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Heat treatment method for large COST-FB2 steel forgings

A technology of COST-FB2 and heat treatment method, applied in the field of heat treatment of large forgings of COST-FB2 steel, can solve the problems of difficult recrystallization, many processes in heat treatment process, complicated forging process, etc., to optimize the distribution of precipitation phases and eliminate the inheritance of structure. phenomenon, the effect of improving the tensile strength

Pending Publication Date: 2022-08-09
NORTHEASTERN UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In the process of manufacturing steam turbine rotors with COST-FB2 steel as raw material, due to the large size and weight of the forgings, the forging process is complicated, and the heat treatment process has many procedures, resulting in structural defects inside the forgings
This structural defect is mainly due to the fact that large forgings of COST-FB2 steel need to go through complex processes such as upsetting, elongation, forging, etc., and the final forging temperature is generally greater than 900 ° C. Overheating leads to the formation of coarse-grained structures, making COST-FB2 steel A non-equilibrium martensite structure of retained austenite is formed. In the alloy steel of this non-equilibrium martensite structure, the austenite grain inherits the coarse grain of the original austenite under certain heating conditions. Grains, including grain size, shape and orientation, cause tissue inheritance, thus affecting the mechanical properties of steel
[0003] At present, there have been some studies on the methods of eliminating tissue inheritance, mainly including ferrite recrystallization, pearlite transformation, austenite recrystallization and rapid heating in the critical region, but these methods are due to the size of COST-FB2 steel forgings. Too large, difficulty in recrystallization of ferrite at high temperature or difficulty in pearlite phase transformation and other reasons lead to incomplete elimination of tissue genetic phenomena and difficulty in application in actual production, etc.

Method used

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  • Heat treatment method for large COST-FB2 steel forgings
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  • Heat treatment method for large COST-FB2 steel forgings

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Embodiment 1

[0038] This embodiment provides a heat treatment method for large-scale forgings of COST-FB2 steel. The COST-FB2 steel in this embodiment is smelted in a vacuum induction furnace. The forging temperature is 1100°C, and the final forging temperature is greater than 900°C. During the forging process, it has undergone upsetting and lengthening twice, and the forging ratio is greater than 3; forgings.

[0039] It is determined that the large forgings of COST-FB2 steel in this embodiment are composed of the following components in mass percentage: C: 0.12-0.14%; Mn: 0.3-0.45%; Cr: 9.0-9.5%; Ni: 0.1-0.2% ; Mo: 1.45-1.55%; Co: 1.2-1.4%; V: 0.15-0.25%; Nb: 0.04-0.08%; N: 0.015-0.03%;

[0040] The specific steps are as follows:

[0041] (1) Preliminary heat treatment: The forgings to be treated are placed in the furnace for a primary normalizing treatment on the high temperature side of the critical zone, heated to 860°C at a heating rate of 60°C / h, kept for 4 hours, and then air-coo...

Embodiment 2

[0044] This embodiment provides a heat treatment method for large-scale forgings of COST-FB2 steel. The COST-FB2 steel in this embodiment is smelted in a vacuum induction furnace. The forging temperature is 1100°C, and the final forging temperature is greater than 900°C. During the forging process, the upsetting and elongation are performed twice, and the forging ratio is greater than 3;

[0045] It is determined that the large forgings of COST-FB2 steel in this embodiment are composed of the following components in mass percentage: C: 0.12-0.14%; Mn: 0.3-0.45%; Cr: 9.0-9.5%; Ni: 0.1-0.2% ; Mo: 1.45-1.55%; Co: 1.2-1.4%; V: 0.15-0.25%; Nb: 0.04-0.08%; N: 0.015-0.03%;

[0046] The specific steps are as follows:

[0047] (1) Preliminary heat treatment: The forgings to be treated are placed in the furnace for a primary normalizing treatment on the high temperature side of the critical zone, heated to 860 °C at a heating rate of 60 °C / h, kept for 4 hours, and then air-cooled to ro...

Embodiment 3

[0050] This embodiment provides a heat treatment method for large-scale forgings of COST-FB2 steel. The COST-FB2 steel in this embodiment is smelted in a vacuum induction furnace. The forging temperature is 1100°C, and the final forging temperature is greater than 900°C. During the forging process, the upsetting and elongation are performed twice, and the forging ratio is greater than 3;

[0051] It is determined that the large forgings of COST-FB2 steel in this embodiment are composed of the following components in mass percentage: C: 0.12-0.14%; Mn: 0.3-0.45%; Cr: 9.0-9.5%; Ni: 0.1-0.2% ; Mo: 1.45-1.55%; Co: 1.2-1.4%; V: 0.15-0.25%; Nb: 0.04-0.08%; N: 0.015-0.03%;

[0052] The specific steps are as follows:

[0053] (1) Preliminary heat treatment: The forgings to be treated are placed in the furnace for a primary normalizing treatment on the high temperature side of the critical zone, heated to 860 °C at a heating rate of 60 °C / h, kept for 4 hours, and then air-cooled to ro...

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Abstract

The invention relates to a heat treatment method of a COST-FB2 steel large forge piece, the heat treatment method comprises pre-heat treatment and final heat treatment, the pre-heat treatment comprises one to three times of normalizing treatment, the normalizing treatment is critical zone high-temperature side normalizing treatment, and the normalizing temperature is 10-15 DEG C lower than Ac3 temperature; the final heat treatment comprises one-time quenching treatment and two-time tempering treatment. According to the heat treatment method, the structure heredity phenomenon can be effectively eliminated, the structure is refined, precipitated phase distribution is optimized, and therefore the mechanical property of the COST-FB2 steel large forge piece is improved.

Description

technical field [0001] The invention relates to the technical field of heat treatment of steel, in particular to a heat treatment method for large COST-FB2 steel forgings. Background technique [0002] As a martensitic heat-resistant steel, COST-FB2 steel is developed by the European COST (CO-operation in Science and Technology) project group and is suitable for medium-pressure and high-pressure steam turbine rotors of thermal power plants under ultra-supercritical conditions of 620℃. steel. In the process of manufacturing steam turbine rotor with COST-FB2 steel as raw material, due to the large size and weight of the forging, the forging process is complicated and the heat treatment process is many, resulting in structural defects inside the forging. This kind of microstructure defect is mainly due to the complex process of upsetting, elongation, forging, etc. for large-scale forgings of COST-FB2 steel. Moreover, the final forging temperature is generally greater than 900 ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D1/28C21D1/18C21D6/00C22C38/04C22C38/44C22C38/46C22C38/48C22C38/52C22C38/54
CPCC21D1/28C21D1/18C21D6/004C21D6/005C21D6/007C22C38/04C22C38/44C22C38/52C22C38/46C22C38/48C22C38/54C22C38/001C21D2211/001
Inventor 耿鑫李扬姜周华陶学儒李花兵刘福斌
Owner NORTHEASTERN UNIV