Effects of Secondary-Phase Formation on the Electrochemical Performance of a Wire Arc Additive Manufactured 420 Martensitic Stainless Steel under Different Heat Treatment Conditions

Abstract

This study aims to investigate the effects of annealing, quenching, and tempering (Q&T) heat treatments on the microstructure, crystallographic orientation, and electrochemical performance of a wall shaped 420 martensitic stainless steel part fabricated by wire arc additive manufacturing technology. The formation of a martensitic matrix with delta ferrite in the as-printed sample, islands of spherical chromium carbides embedded in a ferritic matrix in annealed sample, and intergranular chromium-rich carbides along the primary austenite grain boundaries in addition to intra-lath Fe-rich carbides in the quenching and tempering heat treated sample were detected. To characterize the corrosion performance of the fabricated samples, open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy tests were performed on all samples in aerated 3.5 wt.% NaCl electrolyte at room temperature. The corrosion morphology of the as-printed sample was characterized by localized corrosion attacks adjacent to the delta ferrite phase, while severe pitting occurred in the annealed sample due to the high susceptibility of ferritic matrix-carbide interface to pitting. In contrast to the as-printed and annealed sample, the electrochemical performance of the quenched and subsequently tempered samples was found to be significantly improved, ascribed to elimination of the chromium depleted regions adjacent to the delta ferrite phase, and enhanced protectiveness of the passive film on the alloy’s surface.

Corrosion response of steels fabricated through arc directed energy deposition additive manufacturing: a review

“…For WAAM-fabricated 420 stainless steel, quenching and tempering were shown to enhance the corrosion performance of the as-printed part. 49 In the case of WAAM-fabricated duplex stainless steel, 52 the optimal heat treatment temperature of 1300 °C within the chosen temperature range was found to improve corrosion resistance due to favorable texturing and reduced microstructural defects. Regarding WAAM-fabricated 316L stainless steel, 42 the highest corrosion resistance did not necessarily correspond to the lowest or highest heat treatment temperature.…”

“…In the case of as-printed 420 stainless steel, post-production heat treatments involving annealing and Quench & Tempering (Q&T) were applied. 49 The sample subjected to Q&T exhibited an active-passive corrosion behavior, while the others displayed active behavior in their PDP curves. Furthermore, the post-corrosion examinations revealed severe localized attack on the as-printed martensitic stainless steel, whereas the annealed as-printed alloy exhibited localized pitting.…”

“…47 On the contrary, the presence of intra-lath carbides, which share a similar chemical composition with the matrix, reduced the susceptibility of the 420 stainless steel to micro-galvanic coupling effect and the corresponding non-uniform passive film formation. 49 This, in turn, resulted in improved corrosion resistance. Likewise, the decreased elemental/phase segregation resulting from the rapid solidification in a novel WAAM process (the BC-TWIAW method) led to the absence of microgalvanic coupling in 18-8 stainless steel.…”

Differences between Tensile Properties of WAAM SS304 Components in Different Directions

“…[10][11][12][13] According to the existing research, the mechanical properties of WAAM stainless steel (SS) components are better than that manufactured by traditional manufacturing methods. [14,15] The relevant research results are summarized in Table 1. Relevant researches show that the mechanical properties of WAAM SS components are significantly better than that of forged ones.…”