Heat treatment method of 42CrMo rail rim

Abstract

The invention belongs to the technical field of heat treatment, and relates to a heat treatment method of a 42CrMo rail rim, which comprises the following steps: hoisting: hoisting the rail rim by adopting a two-point hoisting mode and then loading the rail rim into a heat treatment furnace; normalizing: heating the rail rim to 920-930 DEG C through a heat treatment furnace, keeping the temperature for 110-120 minutes, discharging the rail rim out of the furnace, and performing air cooling; the rail rim is heated to 855-865 DEG C, heat preservation is conducted for 50-55 min, then quenching is conducted, and a PAG aqueous solution is adopted as a quenching medium; and high-temperature tempering: heating the rail rim to 520-530 DEG C, tempering, preserving heat for 4.0-4.5 hours, and cooling by adopting a PAG aqueous solution. According to the method, banded segregation is eliminated by increasing the temperature of the normalizing procedure, the grain size reaches 8-9 grades, and PAG cooling after hardening and tempering and high-temperature tempering meets the mechanical property, so that the uniformity of quenching hardness of different parts of the rim is within 2HRC, and the stability and consistency of low-temperature impact are ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment and relates to a heat treatment method for a 42CrMo track wheel rim. Background Art

[0002] The rail rim is a key part of the rail vehicle wheel, which is in direct contact with the rails, responsible for bearing the train load and ensuring smooth operation. It is made of high-strength materials and has a reasonable design of tread and rim to optimize wear resistance, impact resistance and guidance, ensuring the safety and stability of train operation.

[0003] Heat treatment of rail rims is a key step to ensure their performance and quality. The heat treatment process mainly includes normalizing, quenching and high-temperature tempering. Normalizing heats the alloy to a high-temperature austenite single-phase region and maintains it at a constant temperature, so that the ferrite phase, pearlite phase, etc. are fully dissolved into the austenite. Quenching heats the rim to a specified temperature and keeps it warm for a period of time before cooling it quickly to obtain a martensitic structure and improve strength. High-temperature tempering heats and keeps it warm at a relatively high temperature, and martensite is transformed into tempered troostite, which obtains good strength, plasticity and toughness, and has good comprehensive mechanical properties. During the heat treatment process, accurate temperature control is essential. For example, during the quenching process, it is necessary to ensure that the rim is hardened evenly over the entire circumference, which requires that the temperature in the heating furnace must be precisely controlled. Modern heat treatment technology adopts the concept of cascade gas-air ratio control, and achieves precise temperature adjustment through program heating and PID controller to ensure that the rim obtains ideal mechanical properties. After heat treatment, machining and painting are also required to ensure the dimensional accuracy and surface quality of the rim. Finally, the rims are subject to rigorous testing, including dimensional testing and surface color flaw detection, to ensure that they meet relevant standards and requirements. Through these complex heat treatments and subsequent processes, the rail rims can have excellent wear resistance, fatigue resistance and guidance, providing a solid guarantee for the safe and stable operation of rail vehicles.

[0004] At present, the rail wheel rim material is mostly 42CrMo, and the heat treatment system is normalizing after forging, followed by quenching + high temperature tempering. However, the 42CrMo rail wheel rim treated by the existing 42CrMo rail wheel rim heat treatment process has problems such as low grain size (coarse), mixed crystals, banded segregation defects, unstable low-temperature impact energy, and excessive out-of-roundness. Therefore, it is urgent to propose a new heat treatment method for 42CrMo rail wheel rim to overcome the problems of the existing 42CrMo rail wheel rim heat treatment process. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a heat treatment method for a 42CrMo track rim to overcome the problems existing in the existing heat treatment process for a 42CrMo track rim.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A heat treatment method for a 42CrMo track rim comprises the following steps:

[0008] Hoisting: The rail rim is hoisted by two-point hanging method and then loaded into the heat treatment furnace;

[0009] Normalizing process: Heat the rail wheel rim to 920-930℃ in a heat treatment furnace, keep it at this temperature for 110-120min, and then air cool it out of the furnace;

[0010] Quenching process: heat the rail wheel rim to 855℃~865℃ and keep it at this temperature for 50~55min before quenching. The quenching medium is PAG aqueous solution.

[0011] High temperature tempering process: heat the rail rim to 520℃~530℃ for tempering, keep it warm for 4.0~4.5h, and then cool it with PAG aqueous solution.

[0012] Furthermore, after the normalizing process is completed, the track wheel rim needs to be rotated 90 degrees along its axis before entering the quenching process to prevent the track wheel rim from being scrapped due to excessive loss of roundness.

[0013] Furthermore, the track rim has an inner hole, and the openings at both ends of the inner hole are respectively large-diameter and small-diameter;

[0014] The tooling for hanging the track rim is inserted into the inner hole of the track rim from the large diameter end of the inner hole for hanging, and the tooling and the track rim have two parallel contact surfaces to realize two-point hanging of the track rim.

[0015] Furthermore, the concentration of the PAG aqueous solution is 3% to 5%.

