For example, according to the article "Understanding the Significance of Duplex Steel 3D Printing for Automotive Additive Manufacturing" by 3D Science Valley, in order to achieve lightweight automobiles, high-strength steels are widely used in automotive body, chassis, suspension and steering parts. Among them, duplex steel is a new type of high-strength steel based on phase transformation, and in terms of microstructure, duplex steel is composed of softer ferrite and hard phase martensitic. In terms of mechanical properties, it has the characteristics of high strength, work hardening index and low yield ratio. Duplex steel can meet the use of a variety of structural parts of automobiles, including body structural parts - stamping parts with complex structures and non-body structural parts - mainly including suspension parts, chassis and wheels.
In this issue, through excerpts from the recent practice and research of stainless steel additive manufacturing in domestic scientific research institutions, 3D Science Valley and Gu You will appreciate the recent research in this field.
© 3D Science Valley White Paper
Effect of solution temperature on microstructure and properties of arc additive martensitic aging steels
Bai Guanshun 1, Duan Mengwei 2, Mingzhu 1, Peng Yong2, Zhang Minglang 1, Wang Wei 1, Wang Kehong 2
Ningbo Branch of China Academy of Ordnance Sciences2. School of Materials Science and Engineering, Nanjing University of Science and Technology
Summary:
The effect of solution temperature on the microstructure and mechanical properties of martensitic aging steel for arc additive manufacturing was studied.
The results show that after solution and aging treatment, inverted austenite is formed in the interdendrite segregation region of martensitic aging steel for arc additive manufacturing. With the increase of solution temperature, the area fraction and size of inverted austenite produced after aging treatment decreased, which is due to the increase of solution temperature accelerating the diffusion of interdendrite alloying elements, thereby reducing the segregation degree of interdentic austenite stabilized elements. Compared with the stacked state, the strength of the arc additive manufacturing martensitic aging steel increases greatly after solution and aging treatment, and the elongation after breaking is almost unchanged. This is due to the gradient distribution of mechanical stability from the core to the edge in a single inverted austenite grain, and the difference in mechanical stability between different inverter austenite grains. With the increase of solution temperature, the strength and post-break elongation of arc additive manufacturing martensite steel after aging treatment decreased slightly, which was due to the decrease of inverter austenite area fraction and mechanical stability due to the increase of solution temperature, and the decrease of the ability to prolong the work hardening stage, resulting in a decrease in strength. At the same time, the decrease of the inverter austenite area fraction weakens the phase transformation-induced plasticity effect under tensile load, resulting in a slight decrease in the elongation after fracture.
Effect of heat treatment process on the microstructure evolution and mechanical properties of 18Ni300 martensitic aging steel formed by laser melting in the selected area
Wu Wenwei1,2, Xiang Chao2, Zhang Tao2, Zou Zhihang2, Sun Yongfei1,2, Liu Jinpeng2, Zhang Tao1, Han Enhou2,3
School of Physics and Materials Science, Guangzhou University2. Guangdong Institute of Corrosion Science and Technology Innovation3. School of Materials Science and Engineering, South China University of Technology
Summary:
In recent years, 18Ni300 martensitic aging steel has been widely used in additive manufacturing conformal cooling molds, and the heat treatment process is an important factor to determine whether the organizationality of the printed parts can meet the service requirements. In this work, the effects of two typical heat treatment processes, direct aging and solution aging, on the microstructure and mechanical properties of 18Ni300 martensitic aging steel formed by selective laser melting.
The results show that austenite exists in the printed state, direct aging state and solution aging samples, and there is a classical Nishiyama-Wassermann orientation relationship with the martensitic matrix. The elements of the printed specimen are evenly distributed, and there is an obvious melt pool structure and cellular structure, which is formed by dislocation entanglement, and there are a small number of long strips of austenite at the grain boundary. After direct aging treatment, the cytoplasm and melt pool structure were partially dissolved, and Ni was enriched at some grain boundaries and cell walls, with a high content of austenite. After solution aging treatment, the near-whole martensitic structure was obtained, the elements were evenly distributed, the cellular structure and melt pool structure basically disappeared, Ni was enriched at some grain boundaries, and trace amounts of austenite existed. The austenite of the printed sample has no obvious chemical composition segregation, and is a residual austenite. However, there was Ni enrichment in the austenite of the direct aging state and the solid solution aging sample, which was the reversal of the austenite. Direct aging and solution aging treatments enriched Ni at some grain boundaries and cell walls, and Ni enrichment promoted the reversal of austenite formation and stabilized it. The yield strength of the printed specimen was (1090±1.5) MPa, and a large number of rods were precipitated from the matrix after direct aging and solution aging.
