Heat treatment method for reducing hardness difference of root crown of large blade for steam turbine

Abstract

The heat treatment method for reducing the hardness difference of the root crown of the large blade for the steam turbine comprises the following steps that S1, solid solution is conducted, specifically, preheating is conducted for a period of time, then heating is conducted, heat preservation is conducted for a period of time, and the large blade is immersed in water for 1 h after being discharged out of a furnace and subjected to oil cooling; s2, aging I: taking out from water, keeping the temperature for 11-12 hours after a period of time, and then discharging and blowing; and S3, aging II: returning to the furnace, continuously preserving heat for 11-12 hours, and then discharging and blowing. According to the method, the problem that the hardness difference of the 0Cr15Ni 7Cu2MoNbVN steel long blade is large is solved, the hardness of a forge piece is also improved, and therefore the product quality and the production efficiency are improved, specifically, preheating is added in the solid solution stage, and grain growth caused by too long heating time of a material in a high-temperature area is avoided; and (2) oil cooling and water cooling are added after the solid solution is completed, so that the cooling speed after the solid solution is completed is accelerated, and rapid cooling is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of steel materials, in particular to a heat treatment method for reducing the hardness difference between the root and crown of a large blade for a steam turbine. Background Art

[0002] With the development of society and the requirements of environmental protection, steam turbines are also being improved towards high efficiency and energy saving, and the installed capacity is also gradually increasing. At present, the domestic main units are critical, supercritical, and ultra-supercritical units. The length of the last-stage blades of these models exceeds 1000mm, the blade structure is complex, the slender blades usually have a twist angle, the root and the crown are different in size (the root and the crown refer to the two ends of the blade). The difference in hardness of the root and crown of the slender blades leads to differences in the deformation resistance of the blades, which reduces the service life of the blades. The current solution to the above problem is heat treatment. During heat treatment, the temperature is directly increased, the temperature is kept warm after the temperature is increased, and then an aging treatment is directly performed after water cooling. This method causes the blades to be at high temperature for a long time, resulting in crystallization, and the difference is still large.

[0003] Therefore, in order to correct the above defects, we proposed a heat treatment method to reduce the hardness difference between the root and crown of large blades for steam turbines. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a heat treatment method for reducing the hardness difference between the root and crown of large blades for steam turbines.

[0005] To achieve the above object, the present invention provides the following technical solution: a heat treatment method for reducing the hardness difference between the root and crown of a large blade for a steam turbine, comprising the following steps:

[0006] S1. Solution: Preheat for a period of time, then increase the temperature, keep warm for a period of time, cool in oil after taking out of the furnace and immerse in water for 1 hour;

[0007] S2, Aging 1: Take it out of the water and keep it warm for 11-12 hours after a period of time, then take it out of the oven and blow it;

[0008] S3, aging time 2: return to the furnace and continue to keep warm for 11-12 hours, then take out of the furnace and blow.

[0009] Furthermore, in the step S1, during the solid solution, the preheating temperature is 900°C, and the temperature after heating is 1028°C-1048°C.

[0010] Furthermore, in step S1, the holding time after preheating is 85-100 minutes, and the holding time after heating is 70-80 minutes.

[0011] Furthermore, in step S1, the temperature after heating is 1038°C.

[0012] Furthermore, the interval time between the solution treatment in step S1 and the aging treatment in step S2 is greater than 8 hours.

[0013] Furthermore, in step S2, the holding temperature of the aging process 1 is 477°C.

[0014] Furthermore, in step S3, the holding temperature of the second aging process is 440°C.

[0015] Furthermore, in step S1, the oil cooling time is 30 minutes.

[0016] Furthermore, the material of the large blades for the steam turbine is 0Cr15Ni 7Cu2MoNbVN.

[0017] Compared with the prior art, the present invention has the following beneficial effects: the present invention improves the problem of large hardness differences in long blades of 0Cr15Ni 7Cu2MoNbVN steel, and also improves the hardness of forgings, thereby improving product quality and production efficiency. Specifically:

[0018] (1) A preheating is added during the solution stage to avoid grain growth caused by excessive heating of the material in the high temperature area;

[0019] (2) Oil cooling and water cooling were added after the solution was completed, which accelerated the cooling rate after the solution and avoided rapid cooling;

[0020] (3) The solution-aging interval is increased to ensure sufficient microstructural transformation. Insufficient time will result in poor aging effect, thus affecting hardness.

[0021] (4) Adding one aging and wind blowing after aging can avoid cooling brittleness and further improve the hardness of the product, thereby increasing product strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a temperature and time curve diagram in the heat treatment process of the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0024] The present invention provides a technical solution:

[0025] A heat treatment method for reducing the hardness difference between the root and crown of a large blade for a steam turbine comprises the following steps:

[0026] S1. Solution: Preheat for a period of time, then increase the temperature, keep warm for a period of time, take it out of the furnace and cool it in oil before immersing it in water;

[0027] S2, Aging 1: Take it out of the water and keep it warm after a period of time, then take it out of the oven and blow it;

[0028] S3, aging time 2: return to the furnace to continue to keep warm, then take out of the furnace and blow.

[0029] Example

[0030] The blade is 1200mm long and made of 0Cr15Ni 7Cu2MoNbVN. After forging, it is heat treated in the following ways:

[0031] A. Solution the product: heat at 900℃ for 90min, then heat to 1038℃ and keep warm for 80min, then cool in oil and immerse in water for 1h;

[0032] B. The interval from solution treatment to aging treatment is ≥8h;

[0033] C. Aging time 1: 477℃ for 12 hours, then blown out of the oven;

[0034] D. Aging II: Keep at 440℃ for 12h, then blown out of the oven;

[0035] E. The hardness values ​​of 8 samples are as follows:

[0036]

[0037] The hardness value difference of the forgings heat treated by the above method is 6, which improves the consistency of the product and greatly increases the product qualification rate.

[0038] Comparative Example

[0039] The heat treatment was carried out using existing technology, and the results were as follows:

[0040] Original process heat treatment hardness value

[0041]

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A heat treatment method for reducing the hardness difference between the root and crown of large blades for steam turbines, characterized by: The steps include: S1. Solution: Preheat for a period of time, then increase the temperature, keep warm for a period of time, cool in oil after taking out of the furnace, and immerse in water for 1 hour; S2, Aging 1: Take it out of the water and keep it warm for 11-12 hours after a period of time, then take it out of the oven and blow it; S3, aging time 2: return to the furnace and continue to keep warm for 11-12 hours, then take out of the furnace and blow.

2. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 1, characterized in that: In the step S1, during the solid solution, the preheating temperature is 900°C, and the temperature after heating is 1028°C-1048°C.

3. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to any one of claims 1 or 2, characterized in that: In step S1, the holding time after preheating is 85-100 minutes, and the holding time after heating is 70-80 minutes.

4. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 2, characterized in that: In the step S1, the temperature after heating is 1038°C.

5. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 1, characterized in that: The interval between the solution treatment in step S1 and the aging treatment in step S2 is greater than 8 hours.

6. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 1, characterized in that: In step S2, the holding temperature of the aging period 1 is 477°C.

7. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 1, characterized in that: In step S3, the holding temperature of the second aging process is 440°C.

8. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 1, characterized in that: In step S1, the oil cooling time is 30 minutes.

9. The heat treatment method for reducing the hardness difference between the root and crown of a large steam turbine blade according to claim 1, characterized in that: The material of the large blades for the steam turbine is 0Cr15Ni7Cu2MoNbVN.

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