Method for refining grains of heavy forging steel of nuclear reactor evaporator

A technology of grain refinement and nuclear reactor, which is applied in furnace types, furnaces, electric furnaces, etc., can solve the problems that large forgings are difficult to meet performance requirements, and achieve the effects of high strength, grain refinement, and good toughness

Active Publication Date: 2011-11-09
CENT IRON & STEEL RES INST
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Problems solved by technology

[0004] The object of the present invention is to provide a method for refining the crystal grains of large forging steels of nuclear reactor evaporators. It can alleviate the mixed crystal phenomenon that may occur due to forging segregation, and solve the problems that it is difficult to meet the performance requirements stipulated in ASME codes in the production of large forgings.

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  • Method for refining grains of heavy forging steel of nuclear reactor evaporator
  • Method for refining grains of heavy forging steel of nuclear reactor evaporator
  • Method for refining grains of heavy forging steel of nuclear reactor evaporator

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Embodiment example 1

[0029] The improved vacuum carbon deoxidation process is used to smelt test steel. The molten steel is treated with aluminum after vacuum treatment and before pouring. The mass fraction of aluminum element is controlled to be 0.02-0.04%, and the mass fraction of nitrogen element is 0.005-0.015%. Because vacuum carbon deoxidation is used, Therefore, the mass fraction of silicon element is figure 2 . The same batch of samples were subjected to quenching and tempering treatment and simulated post-weld stress relief heat treatment, and processed into tensile and impact samples conforming to national standards for mechanical performance tests. The test results are shown in Table 4. Experimental results show that the present invention obtains a fine grain size (<20 μm), and at the same time, obtains good comprehensive mechanical properties, especially impact toughness. In the heat treatment furnace of the heat treatment process of the present invention, the temperature control accu...

Embodiment example 2

[0031] The test steel was smelted by silicon-killed deoxidation. During vacuum treatment, silicon deoxidation is added, aluminum is added to the molten steel after vacuum treatment and before pouring, the mass fraction of aluminum element is controlled to be 0.02-0.04%, the mass fraction of nitrogen element is 0.005-0.015%, and the mass fraction of silicon element is 0.1-0.3 %, the specific chemical composition is shown in Table 3. After the test steel was forged and opened at 1150°C, two normalizing heat treatment processes were adopted: furnace was charged at 400°C and heated at 150°C / h to 900°C for 5 hours, then air-cooled to room temperature, followed by 640°C for 8 hours, air-cooled to room temperature. Cut samples for metallographic analysis, metallographic structure and grain size see image 3 . The same batch of samples were subjected to quenching and tempering treatment and simulated post-weld stress relief heat treatment, and processed into tensile and impact samp...

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Abstract

The invention relates to a method for refining grains of heavy forging steel of a nuclear reactor evaporator, which belongs to the technical field of heat treatment of steel. The method comprises the following steps of: performing electric furnace smelting and ladle seconclary refining during steel production; performing vacuum pouring by an improved vacuum carbon deoxidation (VCD) process or a silicon killed deoxidation process and a subsequent multi-furnace pouring (MP) process to obtain 200 to 600 tons of steel ingots; accurately controlling the components of the steel in the smelting process, wherein the mass fraction of aluminum elements is between 0.02 and 0.04 percent, the mass fraction of nitrogen elements is between 0.005 and 0.015 percent, the mass fraction of silicon elements is less than 0.1 percent when the improved VCD process is used, and the mass fraction of the silicon elements is between 0.1 and 0.3 percent when the silicon killed deoxidation process is used; and homogenizing a forging state structure by a two-time normalizing preheating treatment process after the ingot is subjected to forging molding, and refining the grains. The method has the advantages that:the grains used for manufacturing the heavy forging steel of the nuclear reactor evaporator are obviously refined; and the level of the grain size is improved from a level 5 to a level 8.5.

Description

technical field [0001] The invention belongs to the technical field of steel heat treatment, and in particular provides a method for refining grains of steel for a large forging of a nuclear reactor evaporator, which is suitable for the grain refinement of a large forging of a nuclear reactor evaporator of a million-kilowatt class of SA508Gr.3Cl.2 low alloy steel. Grain refinement makes the large forging steel structure of the evaporator uniform, the grain size is increased from 5 grades to 8.5 grades, and the average grain size is less than 20 μm, and finally good comprehensive mechanical properties are obtained. Background technique [0002] With the depletion of fossil fuel-based energy resources and the continuous deterioration of the global ecological environment, nuclear power has once again entered a period of rapid development. In recent years, the requirements for the economy and safety of nuclear power plants, and the continuous increase in reactor output power hav...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D8/00C21D1/18C21D1/28C21C7/06C21C5/52C22C38/06
CPCY02P10/20
Inventor 刘正东林肇杰何西扣杨钢干勇
Owner CENT IRON & STEEL RES INST
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