Improving the Defect Tolerance of PBF‐LB/M Processed 316L Steel by Increasing the Nitrogen Content

Abstract

Nitrogen (N) in steels can improve their mechanical strength by solid solution strengthening. Processing N‐alloyed steels with additive manufacturing, here laser powder bed fusion (PBF‐LB), is challenging as the N‐solubility in the melt can be exceeded. This degassing of N counteracts its intended positive effects. Herein, the PBF‐LB processed 316L stainless steel with increased N‐content is investigated and compared to PBF‐LB 316L with conventional N‐content. The N is introduced into the steel by nitriding the powder and mixing it with the starting powder to achieve an N‐content of approximately 0.16 mass%. Thermodynamic calculations for maximum solubility to avoid N outgassing and pore formation under PBF‐LB conditions are performed beforehand. Based on the results, a higher defect tolerance under fatigue characterized by Murakami model can be achieved without negatively influencing the PBF‐LB processability of the 316L steel. The increased N‐content leads to higher hardness (+14%), yield strength (+16%), tensile strength (+9%), and higher failure stress in short time fatigue test (+16%).

Moisture Effects on Qualities and Properties of Laser Powder Bed Fusion (LPBF) Additive Manufacturing of As-Built 17-4PH Stainless Steel Parts

“…In this case, is 3.06 [49], α is 0.30 [50], G is 81 GPa [48], and Δρaus is ab 3.092 × 10 12 m −2 . Therefore, it is understandable that the YS of DP3.4 can be higher t that of HP60 due to the higher dislocation density of the γ phase in DP3.4, as discusse Section 3.2 (Figure 7), contributing approximately 33.5 MPa to the strength improvem Second, the more nitrogen elements in DP3.4, as shown in Table 4, can result in the str solid solution strengthening of interstitial nitrogen atoms, further enhancing the YS UTS of DP3.4 [51,52].…”

“…Therefore, it is understandable that the YS of DP3.4 can be higher than that of HP60 due to the higher dislocation density of the γ phase in DP3.4, as discussed in Section 3.2 (Figure 7), contributing approximately 33.5 MPa to the strength improvement. Second, the more nitrogen elements in DP3.4, as shown in Table 4, can result in the strong solid solution strengthening of interstitial nitrogen atoms, further enhancing the YS and UTS of DP3.4 [51,52]. Finally, the higher fraction of the γ phase in DP3.4 can also, at least in part, contribute to the increase in the UTS, attributed to a higher transformation-induced plasticity (TRIP) effect during deformation [53].…”

Synthesis and Characterization of Innovative Fe–Cr–Mn Ferritic Stainless Steel by Laser Powder Bed Fusion

“…[2,3,11] However, the significant consumption of expensive nickel element and their negative effect on biocompatibility requires the development of nickel-saving or nickel-free stainless steels. Boes et al [12][13][14][15][16][17] developed several types of stainless steels with the introduction of nitrogen, carbon, and manganese to partially replace nickel or eliminate nickel by LPBF. The austenitic and ferritic-austenitic microstructures can be produced via the partial substitution of Ni by Mn [17] or the mixture of austenitic stainless steel powders and super duplex stainless steel powders in different proportions.…”