Method for siliconizing surface of CLA16 steel

Abstract

The invention discloses a method for siliconizing the surface of CLA16 steel, and relates to the technical field of surface treatment. The method comprises the three steps of pretreatment, siliconizing agent preparation and siliconizing. The thickness and the surface silicon content of a siliconizing layer obtained on the surface of the CLA16 steel through the method are controllable, and the siliconizing layer is uniform in thickness, compact in structure and firm in combination with a matrix. The Si-rich surface layer obtained on the CLA16 steel surface through the method has excellent corrosion resistance, and the method is easy to operate, good in process stability and suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of surface treatment, and in particular relates to a method for siliconizing the surface of CLA16 steel. Background Art

[0002] In order to improve the safety of nuclear power, the international community is accelerating the development of fourth-generation nuclear power technologies such as lead-cooled reactors. As one of the six main types of fourth-generation nuclear reactors, lead-cooled reactors have the characteristics of high load tracking, high inherent safety, high power density and long refueling cycle, which well meet the safety, economy, sustainability and nuclear non-proliferation requirements of fourth-generation reactors. Therefore, the application prospects of lead-cooled reactors are very broad.

[0003] Lead-cooled reactor is a fast neutron reactor cooled by liquid lead or lead-bismuth alloy. Lead or lead-bismuth alloy is highly corrosive to structural materials, and complex oxygen control technology or excellent corrosion-resistant materials must be used to ensure the long-term safe operation of the reactor. Studies have found that after adding appropriate amounts of strong oxide-forming elements Si and Al to steel, a dense self-passivating oxide film (SiO2, Al2O3) is formed in liquid lead or lead-bismuth alloy with a certain oxygen content to protect the matrix, preventing the matrix elements from dissolving outward and blocking the inward diffusion of lead and bismuth and the inward diffusion of O elements. Although the addition of Si element can significantly improve the resistance of the matrix material to liquid lead-bismuth corrosion, the addition of Si element will also significantly reduce the toughness of the material, increase the sensitivity of welding cracks, and promote radiation embrittlement and liquid metal embrittlement effects.

[0004] Surface siliconization treatment is an effective way to increase the Si content on the surface of the material. A surface silicon-rich layer with a high Si content can be obtained on the surface of the material, which will not cause the embrittlement effect of the main material and can avoid the problem of early peeling of the coating caused by the use of the coating. The Si-rich surface layer has excellent corrosion resistance and is metallurgically bonded to the main body of the material with good bonding performance. Therefore, exploring the Si-diffusion technology on the surface of materials that does not affect the mechanical properties and embrittlement transition of the main body of the structural material can provide guidance for the practical application of CLAM steel in future lead-based reactors, which has important theoretical significance and practical application value. Summary of the invention

[0005] The purpose of the present invention is to provide a method for siliconizing the surface of CLA16 steel in view of the problems existing in the prior art.

[0006] To achieve this object, the technical solution provided by the present invention is: to provide a method for siliconizing the surface of CLA16 steel, the method comprising the following steps: S1. Pretreatment: Use 320# and 800# sandpaper to grind the surface of CLA16 steel in turn, put the grinded CLA16 steel into deionized water for ultrasonic cleaning for 3~5 minutes, then put it into alcohol for ultrasonic cleaning for 3~5 minutes, and finally take it out and dry it for use; S2. Preparation of siliconizing agent: Weigh ferrosilicon powder, sodium fluoride and ammonium chloride according to a certain proportion and put them into a ball mill, and use a planetary ball mill to mix the three powders evenly; S3, siliconization: put the siliconizing agent into the corundum crucible, bury the CLA16 steel in the center of the siliconizing agent during the loading process, cover the crucible after the siliconizing agent is installed, and control the distance between the CLA16 steel and the crucible wall and the crucible cover to be no less than 5mm. Finally, put the crucible into the corundum tube furnace for vacuuming and heating operations, and the heating rate is 5~10℃ / min. After the temperature in the tube reaches 100~300℃, introduce a mixed gas of Ar and H2 into the tube, close the vacuum valve after 5~30min, and the air pressure in the tube gradually increases. When the air pressure in the tube reaches 1~1.5 atmospheres, close the charging valve. Continue to heat up to 800~1050℃ and keep warm for 0.5~5h, and finally take out the CLA16 steel for air cooling.