[0016] The beneficial effects of the present invention are:

[0017] The present invention provides a heat treatment method for a 42CrMo rail rim, which eliminates band segregation by increasing the temperature of a normalizing process, and the grain size reaches level 8 to 9. The mechanical properties are met by PAG cooling after quenching and high-temperature tempering, so that the uniformity of the quenching hardness of different parts of the rim is within 2HRC, and the stability and consistency of low-temperature impact are guaranteed.

[0018] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0020] Figure 1 Schematic diagram of the structure of the track rim in the embodiment. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0022] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0023] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0024] See also Figure 1 , a rail rim in a heat treatment method of a 42CrMo rail rim, the rail rim having an inner hole, and openings at both ends of the inner hole are respectively a large diameter and a small diameter;

[0025] The heat treatment method specifically comprises the following steps:

[0026] Step 1: The rail rim is hoisted by a two-point hanging method and then loaded into a heat treatment furnace; specifically, a tool for hanging the rail rim is inserted into the inner hole of the rail rim from the large diameter end of the inner hole for hanging, and the tool and the rail rim have two parallel contact surfaces to achieve two-point hanging of the rail rim.

[0027] Step 2 (normalizing process): heat the rail wheel rim to 920-930°C in a heat treatment furnace, keep it at this temperature for 110-120 minutes, and then air-cool it to eliminate the band segregation defect of the wheel rim, and the grain size reaches 8-9 levels;

[0028] The normalizing process breaks the theoretical and conventional normalizing temperature of 860-880℃, eliminates the band segregation defect of the rim, and meets the requirement of grain size ≥ 7 level;

[0029] Step 3: After the normalizing process is completed, the track rim is rotated 90 degrees along its axis and then enters the quenching and tempering process, which includes a quenching process and a high-temperature tempering process;

[0030] By rotating the rail rim, the rail rim is prevented from being excessively out of round and scrapped during the normalizing process and the quenching and tempering process, and the rail rim is prevented from being hung in the converter at the same position, so that the scrap rate is zero. And it can be directly transferred to the quenching and tempering process after the normalizing process, shortening the production cycle and improving production efficiency.

[0031] Step 4 (quenching process): heat the rail rim to 855°C to 865°C, keep it warm for 50 to 55 minutes, and then quench it. The quenching medium uses a PAG aqueous solution (polyalkylene glycol) with a concentration of 3% to 5% to ensure that the uniformity of the quenching hardness of different parts of the rail rim is within 2HRC;

[0032] Step 5 (high temperature tempering process): heat the rail rim to 520°C to 530°C for tempering, and keep the temperature for 4.0 to 4.5 hours, and then cool it with a PAG aqueous solution;

[0033] By strictly controlling the tempering temperature and time, the uniformity of hardness after tempering is ensured; and at the end of tempering, PAG aqueous solution is used for cooling to prevent high-temperature tempering brittleness. In this embodiment, PAG aqueous solution is used for cooling in the tempering process to ensure that the uniformity of tempering hardness of different parts is within 2HRC, and the metallographic structure is level 2 uniform tempered troostite.

[0034] Although the rims made of this material theoretically do not have high-temperature temper brittleness, when the mechanical properties of the rims treated by the existing heat treatment process were tested, it was found that the low-temperature impact energy did not meet the requirements and the data fluctuated greatly. In this embodiment, the problem of large fluctuations in the low-temperature impact energy data was solved by using a PAG aqueous solution for rapid cooling in the tempering process.

[0035] After the heat treatment, the rim body is sampled and tested for tensile strength, yield strength, elongation, shrinkage, normal temperature and low temperature impact energy, all of which meet the user's requirements. In particular, the stability and consistency of low temperature impact are guaranteed.

[0036] 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 heat treatment method for 42CrMo track rim, characterized in that: The following steps are involved: Hoisting: The rail rim is hoisted by two-point hanging method and then loaded into the heat treatment furnace; Normalizing process: Heat the rail wheel rim to 920-930℃ in a heat treatment furnace, keep it at this temperature for 110-120min, and then air cool it out of the furnace; Quenching process: heat the rail wheel rim to 855℃~865℃ and keep it at this temperature for 50~55min before quenching. The quenching medium is PAG aqueous solution. High temperature tempering process: heat the rail rim to 520℃~530℃ for tempering, keep it warm for 4.0~4.5h, and then cool it with PAG aqueous solution.

2. The heat treatment method of the 42CrMo track rim according to claim 1, characterized in that: After completing the normalizing process, the track wheel rim needs to be rotated 90° along its axis before entering the quenching process to prevent the track wheel rim from being excessively out of round and scrapped.

3. The heat treatment method of 42CrMo track rim according to claim 1, characterized in that: The track rim has an inner hole, and the openings at both ends of the inner hole are respectively large-diameter and small-diameter; The tooling for hanging the track rim is inserted into the inner hole of the track rim from the large diameter end of the inner hole for hanging, and the tooling and the track rim have two parallel contact surfaces to realize two-point hanging of the track rim.

4. The heat treatment method of 42CrMo track rim according to claim 1, characterized in that: The concentration of the PAG aqueous solution is 3% to 5%.

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