The industry's focus on stainless steel is often associated with automotive manufacturing, but the adoption of stainless steel materials in aerospace, energy and other fields is showing a trend of diversified demand. A typical example is that one of SpaceX's major efforts is to replace as many materials as possible with stainless steel, initially avoiding the replacement of parts that were exposed to the combustion of high-temperature oxygen-rich gases, but eventually Elon Musk succeeded in replacing most of the parts with stainless steel. As SpaceX builds a full-scale Starship, Elon Musk said that the material cost of a rocket will not cost $400 million to $500 million, only $10 million, and that it will be a reusable spacecraft, thanks to the use of steel. Steel is not only low-cost, but also has a high melting point, where stainless steels with a high chromium-nickel content retain sufficient ductility and strength even at temperatures of -160°C.
Not only aerospace, according to the "China Nuclear Power Research and Design Institute: Research Status of 316L Stainless Steel Powder Additive Manufacturing for Nuclear Power", the application of steel in the field of nuclear power also has great potential, and the structure and properties of additive manufacturing 316L stainless steel are anisotropic, but the anisotropy can be eliminated by additive manufacturing post-processing technology. At present, the most commonly used post-processing technology for additive manufacturing is heat treatment. Compared with forged 316L stainless steel, the mechanical properties and irradiation properties of additively manufactured 316L stainless steel treated by HIP are better. At present, the additive manufacturing technology of nuclear stainless steel is still in its infancy, and the subsequent attention should be paid to the forming mechanism of additive manufacturing and the neutron irradiation performance of forming materials.
In this issue, by focusing on the recent domestic practice and research in stainless steel additive manufacturing, 3D Science Valley and Gu You will appreciate the recent research in this field.
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2205 Duplex Stainless Steel in Additive Manufacturing and
Changes in microstructure and mechanical properties during heat treatment
Yuan Xueting1,2, Li Yinshan2, Zang Wei1,2,3, Guo Kexing2, Ma Xuan1,2, Dong Chao1,2
1.CNPC National Petroleum Pipe Engineering Technology Research Center Co., Ltd. 2. PetroChina Baoji Petroleum Steel Pipe Co., Ltd. 3. Shaanxi Provincial Key Laboratory of High Performance Coiled Tube
Summary:
In order to study the changes in the solid-state phase transformation and mechanical properties of duplex stainless steels during laser powder bed melting (LPBF), the properties of the materials were characterized by electron backscatter diffraction (EBSD), electron probe (EPMA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atom probe chromatography (APT) and mechanical property testing. The results show that the duplex stainless steel (DSS) prepared by LPBF technology is mostly ferrite, and the columnar ferrite grains grow along the BD direction with strong texture, and the yield strength and ultimate tensile strength are greatly improved compared with the conventional DSS, but the ductility is reduced. After annealing at 1 000°C, the microstructure of 2205 duplex stainless steel processed by LPBF technology can be restored to the phase equilibrium state, the plasticity is significantly improved, and the impact toughness is excellent at -110°C. In addition, the LPBF specimen has higher strength and lower plasticity, which is mainly due to the higher N supersaturation in the ferrite structure, the formation of more Cr2N particles, so the dislocation density is larger, after heat treatment, the fine austenite grains are diffusely distributed in the ferrite matrix, forming twins during plastic deformation and resulting in dislocation plugging, thereby inhibiting the plastic deformation of ferrite and making the material have a large plastic deformation limit.
