Stress Corrosion Cracking Probability of Selective Laser Melted 316L Austenitic Stainless Steel under the Effect of Grinding Induced Residual Stresses

Arshad Yazdanpanah,Mattia Lago,Claudio Gennari,Manuele Dabalà

doi:10.3390/met11020327

Abstract

Surface quality and dimensional tolerances of the selective laser melting (SLM) process are not good enough for many industrial applications and grinding as a common finishing process introduces many surface modifications. Investigation on the effect of grinding induced surface residual stress (RS) on early stages of stress corrosion cracking (SCC) of SLM manufactured 316L austenitic stainless steel was conducted. Potentiodynamic and galvanostatic tests in a 3.5% NaCl aqueous solution, XRD, SEM and energy-dispersive X-ray spectroscopy (EDX) analysis were performed. For annealed and specimens with a low RS magnitude, the dominant observation was pit initiation from existing pores and growth in the build direction. For specimens with medium RS level, SCC initiation from pore sites and propagation along melt pool boundaries and for specimens with the highest detected RS, crack initiation from melt pool boundaries, grains, machining marks, and pore sites were observed. Cracks propagated in different directions, i.e., along melt pool boundaries, near-surface transgranular, and transgranular through columnar microstructure. Galvanostatic tests showed three distinctive regions that corresponded to crack and pit initiation and growth. The synergistic effect of high dislocation density along melt pool boundaries, stress concentration in pore sites, molybdenum segregation, and surface RS was the cause of SCC susceptibility of specimens with high RS magnitude.

Highlights

Selective laser melting (SLM) is one of the additive manufacturing (AM) methods that have been widely used for the manufacturing of metallic components with complex geometries [1,2]
This paper aims to clarify the effect of grinding-induced residual stress (RS) on corrosion behavior and stress corrosion cracking (SCC) susceptibility of selective laser melting (SLM) manufactured specimens after grinding with different process parameters
Following the SLM process, samples were solution annealed in an Argon-controlled atmosphere at 1050 ◦C for 30 min and air quenched, to reduce the thermal RS produced by the SLM process and to avoid any possible sensitization effects

Summary

Introduction

Selective laser melting (SLM) is one of the additive manufacturing (AM) methods that have been widely used for the manufacturing of metallic components with complex geometries [1,2]. High heating and cooling rates, due to the interaction of a highly concentrated laser beam with the micro-sized particles, coupled with the thermal effects of previously manufactured layers, leads to the formation of a unique columnar–hierarchical and highly textured microstructure, which is different from other traditional manufacturing methods such as casting and forging [3,4]. Extensive efforts have been made to reduce metallurgical defects such as entrapped gas, not melted particles, micro-cracks, balling, and oxidation to enhance the mechanical characteristics and to obtain the quality of the manufactured parts by the SLM process that required for industrial needs [9,10,11,12]. In the presence of tensile stresses, corrosioninduced defects such as pits could act as precursors for SCC initiation as a result of stress concentration [16,17]

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