloying ensure the composition of the molten steel; The molten steel is subjected to calcium treatment. The addition amount of pure calcium wire is 0.25 Kg per ton of molten steel. After calcium treatment, the molten steel is subjected to soft blowing with argon for 7 min; RH vacuum treatment is carried out for 43 min with a vacuum degree of 42 Pa. During RH vacuum treatment, Re wire is fed into the molten steel. After the end of RH vacuum treatment, soft blowing for 7 min is carried out.

[0084] 3) Continuous casting of molten steel is carried out. Protective casting is adopted with a large ladle long nozzle and a submerged entry nozzle in the mold. A heat preservation cover is covered on the cast billet for slow cooling to promote the escape of hydrogen in the steel billet and reduce the hydrogen content in the steel billet. The slow cooling time is 64 hours;

[0085] 4) The steel billet is heated to 1238 °C, rough rolling is carried out, and after finishing rolling, it becomes a rail, and it is slowly cooled to room temperature with a slow cooling rate of 0.29 °C / s.

[0086] The test steel is compared with the reference steel U75V in terms of conventional mechanical properties, and the results are shown in Table 1; At the same time, the hydrogen-induced delayed cracking properties of the test steel and the reference steel are compared. It is carried out in 0.5 mol / L H2SO4, and a hydrogen charging current is dynamically applied with a hydrogen charging current density of 0.5 mA / cm 2 , and the tensile strain rate is 1.0 10 -5 / s. The hydrogen embrittlement index I HE is calculated through the reduction of area loss to evaluate the hydrogen-induced delayed cracking resistance. The smaller the I value, the better the hydrogen-induced delayed cracking resistance. The comparison of the hydrogen-induced delayed cracking resistance between the reference steel and the hydrogen embrittlement-resistant hot forming steel produced by this method is shown in Table 1. ε Table 1 shows the performance test results of each example and comparative example of the present invention

[0087] Table 1 shows the performance test results of each example and comparative example of the present invention

[0088]

[0089] It can be seen from the test results in Table 1 that all of the implementation cases 1-8 have good performance. Their tensile strength is between 1028-1064 MPa, and the elongation rate is between 12.4-13.8%. These two performances are higher than those of Comparative Examples 1-4 and much higher than those of the traditional steel U75V. The hydrogen embrittlement law shows that the higher the strength of the steel, the greater the hydrogen embrittlement sensitivity index. Although the implementation cases 1-8 have higher strength, they have the lowest hydrogen embrittlement sensitivity. Their hydrogen embrittlement sensitivity index does not exceed 40%, lower than 41-43% of Comparative Examples 1-4, while the hydrogen embrittlement sensitivity index of the traditional U75V product is as high as 52%. Among them, the implementation cases 3-6 are the products of the optimized process, and their hydrogen embrittlement sensitivity index is only 31-33%, with more excellent performance, indicating that the performance of the steel is further improved after optimization. To sum up, this new method for producing heavy rail steel, especially the optimized process method, can effectively improve the anti-delayed cracking performance of the steel.

[0090] The above embodiments are only the best examples and are not restrictive implementations of the technical solutions of the present invention.

Claims

1. A manufacturing method for improving the anti-delayed cracking performance of heavy rail steel, characterized in that, The steel composition by weight percentage includes C: 0.68% - 0.78%, Si: 0.43% - 0.63%, Mn: 1.2% - 2.2%, P ≤ 0.010%, S ≤ 0.004%, (Nb + V + Ti): 0.020 - 0.050%, Als ≤ 0.003%, Cr: 2.2% - 3.2%, Re: 0.0010 - 0.0020%, H ≤ 0.00005%, and the rest is Fe and impurity elements. It is completed through deep desulfurization of molten iron, LF refining, continuous casting of molten steel, and rolling. Among them, in the LF refining step: First, soft blowing is carried out for 3 - 8 minutes, controlling T[O] ≤ 0.0020 wt%. At the same time, aluminum pellets or aluminum wire, lime, and calcium carbide are added to the molten steel to form slag and carry out desulfurization operations, controlling the composition of the slag by mass percentage W(CaO) / W(Al2O3) to be 2.0 - 2.

5. Then, calcium treatment is carried out. The specific treatment process is to feed pure calcium wire into the molten steel. The addition amount of pure calcium wire is 0.15 - 0.40 kg per ton of molten steel. After calcium treatment, the molten steel is soft blown with argon for 5 - 10 minutes. Finally, RH vacuum treatment is carried out for 30 - 50 minutes, with a vacuum degree ≤ 50 Pa. During RH vacuum treatment, Re wire is fed into the molten steel, and after the RH vacuum treatment ends, soft blowing is carried out for 5 - 10 minutes.

2. The manufacturing method for improving the anti-delayed cracking performance of heavy rail steel according to claim 1, characterized in that, The Re is 0.0013 - 0.0018%.

3. The manufacturing method for improving the anti-delayed cracking performance of heavy rail steel according to claim 1, characterized in that, The Cr is 2.5 - 3.0%.

4. The manufacturing method for improving the anti-delayed cracking performance of heavy rail steel according to claim 1, characterized in that, During the RH vacuum treatment, the addition amount of Re wire is 0.1 - 0.25 Kg / ton of molten steel.

5. The manufacturing method for improving the anti-delayed cracking performance of heavy rail steel according to any one of claims 1-3, characterized in that, In the continuous casting step of molten steel: Control the slow cooling time of the cast slab after pouring to be 36 - 72 hours.

6. The manufacturing method for improving the anti-delayed cracking performance of heavy rail steel according to any one of claims 1-3, characterized in that, In the rolling step, the steel billet is heated, rough rolled, and then finished rolled into a rail, and slowly cooled to room temperature with a slow cooling rate of 0.2°C / s - 0.5°C / s.

7. The manufacturing method for improving the anti-delayed cracking performance of heavy rail steel according to claim 6, characterized in that, In the rolling step, the heating temperature of the steel billet is 1230 - 1280°C.

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