High temperature wear behaviour of selective laser melted (SLM) 316L stainless steel (SS) was studied to elucidate the influence of characteristic microstructure of SLM 316L SS on the wear properties. The wear tests were conducted from room temperature (RT) to 600 °C using ball-on-disc setup with alumina counter ball. The effect of temperature on the wear rate and the underlying mechanisms were evaluated and compared with conventional 316 SS. The RT coefficient of friction (COF) and wear rate of SLM 316L SS and conventional 316 SS were 0.5 and 4.6 ± 0.4 x 10−4 mm3/Nm and 0.7 and 4.5 ± 0.1 x 10−4 mm3/Nm, respectively. The wear rate of conventional 316 SS slightly decreased with increasing temperature from 4.5 ± 0.1 x 10−4 mm3/Nm at RT to 3.2 ± 0.1 x 10−4 mm3/Nm at 300 °C, followed by increasing to 4.9 ± 0.4 x 10−4 mm3/Nm at 400 °C, while the wear rate of SLM 316L SS was twofold lower with 2.3 ± 0.6 x 10−4 mm3/Nm at 300 °C and 2.7 ± 0.3 x 10−4 mm3/Nm at 400 °C. The wear rate at 600 °C was found to be comparable between SLM 316L SS and conventional 316 SS with a wear rate of 6.4 ± 0.7 x 10−4 mm3/Nm and 6.6 ± 0.6 x 10−4 mm3/Nm, respectively. The lower wear rate in SLM 316L SS at higher temperatures of 300 °C and 400 °C was due to its stable hierarchical microstructure, cellular subgrains, formation of stable oxide glaze and higher hardness. Moreover, the cross-sectional microscopy of wear track after 600 °C wear tests showed that the deformation zone below the wear track in SLM 316L SS was 10–15 μm compared to 30–40 μm for conventional 316 SS. The two folds low wear rate of the SLM 316L SS at 300 °C and 400 °C compared to conventional 316 SS could potentially render it for usage in applications where high temperature wear resistant SS are needed.

Duplex stainless steel, 71 wt.% austenite, 13 wt.% ferrite and 16 wt.% sigma, was made upon heat treating of fully ferritic as-built selective laser melted (SLM) 2507 stainless steel at 1200 °C. Formation of sigma phase in the heat treated SLM 2507 was investigated using optical microscopy and scanning electron microscopy (SEM). The heat treated SLM 2507 demonstrated a yield strength of 686 MPa, ultimate tensile strength of 920 MPa and an elongation of 1.8% at room temperature with a brittle fracture morphology. Precipitation of sigma phase during heat treatment and slow cooling improved the mechanical and wear properties at high temperatures (1200 °C and 800 °C, respectively). The tensile strength and elongation of the heat treated SLM 2507 was measured 400 MPa and 20% as compared to casted duplex steel with 19 MPa and 30% elongation at 1200 °C. The 20 times higher mechanical strength as compared to casted duplex steel was attributed to sigma precipitates. Tribological behaviour of heat treated duplex SLM 2507 containing sigma at 800 °C showed very low wear rate of 4.5 × 10⁻⁵ mm³/mN compared to casted duplex steel with 1.6 × 10⁻⁴ mm³/mN.

Martensitic 420 stainless steel was successfully fabricated by Selective laser melting(SLM) with >99% relative density and high mechanical strength of 1670 MPa, yield strength of 600 MPa and elongation of 3.5%. X-ray diffraction (XRD) and scanning electron microscopy disclosed that the microstructure of SLM 420 consisted of colonies of 0.5–1 μm sized cells and submicron martensitic needles with 11 wt. % austenite. Tempering of as-built SLM 420 stainless steel at 400 °C resulted in ultra-high strength material with high ductility. Ultimate tensile strength of 1800 MPa and yield strength of 1400 MPa were recorded with an elongation of 25%. Phase transformation analysis was carried out using Rietveld refinement of XRD data and electron backscattered diffraction (EBSD), which showed the transformation of martensite to austenite, and resulted in austenite content of 36 wt. % in tempered SLM 420 stainless steel. Transformation induced plasticity (TRIP), austenite formation and fine cellular substructure along with sub-micron martensite needles resulted in stainless steel with high tensile strength and ductility. The advanced mechanical properties were compared with conventionally made ultra-high-strength steels, and the microstructure-properties relationships were disclosed.

Austenitic stainless steel 316L was fabricated for withstanding elevated temperature by selective laser melting (SLM). Tensile tests at 800 °C were carried out on laser melted 316L with two different strain rates of 0.05 S^− 1 and 0.25 S^− 1. The laser melted 316L showed tensile strength of approximately 400 MPa at 800 °C, which was superior to conventional 316L. Analysis of fracture surface showed that the 316L fractured in mixed mode, ductile and brittle fracture, with an elongation of 18% at 800 °C. In order to understand the mechanical response, laser melted 316L was thermally treated at 800 °C for microstructure and phase stability. X-ray diffraction (XRD) and Electron back scattered diffraction (EBSD) of 316L treated at 800 °C disclosed a textured material with single austenitic phase. SEM and EBSD showed that the characteristic and inherent microstructure of laser melted 316L, consisting of elongated grains with high angle grain boundaries containing subgrains with a smaller misorientation, remained similar to as-built SLM 316L during hot tensile test at 800 °C. The stable austenite phase and its stable hierarchical microstructure at 800 °C led to the superior mechanical response of laser melted 316L.