Study On Microstructure And Properties Of 30crmnsi Alloy Steel Fabricated By Selective Laser Melting

Additive manufacturing(also known as 3D printing technology)is considered a revolutionary technology,because it fundamentally changes the design and manufacturing of products,and selective laser melting technology is also one of the most widely developed and most advanced technologies.It is a rapid manufacturing technology developed based on SLS technology.Compared with other rapid prototyping technologies,SLM technology has the advantages of more efficient,more convenient and broader development prospects.The vigorous development of society is inseparable from the innovation in the fields of bridges,ships and aerospace,and high-strength engineering structural steel came into being.As a high-strength medium-carbon alloy steel,30CrMnSi alloy steel has large tensile strength and yield point,and is widely used in aerospace and military fields.However,in the current research status,there are many studies on SLM forming Al-based alloys,stainless steel and cobalt-chromium alloys and other metals.The exploration of the SLM forming process of 30CrMnSi alloy steel is not yet mature.The relevant research data has not formed a set of process systems.Therefore,this subject uses 30CrMnSi medium carbon alloy steel as the forming material to conduct the SLM process test,mainly to discuss the influence of the process parameters(powder thickness,laser power,scanning speed,scanning interval)on the mechanical properties and density of the formed parts,and to study in detail The microstructure,alloy phase and fracture mechanism of 30CrMnSi medium-carbon alloy steel SLM samples are provided,which provides a theoretical basis for further research on the SLM forming process.The main research contents and conclusions are as follows:(1)Design the process parameters by orthogonal experiment method to prepare the samples,and test and analyze the density,microhardness and strong tensile strength of the formed samples to obtain the relationship between each process parameter and the performance of the parts.Obtained the best forming process parameters under different investigation indexes,and 30CrMnSi alloy steel is mostly used in the aerospace field.Its most important performance index is tensile strength Under these conditions,the optimal process parameters are P=270 W,V=900 mm/s,S=0.10 mm,H=0.02 mm.The density of the 30CrMnSi alloy powder formed by SLM has a tendency to increase first and then decrease with the increase of energy density,and in a certain The density of the sample in the energy density interval gradually decreases with the increase of the thickness of the powder layer.The energy density of the sample formed in the interval of 120 J/mm3-210 J/mm3 has the highest density,about 94%;when the energy density is 45.0 J/mm3,357.1 J/mm3,the minimum density of the samples was 77.5%and 80.2%respectively.(2)The 30CrNnSi alloy sample formed by the SLM process was polished and corroded under the process parameters of the orthogonal test design.Observation under a microscope revealed that a large number of ferrite phases and austenite phases were formed in the sample during the initial cooling period.The internal microstructure of the sample is composed of the ?-Fe(Cr)matrix and the second phase of ?-Cr1.36Fe0.52.The great degree of supercooling and cooling rate lead to the solute being too late during the crystallization process to be the main reason for the formation of the new phase ?-Cr1.36Fe0.52.At the same time,under the combined effect of fine grain strengthening and solid solution strengthening,the microhardness of the SLM sample is much greater than the microhardness of the casting.In the tensile strength test,the macro-necked phenomenon appeared in each group of samples.According to the fracture SEM morphology,the fracture mechanism of the 30CrMnSi alloy sample fonned by SLM is brittle fracture,which shows that a large number of tough sockets and Brittle stripes.(3)In the process of forming 30CrMnSi alloy steel samples by laser selective melting process,it was found that the samples after nine groups of parameters have such metallurgical defects as pores,cracks and residual stress,which are also common types of defects in SLM process.Pores are mainly caused by insufficient powder melting,and pores with uneven shapes are more likely to form macro defects of components,and the number of pores can be controlled by improving process parameters;the formation of cracks is mainly due to the internal stress or other to brittle effects.The bonding force between the metal atoms inside the member is reduced and the gap formed by the new interface is damaged,and it has a great relationship with the material's own properties;the appearance of residual stress will cause micro-defects and macro-destruction of parts,micro-defects will lead to the formation of internal cracks in the metal and macro-destruction is reflected in the phenomenon of warpage and deformation of parts.