Key Takeaways & Executive Findings
- •• WAAM-fabricated 308L stainless steel exhibits anisotropic tensile properties, with higher strength in the horizontal orientation and higher ductility in the vertical orientation. • At 600°C, dynamic strain aging (DSA) occurs, leading to serrated flow and a transition from ductile to mixed ductile-brittle fracture with intergranular facets. • The ferrite number (FN) varies along the build direction (2.30–4.80), influencing mechanical behavior and microstructural stability at elevated temperatures. • The study provides critical data for the application of WAAM 308L in high-temperature structural components, highlighting its potential and limitations.
Abstract
Wire arc additive manufacturing (WAAM) presents a promising approach for fabricating medium-to-large austenitic stainless steel components, which are essential in industries like aerospace, pressure vessels, and heat exchangers. This research examines the microstructural characteristics and tensile behaviour of SS308L manufactured via the gas metal arc welding-based WAAM (WAAM 308L) process. Tensile tests were conducted at room temperature (RT, 25°C), 300°C, and 600°C in as-built conditions. The microstructure consists primarily of austenite grains with retained δ-ferrite phases distributed within the austenitic matrix. The ferrite fraction, in terms of ferrite number (FN), ranged between 2.30 and 4.80 along the build direction from top to bottom. The ferrite fraction in the middle region is 3.60 FN. Tensile strength was higher in the horizontal oriented samples (WAAM 308L-H), while ductility was higher in the vertical ones. Tensile results show a gradual reduction in strength with increasing test temperature, in which significant dynamic strain aging (DSA) is observed at 600°C. The variation in serration behavior between the vertical and horizontal specimens may be attributed to microstructural differences arising from the build orientation. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of WAAM 308L at 600°C were (240 ± 10) MPa, (442 ± 16) MPa, and (54 ± 2.00)%, respectively, in the horizontal orientation (WAAM 308L-H), and (248 ± 9) MPa, (412 ± 19) MPa, and (75 ± 2.80)%, respectively, in the vertical orientation (WAAM 308L-V). Fracture surfaces revealed a transition from ductile dimple fracture at RT and 300°C to a mixed ductile–brittle failure with intergranular facets at 600°C. The research explores the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions, offering crucial insights for its use in thermally resistant structural and industrial components.
1. Introduction
Low-carbon stainless steel 304L (SS304L) is a variation of the popular austenitic stainless steel 304. The extra lower carbon content (≤0.03wt%) in SS304L improves its resistance to sensitization, reducing its susceptibility to intergranular corrosion in hot environments. For cryogenic and moderately high-temperature applications, SS304L is a good choice due to its strength and durability over a broad temperature range [1]. Due to its exceptional weldability, mechanical properties, and corrosion resistance at elevated temperatures, SS304L is highly valued and used in a variety of industries, including structural applications, heat exchangers, turbine buckets, and chemical processing [2–3]. For SS304L exposed to continuous service conditions, a maximum service temperature of less than 750°C is recommended. SS304L has a tensile strength of ~339 MPa at 600°C [4]. The extra low carbon in SS304L makes it less prone to intergranular corrosion. Manufacturing complex and customized components in fewer numbers through conventional processing methods is not feasible at a low cost [5].
Additive manufacturing (AM) presents a significant opportunity to produce near-net-shaped critical components through a layer-by-layer deposition strategy, reducing material waste [6–8]. This advantage makes AM an attractive option for manufacturing structural components using various engineering alloys, including austenitic stainless steel, with better efficiency, particularly in industries that demand customization and efficiency, such as aerospace, medical, chemical, and automotive sectors [9–12]. The cost, speed, material versatility, and ease of operation of arc-based AM techniques make them a competitive alternative for applications where these attributes are more important than the acceptable resolution and surface finish that electron and laser beam-based processes can provide [13]. Arc-based AM systems, such as wire arc additive manufacturing (WAAM), offer several advantages, including high deposition rates, cost-effectiveness, broad material compatibility, operational simplicity, and robustness. These characteristics make them suitable for fabricating structures from stainless steel, aluminum, and other alloys.
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A. Rajesh Kannan, Yasam Palguna, Hafiz Muhammad Rehan Tariq, N. Siva Shanmugam, Tea-Sung Jun (2025). Elevated temperature tensile properties of wire arc additively manufactured 308L austenitic stainless steel. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3166-y
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Frequently Asked Questions
What is the effect of build orientation on the tensile properties of WAAM 308L stainless steel?
The horizontal orientation (WAAM 308L-H) exhibits higher tensile strength, while the vertical orientation (WAAM 308L-V) shows higher ductility. This anisotropy is attributed to microstructural differences arising from the build orientation.
How does temperature affect the tensile behavior of WAAM 308L?
As the test temperature increases from room temperature to 600°C, the tensile strength gradually decreases. At 600°C, significant dynamic strain aging (DSA) is observed, leading to serrated flow and a transition from ductile to mixed ductile-brittle fracture.
What is the ferrite number (FN) range in WAAM 308L and its significance?
The ferrite number ranges from 2.30 to 4.80 along the build direction, with a middle region value of 3.60 FN. This retained δ-ferrite influences the mechanical properties and microstructural stability at elevated temperatures.
What are the yield strength, ultimate tensile strength, and elongation of WAAM 308L at 600°C?
At 600°C, the horizontal orientation has YS of 240 ± 10 MPa, UTS of 442 ± 16 MPa, and elongation of 54 ± 2.00%. The vertical orientation has YS of 248 ± 9 MPa, UTS of 412 ± 19 MPa, and elongation of 75 ± 2.80%.
What is the significance of this research for industrial applications?
This research provides crucial insights into the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions, offering valuable data for its use in thermally resistant structural and industrial components such as pressure vessels and heat exchangers.
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