[0007] Among them, the particle size of the ferrosilicon powder used in the S2 siliconizing agent preparation step is 10~300 mesh, and the mass fraction of silicon in the chemical composition is 75~95%.

[0008] Among them, the proportions used in the S2 siliconizing agent preparation step are 90-98% by mass of ferrosilicon powder, 1-10% by mass of sodium fluoride, and 0-5% by mass of ammonium chloride.

[0009] The structure of the siliconized layer obtained by the method is a silicon-containing solid solution, the silicon content of the surface layer of the siliconized layer is 1-5%, and the thickness of the siliconized layer is 5-100 μm.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: the method for siliconizing the surface of CLA16 steel provided by the present invention performs vacuum treatment on the corundum tube in the early stage of siliconizing, which can discharge the residual air in the tube, and then introduces a mixed gas of Ar and H2, which can control the oxygen content in the siliconizing process to an extremely low level, effectively preventing the oxidation of CLA16 steel during the siliconizing process. In addition, after the siliconizing is completed, the CLA16 steel is directly taken out for air cooling and quenching, and a ferrite and martensite dual-phase structure is directly obtained, which simplifies the subsequent heat treatment process operation; finally, the method is simple to operate, has good process stability, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1The cross-sectional microstructure and composition of the siliconized layer prepared on the surface of CLA16 steel by the method for siliconizing the surface of CLA16 steel provided in Example 1 of the present invention.

[0012] Figure 2 This is the XRD spectrum of the siliconized layer prepared on the surface of CLA16 steel by the method for siliconizing the surface of CLA16 steel provided in Example 1 of the present invention.

[0013] Figure 3 The cross-sectional microstructure and composition of the siliconized layer prepared on the surface of CLA16 steel by the method for siliconizing the surface of CLA16 steel provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0014] The present invention is further described below by means of specific embodiments, but the protection content of the present invention is not limited to the following embodiments, and any non-creative changes made by those skilled in the art on the basis of the present invention belong to the protection scope of the present invention.

[0015] Example 1

[0016] Taking CLA16 steel as the matrix, the surface of CLA16 steel was polished with 320# and 800# sandpaper in turn. The polished CLA16 steel was ultrasonically cleaned in deionized water for 3 minutes, then ultrasonically cleaned in alcohol for 3 minutes, and finally taken out and dried for use. Next, 100 mesh ferrosilicon powder with a silicon mass fraction of 75%, sodium fluoride and ammonium chloride were weighed in a ratio of 95.5%: 3.5%: 1.0% and put into a ball mill, and the three powders were mixed evenly using a planetary ball mill. Then the siliconizing agent was loaded into the corundum crucible, and the CLA16 steel was buried in the center of the siliconizing agent during the loading process. After the siliconizing agent was loaded, the crucible cover was covered, and the distance between the CLA16 steel and the crucible wall and the crucible cover was controlled to be 8mm. Finally, the crucible was placed in a corundum tube furnace for vacuum and heating operations, and the heating rate was 5℃ / min. After the temperature in the tube reaches 200℃, a mixed gas containing 95% Ar and 5% H2 is introduced into the tube. After 10 minutes, the vacuum valve is closed, and the air pressure in the tube gradually increases. When the air pressure in the tube reaches 1.02 atmospheres, the charging valve is closed. Continue to heat up to 1050℃ and keep it warm for 2 hours. Finally, the CLA16 steel is taken out and air-cooled. The cross-sectional morphology of the siliconized layer is analyzed. The thickness of the siliconized layer is about 78.3μm, the surface silicon content is about 4.6%, the siliconized layer is dense, the thickness is relatively uniform, and it is firmly bonded to the substrate. XRD shows that the siliconized layer is mainly Fe phase.