Fatigue crack propagation rate of carbon steel and high-strength steel plate additively manufactured by arc fuse
Zheng Yuanpeng1,2, Chen Tao1,2, Shao Zhenwei3, Huang Cheng4
Key Laboratory of Performance Evolution and Control of Engineering Structures, Ministry of Education, Tongji University2. Department of Architectural Engineering, Tongji University3. Fujian Provincial Institute of Product Quality Inspection and Inspection4. Department of Civil and Environmental Engineering, Imperial College London
Summary:
Fatigue crack growth rate (FCGR) tests were carried out on Wire arc additive manufacturing (WAAM) carbon steel and high-strength steel plates. Compact-tension (CT) specimens were processed from WAAM carbon steel plates with nominal thicknesses of 8 mm and 3 mm and WAAM high-strength steel plates with nominal thickness of 3 mm produced by parallel path printing method and WAAM high-strength steel plates with nominal thickness of 3 mm, and the stress ratio R was 0.1. The Paris formula was used to describe the fatigue crack growth rate, and the mean constants C and m of the Paris formula and the eigenvalues of WAAM carbon steel and high-strength steel plates were obtained by fitting and summarizing. The fatigue cross-section of the specimen was observed by scanning electron microscope, and the reason for the difference in the macroscopic fatigue crack growth rate of the two WAAM steel plates was analyzed from a microscopic perspective. Compared with the recommended values of the code and the fatigue crack growth rate of other steels in the literature, it is pointed out that the fatigue crack growth rate of the two WAAM steel plates is similar to that of ordinary steel, and the fatigue crack growth rate of WAAM high-strength steel plate is better than that of WAAM carbon steel, and is lower than the commonly used mean value recommended by the code, which is related to its cross-sectional characteristics at the microscopic level. The fatigue crack growth rate is not significantly affected by the loading angle. The fatigue crack growth rate of carbon steel plate printed by parallel path and oscillation path is similar, while the fatigue crack growth rate of high-strength steel printed by parallel path is more stable and uniform than that printed by oscillating path.
Numerical analysis of the deformation of 316L stainless steel Joule heating 3D printing process
LIU Wei1, YUE Zuolin2,3, XU Chao2,4, LI Suli2
Shaanxi National Defense Industry Vocational and Technical College Intelligent Manufacturing College 2. School of Mechanical Engineering, Xi'an University of Science and Technology3. Shaanxi Coal Group Shenmu Ningtiaota Mining Co., Ltd.4. Xi'an Taihui Machinery Technology Co., Ltd
Summary:
In order to solve the deformation problem in the 316L stainless steel Joule heating 3D printing molding, the method of control variables was used to summarize the influence of different parameters on the deformation of 316L stainless steel Joule heating 3D printing process according to the changes of different speeds, different pressures and different currents. After changing the parameters, the deformation of the first step and the last step of each layer in each group of parameters were intercepted as reference data. The results show that when the current increases, the deformation also increases. When the velocity decreases, the amount of deformation also decreases; When the pressure increases, so does the amount of deformation. Through the analysis of the deformation of 316L stainless steel Joule heating 3D printing process, the deformation distribution of the material in various situations can be accurately and effectively summarized, which provides a basis for its application in actual production.
Study on the air permeability mechanism of laser selective melting of 3D printed breathable steel
ZHANG Liangliang1, WANG Minjie1, LI Hongxia1, LIU Jianye2, WANG Jinhai2, NIU Liuhui2
National Key Laboratory of High Performance Precision Manufacturing, School of Mechanical Engineering, Dalian University of Technology2. Guangdong Hanbang Laser Technology Co., Ltd
Summary:
Based on the preparation method of laser selective melting (SLM) process and layered printing, the air permeability mechanism of laser 3D printing breathable steel was studied by combining theoretical analysis and experiment. A theoretical model of the permeability of breathable steel was constructed, the relationship between its permeability coefficient and printing process parameters was analyzed, and the SLM process was used to 3D print the permeable steel with micron-level pore structure, and the influence of printing process parameters on the pore characteristics and permeability of the permeable steel was studied, and the effectiveness of the theoretical model was verified, in order to optimize the preparation process of 3D printing of permeable steel. The results show that the porosity and pore size of the breathable steel can be effectively adjusted by controlling the scanning spacing, which is conducive to the formation of a regular pore structure with grid-like distribution, and the porosity of the breathable steel is 5.91%~19.97%, and the pore size is 39.18μm~138.67μm. Based on the gas permeability test, the air permeability coefficient of the breathable steel showed a significant upward trend with the increase of the scanning spacing, and the measured results were 2.48×10-12 m2~4.05×10-12 m2, indicating that the formed connected pore structure provides a strong basis for gas penetration. By comparing and analyzing the calculated results of the air permeability coefficient and the experimental results, the effectiveness of the theoretical model for predicting the air permeability coefficient is verified.
Arc additive manufacturing process for multi-directional steel joints of large steel structures
Wang Yang1, Yu Shengfu1, Quan 2, Wang Neng2, Chen Shengyuan2
State Key Laboratory of Material Forming and Mold Technology, Huazhong University of Science and Technology2. Hubei Honglu Steel Structure Co., Ltd
Summary:
As a key component connecting large steel structures, multi-directional steel joints carry forces in all directions of steel structure buildings and play a vital role in their safety. Based on the structural characteristics of seven-way steel joints, the seven-way steel joints of arc additive manufacturing steel structure buildings are studied, and the path planning methods of partition forming, planar surface slicing and swing filling are used to divide them into three areas: straight-arm round pipe area, intersecting area and branch pipe extension area, and the intersecting area includes three types: two-pipe intersection, three-pipe intersecting and four-pipe intersection. The straight-arm round pipe area and the branch pipe extension area were stacked by swing technology, and the two-pipe intersecting, three-pipe intersecting and four-pipe intersecting areas were stacked by the path planning of curved surface slices, respectively. The forming accuracy of the stacked components is tested, the microstructure is observed and the mechanical properties are measured. The results show that the forming size deviation of the seven-way steel joint member is ±1.32 mm, and the forming accuracy is high. The microstructure is ferrite and pearlite, and the tensile strength and yield strength of the components are increased by about 30% and 105% respectively compared with the same component castings, and the seven-way steel joints of arc additive manufacturing meet the requirements of use.
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