Manufacturing method of LZ50 axle steel and intelligent temperature control process after forging of LZ50 axle steel

Abstract

The invention relates to a manufacturing method of LZ50 axle steel and an intelligent temperature control process after forging, the LZ50 axle steel comprises the following chemical components in percentage by weight (wt.%): 0.47-0.57% of C, 0.17-0.4% of Mn, 0.6-0.9% of Si, less than or equal to 0.03% of S, less than or equal to 0.03% of P, less than or equal to 0.3% of Cr, less than or equal to 0.3% of Ni, more than or equal to 0.02% of T.Al and the balance of Fe and inevitable impurities, and the manufacturing method comprises the steps of converter smelting, external refining, casting blank heating and forging; on the basis of continuous cooling phase transformation behavior research, the cooling process of high-temperature water cooling and low-temperature air cooling is adopted, the structure of the forged piece obtained through the scheme is martensite and a small amount of feather-shaped bainite, the low-temperature toughness of the forged piece is improved while high strength is kept, the production cost is reduced, and the performance requirement of the high-performance axle steel can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy steels and relates to a method for manufacturing LZ50 axle steel, and in particular to an intelligent temperature control process after forging. Background Art

[0002] Large shaft parts are transmission parts of heavy-duty equipment and preforms of large forgings. They are key basic parts of large-duty equipment and are widely used in equipment industries such as transportation, engineering machinery, and national defense. Among them, large axles, as important load-bearing components of bogies, not only have to bear the weight of the train itself, but also are subject to composite stresses such as impact vibration and torsion bending when the train is running at high speed. Its performance changes during transportation have an absolute impact on the safe transportation of the train. With the rapid development of China's high-speed railways, the demand for train axles is also increasing rapidly, and higher requirements are placed on the performance of train axles.

[0003] Chinese patent application number: 2010106013168, a railway locomotive axle steel and a manufacturing method thereof, the mass percentage of the components of the axle steel is: C: 0.42-0.46%; Mn: 0.65-0.80%; Si: 0.20-0.30%; Cr: 0.10-0.20%; V: 0.030-0.050%; Alt: 0.020-0.050%; P≤0.015%; S≤0.005%; the rest is Fe and unavoidable impurities. The manufacturing method includes the following steps: I. Electric furnace smelting: first add scrap steel into the electric furnace and then add molten iron, then start blowing oxygen and add slag-making materials to remove C and P at the same time, and after P≤0.015%, the electric furnace taps steel; before the electric furnace taps steel, add ferroalloys containing corresponding elements, and then perform preliminary alloying; II. Ladle furnace refining: further deoxidation and S removal to S≤0.005% under reducing conditions, and at the same time add ferroalloys with corresponding elements to adjust the composition of molten steel. The axle steel made by this method for manufacturing steel for railway locomotive axles has high strength and good plasticity. This invention only optimizes the forging process, and its main technical feature is to complete melting and oxidation in electric furnace smelting, but there is no corresponding description of subsequent cooling.

[0004] The continuous cooling transformation curve (CCT) of supercooled austenite of steel is a very important means in material research. It can systematically reflect the law of phase transformation. Through CCT curve, experimental characterization and statistical analysis, the microstructure characteristics and change law of steel can be studied, and the heat treatment control mechanism of steel structure can be explored. The heat treatment process of steel can be comprehensively analyzed, which is of great significance for adjusting the chemical composition of steel, formulating reasonable process and improving the mechanical properties of steel. Therefore, it is necessary to analyze the influence of different cooling methods on the microstructure and mechanical properties of axles, and provide theoretical support for the subsequent axle manufacturing technology upgrade, the process and design of new production lines. Summary of the invention