[0017] Example 2

[0018] Taking CLA16 steel as the matrix, the surface of CLA16 steel was polished with 320# and 800# sandpaper in turn. The polished CLA16 steel was ultrasonically cleaned in deionized water for 3 minutes, then ultrasonically cleaned in alcohol for 3 minutes, and finally taken out and dried for use. Next, 100 mesh ferrosilicon powder with a silicon mass fraction of 75%, sodium fluoride and ammonium chloride were weighed in a ratio of 95.5%: 3.5%: 1.0% and put into a ball mill, and the three powders were mixed evenly using a planetary ball mill. Then the siliconizing agent was loaded into the corundum crucible, and the CLA16 steel was buried in the center of the siliconizing agent during the loading process. After the siliconizing agent was loaded, the crucible cover was covered, and the distance between the CLA16 steel and the crucible wall and the crucible cover was controlled to be 8mm. Finally, the crucible was placed in a corundum tube furnace for vacuum and heating operations, and the heating rate was 5℃ / min. After the temperature in the tube reaches 200℃, a mixed gas containing 95% Ar and 5% H2 is introduced into the tube. After 10 minutes, the vacuum valve is closed, and the air pressure in the tube gradually increases. When the air pressure in the tube reaches 1.02 atmospheres, the charging valve is closed. The temperature is continued to rise to 1000℃ and then kept for 2 hours. Finally, the CLA16 steel is taken out and air-cooled. The cross-sectional morphology of the siliconized layer is analyzed. The thickness of the siliconized layer is about 46.1μm, the surface silicon content is about 3.0%, the siliconized layer is dense, the thickness is relatively uniform, and it is firmly bonded to the substrate.

Claims

1. A method for siliconizing the surface of CLA16 steel, characterized in that: The method comprises the following steps: S1. Pretreatment: Use 320# and 800# sandpaper to grind the surface of CLA16 steel in turn, put the grinded CLA16 steel into deionized water for ultrasonic cleaning for 3~5 minutes, then put it into alcohol for ultrasonic cleaning for 3~5 minutes, and finally take it out and dry it for use; S2. Preparation of siliconizing agent: Weigh ferrosilicon powder, sodium fluoride and ammonium chloride according to a certain proportion and put them into a ball mill, and use a planetary ball mill to mix the three powders evenly; S3. Siliconizing: Load the siliconizing agent into the corundum crucible, bury the CLA16 steel in the center of the siliconizing agent during the loading process, cover the crucible after loading the siliconizing agent, and control the distance between the CLA16 steel and the crucible wall and the crucible cover to be no less than 5mm. Finally, put the crucible into the corundum tube furnace for vacuuming and heating operations. The heating rate is 5~10℃ / min. After the temperature in the tube reaches 100~300℃, a mixed gas of Ar and H2 is introduced into the tube. After 5~30min, the vacuum valve is closed, and the air pressure in the tube gradually increases. When the air pressure in the tube reaches 1~1.5 atmospheres, the charging valve is closed, and the temperature continues to rise to 800~1050℃ and then kept warm for 0.5~5h. Finally, the CLA16 steel is taken out and air-cooled.

2. A method for siliconizing the surface of CLA16 steel according to claim 1, characterized in that: The particle size of the ferrosilicon powder used in the S2 siliconizing agent preparation step is 10-300 meshes, and the mass fraction of silicon in the chemical composition is 75-95%.

3. A method for siliconizing the surface of CLA16 steel according to claim 1, characterized in that: The proportions used in the S2 siliconizing agent preparation step are 90-98% by mass of ferrosilicon powder, 1-10% by mass of sodium fluoride, and 0-5% by mass of ammonium chloride.

4. A method for siliconizing the surface of CLA16 steel according to claim 1, characterized in that: The structure of the siliconized layer obtained by the method is a silicon-containing solid solution, the silicon content of the surface layer of the siliconized layer is 1-5%, and the thickness of the siliconized layer is 5-100 μm.

Images