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ML00080 - Sep.2017

MIC of Stacking Disc Springs

Micrographic aspect of the disc fracture (in the right side of the figure). It is possible to see that the structure is martensitic and there are secondary intergranular cracks associated to the fracture.

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Micrographic aspect of the disc (in the right side of the figure). It is possible to see that the is martensitic and there are secondary intergranular associated to the .
M

Material

Low Alloy Medium Carbon QT
  • AISI 6150
Ds

Description

The of this disc spring was detected during inspection after two years in operation in a . The initiation is associated to a pit 0.5 mm depth. The intergranular morphology was identified in a small extension from the pit, suggesting that the was assisted by localized (MIC). The fracture propagation occurred by quasecleavage through the rest of the disc section

C

Chemistry (% in weight)

Disc Analysis

0.48C; 0.19Si; 0.84Mn; 0.012P; 0.003S; 0.84Cr; 0.07Ni; 0.03Mo; 0.03Cu; 0.011V.

Associated Images
Aspect of the broken disc spring, 1/4" thick, OD 10". The fracture is flat and transverse to the disc.
604
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Aspect Before AnalysisDf - Brittle Fracture
Macroscopic aspect of the fracture surface, showing a brittle behavior (chevron marks) and a starting point at the bottom of the groove in the right side of the figure.
42
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fracture Surface AspectDf - Brittle Fracture
Detail of the fracture starting point, in the bottom of the groove, where there is a pit about 0.5 mm depth.
36
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fracture Surface AspectDf - Brittle Fracture
Microscopic detail of the fracture surface in the position where the fracture is intergranular, probably due to the MIC attack creating an embrittled condition of the material.
31
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fractography by SEMDf - Intergranular Fracture
Microscopic detail of the fracture surface in the position where the fracture is intergranular, probably due to the MIC attack creating an embrittled condition of the material. A surface film is evident in this position suggesting that the fracture remained open and exposed to the environment during a certain time before the failure was detected.
29
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fractography by SEMDf - Intergranular Fracture
Fracture micromechanisms. Intergranular fracture in the top of the figure (close to the groove) and transgranular fracture in the bottom of the figure, where the mechanism changed to transgranular by quasecleavage.
27
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fractography by SEMDf - Intergranular Fracture
Microscopic detail of the fracture surface where it is transgranular, by quasecleavage. This aspect is similar to the one expected for this high strenght material without any embrittlement.
27
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fractography by SEMDf - Transgranular Fracture
Microscopic detail of the fracture surface where it is transgranular, by quasecleavage. This aspect is similar to the one expected for this high strenght material without any embrittlement.
26
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Fractography by SEMDf - Transgranular Fracture
The disc spring presented several small pits, as this one, that did not propagate.
24
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Nital Etched Micrography by OMDf - Pitting
Micrographic aspect of the disc in the longitudinal section. Tempered martensitic structure, probably strain hardened.
30
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Nital Etched Micrography by OMDf - Martensite
Micrographic aspect of the disc in the transverse section. Tempered martensitic structure, probably strain hardened.
31
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Nital Etched Micrography by OMDf - Martensite
Micrographic aspect of the disc fracture (in the right side of the figure). It is possible to see that the structure is martensitic and there are secondary intergranular cracks associated to the fracture.
25
VIEW
ML00080 / Sep.2017
MIC of Stacking Disc Springs
M - Low Alloy Medium Carbon QTP - SpringAp - SubseaCd - Brittle Behavior
Cm - Nital Etched Micrography by OMDf - Intergranular Cracking