[0005] The object of the present invention is to provide a method for manufacturing LZ50 axle steel and an intelligent temperature control process after forging thereof, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions: a method for manufacturing LZ50 axle steel and a post-forging intelligent temperature control process thereof, wherein the chemical composition of LZ50 axle steel is as follows by weight percentage (wt.%): C: 0.47-0.57%, Mn: 0.17-0.4%, Si: 0.6-0.9%, S≤0.03%, P≤0.03%, Cr: ≤0.3%, Ni: ≤0.3%, T.Al: ≥0.02%, and the rest is iron Fe and unavoidable impurities; the manufacturing method is as follows, S1, smelting: the raw materials are smelted by converter smelting + ladle refining + vacuum treatment to make the chemical composition of molten steel reach the set target range; S2, heating the ingot: heating the steel ingot with the above composition to 860-870°C in a nitrogen protection furnace, keeping the temperature for 4 hours for homogenization treatment, and obtaining a single-phase austenite structure; S3, forging: final forging temperature 820 ℃; repeated upsetting and drawing, forging ratio ≥5; during the forging process, the forging is carried out by rotating anvil downward pressure; after the final forging is completed, the forging is transferred to the cooling medium for cooling, and the transfer time from the final forging of the forging to the transfer to the cooling medium is controlled within 30 s; S4, cooling after forging: The forgings are cooled by alternating high-temperature water cooling and low-temperature air cooling. Enter the cooling step for rapid cooling. When the forging temperature is lower than 400 °C, stop cooling, remove the forgings and cool them naturally. The specific steps are as follows: The forgings after final forging are transferred to the water tank for cooling. The transfer time from the forgings being taken off the machine to being transferred to the water tank is controlled within 30s. The water temperature in the water tank is 20~50℃. The cooling rate of the forgings needs to be greater than 10℃ / s. After a certain period of time, the cooling is stopped when the forging temperature is cooled to less than 400℃, and the forgings are removed from the water tank for natural air cooling.

[0007] Compared with the prior art, the present invention has the following beneficial effects: The invention rationally designs the chemical composition of LZ50 axle steel and provides a manufacturing method with simple process and low cost.

[0008] The invention effectively regulates the structural transformation of the LZ50 axle steel forging during the cooling process through the innovative design of the post-forging cooling process, optimizes the final product quality, and improves the production efficiency.

[0009] The preferred solution uses high-temperature water cooling + low-temperature air cooling, which also has the following advantages: Reduced energy consumption: The high-temperature water cooling system can effectively utilize the heat capacity of water and quickly remove heat at high temperatures. Combined with low-temperature air cooling, it can reduce the consumption of cooling water at low loads, thereby reducing overall energy consumption; Cost-effectiveness: The combination of high-temperature water cooling and low-temperature air cooling reduces the need for large cooling towers and complex water treatment systems, reducing initial investment and operating costs; Flexibility and adaptability: The cooling method can be flexibly adjusted according to the different needs of the production process and changes in the external environment. Different cooling methods can be used in summer and winter to improve efficiency; Improve cooling efficiency: High-temperature water cooling can provide rapid heat removal in the initial cooling stage of steel, while low-temperature air cooling can maintain the appropriate temperature in the later stage to prevent material defects caused by uneven cooling; Environmentally friendly: It is not dependent on water resources and is relatively more environmentally friendly, especially in areas where water resources are scarce, reducing dependence on water sources and improving production reliability.

[0010] Easy maintenance: Air-cooled equipment is usually easy to maintain and is not easily affected by water quality problems, reducing equipment damage or reduced efficiency due to poor water quality.

