Ultrafine lamellar pearlite structure corrosion-resistant steel rail steel and preparation method

Abstract

The application discloses a kind of ultrafine lamellar pearlite structure corrosion-resistant steel rail steel and preparation method, belong to steel rail steel technical field, solve the existing technology in high bridge tunnel ratio or marine climate conditions steel rail steel poor corrosion resistance, at least one of the problems such as existing corrosion resistance improvement method process operation complex, high cost, influence railway signal, exist local damage after accelerated corrosion, coating aging etc..The corrosion-resistant steel rail steel, composition includes C0.60~0.70, Si0.50~0.60, Mn0.70~0.80, Cr0.25~0.35, Cu0.25~0.35 and Nb0.02~0.04 according to mass percentage.The preparation method includes smelting, casting, heating, heat preservation, rolling, on-line heat treatment and straightening.The application can be used for railway rail.

Description

Technical Field

[0001] This invention belongs to the technical field of steel for rails, and particularly relates to a corrosion-resistant steel for rails with an ultrafine lamellar pearlite structure and its preparation method. Background Technology

[0002] Railway transportation plays a vital role in my country's economic and social development. Steel rails are a key material in railway construction, and their service performance and lifespan significantly affect the safety and reliability of railway transportation. As railway construction extends to more complex environments, these environments place higher demands on the service performance of steel rails. For example, railways built in complex environments exceeding 1,500 kilometers in length have a bridge-to-tunnel ratio of over 80%. Tunnels experience large temperature differences between day and night and are dark and humid environments, making in-service steel rails susceptible to corrosion from humid gases. Furthermore, corrosion problems are common in rails and fasteners under marine climate conditions, further challenging the corrosion resistance and other service performance characteristics of steel rails.

[0003] Currently, methods to improve the corrosion resistance of rails mainly include sacrificial anode protection, surface thermal spraying, and adding corrosion-resistant microalloying elements. Among these, the application of sacrificial anode protection is limited due to its complex process, high cost, and impact on railway signaling. Surface thermal spraying methods, such as aluminum-zinc alloy, chromium alloy, and nano-coatings, also suffer from problems such as accelerated corrosion after localized damage and coating aging. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a corrosion-resistant rail steel with an ultra-fine lamellar pearlite structure and a preparation method thereof, which solves at least one of the following problems in the prior art: poor corrosion resistance of rail steel under high bridge-tunnel ratio or marine climate conditions; complex and costly processes for improving corrosion resistance; impact on railway signaling; accelerated corrosion after local damage; and coating aging.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] This invention provides a corrosion-resistant rail steel with an ultrafine lamellar pearlitic structure, the composition of which, by mass percentage, includes C 0.60-0.70, Si 0.50-0.60, Mn 0.70-0.80, Cr 0.25-0.35, Cu 0.25-0.35 and Nb 0.02-0.04.

[0007] Furthermore, the composition of the steel for corrosion-resistant rails, by mass percentage, also includes at least two of the following: Mo 0.00–0.08, Sb 0.00–0.10, and Sn 0.00–0.10.

[0008] Furthermore, the composition of the corrosion-resistant rail steel, by mass percentage, includes C 0.62–0.65; Si 0.50–0.53; Mn 0.72–0.74; Cr 0.30–0.33; Cu 0.35–0.37; Nb 0.02–0.04; Mo 0.05–0.06; and Sb 0.07–0.08.

[0009] Furthermore, the composition of the corrosion-resistant rail steel, by mass percentage, includes C 0.63–0.64; Si 0.51–0.53; Mn 0.74–0.76; Cr 0.30–0.33; Cu 0.36–0.37; Nb 0.02–0.04; Mo 0.05–0.06; Sn 0.07–0.08.

[0010] Furthermore, the composition of the corrosion-resistant rail steel, by mass percentage, includes C 0.62–0.65; Si 0.50–0.52; Mn 0.74–0.76; Cr 0.31–0.34; Cu 0.36–0.37; Nb 0.02–0.04; Sb 0.07–0.08; Sn 0.07–0.08.