© Springer
SLM additive manufacturing remelts the number of times on 316L components
Effect of surface roughness and wear properties
LI Qiang1,2, LIU Songyong1, WANG Qingyang2
1.School of Mechanical and Electrical Engineering, China University of Mining and Technology2. School of Mechanical and Electronic Engineering, Suzhou University
Summary:
The number of remelting has an important impact on the surface roughness and wear resistance of selective laser melting additive manufacturing components, and it is of great significance to study its influence mechanism and determine the economical remelting times for the development of selective laser melting additive manufacturing technology. The 316L sample was prepared by selective laser melting additive manufacturing equipment, and 0, 1, 2 and 3 laser remelting times were carried out in groups during the sample preparation process, the surface of the sample under different laser remelting times was characterized by 3D profile scanner and scanning electron microscope, the friction and wear test of the sample was carried out by using a high-speed reciprocating friction and wear testing machine, and the quality before and after wear was determined by an electronic analytical balance, and the characterization and wear performance were analyzed. The results show that the surface roughness of SLM additive manufacturing samples decreases gradually with the increase of remelting times, and the average surface roughness values of Sa, Sq, Sv and Sz after remelting decrease from 8.437, 11.88, 82.68 and 252.2 μm in 0 remelting (normal printing) to 6.18, 7.735, 37.597 and 104.36 μm in 3 remelting, respectively, decreasing by 26.75%, 34.89%, 54.53% and 58.62%, respectively. With the increase of the number of remelting, the average friction factor gradually increases, and the mass wear decreases gradually. 2. In the second half of the wear test, the instantaneous maximum friction factor of the 3rd remelting sample is greater than 1, which is due to the "contact growth" before the obvious sliding, and the contact area continues to increase, resulting in the friction exceeding the positive pressure. The reason for the above changes in surface roughness and abrasive properties is that each remelting will further melt and collapse the powder particles adsorbed on the surface and the weld marks until they disappear, and the "peak-to-valley" phenomenon at the adjacent melt path lap will be suppressed, and the defects such as porosity and spheroidization will be gradually repaired, and the surface will become smoother. It is found that the degree of change of surface roughness and wear is different with different remelting times. The concept of economic remelting times is defined, and the comprehensive change rates of surface roughness and friction and wear properties of 1, 2 and 3 remelting times are ζ1=26.61%, ζ2=43.60% and ζ3=23.68%, respectively, and the economic remelting times are determined to be 2. According to the research results, the application example of economic remelting times in mining machinery is given, and the concept of economic remelting times is proposed and applied, which can provide new ideas for improving the surface quality and wear resistance of additive manufacturing components.
Cold metal transition arc additive manufacturing
CHW-90C钢组织性能试验研究
Wei Wenyi, Liaoning Open University[Liaoning Equipment Manufacturing Vocational and Technical College]
Summary:
In this study, the thin-walled components of CHW-90C steel were prepared by using arc fuse additive manufacturing technology. The evolution of the overall structure and mechanical properties of the thin-walled components in the single-layer sedimentary layer and in the single-layer sedimentary layer were systematically studied. The results show that the structure of the single-layer sedimentary layer can be divided into solidification zone and heat-affected zone, and the heat-affected zone can be divided into normalizing zone and tempering zone, the structure of the solidification zone is mainly composed of massive ferrite, while the structure of the tempering zone and the heat-affected zone of normalizing zone is dominated by acicular ferrite. Due to dynamic recrystallization and carbide precipitation in the tempering zone, the grains in the tempering zone are further refined compared with those in the normalizing zone. The overall structure of the parenchyma is relatively uneven from bottom to top, with fine needle-like ferrite and a small amount of martensite at the bottom, coarse massive ferrite in the middle, and a mixed structure of massive ferrite and needle-like ferrite at the top. In addition, the overall mechanical properties of the specimen are anisotropic, in which the tensile strength of the horizontal specimen is higher than that of the vertical direction, reaching 1060 MPa, and the impact toughness of the vertical specimen is higher than that of the horizontal direction, reaching 226.6 J.
Additive manufacturing of low-activation steel
Research status and prospects
CHEN Wei1,2, ZHAO Jie3, ZHU Libin4, CAO Haibo1 1. Hefei Institute of Physical Sciences, Chinese Academy of Sciences2. University of Science and Technology of China3. Anhui Huizheng Electronic Technology Co., Ltd. 4. School of Mechanical Engineering, Hefei University of Technology
Summary:
Reduced activation ferritic/martensitic (RAFM) steel is one of the most mature fusion reactor structural materials, and the oxide dispersion strengthened (ODS) steel with low activation characteristics has both irradiation stability and good high-temperature strength, making it the most promising structural material for fusion reactors. Typical cases of additive manufacturing technology in the field of fusion reactor structural materials are summarized. The research progress of microstructure regulation and mechanical property optimization of additive manufacturing RAFM steel was analyzed in terms of heat input, scanning strategy, printing size, powder characteristics, and heat treatment optimization. The research strategies of additive manufacturing of low-activation ODS steel powder preparation, defect control and nanophase control are reviewed. Finally, the opportunities and challenges of additive manufacturing RAFM steel are summarized, and the development trend and technical difficulties are prospected.