[0011] 4. Based on the above research results, the present invention adopts a reasonable post-forging cooling process to obtain a microstructure of a small amount of feathery bainite and needle-shaped bainite, which significantly improves the strength and wear resistance of the axle steel. It can be better applied to large axles of high-speed railways and has high practical value and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The continuous cooling phase transformation curve of LZ50 axle steel at different cooling rates of the present invention; Figure 2 This is a metallographic structure diagram of LZ50 axle steel 1 / 2R of the present invention under a cooling mode of high-temperature water cooling + low-temperature air cooling; Figure 3 This is a metallographic structure diagram of LZ50 axle steel 1 / 2R of the present invention under a cooling mode of high-temperature air cooling + low-temperature water cooling; Figure 4 This is a metallographic structure diagram of LZ50 axle steel 1 / 2R of the present invention under the cooling mode of full air cooling; Figure 5 This is a metallographic structure diagram of LZ50 axle steel 1 / 2R of the present invention under the cooling mode of full water cooling; Figure 6 The following is a comparison table of mechanical properties between the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0013] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] The invention discloses an intelligent temperature control technology for axle steel after forging. The chemical composition of LZ50 axle steel is as follows by weight percentage (wt.%): C: 0.47-0.57%, Mn: 0.17-0.4%, Si: 0.6-0.9%, S≤0.03%, P≤0.03%, Cr: ≤0.3%, Ni: ≤0.3%, T.Al: ≥0.02%, and the rest is iron Fe and unavoidable impurities.

[0015] Based on the manufacturing method of LZ50 axle steel of the present invention, the above LZ50 and IDC 35E axle steel formula alloy is sequentially smelted in a converter, refined outside the furnace, slab continuously casted, continuously cast billet heated, and forged.

[0016] 1. Smelting The raw materials are smelted by the method of "converter smelting + ladle refining + vacuum treatment" to make the percentage of chemical elements in the molten steel reach: C: 0.47~0.57%, Mn: 0.17~0.4%, Si: 0.6~0.9%, S≤0.03%, P≤0.03%, Cr≤0.3%, Ni≤0.3%, T.Al≥0.02%, and the rest is iron Fe and unavoidable impurities; Composition adjustment: alloying the prepared molten steel to achieve the set target composition range; Ingot casting: Cast the molten steel after smelting to obtain continuous casting billet; 2. Heating of ingot The steel ingot with the above composition is subjected to homogenization normalizing treatment in a nitrogen protection furnace at 860-870°C for 4 hours to obtain a single-phase austenite structure; 3. Forging Final forging temperature is 820℃; repeated upsetting and drawing, forging ratio ≥5; during the forging process, the forging is carried out by rotating anvil downward pressure; after the final forging is completed, the forging is transferred to the cooling medium for cooling, and the transfer time from the final forging of the forging to the transfer to the cooling medium is controlled within 30 seconds; 4. Cooling after forging After the final forging is completed, the final forging temperature is about 820 ℃. The forging is transferred to the water tank for cooling using a hanger. The transfer time from the final forging of the forging to the transfer to the cooling medium is controlled within 30 s. Enter the cooling step for rapid cooling. The cooling rate of the forging needs to be greater than 10 ℃ / s. Use an infrared thermometer to detect the outlet water temperature of the forging. When the forging temperature is lower than 400 ℃, stop cooling and remove the forging. Rapid cooling after final forging can avoid the formation of ferrite and pearlite. After cooling, remove the forging and air cool it. Slow natural air cooling can eliminate the temperature stress caused by too fast cooling, and removing it for air cooling will not produce excessive structural stress. Embodiment 1:

[0017] Firstly, a vacuum induction furnace was used to smelt 150 kg of molten steel with a chemical composition within the above target range. Then, the ingot was cast and hot forged into a billet with a cross-section of 120 mm × 120 mm at a temperature of 820 °C. The forging was then transferred to a water tank for cooling for 20 s. An infrared thermometer was used to detect the outlet water temperature of the forging. After the outlet water temperature was lower than 400 °C, the forging was taken out and naturally air-cooled.

[0018] Comparative Example 1: Firstly, a vacuum induction furnace was used to smelt 150 kg of molten steel with a chemical composition within the above target range. Then, the ingot was cast and hot-forged into a billet with a cross-section of 120 mm × 120 mm at a temperature of 820 °C. The forging was then removed. An infrared thermometer was used to detect the temperature of the forging. After the forging temperature was lower than 400 °C, the forging was taken out and naturally cooled to room temperature.

[0019] Comparative Example 2: First, a vacuum induction furnace was used to smelt 150 kg of molten steel with a chemical composition within the above target range. The ingot was then cast and hot-forged into a billet with a cross-section of 120 mm × 120 mm at a temperature of 820 °C. The forging was then removed and the temperature of the forging was detected using an infrared thermometer to ensure that it cooled naturally to room temperature.