[0011] Furthermore, the composition of the corrosion-resistant rail steel, by mass percentage, includes: C 0.65–0.68; Si 0.52–0.54; Mn 0.74–0.76; Cr 0.30–0.33; Cu 0.36–0.37; Nb 0.02–0.04; Mo 0.05–0.06; Sb 0.03–0.05; Sn 0.03–0.05.

[0012] This invention also provides a method for preparing corrosion-resistant rail steel with an ultrafine lamellar pearlitic structure, used for the preparation of the aforementioned corrosion-resistant rail steel. The preparation method includes the following steps:

[0013] Step 1: Smelt and cast the raw materials according to the composition of the steel used for corrosion-resistant rails to obtain a cast billet;

[0014] Step 2: Heat the billet to the austenitizing and homogenizing temperature and hold it at that temperature;

[0015] Step 3: After heat preservation, the cast billet is removed from the furnace and rolled.

[0016] Step 4: After rolling, hot rolling or online heat treatment using residual heat from rolling is used to obtain the rail to be straightened;

[0017] Step 5: Straighten the rails to be straightened.

[0018] Furthermore, in step 1, Sb is added in the form of an Sb-Fe alloy with an Sb content of 20-30%.

[0019] Furthermore, in step 3, the residual heat from rolling is used for online heat treatment.

[0020] Furthermore, the cooling rate during the online heat treatment process is 0.8–2.0 °C / s.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] The ultrafine lamellar pearlitic corrosion-resistant rail steel provided by this invention belongs to the high-carbon Cr-Cu-Mo-Sb-Sn system of high-strength and high-corrosion-resistant rail steel. It adopts a multi-component composite microalloying approach combining high C with the synergistic effect of Mo, Sb, and Sn. Through the rational matching of Mo, Sb, and Sn elements, their corrosion-inhibiting effect in rail steel is fully utilized. By using microalloying, a corrosion-resistant rail steel with good corrosion resistance, resistance to marine atmospheric corrosion, and resistance to industrial atmospheric corrosion is developed, providing an effective and economical means to solve the harsh corrosive service environment such as coastal areas or tunnels.

[0023] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description. Attached Figure Description

[0024] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0025] Figure 1a This is a metallographic diagram of Embodiment 1 of the present invention;

[0026] Figure 1b This is a scanning electron microscope (SEM) image of Embodiment 1 of the present invention;

[0027] Figure 2a This is a metallographic diagram of Embodiment 2 of the present invention;

[0028] Figure 2b This is a scanning electron microscope (SEM) image of Embodiment 2 of the present invention;

[0029] Figure 3a This is a metallographic diagram of Embodiment 3 of the present invention;

[0030] Figure 3b This is a scanning electron microscope (SEM) image of Embodiment 3 of the present invention;

[0031] Figure 4a This is a metallographic diagram of Embodiment 4 of the present invention;

[0032] Figure 4bThis is a scanning electron microscope (SEM) image of Embodiment 4 of the present invention;

[0033] Figure 5a This is a metallographic diagram of Comparative Example 1 of the present invention;

[0034] Figure 5b This is a scanning electron microscope (SEM) image of Comparative Example 1 of the present invention. Detailed Implementation

[0035] Preferred embodiments of the present invention are described in detail below.

[0036] This invention provides a corrosion-resistant rail steel with an ultrafine lamellar pearlitic structure, the composition of which, by mass percentage, includes C 0.60-0.70, Si 0.50-0.60, Mn 0.70-0.80, Cr 0.25-0.35, Cu 0.25-0.35 and Nb 0.02-0.04, and also includes at least two of Mo 0.00-0.08, Sb 0.00-0.10 and Sn 0.00-0.10, with the balance being Fe and unavoidable impurities.

[0037] It should be noted that the pearlite lamellar spacing of the above-mentioned ultrafine lamellar pearlite structure corrosion-resistant rail steel can reach 0.10 to 0.13 μm, which is significantly smaller than that of the prior art. The volume fraction of pearlite is ≥95%, which is much higher than that of the prior art. This structure has high strength, toughness and fatigue resistance.

