| Selective laser melting(SLM)of high-strength stainless steel can effectively improve the forming efficiency,reduce the waste of raw materials,and is suitable for all kinds of complex shape parts.It is an important way of forming high-strength stainless steel in the future.However,due to the problem of high oxygen content in PH13-8Mo stainless steel powder prepared by vacuum induction melting gas atomization(VIGA),the performance of SLM forming parts is seriously affected.In order to improve the mechanical properties of SLM PH13-8Mo high-strength stainless steel,high quality powder prepared by plasma rotating electrode processing(PREP)with very low oxygen content was used as SLM raw material.Therefore,PH13-8Mo stainless steel powder with high sphericity and good fluidity was prepared by the PREP and the formed parts with ultra-high purity were manufactured by SLM.The tensile and impact mechanical properties of the printed parts under six heat treatment regimes were compared to those without heat treatment.The effects of heat treatment on microstructure and mechanical properties of SLM PH13-8Mo stainless steel were characterized by electron-backscatter diffraction(EBSD),X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscopy(TEM).The strengthening and toughening mechanism of the optimal heat treatment process was studied and analyzed.At the same time,the corrosion resistance of SLM PH13-8Mo stainless steel in 3.5 wt.%Na Cl solution under seven heat treatment regimes was researched by electrochemical experiments(polarization curve,potentiodynamic electrochemical impedance method),and the passive film stability and corrosion resistance mechanism were compared and analyzed.The results show that:1.The oxygen content,that was only 0.0079%,in the powder prepared by the PREP was extreme low,which met the UNS S13800 standard(less than 0.008%).However,the oxygen content,that reached 0.0330%,in the powder prepared by the VIGA was extreme high,which was far beyond the UNS S13800 standard.Compared with the VIGA powder,the physical properties of the powder prepared by the PREP were more excellent,the powder fluidity was increased from 30.66 s/50g to 14.36 s/50g and the apparent density was increased from 4.20g/cm~3to 4.43 g/cm~3.The sphericity of the PREP powder was also significantly improved,and the satellite powder on the PREP powder surface was significantly reduced.Therefore,the PREP process had natural advantages in physical properties,morphology and chemical composition.2.The PH13-8Mo powder prepared by the PREP is printed and formed by SLM technology.The density of the formed part can be controlled at about 99.9%by adjusting the printing parameters.The optimal heat treatment process was 925℃×1 h WC+0℃×2 h AC+540℃×4 h AC.Using this heat treatment p~-r~Io~Ic e~-ss,PH13-8Mo formed parts had the optimal comprehensive mechanical properties:the tensile strength,yield strength and impact energy KU2were 1492 MPa,1432 MPa and 63 J,respectively.The strengthening and toughening mechanism via heat treatment on PH13-8Mo stainless steel is attributed to dislocation strengthening,precipitate strengthening,grain boundary transformation and phase structure transformation.3.The corrosion resistance of SLM PH13-8Mo stainless steel in 3.5 wt.%Na Cl solution under seven heat treatment regimes was researched.The formed part after No.2 heat treatment process(only solution treatment,no aging treatment)had the worst corrosion resistance.However,the shaped part after No.3 heat treatment process(925℃solution+0℃cryogenic treatment)had the best corrosion resistance. |
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