PSI - Issue 24

Jacopo De Nisi et al. / Procedia Structural Integrity 24 (2019) 541–558 Paolo Folgarait et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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The solid alloy (hot rolled bars, hot forgings) has good strength, transverse toughness and ductility, hardness capability and corrosion resistance compared with 304 stainless. It is used in applications requiring high strength and toughness in all directions, in the solution treated condition or heat treated to obtain a wide variety of properties. For the most demanding applications, 15-5 TM PH is produced by Vacuum Arc Re-melting (VAR), to lower gas content and reduce and disperse inclusions, while minimizing alloy segregation during solidification. These factors, coupled with the elimination of delta ferrite, result in superior transverse toughness compared to 17-4 TM PH. Samples have been processed on an EOS M290 equipment, set working parameters are laser power P =195W, laser speed v =1.085mm/s, hatching distance h =0.09mm, layer thickness t =20µm. Designed specimens accounted for subsequent metallographic evaluation, hardness and tensile testing in both as-built condition and after heat treatment. The building job involved the production of samples with their main axes along different building directions and a reasonable number of specimens have been produced with following geometry: metallographic samples with dimensions 25 x 15 x 6 mm (length x depth x height) and standard tensile specimens with nominal diameter 5.0 mm (according to ISO 6892-1:2016 Standard). They have been homogeneously located on the building platform, assuming to subdivide the working area in 9 (nine) quadrants, as schematized in Fig. 1(a). As-built samples, still attached to the building platform, can be seen in Fig.1(b).

Table 1 . Chemical composition of 15-5 PH metal powder (called PH1, according to EOS internal code).

Minimum content [wt%]

Maximum content [wt%]

Element

Cr Ni Cu Mn

14,0

15,5

3,5 2,5

5,5 4,5

-- -- --

1,00 1,00 0,07

Si

C

Mo Nb

<0,1 0,15

0,5

0,45

Fe

balance

balance

Metallographic samples have been classified in 6 (six) different groups, depending on the condition under which they were tested. Specific heat treatment conditions (six in total) are reported in Table 2. Metallographic investigations and hardness indentation tests (Rockwell C and Vickers) have been performed on properly pre-processed samples, as per specific identified Standard, on both as-built (0 group) and heat treated (A1, A2, B1, B2, C groups) specimens. HRC and HV1 hardness tests have been performed on the same specimens and compared for cross validation; HV1 hardness tests were also performed to support metallurgical investigations and the interpretation of specific microstructure features.

Table 2 . Selected heat treatment conditions performed on L-PBF 15-5 alloy samples. Group Heat treatment condition 0 No further heat treatment. Samples tested in the as-built condition A1 H900 as per ASTM A564 - 480°C, 1h holding time (STANDARD) A2 Solution treatment + H900 – 1038°C, 0.5h + air cooling + 480°C, 1h B1 Modified H900 – 480°C, 4h (as per EOS datasheet) B2 Solution treatment + modified H900 – 1038°C, 0.5h + air cooling + 480°C, 4h C Solution treatment + H1025 as per ASTM A564 - 1038°C, 0.5h + air cooling + 550°C, 4h

Tensile properties characterisation has been realized for the 0 group and after heat treating at 480°C for 1 hour (standard H900 heat treatment according to Table 2 – A1 group).