Arc additive manufacturing of T-piece bolts
Experimental study on the mechanical properties of connection joints
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ZHANG Bo1, YE Jun2,3, LIU Nianwu1, LIN Xiaoyang2,3, WANG Zhen4, TANG Huiping4, 1.School of Civil Engineering and Architecture, Zhejiang Sci-Tech University2. School of Civil Engineering and Civil Engineering, Zhejiang University3. Research Center for Balanced Building, Zhejiang University4. School of Engineering, City College of Zhejiang University
Summary:
Arc Additive Manufacturing (WAAM) technology has a wide range of applications in the field of structural engineering, with the advantages of high production efficiency, low equipment cost, high material utilization and environmental sustainability. In order to explore the mechanical properties of the bolted joints of WAAM carbon steel T-pieces, a series of 12 groups of WAAM carbon steel T-shaped pieces were designed, which were connected with high-strength steel (HSS) T-pieces to form bolted joint specimens, and the effects of bolt line position and bolt arrangement on the initial stiffness, failure mode and ultimate bearing capacity of the specimens were studied through experiments. Firstly, the relevant geometric parameters of the specimen were measured by 3D laser scanning technology, and then the mechanical test was carried out and the loading response of the node was measured by digital image correlation technology (DIC). By comparing the test results with the calculation results of the existing design procedures, the applicability and accuracy of the relevant calculation methods are evaluated, and finally the existing calculation models are revised.
The results show that the WAAM carbon steel T-shaped piece has good mechanical properties, and when the distance between the bolt line and the web flange connection decreases, the initial stiffness and ultimate bearing capacity of the specimen show an upward trend, and the failure modes are expected flange failure and the bolt does not break. The existing design methods overestimate the initial stiffness of the specimen, and the prediction of the failure mode is more accurate, but the prediction of the ultimate bearing capacity is conservative, and the modified ultimate bearing capacity prediction model has a good effect, and the design method for the bolted joint of WAAM carbon steel T-shaped piece still needs further research.
H13 steel surface at different preheating temperatures
电弧增材20Cr9Mo3Ni2钢的组织与性能
XIE Jin-ping1, ZENG Da-xin1, SHI Qiu-yue1, YIN Yi-jun2 1. School of Materials Science and Engineering, Hubei Institute of Automotive Technology2. Dongfeng Forging Co., Ltd
Summary:
20Cr9Mo3Ni2 steel was additively manufactured by arc on H13 steel substrate, and the macroscopic morphology, microstructure and mechanical properties of the parts under different preheating temperatures were studied. The results show that the increase of preheating temperature reduces the crack formation tendency of the part, and when the preheating temperature is higher than 300°C, there is no crack in the part. The effects of preheating temperature on the microstructure of different parts of the workpiece are different, and the bottom and middle tissues of the additive zone are mainly tempered martensite when there is no preheating and the preheating temperature is 150°C, and tempered martensite and quenched martensite when the preheating temperature is 300°C. When the preheating temperature is 450°C, the bottom is martensite and a small amount of bainite, and the middle area is mainly martensite; The preheating temperature had little effect on the top tissue, which was mainly martensite and residual austenite. A small amount of ferrite is present between the grains at different preheating temperatures and regions. The structure of the heat-affected zone of the H13 steel substrate is tempered martensite when the preheating temperature is lower than 300°C, and coarse martensite when the preheating temperature is 450°C. With the increase of preheating temperature, the tensile strength of the additive zone increases, the elongation decreases, the transverse tensile strength is slightly higher than the longitudinal tensile strength, and the transverse elongation is lower than the longitudinal elongation. The tensile strength of the bonding zone is lower than that of the additive zone, and the fracture position of the specimen is located in the substrate when the preheating temperature is lower than 300°C, and the fracture position is located in the heat-affected zone of the substrate when the preheating temperature is 450°C. The hardness of the additive zone is low at the bottom and middle and high at the top without preheating and at a preheating temperature of 150°C; When the preheating temperature is 450°C, the hardness is high, and the distribution is relatively uniform from the top to the bottom. It can be seen that the microstructure and properties of the preheating temperature change greatly when the Ms point is crossed.
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