[0038] Compared with existing technologies, the ultrafine lamellar pearlite-structured corrosion-resistant rail steel provided by this invention belongs to the high-carbon Cr-Cu-Mo-Sb-Sn system of high-strength and high-corrosion-resistant rail steel. It adopts a multi-component composite microalloying approach combining high C with the synergistic effect of Mo, Sb, and Sn. Through the rational matching of Mo, Sb, and Sn elements, their corrosion-inhibiting effects in rail steel are fully utilized. By using microalloying, a corrosion-resistant rail steel with good corrosion resistance, resistance to marine atmospheric corrosion, and resistance to industrial atmospheric corrosion is developed, providing an effective and economical means to solve the problem of harsh corrosive service environments such as coastal areas or tunnels.

[0039] Specifically, the functions and proportions of the above elements are based on the following:

[0040] Carbon (C): A key element for improving the wear resistance of rail steel. As the C content increases, the strength, hardness, and wear resistance of rail steel all improve; however, its ductility, toughness, and weldability decrease. It is worth noting that wear resistance is the most critical indicator for rail steel; therefore, this invention employs a high-carbon composition design to ensure high strength and high hardness, with the C content controlled at 0.60–0.70%.

[0041] Si (Si): As a deoxidizing element in steel, Si significantly strengthens through solid solution and refines the interlamellar spacing of pearlite, thereby improving the strength and hardness of rail steel. Si reduces oxidation during frictional heating, increasing the cold work hardening rate of rail steel and thus improving wear resistance. Si also raises the eutectoid transformation temperature of steel, allowing the pearlite transformation to occur at higher temperatures. However, excessive Si will reduce the toughness of rail steel; therefore, its content should be controlled at 0.50–0.60%.

[0042] Mn is one of the effective solid solution strengthening elements in steel. It can significantly improve the hardenability of rail steel, refine the pearlite lamellar spacing, and improve the strength and hardness of rail steel. Therefore, the present invention controls its content to be 0.70-0.80%.

[0043] Cr can significantly improve the hardenability of steel, refine the interlamellar spacing of pearlite, and improve the strength and hardness of rail steel; at the same time, it can form alloy cementite and improve the stability of pearlite structure. Therefore, the content of Cr is controlled at 0.25-0.35% in this invention.

[0044] Cu: It is an effective corrosion-resistant element in rail steel. Cu microalloying can inhibit anodic dissolution and increase the self-corrosion potential, forming a stable enrichment layer in the inner rust layer and preventing the penetration of corrosive ions. However, excessive addition will lead to a decrease in the plasticity of rail steel, and in severe cases, it may even lead to hot rolling cracking. Therefore, the present invention controls its content to be 0.25-0.35%.

[0045] Nb is an effective microalloying strengthening element in rail steel. It precipitates mostly in the form of NbC in the austenite phase region, exhibiting precipitation strengthening and grain refinement effects. Nb microalloying shifts the high-temperature phase transformation curve to the upper right during continuous cooling, which can refine the pearlite lamellar spacing and improve the strength and hardness of rail steel. However, excessively high Nb content can lead to an increase in the NbC precipitation temperature, resulting in coarsening and hindering the refinement of austenite grains. Therefore, this invention controls its content to be 0.02–0.04%.

[0046] Mo, Sb, and Sn are effective corrosion-resistant elements in rail steel; among them, Mo forms MoO4 during corrosion. 2-It has a corrosion-inhibiting effect and can promote the formation of a dense oxide film on the surface of rail steel, preventing the penetration of corrosive ions. The combined addition of Mo with Sb and / or Sn has a synergistic effect, which can form a denser oxide film on the surface of rail steel. At the same time, it slows down cathodic or anodic reactions, further improving the corrosion resistance of rail steel. Considering the synergistic matching with Sb and Sn, the content of Mo in this invention is controlled at 0.00-0.08%. Sb and Sn can effectively slow down cathodic and anodic reactions, and at the same time form a dense corrosion-resistant oxide film on the surface of rail steel, preventing the penetration of corrosive ions and promoting the formation of α-FeOOH, which plays a protective role in the rust layer, thus improving the corrosion resistance of rail steel. Therefore, the content of Sb in this invention is controlled at 0.00-0.10%, and the content of Sn is controlled at 0.00-0.10%.

