Effect of Heat Treatment on the Corrosion Behavior of Selective Laser Melted CX Stainless Steel

The effects of different heat treatment regimes on the microstructure and corrosion behavior of selectively laser melted (SLM) Corrax (CX) stainless steel were systematically investigated. Three distinct thermal processing approaches solution treatment (ST), aging treatment (AT), and combined solution aging treatment (ST + AT) were comparatively examined to assess their microstructural evolution and corrosion performance. The results demonstrated that the SLM-processed CX sample initially consisted of martensite and retained austenite. After solution treatment at 900 °C for 0.5 h, microsegregation was eliminated, and the retained austenite fully transformed into martensite. During direct aging at 525 °C for 3 h (AT), a portion of the martensite reverted to austenite, accompanied by grain refinement that reduced the average grain size to 1.79 μm. When the CX was solution-aged at 900 °C for 0.5 h and then 525 °C for 4 h (ST + AT), the retained austenite transformed completely into martensite. The results of potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) revealed that the aged specimen demonstrated comparatively superior corrosion resistance with reduced surface accumulation of corrosion products relative to both ST and ST + AT specimens. The electrochemical test results indicate that the selection of heat treatment parameters has a significant impact on the corrosion resistance of SLM-formed CX samples. Compared to ST and ST + AT, the corrosion performance of AT-treated samples is improved to a certain extent, with the highest Epit (322 mV) and the largest ΔE (742). The corrosion potential is relatively high (Ecorr, −414 mV vs. SCE), and the corrosion current density is relatively low (Icorr, 0.405 μA·cm−2). This indicates that the AT samples exhibit good corrosion resistance.