Failure analysis of PSV springs of 17-4PH stainless steel

Is the temperature plateau of a self‐heating test a robust parameter to investigate the fatigue limit of steels with thermography?

“…In fact, referring to Figure at loading level in the plastic regime (145 MPa) near the failure, the maximum temperature variation of duplex steel is approximately of 1°C, while 3.5°C at 115 MPa and 2°C at 220 MPa were obtained for AISI 316 and 17‐4 PH, respectively. It is worth noting that the temperature variations of austenitic and martensitic stainless steels are in agreement with the temperature changes reported in literature …”

“…However, as reported in others works, , the temperature trend does not always present a plateau value, and in this case, the described approach can no longer be used. This is the case, for instance, with brittle and high thermal diffusivity materials such as aluminium alloys and martensitic steels . Moreover, the intrinsic heterogeneity can determine differing thermal behaviour of the material due to the presence of internal microstructural processes associated with fatigue damage, as in the case of biphasic microstructures.…”

“…To verify the proposed approach, 3 stainless steels were investigated by performing fatigue tests at R = 0.5 with a stepwise loading procedure, the AISI 316, 17‐4 PH and ASTM A 890 grade 4a steels, respectively, fully austenitic, fully martensitic, and biphasic austeno‐ferritic steels used in the gas and oil industrial field. All the aspects concerning the mechanical characterization of austenitic AISI 316 and martensitic 17‐4 PH are extensively described in other works . ASTM A 890 grade 4a consists of austenitic clusters of grain embedded into a ferritic lattice: the presence of both austenite and ferrite promotes a global heterogeneity.…”

“…This is the case, for instance, with brittle and high thermal diffusivity materials such as aluminium alloys and martensitic steels. 23 Moreover, the intrinsic heterogeneity can determine differing thermal behaviour [24][25][26][27][28][29] of the material due to the presence of internal microstructural processes associated with fatigue damage, 30,31 as in the case of biphasic microstructures. Following these considerations, the validity of the method based on the plateau temperature measurements should be verified.…”

“…All the aspects concerning the mechanical characterization of austenitic AISI 316 and martensitic 17-4 PH are extensively described in other works. [4][5][6]23,32 ASTM A 890 grade 4a consists of austenitic clusters of grain embedded into a ferritic lattice: the presence of both austenite and ferrite promotes a global heterogeneity. The texture of the material is composed by lattice mismatch, 24 lattice discontinuities (grain interfaces, distribution of grain orientation, and interstitial/ substitutional atoms in the matrix 25 ), and different grain shapes ("equiassic" or "columnar/elongated").…”