[0047] For example, considering the synergistic effect of Mo, Sb, and Sn, they can be selectively added in the following ways:

[0048] The first method involves adding Mo and one of Sb or Sn, resulting in an Sb or Sn content of 0.05–0.10% and a Mo content of 0.05–0.08%.

[0049] For example, the composition of the above-mentioned ultrafine lamellar pearlitic corrosion-resistant rail steel, by mass percentage, includes C 0.62-0.65; Si 0.50-0.53; Mn 0.72-0.74; Cr 0.30-0.33; Cu 0.35-0.37; Nb 0.02-0.04; Mo 0.05-0.06; Sb 0.07-0.08.

[0050] Alternatively, C 0.63~0.64; Si 0.51~0.53; Mn 0.74~0.76; Cr 0.30~0.33; Cu 0.36~0.37; Nb 0.02~0.04; Mo 0.05~0.06; Sn 0.07~0.08.

[0051] The second method involves adding only Sb and Sn, resulting in Sb and Sn contents of 0.05–0.10%.

[0052] For example, the composition of the above-mentioned ultrafine lamellar pearlitic corrosion-resistant rail steel, by mass percentage, includes C 0.62-0.65; Si 0.50-0.52; Mn 0.74-0.76; Cr 0.31-0.34; Cu 0.36-0.37; Nb 0.02-0.04; Sb 0.07-0.08; Sn 0.07-0.08.

[0053] The third method involves adding Sb, Sn, and Mo simultaneously, resulting in Sb and Sn contents of 0.03–0.05% and Mo contents of 0.05–0.08%.

[0054] For example, the composition of the aforementioned ultrafine lamellar pearlitic corrosion-resistant rail steel, by mass percentage, includes C 0.65–0.68; Si 0.52–0.54; Mn 0.74–0.76; Cr 0.30–0.33; Cu 0.36–0.37; Nb 0.02–0.04; Mo 0.05–0.06; Sb 0.03–0.05; Sn 0.03–0.05.

[0055] This invention also provides a method for preparing corrosion-resistant rail steel with an ultrafine lamellar pearlite structure, comprising the following steps:

[0056] Step 1: Vacuum induction smelting and casting of the raw materials according to the composition of the steel used for corrosion-resistant rails to obtain a cast billet;

[0057] For example, the smelting method is vacuum induction smelting, electric arc furnace smelting, or converter smelting. It should be noted that if electric arc furnace smelting or converter smelting is used, LF+RH refining is required after smelting before casting.

[0058] Step 2: Heat the billet to the austenitizing and homogenizing temperature of 1200-1250℃ and hold for 1-3 hours;

[0059] Step 3: After heat preservation, the billet is taken out of the furnace, the oxide scale is removed, and it is directly rolled using a universal rolling mill. The final rolling temperature is not lower than 920℃.

[0060] Step 4: After rolling, hot rolling or online heat treatment using residual heat from rolling is used to obtain the rail to be straightened;

[0061] Step 5: Straighten the rails to be straightened.

[0062] Compared with the prior art, the beneficial effects of the preparation method of the ultrafine lamellar pearlite structure corrosion-resistant rail steel provided by the present invention are basically the same as the beneficial effects of the ultrafine lamellar pearlite structure corrosion-resistant rail steel provided above, and will not be repeated here.

[0063] It should be noted that when Sb needs to be added, in order to improve the Sb yield, in step 1 above, Sb is added as an Sb-Fe alloy with an Sb content of 20-30%, rather than directly adding metallic Sb. This is because Sb has a low melting point, and direct addition results in a low yield. Furthermore, the volatilization of Sb will produce biological toxicity and pollute the environment. The Sb-Fe alloy raw material with an Sb content of 20-30% has a melting point between 1300-1400℃ and a density similar to Fe, which can effectively improve the Sb yield.

