Short CommunicationOn the unusual intergranular corrosion resistance of 316L stainless steel additively manufactured by selective laser melting
Introduction
Austenitic stainless steels are widely used in engineering structures operating at elevated temperatures such as in steam generating plants as piping and superheating tube materials. Under such harsh environmental conditions, intergranular corrosion (IGC) of conventional stainless steels is frequently observed, especially in sections joined by welding at temperatures between 500 and 850 °C. Additive manufacturing (AM), an emerging net-shape layer-wise fabrication process, is being adopted for producing structural components used at elevated temperatures because of its ability to produce integrated complex parts in a single step without the need for joining like welding. Selective laser melting (SLM) is a powder-bed AM technique, in which a component is produced by selectively melting consecutive layers of powder on top of each other using a high-energy laser beam [[1], [2], [3]]. Upon irradiation, the powder is melted and forms a tiny melt pool. This generates extremely high temperatures up to 105 °C and rapid cooling up to 106-108 °C/s within the melt pool [4,5]. The thermal history that materials experience during SLM processing is very different from that established by conventional manufacturing techniques [6,7]. The rapid melting and solidification in combination with cyclic heating and cooling upon the deposition of subsequent layers result in a microstructure that differs from traditionally-produced parts [[8], [9], [10]]. This has resulted in unusual properties such as weaker erosion-corrosion resistance of SLM-produced 316L stainless steel (hereafter 316L SS) [11].
It is well-known that an important microstructural characteristic of a crystalline material that could be highly influenced by the thermal history during the production process is the grain boundary (GB) character. Such change in GB character could lead to changes in the IGC behaviour of SLM-produced stainless steels. Research on IGC resistance over the years has shown that the GB character has a crucial influence on precipitation behaviour and IGC susceptibility [[12], [13], [14], [15], [16]]. Measurements of GB character, with special emphasis on coincidence site lattice (CSL) boundaries, have been the focus of GB engineering in improving corrosion resistance. In spite of extensive studies on the microstructural evolution and properties of SLM-produced 316L SS [[17], [18], [19], [20], [21], [22]], the IGC behaviour of SLM-produced stainless steels has yet to be studied in any detail. A recent report has found that the SLM-produced 316L SS exhibited a more rapid sensitization of GBs upon exposure to elevated temperature compared to the wrought counterpart, however, the precipitation behaviour and its subsequent influence on the IGC resistance are not well understood [23].
In the present study, an attempt was made to provide insight into how the nonconventional thermal history associated with SLM processing can influence the GB character, precipitation behaviour and IGC susceptibility with the support of microscopy analysis and electrochemical measurements.
Section snippets
Materials and heat-treatment
Commercially available gas-atomized spherical 316L SS powder, with a particle size range between 5 and 40 μm, was used to produce specimens. Gas-atomisation was performed under argon gas atmosphere. An SLM®-125HL machine was used to produce cubic specimens with dimensions of 1.0 × 1.0 × 1.0 cm3. Prior to the SLM fabrication, the build plate was pre-heated to a temperature of 200 °C and the build chamber was purged with purified argon until the oxygen level was reduced to below 100 ppm. The main
Results and discussion
In general, it is believed that the loss of intergranular corrosion resistance at the GBs in stainless steels is due to the formation of GB chromium carbides that cause localised Cr depletion in the region adjacent to these precipitates [[25], [26], [27]]. The intergranular attack is believed to be accelerated by the increasing potential difference between grain interiors (cathode) and GBs (anode). The DL-EPR test is a common method for assessing such behaviour based on the assumption that only
Summary
The IGC resistance of an additively manufactured 316L SS was studied using a combination of microscopy analysis and electrochemical measurements. The relationship between the IGC and GB character of the SLM-produced 316L SS was established for the first time. No Cr-rich precipitates were detected for SLM-produced specimens after a long-term sensitisation heat-treatment. Subsequently, DL-EPR tests showed substantially lower DOS values for the SLM produced 316L SS compared to its commercial
Data availability statement
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
Acknowledgement
Financial support from Deakin University Postgraduate Research Scholarship (DUPRS) is greatly appreciated. Deakin University’s Advanced Characterisation Facility is acknowledged for use of the microscopy instruments and assistance from Dr Adam Taylor and Dr Mark Nave.
References (48)
- et al.
Additive manufacturing of metals
Acta Mater.
(2016) - et al.
Laser processing of SiC-particle-reinforced coating on titanium
Scr. Mater.
(2010) - et al.
Effect of processing parameters on microstructure and tensile properties of austenitic stainless steel 304L made by directed energy deposition additive manufacturing
Acta Mater.
(2016) - et al.
Signatures of the unique microstructure of additively manufactured steel observed via diffraction
Scr. Mater.
(2018) - et al.
Twinning induced plasticity in austenitic stainless steel 316L made by additive manufacturing
Mater. Sci. Eng. A
(2017) - et al.
Unexpected erosion-corrosion behaviour of 316L stainless steel produced by selective laser melting
Corros. Sci.
(2019) - et al.
Austenite-ferrite interface crystallography dependence of sigma phase precipitation using the five-parameter characterization approach
Mater. Lett.
(2017) - et al.
Suppression of chromium depletion and sensitization in austenitic stainless steel by surface mechanical attrition treatment
Mater. Lett.
(2011) - et al.
Improving the intergranular corrosion resistance of austenitic stainless steel by high density twinned structure
Scr. Mater.
(2017) - et al.
Optimization of grain boundary character distribution for intergranular corrosion resistant 304 stainless steel by twin-induced grain boundary engineering
Acta Mater.
(2002)
Additively manufactured hierarchical stainless steels with high strength and ductility
Nat. Mater.
Hardened austenite steel with columnar sub-grain structure formed by laser melting
Mater. Sci. Eng. A
On the enhanced corrosion resistance of a selective laser melted austenitic stainless steel
Scr. Mater.
Excellent mechanical and corrosion properties of austenitic stainless steel with a unique crystallographic lamellar microstructure via selective laser melting
Scr. Mater.
A study of intergranular corrosion of austenitic stainless steel by electrochemical potentiodynamic reactivation, electron back-scattering diffraction and cellular automaton
Corros. Sci.
Relation between carbide precipitation and intercrystalline corrosion of stainless steels
Corros. Sci.
Determination of susceptibility to intergranular corrosion and electrochemical reactivation behaviour of AISI 316L type stainless steel
Corros. Sci.
The structure of high-angle grain boundaries
Acta Metall.
Changes in the five-parameter grain boundary character distribution in α-brass brought about by iterative thermomechanical processing
Acta Mater.
The effect of phase transformation route on the intergranular corrosion susceptibility of 2205 duplex stainless steel
Mater. Lett.
Identification of sigma and chi phases in duplex stainless steels
Mater. Charact.
In situ phase transformation of Laves phase from Chi-phase in Mo-containing Fe–Cr–Ni alloys
Mater. Lett.
On the effect of long-term creep on the microstructure of a 12% chromium tempered martensite ferritic steel
Acta Mater.
On the formation and growth of Mo-rich Laves phase particles during long-term creep of a 12% chromium tempered martensite ferritic steel
Scr. Mater.
Cited by (91)
Effect of post-processing heat treatments on the high-temperature oxidation of additively manufactured 316L stainless steel
2024, Journal of Materials Research and TechnologyCorrosion behavior of different building planes of selective laser melting 316L stainless steel in 0.1 M HCl solution
2024, Journal of Materials Research and TechnologyEffect of Ce content on precipitation behavior in S31254 super austenitic stainless steel
2023, Journal of Alloys and Compounds