[0020] Comparative Example 3: Firstly, a vacuum induction furnace was used to smelt 150 kg of molten steel with a chemical composition within the above target range. Then, the ingot was cast and hot forged into a billet with a cross-section of 120 mm × 120 mm at a temperature of 820 °C. The forging was then transferred to a water tank for cooling for 20 s. An infrared thermometer was used to detect the outlet water temperature of the forging, and the forging was taken out when the outlet water temperature was close to the water temperature.

[0021] Example 1 adopts a cooling method of high temperature water cooling + low temperature air cooling, while Comparative Examples 1 to 3 respectively adopt cooling methods of high temperature air cooling + low temperature water cooling, full process water cooling and full process air cooling. The mechanical properties of Example 1 and Comparative Examples 1 to 3 are compared in Table 1. Figure 1The CCT curve of comparative example 1 shows that when the forging is cooled to 400 °C by air, ferrite transformation and pearlite transformation have occurred in the forging. Figure 3 The ferrite and pearlite structures shown in the figure make the forging have good toughness, but also significantly reduce its strength and hardness, which cannot meet the requirements of practical engineering applications; when the comparative example 2 is removed after forging and naturally cooled, ferrite and pearlite are generated in the same way as the comparative example 1 ( Figure 4 ), although it has good toughness, the overall strength is low; after the forgings of comparative example 3 are removed, they are directly placed in a water tank for cooling. The large degree of supercooling causes a large amount of martensite and a small amount of feathery bainite to form in the structure. The strength of the forgings is significantly improved compared with comparative examples 1 and 2, but its toughness is significantly deteriorated, making it difficult to use in practice. Example 1 uses the same cooling process as comparative example 3, but adds a low-temperature air cooling process. When the forgings are moved to a water tank and cooled to below 400 ° C, the forgings are removed for natural air cooling. The feathery bainite content in the structure of the forgings is ( Figure 2 ) is increased compared with comparative example 3, so that the forging has higher strength and improved toughness. While reducing the production cost, its comprehensive performance can meet the requirements of practical application.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for manufacturing LZ50 axle steel and an intelligent temperature control process after forging, characterized in that: The chemical composition of LZ50 axle steel is as follows by weight percentage (wt.%): C: 0.47~0.57%, Mn: 0.17~0.4%, Si: 0.6~0.9%, S≤0.03%, P≤0.03%, Cr: ≤0.3%, Ni: ≤0.3%, T.Al: ≥0.02%, and the rest is iron Fe and unavoidable impurities; the manufacturing method is as follows, S1, smelting: the raw materials are smelted by converter smelting + ladle refining + vacuum treatment to make the chemical composition of molten steel reach the set target range; S2, heating the ingot: heating the steel ingot with the above composition to 860-870°C in a nitrogen protection furnace, keeping the temperature for 4 hours for homogenization treatment, and obtaining a single-phase austenite structure; S3, forging: final forging temperature 820 ℃; repeated upsetting and drawing, forging ratio ≥5; during the forging process, the forging is carried out by rotating anvil downward pressure; after the final forging is completed, the forging is transferred to the cooling medium for cooling, and the transfer time from the final forging of the forging to the transfer to the cooling medium is controlled within 30 s; S4, cooling after forging: The forgings are cooled by alternating high-temperature water cooling and low-temperature air cooling. Enter the cooling step for rapid cooling. When the forging temperature is lower than 400 °C, stop cooling, remove the forgings and cool them naturally. The specific steps are as follows: The forgings after final forging are transferred to the water tank for cooling. The transfer time from the forgings being taken off the machine to being transferred to the water tank is controlled within 30s. The water temperature in the water tank is 20~50℃. The cooling rate of the forgings needs to be greater than 10℃ / s. After a certain period of time, the cooling is stopped when the forging temperature is cooled to less than 400℃, and the forgings are removed from the water tank for natural air cooling.

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