[0064] In order to further improve the overall performance of the corrosion-resistant rail steel with ultrafine lamellar pearlite structure, in step 3 above, online heat treatment is carried out using the residual heat of rolling, and the cooling rate is 0.8 to 2.0℃ / s.

[0065] In summary, by improving the composition and preparation method of corrosion-resistant rail steel with ultrafine lamellar pearlite structure, the present invention can obtain a microstructure consisting of pearlite and a very small amount of proeutectoid ferrite, wherein the volume fraction of pearlite is ≥95% and the interlamellar spacing of pearlite is 0.10~0.13μm.

[0066] Accordingly, the ultrafine lamellar pearlite-structured corrosion-resistant rail steel prepared by this invention is a 1080 grade rail steel with a tensile strength of 1090-1110 MPa, a yield strength of 610-630 MPa, an elongation after fracture of 15-17.5%, and a Brinell hardness of 305-315.

[0067] It should be noted that, compared with existing rail steel, the comprehensive corrosion resistance of the ultrafine lamellar pearlite-structured corrosion-resistant rail steel of the present invention is as follows:

[0068] Resistant to atmospheric corrosion: corrosion rate 2.0~3.0g / m 2 The average corrosion rate is 2.14–2.78 g / m·h. 2 ·h.

[0069] The corrosion resistance of the ultrafine lamellar pearlite structure corrosion-resistant rail steel of this invention is significantly better than that of U71Mn. Its resistance to marine atmospheric corrosion is 1.6 to 2 times that of U71Mn, and its resistance to industrial atmospheric corrosion is 1.4 to 1.8 times that of U71Mn.

[0070] The chemical composition of the rail steel in Examples 1 to 4 and Comparative Example 1 of the present invention is shown in Table 1. Among them, Comparative Example 1 is U71Mn produced and sold by a steel mill.

[0071] Examples 1-4 were smelted, cast, and shaped. After the ends were removed, the billets were held at 1230℃ for 1 hour, then forged at a final forging temperature above 920℃. The billet dimensions were 60mm (thickness) × 150mm (width). The forged test steel was heated to 1200-1250℃ and held for 1 hour. After removing the oxide scale, it was rolled according to the following tolerances: 60mm-52mm-42mm-34mm-30mm (positive tolerance). The finished product was approximately 1m long. The final rolling temperature was not lower than 920℃. The steel was then air-cooled to room temperature. Table 2 shows the specific rolling process parameters for Examples 1-4 and Comparative Example 1.

[0072] Table 1 Chemical composition (wt.%) of Examples 1-4 and Comparative Example 1

[0073] C Si Mn Cr Cu Nb Mo Sb Sn P S Example 1 0.64 0.51 0.73 0.31 0.36 0.03 0.06 0.08 / 0.003 0.002 Example 2 0.63 0.52 0.75 0.31 0.35 0.03 0.06 / 0.08 0.003 0.002 Example 3 0.64 0.50 0.75 0.32 0.35 0.03 / 0.08 0.08 0.003 0.002 Example 4 0.65 0.52 0.74 0.31 0.36 0.03 0.06 0.04 0.04 0.003 0.002 Comparative Example 1 0.70 0.34 0.95 0.01 0.01 / / / / 0.009 0.010

[0074] Table 2 Hot rolling process parameters of Examples 1-4 and Comparative Example 1

[0075] Heating temperature / ℃ Final rolling temperature / ℃ Example 1 1230 925 Example 2 1225 920 Example 3 1230 920 Example 4 1228 923 Comparative Example 1 1235 925

[0076] Table 3 shows the room temperature mechanical properties of Examples 1-4 and Comparative Example 1. It can be seen from Table 3 that Examples 1-4 all meet the mechanical property requirements of YB / T 4817. At the same time, the mechanical properties of Examples 1-4 are better than those of Comparative Example 1.

[0077] Table 3. Room temperature mechanical properties of Examples 1-3 and Comparative Example 1

[0078]

[0079]

[0080] Table 4 shows the pearlite lamellar spacing in the rail steel of Examples 1-4 and Comparative Example 1. As can be seen from Table 4, Examples 1-4 obtained ultrafine pearlite microstructure, which has good strength and toughness matching and good corrosion resistance in various environments, resulting in corrosion-resistant rails.

