| Selective laser melting technology(SLM)is an advanced digital and intelligent processing technology.It has the advantages of short manufacturing cycle,high material utilization rate,and is not restricted by the complexity of the structure.It can directly produce metal with excellent performance and complex structure.17-4PH stainless steel has the characteristics of high strength,high toughness and high corrosion resistance.It is an important structural material in the field of shipbuilding.It is often used in the manufacture of sonar shrouds,ship propellers,propeller shafts and other key ship components.Due to the complex structure and shape of these parts,SLM forming shows a huge potential for application compared with traditional manufacturing processes.In the SLM forming process,due to the continuous rapid melting and solidification process of the material,the microstructure of the formed part is different from the traditional preparation method,and defects such as pores and inclusions may appear inside.The heat treatment process can effectively improve the metal microstructure and optimize the comprehensive mechanical properties of the formed parts.It is also the most commonly used post-treatment process in the SLM forming process.This thesis uses commercial SLM forming equipment to prepare high-density 17-4PH samples,and forged 17-4PH samples as a control.H1075 solution aging heat treatment was performed on the two samples to reveal the influence of the heat treatment process on the microstructure,mechanical properties and corrosion properties of the 17-4PH stainless steel prepared by SLM.The difference in microstructure is the root cause of the difference in corrosion and mechanical properties of SLM forming and forging 17-4PH stainless steel.Therefore,this article firstly used XRD diffractometer,metallographic microscope,field emission scanning electron microscope and transmission electron microscope to characterize the unheated,solution heat-treated and H1075 from the three perspectives of metallographic structure,texture orientation,inclusions and precipitation phase.The microstructure of SLM formed17-4PH stainless steel under three states of solution aging heat treatment,so as to systematically study the effect of H1075 heat treatment on the microstructure of SLM formed17-4PH stainless steel.On this basis,the Vickers microhardness test was performed on SLM formed and forged 17-4PH stainless steel to study the mechanism of heat treatment on the mechanical properties of SLM formed 17-4PH stainless steel.The experimental results show that after H1075 heat treatment,the microstructure of SLM formed 17-4PH stainless steel is similar to that of forged 17-4PH stainless steel,but the mechanical properties are better than that of forged 17-4PH stainless steel.Subsequently,this article studied the corrosion resistance of 17-4PH stainless steel formed by SLM by using an electrochemical workstation and taking the forged 17-4PH stainless steel as a control.In this paper,the open circuit potential(OCP),polarization curve,cyclic polarization and electrochemical impedance spectroscopy tests are carried out to characterize the effect of heat treatment on the corrosion resistance of SLM formed 17-4PH stainless steel from three aspects: corrosion type,corrosion rate and pitting performance.The analysis of the test results shows that the SLM formed 17-4PH stainless steel in the three different states before and after heat treatment showed strong uniform corrosion resistance and poor pitting corrosion resistance,and aging treatment has an adverse effect on the corrosion resistance of SLM formed 17-4PH stainless steel.At the end of this paper,the corrosion behavior of 17-4PH stainless steel formed by SLM under different heat treatment conditions is studied by means of metallurgical microscope and field emission scanning electron microscope.Analysis of the experimental results shows that the corrosion behavior of 17-4PH stainless steel formed by SLM in the untreated and solution treated state is pitting corrosion,and the corrosion behavior is transformed into active dissolution after aging treatment.The pore distribution on the surface of the 17-4PH stainless steel formed by SLM under three different conditions was observed by a metallurgical microscope,and combined with the difference between the microstructures,the mechanism of heat treatment on the corrosion performance of the 17-4PH stainless steel formed by SLM was systematically analyzed. |
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