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ML00161 - Mar.2020

Brittle Fracture of a High Strength Socket

Micrographic detail of a secondary crack transverse to the fracture (in the top), showing its transgranular appearance at this position.

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Micrographic detail of a secondary transverse to the (in the top), showing its transgranular appearance at this position.
M

Material

Medium Carbon Tool Steel
  • Modified
Ds

Description

A new socket broke during tightening of 3 ¾” , at 75% of the torque capacity. The material is a medium carbon tool , with low alloy additions of , and W, and the occurred in a brittle way, starting from a raiser; suggesting that the socket configuration is not compatible with the service requirements for this too high strength steel, that also evidenced low absorbed energy at room temperature .

C

Chemistry (% in weight)

Tool analysis

0.33C; 0.72Mn; 0.23Si; 0.011P; 0.009S; 0.90Cr; 0.18Ni; 0.49Mo; 0.58W.

Associated Images
General view of the broken socket. The failure occurred during service, when the tool was tightening 3 3/4" bolts at 75% of the torque capacity. The fracture occurred associated to the smaller section of the socket, thickness of 13 mm, at the corner of the radio, that is a stress concentration raiser.
602
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
General view of the broken socket. It was broken in two parts and shows no evidences of plastic deformation associated to the rupture.
93
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
General view of the broken socket, showing no plastic deformation asociated to the rupture. Looking from this side it is possible to see that the fracture followed the interface of the stem with the socket head.
80
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
Micrography of a longitudinal section of the socket at the position where the fracture occurred. Uniform tempered martensitic structure. The hardness of this microstructure is 639 HV1Kg.
74
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite
Micrography of a longitudinal section presenting an uniform tempered martensitic structure.
81
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite
Micrographic detail of the tempered martensitic structure.
80
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite
Fracture appearance of one side of the broken part showing chevron marks coming from the thinner part of the fracture. The socket thickness is only 13 mm at this point.
77
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Fracture Surface AspectDf - Brittle Fracture
Fracture appearance of the other side of the broken part, also evidencing chevron marks coming from the thinner part of the fracture.
63
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Fracture Surface AspectDf - Brittle Fracture
Detailed macroscopic aspect of the chevron marks in the fracture, starting at the internal surface of the socket, in a region in contact with the bolt that was being torked. The thickness socket is 13 mm at this point.
54
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Fracture Surface AspectDf - Chevron Marks
Detailed macroscopic aspect of the chevron marks in the other side of the fracture, starting at the internal surface of the socket, in a region in contact with the bolt that was being torked. The thickness socket is 13mm at this point.
51
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Fracture Surface AspectDf - Chevron Marks
Micrography, as polished, of the socket in a section transverse to the fracture, showing the fracture in the top and secondary brittle cracks.
45
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - As polished micrographyDf - Secondary Cracks
Micrographic aspect, as polished, of the secondary cracks with brittle aspect (straight cracks).
43
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - As polishedDf - Brittle Cracks
Micrographic details of cracks with brittle aspect (straight and multiple cracks).
42
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - As polished micrographyDf - Cracks
Micrography of the socket in a section transverse to the fracture, showing the fracture in the top and some secondary brittle cracks.
42
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Secondary Cracks
Micrographic detail of a secondary crack transverse to the fracture (in the top), showing its appearance as multiple openings, straight and with intergranular and transgranular characteristics .
35
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Brittle Cracks
Micrographic detail of a secondary crack transverse to the fracture (in the top), showing its transgranular appearance at this position.
34
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Brittle Cracks
Fractography of the broken Charpy V testpiece, in a high strength steel that absorbed 11 Joules at 20°C. Quasicleavage and dimples are the main fracture micromechanisms with some secondary cracks that appear to be intergranular, exactly as the fracture of the part.
48
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Fractography by SEMDf - Broken Testpiece
Fractography of the broken tensile testpiece, in a high strength steel (about 260Ksi Yield Strength) that presented 10% elongation. The fracture micromechanism in a static test is quasicleavage and dimples, with some secondary cracks that appear to be intergranular, exactly as the fracture of the part.
53
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Fractography by SEMDf - Broken Testpiece
Brittle Fracture of a High Strength Socket
4
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite
Micrographic details of cracks with brittle aspect (straight and multiple cracks).
2
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - As polished micrographyDf - Cracks