[0081] Table 4 Pearlite lamellar spacing of Examples 1-4 and Comparative Example 1

[0082] Pearlite lamellar spacing / μm Example 1 0.10 Example 2 0.11 Example 3 0.13 Example 4 0.12 Comparative Example 1 0.18

[0083] Accelerated corrosion tests were conducted in simulated marine atmospheric corrosion and industrial atmospheric corrosion conditions on Examples 1-4 and Comparative Example 1, and compared with Comparative Example 1 (i.e., U71Mn) under the same test conditions to evaluate the corrosion resistance performance of the present invention in marine atmospheric corrosion and industrial atmospheric corrosion environments. The results of the above two accelerated corrosion tests are shown in Table 5.

[0084] The corresponding test conditions are as follows:

[0085] The first method simulates marine atmospheric corrosion. The corresponding immersion corrosion conditions are as follows: solution: 3.5% NaCl solution; RH: 70±5%; test temperature: 45±2℃; each cycle: 60±3min, immersion time 12±1.5min; test period: 72h.

[0086] The second method simulates industrial atmospheric corrosion, with the following corresponding periodic immersion corrosion conditions: solution: (1.0±0.05)×10 -2 mol / L NaHSO3 solution; RH: 70±5%; test temperature: 45±2℃; cycle time: 60±min, immersion time: 12±1.5min; test period: 72h.

[0087] Three parallel samples were set up for each group of tests.

[0088] As shown in Table 5, under both accelerated corrosion conditions, the corrosion resistance of Examples 1 to 4 was superior to that of Comparative Example U71Mn. Their resistance to marine atmospheric corrosion was 1.6 times, 1.6 times, 2.0 times, and 2.1 times that of U71Mn, respectively, and their resistance to industrial atmospheric corrosion was 1.7 times, 1.4 times, 1.8 times, and 1.9 times that of U71Mn, respectively.

[0089] Table 5. Indoor accelerated corrosion test data for Examples 1-4 and Comparative Example 1

[0090]

[0091]

[0092] Figures 1a-5b The images show metallographic structures and scanning electron microscope (SEM) images of Examples 1-4 and Comparative Example 1. It can be seen from these images that the ferrite content in the microstructure of Examples 1-4 is significantly lower than that of Comparative Example 1. At the same time, the pearlite lamellar spacing in Examples 1-4 is also significantly smaller than that in Comparative Example 1.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing corrosion-resistant rail steel with an ultrafine lamellar pearlitic structure, characterized in that, The preparation method includes the following steps: Step 1: Smelt and cast the raw materials according to the composition of the steel used for corrosion-resistant rails to obtain a cast billet; Step 2: Heat the billet to the austenitizing and homogenizing temperature and hold it at that temperature; Step 3: After heat preservation, the cast billet is removed from the furnace and rolled. Step 4: After rolling, hot rolling or online heat treatment using residual heat from rolling is used to obtain the rail to be straightened; Step 5: Straighten the rails to be straightened; The steel used for corrosion-resistant rails comprises, by mass percentage: C 0.65~0.68; Si 0.52~0.54; Mn 0.74~0.76; Cr 0.30~0.33; Cu 0.36~0.37; Nb 0.02~0.04; Mo 0.05~0.06; Sb 0.03~0.05; Sn 0.03~0.

05. In step 1, Sb is added in the form of an Sb-Fe alloy with an Sb content of 20-30%. The volume fraction of pearlite in the corrosion-resistant rail steel is ≥95%, and the interlamellar spacing of the pearlite is 0.10~0.13μm.

2. The method for preparing corrosion-resistant rail steel with ultrafine lamellar pearlitic structure according to claim 1, characterized in that, In step 4, the residual heat from rolling is used for online heat treatment.

3. The method for preparing corrosion-resistant rail steel with ultrafine lamellar pearlite structure according to claim 2, characterized in that, The cooling rate during the online heat treatment process is 0.8~2.0℃ / s.

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