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ML00131 - Apr.2018

Brittle Failure of a Soft Roller Bearing

Macrography of a circumferential section of the roller bearing, showing two different structures: one, white and hard (64 HRc), close to the external surface; and the other, dark and soft (21 HRc), close to the internal surface. The hardness in the thickness, close to the interface, is about 50 HRc.

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of a circumferential section of the roller , showing two different : one, white and hard (64 ), close to the ; and the other, dark and soft (21 ), close to the . The hardness in the thickness, close to the interface, is about 50 .
M

Material

Wear Resistant Steel
  • AISI D2
Ds

Description

The cylindrical roller , manufactured in to meet hardness range from 58HRc to 62HRc, failed in a brittle way after a short time in operation. The bad functioning that to the was caused by and at the soft internal diameter that was in contact with a . The unsuitable hardness level with is associated to problems of . The desired should be martensitic with carbides through the section.

C

Chemistry (% in weight)

Bearing analysis

1.44C; 0.27Si; 0.30Mn; 0.030P; 0.008S; 11.4Cr; 0.21Ni; 0.70Mo; 0.76V.

Associated Images
Aspect of the external surface of the broken cylindrical roller bearing presenting a polished external diameter and a the rupture with brittle characteristics (flat and parts that were lost).
726
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Aspect Before AnalysisDf - Fracture
Macrography of a circumferential section of the roller bearing, showing two different structures: one, white and hard (64 HRc), close to the external surface; and the other, dark and soft (21 HRc), close to the internal surface. The hardness in the thickness, close to the interface, is about 50 HRc.
122
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - NItal Etched MacroDf - Duplex structure
Aspect of the broken cylindrical roller bearing, presenting the internal diameter full of cracks; and the fracture revealing two different morphologies, flat and smooth close to the external diameter (that appeared white in the macrography); and rough close to the internal diameter (that appeared dark in the macrography).
107
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Aspect Before AnalysisDf - Fracture
Aspect of the internal diameter surface presenting several cracks in the axial direction, caused by the contact with the shaft. The roller bearing presented a too low hardness level (21 HRc average) in this ID position.
90
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Aspect Before AnalysisDf - Internal Surface
Detailed aspect of the cracks in the internal diameter surface, where the hardness level was too low. These are typical overloading cracks.
76
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Surface AspectDf - Cracks
Micrography of an axial section of the roller bearing, at the external surface, where the hardness level was about 64 HRc (higher than the limit of 58HRc to 62 HRc).
86
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Close to the External Surface
Micrographic detail of the roller bearing microstructure, close to the external surface, presenting 64 HRc and a microstructure that is martensitic with large carbides.
86
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Martensite
Micrographic detail of the roller bearing microstructure, close to the external surface, presenting 64 HRc and a microstructure that is martensitic with large carbides, several presenting internal cracks.
82
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Cracks
Fractography of the roller bearing, close to the external surface. In this position the fracture of the cylindrical roller bearing shows micromechanisms of decohesion at large carbides (cracked) and quasecleavage, typical of overloading this high strength tool steel (martensitic with carbides at 64 HRc).
75
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Fractography by SEMDf - Close to the External Surface
Micrography of an axial section of the roller bearing, at the internal surface, where the hardness level was about 21 HRc, indicating that in this region the material was not properly quenched and tempered.
75
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Close to the Internal Surface
Micrographic detail of the roller bearing microstructure, close to the internal surface, presenting 21 HRc that reveals that the matrix is not martensitic. It is ferritic with large aligned carbides (cracked).
72
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Ferrite
Micrographic detail of the roller bearing microstructure, close to the internal surface, presenting 21 HRc and a microstructure that is ferritic with large carbides (cracked) and small round carbides.
63
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Cracks
Aspect of the roller bearing fracture surface, by scanning electron microscopy, close to the internal surface. In this position the fracture shows ductile micromechanisms (dimples) as well as decohesion of large carbides and (brittle) cleavage facets, typical of overloading this low strenght, and low toughness, ferritic structure (21 HRc). The structure in this region, ferritic with large broken carbides and small rounded carbides, is of a low toughness, as indicated by the fracture.
54
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Fractography by SEMDf - Close to the Internal Surface
Micrography of a transverse section of the roller bearing, in the region of the interface where, to the top, it is the high hardness structure and, to the bottom, is the low hardness structure. There are several cracks at the interface.
40
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Cracks
Micrographic details of the cracks at the interface.
37
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Cracks
Micrographic details of the cracks at the interface, most part of them associated to the ferritic structure.
41
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Cracks
Fracture micromechanism at a region close to the internal surface. In this position the fracture shows ductile micromechanisms (dimples) as well as decohesion of large carbides and (brittle) cleavage facets, typical of overloading this low strenght ferritic structure (21 HRc). The structure in this region, ferritic with large broken carbides and small rounded carbides, is of a low toughness, as indicated by the fracture.
44
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Fractography by SEMDf - Close to the Internal Surface
Ferritic structure close to the internal diameter of the cylindrical roller bearing, in the circuferemtial direction, presenting large carbides (not aligned due to the direction of the section) and small round carbides. in this region the fracture presented ductile micromechanisms (dimples) as well as decohesion of large carbides and cleavage facets, typical of overloading of this low toughness material.
52
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Ferrite
Fracture micromechanism at a region close to the external surface. In this position the fracture shows quasecleavage, as well as decohesion of large carbides. typical of overloading this high strenght martensitic structure (64 HRc).
44
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Fractography by SEMDf - Close to the External Surface
Martensitic structure close to the external diameter of the cylindrical roller bearing, in the circuferemtial direction, presenting large carbides (not aligned due to the direction of the section) and a martensitic matrix. in this region the fracture presented quasecleavage micromechanism as well as decohesion of large carbides.
36
VIEW
ML00131 / Apr.2018
Brittle Failure of a Soft Roller Bearing
M - Wear Resistant SteelP - Roller BearingAp - Mechanical IndustryCd - Heat Treatment Defect
Cm - Nital Etched Micrography by OMDf - Martensite