Effect of post-heat treatments on the corrosion behaviour of additive manufactured M300 maraging steel

Abstract

M300 maraging steel, with its exceptionally high strength, toughness and weldability, is widely employed in critical applications of space industry. In the present study, M300 alloy has been fabricated using laser powder bed fusion method and the effect of different post-heat treatments and build orientation on the corrosion and stress corrosion cracking (SCC) resistance have been examined using electrochemical polarisation and slow strain rate test methods. The results in general indicate that the fabricated alloy in the as-received condition exhibits fibrous texture in the 〈001〉 direction when compared to XY orientation. The microstructural heterogeneities have been partially improved after solution treatment and aging (STA) and significantly improved after hot isostatic processing (HIP) treatment at high temperature and pressure. As a result of this, the corrosion and SCC resistance of the alloy greatly improved wherein the SCC index value of the alloy was found to be 0.88 when compared to STA condition (0.52). With respect to the build orientation, corrosion resistance of XZ plane is high when compared to XY plane, which can be attributed to microstructural variations. In spite of the high SCC index of the alloy in the HIP condition, the alloy exhibits predominantly intergranular cracking morphology revealing that SCC problem could not be eliminated completely in M300 alloy. However, the high K_ISCC values of the alloy in HIP condition clearly reveal the improved SCC resistance, which was shown to be due to reduction in pores, texture and improved austenite content of the alloy.