热处理对SLM 18Ni300马氏体时效钢组织及腐蚀性能的影响

Effect of Heat Treatment on Microstructure and Corrosion Properties of SLM 18Ni300 Maraging Steel

目的探究热处理对激光选区熔化(Selective Laser Melting,SLM)成形18Ni300马氏体时效钢组织和耐腐蚀性能的影响。方法利用激光选区熔化技术成形18Ni300马氏体时效钢试样,分别对成形试样进行时效处理和固溶+时效处理。通过金相显微镜、扫描电镜、显微硬度计和电化学工作站,分别测试分析了不同热处理SLM 18Ni300马氏体时效钢的微观组织、显微硬度和耐蚀性。结果热处理后,试样微观组织发生显著变化,时效试样组织细化,得到板条马氏体组织;固溶+时效试样激光熔池消失,组织为均匀致密的板条马氏体,且均有细小析出物弥散分布于晶界和板条间。时效处理和固溶+时效处理显著提高了SLM 18Ni300马氏体时效钢硬度,SLM试样硬度为376.6HV1,时效试样和固溶+时效试样硬度分别为651.5HV1和641.8HV1。0.5 mol/L H2SO4溶液中,SLM试样的Jcorr最小,为1.375×10^-3 A/cm^2,耐腐蚀性最好,各试样耐蚀性优劣有SLM试样>固溶+时效试样>时效试样。3.5%NaCl溶液中,SLM试样的极化曲线有明显的钝化平台,且Jcorr最小,为3.630×10^-6A/cm^2,耐腐蚀性最好,各试样耐蚀性优劣有SLM试样>时效试样>固溶+时效试样。结论时效处理和固溶+时效处理后,SLM 18Ni300马氏体时效钢得到板条马氏体组织,硬度显著提高,但在H2SO4溶液和Na Cl溶液中的耐腐蚀性能有所下降。

The work aims to investigate the effects of heat treatment on the microstructure and corrosion properties of 18Ni300 maraging steel fabricated by Selective Laser Melting(SLM).18 Ni300 maraging steel samples were fabricated by selective laser melting and aging treatment and solution-aging treatment were respectively conducted to the SLM samples.The microstructure,microhardness and corrosion properties of the SLM 18Ni300 maraging steel samples under different heat treatment were studied by means of metallographic microscope,scanning electron microscope,hardness tester and electrochemical workstation.It was found that the microstructure of these samples changed significantly after heat treatment.The microstructure of the aged sample was refined and composed of lath martensites.The molten pools of the solution-aged sample disappeared,and the microstructure was composed of dense uniform lath martensites.Fine precipitates were distributed between the grain boundaries and the laths in the heat treatment samples.Both aging treatment and solution-aging treatment improved the hardness of SLM 18 Ni300 maraging steel.The hardness of the SLM sample was 376.6 HV1,and the hardness of the aged sample and the solution-aged sample were 651.5 HV1 and 641.8 HV1,respectively.In 0.5 mol/L H2 SO4 solution,the SLM sample had the best corrosion resistance,as its Jcorr was the smallest(1.375×10^-3 A/cm^2).The corrosion resistance in 0.5 mol/L H2 SO4 solution was:the SLM sample>the solution-aged sample>the aged sample.In 3.5%NaCl solution,the SLM sample had the smallest Jcorr(3.630×10^-6 A/cm^2),and an obvious passivation platform appeared in its polarization curve,so its corrosion resistance was the best.The corrosion resistance in 3.5%NaCl solution was:the SLM sample>the aged sample>the solutionaged sample.After aging treatment and solution-aging treatment,the microstructure of SLM 18 Ni300 maraging steel is lath martensite,and the hardness increases significantly,but the corrosion resistance in H2 SO4 solution and NaCl solution decrease.